Melt Rheological Behaviour of Short Sisal Fibre Reinforced Polypropylene Composites

Abstract

The melt rheological properties of short sisal fibre reinforced polypropylene composites have been studied using a capillary rheometer. The dependence of the relative composition of component reinforcements and their aspect ratio and also the extent of chemical modification on the overall rheological behaviour have been studied. Incorporation of sisal fibre into polypropylene results in an increase in melt viscosity and a decrease in melt elasticity. The melt viscosity was found to have increased with fibre loading. Incorporation of fibres decreased the extrudate deformation and die-swell and this improvement was more prominent at higher fibre loading. A comparison was made between the two techniques employed for the preparation of the composites, i.e. melt mixing in a Haake Rheocord and solution mixing using toluene-xylene mixture as the solvent. It is found that composites prepared by solution mixing showed a higher viscosity as compared to melt mixed composites. Various chemical modifications using chemicals such as isocyanate, maleic anhydride and permanganate treatment have been carried out to improve the interaction between the matrix and fibre. The influence of chemical treatment on the viscosity of the system has been analysed. The fibre breakage analysis during extrusion was carried out using optical microscopy. The morphology of extrudate has been studied by optical and scanning electron microscopes. Master curves have been generated using modified viscosity and shear rate functions that contain the melt flow index (MFI) as a parameter. A comparison was made between theoretical and experimental viscosity values and it was found that experimental viscosity is slightly higher than theoretical viscosity because of the misalignment of fibres.