Microhardness Studies of Chain-Extended PE: I. Correlations to Microstructure

摘要

The hardness-microstructure correlation of various polyethylene(PF) samples crystallized at high pressure from the memlt(chain-extended), with different molecular weights, has been investigated and compared to melt crystallized samples at atmospheric pressure(chain-folded). The hardness, H, of melt crystallized PE is confirmed to increase linearly with the logarithm of the annealing time, t_a, at a constant annealing temperature. The H increase with t_a is discussed in terms of the crystallinity and crystalline lamellar thickness variation. Unusually high hardness values are obtained for samples crystallized or annealed at high pressure as a consequence of the resulting high degree crystallinity and large crystalline lamellar thickness values. However, it is shown that the high surface free energy value of the chain-extended crystals considerably lowers the hardness values from that of an ideal infinitely thick PE crystal. Analysis of the crystal hardness and the melting temperature data of different polymeric materials emphasizes the close existing relationship between both quantities.