均相法、非均相法三醋酸纤维素

三醋酸纤维素的生产工艺有均相法和非均相法两种。均相法是将纤维素或木浆泊在醋酐、催化剂的存在下,于有机溶剂中进行乙酰化反应。反应过程中,固体纤维素逐渐消失,得均相浆液,经水解、中和后沉析,得片,粒状的三醋酸纤维素。非均相法的原理与均相法基本相同,     

纤维素硫酸酯制备研究进展

纤维素硫酸酯是一种具有独特生物学性质的纤维素衍生物,由于其具有抑菌、抗病毒及抗凝血等功效,并且具有良好的生物降解性和生物相容性,无毒无害、绿色环保,所以在食品、医药、化工等领域有着广泛的应用前景。但是目前纤维素硫酸酯还未被用于商品化,其制备方法尚处于研究开发阶段。目前纤维素硫酸酯的制备方法主要分为3类,分别是均相制备法、非均相制备法及准均相制备法。总结归纳了纤维素硫酸酯的制备方法,并介绍分析了各种制备方法各自的特点,为制备取代度、分子量等性质可控的纤维素硫酸酯提供理论依据。     

醋酸纤维素/TiO_2复合膜的制备及性能研究

用溶胶-凝胶法制备纳米TiO2,以纳米TiO2作为无机相添加剂,以醋酸纤维素(CA)作为成膜剂,乙酸甲酯为溶剂,使用流延法制备醋酸纤维素/TiO2复合膜。运用FT-IR、UV-Vis等方法对复合膜进行表征。结果表明,复合膜的热稳定性、耐碱性以及对紫外线的吸收均有所提高。在光照下,对E.coli的抗菌性有所提高。     

二氯甲烷均相法制造三醋酸纤维素文献总结

在这篇文献总结中,比较了均相法和非均相法技术路线的优缺点,着重讨论了国外二氯甲烷均相法制造三醋酸纤维素的情况和工艺条件的选择,供有关单位参考。     

静电纺丝制备多孔醋酸纤维素超细纤维

采用静电纺丝法制备了大量尺寸为60 nm～750 nm椭圆形多孔醋酸纤维素(CA)纤维.利用扫描电镜(SEM)表征了纤维及孔的形态和大小,液氮吸附法(BET)测定了纤维的比表面积.探讨了溶刑种类、溶剂配比和溶液浓度对多孔CA纤维的影响.通过调节纺丝溶液性质和纺丝参数,CA纤维表面多孔大小和分布密度是可调控的.成孔机理是...     

聚己内酰胺/醋酸纤维素合金膜材料的制备及性能表征

采用溶液共混和液-固相转变法制备聚己内酰胺/醋酸纤维素的共混物(PA-6/CA)作为高效液相色谱(HPLC)柱填料。以小分子量化合物为探针分子,用HPLC法测定其界面性能,并研究其共混物的相容性、热稳定性。实验结果表明,PA-6与CA有很好的相容性,且PA-6/CA的热稳定性比纯CA有所提高;PA-6/CA(50∶50)合金膜材料对不离解极性有机物分离效果最佳,适合作脱盐膜材料;CA可有效改善PA-6的亲水性。     

Fe-MCM-41/CA共混膜的制备及其吸附NOR性能研究

采用水热合成法制备Fe-MCM-41介孔分子筛。以Fe-MCM-41和醋酸纤维素(CA)为原料,采用浸没相转化法制备Fe-MCM-41/CA共混膜,用以吸附去除溶液中的诺氟沙星(NOR)。SEM、FTIR和机械性能表征证实了Fe-MCM-41成功共混入膜中,且膜的综合性能得到改善.考察pH、离子强度和温度对共混膜吸附NOR的影响,并探讨了吸附动力学和热力学.结果表明:中性条件有利于Fe-MCM-41/CA膜对NOR的吸附;Na~+和Ca~(2+)均能抑制吸附过程的进行,且Ca~(2+)抑制作用更为明显;NOR吸附过程符合准二级吸附动力学模型和Freundlich吸附等温方程;升高温度有利于Fe-MCM-41/CA膜对NOR的吸附.吸附过程存在静电,氢键,表面络合等作用力.吸附/脱附实验表明共混膜具有良好的再生性能.     

以纳米Al2O3为添加剂CA/PAN共混超滤膜的制备

以纳米Al2O3为添加荆,采用相转化法制备了醋酸纤维素/聚丙烯腈(CA/PAN)共混超滤膜.采用扫描电镜(SEM)及透射电镜(TEM)观察不同条件下制备的CA/PAN共混超滤膜的表面、截面及内部的微观结构.结果表明,纳米Al2O3可有效的控制大孔的形成,不同的凝固浴温度时膜的表面及截面结构有很大影响.     

PAN/CA共混复合膜的气体分离与力学性能

聚丙烯腈（PAN）具有较高的气体渗透性,但拉伸强度低,不适宜直接制膜。为达到气体分离膜在力学强度方面的使用要求,利用PAN与乙酸纤维素（CA）共混改善其拉伸性能。结果表明,采用相转化法制备的PAN/CA共混基膜,随着CA与PAN共混比的增加,拉伸强度有明显的上升趋势,由1.74MPa增加到2.08MPa。当共混比为0....     

硬模法制备无机空心球的研究进展

结构与组成可控、性能可调的微米-亚微米尺度的无机空心球具有极大的应用潜力.系统评述了胶粒模法和胶囊模法等无机空心球的硬模制备方法,阐述了硬模法在均相母液和非均相母液中的不同成壳机制,综述了硬模法制备无机空心球的相关应用及最新进展.     

An Improved Method for Predicting Pressure Drop along Slurry Pipeline

Based on extensive analysis of experimental data, the Kaushal and Tomita (2002) model for composite and solids concentration profiles is modified by considering the effect of particle size and efflux concentration on particle diffusivity. Using a modified model, the ratio of the homogeneously and heterogeneously distributed portion of each particle size is calculated. Pressure drop is predicted by summing the pressure drops due to homogeneously and heterogeneously distributed portions of different particle sizes. Comparison with experimental data for pressure drop shows that the proposed model gives better predictions than the models available in literature. The root-mean-square differences between predicted and measured values of pressure drop in percentage of the mean of measured values are for Wasp the et al. (1977) model: 5.0-21.8%; for the Gillies et al. (1991) model: 6.0-9.2%; for the Kaushal and Tomita (2002) model: 1.7-3.5%; and for the proposed model: 1.6-2.0%.     

An Improved Method for Predicting Pressure Drop along Slurry Pipeline

Based on extensive analysis of experimental data, the Kaushal and Tomita (2002) model for composite and solids concentration profiles is modified by considering the effect of particle size and efflux concentration on particle diffusivity. Using a modified model, the ratio of the homogeneously and heterogeneously distributed portion of each particle size is calculated. Pressure drop is predicted by summing the pressure drops due to homogeneously and heterogeneously distributed portions of different particle sizes. Comparison with experimental data for pressure drop shows that the proposed model gives better predictions than the models available in literature. The root-mean-square differences between predicted and measured values of pressure drop in percentage of the mean of measured values are for Wasp the et al. (1977) model: 5.0-21.8%; for the Gillies et al. (1991) model: 6.0-9.2%; for the Kaushal and Tomita (2002) model: 1.7-3.5%; and for the proposed model: 1.6-2.0%.     

Morphology and pore characteristics of bacterial cellulose/multiwalled carbon nanotube composite cryogels

Bacterial cellulose/multiwalled carbon nanotube (MWCNT) composite cryogels were prepared via sol-gel chemistry using epichlorohydrin as a crosslinker. Their morphology and pore characteristics were examined under various conditions. The bacterial cellulose/MWCNT composite cryogels had a macroporous structure that contained mesopores and micropores due to the MWCNTs that were homogeneously incorporated in the macroporous network structure.     

羧甲基纤维素-Fe_3O_4复合纳米磁性材料的制备及其渗透性能

采用改进的氧化沉淀法在羧甲基纤维素(CMC)溶液中制备了以磁性纳米Fe3O4为核心,外包CMC的复合磁性纳米粒子。用透射电镜、X射线衍射、红外光谱、Zeta电位和震动样品磁强计对复合粒子进行了表面形貌、结构和磁学的表征。实验结果表明,CMC-Fe3O4复合纳米粒子为反尖晶石型,平均粒径约为40 nm;CMC在Fe3O4粒子表面是化学吸附;在相同pH值下,CMC-Fe3O4的表面Zeta电位低于纯相Fe3O4;CMC-Fe3O4的饱和磁化强度为36.74 emu.g-1;CMC-Fe3O4复合粒子在土壤介质中的过滤系数约为0.03 cm-1;在10 cm土柱渗透实验中,72%的CMC-Fe3O4复合粒子悬浊液穿过了土壤介质。     

碳气凝胶载铂催化剂对甲醇的电催化氧化性能

以用溶胶凝胶法制备的碳气凝胶(CA)作为催化剂载体,用间歇微波法制备了碳气凝胶载铂催化剂。用电感耦合等离子光谱仪(ICP)测定了催化剂中Pt的含量,用透射电镜(TEM)和X射线衍射(XRD)对催化剂的形貌、粒径分布以及颗粒粒度进行了表征。结果表明,碳气凝胶载铂催化剂粒子分布均匀、粒径集中,平均粒经为4 nm.用能量散射X射线能谱(EDX)分析了催化剂的化学成分,用循环伏安法、线形扫描伏安法和计时电流法对催化剂的电化学性能进行了表征.结果表明,以碳气凝胶为载体的催化剂比以活性炭为载体的催化剂具有更高的催化活性。     

Rigid polyurethane foam/cellulose whisker nanocomposites: preparation, characterization, and properties

Novel rigid polyurethane nanocomposite foams have been prepared by the polymerization of a sucrose-based polyol, a glycerol-based polyol and polymeric diphenylmethane diisocyanate in the presence of cellulose whiskers. Varying amounts of sulfuric acid hydrolyzed cellulose whiskers (0.25, 0.50, 0.75 and 1.00 wt%) prepared from a commercial fully bleached softwood kraft pulp were incorporated to investigate the effect of its dosage on the mechanical and thermal properties of polyurethane nanocomposites. Fourier transform infrared spectra of the nanocomposite foams suggested that additional hydrogen bonds were developed and crosslinking occurred between the hydroxyl groups of cellulose whiskers and isocyanate groups which increased the phase separation of soft and hard segments in the polyurethane. The closed cells of control foam and nanocomposite foams were homogeneously dispersed and the cell sizes were approximately 350 microm in diameter as observed by scanning electron microscope. A substantial improvement of mechanical properties at low whisker content (< or = 1.00 wt%) was obtained, especially the compressive strength and modulus at 1.00 wt% whiskers content which were increased by 269.7% and 210.0%, respectively. Thermal stability of the nanocomposites was also enhanced as determined by differential scanning calorimetry and thermogravimetric analysis.     

半纤维素含量对蔗渣纤维基膜结构和性能的影响

目的 为了更好地了解甘蔗渣半纤维素在加工过程中与原纤化纤维之间的化学反应性,并为甘蔗木聚糖生物聚合物在材料和产品中的应用创造可能性。方法 以甘蔗渣纤维为原料,通过机械法制备原纤化纤维,采用NaOH对纤维素进行处理。通过纳米粒度仪(FLA)、激光粒度仪(LPS)、接触角测试仪(CA)、水蒸气透过率测试仪(WVTR)、扫描电镜(SEM)、X-射线衍射(XRD)等手段对原纤化纤维悬浮液和纤维基薄膜进行表征。研究处理后纤维素悬浮液的组成、粒径与电荷量,以及纤维基薄膜的表观形貌、纤维结构和性能的变化。结果 经质量分数大于10%的NaOH处理后,半纤维质量分数降低约6%,纤维素的结晶区发生变化,纤维悬浮液的稳定性大幅度降低。当半纤维素质量分数大于20%时,原纤化纤维薄膜具有优异的水蒸气阻隔性能及疏水性能,接触角为94°±4°。结论 蔗渣中的半纤维素与原纤化纤维之间的相互作用及半纤维素侧基取代反应对纤维素材料的组成、结构和性能有重要影响。     

The effects of urease immobilization on the transport characteristics and protein adsorption capacity of cellulose acetate based hemodialysis membranes

In this study, cellulose acetate (CA) based hemodialysis membranes were prepared by a dry phase inversion method and the influences of urease immobilization on the clearing performance and protein adsorption capacity of the membranes were investigated. Permeation experiments have shown that modification of CA membranes with urease immobilization not only enhanced the transport rate of urea but also increased the permeation coefficients of uric acid and creatinine by changing the structure of the membrane. Furthermore, the protein adsorption capacity of the CA membranes decreased. On the other hand, the mechanical strength of the modified CA membrane did not change significantly compared with that of the unmodified one. A mathematical model was derived to determine the rate of mass transfer of urea through modified CA membranes. Model predictions along with the experimental data suggest that urease immobilization can be used as an alternative method in preparing CA based hemodialysis membranes with improved transport characteristics and biocompatibility through reduced protein adsorption capacities.     

Influence of CaCO3 pore-forming agent on porosity and thermal conductivity of cellulose acetate materials prepared by non-solvent induced phase separation

Thermal insulation materials with a low thermal conductivity are indeed demanded because they play the main role in the enhancement of energy conservation in various industries, especially lightweight constructive materials. Therefore, tubular cellulose acetate (CA) materials were firstly prepared by non-solvent induced phase separation (NIPS). In the NIPS process, the concentration of CA was varied in a range of 20–40?wt%. Also, the temperature of water used as a non-solvent was studied from 5?°C up to 50?°C. According to the FE-SEM results, the 30?wt% CA solution at 20?°C provides tubular CA materials with a higher porous structure than an original CA material but the pore size is quite larger than the mean free path of air leading to achieve a material with high thermal conductivity. To overwhelmed such a problem, the calcium carbonate (CaCO₃) was used to be pore forming agents in order to decrease pore size of prepared CA sheet materials. The amount of CaCO₃ particles in the CA sheet materials was varied as 50 and 60?wt% to investigate its effect on porosity and thermal conductivity of the prepared materials. As the results, the CA sheet materials prepared using NIPS process and after removing 60?vol% CaCO₃ have an enlargement of pores with a size lower than the mean free path of air. They exhibit high porous materials leading to the reduction of their thermal conductivity, which has the lowest value about 0.043?W/mK. Consequently, the CA materials are potentially applied for constructive materials in order to reduce energy consumption in buildings.