Composite materials based on natural bast fibres offer potential commercial and environmental benefits due to the low cost, availiability, and biodegradability of the fibres. However, such benefits cannot be realised without a comprehensive evaluation of processing and properties. This thesis involved a comprehensive evaluation of composites based on two types of natural bast fibre (hemp and flax), and two types of matrix - synthetic (epoxy), and biodegradable (Novamont Mater-Si). The experimental work involved four strands: the effects of growing conditions and fibre processing on the properties of raw bast fibres; the optimisation of a pultrusion process for epoxy-matrix composites; development of a film stacking process for Mater-Bi composites, and a detailed evaluation of the mechanical properties of the composites themselves. Fibre bundles and individual fibre cells were investigated to characterise their structure, with particular focus on compressive kink defects. The kink bands were sectioned using a novel technique of focused ion beam milling, and kinking was found to induce delamination and voiding of the lamellar fibre structure. The defect concentration per unit length was assessed for conventionally-processed fibres and for hemp fibres from plants grown under controlled conditions to assess the effect of wind shear and stem flexure on fibre defect concentration. No effect was found for plant flexure, while industrially processed fibre was found to have increased defect concentration. The loading behaviour of both types of composite was seen to be initially linear with a yield point at 20 - 30 MPa and a transition to nonlinear deformation dominated by damage mechanisms as a result of fibre kinks. Epoxy composites possessed an inital modulus of 30 GPa with a 30 - 60% reduction in modulus after yield. Flax reinforcement was found to increase the modulus of Mater-Bi from 0.1 to 20 GPa and strength from 24 to 169 MPa. Fibre addition was also found to significantly embrittle the polymers.
| Identifer | oai:union.ndltd.org:ADTP/258355 |
| Date | January 2007 |
| Creators | Ruys, David Julian, Materials Science & Engineering, Faculty of Science, UNSW |
| Publisher | Awarded by:University of New South Wales. Materials Science & Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Ruys David Julian., http://unsworks.unsw.edu.au/copyright |
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