高残炭硼酚醛树脂的制备

酚醛树脂(PF)因其具有良好的耐热性能和机械性能而被广泛应用。但其耐热性能已经满足不了现代航空航天技术的需求,研究发现,采用硼酸对酚醛树脂进行改性,可以制得具有优良耐高温性能的硼酚醛树脂(BPF)。采用硼酸酯法合成硼酚醛树脂,n(苯酚)∶n(甲醛)=1∶1.5时耐热性最佳。热分析结果表明,合成的BPF在1000℃条件下的残炭率为78%,其耐热性能明显优于传统的酚醛树脂。同时讨论了不同硼酸含量对BPF耐热性能的影响,当n(硼酸)∶n(苯酚)0.33∶1时,残炭率趋于稳定。此外,利用差示扫描量热仪(DSC)方法确定BPF预固化温度为160℃,后固化温度为220℃。     

Chemorheological study of the curing kinetics of a phenolic resol resin gelled

The changes in the resin viscosity, conductivity, mass, and enthalpy during curing reactions have been studied to obtain kinetic parameters that allow modeling of the resin behavior throughout its industrial application. In this work, isothermal rheological tests of a phenolic resol resin were performed in order to study its complex viscosity during crosslinking reactions. Samples were prepared by a precuring treatment in a heated plate press to reach gel point of the resin. Rheological analyses of resol resin curing were carried out at five different temperatures (80-100 °C), and the kinetic models of Arrhenius and Kiuna were applied. The resol resin curing presented an activation energy of 72.1 kJ/mol according to the Arrhenius model. The Kiuna model was proposed to fit the non-linear evolution of the resin’s complex viscosity at the highest temperatures. This kinetic model was suitable for predicting the changes in the complex viscosity of the resol resin after its gelation, and the process activation energy obtained for the second order polynomial applied in this model was 88.1 kJ/mol. In addition, the profile for the degree of curing of resol resin was determined from measurements of the material’s elastic modulus.     

Studies on curing kinetics of a novel combined liquid crystalline epoxy containing tetramethylbiphenyl and aromatic ester‐type mesogenic group with diaminodiphenylsulfone

The curing kinetics of a novel liquid crystalline epoxy resin with combining biphenyl and aromatic ester‐type mesogenic unit, diglycidyl ether of 4,4′‐bis(4‐hydroxybenzoyloxy)‐3,3′,5,5′‐tetramethyl biphenyl (DGE‐BHBTMBP), and the curing agent diaminodiphenylsulfone (DDS) was studied using the advanced isoconvensional method (AICM). DGE‐BHBTMBP/DDS curing system was investigated the curing behavior by means of differential scanning calorimetry (DSC) during isothermal and nonisothermal processes. Only one exothermal peak appeared in isothermal DSC curves. A variation of the effective activation energy with the extent of conversion was obtained by AICM. Three different curing stages were confirmed. In the initial curing stage, the value of E_a is dramatically decreased from ～90 to ～20 kJ/mol in the conversion region 0–0.2 for the formation of LC phase. In the middle stage, the value of E_a keeps about ～80 kJ/mol for cooperative effect of reaction mechanism and diffusion control. In the final stage, a significant increase of E_a from 84 to 136 kJ/mol could be caused by the mobility of longer polymer chains. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3922–3928, 2007     

Studies on the effect of different levels of toughener and flame retardants on thermal stability of epoxy resin

A thermoplastic toughener, polyether sulphone (PES) and a number of different types of flame retardants were blended in different ratios with a commercial epoxy resin triglycidyl-p-aminophenol (TGAP) and 4,4-diamino diphenyl sulphone (DDS) a curing agent. The effect of type and levels of flame retardants (FR) and the toughening agent on the curing, thermal decomposition and char oxidation behaviour of the epoxy resin was studied by the simultaneous differential thermal analysis and thermogravimetric techniques. It was observed that the toughener slightly increases the curing temperature (by up to 20 °C) but had minimal effect on the decomposition temperature of the resin. Flame retardants, however affected all stages depending upon the type of flame retardant used. The curing peak for samples containing tougher and flame retardants although slightly changed depending upon the type of FR, was not more than ± 20 °C compared to that of samples containing toughener only. All flame retardants lowered the decomposition temperature of the epoxy resin. Phosphorus- and nitrogen-containing flame retardants reduced the char oxidation leading to more residual char, whereas halogen- containing flame retardants had less effect on this stage.     

Chemorheological analysis of a gelled resol resin curing under non-isothermal conditions by shear strain

The chemorheological behavior of curing of a resol resin was analyzed under non-isothermal conditions beyond the gelation point. Two heating ramps (0.5 and 1 °C/min) from 0 to 100 °C were performed. The rheological measurements of the resin were performed using oscillatory shear strain. The obtained profiles for the resin’s complex viscosity were applied, after treatment by two calculation methods, to the four- and six-parameter Arrhenius models. These models allow one to establish the viscous flow region of the resin and the kinetic parameters of the material’s curing process. The six-parameter Arrhenius model was selected as the best method for modeling of the resin’s rheological behavior during its curing process. The viscous-flow activation energies determined for the gelled resol resin curing were 67.1 and 58.3 kJ/mol for the 0.5 and 1 °C/min heating rates, respectively. The activation energies of the resin curing process were 41.7 and 67.0 kJ/mol for each temperature ramp.     

Studies on borate esters 1 : The ph dependence of the stability of esters of boric acid and borate in aqueous medium as studied by 11B NMR

The pH dependent stability of esters of boric acid and borate with glycol, glycolic acid, oxalic acid and glyceric acid as dihydroxy compounds has been studied. ¹¹B NMR provides a suitable analytical tool for the quantitative determination and structure elucidation of the various esters in aqueous medium. The pH dependent stability of esters of boric acid and borate is formulated in a general rule of thumb: esters of boric acid and borate with dihydroxy compounds in aqueous medium show the highest stability at that pH where the sum of the charges of the free esterifying species is equal to the charge of the ester.     

Significant evaluation of three factors affecting the pre-curing behavior of urea formaldehyde resin: temperature,solid content,and pH

Journal of Thermal Analysis and Calorimetry - In order to evaluate the significant effects of curing temperature, solid content, and pH on the pre-curing behavior of the UF resin, the isothermal...     

D152树脂对铜(Ⅱ)的吸附性能

The sorption behavior and mechanism of D152 resin for Cu~(2+) is investigated.D152 resin has a good adsorptivity for Cu~(2+) in the HAc-NaAc medium at pH=4.73.The statically saturated sorption capacity is 309mg/g·(resin).Cu~(2+)adsorbed on D152 resin can be eluted quantitatively by using 0.1-2.0mol/L hydrochloric acid as an eluant.The apparent rate constant and activation energy are k_(298)=1.86×10~(-5) sec~(-1) and Ea=12.3kJ/mol.The sorption behavior of D152 resin for Cu~(2+) obeys the Freundlich isotherm.The sorption thermodynamic parameters of D152 resin for Cu~(2+)are enthalpy change ΔH=14.6 kJ/mol,free energy change ΔG=-0.72kJ/mol,entropy change ΔS=51.4J/(mol·K).respectively.     

Effects of modified multi-walled carbon nanotubes on the curing behavior and thermal stability of boron phenolic resin

One kind of boron phenolic resin (BPR) was prepared from the solvent-less reaction of resoles with boric acid. X-ray photoelectron spectroscopy (XPS) showed that the reaction degree of boric acid was 83.8%. Multi-walled carbon nanotubes (MWCNTs) were modified by nitric acid, 4,4′-Diaminodiphenyl methane and boric acid. The effect of modification was determined by Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA) techniques and XPS. The cure kinetics and thermal behavior of BPR and modified multi-walled carbon nanotubes (m-MWCNTs)/BPR were studied. It was found that the curing apparent activation energy (E_a) decreased with the increasing amount of m-MWCNTs. But there was no obvious change in the orders of curing reactions. The results of TGA showed that 1.0 wt% of the m-MWCNTs could increase the thermal decomposition temperature (T_d) and the char yield of m-MWCNTs/BPR nanocomposites by 36.7 °C and 6.2%. These critical enhancements will definitely help to attract more researches on this area.     

聚酯型扩链脲改性环氧树脂E-51/DDS体系反应活性研究

提高二氨基二苯砜(DDS)固化环氧树脂体系的反应活性,降低反应温度、提高反应速率,具有重要的研究意义和实用价值.本研究以聚酯(PEGA1000,2000,PNGA1000,2000)、甲苯-2,4-二异氰酸酯(TDI)、二甲胺为原料合成了含有聚酯型柔性间隔基的扩链脲U-PEGA1000,2000,U-PNGA1000,2000,用其改性环氧树脂E-51/DDS体系,采用DSC系统考察了改性体系的固化反应活性.结果表明,改性体系固化反应活性明显提高,固化反应表现活化能降低,固化反应峰顶温度从230℃降至170℃,固化反应的表观活化能由67.74kJ/mol降至47.80kJ/mol.     

柱前衍生-高效液相色谱法测定香精香料中硼酸和硼砂

香精香料样品中的硼酸经姜黄素的乙酸溶液在室温下进行衍生化,所得硼的衍生物用高效液相色谱法分析。选用Hypersil ODS2色谱柱(4.6mm×250mm,5μm)为固定相,以甲醇与0.012mol·L-1四丁基溴化铵(TBABr)溶液按体积比80比20混合所得溶液为流动相进行淋洗,于波长550nm处进行检测。根据硼砂在硫酸环境下定量转化成硼酸的原理间接测定硼砂。硼的色谱峰面积与其质量浓度在0.004～0.2 mg·L-1范围内呈线性关系,检出限(3s)为4.0×10-4 mg·L-1。在3个浓度水平下做加标回收试验,所得硼酸和硼砂的平均回收率分别在92.1%～106.6%和92.9%～107.1%之间。     

Curing mechanism,heat resistance,and anticorrosion properties of a furan/methyl phenyl silicone coating

A coating composed by methyl phenyl silicone resin (PSi) and furan resin (FR) was prepared, and its curing mechanism, heat resistance, and anticorrosion properties were investigated by Fourier transform infrared spectroscopy, thermogravimetric analysis, electrochemical test, and chemical resistance test. Aldol condensation reaction between FR and PSi occurred at below 200°C, and PSi underwent self‐multidehydrogenation at above 200°C. These curing reactions gave excellent thermal stability and anticorrosion properties. Compared with pure PSi, the blended containing lower than 20 wt% FR had better thermal properties, manifested as over 390°C of 5 wt% weight loss temperature and over 40% of char yield at 800°C. The adhesion property of cured blended system on the metal surface reached the first level which exceeded that of pure PSi coating (the third level). Furthermore, the corrosion resistances of coating in acid, alkali, and salt environments were all improved compared with those of monomeric polymer coating. The impedance of blended coating in 3.5% NaCl solution decreased with increasing FR content, which was 1.8 × 10⁶ Ω cm² when the FR content was 40%, being higher than that of pure PSi coating (7.12 × 10⁵ Ω cm²). This was mainly due to the formation of a cross‐linked network structure based on Si―O―C bond and the enhanced adhesion of cured blended coating. In addition, the surface roughness of cured blended coating was below 2.0 μm, which may have a positive effect on drag reduction in real applications.     

Combined effect of zeolite and boric acid on thermal behavior of epoxy composites

The particles of natural zeolite in combination with boric acid were incorporated into the epoxy resin ED-20 in order to improve the thermal stability of epoxy polymer. Epoxy resin was cured using polyethylenepolyamine. Characterization of the epoxy composites was carried out by using Fourier transform infrared spectrometry, thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) under flow of air and argon. The thermal behavior of the zeolite/boric acid-based epoxy composites (total percentage 15 mass%) were compared with that of 15 mass% boric acid-based epoxy system and the neat epoxy resin. TG and DSC results revealed that the combination of 5 mass% zeolite and 10 mass% boric acid significantly increased the mid-point temperature and residue, and decreased the maximum decomposition rate of the epoxy composites at the heating.     

Multiple-SO3H functioned ionic liquid as efficient curing agent for phthalonitrile-terminated poly(phthalazinone ether nitrile)

Combined with the advantages of low melting point,high thermal stability and strong acidity,a multipleSO_3H functioned ionic liquid(MIL) was developed successfully as a curing agent to promote the curing reaction of phthalonitrile-terminated poly(phthalazinone ether nitrile)(PPEN-Ph).The curing kinetics over differential scanning calorimetry(DSC) showed that both the initial curing temperature T_(p0') and apparent activation energy Ea'(based on Kissinger equation) were reduced significantly over MIL(207.9℃ and 101.5 kJ/mol) compared to the common curing agent ZnCl_2(268.5℃ and 201.5 kJ/mol).Moreover,under identical curing conditions,the resulting thermosetting resin over former(T_(d5%)=526.1℃) showed better thermal stability than that over latter(T_(d5%)=512.1 ℃).These results indicated that MIL should be a good candidate as a curing agent for phthalonitrile resins.     

Preparation of ZnO nanoparticles by a surfactant-assisted complex sol–gel method using zinc nitrate

This paper presents a surfactant-assisted complex sol–gel method for the controlled preparation of Zinc Oxide (ZnO) nanoparticles using zinc nitrate and citric acid as starting material. ZnO nanoparticles with a pure wurtzite structure were obtained after calcination at 773 K. The effects of the citric acid concentration, the pH, and the surfactants on the average particle size and morphology of the ZnO nanoparticles were investigated using X-ray diffraction and scanning electron microscopy. Well dispersed ZnO nanoparticles with a uniform size distribution were obtained using polyethylene glycol (PEG) 2000 as a surfactant. During sintering, the ZnO nanoparticles revealed isotropic growth below 1,373 K and anisotropic growth above 1,473 K. The particles’ activation energy was calculated to be 140 ± 6 kJ/mol between 773 and 1,373 K.     

Determination of the mode and efficacy of the cross-linking of guar by borate using MAS 11B NMR of borate cross-linked guar in combination with solution 11B NMR of model systems

The reaction product of boric acid and the polysaccharide guaran (the major component of guar gum) has been investigated by 11B NMR spectroscopy. By comparison with the 11B NMR of boric acid and phenylboronic acid complexes of 1,2-diols (HOCMe2CMe2OH, cis-C6H10(OH)2, trans-C6H10(OH)2, o-C6H4(OH)2), 1,3-diols (neol-H2), monosaccharides (L-fucose, mannose and galactose) and disaccharides (cellobiose and sucrose) it is found that the guaran polymer is cross-linked via a borate complex of two 1,2-diols both forming chelate 5-membered ring cycles ([B5(2)]), this contrasts with previous proposals. Based upon steric constraints we propose that preferential cross-linking the guaran polymer occurs via the 3,4-diols of the galactose side chain. The DeltaH and DeltaS for complexation of boric acid to cis- and trans-1,2-cyclohexanediol have been determined, from the temperature dependence of the appropriate equilibrium constants, and used in conjunction with ab initio calculations on model compounds, to understand prior conflicting proposals for guaran-boric acid interactions. 11B NMR derived pH dependent equilibrium constants and ab initio calculations have been used to understand the reasons for the inefficiency of boric acid to cross-link guaran (almost 2 borate ions per 3 monosaccharide repeat units are required for a viscous gel suitable as a fracturing fluid): the most reactive sites on the component saccharides (mannose and galactose) are precluded from reaction by the nature of the guar structure; the comparable acidity (pKa) of the remaining guaran alcohol substituents and the water solvent, results in a competition between cross-linking and borate formation; a significant fraction of the boric acid is ineffective in cross-linking guar due to the modest equilibrium (Keq). In contrast to prior work, we present evidence for the reaction of alcohols with boric acid, rather than the borate anion. Based upon the results obtained for phenylboronic acid, alternative cross-linking agents are proposed.     

Separation and sensitive determination of i-urobilin and 1-stercobilin by high-performance liquid chromatography with fluorimetric detection.

i-Urobilin and 1-stercobilin were separated by high-performance liquid chromatography on a reversed-phase octadecylsilane-bonded column and detected fluorimetrically through formation of phosphor with zinc ions in the eluent. The separation and the intensity of the fluorescence response were affected by concentrations of zinc acetate and sodium borate buffer, pH and methanol content in the eluent. The optimal eluent used consisted of 0.1% zinc acetate in 75 mM boric acid buffer (pH 6.0)-methanol (25:75). The detection limit was 0.2 microgram/l for both i-urobilin and 1-stercobilin (signal-to-noise ratio 2), which makes the method 250-2500 times more sensitive than conventional methods.     

D301大孔树脂吸附钒(V)的性能研究

研究了D301大孔树脂对钒的吸附性能.结果表明,pH值对D301树脂吸附钒的影响很大,与钒在溶液中的赋存状态有关,且在pH=2时吸附效果最好:测得吸附热力学参数分别为:△H=8.97kJ/mol,△G_(313)=-5.69kJ/mol,△G_(303)=-5.2kJ/mol,△G_(293)=-4.9kJ/mol,△S=46.84J/mol·K.等温吸附服从Freundlich经验式;考察了溶液浓度、搅拌速率对交换过程的影响,并对实验数据运用相关理论模型进行拟合,结果显示钒(V)在D301树脂上吸附交换过程控制步骤为颗粒扩散控制,反应级数n为0.2391.     

Reduced curing kinetic energy and enhanced thermal resistance of phthalonitrile resins modified with inorganic particles

The effects of inorganic particles such as Al₂O₃ and B₄C on the solidification kinetics and heat resistance of phthalonitrile resin were investigated. The properties of the blends and the cured products were tested by rheometer, differential scanning calorimetry, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The results revealed that B₄C and Al₂O₃ inorganic particles could prolong the gel time of phthalonitrile resin and broaden the processing window. The curing kinetic analysis showed that the presence of the particles could significantly reduce the curing activation energy of phthalonitrile resins by 72.38 kJ/mol down to 43.03 kJ/mol. Meanwhile, the heat resistance of the phthalonitrile resin was improved. Among them, the blend system combined with 30% B₄C showed prominent thermoresistance. And while the T_d5% weight loss temperature was 600°C, char yield at 1000°C was higher than 86% under nitrogen atmosphere; while the T_d5% weight loss temperature was 581°C, char yield at 1000°C was higher than 80% under air atmosphere. Hence, the resulting resins were good candidate matrix of high‐temperature structural composites.     

三角形法和四面体法优化选择毛细管区带电泳背景电解质

建立了两种高效、快速的毛细管区带电泳背景电解质(BGE)的优化方法三角形优化法和四面体优化法。以色谱指纹图谱指数F和色谱指纹图谱相对指数Fr作为评价毛细管电泳分析系统的目标函数,以雪莲药材水提取液为样品,考察一定浓度的硼砂、硼酸、磷酸氢二钠和磷酸二氢钠溶液按三角形优化法和四面体优化法构成背景电解质时对样品的分离情况,通过添加有机改性剂和调节pH进行再优化。用三角形法优化出以50 mmol/L硼砂-含3%乙腈的150 mmol/L磷酸二氢钠(体积比为1∶1)作为BGE时分离效果最佳,用四面体法优化出以50 mmol/L硼砂-150 mmol/L磷酸二氢钠-200 mmol/L硼酸(体积比为1∶1∶2,用0.1 mol/L氢氧化钠调pH 8.55)作为BGE时分离效果最佳,分别获得28个和25个电泳峰。所建立的方法操作简捷,适用于中药材水提取液或醇提取液的毛细管区带电泳BGE的选择。