ULTIMATE TENSILE PROPERTIES OF ACRYLONITRILE-METHYLACRYLATE COPOLYMERIC FIBERS

Abstract

The ultimate tensile properties for an after-heat stretched and a heat-relaxed fiber of acrylonitrile-methylacrylate copolymer have been measured under a condition of constant load and the results obtained are summarized as follows:(1) The tensile strength and the ultimate elongation vary with the after-treatments, but the shape of the composite curve of the logarithmic tensile strength plotted against the logarithmic time to break is unchanged and independent of the after-treatments. Therefore it may be assumed that the after-treatments have no effects on a critical condition for rupture. The temperature dependence of the shift factor along the axis of the time to break can be also assumed to be independent of the after-treatments.(2) From the previous result that the location on the logarithmic axis of the time to break for the composite curve of the tensile strength is linearly related to the reciprocal of a characteristic temperature Tc, it is deduced that Tc for the heat-relaxed fiber is nearly the same as the value for the untreated and that of Tc for the heat-stretched fiber is lower than that of the untreated.(3) Assuming that the shift factor along the logarithmic axis of the ultimate elongation represents a relative concentration of active chain, the free energy difference ΔF_??_ between active and inactive chains is calculated. From the maximum values of ΔF_??_ it is concluded that the active chains in the heat-stretched fiber are in restricted state and those of the heat-relaxed fiber are in relaxed and stable state.(4) The effective stretch ratios for the untreated and the heat-relaxed fibers calculated from the maximum value of the ultimate elongation (εb)max coinside with those values calculated from the shrinkage in a I2-KI aqueous solution of high I2 concentration, and for the after-heat stretched fiber the value calculated from (εb)max coinsides with that obtained in a low I2 concentration ofthe solution, The tensile strength of the after-stretched fiber depends on a lower order region of the fiber structure, and this consideration associates with the decrease in Tc observed for the after-heat stretched fiber.