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The influence of processing on properties of injection-moulded and lomolded components

Johnson, B. A. (2006-03)

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2006.


Rectangular components were produced by both standard injection moulding and by a process called Lomolding. Both moulding grade polypropylene homopolymer and glass-filled polypropylene were used. The effect of processing parameters on material properties, as measured by tensile and impact strength, and warpage were determined for both injection moulding and lomolding, for both unfilled and glass-filled polypropylene materials. Sampling of the components allowed for critical evaluation of processing parameters’ effect on material properties at points close to and distant from the injection point, as well as in the direction of materials flow and transverse to material flow. Glass-filled components were also evaluated in terms of glass fibre length and fibre distribution (post-injection). Overall conclusions could be drawn with respect to the 2 different processes and the materials used. It was seen, inter alia, that the specimen orientation had no effect on the mechanical properties when using unfilled polypropylene, but that the orientation of the glass fibres in the testing direction resulted in an increase in the tensile strength and the impact strength for the injection moulded samples. Similar results were seen for lomolded samples, except that the fibre orientation effects were different. In the same vein, other notable differences could be observed for samples produced by lomolding and injection molding. Fibre length and distributions obtained by polymer burn-off experiments served to help explain differences in properties of glass-filled products produced by the two processes.

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