Stress Relaxation of Oriented Nylon 6 Fibers

The stress relaxation of oriented and dried nylon 6 fibers was measured at temperatures ranging from room temperature to 423°K by a simple tensile method. After the reduction for temperature and crystallinity by Takemura's procedure, the relaxation modulus curves were shifted along time axis, and the master curves were successfully obtained. The Arrhenius plots of shift factor were represented by two straight lines having a break point, the temperature of which was in agreement approximately with those of breakdown of hydrogen bonds in the amorphous region. The relation between the breakdown of hydrogen bonds and the values of apparent activation energies for relaxation was discussed. It has been 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 C_1 and C_2 of the W.L.F. equation, the free volume fraction at Tg, (f_g), and the expansion coefficient of free volume at Tg, (α_f), were estimated to be 0.013 and 4.2×10^<-5>, respectively. Finally, by 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 hight of distribution of the box-type becomes higher and its position shifts to longer time side, whereas those of the wedge-type remains almost unchanged.