Impact Properties and Microhardness of Glass Reinforced Polypropylene

MARTINEZ GAMBA, M.; P- FRONTINI; POUSADA, A

Engineering with Polymers: an Europe – Latin America Research Experience

Año: 2007; p. 37 - 44

Short-fibre reinforced polymer–matrix composites constitute an important class of technical materials, because of their technological and economical advantages. Polypropylene (PP) is characterized as a commonly used material due mainly to its very attractive cost/performance ratio [1, 2]. Different grades of glass reinforced PP are being chosen by manufacturers for multiple injection moulded structural parts. However, the presence of weld lines (WL) generated by the impingement of the advancing flow fronts reduces their mechanical performance. Besides, composites are usually anisotropic because of the non-random orientations of the fibres. It was found that during injection moulding, the final orientation of the fibres in an injection-moulded article is in agreement with the Tadmor flow model [3]. The flow-aligned shell layer is formed by shearing across the part thickness, while the skin layer probably contains material that passed through the fountain region at the flow front and froze rapidly on the mould wall. It has been proposed that microhardness may give useful information about the correlation between processing parameters near and on the weld line, and also about the correlation between mechanical properties and microstructure of polymer structural parts [4, 5]. Several commercial glass fibre reinforced polypropylene grades were injected into final parts using a two-gated hot runner mould. Properties of the mouldings were recorded at different points of the final parts aiming to obtain data from the bulk and from the weld lines induced by the meeting of the two flow fronts. Microhardness [6], tensile impact strength [7] and instrumented falling weight impact [8] tests were preferred as characterizing techniques.