Recent Progress in Polymer Matrix Composites with Chemically Modified Natural Fiber Reinforcement

The rising interest in eco-friendly materials has sparked extensive work on polymer matrix composites (PMCs) reinforced with plant-derived fibers, which are both renewable and biodegradable substitutes for traditional synthetic inputs. Although these composites present substantial environmental advantages, the inherently low bonding strength between the polymer matrix and the natural fibers restricts their mechanical robustness and durability under service conditions. Chemically modifying the fibers has therefore become the predominant strategy for achieving stronger interface adhesion and, in turn, for raising the composites’ overall performance thresholds. This paper surveys the latest contributions concerning the chemical alteration of vegetable and lignocellulosic fibers, with emphasis on alkali, acid, silane, enzyme, and grafting techniques. For each treatment, the review examines the corresponding gains in mechanical strength, thermal stability, and environmental resistance, supported by experimentally validated trends. It further maps the expanding footprint of these composites within automotive, civil, packaging, and consumer-products supply chains. Finally, the article candidly addresses prevalent barriers—such as variability in raw-material properties and prohibitive treatment costs— while outlining targeted research trajectories, including the synergistic combination of treatment techniques and the design of biodegradable matrices, which could extend performance and market acceptance.