The Correlation Between Microstructural Evolution and Slow Crack Growth Resistance of UHMWPE/Bi-HD Blends: A Focus on UHMWPE Content and Molecular Weight

Abstract

This study systematically evaluates the interplay between microstructural characteristics and slow crack growth (SCG) resistance in blends of ultra-high-molecular-weight polyethylene (UHMWPE) and bimodal high-density polyethylene (bi-HD), varying in UHMWPE content and molecular weight (MW). At 1 and 5 wt% UHMWPE, cocrystallization and crystallinity were promoted, while higher contents (10 and 15 wt%) induced phase separation, thicker lamellae, and broader lamellar thickness distribution, as confirmed by thermal, morphological, and X-ray diffraction analyses. The probability of tie molecules (TMs) and zero shear viscosity were strongly correlated with UHMWPE content, underscoring the entangled network structure's dominant role in SCG. This was further evidenced by a 21% increase in strain-hardening modulus < G_p > (52.18 MPa), and a 25% reduction in natural draw ratio (3.2). Quantitative assessment of lamella area offered a more precise reflection of UHMWPE's influence on SCG, with higher MW UHMWPE exhibiting superior <G_p > due to a larger TMs fraction and lamella area. For the first time, the strain-hardened samples revealed a distinctive alternating lamellar structure with slit-like micropores. Incorporating up to 5 wt% UHMWPE into bi-HD increased micropore density while reducing pore size and uniformity. At 10 and 15 wt% UHMWPE, closed micropores predominated, indicating a restricted slippage mechanism.