Application of Contact Angle Measurement to the Manufacture of Textiles Containing

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Textile Research Journal

DOI: 10.1177/0040517508100724 2009; 79; 1202 Textile Research Journal

Fabien Salaün, Eric Devaux, Serge Bourbigot and Pascal Rumeau Microcapsules

Application of Contact Angle Measurement to the Manufacture of Textiles Containing

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Textile Research Journal Article

Textile Research Journal Vol 79(13): 1202–1212 DOI: 10.1177/0040517508100724 © The Author(s), 2009. Reprints and permissions:http://www.sagepub.co.uk/journalsPermissions.nav

Application of Contact Angle Measurement to the Manufacture of Textiles Containing Microcapsules

Fabien Salaün1 and Eric DevauxLaboratoire de Génie et Matériaux Textiles (GEMTEX), UPRES EA2461, Ecole Nationale Supérieure des Arts et Industries Textiles (ENSAIT), BP 30329, 59056 Roubaix Cedex 01, France

Serge BourbigotLaboratoire des Procédés d’Elaboration des Revête-ments Fonctionnels (PERF), UPRES EA1040, Avenue Dimitri Mendeleïev – Bât. C7a, BP 108, 59652 Villeneuve d’Ascq Cedex, France

Pascal RumeauInstitut Français du Textile et de l’Habillement, Direction Régionale Rhône-Alpes PACA, Avenue Guy de Collongue, 69134 Ecully Cedex, France

For the last decade, functional textiles have been devel-oped to enhance textile performances according to theconsumers’ demand and to include a large range of proper-ties with a higher added value. One of the possible ways tomanufacture functional textile products is the incorpora-tion of microcapsules or the use of microencapsulationprocesses for textile finishing. Although microencapsula-tion has been in use for a long time in many industries,including pharmaceutical, carbonless copy, agricultural,food processing, cosmetics and bulk chemistry, it has onlyrecently been introduced in the textile industry [1]. Manyof the substances are encapsulated for potential textileapplications. During the 1990s, this technique madeprogress in the field of phase change materials (PCMs) forthermoregulation [2], in durable fragrances for aromather-apy or controlled release [3], and in cosmetics for cosmeto-textiles which can impart skin care benefits and promote afeeling of well-being. Other applications developed includedyes (thermochromic, photochromic, reactive or dis-persed) [4], insect repellents [5], antimicrobials [6], andfire retardant or intumescent compounds [7].

Microencapsulation is a technique that allows an activesubstance to be entrapped by a suitable polymer wall on avery small scale. The functional performance of the micro-capsules depends on the morphology, the chemical nature

and the surface characteristics of the polymeric shell influ-enced by the process parameters [8]. The choice of a partic-ular process is determined by the solubility characteristics ofthe active compound and the shell material. Thus, the for-mulation of sophisticated shell and the development of thetechnologies allow a wide variety of functionalities to beobtained.

The step of encapsulation allows the active substance tobe integrated in a textile coating, in a textile by impregna-tion or exhaust bath [9], or directly incorporated in differ-ent artificial fibers, e.g. polyacrylonitrile fiber [10],polypropylene fiber [11], or polyacrylonitrile-vinylidenechloride fiber [12]. They will remain effective as long as thecoating or the fibers stay intact [13–15]. All common coat-ing processes, such as knife over roll, knife over air, orscreen printing, can be adapted to apply microcapsules tofabric. The method for manufacturing coating compositionhas been widely described in the patent literature. Never-theless, few papers published in the literature give account

Abstract The efficiency of a binder to link micro-capsules on a textile surface depends on the com-patibility of the different interfaces of the productsinvolved in the coating process. The choice of abinder adapted to the microcapsules was deter-mined in this study by the comparison of the surfaceenergy components induced by the contact anglemeasurement method and washing tests. It wasfound that a polyurethane-based binder was themost suitable to link melamine formaldehyde micro-capsules. Furthermore, the adhesion of micro-capsules was closely dependent on the chemicalnature and structure of the textile support.

Key words binder, coating textiles, microen-capsulation, surface energy, washing test

1 Corresponding author: Laboratoire de Génie et MatériauxTextiles (GEMTEX), UPRES EA2461, Ecole Nationale Supérieuredes Arts et Industries Textiles (ENSAIT), BP 30329, 59056 Rou-baix Cedex 01, France. e-mail: [email protected]



Application of Contact Angle Measurement to the Manufacture of Textiles Containing Microcapsules F. Salaün et al. 1203 TRJ

of the formulation of coating, finishing of fabrics, and there-fore the evaluation of their characteristics, more specificallythermal and durability properties [16, 17]. However, thechoice of the process influences the microencapsulated fab-ric behavior and the yield [9].

The choice of the appropriate fibrous structure is linkedto the capacity of the textile structure to carry a sufficientquantity of the microcapsules and whether it can providean appropriate heat transfer to microcapsules. The follow-ing study developed the different steps taken into consider-ation in order to link efficiently the microcapsules to textilesupports with a binder. It was based on two approaches;the first one was a thermodynamical approach of the wet-ting that characterizes the interfaces between the textileitself, the binder and the microcapsules, and the secondone was the washing fastness of the microcapsules oncelinked on the textile with the binder. A knowledge of thewettability and surface free energy of microcapsules is veryimportant in the design of textile formulations. This type ofinformation can help in the selection of the components ifthe interfacial interactions and compatibility of the formu-lation components are known. Thus, the first step consist-ing of the comparison between the components of thebinder’s surface energy and those of the resins that formthe microcapsule shells helped us to perform our formula-tion. Then, the second step, validated by the ISO 6330norm – washing fastness – picked up the best binderaccording to the best washing fastness results.

Background

Contact Angle Measurement: Surface Energy DeterminationSurface energy determination by means of contact anglemeasurement has been frequently used to investigate thesurfaces properties of textiles [18–20]. These studies showedthat surface energy determination is an appropriate methodto investigate textile surface characteristics such as adhesionproperties. Contact angle measurement (Figure 1) is awell-known technique in many fields such as contamina-tion control, adhesion, surface treatments, and polymerfilm modification. The measurement of contact anglesyields data which reflect the thermodynamics of a liquid/solid interaction.

In this study, surface energies were estimated using thegeometric mean approach of Owens-Wendt [21], takinginto account the dispersive and polar components of thesurface energy and based on Young-Dupré equation(equation (1)) [22]:

(1)

where θ is the equilibrium contact angle, measures betweenthe tangents to the liquid-vapor and solid-liquid interfaceswithin the liquid phase, under the action of the three interfa-cial forces, i.e. solid-vapor (γSV) (mN.m−1 or mJ.m–2), solid-liquid (γSL) (mN.m−1 or mJ.m–2), and liquid-vapor (γLV)(mN.m−1 or mJ.m–2) tensions (Figure 2).

The relationship between the contact angle (θ) of theliquid phase deposited onto a solid phase is derived fromthe general Fowkes expression which considers the polarand dispersive contributions for both solid and liquid des-ignated as γS and γL, with a superscript ‘d’ or ‘p’ for the dis-persive and polar contribution, respectively.

(2)

Thus, from equation (2) for two different test liquids it ispossible to determine the surface energy of the solid phase(γS) as the sum of two components: a dispersive component( ) attributable to London attraction, and a specific (orpolar) component ( ) owing to all other types of polarinteractions such as hydrogen bonding.

γSV– γSL γLVcosθ+ + 0=

Figure 1 Contact angle measurement system

Figure 2 Schematic of a sessile drop, contact angle (θ),and the three interfacial tensions (γlv: liquid–vapor, γsv:solid–vapor, and γsl: solid–liquid) on substrate.

γL 1 cosθ+( ) 2 γLdγS

d( )

12---

2 γLpγS

p( )

12---

+=

γSd

γSp



1204 Textile Research Journal 79(13)TRJTRJ

Relation between Surface Energy and Adhesion

Adhesion is a manifestation of the attractive forces thatexist between all atoms or molecules and which fall intotwo broad categories, i.e. primary (chemical bond) and sec-ondary (van der Waals force and hydrogen bonds). Toassess wetting and adhesion properties, it is necessary toconsider the work of adhesion between two phases. Thework of adhesion (Wadh) describes the work necessary toseparate two solid phases (S1 and S2) so that two new sur-faces of unit area are formed. Therefore, it refers to thefree energy difference between two defined states, the firstof two phases in contact in equilibrium and the secondcomprising the two phases separate in equilibrium in vacuo[23]. The work of adhesion (Wadh) of the liquid drop on asubstrate is given by:

(3)

Combining equations (1) and (3) yields the following equa-tion, relating the contact angle to the work of adhesion:

(4)

In our case, it was important to know whether this inter-face was stable towards liquids and more especiallytowards water. Thus, the work of adhesion is:

(5)

Adhesion is not assured when the interface is immersed ina liquid like water and Wadh is negative, since the freeenergy of the system is reduced and therefore the separa-tion of the two solids is favored.

Experimental

MaterialsMelamine (99%, Acros Organics) and formaldehyde(37 wt% aqueous, Acros Organics) were used as mono-mers; n-hexadecane, n-eicosane and tetra ethyl orthosili-cate (TEOS) (Acros Organics) were used as core material.Nonionic surfactants, Tween 20 and Brij 35 (Acros Organ-ics), were used as emulsifiers. Methanol (99.8%) and 1,6-hexanediol (99%) were also obtained from Acros Organ-ics. For pH control, triethanolamine, sulfuric acid and cit-ric acid were used (Aldrich).

Preparation of Microcapsules

Prepolymer solution synthesis: 100 ml of a 37 wt% strengthaqueous formaldehyde solution was adjusted to pH 9 withtriethanolamine in 500 ml three-neck flask equipped withan anchor stirrer and a condenser at 80 °C. After adding21 g of melamine, a clear solution was formed and wasstirred until boiling occurred. After cooling down to 62 °C,pH was reduced to 1 with sulfuric acid (10 wt%). When thecontents had acquired a milky turbid appearance, 76 ml ofmethanol was added. The content of the flask was cooledto 40 °C over the course of an hour. The solution was neu-tralized with triethanolamine, which terminated the reac-tion and the excess alcohol was distilled off. This resin maybe written as MF5.6Me, where M represents the melamine,F the formaldehyde, Me the methanol, and the subscript isthe molar ratio of formaldehyde per melamine. TheMF5.6Me-He was synthesized by the process as describedabove, where the methanol solution was replaced by amethanol/1,6-hexanediol mixture. The reaction scheme forthe synthesis is given in Figure 3.

Microencapsulation: the microencapsulation of corematerial was carried out in a 500 ml three-neck round-bot-tomed flask equipped with a mechanical stirrer via an insitu polymerization. Prior to the encapsulation, 24 g of n-hexadecane, 24 g of n-eicosane and 2 g of TEOS wereemulsified into a continuous phase containing 125 g of theprepolymer solution (MF5.6Me or MF5.6Me-He), 200 ml ofdistilled water and 10 g of a binary mixture of Tween 20and Brij 35 at pH 4 stirring at 13,500 rpm using an ultraturrax high speed homogenizer (Ika T 25 basic, Germany)at room temperature. The stirring speed was decreased to700 rpm with an anchor stirrer after 15 min, and the emul-sion was stirred for 4 h at 55 °C. Then, the pH of the solu-tion was adjusted to 9 with 50 wt% triethanolaminesolution to complete the reaction.

Sample Preparation

Textile supports: a 100% cotton fabric (566 dtex warp and564 dtex weft yarns at densities of 26 ends/cm × 16 picks/cm, weighing 270 g/m2, thickness of 0.50 mm) (COTTON)and a 100% polyester fabric (345 dtex warp and 290 dtexweft yarns at densities of 18 ends/cm × 17 picks/cm, weigh-ing 120 g/m2, thickness of 0.22 mm) (PES) were chosen asthe specimens.

Binders: the commercial binders used in this studywere: Alcoprint PB-66 (ethyl butyl acrylate from Ciba Spe-cialty Chemicals), Alcoprint PB-HC (polyethyl acrylatefrom Ciba Specialty Chemicals), Dicrylan AS (polydimeth-ylsiloxane polyacrylate from Ciba Specialty Chemicals),Dicrylan PMC (polyurethane from Ciba Specialty Chemi-cals), Airflex EP 177 (ethylene vinyl acetate copolymersfrom Air Products), and Airflex EN 428 (ethylene vinylacetate copolymers from Air Products).

Wadh γSV γSL γLV––=

Wadh γLV 1 cosθ+( )=

Wadh γS1/water γS2/water γS1/S2–+=




Impregnation: the textile impregnation of the two fab-rics was made under the different baths containing thebinder and the microcapsules at different concentrations.It was carried out by immersion of the fabrics at 2 metersper min in the different formulation baths. Once impreg-nated, the samples were pressed by a BENZ vat paddingdevice without pressure in order to keep the microcapsulesintact. Then, the drying treatment step was performed in aBENZ frame under ventilation at 0.5 meter per min speedduring 4 min at 100 °C (to evaporate the water) and 4 minat 150 °C (to ensure adequate binder crosslinking).

Characterization TechniquesCharacterization of the Solid Surface: Contact Angle MethodThe thermodynamic theory on surface properties allowedthe relation describing the surface adhesion properties tobe obtained. Thus, the interface study of the binder/micro-capsule was based on a wetting approach by the contactangle measure that characterizes the interaction between aliquid and a solid. Contact angles were estimated with agoniometer equipped with a special optical system and acamera (Figure 1). A drop of liquid was placed on a poly-mer film and the image was immediately sent via the cam-era to the computer for analysis. The volume of the dropwas about 6 µl. Constant values for the test liquids used forcontact angle measurements were as follows [24]:

Water: γl = 72.8 mJ/m2, γld = 21.8 mJ/m²,γlp = 51.0 mJ/m²;

Diiodomethane: γl = 50.8 mJ/m2, γld = 48.5 mJ/m²,γlp = 2.3 mJ/m².

The contact angles were measured by two referent liquids,which were water and diiodomethane on two melamineformaldehyde resin films (MF5.6Me or MF5.6Me-He).MF5.6Me film was obtained from the polycondensation of amethanol-etherified methylolmelamines prepolymer, andMF5.6Me-He film from the polycondensation of a hexane-diol-etherified methylolmelamines prepolymer and thencompared with the measures obtained on films of sixcrosslinked binders that had been put into an oven at 150°C for 5 min. These films were very uniform spatially, butdid exhibit hydration, which meant that their contact anglevaried according to the exposure of the tested liquid on thevapor. Therefore, each contact angle was measured twice,as a function of time, with t = 0 corresponding to the firstcontact of the liquid with the dry surface and at the timethe angle became steady-stable, when the two surfaceswere equilibrated – generally after a few seconds. Duringthe rest of this study, we took only the second angle meas-ures into account.

Each surface was measured with five independent dropsof the two referent liquids, allowing us to distinguish inde-pendently the dispersed and the non-dispersed compo-nents of each material. No significant variations werefound within any single surface. Drops were always placedat least 10 mm apart and never closer than 10 mm to anedge.

Figure 3 Formation of cross-linked amino resin shell.




Washing Machine ISO TestThe washing fastness tests of the interface binder/micro-capsules/textile were made in the Wascator washingmachine, half charged, at 40 °C, wool program, under thenorm NF EN ISO 6330. After each washing cycle, the sam-ples were conditioned under normal values: 20 °C for thetemperature and 65% humidity for the humidity rate.

Scanning Electron Microscope (SEM) ImagesThe conditions of the attached microcapsules and the char-acterizations of the interface binder/microcapsules andbinder/textile were observed by electronic scanning micros-copy (Philips XL 30 ESEM), with an accelerating voltageof 20.0 or 25.0 kV and 2,000 or 5,000 × magnifications.

Fourier Transform Infrared (FTIR) SpectroscopyThe structure of the shell polymer was analyzed by FTIRspectra. Samples were ground and mixed with KBr to makepellets. FTIR spectra in the transmission mode wererecorded using a Nicolet Nexus, connected to a PC, in whichthe number of scan was 32 and the resolution was 4 cm–1.

Results and Discussion

Microcapsule Characteristics

Two types of microcapsules containing PCMs wereobtained by an in situ polymerization. The surface mor-phology of the microcapsules and chemical structure of thepolymeric shells were investigated using SEM and FTIRspectroscopy, respectively (Figures 4 and 5). As shown inFigure 6, the resulting microcapsules had relatively uniformsizes, spherical shape and smooth surface. No destruction ofthe capsule walls due to mechanical agitation was perceiva-ble. The main difference between the two samples wastheir mean diameter. The particles from MF5.6Me resinhad a mean diameter of about 1.5 µm, whereas those ofMF5.6Me-He had one of about 5 µm.

The FTIR spectra of the microcapsule shells (MF5.6Meand MF5.6Me-He) are shown in Figure 5. Characteristicbroad band responsible for hydroxyl, imino and aminostretching was observed around 3350 cm–1. Alkyl C-Hstretching vibration was found around 2950 cm–1. The C-Nmultiple stretching in the triazine ring was observedaround 1551 cm–1. C-H bending vibration in CH2 wasfound at 1490 cm–1 and 1360 cm–1 due to methylenebridges. The characteristic absorption bands of aliphatic C-N vibration appeared between 1200 and 1170 cm–1. Theband at 1650 cm–1 corresponded to the stretching mode ofC=N. Characteristic triazine ring bending could also beobserved at 810 cm–1. C-O-C stretching due to ether bridgeat 1110 cm–1 was also present in Figure 5.

As shown in Table 1, the surface free energy and its spe-cific components decreased with the incorporation of hex-anediol in the polymer shell, while the London dispersivecomponent increased. As expected, the work of adhesionfor water on microcapsules with MF5.6Me shell (127.4 mJ/m2) was higher than MF5.6Me-He microcapsules (99.2 mJ/m2) (Table 1). These results indicated that the surface ofmicrocapsules was modified with increased hydrophobicgroups during the polymerization. The chemical differencebetween the two amino polymers was based on the triazinesubstitution lengths that varied from 2 to 6 atoms of car-bon. This modification involved a higher non-dispersivebehavior for MF5.6Me microcapsules than MF5.6Me-Hemicrocapsules.

Surface Energy of BindersThe results of the contact angles and the surface energycalculations are shown in Table 1. The test results indicatedthat the polyacrylate binders all had much higher surfaceenergies than the other polymers. These higher surfaceenergies were mainly due to the contribution of the polar

Figure 4 SEM images of microcapsules from MF5.6Me (a)and MF5.6Me-He (b) resins.




component. The presence of ester groups in the polyacr-ylate backbone may explain this high polarity. Further-more, the presence of butyl groups to polyacrylate resultedin an increase of the contact angle with water correlated toa decreased diiodomethane contact angle value. Thus, thelength of the lateral chain led to a decrease in the polarcomponent and governed the surface energy of the poly-acrylate binders. The vinyl acetate copolymers and the pol-yester urethane presented low surface energy. It seemedthat the values were closely linked to the dispersive compo-nent of the materials. The contact angle values with water

and diiodomethane decreased in the presence of acrylicacid in vinyl acetate copolymer (Airflex EN 428). There-fore, this binder was more hydrophobic than the AirflexEP 177. From these results, the component of surfaceenergy and therefore their wetting behavior were closelydependent on the chemical structure of the binders.

Figure 5 FT-IR spectra of MF5.6Me(a) and MF5.6Me-He (b) resins.

Figure 6 Washing fastness of coated samples.




Interface Binder/MicrocapsulesBinder ResultsThe results of the Wadh calculations with water showed thatthe adhesion was assured for the binders Alcoprint PB-66,Dicrylan PMC, Airflex EP 177 and Airflex EN 428 witheither MF5.6Me or MF5.6Me-He. The measures of the con-tact angles allowed us to find out the more suitable bindersfor the link binder/microcapsules (made of MF5.6Me orMF5.6Me-He). They were Alcoprint PB-66, Dicrylan PMC,Airflex EP 177 and Airflex EN 428, because their disper-sive and non-dispersive components were close to the onesof the microcapsule wall and because their Wadh was posi-tive when wetted by water. The values of the componentsof the surface energy that we measured were parallel to thevalues given in the literature, even if they were slightlyhigher [25].

Interface Binder/Microcapsules/TextileThe wetting of textile fabrics can be explained by a physicalphenomenon basis of the system solid-liquid-air. Themeasurement of the fabric surface wetting is a very sophis-ticated and complicated process because of the fabricroughness, heterogeneity and because of the diffusion ofthe liquid into the fiber and the capillarity of the fiber

assembly. Contact angles can range from 0° (complete wet-ting) to 180° (non-wetting). Therefore, on a fiber it is moreconvenient to visualize its wet ability by observing thewater’s contact angle on its surface; when it is near 0°, thenit means that the fiber is hydrophilic and almost completelywettable. However, on the textile fabric itself, the porescreated by the yarn twilling involves the ability of the liquidto withdraw or to spread. Therefore, the experimentallymeasured contact angles on a textile surface can vary con-siderably from the contact angle for an ideal system. Directcontact angle measurements on textile surfaces were notreliable for our study. Thus, the adhesion of the adequatebinders determined with the interface binder/microcapsulemethod with the textile surfaces was characterized by thewashing fastness (NF EN ISO 6330) of the coated samples.Furthermore, as Airflex EP 177 and Airflex EN 428 hadthe same component surface energies, we chose to workwith Airflex EN 428 only.

The binders did not react the same way depending onthe chemical structure and the contexture of the textilesfabrics; this was due to their internal physical characteris-tics, but also to their different surface energies. On allSEM micrographs (Figures 7 and 8), we observed a totalwrapping of the binder around the textile fiber. However,the behavior of the binder on the cotton fabric and on thePES fabric varied. On the cotton, the binder tended to coat

Table 1 Contact angle measures and surface energy components.

Polymer Contact angle Component of surface energya (mJ/m²)

Work of adhesion (mJ/m²)

θwater

(°)θdiiodomethan

e (°)γs

d γsp γs

MF5.6Me methanol-etherified methylolmelamine

27.4 39.4 26.0 39.6 65.6 Wadh MF5.6Me -waterb

137.4

MF5.6Me-He hexanediol-etheri-fied methylol-melamine

68.7 42.0 32.0 10.6 42.6 Wadh MF5.6Me-He -waterb

99.2

Wadh MF5.6Me -Bic Wadh MF5.6Me-He -Bic

Alcoprint PB-66 ethyl butyl acrylate 28.7 38.2 26.7 38.3 65.0 –14.1 –12.1

Alcoprint PB-HC polyethyl acrylate 22.6 70.6 10.1 59.7 69.8 1–4.3 –22.8

Dicrylan AS polydimethylsiloxane polyacrylate

20.5 65.9 12.1 57.7 69.8 1–3.4 –20.5

Dicrylan PMC polyurethane 79.5 49.5 30.1 16.0 36.1 –13.6 –54.1

Airflex EP 177 ethylene vinyl acetate copolymers

91.1 54.2 29.9 12.0 31.9 –14.1 –64.3

Airflex EN 428 ethylene vinyl acetate copolymers

83.8 51.8 29.7 14.3 34.0 –13.8 –58.2

a γs is the surface energy, and γsd and γs

p are the dispersive and polar components, respectively (equation (2)); b Bi: binder; c calculated from equation (4).




the twilling parts of the yarns, which involved a surfacecoating by creating crosslinked areas as the binder couldnot penetrate the pores of the fabric. On the PES, thebinder wrapped the fibers homogeneously inside the coreof the fabric.

The incorporation of the microcapsules in the binderformulation did not modify the cotton surface coating. Itseemed that the microcapsules created crosslinked areas ofcoating between the PES fibers attributed to an increase inviscosity of the formulation.

The microcapsules were linked to the surface of the fib-ers either by being completely wrapped by the binder, or bycreating a linkage with the binder between the fibers.

The different binders did not have the same behavior;Alcoprint PB-66 seemed to have a better adhesion to thefiber than to the microcapsules, as it created agglomeratesof microcapsules instead of fixing them individually to thefiber. The washing test (Figure 6) confirmed this trend,

since after 20 washing cycles, the loss of weight was higherfor fabrics treated with Alcoprint PB-66 than with theother binders for both cotton and PES.

The coatings on PES fabric were more resistant than oncotton, as more impregnated in the core of the fabric, somore protected by the friction during washing.

On the SEM micrographs (Figures 7 and 8) of the coatedtextiles after 20 washing cycles, we observed holes at thefiber surface, which was more subject to frictions. Theseholes represented the place where a microcapsule waslinked with the fiber, so it meant that the adhesion was bet-ter for the binder and the microcapsule than for the binderand the fiber – especially in the case of Alcoprint PB-66.This involved the problem of the adhesion of the binder tothe fiber that appeared more brittle than the adhesion ofthe microcapsules and the binder.

The behavior differences between the binders with thewashing fastness tests were in accordance with the differ-

Figure 7 SEM micrographs of PEScoating with Alcoprint PB-66 (a),Dicrylan PMC (b), Airflex EN 428 (c);with Alcoprint PB-66 + microcap-sules (d), Dicrylan PMC + micro-capsules (e), Airflex EN 428 +microcapsules (f); with AlcoprintPB-66 + microcapsules after wash-ing test (g), Dicrylan PMC + micro-capsules after washing test (h),Airflex EN 428 + microcapsulesafter washing test (i).




ences already noticed on the adhesion of the binder andthe microcapsules, as for Alcoprint PB-66, the values ofwork adhesion were already worse than the other ones.

According to the different tests, surface energy calcula-tions and washing tests, it appeared that Dicrylan PMCwas the more efficient binder to confine the melamine for-maldehyde microcapsules to the textiles, both cotton andPES.

Binder Concentration InfluenceThe efficiency of adhesion was linked to the nature of thebinder and to its proportion used for the coating formula-tion (Table 2). When the weight of the binder represented33% of the coating formulation, less weight loss wasobserved with a formulation of 45 g/m² on the fabrics.Thus, the impregnation mechanism could be divided intotwo steps. First, the binder and the microcapsules filled the

core of the textile, and second, once this area was full, therest of the formulation settled at the surface of the coatedstructure. Therefore, the more binder/microcapsules onthe textile surface (g/m2), the higher the loss of weight after20 washing cycles, because the coating settled on the sur-face was more sensitive to frictions than the coating pene-trated through the textile.

On the PES fabric, it was clear that a high concentra-tion of microcapsules reduced the adhesion of the coatingto the textile fabric. On the cotton fabrics, adhesion wasnot affected by the microcapsule concentration. This wasprobably due to the cotton fiber surface that was notsmooth enough, so the presence of the microcapsulesincreased the specific contact surface, and thus a betteradhesion. This adhesion could be improved by the pres-ence of hydroxyl groups on the cotton, which could createa covalent bond with the functional groups attached to thepolymer binder.

Figure 8 SEM micrographs ofCOTTON coating with Alcoprint PB-66 (j), Dicrylan PMC (k), Airflex EN428 (l); with Alcoprint PB-66 +microcapsules (m), Dicrylan PMC +microcapsules (n), Airflex EN 428 +microcapsules (o); with AlcoprintPB-66 + microcapsules after wash-ing test (p), Dicrylan PMC + micro-capsules after washing test (q),Airflex EN 428 + microcapsulesafter washing test (r).




The presence of blocked isocyanate in the formulationreduced the weight lost after washing. The unblocking dur-ing the binder’s reticulation allowed the formation of cova-lent bonds the binder/fiber and microcapsule/binder. Wenoticed that we could fix up to 15% of microcapsules oncotton and 65% on PES without requiring the use of thebinder. In fact, the microcapsules were locked between thetwilling of the fibers and the isocyanate helped to increasetheir adhesion. Indeed, the loss of weight of the coating onthe textile surfaces that were impregnated by microcap-sules alone was of 100% after several washing cycles.

Conclusion

The adhesion of microcapsules on a textile support is acomplex phenomenon linked to the physical and chemicalcharacteristics of the different involved compounds. Theadhesion study was divided into two steps; the analysis ofthe binder/microcapsules based on the thermodynamicwetting approach and the analysis of the binder/textileinterface based on the NF EN ISO 6330 test norm. Wenoticed a good result correlation of these two approaches.

By the wetting and washing approaches, binder basedon polyurethane polymer was the most suitable for mela-mine formaldehyde microcapsules. The use of a blockedisocyanate in the coating formulation allowd the washingfastness to improve. Better results were obtained with PESfabric than cotton fabric, mainly influenced by the struc-ture of the textile substrate. A dense structure led to a brit-tle coating on the surface, whereas with a less densestructure, the binder wrapped the fibers homogeneouslyinside the core of the fabric which ensured a better adhe-sion.

Regarding the concentration of binder/microcapsulesthat should be used for the best washing fastness, accord-ing to the final desired effect of the microcapsules, it hasbeen proved that it was not necessary to have high concen-trations of both binder and microcapsules. Indeed, it wasmore judicious to determine a good proportion of micro-capsules/binder (66/33 wt%) to limit the loss of coatingweight after washing.

Table 2 Washing fastness of coated samples (μc: microcapsules).

Textile supports Formulation (g/m²) (µc + Dicrylan PMC)

Weight of binder in the formulation (wt%)

Weight loss of coating after 20 washing cycles

PES

59 15 43

70 25 26

53 33 20

44 33 10

26 33 17

90 45 12

66 100 10

32 30/(3)a 17

23 (5)a 35

COTTON

57 15 38

68 25 20

47 33 19

29 33 27

28 33 28

63 45 12

16 100 43

26 30/(3)a 22

17 (5)a 85

a Weight of blocked isocyanate in the formulation (wt%).




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Documents

Application of Contact Angle Measurement to the Manufacture of Textiles Containing