Study on multi-response optimization of mechanical, dielectric properties and fracture surface of alkali-treated sisal fibre rei

https://doi.org/10.3221/IGF-ESIS.78.22

This study investigates alkali-treated sisal fibre reinforced polypropylene composites produced by compression moulding, with particular attention to how fibre treatment, fibre length and fibre loading jointly influence mechanical and dielectric performance. A Central Composite Design under Response Surface Methodology was used to model tensile, flexural and impact responses and to identify a balanced processing window. Alkali treatment improved fibre–matrix adhesion by removing surface impurities and increasing fibre roughness, which strengthened stress transfer and reduced fibre pull-out. The results show that fibre loading and fibre length strongly affected the measured properties; however, excessive reinforcement or longer fibres reduced performance because of poor dispersion, void formation and local stress concentration. The regression models showed good agreement with the experimental data and were suitable for multi-response optimization within the selected design space. Dielectric measurements indicated acceptable insulating behaviour, particularly in composites with better fibre dispersion and fewer interfacial defects. SEM observations further supported these trends by revealing improved fibre embedding and reduced interfacial gaps in treated composites. Overall, the work shows that alkali treatment, combined with statistical optimization, is a practical route for developing lightweight sisal fibre reinforced polypropylene composites with balanced mechanical and dielectric properties. The novelty of this study lies in integrating mechanical characterization, dielectric evaluation, SEM-based fracture analysis and Response Surface Methodology within a single multi-response optimization framework. The optimum treated composite exhibited a tensile strength of 19.20 MPa, flexural strength of 36.20 MPa and impact strength of 178 J/m. The developed regression models showed good agreement with experimental observations, with R² values of 97.42%, 92.76%, 97.89% and 91.92% for tensile strength, flexural strength, impact strength and dielectric constant respectively.