A Direct Comparison of the Fragmentation Test and the Microbond Pull-out Test for Determining the Interfacial Shear Strength

Experiments were conducted to compare the fragmentation test with the microbond pull-out test for determining the interfacial shear strength between carbon AS4 fibers and a thermoset matrix consisting of a Di-Glycidyl Ether of Bisphenol A (DGEBA) resin cured with a diamine (meta-phenylenediamine, m-PDA) curing agent. The results indicate that, for the microbond test, diffusion of the rather volatile m-PDA curing agent at early stages of cure leads to low values of interfacial shear strengths when compared with results obtained for the same system with the fragmentation test.

With the microbond test, a distinct relationship between the glass transition temperature of the droplets and their size is noticed. Smaller (< 150 μm) droplets have very low Tg's and are incompletely cured. While changing to a modified curing cycle and/or using a m-PDA-rich curing environment alleviates the diffusion problem, the interfacial shear strength values are still not in good agreement with the fragmentation test results. Microbond data from another system consisting of DGEBA resin cured with a different, less volatile dimaine curing agent indicates that diffusion of the curing agent becomes less severe as the volatility of the curing agent decreases and the corresponding microbond interfacial shear strengths agree better with fragmentation test results.     

Curing kinetics and properties of epoxy resin-fluorenyl diamine systems

Diglycidyl ether of bisphenol fluorene (DGEBF), 9,9-bis-(4-aminophenyl)-fluorene (BPF) and 9,9-bis-(3-methyl-4-aminophenyl)-fluorene (BMAPF) were synthesized to introduce more aromatic structures into the epoxy systems, and their chemical structures were characterized with FTIR, NMR and MS analyses. The curing kinetics of fluorenyl diamines with different epoxy resins including DGEBF, cycloaliphatic epoxy resin (TDE-85) and diglycidyl ether of bisphenol A (DGEBA) was investigated using non-isothermal differential scanning calorimetry (DSC), and determined by Kissinger, Ozawa and Crane methods. The thermal properties of obtained polymers were evaluated with dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). The results show that the values of activation energy (E_a) are strongly dependent on the structures of epoxy resin and curing agent. The curing reactivity of epoxy system is restrained by the introduction of rigid fluorene into chain backbone and flexible methyl into side groups. The cured DGEBF/fluorenyl diamine systems exhibit remarkably higher glass transition temperature, better thermal stability and lower moisture absorption compared to those of DGEBA/fluorenyl diamine systems, and display approximate heat resistance and much better moisture resistance relative to those of TDE-85/fluorenyl diamine systems.     

Improvement of Elastic Modulus and Thermal Stability of Epoxy Resin Using New Curing Agents

New curing agents 2,5-diamino-1,3,4-thiadiazole (DATD) and N-(4-hydroxybenzal) N'(4′-hydroxyphenyl) thiourea (HHPT) were synthesised and characterized using FT-IR, 1H-NMR and 13C-NMR analysis. The curing reactions were studied for the epoxy resin diglycidyl ether of bisphenol-A (DGEBA) using new curing agents along with the conventional aromatic diamine 4,4′-diamino diphenyl methane (DDM) for comparison purpose. The curing profiles of DDM, DATD and DATD/HHPT towards DGEBA were examined by Differential Scanning Calorimetry (DSC). Elastic modulus and thermal stability of the cured resins were evaluated using DMA and TGA analysis. When compared with DDM and DATD, the DATD/HHPT curing system accelerated the curing rate due to the presence of phenol molecules in the HHPT. Furthermore, the DATD/HHPT-cured epoxy resin demonstrated higher elastic modulus along with better thermal stability.     

The research on syntheses and properties of novel epoxy/polymercaptan curing optical resins with high refractive indices

A novel thioether glycidyl resin bis[3-(2,3-Epoxypropylthio)phenyl]-sulfone (BEPTPhS) with high refractive index was synthesized by condensation of bis(3-mercaptophenyl)sulfone (BMPS) with epichlorohydrin. It's structure was characterized by FTIR, MS and NMR. It was the first time that trimercaptothioethylamine (TMTEA) was used as curing agent to cure epoxy resins. Optical resins possessing high refractive index were prepared by curing diglycidyl ether of bisphenol A (DGEBA) with the mixture of TMTEA and ethylendiamine (EDA) and by curing BEPTPhS/DGEBA with TMTEA. The research on the optical properties of resins of DGEBA cured by the mixtures of TMTEA and EDA indicated that these resins possess higher refractive index (n_d>1.60), lower dispersity (ν_d>34), high impact strength (IPS>30 kJ m⁻²) and higher transmittance. The n_d, ν_d and density of these resins varied linearly with the EDA content in the curing agent mixtures. The optimum ratio of the EDA content to that of TMTEA is 20:80 (molar ratio), at this ratio the cured resin has the optimum optical properties (n_d²⁰=1.61, v_d=35.4). The cured resins of BEPTPhS/TMTEA have a high refractive index (the highest is n_d=1.67). The optical, physical and thermal properties of the cured optical resins of BEPTPhS/TMTEA were discussed in this paper.     

Preparation and properties of soybean oil–based curing agents for epoxy resin

In order to improve the flexibility properties of conventional epoxy resin, two novel soybean oil–based curing agents were synthesized. The curing agent obtained from the reaction between epoxy soybean oil and ethylene diamine was named EEDA, and another curing agent derived from epoxy soybean oil and isophorone diamine was named EIPDA. Several techniques were used to systematically investigate the effects of the structure and content of the two curing agents on the properties of the cured products. The Fourier transform infrared analysis demonstrated that epoxy resin reacted with soybean oil–based curing agents. The differential scanning calorimetry analysis showed that the curing process between diglycidyl ether of bisphenol‐A (DGEBA) and soybean oil–based curing agents only had an exothermic peak. Thermogravimetric analysis indicated that the cured DGEBA/EIPDA system was more stable than the DGEBA/EEDA system below 300 °C. Mechanical tests and Shore D hardness tests suggested that excessive EEDA greatly enhanced the toughness of cured products because of the introduction of aliphatic chains.© 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44754.     

Preparation and Application of a New Curing Agent for Epoxy Resin

A new curing agent based on palmitoleic acid methyl ester modified amine (PAMEA) for epoxy resin was synthesized and characterized. Diglycidyl ether of bisphenol A (DGEBA) epoxy resins cured with different content of PAMEA along with diethylenetriamine (DETA) were prepared. The mechanical properties, dynamic mechanical properties, thermal properties, and morphology were investigated. The results indicated that the PAMEA curing agent can improve the impact strength of the cured epoxy resins considerably in comparison with the DETA curing agent, while the modulus and strength of the cured resin can also be improved slightly. When the PAMEA/epoxy resin weight ratio is 30/100, the comprehensive mechanical properties of the cured epoxy resin are optimal; at the same time, the crosslinking density and glass transition temperature of the cured epoxy resin are maximal.     

Curing of DGEBA epoxy resin by low generation amino‐group‐terminated dendrimers

Low generation amino‐group‐terminated poly(ester‐amine) dendrimers PEA1.0 (NH₂)₃ and PEA1.5 (NH₂)₈, and poly(amido‐amine) dendrimer PAMAM1.0 (NH₂)₄ were used as diglycidyl ether of bisphenol A (DGEBA) epoxy resin hardeners. Thermal behavior and curing kinetics of dendrimer/DGEBA systems were investigated by means of differential scanning calorimetry (DSC). Compared with ethylene diamine (EDA)/DGEBA system, the dendrimer/DGEBA systems gradually liberated heat in two stages during the curing process, and the total heat liberated was less. Apparent activation energy and curing reaction rate constants for dendrimer and EDA/DGEBA systems were estimated. Thermal stabilities and mechanical properties of cured thermosetting systems were examined as well. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3902–3906, 2006     

Curing behavior and properties of epoxy resins cured with the diamine having the quinoxaline or triazine structure

2,3-Bis(4-aminophenyl)quinoxaline (1a), 2,3-bis(4-aminophenyl)-6-methylquinoxaline (1b), and 5,6-bis(4-aminophenyl)-3-(2-pyridyl)-1,2,4-triazine (2) were studied as curing agents of epoxy resins. The exotherms on differential scanning calorimetry thermograms of the mixtures of diglycidyl ether of bisphenol A (DGEBA) with 1a, 1b, and 2 were observed at higher temperatures than that of the mixture of DGEBA with a commercially used diamine, for example, 4,4′-diaminodiphenylsulfone (DDS). However, the epoxy resin cured with 1a (EP-1a) showed higher tensile strength to stainless steel at 20°C than that cured with DDS, and the high tensile strength of EP-1a was maintained even at 180°C. The epoxy resin cured with 1b or 2 also possessed higher tensile strength at 20°C than that cured with DDS, but the high tensile strength lowered somewhat at 120°C. Using diamines 1a, 1b, and 2 as a curing agent improved heat distortion temperatures of the cured epoxy resins. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 1737–1741, 1998     

用FTIR研究环氧树脂的固化反应

采用傅里叶变换红外光谱研究了双酚Ａ型环氧树脂／马来酸酐固化剂／咪唑类固化催化剂体系的固化反应。结果表明,固化催化剂的用量在０．２％～２．０％（质量分数）时,对环氧树脂与固化剂的反应可起到明显的催化作用;大于２．０％时反应机理发生显著变化,环氧树脂与催化剂优先反应,抵制环氧树脂与固化剂的反应。     

苯并(口恶)嗪改性环氧酸酐体系的固化机理及动力学

利用一种二胺型苯并(口恶)嗪改性环氧酸酐体系。通过FT-IR和DSC分析了改性体系的固化机理。结果表明：共混树脂体系在固化时存在两个反应,首先是环氧树脂与足量的酸酐在咪唑作用下在100℃先开始固化,并在150℃固化2 h后固化完全,之后苯并(口恶)嗪在180℃发生开环聚合。用非等温DSC法研究了该共混体系的固化动力学。采用Flynn-Wall-Ozawa方法求出了共混体系在固化时两个固化反应的活化能,分别为65.27 kJ·mol^-1和92.8 kJ·mol^-1,并利用Friedman方法判断了两个反应都是自催化反应,计算得到自催化模型曲线与实验曲线能较好地吻合。     

Processing–morphology–property relationships in epoxy resins

An investigation was conducted into processing–morphology–property relationships of a series of epoxy resin formulations. Diglycidyl ether of bisphenol A (DGEBA) epoxy resin was cured with diethylene triamine (DETA) and 2,5-dimethyl 2,5-hexane diamine (DMHDA). The two systems were compared by electron microscopic investigation and thermomechanical and fracture property measurements. Transmission electron microscopy has revealed a difference in the morphology of fracture surfaces. On the other hand, thermomechanical and fracture properties of DETA- and DMHDA-cured formulations were found to be very similar. Three different processing (curing) conditions were used for DMHDA-cured formulations, without an apparent effect on their properties. The previously reported improvement in impact energy of DMHDA-cured formulations is unfounded.     

Preparation of a light color cardanol-based curing agent and epoxy resin composite: Cure-induced phase separation and its effect on properties

A light color cardanol-based epoxy curing agent (MBCBE) was synthesized from cardanol butyl ether, formaldehyde and diethylenetriamine. In comparison, a phenalkamine with a similar structure was also prepared. The chemical structures were confirmed by GC–MS and FTIR. The cure behaviors of diglycidyl ether of bisphenol A (DGEBA) with these two curing agents was studied by differential scanning calorimetry (DSC). The morphology, mechanical properties, thermal properties of the cured epoxies were also investigated. The DSC results indicated that MBCBE is less reactive than the phenalkamine. The morphology of the cured MBCBE/DGEBA consisted of cavities dispersed within a continuous epoxy matrix. The cavities markedly improved the lap shear strength and impact strength of the cured resin. Both the two cured resins indicated a two-stage decomposition mechanism. Compared with PKA/DGEBA, the weight loss of MBCBE/DGEBA at the first stage was mainly resulted from the dispersed phase in the epoxy matrix.     

有机硅改性水性环氧固化剂的合成及表征

A novel waterborne epoxy curing agent was prepared using 3-glycidoxypropyl trimethoxysilane （GPTMS） as a termination agent of adduct, which was synthesized by triethylene tetramine （TETA） and liquid epoxy resin （E-51）. The effects of the reaction temperature and time on the synthesis process were investigated experimentally. The particle size and the distribution of water dispersion of the curing agent were measured by dynamic light scattering（DLS）. The structure of the products was characterized by Fourier transform infrared spec-trometer （FTIR） and ^1H-nuclear magnetic resonance （^1H NMR）. The properties of the synthesized curing agent and the epoxy resin film cured by it were also measured. The results showed that the appropriate temperature for the synthesis of adduct was at 65-75℃ and the reaction time was 4-5h, and that the suitable reaction temperature of curing agent synthesis was 75-85℃ and the reaction time was 3-4h. When the mass ratios of GPTMS and acetic acid were 3%-5% and 5%-10% respectively, the hardness, water resistance and adhesion of the cured film were improved significantly.     

固化剂对环氧包封料性能的影响

研究了以甲基四氢苯酐和间苯二胺作固化剂时 ,环氧树脂包封料的固化放热现象 ,测定了不同固化剂体系的包封料力学性能、电性能、密度和吸水性。结果表明 ,间苯二胺的活性大于酸酐固化剂的活性 ,但填料的加入使胺固化的放热降低 ,酸酐固化的升高。胺固化的冲击强度较高 ,加入填料可提高拉伸强度。胺固化的介电常数 ,介电损耗角较高 ,但体积电阻率较低 ,其吸水性较高     

Curing Behavior of Wood Adhesives Under High Steam Pressure

Steam-injection pressing is a recent development for manufacturing wood products. The curing mechanism and behavior of wood adhesives during steam-injection heating and hot-platen heating may cause differences in both chemical and physical aspects. The curing of wood adhesives under high steam pressure using an especially designed reaction cell is discussed. The adhesives used in this study were phenol-formaldehyde (PF), urea-formaldehyde (UF), melamine-formaldehyde (MF), and isocyanate (IC) resins. At different curing times, the heating temperature (steam pressure) applied to cure the adhesives was 160°C (6 kgf/cm²). Results were examined by analytical methods using FR-IR, ¹³C-NMR, dynamic mechanical analysis and solvent extraction. (1) By steam-injection heating, PF resin immediately cured to some degree in a few minutes and maintained an equilibrium situation. In this case, the reaction was accompanied by the disappearance of the ether structure. (2) In UF resin, results from IR data clarified different reactions between hot-platen heating and steam-injection heating. During steam-injection heating, as heating time increased, UF resin returned to its liquid state under the influence of hydrolysis. (3) MF resin was almost cured under steam-injection in a short heating time compared with hot-platen heating. (4) IC resin foamed and cured in a short heating time under steam-injection. It was proved that steam-injection heating was more effective than by hot-platen heating for IC resin.     

Curing and thermal behaviour of epoxy resin in the presence of pyromellitic dianhydride and imidazole

The curing behaviour of DGEBA was investigated by differential scanning calorimetry in the presence of varying amounts of PMDA. The molar ratio of DGEBA : PMDA was varied as 1 : 0.8, 1 : 1, 1 : 1.5, 1 : 2.0, and 1 : 2.5. The heat of polymerization (ΔH) was found to be maximum at a molar ratio of 1 : 0.8 (DGEBA : PMDA). To study the effect of imidazole content on the curing behaviour, varying amounts of imidazole, i.e., 0.1, 0.15, 0.2, and 0.3% (w/w) were used keeping the ratio of DGEBA : PMDA (1 : 0.8) constant. A broad exotherm was observed in all the samples. A significant decrease in the peak exotherm was observed when 0.1% imidazole was used. Further increase in the imidazole concentration up to 0.2% resulted in a marginal decrease in the peak exotherm temperature. Thermal stability of epoxy resin, cured isothermally, was evaluated by recording thermogravimetric traces in nitrogen atmosphere. The percent char yield was highest in case of resin sample, IP1‐30 (i.e., DGEBA (1 mole) cured using 0.8 mole of PMDA in the presence of 0.3 (w/w) of imidazole). © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

混合芳香胺固化环氧树脂的研究

用4,4'-二氨基二苯甲烷(DDM)、4,4'-二氨基二苯砜(DDS)和4,4'-二氨基二苯醚(DDE)三种芳香胺混合固化双酚A型环氧树脂,研究了固化网络的机械性能和热性能,当DDM∶DDS∶DDE质量比为5∶2.5∶1时,可使固化网络的冲击强度得到一定的提高。SEM对固化网络冲击断面的微观结构分析表明,树脂呈韧性断裂。     

用DTA研究环氧树脂固化反应动力学

本文用ＤＴＡ和ＦＩＲ研究双酚Ａ二缩水甘油醚型环氧树脂与２－乙基－４－甲基咪唑固化反应动力学,探讨了固化反应的机理。结果表明：此固化反应是分步进行的。第一步是加成反应,第二步是催化聚合反应,由此确定适宜采用分段固化工艺。通过ＤＴＡ曲线推得固化工艺温度,并计算固化反应各步活化能：Ｅ１＝３６８ｋＪ．ｍｏｌ－１,Ｅ２＝５３９ｋＪ．ｍｏｌ－１     

Effect of microencapsulated curing agents on the curing behavior for diglycidyl ether of bisphenol A epoxy resin systems

Microcapsules containing a curing agent, 2‐phenyl imidazole (2PZ), for a diglycidyl ether of bisphenol A (DGEBA) epoxy resin were prepared by a solid‐in‐oil‐in‐water emulsion solvent evaporation technique with poly(methyl methacrylate) (PMMA) as a polymeric wall. The mean particle size of the microcapsules and the concentration of 2PZ were about 10 μm and nearly 10 wt %, respectively. The onset cure temperature and peak temperature of the DGEBA/2PZ–PMMA microcapsule system appeared to increase by nearly 30 and 10°C, respectively, versus those of the DGEBA/2PZ system because of the increased reaction energy of curing. The former could take more than 3 months at room temperature, whereas the latter was cured after only a week. The values of the reaction order (a curing kinetic parameter) for DGEBA/2PZ and DGEBA/2PZ–PMMA microcapsules were quite close, and this showed that the curing reactions of the two samples proceeded conformably. The curing mechanism was investigated, and a two‐step initiation mechanism was considered: the first was assigned to adduct formation, whereas the second was due to alkoxide‐initiated polymerization. The glass‐transition temperature of DGEBA/2PZ was 165.2°C, nearly 20°C higher than the glass‐transition temperatures of DGEBA/2PZ–PMMA microcapsules and DGEBA/2PZ/PMMA microspheres, as determined by differential scanning calorimetry measurements. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

环氧树脂/胺化酰亚胺潜伏性固化体系的制备

为了深入了解新型环氧树脂/胺化酰亚胺潜伏性固化体系的使用条件,采用差示扫描量热（DSC）技术考察了E–51型环氧树脂/脂肪族胺化酰亚胺体系的非等温固化反应过程,研究了体系的固化条件及固化物性能。结果表明：E–51与固化剂的物质的量比为1∶0.1;体系的固化条件为固化150℃/2 h,后固化180℃/1 h。树脂试样制备工艺简单,无挥发性有机溶剂,树脂混合物贮存稳定性好。体系固化反应平稳且放热量较少,完全固化后的树脂试样具有良好的耐水性、耐热性和物理机械性能。