Background: Natural fiber–reinforced polymer composites (NFPCs) have emerged as compelling sustainable alternatives to conventional synthetic-fiber composites because of their renewable origins, low density, and favorable specific mechanical properties (Bledzki et al., 1998; Chawla, 1987). Over the last three decades, research has progressed from basic characterization and processing of wood-flour and plant-fiber filled thermoplastics to sophisticated chemical surface treatments, hybridization strategies combining multiple natural and synthetic reinforcements, and the integration of data-driven predictive methods to anticipate mechanical performance (Hull & Clyne, 1996; Bledzki & Gassan, 1999; Kumar et al., 2025).
Objectives: This work synthesizes the theoretical foundations, mechanistic understanding, empirical trends, and predictive modeling approaches relevant to NFPCs, with explicit attention to cellulose-based fibers, wood-flour fillers, and hybrid fiber systems. The goal is to provide a rigorous, publication-ready synthesis that links microscale interfacial chemistry, mesoscale morphology, and macroscale mechanical response—while mapping how chemical modification, processing variables, moisture, and hybrid architectures combine to determine static and dynamic properties.
Methods: The article integrates classical composite micromechanics, interfacial adhesion theory, extensive literature-derived empirical observations, and contemporary machine learning–enabled predictive approaches to create a coherent narrative. Methods are presented descriptively—detailing experimental designs commonly used in the literature (tensile, flexural, impact, dynamic mechanical analysis, moisture absorption tests), chemical and physical fiber treatments, hybrid stacking strategies, and data-driven model development pipelines (feature selection, supervised learning, cross-validation). Each methodological element is linked to its mechanistic rationale and to reported results across the cited literature (Chawla, 1987; Bledzki & Gassan, 1999; Wang et al., 2006; Karamov et al., 2022).
Results: Collated findings indicate consistent patterns: (1) chemical treatments (alkali, silane, acetylation, fatty acid plasticization) systematically improve fiber–matrix adhesion and tensile strength when optimized, though excessive treatment degrades fiber integrity (Suardana et al., 2010; Marion et al., 2003); (2) hybridization employing wood flour, short natural fibers (jute, hemp, kenaf, sisal, banana), and controlled synthetic phases can be tuned to balance stiffness, toughness, and moisture sensitivity (Mwaikambo & Ansell, 2003; Thiagamani et al., 2022; Balaji et al., 2019); (3) moisture absorption remains a critical degradation mechanism that compromises interface and mechanical properties unless mitigated via coupling agents, matrix selection, or encapsulation strategies (Wang et al., 2006); (4) machine learning models trained on curated material descriptors and processing parameters show promising predictive accuracy for tensile strength and other mechanical endpoints, but their reliability depends on dataset quality, descriptor selection, and interpretability strategies (Karamov et al., 2022; Kumar et al., 2025).
Conclusions: The literature collectively supports a paradigm in which successful NFPC design arises from multipronged control of fiber chemistry, interface engineering, microstructural architecture, and moisture management—augmented increasingly by data-centric predictive frameworks. Future work should target standardized datasets, mechanistically informed descriptors, and systematic studies of long-term environmental durability.
