Thermal behavior of drawn acrylic fibers

The effect of stretching on the thermal behavior of acrylic fibers was investigated with differential scanning calorimetry (DSC), thermogravimetric analysis, and Fourier transform infrared spectroscopy (FTIR). In air atmosphere, the peak temperature of the dynamic DSC thermogram was significantly lowered from 289 to 273 degreesC when the gel fibers (undrawn) were drawn to a draw ratio of 11.2. However, the initiation temperature was unchanged at 202 degreesC. The shoulder in the region of 310-380 degreesC was gradually converted to a sharp peak during the drawing process. However, the dynamic DSC in nitrogen atmosphere did not change in all cases. In air atmosphere the total heat liberated, DeltaH, for gel fiber was 851 J g(-1). However, upon drawing to 11.2, DeltaH increased to 1580 J g(-1) showing an increase in the total chemical changes. An intimate relationship of chemical changes during the heating process was observed with FTIR of heated samples at various temperatures. The initiation of a DSC exotherm in air begins with nitrile cyclization, and subsequently dehydrogenation was initiated between 220 and 260 degreesC. An increase in the X-ray orientation factor and sonic modulus gave a correlation between the stretching draw ratio and crystalline/overall molecular orientation. (C) 2003 Wiley Periodicals, Inc.