Nylon Comfort Fiber Containing Poly(N,N-Dimethylacrylamide)

This invention relates to an apparel fiber of nylon containing 5 to 15 % by weight poly(N,N-dimethylacrylamide) useful for improved comfort for wearers of apparel fabric made therefrom.

Consumers have long perceived cotton as one of the most comfortable apparel fibers, and have credited this perception largely to its moisture regain. Since the invention of nylon, researchers have sought techniques which confer to nylon an equivalent sense of comfort, and have centered this effort on increasing its moisture regain. In Japanese Publication No. 73-13 337 an N,N-dimethylacrylamide-methyl acrylate copolymer was added to polyamide spinning compositions to increase the hygroscopicity of the filaments. Also, a methyl acrylate-N,N-dimethylacrylamide copolymer was used for the same purpose in Japanese Publication No. 72-42 134. It is also known in Japanese Publication No. 72-41 744 to use poly(N,N-dimethylacrylamide) to increase the melt viscosity of polyamide. In Japanese Publication No. 77-25 895, N,N-dimethylacrylamide was grafted onto a polyester or similar polymer by radiation in the presence of a catalyst and in Japanese Publication No. 71-16893-R the graft copolymer of polyamide was an acrylamide and was taught to improve hygroscopic properties. U.S. Pat. No. 4 135 877 teaches the grafting onto a polyamide fiber of N,N'-methylenebis-acrylamide in the presence of an acid to improve hygroscopic properties. A similar teaching was found in U.S. Pat. No. 4,238,193 and a general teaching along the same lines is found in G.B. No. 1 355 846. Acrylamides are grafted onto a hollow fiber in Japanese Publication No. 55057-071.

Poly(N,N-dimethylacrylamide), hereinafter PDMAA, is prepared from a commercially available monomer and polymerizes readily using free radical initiators. The polymer is also available commercially.

This invention is a nylon fiber, useful for improved comfort for wearers of apparel fabric made therefrom, comprising (a) from about 5 to 15% of poly(N,N-dimethylacrylamide) having a molecular weight which in a 25% aqueous solution gives a viscosity of from about 20 to 1 000 centipoise (0.02 to 1.0 Pa.s) at 25.degree. C. and (b) correspondingly from about 85 to 95% by weight nylon. The invention is also the method of preparing a nylon fiber useful for improved comfort for wearers of apparel fabric made therefrom comprising adding from about 5 to 15% by weight of poly(N,N-dimethylacrylamide) having a molecular weight which in a 25% aqueous solution gives a viscosity of from about 20 to 1 000 centipoise (0.02 to 1.0 Pa.s) at 25.degree. C. to from about 85% to 95% by weight of caprolactam, then polymerizing the mixture conventionally, then extruding and washing the resultant polymer conventionally, then forming the resultant polymer into fiber by conventional spinning. Preferably, during the method, a grafting reaction occurs during polymerization. It is also preferable to use at least 10% poly(N,N-dimethylacrylamide) adding to the caprolactam. It is preferable to form the resultant polymer into fiber by spinning through a spinnerette hole having a length to diameter ratio of from about 4:1 to 8:1.

Nylon polymers were actually made containing up to 10% of PDMAA. Nylon fiber containing 10% PDMMA could be spun only when the molecular weight of the PDMAA was such that a 25% aqueous solution gave a viscosity of between 20 and 1 000 centipoise. When the PDMAA molecular weight was high, only nylons containing low concentrations could be spun into yarn. At 65% relative humidity and 68.degree. F. (20.degree. C.) and at 95% relative humidity and 90.degree. F. (32.degree. C.), nylon fibers containing 10% PDMAA had a moisture regain similar to that of cotton. No antioxidants were necessary for satisfactory retention of mechanical properties in hot-wet processing of the nylon fiber and the PDMAA did not affect the light stability or dyed wash fastness in draw twist yarn.

During the research carried out to make this invention, various polymers listed in Table I were evaluated. Because of the concern that low molecular weight polymers may leach out during polymer washing and drying and fiber laundering, copolymers containing PDMAA and small quantities of acrylic acid were also prepared for evaluation. This polymeric system was expected to react with the nylon amine end group forming a stable branched copolymer. These copolymers did not, however, produce processable nylon due to excessive crosslinking reactions (see Table III). It turned out that this modification is unnecessary due to a slow amine-amide interchange reaction that occurred with the PDMAA homopolymer during caprolactam polymerization. This reaction was sufficient to form a stable branched copolymer, which was not affected by the washing process.

Technical data from polymers containing PDMAA are listed in Tables II and III. These tables show that polymers prepared with the lower molecular weight PDMAA samples tended to have fewer amines and fewer carboxyls, particularly at longer polymerization residence times.

The decrease in amines can be explained by a relatively slow amine-amide interchange reaction. The mechanism is probably as follows: ##STR1##

To confirm this mechanism, the effluent sweep gas was collected from a nylon polymerization containing 10% PDMAA. The analysis by gas chromatograph and mass spectrometer found 3.8 grams of dimethylamine, equivalent to 7.5% of the dimethyl amine present in the PDMAA polymer. Details of this experiment are given in Example I. This indicated that a grafting reaction occurred during polymerization. The decrease observed in carboxyls may result from the decarboxylation of any polyacrylic acid formed in the grafting reaction. Polyacrylic acid is known to decarboxylate at about 250.degree. C.

The melt viscosity of polymers containing PDMAA is much lower than nylon homopolymers of the same formic acid viscosity (measured conventionally). This is shown in Table IV. This is consistent with the grafting reaction shown above, since graft polymers have lower melt viscosity, in which the branching segments are tightly coiled, and higher solution viscosities in which the branching segments are extended or loosely coiled than ungrafted polymers. The presence of PDMAA did not significantly lower the melting point of the nylon, nor did it significantly slow the rate of crystallization on cooling. These data are given in Table V.

Initial evaluations showed that at least 10% PDMAA in nylon was required to achieve the 13% to 14% moisture regain attributed to cotton. At this level, attempts to spin polymers containing 10% high molecular weight PDMAA resulted in filaments breaking off at the spinnerette face. In no instances, however, were there high spin pack pressures. This was true even with nylon having formic acid viscosity (FAV) of 90. When the molecular weight of the PDMAA was decreased, and the spinnerette hole length/diameter ratio increased to between 4 and 8:1, spinning performance was good. Summaries of the spinning trials and the yarn physical properties are shown in Table VI.

The moisture regains of the yarns were tested after they were scoured to remove spin finish. The data given in Table VII, show that at room temperature and 65% relative humidity, the regain of yarn with the 10% PDMAA is similar to that of scoured cotton. No change in the moisture regain was seen when the yarns were given twenty-five scouring washes.

Nylon yarns containing PDMAA were submerged in boiling water for thirty minutes, then oven dried at 150.degree. C. The percent loss in strength was less than the control as shown in Table VIII. An antioxidant to stabilize the polymer is unnecessary. PDMAA did not affect the retention of breaking strength or of elongation after being exposed to twenty hours of carbon arc as shown in Table IX. PDMAA did not affect dyed washfastness of draw twist yarns as shown in Table X.

The starting materials were mixed together at 90.degree. C. and poured into a 3-liter glass reactor equipped with a heating mantle and an agitator. The melt was swept with nitrogen gas and stirred and heated to 255.degree. C. over a one-hour period at atmospheric pressure. The melt was held at 255.degree. C. for 31/4 hours with the nitrogen sweep.

The nitrogen gas was passed through a large flask, where much of the water vapor present in the sweep gas condensed, and then two bubblers in series which originally contained solutions of 10 cc of concentrated HCl, and 40 cc of distilled water.

After polymerization was completed the contents of condensate flask and the two bubblers were analyzed for dimethylamine by use of the gas chromatograph. A total of 3.85 grams of dimethyl amine was found; 2.8 grams in the condensate flask, 1.0 gram in the first bubbler, and 0.05 gram in the final bubbler.

The nylon polymer was extruded, washed, dried and submitted for analysis. It had a 67 FAV with 42 carboxyls and 23 amines.

The loss of 3.85 grams of dimethyl amine in 1133 grams of washed and dried polymer is 75 equivalents of amine per 10.sup.6 grams of polymer. Since the difference of ends in the nylon polymer is not 75, but only 19, there must have been some simultaneous loss of carboxyls. Since polyacrylic acid, a possible decomposition product, is known to lose carboxyl groups at 250.degree.-260.degree. C., this could explain the decrease in carboxyls.

The polymer was then extruded into water cut into pellets and washed and dried conventionally to remove water extractables such as lactam monomers, oligomers and the like.

The pellets were melted in a conventional melter and the molten polymer was pumped through a conventional spinnerette, and conventionally quenched to form fiber.

Note that a thorough discussion of N,N-(dimethylacrylamide) that its uses are found in a paper by that name, Chemical Abstracts, Vol. 83, Dec, 1975. This paper includes a thorough discussion on polymerization. However, the following example provides the method to plymerize dimethylacrylamide.

Dimethylacrylamide Polymerization--Materials Required:

N,N-dimethylacrylamide

Isopropyl Alcohol

Potassium Persulfate

Sodium Bisulfite

Boil 580 ml of deionized water while bubbling nitrogen through the water. Then allow the boiled water to cool while passing nitrogen through the water.

Dissolve 3 grams of potassium persulfate (K.sub.2 S.sub.2 O.sub.8) in 50 ml of the boiled water. Dissolve 1.5 grams of sodium bisulfite (Na.sub.2 HSO.sub.3) and another 50 ml of the boiled water.

Pour 160 grams of dimethylacrylamide into the 480 ml of boiled water which remains. Add 20 ml of isopropyl alcohol and cool in an ice bath to 0.degree. C.

Add 10 ml of the potassium persulfate solution and stir. Add 10 ml of the sodium bisulfite solution and stir. Bubble nitrogen through the solution for one-half hour and then allow the solution to warm to room temperature. Then heat the solution to 50.degree. C. for one-half hour. Allow the solution to cool, and store the solution in a dark brown bottle.