Temperature-Induced Structural Changes in Strain-Hardening Behaviour of Semi-Crystalline Polymer
Strain-hardening is essential in processing semi-crystalline polymers such as high-density polyethylene (HDPE).
Although the behavior has been ascribed to the network density, its temperature dependence seems somewhat
contradictory. This work aims to reveal the effect of temperature on HDPE's strain-hardening behavior from the
structural point of view. HDPE samples with different Mw/Mn with almost identical Mw are used to investigate the
influence of the amorphous network. Dynamic response of polymer chains is detected by in situ Raman spectroscopy combined with step-cycle tests to monitor changes in the amorphous region and crystalline phase
during strain-hardening. While the step-cycle response of the stress is more elastic for higher Mw due to higher
network density, the inter-crystalline motion above the a1 relaxation region decreases pressure on the polymer
chains. Thus, it is suggested that the inter-and intracrystalline relaxation is responsible for discrepancy from the
prediction by Haward theory based on the amorphous network.
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