Improving coconut fiber sheet performance via stepwise chemical treatments

Abstract

Coconut fibers have gained increasing attention due to their sustainability, eco-friendly characteristics, and potential as a reinforcing component in composite materials. However, coconut fibers possess a hydrophilic nature, a heterogeneous structure, and poor interfacial adhesion with matrix materials. Therefore, surface modification is essential to enhance their properties before application. This research aims to improve the physical, mechanical, hydrophobic, and interfacial adhesion properties of coconut fibers for the development of interior decorative wall panels, using polyvinyl alcohol (PVA) as a binder. Sequential chemical surface treatments were investigated using potassium permanganate combined with sulfuric acid and benzoyl chloride as well as a treatment sequence starting with sodium hydroxide followed by potassium permanganate combined with sulfuric acid and benzoyl chloride. The morphological characteristics of the fibers were analyzed using scanning electron microscopy (SEM) and the elemental composition was detected by energy-dispersive X-ray spectroscopy (EDX). Physical and mechanical properties of the fiber sheets were underwent testing. The sodium hydroxide pre-treatment effectively removed some of the outer layer of fibers that were damaged and peeled off during the grinding process, resulting in improved accessibility of reactive sites for subsequent chemical modifications and reduced water absorption. Subsequent oxidation with potassium permanganate combined with sulfuric acid increased surface roughness and surface area, leading to a significant enhancement in tensile strength and interfacial bonding with the PVA matrix. In the final step with benzoyl chloride treatment, the hydrophilicity was reduced and the flame-retardant properties were improved, although a slight decrease in tensile strength was observed. Overall, the results indicate that sequential chemical modification significantly influences the structural, morphological, physical, and mechanical properties of coconut fibers and coconut fiber sheets. The most effective treatment was the sodium hydroxide pre-treatment followed by potassium permanganate / sulfuric acid oxidation, which provided optimal improvement for composite applications requiring high mechanical strength, reduced water absorption, and enhanced fiber–matrix interfacial adhesion with PVA binders.