Hydrothermal assisted isolation of microcrystalline cellulose from pepper (Piper nigrum L.) processing waste for making sustainable bio-composite

Conversion of industrial pepper bio-waste (PW) to microcrystalline cellulose (MCC) was investigated as reinforcement agent of natural polymer bio-composites. The investigation highlighted the importance of hydrothermal assisted alkalization step for efficient separation of cellulose from lignin in PW in order to enhance the yield and the crystallinity of MCC. Cellulose was isolated from industrial pepper bio-waste via three steps i.e. alkalization, bleaching and hydrothermal assisted re-alkalization. Hydrothermal treatment during re-alkalization step increased the release of lignin that was bound within the cellulose domain via dissociation of the multiple bonds in the three-dimensional polymer and significantly reduced the lignin concentration. Optimization of hydrolysis parameters i.e. the concentration of HCl, the hydrolysis temperature and time, and also the solid/liquid ratios produced 86% of MCC with high crystallinity index ∼78.9%. The physicochemical properties of MCC isolated from PW exhibited a highly crystalline microcellulose structure with high thermal stability that were comparable to the physicochemical properties of the commercial MCC. Incorporation of MCC with seaweed and chitosan natural polymer showed the enhancement of the tensile strength and the elongation of the bio-composites, which exhibited the potential use of MCC as reinforcement agent in bio-composites to replace traditional plastic.