Hydrothermal extraction of microcrystalline cellulose from post-consumer indigo denim fabrics and evaluation of its UV blocking property

Abstract Waste cotton clothes, including post-consumer denim fabrics, are abundant biopolymer sources due to their high cellulose content. These waste materials commonly end up in landfills, posing health and environmental concerns and losing valuable cellulosic materials. To address these, this study aims to extract and characterize microcrystalline cellulose (MCC) from post-consumer indigo denim fabrics using a one-step hydrothermal method and evaluate its UV-blocking properties. FTIR and TGA analysis of raw and bleached denim confirmed the presence and purity of cotton cellulose and the indigo dye. Extracted MCC yielded 70-84%, with a degree of polymerization (DP) of 281-299. XRD analysis of the MCC showed a cellulose Type I structure. FTIR suggests the removal of amorphous phases of cellulose, leaving the crystalline structure. SEM meanwhile revealed rod-shaped and rough-surfaced MCC particles with diameters of 10-20 μm and lengths of 45-60 μm. Both FTIR and SEM indicated the retention of indigo dye on MCC surface. Increased acid hydrolysis time led to smaller particle sizes and higher degree of crystallinity (CrI). Indigo PVA-MCC films showed good transparency and effective UV blocking. These results indicate the successful conversion of denim to MCC via the hydrothermal method and the stability of indigo dye in the cellulose matrix.