EFFECTS OF ACID HYDROLYSIS ON THE EXTRACTION OF CELLULOSE NANOCRYSTALS (CNCs): A REVIEW

"The potential utilization of cellulose nanocrystals (CNCs) as reinforcing materials has lately attracted significant research attention. This is mainly due to their versatility and suitability for various applications in fields such as food packaging, cosmetics, biomaterials and pharmaceuticals. Several methods have been reported in the literature for isolating CNCs from plant sources, including acid hydrolysis, mechanical treatment and enzymatic hydrolysis, resulting in CNCs with different dimensions, crystallinities and thermal stabilities. However, acid hydrolysis using sulphuric acid (H2SO4) remains the favourite, as it requires shorter time and produces a stable suspension, with high crystallinity, compared to other methods. Sulphuric acid hydrolysis is generally performed with 64% acid concentration, with varying acid to fibre ratios, at temperatures around 45-50 °C, for 30-75 min duration under vigorous stirring. It typically produces needle-like structures, with the diameter and length in the range of 4–25 nm and 100–300 nm, respectively. This review analyses the results reported in the literature regarding the influence of hydrolysis parameters on the extraction of CNCs from various cellulosic materials. The study examines various hydrolysis parameters, specifically extraction time, temperature and acid concentration, to isolate CNCs with controlled morphology, crystallinity and thermal stability."