A study on reproducibility of cellulose acetate membranes

The variation in flux and rejection of replicate cellulose acetate membranes is measured within a membrane sheet as well as between membranes. Although the casting conditions were carefully controlled and various influences were studied. the source of variation in replicates was not identified. It is shown that the cause of variation is not due to hand or machine casting technique, casting solution composition, heat treatment, dust, overall film thickness or pressure history.     

Configuration of cellulose trinitrate in solution

Cellulose trinitrate was prepared from cotton (Deltapine) under a variety of conditions and investigated in solution with ethyl acetate as solvent using the techniques of light scattering, osmometry and viscometry. The more mildly nitrated samples (e.g. 1 h at 20°C) exhibited downward curvature in the Zimm plots and a fractional precipitation experiment showed that this was due to the presence of large gel-like aggregates. Light scattering, viscometry, infra-red and ultracentrifuge measurements were made on the fraction of gel-like material and the effect of further nitration investigated. The possible nature of the aggregates is discussed. Light scattering measurements made on a mildly nitrated sample with this fraction removed yielded a straight line Zimm plot from which chain statistics similar to those found by other authors could be deduced. Samples obtained by more extensive nitration (2–25 h at 20°C) were considerably degraded but yielded straight line Zimm plots and osmotic pressure measurements showed the polydispersities to be low (DP_w/DP_n 1.3). Values of effective bond length, b, calculated from these Zimm plots (4.6 to 5.6 nm) were much larger than those found for the more mildly nitrated samples and those found by other authors. Also, in contrast to the results of other authors, second virial coefficients obtained by light scattering and osmotic pressure were found to be in fair agreement. The effect of gel-like material on measured second virial coefficients is discussed. It is suggested that the discrepancy in b arises because gel-like material remains in more mildly nitrated samples even after the larger aggregates have been removed by fractional precipitation. This material consists of particles denser than the single coils but of comparable or smaller size so that values obtained for the effective bond length are too low. The results of previous investigations on all the cellulosic polymers which have been investigated are discussed in the light of the present work with particular reference to the effect of gel-like material. It is suggested that the apparent disagreement between the conformational analysis of cellulose and experimental results arises from the presence of gel-like material in solutions rather than any fault in the molecular model.     

醋酸丁酸纤维素与聚丙烯酸乙酯共混体系的研究

通过差热分析和拉伸试验研究了醋酸丁酸纤维素CAB－35－1与聚丙烯酸乙酯（PEA）物理共混、半一互穿网络共混体系的相容性和力学性能，并用扫描电镜观察了共混物的形态。     

Electric birefringence of cellulose trinitrate in acetone

Electric birefringence studies have been made on a sample of high molecular weight cellulose trinitrate in acetone. The molecule is shown to have only a permanent dipole moment and no significant anisotropic polarisability in this solvent. Both the rotary relaxation times obtained from transient time dependent effects and the amplitudes of the observed birefringence have been analysed in terms of theories for rigid rods, weakly bending rods, worm-like chains and both flexible and stiff random coils. The study indicates that (a) electric birefringence data are sensitive to molecular flexibility and (b) that in this solvent, nitrocellulose of 12% nitrogen content appears to be a stiff, non free draining coil with a dipole moment of the order of a few debye (i.e. ? 10^?29 C m) per monomer unit.     

醋酸纤维素的制备及其结构与性能

将微晶纤维素(MCC)在冰醋酸/醋酸酐/氯化铁体系下乙酰化,制备醋酸纤维素(CA),考察了催化剂类型及用量、反应温度、反应时间和醋酸酐用量等对CA的取代度和聚合度的影响。研究表明,以氯化铁为催化剂,在冰醋酸/醋酸酐体系下,MCC乙酰化最佳工艺为:0.5 g MCC,0.1 g氯化铁,反应温度50℃,反应时间40 min,5 mL醋酸酐。醋酸纤维素的各项性能均接近商品醋酸纤维素,具有一定的应用价值。     

On the structure of concentrated cellulose acetate solutions

The supermolecular structure of cellulose acetate membrane casting solutions was determined by measuring their rheological behavior. The method was applied to both clear and turbid casting solutions. The resulting data on activation energy of viscous flow are shown to depend on the cellulose acetate content of the casting solution and on the nature of solvent used. The separation properties of the prepared asymmetric membranes determined by reverse osmosis testing indicate a good correlation with the data obtained by the rheological measurements of the casting solutions. The latter can, therefore, be used as a practical tool for the investigation of early stages in the asymmetric membrane formation process.     

新型两性壳聚糖的制备及结构表征

为了制备一种新型的两性壳聚糖,拓展壳聚糖的应用范围,以甲壳素为原料,通过化学修饰,制备一种亲疏水结构的两性壳聚糖。首先甲壳素的C6-OH与2-氯乙胺盐酸盐(ACH)反应,接着C2-氨基脱乙酰化,最后与柠檬醛进行希夫碱反应。采用紫外、红外和X-射线衍射(XRD)对目标产物进行结构表征。结果表明,两性壳聚糖在253 nm处具有最大紫外吸收峰,其酰胺Ⅰ、Ⅱ、Ⅲ谱带的特征吸收峰分别位于1 650,1 575,1 380 cm^(-1);与甲壳素在9°和19°处明显的特征衍射峰相比,两性壳聚糖9°处的特征峰消失,19°处的特征衍射峰变得弱而宽。一种新型两性壳聚糖已成功制备,工艺简便。     

Effect of molecular and compositional heterogeneity on the rheological properties of cellulose acetate solutions

The properties of acetate fibers are essentially a function of the physical and chemical heterogeneity and the rheological properties of solutions of secondary cellulose acetates (SCA). For this reason, the study of the effect of the molecular and compositional heterogeneity of cellulose acetates on the rheological properties of solutions is important.Scientific-Research Institute of Cotton Cellulose Chemistry and Technology, Tashkent. Translated from Khimicheskie Volokna, Vol. 25, No. 1, pp. 15–17, January–February, 1993.     

乙酸丁酸纤维素酯流变学特性及其在壁材上的应用

对机械活化固相共反应剂法合成的乙酸丁酸纤维素酯进行流变学特性分析,并以其为壁材制备载药微囊。研究表明:机械活化乙酸丁酸纤维素酯溶液为非牛顿流体中的假塑性流体,随温度的升高粘度和动态模量变化都较为明显;纤维素酯溶液的动态模量(G’,G")随角频率的增加呈近似线性增加,并且损耗模量G"大于储能模量G’,表现为粘性特征;以机械活化乙酸丁酸纤维素酯为壁材材料制备阿维菌素微胶囊,所得微胶囊颗粒圆滑,形状均一。     

A light-scattering and membrane formation study on concentrated cellulose acetate solutions

An improved explanation of the mechanism of the porous membrane formation with asymmetric structure has been proposed. It emerged from the correlation of the results obtained by the light-scattering measurements of the ternary membrane casting solutions and by the reverse osmosis and ultrafiltration testing of the asymmetric membranes prepared from these solutions. The results of anisotropic light-scattering measurements indicated the extent of supermolecular structurization of the casting solution which affected the porous structure formation in the membrane surface region. The variation of the casting solution composition and, particularly, the role of the CA/F ratio, the formamide content, and their influence on the asymmetric membrane properties were investigated and explained using the improved concept of the membrane-making mechanism.     

Characterization of water structure in cellulose acetate membranes by calorimetric measurements

The heat capacities of homogeneous and asymmetric cellulose acetate membranes have been measured at different water contents within the temperature range of ?40 to +20°C. The experimental heat capacity–temperature curves were verified by DTA measurements within a temperature range of ?120 to +20°C. The results for the partial heat capacity of water within the membranes as well as for the heat of fusion were interpreted by assuming two different states of water—unfreezing bound water due to a sorption process and unbound water due to capillary phenomena, which freezes with a freezing point depression and a reduced heat of fusion.     

A structure rheological study with poly (oxyethylene)

Four samples of poly(oxyethylene) dissolved in water have been studied rheologically. Flow curves have been obtained for different molecular mass and concentration. From no the mass of network strand, the apparent chain element and the penetration hindrance have been obtained. The polymer turns out to form in water entanglement network solutions with somewhat hindered penetration.     

乙酸乙酯介质中脱氨基反应

在乙酸乙酯介质中，2，6-二氯-4-硝基苯胺（DCNA）经重氮化和还原脱氨基“一锅煮”方法合成出3，5-二氯硝基苯。乙酸乙酯不仅作两相反应的溶剂，而且也提供还原剂乙醇。反应过程中没有棕色的二氧化氮废气产生，酸耗量少．且无副产物如醚类生成。对反应中亚硝酸钠用量、硫酸浓度及用量、乙酸乙酯用量、反应温度等因素进行了研究。     

Preparation of Rh-containing cellulose acetate films and the chemistry of Rh in cellulose acetate

RhCl [P(C₆H₅)₃]₃ complexes have been incorporated in cellulose acetate as a dispersion medium using cosolvent (tetrahydrofuran). The interactions between Rh (I) complexes and cellulose acetate (CA) are examined by infrared spectroscopy and thermal analysis. The chemical reactivities of Rh–CA films have been investigated by reacting Rh sites with CO, H₂, O₂, and C₂H₄ in the temperature range 90–150°C and at a pressure of less than 1 atm. Three different Rh-carbonyls and a Rh-hydride species formed in CA are characterized by their infrared spectra. Treatment of 10 or 20 wt % Rh–CA films with hydrogen (600 torr) at 150°C produces small Rh metal particles of ca. 10 Å or less in diameter in CA, which show catalytic activities under mild conditions in various reactions such as hydrogenation of C₂H₄, oxidation of CO, and Fischer–Tropsch type reactions.     

Porous structure and rheological properties of hydrogels of highly water-absorptive cellulose graft copolymers

The porous structures of the highly swollen hydrogels of cellulose—acrylamide graft copolymers were studied by the solute exclusion technique. For these hydrogels, the cumulative volume of pores up to 560 Å in pore width was between 450 and 850 mL/g, and was between 20 and 30% of the total pore volume. With an increasing in the amount of crosslinker added in the grafting procedure, the cumulative pore volume up to 560 Å decreased. Furthermore, larger pores shrunk preferentially. In the range of concentration from 0.003 to 0.3%, the viscosity of the hydrogels increased remarkably with an increase in concentration. The concentration dependence of the viscosity showed a transition at about 0.03%, which corresponded to the reciprocal of the water retention values for each copolymer. At concentrations over 3%, fluidity of the hydrogels was lost and the water swollen copolymers became viscoelastic. This dynamic viscoelasticity remained essentially unchanged in the temperature range of 20 to 80°C. The dynamic viscoelasticity was dependent on the concentration, but the concentration dependence was smaller than that of the viscosity. The larger the amount of the crosslinker added, the larger the value of dynamic modulus became.     

催化精馏合成乙酸乙酯的工业试验

以固体酸为催化剂,在中试催化精馏塔中进行了乙酸与乙醇反应制备乙酸乙酯的工业试验,试验塔的精馏段塔径为600 mm,内装陶瓷规整填料,反应精馏段塔径为1 000mm,内装7层立体催化精馏塔板.采用连续操作,考察了不同的回流比、釜酸质量分数、进料流量对反应和分离过程的影响,同时测定了塔板上气液相质量分数的分布.通过试验得到...