Crystalline Structures in Glass Fibre Reinforced Thermoplastic Composites
Ulrich Göschel, Wolfgang Lutz, Nicholas Craig Davidson, Peter Eyerer
University of Stuttgart, Institute for Polymer Testing and Polymer Science
Germany

Keywords: thermoplastic composites, crystalline structure, dimensional stability

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The thermo-mechanical behaviour of glass fibre reinforced thermoplastic composites depends on the fibre geometry, orientation and content as well as the structure in the polymeric matrix and interphase. Despite a high fibre content of about 30 % up to 50 % at most and a well-oriented fibre structure, the thermally induced dimension changes in the fibre direction are only reduced by about a factor of three, whereas the dimensional changes in the perpendicular directions are worse, often less than those for the unfilled isotropic matrix material. Such a phenomenon is crucial for the warpage behaviour immediately after processing and the thermal limitations for application.
The present paper aims to improve the thermo-mechanical behaviour of glass fibre reinforced thermoplastic composites by a controlled crystallisation both in the matrix and adjacent to the fibre taking into account the role of temperature, orientation and nucleation additives.
Using a fibre content of about 30 %, polyamide (PA 6) and isotactic polypropylene (iPP) are chosen as the matrix materials. Based on well-defined processing conditions such as in injection moulding, the resulting fibre orientation and fibre length have been precisely determined. Differential calorimetrical (DSC) and optical hot stage studies are used to characterise the spherulitic growth. Atomic force microscopy (AFM) have been applied to characterise the crystalline structure in the polymeric matrix and the transcrystallinity near the fibre. By means of the pulsed force mode, an additional tool of the AFM, the local stiffness and adhesion forces in the proximity of the fibre are investigated