Abstract
Blends of polypropylene (PP) and liquid crystalline polymer (LCP) processed without melting the LCP were compared with conventional melt processed blends. In a first stage, PP was blended with 20 wt.% of LCP in a twin-screw extruder with the take-up speed varied to achieve blends with different LCP fibre dimensions. In the second stage these blends were processed both below and above the T m of the LCP by extrusion and injection moulding.
At lower temperatures (180–200°C), where the material was processed without melting the LCP, a real composite structure was formed with solid LCP fibres in the PP matrix. When processed above the T m of the LCP (280°C) all the material was molten during processing and a composite-like blend morphology was created in-situ during cooling of the oriented melt phase. These blends exhibited a skin/core morphology, whereas the composites contained fibres throughout the sample. Due to this difference the impact strength of the composites was significantly higher than that of the blends. The blends exhibited higher modulus than the composites. Moreover, additional drawing can greatly improve the strength and stiffness of the blends. In composites the solid LCP fibres slightly increased the viscosity of PP, while in blends the molten LCP reduced the matrix viscosity and acted as a processing aid.
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