Impact of the surface chemistry of rice hull ash on the properties of its composites with polypropylene

Khalil, R 2008, Impact of the surface chemistry of rice hull ash on the properties of its composites with polypropylene, Doctor of Philosophy (PhD), Civil, Environmental and Chemical Engineering, RMIT University.

Document type: Thesis
Collection: Theses

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Title Impact of the surface chemistry of rice hull ash on the properties of its composites with polypropylene
Author(s) Khalil, R
Year 2008
Abstract Rice hull ash (RHA) is a by-product of the rice industry. RHA is produced when rice hulls are incinerated, for example, when they are used to power steam engines in rice milling plants. Typically, this ash is disposed of in landfill sites, which may cause environmental problems. RHA has a naturally occurring silica content that is very high, ranging from 95 to 98%. This high silica content makes RHA a potential filler for polymer products. The aim of this project was to investigate the application of RHA as a filler in polypropylene. The study used a systematic approach to characterising the RHA physiochemical properties and comparing these to another commercially available grade of silica filler. The processing conditions for mixing RHA with Polypropylene (PP) were optimised to obtain the maximum tensile modulus value. Attempts were made to improve the interaction of RHA and PP by treating the RHA surface with silane coupling agents and adding functionalised polymers to the composite. Mechanical, rheological and morphological properties of the non-silanated, silanated and coupled composites were characterised and compared to determine their structure -property relationships. Rice hull ash (RHA) has a similar chemical structure to other silicas. Like any metals and metalloids, the surface of RHA contains -OH functional groups but these are very limited in quantity. RHA and PP composites have a wide processing window and the optimised processing conditions in a small batch mixer are 12 minutes, 60 rpm and 180°C. Addition of RHA into PP increases the modulus but decreases the tensile strength of the composites, attributed to poor compatibility between RHA and PP, as RHA is hydrophilic and PP is hydrophobic. The optimum loading of RHA is 20wt%. To improve the RHA and PP composites, 2 grades of silane and maleic anhydride grafted PP (MAPP) is used. Silane treated RHA composites have improved mechanical properties, especially tensile strength, attributed to enhanced interfacial interaction. The optimum is 1.5wt% for APS and 2.wt% for MPS in this system. The optimum MAPP concentration in this system is 3wt%. Properties of the RHA / PP composites show modest improvements compared to PP. The properties are not sufficient to make RHA a commercially attractive reinforcing filler for PP for high performance composite. It has potential for a cost reduction filler for low end application composites.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Civil, Environmental and Chemical Engineering
Keyword(s) Rice hulls -- Testing
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