Crystalline behavior and critical crystalline sequence length of propylene/alpha-olefin copolymer

The melting points(T-m), crystalline temperature(T-c) and crystallinity(chi(c)) of propylene/alpha-olefin (pentene-l, octene-1 and decene-1) copolymers have been investigated, The results show that the T-m, T-c and chi(c) of the copolymers are lower than those of propylene homopolymer, indicating that lower alpha-olefin incorporation in copolymer has strongly hampered the crystallization of propylene, From critical crystalline sequence length of several propylene/alpha-olefin copolymers, it can be seen that a long chain alpha-olefin has much stronger effect on crystallization of PP than a short alpha-olefin does.

TEMPERATURE EFFECT ON IMPACT FRACTURE-TOUGHNESS AND FRACTURE MECHANISM OF PHENOLPHTHALEIN POLY(ETHER KETONE)

Phenolphthalein poly(ether ketone) (PEK-C) was tested using an instrumented impact tester to determine the temperature effect on the fracture toughness K-c and critical strain energy release rate G(c). Two different mechanisms, namely the relaxation processes and thermal blunting of the crack tip were used to explain the temperature effect on the fracture toughness. Examination of the fracture surfaces revealed the presence of crack growth bands. It is suggested that these bands are the consequence of variations in crack growth along crazes that are formed in the crack tip stress field. As the crack propagates, the stress is relaxed locally, decreasing the growth rate allowing a new bundle of crazes to nucleate along which the crack advances.