2.1 Introduction - INFLIBNETshodhganga.inflibnet.ac.in/bitstream/10603/34650/7/07_chapter 2.pdf · called as the acetone process. This process is easily performed and very reproducible

Chapter 2

Department of Chemistry, S. P. University Page 43

This chapter deals with the synthesis of polyurethane dispersions.

2.1 Introduction

Aqueous polyurethanes are two-fold systems in which polyurethane

particles are dispersed in continuous aqueous medium i.e. water.

Polyurethane dispersions belong to a unique class of colloidal

dispersions that are mixtures of different chemical species where the

interfacial area plays a dominant or at least important role, so that their

properties depend robustly on the interfacial forces or physicochemical

interactions [1, 2]. A colloidal dispersion is stable when the droplets

(discontinuous phase) persist uniformly in the liquid medium (continuous

phase). The dispersion becomes unstable when the droplets diffuse together

to form a single bigger droplet that leads to a reduction in the total surface

area (coalescence) or to form an aggregate of particles without producing a

new particle (flocculation). The role of polymer in stabilization or flocculation

of colloidal dispersion has been studied extensively in the recent past. [1-5].

Waterborne polyurethane is constituted by a linear thermoplastic

polyurethane backbone which is dispersible into water due to the presence of

ionic groups in its structure (i.e. a polyurethane ionomer) which act as an

internal emulsifier. These ionic groups could be cationic (quaternary

ammonium groups), anionic (carboxylated or sulfonated groups), or non ionic

(polyols with ethylene oxide end groups).

The ionic groups in the ionomer impart the ability of dispersion of

polyurethane into water, normally producing stable dispersions. In water, the

stabilization effect of the ionic sites is due to the formation of tiny spheres

which contain a core of aggregate hydrophobic segment and a boundary layer

carrying the ionic groups. The result is a surprisingly stable hydrosol or

aqueous dispersion. [6]

Among all the most common are anionic groups. Anionic waterborne

polyurethane can be prepared from polyols containing carboxylic acids and

Chapter 2


sulfonic acid groups. Steric hindrance of the polyols prevents the potential

reaction of the acid groups with the isocyanate during the preparation. To

achieve solubility, the acid groups are neutralized using basic compounds,

e.g. tertiary amines. The choice of neutralizing agent also influences the

properties of the dispersions. Scheme is shown in Figure 2.1.

Figure 2.1. Anionic polyurethane dispersion with carboxylate groups

Cationic polyurethanes are the reaction products of isocyanate

prepolymers with building blocks containing tertiary amines, quaternized

withprotonic acid or alkylating agent which forms the water soluble groups in

the polymer. Generally, due their application properties cationic polyurethanes

are of lesser importance except in special applications.

Water-emulsifiable polyurethanes of non-ionic type are yielded by

incorporating hydrophilic, non-ionic building blocks. They are the mostly water

soluble polyethers based on ethylene oxide. The functional ether can be part

of the backbone or preferably, located in the termination of the polyurethane

chain. Scheme is shown in Figure 2.2.

Chapter 2


Figure 2.2. Non-ionic polyurethane dispersion

Basically, waterborne polyurethane can be described as reactive or

non-reactive polymers containing urethane and urea groups which are

stabilized in water by internal or external emulsifiers. These different

hydrophilic modifications allow the production of stable waterborne

polyurethanes with average particle sizes between 10 to 400nm.

2.2 Chemistry of polyurethane dispersions

Many of the scientists have worked on these systems by many

different pathways. Within the decades of research work and by using several

processes this dispersion are described on the principle of incorporating

hydrophilic centers into a macromolecular chain of a polyurethane poylurea

molecule. In the known dispersions, these hydrophilic centers are so called

“internal emulsifiers” are ionic groups or ether functions. The ionic groups are

either incorporated in the prepolymer in the form of certain diols or used as

modified amines for chain lengthening the prepolymers.

Several processes have been developed for the synthesis of

polyurethane dispersions discussed briefly by Dieterich, fosthauser and Kim et

Chapter 2


al [7, 8, 9,]. The basic principle involved in producing NCO-terminated

polyurethane prepolymer with appropriate molecular weights.

All of these have in common the first step, in which a medium

molecular wight polymer ( theprepolymer) is formed by the reaction of

suitable diols or polyols, (usually macrodilos such as polyethers or polyesters )

with a molar excess of disocynates or polyisocynates. In this reaction mixture

and internal emulsifier is usually a diol with an ionic groups (carboxylate,

sulfonate, or quaternary ammonium salt) or a nonionic group (poly ethylene

oxide). Internal emulsifier becomes part of the main chain of the polymer.

The critical step in which the various synthetic pathways differ is the

dispersion of the prepolymer in water and the molecular weight buildup. [10-

13]. There are four main processes.

(A) Solution Process (Acetone process):

First, hydrophilically modified isocynate prepolymer or ionomer is

prepared in a lot of hydrophilic solvent, with low boiling point e.g. acetone,

methyl ethyl ketone or tetrahydrofuran. The solution is subsequently chain

extended in solution in order to prevent high viscosity and dispersed by slow

mixing with water. As more water is added a phase inversion occurs, water

becomes the continuous phase and dispersion is formed. Then the solvent is

removed by distillation. Solvent free aqueous polyurethane dispersion can

only be yielded after the removal of the solvent by distillation. An aqueous

dispersion of the polyurethane ionomer is obtained by this process is

discussed in detail in literatures. [7-9 ]

The preferred solvent is acetone and therefore this process is often

called as the acetone process. This process is easily performed and very

reproducible since the polymer formation is accomplished in a homogenous

solution. This process is limited to uncrosslinked, acetone soluble polymers.

This process also suffers from a low reactor volume yield due to large

quantities of solvent which are used. This method is discussed and

understood by the work done my scientists Xio HX, Duan Y, Pedian J, Cheng

Chapter 2


KL, Trieber RL, Yang CH, Brani A, Tripak RL, Chenwanitcharoen C [14-20, 21-

31]. Scheme is shown in Figure 2.3.

Figure 2.3. Preparation of aqueous polyurethane dispersion by acetone

process

(B) Prepolymer mixing process:

Another way to synthesize polyurethane dispersion is the so-called

prepolymer mixing process discussed in literatures [1, 2, 32-42]. This process

avoids the use of large amounts of solvents as necessary in acetone process.

In this process, a medium molecular weight polymer (the prepolymer) is

synthesized by the reaction of suitable diols or polyols (usually polyether or

polyester macrodiols) with a molar excess of diisocynates or polyisocynates.

In this reaction mixture, an internal emulsifier is added to allow the dispersion

of the polymer in water; this emulsifier is usually a diol with ionic groups

(carboxylate, sulfonate or quaternary ammonium salt) or nonionic groups.

The internal emulsifier becomes part of the main chain of the polymer.

Approximately, 15-20 % water miscible organic solvent, typically N-methyl

pyrrolidinone (NMP) is used to reduce the viscosity of the medium as well to

Chapter 2


dissolve the internal surfactant. This prepolymer is dispersed by the addition

of water and the use of high speed agitation. External emulsifier and high

shear forces are not required. The final step is the chain extension with a

water soluble diamine or polyamine to build up the molecular weight of the

polymer. Scheme is shown in Figure 2.4.

Figure 2.4. Preparation of aqueous polyurethane dispersion by prepolymer

mixing process

(C) Hot melt process:

The hot melt process is a solvent free method of preparing aqueous

polyurethane dispersions. It combines the isocynates poly-addition reaction

followed by an amino-plast polycondensation reaction. The first step is the

synthesis of an isocynate terminated prepolymer at an elevated temperature

(>130) with an excess of urea to form biuret. The capped polyurethane is

dispersed with hot water (100) to minimize the reaction viscosity. Chain

extension is carried out with formaldehyde in the presence of water. In this

way methylol groups are formed which self-condense to give a high molecular

weight product. Production of this type of dispersion requires special powerful

Chapter 2


agitators since even at temperature around 100 C the viscosity of the

prepolymer is usually high. Water dispersed polyurethane prepared by this

process are generally branched and of lower molecular weight.

Among the known solvent-free methods of preparing polyurethane

dispersions, there should also be mentioned the so-called melt dispersion

process as described in German patents [43-45]. In this process, an

oligourethane which has been modified with ionic groups and contains and

contains acylated amino end groups is converted by means of formaldehyde

into the corresponding oligourethane containing methylol end groups

attached to acylated amino groups, and this oligourethane is then chain

lengthened by heat treatment which effects condensation of the reactive

methylol end groups. This chain lengthening reaction may be carried out in

the presence of water so that an aqueous dispersion of polyurethane is

directly obtained. The process is particularly suitable for the preparation of

cationically-mocified polyurethanes or the preparation of ppolyurethanes

containing anionic carboxylate groups. The required combination of an

isocynate polyaddition reaction with the aforesaid chain lengthening reaction

by way of polycondensable methylol groups which are attached to acyl amono

end groups is a more complicated procedure than the usual isocynate

polyaddition by the prepolymer process in which prepolymer containing

isocynate groups are reacted with conventional chain lengthening agents such

as water or diamines.

(D) Ketamine/Ketazine process:

The ketamine process is similar to the prepolymer mixing method, with

one important difference. The blocked diamine is used as latent chain

extender. The blocked diamine, called ketamine can be added to a hydrophici

isocyanate terminated prepolymer without a reaction taking place. As water is

added to disperse the mixture, the ketamine is hydrolyzed at a rate which is

appreciably faster than the isocynate reaction with water. The librated

diamine then reacts with the dispersed particles of polymer to give a chain

extended polyurethane-polyurea. The chain extension and dispersion step

Chapter 2


occur simultaneously and the viscosity increases steadily until a phase

inversion takes place. For this reason powerful agitation and/or some

cosolvent is often required. A variation of the ketamine process uses ketazine

as the latent chain extender. In this case the ketazine hydrolyzes the

hydrazine. Hydrolysis is slower compared to that of ketamine. This is an

advantage when aromatic isocyanate prepolymers are used. Scheme is shown

in Figure 2.5

Figure 2.5. Preparation of aqueous polyurethane dispersion by Ketimine and

ketazine process

2.3 Morphology:

Polyurethanes owe their versatility of application to the wide range of

properties possible. This is due to their morphology in which the soft segment

is usually formed by a polyol and the hard segment by the diisocynates.

Phase separation results in the hard segment aggregating into domains in the

soft segment matrix. Polyurethane dispersions (PUDs) share morphology with

conventional solvent based and moisture curing PU and so wide range of

properties are possible. A further advantage of this type of morphology is the

excellent film forming properties due to the soft, i.e. low, glass transition

temperature (Tg) segment.

Chapter 2


Thus polyurethane are segmented polymers comprising of alternating

sequences of soft segments and hard segments, which constitute a unique

microphase separation structure discussed in literature. Since ions are

introduced into either hard or soft segments, and imparting many properties

to the polyurethane matrix, attention being drawn to these polyurethane

ionomers. There has been a wide range of work done in the field of synthesis

and characterization of various kinds of conventional segmented PU,

polyurethane ionomers contain low-polarity flexible segments and urethane

groups, which are polar and capable of interaction via hydrogen bonds. Ionic

groups in polyurethane tend to interact with each other and aggregate but

are attached to the “alien” hydrophobic neighborhood.

The properties of poly (urethane urea) dispersions are dependent on

the chemical structure and compositional variation, the block length, and the

ionic and urea content. Primarily because of inter-urethane/urea hydrogen

bonding, the two segment types tend to phase-separate in PU, forming

microdomains [46, 47]. The driving force for microdomains formation includes

hydrogen bonding in urethane/urea groups, the electrostatic interaction

(Columbic forces) between the ionic groups, and the crystallization of both

hard and soft segments. Waterborne PU has extremely good cohesion and

adhesion as well as good mechanical properties because of the presence of

microdomains. Factors influencing this phase behavior include polarity

difference, segment length, crystalline ability of each segment, intra and

inter-segment interactions, over all composition of the PUDs [48-54].

Polyurethane dispersions are thus segmented which generally consist high Tg

hard segment and low Tg soft segment and the properties of the polyurethane

ionomers are mainly determined by the interactions between the hard and

soft segments and by the interactions between the ionic groups.

Dispersed polymeric systems show viscosity, which depends on the

particle size and volume proportion of the dispersed polymer, but which is

insensitive to the variation of molecular weight of the dispersed polymer. In

the formulation of one component coatings advantage can thus be taken from

Department of Chemistry, S. P. University

the resistance properties resulting from high viscosity. As a consequence,

dispersion technology enables preparation of high performance, one

component dispersions with low viscosity an

low VOCs content and high molecular weight

Polyurethane dispersion is shown in Figure.2.6.

Figure 2.6 Schematic representation of Polyurethane dispersion.

2.4 Review Of Literatrue

Synthesis of polyurethane dispersions is

complex heterogeneous morphology of these important classes of systems so

that they can be prepared and used in controlled and reproducible manner. In

addition, the stability, digestibility, film

properties of PUDs are expected to be strongly dependent on their colloidal

state, structure and composition.

Department of Chemistry, S. P. University



component dispersions with low viscosity and comprising simultaneously both

ntent and high molecular weight. Schematic representation of

Polyurethane dispersion is shown in Figure.2.6.

Schematic representation of Polyurethane dispersion.

Review Of Literatrue

of polyurethane dispersions is necessary to understand



addition, the stability, digestibility, film forming properties, and viscoeleastic


state, structure and composition.

Chapter 2

Page 52



d comprising simultaneously both

Schematic representation of

Schematic representation of Polyurethane dispersion.

necessary to understand the



forming properties, and viscoeleastic


Chapter 2


The reaction conditions i.e. the amount of neutralization of the

dispersion and the chain extension methods are proved to be most important

in deciding the colloidal properties of final dispersion as well as it also affect

mechanical properties the PUDs films.

Anita Barli, et al [55] have prepared PUD of the same composition with

different preparation processes like solution process and prepolymer mixing

process. The quality and morphology of the dispersion of different processes

were studied and compared.

M. Barikani, et al [56] have studied the effect of DMPA content on the

state of dispersion, particle size distribution, mechanical, and thermal

properties of the PUD cast film.

Da-Kong Lee, et al [57] have discussed the method of obtaining higher

molecular weight aqueous PUDs form various polycarbonatediols, di(4-

isocyanatocyclohexyl) methane (HMDI), and various carboxylic diols, including

dimethylol propionic acid (DMPA) and a carboxylic polycaprolactonediol. The

molecular weights, particle size, thermal and dynamic mechanical properties

of the PUD were investigated.

Kibret Mequatint, et al [58] have studied and discussed the hydrolytic

stability of nano-particle PUD with ions either on soft segment or on hard

segment.

Mohammand M. Rahman, Han-Do et al [59] discussed synthesis and

characterization of waterborne PUD adhesives containing different amount of

ionic groups.

Chang Kee Kim, Byung Kyu Kim [60] investigated effect of ionic,

nonionic hydrophilic segments, and extender on particle size and physical

properties of emulsion cast film.

M. G. Lu, et al [61] have discussed preparation of series of aqueous

PUDs containing pendant carboxylated anion as the hydrophilic group and the

particle size and the mechanical properties of the dispersion were measured.

Chapter 2


The effects of the molar ratio of NCO/OH groups of the other functional

groups on the chemical structure and the properties were discussed. The

particle size mainly depended on the molar ratio of the functional groups. The

particle size is also governed by the NCO/OH mole ratio. The -NH groups in

urethane and urea linkage formed hydrogen bonding with the carbonyl group

(C=O) of other urethane group in the hard segments or either (C-O-C) in the

soft segments.

Seiji Asaoka et al [62] have prepared segmented polyurethane

dispersions (SPUD) having carboxyl groups in soft segments or in hard

segments. Phase separation, surface, and interface structures of films made

from those SPUDs were examined by differential scanning calorimeter (DSC),

contact angel, and X-ray photoelectron spectroscopy (XPS) measurements.

O. Lorenz, et al [63] have discussed investigation of the particle

surface of anionic polyurethane dispersion with COO- groups prepared by

acetone process using 1,2,4-benzenetricarboxylic acid anhydride as a

potential ionic center.

Stefano Turri, et al [64] prepared series of anionic polyurethane-urea

containing perfluoropolyether (PFPE) segments with a process consisting of a

prepolymerisation step, followed by dispersion in water, and chain extension.

Fluid dynamics and process engineering of the dispersion step were finally

discussed, defining optimal mixing conditions for obtaining controlled and

highly reproducible results.

Mika Lahtinen et al [65] have discussed the chain extension of anionic

prepolymers in the preparation of aqueous poly (urethane-urea) dispersions

and importance of stoichiometric balance of isocyanate to amine molar ratio.

Byung Kyu Kim, et al [66] have obtained novel anionmer-type

waterborne PUDs from (β-methyl-δ-valerolactone) glycol (PMVL) and

isophorone diisocyanate (IPDI) following a prepolymer mixing process. The

soft-hard segment phase separation in response to the variations of

Chapter 2


composition and structure of PU have been studied from the dynamic

mechanical measurements of the emulsion cast films.

Jong Cheol Lee et al [67] have synthesized polyurethane (PU)

cationomers from polytetramethylene adipate glycol (PTAd), ispphorone

diisocyanate (IPDI), N-methyl diethanolamine (MDEA) according to a

prepolymer mixing process. Basic structure-property behavior of the emulsion

and cast film was studied with regard to molecular weight of PTAd.

Samy A. Madbouly, et al [68] have studied the Thermal-induced

gelation for waterborne PUD rheological under isothermal conditions by

characterizing elastic storage modulus and viscous loss modulus.

Ten-Chin et al [69] have studied the effect of DMPA units on ionic

conductivity of PEG-DMPA-IPDI waterborne polyurethane as a single ion

electrolytes. Alternating current (AC) impedance experiments were performed

to determine the ionic conductivies of WPU films and their corresponding gel

electrolytes.

Suk-Hye Son et al [70] have reviewed effect of carboxyl groups

dissociation and dielectric constant on particle size of PUD prepared from

prepolymer mixing process.

Byung Kyu Kim et al [71] have prepared aqueous PUDs of

ionic/nonionic PU from hydrogenated diphenylmethane disocyanate (H12MDI),

poly (tetramethylene adipate) glycol (PTAd), polypropylene glycol (PPG),

monofunctional ethylene-propylene oxide ether, and dimethylol proponic acid

(DMPA). The effects of DMPA, PTAd/PPG ratio, and the average molecular

weight of PPG on the state of dispersion, mechanical, and viscoeleastic

properties of the emulsion cast films were determined.

Young Min et al [72] have prepard and characterized aqueous PUDs

conataining ionic and nonionic hydrphylic segments from (IPDI), (PTMG),

(PPG), and (DMPA) as anionic center. The effects of the PEG/PTAd mixing

ratio, type of polyether polyols, and hard segment content on the state of

Chapter 2


dispersion, surface, dynamic, and tensile properties of emulsion-cast film

were determined.

Hong Xia et al [73] have prepared polyurethane-urea anionomer

dispersion with different stoichiometric DMPA/polyol and NCO/OH ratios were

prepared from poly (oxypropylene) glycol, toluene diisocyanate (TDI),

(DMPA), and ethylenediamine (EDA). The dispersion-cast films were prepared

and characterized by mechanical properties, dynamic mechanical analysis

(DMA), and differential Scanning calorimetry (DSC).

Jung-Eun Yang et al [74] have prepared series of waterborne

polyurethane-urea anionomers by a polyaddition reaction with isophorone

diisocynate, poly (tetramethylene oxide). The effect of the degree of

neutralization and counterion on the particle size of the dispersions, the

conductivity, and the antibacterial properties of PUDs were investigated.

Quing-An Li et al [75] have prepared aqueous polyurethane dispersions

having a solid content of 50% and dimethylol propionic acid as the stabilizing

moiety. The effects of the COOH content, NCO/OH molar ratio, and molecular

weight (Mn) of polyol on the properties of PUD and its cast film were studied.

Charoen Chinwanitcharoen et al [76] have prepared and discussed

preparation of aqueous dispersible polyurethane form hydroxyl-terminated

poly (ethylene adiapte), dimethylol propionic acid, 4,4-diphenylmethane

diisocyanate, ethylene glycol and acetone as a solvent and discussed effect of

acetone on the particle size and storage stability of polyurethane emulsion.

D. J. Hourston et al [77] have prepared number of polyurethane

anionomers based dimethylol propionic acid, dimethylol butanoic acid and

suphonate diol as principal ionic moieties. The consequence of the

neutralization step, the degree of neutralization, the type of ionic component,

and the type of counterion were investigated for their effect on the

mechanical and colloidal properties of the polyurethanes.

Chapter 2


Tania Trombetta et al [78] have prepared model structures of linear

segmented anionomeric polyurethanes based on perfluoropolyether

dimethylol-terminated oligomers, isophorone diisocyanate, and dimethylol

propionic acid in the form of aqueous dispersion. The structures differed from

each other in the chemical nature of the chain extender and in the content of

carboxylic acid. Dispersion and polymer films were characterized.

J. S. lee et al [79] have synthesized polyurethane cationomers form

polypropylene glycol (PPG), isophorone diisocyanate and N-

methyldiethanolamine (MDEA) following a prepolymer mixing process.

Emulsions were obtained by adding water to the prepolymer solusions.

Particle size and emulsion viscosity were studied in response to the MDEA

content, degree of neutralization and solid content of emulsion.

Young Min Lee, Jong cheol Lee and et al [80] have prepared aqueous

polyurethane anionomer dispersions form isophorone diisocynate, poly (tetra-

methylene adipate glycol (PTAd) and dimethylol propionic acid as potential

anionic centers. The effects of polyol Molecular weight (Mn) on the state of

dispersion, thermal, mechanical and visco-eleastic properties and swelling of

emulsion cast film were determined. These results could be interpreted in

terms of soft segment-hard segment phase separation and crystallization of

high molecular weight PTAd.

2.5 Ingredients for Polyurethane Dispersions

2.5.1 Polyols:

The chain length (molecular weight) of the linear polyol used as soft

segment contributes to the elasticity of the resulting polymer. Consequently,

an increase of the soft segment provides soft, elastomeric products. They are

also included for appropriate structure property balance of the dispersion and

also for ease of polymerization. The types of the soft segments are;

Chapter 2


(A) Polyethers:

Polyether polyolys like PEGs (polyethylene glycols), PPGs

(polypropylene glycols) and PTMGs (polytetramethylene glycol), etc are

generally used for providing flexible films and enables films with high water

vapor permeation rate.

(B) Polyesters:

Different polyester polyols derived from different available esterification

monomers are used. For preparation of PUD linear type of polyester are used.

Most commons are polyneopentylglycol adipates, polyhexamethylene

adipates, polyethyleneglycol adipates, etc. Polycaprolactones are also used for

enhancing the hydrolytic stability and good mechanical properties. Hydroxyl

terminated alkyld resins are also used for the Preparation of PUDs.

Renewable resources and their esterified products are also used as

polyol for PUD preparations. Other polymeric diols are also used for tailoring

the properties of PUDs like for hybridizations, special formulations and for

extreme hydrolytic stability; like poly (hydroxyacrtlate), Bishydroxy

polydimethylsiloxane, polybutadine glycols, Polycarbonates, etc.

2.5.2 Isocyanates:

Isocyanates are used as reactive components and typically added from

1.4 to 2.0 times the equivalents of hydroxyl components of the polyols and

DMPA and DMBA. The free isocyanate functionality is than utilized for further

polymerization. Many types are available like aliphatic Isocyanates (HDI),

cycloaliphatic Isocyanates (IPDI and HMDI) and aromatic isocynates (TDI).

Aromatic diisocyanates react rapidly at the water dispersion and may prove to

be difficult to handle. They promote good rigidity in the film. Cycloaliphatic

diisocyanates are preferred choice for combining good reactivity and

weathering resistance. Aliphatic diisocyanates are sluggish to react and

require either catalysis or elevated temperature for completing the

prepolymer reaction.

Chapter 2


2.5.3 Ionic Monomer or Internal Emulsifiers:

DMPA Dimethylolpropionic Acid is a unique, trifunctional compound

incorporating a hindered, tertiary carboxylic acid group and two reactive,

primary hydroxyls. The hindered carboxyl is less reactive than most acid

groups. Therefore, DMPA reacts as a diol. The hindered carboxyl of DMPA is

less reactive to isocyanate compare to hydroxyl group. The hydroxyls of

DMPA are reactive to isocyanate. Therefore, DMPA is often chosen as a

source of free acid groups in urethane polymers. Incorporation of this ionic

monomer in the polymer backbone forms the basis of anionic polyurethane

dispersions. Incorporation is accomplished by the reaction of the two

hydroxyls with diisocyanate. The primary hydroxyls of monomers react readily

with Isocyanates and carboxylic acid group remains unreacted and can be

neutralized with base forming ionic moieties for anionic stabilization of the

dispersion.

2.5.4 Chain Extenders:

Chain extenders are the reactive partner for linking the isocyanate

groups. Different diamines like EDA (Ethylene diamine), TMDA

(Tetramethylene diamine), HAD (Hexamethylene Diamine), etc. Polyamines

like DETA (Diethylene triamine), ADZ (Adipic dihydrazide) are also used as

chain externders. Diols like butanediol is also commonly used to increase the

molecular weight in acetone process.

Chain extender composition or addition is controlled by the NCO

content of the prepolymer. Diamines react rapidly with the isocyanate thus

increasing the polymer size by forming urea linkage. Diols react much slower

with the isocyanate compare to diamines. Polyamines of higher functionality

can be used if inter-particle crosslinking is required.

2.5.5 Neutralizing Agents:

Neutralizing agent is used to convert carboxyl functionality into

carboxylate anions which brings the dispersibility of polymer into water.

Chapter 2


Tertiary amine like TEA (Triethyl amine), DMEA (Demethylethanol amine),

DMAP (Dimethylamino propanol) are used as neutralizing agents in PUDs.

Inorganic base like NaOH, KOH, are also used for the same purpose.

Neutralization degree can be varied with brad limits, ranging from 40% to

over 100%. Appropriate neutralization is required for the dispersion stability.

2.5.6 Solvents:

Solvents are primarily used to reduce viscosity of the prepolymer and

make them pourable to perform subsequent steps easily. Generally water

miscible solvents like NMP (N-methyl pyrrolidone), DMF (dimethyl

formamide), Acetone and MEK (Methyl ethyl ketone) are used for PUDs.

Solvent is added in minimum quantity and can be easily evaporated at the

end of the process in order to get totally solvent-free formulations.

2.6 Exprimental

2.6.1 Materials:

Polyethylene glycols were obtained from Aldrich Co. Castor oil and

Coconut oil based alkyd resin as polyol was obtained from Reliable Paints.,

Makarpura G.I.D.C., Vadodara. Its specifications are shown in Table 2.1.

Tabel 2.1 Specification of Various Polyols

Polyols-OH Value

(mg KOH/gm)PH

% Non

Volatiles

Viscosity

(CSt@ 40oC)

PEG-200 500-620 5-7 5max 21-25

PEG-400 260-303 5-7 5max 40-45

PEG-600 170-205 5-7 5max 50-60

PEG-1000 100-119 5-7 5max 60-65

Castor Oil 160-165 6-7 6 max 70-72

Coconut Oil-

Alkyd Resin130-135 5-7 70 ± 2 70-75

Chapter 2


Figure 2.7: General structure of hydroxyl terminated Alkyd resin

derived from coconut oil.

Figure 2.8: Structure of Castor Oil

Various aliphatic and aromatic diisocyanates like Isophorone

diisocyanate (IPDI) and toluene diisocyanate (TDI) are obtained from Aldrich

Co. as technical grade. Their specifications and structure are shown in

Table. 2.2. and Figure 2.9 respectively.

Chapter 2


Table 2.2: Specifications of Aliphatic and Aromatic Diisocyanates.

Material Mol. Wt.

g/mole

Physical

appearance

Density

g/cm3 @

20oC

Boiling

Point

(oC)

IPDI 222.3Colorless,

Liquid1.062 158

TDI 174.2Pale yellow,

Liquid1.214 251

Figure 2.9: Structure of Aliphatic and Aromatic Diisocyanates.

Ionic polyol 2, 2-dimethylol propionic acid (DMPA) was purchased from

Hi-media Co. It was dried at 80o C before used. Their specifications and

structure are shown in Table. 2.3. and Figure 2.10.

Table 2.3: Specifications of 2, 2-dimethylol propionic acid

Monomer Apperance Mol.Wt.OH-Value

(mgKOH/gm)AV

(mgKOH/gm)Mp

DMPAWhite

crystal134.4 830 415 180

Isophorone Diisocyanate Toluene Diisocyanate

Chapter 2


Figure 2.10 2, 2-dimethylol propionic acid

Dibutyltindilurate (DBTDL) was used as catalyst was purchased from

Hi-media Co. Its specifications are shown in Table. 2.4 and structure of

Dibutyltindilurate is shown Figure 2.11. Triethyl amine, Ethylene diamine is

purchased from Adlrich and used as such, without purification. Double

distilled water was used for the dispersions.

Table 2.4: Specification of Dibutyltindilurate.

MaterialMol. Wt.

g/mole

Physical

appearance

Density

g/ml @

25oC

Boiling

Point

(oC)

DBTDL 631.56Pale Yellow,

Liquid1.066 -

Figure 2.11 Structure of Dibutyltindilurate.

Chapter 2


2.6.2Preparation of Polyurethane dispersions:

Preparation of Polyurethane dispersion is divided into four steps

NCO terminated prepolymer

Neutralization of carboxyl ion of perpolymer

Dispersion of prepolymer in water.

Chain extension of the prepolymer.

In a 500 ml four necked round bottom flask equipped with a

condenser, a mechanical stirrer, a thermometer and nitrogen inlet; diol,

diisocyanate, DMPA and catalyst DBTDL were charged in the flask. The

reaction was mixture was heated at 80-90o C for 2 to 3 hours in water bath

under nitrogen atmosphere. Minimum amount of ethyl methyl ketone as

solvent was used to adjust the viscosity of the perpolymer. The reaction was

allowed to carry out until desired NCO value was reached. The amount of free

NCO groups on a percentage basis was determined by the standard di-

butylamine back titration method. The prepolymer temperature was allowed

to drop to 45o C. The carboxylic acid groups were neutralized by the addition

of triethylamine and reaction was allowed to stirrer for 30 min in order to

ensure complete neutralization of COOH group. The mixture is stirred for

further 40 min to ensure the reaction was completed. Dispersion of the

neutralized prepolymer was carried out by adding double distilled water to the

mixture at vigorous stirring. Chain extension of the neutraliszed prepolymer

was carried out simultaneously and after the addition of water. The reaction

scheme is shown in Figure 2.12.

The different compositions of the prepolymer samples and

polyurethane dispersions that were prepared are shown in Tables 2.5 –

2.16.

Chapter 2


Figure 2.12: Reaction Scheme for the Polyurethane dispersion

Chapter 2


Table 2.5 Compositions of prepolymer based on (PEG) and (IPDI)

Sr.No

CompositionCode

Composition by wt (gms)Polyol IPDI DMPA CAT.*

PEG200

1 PPUI1 12.06 24.05 4.05 0.052 PPUI2 10.85 25.10 4.03 0.053 PPUI3 9.50 26.37 4.02 0.054 PPUI4 8.75 27.05 4.01 0.055 PPUI5 7.80 28.10 4.00 0.056 PPUI6 6.90 31.00 3.99 0.05

PEG400 IPDI DMPA CAT.*






Chapter 2


Table 2.6 Compositions of prepolymer based on (PEG) and (TDI)

Sr.No

CompositionCode

Composition by wt (gms)Polyol TDI DMPA CAT.*

PEG200

1 PPUT1 12.06 18.84 4.05 0.052 PPUT2 10.85 19.67 4.03 0.053 PPUT3 9.50 20.68 4.02 0.054 PPUT4 8.75 21.22 4.01 0.055 PPUT5 7.80 22.04 4.00 0.056 PPUT6 6.90 24.31 3.99 0.05

PEG400 TDI DMPA CAT.*






Chapter 2


Table2.7 Compositions of Polyurethane dispersion based on (PEG)

and IPDI

Sr.No

CompositionCode

Dispersioncode

Neutralizing Agent (TEA)

Chain Extender

(EDA)

D.I water

1 PPUI1 PPUDI1 1.12 0.72 55.552 PPUI2 PPUDI2 1.10 0.89 54.253 PPUI3 PPUDI3 1.08 1.05 54.004 PPUI4 PPUDI4 1.05 1.20 53.755 PPUI5 PPUDI5 1.02 1.36 53.506 PPUI6 PPUDI6 1.00 1.65 53.007 PPUI7 PPUDI7 1.12 0.72 55.558 PPUI8 PPUDI8 1.10 0.89 54.259 PPUI9 PPUDI9 1.08 1.05 54.0010 PPUI10 PPUDI10 1.05 1.20 53.7511 PPUI11 PPUDI11 1.02 1.36 53.5012 PPUI12 PPUDI12 1.00 1.65 53.0013 PPUI13 PPUDI13 1.12 0.72 55.5514 PPUI14 PPUDI14 1.10 0.89 54.2515 PPUI15 PPUDI15 1.08 1.05 54.0016 PPUI16 PPUDI16 1.05 1.20 53.7517 PPUI17 PPUDI17 1.02 1.36 53.5018 PPUI18 PPUDI18 1.00 1.65 53.0019 PPUI 19 PPUDI19 1.12 0.72 55.5520 PPUI20 PPUDI20 1.10 0.89 54.2521 PPUI21 PPUDI21 1.08 1.05 54.0022 PPUI 22 PPUDI22 1.05 1.20 53.7523 PPUI23 PPUDI23 1.02 1.36 53.5024 PPUI24 PPUDI24 1.00 1.65 53.00

Chapter 2


Table2.8 Compositions of Polyurethane dispersion based on (PEG)

and TDI

Sr.No

CompositionCode

Dispersioncode


Chain Extender

(EDA)

D.I water

1 PPUT1 PPUDT1 1.12 0.72 55.552 PPUT2 PPUDT2 1.10 0.89 54.253 PPUT3 PPUDT3 1.08 1.05 54.004 PPUT4 PPUDT4 1.05 1.20 53.755 PPUT5 PPUDT5 1.02 1.36 53.506 PPUT6 PPUDT6 1.00 1.65 53.007 PPUT7 PPUDT7 1.12 0.72 55.558 PPUT8 PPUDT8 1.10 0.89 54.259 PPUT9 PPUDI9 1.08 1.05 54.0010 PPUI10 PPUDT10 1.05 1.20 53.7511 PPUI11 PPUDT11 1.02 1.36 53.5012 PPUI12 PPUDT12 1.00 1.65 53.0013 PPUI13 PPUDT13 1.12 0.72 55.5514 PPUI14 PPUDT14 1.10 0.89 54.2515 PPUI15 PPUDT15 1.08 1.05 54.0016 PPUI16 PPUDT16 1.05 1.20 53.7517 PPUI17 PPUDT17 1.02 1.36 53.5018 PPUI18 PPUDT18 1.00 1.65 53.0019 PPUI 19 PPUDT19 1.12 0.72 55.5520 PPUI20 PPUDT20 1.10 0.89 54.2521 PPUI21 PPUDT21 1.08 1.05 54.0022 PPUI 22 PPUDT22 1.05 1.20 53.7523 PPUI23 PPUDT23 1.02 1.36 53.5024 PPUI24 PPUDT24 1.00 1.65 53.00

Chapter 2


Table 2.9 Compositions of prepolymer based on Hydroxylterminated Alkyd resin and (IPDI):

Sr.No

CompositionCode


1 HPUI1 22.56 6.66 2.01 0.052 HPUI2 22.56 7.77 2.01 0.053 HPUI3 22.56 8.88 2.01 0.054 HPUI4 22.56 6.66 2.42 0.055 HPUI5 22.56 6.66 2.68 0.056 HPUI6 22.56 6.66 2.95 0.057 HPUI7 22.56 6.75 2.42 0.058 HPUI8 22.56 7.77 2.68 0.059 HPUI9 22.56 8.88 2.95 0.0510 HPUI10 25.63 6.66 2.01 0.0511 HPUI11 27.68 7.77 2.01 0.0512 HPUI12 29.74 8.88 2.01 0.05

Table 2.10 Compositions of prepolymer based on Hydroxylterminated Alkyd resin and (TDI):

Sr.No

CompositionCode


1 HPUT1 22.56 5.26 2.01 0.052 HPUT2 22.56 6.10 2.01 0.053 HPUT3 22.56 6.97 2.01 0.054 HPUT4 22.56 5.26 2.42 0.055 HPUT5 22.56 5.26 2.68 0.056 HPUT6 22.56 5.26 2.95 0.057 HPUT7 22.56 5.50 2.42 0.058 HPUT8 22.56 6.10 2.68 0.059 HPUT9 22.56 6.97 2.95 0.0510 HPUT10 25.63 5.50 2.01 0.0511 HPUT11 27.68 6.10 2.01 0.0512 HPUT12 29.74 6.97 2.01 0.05

Chapter 2


Table2.11 Compositions of Polyurethane dispersion based on Hydroxyl terminated Alkyd resin and IPDI

Sr.No

CompositionCode

Dispersioncode


Chain Extender

(EDA)

D.I water

1 HPUI1 HPUDI1 1.51 1.30 60.002 HPUI2 HPUDI2 1.51 1.25 65.003 HPUI3 HPUDI3 1.51 1.20 70.004 HPUI4 HPUDI4 1.81 1.30 60.005 HPUI5 HPUDI5 2.02 1.30 60.006 HPUI6 HPUDI6 2.22 1.30 60.007 HPUI7 HPUDI7 1.81 1.35 60.008 HPUI8 HPUDI8 2.02 1.32 60.009 HPUI9 HPUDI9 2.22 1.30 60.0010 HPUI10 HPUDI10 1.51 1.30 60.0011 HPUI11 HPUDI11 1.51 1.25 65.0012 HPUI12 HPUDI12 1.51 1.20 70.00

Table2.12 Compositions of Polyurethane dispersion based on Hydroxy terminated Alkyd resin and TDI

Sr.No

CompositionCode

Dispersioncode


Chain Extender

(EDA)

D.I water

1 PPUT1 HPUDT1 1.51 1.25 65.002 PPUT2 HPUDT2 1.51 1.20 65.253 PPUT3 HPUDT3 1.51 1.15 64.004 PPUT4 HPUDT4 1.81 1.15 65.755 PPUT5 HPUDT5 2.02 1.20 65.506 PPUT6 HPUDT6 2.22 1.15 65.007 PPUT7 HPUDT7 1.81 1.25 65.558 PPUT8 HPUDT8 2.02 1.20 65.509 PPUT9 HPUDT9 2.22 1.15 65.0010 PPUT10 HPUDT10 1.51 1.25 65.5511 PPUT11 HPUDI11 1.51 1.20 65.5012 PPUT12 HPUDT12 1.51 1.15 65.00

Chapter 2


Table 2.13 Compositions of prepolymer based on Castor oil and (IPDI)

Sr. No

CompositionCode


1 CPUI1 20.60 12.46 3.72 0.052 CPUI2 20.60 16.20 3.72 0.053 CPUI3 20.60 16.20 3.72 0.054 CPUI4 20.60 16.20 3.72 0.055 CPUI5 20.60 16.20 3.72 0.056 CPUI6 20.60 16.20 3.72 0.05

Table 2.14 Compositions of prepolymer based on Castor oil and(TDI)

Sr. No

CompositionCode


1 CPUT1 20.60 9.75 3.72 0.052 CPUT2 20.60 12.68 3.72 0.053 CPUT3 20.60 12.68 3.72 0.054 CPUT4 20.60 12.68 3.72 0.055 CPUT5 20.60 12.68 3.72 0.056 CPUT6 20.60 12.68 3.72 0.05

Table2.15 Compositions of Polyurethane dispersion based on Castor oil and IPDI

Sr. No

CompositionCode

Dispersioncode


Chain Extender

(EDA)

D.I water

1 CPUT1 CPUDI1 1.51 1.30 60.002 CPUT2 CPUDI2 1.51 1.25 65.003 CPUT3 CPUDI3 1.51 1.20 70.004 CPUT4 CPUDI4 1.81 1.30 60.005 CPUT5 CPUDI5 2.02 1.30 60.006 CPUT6 CPUDI6 2.22 1.30 60.00

Chapter 2


Table2.16 Compositions of Polyurethane dispersion based on Castor oil and TDI

Sr. No

CompositionCode

Dispersioncode


Chain Extender

(EDA)

D.I water

1 CPUT1 CPUDT1 1.51 1.30 60.002 CPUT2 CPUDT2 1.51 1.25 65.003 CPUT3 CPUDT3 1.51 1.20 70.004 CPUT4 CPUDT4 1.81 1.30 60.005 CPUT5 CPUDT5 2.02 1.30 60.006 CPUT6 CPUDT6 2.22 1.30 60.00

Chapter 2


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Documents

2.1 Introduction - INFLIBNETshodhganga.inflibnet.ac.in/bitstream/10603/34650/7/07_chapter 2.pdf · called as the acetone process. This process is easily performed and very reproducible