Bioconversion of walnut shell residue into microcrystalline cellulose as reinforcement in polymer composites: driving...

The growing volume of agricultural waste presents both an environmental challenge and an opportunity for sustainable resource utilization. In this study, microcrystalline cellulose (MCC) was extracted from an abundant and underutilized walnut shell agro-waste. The process involved sequential alkali treatment, acid hydrolysis, and dual-stage bleaching. The extracted walnut shell microcrystalline cellulose (WSMCC) was extensively characterized to evaluate its physical, chemical, thermal, and morphological properties. The process yielded 42.3 ± 1.2% MCC with a high cellulose content of 95.5% and a density of 1.54 ± 0.02 g cm^-3. Fourier-transform infrared spectroscopy (FTIR) confirmed the removal of lignin and hemicellulose, while X-ray diffraction (XRD) analysis revealed a crystallinity index of 71.53%, suggesting a highly ordered structure. Thermal analysis demonstrated robust thermal stability with a decomposition peak at 332.96 °C and an activation energy of 66.84 kJ mol^-1. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and particle size analysis further confirmed the irregular but consistent particle morphology and surface roughness conducive for polymer reinforcement. The findings establish walnut shell-derived microcrystalline cellulose (MCC) as a promising bio-filler with favourable properties for green composite applications. These applications offer a sustainable alternative to wood-based cellulose, contributing to the circular bioeconomy in walnut-producing regions. This aligns with Sustainable Development Goal (SDG) 12 on responsible consumption and production.