醋酸纤维素的研究现状及展望

醋酸纤维素是纤维素与醋酸酯化而成的一种衍生物,具生物可降解、原料可再生和易加工等优点,随着资源匮乏及环境污染问题的日益严重,绿色环保材料醋酸纤维素越来越受到专家学者的关注.综述了醋酸纤维素在水处理、生物医学、烟嘴过滤及纺织面料等领域应用的研究现状,并指出目前醋酸纤维素的应用缺陷和问题.同时,分别从物理改性和化学改性两方面对醋酸纤维改性技术的研究进行分析,最后,对醋酸纤维素发展趋势进行了展望.     

纤维素醋酸酯接枝己内酯的合成与表征

以冰醋酸为溶剂,浓硫酸为催化剂,将三醋酸纤维素水解为不同取代度的醋酸纤维素(CA),再用此醋酸纤维素同ε-己内酯(ε-CL)接枝共聚合成醋酸纤维素/聚己内酯接枝共聚物(CA-g-PCL).研究了醋酸纤维素取代度和原料配比对单体转化率(C)、接枝率(G)、接枝效率(EG)的影响,结果表明在醋酸纤维素取代度为0.7时接枝共聚反应C、G、EG可分别达到46%、238.6%、88.5%;m(ε-CL)m(CA)=51时可分别达48.3%、140.553%、58.2%,并对相应的接枝共聚物进行了FTIR和1H-NMR的表征分析.     

大麻秆浆制备醋酸纤维素的研究

以大麻秆浆和醋酸为原料制备了醋酸纤维素。考察了硫酸用量、保温温度、保温时间、醋酐用量和冰醋酸用量对醋酸纤维素取代度和聚合度的影响。采用红外光谱和X射线衍射分析对醋酸纤维素进行了表征。实验结果表明:增加硫酸用量、提高保温温度和延长保温时间可提高醋酸纤维素的取代度,但聚合度下降;增加醋酸酐用量可提高醋酸纤维素的取代度,对聚合度影响不大;增加冰醋酸用量可提高醋酸纤维素的聚合度,对取代度影响不大。制备醋酸纤维素的适宜条件为:硫酸、醋酸酐和冰醋酸对大麻秆浆的质量比分别为0.13、9.0和9.0,保温温度为50℃,保温时间为1 h。该条件下制备的醋酸纤维素取代度为2.92,聚合度为121。由醋酸纤维素的红外光谱可证实纤维素与醋酸酐之间醋化反应的发生。X射线衍射分析表明大麻秆浆经醋化反应后,纤维素晶型发生了明显的变化。     

~(13)C-NMR法研究醋酸纤维素的取代基分布

用常规醋酸纤维素的13C-NMR法计算取代基分布难以准确。采用先将二醋酸纤维素中的剩余羟基完全丙酰化,再用13C-NMR法测定二醋酸纤维素乙酰基的取代分布的方法,其研究结果表明,完全丙酰化的二醋酸纤维素的碳谱中羰基碳区两组三重峰可较好地分开,因而可以根据它们的面积比算出其总取代度及在2,3和6位碳原子上的取代基分布。     

醋酸纤维素氨基甲酸酯的合成及其膜性能的研究

研究了用甲苯二异氰酸酯对醋酸纤维素进行改性,合成醋酸纤维素氨基甲酸酯,以增强高聚物的物理性能和耐菌性能。探讨了反应时间、原料配比、反应温度、催化剂用量及产物分离用溶剂等因素对此高聚物材料合成的影响。对醋酸纤维素苯基氨基甲酸酯铸成的反渗透膜的水通量、脱盐率、耐水解和耐微生物的稳定性能的测试表明,经改性的醋酸纤维素膜具有较好的上述性能,是一种良好的膜材料。     

纤维素醋酸酯接枝己内酯的聚合研究

以冰醋酸为溶剂,浓硫酸为催化剂,将取代度为2 4的二醋酸纤维素水解为取代度为1 4的醋酸纤维素(CA)。以此醋酸纤维素为接枝骨架,ε 己内酯(ε CL)为接枝单体,在辛酸亚锡的引发下,合成了醋酸纤维素/聚己内酯接枝共聚物(CA g PCL)。研究了反应物纯度、原料配比、引发剂与单体摩尔比、反应时间、反应温度对单体转化率(C%)、接枝率(G%)、接枝效率(GE%)的影响。结果表明,当反应温度为140℃,单体ε 己内酯与醋酸纤维素的质量比为4∶1,引发剂辛酸亚锡与单体ε 己内酯的摩尔比为0 005,反应时间为16h,C%,GE%和G%分别为46 8%,65 2%和122 1%。     

醋酸纤维素的应用开发研究进展

醋酸纤维素是重要的纤维素衍生物和理想的高分子膜材料。醋酸纤维素纤维具有无毒、无味、吸湿性好、截滤效率高等优点,近年来备受研究者关注。重点介绍了醋酸纤维素的衍生开发及其材料在渗滤、纺织、医疗卫生、包装及功能改性等方面的具体应用研究。     

醋酸纤维素衍生物反渗透膜对低分子量有机物分离特性研究

研究用醋酸纤维素衍生物氰乙基醋酸纤维素、羟丙基醋酸纤维素和醋酸纤维素反渗透膜对有机醇、有机酸及有机胺类水溶液的分离特性,考察操作压力对反渗透分离特性的影响,并应用不可逆热力学过程得出的Spiegler—Kedem膜输送方程解析实验数据,获得了反射系数σ、溶质渗透系数ω和溶剂水渗透系L_p等膜参数。     

醋酸纤维素超滤膜γ射线辐照改性

本文探讨醋酸纤维素超滤膜Ｃｏ＾６０γ射线辐照改性的可能性，分析了γ射线辐照改性机理，研究了吸收剂量，膜形态，铸膜液的组成对改性的影响。结果表明，γ射线辐照是醋酸纤维素超滤膜改性的一个有效方法。     

高性能抗菌纳滤膜的开发

采用等离子体技术对抗菌纳米粒子表面进行化学修饰,把修饰后的抗菌纳米粒子加入到醋酸纤维素的铸膜液中,制备出具有抗菌功能的新型醋酸纤维素纳滤膜。系统地研究了不同改性气体和抗菌纳米粒子浓度对纳滤膜性能的影响,同时借助于光电子能谱对醋酸纤维素纳滤膜的表面组成进行了分析。     

电子束预处理对醋酯纤维降解性能的影响

利用电子束辐照对醋酯纤维进行预处理,研究电子束辐照对醋酯纤维结构、性质及生物降解性能的影响。通过扫描电镜、红外光谱、黏度测试等方法证明:电子束辐照使醋酯纤维表面产生刻蚀,纤维大分子链断裂,聚合度降低,提高了酯酶和纤维素酶对醋酯纤维的降解能力,且辐照剂量越大,处理后醋酯纤维生物降解性能越好。     

Modification of cellulose acetate with oligomeric polycaprolactone by reactive processing: Efficiency,compatibility, and properties

Oligomeric polycaprolactone (oPCL) was used for the modification of cellulose acetate by reactive processing in an internal mixer at 180°C, 50 rpm, 60 min reaction time, and 45 wt % caprolactone (CL) content. The product of the reaction was characterized by several analytical techniques and its mechanical properties were determined by dynamic mechanical thermal analysis and tensile testing. The synthesized oPCL contained small and large molecular weight components. The small molecular weight fraction plasticized cellulose acetate externally and helped fusion. Although composition and structure did not differ considerably from each other when CL monomer or polycaprolactone oligomer was used for modification, the grafting of a few long chains had considerable effect on some properties of the product. The large molecular weight chains attached to CA increased the viscosity of the melt considerably and resulted in larger deformability. oPCL homopolymer is not miscible with cellulose acetate and migrates to the surface of the polymer. Exuded polycaprolactone oligomers crystallize on the surface but can be removed very easily. More intense conditions may favor the grafting of long chains leading to polymers with advantageous properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Electrical conductance of some cellulose derivatives

Summary The interrelation between the electrical conductance, and some chemically modified cellulose molecule produced through partial substitution of the hydroxyl groups by different groups namely, acetate, methoxyl, carboxymethyl and sodium carboxymethyl has been studied in the temperature ranges 283–333 k. The results show that of the examined samples change in the descending order: sodium carboxymethyl cellulose >carboxymethyl cellulose >methyl cellulose>cotton cellulose>cellulose acetate. The variable response of to the chemical modification and the physical changes of cellulose accompanying such modification has been discussed in terms of the molecular structure, chain flexibility and degree of polymerization of the examined samples.     

Thermogravimetric analysis of some chemically modified celluloses

Thermal degradation of carboxymethylcellulose, cellulose acetate, grafted wood pulp, and viscose rayon have been studied using thermogravimetric analysis and differential thermal analysis. The values of rate constant K and the activation energy E were calculated from the kinetic of weight loss using the theory of the first-order reaction. The activation energy of grafted cellulose and viscose rayon was > cellulose acetate > carboxymethylcellulose.     

Aerobic biodegradation of cellulose acetate

Two separate assay systems were used to evaluate the biodegradation potential of cellulose acetate: an in vitro enrichment cultivation technique (closed batch system), and a system in which cellulose diacetate (CDA) films were suspended in a wastewater treatment system (open continuous feed system). The in vitro assay employed a stable enrichment culture, which was initiated by inoculating a basal salts medium containing cellulose acetate with 5% (v/v) activated sludge. Microscopic examination revealed extensive degradation of CDA (DS = 2.5) fibers after 2–3 weeks of incubation. Characterization of the CA fibers recovered from inoculated flasks demonstrated a lower average degree of substitution and a change in the mol wt profiles. In vitro enrichments with CDA (DS = 1.7) films were able to degrade > 80% of the films in 4–5 days. Cellulose acetate (DS = 2.5) films required 10–12 days for extensive degradation. Films prepared from cellulose triacetate remained essentially unchanged after 28 days in the in vitro assay. The wastewater treatment assay was less active than the in vitro enrichment system. For example, approximately 27 days were required for 70% degradation of CDA (DS = 1.7) films to occur while CDA (DS = 2.5) films required approximately 10 weeks before significant degradation was obtained. Supporting evidence for the biodegradation potential of cellulose acetate was obtained through the conversion of cellulose [1-¹⁴C]-acetate to ¹⁴CO₂ in the in vitro assay. The results of this work demonstrate that cellulose acetate fibers and films are potentially biodegradable and that the rate of biodegradation is highly dependent on the degree of substitution. © 1993 John Wiley & Sons, Inc.     

Rheological studies of cellulose derivatives solutions

The rheological behavior of solutions of cellulose derivatives, acetate, and hydroxypropyl was studied as a function of different parameters; molecular weight, concentration,…, at T = 25°C in the vicinity of the liquid crystal phase transition. A variation of the strain rate sensitivity parameter with concentration is found. A degradation of the solution in trifluoroacetic acid is demonstrated.     

Decrement of cellulose recalcitrance by treatment with ionic liquid (1‐ethyl‐3‐methylimidazolium acetate) as a strategy to enhance enzymatic hydrolysis

BACKGROUND: The high crystallinity of cellulose underlies the recalcitrance that this polymer presents in enzymatic degradation. Thus, a pre‐treatment step is applied in most bioconversion processes. Treatments with ionic liquids are considered an emerging pre‐treatment technology, owing to their high efficiency in solvating cellulose, over molecular solvent systems. RESULTS: Crystalline cellulose with and without ionic liquid (1‐ethyl‐3‐methylimidazolium acetate) treatment, both commercially available, were used as substrates in enzymatic hydrolysis reactions using the earlier evaluated cellulolytic system of Fusarium oxysporum. The in situ removal of the hydrolysate during reactions enhanced the reaction rate as well as the overall glucose production. Ionic liquid treatment significantly decreased cellulose crystallinity and enhanced bioconversion yields and rates. The effects of cellulose structural changes during treatment on hydrolysis rate were investigated and the recalcitrance constants were determined. CONCLUSION: The study showed that ionic liquid‐treated cellulose became more homogeneous and more easily degradable than the untreated cellulose, a conclusion that was expressed mathematically by the difference in the recalcitrance constants for the two substrates. It was concluded that glucose production from ionic liquid‐treated cellulose could achieve very high conversion yields in consolidated bioprocesses or during simultaneous saccharification and fermentation. Copyright © 2012 Society of Chemical Industry     

预处理结合纤维素酶处理对醋酯纤维降解的研究

采用纤维素酶降解经氢氧化钠预处理过的醋酯纤维,考察了pH值、温度、酶用量、处理时间以及助剂对酶解效果的影响,并初步探索了超声波对氢氧化钠预处理效果的影响。结果表明,氢氧化钠预处理后,使用纤维素酶降解醋酯纤维的工艺条件为:pH值4.5,温度55℃,酶用量3 mL/L,反应时间4 h;使用超声波辅助氢氧化钠预处理后,醋酯纤维的取代度较单一碱处理略有降低,酶解活性提高;在纤维素酶催化水解反应中,加入非离子表面活性剂可以提高醋酯纤维的酶解效果。     

醋酸纤维素/壳聚糖复合膜制备与性能优化

为拓展醋酸纤维素(CA)在可降解包装材料中的应用,采用溶液共混法制备了醋酸纤维素(CA)和壳聚糖(CS)复合膜,研究了CS含量对CA/CS二元复合膜性能的影响。通过观察并分析复合膜的形貌、断面结构、化学键发现,CS能够充分结合膜内外的孔隙结构,两者之间强烈的相互作用增强了复合膜的各项性能。性能测试结果表明,当CS含量为10%时,复合膜的力学性能达到最大,断裂伸长率及抗拉强度分别增加12.37%和38.62 MPa,降解损失率提高了50.14%。同时,抑制了大肠杆菌及金黄色葡萄球菌的生长,抗菌率最高能够达到73.9%和54.6%。因此,CS在提高CA膜的力学性能和降解性能的同时,还赋予了复合膜优异的抗菌性。