Morphology-performance relationship of polypropylene-nanoclay composites processed by shear controlled injection moulding

Abstract

A nanoclay based masterbatch was mixed with polypropylene and direct injection moulded by conventional (CIM) and shear controlled orientation (SCORIM) injection moulding techniques. The aim was to correlate the morphologies induced by SCORIM and CIM processing with the thermal, mechanical and fracture performance of PP/nanoclay thick mouldings. In SCORIM, two extreme shear levels were applied by changing processing conditions. A complete characterization is reported, and statistical analysis is carried out to obtain a relationship between mouldings? properties. Nanoclay acted as polymer morphology directors, and in combination with SCORIM it induced the formation of γ-polymorph of PP. The nanoclay has a strong positive effect on thermal degradation of PP under oxidative atmosphere, due to the barrier effect of clay and the physico-chemical adsorption of the volatile degradation products on the silicates, but there were no differences between processing techniques. SCORIM samples of neat PP showed non linear brittle behavior, while nanocomposites exhibited quasi-stable behavior induced by a large deformation capability of the skin. Despite, fracture initiates at practically the same loading levels, the overall propagation energy values varied with processing conditions. Statistical analysis indicates that the decrement of the core region achieved by the SCORIM processing, the differences between skin and core and the PP γ-phase induced by the presence of nanoclay, are responsible for the toughening of SCORIM PP/nanoclay mouldings.