Stress relaxation of oriented nylon 6 fibers

Abstract

The stress relaxation of oriented and dried nylon 6 fibers was measured at temperatures ranging from room temperature to 423 K using a simple tensile method. After the reduction for temperature and crystallinity by Nagamatsu et al.'s procedure,2 the relaxation modulus curves were shifted along a time axis, and master curves were obtained. The Arrhenius plots of shift factor was represented by two straight lines having a break point, the temperature of which was in approximate agreement with those of the breakdown of hydrogen bonds in the amorphous region. The relationship between the breakdown of hydrogen bonds and the values of apparent activation energies for relaxation is discussed. It was found that the effects of hydrogen bonds on the relaxation behavior are similar to those of crosslinking points in crosslinked polymers. Moreover, from the constants C1 and C2 of the WLF equation, the free volume fraction at Tg(fg) and the expansion coefficient of free volume at Tg(fg) were estimated to be 0.013 and 4.2 × 10−5, respectively. Finally, through the use of the usual primary approximation method, the relaxation time spectra were obtained from the relaxation master curves. The obtained spectra showed two distributions of wedge type and box type. When the draw ratio increases, the height of distribution of the box type becomes higher and its position shifts to a longer time side, whereas those of the wedge type remain virtually unchanged.