Temperature dependence of the Young's modulus of oriented polyethylene

The neg. dependence on temp. of the Young's modulus of soln.-spun/drawn ultrahigh-mol.-wt. polyethylene (I) fiber was examd. at 25-125°. The data were analyzed employing a previously published model, wherein the oriented fiber was regarded to be of 2 components only, i.e., perfectly oriented and unoriented segments, denoted helical and coil, resp. The modulus of the helical elements, which was equiv. to the theor. axial modulus, was const. in the temp. range of interest. Consequently, the decrease in Young's modulus was discussed in terms of a decrease of the modulus of the coil segments (Ec) with increasing temp. The obsd. variation of Ec correlated surprisingly well with the calcd. change in the cryst. shear modulus resulting from the increase with temp. of the a-axis of the orthorhombic unit cell of I.