微晶纤维素的微细结构研究

研究了各种纤维素材料及不同酸浓度水解制成的微晶纤维素的聚合度，并用X-射线衍射法研究结晶度、结晶形态、晶粒尺寸和颗粒大小；用透射电镜（TEM）观察颗粒形状和大小，发现不同纤维素材料达到平衡聚合度（LODP）的盐酸浓度略有不同；在酸水解过程中纤维素的结晶形态、晶粒尺寸和颗粒大小基本不变，而且用X-射线衍射及TEM测出的颗粒不是纤维素晶粒，而是微原纤。     

稻草微晶纤维素的制备及其形态结构

研究从稻草制备微晶纤维素的工艺以及所制得微晶纤维素的形态结构。研究结果表明,除杂稻草经过质量分数为0.015的氢氧化钠水溶液蒸煮约2小时便可除去绝大部分的木素,所得纤维素用浓度为2mol/L盐酸在80～100℃的温度下水解1—2小时即可达到所谓平衡聚合度(LODP),分别用X—射线仪和电镜等对其结晶度、晶粒尺寸和外观形态等进行了表征。     

微波-NaOH预处理稻杆纤维素的实验研究

利用正交试验对稻秆进行微波-NaOH联合预处理,通过硝酸-乙醇法测定处理后的稻秆中纤维素所占比例,考察微波功率、处理时间、固液比、NaOH溶液浓度对稻秆纤维素所占比例的影响。通过扫描电镜对处理前后的稻秆进行形貌观察,发现处理后的稻秆仍为杆状结构,但表面呈现深度腐蚀状。X-射线衍射实验表明：经过微波-NaOH处理的稻秆其结晶形态未发生明显变化,仍是结晶相和非结晶相两相共存,但处理后的试样结晶度显著增加、微晶尺寸减小。     

乙醇再生微晶纤维素的分级及其结构表征

在微晶纤维素（MCC）的Na OH/尿素溶液中加入不同质量的无水乙醇进行分级沉降，得到分级再生微晶纤维素。通过黏度法测定了再生微晶纤维素的聚合度，采用FTIR、XRD、XPS、TG和SEM对再生微晶纤维素的结构、结晶度、热稳定性和形貌进行了表征。结果表明，随着分级次数的增加，再生微晶纤维素的聚合度逐渐降低，3次分级后微晶纤维素的聚合度由MCC的203降至77；微晶纤维素形貌由表面光滑的棒状纤维结构变为粗糙多孔的结构；再生微晶纤维素的晶型由MCC的Ⅰ型转变为Ⅱ型，3次分级后微晶纤维素的结晶度由MCC的65.58%降至32.05%。分级再生微晶纤维素的自由羟基增加，参与成键的羟基减少；再生微晶纤维素的热稳定性随着分级次数的增加而降低，3次分级后初始分解温度由MCC的310℃降至257℃。     

纤维素的酸处理及醋酸酯化表面改性研究

分别用HCl和H2SO4处理从棉纤维中提取的纤维素,100℃下回流水解30～60 min得到微晶纤维素(MCC),并对其进行醋酸酯化表面改性.采用X-射线衍射(XRD)、热重分析(TG)、红外光谱(IR)技术研究酸处理对MCC的聚合度、结晶度和热稳定性的影响,探讨了改性方法对产物性能的影响.结果表明,纤维素微晶化后仍保持原来的晶型以及晶区和非晶区共存的微细结构,结晶度不能达到100%.扫描电子显微镜(SEM)测试结果表明,不同酸处理后所得产物的形态和热性能有所不同,MCC的最高适用温度不宜超过270℃.适宜的醋酸酯化改性条件为:硫酸和水体积比1∶8、温度60～70℃、改性处理3～5 h.改性后微晶纤维素的内部结晶区结构没有变化,在有机溶剂中的分散性得到良好的改善.     

离子液体与水混合溶剂应用于微晶纤维素溶剂液化研究

将离子液体氯化1-丁基-3-甲基咪唑（[BMIM]C1）、水、固体酸催化剂组成的混合溶剂应用于微晶纤维素的预处理过程中,并尝试把经过预处理的微晶纤维素应用于随后的溶剂液化的研究中,对经过混合溶剂处理后的微晶纤维素进行表征分析。通过测定纤维素的聚合度、官能团基变化、热重分析、结晶结构和表面结构等对微晶纤维素结构进行比较分析。通过对苯酚溶剂液化的基本表征、残渣物的结晶结构以及生成物相对分子质量的变化了解了混合溶剂对微晶纤维素的处理效果。结果表明,通过混合离子液体[BMIM]C1和水并且添加固体酸催化剂形成新的混合溶剂体系对微晶纤维素进行预处理,发现溶剂在保留纤维素主要葡萄糖单元的同时能够有效地降低聚合度。聚合度从未处理时的190降到样品[B]C1（10）的165和样品[B]C1（10）＋NR50的151。混合溶剂对非结晶或低结晶物质具有一定的溶解能力,并且对高结晶性纤维素部分的氢键结构起到破坏作用和造成整体结晶结构的歪曲。在随后的液化过程中,处理后的纤维素液化效率有所提高,在反应2min时,固体酸加混合溶剂处理的微晶纤维素液化残渣率为19％,而未处理的液化残渣率29％。表明使用了混合溶剂添加固体酸的溶剂体系对加速液化的效果更佳,预处理对最终液化生成物的性质影响不大。     

微晶纤维素的性质与应用

微晶纤维素是一种新兴的纤维素功能材料。微晶纤维素的独特性质使它在医药、食品、日用化学品等领域获得广泛的应用。本文从应用角度阐述了微晶纤维素的理化性质和形态结构，介绍了微晶纤维素的工业产品的主要应用途径。     

轻烧氧化镁的微观特征及其活性

活性是轻烧氧化镁的主要应用特性，它与轻烧氧化镁的微观结构密切相关。将新疆某粗晶菱镁矿粉在700～1 100℃煅烧制得轻烧氧化镁，对不同温度轻烧氧化镁的晶胞参数、晶粒尺寸、结晶度、比表面积、孔径分布、比孔容、平均孔径、活性和显微结构等进行表征，利用TG结合非等温反应动力学理论研究轻烧氧化镁的微粒结构，分析该微粒结构随温度变化的机理及其对轻烧氧化镁活性的影响。结果表明：从700℃至1 100℃，轻烧氧化镁晶胞参数a0缩小并趋于稳定，晶粒尺寸逐渐增大，比表面积逐渐减小，但其活性变化并不遵从这一规律，在800℃时活性最高；粗晶菱镁矿粉的热分解受相界面上的化学反应所控制，分解产物—轻烧氧化镁“假象”微粒由氧化镁微晶和贯通的气孔网络结构组成；随煅烧温度升高，氧化镁微晶的烧结影响轻烧氧化镁“假象”微粒结构，进而影响其活性；800℃轻烧试样晶粒尺寸较小，结晶度较低，比孔容较大，且由于晶格调整使其平均孔径最大，大的孔径有利于溶液进入微粒内部，促进反应进行，因此其活性最高。     

1-丁基-3-甲基咪唑氯盐离子液体水溶液对纤维素的作用

在温度90℃, 压力1 MPa条件下, 研究[C₄mim]Cl-水溶液对纤维素的溶解和结构变化的影响。在离子液体含量为60%～95%时, 无定形纤维素可以部分溶解, 并且加去离子水后有纤维素再生。经过[C₄mim]Cl-水溶液处理一段时间后, 微晶纤维素的晶型并没有发生改变, 但纤维素的结晶指数和晶粒尺寸的大小都有明显的变化, 纤维素的分子内和分子间氢键相对强度也有明显变化。离子液体含量不同对微晶纤维素的作用程度不同。     

基于溶胶-凝胶技术制备纳米纤维素的表征

通过傅里叶变换红外光谱、X射线衍射、热重、透射电子显微镜分析及激光粒度分析对基于溶胶-凝胶技术制备的纳米纤维素进行表征,结果表明原料微晶纤维素超分子结构为纤维素Ⅰ型,制备的纳米纤维素为纤维素Ⅱ型;微晶纤维素的结晶度为87.54%,纳米纤维素的结晶度为73.49%,纳米纤维素结晶度较微晶纤维素有所下降;制备的纳米纤维素热稳定性低于微晶纤维素;纳米纤维素平均粒度425 nm,粒度分布呈现正态分布;纳米纤维素长径比为5∶1～40∶1。     

Effect of low temperatures on polymorphic structures of cotton cellulose

Effects of low temperatures upon fine structures of cotton pretreated with either liquid ammonia or caustic of mercerizing strength were investigated. Temperatures of cotton after impregnation with liquid ammonia were lowered by (1) liquid nitrogen, (2) acetone–Dry Ice, (3) acetone, or (4) simple evaporation. With alkali-impregnated fabrics, temperature was lowered by immersion in liquid nitrogen. Changes in fine structure of ammonia- and alkali-celluloses were evaluated by x-ray diffraction before and after removal of each swelling reagent. After treatment with either ammonia or caustic soda, extent of crystalline modification was increased as temperature was reduced. X-ray diffractograms taken while liquid ammonia was still present indicated that the cellulose I structure of cotton sheeting was converted to cellulose III at liquid nitrogen temperatures; extent of conversion was approximately that obtained when a looser yarn structure was treated with liquid ammonia and the ammonia was removed by evaporation. When ammonia was removed with water, the cellulose I lattice was regenerated. In the presence of 23% NaOH, diffractograms indicated a significant decrease in order after a similar drop in temperature, but patterns were not of cellulose II until the NaOH was removed with water. Conversion to cellulose III or to cellulose II was achieved instantaneously when ammonia- and alkali-impregnated fabrics were immersed in liquid nitrogen.     

注射速度对制品成型结晶形态的影响

以某平板塑件为例,以聚丙烯（PP）为实验材料,通过成型取样、X射线衍射实验及数据处理技术相结合的方法研究了注射速度对制品结晶形态的影响规律及影响效应。结果表明,在正常情况下,PP塑件的结晶类型主要为α、β两种晶型;制品的结晶度随注射速度的增大存在极点,呈现倒V字形的变化趋势;制品整体取向度与晶格畸变量具有类似的变化趋势,均随注射速度的增大而增大,而晶粒尺寸的变化则与注射速度呈现负相关性;注射速度对制品晶粒的影响最为显著,结晶度影响其次,影响显著性顺序依次为晶粒尺寸>结晶度>晶格畸变>取向度>晶型,对于本试样,最佳注射速度应控制在180 mm/s。     

一种棒状纳米微晶纤维素的物性研究

通过X -射线衍射、透射电镜 (TEM)、激光光散射、示差扫描量热分析 (DSC)、热重分析 (TGA)以及红外光谱等分析手段 ,研究了一种具有纳米尺寸的棒状微晶纤维素的物理化学性质 ,着重研究了它在不同温度下的热行为。结果表明 ,由于粒径及比表面积的变化 ,这种棒状微晶纤维素的热行为与天然纤维素以及经过DMSO前处理的纤维素相比较 ,具有一些独特的性质     

Crystalline Structure of Microbial Cellulose Compared with Native and Regenerated Cellulose

Microbial cellulose is a chemically pure form of plant cellulose with an ultrafine reticulated structure. In this study, microbial cellulose was biosynthesized in a static condition by acetobacter xylinium (Gluconacetobacter xylinus) of three different mono- and disaccharides, and its crystallinity structure was investigated and compared with each other and also with the crystalline structure of cellulose existing in cotton and ordinary viscose rayon fibers. According to the results, the cellulose production efficiency of monosaccharide (glucose) was higher than that of disaccharides (lactose and sucrose). The crystalline structures of all biosynthesized cellulose were cell I and their dominant allomorphs were I(alpha), contrary to native cellulose, which was I(beta). The crystallinity amount of microbial cellulose was less than 10-15% of cotton and greater than 9% of viscose.     

Further studies on the action of alkali metal hydroxides on cotton

X-Ray diagrams revealed that the conversion of the lattice structure from cellulose I to cellulose II is substantially complete in cotton treated at 0°C with LiOH, NaOH, or KOH of approximately 5N concentration. With concentrations less than 5N, there were marked differences in the ability of these reagents to cause lattice conversions in cotton. Below a minimum concentration which is dependent on both the alkali and the treatment temperature, conversion from cellulose I to cellulose II cannot take place in cotton irrespective of the swelling caused by the reagent. We suggest that extensive swelling by one of these alkalis is not sufficient by itself to cause conversion from cellulose 1 to cellulose II and that the concentration of the alkali is of prime importance. There was no direct relation between the swelling induced in cotton by treatment with LiCH, NaOH, or KOH at 0°C and the sorption ratio of the resulting product. Also, although treatment with 5N KOH caused less swelling than that obtained with either 5N NaOH or LiOH, KOH reduced the level-off degree of polymerization (LODP) of cotton most, indicating the importance of the size of alkali cation in reducing crystallite length. In additional experiments, cotton was treated at 21°C with a solution of 4.7N NaOH to which boric acid had been added. Although the swelling of the cotton was little affected, the addition of the boric acid caused the sorption ratio of the product to decrease, whereas the LODP increased. Also conversion of the lattice structure from cellulose I to cellulose II was inhibited.     

Crystalline character of native and chemically treated egyptian cottons. II. Computation of variance of x-ray line profile and paracrystalline lattice distortions

A variance range analysis of the x-ray line profiles for seven cottons (native, ureatreated, and mercerized) has been carried out to get two estimates of the crystallite size from (1) the slope and (2) the variance intercept. Assuming the crystallite length of cellulose to be the same in ramie and native cottons under ideal conditions of growth, the relative fluctuation of the repeat length along the b-axis has been calculated for all the samples. This degree of paracrystalline lattice distortions is negatively correlated with the fiber bundle strength at zero gauge and appears to be the same as the imperfections referred to in the weak link theories of fiber strength. While the orientation parameters are also well correlated with strength, the degree of crystallinity does not seem to have any influence. Wilson's rigorous mathematical treatment of the number-average particle size, in relation to the two estimates from the variance slope and intercept as well as the particle size distribution, has been successfully applied for the first time to cotton fibers leading to a clearer understanding of crystallite size–strength relationship.     

Hydrolysis of mercerized cotton fibers due to cellulase treatment

Cotton fibers mercerized under the relaxed state were hydrolyzed with crude cellulase. The mercerization treatment examined included ammonia treatment, sodium hydroxide treatment, and two combined treatments using ammonia and sodium hydroxide. Crystalline regions of the mercerized fibers were hydrolyzed in the first step of hydrolysis. In this step, ammonia treatment decreased the crystallite size to a great extent due to the hydrolysis of the cellulose III crystalline phase. Cellulase treatment rendered the crystallite surface highly accessible to water molecules. The crystalline phase was closely related to water sorption of cellulase‐treated fibers. The sequence of treatment had an influence on the fiber structure in the case of the combined mercerization treatment with ammonia and sodium hydroxide. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 364–370, 2000     

Deuteration of cotton fibers. I. Partially decrystallized celluloses

Deuteration of cellulose in the fiber form has been studied by the new technique developed recently. Infrared spectra in the 3-μ region were recorded to obtain four well-resolved bands due to H-bonded hydroxyl groups in the ordered regions. The peaks at 3298 and 3400 cm^?1 were assigned to cellulose I, while those at 3445 and 3493 cm^?1 were assigned to the cellulose II lattice structure. Cotton fibers containing both cellulose I and cellulose II lattice structures (50:50%) gave six bands in the 3-μ region at 3230, 3298, 3350, 3400, 3445, and 3493 cm^?1. Deuteration of swollen and decrystallized cotton fibers revealed that ethylenediamine brings about partial conversion of cellolose I lattice structure to cellulose II lattice structure, giving the characteristic cellulose II band at 3493 cm^?1. Swelling mechanism with ethylenediamine to account for formation of cellulose II in cotton fibers has been put forward. Zinc chloride was found to retain the cellulose I structure intact. In both the decrystallized celluloses, the band at 3400 cm^?1 has been found to be completely wiped out. This band has been assigned to the group of H bonds mainly lying in rather imperfectly ordered crystalline regions in the fiber structure, which are attacked first during swelling treatment by both the swelling agents irrespective of their different mechanisms of swelling.     

Physical and fine structure properties of cotton fibers swollen with trimethylbenzylammonium hydroxide

Cotton fiber was treated with aqueous trimethylbenzylammonium hydroxide (Triton B) at concentrations over the range 25%–40%. After complete removal of the swelling agent, the samples were evaluated for the extent of swelling, strength and elongation, birefringence, moisture regain, density, crystallinity, x-ray diffraction patterns, and microfibrillar morphology. Electron-microscopical examination and other evaluation of fine structure properties revealed that the nature of swelling is intercrystalline up to 30% concentration of Triton B, and intracrystalline beyond that. Although the swelling as measured by propanol-2 retention after treatment with 30% Triton B is about twice as much as that of the control, the original structure remains almost unchanged except for some gain in strength and elongation and increase in moisture regain. At 32% Triton B concentration and beyond, rapid decrystallization takes place, accompanied by a fall in birefringence, density, and crystallinity index. X-Ray analysis showed significant loss of lateral order and partial conversion of cellulose I to cellulose II at 35% and 40% Triton B concentrations. The results indicate that, used at the critical concentration of 30%, Triton B can be a useful swelling agent for cotton fibers as it opens up the fine structure of cellulose considerably without impairing any important physical properties.