Surface and pore structure modification of cellulose fibers through cellulase treatment

The surface and pore structure of cellulose fibers have a significant impact on the properties and performance in applications. Cellulase enzymatic hydrolysis of cellulose fibers can result in changes to the surface and pore structure, thus providing a useful tool for fiber modification. This research characterizes these changes using various test methods such as fiber dimension, water retention value (WRV), hard‐to‐remove (HR) water content, freezing and nonfreezing bound water content, polymer adsorption, and crystallinity index. For a high‐dosage cellulase treatment (600 U/g dry solid), the fiber length was significantly decreased and the fibers were “cut” in the cross direction, not in the axial direction. The swelling capacities as measured by the WRV and HR water content increased for the high‐dosage treatment. Three independent measurements (nonfreezing bound water, polymer adsorption, and crystallinity index) are in good agreement with the statement that the amorphous regions of cellulose fibers are a more readily available substrate relative to crystalline regions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3833–3839, 2007     

Effect of solvent exchange on the structure and rheological properties of cellulose in LiCl/DMAc

Effect of solvent exchange on the structure of cellulose was investigated by Fourier transform infrared spectroscopy, wide angle X‐ray diffraction, and scanning electron microscopy analysis. The solvent exchange facilitated the dissolution of cellulose in LiCl/DMAc with no change of the crystalline structure of cellulose. In contrast, solvent exchange led to the fibrillation on the treated fiber surface and the trimmed rod‐like particles, further confirming the occurrence of particle disintegration. The rheological properties of three cellulose samples with different degrees of polymerization (DP) and different concentrations were investigated. Results indicated that the cellulose LiCl/DMAc solutions were non‐Newtonian fluids. At low deformation rates the cellulose solution behaved like a viscous liquid (loss modulus G″ being larger than storage modulus G′), but elastic properties developed at high angular frequency. The two domains of viscoelastic behavior were separated by the so‐called crossover point for G′ and G″, which was slightly shifted to lower frequencies as the testing temperature increased from 50 to 80°C. As the concentration and the average molecular weight (or DP) increased, the angular frequency at the crossover point increased also under the experimental conditions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Regulating the pore structure of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) oxidized cellulose membranes: impact of drying method and organic solvent processing

Cellulose‐based membrane is a satisfactory candidate for the separator of lithium‐ion batteries due to its renewability, abundant pore structure and outstanding thermal–chemical stability. In this study, 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) oxidized cellulose fiber (TOCF) membranes with different oxidation degrees were prepared. Membranes with high oxidation degree are faced with a pore closure issue, resulting in low porosity. In order to improve the pore structure, the TOCF membranes were dried differently through air drying, vacuum drying and freeze drying. Furthermore, air‐dried membranes were processed by three organic solvents – n‐butyl alcohol, carbon tetrachloride and n‐heptane. The physical properties, pore structure characteristics, mechanical properties and the electrochemical performance of the membranes were measured and characterized. From the results, freeze drying is found to provide the highest porosity and mean pore diameter. Unfortunately, Young’s modulus of the freeze‐dried membranes is the smallest as well. However, membranes processed by n‐butyl alcohol have weak tensile properties. Compared to non‐processed membranes, membranes processed by organic solvents present better pore structure and significantly better electrochemical performance. With all properties considered, TOCF membranes processed by carbon tetrachloride or n‐heptane are qualified for serving as battery separators as they possess improved pore structure, enhanced Young’s modulus, considerable tensile strength and improved electrochemical properties. © 2020 Society of Chemical Industry     

黏结剂对FCC催化剂孔结构的影响

黏结剂的性能直接影响FCC催化剂的孔结构。运用电镜等分析方法分析黏结剂的粒子特征,根据黏结剂的粒度分布计算黏结剂粒子堆积孔的孔分布,研究黏结剂对FCC催化剂孔结构的影响。结果表明,FCC催化剂的中孔主要来自黏结剂粒子间松散堆积形成的堆积孔。     

不同预处理条件下纤维素的结构变化及其在DMAc/LiCl中的溶解

介绍了乙二胺、氢氧化钠和高温等三种不同的纤维素预处理方法。研究预处理后纤维素的结构变化,讨论预处理过程中的转化机理,并通过X射线衍射对纤维素结晶度的变化进行表征,证明乙二胺预处理后纤维素的结晶度下降最大。纤维素经过预处理后可以溶解在DMAc/L iC l中,讨论其溶解机理,通过对比三种预处理纤维素的溶解性能,表明经过乙二胺预处理之后的纤维素在DMAc/L iC l中溶解性能最好,氢氧化钠预处理的纤维素次之,高温预处理的纤维素溶解性能相对较差。     

不同预处理条件下纤维素的结构变化及其在DMAc／LiCI中的溶解

介绍了乙二胺、氢氧化钠和高温等三种不同的纤维素预处理方法。研究预处理后纤维素的结构变化，讨论预处理过程中的转化机理，并通过X射线衍射对纤维素结晶度的变化进行表征，证明乙二胺预处理后纤维素的结晶度下降最大。纤维素经过预处理后可以溶解在DMAc／LiCI中，讨论其溶解机理，通过对比三种预处理纤维素的溶解性能，表明经过乙二胺预处理之后的纤维素在DMAc／LiCI中溶解性能最好，氢氧化钠预处理的纤维素次之，高温预处理的纤维素溶解性能相对较差。     

ISEC法在评价色谱介质孔径结构方面的应用

层析是生物大分子分离纯化的一种重要手段,层析介质作为层析过程的关键的一部分受到了广泛的关注。层析介质的孔径结构对其分离纯化的效果有着显著的影响,因此探究层析介质的孔径结构至关重要。介绍了测定色谱介质孔径结构常用的方法,如：压汞法、氮气吸附法、小角X射线散射法、电镜扫描法（SEM和TEM）和逆体积排阻色谱法(ISEC)。重点阐述了ISEC法的基本原理和常用的探针类型,总结了ISEC法应用中的优点及不足,介绍了ISEC法的发展历史及其在国内外的研究现状。     

纤维素在丝光化处理过程中结构变化的研究

本文研究了纤维素在丝光化过程中其结构的变化，着重讨论不同再生条件对其晶型结构的影响。碱处理纤维素在水中再生，当碱含量＞12％时纤维素Ⅰ开始向纤维素Ⅱ转变；当碱含量＞18％时则完全转变为纤维素Ⅱ。在水中再生而晶型未发生变化的碱处理纤维素在不同醇中（如甲醇、乙醇和异丙醇等）再生时，则以分子体积大小不同发生部分或全部的晶型转变。在体积较大的异丙醇中再生时转变开始的碱含量降至3％。我们认为，上述现象源于醇的体积效应，以及相对于水较少形成氢键的能力，并从醇中再生这一角度初步探讨纤维素丝光化的机理。     

Structural aspects of the thermally accelerated ageing of cellulose: effect of cellulose source and ageing conditions

Small angle X‐ray scattering has been used to study the void parameters of filter paper, kraft paper and ramie after ageing in air and in vacuo at 160 °C and 120 °C. The cellulose fibres contain long thin voids oriented with their long axis roughly parallel to the fibre axis. The aged samples were observed both dry and fully hydrated. Hydration caused small voids to open up between the fibrils which compose a single fibre. The void parameters of dry cellulose remained largely unchanged on ageing, but the wet values of aged material approached those of dry. This effect was more profound the more extreme the ageing conditions. The conclusion is that high temperatures and chain scission encourage chain mobility and facilitate hydrogen bonding between the fibrils in a mechanism similar to that proposed for hornification. Conventional hornification, whereby intrafibre hydrogen bonding increases due to dehydration below a threshold value is also likely. The additional hydrogen bonding means that the fibre is less able to open small voids and absorb water after ageing. Measurements of water retention values of filter paper support the model of structure closure. Zero span and wide span tensile strengths of filter paper fall by greater amounts, the more severe the ageing conditions. The effect of chain scission evidently dominates any internal structural modifications in determining the mechanical strength of aged fibres. © 2002 Society of Chemical Industry     

渣油加氢催化剂孔结构对反应活性的影响

在3L中型加氢试验装置上考察了渣油加氢脱硫催化剂孔结构对反应活性的影响，试验结果表明，当孔结构发生变化时，催化剂的脱硫、脱氮、脱残炭及脱金属反应活性呈现不同的变化规律。     

孔道结构对渣油加氢脱金属催化剂活性的影响

选择性制备3种不同孔道结构的渣油加氢脱金属催化剂,并进行渣油加氢脱金属和加氢脱硫活性评价。结果表明,一定量大孔(>50 nm)的存在,能够提高催化剂单位表面积的加氢脱金属活性;加氢脱硫活性与体积比表面积成正比。     

燃烧过程对页岩灰孔隙结构的影响

页岩灰为油页岩及其半焦的燃烧产物,可作为建筑原材料、化工填料和吸附剂等,具有一定的工程应用价值。采用氮气等温吸附/脱附法对油页岩燃烧生成的页岩灰的孔隙结构进行了测量,并对不同升温速率和不同终温所得到的页岩灰的孔隙结构进行了比较,结果表明：如果油页岩在快速升温条件下燃烧所放出的热量能够被周围环境吸收而使得油页岩颗粒温度始终低于其灰熔点温度,所得到的页岩灰的孔容积和孔比表面积较大,适宜工业应用。     

Swelling behavior of crosslinked hydroxypropyl cellulose films retaining cholesteric liquid crystalline order. I. Effect of temperature

Temperature dependence of the swelling behavior in both water and propanol was determined for the crosslinked hydroxypropyl cellulose (HPC) films retaining cholesteric liquid crystalline order (CLCO) and for the crosslinked amorphous HPC films. The dependence of swelling behavior in water for the films retaining CLCO was different from that of the amorphous films. With increasing temperature, the equilibrium swelling ratio (B_e) for the films retaining CLCO decreased, whereas B_e for the amorphous films increased. In propanol, both films exhibited the same temperature dependence. B_e increased with increasing temperature. The increasing rate of the swelling in transient state showed similar temperature dependence on B_e. The increasing rate for the films retaining CLCO decreased with temperature, but that for the amorphous films increased in water; in propanol, the increasing rate for two types of films increased. The difference in the swelling behavior between the two types of films may be due to the difference in the number-average molecular weight between crosslinks. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1015–1022, 1999     

纤维素在NMMO水溶液中的溶胀行为研究

通过离心分离法表征纤维素在N-甲基吗啉-N-氧化物水溶液中的溶胀行为,研究了NMMO浓度、温度对纤维素浆粕溶胀的影响;用显微镜追踪拍摄纤维素的溶胀过程,测定纤维的溶胀率,验证了离心分离法的可行性。结果表明:随着NMMO浓度、溶胀温度的升高,纤维素溶胀率增大,溶胀效果变好;纤维素在NMMO水溶液中的最佳溶胀条件为NMMO质量分数78%、温度75℃,溶胀时间40 min。     

Effect of solvent on morphology of electrospinning ethyl cellulose fibers

The influence of the composition of a multicomponent solvent on the surface morphology and diameter distribution of ethyl cellulose fibers produced by electrospinning technology was investigated. The results showed that the average diameter of the fibers using the multicomponent solvent was thinner than when using either of the two components and the diameter distribution of the fibers became narrower. Tiny tubercles formed on the fiber surface, which may improve the specific surface area and broaden the applications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1292–1297, 2005     

Effect of moisture distribution in pore structure on fragmentation characteristics of lignite

ABSTRACT

The experiments were performed to explore the effect of moisture on fragmentation properties of Mengdong (MD) lignite, Xiao Longtan (XLT) lignite, and Zhaotong (ZT) lignite with temperature of 200°C and particle size of 13–10?mm using the fixed bed reactor. It showed fragmentation ratio and pulverization ratio increased, and particle size variation ratio decreased with an increase in initial moisture of lignite. The distribution of moisture in pores under different initial moisture contents was analyzed by nuclear magnetic resonance. The distribution of moisture in pores between raw and dried lignite was different. The water content in macropores rapidly decreased, but water content in mesopores remained constant in prior period and then slightly decreased with the residence time increasing. There was a good connectivity between macropores and mesopores. The water in micropores, which hardly influenced fragmentation, was generally closed and not favored for the mobility of water. The water in macropores had a significant effect on fragmentation of lignite. However, when the moisture content in macropores was less than 0.10?g/g coal, the degree of fragmentation became little.     

磷渣颗粒级配对水泥石孔结构的影响

采用压汞法对磷渣水泥石的孔结构进行了试验研究,又用灰色关联分析不同磷渣颗粒分布对水泥石孔结构的影响,并用Origin作图分析磷渣水泥石孔径分布的变化趋势。结果表明:对于不同的磷渣,其颗粒级配对水泥石的孔结构的影响有显著差异,并不是细颗粒含量越高水泥石总的孔隙率越低,而要根据具体的磷渣选择适当的粉磨细度。     

The pore structure of chrominophosphate catalysts

A series of chrominophosphates (CrPs) with various P/Cr ratios were prepared by the precipitation method. The pore structures of these catalysts were characterized by nitrogen adsorption and mercury-penetration porosimetry. The results indicated that the micro-pores with diameters less than 20 nm were due to the dehydration process and had a slit-shaped geometry. There were two types of large pores (meso- and macro-) with diameters greater than 20 nm. These pores had a cylindrical pore-shape. The meso-pores can be attributed to the packing of particles and the macro-pores are essentially due to the packing of the aggregates of the particles.     

载体孔结构对银基催化剂性能影响

乙烯氧化制环氧乙烷银催化剂所用载体为大孔惰性α-Al2 O3.载体孔道结构对金属银的分布有调控作用,通过选择适宜的孔道结构,采用银胺溶液浸渍,热分解可以获得特定尺寸分布的负载银催化剂.以不同粒度和晶相的氧化铝复配,添加不同的扩孔剂,制备了孔结构不同的三种载体负载银制得银催化剂.对银催化剂进行TGA和SEM分析,并考察其...     

矿渣掺量对偏高岭土基土聚水泥抗压强度及孔结构的影响

为提高偏高岭土基土聚水泥的力学性能,在偏高岭土中加入不同掺量(质量分数10%~50%)的矿渣,分析其对土聚水泥抗压强度的影响,并利用压汞仪和扫描电镜对80℃蒸养3 d的土聚水泥试样进行孔结构和断面形貌分析.实验结果表明:随着矿渣掺量的增加,土聚水泥的抗压强度显著提高,孔隙率呈线性减小,孔径分布逐步向微孔方向移动.当矿渣掺量为50%时,80℃蒸养3 d和7 d后抗压强度分别达到73.4和74.4MPa,3 d龄期试块的孔隙率仅为4.46%,孔径尺寸小于20 nm.微观结构分析表明,矿渣的加入使土聚水泥结构更加致密,有利于土聚水泥抗压强度的提高.