Invention of novel continuous nitropulper technology for producing commercial nitrocellulose of wood pulp sheet

Nitrocellulose is one of the most important cellulose derivatives used in industry and commerce, produced from raw materials such as cotton linters, dissolving wood pulp, or pure/mixed cellulose pulp. This study aims to develop an efficient process for converting pulp into nitrocellulose while minimizing particle and dust formation, acid waste, fiber damage, and production bottlenecks during nitration and boiling stages. The research involved opening dense wood pulp sheets (88-90% purity) using a laboratory mixer and a pilot-scale nitropulper. Simultaneous nitration was conducted in a mixed acid solution (27% nitric acid, 65% sulfuric acid, 8% water) with varying acid-to-cellulose ratios (65:1 to 15:1) for 1 to 5 min. Pre-nitration was carried out for 4 min, followed by post-nitration (16-36 min) to ensure complete reaction. The nitrocellulose was then deacidified, boiled in an autoclave (with water-to-nitro pulp ratios of 30:1 to 5:1), milled, and washed. Results showed that sheet opening was incomplete at 1-2 min, but after 3 min-even at the lowest acid ratio (15:1, 5% consistency)-full opening and nitration were achieved. The final nitrocellulose exhibited excellent quality: no unnitrated particles, low lacquer turbidity (11), high stability (Bergmann stability ≤ 1.4 mg), low alkalinity (0.01), minimal acetone insolubility (0.11%), and few physical impurities. Additionally, blending 90%-purity wood pulp with 99%-purity cotton linters improved lacquer quality. FT-IR and DSC analyses confirmed structural similarity between wood-pulp-derived nitrocellulose and cotton-based nitrocellulose, with comparable NO₂/OH peaks (FT-IR) and decomposition temperatures (~ 202 °C vs. 201 °C). GPC tests showed average molecular weights of 55,303 Da (wood pulp) and 59,402 Da (cotton). The optimized process reduced acid-to-cellulose ratios (from 65:1 to 15:1 in nitration; 30:1 to 15:1 in boiling), increasing pre-nitrator and autoclave capacity. Cost-effective, high-quality nitrocellulose was successfully produced using a 70:30 wood pulp-to-cotton linter blend.