Effect of entanglement on brittle-ductile transition in polyethylene

The brittle-ductile transition temperature (BDTT) of polyethylene with different degrees of entanglement density produced by crosslinking was evaluated using the Charpy impact test. BDTT was defined as the temperature at which the Charpy impact value Et changed abruptly from low to higher values. The increase In entanglement density brought about only a slight fall in BDTT, although that led to an increase in Et at ambient temperature corresponding to the occurrence of a dimple type fracture. A transition model between brittle fracture, patchwork type fracture (craze-like) and yielding deformation, depending on the degree of crosslinking, was proposed to explain those experimental results.