Structure development during dry-jet-wet spinning of acrylonitrile/vinyl acids and acrylonitrile/methyl acrylate copolymers

Dry-jet-wet spinning of three copolymers, poly(acrylonitrile/methyl acrylate), poly(acrylonitrile/methacrylic acid), and poly(acrylonitrile/itaconic acid), was performed with a dimethylformamide/water (60:40 v/v) coagulation bath at different temperatures (10-40degreesC). The fibers were stretched to different levels (1.1-6x) in boiling water, collapsed, and annealed over a heater plate at 130degreesC. The effects of the polymer composition, coagulation bath temperature, and draw ratio on the cross-sectional morphology, structure, and tensile properties are reported. The cross-sectional shape of the gel fibers underwent a transition from a kidney shape to an oval shape, and macrovoids began to appear at higher temperatures. However, F(AN/IA) gel fibers changed from a kidney shape to an irregular shoe type with a gel network of interconnected polymer fibrils. For F(AN/MAA) gel fibers, the diameter increased from 45 to 67 gm when the coagulation bath temperature was increased from 10 to 40degreesC, and the denier value decreased from 17.5 to 14.3 den/filament. The strength, modulus, and elongation at break decreased with an increase in the coagulation bath temperature. For F(AN/MAA) fibers coagulated at 10degreesC in a spin bath, the strength increased from 0.43 to 2.213 g/den, the modulus increased from 27 to 76 g/den, and the density increased from 1.177 to 1.196 g cm(-3) when the gel fibers were drawn to 6x. However, 6x drawn F(AN/MA) fibers had a higher strength (3.1 g/den) and elongation (14.6%) in a 40degreesC coagulation bath. F(AN/IA) fibers could be drawn only to a draw ratio of 4x instead of the 6x draw ratio for F(AN/MAA) and F(AN/MA) fibers. Therefore, the final F(AN/IA) fibers exhibited poor mechanical properties (tenacity 0.81 g/den, modulus = 22 g/den, and elongation at break 8%). The crystallinity did not change significantly (chi(c) = 61-63%) with the draw ratio, but the crystal size increased from 22.9 to 43.4 Angstrom and orientation factor from 0.41 to 0.78. The dichroic ratio, measured with Fourier transform infrared, decreased with an increase in the draw ratio, but the sonic modulus and crystalline orientation values increased with an increase in the draw ratio. Thermomechanical data show a maximum physical shrinkage of 51.7% for 6x drawn F(AN/MA) and a minimum physical shrinkage of 30.5% for 4x drawn F(AN/IA) fibers. (C) 2002 Wiley Periodicals, Inc.