The brittle‐ductile transition temperatures (BDTT) of polyethylenes with different degrees of crystallinity, such as LDPE, LLDPE, MDPE, and HDPE, were evaluated using Charpy impact test. The effect of the specimen cooling condition on the BDTT was a main concern in the study. A rise in the cooling plate temperature (Tp) for high density resins brought about a fall in BDTT and an increase in the Charpy impact value Et. However, embrittlement was observed during a tensile test for HDPE samples with a rise in Tp. A crack shielding effect by microvoid formation is proposed as the toughening mechanism for HDPE.
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.
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