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     

Preparation,curing kinetics,and thermal properties of bisphenol fluorene epoxy resin

Diglycidyl ether of 9,9‐bis(4‐hydroxyphenyl) fluorene (DGEBF) was synthesized to introduce more aromatic structures into an epoxy resin system. The structure of DGEBF was characterized with Fourier transform infrared and ¹H‐NMR. 4,4′‐Diaminodiphenylmethane (DDM) was used as the curing agent for DGEBF, and differential scanning calorimetry was applied to study the curing kinetics. The glass‐transition temperature of the cured DGEBF/DDM, determined by dynamic mechanical analysis, was 260°C, which was about 100°C higher than that of widely used diglycidyl ether of bisphenol A (DGEBA). Thermogravimetric analysis was used to study the thermal degradation behavior of the cured DGEBF/DDM system: its onset degradation temperature was 370°C, and at 700°C, its char yield was about 27%, whereas that of cured DGEBA/DDM was only 14%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Cure kinetics of a diglycidyl ether of bisphenol a epoxy network (n = 0) with isophorone diamine

The study of the cure reaction of a diglycidyl ether of bisphenol A epoxy network with isophorone diamine is interesting for evaluating the industrial behavior of this material. The total enthalpy of reaction, the glass‐transition temperature, and the partial enthalpies at different curing temperatures have been determined with differential scanning calorimetry in dynamic and isothermal modes. With these experimental data, the degree of conversion and the reaction rate have been obtained. A kinetic model introduces the mechanisms occurring during an epoxy chemical cure reaction. A modification of the kinetic model accounting for the influence of the diffusion of the reactive groups at high conversions is used. A thermodynamic study has allowed the calculation of the enthalpy, entropy, and Gibbs free energy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

新型环氧树脂胶粘剂的固化动力学研究

在不同升温速率下采用非等温差示扫描量热（DSC）技术对一种新型改性环氧树脂胶粘剂的固化反应过程进行了跟踪,并利用Kissinger、crane方程以及Arrhenius方程对该固化反应进行了动力学分析。结果表明,该固化反应的活化能为59.18kJ／mol,反应级数为0．89;结合Dsc谱图确定其固化工艺为130℃／1h＋150℃／2h＋175℃／3h。     

Preparation and curing kinetics of bisphenol A type novolac epoxy resins

A bisphenol A type novolac resin (Bis‐ANR) was synthesized from bisphenol A and formaldehyde; the resulting novolac was epoxidized to generate a bisphenol A type novolac epoxy resin (Bis‐ANER). The chemical structures of Bis‐ANR and Bis‐ANER were confirmed by ¹H‐NMR spectroscopy and IR spectroscopy; the molecular weights and molecular weight distributions were determined by gel permeation chromatography. In addition, the curing process of Bis‐ANER with 4,4′‐diaminodiphenyl sulfone was studied in both dynamic and isothermal modes with differential scanning calorimetry. The dynamic curing kinetic analysis was evaluated with both the Kissinger and Flynn–Wall–Ozawa methods, and the curing activation energy values were obtained. The isothermal curing reaction exhibited autocatalytic behavior, and the curing kinetics were described with the Kamal kinetics model, which accounted for both the autocatalytic and diffusion‐control effects. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 858–868, 2006     

Novel nitrogen‐containing epoxy resin. I. Synthetic kinetics

A novel nitrogen‐containing epoxy resin was synthesized by two steps: (1) condensation reaction between xyleneformaldehyde resin and phenol, to obtain thermoplastic xylenephenolformaldehyde (XPF) resin; and (2) addition reaction between XPF resin and triglycidyl isocryanurate (TGIC). The synthetic kinetics of XPF resin were intensively investigated by gel permeation chromatography (GPC). The results showed that XPF resin, with different molecular weights and low content of free phenol, could be obtained by changing the reaction conditions. The kinetics of reaction between XPF resin and TGIC was monitored by GPC and epoxy value titration. The results showed that the percentage conversion of TGIC was >85% within 60 min at 140°C and the epoxy value, about 0.3–0.4 mol/100 g, varied with the reaction conditions. This novel epoxy resin exhibited good stability of storage and could be used as a basic resin for making prepreg and laminate. The structures of XPF and XT resins were characterized by IR and ¹H‐NMR spectra. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96:723–731, 2005     

环氧树脂/双环戊二烯双酚型氰酸酯树脂共聚体系固化动力学研究

采用Ozawa方法和Kissinger方法研究了环氧树脂和双环戊二烯双酚型氰酸酯树脂(DCPDCE)共聚体系的固化动力学,并计算了活化能、指前因子、不同温度下的反应速率常数和共聚物的总反应级数。研究结果表明,体系中加入环氧树脂后,提高了体系的反应活化能,明显降低了室温时的反应速率常数,而对固化温度(180℃)时的反应速率常数影响不大。不同环氧树脂含量的共聚体系固化反应级数均接近1级反应。     

Kinetic analysis of relaxation process for the epoxy network diglycidyl ether of bisphenol A/m‐xylylenediamine

The relaxation kinetic of the epoxy network diglycidyl ether of bisphenol A (BADGE n = 0) and m‐xylylenediamine (m‐XDA) was analyzed from DSC experimental data, using different theoretical models. Based on a Petrie model, which involved separate contributions of temperature and structure, three characteristic parameters were calculated: a preexponential factor A, an apparent activation energy E_H, and a parameter C, which indicate the dependency of relaxation time on structure. This model allowed us to calculate the relaxation function at different ageing temperatures. Another method used to study a relaxation kinetic was the Kovacs–Hutchinson model, which takes into account the dependency of the relaxation time on temperature and structure. The last model used was a two‐parameter equation from Williams–Watts, where the relaxation time is independent of temperature. Using data of characteristic times a master curve for the relaxation function was obtained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1591–1595, 2005     

环氧树脂固化反应动力学研究及其活性增韧

采用动态DSC法跟踪环氧树脂E-51／固化剂5784体系的反应历程,确定固化温度,利用Kissinger方程和Crane方程对固化反应动力学进行分析,通过红外分析确定聚硫橡胶的增韧方式,研究不同聚硫橡胶用量列固化产物力学性能的影响,采用扫描电镜分析试样断口形貌。研究结果表明：该固化体系的动力学参数为表观活化能△E=63．946kJ／mol,指前因子Ak=1．90×10^5,反应能级n=0．91,聚硫橡胶增韧环氧树脂通过化学键合来实现,并且效果明显。     

汽车用环氧树脂结构胶固化动力学研究

运用非等温DSC(差示扫描量热)法对Sikapower-492G型汽车用EP(环氧树脂)结构胶在动态升温过程中的固化动力学进行了研究。根据不同升温速率时的DSC曲线,采用Kissinger法、Crane法、Ozawa法和温度-升温速率(T-β)外推法等得到该EP胶粘剂的动力学参数。结果表明:该EP胶粘剂体系的固化动力学可用1级固化动力学模型进行表征;该EP胶粘剂的凝胶化温度、固化温度和后处理温度约分别为123、164、224℃,其表观活化能、频率因子和反应级数等动力学参数分别为117 kJ/mol、1.80×1013 s-1和0.934。     

酚醛型环氧树脂/双酚A型氰酸酯树脂体系固化动力学的研究

应用差示扫描量热分析(DSC)对不同比例的酚醛型环氧树脂/双酚A型氰酸酯树脂体系固化动力学进行了研究,并通过Kissinger法、Ozawa法和Crane法求得了体系的固化动力学参数。结果表明,当环氧树脂与氰酸酯的摩尔比为2∶1时,由Kissinger法和Ozawa法计算得到的表观活化能在体系中最小,分别为49.05 kJ/mol和54.86 kJ/mol,Crane方程求得的表观反应级数为1~2。     

FTIR法研究芳胺固化四溴双酚A环氧树脂反应动力学

用傅里叶变换红外光谱法研究了芳香二胺在恒温下固化四溴双酚A环氧树脂的固化反应动力学,得出了各固化反应的表观活化能。     

腰果酚缩醛胺与环氧树脂的固化反应动力学的研究

在不同升温速率下,用差示扫描量热分析(DSC)研究了腰果酚缩醛胺固化剂(PCD)与环氧树脂的固化反应动力学。通过Kissinger、Crane方程和等转化率的方法求得了其表观活化能E=39.89kJ/mol,固化反应级数n=0.906。     

水性环氧树脂固化反应的研究

通过测定凝胶时间,利用红外光谱仪、差示扫描量热仪等对水性环氧树脂的固化反应进行了研究,并根据K issinger和Ozawa方法分别求得水性环氧树脂体系固化反应的表观活化能。结果表明,凝胶时间随着环氧与胺氢物质的量比的增大而增加,且环氧与胺氢物质的量比为1∶1时较好。环氧基特征吸收峰的强度随着固化反应时间的延长明显变弱,且固化4 h后,环氧的特征峰几乎全部消失。水性环氧体系固化的初始温度、峰值温度和终止温度随着升温速率的增加,均向高温方向移动,用Kissinger和Ozawa法求得水性环氧树脂固化的表观活化能分别为27.35 kJ/mol、32.77 kJ/mol,表明体系的表观活化能很低,固化反应很容易进行。     

Cationic curing of diglycidyl ether of bisphenol A and 2,2,5,5‐tetramethyl‐4,6‐dioxo‐1,3‐dioxane and degradation of the thermosets obtained

Ytterbium and lanthanum triflates were used as cationic initiators to cure mixtures of diglycidyl ether of bisphenol A and 2,2,5,5‐tetramethyl‐4,6‐dioxo‐1,3‐dioxane in several proportions. The evolution of the epoxy and lactone during curing and the linear ester groups in the final materials were evaluated with Fourier transform infrared in the attenuated total reflection mode. The shrinkage after curing and the thermal degradability of the materials with variations in the comonomer ratios and initiator used were evaluated and related to the chemical structure of the final network. The expandable character of 2,2,5,5‐tetramethyl‐4,6‐dioxo‐1,3‐dioxane was confirmed. The obtained materials were more degradable than conventional epoxy resins because of the tertiary ester groups incorporated into the network by copolymerization. The kinetic parameters of the curing and degradation processes were calculated with differential scanning calorimetry and thermogravimetric analysis, respectively, with isoconversional procedures applied in both cases. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

环氧树脂/苯乙烯-马来酸酐共聚物体系固化动力学研究

用示差扫描量热仪(DSC)对环氧树脂/苯乙烯-马来酸酐共聚物/甲基咪唑体系的固化反应过程进行了分析,并用Kissinger和Ozawa方法分别求得固化反应的表观活化能ΔE为58.27 kJ/mol和64.93 kJ/mol;根据Crane理论计算得到该体系的固化反应级数n=0.85,为该环氧树脂体系的固化工艺确定提供理论依据。     

Effect of amino-polycarbonate on the curing kinetics and morphology of epoxy resin

The curing kinetics and the glass transition behavior of amino-polycarbonate with diglycidyl ether of bisphenol-A epoxy resin systems were studied by differential scanning calorimetry (DSC). The ASTM E-698 method was chosen to determine the kinetics parameters of the curing reaction, including the activation energy, preexponential factor, rate constant, and 60-min half-life temperature. The amino-polycarbonate was able to accelerate the curing reaction, reduce the apparent active energy, and decrease T_g of the systems. A homogeneous amino-polycarbonate/epoxy resin network was observed in scanning electron microscopy (SEM) pictures. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 833–838, 2001     

Nonisothermal degradation kinetics for epoxy resin systems containing polymethylphenylsilsesquioxane

The thermal degradation behaviors of polymethylphenylsilsesquioxane/epoxy resin (PMPSQ/EP) systems were investigated by thermogravimetric analysis (TGA) under nonisothermal conditions in nitrogen atmosphere. During nonisothermal degradation, Kissinger's and Flynn‐Wall‐Ozawa's methods were both used to analyze the thermal degradation process. The results showed that a remarkable increase of activation energy was observed in the presence of PMPSQ, which indicated that the addition of PMPSQ retarded the thermal degradation of EP. Flynn‐Wall‐Ozawa's method further revealed that PMPSQ significantly increased the activation energy of EP thermal degradation especially in the early and final stage of thermal degradation process, which illustrated that the PMPSQ stabilized the char layer and improved the flame retardancy of EP. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Curing of diglycidyl ether of bisphenol‐A epoxy resin using a poly(aryl ether ketone) bearing pendant carboxyl groups as macromolecular curing agent

BACKGROUND: Reactive thermoplastics have received increasing attention in the field of epoxy resin toughening. This paper presents the first report of using a novel polyaryletherketone bearing one pendant carboxyl group per repeat unit to cure the diglycidyl ether of bisphenol‐A epoxy resin (DGEBA). The curing reactions of DGEBA/PEK‐L mixtures of various molar ratios and with different catalysts were investigated by means of dynamic differential scanning calorimetry and Fourier transform infrared (FTIR) spectroscopy methods. RESULTS: FTIR results for the DGEBA/PEK‐L system before curing and after curing at 135 °C for different times demonstrated that the carboxyl groups of PEK‐L were indeed involved in the curing reaction to form a crosslinked network, as evidenced by the marked decreased peak intensities of the carboxyl group at 1705 cm^?1 and the epoxy group at 915 cm^?1 as well as the newly emerged strong absorptions of ester bonds at 1721 cm^?1 and hydroxyl groups at 3447 cm^?1. Curing kinetic analysis showed that the value of the activation energy (E_a) was the highest at the beginning of curing, followed by a decrease with increasing conversion (α), which was attributed to the autocatalytic effect of hydroxyls generated in the curing reaction. CONCLUSION: The pendant carboxyl groups in PEK‐L can react with epoxy groups of DGEBA during thermal curing, and covalently participate in the crosslinking network. PEK‐L is thus expected to significantly improve the fracture toughness of DGEBA epoxy resin. Copyright © 2009 Society of Chemical Industry