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.

能够在较低温度下溶解纤维素的NaOH /脲（或硫脲）溶剂系统是纤维素化学领域的一项突破，据报道，当将纤维素添加到氢氧化钠（NaOH）和添加剂的预冷水溶液中时，纤维素会迅速溶解。实际上，在开始这项工作时，我们计划基于溶解浆在NaOH /添加剂水溶液中的部分溶解来制造基于浆纤维的缓冲包装材料，并且发现添加到预冷水溶液中的某些溶解浆没有显示出更好的溶解性。因此，这项工作比较了直接溶解法和冻融法在溶解纸浆纤维和纯纤维素中的有效性。检查了三种水溶液：7％NaOH / 12％尿素，9.5％NaOH / 4.5％硫脲和8％NaOH / 8％尿素/6.5%硫脲。通过偏振光学显微镜分析三种NaOH /添加剂水溶液的溶解能力，并确定溶解的纤维素比例。结果表明，在三种水溶液中，冻融法未干燥的针叶木溶解浆和竹子溶解浆均比直接溶解法具有更好的溶解度。溶解方法对每种溶解浆在8％NaOH / 8％尿素/6.5%硫脲溶液中的溶解影响可忽略不计。似乎直接溶解法更适合于聚合度（DP）较低的烤箱干燥微晶纤维素，而冻融法更适合于具有较高DP的永不干燥的纸浆纤维素纤维。