Flexural creep behaviour of PP matrix woven composite

In this work the flexural creep behaviour of polypropylene and glass fibre commingled woven composite (Twintex) sheets has been studied. Test samples were obtained in a compression moulding apparatus at different plate temperatures. Short-term flexural creep tests were run at multiple stress levels. Varying the applied stress level and using the Boltzmann superposition principle the linearity of creep behaviour was tested. In the linear viscoelastic region, creep tests were performed at different temperatures, ranging between 303 and 425 K. Time–temperature superposition principle was applied to build master curve, to predict the creep behaviour of the composite at a single reference temperature and long time scales. The obtained results indicate that higher temperatures of the plates lead to a composite with a lower creep compliance, which was related to the crystalline structure developed in the polymer matrix during cooling, and to a better fibre impregnation. An increase of the temperature of the mould resulted in higher degree of crystallinity of the polymer matrix, and lower final void fraction of the composite, as evidenced by results obtained from density tests, X-ray and DSC analysis. In turn, the higher crystalline fraction and lamellar thickness of crystallites were found to decrease the ductility of the composite, as evidenced from Charpy impact tests.