Kinetics of epoxy cure: 2. The system bisphenol-A diglycidyl ether/polyamide

Differential scanning calorimetry, infra-red absorption and d.c. conductivity were used to study the cure of the system bisphenol-A diglycidyl ether/polyamide in the range 23–110°C. At elevated temperatures, two reactions were found to occur subsequent to the cure reaction. In addition, glass transition data indicate that, where network mobility permits, large-scale reorganization of the network occurs subsequent to cure to give an ‘equilibrium’ glass.     

Kinetics of epoxy cure: 3. The systems bisphenol-A epoxides/dicy

Differential scanning calorimetry was used to study the cure of several bisphenol-A epoxide/dicy (dicyandiamide, cyanoguanidine) systems in the temperature range 170–220°C. It was found that, simultaneously with curing, the dicy decomposed into melamine, which was capable of further decomposition. With a higher molecular weight epoxide, reaction subsequent to cure resulted in a more rigid epoxy than expected. The addition of surfactant caused reaction to occur at lower temperatures, although the rate decreased and a change in mechanism appeared to have occurred.     

水溶性双酚A型环氧树脂乳液的制备

采用E-Ⅱ型乳化剂和相反转技术制备水溶性双酚A型环氧树脂乳液,研究了乳化剂的用量、乳化时间、搅拌速率和乳化温度对乳液稳定性的影响.得出了最佳乳化工艺条件:乳化剂质量分数为7.25%～8.0%、乳化温度为60～70 ℃、搅拌速度为700～900 r/min、乳化时间为40～50 min.采用激光粒度衍射分析仪表征了水溶性环氧乳液的粒径为400～500 nm.     

湿固化聚氨酯/环氧树脂固化体系的研究

以聚丙二醇(PEG)、甲基六氢苯酐(MHHPA)、异佛尔酮二异氰酸酯(IPDI)、二苯基甲烷二异氰酸酯(MDI)以及甲苯二异氰酸酯(TDI)为原料,分别合成出了三种末端含有异氰酸酯的反应性聚氨酯。评价了这三种反应性聚氨酯的物理机械性能,并将这三种聚氨酯分别与低黏度双酚A型环氧树脂按不同的比例混合,考察了三个不同的聚氨酯/环氧树脂固化体系的力学性能。研究表明,当反应性聚氨酯预聚体与环氧树脂的质量比为95∶5,固化条件为室温下7d或者室温下12h后,再在80℃放置4h时,这三种共混体系均能达到理想的黏结效果。     

Kinetics of a sterically hindered amine-cured epoxy resin system

Fourier transform infrared spectroscopy (FT-IR) and torsional braid analysis (TBA) were used to study the reaction of an epoxy resin system cured with a sterically hindered amine. Isothermal torsional braid analysis showed the apparent activation energy to be approximately 42 kJ/mol. The reaction kinetics were also considered from the unreacted freshly mixed condition and a partially reacted “B-staged” condition using infrared spectroscopy, The B-staged condition is unreactive and stable at room temperature due to the quenching of the primary amine reaction by the glassy structure and the steric hindrance of the secondary amine reaction. Apparent activation energies for these two conditions were found to be 49.4 kJ/mol and 49.0 kJ/mol respectively. The storage life at room temperature of the B-staged resin system is predicted to be at least three months based on extrapolation of the experimental kinetic data.     

Viscosity modeling during epoxy resin cure

A model is presented that describes the changing melt viscosity of an epoxy laminating resin during its cure. The model incorporates chemical as well as physical factors. The predictions of the model are compared to experimental data using resin cured at several rates of heat-rise, and at a fixed heat-rise profile using resin preadvanced to different extents of reaction. Agreement is good, particularly at rapid heat-rise rates, typical of those used in production.     

A DSC kinetic study of the epoxy network system bisphenol-A diglycidylether- bis(4-aminocyclohexyl)methane

Summary The kinetics of the curing reaction of an epoxy resin based on bisphenol-A diglycidylether with a cycloaliphatic diamine, bis(4-aminocyclohexyl)methane, was studied by differential scanning calorimetry. The measurements were performed both under isothermal conditions and as a function of heating rates. The reaction was also followed by determining the Tg of the resin cured for different time intervals at 150°C. The enthalpy of the reaction was derived from these measurements. The rates and extent of cure were determined. The cycloaliphatic amine used for this study was demonstrated to be more reactive than analogous aromatic systems and yet provided rigid networks with a desirably high Tg.     

分子蒸馏双酚A环氧树脂的性能研究

采用普通市售128环氧树脂经过分子蒸馏,去除轻馏分和多聚体重组分后,得到双酚A分子环氧树脂,牌号为JF-9955A。通过红外光谱和液相色谱分析,基础性能和Na+含量检测以及对其酸酐固化物性能的测试将JF-9955A与国外陶氏化学的DER 332、BakeliteEPR 162高纯度双酚A环氧树脂进行了对比。结果表明,JF-9955A具有粘度低,纯度高,可水解氯及其他离子杂质含量低等特点,各项性能指标达到国外同类产品水平。     

Advanced isoconversional cure kinetic analysis of epoxy/poly(furfuryl alcohol) bio‐resin system

Furfuryl alcohol as a biomass‐derived monomer was used for synthesizing poly(furfuryl alcohol). A diglycidyl ether of bisphenol A (DGEBA) epoxy resin along with 3% and 15% by weight of the poly(furfuryl alcohol) was cured using an aliphatic amine hardener. The cure kinetics of the DGEBA/poly(furfuryl alcohol)/amine systems were investigated by nonisothermal differential scanning calorimetry. The kinetic triplets [E_α, A_α, and f(α)] were computed by using an integral isoconversional method. Based on the E_α‐dependency results a single‐step autocatalytic model was suggested for the reactions mechanism, however, the A_α‐dependency and f(α) analysis did not confirm the suggested model. Detailed kinetics analysis revealed that the cure reaction mechanism of the DGEBA did not change due to the presence of the poly(furfuryl alcohol) in the degree of conversion range < 0.75, nevertheless, it dramatically changed in the degree of conversion range > 0.75 due to the presence of 15 wt % poly(furfuryl alcohol). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45432.     

A thermoanalytical study of the cure characteristics of an epoxy resin system

Rates and extents of cure at different times and temperatures are determined for a modified epoxy resin system and related to gel time measurements. An empirical equation based on time-temperature superposition determines cure time as a function of degree and temperature of cure. The dependence of glass transition temperature on degree of cure, and heat capacity measurements on the cured resin, are discussed.     

Toughness and reinforcement of diglycidyl ether of bisphenol-A by hyperbranched poly(trimellitic anhydride-butanediol glycol) ester epoxy resin

Hyperbranched epoxy resin shows best comprehensive performance in epoxy resin system and is considered as a kind of toughness and reinforcement additive. This article reports on the use of novel hyperbranched poly(trimellitic anhydride-butanediol glycol) ester epoxy resin (HTBE) prepared by us as a functional additive to an epoxy amine resin system. The effect of molecular weight and content of the HTBE on the performance of the diglycidyl ether of bisphenol-A (DGEBA)/HTBE hybrid resin are discussed in detail, and their performance has maximum with the increase of content and molecular weight of HTBE. The impact strength and fracture toughness of the hybrid resin containing 9 wt% second generation of HTBE are 48.2 kJ/m² and 2.71 MPa m^1/2, and which almost are 2.77 and 1.5 times of DGEBA performance respectively. Furthermore, the tensile and flexural strength can also be enhanced about 17%. The fracture surface micrograph of hybrid resin shows no microphase separation of the HTBE/DGEBA blends that facilitates an enhanced interaction to achieve excellent toughness and strength enhancement of the cured systems by scanning electron microscope (SEM). A novel situ reinforcing and toughening mechanism and model are discovered and confirmed by SEM, molecular simulation, and dynamic mechanical thermal analysis technology. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Kinetics of epoxy resins formation from bisphenol-A,bisphenol-S,and epichlorohydrin

The kinetics of formation of epoxy resins derived from bisphenol-A, bisphenol-S, and epichlorohydrin under stoichiometric conditions was considered. The kinetics of reaction was studied by taking into account the consumption of the added alkali and epoxide value of epoxide oligomers. The obtained results satisfactorily explained that the reactivity of bisphenol-A with epichlorohydrin is higher than that of bisphenol-S, the rate of dehydrochlorination of chlorohydrin ether in the presence of alkali and water is much higher than that of the rate of condensation of phenolic hydroxyl group with epichlorohydrin. The apparent reaction order of phenolic groups with epichlorohydrin and terminal epoxide group in the oligomer are all second order. The rate constants and activation energy were determined. The results are discussed. © 1993 John Wiley & Sons, Inc.     

Rheological cure characterization of a polyfunctional epoxy acrylic resin

The curing reaction of a well-controlled epoxy functional acrylic resin based on glycidyl methacrylate (GMA), specifically a statistical copolymer with butyl acrylate (BA), and a commercial linear diamine (Jeffamine® D-230) was monitored using rheological measurements. The evolution of viscoelastic properties, such as storage modulus (G′) and loss modulus (G′′) and complex viscosity (η^*) was recorded in both dynamic and isothermal conditions, at six different temperatures (50–100 °C). An autocatalytic kinetic model was proposed, and all the kinetic parameters including reaction orders and kinetic constants were determined for the cross-linking reaction at temperatures above glass transition temperature of fully cured network (T_g∞). The overall curing process was described by a second-order phenomenological rheokinetic equation based on the model of Kamal. In addition, an empirical model was used to predict the change in viscosity of this system with time until gelation is reached.     

纳米氮化硅对环氧树脂固化反应的影响研究

通过DSC、红外光谱研究了纳米氮化硅粒子的加入对环氧树脂体系固化反应的影响。结果表明,一方面由于纳米Si3N4高的表面活性会促进环氧树脂体系的固化过程;另一方面,由于纳米粒子的加入增大了体系的粘度阻碍了反应分子的运动使得复合材料固化反应速度变慢。环氧树脂体系在不同反应时期表现出的不同的固化行为正是这两种因素综合作用的结果。此外,还研究了不同添加量的纳米Si3N4对复合材料拉伸强度和固化时间的影响。当纳米Si3N4添加量为3%(以环氧树脂质量计)时,复合材料拉伸强度达到最大值,提高了145%。     

Calorimetric and microwave dielectric monitoring of epoxy resin cure

The cure process of a BADGE (diglycidyl ether of bisphenol-A) resin (Epon 828) and ethylenediamine has been investigated by means of calorimetry and dielectrometry in the microwave region (10⁷–10¹⁰ Hz) in the temperature range 50 to 70°C. Kinetic data from calorimetry were analyzed in detail. An overall kinetic order of 2.5 has been obtained. The time domain reflectometry (TDR) has been used to characterize pure components and their mixtures. Cure monitoring was carried out with both TDR and a cavity method at fixed frequency (9.5 × 10⁹ Hz). A very good agreement was obtained between the reaction rate as measured by calorimetry and the rate of decrease of dielectric constants up to very high conversion. This was explained by admitting that the rates of disappearance of dielectric dipoles and of reactive species coincided.     

The effect of state of cure on bond performance for an epoxy resin system

A study of the influence of the state and mode of cure of an epoxy resin, diglycidyl ether of bisphenol A cured with 4,4′-diaminodiphenylmethane, has been made. The state of cure was assessed by differential scanning calorimetry as residual heat of reaction and a transition temperature T^* corresponding to either the melting point or the glass transition temperature. The state of cure was varied by controlling both the time and temperature of cure. Bond strengths can be related to either T^g or residual heat of reaction, but the different cure schedules produce different relations; simultaneous measurement of both parameters is necessary to specify the state of cure. Some additional work has been carried out on the effect of delayed cure on bond performance and on the effect of varying the cure schedule for a phenol-formaldehyde adhesive. Both single- and double-overlap joints have been used and a constant single/double bond strength ratio has been found. This constant is different for the two adhesives, reflecting their different behavior in shear.     

光引发阳离子聚合及其在环氧树脂固化研究中的进展

从光引发阳离子聚合的特点、常见阳离子型光敏引发剂及其引发聚合机理、光引发环氧树脂阳离子聚合体系及发展前景等几个方面进行了简要概述。     

Adhesion promotion at high temperature for epoxy resin or polyimide onto metal by a two-component coupling system of polybenzimidazole and 4-aminophenyl disulfide

A two-component coupling agent layer consisting of polybenzimidazole and 4 aminophenyl disulfide showed better anticorrosive performance and higher adhesive strength for copper and resins than did each single component even at high temperature. © 1995 John Wiley & Sons, Inc.     

Chemical interpretation of the relaxed permittivity during epoxy resin cure

The isothermal cure of a diglycidyl ether of Bisphenol-A (DGEBA) epoxy resin with diaminodiphenylsulfone has been characterized by microdielectrometry and differential scanning calorimetry. The cure temperatures ranged from 410 to 460K. The behavior of the relaxed (or static) dielectric permittivity vs. cure time and temperature was determined from the microdielectrometry data. The DSC data was fit to an autocatalyzed reaction kinetics model, which was then used to predict reactive group concentrations as a function of cure time and temperature. The temperature dependence of the relaxed permittivity at constant chemical conversion was examined in the context of the Onsager theory for the relaxed permittivity of a system of independent dipoles. This analysis indicated that the dipoles in the resin are not independent, as assumed by the Onsager theory, and that the behavior is similar to that observed in polyethers. An empirical modification to the Onsager theory was used in conjunction with the kinetic model to estimate dipole moments for the epoxide, primary amine, and reacted (secondary and tertiary) amine groups. The relative and absolute values of the dipole moments were in good agreement with estimates based on the structures, leading to the conclusion that the observed decrease of the relaxed permittivity during cure of this epoxy/amine system is due to the changing concentrations of polar reactive groups.