In this work, optimal and waste-free technologies for the production of nanocrystalline cellulose (NCC) and its composites with an inorganic pigment, as well as semi-finished products containing aggregates of nanoparticles were developed. The following optimal conditions of cellulose hydrolysis were proposed: the concentration of sulfuric acid was 40 wt %, temperature 80?, duration 1 h, and liquid to solid ratio 7. After the hydrolysis stage, the hydrolyzed cellulose was washed, diluted with water, and disintegrated to isolate individual nanoparticles. After that, the dilute dispersion of NCC was evaporated to obtain a commercial product, concentrated NCC paste. To obtain a composite, the acid in the unwashed hydrolyzed cellulose was neutralized with calcium hydroxide to precipitate a white pigment, calcium sulfate. Moreover, the spent acid and acidic wastewater were collected and treated with hydroxylapatite to produce a valuable by-product, superphosphate, the sale of which greatly reduces the cost of the primary product, NCC. The wastewater collected after washing, neutralization, and evaporation was purified and returned to the technological cycle. To reduce the production cost, such expensive stages as disintegration and evaporation of a dilute aqueous dispersion were eliminated, which made it possible to obtain cheap semi-finished products containing NCC-aggregates or its composite with inorganic particles of calcium sulfate.
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