4
Ind. Eng. Chem. Prod. Res. Dev. 1982, 21, 4-11
of isomers hindered crystallization. These compounds are tetrafunctional in reactions with alcohols as contrasted with the difunctional 4,5-dihydroxyimidazolidinones (Figures 1 and 2). When the compounds were used as cross-linking agents for cotton the higher functionality gave slightly higher contents of bound nitrogen. The higher nitrogen contents indicated a small increase in reactivity although not necessarily an increase in the degree of cross-linking. However, isolation of the compounds from the reaction mixture was needed for the best results. The difficulty of isolation and the cwt of reagents for preparing the compounds suggests that the a,w-bis(4,5-dihydroxy3-methyl-2-oxoimidazolidin-l-y1)alkanes will be more expensive than the dihydroxyimidazolidinones. Acknowledgment The authors thank the Textile Properties Unit of the Southern Regional Research Center for physical testing of fabric, A. M. Hammond for nitrogen analyses, J. E. Helffrich for assistance in fabric treatment, and J. M. Simoneaux for chromatography. Mention of companies or commercial products does not imply recommendation or endorsement by the US. Department of Agriculture over others not mentioned.
Literature Cited Amerlcan Assoclatlon of Textlle Chemists and Colorists, AATCC Technical Manual, 1977. Voi. 53. Beachem. M. T. U.S. Patent 3304312, 1967. Dlnwoodle, A. H.; Fort, G.; Thompson, J.M.C. J. Chem. SOC. C 1987. 2565-2568.
Frick, J. G.,Jr.; Harper, R. J., Jr. “Adducts of Glyoxal and Amides as Flnishing Agents for Cotton”;Amerlcan Chemlcal SocletylChemical Society of Japan Chemlcal Congress, Honolulu, HI, April 3, 1979 (Abstract Cell 072 In Abstract of Papers, Part 1). Gonzales, E. J.; Benerlto, R. R.; Berni, R. J . Text. Res. J. 1988, 36, 565-571.
Vail, S. L.; Barker, R. H.; Mennitt, P. G. J . Org. Chem. 1985, 30, 2179-2182.
Vail, S. L.: Mruphy, P. J., Jr.; Frlck, J. G., Jr.; ReM, J. D. Am. Dyest. ffept. 7967, 50 (15), 27-30. Weakly, M. L.; Moffett, S. M.; Crab, L. E. U.S. Patent 3119865. 1964. (Chem. Abstr. 1984, 60, 11941.) Yamamoto, K. “Non-formaklehyde Resin Finlhing of Cotton”; Amerlcan Chemical SocletylChem!cal Society of Japan Chemlcal Congress, Mnob Iu, HI, Apr 3, 1979. (Abstract CELL 071 in Abstract of Papers, Part 1).
Received for review June 16, 1981 Accepted August 21, 1981 Paper derived from presentation at the 181st National Meeting of the American Chemical Society, Division of Cellulose, Paper and Textile Chemistry Symposium on Functional Finishes for Cotton Cellulose, Atlanta, GA, Apr 1, 1981.
Urethane Prepolymers as Durable Press Finishes Charles Tomaslno’ and Thomas W. Wllson Department of Textile Chemistry, North Carolina State University, Ralebh, North Carolina 27650
Wllton R. Goynee Southern Regional Research Center, New Orleans, Louisiana 70 179
Partially blocked, fully extended polyurethane prepolymers and completely blocked diisocyanates are evaluated
as durable-press (DP) finishes on five fabrics made from polyester and cotton. Data are presented comparing various compositions applied as emulsions and as solutions from N-methyl-2-pyrrolidlnone. Elastomer-forming prepolymers were found to improve the DP wash appearance of polyester/cotton blended fabrics; however, on all-cotton fabrics, only dry wrinkle recovery was increased without any improvement in DP wash appearance. Data are presented to show that blocked diisocyanates will unblock and cross-link cotton when applied by a paddrycure procedure provided the reagent penetrates into the fiber cross section. Size and physical state of the reagent appear to be important factors influencing penetration. Microscopic data are presented to document the conclusions.
The future status of aminoplast resins for use by the textile industry is clouded by impending regulations restricting human exposure to formaldehyde vapors. Depending on where the exposure limits are set, there is the distinct possibility that the use of these products as durable-press finishes will be severely restricted. If so, the quality of durable-press fabrics will suffer. The search for viable substitutes, therefore, becomes a timely and commercially important subject. The application of polymers to washable fabrics has been an active field of textile f i i research. There are many reasons why polymers are applied: to modify the surface of the fiber; to increase the bulk of the fabric; to impart stiffness or fullness of hand; to improve abrasion resistance, tensile properties, stability to W radiation, and to impart water repellency. For washable fabrics containing cellulose, 0196-4321/82/1221-0004$01.25/0
aminoplast resins are very effective in producing durable-press qualities; i.e., resistance to wrinkling, minimal residual shrinkage during laundering, and self-smoothing, no-iron features after drying. Nonformaldehyde-containing polymers are sometimes added to aminoplast formulations for improved abrasion resistance, wrinkle recovery, and other properties, Vail et al. (1968). In most cases the polymers that are used are chosen for their ability to improve the abrasion resistance and/or hand of a cross-linked fabric rather than for their ability to improve wrinkle resistance. Various authors have affirmed that elastomeric polymers (polymers having high elastic recovery, low glass-transition temperature and low permanent set) substantially improve wrinkle recovery. Olson et al. (1962),investigated the effects of a wide range of polymers on cotton fabrics and 0 1982 American Chemlcal Society
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 1, 1982 5
compared the results of 12 different polymer types. Welsh et al. (1967) attributed the improved wrinkle recovery of a polysiloxane-treated fabric to the elasticity of the polysiloxane. Rawls et al. (1970) concluded that elasticity must play an important role in the ability of a polymer to improve wrinkle recovery since nonelastic polymers have never been reported to improve wrinkle recovery except when they cross-link cellulose. Chapman (1976) theoreti d y analyzed the wrinkle recovery of blended fabrics and concluded that wrinkle recovery is biased toward the stiffer fiber and that friction between fibers decreases recovery. He further states that elastomers replace the frictional contacts between fibers with elastic connections and that the strains in the elastomer are about two orders of magnitude greater than those in the fiber. Polyurethanes can be made with a wide range of properties depending on the selection of polyols and crosslinking triols. Polyurethane dispersions are commercially available, and Blanchard et al. (1967) reported their influence on the durable-press performance of all-cotton fabrics. Blumenstein (1968) discussed "B" stage urethane prepolymers having a reasonable shelf life where the elastomeric properties are developed by curing at elevated temperatures. A portion of the isocyanate groups is blocked with a thermally unstable reagent. When heated, the isocyanate is regenerated and reacts with any available hydroxyl group. Blumenstein suggests that reaction between the polymer and fiber surface can occur since the water is removed prior to regenerating the isocyanate. Verburg and Snowden (1967) have reported that cotton is cross-linked when it reacts with HMDI in DMF. Ellzey and Mack (1962) treated cellulose with aromatic diisocyanah and obtained mixed results. Aromatic isocyanates react rapidly with water, and the bound water in cellulose may have influenced their results. Traditional washable fabrics have been constructed from cotton or polyester/cotton yarns, whereas new fabric constructions utilizing 100% textured polyester and yarns of higher polyester content are finding their way into washable fabric markets. Many of the polymer studies have been done on 100% cotton fabrics or on specific market fabrics. In some cases conclusions are based on a single fabric property-usually wrinkle recovery. For a fabric to perform successfully as a durable-press fabric it must possess good wrinkle recovery, low residual shrinkage, and good self-smoothing properties while drying. Objective The ultimate objective of this ongoing research project is to develop formaldehyde-free durable-press finishes. The investigations described herein are part of a continuing project directed toward determining the durable-press performance of model fabrics treated with elastomeric finishes where all the criteria important to durable-press are used as the basis for conclusions. Materials and Methods The urethane elastomers used in this study were laboratory preparations based on technology developed by the research department of a leading textile company. The diisocyanates used were HMDI (4,4'-dicyclohexylmethane diisocyanate) and IPDI (isophorone diisocyanate) (Figure 1). The polyols listed in Figure 2 were used as received from the chemical supplier. Multrathane R-26 (Mobay) is a saturated polyester resin glycol with a number average molecular weight of 1870. Teracol2000 and 650 (du Pont) are poly(tetramethy1ene ether) diols with number average molecular weighta of 2000 and 650, respectively. The triol, PCP-0301 (Union Carbide) is the propylene oxide adduct
O = C = N e C H , a N = C = O 4 , 4 ' - Dicyclohexylmethane
Diisocyanate
.
(HMDI)
0 II
C
i CH&CH,
c H3
CH,-N=C=O
Itophorone Dlltocyanate (IPDI)
Figure 1. Diisocyanates.
W
S
0
f? 8 H 2 C H 2 0 H
II
H 0 [C H 2 C H 2 0 C (C H 2 14 C 03 Polyester D i o l H [ O C H 2 C H 2 C H ,CH2]
,OH
P o l y e t h e r Diol
L-T
y 3
+
C H ~O C H ~ ~ H S ~ O H
I I
y43 C 2H gC- CH 2 4 O C H 2 C H j y OH F"3 C H 2 t O C H z C H +,OH Trimethylolpropane/Propylene Triol
Oxide
Figure 2. Polyols. Table I. Composition of Experimental kinishes molar ratiosa chemicals HMDI IPDI poly(ester) diol poly(ether) diol 2000 poly(ether) diol 650 triol butanone oxime
A
B
C
6
6
1
D 2
3 3
1 2 2.4
2 2.4
2
2
a A, 20% blocked poly(ester urethane); B, 20% blocked poly( ether urethane); C, 100% blocked diisocyanate; D, extended and 50% blocked diisocyanate.
of trimethylolpropane with a number average molecular weight of 301. The blocking agent was 2-butanone oxime obtained from Tenneco. M-Pyrol (N-methylpyrrolidinone) was obtained from GAF. The compositions listed in Table I were prepared as a 60% xylene solution. When the xylene evaporated from compositions A and B, a viscous, sticky gum was obtained. The gum is a partially blocked, fully extended "B" stage prepolper which cures into a tough elastic film at 150 "C. The xylene solution was either emulsified with Pluronic
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 1, 1982
0
Table 11. Heat Treatment vs. Fabric ProDerties heat treatment, min sample
a
untreated control
20
Original fabric.
15
0
0
15
10
15
10
20
Applied as an emulsion.
50/ 50 polyester/cotton %
165°C
untreated control
10% poly(ester urethane)b (composition A)
a
110°C
100%cotton
%
Ldy
DP
CRAC
SHRd
DP
CRAc
SHRd
1 5 1 5 1 5 1 5 1 5 1 5
1 1 1 1 1 1 1 1 1 1 1 1
188 195 159 157 24 0 21 5 224 23 1 225 225 223 21 5
8.1 9.7 6 7.3 4.7 6.3 2.5 3.7 3.9 5.3 3.7 4.7
1 1 2 2 3 2 3 3 3 3 3 3.5
268 256 265 286 29 2 278 253 277 27 8 281 276 27 8
2 3 1.3 2.0 1.3 1.9 1.2 1.7 1.3 1.5 1.3 1.7
Sum warp
+ fill.
Warp shrinkage.
Table 111. Add-on vs. Fabric Properties; Poly(ester urethane) (Composition A) 100% cotton sample untreated control, heat -set 5% poly( ester urethane) (composition A) 10%poly(ester urethane) (composition A) a
Ldy 1 5 1 5 1 5
DP 1 1 1.5 1.0 1.0 1.0
CRA 159 157 249 238 2 24 231
50/50 polyester/cotton % SHR
DP
CRA
%SHR
6.0 7.3 3 3.7 2.5 3.7
2 2 3 2.5 3 3
26 5 283 284 274 253 277
1.3 2.0 1.3 1.7 1.2 1.7
Dried 10 min at 110 "C;cured 1 5 min at 1 6 5 "C.
P-75 (BASF-Wyandotte) or diluted with a polar solvent to 10% solid. Fabric Description. The fabrics used were an 80 X 96,100% cotton sheeting; a 54 X 65,100% spun polyester plain weave; a 71 X 102,50/50 polyester/cotton sheeting; .a 51 X 84,100% textured filament polyester f i n g , 50/50 spun polyester/cotton warp 2 X 2 twill, and a 69 X 83, 100% spun polyester filling, 100% spun cotton warp plain weave. This selection includes fabrica containing 100%of either fiber and several combinations of the two. All fabrics were prepared for finishing by appropriate methods. Fabric Applications. All finishes were applied at 100% wet-pick-up by padding. The premarked fabrics were placed on pin frames to the exact untreated dimensions, dried at 110 "C, and cured a t 165 "Cfor the specified times. Microscopical Procedures. Location of polymers within fibers was studied by transmission electron microscopy as described by Rollins et al. (1972). Microsolubility testa, using cupriethylenediamine hydroxide (cuene) on ultrathin fiber cross sections indicate penetration into the fiber and interaction of the polymer with cellulose. Unmodified cellulose is removed by the dispersing action of the cuene, leaving only noncellulosic materials in the primary wall and lumen areas, as well as any cellulose that has been protected by the polymer. Expansion swelling of fibers in a water-methanol solution prior to embedding in methacrylate produces separation of fibrils into layer patterns that are recognized when cross sections of the swelled fibers are studied. Unmodified fibers exhibit extensive swelling and fibril separation. Chemical modification reduce the degree of swelling, and layering patterns that correlate with the amount of chemical add-on in modification procedures can be seen. Surface examination of fabrics to determine amount of polymer deposited on and between fibers was carried out by scanning electron microscopy.
Results and Discussion Effect of Curing. Application of the poly(ester urethane) (composition A, Table I) emulsion on both the 100% cotton and the 50/50 polyester/cotton fabrics resulted in a tacky hand after the fabrics were dried at 110 "C. The tack disappeared and the fabric became somewhat stiffer when the fabrics were cured at 165 "C. The stiffness at the 5 % add-on level was less apparent than at 10% add-on. The uncured gum increased crease recovery, reduced shrinkage of the cotton fabric, and improved the DP rating (wash appearance) of the polyeater/cotton fabric; however, the noted improvements were not permanent to repeated laundering. This can be seen in Table I1 by comparing the data for the untreated fabrics vs. those for the fabrics that were treated and dried. The data show that while curing does not further improve the properties, it is essential for making the improvements permanent to repeated laundering. Cotton's improvement in wrinkle recovery did not translate into an improvement in DP wash appearance. Apparently, cotton's response to hot, wet conditions was not significantly altered by the elastomeric finish. On the other hand, the blended fabric's improvement in DP rating was significant, yet there was very little change in the fabric's original crease recovery. The effect of add-on can be seen in Table 111. The data show that 5% is just as effective as 10% add-on for either fabric. Since regenerated isocyanate groups are capable of reacting with cellulose hydroxyls as well as the extender polyols (see Figure 31, composition C in Table I was prepared as an aqueous emulsion and applied to fabrics. A completely blocked, larger diisocyanate (composition D) was also prepared and applied from solvent. For both preparations, the 2-butanone oxime-to-isocyanate mole ratio was 1.1 to 1 to ensure against residual unblocked isocyanates. Also the extender polyols were completely omitted.
I d . Eng. Chem. Prod. Res. Dev.. VoI. 21. No. 1. 1982 7
Table IV. Comparison of Various HMDI Compositions 100% cotton
50150
polyesterlcotton
Ldy
DP
CRA
%SHR
DP
CRA
% SHR
10% poly(ester urethane) (composition A) emulsion
1 5
1 1
225 225
3.9 5.3
3 3
27 8 281
1.3 1.5
1 0 % poly(ether
1 5
1 1
222 212
3.7 5.0
4 4
308 296
0.7
1
1 1
151 175
4.0 5.3
3
5
259 248
2.0 2.7
sample
urethane) (composition B)
1.0
emulsion (10%
blocked) HMDI
(composition C)
3
Table V. Solution vs. Emulsion Application 100% cotton
MY
DP
1 0 % blocked HMDI
1
P
(composition C) emulsion 1 0 % blocked HMDI (composition C) solution" 10% poly(ether urethane) (composition B) emulsion 10% poly(ether urethane) (composition B) solutiona
5
1
sample
10%extended and blocked
50/50
polyesterlcotton
3' % SHR
DP
CRA
%SHR
1
151 175
4.0 5.3
259 24 8
2.0 2.7
5
2e 2
179 186
2.7 3.2
3 3 3 3
291 298
0.9 1.7
1 5
1 1
3.7
1
5
1
6.3
4 4 4 46
308 296 308 298
0.1
1
222 212 199 186
1
1
139 143
3.7 5.0
3 3
24 9 252
IPDI diisocyanate 5 1 (composition D) solution' "Solvent N-methylpyrrolidione. Breaking strength 24.5 Ib.
CRA
e
5.0 4.7
Breakingstrength 18.7 Ib.
1.0 0.7
1.3 0.8 1.5
DP = 4 after
15
MY.
0
Cell OH LV
3
C~IIO~NHR
* RNHCON=C
K(OH),
HOR'OCNHR
!OH CH,CC,H,
Figure 3. Resetions of blocked isocyanates.
In Table IV,data are presented to show that the blocked HMDI (composition C in Table I) had little effect on cotton when applied as an emulsion. The blocked HMDI (C) improved the DP rating for the polyester/mtton blend, yet the crease recovery was lower than that of the untreated fabric. Both fabrics were stiff and boardy prior to washing. These results indicated that the HMDI ( C ) did not penetrate the cotton fiber: instead, it formed an intractable polymer (probably a polyurea) on the surface of the fabric and, at best, only reacted with surface hydroxyls. Microscopic examinations (Figure 4) confirmed this conclusion and will be discussed in a later section of this report. Table IV also includes data obtained from the application of a poly(ether urethane) (composition B) applied as an emulsion. The prepolymer was prepared by substituting poly(tetramethy1ene ether) diol for the polyester diol and was included in this study for the purpose of determining the influence of the extender polyols. Comparing poly(ether urethane) (B) with poly(ester urethane) (A), the data show that (B) is superior to (A) on polyester/cotton. A DP rating of 4 VB. 3 and higher wrinkle recovery were obtained. Both compositions were equally poor on the all-cotton fabric. The poly(ether urethane) (B) resulted in a much softer, silkier hand than the poly(ester urethane) (A). Solution VB. Emulsion. A series of experiments was amducted to determine the influence of the surfactant and
."
,!,,, ,,.! ,,-,I, ,,-. ._.. n , h ...," ;,;,,,I,",
";,,.;,. *,I,,.,./"
/,"#,..
I*".
,,
;,:,,,I,,.!
Figure 4. Cuene c r m sections. of water itself on the final properties; therefore, nonaqueous solutions were prepared from the various compositions. Even though xylene was used to prepare the prepolymers, the reaction mixture became hazy when cooled to room temperature. A clear solution was obtained only when the concentrate was diluted with more polar solvents. N-Methylpyrrolidinone was chasen as the solvent because it is a known swelling agent for cellulose fibers. Data are presented in Table V comparing emulsion-applied and solution-applied blocked HMDI (composition C). On cotton, the solution data showed an increase in DP ratings and reduced shrinkage plus a reduction in breaking strength when compared to the emulsion data. On polyester/cotton, the solution data showed an increase in wrinkle recovery. The solution-applied large diisocyanate (composition D) did not even improve the wrinkle recovery of cotton. It did however give rise to an improvement of DP ratings on polyester cotton. These results indicated that the blocked HMDI ( C ) cross-linked cotton only when it was applied as a solution from a cellulose swelling solvent and that the larger diisocyanate (D) did not penetrate, even from the swelling solvent; only surface polymer was formed. Table V also compares the results obtained when the
8
Ind. Eng. Chem. Prod. Res. Dev., Vol. 21, No. 1, 1982
poly(ether urethane) (B) was applied from solvent and as an emulsion. The data are s i m i i regardless of how it was applied. The solvent data again show excellent DP ratings and improved wrinkle recovery on polyester/cotton. The improvement was durable through 15 launderings as the DP wash rating was unchanged. On all-cotton,the solution data duplicated the emulsion data for DP ratings. The wrinkle recovery, while improved over the untreated fabric, was lower than that obtained by the emulsion treatment. A possible explanation for this difference is the observation (shown in a later section) that more fiber-to-fiber bonding was obtained by the emulsion treatments over the solution treatment. The solution appeared to promote more uniform fiber coating and less fiber bridging. These comparisons taken as a whole indicate that neither the surfactant nor the water influence the final fabric properties imparted by the elastomer. Aminoplast vs. Urethane Elastomers. The data in the foregoing section show that urethane elastomers, in particular the poly(ether urethane) (B)elastomer, give excellent DP wash ratings on a polyester/cotton intimate blend fabric and extremely poor results on a 100% cotton fabric. The data further show that elastomeric polyurethanes applied as an emulsion are just as effectve as when applied from solutions. In Table VI, data are presented comparing the two elastomeric urethanes on five fabrics. Data for a conventional cross-linking aminoplast, dimethylol-dihydroxyethyleneurea,are included to complete the comparison. On all fabrics containing cotton, the conventional aminoplast's ability to cross-link the fiber was manifested by the fabric's response to hot, wet conditions. Residual shrinkage was markedly reduced, the wrinkle recoveries for those yarns containing cotton was vastly improved and durable-press (wash appearance) ratings were excellent. It is interesting to note that on 50/50 polyester/cotton, the wrinkle recovery of the unwashed DMDHEU treated fabric was lower than that of the untreated fabric. The wrinkle recovery improved as the fabric was laundered, eventually approaching the original untreated values. The phenomenon was very noticeable on the 100%polyester fabric and was observed on all polyester-containing fabrics. The unwashed fabrics treated with DMDHEU were stiffer than the original untreated sample; however, the stiffness was reduced when the fabrics were laundered. The elastomeric urethanes, in particular the poly(ether urethane) (B),did not follow this trend. The wrinkle recovery of the unwashed samples were equal-to or better-thanthe original values and were maintained through repeated laundering. The poly(ether urethane) (B), however, stood out as an exceptional finish for the 50/50 blended fabric. The DP rating was higher than that of the conventional DMDHEU, and the wrinkle recovery was as good. The data are not as dramatic for those fabrics containing a high percentage of polyester because the untreated fabrics perform so well. The fabric woven from 100% cotton warp, 100% polyester filling is an interesting case. While the overall fabric blend is 50% cotton and 50% polyester, the DP performance responded to DMDHEU and not to the elastomer finish. In this respect, the fabric acta like an all-cotton fabric. One can conclude that some polyester fibers must be intimately blended with cotton in order for the elastomer to be effective. Microscopical Examinations Blocked HMDI Treatment. The interior of ultrathin cotton-fiber cross sections treated with an emulsion of blocked HMDI (C)was completely dissolved by cuene, leaving a ring of undissolved material; however, the cross
I
rim
c:
00
Z?
mom
(Dm0 mmm
Y
;
mm
mm
mm
mm
**
n!
mrlw mmm mmm
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v!?
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I d . Eng. C b m . Rod. Res. Dev.. VoI. 21, No. 1. 1982 0
