摘要
常见的纤维素溶剂体系对溶解温度要求苛刻,研究室温下可高效溶解纤维素的溶剂体系与溶液性能是提高纤维素资源利用与加工的关键步骤。本文以浊度值为量化指标,通过单因素实验探究四乙基氢氧化铵(TEAOH)/H_(2)O体系溶剂质量分数、温度、溶解时间等因素对溶解能力的影响,以探究相对最优溶解工艺。分析了纤维素固含量、溶液温度对稳态流变的影响,并得出结构黏度指数与黏流活化能。通过凝固再生制备纤维素膜,并对再生膜形貌结构与力学性能进行表征。实验结果显示,溶剂质量分数为35%时,25℃下10 min内可以将固含量8%聚合度(DP)540纤维素直接溶解,TEAOH/H_(2)O体系下纤维素溶液呈切力变稀的非牛顿流体,稳态流变中结构黏度指数与黏流活化能均较好,凝固再生制备的纤维素膜内部结构致密,再生膜力学性能良好。
Cellulose is one of the most abundant natural polymers in the nature,and it has many attractive advantages,such as renewability,biodegradability,and biocompatibility.With the decrease of non-renewable resources such as coal and oil,the use of cellulose resources can significantly reduce mankind’s dependence on non-renewable resources.Nevertheless,on account of the large amount of network connecting hydrogen bonds and partially dense crystal structure,cellulose is hard to dissolve in common solvent,nor can it be heated to a molten state.Thus,finding new solvents to dissolve cellulose is still the most effective way to process cellulose at present.Numerous solvent systems,including alkali/urea,N-methylmorpholine-N-oxide(NMMO),ionic liquids,molten salt hydrates,and low eutectic solvents,have been applied to dissolving cellulose.However,the majority of these solvents require strict temperature conditions(at low or high temperatures)for effective dissolution.Currently,quaternary ammonium hydroxide solvents have been extensively investigated because of their efficiency in dissolving cellulose under room temperature,but the majority of these solvents are costly,which prevents their further application.Therefore,we choose the relatively inexpensive tetraethylammonium hydroxide(TEAOH)/H_(2)O solvent system to study its solubility and solution properties.To develop new solvent systems for cellulose,the solubility of cellulose in TEAOH/H_(2)O and the rheological properties,film-forming properties of cellulose solutions were investigated.The effects of solvent concentration,temperature,and dissolution time on dissolution capability were investigated by using the single factor experiments.The optimal dissolution factors were determined as follows:8%degree of polymerization(DP)540 cellulose can be directly dissolved within 10 minutes at 25℃when the TEAOH concentration is 35%.The relationship between the steady rheological properties of cellulose solutions and the cellulose concentrations,and temperature was analyzed.Cellulose solutions in the TEAOH/H_(2)O system exhibited shear-thinning non-Newtonian fluid behavior.The structural viscosity index of cellulose solutions with 6%-8%concentrations is 4.72-7.40 at 10-50℃,and the viscous flow activation energy at zero shear rates are respectively 29.08 kJ/mol,33.24 kJ/mol and 30.75 kJ/mol.The structural viscosity index of cellulose solutions decreases with increasing temperature or decreasing concentrations.There is no obvious law between the change of viscous flow activation energy and cellulose solid content.The structural viscosity index and viscous flow activation energy in this system are suitable for the preparation of cellulose products.Finally,the morphological structure and mechanical properties of the regenerated cellulose films were characterized.The surface and cross-sectional structures of the regenerated cellulose films in this system exhibited dense and homogenous surface and cross-sectional structures without any layering or obvious pores.With the increase in cellulose concentrations(6%-8%),the tensile strength increased from 62.8 MPa±1.4 MPa to 82.3 MPa±2.3 MPa,while the elongation at break increased from 6.5%±1.2%to 9.2%±1.5%.The quaternary ammonium hydroxide aqueous solution has mild dissolution conditions and a lot of water is allowed in the system,which is highly efficient for dissolving cellulose and biomass components.By investigating the solubility effect,rheology and film-forming properties of cellulose in TEAOH/H_(2)O solvent system,we provide predictions for adjusting cellulose dissolution capability and mechanical performance of regenerated products in this study,offering reference for high-value utilization of cellulose resources and the development of efficient cellulose solvents under room temperature.
作者
吴奇龙
王文聪
WU Qilong;WANG Wencong(College of Textile Science and Engineering,Jiangnan University,Wuxi 214122,China)
出处
《丝绸》
CAS
CSCD
北大核心
2023年第10期1-7,共7页
Journal of Silk
基金
国家自然科学基金项目(51703085)
关键词
纤维素
溶解
四乙基氢氧化铵(TEAOH)
流变性能
再生纤维素膜
力学性能
cellulose
dissolution
tetraethylammonium hydroxide(TEAOH)
rheological property
regenerated cellulose films
mechanical properties
