纤维素科学与技术研究进展

本文综述纤维素科学与技术的研究进展。阐述了纤维素结构、纤维素的合成、纤维素液晶、功能纤维素、纤维素溶剂、纤维素裂解和纤维素的废物利用等的最新动态。     

纤维素及其衍生物液晶

从纤维素及其衍生物的化学结构出发,综合论述了纤维素衍生物的合成方法,液晶态的形成理论,液晶性能及其在塑料中的应用。     

纤维素及其衍生物液晶的形成及应用

系统地介绍了液晶的特性、纤维素及其衍生物液晶的形成及其在纤维与膜技术上的应用。     

纤维素及其衍生物的液晶态与应用

本文讨论了纤维素及其衍生物的液晶态与应用。     

纤维素膜、纤维素功能材料及纤维素医用材料的发展

概述了纤维素膜、纤维素功能材料及纤维素医用材料的发展状况,指出纤维素膜、纤维素功能材料及纤维素医用材料是纤维素科学发展的重要方向之一,成为当代新材料的一个重要组成部分,具有极为广阔的发展和应用前景。     

醋酸纤维素的现状与发展趋势

介绍了醋酸纤维素的性质、用途以及国内外动态。概述了它的发展障碍以及解决问题的途径。     

纤维素衍生物液晶相转变和织态结构

本文综述了纤维素衍生物液晶态相转变和织态结构。描述了纤维素衍生物从各向同性态向液晶态的转变过程和液晶态的织构特征。讨论了溶液浓度和温度对液晶相织构的影响。探讨了各种因素,如溶剂、取代基含量、外加力场和外加磁场等对液晶相的形成及织态结构的影响。     

纤维素衍生物

纤维素衍生物１概况我国纤维素衍生物工业已有数十年历史,除硝酸纤维素和粘胶纤维已有相当规模的大、中型厂外,羧甲基纤维素近年来已发展至数十家中小型厂,形成了年产２万ｔ以上的规模。但醋酸纤维素尚不足５０００ｔ／ａ规模。我国纤维素衍生物与国外相比,不论在品种...     

纤维素液晶研究领域取得重要进展

纤维素是一种生长和存在于绿色植物中的丰富的可再生的(年再生850亿吨)天然高分子材料,纤维素材料的开发利用在高分子科学的建立、发展和工业应用方面都起到了重要的作用。特别是在石油资源开始逐步枯竭的时期,纤维素资源有可能代替石油成为现代化学工业的基本原料之一。中国科学院广州化学研究所纤维素化学重点实验室黄勇研究员和王林格博士领导的研究小组长期以纤维素衍生物所形成的液晶相为主要对象开展基础和应用方面的研究。最近在国家杰出青年基金项目的支持下,该研究小组利用可聚合单体作为溶剂对纤维素衍生物胆甾型液晶相溶液中各织…     

我国纤维素油田化学品的应用与发展前景

本文全面介绍了纤维素油田化学品在我国石油工业钻井完井、固井作业、压裂、酸化以及强化采油中的应用研究状况，同时根据目前我国油田化学处理剂和油气钻探技术发展的特点，探讨和展望了纤维素油田化学品在我国的发展前景。指出要进一步开拓纤维素油田化学品就必须大力开发新品种，努力提高原有产品效能。     

丙烯酸铅对乙基纤维素胆甾型液晶的影响

本文利用紫外-可见分光光度计研究了丙烯酸铅(PbA)对乙基纤维素(EC)/丙烯酸(AA)胆甾型液晶的影响,研究发现:在EC/AA胆甾型液晶中,其最大选择性反射波长和螺距随溶液浓度增加而降低;PbA的加入也使反射波长和螺距降低,并且溶液中PbA浓度越大,反射波长和螺距降低越多,这可能是由于Pb2+与纤维素分子的络合作用,拉近了相邻EC分子链距离,导致胆甾型液晶溶液中的层间分子距离减小所致。利用这种性质调节纤维素胆甾型液晶的光学反射性能。     

Thermal degradation of cellulose and cellulose esters

Cellulose, cellulose diacetate (CDA), cellulose triacetate (CTA), cellulose nitrate (CN), and cellulose phosphate (CP) were subjected to dynamic thermogravimetry in nitrogen and air. The thermostability of the cellulose and its esters was estimated, taking into account the values of initial thermal degradation temperature T_d, the temperature at the maximum degradation rate T_dm, and char yield at 400°C. The results show that these polymers may be arranged in the following order of increasing thermostability: CN < CP < regenerated cellulose < filter cotton < CDA < CTA. The activation energy (E), order (n), and frequency factor (Z) of their degradation reactions were obtained following the Friedman, Chang, Coats–Redfern, Freeman–Carroll, and Kissinger methods. The dependence of T_d, T_dm, E, n, Ln Z, and char yield at 400°C on molecular weight and test atmosphere is also discussed. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68:293–304, 1998     

Gel formation and liquid crystalline order in cellulose triacetate solutions

The formation of a liquid crystalline state of cellulose triacetate solution in trifluoroacetic acid was studied using optical microscopy, polarimetry and circular dichroism measurements. Below a critical concentration of $\text{34}\text{g}\text{100}\text{ml}$ a clear isotropic solution was formed. Solutions more concentrated than this were in the cholesteric liquid crystalline state. If water was added to the solution, a gel phase was formed if the polymer concentration was above a critical value. We interpret our observations in terms of the Pincus-de Gennes theory and show that the formation of liquid crystalline order involves both inter-and intramolecular forces.     

Characterisation of cellulose treated by the steam explosion method. Part 3: Effect of crystal forms (cellulose I,II and III) of original cellulose on changes in morphology,degree of polymerisaion,solubility and supermolecular structure by steam explosion

An attempt was made to clarify the effect of the crystal form of untreated cellulose on the morphological and structural changes of cellulose during steam explosion treatment (steam pressure P = 2.9MPa (T = 508K), treatment time t = 15-300 s). For this purpose, the crystal form of soft wood pulp (cellulose I) was converted by solid-to-solid transition, with minimal unavoidable change in other structural characteristics including morphology and average degree of polymerisation, into cellulose II or cellulose III. It was proved by both X-ray and solid-state cross-polarisation/magic-angle sample-spinning (CP/MAS) ¹³C NMR analyses that even a simple addition of water at room temperature brought about a significant structural change in the steam-untreated cellulose samples. The solubility towards 9.1 wt% aqueous sodium hydroxide, S_a, of the cellulose samples of crystal forms I and III could be improved from 31-33% up to almost 100% by selecting appropriate steam explosion conditions (for example, P = 2.9MPa, t = 30 s). Such a magnificent increase in S_a by the steam explosion treatment was not observed for the cellulose II sample, even under the rather severe conditions of the steam explosion treatment at which the cellulose III crystal was converted to a large extent to cellulose I, as confirmed by X-ray diffraction. X-ray diffraction analysis showed that crystallisation of samples with cellulose I or II crystal occurred to some extent during the steam explosion treatment. Contrary to this, the degree of breakdown of the intramolecular hydrogen bond O₃…O'₅, as estimated by CP/MAS ¹³C NMR analysis, significantly increased for cellulose I and I11 during the treatment. The decrease in the viscosity-average degree of polymerisation, P, observed for all treated samples can be roughly categorised into two or three steps of the first-order decomposition reaction with different reaction rates.     

Morphological and grafting modification of natural cellulose fibers

Crystal structure and mechanical properties of cellulose fibers were studied to investigate the effect of chemical treatment on the fiber. Pretreatment by acetone extraction, mercerization with 3–20% wt/v sodium hydroxide (NaOH), and acrylonitrile (AN) grafting initiated by azo‐bis‐isobutylonitrile were performed. From Fourier transform infrared spectroscopy and wide‐angle X‐ray diffraction quantitative measurements, the pretreated fibers showed an induced slight decrease of crystallinity index. The structural transformation of the fibers from cellulose I to cellulose II was observed at high NaOH concentration of 10–20% wt/v. The amount of grafting, 1.56, 2.94, 6.04, 8.34, or 10.46%, was dependent upon the initiator concentration and the volume of monomer in the reactor. The AN grafted fibers had no transformation of crystalline structure as observed after mercerization. Only a variation of X‐ray crystallinity index with grafting amount was observed. Moisture regain of pretreated and modified fibers depended on the structure of the fiber and the amount of grafting. The mechanical properties performed by a single fiber test method were strongly influenced by the cellulose structure, lateral index of crystallinity, and fraction of grafting. Scanning electron microscopy was used for analysis of surface morphologies of treated fibers. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2456–2465, 2004     

Solubility of bacterial cellulose and its structural properties

Based on experiments conducted, it has been found that bacterial cellulose, like spruce cellulose, is soluble in an aqueous NaOH solution with the concentration of 8.5% at a temperature of −5°C if the polymerization degree of the cellulose does not exceed 400. When 1% of urea is added to the NaOH solution, the solubility of cellulose increases; and, in this solvent, bacterial cellulose may be dissolved so long as its polymerization degree is below 560. The results of these experiments are of great practical importance since they point to the possibility of the preparation of cellulose spinning solutions suitable for fiber formation. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1871–1876, 1998     

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。     

一种新型纤维素衍生物固定相的制备及对硝基苯胺异构体的分离

利用自制的环十二烷基胺对纤维素进行了改性,考察了将其作为高效液相色谱固定相对硝基苯胺3种异构体的分离,结果表明分离效果良好。     

Crystal structure of cellulose polymorphs by potential energy calculations: 1. Most probable models for mercerized cellulose

An attempt is made to establish the crystal structure of mercerized cellulose through combined optimization of the crystallographic discrepancy factor and potential energy of the system. The potential energy is calculated using the semi-empirical atom—atom potential method. Several low-energy structures are found, all consistent with the available X-ray diffraction data. The most preferable model possesses a mobile hydrogen bonding network capable of facile rearrangement through thermal migration of protons.