Optimized alkaline treatment of date palm petiole fibers for biocomposites: Multi-technique characterization and digital image correlation (DIC) analysis

Biomaterials engineering today demands a redefinition of tomorrow's materials, integrating renewable and sustainable resources. In this context, natural fibers are attracting growing interest, provided that certain technological barriers related to their compatibility with polymer matrices can be overcome. This study explores, for the first time, the potential of date palm petiole fibers (DPF), an abundant and underutilized lignocellulosic resource, for designing high-performance biocomposites through optimization of alkaline treatment. The influence of increasing NaOH concentrations (0.5–5 %) applied at room temperature and at 60°C was evaluated on the physicochemical and mechanical properties of DPF. A multi-technique approach including scanning electron microscopy coupled with EDX, Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), thermal analysis (TGA/DTG), uniaxial tensile testing, and digital image correlation (DIC) enabled correlation of structural modifications with mechanical performance. The results reveal that mild treatment (1 % NaOH) induces partial delignification favorable to cellulosic accessibility, maximizing the strength of both fibers and composites (244.22 MPa, 6.16 % elongation). AFM analysis reveals surface modifications promoting interfacial bonding, while TGA/DTG demonstrates enhanced thermal stability of the optimized composites.While heat treatment (HT) improves ductility (up to 7.17 %), severe treatments degrade the structure and impair performance. This study identifies 1 % NaOH as the optimal treatment for structural applications, while NaOH-HT combinations open pathways for composites with tailored ductility. • Optimized 1 % NaOH treatment enhances date palm petiole fiber strength. • Multi-technique analysis links fiber structure to composite performance. • Digital Image Correlation (DIC) reveals strain distribution in composites. • Alkali–heat synergy tailors ductility but may reduce tensile resistance. • Valorization of palm petiole waste enables sustainable high-performance biocomposites.