Processing-induced morphology: Its relationship with tensile impact behaviour in injection-moulded polypropylene

Eric Lafranche (1) , Grέgory Brassart (1) , Patricia Krawczak (1)

1 Mines Douai EMD - École des Mines de Douai

This paper aims at identifying the main parameters that govern the tensile-impact strength of injection-moulded polypropylene. A Taguchi Design of Experiments (DOE) analysis has shown that the key parameters in both flow and transverse directions are the polymer melt and mould temperatures and the volumetric flow rate. The differences in high-speed mechanical behaviour have been explained on the basis of an investigation of the processing-induced morphology/tensile-impact behaviour relationship. The microstructure of parts manufactured under two extreme sets of moulding conditions has been analysed through-the-thickness by means of microscopy observations and by measurements of crystallinity, molecular orientation and thermal expansion. The impact brittleness originates from the skin layers, the major influential parameters being the skin/core ratio and the crystalline structure. The crack initiation energy increases with the oriented skin layer thickness, whereas the brittleness increases with the crystallinity level and the spherulite size.

Domaines: Science des matériaux [cond-mat.mtrl-sci]; Polymères; Mécanique des matériaux [physics.class-ph]; Matériaux; Génie des procédés

Eric Lafranche, Grέgory Brassart, Patricia Krawczak. Processing-induced morphology: Its relationship with tensile impact behaviour in injection-moulded polypropylene. Polymers and Polymer Composites, 2006, 14 (6), pp.563-576. ⟨10.1177/096739110601400602⟩. ⟨hal-01773356⟩