Cure behavior of epoxy resin/MMT/DETA nanocomposite

The Flory's gelation theory, non-equilibrium thermodynamic fluctuation theory and Avrami equation have been used to predict the gel time t _g and the cure behavior of epoxy resin/organo-montmorillonite/diethylenetriamine intercalated nanocomposites at various temperatures and organo-montmorillonite loadings. The theoretical prediction is in good agreement with the experimental results obtained by dynamic torsional vibration method, and the results show that the addition of organo-montmorillonite reduces the gelation time t _gand increases the rate of curing reaction, the value of k, and half-time of cure after gelation point t_1/2 decreases with the increasing of cure temperature, and the value of n is ~2 at the lower temperatures (<60°C) and decreases to ~1.5 as the temperature increases, and the addition of organo-montmorillonite decreases the apparent activation energy of the cure reaction before gelation point, but has no apparent effect on the apparent activation energy of the cure reaction after gelation point. There is no special curing process required for the formation of epoxy resin/organo-montmorillonite/diethylenetriamine intercalated nanocomposite. This revised version was published online in July 2006 with corrections to the Cover Date.     

Speciation analysis of chromium by separation on a 5-palmitoyl oxine-functionalized XAD-2 resin and spectrophotometric determination with diphenylcarbazide

The method developed in this work for the separation and preconcentration of Cr(III) is based on its retention by an Amberlite XAD-2 copolymer resin functionalized with 5-palmitoyl-8-hydroxyquinoline (oxine), abbreviated XAD-POx, with the ligand covalently bound to the copolymer. Cr(III) sorption was quantitative within the pH range 4.5–7.0 and Cr(VI) was not retained. The Cr(III) held by the resin column was eluted with a hot solution of H₂O₂ in pH9.0 aqueous NH₃–NH₄Cl buffer, and Cr oxidized to CrO₄^2– was rejected by the chelating cation-exchanger column. Any Cr(VI) originally present with Cr(III) could be reduced with an acidic solution of H₂O₂, and retained by the column yielding total Cr results, Cr(VI) being determined from the difference. The resin showed a maximal preconcentration factor of 60 for Cr(III), the LOD and LOQ being 9.3 and 30.1 nmol L^–1, respectively. The developed preconcentration-speciation analysis was finished with a diphenylcarbazide (DPC) spectrophotometric procedure suitable for conventional laboratories. The resin showed excellent salt tolerance, enabling Cr analysis in seawater, and was stable over extended use. All the interferents of this procedure that normally occur in an electroplating effluent, a blended coal CRM, and a standard steel sample could be removed by the recommended procedure, by use of partial and total selectivity at the adsorption and desorption stages, respectively, enabling preconcentration and colorimetric determination of chromium in various complex matrices.     

Evaluation of behaviour of linear monoamines CH3-(CH2)n−1-NH2 (n=1-6) in ion chromatography

This paper reports the results on a study of ion chromatography (IC) behaviour on strong cationic exchange column of CH₃-(CH₂)_n−1-NH₂ (n=1-6) type linear monoamines. The eluents were mixtures of HCl-NaCl, HNO₃-NaNO₃, HClO₄-NaClO₄, H₂SO₄-Na₂SO₄, HClO₄-NaClO₄-CH₃CN. Amines were revealed with an amperometric detector. The influence of different counter-ions on retention factors, k′, is discussed. Relationships between k′ and pE (E=sum of Na⁺ and H⁺ concentrations), and length of alkylic chain, and sensitivity coefficient S, are reported and discussed. The addition of acetonitrile (ACN) in the eluent was also taken into account. Suitable considerations are derived from these data. An example of monoamines separation is given.     

Synthesis, characterisation and evaluation of polydithiocarbamate resin supported on macroreticular styrene-divinylbenzene copolymer for the removal of trace and heavy metal ions

A new chelating resin was synthesised by the modification of styrene-divinylbenzene (2%) copolymer and incorporation of dithiocarbamate groups. The polydithiocarbamate resin was characterised by elemental analysis, thermal studies and IR studies. The analytical characteristics of the sorbent were established and optimum sorption conditions for Cu, Ni, Pb, Fe, As and Mn determined. The total sorption capacity of the resin was 37 mg g⁻¹ for Ni(II), 35 mg g⁻¹ for Cu(II), 29 mg g⁻¹ for Fe(III) and 23 mg g⁻¹ for Pb(II). The optimum pH for the removal of metal ions was 3-5 for Ni(II), 5 for Cu(II), 4 for Fe(III) and 4-5 for Pb(II). High sorption capacity was observed when compared with other conventional chelating polymers. The sorption kinetics was fairly rapid, as apparent from the loading half time t_1/2 values, indicating a better accessibility of the chelating sites.     

Synthesis and properties of novel fluorinated epoxy resins based on 1,1-bis(4-glycidylesterphenyl)-1-(3′-trifluoromethylphenyl)-2,2,2-trifluoroethane

A novel fluorinated epoxy resin, 1,1-bis(4-glycidylesterphenyl)-1-(3′-trifluoromethylphenyl)-2,2,2-trifluoroethane (BGTF), was synthesized through a four-step procedure, which was then cured with hexahydro-4-methylphthalic anhydride (HMPA) and 4,4′-diaminodiphenyl-methane (DDM). As comparison, a commercial available epoxy resin, bisphenol A diglycidyl ether (BADGE), cured with the same curing agents was also investigated. We found that the BGTF gave the exothermic starting temperature lower than BADGE no mater what kind of curing agents applied, implying the reactivity of the former is higher than the latter. The fully cured fluorinated BGTF epoxy resins have good thermal stability with glass transition temperature of 170-175 °C and thermal decomposition temperature at 5% weight loss of 370-382 °C in nitrogen. The fluorinated BGTF epoxy resins also showed the mechanical properties as good as the commercial BADGE epoxy resins. The cured BGTF epoxy resins exhibited improved dielectric properties as compared with the BADGE epoxy resins with the dielectric constants and the dissipation factors lower than 3.3 and dissipation 2.8 × 10⁻³, respectively, which is related to the low polarizability of the C-F bond and the large free volume of CF₃ groups in the polymer. The BGTF epoxy resins also gave low water absorption because of the existence of hydrophobic fluorine atom.     

2-{[1-(3,4-Dihydroxyphenyl)methylidene]amino}benzoic acid immobilized Amberlite XAD-16 as metal extractant

2-{[1-(3,4-Dihydroxyphenyl)methylidene]amino}benzoic acid (DMABA) was loaded on Amberlite XAD-16 (AXAD-16) via azo linker and the resulting resin AXAD-16-DMABA explored for enrichment of Zn(II), Mn(II), Ni(II), Pb(II), Cd(II), Cu(II), Fe(III) and Co(II). The optimum pH values for extraction are 6.5-7.0, 5.0-6.0, 5.5-7.5, 5.0-6.5, 6.5-8.0, 5.5-7.0, 4.0-5.0 and 6.0-7.0, respectively. The sorption capacity was found between 97 and 515 μmol g⁻¹ and the preconcentration factors from 100 to 450. Tolerance limits for foreign species are reported. The kinetics of sorption is fast as t_1/2 is ≤5 min. The chelating resin can be reused for 50 cycles of sorption-desorption without any significant change (<1.5%) in the sorption capacity. The limit of detection values (blank +3 s) are 1.12, 1.38, 1.76, 0.67, 0.77, 2.52, 5.92 and 1.08 μg L⁻¹ for Zn(II), Mn(II), Ni(II), Pb(II), Cd(II), Cu(II), Fe(III) and Co(II), respectively. The enrichment on AXAD-16-DMABA coupled with monitoring by flame atomic absorption spectrometry (FAAS) is used to determine all the metal ion ions in river and synthetic water samples, Co in vitamin tablets and Zn in milk samples.     

STUDY ON THE EPOXY RESIN TOUGHENED BY HYDROXY-TERMINATED BUTADIENE-ACRYLONITRILE COPOLYMER

Toughened epoxy resin with excellent properties was obtained by adding organic acid anhydride curing agent and hydroxy-terminated butadiene-acrylonitrile copolymer (HTBN), which is cheaper than CTBN. The anhydride reacts with both epoxy groups on epoxy resin and hydroxyl groups on HTBN. As a result the soft long chains of HTBN and the rigid chain of epoxy resin form one network, giving the resin toughness. Two-phase structure of the toughened resin was observed by SEM and TEM.     

酚醛基活性炭纤维孔结构及其电化学性能研究

利用水蒸汽活化法制备了酚醛基活性炭纤维(ACF-H2O), 对其比表面积、孔结构与在LiClO4/PC(聚碳酸丙烯酯)有机电解液中的电容性能之间的关系进行了探讨. 用N2(77 K)吸附法测定活性炭纤维的孔结构和比表面积, 用恒流充放电法和交流阻抗技术测量双电层电容器(EDLC)的电容量及内部阻抗. 研究表明, 在LiClO4/PC有机电解液中, ACF-H2O电极的可用孔径(d)应在0.7 nm以上. 随着活化时间的延长, ACF-H2O的孔容和比表面不断增大, 但微孔(0.7 nm ＜ d ＜ 2.0 nm)和中孔(d ＞ 2.0 nm)率变化很小, 活化过程中孔的延伸和拓宽同步进行, 但过度活化则造成孔壁塌陷, 孔容和比表面迅速下降. 因此, 除活化过度的样品外, 电容量随比表面积呈线性增长, 最高达到109. 6 F•g-1. 但中孔和微孔的孔表面对电容的贡献不同, 其单位面积电容分别为8.44 μF•cm-2和4.29 μF•cm-2, 中孔具有更高的表面利用率. ACF-H2O电极的电容量、阻抗特性和孔结构密切相关. 随着孔径的增大, 时间常数减小, 电解液离子更易于向孔内快速迁移, 阻抗降低, 电极具有更好的充放电倍率特性. 因此, 提高孔径和比表面积, 减少超微孔(d ＜ 0.7 nm), 是提高 EDLC能量密度和功率密度的重要途径. 然而仅采用水蒸汽活化, 只能在小中孔以下的孔径范围内进行调孔, ACF-H2O电极电容性能的提高受限.     

丁腈羟增韧环氧树脂形态与力学性能

研究了丁腈羟增韧环氧树脂的力学性能和形态结构，丁腈羟的用量、丁腈羟中丙烯腈的含量、固化条件对所形成的微区尺寸都有较大影响，并进一步影响固化物的力学性能。     

The mechanical properties and tribological behavior of epoxy resin composites modified by different shape nanofillers

Mechanical properties and tribological behavior of epoxy resin (EP) and EP nanocomposites containing different shape nanofillers, such as spherical silica (SiO₂), layered organo‐modified montmorillonite (oMMT) and oMMT‐SiO₂ composites, were investigated. The SiO₂‐oMMT composites were prepared by in situ deposition method and coupling agent modification, and transmission electron microscopy (TEM) analysis shows that spherical SiO₂ is self‐assembled on the surface of oMMT, which forms a novel layered‐spherical nanostructure. The mechanical properties test results show that oMMT obviously improves the strength of EP and SiO₂ enhances its toughness, but oMMT‐SiO₂ exhibits a synergistic effect on toughening and reinforcing EP simultaneously. A pin‐on‐disc rig was used to test friction and wear loss of pure EP and EP nanocomposites. The tribological test results prove that these nanofillers with different shapes play different roles for improving the wear resistance of EP nanocomposites. Morphologies of the worn surfaces were studied further by scanning electron microscopy (SEM) observations, and it was clarified that the EP and EP nanocomposites undergo similar wear mechanisms. Copyright © 2006 John Wiley & Sons, Ltd.