Nanocomposites based on liquid‐crystalline epoxy–clay: synthesis and morphology

Liquid‐crystalline epoxy–organoclay nanocomposites were synthesized based on two different liquid‐crystalline epoxy monomers, 4, 4′‐diglycidyloxybiphenyl (BP) and hydroquinone bis(4‐epoxypropylbenzoate) (HB). The X‐ray diffraction patterns of BP–organoclay (93A) hybrids indicate that BP diffuses into the organoclay layers and increases d‐spacing from 2.3 to 3.7 nm either in a solvent or in the melting state. The dynamic differential scanning calorimetry results indicate that the alkylammonium ion in the clay gallery catalyzes the epoxy ring‐opening reaction with a diamine curing agent. The fast intergallery polymerization forms the exfoliated nanocomposite if the content of organoclay is below 2 %. But an intercalated nanocomposite is obtained with an increase of organoclay to 10 %. The nanocomposite with 5 % of organoclay is a mixture of the two types. Polarizing optical microscopy photographs of the cured products showed that the liquid‐crystalline phase is formed with or without organoclay. Copyright © 2005 Society of Chemical Industry     

Study of the isothermal curing of an epoxy prepreg by near‐infrared spectroscopy

The commercial epoxy prepreg SPX 8800, containing diglycidyl ether of bisphenol A, dicyanodiamide, diuron, and reinforcing glass fibers, was isothermally cured at different temperatures from 75 to 110°C and monitored via in situ near‐infrared Fourier transform spectroscopy. Two cure conditions were investigated: curing the epoxy prepreg directly (condition 1) and curing the epoxy prepreg between two glass plates (condition 2). Under both curing conditions, the epoxy group could not reach 100% conversion with curing at low temperatures (75–80°C) for 24 h. A comparison of the changes in the epoxy, primary amine, and hydroxyl groups during the curing showed that the samples cured under condition 2 had lower initial epoxy conversion rates than those cured under condition 1 and that more primary amine–epoxy addition occurred under condition 2. In addition, the activation energy under cure condition 2 (104–97 kJ/mol) was higher than that under condition 1 (93–86 kJ/mol), but a lower glass‐transition temperature of the cured samples was observed via differential scanning calorimetry. The moisture in the prepreg was assumed to account for the different reaction kinetics observed and to have led to different reaction mechanisms. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2295–2305, 2003     

Nonisothermal cure kinetics of DGEBA with novel aromatic diamine

The effect of the molar ratio of diglycidyl ether of a bisphenol‐A based epoxy (DGEBA) and synthesized 4‐phenyl‐2,6‐bis(4‐aminophenyl)pyridine (PAP) as curing agent during nonisothermal cure reaction by the Kissinger, Ozawa, and isoconversional equations was studied. The cure mechanism was studied by FTIR analysis. Kinetic analysis of the curing reaction of DGEBA at two different concentrations (42 and 32 phr) of the curing agent was studied by using DSC analysis. With an increasing PAP content, the pre‐exponential factor increased by increasing collision probability between epoxide and primary or secondary amine groups in noncataltyic or catalytic modes. The activation energy also increased because of the increasing content of crosslink density. The activation energies obtained from three equations were in good agreement. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3076–3083, 2007.     

丁腈羟_丁二酸酐加成物与环氧树脂反应动力学的研究

用红外光谱仪和差示扫描量热计,研究了端羟基液体丁二烯-丙烯腈共聚物与丁二酸酐反应得到的加成物与环氧树脂的固化反应动力学。结果表明,在此固化反应体系中,反应前期主要是羧基与环氧基的反应,后期则主要是环氧基的聚合;树脂中仲羟基与环氧基的反应可以忽略。用DSC法测得的固化反应表观活化能为66.5 kJ/mol。     

Effect of backbone moiety in epoxies on thermal conductivity of epoxy/alumina composite

We chose two commercial epoxies, bisphenol A diglycidyl ether (DGEBA) and 3,3′,5,5′‐tetramethyl‐4,4′‐biphenol diglycidyl ether (TMBP), and synthesized one liquid crystalline epoxy (LCE), 4′4′‐bis(4‐hydroxybenzylidene)‐diaminophenylene diglycidyl ether (LCE‐DP) to investigate the effect of backbone moiety in epoxies on the thermal conductivity of epoxy/alumina composite. The DGEBA structure shows an amorphous state and the TMBP structure displays a crystal phase, whereas the LCE‐DP structure exhibits a liquid crystalline phase. The curing behaviors of them were examined employing 4,4′‐diaminodiphenylsulfone (DDS) as a curing agent. The heat of curing of epoxy resin was measured with dynamic differential scanning calorimetry (DSC). Alumina (Al₂O₃) of commercial source was applied as an inorganic filler. Thermal conductivity was measured by laser flash method and compared with value predicted by two theoretical models, Lewis‐Nielsen and Agari‐Uno. The results indicated that the thermal conductivity of the LCE‐DP structure was larger than that of the commercial epoxy resins such as TMBP and DGEBA and the experimental data fitted quite well in the values estimated by Agari‐Uno model. POLYM. COMPOS., 2013. © 2013 Society of Plastics Engineers     

Analysis of the crosslinking process of epoxy–phenolic mixtures by thermal scanning rheometry

The curing reaction of different mixtures of an epoxy resin (diglycidyl ether of bisphenol A type) and a phenolic resin (resole type) cured with different amine concentrations (triethylene tetramine) was studied with thermal scanning rheometry under isothermal conditions from 30 to 95°C. The gel time, defined by several criteria, was used to determine the apparent activation energy of the process. Moreover, with an empirical model used to predict the change in the complex viscosity versus time until the gel time was reached, and under the assumption of first‐order kinetics, the apparent rate constant and the apparent activation energy for the curing process were calculated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 818–824, 2005     

反应型DOPO基阻燃剂在环氧树脂中的应用

综述了近年来在反应型DOPO基(9,10-二氢-9-氧-10-磷杂菲-10-氧化物)阻燃剂中引入羟基、羧基、氨基等基团以及与氰酸酯加成得到具有阻燃性的环氧树脂固化剂以及在DOPO衍生物中引入环氧基,制备本质阻燃环氧树脂的研究进展。     

Comparison of the curing kinetic behavior for two epoxy resin systems containing EPIKOTE 828–EPIKURE 3090 and DURATEK KLM 606A–DURATEK KLM 606B

The aim of the study is to determine the optimum cure temperatures and kinetics for two different epoxy resin systems without using solvent. Two resin systems consist of EPIKOTE 828® epoxy resin–EPIKURE® 3090 polyamidoamine curing agent and DURATEK® KLM 606A epoxy resin–DURATEK® KLM 606B polyamide curing agent. The ratio of resin to curing agent was kept as 1:1 for both the systems. Curing temperatures of both the systems were determined and kinetic parameters were calculated with respect to the experimental results following nth‐order kinetics. Then, a series of isothermal temperatures was applied to the resin systems in order to assess the cure process in terms of conversion, time, and temperature by using differential scanning calorimeter (DSC). The test results of both systems show that the rate of degree of cure for EPIKOTE 828® epoxy resin–EPIKURE® 3090 polyamidoamine curing agent system is approximately 10 times higher than that of DURATEK® KLM 606A epoxy resin–DURATEK® KLM 606B polyamide curing agent system at 230°C. POLYM. COMPOS., 28:762–770, 2007. © 2007 Society of Plastics Engineers     

Relationship between anisotropic orientation and curing of liquid crystalline epoxy resin

The effect of macroscopic orientation of liquid crystalline epoxy (LCE) resin, 4,4′‐di(2,3‐epoxypropenyloxy)phenyl benzoate, on the curing and liquid crystalline phase of LCE/diaminodiphenylester (DDE) mixture was investigated. Birefringence and curing rate of uniaxially aligned LCE/DDE on rubbed PI surface was compared with those of unaligned LCE/DDE. Anisotropic orientation accelerated the curing of LCE and facilitated the formation of liquid crystalline phase. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1712–1716, 2006     

Poly(phenylene ether)/epoxy thermoset blends based on anionic polymerization of epoxy monomer

Low molar mass poly (phenylene ether) (LMW‐PPE) with phenol‐reactive chain ends was used as modifier of epoxy thermoset. The epoxy monomer was diglycidylether of bisphenol A (DGEBA), and several imidazoles were used as initiators of anionic polymerization. The curing and phase separation processes were investigated by different techniques: Differential Scanning Calorimetry, Size Exclusion Chromatography, and Light Transmission measurements. The final morphology of blends was observed by Environmental Scanning Electron Microscopy and Transmission Electron Microscopy. The epoxy network is obtained by imidazole initiated DGEBA homopolymerization. Initial LMW‐PPE/DGEBA mixtures show an UCST behavior with cloud point temperatures between 40 and 90°C. PPE phenol end‐groups can react with epoxy, leading to a better interaction between phases. The curing mechanism and phase separation process are not influenced by the chemical structure of initiators, except when reactive amine groups are present. The phase inversion is observed at 30 wt % of PPE. The mixtures with amine‐substituted imidazole present important differences in the initial miscibility and curing process interpreted in terms of fast room temperature amine‐epoxy reaction during blending. Final domain size is affected by this prereaction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2678–2687, 2004     

Cure behavior and kinetic study of diglycidyl ether of bisphenol A with a tertiary amine salt by differential scanning calorimetry

To favor the curing process of epoxy resin by cross ‐ linking and not by vitrification, the use of a tertiary amine salt is proposed. The curing reaction between diglycidyl ether of bisphenol A and tris‐(dimethylaminomethyl) phenol tri(2‐ethyl hexanoate) is studied by differential scanning calorimetry (DSC). Studies are carried out at different concentrations of amine salt: 5, 7.5, and 10 wt%. The vitrification is observed at low concentrations of the amine salt in curing experimental assessments. Furthermore, the experimental characterization of the glass transition temperature at different amine salt concentration allows inferring the polymer network connectivity. Later, the Kissinger method is used to calculate the activation energy. Finally, a reaction mechanism between the epoxy resin and the curing agent is proposed. The reaction mechanism is based on four reactions that may occur. In the most likely reaction happening in the curing, the 2‐ethyl hexanoate behaves as a catalyst through three types of esterification. The characterization and mechanism of the curing reaction of the epoxy resin DER 331 and the amine salt tris‐(dimethylaminomethyl) phenol tri(2‐ethyl hexanoate) have not been reported previously, so it is a novel support of technological relevance for the cure of epoxy community. POLYM. ENG. SCI., 2017. © 2017 Society of Plastics Engineers     

Curing characteristics of epoxy resin systems that include a biphenyl moiety

The curing characteristics of epoxy resin systems that include a biphenyl moiety were investigated according to the change of curing agents. Their curing kinetics mainly depend on the type of hardener. An autocatalytic kinetic reaction occurs in epoxy resin systems with phenol novolac hardener, regardless of the kinds of epoxy resin and the epoxy resin systems using Xylok and DCPDP (dicyclopentadiene‐type phenol resin) curing agents following an nth‐order kinetic mechanism. The kinetic parameters of all epoxy resin systems were reported in terms of a generalized kinetic equation that considered the diffusion term. The fastest reaction conversion rate among the epoxy resin systems with a phenol novolac curing agent was obtained in the EOCN‐C epoxy resin system, and for systems with Xylok and DCPDP hardeners, the highest reaction rate values were obtained in NC‐3000P and EOCN‐C epoxy resin systems, respectively. The system constants in DiBenedetto's equation of each epoxy resin system with different curing agents were obtained, and their curing characteristics can be interpreted by the curing model using a curing agent as a spacer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1942–1952, 2002     

Epoxy‐montmorillonite clay nanocomposites: Synthesis and characterization

Nanocomposites of epoxy resin with montmorillonite clay were synthesized by swelling of different proportions of the clay in a diglycidyl ether of bisphenol‐A followed by in situ polymerization with aromatic diamine as a curing agent. The montmorillonite was modified with octadecylamine and made organophilic. The organoclay was found to be intercalated easily by incorporation of the epoxy precursor and the clay galleries were simultaneously expanded. However, Na‐montmorillonite clay could not be intercalated during the mixing or through the curing process. Curing temperature was found to provide a balance between the reaction rate of the epoxy precursor and the diffusion rate of the curing agent into the clay galleries. The cure kinetics were studied by differential scanning calorimetry. The exfoliation behavior of the organoclay system was investigated by X‐ray diffraction. Thermogravimetric analysis was used to determine the thermal stability, which was correlated with the ionic exchange between the organic species and the silicate layers. The morphology of the nanocomposites was evaluated by scanning electron microscopy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2201–2210, 2004     

Using silica nanoparticles as curing reagents for epoxy resins to form epoxy–silica nanocomposites

Nanoscale colloidal silica showed high reactivity toward curing epoxy resins to form epoxy–silica nanocomposites under mild conditions. Adding a certain amount (5000 ppm) of magnesium chloride lowered the activation energy of the reaction from 71 to 46 kJ/mol. Less and more magnesium chloride both exhibited counter action on lowering the activation energy of the curing reaction. Tin chloride dihydrate and zinc acetylacetonate hydrate were also added into the curing compositions, however, showing no significant effect on promoting the curing reaction. Through this curing reaction, epoxy–silica nanocomposites containing high silica contents up to 70 wt % were obtained. Therefore, this reaction provided a novel and convenient route in preparation of epoxy–silica nanocomposites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1237–1245, 2005     

Synthesis,characterization, and curing of {2,6–bis‐[2‐(bis‐oxiranylmethyl‐amino)‐methylbenzyl]‐phenyl}‐bis‐oxiranylmethylamine (BPBOMA)

The curing behavior of epoxy resin prepared by reacting epichlorohydrin with amine functional aniline acetaldehyde condensate (AFAAC) was investigated using AFAAC as a curing agent. The epoxy resin, {2,6‐bis‐[2‐(bis‐oxiranylmethyl‐amino)‐methylbenzyl]‐phenyl}‐bis‐oxiranylmethylamine (BPBOMA), was characterized by FTIR and ¹H‐NMR spectroscopy, viscosity measurement, and determination of epoxy content. Analysis of the curing reaction was followed by differential scanning calorimetry (DSC) analysis. To investigate the curing kinetic with AFAAC, dynamic DSC scans were made at heating rates of 5, 10, 15, and 20°C/min. The activation energy and frequency factor of the AFAAC formulation were evaluated. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3168–3174, 2006     

Study on reaction kinetics of epoxy resin cured by a modified dicyandiamide

To improve the disadvantage of the low reactivity and reduce the high curing temperature of epoxy resin cured by dicyandiamide (DICY), DICY is chemically modified with phenyl hydrazine and a new curing agent, LB‐A, is developed in this research. The structure, the curing behavior, and reaction kinetics of LB‐A curing epoxy resin are investigated. Results show that the DICY is modified successfully and the well‐defined structure of DICY is destroyed after modification. Consequently, a new curing agent in a noncrystal form is resulted. Thereupon, the reactivity and compatibility between the epoxy resin and the curing agent are improved appreciably using LB‐A instead of DICY. Meanwhile, the curing temperature and activation energy of the curing reaction decrease outstanding, whereas the rate constant increases remarkably. In addition, the compressive strength and the adhesive strength in shear by tension loading of the resulting epoxy resins have been increased using LB‐A instead of DICY as the curing agent. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

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.     

Influence of the epoxy functionalization of multiwall carbon nanotubes on the nonisothermal cure kinetics and thermal properties of epoxy/multiwall carbon nanotube nanocomposites

Multiwall carbon nanotubes were functionalized with epoxy groups by chemical modification in four stages. At each stage, the compound was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy (SEM). Epoxy composite samples were prepared by mixing diglycidyl ether of bisphenol A‐based epoxy resin and synthetic epoxy‐functionalized multiwall carbon nanotube (E‐MWCNT) with different percentages (1, 3, 6, 9, 12, and 15%) in acetone. Ultrasonic dispersion was used to produce homogenous blends. The optimum ratio of the reacting components (9%) was investigated by total enthalpy of the curing reaction from differential scanning calorimetry (DSC) thermograms. The kinetics of the curing reaction for epoxy composites with 4,4′‐diaminodiphenylsolfon as a curing agent was studied by means of a DSC nonisothermal technique. The kinetic parameters such as activation energy, pre‐exponential factor, and rate constant were obtained from DSC data. The structure ofthe nanocomposites and dispersion of the E‐MWCNTs in the nanocomposites were observed using SEM, and the thermal properties were studied by thermogravimetric analysis. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Hybridization of aqueous PU/epoxy resin via a dual self‐curing process

Amino‐terminated and carboxyl‐containing polyurethane (PU) is prepared by an isocyanate‐terminated PU prepolymer process. Carboxyl‐containing epoxy resin is obtained from a half‐esterification of epoxy resin with maleic anhydride. These two aqueous resins are obtained after neutralization with triethylamine and dispersion into water phase, respectively. A latent curing agent (TMPTA‐AZ) is prepared by a Michael addition of aziridine with trimethylolpropane triacrylate (TMPTA). A self‐curing system of PU/epoxy hybrid is obtained from a blending of these two aqueous resins with latent curing agent. PU/epoxy hybrid is derived from two self‐curing reactions on drying. The first curing for hybridization between PU amino groups with oxirane groups of epoxy resin is via a ring‐opening reaction and the secondary curing takes place on carboxyl groups of PU/epoxy hybrid with aziridine of TMPTA‐AZ. The final properties of these dual self‐cured PU/epoxy hybrids are reported. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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