Influence of comonomer distribution on crystallization kinetics and performance of polyethylene of raised temperature resistance

Abstract

Three polyethylene of raised temperature resistance (PE‐RT) materials have been used to explore the factors that cause the differences in crystallization kinetics and mechanical performance between different classes and between the same classes. 1‐PE‐RT and 3‐PE‐RT belong to the same class (type II) but with different comonomer, while 2‐PE‐RT (type I) and 3‐PE‐RT use the same comonomer. The results of tensile and bending tests and isothermal crystallization indicate that different classes or even the same classes of PE‐RT have differences in high‐temperature resistance and long‐term performance. Characterization of the molecular chain structure shows that the comonomer content within the high molecular weight chains is significantly higher than that within the low molecular weight chains, and the comonomer is not uniformly distributed over the short‐chain molecules, which makes 1‐PE‐RT have higher modulus and better long‐term performance. Because the difference of comonomer content in long‐chain molecules and short‐chain molecules is small and the comonomer is relatively uniformly distributed over the short‐chain molecules, 3‐PE‐RT cannot balance the stiffness and the long‐term performance very well. For 2‐PE‐RT, the comonomer content in the long‐chain molecules and the short‐chain molecules is approximately the same and there is no intramolecular comonomer distribution, and thus it has the best long‐term performance but the lowest modulus. 2‐PE‐RT cannot have rigidity and good long‐term performance at the same time. © 2019 Society of Chemical Industry

Experimental study on the effect of molecular weight and chemical composition distribution on the mechanical response of high‐density polyethylene

“…Much prior research explored the impact of polyolefin's microstructure properties on the properties of the final product, and microstructural features of semicrystalline materials affect their mechanical and long-term performance. [13][14][15][16][17][18][19][20][21][22] Brown et al [23] have investigated the influence of morphology and MW on ductilebrittle transitions in linear polyethylene. They found that the brittle fracture stress of linear polyethylene increases with the number of tie molecules, and the number of tie molecules increases with MW and the cooling rate.…”