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。     

流动床离子交换工艺在己二酸催化剂回收中的应用

介绍流动床离子交换装置回收催化剂的生产工艺，从交换装置的选择到运行，分析了流动床的优点、影响因素以及生产中应注意的问题和要求。     

指数曲线贮仓的设计剖析

贮仓是许多工业过程中的常用设备，起拱是贮仓使用时常出现的故障，如何解决起拱问题是贮仓设计的关键，除常采取增大仓壁倾角、设置破拱装置等方法外，设计成曲线贮仓也是行之有效的措施之一。分析了指数曲线贮仓的工作原理和特点，建立了仓壁指数曲线方程，阐述了设计步骤与注意事项，并举例说明。     

Vinyl‐containing silicone resin as the crosslinking agent of heat‐curable silicone rubber

Heat‐curable silicone rubber (HCSR) was prepared by using vinyl‐containing silicone resin (VSR) as the crosslinking agent instead of polyvinylsilicone oil (C gum). Mechanical properties and crosslink density of the vulcanizates were measured. The results indicate that VSR is a good crosslinking agent for HCSR. The tensile strength, tearing strength, elongation at break, and hardness of the vulcanizate can reach 10.2 MPa, 29.1 kN/m, 720%, and 58 SHA, respectively. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 3123–3127, 2002; DOI 10.1002/app.10054     

Diterpene resin acids: Major active principles in tall oil against Variegated cutworm,Peridroma saucia (Lepidoptera: Noctuidae)

Tall oil, a by-product of the kraft process for pulping softwood, has been shown to have insecticidal properties. In the present study, the active principles in tall oil against the variegated cutworm,Peridroma saucia Hübner, were investigated. GC-MS analysis showed that abietic, dehydroabietic, and isopimaric acids were major resin acid components of crude tall oil and depitched tall oil. When crude tall oil samples of differing resin acid composition were incorporated into artificial diet at a concentration of 2.0% fresh weight, they suppressed larval growth by 45–60% compared to controls. This suppression was significantly (P0.05) correlated with the equivalent contents of abietic, dehydroabietic, isopimaric, and total resin acids. These results were also evident from a diet choice test, showing that the second-instar larvae obviously selected diets with low levels of resin acids when different diets were randomly arranged in a Petri dish. Bioassays with pure resin acids (abietic, dehydroabietic, and isopimaric acids) demonstrated that all individual chemicals have similar bioactivity against this insect. Comparison of the bioactivities of depitched tall oil and an equivalent mixture of pure resin acids in thePeridroma chronic growth bioassay indicated that pure resin acids and depitched tall oil share a common mode of action to this insect. This study confirms that resin acids are major active principles in tall oil against the variegated cutworm, but other chemicals likely also contribute to the bioactivity of tall oil.     

Catalytic and inhibitory effects of dissolved Cd2+ on C3H8 electro-oxidation

Studies have been made of the effect of Cd²⁺ on the oxidation rate of C₃H₈ in 80% H₃PO₄ at 130 C on platinized Pt electrodes.Dissolved Cd²⁺ discharges, probably as Cd⁰, and forms a stable sub-monolayer on a Pt electrode at potentials as high as 0·5 V versus RHE. Although this Cd⁰ layer is apparently substantially desorbed in favor of adsorbed hydrocarbon, C₃H₈ adsorption is inhibited in its presence. C₃H₈ oxidation is also inhibited. However, the C₃H₈ oxidation rate is observed to increase under some circumstances, and this appears to be because Cd isabsorbed into the Pt lattice. Co-plating of Cd and Pt leads to an electrode which, once the excess Cd has been removed, appears to be stable, and which catalyses C₃H₈ oxidation by about a factor of three at 0·25 V. Above 0·3 V, this absorbed Cd somewhat inhibits C₃H₈ oxidation.     

Synthesis and Morphology of TiO2 Nanotube Arrays by Anodic Oxidation Using Modified Glycerol-Based Electrolytes

Titanium dioxide (TiO₂) nanotube arrays were prepared by electrochemical anodization of titanium sheets in the glycerol 176 mL/H₂O 44 mL/NH₄F 0.5 wt% electrolytes modified with H₂SO₄ and NaAc addition. The surface morphologies, average inner diameter, and the length of the nanotube arrays changed with the solution pH in the range from 5.6 to 4.0 by adding H₂SO₄. A uniform surface morphology of the nanotubes with average inner diameter of ∼80 nm and a length of ∼1000 nm was obtained when the solution pH was 5.0. The growth rates of the nanotubes were remarkably enhanced by NaAc addition in the range of 0.04–0.14 M . With NaAc addition of 0.10 M , the length of the nanotube arrays reached 4.16 μm after an 8-h anodization, increasing 3.23 μm compared with no NaAc addition. The relationship between solution pH and growth of TiO₂ nanotubes was analyzed by current–time curves, solution electrical conductivities, and scanning electron microscopy (SEM), and the role of NaAc was also discussed based on SEM and solution electrical conductivities.     

A growth mark method for studying growth mechanism of carbon nanotube arrays

A novel and simple growth mark method was developed to make marks during the growth process of carbon nanotube arrays. These marks can be read out under scanning electron microscope or optical microscope. Based on this method, the growth rates at different temperatures and under different acetylene partial pressures were measured, from which the activation energy and the order of reaction were determined. Based on our experimental results, the growth of carbon nanotube arrays in our experimental condition could not be diffusion-limited. The measured activation energy could possibly be attributed to the heterogeneous decomposition of acetylene over the catalyst particle. Furthermore the marked array with special segmental structure may be found some applications in the future.     

Isomerization Dynamics of Dicyanine A in n-Alcoholic Solution

The radiationless relaxation of dicyanine A molecules in n-alcohols methanol to butanol has been studied by picosecond fluorescence spectroscopy and time-resolved nonlinear spectroscopy. The fluorescence decay rates have been measured as a function of viscosity, temperature, and fluorescence wavelength. It is shown that the wavelength dependence can be explained by coexistence of two ground-state conformers. The intrinsic activation barrier for the nonradiative decay from the excited surface is very small, much less than 1 kcal/mol. In a particular solvent the time constants of the nonradiative relaxation show a linear dependence on the variation of viscosity. The experimental data are discussed in relation to the BFO theory (Bagchi, B.; Fleming, G.R.; Oxtoby, D.W. J. Chem. Phys. 1983, 78: 7375).     

The kinetics of B‐a and P‐a type copolybenzoxazine via the ring opening process

The structure of benzoxazines is similar to that of phenolic resin through thermal self‐curing of the heterocyclic ring opening reaction that neither requires catalyst nor releases any condensation byproduct. These polybenzoxazine resins have several outstanding properties such as high thermal stability and high glass transition temperature. To better understand the curing kinetics of this copolybenzoxazine thermosetting resin, dynamic and isothermal differential scanning calorimetry measurements were performed. Three models, the Kissinger method, the Flynn–Wall–Osawa method, and the Kamal method, were used to describe the curing process. Dynamic kinetic activation energies based on Kissinger and Flynn–Wall–Osawa methods are 72.11 and 84.06 KJ/mol, respectively. The Kamal method based on an autocatalytic model results in a total order of reaction between 2.66 and 3.03, depending on curing temperature. Its activation energy and Arrhenius preexponential are 50.3 KJ/mol and 7959, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 730–737, 2005