Development and optimization of sustainable sisal fibre/karaya gum reinforced polyester composites: Mechanical, thermal, dielectric and moisture absorption performance

Sustainable hybrid composites were created by using sisal fibre as a reinforcement and karaya gum as a natural filler in a polyester matrix. Systematically changing the amount of karaya gum (0–25 wt%) affected the mechanical, thermal, dielectric, and moisture absorption properties. The composite with 15 wt% karaya gum (SK3) had the best performance, with a maximum tensile strength of 42.5 MPa, a flexural strength of 64.1 MPa, and an impact strength of 5.4 kJ/m². These values were much better than those of neat polyester. Dynamic mechanical analysis revealed an increase in storage modulus from approximately 1300 MPa to 2500 MPa and a shift in glass transition temperature from around 78 °C to 90 °C, signifying improved stiffness and limited polymer chain mobility. Thermogravimetric analysis showed that the material was more thermally stable, with the start of degradation moving from about 310 °C to about 345 °C and the amount of char residue rising to about 55%. The dielectric strength also went up from 14.2 kV/mm to 18.6 kV/mm, which shows that the electrical insulation works better. But because the filler was hydrophilic, the water absorption went up from 0.35% to 2.41%. FTIR analysis revealed the interfacial bonding between sisal fibre, karaya gum, and polyester matrix. Optimization results were able to pinpoint SK3 (15 wt% karaya gum) as the best composite formulation exhibiting the highest performance in all aspects.