Abstract:
This invention is a nylon fiber useful for improved comfort for wearers of apparel fabric made therefrom comprising (a) from about 5 to 15 percent 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° C. and (b) correspondingly from about 85 to 95% by weight nylon.

Description:
BACKGROUND OF THE INVENTION 
     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&#39;-methylene-bis-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. 
     SUMMARY OF THE INVENTION 
     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° 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 1000 centipoise (0.02 to 1.0 Pa.s) at 25° 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) added 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% PDMAA 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 1000 centipoise. When the PDMAA molecular weight was high, only nylons containing low concentrations could be spun into yarn. At 65% relative humidity and 68° F. (20° C.) and at 95% relative humidity and 90° F. (32° 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. 
     DESCRIPTION OF THE INVENTION 
     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° 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° 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. 
    
    
     EXAMPLE 1 
     
         ______________________________________Caprolactam     1088    gramsAminocaproic Acid           52      gramsMnCl.sub.2.4 H.sub.2 O           0.0674  gramH.sub.3 PO.sub.2 m 50% Solution           0.1675  gramPDMAA, Sample No. 11           455     grams    (113.75 g solids)(25% Solids)______________________________________ 
    
     The starting materials were mixed together at 90° 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° C. over a one-hour period at atmospheric pressure. The melt was held at 255° 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. 
     
         ______________________________________Dimethyl Amine Found, Grams                  3.85Dimethyl Amine Added as PDMAA:Molecular Wt. (CH.sub.3).sub.2 NH                  45.1 ##STR2##              99.1 ##STR3## ##STR4##______________________________________ 
    
     The loss of 3.85 grams of dimethyl amine in 1133 grams of washed and dried polymer is 75 equivalents of amine per 10 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°-260° 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) and its uses are found in a paper by that name, Chemical Abstracts, Vol. 83, December, 1975. This paper includes a thorough discussion on polymerization. However, the following example provides the method to polymerize dimethylacrylamide. 
     EXAMPLE 2 
     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 2  S 2  O 8 ) in 50 ml of the boiled water. Dissolve 1.5 grams of sodium bisulfite (Na 2  HSO 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° 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° C. for one-half hour. Allow the solution to cool, and store the solution in a dark brown bottle. 
     
                       TABLE I______________________________________PDMAASample % Acrylic % Conc., Viscosity,                             PascalNumber Acid      Aqueous  Centipoises                             Seconds (Pa · s)______________________________________1      0         100      --      --2      0         25.4     20 000  20.0003      0         25.4     354     0.3544      0         25.6     4 000   4.0005      0         25.0     10 000  10.0006      2.0       24.5     175     0.1757      5.0       24.6     200     0.2008      0         25.0     25      0.0259      2.0       25.0     21      0.02110     0         25.5     74      0.07411     0         25.0     156     0.15612     2.5       25.1     79      0.07913     2.5       25.5     153     0.15314     5.0       25.7     76      0.07615     5.0       25.2     152     0.15216     0         25.6     76      0.07617     0         25.0     302     0.302______________________________________ 
    
     
                                           TABLE II__________________________________________________________________________POLYMERIZATION CONDITIONS AND PROPERTIESOF PDMMA MODIFIED NYLONS     Conc.NylonPDMAA     in  HoursPolymerSample     Nylon,         at   ExtrusionNumberNumber     %   255° C.              Ribbon                   *FAV **COOH                             **NH.sub.2__________________________________________________________________________1    1    10  1    None 87   76   622    1    4   2    Fair 96   62   603    1    1   2.6  Good 51   62   584    5    5   1.8  Fair 93   68   625    5    1   2.5  Good 71   53   506    4    10  1.5  Good 102  56   477    4    5   2.2  Good 90   59   588    4    1   2.5  Good 81   52   449    3    7.3 2.5  Good 54   56   4210   3    5   3.3  Good 89   53   4811   3    1   3.0  Good 65   56   5112   8    6   7.5  Good 53   16   1313   8    5   7    Good 64   24   1514   10   10  5.2  Good 57   24   1215   11   10  5.7  Good 74   23   1516   16   10  3.5  Good 46   40   2317   17   10  2.2  Good 96   40   2818   10   10  6    Good 54   20   1119   10   10  5    Good 55   63   1820   10   10  4    Good 53   35   2221   10   5   3    Good 72   41   33__________________________________________________________________________ *FAV is relative formic acid viscosity obtained by measuring the viscosit at 25° C. of a 11% solution of the polymer in formic acid (ASTM 78962T). **COOH indicates carboxyl groups per 10.sup.6 g polymer and NH.sub.2 indicates amine groups per 10.sup.6 g polymer measured as in U.S. Pat. No 4 356 280, Col. 4, lines 55 through 68, and column 5, lines 1 through 46, hereby incorporated by reference. 
    
     
                                           TABLE III__________________________________________________________________________POLYMERIZATION CONDITIONS AND PROPERTIESOF PDMAA/ACRYLIC ACID COPOLYMERS     Conc.NylonPDMAA     in  HoursPolymerSample     Nylon,         at   ExtrusionNumberNumber     %   255° C.              Ribbon                   *FAV **COOH                             **NH.sub.2__________________________________________________________________________C-1  6    5   6    Good 109  52   10C-2  6    1   2.5  Good 86   53   43C-3  7    5   5.2  Fair 73   78   14C-4  7    1   2.2  Good 83   61   44C-5  9    7.5 6.5  None 20   33   18C-6  9    5   6    Good***                   48   43   17C-7  12   10  9    None 24   52   21C-8  12   5   6    Fair***                   36   13   11C-9  13   10  9    None 30   56   14 C-1013   10  6    None 22   65   20__________________________________________________________________________ *FAV is relative formic acid viscosity obtained by measuring the viscosit at 25° C. of a 11% solution of polymer in formic acid (ASTM 78962T). **COOH indicates carboxyl groups per 10.sup.6 g polymer and NH.sub.2 indicates amine groups per 10.sup.6 g polymer measured as in U.S. Pat. No 4 356 280, supra.  ***These were the only batches containing a copolymer which could be spu into yarn. 
    
     
                       TABLE IV______________________________________MELT VISCOSITY OF NYLON POLYMERS CONTAININGPDMAA (500° F. (260° C.), 33:1 Orifice at 2 000Seconds.sup.-1)Nylon  PDMAA    Conc.Polymer  Sample   in Nylon,        Viscosity,Number Number   %          FAV   Pascal · seconds______________________________________Control*  --       --         53    120.0C-3     7       5          73    35.014     10       10         57    49.015     11       10         74    50.59       3       7.3        54    80.0______________________________________ The viscosity was measured on a Monsanto Automatic Capillary Rheometer Model 3501. *The control polymer was an acetic acid terminated polymer containing 0.06% TiO.sub.2 of about 50 FAV, 50 carboxyls and 18 amines stabilized with 8 ppm of manganese and 10 ppm of phosphorus. 
    
     
                       TABLE V______________________________________DSC ANALYSIS OF NYLON CONTAINING PDMAAPoly-mer   Conc. ofNum-  PDMAAber   Sample Number             Tm, °C.                      Tg, °C.                            Tch, °C.                                   Tcc, °C.______________________________________NO*   0           223      36    65     176Con-  0**         225      40    66     174trol14    10% of No. 10             222      41    69     17215    10% of No. 11             222      41    69     17321     5% of No. 10             224      39    69     175______________________________________ *NO is polymer without additive or stabilizers of about 55 FAV, 55 carboxyls and 55 amines. **The control polymer is an acetic acid terminated polymer containing 0.06% TiO.sub.2 of about 50 FAV, 50 carboxyls and 18 amines stabilized with 8 ppm of manganese and 10 ppm of phosphorus. The DSC (Differential Scanning Calorimeter) analysis was performed on a duPont Model 1090 Thermal Analyzer. The solid polymer was heated in nitrogen at the rate of 10° C. per minute. The temperature at the peak of the endotherm was taken as the melting point, Tm. The temperature was raised to 255° C. and held for five minutes. It was then quenched in liquid nitrogen to produce an amorphous solid. The polymer wa then heated at 10° C. per minute. The temperature at which the hea flow increased, before becoming steady again, was taken as the glass transition temperature, Tg. The heating was continued at 10° C. minute. The temperature at the peak of the exotherm was taken as the temperature of crystallization on heating, Tch. The heating was continued to 255° C. and then cooled at 10° C. per minute. The temperature at the peak of the exotherm was taken as the temperature of crystallization on cooling, Tcc. 
    
     
                                           TABLE VI__________________________________________________________________________SPINNING CONDITIONS AND YARN PHYSICAL PROPERTIESNylonConc. &amp;     Spin         Pot                UTS                               %PolymerPDMAA     Temp.,         Pressure,  %   **UTS                            mN/                               Shrink-NumberSample     °C.         psig            kPa FAV*                    UE**                        gpd dtex                               age__________________________________________________________________________Control   275 2200            15 200                45  61  5.4 48 1710    6% of     275 2000            13 800                53  59  4.4 39 21No. 8Control   268 750            5200                40  55  4.4 39 18C6    5% of     263 600            4100                48  48  3.6 32 20No. 913    5% of     273 1050            7200                64  57  4.1 36 22No. 8Control   276 500            3400                45  65  4.5 40 1714   10% of     275 400            2800                57  38  2.8 25 25No. 1015   10% of     276 500            3400                74  53  3.1 27 25No. 1121    5% of     276 1150            7900                72  60  4.1 36 21No. 10Control   270 700            4800                45  54  4.6 41 1618   10% of     274 500            3400                54  56  3.1 27 21No. 1019   10% of     271 500            3400                55  49  2.9 26 21No. 1020   10% of     270 500            3400                53  52  3.1 27 20No. 10Control   264 1300            9000                45  54  4.7 41 --C8    5% of     265 1800            12 400                36  20  2.8 25 --No. 1216   10% of     265 1400            9700                46  37  3.0 26 --No. 16__________________________________________________________________________ All cross sections were round; draw ratios 3.0; and deniers 110/30. *FAV is relative formic acid viscosity obtained by measuring the viscosit at 25° C. of a 11% solution of polymer in formic acid (ASTM 78962T). **UE is ultimate elongation, %. UTS is ultimate tensile strength in grams per denier and millinewtons/decitex. 
    
     
                       TABLE VII______________________________________YARN MOISTURE REGAIN             Moisture Regain, %     Concentration 65% RH   95% RHPolymer   and PDMAA     at 68° F.                            at 90° F.Number    Sample Number (18° C.)                            (32° C.)______________________________________Control*                4-5      7-812         6% of No. 8  5-6       9-10Control*                4-5      7-814        10% of No. 10 6-7      13-1415        10% of No. 11 6-7      13-1421         5% of No. 10 5-6      10-11Control*                4-5      7-818        10% of No. 10 6-7      13-1419        10% of No. 10 6-7      13-1420        10% of No. 10 6-7      13-14______________________________________ All yarns were scoured once, AATCC 96 II E, to remove finish oils. The test method is described in ASTM Procedure D885, Section 10. *The control is an is acetic acid terminated polymer containing 0.06% TiO.sub.2 of about 50 FAV, 50 carboxyls and 18 amines stabilized with 8 ppm of manganese and 10 ppm of phosphorus. 
    
     
                       TABLE VIII______________________________________YARN STABILITYYARN BREAKING STRENGTH AFTER HOT/WETTREATMENT 110/30 YARN, ROUND CROSS SECTIONNylon  Conc.      Breaking Strength, GramsPolymer  &amp; PDMAA    Un-     TreatedNumber Sample No. treated (1)  5   (2)  %   (3)  %______________________________________Control*          455     337  74  337  74  301  6614     10% of # 10             285     247  86  263  92  237  8315     10% of # 11             297     251  85  259  87  226  7621      5% of # 10             395     357  90  362  92  287  73______________________________________ (1) Exposed to boiling water 30 minutes and dried in an air oven 10 minutes at 150° C. (2) Exposed to boiling water 30 minutes and dried in an air oven 20 minutes at 150° C. (3) Exposed to boiling water 30 minutes and dried in an air oven 30 minutes at 150° C. 
    
     
                                           TABLE IX__________________________________________________________________________LIGHT STABILITY, CARBON ARC                    10 Hours   20 HoursConc.        Initial            UTS,         UTS,Polymerand PDMAA        **UE            **UTS,                 m/N                    UE UTS,                           m/N **UE                                   **UTS,                                        m/NNumberSample Number        %   gpd  dtex                    %  gpd dtex                               %   gpd  dtex__________________________________________________________________________Control*     26  4.8  42 24 5.1 45  45  25   4414   10% of No. 10        22  3.6  32 20 3.7 33  33  21   3115   10% of No. 11        24  3.5  31 21 3.4 30  30  20   3121    5% of No. 11        24  4.5  40 24 4.8 42  42  23   40__________________________________________________________________________ The test method is that described in AATCC Test Model 111C1978 but withou the humidity control. *The control is an acetic acid terminated polymer containing 0.06% TiO.sub.2 of about 50 FAV, 50 carboxyls and 18 amines stabilized with 8 ppm of manganese and 10 ppm of phosphorus. **UE is ultimate elongation, %. UTS is ultimate tensile strength in grams per denier and millinewtons per decitex. 
    
     
                       TABLE X______________________________________CROSS STAINING AND DYED WASHFASTNESS OFYARNS CONTAINING PDMAA BY AATCC TEST 61-1975IIIA (GRAY SCALE)NylonPolymer Conc. and PDMAA                  Staining       ShadeNumber  Sample Number  Nylon    Cotton                                 Change______________________________________Control 0              4-5      5     314      10% of No. 10  4        5     3-415      10% of No. 11  4        5     3-421       5% of No. 10  3-4      5     3______________________________________ 
    
     All yarns were 110/20 round cross section. They were dyed with 0.,13% Telon fast violet A-BB (Acid Violet 103), and then washed for 45 minutes at 120° F. (49° C.) using the AATCC standard detergent.