Rotational shear-induced shish-kebab structures in UHMWPE/HDPE pipes for enhanced hoop strength

Polymer chain entanglement remains a major challenge in fabricating polyethylene pipes with desired circumferential mechanical properties. Conventional self-reinforcement methods fall short in the processability of ultra-high-molecular-weight polyethylene (UHMWPE)/high-density polyethylene (HDPE) blends. In this study, a rotating shear system (RSS) was adopted to improve UHMWPE dispersion in the HDPE matrix and promotes the formation of highly oriented shish-kebab structures. Under the optimized shear condition (8 rpm), the molecular orientation degree was 0.93, accompanied by a transition from isotropic spherulites to dense, fibrous lamellae uniformly distributed across the pipe wall. The RSS-generated shear field reduced molecular entanglement and lowered the energy barrier for chain folding into the crystal lattice, thereby facilitating the formation of interlocking shish-kebab structures. The sample processed at 8 rpm exhibited a shish length of 315.42 nm, crystalline thickness (L_c) of 33.55 nm, and kebab lateral size (L_kebab) of 62.46 nm, corresponding to hoop strength of 89.0 MPa, a threefold increase compared to the static (0 rpm) sample. It demonstrates that applying an appropriate shear field effectively tunes the crystalline structure of polyethylene, enabling the fabrication of UHMWPE/HDPE composites with superior mechanical properties.