Effect of Hydrolysis Acid Concentration on Microcrystalline Cellulose Derived from Denim Fibers for UV-Shielding Applications

Despite their widespread use due to affordability, ease of use, and corrosion resistance, polymers are susceptible to ultraviolet (UV) degradation. Recent advancements on UV-blocking technologies however, suffer from chemical incompatibility with organic polymer substrates such as polyvinyl alcohol (PVA). Thus, there is a need to explore sustainable and green alternatives for compatible UV-blocking materials. This study investigates the UV blocking performance of PVA reinforced with microcrystalline cellulose (MCC) extracted from used denim fabrics using mild acid hydrolysis. Optical microscopy and FTIR analysis of raw denim showed the structure of cotton fiber and the presence of indigo dye. MCC yield ranges from 43-83% with degree of polymerization (DP) of 146-173 after extraction at varying hydrochloric acid (HCl) concentrations. XRD and SEM analysis showed cellulose Type I structure and rod-shaped MCC with particle lengths of 37-78 μm. Increasing HCl concentration during hydrolysis led to shorter particle lengths and higher degree of crystallinity, indicating an increase in the crystalline phases due to conversion of cellulose to MCC. These results indicate the successful conversion of denim fabric to MCC. Lastly, the fabricated PVA-indigo MCC films were effective in blocking UV light while maintaining good transparency. When compared to bleached MCC, PVA with indigo MCC resulted to 12% more UV blocking. This can be attributed to the indigo retention and stability in MCC even after increased acid concentration, which is also shown in the FTIR and SEM analysis. These findings contribute to waste reduction efforts by utilizing cotton waste and offer a sustainable solution to produce UV-resistant PVA films.