OPTIMIZATION OF PROCESS FOR PRODUCTION OF NANOCRYSTALLINE CELLULOSE AND ITS COMPOSITES
In this work, optimal and waste-free technologies were proposed for the production of nanocrystalline cellulose (NCC) and its composites with inorganic pigment, as well as semi-finished products containing aggregates of nanoparticles. The following optimal hydrolysis conditions were found: concentration of sulfuric acid 40 wt%, temperature 80°C, duration 1 h, acid/cellulose ratio 7. After hydrolysis stage, the hydrolyzed cellulose was washed, diluted with water and disintegrated to isolate individual nanoparticles. Then, the diluted NCC dispersion was evaporated to obtain a commercial product - concentrated NCC paste. In order to obtain a composite, the acid in the unwashed hydrolyzed cellulose was neutralized with calcium hydroxide to precipitate a white pigment, calcium sulfate. In addition, the spent acid and acidic washings were collected and treated with hydroxylapatite (HAP) to produce a valuable by-product, superphosphate (SUP), the sale of which significantly reduces the cost of the primary product, NCC. Contaminated water collected after washing, neutralization and evaporation was purified and returned to the technological cycle. To reduce the cost of production, such expensive process steps as disintegration and evaporation of diluted dispersion were eliminated, which made it possible to obtain cheap semi-finished products containing NCC aggregates or composite of NCC with inorganic calcium sulfate particles.