Interphase Engineering in Lignin-Containing Nanocellulose Composites from Tropical Biomass: Evidence-Weighted Comparative Framework, Product Windows, and Biorefinery Constraints

Tropical lignocellulosic residues offer regionally abundant feedstocks for lignin-containing nanocellulose composites, but their value cannot be inferred from biomass origin or bulk lignin content alone. This review reframes the field as an interphase engineering problem, distinguishing between residual-lignin nanofibrils, redeposited-lignin systems, lignin-nanoparticle assemblies, compatibilized thermoplastic hybrids, and all-lignocellulosic sheets. The evidence is weighted according to feedstock geography, lignin state, nanocellulose morphology, moisture history, shaping route, and application-relevant testing. The synthesis indicates that tropicality matters through ash, extractives, contamination, water retention, storage stability, and processing logistics. Mill-concentrated residues, especially oil palm streams and sugarcane bagasse, offer the most credible near-term platforms because wet preprocessing and fractionation can be integrated locally. Decentralized residues, including pineapple leaf fiber and banana pseudostem, remain promising only when stabilization and contamination control are solved near the source. Finely distributed lignin often enhances UV shielding, antioxidant response, oil resistance, and selective wetting, whereas coarse or redeposited lignin often compromises fibrillation, transparency, and interphase continuity. Packaging layers, paper-like structures, coatings, and selected porous media emerge as high-confidence product windows; thermoplastics are medium-confidence, and biomedical, additive-manufacturing, and nano-reactor claims remain conditional.