Natural fiber composites – examining the effect of physical and chemical pretreatments on the mechanical, thermal and morphological performance

Abstract Natural fiber‐reinforced composites have received a lot of interest recently because of their advantages of being inexpensive, environmentally sustainable, biodegradable, nontoxic, lightweight and nonabrasive. Natural fibers such as flax, bamboo, sisal, hemp, ramie, jute, wood, etc., are primarily used as reinforcements in polymer matrices. However, the broader application of these has been limited due to various impediments, such as poor interfacial adhesion with polymeric matrices, high moisture absorption, low processing window and inadequate flame retardancy. To address these limitations, various surface modification techniques, both chemical and physical, on the surface of natural fibers have been explored to enhance fiber–matrix compatibility, reduce hydrophilicity and improve the mechanical and thermal properties of the resulting composites. Among these, plasma treatment, a physical technique for surface modification, has emerged as a promising eco‐friendly approach due to its ability to modify natural surface properties without using harmful chemicals. Other widely studied chemical modifications include alkali treatment, acetylation, silane coupling, bleaching, benzoylation and hybrid treatments. This review paper critically analyzes recent research on surface modification of natural fibers and its influence on the mechanical strength, thermal behavior and morphological characteristics of fiber‐reinforced polymer composites. The aim is to provide a complete understanding of the effect of pretreatment processes and their optimization on the performance of natural fiber composites for advanced material applications. © 2025 Society of Chemical Industry.