2018 Volume 75 Issue 6 Pages 497-506
In situ Raman spectroscopy was performed to evaluate microscopic deformation behavior such as the load sharing of molecular chains and the molecular orientation for high-density polyethylene and isotactic polypropylene under uniaxial stretching. Below the α1 relaxation temperature, the compression stress is applied to the crystalline chains in the yielding region due to the macroscopic shrinkage with necking. Moreover, the crystalline chains orient in the 30–50° direction, suggesting that the molecular orientation of the crystalline chains is hindered by the excluded volume effect of the lamellar cluster units. On the other hand, above the α1 relaxation temperature, the crystalline chains immediately orient in the stretching direction after the yielding point and the stretching stress is applied on the crystalline chains. The enhancement of the molecular orientation of the crystalline chains is caused by the thermal activation of the molecular motion within the crystalline phase owing to the onset of α1 relaxation.
