木质素改性酚醛树脂的研究进展

人造板工业用的酚醛树脂胶,虽然粘接性能好,但在制造和使用的过程中都会释放出污染物甲醛,而木质素分子中有酚羟基和醛基,使用木质素,既可改善胶粘剂的性质,又可节约苯酚的用量,降低甲醛释放量,达到废物利用与保护环境的目的本文综述了木质素磺酸盐、碱木质素、甘蔗渣木质素、酶解木质素等代替部分苯酚应用于环保树脂胶的制备工艺及研究发展现状,并对其发展前景作了展望     

The thermal expansion behaviour of oriented polypropylene

The thermal expansion behaviour of die drawn polypropylene rods has been measured over the temperature range −50°C to +10°C. For high draw samples the values for the thermal expansion coefficient in the axial direction α_∥ are negative and increase in magnitude with increasing temperature. It is shown that this result is consistent with the presence of an internal shrinkage stress. For low draw samples and most high draw samples after annealing, the value of α_∥ is positive and increases in magnitude with increasing temperature. It is shown that this result can also be explained in terms of an internal shrinkage stress, on the basis of a simple relationship between the axial and radial expansion coefficients.     

Effect of different modified lignins on the properties of xylan composite hydrogels

To improve the mechanical properties of hemicellulose hydrogel, a green, adjustable mechanical property, high swelling ratio (SR) composite hydrogel was successfully prepared by using modified lignin as a reinforcing agent. The structure and characteristics of the composite hydrogels were investigated by TGA, FTIR, SEM, rheological analysis, and SR. It can be found that the modified lignin could significantly improve the mechanical properties of the composite hydrogels. The maximum compressive stress of unmodified lignin hydrogel was 61.72 kPa and the compressive deformation was 75%. Compared with the unmodified lignin hydrogel, the mechanical properties were significantly improved, with the maximum compressive stress of the modified lignin hydrogel was 145.2 kPa and the compressive deformation was up to 90%. After adding modified lignin, the SR of the as-prepared hydrogel was up to 155.17 g/g, which was much higher than that of unmodified lignin hydrogel (105.79 g/g). The composite hydrogel had good antioxidant properties, and the free radical removal rate can reach 85.3%, which is twice as much as that without the modified lignin. With cost-effective lignin as a reinforcing agent, the as-prepared hemicellulose hydrogel with adjustable mechanical properties is favorable for great application potential.     

The thermal expansion behaviour of highly oriented polyethylene

The thermal expansion behaviour of oriented polyethylene has been studied over the temperature range ?50°C to +20°C. In general the values for the thermal expansion coefficient in the orientation direction are negative and of a greater magnitude than the c-axis expansion for the crystal, which is approached at ?50°C. This remarkable effect has been quantitatively related to the influence of an internal shrinkage force, and the changes in expansivity with temperature shown to relate primarily to the change in modulus with temperature.     

Halogeno‐modified polystyrene: monomer reactivity ratios,thermal behaviour and flammability

Chemical modification based on incorporation of flame retardants into polymer backbones was used in order to reduce flammability of polystyrene (PSt). The halogeno‐substituted styrenes: 4‐chlorostyrene (ClSt), 4‐bromostyrene (BrSt) and 2,3,4,5,6‐pentafluorostyrene (5FSt) were applied as reactive flame retardants. Homo‐ and copolymers of these halogeno‐substituted styrenes and styrene (St) were synthesized with various feed ratios using free radical bulk polymerization with azobisisobutyronitrile as a initiator. This yielded series of (co)polymers with various amounts of included ClSt, BrSt and 5FSt (5–50 mol% of modified St). Copolymer compositions were determined using ¹H NMR spectroscopy. The relative reactivity ratios of the used comonomers were determined by applying conventional linearization methods. The Jaacks (J) method was used for systems including BrSt and ClSt monomers whereas the Fineman–Ross method was additionally used to confirm the values of reactivity ratios of St–5FSt. The reactivity ratios of comonomer pairs obtained from J plots were 0.75 and 0.38 (St–ClSt), 1.65 and 0.46 (St–BrSt), 0.44 and 0.42 (St–5FSt). Glass transition temperature and thermal stability of obtained (co)polymers were determined using differential scanning calorimetry and thermogravimetric analysis (TGA), respectively. The thermal degradation kinetic of PSt, PClSt, PBrSt and P5FSt was studied applying TGA. Kinetic parameters such as thermal decomposition activation energy (E) and frequency factor (A) were estimated using Ozawa and Kissinger models. The resulting activation energies estimated using these two methods were quite close. The values of activation energy (kJ mol^?1) increased in the following order: PClSt (E(O) = 216.1) < PSt (E(O) = 219.9) < PBrSt (E(O) = 224.7) < P5FSt (E(O) = 330.9). A pyrolysis combustion flow calorimeter was applied as a tool for assessing the flammability of the synthesized (co)polymers. © 2014 Society of Chemical Industry     

Succinylation of three different lignins by reactive extrusion

Succinate esters of three lignin materials were prepared by reactive extrusion. Reactive extrusion was developed as a facile route to chemically modify lignin with the benefits of being a scalable, solvent‐free, and economic process. Kraft lignin and crude and purified enzyme saccharification lignins were reactively extruded with varying amounts of succinic anhydride. The resulting products were characterized chemically and thermally. Succinylation occurred preferentially at the aliphatic hydroxyl groups of kraft lignin, with phenolic substitution occurring at higher amounts of succinic anhydride addition. The degree of substitution was dependent on the relative amounts of succinic anhydride and lignin substrate. Thermal stability of the products decreased with increasing levels of substitution, primarily due to the loss of succinate groups on heating. The degree of substitution influenced the glass transition temperature, which reflected the melt flow and solubility of the products. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The thermal shock behaviour of ductile particle toughened alumina composites

Over recent years, it has been established that the incorporation of metallic particles into a ceramic matrix can lead to enhanced fracture properties. Relatively few attempts, however, have been made to establish whether or not the improved fracture toughness typically observed in such composite systems can offer improved performance in demanding environments. The current study is concerned with the thermal shock behaviour of a ceramic matrix composite consisting of an alumina matrix containing 20 vol% of discrete iron particles. The composite material has been produced by both hot pressing and conventional sintering techniques. The hot pressed composite shows a greater resistance to thermal shock than the monolithic matrix, both in terms of the critical temperature differential and retained strength, whereas the sintered material has been found to behave as a typical low strength refractory ceramic. The calculation of thermal shock resistance parameters for the composites and the monolith has indicated possible explanations for the differences in thermal shock behaviour.     

High temperature thermal stabilization of alumina modified by lanthanum species

The effects of precursor pretreatment and addition methods of lanthanum species on stabilization of alumina (surface area loss, phase transformations and high temperature interaction with lanthanum species) have been investigated by BET specific surface area measurements (BET), X-ray powder diffraction (XRD), N₂ adsorption–desorption isotherms, thermal analysis and X-ray photoelectron spectroscopy (XPS) in the range of 600–1150°C. Although powder La₂O₃, which is mechanically mixed with γ-Al₂O₃ or pseudo boehmite, can effectively retard the α phase transformation by solid phase interaction with Al₂O₃, it does not show a positive effect on retarding the loss of surface area. Compared with the direct impregnation of γ-Al₂O₃, the gelation of pseudo boehmite by acidification accelerates phase transformations and weakens the stabilizing influence of lanthanum species. At 600°C and for atomic ratio of La/Al up to 0.1 or at 1150°C and La/Al≤0.02, the lanthanum species is highly dispersed in alumina. With the increase of calcination temperature or lanthanum content, lanthanum species is present as dispersed La₂O₃, LaAlO₃ and crystalline La₂O₃. At T≤1000°C the surface area loss of alumina is mainly attributed to the sintering of particles. The follow-up loss at T>1000°C results from both sintering and phase transformations. The highly dispersed lanthanum species retard both sintering and phase transformations, and their associated surface area loss. However, the formation of LaAlO₃ mainly retards the surface area loss resulting from the α phase transformation. Having considered the purely mechanical mixing effect of additive on the surface area loss of alumina, an influence criterion of lanthanum species on retarding the surface area loss whether resulting from sintering or from α phase transformation at high temperature ≥1000°C has been proposed in this paper.     

负载硅钨杂多酸纳米银修饰电极的电化学性质研究

以硅钨杂多酸作为光催化还原剂制备了纳米银(SiW12-NS)。用PVP作偶联剂,将SiW12-NS修饰到玻碳电极表面,用循环伏安法(CV)研究其电化学行为。结果表明,修饰电极具有良好的电化学响应和电极稳定性,对BrO3-,NO2-具有良好的电催化还原性能。     

Crystallisation behaviour of blast furnace slag modified by adding fly ash

Crystallisation of molten blast furnace (BF) slag can increase its viscosity, which can in turn affect the quality of slag fibres. Fly ash was added to BF slag to control its crystallisation and modify its chemical composition. FactSage simulation and analyses using X-ray diffraction (XRD), scanning electron microscope-backscattered electrons (SEM-BSE) coupled to an energy dispersive spectrometer (EDS), and single hot thermocouple technique (SHTT) were performed to explore the crystallisation behaviour of the modified BF slag. The relationship between temperature, mineral precipitation, and added fly ash content was investigated. The minerals contained in the modified BF were melilite, anorthite, clinopyroxene, and spinel. Variation in the fly ash content did not change the composition of the precipitate, but changed its content and the crystallisation temperature of the minerals, which affects the initial crystallisation temperature of the modified BF slag. It decreased as fly ash content increased, and was influenced by the crystallisation of melilite when the added fly ash content was between 5% and 20%. When the added fly ash content increased to 25%, the initial crystallisation temperature was influenced by the precipitation of anorthite. The initial crystallisation temperatures obtained by FactSage simulation, XRD analysis, and SHTT experiments differed due to kinetic effects. The modified BF slag with a fly ash content of 15% is considered suitable for manufacturing of slag fibres due to its low initial crystallisation temperature and cost.     

The influence of ultrasound on the thermal behaviour of clay minerals

The aim of this work is to compare the influence of sonication on the thermal behaviour of kaolinites (KGa-1, KGa-2), pyrophyllite, talc and muscovite. Sonication produces a significant increase of the specific surface area due to particle size reduction. As sonication time increases and the particle size decreases, the thermal behaviour of these clay minerals is strongly modified. Thus, there is a significant increase of the weight loss at low temperature which is related to the loss of some outer hydroxyl groups and protonated hydroxyls whose proportion in the minerals increase as the new surface generated increases. Additionally, the original endothermic dehydroxylation effects of all these minerals shift to lower temperatures. Disordered kaolinite shows the smallest shift (9 °C) while muscovite presents the largest (184 °C). A linear relation has been established between the temperature shift of the dehydroxylation and the percentage of increase in the specific surface area. The influence of sonication on the high temperature DTA effects of kaolinite, pyrophyllite, and muscovite is also studied.     

A study of spalling behaviour of PAN fibre-reinforced concrete by thermal analysis

Comparisons are made between polypropylene (PP) fibres and polyacrylonitrile (PAN) fibres in order to relate the thermal properties of fibres with the respective fibre mortar behaviour under thermal exposure. Thermogravimetry (TG), differential scanning calorimetry (DSC) and thermochromatography (ThGC) are utilized. When a cementitious fibre mortar is being heated, several physical phenomena occur in the temperature range between 100°C and 200°C. There is a significant difference in the thermal behaviour between PP and PAN fibres. PP fibres melt at 160–170°C. The non-melting behaviour of PAN fibre together with its rapid exothermic degradation reactions at around 300°C may add risk to the spalling of fibre mortar under rapid thermal exposure.     

环氧树脂改性聚氨酯耐热性能的研究

端异氰酸酯基聚氨酯预聚体与环氧树脂E-51形成了互穿网络,通过热重分析仪(TGA)研究了完全固化后的互穿网络的热分解行为、透射电镜研究了IPN的相分离行为,及拉伸强度、硬度等对其进行了表征。结果表明,经过环氧树脂改性的聚氨酯的耐热性能比纯聚氨酯得到了提高,且力学性能也有所改善,并对其机理进行了阐述。     

Enhanced fluorescence and thermal sensitivity of polyethylenimine modified by Michael addition

Polyethylenimine (PEI) with enhanced fluorescence and thermal sensitivity was achieved by Michael addition of divinylsulfone (DVS) and N-isopropylacrylamide (NIPAm) respectively. The fluorescence enhancement is quantitatively studied by tailoring the amount of DVS, the medium pH, the substituting acrylates, the substrate polymers with different type amine groups, and the substrate molecular weights. The results suggested that different amine groups affected the performance of fluorescence with quantum yields varied from 0.340 for primary amine (NH₂-) to 0.090 for tertiary amine (N(-C)₃), and further to 0.049 for secondary amine (-NH-). It was also found that the fluorescence enhancement was attributed to the specific molecular structure of DVS-substituted product. The fluorescence moiety is believed to involve a proton-transfer process and have O₂-dependent and pH-sensitive fluorescence properties. From the current study, it can be expected that the accurate prediction of the O₂-dependent fluorescence would be dependent on molecular orbital calculation of the small amine molecules (oxidized with O₂) and their DVS-substituted products.     

Carbonization behaviour of modified synthetic mesophase pitches

Stabilization of naphthalene-derived synthetic mesophase pitch was achieved by controlled oxidation or reaction with phenanthrenequinone (PHQ) in order to suppress the swelling during high-temperature treatments. The modified pitches were characterized and their carbonization behaviour was studied by thermogravimetry-mass spectrometry. The results show that naphthenic groups are involved in the stabilization process. PHQ reacts via cycloaddition reactions, yielding oxygen-containing non-planar structures, a feature that accounts for the loss of anisotropic properties of the final material.     

The effect of magnetic stabilization on the thermal behaviour of fluidized beds

The effect of a magnetic field on the thermal behaviour of a fluidized bed of magnetizable particles with an immersed heating surface has been studied. The temperature distribution inside the bed has been determined, both in the radial and axial directions. A model has been developed which allows calculation of the effective thermal conductivity of the bed from experimental data.     

聚砜改性环氧树脂复合材料热老化性能研究

以聚砜(PSF)改性环氧树脂(EP)为基体树脂,玻璃纤维为增强材料,采用高温模压成型法制备出PSF改性EP/玻璃纤维复合材料。结果表明:PSF能有效提高EP基体的热稳定性能;经200℃热老化72 h后,PSF改性EP/玻璃纤维复合材料的热失重率<1%,其冲击强度和弯曲强度呈先升后降态势,电绝缘性能仍然较好(其体积电阻率和表面电阻率的数量级仍保持在1012左右);该复合材料在高温绝缘场合中具有良好的应用前景。     

Reaction between chlorophosphazenes and silicon alkoxides—formation of temperature-stable thermosetting materials

The reaction between chlorophosphazenes and silicon alkoxides has been studied as a means of preparing temperature-stable thermosetting resinous materials. If the silicon alkoxide is polyfunctional in straight-chain lower alkoxy groups the usual reaction is elimination of alkyl chloride and formation of a thermosetting resinous product. The mechanism of this reaction is discussed. Other reactions occurring in the treatment of chlorophosphazenes with silicon alkoxides are also discussed. Asbestos laminates which retain much of their strength when heated to 500° for 50 hours in air can be prepared from the thermosetting resinous products resulting from the reaction between chlorophosphazenes and silicon alkoxides.     

Fractionation of woodmeal by prehydrolysis and thermal organosolv. Process strategy,recovery of constituents,and solvent fractionation of lignins so produced

A prototype hardwood Populus deltoids has been fractionated in kg quantities into its primary constitutive polymers, namely, cellulose, hemicelluloses, and lignin, under optimal recovery conditions for each fraction. Our approach is targeted at processing sawdust or finally divided wood (d_p ≤ 0.5 mm) and involves a thermomechano-solvolytic treatment of medium consistency suspensions in two process development units operated sequentially. Firstly, the hemicellulose fraction is removed from the initial wood by a aqueous-steam pretreatment (auto-hydrolysis) at conditions where nearly 90% of the hemicelluloses are solubilized. Secondly, the treated wood (lignocellulose) is separated into cellulose and lignin rich fractions by subjecting it to an organosolvolytic treatment using ethylene glycol as solvent. An experimental unit which can be operated in semi-continuous or continuous modes is described and was employed for this step. The recovery of each fraction via appropriate mass balances is presented. Also, a comparative characterization of the lignins isolated via (a) the direct solvolysis route and (b) the sequential aqueous-steam pretreatment followed by solvolysis approach is made using solvent fractionation, molar mass distribution, and ¹³C NMR spectroscopy methods.     

The methanogenic toxicity of wastewater lignins and lignin related compounds

Lignin derivatives are major components of wastewater streams generated in the chemical processing of wood. The objective of this study was to evaluate the inhibitory effect of various lignins isolated from forest industry wastewaters, and selected lignin model compounds, on methanogenic bacteria. The methanogenic inhibition was determined at 30°C in standard toxicity assays, utilizing anaerobic granular sludge as inoculum. The wastewater lignins differed considerably in their inhibitory activity. Some lignin samples were nontoxic, whereas others caused 50% inhibition at concentrations ranging from 3320 to 5950 mg COD dm^?3. Experiments with ultrafiltered lignins revealed that the toxicity of the inhibitory lignin samples originated from the low molecular weight fraction. In additional studies with low molecular weight lignin model compounds, it was observed that the inhibitory activity of these compounds was related to the functional groups on the aromatic ring. Compounds with aldehyde groups or apolar substituents were highly toxic, whereas those with carboxylic groups only caused significant inhibition at high concentrations. These results indicate that low molecular weight lignin derivatives in forest industry wastewaters are potential inhibitors of anaerobic treatment systems.