Role of tie molecules in the yielding deformation of isotactic polypropylene

✍ Scribed by Koh-Hei Nitta; Motowo Takayanagi

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 202 KB
• Volume: 37
• Category: Article
• ISSN: 0887-6266
• DOI: 10.1002/(sici)1099-0488(19990215)37:4<357::aid-polb9>3.0.co;2-i

✦ Synopsis

We examined the effects of the tie-molecule fraction on the yielding behavior of two isotactic polypropylenes, one having little ethylene content and the other as the homopolymer with no ethylene. The tie-molecule fraction of the samples used in this study was controlled by blending ethylene-␣-olefin of an ␣-olefin content above 50 mol % in the blend of which the copolymers were incorporated into the amorphous regions of polypropylene (PP). An excellent linear relationship was observed between the measured yield stress and the tie-molecule fraction estimated from the Huang-Brown model, suggesting that the tie-molecule fraction and lamellar stiffness determine whether the lamellar fragmentation is easily activated or not, depending on the PP composition. Furthermore, an extended Huang-Brown model predicts a lamellar cluster connecting about five lamellae, which has a potential to account for morphological transformation of the spherulitic structure into a fibrillar one. Comparing the immiscible blends showing a phase-separated morphology with the partially miscible blends mentioned above, the yield stress was lowered by the presence of rubber phase, apparently in a similar manner; but the yielding processes were clearly discriminated between both cases when the yield stress was plotted against the tie-molecule fraction.