The growing generation of leather waste poses severe environmental challenges, demanding sustainable valorization strategies. This study presents an innovative approach to developing high-performance composites by extracting cellulose nanocrystals (CNC) from Nypa fruticans, a locally abundant mangrove biomass, and integrating them into PVC-leather scrap matrices reinforced with Al2O3. CNC was obtained via oxidation, yielding nanocrystals with a diameter of ~100 nm and 78.07% crystallinity, as confirmed by FTIR, XRD, FESEM, and DLS analyses. Composite sheets were fabricated with optimized CNC loadings (1-4 %) and evaluated for mechanical, thermal, and moisture-resistance properties. The hybrid composite containing 3 % CNC and 4 % Al2O3 exhibited improved performance, achieving a tensile strength of 3.43±0.14 Nmm⁻², an enhancement of about 120% compared to the control, and an elongation at break of 25.13±1.11%. Thermogravimetric analysis showed improved thermal stability, with a degradation onset near 380 °C and an increased char yield (5.09 % vs. 1.02 % for the control). Water absorption decreased to 19.63 %, indicating enhanced compactness and interfacial bonding. The study establishes Nypa fruticans as a novel, renewable feedstock for CNC production and demonstrates a synergistic reinforcement effect between bio-derived CNC and inorganic Al2O3 within the PVC-leather matrix. These results contribute to the theoretical understanding of structure-property relationships in hybrid nanocomposites and offer a scalable, eco-efficient route for transforming industrial leather waste into functional materials. The developed composites exhibit strong potential for use in footwear, insole boards, and leather goods, aligning with circulareconomy and sustainable-manufacturing objectives.

bio-composite, cnc, waste-upcycling, leather scrap, sustainable materials