共查询到20条相似文献,搜索用时 15 毫秒
1.
J. Macan I. Brnardić M. Ivanković H. J. Mencer 《Journal of Thermal Analysis and Calorimetry》2005,81(2):369-373
Summary A kinetic study of cure kinetics of epoxy resin based on a diglycidyl ether of bisphenol A (DGEBA), with poly(oxypropylene) diamine (Jeffamine D230) as a curing agent, was performed by means of differential scanning calorimetry (DSC). Isothermal and dynamic DSC characterizations of stoichiometric and sub-stoichiometric mixtures were performed. The kinetics of cure was described successfully by empirical models in wide temperature range. System with sub-stoichiometric content of amine showed evidence of two separate reactions, second of which was presumed to be etherification reaction. Catalytic influence of hydroxyl groups formed by epoxy-amine addition was determined. 相似文献
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Investigation of the dissolution of cellulose in Ethylene Diamine (EDA)/Potassium thiocyanate (KSCN) solutions by infrared
spectroscopy (FTIR) and thermal analysis (DSC) indicated that changes to the solvent during freeze thaw cycling of mixtures
was consistent with increased interaction between cellulose and solvent. Thermal transitions in the system, however, occurred
at temperatures outside the range used in thermal cycling to promote dissolution. Further exploration of the dissolution and
mixing process indicated that mixing was the limiting step in solution formation. The dissolution of two types of cellulose
with different molecular weights (Degree of Polymerization (DP)=210 and >1000) was studied using EDA/KSCN solution as the
solvent. The solubility and the dissolution rate of cellulose depended on both the solvent composition and cellulose molecular
weight. Cellulose could dissolve faster in the solvent with lower salt concentration but the highest cellulose concentration
was obtained in the solvent with 30~35% KSCN. Rheological measurements showed that cellulose solutions exhibited viscous solution
behavior at low KSCN concentration but primarily elastic behavior at high salt concentration. 相似文献
4.
T. S. Chung Wei‐Yu Chen Yuhui Lin Kumari P. Pramoda 《Journal of Polymer Science.Polymer Physics》2000,38(11):1449-1460
We studied three kinds of ladderlike polyepoxysiloxanes, which have different side groups grafted on the ladderlike backbones. 1,3‐Bis(aminopropyl)tetramethyl disiloxane (diamine) was used as the curing agent. The reaction between ladderlike polyepoxysiloxanes and diamine was investigated by contact angle measurements and surface free energy study. Several factors such as diamine amount, reaction time, and temperature can affect the systems' surface tension (or surface free energy), which were determined by two‐liquid geometric and three‐liquid acid‐base methods. The experimental results showed that an increase in the diamine amount in the reaction systems results in an increase in the polar part of surface free energy because of electron donate characteristics of the diamine. However, because epoxy (electron acceptor) and diamine (electron donor) react fast at elevated temperatures, increasing reaction temperature decreases the polar part of the surface free energy, while increases the nonpolar part of the surface free energy. The evolution of surface free energy with time for various epoxy–diamine reaction systems at various temperatures has also been studied. It was found that it took a relatively long time (50–60 h) to reach the equilibrium state. The experimental results can be well interpreted by the epoxy–diamine reaction mechanism and van Oss–Good's Lewis acid‐base theory. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1449–1460, 2000 相似文献
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Leonel Silva Sebastián Tognana Walter Salgueiro 《Journal of Polymer Science.Polymer Physics》2013,51(8):680-686
A differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) study of miscibility in blends of the semicrystalline polyester poly(3-hydroxybutyrate) (PHB) and amorphous monomer epoxy DGEBA (diglycidyl ether of bisphenol A) was performed. Evidence of the miscibility of PHB/DGEBA in the molten state was found from a DSC study of the dependence of glass transition temperature (Tg) as a function of the blend composition and isothermal crystallization, analyzing the melting point (Tm) as a function of blend composition. A negative value of Flory–Huggins interaction parameter χPD was obtained. Furthermore, the lamellar crystallinity in the blend was studied by SAXS as a function of the PHB content. Evidence of the segregation of the amorphous material out of the lamellar structure was obtained. © 2013 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013 相似文献
7.
In this work the curing kinetics behaviour of a rubber modified epoxy amine system is investigated through calorimetric analysis.
This study is part of a wider investigation on new epoxy formulations to be used as matrices of composite materials. The aim
is to enhance both the processing behaviour and the mechanical properties of the matrix in order to obtain higher performance
composites for more demanding applications. The epoxy system is blended with a high molecular mass rubber containing functional
groups reactive towards the epoxies. The formation of a rubber/epoxy network can be achieved by means of a 'pre-reaction'
between the epoxy monomers and the rubber functional groups, carried out in the presence of a suitable catalyst and before
the resin is cured with the amino hardener. In this work the influence of both the rubber and the catalyst on the resin cure
kinetics is analysed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Ethylene diamine (EDA)/salt solvent systems can dissolve cellulose without any pretreatment. A comparison of the electrical
conductivity of different salts in EDA was made at 25 °C, and conductivity decreased in the order of KSCN>KI>NaSCN at the
same molar concentration. Among the salts tested, potassium thiocyanate (KSCN) was capable of dissolving both high molecular
weight (DP>1000) and low molecular weight (DP = 210) cellulose, and this was confirmed by polarized light microscopy. 39K and 14N NMR experiments were conducted at 70 °C as a function of cellobiose concentration with EDA/KSCN as the solvent. The results
showed that the K+ ion interacts with cellobiose more than the SCN− ion does. Recovered cellulose was studied by infrared spectroscopy (FTIR) and wide angle X-ray diffraction (WAXD). Changes
in the FTIR absorption bands at 1,430 and 1,317 cm−1 were associated with a change in the conformation of the C-6CH2OH group. The changes in positions and/or intensities of absorption bands at 2,900, 1,163, and 8,97cm−1 were related to the breaking of hydrogen bonds in cellulose. X-ray diffraction studies revealed that cellulose, recovered
by precipitating cellulose solutions with water, underwent a polymorphic transformation from cellulose I to cellulose II. 相似文献
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2,4,6-三(羟基苯甲基氨基)-均三嗪的合成及其与双酚A型环氧树脂的固化行为研究 总被引:2,自引:0,他引:2
合成了一种含三嗪环结构的环氧树脂固化剂2,4,6-三(羟基苯甲基氨基)-均三嗪(MFP).用动态DSC和原位红外光谱对MFP/DGEBA(双酚A型环氧树脂)体系的固化行为进行了研究.动态DSC研究表明,由于MFP分子结构中存在两种活泼氢(酚羟基氢和仲胺氢),固化反应存在明显的两个峰,相对应的表观活化能分别为70.5 kJ.mol-1和86.5 kJ.mol-1(Kissinger法),通过与另一相似化合物固化DGEBA的比较可知,在MFP固化DGEBA的过程中,酚羟基与环氧基反应相对较难.原位红外动力学结果很好地支持了上述结论. 相似文献
11.
Differential scanning calorimetry (DSC) was used to indicate the relative extents of the different cure reactions of the 4-glycityloxyl-N, N-diglycidylaniline (MY0510), polyglycidyl ether of phenol formaldehyde novolac (DEN431) and 3,3 diamino diphenylsulphone (3,3 DDS) resin systems and how these were affected by the presence of polyethersulphone (PES). The extent of reactions at any given time decreased with increasing PES concentration and the reaction rate maximum shifted to longer times. The cured resin systems were examined using dynamic mechanical analysis (DMA). Broader β-transitions of lower intensities were observed in specimens containing PES, suggesting an increased range of relaxations within the transition. 相似文献
12.
F. Benard J.Y. Buzaré I. Campistron A. Laguerre F. Laval 《Polymer Degradation and Stability》2007,92(5):785-794
The influence of silica fillers on chemical modifications of diglycidyl ether of bisphenol A/triethylene tetramine (DGEBA/TETA) epoxy resins induced by electron beam irradiation has been studied by 13C CP-MAS (Cross Polarisation and Magic Angle Spinning) NMR. Four kinds of silica filler were investigated: a pure micrometric silica, a treated micrometric silica, a pure nanometric silica and a treated nanometric silica. On the unirradiated epoxy resins, the magnetization transfer curves reveal structural differences due to the kind of silica fillers. A decrease of the epoxy network rigidity in the presence of nanometric silica fillers is shown. During irradiation, the formation of phenolic ends and enamine functions is confirmed. The slowing of the magnetization transfer of the pure and treated micrometric silica filled epoxy resin reveals an important decrease of the rigidity of these resins. On the pure and treated nanometric silica filled epoxy resins, reactions of the reactive species created by the irradiation in the epoxy resin and the silica particles surface are shown. 相似文献
13.
C. C. Riccardi J. Dupuy R. J. J. Williams 《Journal of Polymer Science.Polymer Physics》1999,37(19):2799-2805
A survey of the literature dealing with the kinetics of epoxy/anhydride polymerizations initiated by tertiary amines, shows inconsistencies in results reported by several authors. Both first-order and autocatalytic expressions have been used to fit experimental results. In the former case, significantly different values of apparent activation energies were found in isothermal and nonisothermal experiments. A simple kinetic model is proposed to explain these inconsistencies, based on the following steps: (a) a reversible reaction transforming an inactive initiator species into an active one, (b) a propagation step, and (c) a chain transfer step regenerating the active initiator (step not relevant to the kinetic analysis). The simple model explains both the first-order and autocatalytic behaviors reported in the literature. It also leads to the experimental values of the apparent activation energies obtained under different conditions. It is also shown that isoconversional methods should not be applied to obtain fundamental kinetic parameters in systems where the reaction rate depends on the concentration of an active species that varies independently of the conversion of functional groups. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2799–2805, 1999 相似文献
14.
John A. Marsella William E. Starner 《Journal of polymer science. Part A, Polymer chemistry》2000,38(5):921-930
Kinetic studies established that the monomethylation of a primary amine leads to significantly higher reaction rates with glycidyl ethers. The relative rates for approximately 25 amines were determined in an alcohol solvent under pseudo‐first‐order conditions (excess epoxy). The rates were referenced to aniline. For the aliphatic amines, reactivity consistently increased upon going from a primary amine to the corresponding N‐methyl secondary amine. This acceleration effect was not seen for aniline. The enhanced reactivity was also seen in curing systems, both with pure methylated amine curing agents and with complex mixtures obtained from the partial methylation of polyamines. Economically viable partially methylated amine curing agents were obtained by the reductive alkylation of commercial polyamines with formaldehyde and by the reaction of monomethylamine with 3‐(N‐methylamino)propionitrile in the presence of hydrogen and a hydrogenation catalyst. Although actual cure performance is based on a complex combination of several factors, the acceleration due to monomethylation could be a useful tool for enhancing amine/epoxy curing reactions. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 921–930, 2000 相似文献
15.
The microwave and thermal cure processes for the epoxy-amine systems (epoxy resin diglycidyl ether of bisphenol A, DGEBA) with 4,4′-diaminodiphenyl sulphone (DDS) and 4,4′-diaminodiphenyl methane (DDM) have been investigated for 1 : 1 stoichiometries by using fiber-optic FT-NIR spectroscopy. The DGEBA used was in the form of Ciba-Geigy GY260 resin. The DDM system was studied at a single cure temperature of 373 K and a single stoichiometry of 20.94 wt% and the DDS system was studied at a stoichiometry of 24.9 wt% and a range of temperatures between 393 and 443 K. The best values of the kinetic rate parameters for the consumption of amines have been determined by a least squares curve fit to a model for epoxy/amine cure. The activation energies for the polymerization of the DGEBA/DDS system were determined for both cure processes and found to be 66 and 69 kJ mol−1 for the microwave and thermal cure processes, respectively. No evidence was found for any specific effect of the microwave radiation on the rate parameters, and the systems were both found to be characterized by a negative substitution effect. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
16.
几种聚醚胺改性蒙脱土对环氧树脂固化过程的影响 总被引:1,自引:0,他引:1
首先制备了五种聚醚胺改性蒙脱土(MMT), 并将这五种聚醚胺改性蒙脱土加入到双酚A 型环氧树脂E51 和聚醚胺D400体系中, 采用差示扫描量热法(DSC)考察了五种聚醚胺改性MMT对环氧树脂升温固化进程的影响. 随后, 优选一种EP/MMT 混合体系即EP/D400-T500-MMT 混合体系, 系统地研究了该体系与纯环氧树脂体系在130, 140, 150 及160 ℃等几个温度下的等温固化过程, 考察了等温固化时间对固化度和固化度变化速率的影响以及固化度与固化度变化速率之间的关系, 并利用Kamal 模型进行拟合计算了固化动力学参数. 研究结果表明, 与纯环氧树脂相比, 几种聚醚胺改性MMT 的固化放热峰均向高温迁移, 同时聚醚胺D400 协同插层MMT 降低了高分子量聚醚胺插层MMT 所导致的环氧树脂DSC 曲线的畸变情况; EP/D400-T500-MMT 混合体系和纯环氧体系的等温固化反应过程符合Kamal 模型;在相同的固化温度下, EP/D400-T5000-MMT 混合体系的反应速率常数k1 和k2 值以及反应级数m 均比纯EP 体系小, 而反应级数n 以及总反应级数m+n 值比纯EP 体系大, 表明两种聚醚胺协同插层的改性蒙脱土D400-T5000-MMT 的加入降低了环氧体系固化反应速率. 另外, EP/D400-T5000-MMT 混合体系的活化能Ea1 和Ea2 与纯EP 体系的相比也略有升高. 相似文献
17.
Pedro Francisco Caamero Jos Luis de la Fuente Marta Fernndez-García 《European Polymer Journal》2009,45(9):2665-2673
The curing kinetics using a glycidyl methacrylate (GMA)-co-butyl acrylate (BA) statistical copolymer synthesized by atom transfer radical polymerization (ATRP) and a commercial linear diamine (Jeffamine® D-230) was investigated in the temperature range between 50 and 100 °C. Isothermal experiments using differential scanning calorimetry (DSC) were performed to determine all the kinetics parameters, such as the reaction orders, the activation energy and the rate constants, based on an autocatalytic mechanism proposed by Kamal. The isoconversion method was used to evaluate the variation of the effective activation energy with the extension of the conversion that seems slightly decrease initially, and then increases as the cure reaction proceeds. In addition, dynamic kinetic parameters were calculated from non-isothermal experiments using the Kissinger and Ozawa methods. The resulting epoxy resin presents similar physical characteristics to some reported in the literature. 相似文献
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In this report, a novel phosphorus/silicon‐containing reactive flame retardant, hexa(3‐triglycidyloxysilylpropyl)triphosphazene (HGPP), was synthesized and characterized by Fourier transform infrared spectrometry and nuclear magnetic resonance spectra (1H, 31P, and 29Si), respectively. To prepare cured epoxy, HGPP had been co‐cured with diglycidyl ether of bisphenol‐A (DGEBA) via 4,4‐diaminodiphenylsulfone as a curing agent. The mechanical, thermal, and flame retardant properties of the cured epoxy were evaluated by dynamic mechanical analysis, thermogravimetric analysis, and limiting oxygen index (LOI). According to these results, it could be found that incorporation of HGPP in the cured epoxy system showed good thermal stability, high LOI values, and high char yield at high temperature. As moderate loading of HGPP in the epoxy system, its storage modulus and glass transition temperature were higher than those of neat DGEBA. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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Mark C. Finzel John Delong Martin C. Hawley 《Journal of polymer science. Part A, Polymer chemistry》1995,33(4):673-689
The bulk phase kinetics of an epoxy (DGEBA) /amine (DDS) thermoset have been studied using DSC, FTIR, and 13C-NMR. In the absence of catalyst, the reaction was found to involve a main exothermic reaction between epoxide and amine hydrogen and a side reaction between tertiary amine formed in the main reaction and epoxide. The main reaction was exothermic while the side reaction had no discernable exotherm. Etherification did not occur to any significant extent. Since only the main reaction is exothermic, DSC was very useful for studying the main reaction kinetics. FTIR was used for determining whether epoxide and amine hydrogen were consumed at different rates as a way of following the side reaction. An IR band previously unused by other investigators was used to monitor the amine hydrogen concentration. NMR confirmed the above mechanism by identifying the formation of a quaternary ammonium ion/alkoxide ion pair as a reaction product of tertiary amine and epoxide. This mechanism has been successfully fit to a rate law valid over the entire extent of reaction. The rate constant for the epoxy/amine addition reaction was found to depend on hydroxide concentration (extent), reaction temperature, and glass transition temperature and included contributions from uncatalyzed and autocatalyzed parts. The side reaction (quaternary ammonium ion formation) formed weak bonds which did not affect the overall system Tg. Both reactions were second order. The rate constants for the main reaction first increase with increasing extent due to autocatalysis by hydroxide before decreasing due to the diffusion limit caused by gelation and vitrification. © 1995 John Wiley & Sons, Inc. 相似文献
20.
Heping Liu Alfred Uhlherr Russell J. Varley Michael K. Bannister 《Journal of polymer science. Part A, Polymer chemistry》2004,42(13):3143-3156
Eleven different epoxy/diamine systems, including tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM), triglycidyl p‐aminophenol (TGAP), and diglycidyl ether of bisphenol A (DGEBA) with 4,4′‐diaminodiphenylsulfone (DDS), diethyltoluenediamine (DETDA), dimethylthiotoluenediamine (DMTDA), and meta‐phenylenediamine (m‐PDA), were studied with near‐infrared spectroscopy at different temperatures. The reactivities of the epoxies were determined and found to be in the following order when reacted with the same amine: DGEBA > TGAP > TGDDM. When the primary amine was reacted with the same epoxy, the order was DETDA > DDS > DMTDA; for the secondary amine, the order was DETDA > DMTDA > DDS. The relative reaction rates of the secondary amine to the primary amine were compared and discussed in terms of the structural differences and the corresponding substitution effect. It was concluded that the increase in the secondary amine reactivity of DETDA and DMTDA was caused by the deconjugation of the benzene‐ring π electrons from the lone pair on the N atom. The overall order of the secondary amine relative reactivity was DMTDA > DETDA > DDS for the same epoxy and TGDDM > TGAP > DGEBA for the same amine. The m‐PDA systems had no significant positive or negative substitution effects. Molecular orbital calculations were performed, and the results showed the most significant deconjugation effect in the secondary amine of DETDA. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3143–3156, 2004 相似文献