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Indexed by:期刊论文

Date of Publication:2011-07-28

Journal:JOURNAL OF CHEMICAL PHYSICS

Included Journals:SCIE、EI

Volume:135

Issue:4

ISSN No.:0021-9606

Key Words:chemical interdiffusion; crystallisation; differential scanning calorimetry; Fourier transform spectra; infrared spectra; nucleation; optical microscopy; phase separation; polymer blends; quenching (thermal)

Abstract:Influence of inter-diffusion on the crystallization dynamics in polyethylene/poly(ethylene-alt-propylene) (PE/PEP) blends was studied by a combination of optical microscopy (OM), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). OM measurements showed that the crystal nuclei may be first generated at phase separated interface where concentration fluctuation is greatly enhanced in the temperature quench process. After the formation of crystal nuclei, the only crystallizable components, PE chains, are necessary to reach the nucleation site via inter-diffusion to continue the secondary nucleation and growth process. DSC showed that there is only one 96 degrees C crystallization peak when PE (M(W) = 52 kg/mol) is blended with low molecular weight PEP (M(W) = 32 kg/mol); while there are two crystallization peaks, which are 96 degrees C and 72 degrees C, respectively, when the same PE is blended with high molecular weight PEP (M(W) = 110 kg/mol). The origin of the 72 degrees C crystallization peak was studied by DSC isothermal crystallization and time resolved FTIR. It was proved that the 72 degrees C crystallization peak is resulted from the smaller inter-diffusion coefficient in the PEP-rich region. Both slow mode theory and fast mode/constraint release models of inter-diffusion can be used to explain the smaller inter-diffusion coefficient in the PEP-rich region, which dynamically results in the disappearance of the 72 degrees C crystallization peak after isothermal crystallization at 90 degrees C for 60 min. Therefore, inter-diffusion plays an important role on crystallization dynamics in multi-component and multi-phase polymeric blends. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3613652]