Chemical Compatibility and Performance Optimization in Natural Fiber-Based Polymer Composites

Natural fiber–reinforced polymer composites (NFPCs) are increasingly regarded as sustainable substitutes for conventional composites owing to their environmental merits, such as inherent biodegradability and comparatively low energy costs during manufacturing. Nonetheless, the intrinsic inadequacy of chemical bonding between the cellulosic fibers and the synthetic polymer matrices limits the realization of their anticipated end-use advantages. To circumvent this barrier and subsequently improve the composite’s mechanical, thermal, and environmental outcomes, selective chemical functionalization of the reinforcements has obtained renewed investigative momentum. This review systematically elaborates on the fundamental mechanisms governing fiber–polymer interlinking and consolidates recent advancements in tailored oxidative, esterification, and silane modification procedures directed toward maximum fibre–matrix matching. A comprehensive quantitative and qualitative assessment of how these interface-engineering strategies modulate composite performance is presented, thereby directing the selection and refinement of treatments toward optimized exploitation across heterogeneous industrial environments ranging from transportation to civil infrastructure.