Effect of ageing on the mechanical properties and the residual stress distribution of hybrid clay–glass fibre–polypropylene injection mouldings

The effects of ageing on the mechanical properties and thermal stresses distribution of injection moulded, short glass fibre/clay/polypropylene composites were studied. Two different clays were studied—talc and sepiolite. The results obtained indicate that the incorporation of short glass fibre into clay/polypropylene composites improves the mechanical properties, independently of ageing treatment. Larger elastic modulus values were obtained for talc-filled samples, whereas higher strength values were obtained with the sepiolite-filled ones. The impact strength increased as a result of the incorporation of glass fibre into the sepiolite-filled composite, while a small decrease was detected for the talc-filled polypropylene sample. Sepiolite-filled compounds show higher mould shrinkage in the bar-axis direction than equivalent talc-filled grades. In contrast, the shrinkage obtained on annealing at various temperatures between 100 and 160 °C was generally greater for talc-filled compounds than for the sepiolite-filled compounds. The shrinkage behaviour in the transverse direction was more complex. The residual stress levels of clay-filled polypropylene compounds were generally lower than those reported in the literature concerning short glass fibre polypropylene compounds under similar conditions. Hybrid composites showed much higher stress levels than the corresponding clay-filled samples independently of ageing conditions.