The in situ synthesis of weakly entangled ultrahigh‐molecular‐weight polyethylene/polyethylene wax blends and its synergetic disentanglement effect on LLDPE reinforcement

Abstract

AbstractHigh‐performance ultrahigh‐molecular‐weight polyethylene (UHMWPE)/low‐molecular‐weight polyethylene (PE) mixture additives were proven to be effective for enhancing commercial high‐density polyethylene (HDPE) resins, which were synthesized by the complicated dual‐site immobilized catalyst system. In this paper, PE wax components were preadded in the polymerization reactor for in situ synthesizing the UHMWPE/PE wax binary blends with just a single SiO2/MgCl2 supported Z–N catalyst modified by the active site isolators. The influence of PE wax addition on the catalytic activity, molecular weight, thermodynamic property, particle size, and entanglement density was systematically researched. It was evidenced that the catalytic activity and molecular weight exhibit a linear relationship with the ethylene solubility caused by the PE wax addition. Besides, the competition between chain propagation/crystallization balance and PE wax long chains entanglement effect arising from the PE wax addition leads to the minimum entanglement density (GNt = 0.59) of UHPE‐20%. The disbalance of chain propagation rate and chain crystallization rate can be broken by PE particle fragmentation, inducing rapidly increased entanglements. Furthermore, with the synergistic disentanglement influence of reduced entanglements for UHMWPE and the chain diffusion ability for PE wax, the LU‐30 sample with a mixture of UHPE‐30% and linear low‐density polyethylene (LLDPE) exhibits the optimum strength/stiffness/toughness properties. The tensile strength, Young's modulus, and impact strength of LU‐30 reach 18.2 MPa (+4%), 172.1 MPa (+53.8%), 60.5 kJ/m2 (+13.1%), respectively, compared with those of pure LLDPE. The overall enhanced mechanical properties are attributed to the intensive signal intensity and tightly stacked form of shish‐kebab structures, which were verified by the two‐dimensional small angle X‐ray scattering and two‐dimensional wide angle X‐ray diffraction patterns. In addition, the in situ polymerization method of UHMWPE/PE wax with SiO2/MgCl2 supported Z–N catalysts exhibits a great probability of efficient utilization of low‐molecular‐weight polyethylene by‐products (PE wax).