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Abstract

Natural Fibre Reinforced Polymer (NFRP) composites offer favorable strength-to-weight ratios, low cost, biodegradability, and CO₂ capture potential, making them viable alternatives to synthetic composites. However, their hydrophilic nature leads to moisture absorption, weak matrix bonding, and microbial vulnerability. This study explores plastination, originally developed for preserving biological tissues, as a promising chemical preservative method to improve the environmental durability and mechanical performance in Western Red Cedar (WRC) softwood bio-composites. This research was completed in two phases. In phase 1, a comparative analysis was conducted to evaluate the influence of different cutting techniques of WRC and orientations during plastination using SS151 silicone as the impregnation material. While phase 2 expanded the scope of this plastination study to investigate the effects of different impregnation materials, SS151 silicone, Poly Furfuryl Alcohol (PFA), and Poly Methyl Methacrylate (PMMA), on WRC. Results from phase 1 indicated that the horizontal orientation and computer numerical control-cut (PH-C) configuration exhibited the lowest moisture absorption content (10.58%), the highest density (0.659 g/cm³) and highest depth of polymer impregnation (44.39%). A formal multicriteria decision-making analysis (Technique for Order Preference by Similarity to Ideal Solution, or TOPSIS) was adopted, and identified the PH-C as the most effective plastination configuration. In phase 2, PFA emerged as the most effective alternative in terms of water activity (0.5498) and flexural strength (53.06 MPa). Volume shrinkage analysis further supported its superior dimensional stability (1.919%). While tensile strength remained comparable to virgin WRC, a significant increase in the modulus of elasticity for both PFA and PMMA indicated improved material stiffness. As in phase 1, the TOPSIS multicriteria decision-making analysis was performed and ranked PFA as the overall optimal impregnation material. Manual and optimization-based sensitivity analyses confirmed the robustness of this decision. Overall, these thesis findings, along with the optimized plastination method, provide a pathway for further advancing the application of natural fibre composites in demanding (e.g. outdoors and moist) environmental conditions, thereby bridging the gap between sustainability and structural durability requirements in design.