Study on the mechanical and thermal degradation properties of hybrid composites containing rice husk, short glass fibre and polypropylene

Abstract

This study aims to investigate the mechanical and thermal properties of hybrid composites containing rice husk (RH), glass fibres (GF) and polypropylene (PP). The objective is to develop the required technology for industrial applications of natural fibres composites. In this study, both binary RH/PP composites and ternary RH/GF/PP hybrid composites had been prepared for investigation. As RH fillers are commercially available in two different forms: rice husk flake (RF) and rice husk powder (RP), their reinforcing effect were also investigated. In order to enhance the interfacial bonding of glass fibre or rice husk with the polypropylene matrix, maleic anhydride grafted polypropylene (MA-g- PP) was used as the compatibilizing agent. In this work, a series of measurements of mechanical, thermal, and water absorption behaviour were conducted to investigate the performance of the obtained composites. The stiffness and fracture resistance of composites were measured by using tensile, flexural, Izod impact, instrumental drop weight impact and the essential work of fracture analysis. Following the mechanical tests, fractography, glass fibres length distribution and orientation were investigated by using scanning electron microscope (SEM), optical microscope and image analysis software. Besides, the water absorption curves and the influences of moisture content to the stiffness of composites were also determined. Finally, the thermal and processing properties of the composites were characterized by using thermogravimetry analysis and rheology measurement. It was found that the application of rice husks and glass fibres brought positive effects to the performance of composites. The addition of RH fillers and glass fibres effectively enhanced the stiffness of composites. However, the content and size of RH or GF affected the interfacial adhesion, orientation and dispersion of them. Up to 20wt% of GF were introduced, the reinforcement effect was reduced. The water absorption behaviour and the influences of water immersion content towards the mechanical strength of composites were illustrated. It was found that the time for achieving saturation and the absorbed moisture content at the equilibrium state was directly proportional to the rice husk content. The bending strength of the composites dropped gradually within the water immersion period. In the thermogravimetric studies, the changes of mass of binary and ternary composites were monitored under different heating rates. And the influences of RF and GF on thermal decomposition behaviours of PP matrix were illustrated. The faster the heating rate, the higher the degradation temperature was obtained. Besides, RF was thermally stable. The result showed that the addition of RF could retard the thermal decomposition of PP in the composites. The RH turned to carbon char after degradation to protect and enhance the thermal stability of PP matrix. However, the presence of RF in the composites did not affect the degradation mechanism of PP.

Date of Award	2 Oct 2008
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Kwok Yiu Robert LI (Supervisor)