Sensitivity of post yield axial deformation properties of high-density ethylene/α-olefin copolymers in relation to molecular structure and slow crack growth resistance

Abstract

1-butene and 1-hexene based bimodal high density polyethylene samples were produced and post yield axial deformation properties, i.e. natural drawing and strain hardening, were investigated at 20 mm/min test speed and at 80 °C in relation to their molecular structure, such as molecular weight, comonomer type and content, viscosity, lamellae thickness and its distribution. Experimental results were evaluated for understanding the sensitivity of maximum natural drawing ratio and strain hardening modulus to amorphous phase entanglement density and tie molecules in relation to slow crack growth properties of polyethylene. It was found that, natural drawing ratio and strain hardening modulus have strong correlations with molecular parameters. Furthermore, it is demonstrated, for the first time, that natural drawing ratio and strain hardening modulus can be predicted with very high level of confidence by product of weight average molecular weight and comonomer content (mol.%) regardless of comonomer type.