【作者】 林春香；

【导师】 詹怀宇；

【作者基本信息】 华南理工大学 ， 制浆造纸工程， 2010， 博士

【摘要】 纤维素是自然界最为丰富的可再生天然高分子资源,具有许多良好的性能,有效利用纤维素资源,对于解决当今面临的资源问题具有重要意义。本论文以新型绿色溶剂离子液体1-丁基-3-甲基咪唑氯盐(BMIMCl)为反应介质,采用不同的聚合方法,包括传统自由基聚合和可控/活性自由基聚合,对纤维素进行均相改性研究,后者可合成结构与分子量大小可控,分子量分布窄的纤维素接枝共聚物。以丙烯酸为单体,过硫酸铵为引发剂,N’N-亚甲基双丙烯酰胺为交联剂,利用传统自由基聚合,在离子液体BMIMCl为反应溶剂的均相条件下制备出纤维素与丙烯酸的接枝共聚物,随后采用反相悬浮技术将接枝共聚物球化,制备出球形纤维素吸附剂。研究了反应条件(包括单体用量,引发剂用量,反应时间和聚合反应温度)对接枝效果的影响,优化了纤维素吸附剂制备的反应条件。研究结果表明,以离子液体BMIMCl为反应介质,不仅可以加快反应速度,提高产物的接枝率,而且所制得的球形纤维素吸附剂对水溶液中重金属离子及阳离子碱性染料具有良好的吸附性能。实验以三种金属离子(Cu2+、Ni2+和Fe3+)和阳离子碱性染料亚甲基蓝为吸附质,采用静态吸附方法综合研究了球形纤维素的吸附性能,包括等温吸附及各影响因素对吸附效果的影响,并对其吸附热力学和动力学进行了研究,探讨了吸附机理。研究结果表明,球形纤维素吸附剂对金属离子及阳离子染料具有很好的吸附效果,对水溶液中Cu2+、Ni2+、Fe3+和亚甲基蓝静态吸附量分别达到174.8 mg/g、61.2 mg/g、63.6 mg/g和307 mg/g,而且再生容易,回收率高,并可以重复使用。吸附剂的静态等温吸附符合Langmuir和Freundlich吸附等温式。吸附热力学和吸附动力学研究结果表明球形纤维素吸附剂对金属离子及染料的吸附以化学吸附为主;吸附过程由表面扩散和颗粒内扩散联合控速,但以颗粒内扩散为主。用微波辐射代替常规加热方式,在离子液体中快速合成纤维素接枝共聚物,考察了反应条件包括微波辐射温度及辐射时间等对接枝效果的影响。研究结果显示,与传统的加热方式相比,微波辐射加热可加快反应速度,大大缩短了聚合反应的时间,仅3min就能得到性能良好的纤维素接枝共聚物。以金属离子Pb2+为印迹分子,在离子液体中通过接枝共聚方法合成了纤维素金属离子印迹聚合物。实验研究了反应条件对印迹聚合物吸附性能的影响以及聚合物对印迹分子的选择性。研究结果表明,所制备的印迹聚合物,在与其他金属离子(Cu2+或Ni2+)的竞争吸附中,对印迹分子表现出较高的吸附选择性,而且还具有良好的再生性能,可以循环使用。活性/可控自由基聚合技术集自由基聚合与活性聚合的优点于一体,可合成具有精致结构的分子量可控、分子量分布窄的聚合物,而且其聚合实施条件与传统自由基聚合相似。本实验分别通过两种活性/可控自由基聚合,原子转移自由基聚合(ATRP)和可逆加成-断裂链转移自由基聚合(RAFT),合成了纤维素与甲基丙烯酸甲酯(MMA)的接枝共聚物。实验通过纤维素与氯乙酰氯在离子液体中的均相乙酰化,一步合成了ATRP大分子引发剂(Cell-ClAc),随后用其引发了MMA在离子液体中的ATRP,构筑纤维素接枝共聚物,并对其反应动力学进行了研究。实验结果表明,MMA在离子液体中的聚合反应动力学呈一级反应动力学规律,并且分子量大小随单体转化率呈线性增加,分子量分布较窄,表明该聚合反应是活性可控的;合成的纤维素与MMA的接枝共聚物在丙酮溶液中具有自组装行为;以离子液体为反应介质可加快聚合反应速度,提高单体转化率,聚合反应的表观活化能较低(ΔEaapp为16.6 KJ/mol),说明反应容易在离子液体中进行;此外,离子液体的使用还可使聚合物容易与无机催化剂有效分离,从而避免了对聚合物的污染;聚合反应温度以及反应体系中各物料配比(例如单体与引发剂摩尔比,配体与催化剂摩尔比等)对聚合反应速率、聚合产物分子量及分子量分布有较大的影响。通过二硫代苯酰基氯化镁与Cell-ClAc的取代反应,将纤维素大分子引发剂转化为RAFT大分子链转移剂Cell-CTA,并以偶氮二异丁腈为引发剂,引发了MMA在离子液体中的RAFT聚合,构筑纤维素接枝共聚物。聚合反应动力学曲线以及接枝共聚物侧链的分子量及分子量分布与转化率关系曲线表明,该聚合反应是活性可控的;以离子液体为反应介质可加快聚合反应速率,提高单体转化率。更多还原

【Abstract】 Cellulose is the most abundant renewable biopolymers on earth, it has many good properties. The effective utilization of the cellulose has a great significance to the crisis of resource. In this paper, cellulose was modified homogeneously via different methods, including traditional radical polymerization and“living”/controlled radical polymerization, using an ionic liquid 1-butyl-3-methylimidazolium chloride (BMIMCl ) as reaction medium.Cellulose was grafted homogeneously with acrylic acid in BMIMCl by traditional radical polymerization, using ammonium persulfate (APS) as an initiator and N,N’-methylene- bisacrylamide(MBA) as a crosslinker. And then the spherical cellulose adsorbent was obtained through a water-in-oil suspension technique. The reaction conditions were optimized to obtained higher graft percentage (GP). The experimental results show that the use of BMIMCl as reaction medium can enhance the reaction rate and increase the grafting efficiency.Comprehensive studies on the adsorption properties of the spherical cellulose adsorbents were conducted in ways of static adsorption using metal ions(Cu2+, Ni2+ and Fe3+) and cationic dye (Methylene blue)as adsorbates.And,static isothermal adsorptions as well as various effecting factors were also studied. Moreover, the adsorption mechanisms including the adsorption thermodynamics and kinetics were explored.The adsorption of the metal ions and cationic dye on the adsorbents have found to be concentration、pH and temperature dependent.Furthermore,excellent adsorption efficiency of the above two adsorbates on the adsorbent can be obtained.And, the cellulose adsorbent has such advantages as easy regeneration, high recovery and reusability etc. The static adsorption process follows Langmuir and Freundlich adsorption isotherm equations. It can be concluded from the adsorption thermodynamics and kinetics that chemical adsorption is predominant for the adsorption of two adsorbates on the adsorbent.The adsorption rate is controlled by two diffusion models of surface diffusion process and intra-particle diffusion process,between which the intra-particle diffusion process plays a more significant role during the adsorption process.The microwave heating was adopted to replace the conventional heating to synthesize the graft copolymer of cellulose with acrylic acid. The effects of reaction conditions on grafting were studied and the results show that the use of microwave resulted in a drastic reduction of reaction time: 3 min irradiation was sufficient, compared with 30 min to 5 hours, as conventional heating was used. A probable free radical mechanism for grafting under microwaves was also proposed.The metal ion imprinted polymer was synthesized by homogeneous radical graft copolymerization of functional monomer acrylic acid onto cellulose with Pb2+ as template in BMIMCl. Investigation on the selective adsorption property of the imprinted copolymer was conducted. It is concluded that the obtained Pb2+-imprinted copolymer shows higher selectivity towards Pb2+ than the non-imprinted polymer.“Living”/controlled radical polymerization combines the advantages of free radical polymerization and living polymerization. Polymers with fine structures, predetermined molecular weights and narrow polydispersities can be synthesized through“living”/controlled radical polymerizations in the polymerization condition which is similar to that of traditional free radical polymerization. In this paper, cellulose graft copolymers were synthesized via two“living”/controlled radical polymerizations, atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer polymerization (RAFT), respectively.Cellulose-based macroinitiator (Cell-ClAc) was first synthesized by direct homogenous acylation of cellulose in BMIMCl in absence of any catalyst. Then the homogeneous ATRP of MMA from cellulose macroinitiator was carried out in BMIMCl without homopolymer byproduct and the polymers were easily separated from the catalyst when the ionic liquid was used as reaction medium. Further the cellulose graft copolymer in solution could aggregate and self-assembly. The kinetic of the ATRP was also investigated and the results showed that the obtained copolymers had grafted polymer chains with well-controlled molecular weight and low polydispersity, and the polymerization was a“living/controlled”system. The reaction temperature and reaction ingredients ratios have great effect on the polymerization rate. The low apparent energy of activation (ΔEaapp , 16.6 KJ/mol) of the polymerization reaction illustrates that the reaction carried in BMIMCl is much easier.Cellulose based RAFT chain transfer agent (Cell-CTA) was obtained through substitution reaction of Cell-ClAc and bis(thiobenzoyl) disulphide. Then the MMA polymer chains were grafted onto the cellulose by RAFT in BMIMCl using 2, 2’-azobis(isobutyronitrile) (AIBN) as initiator. The experiment results demonstrate that the use of the ionic liquid as a reaction medium enhanced the polymerization rate to a moderate extent. Additionally, a controlled/living polymerization character was proven for cellulose-CTA-mediated RAFT polymerization in BMIMCl as a result of the first-order kinetics of the copolymerization, linear increase in Mn with conversion, and low PDIs.更多还原