The fractionation and characterisation of propylene-ethylene random copolymers

[摘要] This study involves the fractionation and characterisation of three propyleneethylenerandom copolymers. The fractionation technique used in the study wastemperature rising elution fractionation (TREF). The TREF fractions weresubsequently analysed offline by crystallisation analysis fractionation (CRYSTAF),differential scanning calorimetry (DSC), 13C NMR, high-temperature gel-permeationchromatography (HT-GPC), and wide-angle x-ray diffraction (WAXD). The effect ofthe ethylene comonomer on the crystallisability of the propylene was investigated,along with the effect of the comonomer on the type of crystal phase formed during thecrystallisation. The results show that the comonomer inhibits the crystallisation of thecopolymer and that as the ethylene content increases, the crystallisation and meltingpoints decrease. It was also shown that the higher the ethylene content, the more ofthe γ-phase crystal type is formed. The distribution of the comonomer throughout thecopolymers was also investigated. The results show that there is an unevendistribution of the comonomer with most of the comonomer accumulating in theamorphous areas, and very little actually being incorporated in the crystalline regions.It was also observed that the fractions eluting at the highest temperatures hadconsiderably higher polydispersities and lower molecular weights than the fractionseluting just before them. The highest temperature fractions also have lower meltingand crystallisation temperatures than the preceding fractions. This has been attributedto a nucleation effect by the sand support used during the TREF fractionation.

[发布机构] Stellenbosch University