Properties of Aqueous Solutions of Mixtures of Methyl Cellulose and Hydroxypropyl Cellulose

Rheological properties of dilute and moderately concentrated aqueous solutions of mixtures of methyl cellulose and hydroxypropyl cellulose and gelation in these solutions were studied. Using the solvent vapor sorption, the compatibility of the polymer pair was examined and the composition range in which the thermodynamic compatibility is realized was determined.     

Pervaporation of Water and Ethanol Using a Cellulose Acetate Butyrate Membrane

Okada and Matsuura's transport equations for pervaporation give rise to three fundamental parameters, namely, interfacial saturation vapor pressure P_*, liquid transport parameter A/δ, and vapor transport parameter B/δ. The effects of the chemical nature of the membrane material and the upstream operating pressures of 101.3 and 303.9 kPa on the above parameters were investigated from the pervaporation data at laboratory temperature (24°C) for water and ethanol using a cellulose acetate butyrate membrane. The results show that the P_*, values are essentially unaffected by the upstream pressure, and that they are generally higher than the literature values of saturation vapor pressure at 24°C. Further, the values for A/δ and B/δ tend to increase with increased upstream pressure for both systems studied. These results are discussed.     

Phase Behaviour of Hydroxypropyl Cellulose/ Polyacrylamide Gels

Summary : Polysaccharide-based materials have gained nowadays a great importance in many fields of industry, e.g., in the pharmaceutical industry. Some characteristics of such compounds are their non-toxicity and the presence of a lower critical solution temperature (LCST) and/or an upper critical solution temperature (UCST). This work presents results on the synthesis and characterization of composites from hydroxypropyl cellulose (HPC) and polyacrylamide (PAAm). The ratio of HPC/PAAm was varied as well as the concentration of the crosslinker and the pH value of the reaction mixture. The compounds prepared were characterized by means of Fourier Transform Infrared spectroscopy (FTIR) and turbidity measurements. FTIR spectroscopy showed the presence of the main structural features of the precursors in the gels. The turbidity measurements of the gels in water showed the presence of a LCST in all samples. The LCST decreased when the quantity of HPC was increased in the gel and diminished also with increasing quantities of crosslinker and pH. The turbidity measurement showed the presence of an UCST when the concentration of the polymer was higher than 1% (w/w). This phenomenon is caused by the presence of the PAAm, which acted as precipitant and influenced over the entropy of the system and provoked phase separation.     

Bioelectrocatalytic and Enzymic Activity of Laccase in Water–Ethanol Solutions

The effect the composition of a water–ethanol mixture has on the enzymic (in the pyrocatechol oxidation reaction) and bioelectrocatalytic in a broad potential range (in the oxygen reduction reaction) activity of laccase (L) is studied. On the basis of obtained results conclusions are made about the influence exerted by ethanol in the composition of the water–ethanol mixture on the activity of laccase solubilized and immobilized in the composition of a composite (laccase–Nafion). The decrease in the activity in both the enzymic and the bioelectrocatalytic reactions is probably caused by the denaturation of laccase, which is due to the replacement of the hydration shell of a protein globule by a solvation shell. Besides, there take place a retardation of the kinetic stage of the formation of a laccase–substrate complex (LHO₂OH) because of the slowness of the diffusion of water into an active center and an inhibiting effect of ethanol, which is capable of binding itself to an enzyme globule in the vicinity of the active center of laccase.     

Viscosities of Aqueous Solutions of Dimethylsulfoxide, 1,4-Dioxane and Tetrahydrofuran

Abstract

Viscosities of the systems, water(W) + dimethylsulfoxide(DMSO), W + 1,4-dioxane (DXN) and W + tetrahydrofuran(THF), are measured at temperatures ranging from 303.15–323.15K. Viscosities and excess viscosities are plotted against the mole fraction of the organic solutes. On addition of solutes to water, viscosities first increase rapidly, pass through maxima and then decline continuously until the pure state of solutes is reached. Excess viscosities are found to be positive and large in magnitude and their curves are similar to those of the viscosity curves. The ascending part of the viscosity curves in the water-rich region is accounted for by both the hydrophobic effect of forming cage structures around solutes and the hydrophilic effect forming H-bonds between water and organic solutes. The descending part of the viscosity curves is explained by the continuous destruction of cages formed. The maxima are thought to be due to competing processes of formation and destruction of cage structures.     

Mesophases in a Gel from Hydroxypropyl Cellulose/Polyacrylamide

The objective of the present work is to analyze the different mesophases observed in a gel synthesized from hydroxypropyl cellulose (HPC) and polyacrylamide (PAAm) and its phase behavior in water. Hydroxypropyl cellulose is a material derived from cellulose it is non toxic and degradable. HPC is widely used in pharmaceutics, food additives, stabilizer, thickener, etc., HPC is approved by the FDA for use in the food industry. HPC has the characteristic that it forms liquid crystals, depending on the solvent and on the concentration of the polymer. In this work a lower critical solution temperature (LCST) and an upper critical solution temperature (UCST) were observed, the resulting gel showed anisotropic, nematic and cholesteric phases in water, the phase formed depended on the concentration of the polymer.     

在水-四氢呋喃中纤维素转化为5-羟甲基糠醛及副产物鉴定

在酸性条件下,水-四氢呋喃混合溶剂中转化纤维素制备了平台化合物5-羟甲基糠醛（HMF）．在纤维素浓度仅为2.4wt%时,可以得到38.6%的HMF,但是随着纤维素浓度的增加,胡敏素和乙酰丙酸成为主要产物．利用液相色谱-多级串联质谱联用技术检测到了分子式为C9H16O4、 C10H14O4、 C11H12O4、C12H10O5 和C12H16O8的一系列副产物．C9H16O4是通过四氢呋喃开环为1,4-丁二醇再与乙酰丙酸酯化反应得到,而C10H14O4是通过四氢呋喃开环后与HMF醚化得到．C11H12O4是由5-羟甲基糠醛与乙酰丙酸发生酯化反应得到,C12H10O5是由HMF自身醚化得到,而C12H16O8是HMF与葡萄糖经过缩醛反应得到．HMF的自身醚化反应及HMF与1,4-丁二醇的醚化反应是主要的副反应．     

Ultrasonic Solution Degradations of Polystyrene and Substituted Polystyrenes in Tetrahydrofuran as Solvent

Abstract

Ultrasonic (70 W, 20 kHz) solution (2% THF) degradations of polystyrene (PS), poly(α-methylstyrene) (PαMeS), poly(p-isopropyl α-methylstyrene) (PpiPrαMeS), poly(p-chlorostyrene) (PpCIS), poly(p-bromostyrene) (PpBrS), and poly(p-methoxystyrene) (PpOMeS) have been carried out in tetrahydrofuran at 27° C. The average number of chain scissions S (where S = [(M _n)₀/(M _n)_t] - 1), computed from the overall values of [(M _n)₀ and (M _n)_t, were found to be different from those of S' (where S' = α([(M _n)₀/(M _n)_t] - 1)) based on the component (only that part of the polymer which is involved in degradation) data of the weight fraction (α), (M _n)₀, and (M _n)_t), S' for polystyrene and substituted polystyrene follows the order PS gt; PpCIS gt; PpiPrαMeS gt; PpBrS gt; PpOMeS gt; PαMeS. In the case of PS where degradations were also carried out at -20°C, lowering of the temperature increased the weight fraction of polymer degraded as well as S. Based on the viscosity and GPC data, it is concluded that the ultrasonic solution degradation of PS does not lead to branched polymers.     

长链烷酸接枝羟丙基纤维素相变材料的制备及其性能

采用酯化的方法将具有相变特征的长链脂肪酸接枝到羟丙基纤维素主链上, 得到了一系列性能稳定, 温度范围适宜的高分子固-固相变材料, 并利用傅里叶红外光谱(FT-IR)、核磁共振(NMR)、差示扫描量热仪(DSC)、热失重分析仪(TGA)和X射线散射等技术手段对其化学结构及相变行为进行了研究。 结果表明, 该材料呈现出可逆的固-固相转变特性, 相变温度范围可通过改变脂肪酸的长度调节。 利用棕榈酸、硬脂酸和花生酸获得的相变材料焓值达到60 J/g, 所获得的材料在250 ℃以内不发生热分解。 通过将两种长链脂肪酸混合同时接枝到羟丙基纤维素主链上, 所得产物的吸/放热温度随着混合脂肪酸组分含量的变化而变化, 同时X射线散射的结果也证明羟丙基纤维素混合酯的分子间距是位于其两种单一酯之间的。这一结果为制备一定温度范围内任意相变温度的高分子固-固相变材料提供了简便的方法。     

Composite Fibers Based on Hydrated Cellulose and Poly-N-vinylpyrrolidone,Prepared from Cellulose Solutions in N-Methylmorpholine-N-Oxide

Russian Journal of Applied Chemistry - Hydrophilic composite fibers of various compositions were prepared from mixtures of solid solutions of cellulose in N-methylmorpholine-N-oxide or its...     

纤维素在离子液体中的降解转化

随着社会对能源资源的需求越来越大,生物质资源得到了广泛的重视,世界上存储量最大的生物质资源--纤维素在新兴溶剂离子液体中的降解转化受到了越来越多的关注。本文简要介绍了近几年来纤维素在离子液体中的溶解、单糖(果糖、葡萄糖)在离子液体中脱水转化为5-HMF(5-羟甲基糠醛)和纤维素在离子液体中一步降解转化为5-HMF的研究。指出目前研究存在的缺点与不足,并提出了可能的解决方法。     

Thermal Degradation of Cotton Cellulose

The thermal degradation of cotton cellulose treated with chemical mixtures containing P and N was studied by thermal analysis, infrared spectroscopy, Char yield and limiting-oxygen-index (LOI). Our experiments demonstrated the following facts. The temperatures and activation energies of pyrolysis were lower for cotton cellulose treated with flame retardants than those for untreated samples and the values of Char yield and LOI were greater for treated cotton than those for untreated one. This revised version was published online in August 2006 with corrections to the Cover Date.     

Nonlinear Dielectric Effect Study of Tetrahydrofuran Association in Benzene and Cyclohexane Solutions

The nonlinear dielectric effect (NDE) has been applied to study the molecular association in tetrahydrofuran (THF) solutions in benzene and in cyclohexane. On the basis of the experimental values of the NDE parameter, electric permittivity, and density, determined as a function of temperature and concentration, and applying the general, statistical theory of NDE, the association constants and dipole moments of the associates were determined. The molecular orbital PM3 method has been applied to calculate the dipole moments and energy of molecular clusters. The results of NDE and PM3 studies are fairly consistent and reveal that a weak dipolar association takes place in the cyclohexane solutions. In the benzene solutions the association, if any, is much weaker probably due to competitive interactions between the solute and the solvent.     

Amphiphilic Graft Copolymers of Hydroxypropyl Cellulose Backbone with Nonpolar Polyisobutylene Branches

The novel amphiphilic graft copolymers with hydrophilic hard polar hydroxypropyl cellulose(HPC) backbone and hydrophobic soft nonpolar polyisobutylene(PIB) branches have been successfully synthesized through nucleophilic substitution reaction of living PIB chains carrying oxonium ions with the-OH groups along HPC backbone. The PIB branch length in the graft copolymers could be designed by living cationic polymerization and the grafting density could be adjusted by PIB~+/-OH molar ratio. The living PIB chains carrying oxonium ion were prepared by transformation of allyl bromide end groups in the presence of AgClO_4 and silver nanoparticles(3.2±0.3 nm, 0.7 wt%-1.8 wt%)generated in situ from AgBr. The phase-separation morphology was formed in the graft copolymers due to their incompatibility between backbone and branches. The hydrophilicity on the surface of graft copolymer films could be turned to hydrophobicity by increasing grafting density or/and length of PIB branches. The soft PIB segments in graft copolymers provided an unique surface via self-assembly for anti-protein adsorption against bovine serum albumin. A small amount of Ag nanoparticles in the copolymers contributed to good antibacterial activities against Staphylococcus aureus or Escherichia coli.     

GC Methods for the Determination of Methanol and Ethanol in Insulating Mineral Oils as Markers of Cellulose Degradation in Power Transformers

Methanol and ethanol in transformer oils have been recently proposed as new markers of thermal and mechanical degradation of cellulose (the solid insulation in power transformers). In this work, we optimized and compared the performance of two headspace gas chromatographic methods based on flame ionization (HS–GC–FID) and mass spectrometry detection (HS–GC–MS) to determine methanol and ethanol in insulating mineral oil. For methanol and ethanol, the detection limits were 12 and 27 μg kg^?1 (HS–GC–FID) and 1.3 and 3.1 μg kg^?1 (HS–GC–MS). Repeatability was evaluated in transformer oils for both the methods at different concentration levels of analytes and RSD values were found to lie between 1.8 and 16 %. The accuracy of the methods was assessed under a proficiency test (Cigré JWG A2/D1.46). The methods were compared by a F-test and a one-sided paired t test performed on 21 transformer oils in service. Correlations of methanol and ethanol content in sampled oils against their actual time of service are provided. For each sample, the content of traditional markers (furan-2-carbaldehyde and CO₂) was also measured, finding a correlation between light alcohols and CO₂ content. This indicates that methanol and ethanol determination may be helpful in providing further information on the thermal degradation conditions of transformers’ solid insulation. The method developed is currently routinely applied by the laboratories of Sea Marconi Technologies for the assessment of transformers’ conditions.     

棉浆粨纤维素的超声波处理

氢键;结晶程度;棉浆粨纤维素的超声波处理     

Excess Molar Volumes and Thermal Expansivities of Aqueous Solutions of Dimethylsulfoxide,Tetrahydrofuran and 1,4-Dioxane

Densities, , of the systems water (W) + dimethylsulfoxide (DMSO), W + tetrahydrofuran (THF) and W + 1,4-dioxane (DO) have been determined in the temperature range 303.15-323.15 K. Excess molar volumes, $V_m^E $ , have been found to be negative and large in magnitude. Thermal expansivities, f , and excess thermal expansivities, f E , have been calculated. Densities, excess molar volumes, thermal expansivities and excess thermal expansivities have been plotted against mole fraction of solutes. All these properties have been expressed satisfactorily by appropriate polynomials. Attempt has been made to explain $V_m^E$ in terms of hydrophobic hydration and hydrophilic effect of the solutes.     

纤维素酶降解纤维素机理的研究

纤维素是自然界中含量最多的一类碳水化合物,同时它也是地球上数量最大的可再生资源。纤维素酶是一种高活性生物催化剂,在纤维素类资源的利用方面发挥重要的作用。本文综述了纤维素、纤维素酶的分子结构和纤维素酶对纤维素的降解机理,影响酶解的主要因素以及提高酶解效率的主要措施,并对纤维素酶研究存在的问题以及今后的发展作了进一步展望。