Influence of different concentrations of glycidylisobutyl‐POSS on the glass transition of cured epoxy resin

In this study, polyhedral oligomeric silsesquioxane glycidylisobutyl‐POSS was dispersed in epoxy resin by ultrasound, and the parameters of a phantom model, the Williams–Landel–Ferry (WLF) and Vogel–Fulcher–Tammann (VFT) equations were modeled using dynamic mechanical analysis (DMA) to evaluate their influence on the glass transition state. The relaxation and retardation time distributions were estimated using a nonlinear regularization method, and the estimated physical parameters were discussed based on the results obtained from transmission electron microscopy (TEM). The TEM analysis indicated higher POSS dispersion with a spherical shape. The POSS dispersion was associated with the formation of micelles due to their hybrid character. The micelles favored the interconnections of the nodular microstructure of the epoxy thermosetting, which led to an increase in their T_g values. These interconnections increased the structure's percolation, promoted a reduction in the thermal expansion coefficient and resulted in a more homogeneous glass transition, in terms of a cooperative distribution in the relaxation times at the time scale measured. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41453.     

Degradation kinetic of epoxy nanocomposites containing different percentage of epoxycyclohexyl—POSS

In this study, epoxy nanocomposites containing 0.5, 1, 2, and 5% (m/m) of epoxycyclohexyl—POSS were prepared by mechanical mixture. The samples were characterized by gel content, thermogravimetric analysis (TGA), transmission electron microscopy, and scanning electron microscopy (SEM). TGA analysis was carried out at different heating rates (5, 10, 20, and 40°C min⁻¹) aiming to evaluate the decomposition by Avrami, Flynn‐Wall‐Ozawa and Criado kinetic models. It was constated an increase in the gel fraction and dispersion of the nanocages only for the sample containing 5% POSS. The degradation study showed two distinct stages of weight loss and only for the first stage a shift in the temperature up POSS incorporation was observed. The Avrami kinetic parameters showed that the incorporation of POSS does not affect the degradation rate constant; however, there is an increase in the time required for the degradation reaction occurs. Also, it was observed an increase in the activation energy values for the sample containing 5% (m/m) of POSS. The degradation kinetic mechanisms in presence of POSS was changed from deceleratory mode (F₁) for diffusion (D_n) in the range corresponded to the second stage of weight loss. SEM analysis showed that the morphology of the epoxy resin was modified by the POSS presence, and for 5% (m/m) of POSS was constated a more homogeneous morphology in relation to other samples. © 2012 Society of Plastics Engineers     

Hygrothermal degradation of the composite laminates from woven carbon/SC‐15 epoxy resin and woven glass/SC‐15 epoxy resin

The degradation mechanism for hygrothermal aging of woven carbon‐epoxy and woven glass‐epoxy composite laminates was investigated in the micro‐scale. Interlaminar shear and cross laminar flexural tests were performed on notched and unnotched specimens to know the mechanical performance of the composite laminates. The Interlaminar Shear Stress (ISS) for both the composites was also evaluated and correlated with the number of hygrothermal cycles. Four‐point bending and tensile or compression shear loading configurations were also used. The stress at the onset of delamination (Delamination Damage Tolerance, DDT) was identified from the load‐deflection curve of the flexural specimens and correlated with the number of hygrothermal cycles. It was found that both the ISS and DDT decrease with the exposure time. Dimensional stability was almost unchanged throughout the aging process, although there was a very little moisture absorption (∼1.3%) in glass‐epoxy and carbon‐epoxy composite laminates. SEM photomicrographs of the delaminated surface show that failure occurs suddenly in a macroscopically brittle mode by crack initiation and propagation method. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers.     

ToF‐SIMS investigation of epoxy resin curing reaction at different resin to hardener ratios

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) and principal components analysis (PCA) were used to analyze diglycidyl ether of bisphenol A (DGEBA) and diglycidyl ether of bisphenol F (DGEBF) epoxy resin blend cured with isophorone diamine (IPD) hardener at different resin to hardener ratios. The aim was to establish correlations between the hardener concentration and the nature and progress of the crosslinking reaction. Insights into the cured resin structure revealed using ToF‐SIMS are discussed. Three sets of significant secondary ions have been identified by PCA. Secondary ions such as C₁₄H₇O⁺, CHO⁺, CH₃O⁺, and C₂₁H₂₄O₄⁺ showed variance related to the completion of the curing reaction. Relative intensities of C_xH_yN_z⁺ ions in the cured resin samples are indicative of the un‐reacted and partially reacted hardener molecules, and are found to be proportional to the resin to hardener mixing ratio. The relative ion intensities of the aliphatic hydrocarbon ions are shown to relate to the cured resin crosslinking density. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Novel adamantane‐containing epoxy resin

A novel adamantane‐containing epoxy resin diglycidyl ether of bisphenol‐adamantane (DGEBAda) was successfully synthesized from 1,3‐bis(4‐hydroxyphenyl)adamantane by a one‐step method. The proposed structure of the epoxy resin was confirmed with Fourier transform infrared, ¹H‐NMR, gel permeation chromatography, and epoxy equivalent weight titration. The synthesized adamantane‐containing epoxy resin was cured with 4,4′‐diaminodiphenyl sulfone (DDS) and dicyandiamide (DICY). The thermal properties of the DDS‐cured epoxy were investigated with differential scanning calorimetry and thermogravimetric analysis (TGA). The dielectric properties of the DICY‐cured epoxy were determined from its dielectric spectrum. The obtained results were compared with those of commercially available diglycidyl ether of bisphenol A (DGEBA), a tetramethyl biphenol (TMBP)/epoxy system, and some other associated epoxy resins. According to the measured values, the glass‐transition temperature of the DGEBAda/DDS system (223°C) was higher than that of the DGEBA/DDS system and close to that of the TMBP/DDS system. TGA results showed that the DGEBAda/DDS system had a higher char yield (25.02%) and integral procedure decomposition temperature (850.7°C); however, the 5 wt % degradation temperature was lower than that of DDS‐cured DGEBA and TMBP. Moreover, DGEBAda/DDS had reduced moisture absorption and lower dielectric properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Environmental degradation of an epoxy resin matrix

With the increased use of graphite-reinforced composites as replacements for metals has come concerns about durability under harsh environmental conditions. Degradation is expected to begin on the surface and progress toward the center of the resin as a function of time, and reflectance infrared techniques are ideal for monitoring structural changes on surfaces. The present paper describes the application of Fourier transform infrared spectroscopy using internal reflectance elements to the determination of the degree of environmental aging of Hercules 3501?6 resin. The results indicate that degradation occurs via hydrolysis, oxidation, and dehydration reactions at specific locations in the polymer chain. Of special interest is the unique reaction of the tertiary amine of the epoxy portion of the molecule.     

Thermal degradation of biomedical polyurethanes—A kinetic study using high‐resolution thermogravimetry

The kinetics of thermal degradation of polyurethanes (PUR) has been studied by means of high‐resolution and constant heating rate thermogravimetry (TG), under nitrogen and synthetic air atmospheres. The high‐resolution TG provided a way to increase resolution with decreasing the time of data acquisition. In this mode, the heating rate is dynamically varied to maximize resolution. A method to calculate the kinetic parameters from this technique was used. The TG curves showed two or three decomposition steps, depending on the atmosphere employed. The parameters calculated for the PUR decomposition were the activation energy, reaction order, and preexponential factor. A method to estimate the polymer lifetime was also used. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 910–919, 2001     

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.     

Curing of epoxy resin using imide‐amines

The curing behavior of diglycidyl ether of bisphenol‐A (DGEBA) was investigated by differential scanning calorimetry, using varying molar ratios of imide‐amines and 4,4′‐diaminodiphenyl sulfone (DDS). The imide‐amines were prepared by reacting 1 mol of pyromellitic dianhydride (P) with excess (2.5 mol) of 4,4′‐diaminodiphenyl ether (E), 4,4′‐diaminodiphenyl methane (M), or 4,4′‐diaminodiphenyl sulfone (S) and designated as PE, PM, PS. Structural characterization was done using FTIR, ¹H NMR, ¹³C NMR spectroscopic techniques and elemental analysis. The mixture of imide‐amines and DDS at ratio of 0 : 1, 0.25 : 0.75, 0.5 : 0.5, 0.75 : 0.25, and 1 : 0 were used to investigate the curing behavior of DGEBA. The multiple heating rate method (5, 10, 15, and 20°C/min) was used to study the curing kinetics of epoxy resins. The peak exotherm temperature was found to be dependent on the heating rate, structure of imide‐amine, and also on the ratio of imide‐amine : DDS used. Activation energy was highest in case of epoxy cured using a mixture of DDS : imide‐amine of a ratio of 0.75 : 0.25. Thermal stability of the isothermally cured resins was also evaluated in a nitrogen atmosphere using dynamic thermogravimetry. The char yield was highest in case of resins cured using mixture of DDS : PS (0.25 : 0.75; EPS‐3), DDS : PM (0.25 : 0.75; EPM‐3), and DDS : PE (0.75 : 0.25; EPE‐1). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3502–3510, 2006     

Influence of partial cross‐linking degree on basic physical properties of RTM6 epoxy resin

Thermo‐physical and mechanical properties of partially and completely cross‐linked RTM6 epoxy resin samples in the glassy state have been investigated. A significant dependence of glass transition temperature, density, and modulus on the curing history and the curing degree is found. Density and modulus decrease with increasing curing degree and show a step‐like irregularity in the so called transition region, which is related to the transition from rubber to glassy state during cross‐linking and the starting of structural relaxation processes. The relationship between the thermo‐physical and mechanical properties, which is important for the development of new processing routes for fiber reinforced polymers, is addressed. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4338–4346, 2013     

Advanced isoconversional cure kinetic analysis of epoxy/poly(furfuryl alcohol) bio‐resin system

Furfuryl alcohol as a biomass‐derived monomer was used for synthesizing poly(furfuryl alcohol). A diglycidyl ether of bisphenol A (DGEBA) epoxy resin along with 3% and 15% by weight of the poly(furfuryl alcohol) was cured using an aliphatic amine hardener. The cure kinetics of the DGEBA/poly(furfuryl alcohol)/amine systems were investigated by nonisothermal differential scanning calorimetry. The kinetic triplets [E_α, A_α, and f(α)] were computed by using an integral isoconversional method. Based on the E_α‐dependency results a single‐step autocatalytic model was suggested for the reactions mechanism, however, the A_α‐dependency and f(α) analysis did not confirm the suggested model. Detailed kinetics analysis revealed that the cure reaction mechanism of the DGEBA did not change due to the presence of the poly(furfuryl alcohol) in the degree of conversion range < 0.75, nevertheless, it dramatically changed in the degree of conversion range > 0.75 due to the presence of 15 wt % poly(furfuryl alcohol). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45432.     

New thermosetting resin from terpenediphenol‐based benzoxazine and epoxy resin

Terpenediphenol‐based benzoxazine was prepared from terpenediphenol, formaline, and aniline. Curing behavior of the benzoxazine with epoxy resin and the properties of the cured resin were investigated. Consequently, the curing reaction did not proceed at low temperatures, but it proceeded rapidly at higher temperatures without a curing accelerator. The properties of the cured resin both from neat resins and from reinforced resins with fused silica were evaluated, respectively. The cured resins showed good heat resistance, mechanical properties, electrical insulation, and especially water resistance, compared with the cured resin from bisphenol A type novolac and epoxy resin. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2266–2273, 1999     

TGA-FTIR研究环氧/酸酐固化物热降解行为

采用TGA-FTIR联用技术在高纯氮气保护下实时研究了环氧树脂酸酐固化物热降解过程和气相产物。TG和DTG曲线表明,环氧树脂酸酐固化物存在着2个热失重阶段,最大热失重速率峰值温度分别在163℃和389℃,其失重温度范围分别在100~210℃和260~570℃。FTIR谱图表明第一失重阶段主要是体系中所含的水分挥发和/或伯醇脱水及一些小分子物质挥发过程。CO和酮类物质分别产生于280℃和305℃,并一直持续到本实验结束;酸酐类物质在455℃以下时吸收峰的强度很微弱,此后逐步增强。此外,环氧树脂酸酐固化物热降解气相挥发物还有各种碳氢混合物。     

Effect of copper oxides on the thermal oxidative degradation of the epoxy resin

The effect of copper oxides on the thermal oxidative degradation of a brominated epoxy resin–dicyandiamide system was studied using Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). The addition of small amounts of Cu₂O or CuO fillers to the epoxy resins affected the relative amounts of highly reacted cyclic species formed during thermal aging and induced catalytic degradation of the epoxy resins. The overall and initial activation energies of the degradation process were found to decrease, and the order in the degradation kinetics of the epoxy resin changed from a near zero order to negative domain (autocatalytic nature) in the presence of copper oxides. © 1994 John Wiley & Sons, Inc.     

Influence of aliphatic amine epoxy hardener on the adhesive properties of blends of mono‐carboxyl‐terminated poly(2‐ethylhexyl acrylate‐co‐methyl methacrylate) with epoxy resin

The adhesive properties have been investigated in blends of mono‐carboxyl‐terminated poly(2‐ethylhexyl acrylate‐co‐methyl methacrylate) with diglycidyl ether of bisphenol A and three different aliphatic amine epoxy hardener. The adhesives properties are evaluated in steel alloy substrate using single‐lap shear test. The copolymers are initially miscible in the stoichiometric blends of epoxy resin and hardener at room temperature. Phase separation is noted in the course of the polymerization reaction. Different morphologies are obtained according to the amine epoxy hardener. The most effective adhesive for steel–steel joints in single‐lap shear test is the blends using 1‐(2‐aminoethyl)piperazine (AEP) as hardener. This system shows the biggest lap shear strength. However, the modified adhesives show a reduction in the mechanical resistance. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Mechanistic kinetic model of an epoxy resin cured with a mixture of amines of different functionalities

The polymerization kinetics of a monoamine (p-toluidine), a diamine (4,4′-diaminodiphenylmethane) or a mixture of both amines reacted with an epoxy prepolymer, diglycidylether of bisphenol A (DGEBA), was analyzed using differential scanning calorimetry. A simple mechanistic model, consisting of an epoxy-hydroxyl complex formation out of equilibrium, including the possibility that amino hydrogens react with free epoxy groups or with the epoxy-hydroxyl complex, and taking into account the possible difference of the reactivity of amino hydrogens, provided a reasonable fitting of the whole set of experimental results with a lonely set of activation energies.     

A comparative study on the properties of the different amino‐functionalized multiwall carbon nanotubes reinforced epoxy resin composites

Multiwall carbon nanotubes (MWCNTs) were amino‐functionalized by 1,2‐ethylenediamine (EDA)' triethylenetetramine (TETA), and dodecylamine (DDA), and investigated by fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and thermogravimetric analysis (TGA). The dispersion of the DDA functionalized MWCNT in DMF is better than that of the MWCNT functionalized by the EDA and the TETA. Carbon nanotubes reinforced epoxy resin composites were prepared, and the effect of the amino‐functionalization on the properties of the composites was investigated by differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA), and TGA. The composites reinforced by the MWCNTs demonstrate improvement in various mechanical properties. The increase of T_g of the composites with the addition of amino‐functionalized MWCNT compared to the T_g of the composites with the addition of unfunctionalized MWCNT was due to the chemical combination and the physical entanglements between amino group from modified MWNTs and epoxy group from the epoxy resin. The interfacial bonding between the epoxy and the amino group of the EDA and the TETA‐modified MWCNT is more important than the well dispersion of DDA‐modified MWCNT in the composites for the improvement of the mechanical properties. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Toughening of a dicyandiamide-cured epoxy resin: Influence of cure conditions on different rubber modifications

Cure kinetics of modified epoxy resins cured with dicyandiamide are studied. The influence of different heating rates in the curing process, such as curing behavior, morphology, and thermo-mechanical properties, is studied. Additionally, three different post-cure cycles at 180°C are employed. Two butadiene-based toughening agents are used, a carboxyl-terminated polybutadiene-co-acrylonitril (CTBN) prepolymer and a functionalized block copolymer of polytetrahydrofuran and hydroxyl-terminated polybutadiene. The amphiphilic block copolymer enables investigations with a bimodal particle size morphology. All results are contrasted with those of the neat resin and butadiene-free block polymer. Faster curing processes result in smaller average particle sizes and better fracture toughness of the modified epoxy resins. Further improvements are achieved with additional post-cure cycles at 180°C. An increased interfacial adhesion between the particles and the epoxy matrix is considered to be the main mechanism. Optimized lengths of the post-cure process can be determined with the butadiene-based toughening agents indicating a competing thermal degradation. Longer post-cures than 40 min lead to lower fracture toughness in the butadiene-based modified materials. In general, similar influences of the curing and post-curing process on the bimodal and unimodal distributed system can be observed differing in more intense dependencies of the bimodal system.     

Thermal degradation of epoxy resin reinforced with polypropylene fibers

The influence of polypropylene fibers on the thermal degradation of epoxy composites was investigated with thermogravimetric analysis. Three composites with 5, 10, or 15 wt % polypropylene fibers were prepared with epoxy as a matrix material. The polypropylene fibers, used as reinforcing materials, retarded the thermal decomposition, and increasing the weight percentage of the fiber material increased the thermal stability to a certain extent. Of the three composites, the 10 wt % polypropylene fiber/epoxy resin composite showed very good thermal stability, which was indicated by the increase in the resin decomposition temperature from 280°C for the 5 wt % polypropylene fiber/epoxy resin composite to 375°C for the 10 wt % polypropylene fiber/epoxy resin composite. The Horowitz–Metzger method was used to calculate the activation energies, and the results were tabulated. A morphological analysis was carried out with scanning electron microscopy to evaluate the dispersion of the fibers in the epoxy matrix. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 500–503, 2007     

Thermal degradation of epoxy novolac-phenol formaldehyde novolac resin systems

The evolution of organic vapors from encapsulants at elevated temperatures has been implicated as the source of the degradation of the gold–aluminum intermetallic of the wire that connects the bond pad to the leadframe in an integrated circuit. Gas chromatography/infrared spectroscopy/mass spectrometry were used to study the decomposition of three commercial epoxy-novolac thermosetting compounds. Outgassing products have been identified and their origins discussed. Insight into the types of initiators used in encapsulants and their possible influence upon ball bond failure rates has been gained.