The use of laser light scattering to study solution crystallization phenomena in polyolefins

[摘要] ENGLISH ABSTRACT: An instrument, named solution crystallization analysis by laser light scattering (SCALLS), that measuresthe solution melting and crystallization of polymers in solution was developed further in this study. Theinstrument was tested in a theoretical study to evaluate the Flory-Huggins relationship of melting pointdepression in solution of copolymers. It was found that the solvent interaction parameter forpropylene/higher 1-alkene copolymers, with low comonomer content is dependent on the comonomer type.It was also showed that the melting point depression is dependent on both the type and amount ofcomonomer included in the copolymer. The instrument was further developed to include a total of threelasers with different wavelengths. Initial problems with laser interference was rectified by the introductionof dichroic mirrors to direct the laser light to the relevant detectors and broad pass filters in front of the thedetectors to ensure that only the relevant laser light passes through. For homogenous polypropylene samplesit was found that even though a slower cooling rate increases the relative peak temperatures as well as therelative temperature differences between the peaks, detail in the peak profiles is the same for the fastercooling rate. The subsequent heating analysis does show that there is a definite dependence on the coolingrate. The ZNPP-4 sample shows that the appearance of a shoulder in the heating analysis becomes moredefined as a peak if the preceding cooling analysis is slower. Complex impact-polypropylene samples,differing only in the amount of ethylene were analysed and even small differences between samples weredetected. The possible application of the SCALLS instrument was investigated. It was proven that theinstrument can be used as a screening method for prep-TREF to determine the fractionation temperatures.

[发布机构] Stellenbosch University