酶处理结合机械法分离纳米纤维素的特性研究

发布时间：2018-06-27 12:20

本文选题：酶处理 + 机械法　；参考：《南京林业大学》2015年硕士论文

【摘要】：纳米纤维素具备比强度高、热膨胀系数低、易化学改性、成本低、可再生、可生物降解、环境友好等特性,是一种理想的用于增强聚合物的材料。使用纳米纤维素改性的聚合物材料具备良好的生物可降解性,可以替代传统的石油化工产品等一些不能生物降解的聚合物材料。传统的酸解法制备纳米纤维素水解剧烈,对环境影响大,对反应设备要求高,因此开发一种简单、低成本和对环境友好的纳米纤维素制备方法极为重要。本研究以纸浆为原料分离纤维素,利用提纯纤维素酶使纤维素在温和的条件下水解,并结合研磨和高压均质机械方法制备纳米纤维素,利用现代分析技术表征其形态和性能;利用制备的纳米纤维素添加到聚乙烯醇树脂中制备纳米纤维素/聚乙烯醇复合薄膜,研究其力学性能、光学特性和电学特性,结果表明:(1)最佳木聚糖酶处理条件下,产物中纤维素相对含量为95.45%;最佳碱处理条件下,产物纤维素相对含量高达98.12%。碱处理提纯的纤维素纯度更高。(2)纸浆原料的纤维素结晶度Cr I值为77.50%。在最优木聚糖酶处理条件下产物Cr I达到81.93%;在最佳碱处理条件下,纸浆中纤维素结晶度Cr I值上升到85.89%。木聚糖酶处理和碱处理都没有使纤维素的晶型发生转变。(3)经硫酸铵分级沉淀法提纯之后,内切葡聚糖酶的比活力显著提高,由0.135IU/mg提高到0.245IU/mg,并且具有高达84.57%的酶活回收率。纤维素酶和提纯纤维素酶的最佳酶添加量均为30IU/g底物。在同样的酶添加量条件下,提纯纤维素酶的酶解得率要低于纤维素酶的酶解得率;无论是提纯后的纤维素酶还是纤维素酶混合酶体系作用于碱法纤维素原料,酶解得率均随着酶解时间的增加而变大,在24h之后增长极为缓慢。(4)经过提纯纤维素酶处理后,纤维素晶型仍然保持为纤维素I型。纤维素的结晶度值随着酶解时间的延长而增大;通过提纯纤维素酶处理,纤维素的平均聚合度有显著下降。纤维素分子的尺寸粒径大小都有很大程度的降低。(5)提纯纤维素酶处理,以及研磨高压均质处理,都没有破坏纤维素的化学结构和热稳定性。酶处理前后和机械处理后的三种纤维素在水分散体系中其表面显电负性。经最优处理工艺条件的提纯纤维素酶处理之后和后续机械研磨均质处理,纤维水分散体系的Zeta电位绝对值分别由16.63m V增大到17.16m V和18.25m V;(6)经提纯纤维素酶处理以后,纤维素原料纤维长度急剧减短,被酶水解为短棒状的纤维,长径比小;纤维表面多处出现了较为明显的断裂和缺口。再经研磨结合高压均质处理后纤维丝束之间互相缠绕内部纤维团聚,直径达到纳米级别。(7)纳米纤维素对PVA树脂有增强作用。纳米纤维素在纳米纤维素/聚乙烯醇复合薄膜中添加量的增加会使得薄膜复合材料的拉伸强度增大和断裂伸长率降低。纳米纤维素的添加量达到5%时,复合材料的拉伸强度增大到105MPa,比纯PVA树脂的拉伸强度相比提升了10.2%;断裂伸长率降低到12.0%,相比纯净的PVA树脂的断裂伸长率降低了57.3%。与纯净PVA薄膜相比,纳米纤维素/聚乙烯醇复合薄膜的透光性下降,由95.92%降低到纳米纤维素添加量为5%时的88.2%,减弱幅度较低。纳米纤维素的添加量增加会引起纳米纤维素/聚乙烯醇复合薄膜表面电阻率的增加,并对其相对介电常数和损耗角正切值等介电性能有影响。
[Abstract]:Nanoscale has the characteristics of high specific strength, low thermal expansion coefficient, easy chemical modification, low cost, renewable, biodegradable, environmental friendly and so on. It is an ideal material for strengthening polymers. The polymer materials modified by nanoscale have good biodegradability and can replace traditional petrochemical products. It is very important to develop a simple, low cost and environmentally friendly nanoscale cellulose preparation method, which is very important for the preparation of nanosulcose, which is simple, low cost and environmentally friendly. This study uses pulp as raw material to separate cellulose and use purification of cellulose. Cellulose was hydrolyzed under mild conditions and nanoscale was prepared by grinding and high pressure homogenization. The morphology and properties of the cellulose were characterized by modern analytical techniques. Nanosol / polyvinyl alcohol composite films were prepared by adding nanoscale to the polyvinyl alcohol resin. The mechanical properties and optical properties of the nanofibers were studied. The results showed that: (1) the relative content of cellulose in the product was 95.45% under the optimal xylanase treatment conditions, and the purity of cellulose was higher than that of 98.12%. alkali treatment under the best alkali treatment conditions. (2) the Cr I value of fibrin crystallinity of pulp raw material was 77.50%. at the optimal xylanase treatment conditions. The lower product Cr I reached 81.93%. Under the optimum alkali treatment conditions, the crystallinity of cellulose Cr I in pulp increased to 85.89%. xylanase treatment and alkali treatment. (3) after purification by ammonium sulfate fractionation, the specific activity of the endosanase was significantly increased from 0.135IU/mg to 0.245IU/mg. The optimum enzyme activity of cellulase and purified cellulase is 30IU/g substrate. The rate of enzymatic hydrolysis of cellulase is lower than that of cellulase in the same amount of enzyme addition. The cellulase or cellulase mixed enzyme system after purification is used in the alkali process. Cellulose raw material, the rate of enzymatic hydrolysis increased with the increase of enzyme hydrolysis time. After 24h, the growth of cellulose was very slow. (4) after purification of cellulase, the crystalline form of cellulose remained the I type of cellulose. The crystallinity of cellulose increased with the prolongation of enzymolysis time; the average degree of polymerization of cellulose by purification of cellulase and the average degree of polymerization of cellulose were obtained. The size of the cellulose molecules decreased greatly. (5) the purification of cellulase treatment, and the high pressure homogenization treatment, did not destroy the chemical structure and thermal stability of the cellulose. The surface of the three cellulose in the water dispersive system after and before and after the enzyme treatment was the best. The absolute value of Zeta potential of fiber water dispersion system was increased from 16.63m V to 17.16m V and 18.25m V, after purification of cellulose enzyme treatment and subsequent mechanical grinding. (6) after purification of cellulase, the fiber length of cellulose fiber was shortened sharply, and the enzyme was hydrolyzed into short rod like fiber, and the ratio of length to diameter was small. There are more obvious breakages and gaps on the surface of the fiber. The fiber bundles are intertwined with the fiber bundles after the grinding and high pressure homogenization. The diameter reaches the nanometer level. (7) the nano cellulose has an enhanced effect on the PVA resin. The addition of nanofibric to the nanofibrine / polyvinyl alcohol composite film will be increased. The tensile strength and elongation at break of the film composite were increased and the elongation at break was reduced. The tensile strength of the composite was increased to 105MPa when the amount of nanoscale was 5%, compared with the tensile strength of the pure PVA resin, the elongation at break was reduced to 12%, and the elongation at break of the pure PVA resin decreased by 57.3%. and purity. Compared with the PVA film, the transmittance of nanoscale / polyvinyl alcohol composite film decreased from 95.92% to 88.2% when the nano cellulose was added to 5%. The increase in the addition of nanoscale would cause an increase in the surface resistance of the nano cellulose / polyvinyl alcohol composite film, and the relative dielectric constant and loss angle of nanoscale cellulose / polyvinyl alcohol composite film. The dielectric properties such as tangent value have an effect.
【学位授予单位】：南京林业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ352.1;TB383.1

【参考文献】