Phase‐separation process in a poly(methyl methacrylate)‐modified epoxy system: A novel approach to understanding the effect of the curing temperature on the final morphology

In this study, the physical and chemical changes of a poly(methyl methacrylate) (PMMA)‐modified epoxy system were examined to understand the effect of the curing conditions on its final morphology. The curing process of the PMMA–epoxy reactive system was complementarily analyzed by Fourier transform infrared spectroscopy in the near range (FT‐NIR) and fluorescence spectroscopy. The relationships among (1) the chemical conversion of the curing reaction, (2) the first moment of the fluorescence emission band (〈ν〉) arising from a chromophore chemically bonded to the epoxy reactive system, (3) the phase‐separation process, and (4) the dynamics of the epoxy thermoset during its curing process are discussed. From a chemical point of view, FT‐NIR did not reveal any significant change in the curing reaction with the presence of 2 wt % PMMA. However, in terms of physical changes, the analysis of the fluorescence response clearly showed variations in the curing reaction due to the presence of the thermoplastic polymer. Also, fluorescence allowed the estimation of the glass‐transition temperature of the system with curing when the reaction was diffusion‐controlled, whereas Fourier transform infrared spectroscopy was not sensible enough. In the second part of this study, scanning electron microscopy images of the PMMA‐modified epoxy system were analyzed to understand the effect of the temperature on the final morphology when the amount of thermoplastic was below the critical volume fraction. A linear dependence between the inverse of the mean area of the thermoplastic‐rich domains and the inverse of the absolute temperature was obtained. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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     

Cure and reaction kinetics of an anhydride‐cured epoxy resin catalyzed by N‐benzylpyrazinium salts using near‐infrared spectroscopy

The cure behavior and the reaction kinetics of an anhydride‐cured epoxy resin catalyzed by cationic thermal latent initiator, N‐benzylpyrazinium salts, have been investigated by a near‐infrared (NIR) spectroscopy. The spectral changes are interpreted in terms of the mechanism of cure. NIR absorption bands are due to protons connected to carbon, nitrogen, and oxygen. In this work, the homogeneous model system involves a simple addition reaction mechanism leading to an exothermic reaction between epoxide and anhydride activated groups. A comprehensive account of the origin, location, and shifts during reaction of all major NIR absorption peaks in the spectral range from 4000 to 7100 cm^?1 is provided. The extent of reaction is calculated from NIR absorption band at 4530 cm^?1, which depends on epoxide concentration. The utility of NIR spectroscopy to study the kinetics of epoxy cure reaction has been established. Consequently, absorbencies in the NIR spectra suitable for quantitative studies of epoxy resin reaction kinetics have been identified.     

Ultraviolet curing kinetics of cycloaliphatic epoxide with real‐time fourier transform infrared spectroscopy

The photo‐induced curing kinetics of cycloaliphatic epoxide coatings were investigated with real‐time Fourier transform infrared spectroscopy with an optical fiber ultraviolet curing system. The consumption of epoxy group as a function of time was obtained by monitoring of the oxirane absorbance in the 789–746‐cm^?1 region. The effect of the type of epoxide, hydroxyl equivalent weight, ratio of oxirane to hydroxyl groups (R), photoinitiator, and exposure time on the curing reaction was investigated. In general, the rate of curing was dependent on the hydroxyl equivalent weight, R, type of epoxide, and photoinitiator. For formulations without polyol, both initiator concentration and exposure time had minimal effects on the curing reaction. However, for formulations with polyol, the curing a reaction was dependent on the initiator concentration. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2485–2499, 2003     

Analysis of a crease‐resisting finish on linen fabrics using Fourier transform infrared spectroscopy and visible and near‐infrared spectroscopy

A wide range of chemical reagents are capable of producing a satisfactory crease‐resisting finish for cellulosic fabrics and are currently available on the market. However, these agents do not work as efficiently on linen relative to cotton or rayon. Untreated linen controls and samples treated with a N‐methylol reagent were investigated for physical and chemical changes, and an attempt was made to quantify the crosslinking bonds formed and assess other changes in the treated fabrics using Fourier transform infrared spectroscopy (FTIR) and visible and near‐infrared spectroscopy (NIR). The results were compared with nitrogen analysis data, crease‐recovery angle measurements, and abrasion‐resistance tests in an attempt to assess the effectiveness of the treatment relative to the responses of the instrumental techniques. This study shows correlations between the visible and NIR and FTIR spectra and the crease‐recovery angle and abrasion resistance. The study also indicates that FTIR may be useful in assessing the crosslinking bonding changes associated with the dimethylol urea treatment of linen to achieve improved crease recovery. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 1886–1896, 2001     

Thermal curing of glass‐epoxy prepregs by luminescence spectroscopy

In this study, we investigated the application of the luminescence spectroscopy technique in steady‐state conditions to study glass fiber‐epoxy F161 prepregs. We conducted this study by comparing the results obtained from the intrinsic fluorescence with Fourier transform near infrared spectroscopy. The extrinsic fluorescence of 9‐anthroic acid (9‐AA) was also used. Fourier transform infrared spectroscopy was also used to characterize the epoxide resin. The prepregs containing 9‐AA and those that did not were heat‐treated at 177°C (F161) for 1100 min at a 2°C/min heating rate. The results obtained by both methods indicated that the crosslinking reaction could be monitored by analysis of the spectral changes of the emission bands of the prepreg and 9‐AA. The intrinsic emission at 320 nm was attributed to the fluorophore group containing the epoxy ring and was used to calculate the conversion degree. The photophysical behavior of the 9‐AA probe indicated a reduction of free volume of the polymeric matrix with curing process. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Thermogravimetric and Fourier‐transform infrared analyses on the cure behavior of polycardanol containing epoxy groups cured by electron beam

In this study, the curing behavior of polycardanol containing epoxy groups (diepoxidized polycardanol) was exploited in terms of thermal stability and the cure reaction conversion by means of thermogravimetric analysis and Fourier‐transform infrared spectroscopy, respectively. The effect of photo‐initiator type and concentration and electron beam absorption dose in the presence of cationic photo‐initiators (triarylsulfonium hexafluorophosphate (P‐type) and triarylsulfonium hexafluoroantimanate (Sb‐type) on the cure behavior of diepoxidized cardanol (DEC) resin was investigated. The thermal stability of DEC with Sb‐type photo‐initiator was higher than that with P‐type one, being increased with increasing the concentration and electron beam absorption dose. The conversion of cure reaction was gradually increased with increasing the dose, showing the maximum at 800 kGy. The results revealed that Sb‐type photo‐initiator, the concentration of 2 or 3 wt %, and electron beam absorption dose of about 800 kGy may be preferable for initiating epoxy ring opening in the DEC molecules as well as for efficiently curing the DEC resin by electron beam irradiation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41599.     

Miscibility and mechanical properties of an amine‐cured epoxy resin blended with poly(ethylene oxide)

Blends composed of diaminodiphenylmethane bisphenol‐A epoxy resin and poly(ethylene oxide) (PEO) were prepared via in situ curing reaction of epoxy in the presence of PEO. The miscibility of the blends before and after curing was established by thermal (differential scanning calorimetry, DSC), microstructural (atomic force microscopy) and dynamic mechanical analysis. Fourier transform infrared spectroscopy indicated that the OH groups developed through cure reactions interact by hydrogen bonding with PEO. After crystallinity analysis by DSC, the interaction parameter was determined through the depression of the equilibrium melting temperature. Mechanical properties of the miscible blends do not show any significant change, although improvement of fracture toughness has been observed with respect to the matrix properties. Copyright © 2006 Society of Chemical Industry     

Preparation and properties of halogen‐free flame‐retarded phthalonitrile–epoxy blends

Halogen‐free flame‐retarded blends composed of 2,2‐bis[4‐(3,4‐dicyanophenoxy) phenyl] propane (BAPh) and epoxy resin E‐44 (EP) were successfully prepared with 4,4′‐diaminodiphenyl sulfone as a curing additive. The structure of the copolymers was characterized by Fourier transform infrared spectroscopy, which showed that epoxy groups, a phthalocyanine ring, and a triazine ring existed. The limiting oxygen index values were over 30, and the UL‐94 rating reached V‐0 for the 20 : 80 (w/w) BAPh/EP copolymers. Differential scanning calorimetry and dynamic rheological analysis were employed to study the curing reaction behaviors of the phthalonitrile/epoxy blends. Also, the gelation time was shortened to 3 min when the prepolymerization temperature was 190°C. Thermogravimetric analysis showed that the thermal decomposition of the phthalonitrile/epoxy copolymers significantly improved with increasing BAPh content. The flexible strength of the 20:80 copolymers reached 149.5 MPa, which enhanced by 40 MPa compared to pure EP. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Radiation degradation of epoxidized natural rubber studied by solid‐state nuclear magnetic resonance and infrared spectroscopy

The mechanism of radiation‐induced structural changes in epoxidized natural rubber was investigated using nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. Samples were irradiated both under vacuum and in air. Because the rubbers crosslinked during irradiation, solid‐state NMR had to be used. The cross polarized/magic angle spinning NMR spectra were used to calculate the radiation yields. Ring opening of the epoxy groups was found to occur during irradiation. Most of the crosslinking was due to epoxy group ring opening, and very little or no C C crosslinking was observed. © 2000 Society of Chemical Industry     

Study of glycidyl ether as a new kind of modifier for urea‐formaldehyde wood adhesives

In this work, the multiepoxy functional glycidyl ether (GE) modified urea‐formaldehyde (UF) resins were synthesized via a traditional alkaline‐acid process under low formaldehyde/urea (F/U) molar ratio. The synthesized resins were characterized by ¹³C magnetic resonance spectroscopy (¹³C‐NMR), indicating that GE can effectively react with UF resins via the ring‐opening reaction of epoxy groups. Moreover, the residual epoxy groups of GE could also participate in the curing reaction of UF resins, which was verified by Fourier transform infrared spectroscopy. The storage stability of GE‐modified UF resins and the thermal degradation behavior of the synthesized resins were evaluated by using optical microrheology and thermogravimetric analysis, respectively. Meanwhile, the synthesized resins were further employed to prepare the plywood with the veneers glued. For the modification on bonding strength and formaldehyde emission of the plywood, the influences of addition method, type, and amount of GE were systematically investigated. The performance of UF adhesives were remarkably improved by the modification of GE around 20–30% (weight percentage of total urea) in the acidic condensation stage during the resin synthesis. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Curing kinetics of a “green” thiol‐containing resin: Oligo(ethylene‐2‐mercaptosuccinate)

This work focuses on examining the curing process of neat oligo(ethylene‐2‐mercaptosuccinate) using differential scanning calorimetry (DSC), rheology, and Fourier transform infrared (FTIR) spectroscopy. The thiol‐containing resin offers much promise as a bioabsorbable polymer in medical field and as a reusable thermoset in sustainable applications. Although curing between thiol groups has been investigated in solutions, studies of neat materials without solvent are rare. Here, the evolution of glass transition temperature (T_g), complex shear modulus (G*), gelation, and chemical structure are monitored as a function of isothermal curing time and temperature. Both T_g and G* increase with curing, indicating the formation of polymer networks. The conversion of the cure is determined from the DiBenedetto equation and is found to follow a second‐order plus second‐order autocatalytic reaction model. Importantly, the intensity of the S–H bond absorption decreases with the extent of curing, which confirms the curing mechanism, i.e., disulfide formation between the thiol groups. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43205.     

Synthesis of a self‐emulsifiable waterborne epoxy curing agent based on glycidyl tertiary carboxylic ester and its cure characteristics

A novel self‐emulsifiable waterborne amine‐terminated curing agent for epoxy resin based on glycidyl tertiary carboxylic ester (GTCE) was synthesized through three steps of addition reaction, capping reaction, and salification reaction of triethylene tetramine (TETA) and liquid epoxy resin (E‐44). The curing agent with good emulsifying and curing properties was gradually obtained under condition of the molar ratio of TETA: E‐44 as 2.2: 1 at 65 °C for 4 h, 100% primary amine capped with GTCE at 70 °C for 3 h, and 20% salifiable rate with glacial acetic acid. The curing agent was characterized by Fourier transform‐infrared spectroscopy (FT‐IR). The curing behavior of the E‐44/GTCE‐TETA‐E‐44 system was studied with differential scanning calorimetry (DSC) and FT‐IR. Results showed that the optimal mass ratio for E‐44/GTCE‐TETA‐E‐44 system was 3 to 1, and the curing agent showed a relatively lower curing temperature. The cured film prepared by the self‐emulsifiable curing agent and epoxy resin under the optimal mass ratio displayed good thermal property, hardness, toughness, adhesion, and corrosion resistance. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44246.     

Physical study of room‐temperature‐cured epoxy/thermally reduced graphene oxides with various contents of oxygen‐containing groups

In this study, the effects of different oxygen‐containing group contents in thermally reduced graphene oxides (TRGs) for enhancing the physical properties of epoxy nancomposites was examined. The epoxy/TRG nanocomposites (ETNs) were prepared by a room temperature curing method in the presence of TRGs containing different oxygen‐containing groups and were then characterized by Fourier transform infrared spectroscopy. TRG contents with higher oxygen‐containing group contents (ca 33%) were found to show better dispersion capability in the epoxy matrix than TRGs with lower oxygen‐containing group contents (ca 11%) based on morphological observations by transmission electron microscopy. The better dispersion capability of TRGs with higher oxygen‐containing group contents in ETN membranes was found to lead to significantly enhanced mechanical strength, thermal stability and thermal conductivity based on measurements of dynamic mechanical analysis, tensile tests, thermogravimetric analysis and by the transient plane source technique. © 2014 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry     

Synthesis,thermal properties,and flame retardance of phosphorus‐containing epoxy‐silica hybrid resins

A novel epoxy resin modifier, phosphorus‐containing epoxide siloxane (DPS) with cyclic phosphorus groups in the Si O network, was prepared from the reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) with polyhedral‐oligomeric siloxanes, which was synthesized by the sol–gel reaction of 3‐glycidoxypropyltrimethoxysilane. DPS was confirmed by Fourier transform infrared and ²⁹Si NMR measurement, and then was employed to modify epoxy resin at various ratios, with 4,4‐diaminodiphenyl‐methane as a curing agent. In order to make a comparison, DOPO‐containing epoxy resins were also cured under the same conditions. The resulting organic–inorganic hybrid epoxy resins modified with DPS exhibited a high glass transition temperature (T_g), a good thermal stability, and a high limited oxygen index. In addition, the tensile strength of cured products was also rather desirable. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Synthesis and curing properties of a novel curing agent based on N‐(4‐hydroxyphenyl) maleimide and dicyclopentadiene moieties

A new type of epoxy resin curing agent, containing pendant phenol functions, was synthesized by the free‐radical copolymerization of N‐(4‐hydroxyphenyl) maleimide with dicyclopentadiene (DCPD) monomer in the presence of a radical initiator. The chemical structure was characterized with Fourier transform infrared spectroscopy and nuclear magnetic resonance. The molecular weight of the new curing agent was determined by gel permeation chromatography. The activity and activation energy of this new curing agent with o‐cresol formaldehyde novolac epoxy (CNE) was investigated with a nonisothermal differential scanning calorimetry technique at different heating rates. The thermal properties of the cured polymers were evaluated with thermogravimetric analysis, and the results exhibit good thermal stability. In addition, this new curing agent with CNE showed low moisture absorption because of the hydrophobic nature of the DCPD structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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     

Influences of different gravity environments on the curing process and cured products of carbon‐nanotube‐reinforced epoxy composites

The influences of different gravity environments on the curing process and the cured products of carbon‐nanotube‐reinforced epoxy composites were investigated in this study. Different gravity environments were simulated with a superconducting magnet on the basis of which resin matrix composites with different amino‐functionalized multiwalled carbon nanotube (NH₂‐MWCNT) concentrations of 0.1, 0.3, 0.5, and 1 wt % were tested. Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, thermomechanical analysis (TMA), thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, and three‐point bending tests were used to analyze the characteristics of different curing processes and cured products. From the results, we observed that the curing rate of the epoxy composites was influenced by different gravity values, and there was anisotropy in the NH₂‐MWCNT‐reinforced epoxy composites cured in the simulated microgravity environment. More effects of gravity on the curing process and cured products could be obtained through detailed experiments and discussion; this is important and fundamental for improving and enhancing the properties of composite materials used in different gravity environments. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41413.     

异氰酸酯/环氧树脂的固化机理

详细研究了异氰酸酯/环氧树脂体系的固化反应和固化机理。采用差示扫描量热法（DSC）和红外光谱法（FTIR）跟踪了异氰酸酯/环氧树脂固化反应过程,定量分析了异氰酸酯、环氧基团和新生成的异氰脲酸酯和口恶唑烷酮的变化。DSC分析结果表明,DSC曲线上出现3个放热峰,说明固化过程中存在至少3种反应;FTIR分析结果表明,在140℃以下固化体系主要发生异氰酸酯的三聚反应生成三嗪环（异氰脲酸酯）;在200℃下,异氰酸酯-NCO基团与环氧基团开环反应生成口恶唑烷酮;在230℃ 下,三嗪环（异氰脲酸酯）进一步与环氧基团开环反应生成口恶唑烷酮。研究了不同温度下环氧基团、异氰酸酯基团、异氰脲酸酯基团、口恶唑烷酮基团随反应时间的变化规律。     

Incorporation of epoxidized soybean oil as co‐matrix in epoxy resin toward developing plastisol/particulate toughened glass fiber composites

Epoxidized soybean oil was incorporated as a co‐matrix into an epoxy resin, and the hybrid resin system was used for preparing glass fiber‐reinforced composites. Effect of addition of poly(vinyl chloride) plastisol and selected particulate fillers (fly ash and wood flour) to epoxy/epoxidized soybean oil matrix on mechanical and water uptake properties of glass fiber‐reinforced composites were studied. Fourier transform infrared spectroscopy was used to reveal the curing state of these composites. It was observed that tensile strengths and moduli decreased with the inclusion of all additives. However, addition of poly(vinyl chloride) plastisol, fly ash, and wood flour particulate fillers showed significant increase in impact strengths compared with neat epoxy composite in a synergistic manner. Water uptake results of the composites were found to be in good agreement with ? OH peak intensities obtained from Fourier transform infrared spectroscopy. Finally, acousto‐ultrasonic nondestructive technique was successfully used to assess damage states and to relate stress wave factors with tensile strength properties of modified epoxy‐based glass fiber composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40586.