Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.596293
Title: An X-ray diffraction and modelling study of branched polyethylenes
Author: Baker, A. M. E.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1996
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Abstract:
Fifteen commercial branched polyethylenes were investigated after crystallisation under uniform, controlled conditions. Additionally, fibres were drawn. The samples were characterised in detail, including determination of heterogeneity in branch placement (using temperature rising elution fractionation). X-ray diffraction traces were measured on unoriented samples using a commercial diffractometer, and analysed using the Rietveld method. Fibre diffraction patterns were recorded digitally using a novel scanning diffractometer equipped with a charge coupled device (CCD), and mapped into cylindrically averaged reciprocal space. The patterns were fitted by a least-squares algorithm to extract peak positions and intensities. In both sets of data, it proved impossible to fit the entire diffraction pattern satisfactorily. Better fits were obtained by fitting separately to low and high angle regions. This is hypothesised to result from the presence of a component, intermediate in order between crystalline and amorphous components. This partially ordered component may represent an interfacial or boundary zone. Accurate cell parameters were obtained from the two sets of experimental data. These showed that unit cell expansion was maximised for random branch placement and that fibre drawing caused rejection of branches from crystallites. Some ratios of peak intensity showed significant trends with branch content and distribution. These were interpreted with reference to molecular modelling as indicating that some branch incorporation occurred, via a axis disorder and possibly a change in chain setting angle in the vicinity of the branch.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.596293  DOI: Not available
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