Zero-discharge Technology for Production of Nanocrystalline Cellulose

In this paper a green zero-discharge technology for production of nanocrystalline cellulose particles (NCP) was proposed. The parameters of acid hydrolysis of bleached kraft pulp were studied. As a result the following optimal conditions were found: concentration of sulphuric acid is 60 wt. %, liquid/solid ratio is 5, temperature is 45oC and time is 1 h. Cellulose hydrolysis under optimal conditions generates NCP with average sizes of 120 x 15 nm, yield of 60-64%, crystallinity degree of 73-75%, DP of 120-140 and content of sulfonic groups of 46-50 meq/kg. The proposed technology provides the complete utilization of acidic wastewater and their use for the production of valuable by-product such as superphosphate fertilizer, the selling of which covers above 70% of the production cost of NCP. Furthermore, all washing water is returned in the production line. Thus, the cheap cellulose nano-product, 40% wetcake of NCP, was obtained without discharge of production waste into the environment. The obtained wetcake of NCP can be used as modifying additive for compositions of papers, glues, coatings, latexes or solutions of polymers, followed by homogenization, casting and drying.

Keywords: Nanocrystalline cellulose; Green technology; Waste utilization; By-product.