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Cork Liquefaction
Improvement of the Process and its Application on Adhesives
Formulation
Ricardo do Ó Carvalho
Thesis to obtain the Master of Science Degree in
Materials Engineering
Supervisor: Dr.ª Maria Margarida Pires dos Santos Mateus
Co-Supervisor: Dr. Rui Miguel Galhano dos Santos Lopes
Examination Committee
Chairperson: Prof.ª Dr.ª Maria de Fátima Reis Vaz
Supervisor: Dr.ª Maria Margarida Pires dos Santos Mateus
Members of the Committee: Prof. Dr. João Carlos Moura Bordado
Eng.ª Ana Cristina Lopes Cardoso
November of 2015
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Agradecimentos
Em primeiro lugar gostaria de agradecer ao Professor João Moura Bordado por me ter apresentado
aos meus orientadores, os quais proporcionaram o trabalho laboratorial que se prolongou ao assunto
da minha dissertação. Obrigado pela oportunidade e por todas as sugestões. Pelas anedotas também.
Aos meus orientadores, Doutora Margarida Mateus e Doutor Rui Galhano, que num ambiente de boa
disposição me transmitiram os conhecimentos necessários e promoveram o meu desenvolvimento
pessoal para além da dissertação.
Aos restantes membros do meu grupo pela entreajuda, partilha de conhecimento e boa disposição ao
longo destes meses.
À Cork Supply, destacando-se a Engenheira Ana Cristina Cardoso, pela oportunidade de trabalhar em
conjunto com uma empresa de renome na indústria corticeira, resultando numa dissertação com
aplicação real que decerto não será só mais uma na base de dados da faculdade.
À Fabrires pela disponibilização de material e know-how para os últimos ensaios, assim como pelos
conhecimentos adquiridos e pelos bons momentos passados com os colaboradores da mesma.
Ao João Rodrigues pela ajuda inicial na conceção da mexedeira, à Carina Domingues pela ajuda no
Karl-Fischer e à Ana Elisa Ferreira por todas as dicas, sugestões e, mais importante, pela “seriedade”
e partilha de receitas gastronómicas.
Aos amigos de sempre e aos mais recentes pelo apoio neste percurso, pelos momentos que passámos
juntos e pelo que aprendi com vocês. Vocês foram (e são) essenciais para ter chegado ao fim desta
etapa da melhor forma.
Finalmente, à minha Família, não só por ser o pilar desta dissertação, do curso que terminei, mas de
tudo o resto. Um grande obrigado.
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Resumo
Nos últimos anos, a indústria corticeira tem feito um grande esforço para substituir componentes
presentes em adesivos de cortiça derivados da indústria petroquímica. Tal necessidade deve-se ao
facto de a legislação para materiais em contacto com alimentos ser cada vez mais rigorosa, e os
consumidores procurarem cada vez mais materiais sustentáveis e amigos do ambiente.
O presente trabalho estudou a liquefação de pó de cortiça, um dos mais abundantes resíduos da
indústria corticeira. Para se obter o liquefeito fez-se uma mistura reacional com 20% de pó de cortiça,
60% de 2-Etil-hexanol, 20% de dietilenoglicol e 3% da mistura reacional total como ácido p-
toluenossulfónico. As reações foram realizadas a 160°C durante 90 minutos, atingindo-se uma
conversão de 94%.
O liquefeito foi posteriormente fracionado em componentes solúveis em água (açúcares) e não-solúveis
(polióis). Ambas as frações foram caracterizadas em termos de valor hidróxido, valor ácido, teor de
humidade e espectroscopia de infravermelho. O espectro ATR-FTIR dos açúcares mostrou-se rico em
grupos hidroxilo, o que também foi comprovado pelo valor hidróxido, ao contrário da fração dos polióis.
Os açúcares foram aplicados em 14 procedimentos de colmatagem. Os que apresentaram melhor
avaliação visual foram testados em água fervente e o teor de resíduos foi contabilizado. Os polióis
foram utilizados em colas de aglomeração, as quais foram caracterizadas em relação ao teor de grupos
NCO livres, gel time e viscosidade. Foi observado que as colas de aglomeração devem ainda ser
aperfeiçoadas, enquanto que os açúcares foram eficazmente introduzidos em adesivos de colmatagem.
Palavras-chave: Liquefação, cortiça, colmatagem, aglomeração, adesivos, cola.
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Abstract
In the last couple of years, the cork industry has put a lot of effort into continuously replacing components
present in cork adhesives formulations derived from petrochemicals. This was necessary since the
legislation for materials in contact with food became stricter and consumers are seeking environmentally
friendly and sustainable materials.
The present work studied the liquefaction of cork powder which is one of the biggest by-products in the
cork industry. In order to produce a liquefied product, a quantity of 20% of cork powder was used with
60% of 2-Etyl-hexanol, 20% of diethylene glycol and 3% of the total reaction mixture as p-toluenesulfonic
acid was used. The reactions were carried at 160°C for 90 minutes, achieving a biomass conversion of
94%.
The liquefied product was fractionated in water soluble (sugars) and non-soluble (polyols) portions. Both
fractions were characterized in terms of hydroxyl value, acid value, humidity content, and infrared
spectroscopy. The ATR-FTIR of sugars fraction was shown to be rich in hydroxyl groups, also proven
by the hydroxyl value, in contrast with the polyols fraction.
The sugars were applied in 14 corks colmation procedures. The ones that presented the best visual
evaluation where tested in boiling water and their residues content acquired. The polyols were used for
agglomeration adhesives, which were characterized regarding the free NCO content, gel time and
viscosity. It was observed that the produced agglomeration adhesives must be refined, whereas the
sugars were effectively introduced in colmation adhesives.
Keywords: Liquefaction, cork, colmation, agglomeration, adhesives, glue.
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Index
Agradecimentos .................................................................................................................................... ii
Resumo.................................................................................................................................................. iv
Abstract ................................................................................................................................................. vi
Figures .................................................................................................................................................... x
Tables ................................................................................................................................................... xii
Abbreviations ...................................................................................................................................... xiv
1. Introduction ........................................................................................................................................ 1
MOTIVATION AND OBJECTIVES ......................................................................................................... 1
CORK ............................................................................................................................................. 1
CORK MARKET ............................................................................................................................... 2
CORK STOPPERS ............................................................................................................................ 4
CORK CELLULAR STRUCTURE .......................................................................................................... 6
CHEMICAL COMPOSITION ................................................................................................................. 7
BIOMASS CONVERSION .................................................................................................................. 13
SYNTHESIS OF ADHESIVES FROM LIQUEFIED BIOMASS ..................................................................... 19
COLMATION PROCESS ................................................................................................................... 23
2. Experimental work ........................................................................................................................... 25
CORK LIQUEFACTION ..................................................................................................................... 25
HYDROXYL VALUE ......................................................................................................................... 27
ACID VALUE .................................................................................................................................. 28
HUMIDITY CONTENT DETERMINATION – KARL FISCHER METHOD....................................................... 28
INFRARED SPECTROSCOPY ............................................................................................................ 29
COLMATION .................................................................................................................................. 30
BOILING WATER TEST .................................................................................................................... 32
RESIDUES CONTENT...................................................................................................................... 32
AGGLOMERATION GLUE PREPARATION ........................................................................................... 33
AGGLOMERATION ........................................................................................................................ 34
NCO CONTENT .......................................................................................................................... 35
GEL TIME .................................................................................................................................... 36
3. Results and Discussion .................................................................................................................. 39
LIQUEFACTION .............................................................................................................................. 39
HYDROXYL VALUE, ACID VALUE AND HUMIDITY CONTENT ................................................................. 39
ATR-FTIR ................................................................................................................................... 40
ix
COLMATION PROCEDURES ............................................................................................................. 42
COLMATION VISUAL INSPECTION .................................................................................................... 49
BOILING WATER TEST .................................................................................................................... 51
RESIDUES CONTENT...................................................................................................................... 52
AGGLOMERATION ADHESIVE .......................................................................................................... 54
CORK BIO-REFINERY ..................................................................................................................... 56
4. Conclusion ....................................................................................................................................... 59
5. Future Work ..................................................................................................................................... 60
6. Bibliography ..................................................................................................................................... 61
7. Appendices ...................................................................................................................................... 66
COLMATION PROCEDURES ............................................................................................................. 66
x
Figures
Figure 1 - Cork harvesting. [2] ................................................................................................................ 2
Figure 2 - Cork production by Mediterranean country (2012). [5] .......................................................... 3
Figure 3 - Natural corks. [6] .................................................................................................................... 4
Figure 4 - Colmated corks. [6] ................................................................................................................ 4
Figure 5 - Punched cork board (left) and granulates (right). [7] ............................................................. 5
Figure 6 - Agglomerated cork. [8] ........................................................................................................... 5
Figure 7 - Technical cork. [6] .................................................................................................................. 6
Figure 8 - Champagne cork. [6] .............................................................................................................. 6
Figure 9 - Capsulated cork. [6] ............................................................................................................... 6
Figure 10 – (Left) Directions on cork relatively to the trunk of the tree (Right) SEM micrographs of natural
cork in the radial section (a) and tangential section (b). [9] ..................................................................... 7
Figure 11 – “Half wall” model proposed by Sitte; (T) tertiary wall, (S) secondary wall, (W) waxes, suberin,
(P) primary wall, (M) medium lamella, (Po) pore. [9] ............................................................................... 8
Figure 12 - Medium chemical composition of virgin and reproduction cork of 10 trees. [3] ................... 8
Figure 13 - Proposed structure for suberin. [9] ....................................................................................... 9
Figure 14 – Monomers present in the lignin biosynthesis. [10] .............................................................. 9
Figure 15 – Model for the Lignin structure in cork. [3] .......................................................................... 10
Figure 16 – Model for the linkage of the phenolic region of suberin with the ligno-cellulosic matrix and
the aliphatic region with the waxes. [9] .................................................................................................. 11
Figure 17 – Cellulose structure consisting of glucose monomers connected by glycoside linkages. [9]
............................................................................................................................................................... 13
Figure 18 - Classification of biomass conversion technologies. ........................................................... 14
Figure 19 - Acid-catalyzed liquefaction of cellulose in EG. Adapted from [18]. .................................... 15
Figure 20 – Procedure for liquefied products separation. [53] ............................................................. 19
Figure 21 - Typical reaction to obtain a polyurethane. [55] .................................................................. 19
Figure 22 - Polymerization of the polyurethane pre-polymer. [55] ....................................................... 20
Figure 23 – (Left) Adhesive formulation without cork; (Right) Adhesive formulation with cork. ........... 22
Figure 24 - Hexamethylene diisocyanate (HDI).................................................................................... 22
Figure 25 – (A) Colmation machine; (B) Mixing blades; (C) Drying drum. ........................................... 24
xi
Figure 26 - Liquefaction apparatus. ...................................................................................................... 26
Figure 27 - 831 KF Coulometer. [58] .................................................................................................... 29
Figure 28 - A) Colmation mixer cross section; B) Grid drum cross section; C) Plastic cover and fan
heater cross section. ............................................................................................................................. 30
Figure 29 - A) Colmation mixer drum; B) Blades axis inside the drum. ............................................... 31
Figure 30 - A) Grid drum and motor; B) Grid drum position inside the plastic box; C) Plastic cover, fan
heater and temperature controller. ........................................................................................................ 31
Figure 31 - A) Open mold; B) Closed mold; C) Mold with metal cylinder and funnel; D) Mold press; E)
Cork extraction. ..................................................................................................................................... 35
Figure 32 - (A) Liquefied cork; (B) Polyols extract; (C) Aqueous extract. ............................................ 39
Figure 33 - ATR-FTIR of the liquefied product and respective extracts. A - Liquefied product; B - Polyols
extract; C - Aqueous extract; D - Carbohydrates fingerprint from aqueous extract. ............................. 41
Figure 34 – Corks cut in the direction of the lenticular cells. (A) Colmation No.6; (B) Uncolmated cork;
(C) Colmation No.7. ............................................................................................................................... 46
Figure 35 - Colmation No.11 glued ends. ............................................................................................. 47
Figure 36 – Commercial (left) and colmation N.7 (right) boiled corks. ................................................. 52
Figure 37 - Colmation No.11 (left) and colmation No.12 (right) boiled corks. ...................................... 52
Figure 38 - Agglomerated corks with adhesive No.1 (left) and adhesive No.1 plus 0.02g of DBTL and
1.5g of water (right). .............................................................................................................................. 55
Figure 39 - Agglomerated corks with adhesive No.2 (left) and No.4 (right). ........................................ 56
Figure 40 - Liquefaction unit flow chart. ................................................................................................ 57
xii
Tables
Table 1 - Cork oak forest, percentage of area by country. [4] ................................................................ 2
Table 2 – Cork sales (exports) by product (2013). [4] ............................................................................ 3
Table 3 - Cell dimensions of cork cells during different periods. [9] ....................................................... 7
Table 4 - Average monosaccharides fraction. [3] ................................................................................. 12
Table 5 – Summary of the parameters used in the liquefaction procedures. The values in the time (t),
Temperature (T), reagents and catalyst columns correspond to the base or higher yields conditions;
Unless indicated, the values are presented in mass percentage; (1) Catalyst % calculated on the solvent
basis; (2) After liquefaction, the polyols were produced by reacting the glycosides with soy, castor and
rice-bran oil; (3) 1 g of Maleic acid anhydride (Ma) was firstly used and subsequently Phthalic acid
anhydride (PA) or trimellitic acid anhydride (TMA) were added from 0 to 0.7g; (4) Microwave heating;
(5) Heating in autoclave with hot compressed ethanol (ET). ................................................................ 16
Table 6 (cont.) – Summary of the parameters used in the liquefaction procedures. The values in the time
(t), Temperature (T), reagents and catalyst columns correspond to the base or higher yields conditions;
Unless indicated, the values are presented in mass percentage; (1) Catalyst % calculated on the solvent
basis; (2) After liquefaction, the polyols were produced by reacting the glycosides with soy, castor and
rice-bran oil; (3) 1 g of Maleic acid anhydride (Ma) was firstly used and subsequently Phthalic acid
anhydride (PA) or trimellitic acid anhydride (TMA) were added from 0 to 0.7g; (4) Microwave heating;
(5) Heating in autoclave with hot compressed ethanol (ET). ................................................................ 17
Table 7 - Adequate range for different properties of agglomerated corks. ........................................... 34
Table 8 - Acid value, hydroxyl value and humidity content for the liquefied cork and respective extracts.
............................................................................................................................................................... 40
Table 9 – Summary of the bands assignment for the ATR-FTIR spectra. ............................................ 42
Table 10 – Summary of the colmation procedures from No. 1 to 7. ..................................................... 43
Table 11 – (Continuation of Table 1) Summary of the colmation procedures from No. 8 to 14. .......... 44
Table 12 - Summarized colmation step changes, objectives and results; Symbols: (↓) Decrease and (↑)
Increase the quantities of …, (→) Substitution of … for …, (X) Removal of, (>) Higher, (<) Lower, (+)
Add. ....................................................................................................................................................... 48
Table 13 – Classification method from 0 to 2 for the several parameters, being 1 equivalent to an
average insufficient performance, 2 to satisfactory and 3 to efficient. .................................................. 50
Table 14 - Visual inspection of the colmated corks according to the various parameters. ................... 51
Table 15 - Filter papers after filtering the alcoholic solutions containing the colmated corks residue with
and without compression in the corking machine. The loosen adhesive (mg) is also presented. ........ 53
Table 16 - Agglomeration adhesives formulation.................................................................................. 54
xiii
Table 17 – Agglomeration adhesives testing. Symbols: Applied () and not applied (X) for
agglomeration. ....................................................................................................................................... 54
xiv
Abbreviations
2-EH 2-Ethylhexanol
AA Acetic anhydride
AV Acid value
CS Cork Supply Portugal SA
DEG Diethylene glycol
DMAP 4-(Dimethylamino)pyridine
EG Ethylene glycol
FR FabriRes – Produtos Químicos, Lda
Gly Glycerol
HDI Hexamethylene diisocyanate
IPDI Isophorone diisocyanate
KOH Potassium hydroxide
MDI Diphenylmethane diisocyanate
MQ MikroQuímica – Produtos Químicos, Lda
N Normality of the titrant
OH Hydroxyl
OHV Hydroxyl value
PEG Polyethylene glycol
PG Propylene glycol
PTSA p-toluenesulfonic
PU Polyurethane
SA Sulphuric acid
TDI Toluene diisocyanate
THF Tetrahydrofuran
xv
1
1. Introduction
Motivation and objectives
In recent years, a huge effort has been made by the cork industries to continuously replace the
components present in cork adhesives formulations derived from the petrochemical exploration, not only
because the legislation on materials in contact with food got more strict over the years, but also because
the market is increasingly seeking for environmentally friendly and sustainable materials.
Not so recent is the problem of the cork sub-products. A large portion of these is usually used in the
production of other types of corks. The remaining sub-products are simply incinerated or landfilled,
representing an additional cost.
Liquefaction has been shown as an effective thermochemical process to convert lignocellulosic
materials into liquid products. From its several applications, biofuels and adhesives are the main studied
fields in this subject [1].
The purpose of this dissertation is to match these two problems faced by the cork industry and to use
the liquefaction process in order to overcome them: by liquefying the cork residues one can produce a
liquid product that can be latter used as a component for the production of cork based polyurethane
adhesives.
Cork
It is believed, that cork was firstly used in the 3rd century BC as amphorae closures to preserve wine.
Although, only in the 17th century, cork stoppers were introduced in the wine industry by the monk Dom
Pérignon as an alternative for the ineffective wooden ones. [2].
Cork is extracted from the cork oak (Quercus Suber L) as it corresponds to the bark of the tree which is
harvested periodically (usually every nine years) in the form of boards (Figure 1) that have an adequate
thickness for the production of cork stoppers. The cork oak is an evergreen tree that as bark regeneration
capability. Therefore, it can be exploited during its life span resulting in a completely sustainable
material. This tree can usually be found in Mediterranean areas such as the Iberian peninsula (Portugal
and Spain), southern France, Italy and North of Africa [3].
2
Figure 1 - Cork harvesting. [2]
Cork Market
Cork oak forest can be found in several Mediterranean countries, accounting for a total area of 2.139.942
hectares. Portugal holds 34% of this area, matching to 736.775 hectares (Table 1) [4]:
Table 1 - Cork oak forest, percentage of area by country. [4]
Country Area (hectares) Percentage (%)
Portugal 736.775 34
Spain 574.248 27
Morocco 383.120 16
Algeria 230.000 11
Tunisia 85.771 4
France 65.226 3
Italy 64.800 3
With a production of 100 thousand tons of cork in 2012, Portugal is the world production leader,
equivalent to 49.6% of the global annual production of 201 thousand tons (Figure 2). The global exports
present a value of 1.305,9 millions of euros, wherein Portugal reached exports of 834.3 million of euros,
corresponding to 63.9% of the global exports [4].
3
Figure 2 - Cork production by Mediterranean country (2012). [5]
From these exports, the principal destination sector of the cork products is the wine industry (66.4%),
followed by the construction sector (24.5%) (Table 2).
Table 2 – Cork sales (exports) by product (2013). [4]
Type of exported product Percentage
Natural cork stoppers 42.02
Other types of stoppers 26.37
Floor and wall coverings, insulation, etc. 23.72
Other cork articles 7.06
Blocks, plates, sheets, strips, etc. 0.83
Of the overall export of Portuguese goods, 2% corresponds to the cork commerce which is equivalent
to 699.6 million euros on the trade balance.
The exploitation of this market results on cork sub-products like crushed and granulated cork and cork
powder. Estimates say that solely in the production of cork-stoppers, about 25-30% of cork powder is
produced as a side product, which was about 25-30 thousand tons in 2012. Although most of these sub-
products are used for agglomerated cork, incinerated or simply landfilled, the exportation of 37
thousands of tons, equivalent to 35,2 millions of euros, was attained for the construction business [4].
4
Cork Stoppers
Cork stoppers are the main focus of the cork companies due to the demand of the wine industry, and in
a smaller amount the sparkling wines and liqueurs industry. These corks are categorized by its quality
classes, according to the porosity and heterogeneity of the cork present on the tops and on the body of
the cork.
Natural corks (Figure 3) are extensively used for wines, presenting different dimensions and different
quality classes. In Portugal, nine different quality classes are considered for the natural corks: “flor,
extra, superior, 1.ª, 2.ª, 3.ª,4.ª,5.ª and 6.ª”.
Figure 3 - Natural corks. [6]
The natural corks with lower quality are not usually commercialized due to their ineffective sealing. In
order to use this resource as an effective stopper, these stoppers are often colmated (Figure 4) so they
can still be sold for a lower price. The colmation process is based on the penetration of an approved
adhesive and cork powder in the cork pores. These corks are usually classified in A, B, C (or I, II, II).
Figure 4 - Colmated corks. [6]
Multi-Piece corks are usually manufactured with two or more pieces of natural cork connected by an
approved glue. They are usually produced with cork strips that are too thin to produce one-piece natural
cork stoppers. The classification is similar to the natural corks.
5
Besides the natural corks, after punching the cork boards some cork powder and scraps result. These
scraps and lower quality boards are then shredded in order to obtain granulated cork, which can be
used to produce other types of corks.
Figure 5 - Punched cork board (left) and granulates (right). [7]
The granulated cork can be used to produce uniform and cheap agglomerated corks (Figure 6) by
using an approved agglomeration adhesive. In general, these corks are not used for wines where the
sealing period does not exceed one year. The general classification usually refers to the size of the used
granulates and also the type of surface finishing.
Figure 6 - Agglomerated cork. [8]
From the granulated cork and punched discs from thinner cork boards, technical corks can be
produced (Figure 7). These corks are usually used for wine bottles that are consumed in a period from
two to three years. The classification is the same as for the colmated corks (A, B, C; according to the
quality of the disks) and the designation depends on the number of disks: 1+1 technical corks for a
granulated cork with 2 disks in both ends, 2+2 with 2 disks in each end, and 2+0 for a granulated cork
with 2 disks just in one side.
6
Figure 7 - Technical cork. [6]
Also considered a technical cork, the champagne cork (Figure 8) has a larger diameter in order to
contain the high pressures in gasified wine bottles. These stoppers are usually graded as “Extra”,
“Superior”, 1st or 2nd.
Figure 8 - Champagne cork. [6]
Capsulated corks (Figure 9) are natural or colmated stoppers that are attached to a capsule that can
be made by different materials. These corks are often used in spirits, liquors and fortified wines, where
they can be easily reused. Their classification usually relies on the size of the cork and the type of
capsule.
Figure 9 - Capsulated cork. [6]
Cork cellular structure
The structure of natural cellular materials was primarily studied by Robert Hooke (1635-1703) [3], where
he first chose cork as the study material. Cork is a cellular tissue with closed cells with thin walls,
arranged without intercellular space, being the interior of the cells hollow and containing air inside. It
7
presents an alveolar structure (Figure 10), whit hexagonal prisms (Figure 10a), similar to a honeycomb.
In the axial and tangential directions the cells reveal a rectangular shape with a base-to-base packing
in column (Figure 10b), resulting in the classification of cork as a transversally isotropic material since
the directions perpendicular to the radial direction are nearly equivalent. Typical cell dimensions for
different growing periods are shown in Table 3.
Figure 10 – (Left) Directions on cork relatively to the trunk of the tree (Right) SEM micrographs of natural cork in
the radial section (a) and tangential section (b). [9]
Table 3 - Cell dimensions of cork cells during different periods. [9]
Cell dimensions Early cork Late cork
Prism height (µm) 30-40 ~ 10
Prism base edge (µm) 13-15
Average base (cm2) 4-6 × 10-6
Wall thickness (µm) 1- 1.5 ~ 2
Number of cells per cm3 4-7 × 107 10-20 107
Cork also contains lenticular channels disposed in the radial direction, which are cylindrical and hollow.
The volume fraction of these channels varies according to the cork type and can dictate the industrial
quality of the corks.
Chemical composition
The specific properties of cork mainly arise from its chemical composition. These properties depend on
factors like geographic origin, climate and soil conditions, genetic origin, tree dimension, age (virgin or
reproduction) and growth conditions.
The cells walls of cork are, like other natural tissues, composed of two different components: structural
components and non-structural components. Structural components are natural polymeric
8
macromolecules that confer shape and most of the physical and chemical properties of the cells.
Suberin, lignin and the polysaccharides cellulose and hemicellulose are known as this type of
components. Non-structural components cover extractable and inorganic components. These
extractable components often are low molecular mass compounds that are soluble and may be
extracted from the cells with adequate polarity solvents, without damaging the cell structure. In cork,
extractable components are usually classified as waxes and phenolics while the inorganic compounds
are usually indirectly accounted by the ashes content.
The structure of cork is different in several regions [3] but it can be related to a typical lignocellulosic
material as follows (Figure 11).
Figure 11 – Structure of cork, based on a typical lignocellulosic material. Adapted from [10].
Figure 12 presents the average chemical composition of virgin and reproduction cork. An increase in
suberin and extractable content in regenerated cork is noticed [9].
Figure 12 - Medium chemical composition of virgin and reproduction cork of 10 trees. [3]
Suberin 35.2%
Lignin22.4%
Polysaccharides21.3%
Extractables 16.9 %
Ashes0.9%
Virgin cork
Suberin39.4%
Lignin24%
Polysaccharides19.9%
Extractables14.2%
Ashes1.2%
Reproduction cork
9
1.6.1. Suberin
The main compound present in the cellular cells is suberin (Figure 13), which is a biopolymer with lipid
nature and a polyester structure, responsible for the low permeability of cork.
Figure 13 - Proposed structure for suberin. [9]
The concept of suberin is restricted to an individualized polymer with a polyaliphatic and polyphenolic
structure [3], that also contains peripheral bonds with the aromatic polymers in the cellular walls of cork.
1.6.2. Lignin
Although the structure of lignin is not fully established yet, as the connection with other cell walls
components, it is well known that lignin is a polymer with aromatic nature and a supramolecular
amorphous structure. Lignin is produced through the monomers of coniferyl, sinapyl and p-coumaryl
alcohols (Figure 14), which, after the introduction in the lignin polymer, are identified as guaiacyl,
syringyl and p-hidroxiphenyl subunits, respectively, by their aromatic ring structure.
Figure 14 – Monomers present in the lignin biosynthesis. [10]
10
Cork lignin belongs to the guaiacyl type due to its high content of 94-96% guaiacyl units. It also contains
2-3% of 4-hydroxyphenyl and 3% of syringil units [3].
Figure 15 – Model for the Lignin structure in cork. [3]
It is proposed [9] that the ligno-cellulosic matrix bonds with the aromatic domain of suberin through the
dicarboxylic acid and hydroxyl acids by ester bonds, and that the waxes interact with the aliphatic area
of suberin (Figure 16).
11
Figure 16 – Model for the linkage of the phenolic region of suberin with the ligno-cellulosic matrix and the
aliphatic region with the waxes. [9]
1.6.3. Polysaccharides
The polysaccharides give structural rigidity to the cork cell, preventing the cells from collapsing.
Polysaccharides present in cork are cellulose (homopolymer) and hemicelluloses (heteropolymer). Cork
contains much less polysaccharides than wood with a content of 20%, being glucose and xylose the
highest fraction (Table 4).
12
Table 4 - Average monosaccharides fraction. [3]
Monosaccharide Structure % of the total
Virgin cork Reproduction cork
Glucose
50,7 ± 6,4 45,4 ± 6,2
Xylose
34,0 ± 5,1 32,3 ± 5,5
Arabinose
6,4 ± 0,8 13,2 ± 2,3
Galactose
3,6 ± 0,9 5,1 ± 2,6
Mannose
3,6 ± 0,7 3,2 ± 1,1
Rhamnose
1,7 ± 0,4 0,8 ± 0,1
Cellulose is a sequence of glucose monomers connected by glycoside linkages (Figure 17). Cellulose
macromolecules are set parallel to each other, in a compact and organized fashion, with hydrogen bonds
between adjacent monomers and also within the macromolecule itself, resulting in crystalline fibrils [3].
Having the highest degree of polymerization and the occurrence of crystallization, cellulose represents
the cork component that is harder to cleave.
13
Figure 17 – Cellulose structure consisting of glucose monomers connected by glycoside linkages. [9]
Hemicellulose differs from cellulose due to its branched structure, smaller degree of polymerization and
mainly due to its monomeric composition. Hemicellulose contains different monosaccharides: pentoses
(xylose, arabinose) and hexoses (glucose, mannose, galactose, rhamnose, glucuronic acid), which may
also contain methyl and acetyl groups. Since hemicellulose as a non-crystalline nature it is also more
prone to deformation.
1.6.4. Extractable components
Extractable components are not usually linked to the main structure of cork resulting in an easy
extraction with solvents. Extractable content ranges from 14 to 18%, which depends mainly on the type
of cork: virgin cork usually has a bigger extractable content [3]. The two most significant components
are waxes and phenolic compounds, which include the chemical families of flavonoids and tannins [9].
1.6.5. Inorganic components
Ashes usually fulfill 1-2% of the cork components, wherein 60% is calcium and the remaining are smaller
values of phosphorus, sodium, potassium and magnesium. These elements are usually found more
abundantly in the exterior layer of cork, where it can reach 10%.
Biomass conversion
In the recent decades, alternative ways to produce materials from biomass have been discussed due to
their non-dependence on petroleum, renewability, accessibility and low environmental impact derived
from its exploitation. Two main classes of technologies are used to obtain bio-based products as shown
in Figure 18: the thermochemical and the biochemical conversion. Biochemical conversion relies on the
enzymatic conversion into ethanol and other depolymerisation by-products and thermochemical
conversion can be further divided in four different categories: combustion, pyrolysis, gasification and
liquefaction, being the last the main focus of this dissertation.
14
Figure 18 - Classification of biomass conversion technologies.
Combustion refers to the burning of fuel in a boiler, furnace or stove to produce heat (800-1200 ˚C).
Pyrolysis is the thermal decomposition of organic matter without air or oxygen at high temperatures
(400-600 ˚C) and subsequent conversion into liquid and gaseous products that can be used for energy
production. Gasification involves pyrolysis and combustion in an oxygen-deficient atmosphere where
thermal decomposition occurs resulting in non-condensable fuel or gases (800-1200 ˚C) [11].
The definition of liquefaction has not remained constant through the years, lately it is used to describe
a thermochemical conversion process used to produce a liquid from organic matter at relatively low
temperature. Liquefaction has been proven to be an attractive method to effectively convert materials
composed of natural polymers (e.g cellulose, lignin, suberin and starch) into fragments of small
molecules. By doing so, one can add value to agro-forestry by-products (e.g. wood residues [11–17],
bagasse [18–20], wheat straw [21,22] and corncob [24]) and end-of-live materials recycling (e.g. paper
[18]). This is a major interest of the polyurethane industry since these fragments are unstable and
reactive and can easily re-polymerize and re-condense. The result is a favourable raw material for the
production of plastics, adhesives or coatings via conventional polymerisation techniques. To the
liquefaction products one usually call bio-polyols, which are a mixture of many different compounds that
own its reactivity to the large amount of highly active hydroxyl groups that can be accounted by the
hydroxyl number. This feature is often taken into the preparation of polyurethanes so that the proportions
of the raw material can be calculated for the desired properties.
There are four main types of liquefaction: direct liquefaction at high temperatures (300-500°C) and under
pressures (5-10 MPa) without a catalyst [25], in sub and supercritical solvents (e.g. water[26], ethanol
[27], [28], phenol [29] and methanol [30]), in ionic liquids [10], [31]–[34] and in reactivate solvents and
catalyst. For the later, the used solvents are usually cyclic carbonates (ethylene carbonate [35], [36],
propylene carbonate [36]), phenol (usually used to achieve phenol-formaldehyde resins [37]) and
polyhydric alcohols (ethylene glycol (EG) [16], [17], [23], [38], [39], diethylene glycol (DEG) [40], [41],
Biomass Conversion Technology
Biochemical Conversion
Thermochemical Conversion
Combustion
Pyrolysis
Gasification
Liquefaction
15
propylene glycol (PG) [41], polyethylene glycol (PEG) [12], [19], [21], [22], [35], [42], [43], [44], glycerol
(Gly) [19], [25], [40], [45], [44]), which are usually used to obtain polyurethane foams.
Recently much attention has been given to liquefaction of bioresources using polyhydric alcohols due
to its high yields and low-cost equipment and reagents, resulting in relatively cheap products. This type
of liquefaction is often conducted at temperatures in the range of 150-180˚C, at atmospheric pressure
and usually with the presence of a catalyst. The liquefaction can be either acid- or base-catalysed with
the former being more common since the base-catalysed liquefactions need higher temperatures (250
˚C) to achieve liquefaction yields comparable to the obtained by acid-catalysed [46]. However, base-
catalysed liquefactions are less prone to metal equipment corrosion.
The liquefaction of lignocellulosic materials in polyhydric alcohols combines the reactions of solvolysis,
depolymerisation, thermal degradation and hydrolysis [19], [47] through the following steps: solvolysis
resulting in micellar-like substructures; depolymerization to smaller and soluble molecules; thermal
decomposition leading to new molecular rearrangements through dehydration, decarboxylation, C - O
and C - C bond ruptures and hydrolysis of glycosidic bonds;
The reaction of hydrolysis cleaves various chemical bonds, like the glycoside bonds in cellulose,
producing smaller molecules named glycosides. The liquefaction of hemicellulose, lignin, suberin and
amorphous cellulose occurs in the beginning of the liquefaction process due to their amorphous
structure which is easily accessible to the liquefaction solvents, corresponding to a fast liquefaction
stage. The following stage is slow and depends mostly in the amount of crystalline cellulose due to its
packed structure that is less accessible to the solvents [19], [48], [49], [50]. Cellulose is initially
converted to glucosides which are then hydrolysed to levulinates [35], [38] (Figure 19). These
intermediate molecular fragments further react with the alcoholic solvents. Monohydric solvents can only
combine with a fragment with one hydroxyl group, but a solvent like DEG (a di-alcohol) or Gly (a tri-
alcohol) can react with multiple fragments. Thereby, the molecular weight of products is increased and
the formation of heavy oil and residue is promoted with polyhydric alcohols.
Figure 19 - Acid-catalyzed liquefaction of cellulose in EG. Adapted from [18].
16
The recondensation reactions among the liquefaction products compete against the liquefaction
reactions during the biomass liquefaction process and when dominant they lower the efficiency of the
reaction. For example, lignin produces free radical fragments which can easily condense after a certain
reaction time, resulting in insoluble residues [35], [38]. In order to avoid the negative effects of these
recondensation reactions, optimization of liquefaction parameters can be done, such as liquefaction
temperature and time, catalyst and solvent/biomass ratio. This recondensation effects can also be
minimized by using an ultrasonic process which inhibits the formation of large molecules by keeping the
reactive segments apart combined whit short reaction times [51], [52]. A more effective liquefaction
heating might also be achieved by the application of microwave heating [14], [41]. A summary of some
studies on liquefaction and the used parameters is shown in Table 5 and 6.
Table 5 – Summary of the parameters used in the liquefaction procedures. The values in the time (t), Temperature
(T), reagents and catalyst columns correspond to the base or higher yields conditions; Unless indicated, the values are presented in mass percentage; (1) Catalyst % calculated on the solvent basis; (2) After liquefaction, the polyols were produced by reacting the glycosides with soy, castor and rice-bran oil; (3) 1 g of Maleic acid anhydride (Ma) was firstly used and subsequently Phthalic acid anhydride (PA) or trimellitic acid anhydride (TMA) were added from 0 to 0.7g; (4) Microwave heating; (5) Heating in autoclave with hot compressed ethanol (ET).
Authors Biomass:solve
nt ratio
Reagent
s Catalyst (1)
t
(min
)
T
(˚C
)
OHV
(mg
KOH/g)
Max.
conv.
(%)
Ugovše
k et al.
[17]
Black poplar
sawdust
(1:1, 1:2, 1:3,
1:4, 1:5)
EG 3 % SA 150 18
0
667 (1:1)
1270 (1:3) 91 (1:3)
Mishra
and
Sinha
[18]
5g of de-inked
paper/150mL (2) EG
0.5 % SA
0.5 % PTSA 150
15
0 200-406
80
93
Briones
et al.
[24]
Rapeseed cake
(0.2)
Date seeds
(0.25)
Olive stone
(0.25)
Corncob (0.3)
Apple pomace
(0.3)
PEG:G
(4:1) 3 % SA 60
16
0
586
395
496
504
428
84
96
92
91
97
17
Kunaver
et al.
[40]
Spruce wood
meal (1:3)
G:DEG
(4:1) 3 % PTSA 120
18
0 1043 78
Table 6 (cont.) – Summary of the parameters used in the liquefaction procedures. The values in the time (t), Temperature (T), reagents and catalyst columns correspond to the base or higher yields conditions; Unless indicated, the values are presented in mass percentage; (1) Catalyst % calculated on the solvent basis; (2) After liquefaction, the polyols were produced by reacting the glycosides with soy, castor and rice-bran oil; (3) 1 g of Maleic acid anhydride (Ma) was firstly used and subsequently Phthalic acid anhydride (PA) or trimellitic acid anhydride (TMA) were added from 0 to 0.7g; (4) Microwave heating; (5) Heating in autoclave with hot compressed ethanol (ET).
Kržan
and
Kunaver
[41]
Poplar, alder,
linden or beech
sawdust (1:5)
PG, EG
or DEG
10 % MA +
PA or TMA
(3)
20
Apr
ox.
28
0
(4)
500-600 100
(+0.5 PA)
Xu et al.
[42] Sawdust (1:5,8)
G:ET
(1:2)
0.3 % SA,
NaOH,
PTSA or PA
60
25
0
(5)
635 97,8
Tohmur
a et al.
[13]
Sugi wood meal
(1:3)
PEG:G
(7:3) 3 % SA 300
15
0 219-273 91.3
Chen
and Lu
[22]
Wheat Straw PEG:G
(8:2) 2 % SA 80
15
0 250-430 ~100
Wang
and
Chen
[23]
Wheat Straw
(1:6)
EG:G
(5:1) 3 % SA 120
14
0 46 87
Ye et al.
[43]
Bamboo shoot
shell (1:6)
PEG:EG
(3:1, v/v) 4% SA 80
15
0 - 99.8
Soares
et al.
[45]
Cork (1:5) PEG:G
(9:1) 4% SA 60
15
0 130-223 71
18
Lee and
Lin [44]
Taiwan acacia
and
China fir (1:3)
PEG:G
(9:1) 9% SA 90
15
0
310
287
80.6
93.5
Maxime
et al.
[25]
Cork (1/10) PEG:G
(3:1)
3% SA or
NaOH 150
15
0 - 93
Zhang et
al. [48] Bagasse (1:3)
PEG:G
(3:1) 3% SA 120
15
0 310-510 98.9
Zhang et
al. [19]
Chinese
Eucalyptus EG:G 3 % SA 120
16
0 - ~95
Maxime et al. [25] liquefied cork with a catalyst to glycerol ratio of 3:100. It was shown that for an
increase in reaction temperature from 150 ˚C to 200, the reaction yield didn’t increase when using SA,
contrarily to NaOH, which proves the efficiency of a basic catalyst only at higher temperatures (200 ˚C).
According to the authors this occurs due to the inability of SA to catalyse the liquefaction of cork suberin,
leading to liquefaction yields around 47%. However, while using NaOH at 150 ̊ C with different G to PEG
ratios, the LY was constant (from 40 to 50%) while for SA the LY increased from about 40% to 93% with
G to PEG ratios from 1:9, 1:3 and 1:1. The addition of PEG thereby showed the ability to aid the
liquefaction of suberin under acidic conditions.
A study on cork was made by Soares et al. [45] that demonstrates a liquefaction yield of 79% in a solvent
mixture of PEG and G at 150˚C with 4% SA as catalyst. This study shows that for temperatures higher
than 150˚C, the decomposition of cork compounds (mainly suberin, lignin and cellulose) was promoted
simultaneously with the condensation of the liquefaction intermediates. This also happens for the
reaction time when it is increased from 60 to 120 minutes, reducing thereby the reaction yield. This
effect was also observed by Zhang et al. [18, 48]. They could prove that out of weight a ratio of 1, 2, 3
and 6 % of SA, 3% seems to be the most appropriate due to the higher LY. Opposed to that 6% of SA
that leads to condensation, thereby decreasing the LY.
Zhang et al. [53] fractionated the liquefied product of bagasse and classified the fractions in water-
soluble, acetone-soluble and insoluble residue fractions. It was shown that acetone-soluble fraction
showed higher Mw due to lignin derivatives.
19
Figure 20 – Procedure for liquefied products separation. [53]
This presence of a wide spectrum of different compounds in biomass liquefaction-derivatives indicates
the complex nature of chemical reaction that occurs and competes against each other simultaneously.
Synthesis of adhesives from liquefied biomass
Polymeric polyols, which mainly consist of polyether and polyester polyols, are used to produce
polyurethanes (PUs) through their condensation polymerization reactions with isocyanates. Even
though other types of resins (like phenolic and epoxy) have already been synthesized, this thesis will
focus on PUs synthesis methods and applications. Polyols from biomass liquefaction are usually suited
for the production of rigid and semi rigid polyurethane foams [14], [22], [23], [54], but the production of
polyurethane adhesives has also been reported.
1.8.1. Polyurethane adhesives for cork stoppers
A large portion of the adhesives used for agglomerated and colmated corks are produced by reacting
an isocyanate and a polyol. Isocyanates are compounds that usually contain two or more isocyanate
groups (-NCO) per molecule whereas a polyol contains two or more hydroxyl groups (-OH) per molecule.
Figure 21 - Typical reaction to obtain a polyurethane. [55]
20
Most of the isocyanates are difunctional, they have two isocyanate groups per molecule like toluene
diisocyanate (TDI), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI) and
isophorone diisocyanate (IPDI). Aromatic isocyanates like MDI and TDI are usually more reactive than
the aliphatic isocyanates such as HDI and IPDI.
The polymerization reaction can also take place in the presence of water, even if it is cork’s moisture,
with water and an isocyanate end (Figure 22 A and B), forming a carbamic acid group, which rapidly
decomposes into an amine group and carbon dioxide (Figure 22 C). It should be noted that the molecule
present in Figure 22 C is an intermediary species and thereby is present in less quantity during the
reaction. The polymerisation occurs when the amine group then reacts with another isocyanate group
(Figure 22 A+C).
Figure 22 - Polymerization of the polyurethane pre-polymer. [55]
All the reaction products are expected to be polymeric and have a molecular weight above 1000g/mol
[55], raising no public health issues since they are not absorbed in the gastro-intestinal tract.
1.8.2. Bio-polyols polyurethane adhesives
Juhaida et al. [56] prepared a wood laminating adhesive from liquefied kenaf core with PEG1000 and
glycerol (3/15) at a temperature of 160 ˚C for 90 min. A weight ratio of kenaf core/solvent of 1/18 was
used along with 3 % of the solvents weight as SA. The polyols were then solubilized in dioxane and
reacted with TDI at 50-60 ˚C for 2 h. Subsequently, 1,4-butanediol was added and the mixture raised to
70-80 ˚C and kept for 3h. The final formulation comprised weight ratios of 55% of polyol, 42.5% TDI,
2.5% 1,4-butanediol, and 1% amine catalyst. The resin was tested on rubber wood blocks which were
cured for 24h and subsequently conditioned at 20 ± 2 ˚C and 65 ± 5% relative humidity for one week.
Carbon dioxide bubbles formed during the curing, resulting in a shear strength of 2.9 MPa when
compared to a commercial one of 4.6 MPa, which also as higher viscosity.
21
Mishra and Sinha [18] prepared PU adhesives using cellulosic waste paper and castor oil. The waste
paper was used in a glycolysis process, which owes its name to the glycosides obtained with this
liquefaction. The paper was first de-ink with 1.5% NaOH solution and dried at 90 ˚C for 24h. Then it was
mixed with 150mL of ethylene glycol (EG) and 0.5% of the EG as p-toluenesulfonic acid catalyst (PTSA)
and heated for 2.5h at 145-150 ˚C, representing a final glycosides yield of 93%. In order to prepare the
adhesive, mixtures with different ratios of glycosides and castor oil were reacted at 220-250 ˚C for 1 h
with lithium hydroxide catalyst, which resulted in different OH values. The polyols were then mixed with
TDI and catalyst for 1 min. It was found that polyols with higher OH values had lower viscosity and
presented higher lap shear strength due to a higher cross-linking. A NCO/OH ratio of 1.2 and curing
time of 5 days showed higher single-lap shear strength than some commercial adhesives.
Lee and Lin [44] produced polyols from the liquefaction of Taiwan acacia and China-fir in PEG and
glycerol with SA at 150 ˚C for 90 min. A weight ratio of polyhydric alcohols/wood/SA of 3/1/0.09 was
used. The PU resins were prepared with NCO/(COOH+OH) ratios of 1, 1.5 and 2 with PMDI, Desmour
L (adduct of toluene diisocyanate with trimethylol propane) and Desmodur N (trimer of hexamethylene
diisocyanate) which correspond to an aromatic isocyanate polymer, aromatic isocyanate monomer and
aliphatic isocyanate, respectively. Wet and dry bonding strength was measured, being the last in 2
different ways: immersion in water for 3 h at 60 ˚C and in boiling water for 4 h. It was shown that the gel
properties of PU resins are influenced by the type of isocyanates, the NCO/(COOH+OH) ratio and the
proportion of catalyst used. The bonding strength was also found to be higher with higher molar ratios
of NCO/(COOH+OH). Desmodur L as shown an appropriate gel time for processing, and when blend
with liquefied Taiwan acacia it showed the better bonding properties.
Wood meal pre-treated with benzyl chloride (benzylated wood) and liquefied with dibasic ester and HCl
as a catalyst at 75-80 ˚C for 3h was done by [57], [58]. PU resins were then prepared with PEG as a
plasticizer and stirred for 30min at 50 ˚C. The diisocyanate and butylacetate mixture was then added
followed by the addition of dibutylin as a catalyst and kept at 50 ˚C for 30 minutes followed by 75-80 ˚C
for 3 hours. Three different isocyanates (IPDI, HDI and TDI) and PEG with different molecular weights
were tested. TDI showed the best performance on PUs for painting applications, contrarily to HDI which
is not suitable for these systems. These PU resins displayed higher thermal stability (280 ˚C) than the
petroleum based ones (<250 ˚C) for which the addition of PEG did not show relevant effect.
After a liquefaction with PEG400 and glycerin (7/3, w/w) and SA, with a solvent/wood radio of 3/1, at a
temperature of 150 ˚C from 1.5 to 5 hours, a water based polyisocyanate adhesive was produced. This
mechanism was proposed by Tohmura et al. [13]. This adhesive was prepared by blending 100 parts of
liquefied wood with 158 parts of pMDI, and afterwards applied on a three layer plywood panels. The
solid content of the adhesive was more than 90%, higher than the usual 66% for the commercial water
based polyisocyanate adhesives, and although it presented a relatively low viscosity and lower shear
strengths than the commercial ones, the produced panels meet the criteria of the Japanese national
standard for plywood.
22
A big part of these polyurethane adhesives are not adequate for the use in the food industry.
Unfortunately, the adhesives used for colmation and agglomeration will not be reviewed here since they
remain confidential information.
1.8.3. Polysaccharides adhesive
The corks polysaccharides can be used to produce an adhesive (Figure 23) by using an isocyanate,
water and cork powder according to the formula developed by our research group, which led to a patent
[1]. Such formulations have the advantage of being water-based, thereby solvent free and safe handling.
Figure 23 – (Left) Adhesive formulation without cork; (Right) Adhesive formulation with cork.
The isocyanate acts as a cross-linker by linking the polysaccharides and water molecules as stated in
1.8.1. The chosen isocyanate was Desmodur DA-L, a hydrophilic and aliphatic based on hexamethylene
diisocyanate (HDI) (Figure 24) with an NCO content of 20% [59]. Since the isocyanate does not contain
aromatic rings and only contains 0.25% of monomeric isocyanate it is not expected to raise any public
health issues when used in articles in contact with food. Furthermore, its hydrophilic character allows it
to be water dispersible like the polysaccharides fraction.
Figure 24 - Hexamethylene diisocyanate (HDI).
Cork powder was added to promote the cohesion of the components that make up the polymeric matrix
by filling the existing porosity and increasing the surface area which promotes a more effective
connection of the various components and also acting as a load, thickening the adhesive. Furthermore,
it as an auto-adhesion character not only because of its high specific area but also due to its waxes and
23
suberin monomers that acts as binders, offering the ability to act as a binding agent of compatible
components by a chemical bond. Similar to cork powder, the polysaccharides fraction also act as a
binding agent which is even easier to homogenise since they are water soluble. It should also be noted
that the adhesion capability also depends on the particle size and on the interfacial adhesion between
the matrix and the cork.
The adhesive formulation consists on a ratio of water/polysaccharides/Desmodur Da-L/cork powder of
20/3/1.2/0.2 (w/w). This formulation is suitable for the gluing of lignocellulosic material surfaces, as cork
and wood at room temperature (15-30 °C) and can attain shear stresses of 9.4 x 10-3 Pa, being possible
to promote its adhesion by heating (hot-melt adhesives).
The compatibility of the adhesive for materials in contact with food is in agreement with the following
documents:
- Resolution ResAP (2004) 2 on cork stoppers and other cork materials and articles intended to
contact foodstuff;
- Technical document No. 1. L of substances to be used in the manufacture of cork stoppers and
other cork materials and articles intended to contact foodstuff;
- Technical document No. 2 - Test conditions and methods of analysis for cork stoppers and other
cork materials and articles intended to contact foodstuff;
- 82/711/EEC;
- 93/8/EEC;
- 97/48/EEC;
- 2002/72/EEC;
- Commission regulation (EU) No 10/2011;
- Regulation (EC) No 1935/2004.
Colmation process
As mentioned before, colmation is the process of removing the porosity of lower quality corks by
covering it with a mixture of an adhesive (approved to be in contact with food) and cork powder. This
operation intends not only to offer market value to these lower class corks by increasing its performance
and visual appearance, but also to make use of the cork powder obtained in the cork manufacture.
“MikroQuímica – Produtos Químicos, Lda.” (MQ) is one the companies that provides colmation services
to Cork Supply (CS). Here, a machine is used to test colmated corks batches before introducing the
process in the industrial scale (Figure 25). The colmation process may vary within different enterprises
and with the type of adhesive. It often starts with pre-humidification of 1500-2000 corks with 2 L of water
in a bucket in order to create an adequate substrate for the glue to spread. The humidified corks are
inserted in the upper drum (Figure 25 C), the glue is added and the blades are set to rotate for 10
minutes with a velocity of 16 rpm, which is approximately constant through the whole process. The
blades rotate in the opposite direction of the drum in order to cause the higher entropy possible so the
glue enters the pores of the corks with the impact among them and the colmation drum and blades.
24
Cork powder (65 L) and water (5L) are poured in the drum cavity and mixed for 25 minutes. After, it is
also common to add some cork powder if the pores aren’t yet covered. The colmation drum is then
opened and the corks are dropped to the lower drum for a process of dedusting for 5 minutes. This
process intends to eliminate the small granules left on the surface of the cork, which are removed
through the grid of the drum, and thereby produce a smooth surface. By subsequently closing the
chamber doors of the lower drum and heating it with ventilated air at 40/50 °C for 25 minutes the corks
are allowed to dry. Finally, the corks just have to be removed from the drum and stored in open air to
allow eventual humidity to be removed.
Figure 25 – (A) Colmation machine; (B) Mixing blades; (C) Drying drum.
A
C
B
25
2. Experimental work
Cork liquefaction
2.1.1. Materials:
Biomass:
- Cork powder (8% humidity), was provided by Cork Supply Portugal (São Paio de Oleiros, Portugal);
Reagents:
- Diethylene glycol (DEG) – Sample provided by Resiquímica (TB = 245°C, µ = 0,04 Pa.s at 25°C);
- 2-Ethylhexanol (2-EH) – Sample provided by Resiquímica (TB = 184,6°C, µ = 0,01 Pa.s at 25°C);
Catalyst:
- P-Toluenesulfonic acid (PTSA) – Sigma-Aldrich (98.5 % purity);
Solvents:
- Acetone – VWR (Technical grade, 99% purity);
- Methanol – Panreac (99,8% purity).
2.1.2. Equipment:
- Mechanical stirrer – IKA;
- Thermocouple – Omega Engineering, ;
- Temperature controller – Honeywell, ;
- Wide-necked 4L reactor;
- Reactor lid;
- Heating mantle – J. P. Selecta, Fibroman-O;
- Condenser;
- Dean-Stark separator;
- Analytical balance – Kern & Sohn (0,1 mg readability);
- Vacuum pump;
- Cellulose filter paper –Whatman, Grade 1 (11 µm pore size).
2.1.3. Method:
The liquefaction reactions were carried out in a 4L wide-necked reactor with a five-socket reactor lid
equipped with a Dean-Stark separator, condenser, mechanical stirrer and thermocouple on a heating
mantle as in Figure 26.
Before the reaction, 220g of cork were mixed with 2 Et Hex and DEG with a weight ratio of 1:3:1,
respectively. The mixture was then introduced in the reactor and mixed along with 3% of the total mixture
weight of p-toluenesulfonic acid catalyst. The chosen reaction temperature and time was 160 °C and
26
130 minutes. Aluminium foil was used to cover the reactor for thermal insulation during the reaction time,
and removed at the end to cool the reaction product to 80 °C. The dean-stark separator was used to
separate and reuse the water and 2-EH phases. Then approximately 3L of water were added in order
to separate the hydrophobic and hydrophilic products, which were left overnight in order to efficiently
permit the phase separation. Since the water soluble portion is denser it can be extracted using the
reactor tap, and filtered under vacuum in a kitasato flask fitted with a Buchner funnel with a cellulose
filter. After the first extraction, water was added, mixed, left for about 30 minutes and removed until the
water soluble portion is colourless. The hydrophilic product was then extracted from the reactor and
filtered with the aid of acetone and methanol. Both filtration products were evaporated under reduced
pressure by rotatory evaporator system at 40-50°C.
Figure 26 - Liquefaction apparatus.
2.1.4. Calculations:
After oven-drying at 120 ºC for one day, the quantity of residue was measured. The liquefaction yield
conversion (LY) was calculated on the basis of the insoluble part, using the equation [48,24]:
𝐿𝑌 (%) = (1 −𝑊𝑅
𝑊𝐶) × 100 (1)
Condenser
Dean-Stark
Reactor lid
Heating mantle
Aluminium foil
Mechanical stirrer
Temperature controller
Thermocouple
27
Where WR is the mass of the solid residue in the reaction mixture and WC is the mass of cork in the
starting mixture.
Hydroxyl value
Hydroxyl value (OHV) measures the milligrams of KOH necessary to neutralize the acetic acid obtained
from the acetylation of free hydroxyl groups per gram of the given substance, basically it is a measure
of the free hydroxyl groups concentration in a given chemical substance.
2.2.1. Equipment:
- Magnetic stirrer;
- Magnetic stirring bars;
- Burette;
- Erlenmeyer flask;
- Pasteur pipette;
- Graduated cylinder.
2.2.2. Reagents:
- Tetrahydrofuran (THF) – Fisher Chemical (99,99% purity);
- Potassium hydroxide (KOH) 0.5 N – Merck;
- 4-(Dimethylamino)pyridine (DMAP) – Aldrich (>99% purity);
- Acetic anhydride (AA) – Sigma-Aldrich;
- Phenolftalein - Sigma-Aldrich (0,5g in 50ml of ethanol)
2.2.3. Procedure:
A solution of 12.5% AA in THF solvent (v/v) along with other of 1% DMPA (w/v) in THF are added to 1g
of sample diluted in THF being then stirred for 10 minutes. Afterwards the acetylation reaction is
quenched with the addiction of water and stirred for 20 min, converting the unreacted acetic anhydride
to acetic acid. The resulting solution is then titrated with KOH, using phenolphthalein as a pH colorimetric
indicator (0,5g in 50ml of ethanol), which often leads to an equivalence point between 8.2 and 10.
2.2.4. Calculation:
The expression for the OHV calculation is the following:
𝑂𝐻𝑉 =(𝑉𝐵 − 𝑉𝑆) × 𝑁 × 56,1
𝑤𝑆+ 𝐴𝑉 (2)
Where:
28
VB – Volume in mL of analyte required for the titration of the blank;
VS – Volume in mL of analyte required for the titration of the sample;
WS – Weight of sample in grams;
N – Normality of the titrant (0,5 in this case);
56.1 – Molecular weight of KOH;
AV – Acid value of the chemical substance (determined separately and explained next).
Acid value
Acid value (AV) is a measure of the KOH necessary to neutralize one gram of chemical substance and
it is usually expressed in milligrams. This value measures the concentration of carboxylic acid groups of
a chemical compound.
2.3.1. Equipment:
- Burette;
- Erlenmeyer flask;
- Pasteur pipette;
- Graduated cylinder.
2.3.2. Reagents:
- Tetrahydrofuran (THF) – Fisher Chemical (99,99% purity);
- Potassium hydroxide (KOH) 0.1 N – Merck;
- Phenolftalein – Sigma Aldrich.
2.3.3. Procedure:
One gram of the sample is dissolved in 40mL of THF and subsequently titrated with KOH 0.1N.
2.3.4. Calculation
The expression for the AV calculation is the following:
𝐴𝑉 =𝑉𝑆 × 𝑁 × 56,1
𝑤𝑠 (3)
Humidity content determination – Karl Fischer method
The determination of the water content in the previously evaporated samples was done using the Karl-
Fischer titration method in an 831 KF Coulometer from Metrohm. It uses methanolic solution of iodine,
29
sulphur dioxide and a base as a buffer. The reactions that occur during the titration can be summarized
by the following equation [60]:
𝐻2𝑂 + 𝐼2 + [𝑅𝑁𝐻]𝑆𝑂3𝐶𝐻3 + 2𝑅𝑁 ↔ [𝑅𝑁𝐻]𝑆𝑂4𝐶𝐻3 + 2[𝑅𝑁𝐻]𝐼
In the above equation, the electrochemically generated I2 by the anodic oxidation of iodine reacts
quantitatively with H2O. An alternating current of constant strength is applied to a double platinum
electrode, for which the voltage difference between the platinum wires drastically lowers in the presence
of minimal quantities of free iodine, representing the end point of the titration.
2.4.1. Materials
- 831 KF Coulometer – Metrohm;
- 5mL syringe;
- Analytical balance – Kern & Sohn (0,1 mg readability).
Figure 27 - 831 KF Coulometer. [58]
2.4.2. Reagents
- Hydranal solution - Fluka
2.4.3. Procedure
The equipment is set at 700 rpm till it stabilizes (the older the solution the longer it takes) and a
reasonable quantity of sample is loaded in the syringe, removing the air bubbles inside. The syringe is
then place on the analytical balance and tared. Subsequently 3 drops of the sample are introduced in
the solution and its weight is introduced in the equipment. After the run the weight of the sample can be
corrected if needed and the water content can be read.
Infrared spectroscopy
MIR (Mid InfraRed) spectra of the liquefied product and respective fractions were analyzed resorting to
an FT-MIR spectrometer from BOMEM FTLA2000-100, ABB CANADA equipped with a light source of
SiC and a DTGS detector (Deuterated Tryglicine Sulfate). The used accessory was an ATR with single
30
horizontal reflection (HATR) containing a ZnSe crystal of 2mm of diameter from PIKE Technologies.
The specters in the range of 600-4000 cm-1 were collected with the BOMEM Grams/32 software.
Colmation
The colmation procedures can only be reproducible if tested in a similar colmation machine. However,
a colmation machine like the one used in MikroQuímica can cost around 20 000 €, which presents an
associated cost that one cannot afford. Based on the machine used in MikroQuímica a colmation mixer
was then constructed for the pilot colmation procedures based on the following initial drafts:
Figure 28 - A) Colmation mixer cross section; B) Grid drum cross section; C) Plastic cover and fan heater cross
section.
The main drum (Figure 28 A and Figure 29 A) was built using a 35 cm high plastic bucket, with one
hole in the center of the basis and another hole in the middle of the cover where the rotational axis is
set. Another hole was made in the middle of the bucket for the introduction of the mixtures without
needing to open the drum from step to step, and covered during the procedure with a rubber stopper.
The four blades are screwed in the metal axis in different directions and inclinations (Figure 29 B) in
order to cause the maximum entropy possible. The cover was tightly screwed in order to serve as the
second support since the blades axis is the one attached to the overhead stirring motor. The mixing
drum is set on a plastic box with two holes in each side in order to support the axis. During the
procedures the motor is set at 40 rpm, the closest and lowest possible rotation compared to the velocity
used in MQ. Opposite rotations of the drum and the blades was not possible due to the friction offered
by the corks, which could not be overcome by the weak rotational power of the motor.
C B
A
31
Figure 29 - A) Colmation mixer drum; B) Blades axis inside the drum.
The same plastic box is used for the support of a grid drum (Figure 30 A, B and C) which also covers it
in order to maintain the temperatures inside the box. This box as a side aperture where the air produced
by the ventilation heater comes in. The grid drum as a grid connected to two plastic covers screwed to
a steel axis that is also attached to the motor which is set at the same rotation. In order to introduce the
corks, one of the covers is unscrewed. The temperature allowed by the fan heater is between 50 and
60 °C, which can be supervised with a temperature controller linked to the heater or simply with a
thermometer (Figure 30 D and E).
Figure 30 - A) Grid drum and motor; B) Grid drum position inside the plastic box; C) Plastic cover, fan heater and
temperature controller.
A B
A B
C
32
2.6.1. Equipment
- Colmation equipment
- Analytical balance – Kern & Sohn (0,1 mg readability);
2.6.2. Materials:
- Cork stoppers (class 6, 24x45 mm)
- Cork powder;
- Hydrocarbons fraction;
- Desmodur DA-L (hydrophilic aliphatic polyisocyanate based on HDI) – Bayer (20% NCO content,
0.25% monomeric isocyanate, viscosity of 3 MPa.s)
- Distilled water;
- Rhodamine B – Keystone
Boiling water test
The present test is often used in the cork industry to determine the attachment efficiency of the colmation
glue. By inserting the colmated/agglomerated corks in boiling water it is expected that if the adhesive is
not adequate it will detach/peel from the cork.
2.7.1. Equipment
- Wide-necked 1L reactor;
- Heating mantle - J. P. Selecta, Fibroman-O;
- Flexible metallic net.
2.7.2. Procedure
The corks are inserted in a reactor and covered with a metallic net in order to keep them constantly
covered by water. The corks are then covered with water and left for 1h after the water starts boiling.
Residues content
The following procedure was conducted in CS to account the solid residues in produced corks, i.e. the
adhesive content that did not adhere to the corks body or that becomes loose after compression in the
corking machine.
2.8.1. Equipment
- Laboratory oven
- Desiccator
- Stirring plate
- Bottling machine - Bertolaso
33
2.8.2. Materials
- Ethanol P.A.
- Tartaric acid
- Cellulose filter paper (11 µm pore size)
2.8.3. Procedure
A residues extraction solution was used as an alternative for wine and was firstly prepared by measuring
180 mL of distilled water in a graduated cylinder, adding 20 mL of ethanol and mixing with a glass rod.
Then 4/5 drops of tartaric acid are added till the pH of the solution ranges from 3 to 4. 100 mL of this
solution is added in a 250 mL Erlenmeyer flask and 5 corks are introduced. The same containers are
placed in the stirrer board at 150 rpm for 30 min.
Cellulose filters were placed over watch glasses and transferred to the laboratory oven under 50 ºC for
30 minutes and subsequently transferred to the desiccator and left for 30 min. These sets were then
weighted (mi). After removing the Erlenmeyer flasks and filtering the content under vacuum the sets of
watch glasses and filters were once again weighted (mf).
The procedure was repeated for previously compressed corks in the bottling machine with the jaws at a
distance of 15.5 mm. The filter papers, corks and white paper under the corking machine were then
observed in order to verify if there was detachment of the gluing material.
Agglomeration glue preparation
“FabriRes – Produtos Químicos Lda” (FR) is a specialist in the production of adhesives for agglomerated
corks. The following method is typically used in the company to produce bio-based agglomeration glues.
An agglomeration adhesive is said to be adequate for the production of corks if the viscosity lies between
4000 and 8000 cP and if the gel time is lower than 15 min.
2.9.1. Equipment
- Thermometer
- Balance
- 600 mL beaker
- Mechanical stirrer
- Hot plate – IKA®, Yellow line, Model MSHB
- DV-E Viscometer - Brookfield
2.9.2. Materials
- Cork polyol
- Phosphoric acid (>85% purity)
- Acetone (>99.4 % purity)
34
- Desmodur H (monomeric aliphatic diisocyanate based on HDI) – Bayer (49.7% NCO, viscosity of 3
MPa.s)
- Desmodur I (monomeric cycloaliphatic diisocyanate based on IPDI) – Bayer (37.5% NCO, viscosity
of 10 MPa.s)
- Desmodur (TDI)
- DBTL – KOSMOS 19.
2.9.3. Procedure
The polyols were mixed with acetone and phosphoric acid in a 600 mL beaker and heated till 40 °C. At
this temperature the isocyanates were added and the mixture was heated till 85 °C and left for 3 hours.
After this time the mixture was left to cool 20°C to and its viscosity, NCO value and gel were analyzed.
If the properties were reasonable the glue was applied for agglomeration.
Agglomeration
Agglomeration uses cork granulates with different granulometries to produce agglomerated corks along
with an approved adhesive. The following method was adapted from the one used by FR for the
production of two agglomerated corks with granulated cork. The corks produced with this method are
considered acceptable if their properties fall into the ranges bellow:
Table 7 - Adequate range for different properties of agglomerated corks.
Density (kg/m3) 260-300
Length (mm) 47,2 – 48,7
Diameter (mm) 26,6 – 26,9
Weight (g) 6,5 – 7,0
2.10.1. Equipment
- Corks molds and press;
- Laboratory oven;
- Analytical balance;
- Hammer;
- Caliper.
2.10.2. Materials
- Fine granulated cork (0,5 - 2mm);
- Cork based adhesive.
35
2.10.3. Procedure
A weight of 12g of granulated cork is inserted in a 600mL beaker and 3g of adhesive are subsequently
added and stirred till the mixture is homogeneous. The metal cylinder is then attached to the open mold
(Figure 31 C) and 7,5g of the mixture are introduced with the aid of a funnel. The mold is then placed
in the press and screwed for compression (Figure 31 D). With a hammer, the mold aperture can be
closed and it can be inserted in the oven at 120 °C for 1 h so the glue can cure. The mold is then
removed from the oven, opened and with a hollow base and a screw press, the cork can be extracted
from the mold (Figure 31 E).
Figure 31 - A) Open mold; B) Closed mold; C) Mold with metal cylinder and funnel; D) Mold press; E) Cork
extraction.
NCO Content
The following method is used by FR to determine the content of free isocyanates groups based on the
standard ASTM D 2572. The method is based on the capacity that the unreacted isocyanates group
react rapidly and equitably with dibutylamine.
A
C
B
D E
36
2.11.1. Equipment
- Analytical balance
- 10 mL burette with automatic zero, graduated at 0,05 mL
- Magnetic stirrer;
- Magnetic stirring bars;
2.11.2. Materials
- Dibutylamine – Synthesis grade, Scharlau
- FIXANAL - Hydrochloric acid (titrisol ampole 1N) – Analytical grade, Fluka
- Bromophenol blue indicator
- Acetone
- Distilled water
- Toluene – Analytical grade
- Isopropyl alcohol - Makeni Chemicals
2.11.3. Procedure
A solution of dibutylamine 1N solution was firstly prepared in a 1000mL volumetric flask with 130g of
dibutylamine and the volume was completed with toluene. Secondly, a bromophenol blue indicator
solution at 0.5% in a 250 mL beaker with 0.5 g of the indicator dissolved in 100 mL of isopropyl alcohol.
In a 250 mL beaker samples from 2 to 4 g were added together with 100 mL of acetone and 10 mL of
the dibutylamine solution measured with a pipette. The mixture was stirred for 10 min on the magnetic
stirrer and 3 drops of the indicator solution were added. Titrating was then accomplished with a 1N HCl
solution. Titrating the blank was also necessary.
2.11.4. Calculation
The expression for the NCO content calculation is the following:
𝐴𝑉 =(𝑉𝐵 − 𝑉𝑆) × 4.2
𝑊𝑆 (4)
Gel time
The present method is used by FR to determine the gelation time of an adhesive. The method is based
on a polymerization reaction in the presence of water, which leads to the curing of resin. The gel time is
the time spent from the introduction of the adhesive in the oil bath till the adhesive thickens.
37
2.12.1. Equipment
- Stirring hot plate;
- Magnetic stirring bars;
- Thermometer
2.12.2. Procedure
A beaker with oil is heated with agitation thill it reaches 120 °C. Another beaker is loaded with 30 g of
the adhesive together with 1.5 mL of distilled water and homogenized for 30 sec with a glass rod. The
flask is then placed in the oil bath and with a chronometer the time from the moment the beaker is dipped
thill it loses its ability to flow is measured.
38
39
3. Results and Discussion
Liquefaction
The liquefaction process yielded a dark bio-oil (Figure 32 A) with 94% conversion rate. Such a result
shows the effectiveness of the chosen reagents, catalyst and reaction conditions developed by the
group. After filtration and concentration, the polyols extract led to a dark brown oil (Figure 32 B) whereas
the aqueous extract presented an amber colored syrup (Figure 32 C). The previously estimated yield
for the polyols and aqueous extract of 70.4 and 23.6 respectively (over the total mass used in the
reaction), respectively, based on each cork component percentage and on the yield of 94%, was in
accordance with the verified ones.
Figure 32 - A) Liquefied cork; B) Polyols extract; C) Aqueous extract.
Usually, lower liquefaction yields are presented not only for cork but also for other types of biomass:
Soares et al. [45] present a liquefaction extent of 71% for cork, Maxime et al. [25] obtained a close value
for cork of 93% although with a much lower concentration of biomass (10%:
biomass/(Biomass+Solvents)), while others presented a higher yield for other types of biomass although
with a lower concentration of biomass too.
Hydroxyl value, acid value and humidity content
The results for the hydroxyl value, acid value and humidity content are presented in the table below
(Table 8). Depending on several factors like the type of biomass, reagents and catalyst used, the OHV
may vary widely from 46 to 1270 mg KOH/g for the liquefied products, and the AV from 0 to 40 mg
KOH/g and therefore the presented values are in accordance with those reported in the literature. After
evaporation, the measured water content of the polyols and aqueous extract was 3.2 and 1.4 %,
respectively.
40
Table 8 - Acid value, hydroxyl value and humidity content for the liquefied cork and respective extracts.
Product Acid Value (mg KOH/g) Hydroxyl Value (mg KOH/g) Water content (%)
Liquefied Cork 6 725 -
Polyols Extract 0.5 271.6 3.2
Aqueous Extract 32.2 621.2 1.4
The OHV of the aqueous extract is higher than the polyols extract due to the polarity of cellulose and
hemicellulose depolimerization products (carbohydrates) and other compounds with higher polarity that
are easily extracted with water. The lower OHV of the polyols extract is due to the fatty-acids of suberin,
the major component of cork, which suffer esterification with the present hydroxyl groups in the mixture,
leading to aliphatic linear-chain esters polyols. Lignin also decreases the OHV as it is expected that a
lignin-based polymer forms due to the condensation reactions between the solubilized lignin with the
present OH groups. Other degradation and condensation reactions between the lignin degradation
fragments and 2EH may also occur, contributing to a smaller OHV of the polyols phase. It should also
be noted that the aqueous extract is also expected to contain traces of unreacted DEG and tannins,
whereas the polyols extract might contain traces of 2-EH and waxes, due to their hydrophilic character.
Even though the rotatory evaporator is not as efficient as desired, it would be expected that the water
content of the aqueous extract would be higher since it is the fraction that initially contains more water.
Although, the polyols extract forms an emulsion with water thereby making it difficult to remove.
In FR the maximum water content accepted in the polyols for the production of agglomeration glues is
0.08% since a higher water content can lead to gelification. As the polyols extract does not have the
appropriate water content, it was furthermore heated to 105 °C while stirring for 3 hours in order to
remove the water excess. After the procedure, a water content of 0.06 % was achieved although with
some recondensation.
ATR-FTIR
Figure 33 represents the obtained ATR-FTIR absorption spectra for the liquefied product (A) and
respective polyols (B) and aqueous extract (C). Every spectra presents a broad and intense band at
3500-3000 cm-1 typical of the hydroxyl groups stretching vibration, and between 2924 and 2856 the
peaks are representative of C-H stretching vibrations [61][14]. As expected, the aqueous extract as a
more prominent O-H stretching peak since it is the fraction that contains hydrocarbons and thereby
represents a higher concentration of OH groups.
41
Figure 33 - ATR-FTIR of the liquefied product and respective extracts. A) Liquefied product; B) Polyols extract; C)
Aqueous extract; D) Carbohydrates fingerprint from aqueous extract.
At 1730 cm-1 another peak is present being representative of the carbonyl groups stretching [14], [61].
In the aqueous extract this peak is more prominent than in the polyols one due to the presence of added
value compounds, furfural and levulinates, which have -C=O groups in their structure.
The intense peaks at 683-1456 cm-1 in Figure 33 D are known as the carbohydrate fingerprint region.
The peaks at 1456 cm-1 and 1215 cm-1 are related to the C-O-H bending and stretching mode,
respectively, of the CH2OH side chain of the monosaccharides thereby being more prominent in the
aqueous fraction [14]. The peak at 1351 is related to the C-H deformation in cellulose and hemicellulose
[41]. A discrete peak at 1150 cm-1 is attributed to the stretching vibrations of C-O-C in the ring structure,
in this case the carbohydrates derivatives and di- and polysaccharides with a 1→4 glycosidic linkage
[14].
Also common in carbohydrates, specifically pyranoses, at 1124 cm-1 one can observe the peak from C-
O-C asymmetric stretching of cyclic ethers [61]. The more intense and sharp peak of the spectra is found
at 1053 cm-1, which is related to the carbohydrates C-O stretching [61]. At 1011 there is a C-H bending
vibration particular from glucose, beings the first one quite common on oligo- and polysaccharides, and
another peak at 921 cm-1 due to the 1→4 glycosidic linkage that confirms the presence of longer chains
of carbohydrates [62].
The out-of-phase ring stretch causes a C-H equatorial deformation vibration band represented at 891
cm-1 and being common in α- and β-pyranoses [14].
Finally, the 683 cm-1 peak is related to the C-H bend of the carbohydrates [61].
42
Table 9 – Summary of the bands assignment for the ATR-FTIR spectra.
Wavenumber (cm-1) Assignment of functional group
3500-3000 -OH stretching
2924-2856 C-H stretching
1730 C=O stretching
1456 C-O-H bending of the CH2OH monosaccharides side chain
1351 C-H deformation in cellulose and hemicellulose
1215 C-O-H stretching of the CH2OH monosaccharides side chain
1150 C-O-C stretching vibrations in the ring structure
1124 C-O-C asymmetric stretching of cyclic ethers
1053 C-O stretching
921 Skeletal mode vibrations of α-1,4 glycosidic linkage
891 β-glycosidic linkages
683 C-H bend in carbohydrates
Colmation procedures
The process used by MQ starts with the pre-humidification of corks, followed by the addition of the
adhesive, then by addition of a water and cork powder mixture and finally just cork dust. After the
colmation steps one move to the dedusting and drying execution. Each single step is covered below:
Pre-humidification is usually done in order to offer a moisturized substrate were the colmation
adhesive is expected to have a higher affinity and consequently an easier attachment;
The cork powder present in the adhesive is expected not only to improve the bonding strength of
the same but also to act as a primary filler in the cork pores, preventing that they look superficially
covered but hollow inside. This is not done in the traditional colmation since the glue is introduced
alone and the cork powder and water mixture is only added afterwards. Although there is no
introduction of cork powder in the first step of the traditional process this might not result in hollow
pores since the usual colmated corks are class 5 or higher, but in lower 6 grade corks were the
pores are bigger this effect may be crucial in the colmation effectiveness.
As stated above, the cork powder and water addition step intends to offer a cork filler to the already
glued pores were the cork is intended to attach. By adding water to the cork dust one offer a fluid
vehicle that allows the cork dust to penetrate the cork;
Finally, the dedusting and drying step is accomplished at a temperature high enough to dry the cork
but not so high that could physically deform them.
43
All the tested colmation procedures are presented in the appendices, as well as an image with 12 corks
for each one. To mention that the mixing times for each step of the procedure were firstly based on the
traditional procedure and subsequently adapted to allow effective mixing. The procedures are
summarized in the following tables:
Table 10 – Summary of the colmation procedures from No. 1 to 7.
Colmation No./
Procedure step
1 2 3 4 5 6 7
Pre-humidification
Yes
25 mL water
No No No No No
Vacuum
Water 1L + pigment
(20min)
Adhesive application
20 mL water
3g sugars
1.2g Desmodur
DA-L
0.2g cork powder
(t=10 min)
60 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=10 min)
60 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=20 min)
60 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=10 min)
60 mL water
9g sugars
3.6g Desmodur
DA-L
1g cork powder
(t=10 min)
60 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=20 min)
60 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=20 min)
Cork powder and water addition
1g cork powder
50 mL water
(t=25 min)
----
1g cork powder
50 mL water
(t=25 min)
1g cork powder
50 mL water
(t=25 min)
1g cork powder
(t=20 min)
1g cork powder
50 mL water
(t=25 min)
1g cork powder
50 mL water
(t=25 min)
Cork powder
addition
1g
(t=5 min)
1g
(t=20 min)
1g
(t=5 min)
1g
(t=5 min) ----
1g (t=5 min)
1g (t=5 min)
1g (t=5 min)
1g (t=10 min)
Drying T=55-65°C
(t=30 min)
T=55-65°C
(t=30 min)
T=55-65°C
(t=30 min) ---- ----
T=55-65°C
(t=30 min)
T=55-65°C
(t=30 min)
Adhesive application
---- ---- ----
60 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=25 min)
60 mL water
9g sugars
3.6g Desmodur
DA-L
1g cork powder
(t=10 min)
60 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=20 min)
----
Cork powder
addition ---- ---- ----
1g (t=5 min)
1g (t=20 min)
1g (t=5 min)
----
Drying ---- ---- ---- T=55-65°C
(t=30 min)
T=55-65°C
(t=30 min)
T=55-65°C
(t=30 min) ----
44
Table 11 – (Continuation of Table 1) Summary of the colmation procedures from No. 8 to 14.
Colmation No./
Procedure step
8 9 10 11 12 13 14
Pre-humidification
No No No No No No No
Adhesive application
60 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=20 min)
60 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=10 min)
90 mL water
18g sugars
7.2g Desmodur
DA-L
1.2g cork powder
(t=20 min)
60 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=20 min)
60 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=20 min)
60 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=20 min)
120 mL water
18g sugars
2g Desmodur
DA-L
1.2g cork powder
(t=20 min)
Cork powder and water addition
1g cork powder
50 mL water
(t=25 min)
1g cork powder
50 mL water
(t=25 min)
1g cork powder
50 mL water
(t=25 min)
1g cork powder
50 mL water
(t=25 min)
1g cork powder
50 mL water
(t=25 min)
1g cork powder
50 mL water
(t=25 min)
5g cork powder
(t=15 min)
Cork powder
addition
1g (t=10 min)
1g (t=5 min)
1g (t=10 min)
1g (t=5 min)
2g (t=5 min)
1g (t=5 min)
1g (t=5 min)
1g (t=5 min)
1g (t=5 min)
1g (t=5 min)
1g (t=5 min)
1g (t=5 min)
----
Drying ---- ---- T=55-65°C
(t=30 min)
Air drying over night
Air drying over night
Air drying over night
T=55-65°C
(t=30 min)
Adhesive application
60 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=20 min)
30 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=10 min)
----
60 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=20 min)
30 mL water
9g sugars
3.6g Desmodur
DA-L
0.6g cork powder
(t=20 min)
30 mL water
9g sugars
3.6g Desmodur
DA-L
1g cork powder
(t=20 min)
----
Cork powder
addition
1g
(t=10 min)
1g (t=10 min)
1g (t=10 min)
---- 1g
(t=5 min)
0.5g
(t=5 min)
1g
(t=5 min) ----
Drying T=55-65°C
(t=30 min)
T=55-65°C
(t=30 min) ----
T=55-65°C
(t=30 min)
T=55-65°C
(t=30 min)
T=55-65°C
(t=30 min) ----
45
Colmation No.1 was structurally based on the colmation procedure used in MQ. Given that the adhesive
properties are different from the commercial ones the quantity of adhesive used is expected to vary, and
so, the initial gluing step was performed with the basic adhesive formulation quantity. It is also worth
mentioning that usually only class 5 or higher are colmated, and by using class 6 corks the worst
foreseeable case is being tested.
It can be observed that the colmation material aggregates at the entrance of the pores, and although
some colmation material was still inside the drum, the pores remained hollow. Thereby, one can allege
that for this specific adhesive the pre-humidification does not aid the primary anchoring of the gluing
material. Contrarily to the pre-humidification objective of the traditional method where the pre-
humidification is intended to act as a binder between the cork and the non-aqueous adhesive, this was
expected since the pre-humidification impregnates the cork and when the adhesive is added the
substrate is already saturated, and instead of anchoring it slips. This is where the cork carbohydrates
enter: by having a similar structure to the cork components they act as a binding agent that is expected
to be more efficient than just water. Finally, although the traditional process does not possess a step
where only cork dust is applied it was found to be necessary to add this final step in order to try to cover
the pores (which were almost all uncovered) with the aid of the existing liquid in the drum. This first
colmation thereby showed lack of adhesive, and consequently an easily detachable material that
ineffectively covered the pores ok the cork.
Parallel to colmation No.1, colmation No.2 was also carried based on the previously tested procedures
of VALOR5 project. This procedure does not contain neither a pre-humidification step nor the cork
powder plus water step. A higher fraction of pores were covered although some seemed to be hollow
inside.
As the removal of the pre-humidification was shown to be necessary, and an increase in the adhesive
quantity was also shown to be effective, colmation No.3 adopted both and kept the cork powder plus
water step since in colmation No.2 the cork powder seemed to not penetrate the cork effectively.
Although a large portion of pores remained unfilled the quantity of cork powder agglomerated at the
entrance of the pores was reduced, as the loose appearance.
In order to improve colmation No.3, additional adhesive and cork dust were added, in two separated
steps, to produce an additional layer of colmation material, resulting in colmation No.4. This colmation
showed no improvement since the water/solid ratio was too high and no efficient anchoring was
achieved due to the relative solid fraction ended up being dragged into the excess water inside the drum.
Following this procedure, Colmation No.5 did not possess the second step of cork dust and water
mixture, being the cork content of this step compensated in the adhesive insertion steps. Still the
adhesive material presented a loose appearance and low filling.
Since an increase of adhesive did not show higher filling of the pores it was added an intermediate
drying step to colmation No.4, which is expected to reduce the liquid/solid ratio and thereby increase
46
anchoring and decrease water dragging on the second step of colmation, resulting in colmation No.6.
In the first colmation row an additional gram of cork powder was added due to the lack of solid fraction
observed in the previous procedures. As expected, by the end of this first colmation, the pores were not
completely covered. The further drying and colmation intended to stack a first layer of colmation glue
that would provide a stable substrate for the second colmation. Besides the water in the adhesive, no
more water was added in the second colmation row because the end of the pores were now more
exposed and so the transport of cork powder by water was not that imperative, and thereby the water
dragging effect was also reduced. Although most of the defects where colmated, in some the attachment
of the adhesive to the pores walls was not total.
Pre-humidification should not be set aside with just one trial and so the first colmation sequence was
tested with a simple pre-humidification with 25 mL of water, under vacuum for 20min (Colmation No.7).
The use of Rhodamine B pigment was implemented in order to track the penetration of water. As it can
be observed in Figure 34, even though some air in the corks was removed, placing the corks under
vacuum did not aid the penetration of cork dust in the cork pores when comparing to colmation No.6.
Figure 34 – Corks cut in the direction of the lenticular cells. A) Colmation No.6; B) Uncolmated cork; C) Colmation
No.7.
Following the statement of Colmation No.6, Colmation No.8 intended to keep the 2 colmation
sequences with the removal of the intermediate drying step, thereby reducing this additional cost in the
procedure. The result was semi-covered but hollow pores since the water bubbles inside the cork pores
were not allowed to dry and liberate the air inside, thereby producing an excess of surface tension that
B A
C
47
did not allow the second colmation material to deposit well in the substrate. It should also be noted that
this process was somewhat dispensable since this was previously observed in colmation No.4 (although
with a smaller portion of cork powder) where it was concluded that the liquid phase of the additional
portion of adhesive would drag the colmation material instead of promoting anchoring. This effect could
not even be overcome by the decrease in water and the increase of cork powder in the second adhesive
step (Colmation No.9), neither by placing approximately the same quantity in a row (Colmation No.10).
These procedures showed that the adhesive was inside the pores instead of agglomerating at the
entrance of the same, but the filling was low.
Since the intermediate drying showed to be an essential step in the colmation of class 6 corks, a
colmation similar to N.6 was tempted but with residence overnight at ambient temperature (Colmation
No.11). This procedure showed colmated cracks and pores but glued ends (Figure 35), being observed
after performing the second colmation sequence. In Colmation No.12 the quantity of water was reduced
to half along with the quantity of cork dust in the final adding step. It resulted on covered pores and
cracks with adequate filling and only the excessively big pores could not be colmated.
Figure 35 - Colmation No.11 glued ends.
Being colmation No.12 already an effective procedure, it was attempted to completely remove the glued
ends and at the same time decrease the quantity of isocyanate, the most expensive component in the
glue. From this decision arises Colmation No.13 in which the quantity of Desmodur DA-L is decreased
from 3.6g to 1g in the adhesive formulation. As expected the decrease in this component affects the
adhesion power due to the lower crosslinking, which could be observed by the contraction of the
colmation material upon cooling and also by its loose appearance.
The reduction of isocyanate was kept and still tested in Colmation N.14. It was attempted the increase
of adhesive in the first step, which by itself increased the water and cork powder in the beginning of the
sequence, thereby showing the dispensability of the water and cork powder mixture added afterwards,
resulting on an increase of the total isocyanate ratio. The quantity of cork solely added alone was left
constant. This colmation also showed completely covered defects while the corks were wet but upon
cooling contraction and posterior detachment could also be observed.
The summarized colmation step changes, objectives and results are present in Table 12.
48
Table 12 - Summarized colmation step changes, objectives and results; Symbols: (↓) Decrease and (↑) Increase
the quantities of …, (→) Substitution of … for …, (X) Removal of, (>) Higher, (<) Lower, (+) Add.
Objective Colmation changes Relative results
1
Test a basic process based on the
starting adhesive formula and
procedure
-
Easily detachable adhesive material
Ineffective penetration in the pores
Lack of adhesive
2 Test the procedure used in VALOR 5 -
Easily detachable adhesive material
Ineffective penetration in the pores
Lack of adhesive
3 ↑ Penetration X Pre-humidification
↑ Adhesive
Increased pores covering
Increased anchoring
4 ↑ Colmation “layers” ↑ Adhesive in a posterior step Decreased filling
Non colmated cracks
5 ↑ Solids fraction
↑ Cork dust in the adhesive
X Cork dust and water mixture
step
Insufficient filling
Loose appearance
6 ↑ Colmation “layers” + Heat drying step Colmated cracks and pores
Reasonable attachment
7 ↑ Initial penetration + Vacuum Vacuum does not increase penetration
8 X Heat drying X Heat drying step Low filling
Cracks not colmated
9 X Heat drying ↑ Solid fraction
↓ Liquid fraction
Effective anchoring
Low filling
Covered but hollow pores
10 X Heat drying ↑ Adhesive and cork powder Effective anchoring
Low filling
11 X Heat drying Heat drying step → Drying at
room temperature
Effective pore penetration
Colmated cracks
Glued ends
12 ↓ Glued ends ↓ Liquid and solid portion
High filling
Big pores and cracks colmated
< fraction of corks with glued ends
13 ↓ Isocyanate ↓ Desmodur DA-L
Good filling
Loose appearance
Detachment when dried
14 ↓ Isocyanate
↓ Colmation steps
↑ Adhesive in the 1st step
↓ Desmodur DA-L
Insufficient filling
Loose appearance
Detachment when dried
49
From factors that control the efficiency of a colmation procedure like the quantity of inserted adhesive,
quantity of cork powder and number of colmation steps, it can be said that the quantity of water played
a crucial effect in the colmation procedures, not only by the necessity of water to transport the cork
powder but also the need of choosing an appropriate quantity that does not promote dragging of the
colmation material. Also related to water is the intermediate drying step that reduces the humidity
content, thereby facilitating the deposition of more adhesive material by reducing the water surface
tension (or even eliminate it), and also promoting curing. It is also worth mentioning that contrarily to the
traditional procedure the pre-humidification was proved not to be necessary for this specific adhesive.
Colmation visual inspection
In order to do the visual classification of the colmated corks different aspects were taken into account:
the covering of small pores, big pores and cracks, the anchoring, the existence of glued ends and the
loose appearance of the adhesive material.
The quantity of glue is the main precursor for filled pores in a cork. It dictates if the inserted quantity of
glue is appropriate for the volume of vacancies present in the corks, leading to a better performance on
the covering of smaller and bigger pores, as well of cracks.
One of the main difficulties of colmation is the complete covering of the cracks since they are narrow
and deep, being less prone to the penetration of the colmation agent. Some colmation procedures may
present covered pores but exposed cracks.
Smaller pores (≤ 2mm) are usually easier to cover since they are not as narrow as cracks, being thus
more reachable and not as wide as big pores which make them a more stable anchoring spot for the
gluing materials.
Big pores (> 2mm) are easily targetable but more difficult to cover due to an increased need of
colmation glue. Although these areas present nucleation points after the first gluing step, as the quantity
of adhesive material is inserted in a big pore the more difficult it is to remain mechanically stable and
the detachment is more prone to occur.
Anchoring is related to the capacity of the adhesive material to penetrate and attach in the interior of
the defects. It may happen that a defect seems to be covered but the anchoring was poor since they
remain hollow.
With the evolution of the procedures, glued ends started to appear. These zones usually possess less
defects and so it is expected that due to the excess of adhesive material there will be its concentration
in the easy anchoring spots: the smooth surfaces of the tops. This is also expected to occur due to the
strong adhesion power of the glue that cannot be surpassed on the dedusting step.
Attachment appearance is related to the capacity of agglomeration of the adhesive material. This factor
may be dependent on the cork powder/adhesive ratio, water dragging effects, as well on reductions on
the quantity of isocyanate in the adhesive tested in the final procedures.
50
The parameters herein discussed are presented in the Table 13, as well as an example for the
considered classification value. In Table 14 the results for each colmation procedure are presented. The
procedure that as the better visual evaluation is expected to be the one with the higher sum of the
different parameters classification.
Table 13 – Classification method from 0 to 2 for the several parameters, being 1 equivalent to an average
insufficient performance, 2 to satisfactory and 3 to efficient.
Parameter/
Classification 0 1 2
Covering
Cracks
Smaller Pores
Bigger Pores
Anchoring
Bottoms not glued
Tight appearance
51
Table 14 - Visual inspection of the colmated corks according to the various parameters.
Co
lma
tio
n n
um
be
r
An
ch
ori
ng
Sm
all
er
po
res
co
vere
d
Big
ge
r p
ore
s
co
vere
d
Cra
ck
s c
ov
ere
d
Bo
tto
ms n
ot
glu
ed
Th
igh
ap
pea
ran
ce
Cla
ss
ific
ati
on
(0-1
2)
1 1 0 1 0 2 1 5
2 1 1 2 1 2 1 8
3 2 1 1 1 2 2 9
4 1 1 1 0 2 0 5
5 1 1 1 0 2 0 5
6 1 2 2 1 2 2 10
7 - - - - - - -
8 1 1 1 1 2 2 6
9 1 1 1 1 2 2 6
10 1 1 1 1 2 2 6
11 2 2 2 2 0 2 10
12 2 2 2 2 1 2 11
13 0 2 2 2 2 0 8
14 0 2 2 0 2 0 6
As expected, it can be observed in the former table that colmation No. 12 attained the highest visual
classification, and when the quantity of isocyanate was reduced the visual classification decreased
several values.
Boiling water test
Commercial colmated and colmation No.6 sets of corks were firstly tested in boiling water. It can be
observed in Figure 36 that the commercial adhesive detaches more easily than the one used for
colmation No.6, although the glue used in the commercial colmated corks should also be tested in the
52
same quantity and with the same procedure as colmation No.6 so one can surely state that the
developed adhesive is more efficient.
Figure 36 – Commercial (left) and colmation N.7 (right) boiled corks.
With a higher visual evaluation, corks from colmation No.11 and 12 were also tested (Figure 37).
Colmation No.11 corks did not pass the test due to the colmation material detachment. Colmation No.
12 showed to be adequate procedures due to the colmation material stability after boiling.
Figure 37 - Colmation No.11 (left) and colmation No.12 (right) boiled corks.
Residues content
The tested colmation procedures were colmation No.11 and 12 since they presented a better
performance on the visual evaluation. The white sheet under the corking machine showed no residues
of the colmation material detached after compression, thereby presenting the necessary attachment and
resilience to support the compressive forces on the corking machine.
Since there was no detachment while compressing the corks they could then be introduced in the
extraction solution that simulates wine not only due to the ethanol content but also due to the tartaric
acid, which is one of the main acids in wine that lowers the pH, acting as a preservative after
fermentation. After comparing the compressed and uncompressed corks filtering papers (Table 15) one
can observe that for the tested colmations the dethatched mass is always smaller than for the traditional
colmation. Even though the tested corks are expected to release a smaller percentage of residues than
53
in the typical environment since the wine is not in contact with the entire corks surface, this is a positive
aspect of the tested procedures because they release less residues than the traditional colmation. One
support for this results would have been to know the weigh difference after colmation to obtain the added
adhesive mass in each cork so one could ensure that the higher residues mass in the traditional mass
is not only higher due to a higher mass of adhesive added.
Table 15 - Filter papers after filtering the alcoholic solutions containing the colmated corks residue with and
without compression in the corking machine. The loosen adhesive (mg) is also presented.
Uncompressed Compressed
Loose adhesive mass (mg) Loose adhesive mass (mg)
Traditional
colmation
15,5
9,6
Colmation
Nº11
2,4
9,4
Colmation
No. 12
2,2
4,4
54
The traditional colmation shows a decrease in the residues mass after compression contrarily to the
tested colmations, evidencing frailty to the alcoholic solution. Although, the residues mass is still
acceptable as it is lower than for the traditional colmation.
With a higher visual classification, colmation No.12 also showed the best performance in this test since,
after compression, the residues mass was the smallest observed, thereby showing to be the most
appropriate colmation procedure. To be noted that this test should comprise more samples in order to
obtain a more solid conclusion, which was not possible because the tested procedures contained 20
corks each.
Agglomeration adhesive
Agglomeration adhesives were produced according to the procedure in point 2.10. The formulations
(Table 16) of the adhesives were proposed in FR based on the ones presently used for natural polyols.
Table 16 - Agglomeration adhesives formulation.
Components (%) /adhesive
1 2 3 4 5
Cork polyol 65 54.98 69.95 79.8 63.64
Soy oil - 5 5 - -
Acetone 0.018 - - 0.1 0.18
Phosphoric acid 0.018 - - 0.1 0.18
HDI 10 32.5 5 - -
TDI - - - 20 36
IPDI 24.84 7.5 20 - -
DBTL - 0.02 0.05 - -
Apart from the main components (cork polyol and isocyanates) acetone, phosphoric acid and DBTL
were also added. Phosphoric acid is often used to neutralize a possible basicity of the commercial
polyols (which was not the case), acetone was used as a dispersing agent, DBTL is the currently used
catalyst used in these adhesives due to its effectiveness (although some efforts are being made to
replace it) and soy oil acts as a plasticizer. It is worth mentioning that when the soy oil was present no
phosphoric acid and acetone were added since it also acts as a dispersive agent. Although more
studied, TDI is also being replaced in the market, thereby some formulations used mixtures of HDI and
IPDI, as different proportions can regulate the viscosity of the adhesive.
The viscosity, free NCO content, solids content and gel time were determined for the previous
formulations, as their agglomeration applicability (Table 17).
Table 17 – Agglomeration adhesives testing. Symbols: Applied () and not applied (X) for agglomeration.
Tests/adhesive 1 2 3 4 5
55
Viscosity (cP) 8480 4545 - 3150 -
NCO (%) 0 3.56 0 8.72 2.12
Gel time (min) >15 >15 - >15 -
Agglomeration X X
The first adhesive was used for two agglomerations: one with the originally prepared formulation and
another with the addition of 0.02 g of DBTL and 1.5 g of water. Being the free NCO equal to 0, the gel
time was higher than 15 min as expected because there were no reactive groups left and thereby none
of the formulations showed to be effective since the corks were easily broken and presented a friable
surface (Figure 38). As expected, the addition of catalyst and water to promote a faster reaction was
shown to be ineffective.
Figure 38 - Agglomerated corks with adhesive No.1 (left) and adhesive No.1 plus 0.02g of DBTL and 1.5g of
water (right).
The formulation for adhesive 2 contains a higher percentage of isocyanates, resulting in a NCO value
of 3.56 %. Even with this positive value the gel time was higher than 15 min, which by itself presents its
unsuitability for the industrial production because the adhesive will not have enough time to cure and a
brittle cork will result (Figure 38). Adhesive No.3 was not applied for agglomeration due to the previous
results and the NCO value equal to 0. Adhesive No.4 possessed a higher NCO value and so
agglomeration was tried although with no success since the corks presented a crumblier surface.
Adhesive No.5 had a viscosity surely above 8000 cP, showing its unsuitability for the industrial
production and so no more tests were carried out.
56
Figure 39 - Agglomerated corks with adhesive No.2 (left) and No.4 (right).
With these poor results it was concluded that the developed adhesives formulations must be refined.
Thereby a higher ratio of adhesive/cork granulate should have been also tested, granulates with a
smaller specific area and/or a higher percentage of catalyst.
Cork bio-refinery
Having an industrial concern, it is hereby presented a flow chart (Figure 40) of a possible bio-refinery
that can function not only for the production of bio-fuel but also jointly with an adhesives formulation unit.
The imputed costs in the industry for each component are presented, in accordance with the prices
employed by the suppliers of FR, as well as their overall used percentage and yield for the process
products and by-products. The cost of water is neglected.
57
2-EHDEGCatalyst
H2O
Polyols(37.9 MJ/Kg)
Sugars(20.3 MJ/Kg)
Cork
LIQUEFACTION UNIT FLOW CHART
58.3 %1,7 €/Kg
19.4%1,3 €/Kg
2.9 %1,9 €/Kg19.4 %
0,40 €/Kg
ResidueLiquefied Product
(26.6 MJ/Kg)
6 %94 %
0.76 €/Kg
70.4 %0.57 €/Kg
23.6 %0.19 €/Kg
Adhesives formulation unit
Desmodur DA-L
7 €/Kg
Water-base adhesive
0,4 €/Kg
Natural polyols adhesive
Polyurethane foams
? €/Kg
Fuel
Figure 40 - Liquefaction unit flow chart.
58
The process would start with the addition of cork powder, catalyst and the reagents DEG and 2-EH in
an industrial reactor. After a residence time of 1.5 h at 160 °C, a yield of 94 % of the liquefaction product
and a residue of 6 % are obtained. Water and 2-EH would be continuously kept in the reactor due to a
demister. If intended, the process can stop at this point and the liquefied product can be used for direct
combustion since it presents a calorific power of 26.618 MJ/Kg (measured by the SECIL accredited
laboratory). If the adhesives production is intended, the liquefied product would follow to an IBC for the
addition of water, and with the aid of a mechanical stirrer the phase separation could be achieved,
representing a yield of 70.4 % for the polyols and 23.6 % for the polysaccharides extract. The polyols
could be inserted again for a following liquefaction due to its high 2-EH content, to combustion (37.905
MJ/Kg) or to an adhesives formulation unit together with the polysaccharides fraction, both needing an
extra drying step. This last calorific powder of polyols is high when compared to a commercial diesel
with 45.710 MJ/Kg. The sugars fraction presents a smaller calorific power of 20.285 MJ/Kg, and so they
are more suitable for adhesives formulation. This fraction can be further analyzed in order to determine
its water content: if the water content is not the pretended in the final adhesive formulation, drying or
water addition is necessary. After formulation, a water-based adhesive is expected to cost around 0.4
€/Kg and the cost of a polyol adhesive will depend on the components used in its improved formula.
59
4. Conclusion
Cork powder was successfully liquefied with DEG, 2-EH and PTSA for 1.5 h at 150°C, yielding a
conversion of 94%. The liquefied product was fractionated, although breaking the emulsion could
increase the efficiency of this phase separation.
The aqueous extract showed a higher hydroxyl value (621.2 mg KOH/g) than the polyols extract (271.6
mg KOH/g) mainly due to the presence of cellulose and hemicellulose depolimerization products, proven
in the ATR-FTIR spectra that present a sharp peak from the C-O stretching of the carbohydrates in the
fingerprint region, along with a more prominent peak representative of the hydroxyl groups stretching.
The liquefied product itself presented an acid value of 6 mg KOH/g, a low enough value for the
production of biodiesel.
Although the typical colmation procedure could not be applied for class 6 corks with the previously
developed adhesive, an alternative colmation procedure was successfully developed, which consisted
in two separated colmation rows with an intermediate drying step at room temperature (colmation No.
12).
A visual inspection method of colmated corks was also proposed, which consisted on a classification
from 0 to 2 for several parameters, resulting in a final classification from 0 to 12. Apart from having a
higher visual classification, colmation No. 12 also presented a higher resistance to boiling water for an
hour, even higher than a commercial colmated cork. The residues content was also smaller than the
traditional colmation corks.
The developed adhesives did not show adequate properties for industrial use due to the excessive
quantity of isocyanate needed, the high gel times and their inability to properly agglomerate. Although,
some adhesives showed an adequate NCO content (adhesive 2, 4 and 5) and viscosity (adhesive 1 and
2) for industrial production. The reason for these poor results might be the high specific area of the used
cork granulates and the low quantity of catalyst.
Finally, a flow chart for a cork bio-refinery together with an adhesives formulation unit was presented
based on the obtained liquefaction yields and currently employed prices for the used material. The
water-based adhesive is expected to cost around 0.4 €/kg. The residue and the polyols can be used as
a fuel that as 34.14 MJ/Kg of calorific power.
60
5. Future Work
A demulsification agent should be tested (i.e. talcum powder) in the liquefied product fractioning in order
to obtain a more effective separation, which could result in a lower water content and OH value for the
polyols fraction. Thereby, the isocyanate contents in the agglomeration adhesives could be lowered,
decreasing the cost of the adhesive, along with the time and energy spent on the samples evaporation;
Test reagents not originated from the oil industry (i.e. amyl alcohol) to produce 100% natural adhesives;
Improve the adhesive composition by studying its wettability properties: an adhesive with high wetting
is expected to penetrate the cork defects easier;
Characterize the sugars fraction with HPLC, which can also prove the results obtained in the particle
size test;
Parameterize the efficiency of the corks colmation procedures by weighting the corks and verifying its
porosity before and after the same using a pycnometer (even though it is not used in the industrial
environment);
Test the produced adhesives in more quantity, with more catalyst and with cork granulates with smaller
specific area.
The adaptability of the liquefaction in an industrial reactor was already proved, now the developed
colmation procedure should also be tested in an industrial colmation mixer.
61
6. Bibliography
[1] C. M. Bordado João Carlos, Silva Elisabete, Lopes Rui Miguel, Mateus Maria Margarida, Avelar
Ana Cristina, “Two-component natural polymeric water-based glues, obtained from derivatives of cork,”
2015.
[2] “HISTÓRIA DA CORTIÇA.” [Online]. Available: http://www.apcor.pt/artigo/historia-cortica.htm.
[Accessed: 01-Jan-2015].
[3] H. Fortes, M. A., Rosa, M. E., Pereira, A Cortiça. Lisboa: IST Press, 2006.
[4] APCOR, “Cortiça/Cork 2014,” 2014.
[5] “Localização do Montado.” [Online]. Available: http://www.amorim.com/a-cortica/localizacao-
do-montado/. [Accessed: 24-May-2015].
[6] “Corksupply Products.” [Online]. Available: http://www.corksupply.com/products/default.aspx.
[Accessed: 24-May-2015].
[7] “Cork punching.” [Online]. Available: http://www.corklink.com/index.php/10-steps-to-make-a-
natural-cork-stopper/cork-punch/. [Accessed: 01-Jan-2015].
[8] “Granulated cork.” [Online]. Available: http://lakewoodcork.com/carat/. [Accessed: 24-May-
2015].
[9] S. P. Silva, M. A. Sabino, E. M. Fernandes, V. M. Correlo, L. F. Boesel, and R. L. Reis, “Cork :
properties, capabilities and applications,” Int. Mater. Rev., vol. 50, no. 6, pp. 345–365, 2005.
[10] A. Brandt, J. Gräsvik, J. P. Hallett, and T. Welton, “Deconstruction of lignocellulosic biomass
with ionic liquids,” Green Chem., vol. 15, no. 3, pp. 550–583, 2013.
[11] Y. Zhang, T. Funk, and G. Riskowski, “Thermochemical Conversion Process of Swine Manure,”
1999.
[12] H. Zhang, H. Yang, H. Guo, C. Huang, L. Xiong, and X. Chen, “Kinetic study on the liquefaction
of wood and its three cell wall component in polyhydric alcohols,” Appl. Energy, vol. 113, pp. 1596–
1600, 2014.
[13] S. I. Tohmura, G. Y. Li, and T. F. Qin, “Preparation and characterization of wood polyalcohol-
based isocyanate adhesives,” J. Appl. Polym. Sci., vol. 98, pp. 791–795, 2005.
[14] H. Pan, Z. Zheng, and C. Y. Hse, “Microwave-assisted liquefaction of wood with polyhydric
alcohols and its application in preparation of polyurethane (PU) foams,” Eur. J. Wood Wood Prod., vol.
70, pp. 461–470, 2012.
[15] A. Sequeiros, L. Serrano, R. Briones, and J. Labidi, “Lignin liquefaction under microwave
heating,” J. Appl. Polym. Sci., vol. 130, pp. 3292–3298, 2013.
62
[16] E. Jasiukaitytė-Grojzdek, M. Kunaver, and C. Crestini, “Lignin Structural Changes During
Liquefaction in Acidified Ethylene Glycol,” J. Wood Chem. Technol., vol. 32, no. February, pp. 342–360,
2012.
[17] A. Ugovšek, F. Budija, M. Kariž, and M. Šernek, “The Influence of Solvent Content in Liquefied
Wood and of the Addition of Condensed Tannin on Bonding Quality,” Drv. Ind., vol. 62, no. 2, pp. 87–
95, 2011.
[18] D. Mishra and V. Kumar Sinha, “Eco-economical polyurethane wood adhesives from cellulosic
waste: Synthesis, characterization and adhesion study,” Int. J. Adhes. Adhes., vol. 30, no. 1, pp. 47–54,
2010.
[19] H. Zhang, J. Luo, Y. Li, H. Guo, L. Xiong, and X. Chen, “Acid-catalyzed liquefaction of bagasse
in the presence of polyhydric alcohol,” Appl. Biochem. Biotechnol., vol. 170, pp. 1780–1791, 2013.
[20] J. Long, W. Lou, L. Wang, B. Yin, and X. Li, “[C4H8SO3Hmim]HSO4 as an efficient catalyst for
direct liquefaction of bagasse lignin: Decomposition properties of the inner structural units,” Chem. Eng.
Sci., vol. 122, pp. 24–33, 2015.
[21] E. B. M. Hassan and N. Shukry, “Polyhydric alcohol liquefaction of some lignocellulosic
agricultural residues,” Ind. Crops Prod., vol. 27, no. 1, pp. 33–38, Jan. 2008.
[22] F. Chen and Z. Lu, “Liquefaction of wheat straw and preparation of rigid polyurethane foam from
the liquefaction products,” J. Appl. Polym. Sci., vol. 111, no. 1, pp. 508–516, 2009.
[23] H. Wang and H. Z. Chen, “A novel method of utilizing the biomass resource: Rapid liquefaction
of wheat straw and preparation of biodegradable polyurethane foam (PUF),” J. Chinese Inst. Chem.
Eng., vol. 38, pp. 95–102, 2007.
[24] R. Briones, L. Serrano, and J. Labidi, “Valorization of some lignocellulosic agro-industrial
residues to obtain biopolyols,” J. Chem. Technol. Biotechnol., vol. 87, no. May 2011, pp. 244–249, 2012.
[25] A. M. C. Yona, F. Budija, B. Kričej, A. Kutnar, M. Pavlič, P. Pori, Č. Tavzes, and M. Petrič,
“Production of biomaterials from cork: Liquefaction in polyhydric alcohols at moderate temperatures,”
Ind. Crops Prod., vol. 54, pp. 296–301, Mar. 2014.
[26] I. Johannes, H. Luik, V. Palu, K. Kruusement, and A. Gregor, “Synergy in co-liquefaction of oil
shale and willow in supercritical water,” Fuel, vol. 144, pp. 180–187, 2015.
[27] W. Zhao, W. J. Xu, X. J. Lu, C. Sheng, S. T. Zhong, S. R. Tang, Z. M. Zong, and X. Y. Wei,
“Preparation and property measurement of liquid fuel from supercritical ethanolysis of wheat stalk,”
Energy and Fuels, vol. 24, no. 19, pp. 136–144, 2010.
[28] S. Brand and J. Kim, “Liquefaction of major lignocellulosic biomass constituents in supercritical
ethanol,” Energy, vol. 80, pp. 64–74, 2015.
[29] S. H. Lee and T. Ohkita, “Rapid wood liquefaction by supercritical phenol,” Wood Sci. Technol.,
vol. 37, pp. 29–38, 2003.
63
[30] Y. Yang, A. Gilbert, and C. (Charles) Xu, “Production of Bio-Crude from Foresty Waste by
Hydro-Liquefaction in Sub-/Super-Critical Methanol,” AlChE J., vol. 55, no. 3, pp. 807–819, 2009.
[31] H. Xie and T. Shi, “Liquefaction of wood (Metasequoia glyptostroboides) in allyl alkyl
imidazolium ionic liquids,” Wood Sci. Technol., vol. 44, pp. 119–128, 2010.
[32] Z. Zhang and Z. K. Zhao, “Bioresource Technology Microwave-assisted conversion of
lignocellulosic biomass into furans in ionic liquid,” Bioresour. Technol., vol. 101, no. 3, pp. 1111–1114,
2010.
[33] Z. Lu, H. Zheng, L. Fan, Y. Liao, B. Ding, and B. Huang, “Liquefaction of sawdust in 1-octanol
using acidic ionic liquids as catalyst,” Bioresour. Technol., vol. 142, pp. 579–584, 2013.
[34] J. Long, X. Li, B. Guo, F. Wang, Y. Yu, and L. Wang, “Simultaneous delignification and selective
catalytic transformation of agricultural lignocellulose in cooperative ionic liquid pairs,” Green Chem., vol.
14, p. 1935, 2012.
[35] T. Yamada, M. Aratani, S. Kubo, and K. Ono, “Chemical analysis of the product in acid-
catalyzed solvolysis of cellulose using polyethylene glycol and ethylene carbonate,” J wood Sci, vol. 53,
pp. 487–493, 2007.
[36] T. Yamada and H. Ono, “Rapid liquefaction of lignocellulosic waste by using ethylene
carbonate,” Bioresour. Technol., vol. 70, no. 1, pp. 61–67, 1999.
[37] S. H. Lee, Y. Teramoto, and N. Shiraishi, “Resol-type phenolic resin from liquefied phenolated
wood and its application to phenolic foam,” J. Appl. Polym. Sci., vol. 84, pp. 468–472, 2002.
[38] T. Yamada and H. Ono, “Characterization of the products resulting from ethylene glycol
liquefaction of cellulose,” J. woo, vol. 47, pp. 458–464, 2001.
[39] A. Ugovšek, A. Sever Škapin, M. Humar, and M. Sernek, “Microscopic analysis of the wood
bond line using liquefied wood as adhesive,” J. Adhes. Sci. Technol., vol. 27, no. February, pp. 1247–
1258, 2013.
[40] M. Kunaver, E. Jasiukaityte, N. Čuk, and J. T. Guthrie, “Liquefaction of wood, synthesis and
characterization of liquefied wood polyester derivatives,” J. Appl. Polym. Sci., vol. 115, no. 3, pp. 1265–
1271, 2010.
[41] A. Kržan and M. Kunaver, “Microwave heating in wood liquefaction,” J. Appl. Polym. Sci., vol.
101, pp. 1051–1056, 2006.
[42] J. Xu, J. Jiang, W. Dai, and Y. Xu, “Liquefaction of sawdust in hot compressed ethanol for the
production of bio-oils,” Process Saf. Environ. Prot., vol. 90, no. January, pp. 333–338, 2012.
[43] L. Ye, J. Zhang, J. Zhao, and S. Tu, “Liquefaction of bamboo shoot shell for the production of
polyols,” Bioresour. Technol., vol. 153, pp. 147–153, 2014.
[44] W. J. Lee and M. S. Lin, “Preparation and application of polyurethane adhesives made from
polyhydric alcohol liquefied taiwan acacia and china fir,” J. Appl. Polym. Sci., vol. 109, pp. 23–31, 2008.
64
[45] B. Soares, N. Gama, C. Freire, A. Barros-Timmons, I. Brandão, R. Silva, C. Pascoal Neto, and
A. Ferreira, “Ecopolyol production from industrial cork powder via acid liquefaction using polyhydric
alcohols,” ACS Sustain. Chem. Eng., vol. 2, pp. 846–854, 2014.
[46] M. Alma, D. Maldas, and N. Shiraishi, “Liquefaction of several biomass wastes into phenol in
the presence of various alkalis and metallic salts as catalysts,” J. Polym. Eng., vol. 18, no. 3, pp. 161–
177, 1998.
[47] M. Balat, “Mechanisms of Thermochemical Biomass Conversion Processes. Part 3: Reactions
of Liquefaction,” Energy Sources, Part A Recover. Util. Environ. Eff., vol. 30, no. 7, pp. 649–659, 2008.
[48] H. Zhang, H. Pang, J. Shi, T. Fu, and B. Liao, “Investigation of liquefied wood residues based
on cellulose, hemicellulose, and lignin,” J. Appl. Polym. Sci., vol. 123, no. 2, pp. 850–856, Jan. 2012.
[49] H. Zhang, F. Ding, C. Luo, L. Xiong, and X. Chen, “Liquefaction and characterization of acid
hydrolysis residue of corncob in polyhydric alcohols,” Ind. Crops Prod., vol. 39, pp. 47–51, 2012.
[50] E. Jasiukaityte-Grojzdek, M. Kunaver, and I. Poljansek, “Influence of cellulose polymerization
degree and crystallinity on kinetics of cellulose degradation,” BioResources, vol. 7, no. 3, pp. 3008–
3027, 2012.
[51] M. Kunaver, E. Jasiukaityte, and N. Čuk, “Ultrasonically assisted liquefaction of lignocellulosic
materials,” Bioresour. Technol., vol. 103, pp. 360–366, 2012.
[52] M. M. Mateus, N. F. Acero, J. C. Bordado, and R. G. Santos, “Sonication as a foremost tool to
improve cork liquefaction,” Ind. Crop. Prod., vol. 74, pp. 9–13, 2015.
[53] T. Zhang, Y. Zhou, D. Liu, and L. Petrus, “Qualitative analysis of products formed during the
acid catalyzed liquefaction of bagasse in ethylene glycol,” Bioresour. Technol., vol. 98, no. 7, pp. 1454–
1459, 2007.
[54] S. Hu and Y. Li, “Polyols and polyurethane foams from acid-catalyzed biomass liquefaction by
crude glycerol: Effects of crude glycerol impurities,” J. Appl. Polym. Sci., vol. 131, pp. 9054–9062, 2014.
[55] T. Six and A. Feigenbaum, “Mechanism of migration from agglomerated cork stoppers. Part 2:
Safety assessment criteria of agglomerated cork stoppers for champagne wine cork producers, for users
and for control laboratories.,” Food Addit. Contam., vol. 20, no. 10, pp. 960–971, 2003.
[56] M. F. Juhaida, M. T. Paridah, M. Mohd. Hilmi, Z. Sarani, H. Jalaluddin, and a. R. Mohamad
Zaki, “Liquefaction of kenaf (Hibiscus cannabinus L.) core for wood laminating adhesive,” Bioresour.
Technol., vol. 101, no. 4, pp. 1355–1360, 2010.
[57] Y. Wei, F. Cheng, H. Li, and J. Yu, “Properties and Microstructure of Polyurethane Resins from
Liquefied Wood,” Appl. Polym. Sci., vol. 95, pp. 1175–1180, 2004.
[58] Y. Wei, F. Cheng, H. Li, and J. Yu, “Thermal properties and micromorphology of polyurethane
resins based on liquefied benzylated wood,” J. Sci. Ind. Res. (India)., vol. 64, no. 6, pp. 435–439, 2005.
[59] Bayer, “DESMODUR DA-L,” 2014.
65
[60] Metrohm, “756/831 KF Coulometer, Intructions for use.” 2003.
[61] X. Zou, T. Qin, L. Huang, X. Zhang, Z. Yang, and Y. Wang, “Mechanisms and main regularities
of biomass liquefaction with alcoholic solvents,” Energy and Fuels, vol. 23, no. 10, pp. 5213–5218, 2009.
[62] R. Kizil, J. Irudayaraj, and K. Seetharaman, “Characterization of Irradiated Starches by Using
FT-Raman and FTIR Spectroscopy,” J. Agric. Food Chem., vol. 50, pp. 3912–3918, 2002.
66
7. Appendices
Colmation procedures
7.1.1. Colmation No.1
Colmating No. 1
25 mL Water
1 g Cork powder + 50 mL Water
1g Cork powder
10 min
25 min
Drying (30 min, 55-65 °C)
5 min
20 mL Water + 3 g Sugars +
1.2 g Desmodur + 0.2 g Cork powder
67
7.1.2. Colmation No.2
Colmating No. 2
60 mL Water + 9 g Sugars +
3.6 g Desmodur + 0.6 g Cork Powder
1 g Cork powder
10 min
20 min
Drying (30 min, 55-65 °C)
68
7.1.3. Colmation No.3
Colmating No.3
60 mL Water + 9 g Sugars +
3.6 g Desmodur + 0.6 g Cork Powder
1g Cork Powder + 50 mL Water
1 g Cork Powder
20 min
25 min
5 min
Drying(30 min, 55-65 °C)
69
7.1.4. Colmation No.4
Colmating No. 4
60 mL water + 9 g Sugars +
3.6 g Desmodur + 0.6g Cork Powder
1g Cork Powder + 50 mL Water
1 g Cork Powder
60 mL Water + 9 g Sugars +
3.6 g Desmodur + 0.6 g Cork Powder
1 g Cork Powder
10 min
15 min
5 min
25 min
Drying (30 min, 55-65°C)
5 min
70
7.1.5. Colmation No.5
Colmating No. 5
60 mL Water + 9 g Sugars +
3.6 g Desmodur + 1 g Cork Powder
1 g Cork Powder
10 min
20 min
Drying (30 min, 55-65°C)
60 mL Water + 9 g Sugars +
3.6 g Desmodur + 1 g Cork Powder
1 g Cork Powder
10 min
20 min
71
7.1.6. Colmation No.6
Colmating No. 6
60 mL Water + 9 g Sugars +
3.6 g Desmodur + 0.6 g Cork Powder
1 g Cork Powder + 50 mL Water
1 g Cork Powder
1 g Cork Powder
Drying (30 min, 55-65°C)
60 mL Water + 9 g Sugars +
3.6 g Desmodur + 0.6 g Cork Powder
1 g Cork Powder
20 min
25 min
5 min
5 min
30 min
20 min
Drying (30 min, 55-65°C)
5 min
72
7.1.7. Colmation No.7
Colmating No. 7
Vacuum: Water + Pigment
60 mL Water + 9 g Sugars +
3.6 g Desmodur + 0.6 g Cork Powder
20 min
1 g Cork Powder + 50 mL Water
20 min
1 g Cork Powder
1 g Cork Powder
25 min
5 min
Drying (30 min, 55-65°C)
10 min
73
7.1.8. Colmation No.8
Colmating No. 8
60 mL Water + 9 g Sugars +
3.6 g Desmodur + 0.6 g Cork Powder
1 g Cork Powder + 50 mL Water
1 g Cork Powder
1 g Cork Powder
60 mL Water + 9 g Sugars +
3.6 g Desmodur + 0.6 g Cork Powder
1 g Cork Powder
20 min
25 min
10 min
5 min
20 min
Drying (30 min, 55-65°C)
10 min
74
7.1.9. Colmation No.9
Colmating No. 9
60 mL Water + 9 g Sugars +
3.6 g Desmodur + 0.6 g Cork Powder
1 g Cork Powder + 50 mL Water
1 g Cork Powder
1 g Cork Powder
30 mL Water + 9 g Sugars +
3.6 g Desmodur + 0.6 g Cork Powder
1 g Cork Powder
20 min
25 min
10 min
5 min
20 min
Drying (30 min, 55-65°C)
10 min
1 g Cork Powder
10 min
75
7.1.10. Colmation No.10
Colmating No. 10
90 mL Water + 18 g Sugars +
7.2 g Desmodur + 1.2 g Cork Powder
1 g Cork Powder + 50 mL Water
2 g Cork Powder
1 g Cork Powder
Drying (30 min, 55-65°C)
20 min
25 min
5 min
5 min
76
7.1.11. Colmation No.11
Colmating No. 11
60 mL Water + 9 g Sugars +
3.6 g Desmodur + 0.6 g Cork Powder
1 g Cork Powder + 50 mL Water
1 g Cork Powder
1 g Cork Powder
Air drying over night
60 mL Water + 9 g Sugars +
3.6 g Desmodur + 0.6 g Cork Powder
1 g Cork Powder
20 min
25 min
5 min
5 min
30 min
20 min
Drying (30 min, 55-65°C)
5 min
77
7.1.12. Colmation No.12
Colmating No. 12
60 mL Water + 9 g Sugars +
3.6 g Desmodur + 0.6 g Cork Powder
1 g Cork Powder + 50 mL Water
1 g Cork Powder
1 g Cork Powder
Air drying over night
30 mL Water + 9 g Sugars +
3.6 g Desmodur + 0.6 g Cork Powder
0.5 g Cork Powder
20 min
25 min
5 min
5 min
30 min
20 min
Drying (30 min, 55-65°C)
5 min
78
7.1.13. Colmation No.13
Colmating No. 13
60 mL Water + 9 g Sugars +
1 g Desmodur + 0.6 g Cork Powder
1 g Cork Powder + 50 mL Water
1 g Cork Powder
1 g Cork Powder
Air drying over night
30 mL Water + 9 g Sugars +
1 g Desmodur + 0.6 g Cork Powder
1 g Cork Powder
20 min
25 min
5 min
5 min
30 min
20 min
Drying (30 min, 55-65°C)
5 min
79
7.1.14. Colmation No.14
Colmating No. 14
120 mL Water + 18 g Sugars +
2 g Desmodur + 1.2 g Cork Powder
5 g Cork Powder
Drying (30 min, 55-65°C)
20 min
15 min
