Acrylic Resins in Textile Processing J
A. C. NUESSLE AND B. B. KINE Research Laboratories, Rohm & Haas Co., Philadelphia, Pa.
Q
1
NTIL a few decades ago, the only polymeric materials employed in the finishing of textiles were naturally occurring substances such as rosin, gelatin, and various starches and gums. Today, however, the industry utilizes a large variety of synthetic polymers to achieve effects not possible with the natural products. One group of synthetics which enjoys such use is the acrylics family, composed of resins derived from acrylic acid and related compounds. A simplified picture of the chemical relationship between the acrylics and other synthetic polymers commonly utilized in textile finishing is shown:
e
ties responsible for their utility in certain applications. Other polymer types are mentioned where it is desirable to show similarities or differences, because the use of acrylics in a particular application will be unique only where other polymers do not have the required properties. GENERAL PHYSICOCHEMICAL CONSIDERATIONS
A linear polymer may exist in any one of three states, depending on its temperature, its chemical nature, and its molecular weight. Below a certain temperature the polymer is frozen in a glassy state, in which it possesses the mechanical properties of a Synthetic Polymers rigid solid. With increasing temperature there occurs a secondorder transition, beyond which the polymer enters a plastic state wherein under small periods of Addition Condensation polymers applied stress it has the reverspolymers ible deformation of a rubber. At a still higher temperature the polymer may enter a state of sym-Ethylenes unsym-Ethylenes Formaldehyde Polyesters viscous flow, in which nonreverscondensates ible deformations take place; this occurs most readily with polymers of low molecular Nitrogenous Nonnitrogenous weight, but may also occur with high polymers if the temperature is sufficiently elevated. Under Maleic derivatives Vinyl esters Phenol F Urea F Melamine F Ketone F (generally Vinylidene normal conditions of use, howhalides copolymers) ever, most linear polymers emStyrene ployed in the textile industry Acrvlics are in either the glassy or the rubbery state. The acrylics are a sdbdivision of the unsymmetrically subThe transition from glassy t o rubbery is a fairly sharp one, stituted ethylene class, which comprises a large number of resins but the observed value of the transition temperature may vary obtained by the polymerization of monomers containing a widely, depending on the method of test; probably the most critical variable is the rate of testing. A number of mechanical CHz=C< group. It is not unexpected, therefore, that in propertests have been proposed, involving softening temperature (1), ties and uses they are more closely related to vinyl polymers such brittle point (9),Young's modulus (9), and the like. A typical as polystyrene or polyvinyl acetate, than to the condensation curve, showing the effect of temperature on torsional stiffness, resins such as the urea-formaldehydes. is given in Figure 1. The acrylic monomers include both acrylic and methacrylic A comparison of test methods is outside the scope of this paper. acids, and their salts, esters, amides, and nitriles: Of greater importance to the present discussion is the fact that, under specific conditions of test, the location of Tg varies markedly CH-CH CH-CH CHFCH CHz=CH with the chemical composition of the polymer. For example, 2I I an ethyl acrylate polymer may have a transition temperature of bOOH COONa COOR CONHz -20' C., while a polymer of ethyl methacrylate may have a Tg Acrylic Acrylate Acrylic Acrylamide of f55" C., as indicated in Figure 2. At room temperature the acid salt ester ethyl polyacrylate would be soft and rubbery, while the ethyl polymethacrylate would be stiff. The stiffness of a polymer in the rubbery state also tends to increase with molecular weight, etc. CHz=CH but most polymers used in textile applications are polymerized CHa=l I to a degree where the effect of molecular size is no longer critical. CN COOH Accordingly, the transition temperatures of the various polymers, and their relative stiffness a t a given temperature, are determined Acrylonitrile Methacrylic primarily by their chemical constitution. acid The following generalizations may be made concerning the The present paper is concerned with textile uses of acrylics, relationship between chemical structure and physical properties of the acrylic polymers. and especially with some of the chemical and physical proper-
I
I
I'
7-
I
I
I
8""
1287
INDUSTRIAL AND ENGINEERING CHEMISTRY
1288
t
60
Vol. 45, No, 6
tion in ethylene dichloride or other suitable solvent. Because of greater fire hazard, toxicity, and expense, this is usually less desirable than an application from water medium, but finds use in applications where a very glossy surface coating is desired. FROMEMULSION POLYMER. The water-insoluble monomers may be polymerized in emulsion form, to produce an aqueouq dispersion or latex. Properly made, such dispersions are stable in storage for a year or more, and may be readily diluted with water to any degree a t time of use. On drying, most dispersions are irreversibly broken, so that the finish is wash-fast. Because of the ease of application, this is the most popular method of applying the water-insoluble acrylics to textiles. APPLIEDAS MONOMER.There are many ways of applying an acrylic monomer (or combination of monomers) to a textile material, and subsequently bringing about polymerization in place. By such means, the polymer can in many instances be built up within the fiber, rather than deposited on the surface. Some attention has been given to this method by various investigators, although thus far little commercial utilization has resulted.
GLASSY
It is evident that the acrylics are most often applied either from water solution or from aqueous emulsion. EMCLSIOM POLYMERS
Tg
TEMPERATURE
-
F i g u r e 1. Effect of Temperature on Torsional Stiffness Because the alkyl group tends to separate the polymer molecules and act as a plasticizer, the lower members of the n-alkyl acrylate series become even softer with increasing length of the alkyl chain. Higher in the series, there is a reversal as a waxy stiffness sets in owing to the tendency of the longer alkyl chains to crystallize. Brittle point measurements, which determine the temperature a t which an arbitrary brittle stiffness is attained, set the minimum a t n-octyl(9); however, a test based on relative hardness a t a fixed, more elevated temperature-e.g., room temperature-would put the minimum somewhat higher. The n-alkyl methacrylates similarly become softer, to a minimum, by brittle point, a t dodecyl ( 8 ) . Branched-chain alkyl esters have greater rigidity than the corresponding straight-chain esters. The tert-butyl esters are especially stiff ( 7 ) . Acrylonitrile and methacrylonitrile polymers are very stiff and have a very high Tg,presumably because of strong hydrogen-bonding tendencies of the compact, polar nitrile group. The polyacids, their amides, and their alkali salts, which are so strongly polar as to be generally water-soluble, give stiff films having relatively little thermoplasticity. The effect of copolymerization tends to be additive, with the copolymer exhibiting physical properties intermediate between those of its components. Thus, the physical as well as chemical properties can be varied over a wide range by suitable choice of monomer combinations. One other important factor which may influence the physical properties of a polymer film is its mode of preparation. A film laid down from emulsion-Le., latex-may be somewhat less continuous than one laid down from solvent, particularly if the transition temperature is high. As is illustrated in a later section, this can influence the type of finish obtained on the textile fabric. METHOD OF APPLICATION
There are four general methods of applying acrylics to textile materials:
FROM WATERSOLUTION.The water-soluble polymers include polyacrylic and polymethacrylic acids, their alkali and ammonium salts, and their amides. Acrylonitrile and the acrylic esters cannot be so applied, unless copolymerized with a substantial proportion of one of the water-soluble acrylics. Applied to textile yarns or fabrics, such materials usually remain matersoluble, unless insolubilized by some special method, and are therefore most useful where wash-fastness is not required. The acrylic esters and their coFROM SOLVENT SOLUTION. polymers with acrylonitrile may generally be applied from solu-
PHYSICAL PROPERTIES AXD ESD USE. One of the most common objectives of textile finishing is the modification of the “hand” or feel of a fabric. By this means it is possible to weave a standard fabri: and modify it later to meet the requirements of the current fashion trend. It is also possible to take a light, inexpensive fabric and build it up to simulate a heavier, more expensive fabric. This is generally done by treating the fabric with a polymeric material which will penetrate the yarns and bind the fibers together, and also bond the yarns a t the crossover points. Thus the fabric becomes less multifilamentous, and
tI
11 EA
- 20
ROOM TEMP
-
+55
PEkrbiYk “6. Figure 2.
Effect of Chemical Composition on Transition Temperature
therefore less flexible. I n order to do this, the polymer must adhere t o the fibers; but assuming good adhesion (as is almost invariably the case with cellulosic fabrics) the effect on fabric Lfhand”is then dependent to a large degree on the physical properties of the polymer. For example, consider the effect of two conlmercially available acrylic dispersions applied to an 80 x 80 cotton sheeting. One of these, designated as emulsion A, when dried doivn on gla% in the absence of fabric, yields a soft, rubbery film, whereas the other, emulsion R,dries to a hard film. Each of these products was padded onto the fabric a t two concentrations and dried a t two temperatures. Stiffness tests were then made using the Gurley tester (9) which measures the force required to bend the fabric sample unilaterally. Although m r h a test cannot take into account all of the many factors Tvhich go to make up the complex property known as hand, it does give an objective meawrement of one important fabric property-flexural stiffness. The data are listed in Table I .
INDUSTRIAL AND ENGINEERING CHEMISTRY
June 1953
It is apparent that stiffness increases with concentration (as would be expected), and also increases slightly with temperature of drying (because of more com lete fusion of the emulsion particles). Far greater, however, is t%e difference between products: Emulsion B, which dries to a hard film, imparts considerable stiffness t o the-fabric, while emulsion A, which dries to a soft, rubbery film, Gves little stiffness b u t imparts full, heavy feel, which unfortunately cannot easily be reduced to a single numerical quantity. As these materials are both acrylics, it is obvious that a range of effects is available, depending on the type of acrylic selected. TABLEI. FILMFORM OF EMULSION POLYMER vs. EFFECTON FABRIC Drying Solids Tfmp., on Fabric, C.
Polymer
Film Form
Water control
......
.... ..
A
Soft, rubbery
B
Hard, stiff
3.9 3.9 7.7 7.7 4.1 4 1 7.7 7.7
%
,.
a
Gurley Stiffnessa, Mg../In. 6.6 6.6 10.2 10.4 12.0 13.2 38 44 59 62
120 150 120 150 120 150 120 150 120 150
Hand of Fabric
E
,Composition
50 EA 50 M M A 100 MMA
M a
EA, ethyl acrylate.
Drying T:mp., C. 25 150 Soft, rubbery 25 E (EA) 150 E M (EA/MMA) Stiff, flexible 25 150 M (MMA) Very stiff, brittle 25 150 a About 4% solids in ethylene dichloride. Solvent Solutions Solvent only
Stiff
Film Form
.......
GurIey Stiffness, Mg./Inch 7.2 7.1 12 11 65 73 112 111
Hand of Fabric Soft Full, heavy Stiff Very stiff
Another way in which a dispersion of a hard polymer such as M may be made to give a continuous film, and therefore stiffness t o fabric, is by plasticizing it with a softer polymer. I n Table IV is shown the effect on fabric stiffness of a physical mixture of polymer dispersions E and M, dried on a t 15OoC.,as compared with each polymer separately. As the two polymers are compatible, they fuse together to form a single-phase mixture having considerable hardness and capable of stiffening the fabric appreciably. By contrast, a mixture of polymer E and an infusible pigment (titanium dioxide) forms a two-phase system having the properties of the soft, continuous phase, and therefore does not stiffen the fabric.
TABLEIV. EFFECTOF MIXTURESOF EMULSIONPOLYMERS Applied Solids % M
% E 8 4
.. 4
.4. .8.
% Ti02
..
.. 4
Gurley Stiffness 11 28 12 11
This is an extreme case; most aqueous dispersions for textile use are of the %ontinuous film" type, and mixtures of these will give effects intermediate between those of the components. Where a polymer such as M is to be used for delustering, however, it is important not to use it in conjunction with a softer CHEMICALCOMPOSITION OF EMULSION POLYMERS polymer which will plasticize it; otherDrying Gurley Solids on TErnZ., Stiffness wise stiffness will result, instead of the Form Fabric, % Mg./Inoh Hand of Fabria desired dulling effect. However, the
. . . . ... 100 E A a
ERI
Film
TABLE 111. EFFECTOF SOLVENT APPLICATIONS
Full, heavy
To illustrate further the variety of effects, and t o show how monomer composition controls the physical properties of the film and therefore the type of finish obtained, the following series of polymers was studied: E 100% ethyl acrylate EM 50% ethyl acrylate, 50% methyl methacrylate M 100% methyl methacrylate Each was polymerized in a similar system, using an anionic dispersing agent, and to an average chain length in a range where variations would not be critical; therefore, any marked differences between the materials may be attributed to their monomer composition. Cotton sheeting was dipped into the polymer dispersions, squeezed, and dried either a t room temperature (ea. 25' C.) or at 150' C. Gurley stiffness values were obtained, and the hand was also evaluated subjectively. In addition, portions of each polymer were dried down in the absence of fabric to determine the film properties, The data, presented in Table 11, indicate the direct relation between the physical properties of the dried-down polymer and the effect on fabric. The soft, rubbery polymer (E) gives a full, heavy hand with little added stiffness; the stiff, brittle copolymer (EM) produces a stiff, rather crisp finish; but the even stiffer polymer (M), which has such a high fusing point that the tiny dispersed particles will not coalesce into a continuous film, has very little effect on the hand. A polymer of the latter type, lacking cohesion, may nevertheless have satisfactory adhesion to certain fibers, and in such a case may be used to deluster a very shiny fabric.
Polymer Water only
The necessity of fusing the dispersed particles to obtain proper cohesion is shown in the effect of drying temperature on copolymer EM. Drying at 150' C. almost doubled the stiffness over that obtained a t room temperature. Each of these polymers, if precipitated from the dispersion and dissolved in a suitable solvent, will then dry down to a continuous film, as there are no longer any discrete particles which need to be fused. The molecular flow required for film formation is maintained during drying by residual solvent, which temporarily lowers the transition temperature. Accordingly, polymer M would be expected to give a stiff finish to fabric if applied from solvent. Data in Table I11 show that this is so. It is also apparent that the drying temperature is much less critical when applying from solvent than when applying from aqueous dispersion.
Soft
Test made in warp direction.
TABLE 11. EFFECTOF
1289
Soft, rubbery
.... 4
4
Stiff, brittle
8 4
Discontinuous, powdery
8 4 4
25 150
6.1 6.7
25 150 I5O 25
7.5 8.9 11 16 31 56 7 5
4
8
MMA, methyl methacrylate.
150 150 25 150 150
8.9 12
Soft Full, heavy Stiff
v:
slightly stiff dielustered"
stiffness produced by the mixture of polymers E and M (28 mg. per inch) is not HO great as was obtained from copolymer E M (56 mg. per inch) (cf. Table 11). AND END USE. CHEMICALPROP~RTIES It should be evident that, in so far as the type of finish obtained on fabric is due to the physical properties of the polymer, any other polymer type hav-
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
1290
Vol. 45, No. 6
TABLE V. AGINGCHARACTERISTICSO F VARIOUS COPOLYMERS ON COTTON F.4BRICR Fabric NO.
0 1 2
Polymer Composition
Effect on Stiffness" Oven, 12 Hours a t Fade-Ometer 1200 c. 50 Hours 100 Hours, Or& units Units % L C Units % i.c Units % i C
Water Ethyl acrylate Ethyl acrylate, methyl methacrylate Vinyl chloride, 2-ethyl hexyl3 acrylate 4 Butadiene, acrylonitrile 5 Vinylidene chloride, vinyl acetate S7inyl acetate 6 a Gurley stiffness, mg./inch. b Reflectance as % of ceramic plate, using Increase in stiffness, as 70of original. d Decrease in whiteness, as % of original.
-
7
11
6 10
.. ..
7 9
0
7 11
I .
0 0
Effect on Colora Oven, 12 Hours Fade-Ometer orig,, a t 120' C. 50 Hours 100 Hours units Refl. % d.d Refl. % d.d Refi. % d.d 99.2 97.2
96.1 92.2
3.1 5.1
98.2 94.9
1.0 2.4
96.5 94.5
2.7 2.8
56
61
9
54
..
69
23
98.5
94.2
4.4
95.1
3.5
94.3
4.3
14 10
29
12
107 20
57 111
307
1010
64 111
357 1010
96.0 88.7
83.5 77.6
13.0 12.5
80.1 64.2
16.6 27.7
78.9 80.7
17.8 31.6
46 78
50 86
9 10
58 89
26
61 89
33 14
92.0 98.3
77.8 93.1
15.4 5.3
45.2 97.0
50 9 1.3
39.8 96.3
56.7 2.0
14
blue filter.
ing the same physical properties will tend to produce a simiHere is shown the effect of eight commercially available aqueous lar result. Thus, the finishes achieved with ethyl acrylate and dispereions, applied at equal solids (about 6%) to a rayon challis, methyl methacrylate, in the above examples, may be closely an acetate satin, and a nylon taffeta. The fabrics vere dipped, duplicated by appropriate combinations of, say, hexyl methacrysqueezed, and dried a t 150°C. The polymers are listed in order late and acrylonitrile. Moreover, the choice is by no means of relative stiffness on rayon, as ranked subjectively by several limited t o the acrylics. Using nonacrylic monomers, a range of observers. Also listed for acetate and nylon is the degree of effects may be obtained from butadiene (soft) and styrene, vinyl crazing, or susceptibility to cracking of the finish, which s h o m up chloride, or vinyl acetate (stiff). As with the acrylics, the range as a white mark when scraped with the fingernail. Conditions from hard t o soft may be obtained by interpolymerization or necessary for crazing are that the polymer be brittle and the admixed homopolymerization, or by incorporation of a nonpolyhesion be insufficient to withstand the abrading force. merizing plasticizer. Against such competition, the choice of an acrylic is often based on more suitable chemical properties. TABLEVI. ADHESIONOF EMULSION POLYMERS TO VARIOGSFIBERS Among these chemical properties is resistance to Rayon, Acetate Nylon, aging, specifically to changes resulting from heat Polymera Film Form Rel. Stiff. Rel. stiff. Crazing Rel. stiff Crazing Rubbery 2 4 Kone 5 None and light. I n Table V are presented the results of A B Rubbery 2 3 None 3 None oven test's (12 hours at 120" C.) and Fade-Ometer C Rubbery 3 5 V. slight 5 None D Stiff flexible 5 6 V. slight . . . exposure (50 and 100 hours) on cotton fabric treated E Stiff: flexible 5 6 Slight 4 V. siight with approximately 8% solids of each of several aqueF Stiff, slightly brittle 8 6 Severe 6 Slight G Stiff, slightly brittle 8 8 Severe 7 Slight ous dispersions, including acrylics, nonacrylics, and V Stiff, brittle 4 Severe 8 8 Severe mixed polymers. The fabrics were dipped, squeezed, a Al! acrylics except V (vinyl acetate) and D and E (mixed). * Stiffness. 0 (untreated fabric); 2 full, heavy; 5 leathery; 8 stiff. dried at 1500 c,,and subjected to the accelerated aaina - - tests. Only the tn-o acrylics (fabrics 1 and 2) and vinyl acetate (6) were resistant to stiffening and discoloration on expoOn acetate, the relative stiffness generally follows in the same sure to heat and light. By contrast, one of the nonacrylics (5) order as on rayon; but on nylon the order is somewhat irregular. and two mixed polymers (3 and 4) showed marked adverse Attempts to relate the adhesion to the monomer composition changes as a result of thc accelerated aging tests-in one case within the series illustrated have not been very successful, althe fabric stiffness showed more than a tenfold increase, and in though it would appear that the vinyl acetate dispersion, which another the whiteness (as measured in blue light) showed a drop is so effective on the acetate and rayon, is inferior to the stiffer to less than half its original value. While no far-reaching conacrylic on the nylon. The vinyl acetate also shows more crazing clusions may be drawn from so brief an experiment, nevertheon nylon than do the acrylics. less, the data illustrate what has been found to be true in many One factor which complicates the situation is the presence of other studies: The acrylics invariably have good aging properties, dispersing agent, a component of practically all emulsion polybut in mixed polymers they cannot overcome inferior properties mers; because of this, the effects of chemical composition on adimparted by other monomers. The addition of ultraviolet abhesion are more easily studied by application from true solution. sorbing agents and other adjuncts would improve the aging The dispersing agent is also primarily responsible for the ionic properties of the more unstable materials, but the acrylics are nature of most dispersions, and with the acrylic emulsion polysatisfactory without such agents. mers, as with all dispersions, the ionic nature is of considerable Not shown in Table V are the excellent aging properties of vinyl importance in determining handling properties. The usual anacetate-acrylic mixed polymers. Vinyl acetate alone will always ionic form is incompatible with most cationic materials, including give a stiff fabric; softer finishes based on plasticized or copolycertain thermosetting resins; the cationic form, ip addition t o merized vinyl acetate will have aging properties dependent on being incompatible with anionics, tends to exhaust onto textile the properties of the plasticizer or other monomer. Some of the fibers, x-hich may be either desirable or undesirable. The nonsofteracrylics, asmight be expected, are ideal for this purpose, even ionic dispersions are the most versatile because not only are they though the extent of interpolymerization is believed to be small. generally compatible with other finishing agents, but, by addition A second property which may be regarded as primarily chemical of a suitable cationic surface active agent, they can be made to in nature is the adhesion of the polymer to the textile fiber. exhaust. It is thus not necessary that the polymer itself be It was stated earlier that the type of bodying or stiffening effect cationic, in order for exhaustion to take place. The ionic nature imparted by a polymer depends on its physical form, provided it must be considered as contributing to the properties of the polyhas good adhesion to the fibers, and that in the case of cellulosic meric dispersions, quite apart from the physical or chemical proptextiles the adhesion is usually satisfactory. This is not always erties of the polymer itself. so with the hydrophobic fibers, as is illustrated in Table VI.
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
June 1953
a
I n considering the degree of wash-fastness of a thermoplastic finish, a distinction, albeit an academic one, must be made between two factors: the weight retention, which is almost always high, and the retention of the finish, which in certain instances-e.@;., those depending on adhesion of polymer to fiber-may be appreciably reduced. For example, washing a fabric which has been treated with a moderately hard acrylic emulsion generally lowers the resin content by less than 10%; but because the adhesion between the polymer and the fibers has been partially destroyed, the fibers are no longer as completely cemented together, and the stiffness may be reduced to a considerable degree. Hot pressing, particularly in the presence of moisture, is helpful in re-establishing the adhesion and, therefore, in restoring much of the original stiffness. This phenomenon is illustrated by the data in Table VII, which show the effects of washing and various aftertreatments on the stiffness of an acrylic-treated cotton fabric.
TABLEVII. EFFECTO F WASHING
AND PRESSING ON FABRIC
STIFFNESS
Original Washed, air-dried (25' C.) Dry-pressed (150' C . ) Sprayed, pressed (150' C.)
Gurley Stiffness, Mg./Ineh Untreated Acrylic 67 6 7 23 31 7 45 6
The fabric, along with an untreated control, was tumbled in a wash wheel for 15 minutes at 60" C. in 0.1% soap and 0.1% sodium tetraphosphate, followed by rinsing, centrifuging, air drying, spraying with water (where indicated), and pressing at 150' C. Despite the changes in stiffness, the resin content (by acetone extraction) remained constant a t 7.5% throughout the series. The possibility of soap pickup on the fabric cannot be completely ruled out as a contributing factor t o both weight retention and softening of the finish. Nevertheless, in other instances where nonionic detergents have been used in washing, the resin content has rarely dropped more than 10% in a single wash; yet there is always some loss of stiffness on tumble washing, and partial regain on damp pressing, even when water alone is used as the washing solution. Thus, the variation in stiffness is due to changes in adhesion (and possibly cohesion) rather than t o loss of polymer. The full hand imparted by the softer acrylics undergoes a similar, though less noticeable, change on washing and pressing. OTHER USES OF WATER-INSOLUBLE ACRYLICS
1291
degree of nonskid; satisfactory adhesion to the fibers; and no stiffening on storage. I n this application, resistance t o ultraviolet light is not a factor, nor is discoloration on storage. Similarly, certain of the acrylic emulsion polymers have shown considerable merit as binders for nonwoven fabrics. In such an application the web of textile fibers is held together by the resin binder, which may either be printed on in the form of stripes or other pattern or applied uniformly throughout the fabric. As in the case of rug backing, only the higher cost of the acrylics has prevented their greater utilization in this use. Pigment binding is another field in which the acrylics have shown promise, Any of the acrylics, soft or stiff, may be employed to bind dulling agents to obtain combination bodyingdelustering effects. As a component of backfilling mixtures, which ordinarily contain clay plus starch or flour and are used to add body, weight, and a closed-up appearance to lowgrade fabrics, the acrylics impart a degree of water resistance and freedom from dusting. Certain of the acrylics have also shown merit in reducing crocking when added to pigment dyeing systems containing other types of resin binders. I n each of these applications the acrylics are especially valuable because of their freedom from discoloration and from change in stiffness on aging, in addition to their adequate binding properties. Acrylic polymers have been used to prepare coated fabrics having excellent resistance to weathering, Coatings may be applied from solvent or from thickened water emulsion, and may be clear or pigmented. By proper selection of monomers, any degree of flexibility may be obtained without need of plasticizers; in the same manner the temperature range (between brittle and tacky) may be modified to suit the specific end use. Adhesion to various textile fibers ranges from good to excellent. The acrylic emulsion polymers, in common with most other thermoplastics, are ineffective in imparting shrinkage control or crease resistance, generally cause a slight increase in tensile and a slight decrease in tear strength, but usually improve the resistance to abrasion. The resistance to flat abrasion, in particular, is often markedly improved. Table VI11 gives typical data on the effect of several acrylic polymers on the properties of a cotton sheeting; an 8% solids application was employed to emphasize the results. WATER-SOLUBLE ACRYLICS
Thus far, only the water-insoluble acrylics, which are available in a wide range of physical forms, have been considered. By contrast, the soluble acrylics-the acids, salts, and amideswith few exceptions dry down to hard, stiff films, by virtue of the fact that the same strongly polar forces that draw the molecules into solution will, in the absence of water, bind the molecules together to form glassy solids having little thermoplasticity. Applied to cellulosic fabrics, each imparts a crisp, starchlike finish. Because they remain water-soluble (except in certain cases), they are not widely used as finishing agents, although sodium polyacrylate is frequently used as an additive to starch formulations to impart greater toughness and flexibility. Of greater importance is their use in sizing warp yarns to protect them during weaving; in this application ready removability is an asset. The function of a warp size is to hold down the loose fibers and protect the yarn from chafing during weaving. The
During World War I1 the problem of keeping drinking water cool in the field was solved by the use of a heavy canvas water bag, so impregnated as to prevent leakage but to permit a slow diffusion of water to the surface, where evaporation exerted a cooling effect on the contents of the bag. This controlled seepage was attained by use of an acrylic polymer in combination with a hydrophilic colloid. The proper diffusion rate and flexible &ish could no doubt have been obtained with other polymers; the choice of the particular acrylic was based on chemical inertness, freedom from toxicity. - , and resistance to change' on storage or exposure to light. TABLE VIII. EFFECTOF ACRYLICS ON FABRIC PROPERTIES A potentially important use for the acrylics is that Grease of rug backing. The function of such material is to ShrinkageQ, RgZo&;b, Elmendorf Tensilec, Abrasio n bind the pile fibers and/or to prevent the rug from Polymer % Tear, TBL Warp, 8% Asslied dolids Waru Fill Waro Fill Wars. Lb. Lb. CYOl& skidding on a polished floor. Although as yet not Untreated 8 . 8 6 . 1 65 61 3.8 45 7 700 widely utilized in this application because of their 47 29 '800 E EA) 6.0 5.7 66 3.2 Eih (EA/MMA) 6.0 5.3 48 2.7 53 20 500 relatively high price, the softer acrylics have all the M (MMA) 6.7 5.8 44 16,900 54 58 2.8 necessary attributes: flexibility without need of a Full Sanforize wash, 40 minutes at 80° C.in 0.1% soap. 6 Monmnto test. plasticizer, thus eliminating the possibility of stained C 1 inch raveled strip. floors through plasticizer migration; any desired
i:
@
:
1292
INDUSTRIAL AND ENGINEERING CHEMISTRY
sizing agent must, of course, form a tough film, neither too brittle nor too soft; but not all polymers having satisfactory physical properties will make good sizes. Unless the polymer has sufficient adhesion to the fiber, it will flake off when subjected to the flexing and abrading forces incurred during weaving. There are many materials which could be used in the warp sizing of cotton; various starches, sodium carboxymethylcellulose, polyvinyl alcohol, and sodium polyacrylate are a few of the many which have sufficient adhesion, in addition to the necessary film properties. Polyacrylic and polymethacrylic acids would also be satisfactory, except that they are too acidic and would tend to degrade the cellulose. Because cornstarch, plasticized with tallow or other softener, is both efficient and economical, it is the most widely used material for sizing cotton warps. The only acrylic having any appreciable commercial utility in this application is sodium polyacrylate, which to date has been employed only as an additive to starch mixes. In the sizing of nylon, however, the situation is different. The various starches, sodium carboxymethylcellulose, and sodium polyacrylate do not have sufficient adhesion to nylon, and tend to flake off. Polyvinyl alcohol, generally employed with boric acid or borax, has slightly better adhesion, and has enjoyed considerable use in this application. More recently it has been found that polymethacrylic and polyacrylic acids have excellent adhesion, Both show up well in laboratory tests, but on a plant scale the polyacrylic has demonstrated a definite superiority and is probably the most effective of the currently available nylon sizes. The reasons for the superiority of polyacrylic acid over polymethacrylic and the other materials have not been clearly elucidated, but the following factor8 are suggested: Both of the acrylics are rather strong acids, which could account for their great specific adhesion to nylon. Polyacrylic acid is somewhat stronger than polymethacrylic acid. The polyacrylic acid molecule is contracted into a coiled configuration, so that solutions of polyacrylic acid have a lower viscosity than would be expected from the degree of polymerization. Polymethacrylic acid exhibits this property to a lesser degree. The lower viscosity a t a given concentration facilitates penetration into the yarn, resulting in more complete bonding o! the individual fibers by mechanical as well a9 specific adhesion. The coiled chain should also confer greater flexibility to the polymer and lessen its tendency to flake off. From steric considerations, a polyacrylic chain should be more flexible than a methacrylic of equal length. On the basis of present information, it is difficult to determine the exact significance of each of these factors. For example, partial neutralization of polyacrylic acid with sodium hydroxide to the extent of 20 to 25% is known to interfere with its efficiency as a nylon size. It cannot be stated, however, that this is due entirely to the decrease in acidity, for neutralization is accompanied by a straightening of the polymer chain, with resulting increase in viscosity and decreased flexibility. On the other hand, the flexibility of the polymer is probably not as important as the other two factors, as it is possible to neutralize the acid with a material-e.g., triethanolamine-which, by acting as a plasticizer, will increase the flexibility of the film, yet still interfere with sizing efficiency because of adverse changes in the other factors. The probability that the efficiency of polyacrylic acid as a size for nylon is due primarily to greater specific adhesion, rather than to physical properties of the polymer, is etrengthened by the finding that polyacrylic acid may be made to combine chemically xvith nylon. Polymethacrylic acid has a much lover degree of reactivity. I n Table IX are shown data obtained on drying measured amounts of polyacrylic acid or polymethacrylic acid onto nylon fabric a t elevated temperatures and determining the quantity retained after a scour in 0.1% soap and 0.1% soda ash for 40 minutes a t 80" C. The possibility that the 175" baking is merely insolubilizing the polyacrylic acid through anhydride formation can be ruled
T.4BLE
Polymer PAA PLIA
Ix.
Vol. 45, No. 6
REACTIOM O F POLYlCRYLIC
Baked 10 Min. a t C. 115 175 115
ACID WITH N Y L O N Amount Applieda, Retained after Retained, G. Washingb, G. %
out by extracting the treated fabric with boiling benzyl alcohol, a nylon solvent. This will dissolve away the unreacted nylon, leaving a gossamerlike residue of the polyacrylic acid-nylon reaction product. In a typical instance, There the amount of polyacrylic acid applied was 5% (on the weight of the nylon), the residue amounted to 9.8%. It contained both nitrogen and unreacted carboxyls. The mechanism of the reaction has not been determined: two possibilities are (1) imide formation and (2) trans-amidixation. HOC=O
+ (PAAjL(PA
K R'-(nylon) I
41
H
The latter seems much more plausible. There is a third possibility-that the combination takes place on end groups; the final result would be similar to Reaction 2 . Aside from the theoretical aspects, tLyo practical considerations are worth mentioning. First, when polyacrylic acid is used as a warp size, it should not be subjected to severe drying conditions; otherffise it will not be completely removed in mashing. Second, if sufficient heat is applied, it should be possible to utilize polyacrylic acid as a durable finishing agent. Data presented in Table X show that this is so. The polyacrylic acid was applied to nylon taffeta by dipping and squeezing to obtain 5 % solids on fabric. Baking a t temperatures up to 176' C. was conducted in an oven; for the 200" treatment a thermostatically controlled hot iron Tas used. Washing was conducted a t 80' for 40 minutes. Because nylon is heat-set a t temperatures around 200" C., it is possible to utilize polyacrylic acid as a warp size, then fix it in the fabric as a durable finish. For a crisp organdy finish, hon-ever, the polyacrylic acid is best applied to the woven fabric,
TABLE x. EFFECTO F HEATO N DURllBILITY ACID ON KYLON Heat Treatment Min. Temp., O C. 10 5
Girley Stiffness, JIg./Inch Unwashed Washed % Retained"
120 150 150 1 173 173 10 0.08 200 0.5 PO0 Not corrected for rtiffness of
30
O F POLYACRYLIC
16 19 17
17
19 18 17
1
3 12
3 16
11 17
fi
16
71 18 84 61 100
a untreated fabric (about 1 t o 2 mg./inoh) , which was not altered by heat treatment or washing.
June 1953
INDUSTRIAL AND ENGINEERING CHEMISTRY
so that all the yarns, both warp and filling, are sized. The treatment is particularly effective for stiffening nylon lace. Further data, outside the scope of the present paper, indicate that polyacrylic acid/glycerol (10 to 3) will give a finish of even greater crispness and durability than polyacrylic acid along, the glycerol apparently not only acting to cross-link the polyacrylic acid molecules, but serving as a flux or solvent medium for the reaction with nylon. The finish is exceedingly resistant to removal by 1 % hydrochloric acid or 1% sodium hydroxide a t the boil. Unfortunately, polyacrylic acid does not have durable adhesion to Orlon or Dacron. OTHER USES OF WATER-SOLUBLE ACRYLICS
The alkali salts of polyacrylic and the polymethaorylic acids exhibit in water solution the high viscosity expected of a polymeric material. Sodium polyacrylate, at present the most readily available salt, finds considerable use as a thickener for natural and synthetic latices, as an ingredient in printing pastes, and 8s a dispersing agent and protective colloid. It is compatible with most anionic and nonionic dispersions and, unlike many natural gums, is unaffected by bacterial or hydrolytic decomposition. Polyacrylamide and polymethacrylamide also tend to be watersoluble. Viscous solutions of the latter may be made by polymerization of the commercially available monomer in aqueous medium a t temperatures below 80” C. Polymethacrylamide prepared under other conditions may be incompletely soluble (10).
Films of the polyamides, unlike those of sodium acrylate or methacrylate, may be insolubilized by heat, which causes crosslinking of the polymer chains through imide formation. Of greater technological importance is the very complete insolubilization which may be obtained by reaction with formaldehyde, glyoxal, or various amino- or phenol-formaldehyde condensates. Such combinations have the properties usually associated with polymeric thermosetting materials, and may be used to obtain such typical effects as durable crispness, stabilization of cellulosic fabrics against shrinkage, durable glazing, and embossing. Ammonium polyacrylate has similar thermosetting properties, but to a much lesser extent. Sodium polyacrylate, when made by hydrolysis of acrylonitrile, may contain a small proportion of amide or ammonium groups, but not to the extent that it is easily insolubilized by formaldehyde or heat. It is possible to prepare copolymers of methacrylamide with acrylic and methacrylic acids and esters, as well as with a variety of nonacrylic monomers, The water solubility of such products varies with the proportion of hydrophilic groups and the degree of polymerization, and no general rule can be given (IO). I
1293
ferrous sulfate was dried into wool, and the wool worked for several hours a t 95” C. in a dispersion of methyl methacrylate, which in some instances contained 0.03% hydrogen peroxide. At 45% add-on the area shrinkage was reduced from 50% (for the untreated) to 0.5% for the treated. The investigators believed the shrink resistance to be due to internally formed polymers. Weight gains up to 240% were reported, but no doubt much of this was due to surface resin. I n another case (II), wool fabric, saturated with dilute persulfate solution, was exposed to the vapors of various monomers a t 90” to 95” C. Effects noted were shrink resistance, decreased affinity for water vapor (possibly because available sites were blocked by the polymer), and a fuller hand (perhaps due in part to surface resin). I n other studies (5),wool fibers containing polymethacrylamide were aftertreated with formaldehyde to obtain a cross-linked polymer, a t least partially within the fibers. Reduced extensibility resulted. More recently, a study of polymerization of vinyl monomers within viscose rayon fibers has been reported by Landells and Whewell (4). Weight gains up to 78% are claimed; the properties of the cellulose are said to have been considerably altered, but no details are given. The above possibilities are of course not limited to acrylics. Theoretically any vinyl monomer or combination of monomers may be utilized in this way, although from a practical standpoint each will probably require its own special conditions for greatest yield. I n addition to polymer formation, it is also possible to obtain reaction of the monomer with the fiber. Thus, Stallings (IS) treated cotton fabric with acrylonitrile in the presence of sodium hydroxide to obtain cyanoethylcellulose. The fabric was said to be stronger, stiffer, less water-absorbent, and more resistant to abrasion. Under other reaction conditions, sodium carboxyethylcellulose was obtained ( l a ) ,and the fabric was stronger and more water-absorbent, and had a linen-like luster. The variation in water absorption reflects the increased hydrophilic tendency of the functional group, going from cyanoethyl to hydroxyl (in the original cellulose) to sodium carboxyethyl. None of the above processes involving monomer applications has as yet attained commercial importance. ACKNOWLEDGMENT
Credit is extended to R. F. Crawford and to Betty Haffner for their valuable contributions to the experimental sections of the paper. LITERATURE CITED
(1) Am. SOC.Testing Materials, “ASTM Standards,” Part 5, p. 1580, 1949.
MONOMER APPLICATIONS
I n the applications thus far discussed, the acrylics have been prepolymerized and have therefore been unable to penetrate the fibers. In many instances, however, it is possible to apply an acrylic in the form of the monomer and polymerize it, at least in part, within the fibers. A number of researches along this line have been reported, and several of these are briefly outlined below. The methods of application are varied. Depending on the physical form, solubility, and vapor pressure of the monomer, each of the acrylics may be applied in several of the following ways: from water or solvent solution, from emulsion, as the pure liquid, or in the vapor phase. The catalyst, which is generally applied to the fiber in a separate operation, is usually a persulfate or peroxide type, sometimes in combination with a ferrous salt or other activator. Speakman and coworkers have made numerous investigations of monomer applications to wool. I n one instance (6), 0.2%
(2) (3)
Conant and Liska, J . Appl. Phys., 15, 767 (1944). Institute Paper Chemistry, P a p e r Trade J., 104, No.
21, 4 3 ;
No. 22, 4 3 (1937).
Landells and Whewell, J . Soc. D y e r s Colourists, 6 7 , 338 (1952). (5) Lipson and Speakman, Ihid., 6 5 , 3 9 0 (1949). (6) Lipson and Speakman, N a t u r e , 157, 590 (1946). (4)
(7) Neher, IND. ENG.CHEM.,28, 267 (1936). (8) Rehberg and Fisher, Ibid., 40,1429 (1948). (9) Rehberg and Fisher, J . Am. Chem. SOC.,66, 1203 (1944). (IO) Rohm and Haas Co., Technical Bulletin “Methacrylamide,” 1950.
(I 1) Speakman and Barr (to Imperial Chemical Industries), Brit. (12)
Patent 559,787 (1944). Stallings (to Rohm & Haas Co.), U. S. Patent
2,390,032
(1945). (13) Ihid., 2,473,308 (1949).
RECEIVED for review August 6, 1952. ACCEPTEDOctober 23, 1952. Presented before the Division of Paint, Varnish, and Plastics Chemistry, Symposium on Resins in Textile Finishes, a t the 122nd Meeting of the AMERICAN CHEMICAL SOCIETY, Atlantic City, N J.
