硫酸水解法和过硫酸铵氧化法制备纳米纤维素及其气凝胶的特性研究

发布时间：2018-06-16 08:15

本文选题：纳米纤维素 + 醇凝胶　；参考：《南京林业大学》2017年硕士论文

【摘要】：气凝胶作为一种新型材料,具有很多优良的性能,如高比表面积、高孔隙率、低密度、低导热系数、低介电常数、低光折射率、极强的气体吸附能力等,已被列为十大热门材料之一。目前气凝胶的研究多集中在有机、无机和有机-无机复合气凝胶。纤维素气凝胶作为新生的第三代气凝胶材料,不仅具备了传统气凝胶的优良性能,同时还融入了纤维素的一些优异性能,如原料充足、可降解、可再生、生物相容性好等,使其具有广阔的应用前景。本论文以纸浆为原料,分别采用硫酸水解法和过硫酸铵氧化法制备纳米纤维素纳米晶须(Cellulose Nanocrystalline(CNC))和纳米纤维(Cellulose Nanofiber(CNF)),并对两种纳米纤维素性能进行分析和表征;分别以纳米纤维素纳米晶须和纳米纤维为原料,采用无机盐凝胶法制备水凝胶,通过溶剂置换得到醇凝胶,最后利用超临界干燥和冷冻干燥制备出球形气凝胶,探讨两种纳米纤维素醇凝胶的最佳超临界干燥工艺,并对气凝胶的性能进行分析和表征。具体结论如下所示:1)两种纳米纤维素依然保持纤维素Ⅰ型结构,结晶度增加,热稳定性降低。纳米纤维素纳米晶须的结晶度为75.4%,热降解初始温度(T_0)和最大失重率温度(T_(max))分别为200℃和265℃,直径主要分布在24-35nm范围内,长度在250-400nm之间,表面引入磺酸基团,为两端尖的短棒状结构;纳米纤维的结晶度为68.9%,热降解初始温度(T_0)和最大失重率温度(T_(max))分别为210℃和344℃,直径主要分布在50-70nm之间,长度为1-2微米,表面部分羟基被氧化成了醛基和羧基,为长纤维状。与纳米纤维素纳米晶须相比,纳米纤维的热降解初始温度和最大失重率温度较高,直径和长度较大,但结晶度较低,两种纳米纤维素的形状也不同。这些差异主要因为制备方法的不同所导致。2)质量分数为1.5%的CNC醇凝胶最佳超临界CO_2干燥工艺为:45℃、2h、12MPa,质量分数为2.5%和3.5%的CNC醇凝胶最佳超临界CO_2干燥干工艺为:45℃、3h、12MPa;质量分数为1.5%的CNF醇凝胶最佳超临界CO_2干燥工艺为:50℃、4h、13MPa,质量分数为2.5%和3.5%的CNF醇凝胶最佳超临界CO_2干燥工艺为:50℃、2h、13MPa。3)采用万能力学实验机测定其力学性能:超临界CO_2干燥后的质量分数分别为1.5%、2.5%、3.5%的CNC气凝胶和CNF气凝胶,其压缩强度分别为0.32MPa、0.40MPa、0.46MPa和0.37MPa、0.67MPa、0.77MPa;经液氮冷冻干燥得到的质量分数分别为1.5%、2.5%、3.5%的CNF气凝胶,其压缩强度分别为0.85、1.32,和1.47MPa。纳米纤维素气凝胶的压缩强度随着纳米纤维素质量分数的增加而增加。4)利用扫描电子显微镜(Sweep Electron Microscope简称SEM)对其内部微观形貌进行观察:超临界CO_2干燥得到的气凝胶内部为三维网络结构,冷冻干燥得到的气凝胶内部为三维层状结构,且纳米纤维素质量分数越高,内部结构越密实。5)通过比表面积分析仪对纳米纤维素气凝胶的吸附量和孔径分布进行分析:纳米纤维素气凝胶的N_2等温吸附线均符合第Ⅱ类等温吸附线,以多层吸附为主,孔径主要以介孔为主。随着纳米纤维素质量分数的增加,吸附量增加,孔径减小。6)当纳米纤维素质量分数相同时,CNC气凝胶的干燥收缩率、内部孔径大于CNF气凝胶,其压缩强度、比表面积比CNF气凝胶小;通过冷冻干燥得到的纤维素气凝胶的密度、压缩强度和收缩率比超临界CO_2干燥得到的气凝胶大,但比表面积和内部孔径小于超临界CO_2干燥得到的气凝胶;随着纳米纤维素质量分数的增加,醇凝胶的干燥收缩率降低,气凝胶的密度升高
[Abstract]:As a new material, aerogels have many excellent properties, such as high surface area, high porosity, low density, low thermal conductivity, low dielectric constant, low refractive index, and very strong gas adsorption capacity. The aerogels have been listed as one of the ten most popular materials. As a new third generation aerogel, gelatin. Not only has the excellent performance of the traditional aerogels, but also integrates some excellent properties of cellulose, such as sufficient raw material, biodegradability, renewable, good biocompatibility and so on, so that it has a broad application prospect. This paper uses pulp as raw material, using sulphuric acid water respectively. Nanofibric nanofibers (Cellulose Nanocrystalline (CNC)) and nanofibers (Cellulose Nanofiber (CNF)) were prepared by solution and ammonium persulfate oxidation. The properties of two kinds of nanofibers were analyzed and characterized. Hydrogels were prepared by nanosilet nanofibers and nanofibers respectively by inorganic salt gel method. The spherical aerogels were prepared by supercritical drying and freeze-drying. The optimal supercritical drying process of two nanosilet gels was investigated and the properties of aerogels were analyzed and characterized. The specific conclusions are as follows: 1) two nanosilics still maintain the structure and crystallinity of cellulose type I. The crystallinity of nanoscale nanofibers was 75.4%, the initial temperature of thermal degradation (T_0) and the maximum weightlessness temperature (T_ (max)) were 200 and 265 C respectively. The diameter of nanofibric nanofibers was mainly in the 24-35nm range, the length was between 250-400nm and the surface was introduced into the short rod like structure at both ends, and the crystallization of nanofibers. The initial thermal degradation temperature (T_0) and the maximum weight loss temperature (T_ (max)) are 210 and 344 C respectively, the diameter is mainly between 50-70nm, the length is 1-2 micron, the surface hydroxyl group is oxidized to aldehyde group and carboxyl group, and it is long fiber. Compared with nanofiber nanofibers, the initial temperature and maximum thermal degradation temperature of nanofibers are compared with nanofibers. The weight loss rate is higher, the diameter and the length are larger, but the crystallinity is low, and the shape of the two kinds of nanoscale is different. The difference is mainly due to the best supercritical CO_2 drying process of the CNC alcohol gel with the mass fraction of.2) with the mass fraction of 1.5%, which is 45, 2h, 12MPa, the CNC alcohol gel with the mass fraction of 3.5% and the optimum overcoming of the gel. The dry drying process of boundary CO_2 is: 45 C, 3h, 12MPa; the optimum supercritical CO_2 drying process of CNF alcohol gel with a mass fraction of 1.5% is: 50 C, 4h, 13MPa, the optimum supercritical CO_2 drying process of CNF alcohol gel 2.5% and 3.5%: 50 C, 2h, 13MPa.3) using the universal mechanical test machine to determine its mechanical properties: the quality after supercritical CO_2 drying The compression strength of CNC aerogels and CNF aerogels of 1.5%, 2.5%, 3.5%, respectively, 0.32MPa, 0.40MPa, 0.46MPa and 0.37MPa, 0.67MPa, 0.77MPa, and CNF aerogels of 1.5%, 2.5%, 3.5%, respectively by liquid nitrogen freeze drying, are divided into 0.85,1.32 and compressive strength of 1.47MPa. nanoscale aerogels. With the increase of the mass fraction of nanoscale cellulose (.4), the internal micromorphology was observed by scanning electron microscope (Sweep Electron Microscope for short). The internal microstructure of the aerogel obtained by supercritical CO_2 drying was three-dimensional network structure, and the interior of the aerogel obtained by freeze-drying was three-dimensional and nanofiber quality. The adsorption capacity and pore size distribution of nano cellulose aerogels are analyzed by the surface area analyzer (.5). The N_2 isothermal adsorption line of nanoshogel aerogels conforms to class II isothermal adsorption line, and the main pore size is mesoporous. With the mass fraction of nanoscale. When the mass fraction of nanoscale is the same, the drying shrinkage of CNC aerogels is larger than that of CNF aerogels when the mass fraction of nanoscale is the same. The compressive strength and specific surface area of the aerogels are smaller than that of the CNF aerogels, and the density, compression strength and shrinkage rate of the cellulose aerogels obtained by freeze-drying are obtained than that of the supercritical CO_2 dry CO_2. Aerogels are larger, but the specific surface area and inner pore size are less than the aerogels obtained by supercritical CO_2 drying. With the increase of the mass fraction of nanoscale, the drying shrinkage of the alcohol gel decreases and the aerogel density increases.
【学位授予单位】：南京林业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TQ352.79;TQ427.26

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