【作者】 李伟；

【导师】 刘守新；

【作者基本信息】 东北林业大学 ， 林产化学加工工程， 2012， 博士

【摘要】 纳米纤维素(NCC)以其大量、可再生、可生物降解以及优良的力学性能,不仅在材料合成上展示出了极高的杨氏模量和强度等性能,加之其具有生物材料的轻质、可降解、生物相容及可再生等特性,使其在高性能复合材料中显示出巨大的应用前景。目前,NCC主要由植物原料通过可控的化学、物理或生物的方法制得,一些特殊的微生物或被囊动物也可被用作NCC的制备原料。如何拓展NCC的制备原料,以及通过优化制备方法,制备出生产成本低,高效快速,绿色的NCC对其进一步的应用有着重要的理论及指导意义。本文旨在以不同纤维素为原料,采用超声辅助酸水解以及高强超声法制备出不同形貌的NCC。以制备的NCC为增强剂用于制备PVA复合薄膜材料；以制备的长丝状的NCC为模板剂制备磁性纳米纤维材料；以制备的棒状NCC为模板剂制备球形纳米TiO2。研究中采用扫描电子显微镜,透射电子显微镜,X射线衍射,热重分析,低温液氮吸附以及振动样品磁强计分析等手段对制备的NCC以及复合材料进行表征。本文首先对NCC的制备以及应用研究进展进行了综述,在此基础上介绍了本课题的研究背景,方案,内容,创新点以及主要的研究方法。以漂白硫酸盐针叶浆(BSKP)为原料采用超声辅助酸水解的方法制备出NCC。超声处理能够引起纤维表面的侵蚀、折叠和细纤维化等变化,这样的变化有利于酸分子更好的渗透到纤维内部同时增加了酸分子与纤维的反应点。由超声辅助酸水解制备的NCC的直径为10-20nm、平均长度为96nm。所制备的NCC主要含有三个热降解过程,其热稳定性降低的主要原因是由于NCC的纳米尺寸和表面含有的大量末端链。同时NCC降解初始温度较低,但其整个降解过程覆盖了一个较宽的温度范围。其最终炭残渣量为43%。所制备的NCC与表面化学结构与BSKP相同,其结晶度由BSKP的74.9%提高为82.3%。以微晶纤维素(MCC)为原料采用高强超声法制备出棒状NCC,所制备的NCC的直径为10-20nm,长度为20-250nm。随着超声时间的增加,NCC的结晶度呈降低的趋势；但超声功率对结晶度的影响变化不大。纤维素中无定形区和结晶区的结构在超声的作用下能够同时被破坏除去。以NCC为增强剂经不同的填加量所制备的聚乙烯醇(PVA)复合膜材料在各个温度下的存储模量都有了不同程度的增加。填加量为4%复合膜的存储模量在30℃和100℃下分别是纯PVA的1.76和1.54倍；填加量为8%复合材料的存储模量在30℃和100℃下分别是纯PVA的2.4和1.73倍。以硫酸盐漂白阔叶浆(BHKP)为原料采用化学预处理结合高强超声法制备出长丝状的NCC。所制备的NCC的直径为20-70nm,长度约500μm。与碱处理后的BHKP相比,NCC的结晶度略有下降,表明结晶区遭到破坏的比例相对较多。与BHKP相比,NCC的热稳定性稍微有所下降,主要是由于NCC表面所含有羟基量的增加。将NCC作为增强剂制备出光透明的PVA复合膜材料,当NCC填加量为4%时,既能够保证复合膜材料的增强效果,同时还保持了良好的透光性。以碱性过氧化氢化机浆(APMP)为原料采用化学预处理结合高强超声法制备出长丝状NCC。所制备的NCC直径为20-90nm,长度约500μm。 APMP经过除木素和碱处理过程,其结晶度和热稳定性得到了提高；经过超声处理所制备的NCC的结晶度仍然有一定的升高,证明在处理过程中,无定形区去除的比例更高。采用NCC气凝胶为模板制备出CoFe2O4铁氧体磁性纳米复合材料,随着反应浓度的增加,复合材料中磁性颗粒所占的比例也随着增加,同时磁性也随着增强。以棒状NCC为模板剂,经酸催化水解法制备出了球形介孔TiO2(SP-TiO2)。所制备Ti02为直径100-200nm的规整球形颗粒,单个球形颗粒由粒径为10-20nm的Ti02小晶粒组成SP-TiO2平均介孔孔径在8.21-13.48nm之间,随煅烧温度升高而增大。NCC长链结构之间羟基键合所形成的狭小空间构成的微反应器,可有效限制Ti02前躯体的生长和团聚,诱导Ti02前躯体晶粒自组装成球形结构,并抑制由锐钛矿相向金红石相转变。600℃煅烧温度SP-TiO2表现出最高活性,对苯酚降解率达89%。更多还原

【Abstract】 Nanocrystalline cellulose (NCC) was a hotspot in nanotechnology field for its advantages of abundant, renewable, biodegradable and excellent mechanical properties. It had high Young’s modulus and strength, and also the properties of lightweight, biodegradable, biocompatible and renewable had exhibited great application prospects in preparing the high-performance composite materials. NCC was prepared form different plant materials through controlling chemical, mechanical or biologic methods. Some special bacterial and tunicate were also excellent materials to prepare NCC. How to expand raw materials, as well as through optimizing the preparation method to produce low costs, efficient and environmental friendly NCC had great theoretical meaning in further application.This paper aimed to preparing NCC with different morphologies through using different cellulose materials via ultrasound assisted method. PVA composites were prepared using rod-shaped and the long web-like NCC as enhanced materials. Magnetic nanomaterials were prepared using long web-like NCC as matrix. Mesoporous TiO2spheres prepared by an acid catalyzed hydrolysis method using rod-shaped NCC as template. SEM, TEM, XRD, DRS, N2adsorption isotherm and VSM were used for characterization of NCC, nanocomposites and SP-TiO2photocatalyst.Nanocrystalline cellulose (NCC) with small particle size and high crystallinity was prepared via the combined method of ultrasonication and acid hydrolysis from bleached softwood kraft pulp (BSKP). The analyses revealed that rod-shaped NCC particles with diameter of10to20nm can be obtained. Ultrasonication can induce cellulose folding, surface erosion, and external fibrillation of BSKP, together with the shorter average length of NCC (96nm) than that prepared without ultrasonication (150nm). Due to the smaller size and larger number of free ends of chains, the thermal stability of NCC was lower than BSKP. The degradation of BSKP exhibited one significant pyrolysis stage within the range of300to420℃. In contrast, UH-NCC exhibited three pyrolysis stages within the range of210to450℃. NCC prepared with ultrasonication decomposed at lower temperature and over a wider temperature range, together with higher char yield of43%(compared with27%for that without ultrasonication). The obtained NCC had similar surface chemical structures but higher crystallinity (82.3%) compared with that of the starting BSKP (74.9%).Rod-shaped NCC was prepared from microcrystalline cellulose (MCC) using the purely physical method of high-intensity ultrasonication. The reinforcement capabilities of the obtained NCC were investigated by adding it to poly (vinyl alcohol)(PVA) via the solution casting method. The results revealed that the prepared NCC had a rod-shaped structure, with diameters between10-20nm and lengths between50-250nm. X-ray diffraction results indicated that the NCC had the cellulose I crystal structure similar to that of MCC. The crystallinity of the NCC decreased with increasing ultrasonication time. The ultrasonic effect was non-selective, which means it can remove amorphous cellulose and crystalline cellulose. Because of the nanoscale size and large number of free-end chains, the NCC degraded at a slightly lower temperature, which resulted in increased char residue (9.6%-16.1%), compared with that of the MCC (6.2%). The storage modulus of the nanocomposite films were significantly improved compared with that of pure PVA films. The modulus of PVA with8wt%NCC was2.40×larger than that of pure PVA.Optically transparent reinforced poly (vinyl alcohol) composites were prepared using NCC from bleached hard kraft pulp (BHKP) isolated by high-intensity ultrasonication. The obtained NCC was used to reinforce PVA to make nanocomposites via the solution casting method. The results revealed that the prepared NCFs were long web-like structure, with diameters between20-80nm and lengths more than500μm. X-ray diffraction results indicated that the NCFs had the cellulose I crystal structure similar to that of BHKP. The crystallinity of the NCFs increased from77.3%(BHKP) to78.3%. The initial pyrolysis temperature shifted to a lower temperature than that of the Al-CFs, because of increased the number of hydroxyl groups of NCFs. The tensile modulus and Young’s modulus of PVA composites were significantly improved with the NCC loading of4%which was1.86×and1.63×that of neat PVA and also retained an excellent transparency.NCC aerogels were prepared from poplar alkaline peroxide mechanical pulp (APMP) using physical ultrasonication method. As raw materials, the unique mechanical effects of APMP cause the fiber folding and loose during the pulping process, which was beneficial to further chemical purification and subsequent treatment for long and entangled NCC. The obtained NCC exhibited higher crystallinity (77.8%) compared with that of APMP (72.6%) together with diameters range from20to90nm and self-assembled to network. The primary thermal degradation of NCC occurred at331.5℃. The prepared NCC network aerogels acted as a novel matrix which can prevent the growth and aggregation of ferromagnetic CoFe2O4nanoparticles. The magnetic properties were all increased with increasing the reaction concentration of FeSO4/CoCl2salt.Mesoporous nanosize TiO2spheres (SP-TiO2) were prepared using rod-like NCC as template. The results showed that SP-TiO2was uniform in size with a diameter of100-200nm. SP-TiO2was composed of smaller crystal particles (10-20nm). The average mesoporous pore diameter of SP-TiO2was8.2-13.5nm, which increased with increasing calcination temperature. A nano-scale reactor that was formed by bonding between the hydroxyl groups of NCC long-chain can inhibit the growth and aggregation of the TiO2precursor, promote its self-assembly into spherical structure, and inhibit the phase transformation from anatase to rutile. SP-TiO2prepared at600℃exhibited the highest activity with the phenol degradation percentage of89%.更多还原