Investigation of the physicomechanical properties of polyester composites reinforced treated sisal fabric

The reinforcement of polymer matrices with natural fibers has emerged as a sustainable pathway to enhance mechanical and environmental performance. In this study, sisal fibers were first mercerized and subsequently modified using potassium permanganate (0.09%) and sodium chlorite (1.5%), with the aim of improving fiber–matrix adhesion and assessing the influence of temperature on composite properties. Twill 2/2 woven laminates were fabricated via vacuum bagging and evaluated in terms of tensile, flexural, and impact performance, as well as water uptake in saline environments. Results showed that alkali treatment significantly increased tensile strength from 129.31 ± 4.32 MPa to 266.12 ± 3.56 MPa, while the addition of KMnO₄ further boosted it to 359.11 ± 2.67 MPa. Water absorption decreased after treatments but rose with temperature from 18°C to 40°C. SEM analysis confirmed improved interfacial bonding, and TGA revealed enhanced thermal stability, particularly in alkali- and KMnO₄-treated composites. The combined alkali and KMnO₄ treatment offered the most balanced improvement, highlighting its potential for marine and structural applications where durability and resistance to aggressive conditions are required.