Optimising fibre-to-resin ratios and post-curing parameters for enhanced mechanical properties of sunn hemp bio-composites

Optimising the fibre-to-resin ratio in bio-fibre reinforced polymer composites is crucial to achieving the mechanical performance and durability required for practical applications in sustainable construction and structural components. This research investigates the influence of fibre volume content on the tensile, flexural, and interlaminar shear strength (ILSS) of sunn hemp fibre bio-composites. Composite laminates were fabricated through compression moulding with fibre volume fractions of 15%, 30%, and 45%, combined with bio-epoxy resin, and subsequently post-cured at various temperatures (60°C, 80°C, 100°C) and durations (2, 4, and 6 hours), respectively. Mechanical characterisation involved tensile (ASTM D638), flexural (ASTM D790), and ILSS (ASTM D2344) tests conducted using a 10 kN universal testing machine. Experimental results show that increasing fibre volume content from 15% to 45% improved tensile strength and modulus by 28% and 11% respectively. Additionally, ILSS exhibited an 83% increase from 15% to 30% fibre content and a further 25% improvement at 45%, indicating enhanced shear stress transfer. Overall, the optimized mechanical properties—tensile strength (91 MPa), flexural strength (125 MPa), and ILSS (15 MPa) were achieved at 30% fibre volume and a post-curing time of 6 hours. Post-curing at 60°C maximized tensile strength, whereas flexural and shear strengths peaked at 100°C. These findings provide valuable insights into optimizing fibre-to-resin ratios and post-curing conditions for the sunn hemp reinforced polymer composites to achieve properties required for potential applications in building, construction, automotive, and structural materials. • Sunn hemp bio-composites optimized for superior mechanical performance • 30% fibre volume content offers peak strength and stiffness • Post-curing at 80°C for 4–6 h enhances tensile and flexural properties • Interlaminar shear strength improved by 133% at 45% fibre volume • RSM and desirability function used to model and optimise bio-composite design