Preparation and Characterization of Multilayered High-density Polyethylene with Tunable Crystalline Structure

In rotationally extruded fittings, high-density polyethylene (HDPE) pipes prepared using conventional processing methods often suffer from poor pressure resistance and low toughness. This study introduces an innovative rotary shear system (RSS) to address these deficiencies through controlled mandrel rotation and cooling rates. We successfully prepared self-reinforced HDPE pipes with a three-layer structure combining spherical and shish-kebab crystals. Rotational processing aligned the molecular chains in the ring direction and formed shish-kebab crystals. As a result, the annular tensile strength of the rotationally processed three-layer shish-kebab structure (TSK) pipe increased from 26.7 MPa to 76.3 MPa, an enhancement of 185.8%. Notably, while maintaining excellent tensile strength (73.4 MPa), the elongation at break of the spherulite shishkebab spherulite (SKS) tubes was improved to 50.1%, as compared to 33.8% in the case of shish-kebab spherulite shish-kebab (KSK) tubes. This improvement can be attributed to the changes in the micro-morphology and polymer structure within the SKS tubes, specifically due to the formation of small-sized shish-kebab crystals and the low degrees of interlocking.In addition,2D-SAXS analysis revealed that KSK tubes have higher tensile strength due to smaller crystal sizes and larger shish dimensions, forming dense interlocking structures. In contrast, the SKS and TSK tubes had thicker amorphous regions and smaller shish sizes, resulting in reduced interlocking and mechanical performance.