Developments in acrylic - based thickeners as substitute of emulsion

13 Pages·2012·2.69 MB·English

Indian Journal of Fibre & Textile Research
Vol. 26, March-June 2001, pp. 143-1SS
Developments in acrylic - based thickeners as substitute of emulsion thickeners for
pigment printing
M Jassal' & P 8ajaj
Department of Textile Technology, Indian Institute of Technology, Hauz Khas, New Delhi 110 016, India
Pigment printing is confronted with growing demands. which, in turn, pose both environmental and technological
challenges to the system. This paper presents a comprehensive review of developments in synthetic thickeners as substitute
of emulsion thickeners for pigment printing.
Keywords: Acrylic thickener, Emulsion thickener, Kerosene emulsion, Pigment printing. Synthetic thickener
1 Introduction 1.1 Why Synthetic Thickeners?
The presence of oil phase in emulsion thickener
Unlike printing with fibre-affinitive dyes, the
causes problems, such as air and water pollution,
pigments are fixed to the substrate by a binder which
flammability lexplosion risk, wasteful use of energy,
adheres to the fibre and forms a continuous film on
and increased cost and decline in availability, some of
the fabric enclosing the pigment particles.The print
which have become quite prohibitive in recent years.
pastes also require a thickening agent to control the
flow and penetration of the paste. Viscosity is Global climatic changes and increasing concern
attributed to the internal friction in the fluid and is towards environment have imposed strict regulations
defined in terms of tangential stress (t) and rate of towards emission Idischarge of harmful solvents into
shear (D, viscosity gradient between parallel plates). the atmosphere or the sewage system. Solvent
The type and solid content of the thickener play a vapours also contribute to unpleasant and unhealthy
dominant role in governing the quality of prints working environment.
obtained. as the thickener remains entrapped with the
This can be eliminated or reduced by either
binder. Therefore, the emulsion thickeners, that
substituting the emulsion thickener or through recycle
develop viscosity due to the resistance of the droplets
Irecovery of used oiLThe recovery studies for
of two immiscible liquids, result in full satisfaction
kerosene have recently been reported by the Bombay
with respect to the print quality. Both water-in-oil Textile Research Association7 The alternate thickener
.
(w/o) and oil-in-water (o/w) have been used with for effective substitution must possess high viscosity
widely varying proportions of oil, but because of the at very low solid content, pseudoplastic behaviour.
technical difficulties, only o/w systems (with nearly inertness towards pigments and other essential
70-80% of oil phase) are preferred. The prints components of print paste, and finally, insolubility in
obtained using this conventional emulsion thickener water, detergent solution, mild alkaline wash liquor
are excellent in terms of clarity of shade, brightness and drycleaning solvents.
and colour yield. These advantages coupled with soft
The natural and modified natural thickeners have
handle have made it the most popular technology for
not gained popularity in pigment printing due to their
printing. In fact, the development of emulsion
inconsistent rheology (no shear thinning) and adverse
thickeners along with the simplicity and versatality of
effect on the feel of prints. However, the synthetic
pigment printing technique is responsible for the
thickeners have pronounced pseudoplastic rheology.
current market share of pigment printing ).6.
They deform under stress and recover to their original
viscosity on removal of stress. As a result, the syn
thetic thickeners have the ability to produce prints
"To whom all the correspondence should be addressed.
with better smoothness, levelness and sharpness than
Phone: 6S91426: Fax: [phone]S8112:
natural Imodified natural thickeners. The rheological
E-mail: [email protected]
144 INDIAN J. FIBRE TEXT. RES., MARCH-JUNE 2001
properties of these synthetic thickeners are identical to Hence, comonomer composition is required to be
emulsion thickeners. optimized to obtain a product with suitable
For full or partial substitution of oil in water rheological properties and printing performance.
emulsions, various synthetic products at relatively Divalent/trivalent monomers, such as divinyl
small concentration have been explored over the past benzene (DYB), N,N' -methylene bisacrylamide
two decades. Among them, the polyanionic (MBA), methylol acrylamide (MA) and ethylene
copolymers prepared from monomers, such as acrylic glycol dimethacrylate (EGDMA) have also been used
acid, methacrylic acid and maleic anhydride, are as one of the components in producing these
widely known for pigment printing. This was the first thickeners. Such loosely crosslinked polymers
sizeable contribution of textile printing industries to provide printable viscosity at a much lower solid
cleaner environment8.This paper discusses the content (0.5-2%) compared to linear polymers (solid
developments in synthetic thickeners towards their content 10-15%). Depending upon the presence and
improved performance for pigment printing. absence of crosslinking agent, these acrylic thickeners
are categorized as alkali soluble and alkali
lo
2 Acrylic-based Thickeners swellable . Certain monomeric combinations
reported in the literature for emulsion polymerization
2.1 Basic Structure
of thickeners and the Brookfield viscosity are shown
Acrylic-based thickeners are generally high
in Tables I and 2 respectively.
molecular weight copolymers of (meth) acrylic acid
and its ester. The acid comonomer is responsible for 2.2 Polymerization Techniques
thickening and development of viscosity on partial Acrylic copolymers have been synthesized by
neutralization with a base9.1O, whereas acrylate emulsion, inverse emulsion, solution and suspension
monomers function as internal plasticizers, resulting techniques. Among these, the emulsion route is
in polymer film with reduced glass transition preferred due to easy control and high molecular
temperature (Tg) II. Lower Tg improves the feel of the weight of the polymer obtained in the readily useable
fabrics, but too Iowa value may lead to poor crock latex. This process also eliminates the use and
fastness. The proportion of comonomers affect the recovery of expensive/polluting organic solvents.
rheological properties and performance of thickeners. Powdered thickening agents are also known to be
Table I-Typical comonomer combinations used for synthesis of thickeners by emulsion polymerization
Acid monomer Ester monomer Other monomer Crosslinking monomer Ref.
EA N-Decyl acrylamide 12-13
EA Ethoxylated stearyl alcohol allyl ether 14
EA Monoester of ethoxylated Diallyl phthalate 15
heptadecanol and methylene
succinic acid
BA EGDMA or MBA (2-17%) 16-20
EA DYB or NMA 21-23
MMA 24
Ethoxylated fatty alcohol
methacrylate
MA EGDMA 25
MMA
BA BDDA 26
EA
MMA PYA 27
EA DYB or EGDMA 28
Cetyl stearyl
Polyoxy sorbate
Conld.
JASSAL & BAJAJ: ACRYLIC-BASED THICKENERS FOR PIGMENT PRINTING 145
Table I- Typical comonomer combinations used for synthesis of thickeners by emulsion polymerization--Collld.
Acid monomer Ester monomer Other monomer Crosslinking monomer Ref.
EA Unsaturated amide Polyoxyethylene crosslinkers 29
Associative monomer Unsaturated sulfonic acid
MMA Glycidyl methacrylate 30
BA
AA BA Partially esterified PV A 31
Aam
MMA 32
2-ethylhexylacrylate
HEMA
BA Styrene NMA 33
EA Polyoxyethylene nonyl phenyl
ether
BA 40% copolymer of 5011101%, Hexamethylenediamine, other di 34
MA maleic anhydride and 50 amines, polyhydric alcohols
11101% vinyl isobutyl ether
Maleic anhydride Di-ethyl maleate 35
Iso-butyl vinyl ether
AMPS TMPTA 36
AA - Acrylic acid; MAA - Methacrylic acid; BA-Butyl acrylate; EA - Ethyl acrylate; EGDMA - Ethylene glycol di
methacrylate; MBA - N,N' - methylene- bis-acrylamide; PV A - Polyvinyl alcohol; DVB - Divinyl benzene; TMPT A - Trimethyl
propane triacrylate; EGDGE - Ethylene glycol diglycidyl ether; PEG - Polyethylene glycol; Aam - Acrylamide; NMA - N
methylol acrylamide; AMPS - 2-acrylamido-2-methyl-I-propane sulphonic acid or its salt; HEMA -hydroxyethyl methacrylate; PS
-olystyrene; BDDA - Butanediol diacrylate; and MA - Methylol acrylamide
Table 2 - Brookfield viscosity of synthetic thickeners based on different monomer combinations
Monomer composition Brookfield viscosity Ref.
MAA/EA (62:38) 43,000 cP (5% soln, 12 rpm,25°C) 12
MAA/EA (65:35) 40,000 cP (5% soln, 12 rpm, 25°C) 12
EA/MAA (100:80) 14000 cP 14
Ethoxylated stearyl alcohol allyl ether (10 mol)
EA (126.8 g) 800 mPas (RVT 20 rpm, 0.5% soln) 28
MAA (92.7 g)
Cetyl slearyl polyoxy sorbate (24.3 g)
DVB(I%)
EA (127.6 g) 2750 cP (Spindle RV 7. 20DC) 29
MAA (92.7 g)
Esters (CI6-IS) of acrylic acid (24.3 g)
2-AMPS (340 g) 1040 pas (At shear rate 0-1 Hz of 1% soln) 36
TMPTA (32g)
AA (200 parts) 3500 cP (VKRV8 Viscometer, 20 rpm, 25°C) 37
Aal11 (60 parts)
AA (95g) 38500 cP 38
A product of benzyl alcohol and allyl glycidyl ether (5g) (0.5% soln, 20 rpm)
Contd.
146 INDIAN J. FIBRE TEXT. RES., MARCH-JUNE 2001
Table 2 - Brookfield viscosity of synthetic thickeners based on different monomer combinations----Collld.
Monomer composition Brookfield viscosity Ref.
AA (30g) 1500 cP (20 rpm, pH 7) 39
Pentaerythritoltetrallyl ether (0.5g)
Maleic anhydride (58.84) 2500 cP (I % soln, 5 rpm, 30°C) 40
isobutylenc (50.5)
n-Oodecylmethacrylate (14.2)
AA (16%), EA (81.9%). 1,4-BOOM (0.1%), NMA (2%) 40 cP (20°C) 41
MAA(41%) 310 cP (30oC) 41
BA (45.1%)
VA (13.9%)
AA (250.28 mg) 4700 cP (1.2% soln) 42
Stearylmethacrylate (5.72 g) 7800 cP (1.5% soln)
Allyl pentaerythritol (0.858 g) 25000 cP (2% soln)
A A (83 g) 25000 cP (20°e, 20 rpm) 43
Aam (12g) 15000 cP (after addition of 0.1% Na]S04)
AN (5g)
AA (84.5%) 26250 cP (20°C, 20 rpm) 43
Aam (12g) 13400 cP (after addition of 0.1% Na2S04)
AN (3.75 g)
AA (87.5%) 38000 cP (20°e, 20 rpm) 43
Aam (l2.5g) 9000 cP (after addition of 0.1% Na2S04 solution)
very effective, but they are difficult to handle due to 0.5-5% aqueous solution of film forming acrylic
dusting and lumping problems. Granules are delivered polymers in cyclohexane. The treatment swells and
in a dust-free form but their application requires an aggregates the thickener particles53.
initial additional step of the preparation of an aqueous Bajaj et 01.54 have synthesized thickeners for
dispersion of the acidic form of the thickener to pigment printing by emulsion method and by post
develop requisite viscosity. crosslinking of hydrolysed acrylic polymers. The
Certain thickener formulations are available in the effective solid contents of the polymers obtained by
paste dispersion forms in volatile hydrocarbons.These both the methods are shown in Table 3. The
dispersions on dilution result in high viscosity. thickeners of varying compositions were emulsion
Although the emission from these hydrocarbons is polymerized using methacrylic acid (MAA),
relatively low, the stricter environmental laws ensure ethylacrylate (EA), ethylene glycol dimethacrylate
that even these small quantities have to be eliminated. (EGDMA) and N,N'-methylene-bis-acrylamide
In such dispersions, the hydrocarbons are eliminated (MBA). The polymerization mechanism, the
either by preparation of powder form user-friendly reactlVlty ratios and detailed characterization of
non-dusting synthetic thickeners or by replaceni'ent of polymers in the above systems have already been
conventional hydrocarbons by native oils. reported54.
Investigations on emulsion polymerization of these The intrinsic viscosity of the MAA-EA copolymers
systems44.S1 have revealed that the reaction rate, prepared by the emulsion route increased form 1.72 to
reaction mechanism, latex stability and properties of 2.70 dl g-I with the increase in EA content from 17.6
final product are greatly affected by the concentration to 49.8 mole%. This was attributed to the increased
and the polarity of the monomers50.5I, feed rate/policy molecular weight and increased size of the side
of monomers52, emulsifier concentration and substituent, i.e. ester group of EA as compared to
polymerization temperature. carboxylic acid group of MAA. The IR absorption
The preparation of water-soluble acrylic thickeners due to carboxyl stretching of acid and ester groups of
in non-dusting form is reported by treating 20% of the copolymer appeared as one broad band in the range
JASSAL & BAJAJ: ACRYLIC-BASED THICKENERS FOR PIGMENT PRINTING 147
Table 3 - Effective solid content of crosslinked acrylic thickeners
Thickener Crosslinker Effective solid Ref.
Type % content, %
Hydrolysed low molecular Formaldehyde 2.4 2.5 55,56
weight acrylic polymer Aluminium sulphate 1.5 2.82
2.0 2.6
2.5 2.4
Hydrolysed high molecular Aluminium sulphate 1.5 1.4 55, 56
weight acrylic polymer 2.0 1.2
2.5 0.9
AA:EA:BA 3.5
(70:15:15)
MAA:EA EGDMA <3 4 54,57
(65:35)
>3 4
MAA:EA MBA \-3 4 54,57
6:;:35
1700-1740 cm -I, which were not resolvable due to the aqueous phase. At MAA concentration of 10 mole%,
close proximity. Therefore, the composition of the average sequence length was found to be 2.42,
copolymers was calculated by measuring the intensity which increased to 9.80 in the sample containing 75
of peak due to OCH (d) protons (0 4.0) of EA and mole% of MAA.
2
then subtracting the contribution of EA from multiplet On the basis of statistical calculations, the
of methyl protons of MAA and EA. The calculated following mechanism was postulated for MAA-EA
concentration of MAA in copolymer was found to be emulsion polymerization.
much closer to feed concentration than those obtained
• In the initial stages of polymerization, EA and
from acidimetric titrations.
MAA get converted to oligomeric radicals.
CI3 NMR was used to calculate the concentration
• The oligomeric radicals with very high MAA
of various M-centered and E-centered triads from the
content remain in aqueous phase and on
relative areas of resonance signals. It has been
termination form water-soluble product, resulting
reported that as the concentration of MAA in the
in high viscosity of latex.
copolymer increased from 50.2 to 61.9 mole%, the
• Later, the oligomeric radicals, with sufficient EA
concentration of NMM triad (N,N' -methylene bis
concentration to provide hydrophobicity,
acrylamide-methacrylic acid-methacrylic acid)
precipitate the radicals out of aqueous phase as
increased from 0.36 to 0.45 moie% ~nd [hat of EME primary particle.
triad (Ethylacrylate-methacrylic acid-ethylacrylate)
In the second approach, the acrylic polymers
decreased from 0.25 to 0.24 mole%. In the case of E
(textile grade acrylic fibre waste and high molecular
centered triads, the concentration of MEM triads
weight acrylic polymers) have been suitably
(Methacrylic acid-ethylacrylate-methacrylic acid)
hydrolysed and crosslinked using organic crosslinker
increased and that of EEE triads (Ethylacrylate
or multivalent metal salts. The crosslinks obtained
ethylacrylate-ethylacrylate) decreased with the
through formylation were not ecofriendly due to the
increase in MAA concentration in the copolymer. At
presence of free formaldehyde while those obtained
82.3 mole% MAA, the concentration of E-centered
by aluminium sulphate were effective for production
triads was found to be negligible. The reactivity ratios
of high viscosities. The high molecular weight
of MAA and EA have been obtained as 2.58 ± 0.13
hydrolysed product was more effective due to the
and 0.157 ± 0.08 respectively.
lower solid content required to realise printable
The possible mechanism for polymerization has viscosity.
been proposed by determining the concentration of Another technique of polymerization, inverse
both the monomers in aqueous phase (prior to polym emulsion process, yields a viscous latex consisting of
erization). The average sequence length of MAA in hydrophilic polymer particles swollen by water in the
creased with the increase in MAA concentration in continuous phase58. Agglomerated particles can be
148 INDIAN J. FIBRE TEXT. RES., MARCH-JUNE 2001
separated by azeotropic distillations after emulsions. The manufacturer also recommends the
po I ymen.zatl.o n5 9.6 0 . use of certain secondary auxiliaries suitable for these
L ate x Ilavi·n g goo d e I ectro I yte resI.s tance 61.6 7- ha s thickeners.
been obtained by polymerization of non-ionic Allied Colloids have summarized7o71 their
.
hydrophobic comonomers, such as acry lam ide at
developmental actiVItIes relating to synthetic
selected pH. A polyacrylic acid thickener synthesised
thickeners. Alcoprint thickeners by Allied Colloid are
by inverse emulsion polymerization technique with
liquid dispersions consisting of very small (approx.
MBA and hydrophobic monomers having long alkyl
l)..l) dehydrated polymer particles suspended in
groups, such as hexadecyl methacrylate (HM),
hydrocarbon solvent, stabilised llsing especially
dodecyl methacrylate (OM), has been reported63. developed stabilizer and emulsifier system. Small size
Results indicated that at a low amount of crosslinking
of particles together with carefully selected surfactant
and in aqueous medium, the crosslinked polymer
ensure good dispersion of polymer particles prior to
using HM was found to be more effective than that
swelling.Thickeners designated OP3-313l and
obtained using OM. Acraconz B were also offered by Allied Colloid72 for
A patentM discloses the preparation of heat
aqueous pigment printing to eliminate loss of print
sensitive thickeners by inverse emulsion technique
definition due to flushing. The Acraconz B was
from N-isopropyl acrylamide with MBA as
known to have minimal effect on handle and could be
crosslinking agent in the presence of hydrophobic
used on all types of printing machines.
emulsifier sorbiton monooleate in hexane. The
disadvantages of inverse emulsion technique include RSA Polymers73 claim RAN 5000 to be a cheaper
the use of costly organic solvents, the extra cost of substitute for kerosene with better performance
solvent recovery step and the additional step required compared to Alcoprint PTF from Allied Colloid.
for conversion of polymer powder to a latex. Morton International company offers two printing
Solution and precIpItation polymerization thickeners Mor-Print PY and Poly thickener OP. The
techniques are not popular due to the disadvantage of key features of some commercial products are
low molecular weight of the polymer obtained which summarized in Table 4.
leads to poor rheological properties. A radiation
induced crosslinking of PYA-PAA polymer for 2.4 Rheological Properties of Acrylic Thickener
pigment printing thickener is also reported The alkali-soluble acrylic polymers of very high
liS.
molecular weight develop high viscosity on
dissolution. But, the thickened solutions are very long
2.3 Commercially Available Acrylic Thickeners
or stringy and exhibit the wrong rheology for printing.
The synthetic thickeners are sold under the name of
The loosely crosslinked thickeners undergo swelling
Lutexal by BASF66 and Acrysol by Rohm & Haasli7.
of polymer particles and not the true dissolution. The
Lutexal HSF is supplied in the form of highly viscous
extremely high thickening action results form the fact
neutral paste with good storage stability. It has
that very long chain polyacid molecules, crosslinked
minimum influence on handle and fastness properties
to defined and limited extent, are swollen in the
and is, therefore, outstanding in suitability for solvent
entangled form. The resultant flow properties are
free or low-solvent pigment printing. Carbopol
similar to those shown by emulsion thickenings
thickeners68 of B.F.Goodrich (USA) are also
composed of defined droplets. These thickeners are
polyacrylic acid based thickeners available under
known to exhibit structural viscosity with yield. The
various grades (mol. wI. ranging from 4,50,000 to
mechanical forces subjected at the moment of printing
34,00,000). These grades are prepared in solvents
cause a temporary reduction in viscosity, enabling the
which dissolve the monomers but not the resulting
use of fine screens and produce sharp prints. The
polymers. The polymer is isolated as light fluffy
swollen structures also ensure that the print pastes
powder. Printofix Thickener CN by Clariant6 is high
<) remain more on the surface and give full and brilliant
molecular weight polymer of completely neutralized
shades.
acrylic acid with pH 8-9 (I % in water). The
manufacturer claims its suitability for flat screen, Guion and Hood76 compared the viscosity profile
rotary and roller printing on both cellulosic and its of various natural and synthetic thickeners at
blends. The handle and fastness properties of prints concentrations necessary for obtaining similar prints.
are comparable to those achieved with white spirit The log-log plots of synthetic thickeners showed
JASSAL & BAJAJ: ACRYLIC-BASED THICKENERS FOR PIGMENT PRINTING 149
Table 4 - Various commercially available acrylic thickeners for pigment printing
Company Product Characteristics Performance Ref.
B.F.Goodrich Carbopol Polyacrylic acid based fluffy powder Can be used with black pigment 68
(USA) successfully
1392 WC
BASF Lutexal P Acrylate based for kerosene-free pigment Good print paste stability 73
printing
Allied Colloid DP3-3131 Pigment prints overcome flushing 73
(U K)
Acraconz B Thickener with small or no white spirit 73
Alcoprint PTF For aq. pigment printing Performance improved with spe 75
cial auxiliaries
Alcoprint PTP For aq. pigment printing (25% stronger Better than Alcoprint PTF 75
than Alcoprint PTF)
RSA Polymers RAN 5000 Anionic aq. pigment printing (30-32% 74
solid content)
Ciariant Printofix thick Based on completely neutralized acrylic Suitable for pigment printing 69
ener CN acid
Morton Interna Mor-Print PV Non-VOC,Non-dusting. free flowing pow- Preneutralized 75
tional Company Poly thickener der Used with appropriate neutralizing
DP agent
profiles which were concave upwards at high shear reported77.78. Viscosity was found to increase with the
rates. The upturn or tail at high shear rates was increase in pH up to 7.5-8 and beyond that the
evident at a shear rate above 400 S·I. viscosity decreased.
In a US patent41 viscosities (Brookfield RVT, 2.4.2 Effect of Crosslinker Concentration
,
20°C) of an acrylic based thickener are claimed to be Crosslinker concentration determines the degree of
136000 cP, 17000 cP and 4400 cP at the spindle networking and, therefore, controls the solid content
speeds 0.5, 10, 100 rpm respectively. of polymer required to obtain printable viscosities and
Besides shear rate,many variables are reported to the rheology of paste. The related data investigated by
alter the apparent visosity of pseudoplastic Bajaj et a154.57 is summarized in Table 3. The first
materials.Those likely to influence viscosity in approach of crosslinking via formylation increased
preparing and using print paste include temperature, the viscosity significantly, thus bringing down the
pH,concentration of thickener, concentration of solid content from 15% to 2.5%. The inorganic
electrolytes, composition of thickener and molecular crosslinks, imparted through trivalent metal salts,
weight of thickener57 showed a dramatic reduction in solid content from
.
2.82% to 2.4% and 1.4% to 0.9% for the low
2.4.1 Role of Ammonia Addition
molecular weight and high molecular weight
Viscosity depends upon the degree of ionization of
hydrolysed products respectively.
carboxylic groups present in the polymer chain. When
NH 0H is added to the polymer emulsion, ionization Emulsion polymers with methacrylic acid were
4
occurs, providing NH/ (ammonium) counter ions and also evaluated for rheological behaviour.
polymeric chains containing COO' (carboxylate) ions. Combinations of these products with kerosene in
After complete neutralization is achieved, further different proportions were compared to acrylic-based
addition of ammonia results in build up of NH/ thickeners and acrylic based/kerosene system
counter ions, leading to decrease in ionization of (Table 5). Among the three synthetic thickeners, the
COOH group by the effect of law of mass action and Brookfield viscosity of P M was the highest
2 3
the common ion effect. The extended chains start (70400cP). The viscosities of P E and P E were
2 4 2 5
recoiling and viscosity decreases. Measurement of 32000 and 26000 cP respectively. This trend is
viscosity over a wide pH range has already been explained by the authors on the basis of gel content or
150 INDIAN J. FIBRE TEXT. RES., MARCH-JUNE 2001
Table 5 - Rheological properties of print pastes in comparison to kerosene emulsion and synthetic thickener
Thickener Solid Viscosity of Visosit~ of J2rint J2aste, cP
(code) . content, % stock paste, cP Red FGR Blue TFB Golden Yellow Black TBR
TRM
Kerosene emulsion (KE) 63000 37400 16400 10000 7000
Alcoprint PTF (AI) 2 1114000 17800 14000 23400 12000
MAA:EA 4 32000 17000 14000 16800 11200
(P2E4)
MAA:EA 4 26000 20400 12000 1160J 7800
(P E,)
2
MAA:EA 4 70400 13400 10000 9200 5600
[MBAI-3%] (P2M3)
PE.j:KE 3.2 33600 30400 14400 15000 12800
2
(80:20)
PE.j:KE 2.4 31400 28400 13800 16600 11600
2
(60:40)
PE,:KE 3.2 43600 16800 7400 9000 7600
2
(80:20)
P E,:KE 2.4 35600 17800 8000 8600 7200
2
(60:40)
PM :KE 3.2 5380 12000 8200 7000 5000
2 3
(80:20)
P2M,:KE 2.4 39400 9800 6200 5200 5000
(60:40)
AL:KE 1.6 96600 22000 18200 17200 7000
(80:20)
AL:KE 1.2 66200 22800 15800 14600 6200
(60:40)
degree of crosslinking of these thickeners. The NaCl to 4% solution of above polymer56. Brookfield
product P2M3 had a gel content of 90.7% compared to viscosity (at 20 rpm, 20°C) of printing paste
83.0% and 80.6% for P2E4 and P2E5 respectively78. containing high molecular weight acrylic thickener
reduced from 25000 cP to 15000 cP upon addition of
43
2.4.3 Interaction with Pigment Colours and Printing 0.1 % Na2S04 solution .
Auxiliaries
Addition of printing auxiliaries, i.e. binder, Any factor causing a decrease in degree of
pigment and fixer, causes an immediate drop in dissociation is known to reduce the viscosity. The
viscosity (Table 5) in all the thickener combinations. electrolytes or salts which are added externally
However, the drop was highest in case of commercial decrease dissociation by common ion effect, and
acrylic based thickener AJcoprint PTF. The reduction partial precipitation of chains occurs, resulting in the
in Brookfield viscosity also varied with different drop of viscosity. Chavan et at.78• found that
pigments. The black pigment resulted in lowest crosslinked polymers are more sensItive to
viscosity because of the increased concentrations of electrolytes than linear polymers. Bajaj et at.55
pigment (2% extra) and binder (5% extra). observed that higher molecular weight products are
A drop in viscosity was observed when ions were more sensitive to electrolytes than lower molecular
added in the form of salt, e.g ammonium sulphate weight products. A similar observation has also been
[(NH4) 2S04], sodium chloride (NaCt). Brookfield made with AJcoprint PTF. This is attributed to the
viscosity (at 6 rpm) of saponified polyacrylonitrile high solid content of the paste of lower molecular
reduced from 8000 cP to 5000 cP on addition of 1% weight products.
JASSAL & BAJAJ: ACRYLIC-BASED THICKENERS FOR PIGMENT PRINTING lSI
2.5 Printing Performance of Acrylic -based Thickener deteric;ated. Crosslinked products obtained through
The comparison of printing performance of syn trivalent metal salts resulted in further improvement
thetic products has recently been highlighted by in brightness and fastness properties. The solid
Bhagwat et al. 79 . content of the thickener was found to affect the
brightness of prints. The feel of the printed fabric in
2.5.1 Colour Value, Handle and Fastness Properties terms of bending length improved as the bending
The colour value and brightness are affected by the
length dereased to 3-4 cm from an original value of>
chemical nature of the monomers used, while the
8 cm. Surprisingly, with the high mol. wt. crosslinked
penetration and sharpness of prints is related to the
product obtained with trivalent aluminium salts, the
rheology of the paste. Despan d e et al. 80.8 1 i. nvesti. gated
handle of the fabric followed a reverse trend. The
the performance of polyacrylamide thickeners with
stiffness increased with the decrease in solid content
Acramine Red FGR, Acramine Blue FFG and
or increase in crosslink density, probably due to the
Acramine Yellow F2G pigments and observed the
higher rigidity of the chains because of the excessive
inferior wash fastness due to the high solubility of
crosslinks (Table 6).
polyacrylamide thickening and that the feel of prints
The incorporation of softer monomers (acrylates)
was comparable to emulsion thickeners. The
during synthesis improves the handle of the fabric.
stickiness of the paste also caused difficulty in
Various synthetic thickeners with varying proportion
washing of screens. of comonomers have been reported 83.84 . B asu et a l.8 3
Acrylic acid-acrylamide copolymers of varying
synthesized synthetic thickeners with high molecular
concentrations of two monomers and crosslinking
weight (Brookfield viscosity 63000 and 23400 cP at
density (N,N' -methylene-bis-acrylamide and bis
4% concentration of polymer). The products exhibited
acrylamide-acetic acid) have been effectively used to
steep rise in viscosity at 2.5-3% concentration. The
replace kerosene in pigment printing. Polyester-cotton
exact composition/degree of crosslinking of the
(65:35) fabric82 with a blue pigment showed bright
thickeners has not been disclosed. Among the two
prints with sharp outlines. Using the same pigment,
synthetic products TX 1 and TX2, the product TX I
the cotton fabric showed uniform prints with excellent
performs better; however, the printing trials with
colour value and good penetration, fastness to
100% TXl showed the prints inferior to that of
abrasion and fastness to washing.
emulsion thickener. The incorporation of 50 parts
Saponified polyacrylonitrile based on low and high emulsion thickeners substantially improved the colour
molecular weight acrylic polymers have also been value, sharpness and brightness of prints.
reported. 56.77. These products, though found suitable Chavan et al.78 studied the performance of
for reactive printing, did not perform well with MAA:EA (65:35) crosslinked copolymers and
pigments due to the lower molecular weight and long commercial acrylic based thickener (A\coprint PTF).
stringy flow of the print paste. On formylation of low The colour value of the samples printed with synthetic
molecular weight saponified polymer, the brightness thickener including A\coprint PTF was lower than
of prints was improved but the feel was seriously those of the samples printed with kerosene emulsion.
Table 6 - Effect of degree of crosslinking and molecular weight 011 the bending length of the
printed samples
Thickener Aluminium Acron Brill Acron Acron Golden
sulphate Red Blue B Yellow
conc., %
Hydrolysed low mol. wt. acrylic polymer >8.0 >8.0 >8.0
crosslinked with aluminium sulphate, % 1.5 3.5 3.2 3.45
2.0 4.8 2.8 3.3
2.5 4.3 3.25 3.0
Hydrolysed high mol. wt. acrylic polymer 5.0 5.2 4.8
crosslinked with aluminium sulphate, % 1.5 3.95 3.5 3.20
2.0 4.6 3.8 3.7
2.5 5.1 4.25 4.30
AA:EA:BA 1.95 1.85 1.60
(70: 15: 15)
152 INDIAN J. FIBRE TEXT. RES., MARCH-JUNE 2001
The wash and rub fastness properties of prints were BASF thickener based on acrylic acid-acrylamide
comparable to those obtained from kerosene emulsion copolymer89 along with a plasticizer (polydimethyl
and Alcoprint PTF. However, the scrub fastness of the siloxane) was tried with blue pigment (C.l. 174160)
samples was inferior, which improved on fixation at on viscose staple yarn fabric. Brilliant blue prints with
170°C. Prints obtained using mixture of synthetic and high levelness, sharp outlines, soft handle and good
kerosene emulsion thickeners were much brighter, all round fastness were claimed.
sharper and more uniform than those obtained with Vargese el al.9o have compared the performance of
100% synthetic or 100% kerosene emulsion thickener.
following three types of thickening systems with
Among the various copolymers, MAA:EA (65:35)
kerosene oil emulsion system:
crosslinked with > 3% EGDMA showed the best
performance. (i) Polycarboxylic acid (PCA)-all aqueous
system,
Another BASF thickener85, based on emulsion
(ii) Polymethylene carboxylate (PMC)-Iow
polymer of methacrylic acid /acrylic acid/allyl ether
kerosene emulsion system, and
(50:40: 10), was used with Imprerom Blue KRR (T.M)
(iii) Non-ionic emulsifying agent (NEA)-all
and Haliamine Bourdeaux on 50:50 polyester/cotton
aqueous system,
blend.The print was dried and cured at 150°C for 5
min. Excellent colour yield, brightness and sharp Considering both the print characteristics and
contour have been claimed in the patent. fastness to various tests, the three kerosene substitutes
have been graded as PMC = NEA > PCA.
Pigment printing in aqueous phase to replace
They also investigated the role of ammonium
kerosene and turpentine on all types of fabrics was
studied by Khanna86. The recommendations were sulphonate (AMS) or ammonium toluene sulphonate
(ATS) as the effective energy saving catalysts in place
made to avoid hard water or catalyst in the print paste.
of diammonium phosphate.
Acrylic based thickeners28 with cetyl stearyl
sorbate as comonomer, when used to fix prints at 3 Developments Towards Improved Performance
160°C for 3 min, resulted in good colour yield as well of Synthetic Thickeners
as contour sharpness on both cotton and polyester/ As discussed earlier, the hydrophilic and
cotton blend (65:35). hydrophobic comonomers govern the viscosity and Tg
of the product respectively and hence necessitate
The incorporation of 50 parts emulsion thickening
optimization to get the best performance. But the
substantially improved the colour value, sharpness
synthetic thickeners obtained through the best
and brightness of prints. The effect of partial
optimized conditions also do not match the overall
substitution of kerosene with synthetic thickeners
(Thixosyn PT) and subsequent fixation of pigment performance of oil- in- water emulsion 78. Continuous
efforts are on and new patents are being filed using
prints on silk using solar oven has been investigated
s7 different co monomers, crosslinkers, special
by Gulrajani el al. .
auxiliaries and surfactants to synthesize thickeners
The alternate to synthetic thickener developed at
and modified printing techniques to obtain improved
ATIRA84, ECO-TA-PRINT (ETP), was synthesised effects. Some common problems associated with
using balanced composition of selected monomers.
synthetic thickeners and possible solutions are
The product was reported to give colour strength
summarized in Table 7.
values higher than the prints obtained with standard
Carboxylic thickeners having improved
commercial thickener and closer to those obtained
with kerosene thickening. The stiffness property also performance91.92 under alkaline conditions (pH/ 10)
are claimed by incorporating 0.05 .. 5% N-substituted
followed the similar trend. The ETP has been claimed
acrylamide monomers (isopropyl acrylamide,
to be better than the commercial products used for
diacetone acrylamide, I-octyl acrylamide or I-butyl
comparison. In another study of ATIRA, Bhagwat and
Srivastava88 demonstrated that by incorporating acrylamide) by weight of polyunsaturated
certain auxiliary chemical (which modify the crosslinking agents.
penetration behaviour of print paste), the brilliance of In a US patent'», high efficiency copolymeric
pigment prints with synthetic thickener can be thickeners with improved tolerance to ionic or
obtained to the level similar to emulsion thickenings. electrolyte content have been disclosed. The