Interfacial Engineering, Physicochemical and Thermal Properties of Bio-Based Natural Fiber Reinforced Composites: A Critical Review with Sustainability Implications

Natural fiber reinforced composites (NFRCs) are increasingly explored as sustainable alternatives to conventional materials; however, their performance is strongly governed by thermodynamic and thermal interactions at the fiber–matrix interface. This review provides an integrated framework linking interfacial phenomena, physicochemical characteristics, thermal behaviour, and sustainability considerations in natural fiber composite design. Using established thermal analysis approaches such as differential scanning calorimetry and thermogravimetric analysis, key parameters including enthalpy changes, thermal stability, and degradation kinetics are evaluated and compared with synthetic fiber composites. The role of moisture-induced physicochemical interactions and interfacial incompatibility is examined through their impact on free energy, adhesion, and heat dissipation mechanisms. Surface modification strategies are critically assessed in terms of their ability to enhance interfacial bonding and improve thermal stability. The compiled findings across the surveyed literature demonstrate that optimized interfacial engineering significantly alters degradation pathways and heat flow characteristics, thereby identifying clear avenues for improving material performance. The thermodynamic insights are further correlated with lifecycle considerations, demonstrating that NFRCs can offer reduced environmental impact while maintaining acceptable thermal performance. This work provides a quantitative framework linking interfacial thermodynamics with sustainable composite design.