基于离子液体溶解/催化双重作用的废弃棉纤维乙酰化及其复合材料研究

The disposal problem created by waste cotton fabrics (WCF) is a serious challenge to our society due to their non-meltable and chemically insoluble nature. Preparation of regenerated cellulose and its ramification using ionic liquid (IL) as solvent has been proposed as a potentially attractive way to reclaim WCF. However, the large IL consumption and hence high costs have restricted its application in industry. Our previous research indicated that the Bronsted acidic IL might be used as both solvent and catalyst for the esterification of mechanochemically pretreated WCF with acetic anhydride. A high conversion (77-100%) can be achieved within a 4-8 h reaction time using 0.9-1.8 molar equivalents of IL per molar of anhydro glucose unit. Moreover, the degree of substitution (DS) of the obtained esters can be easily controlled by varying IL content. The focus of this study is to reveal the solvent/catalyst dual function mechanism of IL during the esterification reaction. For this purpose, the effect of reactant proportion, reaction time and temperature, the structure and content of ILs on the conversion, DS and substitution position of the obtained esters were investigated in detail. The effect of mechanochemical pretreatment on the accessibility of cellulose ramification was illustrated as well. Furthermore, the unconverted ultrafine cellulose powder was used as a reinforcement of the obtained esters to prepare self-reinforced cellulose composites. The technology presented in this study not only alleviates the environmental pollution from waste textiles, but also provides alternative resource for the textile industry.

废旧棉纺织品的回收利用是亟待解决的难题，采用离子液体作为溶剂制备再生纤维素及其衍生物是缓解该问题的有效途径。然而，离子液体耗用量大、生产成本高，成为制约该技术推广应用的主要瓶颈。前期实验发现，以少量Bronsted酸性离子液体为反应介质，经机械活化后的废弃棉纤维乙酰化反应的转化率高达77～100%，且可通过调控离子液体用量一步得到不同取代度的纤维素酯，推测离子液体在酯化反应中具有溶剂/催化剂的双重功能。本项目通过系统研究反应物配比、反应时间、温度、离子液体的结构和用量等因素对产物酯的收率、取代度和取代位置的影响规律，揭示Bronsted酸性离子液体促进纤维素酯化反应的溶解/催化双重作用机制。阐明机械活化对纤维素衍生化反应可及性的影响规律，发展将酯化反应中未转化的纤维素超微粉作为纤维素酯的增强填料，高效制备全纤维素复合材料的新技术，为废弃棉纺织品的低成本/绿色化回收利用提供新方法和理论指导。

针对废旧纺织品的回收利用这一亟待解决的难题，采用Brønsted酸性离子液体作为纤维素乙酰化反应的新型绿色催化剂，以废弃棉纤维为原料制备醋酸纤维素及其复合材料。阐明了机械应力作用对废弃棉纤维的粒径及其分布、分子量、结晶结构、氢键结构及衍生化反应可及性的影响规律；研究了反应物配比、反应时间、温度、离子液体的组成、结构和用量等因素对纤维素酯化反应的影响，揭示了Brønsted酸性离子液体促进纤维素酯化反应的溶解/催化双重作用机制；进而，通过调控反应条件经一步法即可高产率制备不同取代度、不同溶解性的醋酸纤维素，并制备了多种功能化复合材料，丰富和发展了纤维素乙酰化反应的理论基础和应用实践。在本项目执行期间，共计发表36篇SCI论文且标注本基金项目资助，其中通讯作者或第一作者SCI论文27篇，申请中国发明专利1项，部分成果已进入产业化阶段，产生了显著的经济效益。