Kinetic parameters of a cyanate ester resin catalyzed with different proportions of nonylphenol and cobalt acetylacetonate catalyst

The isothermal cure of a dicyanate ester monomer has been investigated by differential scanning calorimetry (DSC) in the presence of different quantities of a catalyst system formed by nonylphenol (NP) and cobalt (II) acetylacetonate (Co(AcAc)₂). Two sets of experiences were studied. Firstly, the NP composition was varied from 0 to 10 per hundred resin (phr) and secondly, the Co(AcAc)₂ loadings were changed at 2 phr of NP. It has been observed that the cyanate conversion increases significantly after the first addition of the metal catalyst and, also, at the same time the thermal stability improves. Moreover, the kinetic data have been fitted with a second-order equation respect to the cyanate conversion in the kinetically conversion regime. Also, both the activation energies and the kinetic order respect to the NP and the Co(AcAc)₂ have been determined.     

A comparative study on the effect of carbon fillers on electrical and thermal conductivity of a cyanate ester resin

Carbon fillers including multi-walled carbon nanotubes (MWCNTs), carbon black (CB) and graphite were introduced in a cyanate ester (CE) resin, respectively. The effects of the fillers on the electrical and thermal conductivity of the resin were measured and analyzed based on the microscopic observations. MWCNTs, CB and graphite exhibited percolation threshold at 0.1 wt%, 0.5 wt% and 10 wt%, respectively. The maximal electrical conductivity of the composites was 1.08 S/cm, 9.94 × 10⁻³ S/cm and 1.70 × 10⁻⁵ S/cm. MWCNTs showed the best enhancement on the electrical conductivity. The thermal behavior of the composites was analyzed by calorimetry method. Incorporation of MWCNTs, CB and graphite increased the thermal conductivity of CE resin by 90%, 15% and 92%, respectively. Theoretical models were introduced to correlate the thermal conductivity of the CE/MWCNTs composite. The interfacial thermal resistance between CE resin and MWCNTs was 8 × 10⁻⁸ m²K/W and the straightness ratio was 0.2. The MWCNTs were seriously entangled and agglomerated. Simulation results revealed that thermal conductivity of the CE/MWCNTs composites can be substantially elevated by increasing the straightness ratio and/or filler content of MWCNTs.     

Electroactive shape memory cyanate/polybutadiene epoxy composites filled with carbon black

Electroactive shape memory composites were synthesized using polybutadiene epoxy(PBEP) and bisphenol A type cyanate ester(BACE) filled with different contents of carbon black(CB). Dynamic mechanical analysis(DMA), scanning electron microscopy(SEM), electrical performance and electroactive shape memory behavior were systematically investigated. It is found that the volume resistivity decreased due to excellent electrical conductivity of CB, in turn resulting in good electroactive shape memory properties. The content of CB and applied voltage had significant influence on electroactive shape memory effect of developed BACE/PBEP/CB composites. Shape recovery can be observed within a few seconds with the CB content of 5 wt% and voltage of 60 V. Shape recovery time decreased with increasing content of CB and voltage. The infrared thermometer revealed that the temperature rises above the glass transition temperature faster with the increase of voltage and the decrease of resistance.     

Oxidation and detection of L-cysteine using a modified Au/Nafion/glass carbon electrode

In this work,the electrochemical oxidation of L-cysteine(CySH)was investigated on a composite film modified electrode with Au nanoparticles dispersed in the fluorocarbon polymer(Nafion).The excellent electrocatalytic effect on CySH oxidation was attributed to the role of Au nanoparticles.The voltammetric studies revealed two anodic peaks for the oxidation of CySH in the pH range of 2.0–8.0.The electrode was used to detect cysteine at pH 2.0 and pH 7.0.At pH 2.0,a determination range of 3.0–50.0?mol/L was ob...     

Cure kinetics of a cobalt catalysed dicyanate ester monomer in air and argon atmospheres from DSC data

A kinetic analysis of the cyclotrimerisation reaction of a dicyanate ester monomer catalysed by cobalt(II) acetylacetonate and nonylphenol in air and argon atmospheres has been carried out by differential scanning calorimetry (DSC). Dynamic and isothermal DSC scans as well as the glass transition temperature are the experimental data obtained. From isothermal scans a higher cyanate conversion in air than in argon was obtained. The cyanate conversions are satisfactorily described with a second-order kinetic equation in the kinetically controlled region, and by m-order (m<1) equation after vitrification is reached. Activation energies determined by different procedures agree among them, showing slightly higher values in argon than in air.     

Understanding the role of clay silicate nanoparticles with organic modifiers in thermal curing of cyanate ester resin

The catalytic effect of montmorillonite clay nanoparticles containing organic modifiers such as quaternary phosphonium salts on cure mechanism of cyanate ester resin (RS-9D) was studied by differential scanning calorimetry (DSC) measurements, FT-IR and NMR spectroscopy as well as mass-spectrometry. The results show that the net catalytic effect arises from the presence of moisture associated with nanoclay particles where organic modifiers act as moisture transport agents. Possible mechanisms for cure pathways are discussed.     

Hybrid cyanate ester resin-based nanocomposites: Increased indentation size effect due to anomalous composition of micron subsurface layer

Hardness of materials increases with decreasing indentation depth from macro-to nano-scales, which is known as the indentation size effect (ISE). This effect has been associated with indenter shape, frictional forces, dislocation models and other features. We show an anomalously high ISE for a 1-μm subsurface layer in the hybrid nanocomposites based on densely cross-linked Cyanate Ester Resins (CER) containing functionalized 3-D POSS or 2-D MMT nanoparticles (NP). This effect disappears after mechanical stripping of the surface layer. Energy dispersive X-ray (EDX) spectral analysis shows that this anomaly was caused by increased content of NP (Si and Al elements), by 2.5 times, in the 1-μm subsurface layer. The hardness of the 1-μm subsurface layer in these brittle nanocomposites is due to its peculiar composition, and must be taken into account when considering mechanical strength and frictional properties.     

Leakage failure in fibre-reinforced polymer composite tubular vessels at elevated temperature

Pressure-containing structures made from fibre-reinforced polymer composites are increasingly used in harsh environments. This is in part due to their good corrosion resistance. Assessing the performance of such structures often requires consideration of different temperature regimes. Compared to metallic structures, pressurized composite structures exhibit complex damage behaviour which commonly includes fluid leakage that is induced by micro-cracking of the polymer matrix. This is an important damage mode to consider since it not only affects the pressure capacity of unlined components but also causes reduced stiffness and, possibly, fluid ingress into the structure. Leakage behaviour, and thus the occurrence of matrix cracking, may conveniently be assessed through pressure testing. Since fluid properties vary with test temperature, an appropriate testing scheme is required to obtain truly comparable leakage thresholds. The work described in the present paper involves a permeability based testing methodology. Fibre-reinforced tubular specimens were used in this study with either an epoxy or bismaleimide matrix material, which are intended for room and elevated temperature service, respectively.     

Mechanism of thermal polymerization of cyanate ester systems: Chromatographic and spectroscopic studies

The mechanisms and kinetics of polymerization of mono- and difunctional cyanate esters are investigated using chromatographic (HPLC) and spectroscopic methods (UV, liquid and solid-state NMR, and FTIR). The results obtained after chromatographic separation and identification of the chemical species present in the reaction medium have enabled us to propose a reaction path and a kinetic model for these thermally polymerized systems. Finally, the polymerization of cyanate ester was studied in the presence of different catalysts (imidazole, AcAcCu and AcAcCr) added directly, without solvent, and showed their influence on mechanisms. © 1996 John Wiley & Sons, Inc.     

Flexural properties of sandwich composite panels with glass laminate aluminum reinforced epoxy facesheets strengthened by SMA wires

Sandwich composite panels are widely used and significant in structural applications such as aerospace, shipbuilding and transportation, etc. This is due to their specific properties such as specific stiffness, strength and energy absorption. Still, many innovations are required to develop and upgrade their mechanical properties in various loadings and conditions, specifically in bending loads. One of the methods to enhance the properties of sandwich structures is to employ various advanced materials in these structures to change their acquired properties. In the present research work, sandwich composite panels made by fiber metal laminate like glass laminate aluminum reinforced epoxy (GLARE) as the facesheets and PVC polymer foam as the core material are investigated in flexural (bending) loading condition. To change or enhance the behaviour of sandwich panel in bending loads, shape memory alloy wires are also embedded in between glass fiber reinforced epoxy composite layers in fiber metal laminate facesheets. The shape memory wires are also pre-strained in fiber reinforced epoxy composite in sandwich panels. To study the flexural properties of sandwich panels with fiber metal laminate facesheets, the effect of shape memory alloy wires and also the effect of pre-straining of the wires, three types of sandwich panels are considered and made including panels without shape memory alloy wire, two wires with 0% tensile pre-strain, and two wires with 5% tensile pre-strain for the same cross section. Due to the importance of bending properties in structural applications, the sandwich composite specimens are subjected to flexural test according to ASTM standards. The maximum of 13% increase in maximum bending load and 84% increase in breaking load for the specimens with 0% pre-strained wires are achieved. Also, the maximum displacement and the energy absorption for the specimen with 5% pre-strain was enhanced by 26.5% and 37%, respectively. The energy absorption during the flexural test is greater in case of the specimen with pre-strained wires. Moreover, the specimens with pre-strained wires show better integrity of the structure after the failure in bending. The results represent the advantage effect of shape memory alloy wires on sandwich composite panel's behaviour in bending.     

Pt/HM、Pd/HM催化剂上CO氧化反应活性和动力学研究

研究了Pt/HM、Pd/HM催化剂上CO氧化反应的活性,求出了各种催化剂的CO氧化反应动力学方程。考察了不同气氛下CO氧化活性的演变规律和V⁴⁺、Co²⁺离子对Pt、Pd的助催化作用,并用催化剂集团结构适应模型对以上结果作出了解释。     

Effect of internal mold release agent on flexural and inter laminar shear properties of carbon and glass fabric reinforced thermoset composites

The study is focused on thermoset composites reinforced with carbon and glass woven fabrics. Two types of thermoset resins, for example, epoxy and vinyl ester were used as the matrix. Varying concentrations of internal mold releasing (IMR) agent was used in the resin. The composites were cured both at room temperature and at 80°C. The flexural properties were studied using 3‐point bending test method. Further theinter‐laminar shear strength (ILSS) was investigated using the short beam shear strength test based on 3‐point bending. The flexural modulus of room temperature cured epoxy resin is higher than that of high temperature cured epoxy resin and cured vinyl ester resin. The flexural modulus is lowest for 1% IMR sample in epoxy system and the modulus for 0% and 2% epoxy are not significantly different. Lowest flexural strength and modulus can be observed for the combination of reinforcement and curing conditions for samples containing 1% IMR for the epoxy systems. Carbon fiber is found to be less compatible with the vinyl ester resin system and the addition of IMR to the resin degraded the properties further. Inter‐laminar shear strength for epoxy‐based composites is not much affected by presence of IMR, but in case of vinyl ester based composites there is a decrease in ILSS on addition of IMR agent. The study explains variation in flexural properties on addition of IMR and change of curing conditions. These results can be used for ascertaining variation in mechanical properties in real use.     

Impact resistance of hybrid glass fiber reinforced epoxy/nanoclay composite

The effect of nanoclay addition in Glass Fiber Reinforced Epoxy (GFRE) composites on impact response was studied. The epoxy nanocomposite matrix with 1.5 and 3.0 wt% loading of I.30E nanoclay was produced by high shear mixing. Hybrid GFRE nanoclay composite plates were manufactured by hand layup and hot pressing techniques using electrical grade-corrosion resistant (E-CR) glass fiber mats. The laminates were then subjected to low-velocity impact with energies between 10 and 50 J. Addition of nanoclay was found to improve peak load and stiffness of GFRE. Nanoclay loading of 1.5 wt% resulted in optimum properties, with 23% improvement in peak load and 11% increase in stiffness. A significant reduction in physical damage was also observed for hybrid nanocomposite samples as compared to GFRE. This was mainly attributed to transition in damage mechanism due to nanoclay addition. Clay agglomeration in samples with 3.0 wt% loading contributed towards limiting the improvement in impact resistance.     

Mn(Ⅱ)和Ce(Ⅳ)离子对铬酸氧化乳酸的影响

The kinetics and mechanism of lactic acid oxidation in the presence of Mn(II)and Ce(IV)ions by chromic acid were studied spectrophotometrically.The oxidation of lactic acid by Cr(VI)was found to proceed in two measurable steps,both of which gave pyruvic acid as the primary product in the absence of Mn(II).2Cr(VI) 2CH3CHOHCOOH→2CH3COCOOH Cr(V) Cr(III)Cr(V) CH3CHOHCOOH→Cr(III) CH3COCOOH The observed kinetics was explained due to the catalytic and inhibitory effects of Mn(II)and Ce(IV)on the lactic acid oxidation by Cr(VI).The reactivity of lactic acid depends upon the experimental conditions.It acts as a two-or three-equivalent reducing agent in the absence or presence of Mn(II).It was examined that Cr(III)products resulting from the direct reduction of Cr(VI)by three-equivalent reducing agents.The oxidation of lactic acid follows the complex order kinetics with respect to [lactic acid].The activation parameters Ea,ΔH#,and ΔS# were calculated and discussed.     

两种表征金属有机双层膜络合和金属薄膜氧化反应动力学的方法

建立了两种新的薄膜反应动力学表征方法, 即透射光谱法和方块电阻法, 以克服传统动力学表征手段在薄膜体系氧化与络合反应过程中应用的局限性. 以透射光谱为表征手段, 得到了Ag/TCNQ(四氰基对醌二甲烷)金属有机双层薄膜的络合反应动力学曲线; 以方块电阻为表征手段, 得到了Cu薄膜的氧化反应动力学过程.     

碳纤维的高温氧化动力学模型

碳纤维的高温氧化动力学模型唐龙贵（浙江大学高分子科学与工程研究所,杭州,３１００２７）关键词碳纤维,氧化,动力学,模型碳纤维是一种具有高比强度、高比模量、耐磨、导电等优良性能的骨架材料,是制造高性能复合材料的基础。它在宇航、军事等高技术工业领域得到了...     

Oxidation of Substituted Benzyl Alcohols by Quinoxalinium Dichromate. A Kinetic Study

Summary. Quinoxalinium dichromate (QxDC) oxidizes benzyl alcohol and substituted benzyl alcohols smoothly in dimethyl sulfoxide (DMSO) and in the presence of acid to the corresponding aldehydes. The reaction has unit dependence on each of the alcohol, QxDC, and acid concentrations. Electron-releasing substituents accelerate the reaction, whereas electron-withdrawing groups retard the reaction, and the rate data obey Hammetts relationship. The reaction constant was –1.09±0.01 at 303K. Oxidation of ,-dideuteriobenzyl alcohol indicated the presence of a substantial primary kinetic isotope effect (k_H/k_D=6.78 at 303K). The reaction failed to induce the polymerization of acrylonitrile. The rates of oxidation were determined at different temperatures and the activation parameters were evaluated. The analysis of the dependence of the kinetic isotope effect on temperature indicated that the reaction involves a symmetrical cyclic transition state. A suitable mechanism is proposed.     

Morphology and properties of cyanate ester/liquid polyurethane/silica nanocomposites

The high‐speed homogeneous shearing method was applied to prepare nanocomposites of cyanate ester (CE) with liquid polyurethane elastomer (PUR) and silica. To investigate the influence of various components on the morphology and properties of the ternary composites, the binary composites of CE/PUR and CE/silica were also involved in this article. The morphology of the cured materials of binary and ternary systems was investigated by transmission electron microscopy (TEM), and the results show that silica nanoparticles were uniformly distributed in the ternary and binary matrix. Phase separation of elastomer in composites was not observed by TEM. FTIR test and dynamic mechanical analysis (DMA) proved that chemical linking was existent between PUR and CE. Scanning electron microscopy examinations and mechanical properties tests were carried out. The results show that ternary composites displayed higher fracture toughness and impact strength compared with most of the binary systems. This suggests that the addition of PUR and nanosilica can synergistically improve the toughness of CE. DMA studies confirmed that the incorporation of silica can increase the storage modulus and T_g for CE and CE/PUR system, since there are a good adhesion and a strong hydrogen bonding between silica and polymers. The thermal property of ternary composites increases with the increase of silica nanoparticle loading. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1243–1251, 2008     

FTIR isothermal cure kinetics and morphology of dicyanate ester resin/polysulfone blends

The isothermal cure of a dicyanate ester monomer by “in situ” Fourier transform infrared spectroscopy (FTIR) has been investigated. The degree of cyanate conversion and the kinetic parameters have been determined for cobalt catalyzed and uncatalyzed resin as well as for polysulfone (PSF) modified systems at different curing temperatures. The cyanate conversion increases with the increment of temperature and with the addition of a catalyst, but it does not vary with the addition of PSF. In all the systems studied, the rate of reaction showed a second-order dependence on the cyanate concentration in the kinetically controlled stage. Moreover, the addition of PSF generates a matrix with two-phases that changes in composition and morphology depending on the percent of added thermoplastic and curing temperature as observed by scanning electron microscopy.     

Thermal conductivity and properties of cyanate Ester/nanodiamond composites

The aim of this study was to improve thermal conductivity, thermal stability, and mechanical properties of bisphenol A dicyanate ester with the addition of nanodiamond. Cyanate ester/nanodiamond composites containing various ratios of nanodiamond were prepared. Thermal stability and thermal conductivity of the samples were evaluated by thermogravimetric analysis, differential scanning calorimetry, and laser flash method, respectively. The samples were characterized with the analysis such as gel content, water absorption capacity, and stress–strain test. Hydrophobicity of the samples was determined by contact angle measurements. Moreover, the surface morphology of the samples was investigated by a scanning electron microscopy. The obtained results prove that the cyanate ester/nanodiamond composites have good thermal and mechanical properties and can be used in many applications such as the electronic devices, materials engineering, and other emergent. Copyright © 2014 John Wiley & Sons, Ltd.