An efficient fully bio‐based reactive diluent for epoxy thermosets: 2‐[(Oxiran‐2‐ylmethoxy) methyl] furan versus a petroleum‐based counterpart

Furfuryl alcohol and bio‐based epichlorohydrin were used to prepare a fully bio‐based reactive diluent, 2‐[(oxiran‐2‐ylmethoxy) methyl] furan (FOM). After spectral characterization, FOM was blended with epoxy resin, diglycidylether bisphenol A (DGEBA), at different ratios for reducing the viscosity. For a comparison, Cardura (one of the most common commercial reactive diluents), was separately incorporated to DGEBA. Amine‐curing process of the blends was recorded by FTIR and DSC. Similar trends of curing progression for DGEBA containing the reactive diluents were observed. Thermogravimetric analysis and dynamic mechanical thermal analysis, mechanical (hardness, adhesion, and stress–strain) and morphological properties were also investigated to study characteristics of the epoxy matrices formulated with FOM or Cardura. It was concluded that FOM could be considered as an efficient reactive diluent in formulations of polymer composites, structural adhesives and surface coatings based on epoxy resins. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44957.     

改性环氧树脂的固化与稀释增韧研究

研究了改性环氧树脂的固化、稀释增韧效果。探讨了不同种类的固化剂及活性稀释剂对改性环氧树脂的冲击强度、拉伸强度及维卡软化点等性能的影响。研究结果表明,在固化剂9032和活性稀释剂的共同作用下,能制得室温固化型增韧环氧树脂,且其具有较高的强度和耐热性。     

Material systems for rapid manufacture of composite structures

A manufacturing process is described that builds complex composite parts using a layered building process in which each layer of pre‐preg composite is laid and cured as the build progresses. In order to employ on‐line curing without molds, resin technologies that provide fast curing at room temperature—ultraviolet curable and epoxy/polyamide—were investigated. UV‐curable resins were tested for their ability to “shadow” cure by exposing carbon fiber composites to ultraviolet light to determine if the cure propagated from areas directly exposed to areas under fibers. Though ultraviolet curing showed advantages in cure time and low volatile production, very minimal “shadow” curing was achieved. A low temperature curing epoxy/polyamide mixture was tested for the effects of cure temperature, cure time, and mix ratio on the final degree of cure (%DOC) and glass transition temperature (T_g). Layers were made using different resin mixtures, partially cured, and used to build layered parts to determine curing characteristics during the lay‐up process. In the epoxy/polyamide mixtures, mix ratio had little effect on the reaction rate but did affect the T_g. A kinetic model was established for the resin epoxy/polyamide system for optimizing processing conditions during fabrication. However, the model failed to correctly predict the fabrication. The reaction of the material was different during the fabrication process than during the isothermal cure due to the presence of oxygen. During the build process, the degree of cure in each layer increased significantly over the prestaged degree of cure in less time than theoretically predicted. However, the final resin properties, such as T_g, were still below the specifications for high performance parts.     

Cure kinetic study of carbon nanofibers/epoxy composites by isothermal DSC

An investigation was carried out into the cure kinetics of carbon nanofibers (CNF)/epoxy composites, composed of tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM) resin and 4,4′‐diaminodiphenylsulfone (DDS) as a curing agent. The experimental data for both neat system and CNF/epoxy composites revealed an autocatalytic behavior. Analysis of DSC data indicated that the presence of carbon nanofibers had only a negligible effect on the cure kinetics of the epoxy. Kinetic analysis was performed using the phenomenological model of Kamal and two diffusion factors were introduced to describe the cure reaction in the latter stage. Activation energies and kinetic parameters were determined by fitting experimental data. Comparison between the two diffusion factors was performed, showing that the modified factor was successfully applied to the experimental data over the whole curing temperature range. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 329–335, 2005     

Study on the curing reaction,dielectric and thermal performances of epoxy impregnating resin with reactive silicon compounds as new diluents

Two silicon compounds including (3‐glycidoxypropyl)trimethoxysilane (A187) and (3‐glycidoxypropyl)methyldiethoxysilane (W78) were used and studied as reactive diluents for aluminum (III) acetylacetonate (Alacac) accelerated epoxy/anhydride impregnating resin systems. The dielectric performances were studied and characterized by the dielectric dissipation factor, dielectric constant, volume resistivity, and breakdown strength. The curing behaviors and thermal properties of the cured impregnants were studied by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and thermogravimetry. The activation energies of different epoxy formulations were determined with Kissinger method. The results showed that W78 was effective to decrease the viscosity and had little influence on the curing reaction. The cured sample of 15 parts‐of‐W78‐containing‐epoxy resin/methyl‐hexahydrophthalic anhydride (MHHPA) accelerated by Alacac exhibits good dielectric and heat resistant performances with a dielectric dissipation factor below 0.04 at 155°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

兆瓦级风力发电机叶片用环氧树脂

针对兆瓦级风机叶片用纤维/环氧复合材料的特殊要求,开展了适用于真空辅助灌注(VARTM)工艺的环氧基体树脂的国产化研究。采用国产环氧树脂与实验室自制的稀释剂制备环氧树脂与胺类固化剂配合使用,通过示差扫描量热分析,IR光谱,力学性能,耐热性、粘度及吸水性测试等研究了环氧树脂与固化剂配比对其工艺和固化物性能的影响,获得了初始粘度低、粘度对温度不敏感、操作时间长的环氧基体树脂,其树脂浇注体的拉伸性能、弯曲性能均优于国外环氧树脂固化体系,可满足兆瓦级风机叶片用高性能复合材料的使用需求。     

Cure behavior of an interpenetrating diglycidyl ether of bisphenol A/poly(ethylene oxide) miscible system

Differential scanning calorimetry (DSC) was performed to investigate the cure behavior of epoxy networks of diglycidyl ether of bisphenol A/poly(ethylene oxide) (DGEBA/PEO) cured with 4,4'-diaminodiphenyl sulfone (DDS). An interesting miscibility has been recently reported for DGEBA/PEO networks of a semi-interpenetrating structure cured with aromatic amine. This study focused on the cure behavior and effects of miscible polymer diluents on cure kinetics. The physical miscible state between the polymer and epoxy was found to exert no alteration on the cure mechanism, which remained to be autocatalytic for DDS amine-curing of all DGEBA/PEO mixtures as well as the pure DGEBA. The PEO component, being in a miscible state with the epoxy/DDS throughout the cure, acted as a diluent for the reactive DGEBA epoxy and DDS components. The dilution effect could be partially compensated by raising the DDS/epoxy ratio in proportion to increased PEO fraction in DGEBA/PEO/DDS mixtures.     

Curing kinetics and viscosity change of a two‐part epoxy resin during mold filling in resin‐transfer molding process

The curing kinetics and the resulting viscosity change of a two‐part epoxy/amine resin during the mold‐filling process of resin‐transfer molding (RTM) of composites was investigated. The curing kinetics of the epoxy/amine resin was analyzed in both the dynamic and the isothermal modes with differential scanning calorimetry (DSC). The dynamic viscosity of the resin at the same temperature as in the mold‐filling process was measured. The curing kinetics of the resin was described by a modified Kamal kinetic model, accounting for the autocatalytic and the diffusion‐control effect. An empirical model correlated the resin viscosity with temperature and the degree of cure was obtained. Predictions of the rate of reaction and the resulting viscosity change by the modified Kamal model and by the empirical model agreed well with the experimental data, respectively, over the temperature range 50–80°C and up to the degree of cure α = 0.4, which are suitable for the mold‐filling stage in the RTM process. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2139–2148, 2000     

Curing kinetics and reaction‐induced homogeneity in networks of poly(4‐vinyl phenol) and diglycidylether epoxide cured with amine

Mixtures of diglycidyl ether of bisphenol‐A (DGEBA) epoxy resin with poly(4‐vinyl phenol) (PVPh) of various compositions were examined with a differential scanning calorimeter (DSC), using the curing agent 4,4′‐diaminodiphenylsulfone (DDS). The phase morphology of the cured epoxy blends and their curing mechanisms depended on the reactive additive, PVPh. Cured epoxy/PVPh blends exhibited network homogeneity based on a single glass transition temperature (T_g) over the whole composition range. Additionally, the morphology of these cured PVPh/epoxy blends exhibited a homogeneous network when observed by optical microscopy. Furthermore, the DDS‐cure of the epoxy blends with PVPh exhibited an autocatalytic mechanism. This was similar to the neat epoxy system, but the reaction rate of the epoxy/polymer blends exceeded that of neat epoxy. These results are mainly attributable to the chemical reactions between the epoxy and PVPh, and the regular reactions between DDS and epoxy. Polym. Eng. Sci. 45:1–10, 2005. © 2004 Society of Plastics Engineers.     

新型脂环环氧树脂/胺体系固化动力学及性能研究

采用DSC研究了脂环环氧树脂稀释剂1,4-环己烷二甲醇二缩水甘油醚(CHDMDGE)与异佛尔酮二胺及聚醚胺D230的固化行为,得出其固化反应的活化能、指前因子和反应级数等动力学参数。通过外推法计算出了固化工艺的特征温度,以此为依据制定了固化工艺并对固化后体系的力学性能进行了测试。结果表明,与线形脂肪族环氧稀释剂1,4-丁二醇二缩水甘油醚和1,6-己二醇二缩水甘油醚相比,CHDMDGE的拉伸强度分别提高了0.4倍和2.7倍,断裂伸长率则提高了1.9倍和5.0倍。     

Modification of a two‐component system by introducing an epoxy‐reactive diluent: Construction of a time–temperature–transformation (TTT) diagram

Curing reactions of a three‐component system consisting of an epoxy resin diglycidyl ether of bisphenol A (DGEBA n = 0), 1,2‐diaminecyclohexane as curing agent, and vinylcyclohexene dioxide as a reactive diluent were studied to calculate a time–temperature–transformation isothermal cure diagram for this system. Differential scanning calorimetry (DSC) was used to calculate the vitrification times. DSC data show a one‐to‐one relationship between T_g and fractional conversion α, independent of cure temperature. As a consequence, T_g can be used as a measure of conversion. The activation energy for the polymerization overall reaction was calculated from the gel times obtained using the solubility test (58.5 ± 1.3 kJ/mol). This value was similar to the results obtained for other similar epoxy systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1190–1198, 2004     

聚乙二醇接枝改性纳米炭黑对环氧树脂固化过程的影响

采用差示扫描量热法研究了以聚乙二醇(PEG)接枝改性的纳米炭黑(NC)(NC-PEG)为填料对环氧树脂/4,4-二氨基二苯砜非等温固化反应的影响,通过Flynn-Wall-Ozawa法和Malek法确定了固化反应的动力学参数.结果表明:两参数的自催化模型能够很好地描述环氧树脂及其复合材料的固化反应过程,各试样的模型拟合结果与实验数据相吻合.NC-PEG能够促进环氧树脂的固化,使固化活化能降低,其中,NC-PEG用量为3 phr时,活化能最低.     

Effect of curing method on mechanical and morphological properties of carbon fiber epoxy composites for solid rocket motor

Microwave (MW) curing and conventional thermal curing techniques were utilized to cure carbon fiber epoxy composites for solid rocket motor to investigate the effect of curing method on their mechanical and morphological properties. In this work, tensile and inplane shear strength properties together with morphological properties were compared between MW cured and thermally cured composites, and the mechanism for MW curing was analyzed. The study shows that 83% cure cycle time reduction is achieved through MW curing. Mechanism analysis for MW curing indicates the resin at the surface layer and interior parts of the composites is cured with different forms. Temperature monitoring during MW processing indicates the uneven electric field distribution in the domestic MW oven. Fourier transform infrared spectrum measurements reveal that MWs do not initiate any new chemical reactions during the curing process of the composites. Thermal analysis using differential scanning calorimeter reveals higher glass transition temperature (T_g) of MW cured composites compared with thermally cured counterparts. Moreover, the MW cured composites show 17% lower tensile strength than thermally cured composites, whereas a 3% increase of the inplane shear strength is observed for MW cured composites, which is also confirmed via scanning electron microscope by means of better coating the fibers with resin, increased fiber wetting and less fiber pullout. POLYM. COMPOS., 36:1703–1711, 2015. © 2014 Society of Plastics Engineers     

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.     

Curing behavior of dicyandiamide/epoxy resin system using different accelerators

Various amounts of dicyandiamide (Dicy), two grades of epoxy resins, i.e. Epiran 06 and Epikote 828, and three different accelerators including benzyl dimethyl amine (BDMA), 3-(4-chlorophenyl)-1,1-dimethyl urea (Monuron) and 2-methyl imidazole (Im) were used in curing of Dicy/epoxy resin system. Both of the used epoxy resins were based on diglycidyl ether of bisphenol A (DGEBA). The effects of type and concentration of accelerators on curing behavior were studied by differential scanning calorimetry (DSC) method in dynamic or non-isothermal mode. The optimum concentration of Dicy for curing of epoxy resins was obtained based on the glass transition temperature of the cured epoxy/Dicy formulations. The maximum glass transition temperature of 139 °C was obtained at the stoichiometric ratio of Dicy to epoxy of 0.65. The results showed that BDMA has a broader curing peak in DSC and starts the cure reaction earlier than the others. However, Monuron has a narrow curing reaction peak with good cure latency. The tensile properties of Dicy-cured Epiran 06 and Epikote 828 epoxy resins reinforced with chopped strand mat showed that these two epoxy resins have similar mechanical properties. For composites based on the Epiran 06 and Epikote 828 reinforced with 40 wt % glass chopped strand mat, tensile strength and modulus were 156 and 153.4 MPa and 11.6 and 12.4 GPa, respectively.     

基于变活化能模型的T800/环氧树脂预浸料固化反应动力学研究

为了深入了解某新型高温固化T800/环氧树脂预浸料的固化行为,借助差示扫描量热仪(DSC),采用非等温DSC法研究了T800/环氧树脂预浸料的固化反应过程。基于唯象模型,系统研究了该预浸料的固化反应特征温度及固化动力学参数,确定该预浸料中环氧树脂的固化反应动力学模型为自催化模型。采用等转化率法,分析了预浸料中环氧树脂的反应活化能随固化度的变化情况,结果表明在整个固化反应过程中,树脂固化反应活化能变化较大,传统模型法基于全固化过程活化能不变的假设无法准确描述该固化反应。采用变活化能自催化模型,利用粒子群全局优化算法,得到了T800/环氧树脂预浸料的固化动力学方程,结果表明该模型能较好地描述实验现象,可为进一步研究该预浸料的热力学性能及其成型过程中的质量控制提供理论基础。     

Ultraviolet‐curing behavior of an epoxy acrylate resin system

Ultraviolet (UV)‐curing behavior of an epoxy acrylate resin system comprising an epoxy acrylate oligomer, a reactive diluent, and a photoinitiator was investigated by Fourier transform infrared (FTIR) spectroscopy. The conversion changes of the resin system containing 20 phr of 1,6‐hexanediol diacrylate as a reactive diluent and 2‐hydroxy‐2‐methyl‐1‐phenyl‐propan‐1‐one as a photoinitiator were measured under different UV‐curing conditions. The fractional conversion was calculated from the area of the absorption peak for the vinyl group vibration occurring at 810 cm^?1. The effects of photoinitiator concentration, total UV dosage, one‐step or stepwise UV irradiation, UV intensity, atmosphere, and temperature on the curing behavior of the resin system were investigated. The conversion of the resin system increased rapidly at the initial stage of the UV‐curing process but increased very slowly after that. The final conversion of the resin system was mainly affected by total UV dosage. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1180–1185, 2005     

Cure characterization of Cycom 977‐2A carbon/epoxy composites for quickstep processing

In this effort, Quickstep, a relatively a new technique, have been employed for manufacturing of composite materials. The cure schedule provided by a prepreg manufacturer is usually designed for autoclave or other traditional processing techniques and thermosetting resin systems are formulated for ramp rate curing 2–3 K min^?1. While in case of Quickstep processing, ramp rates of 15 K min^?1 can be achieved, thus changing the chemorheology of resin. The cure process of 977‐2A carbon/epoxy composites was evaluated for Quickstep processing using differential scanning calorimetry (DSC), dynamic mechanical and thermal analysis, and Fourier transformed infrared and results were compared with cure cycle employed for autoclave curing. Optimum hold time for Quickstep processing at upper curing temperature (180°C) was determined using DSC. The hold time of 120 min at 180°C was found to be suitable for Quickstep cure cycle, producing a panel of similar degree of cure to that achieved through autoclave processing schedule. Final degree of cure was dependent on time spent at upper cure temperature and slightly on initial steps of the cure cycle which was used to control the resin flow, fiber wetting, and void removal. Quickstep processed samples exhibited higher T_g and crosslink density and similar molecular network structure to the autoclave cured samples. POLYM. ENG. SCI., 54:887–898, 2014. © 2013 Society of Plastics Engineers     

Synthesis and evaluation of tetra(2,7-octadienyl) titanate as a reactive diluent for air-drying alkyd paints

Environmental regulations are forcing the reformulation of many decorative and protective coatings systems. In particular, air-drying solventborne alkyd paints need to meet increasingly stringent emission limits and often must be reformulated with suitable exempt solvents or reactive diluents to achieve volatile organic compound (VOC) reduction. In the research summarized in this article, a new reactive diluent, tetra(2,7-octadienyl) titanate, was synthesized and evaluated in alkyd formulations for VOC reduction and property enhancement. A soy-based long-oil alkyd resin; a soy-based high-solids, long-oil alkyd resin; and a linseed-based, high-solids long-oil alkyd resin were evaluated in combination with the new reactive diluent at weight percentages ranging from 10% to 50%. Characterization included measuring viscosity, film dry times, and film performance of the reactive diluent formulations in comparison to neat alkyd resins used as control. The tetra(2,7-octadienyl) titanate formulations consistently exhibited reduced viscosities and dry times as a function of concentration. The resulting films were harder and more thoroughly cured than the control systems.     

DSC study of the cure kinetics during nanocomposite formation: Epoxy/poly(oxypropylene) diamine/organically modified montmorillonite system

The effect of an organically modified montmorillonite (OMMT) on the curing kinetics of a thermoset system based on a bisphenol A epoxy resin and a poly(oxypropylene)diamine curing agent were studied by means of differential scanning calorimetry (DSC) in isothermal and dynamic (constant heating rate) conditions. Montmorillonite and prepared composites were characterized by X‐ray diffraction analysis (XRD) and simultaneous differential scanning calorimetry–thermogravimetric analysis (DSC–TGA). Analysis of DSC data indicated that the presence of the filler has a very small effect on the kinetics of cure. A kinetic model, arising from an autocatalyzed reaction mechanism, was applied to the DSC data. Fairly good agreement between experimental and modeling data was obtained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 550–557, 2006