Comprehensive Study of Preparation of Carboxy Group-Containing Cellulose Fibers from Dry-Lap Kraft Pulps by Catalytic Oxidation with Solid NaOCl

Catalytic oxidation of commercial and dry-lap hardwood and softwood bleached kraft pulps (HBKP and SBKP, respectively) with 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) and NaBr has been comprehensively studied using solid NaOCl·5H2O as the primary oxidant for the preparation of carboxy group-containing cellulose fibers. When the amount of solid NaOCl added to the pulp suspension at pH 10 was 5 mmol/g pulp, a high initial reaction rate, a short time for complete oxidation, and high carboxy content and viscosity-average degree of polymerization for both the oxidized HBKP and SBKP were achieved. When they were prepared with 15 mmol NaOCl/g pulp, the mass recovery ratios of the water-insoluble oxidized cellulose fibers decreased to 40 and 26% for HBKP and SBKP, respectively, and their viscosity-average degrees of polymerization decreased to 180–230; side reactions always occurred on the pulps during oxidation. Solid-state 13C NMR and X-ray diffraction showed that the crystallinity and crystal size of cellulose I in the original pulps were preserved for the oxidized cellulose fibers prepared with 2.5 to 15 mmol of NaOCl/g pulp. The obtained carboxy group-rich cellulose fibers can be used as scaffolds for diverse cationic compounds and are suitable to be used as new functional group-containing sheet materials using the conventional papermaking process.