Properties of Kenaf (Hibiscus Cannabinus L.) Bast Fibre Reinforced Unsaturated Polyester Composite

The main purpose of this research is to exploit new bio-fibre resources for the structural composite industries. Kenaf bast fibre was combined with thermosetting resin matrix to produce advance composites and its mechanical and dimensional stability properties were investigated. Unsaturated polyester was used as matrix resin in this project which consist 44-48% of styrene monomer and form gel in 24-30 minutes with 1% methyl ethyl ketone peroxide. Biological retting and chemical retting were introduced to prepare the fibre. In biological retting, the bast layer of kenaf was submerged into a water-bath filled with sandy soil (pH = 8.9) and water for 3 days under constant temperature of 30 ± 2 ºC. For chemical retting, the bast layer is submerged in 5% sodium hydroxide (NaOH) and boiled under high temperature (80 ºC) for 75 minutes. Modified water retting reduced the retting time to 3 days compared to normal water retting process which required 5 to 30 days. However, chemical retting produced weaker fibres due to the extreme processing condition. The kenaf bast fibre was well incorporated in the unsaturated polyester resin matrix and successfully hot-pressed into panels. The composites were fabricated using unidirectional and cross-ply lamination with different fibre volume fraction (40%, 50% and 60%). Chemical analysis, mechanical tests, Izod pendulum impact test and analytical test were carried out. Specimens were further observed under Phillips XL30 scanning electron microscope (SEM). Generally, the main effects of fibre content, lay-up method and fibre type significantly influenced the properties of kenaf bast fibre reinforced unsaturated polyester composites, except the fibre type has no significance influence on the impact resistance, water absorption and thickness swelling of kenaf composites. However, interactions of the main effects were dominated in each mechanical and dimensional stability properties such as the influence of interaction between fibre content - lay-up and fibre type - lay-up method. Overall, biological retted fibre composites showed better physical and mechanical properties compare to chemical retted fibre composites at the same fibre content and lay-up method. The tensile strength and flexural strength of 60% fibre content composites with biological retted fibre was 232 MPa and 248 MPa, respectively.

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