Annealing-induced high impact toughness of isotactic polypropylene realized by introducing ultra-high molecular weight polyethylene

In present work, a small amount of ultra-high molecular weight polyethylene (UHMWPE) was introduced into isotactic polypropylene (iPP), and the blend was further annealed at different temperatures to tailor the microstructure. The changes in microstructure and mechanical properties of iPP and iPP/UHMWPE blend upon annealing were investigated and compared in detail. It was found that UHMWPE acting as organic rigid particles could insert and segment iPP crystal grains, facilitating the enhancement of compatibility of immiscible iPP/UHMWPE blend. The introduction of UHMWPE and annealing treatment has synergistic toughening effect on iPP. The impact strength of iPP/UHMWPE blend reaches 7.3 kJ m⁻², 128% higher than that of pure iPP. After annealing at 120 °C for 3 h, the impact strength of iPP alone is increased by 75% in contrast to that of its unannealed counterpart, while this value is increased dramatically by 372% for the iPP/UHMWPE blend. The remarkably elevated impact toughness of iPP blended with a small amount of UHMWPE upon annealing could be ascribed to the rigid-particle function of UHMWPE, promoted mobility of chain segments in the amorphous region, and enhanced interfacial interaction between the iPP and UHMWPE upon annealing.