Effect of the Dissolving Method on the Dissolution of Dissolving Pulp Cellulose Fibers with Different Dried-States in Different NaOH/Additives Aqueous Solutions

• Published in: Journal of polymers and the environment 2021-12, Vol.29 (12), p.3909-3917
• Main Authors: Kong, Weiwei, Yu, Guangrong, Xing, Jiong, Zhang, Hongjie, Liu, Meihua, Shi, Yan
• Format: Article
• Language: English
• Subjects: Additives; Aqueous solutions; Bamboo; Cellulose; Cellulose fibers; Chemistry; Chemistry and Materials Science; Crystalline cellulose; Degree of polymerization; Dissolution; Environmental Chemistry; Environmental Engineering/Biotechnology; Fibers; Freezing; Industrial Chemistry/Chemical Engineering; Light microscopy; Low temperature; Materials Science; Optical microscopy; Original Paper; Packaging materials; Polymer Sciences; Pulp; Sodium hydroxide; Softwoods; Thiourea; Thioureas; Urea; Ureas
• ISSN: 1566-2543; 1572-8919
• DOI: 10.1007/s10924-021-02149-8

A NaOH/urea (or thiourea) solvent system capable of dissolving cellulose at lower temperatures is a breakthrough in cellulose chemistry, and it was reported that cellulose rapidly dissolved when it was added to a precooled aqueous solution of sodium hydroxide (NaOH) and additives. In fact, upon initiating this work, we plan to fabricate pulp fibers based cushioning packaging material based on part dissolution of dissolving pulp in aqueous NaOH/additives solutions, and found certain dissolving pulp added to a precooled aqueous solution did not show better dissolution. Therefore, this work compared the effectiveness of the direct dissolution method and freezing-thaw method in dissolving pulp fiber and pure cellulose. Three aqueous solutions were examined: 7% NaOH/12% urea, 9.5% NaOH/4.5% thiourea, and 8% NaOH/8% urea/6.5% thiourea. The dissolving capacity of three NaOH/additives aqueous solutions was analyzed by polarized optical microscopy and the dissolved cellulose proportion was determined. The results showed that the never-dried softwood dissolving pulp and bamboo dissolving pulp achieved better dissolution using freezing-thaw method than using direct dissolution method in the three aqueous solutions. The dissolving method had a negligible effect on the dissolution of each dissolving pulp in the 8% NaOH/8% urea/6.5% thiourea solution. It seems that the direct dissolution method was more suitable for oven-dried microcrystalline cellulose with a low degree of polymerization (DP) and the freezing-thaw method was more suitable for never-dried pulp cellulose fibers with a higher DP.