| Résumé | The automotive industry is seeking new solutions for lighter, more fuel efficient vehicles. To achieve this goal, light materials for semi-structural and structural automotive applications in both aesthetic and nonaesthetic parts are of strategic importance. Long fibre thermoplastics (LFT) based on polypropylene/glass fibre (PP/GF) composites represent an interesting alternative when it comes to light weight materials. LFTs are commercially available in pre-compounded pellets for injection moulding and are developed with specific properties for targeted functions. LFTs are now prepared by in-line compounding (ILC) of base materials including resin, additives (heat stabilizers, colors, coupling agents, etc.), and glass roving reinforcements for direct moulding of LFT parts (D-LFT) to reduce costs, heat histories, and create in-house flexibility of material blending. There are two major technologies for D-LFT moulding, both relying on twin-screw extrusion (one-stage or two-stage) for ILC: one utilizing compression moulding and the other injection moulding. These technologies share several similarities, but also present significantly different features in terms of fibre length, orientation and mechanical properties. The objective of this paper is to address some of them. A compression moulding process (Dieffenbacher LFT Direct system) and an injection moulding process (Krauss-Maffei Injection Moulding Compounder) were used to compare their specific features. Samples were taken from the parts and from machine purges for a comparison of the respective fibre distribution patterns using micro focus X-ray computed tomography. Their fibre length distribution was also obtained from pyrolysis and image analysis. Resulting mechanical properties were then compared to provide a more complete understanding of the two moulding technologies. The paper will focus on presenting the respective advantages and specific features of the two moulding technologies. The advantages of using ILC for natural fibre-filled PP composites will also be presented. |
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