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20. Effect of Heterogeneous Short Chain Branching Distribution on Acceleration or Retardation of the Rate of Crystallization from Melts of Ethylene Copolymers Synthesized with Ziegler-Natta Catalysts.

Author

Ren, Minqiao, Chen, Xuejian, Sang, Yuan, and Alamo, Rufina G.

Subjects
*LOW density polyethylene, *COPOLYMERIZATION, *CATALYSTS, *CHAIN-propagating reactions, *CRYSTALLIZATION, *MACROMOLECULES
Abstract

Ethylene 1-alkene copolymers with the same molar mass, same molar mass distribution and very similar average comonomer content of 3.8 +/− 0.4 mol% but different broad interchain comonomer content distribution (CCD), are found to display different extents of melt memory effect on crystallization rate. With decreasing the initial melt temperature, all broadly distributed copolymers show enhanced crystallization followed by a decrease of crystallization rate. However, copolymers with a higher content of molecules in the medium composition range (6-2 mol% comonomer) and a lower content of lightly branched molecules (<2 mol% comonomer), display the highest effect of memory of a prior crystallization in their high temperature melts. The increase in crystallization peak temperature is up to 4 °C. The acceleration and further retardation of the crystallization are associated with self-seeds that remain in one-phase or two liquid phases melts respectively. The magnitude of the effect on crystallization is proportional to the number of surviving seeds in the initial melt. [ABSTRACT FROM AUTHOR]

Published
2015
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35. The effect of 60Co γ‐rays on the crystal structure, melting and crystallization behavior of poly(butylene succinate)

Author

Song, Jianbin, Ren, Minqiao, Song, Chunlei, Wang, Shuyun, Zhang, Hongfang, and Mo, Zhishen

Abstract

The results obtained for poly(butylene succinate) (PBS) after 60Co γ‐ray irradiation, studied by wide‐angle X‐ray diffraction (WAXD), differential scanning calorimeter (DSC) and polarizing optical microscopy (POM), revealed that the degree of crystallinity, melting temperature and enthalpy decreased with increasing irradiation dose, but that the crystal structure of PBS did not vary when compared to non‐irradiated PBS. By using Scherrer equation, small changes occurred in the crystal sizes of L020, L110 and L111. The spherulitic morphology of PBS was strongly dependent on irradiation dose and changed significantly at higher irradiation dosages. The crystallization kinetics of PBS indicated that the Avrami exponent (n) for irradiated PBS was reduced to 2.3, when compared to non‐irradiated PBS (3.3). Copyright © 2004 Society of Chemical Industry

Published
2004
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