【作者】 何建新；

【导师】 王善元；

【作者基本信息】 东华大学 ， 纺织材料与纺织品设计， 2007， 博士

【摘要】 纤维素葡萄糖单元上的三个羟基几乎完全乙酰化,得到三醋酸纤维素,其取代度为2.9-3.0。三醋酸纤维素水解到取代度2.6─2.4,称为二醋酸纤维素。三醋酸纤维素广泛运用于胶卷、塑料、纺织纤维、膜材料等,而二醋酸纤维素广泛运用于香烟滤嘴和纺织纤维。醋酸纤维素对纤维素的来源有较高的要求,其a-纤维素含量要高于95%,因而能够用于制备醋酸纤维素的原料通常是棉绒和高级木溶解浆,商业上广泛使用的是高级木溶解浆。竹子具有可再生,低成本的优势,不过到现在为止,还没有竹浆粕用于制备醋酸纤维素的报道。本文选择慈竹为原料,通过结合酸预水解工艺和两道中温硫酸盐蒸煮工艺以及木聚糖酶和DMD用于漂前预处理,制备高a-纤维素含量、高聚合度和高白度的醋化用高级溶解竹浆粕(高级竹浆)。确定了合理的预水解、蒸煮和漂白的工艺条件,研究表明蒸煮过程中适当提高硫化度能够增加脱木素选择性,可以有效防止碳水化合物降解的同时获得深度脱木素的浆粕。在木聚糖酶和DMD处理(包括碱抽提段)阶段,竹浆的白度的增加占整个漂白流程白度增加量的15.29%;卡伯值的降低量占整个漂白流程降低量的37.87%;而特性粘度降低量仅占整个漂白流程降低量13.77%。通过两种处理能够减少纤维素的降解,而能有力地脱除木质素,明显的提高浆粕的白度。红外光谱证明了木聚糖酶对竹浆中半纤维素(木聚糖)的水解作用,而X-衍射分析间接的证明了DMD的脱木素作用,因为2θ角29.4°处归属于无机成分的衍射峰在DMD处理后完全消失。通过X射线光电子能谱(XPS)探测浆粕表面的氧碳原子比(O/C)和四种C原子的相对含量,详细地分析了漂白各阶段浆粕表面化学组成的相对变化,特别是在过氧化氢漂白段,抽提物的含量有明显增加,终漂后浆粕的抽提物表面覆盖率要明显的高于木质素的表面覆盖率。在漂白流程中,DMD处理会降低样品的结晶度和晶粒尺寸,不过其它阶段浆粕的结晶度晶粒尺寸增加,总的说来,最终浆粕的结晶度和晶粒尺寸要高于漂前的。SEM观察到了制备的高级竹浆表面的裂缝、沟槽和整齐微纤以及内部大大小小的空洞,这表明制浆过程中半纤维素和木质素等非纤维素成分充分去除。分析也表明,与加工烟用醋酸纤维的高级硬木溶解浆(高级木浆)相比,虽然高级竹浆的木聚糖、灰分和抽提物的含量有一些偏高,不过其主要的物理化学指标基本达到了醋化用浆粕的要求。然而相比高级木浆,高级竹浆有较高的结晶度、晶粒尺寸以及更多的氢键,这会影响到后续的反应性能,因而乙酰化之前,必须进行合适的预处理增加醋化反应的可及性。研究了温度、时间和催化剂用量对高级竹浆的高温乙酰化反应的影响,发现增加温度和提高催化剂的用量均可增加醋酸纤维素的取代度,不过温度对聚合度的影响更为显著。因而我们选择了乙酰化反应采用较低的温度(50℃)相对较高的催化剂用量3%。在预处理方式中,利用醋酸和1%的硫酸活化具有最好的效果,可以保持较高的聚合度而缩短反应时间。高级竹浆直接乙酰化后,反应介质中有一些不溶性残余,这会影响反应溶液的透光度,导致沉淀后的三醋酸纤维素呈现淡黄色。分析表明这些对不溶性残余的形成与溶解性能较差的木聚糖二醋酯(XDA)有关,通过加入少量XDA的良溶剂如1,2-二氯甲烷到高级竹浆的乙酰介质中,能在分子水平溶解这些不溶性残余,而使三醋酸纤维素的白度有了明显的改善,此外,由于溶液中XDA溶解状态的改变,沉淀后产物的结晶度和热性能有了提高。不过高级竹浆直接乙酰化后水解得到的二醋酸纤维素的物理性能如聚合度、白度和丙酮溶液中的颗粒物的测试表明其性能接近商业烟用二醋片,具有较高的质量,这可能是由于木聚糖在高级竹浆中的含量不是很高(3.7%),经过硫酸催化水解后,大部分的XDA会被水解。TG分析表明三醋酸纤维素的热稳定性要好于二醋酸纤维素,乙酰基的存在能够增加醋酸纤维素的热稳定性;DTA分析显示三醋酸纤维素的熔融峰和分解峰发生了重叠,而二醋酸纤维素因为结晶不完善,晶区分子链和链段可较自由的活动,因而其熔融峰在较低温度出现,拉开了分解峰和熔融峰之间的距离;不过二醋酸纤维素的玻璃化转变区比较明显且Tg高于三醋酸纤维素。高级竹浆合成的二醋酸纤维素能够顺利纺丝,纤维的拉伸性能也表明其完全适合作为烟用醋酸纤维。其动态力学分析(DMA)显示,除了a转变(玻璃化转变)外,玻璃化温度以下的β~*和γ松弛与纤维的含水有关,而β松弛可能是由主链的局部曲柄运动引起的,不过也不能排除侧基和主链协同运动的可能性。本文对降解二醋酸纤维的研究表明醋酸纤维在碱处理过程中的重量损失主要是由去乙酰化作用,这种去乙酰化促进了随后的酶降解,当取代度降低到0.8时醋酸纤维的酶降解增加最为显著。~1HNMR分析显示只有在较低氢氧化钠浓度,碱溶液中的去乙酰化反应才与醋酸纤维素三个位置酯基的反应性能有关,但是没有沿着理论上的顺序进行,碱溶液中醋酸纤维脱乙酰化产物的取代度并不均一,而是有一定的分布,这些产物经过纤维素酶处理后,由于类纤维素结构的低取代度的醋酸纤维素的降解,取代度会增加,这也被红外光谱和X衍射对结晶结构的分析所证明。更多还原

【Abstract】 Cellulose triacetate（CTA）can be used for cellulose acetate（CA）with a degree of substation（DS）above 2.9,which is obtained through acetylation for all three hydroxyl groups of anhydroglucose unit in cellulose.Cellulose diacetate（CDA）with a DS of 2.4-2.6 can be obtained by hydrolysis for CTA.The field of application for CTA includes photographic film base,plastics,textile fiber,membrane materials,and CDA can be used as cigarette filters and textile fiber.Original materials used for preparing cellulose acetate are generally high quality celluloses with an a-cellulose content of more than 95%,therefore,cellulose materials capable of being used for preparing CA are usually cotton linters,as well as high-grade wood dissolving pulps,which are applied in commerce widely.Bamboo has the advantages of low cost and regeneration,but there is no report about bamboo pulps used in CA preparation.High-grade bamboo dissolving pulp for CA（high-grade bamboo pulp）with a higher a-cellulose content,degree of polymerization（DP）and brightness was prepared in the study through the process flows of acidic prehydrolysis,twice sulphate cook with moderate temperature,and bleaching using pretreatment of xylanase and DMD,and the optimal conditions in these flows was determined.The investigations showed that suitable enhancement of sulfidity can improve selectivity of delignify in cooking and avoid degradation of carbohydrate.The increment of brightness in the stage of xylanase and DMD treatment occupied for 15.29%of the total of the increment in whole bleaching process;the decrease of Kappa number occupied for 37.87%of the total of decrease in whole bleaching process;while the decrease of intrinsic viscosity only occupied for 13.77%the total of decrease in whole bleaching process.Therefore,the two treatments can reduce cellulose degradation,enhance delignification,and improve the brightness of bamboo pulp.Hydrolytic action of xylanase for hemicellulose was demonstrated by FTIR,and X-ray diffraction proved the delignification of DMD for bamboo pulp because of complete disappearance of the diffraction peak at 2θof 29.4（?） attributed to inorganic constituents after DMD treatment.The change of chemical compositions on the surface of bamboo pulps in each stage of bleaching was analyzed in detail by monitoring the ratio of O/C and the contents of four components of C1s indicative of C atoms with 0,1,2 or 3 bonds to neighboring O atom（s）.Extractive content on the surface of pulp increased markedly during the stage of H₂O₂ bleaching, and the surface coverage of extractives for the pulp of final bleaching was more than that of lignin.DMD treatment resulted in the decrease of crystallinity and crystallite size of bamboo pulp during bleaching;however,they increased in other stage of bleaching,and on the whole crystallinity and crystallite size of pulp after bleaching were more than these before bleaching.This entirely removing of lignin and hemicellulose in high-grade bamboo pulp can be seen demonstrated by SEM observation,because of full of grooves,splits, apertures,filaments and fibrils in surfaces of the pulps,and large numbers of apertures and cracks with uneven sizes distributing over the lengthwise section.As compared with high-grade hardwood pulp used for preparing CA,in spite of higher contents of xylan,ash and extractive in high-grade bamboo pulp,its physical and chemical properties came up to the requirement for acetylation;however,the higher crystallinity and crystallite size,as well as more hydrogen bond can affect its reactivity of acetylation.The influence of temperature,time and catalyst to acetylation of high-grade bamboo pulp was investigated,and found that the increases of both temperature and catalyst could raise the DS of CA,but increasing temperature is more prominent for the decrease of the DP.Therefore,a lower temperature（50℃）and a higher catalyst dosage were adopted in acetylation of high-grade bamboo pulp.Among various pretreatment modes,it was optimal for the activation of the pulp to use acetic acid and 1%sulfuric acid because reactive time of acetylation could be reduced while CA prepared maintained a higher DP.Some insoluble residues remained in acetylation medium of high-grade bamboo pulp,which resulted in the decrease of the transmittance of reaction solution and the brightness of CTA prepared. Characterization of the insoluble residue indicated that its formation was associated with XDA,which has poor solubility in acetylation medium,An addition of good solvent of XDA such as 1,2-dichloroethane to acetylation medium of high-grade bamboo pulp could release the aggregation of XDA and CTA and dissolve the insoluble residue,which led to the improves of the properties of CTA prepared such as brightness,crystallinity and thermal stability.However,measuring the properties such brightness,DP and particles in acetone for CDA prepared by acetylation and subsequent hydrolysis for high-grade bamboo pulp,indicated that it had high quality and had access to commercial CDA for cigarette filter because of a lower content of xylan in high-grade bamboo pulp（3.7%）,most of which can be hydrolyzed by sulfuric acid catalysis.TG analysis indicated that thermal stability of CTA was more than that of CDA and the existence of acetyl group could improve thermal property of CA.The two peaks corresponding to crystallization and melting overlapped in DTA curve of CTA,while owing to less perfect and smaller crystallites in CDA,more facile motility for the molecule chains or chain segment within its crystalline region resulted in the melting peak appearing in a lower temperature,and the interval between the melting and decomposition temperature enlarged,accordingly;on the other hand as compared with CTA,the peak corresponding to gamma transition for CDA was more conspicuous and Tg appeared in a higher temperature.CDA prepared from high-grade bamboo pulp could be spinned favorably,and tensile properties of the CDA fibers spinned indicated of suitability for cigarette filter. DMA of the fibers demonstrated that a-relaxation was related to the glass-to-rubber transition;theβ^* shoulder was due to loss of moisture;theβrelaxation is tentatively assigned to local motions of the main chain（glucose unit）;the low-temperatureγrelaxation was humidity-dependent.The study on degradation of CDA fibers showed that weight loss of CA fibers immersed in NaOH solution chiefly depended on acetylation,and alkaline treatment promoted the degradation of CA fibers in cellulase solution by reason of deacetylation,especially when DS of CA fibers reached 0.8,cellulase degradation increased most markedly.¹NMR spectra suggested that only in a lower NaOH concentration（=0.25 N）deacetylation reaction was affected by the reactivities of ester groups at position 2,3 and 6 in anhydroglucose unit,but did not follow the theoretical trend in the three positions.Moreover,the DS for polymer molecules in CA fibers were dispersive after alkaline treatment in heterogeneous condition and the DS of the product increased during sequent cellulase degradation.This was also demonstrated by the result of IR analysis and X-ray diffraction.更多还原