Molecular and Morphological Studies to Understand the Strain Hardening Behavior of UHMWPE/HDPE blends

The most common route to improve the properties of bimodal high-density polyethylene (bi-HDPE) pipes is to add the controlled-amounts of high molecular weight (HMW) chains, without compromising the melt flowability. To elucidate the influence of HMW chains on slow crack growth (SCG), blends of bi-HDPE and ultra-high molecular weight polyethylene (UHMWPE) at different contents (1, 5 and 10 wt.%.) were examined through strain hardening (SH) test. Meanwhile, the correlation between SH modulus ( Gp ), entanglement density and crystallization behavior have been investigated thorough rheological and thermal analysis. Addition of UHMWPE up to 10 wt.%, augmented the Gp value of bi-HDPE from 44 to 56 MPa. This is attributed to the higher amounts of inter-cluster links of UHMWPE and the ability of co-crystallization between components. The detailed examination of the longitudinal morphology of strain-hardened samples revealed an alternating banded structure of etched defects. When UHMWPE content is beyond 1 wt.%, the defect size and bands thickness become considerably smaller, indicating a more oriented structure.