Thermal characterization of carbon‐nanofiber‐reinforced tetraglycidyl‐4,4′‐diaminodiphenylmethane/4,4′‐diaminodiphenylsulfone epoxy composites

The thermal properties of carbon nanofibers (CNF)/epoxy composites, composed of tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM) resin and 4,4′‐diaminodiphenylsulfone (DDS) as a curing agent, were investigated with differential scanning calorimetry (DSC), thermogravimetric analysis, and dynamic mechanical thermal analysis. DSC results showed that the presence of CNF had no pronounced influence on the heat of the cure reaction. However, the incorporation of CNF slightly improved the thermal stability of the epoxy. Furthermore, the storage modulus of the TGDDM/DDS epoxy was significantly enhanced, whereas the glass‐transition temperature was not significantly affected, upon the incorporation of CNFs. The storage modulus of 5 wt % CNF/epoxy composites at 25°C was increased by 35% in comparison with that of the pure epoxy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 295–298, 2006     

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.     

Reaction kinetics and thermal properties of epoxidised cresol novolac/4,4′‐diglycidyl (3,3′,5,5′‐tetramethylbiphenyl) epoxy resin composite cured with aromatic diamine

A series of novel composites based on different ratios of epoxidised cresol novolac (ECN) and 4,4′‐diglycidyl(3,3′,5,5′‐tetramethylbiphenyl) epoxy resin (TMBP) have been prepared with the curing agent 4,4′‐methylenediamine (DDM) and 4,4′‐diaminodiphenylsulfone (DDS), respectively. The investigation of cure kinetics was performed by differential scanning calorimetry using an isoconversional method. The high thermal stabilities of the cured samples were also studied by thermogravimetric analysis. In addition, no phase separation was observed for cured ECN/DDM and ECN/DDS blending with different amounts of TMBP by dynamic mechanical analysis and scanning electron microscopy. Moreover, the cured systems also exhibited excellent impact properties and low moisture absorption. All the results indicate that the ECN/TMBP/DDM and ECN/TMBP/DDS systems are promising materials in electronic packaging. Copyright © 2011 Society of Chemical Industry     

Effects of modifiers in organoclays on the curing reaction of liquid‐crystalline epoxy resin

The effects of three organoclays (Cloisite 10A, 93A, and 30B) with different modifiers on the curing reaction of a liquid‐crystalline epoxy (LCE) resin based on 4,4′‐diglycidyloxybiphenyl and the curing agent sulfanilamide were studied. The curing kinetics of the LCE and clay composites were analyzed with differential scanning calorimetry. The Flyann–Wall–Ozawa and Kissinger–Akahira–Sunose methods were used to calculate the activation energies at different conversions. All three alkylammonium ions lowered the reaction activation energy and catalyzed the epoxy ring‐opening reaction with the diamine curing agent. 30B, with two hydroxy groups of quaternary ammonium, showed the highest catalysis because the hydroxy groups facilitated the curing process. 10A and 93A had similar catalytic abilities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1329–1334, 2005     

Cure kinetics and modeling of an epoxy resin cross‐linked in the presence of two different diamine hardeners

An epoxy resin diglycidyl ether of bisphenol A (DGEBA) is cross‐linked with the help of two aromatic diamine 4,4′‐diaminodiphenylsulfone (DDS) + 4,4′‐methylenebis 3‐chloro 2,6‐diethylaniline (MCDEA) of nearly equal flexibility but different reactivities. The ratio of the two amines is varied while keeping the stoichiometry of the epoxy/amino hydrogen groups constant. The experimental cure kinetics are studied at four different isothermal temperatures. Their modeling is carried out by a phenomenological Kamal‐Sourour kinetic model. The procedure is two‐fold: 1) linear combinations of the values of rate constants from the two neat thermosets (based on only one amine) and 2) values calculated directly from isothermal cures of reactive amine mixtures. A good correlation was observed between the experimental data and the model predictions (both procedures). These amine formulations provide “mixed” epoxy thermosets and will be used later to control thermoset/thermoplastic blend morphologies for which reaction kinetics need to be predicted. POLYM. ENG. SCI. 45:1581–1589, 2005. © 2005 Society of Plastics Engineers     

Composites of carbon nanofibers and thermoplastic polyurethanes with shape‐memory properties prepared by chaotic mixing

Composites of carbon nanofibers (CNFs), oxidized carbon nanofibers (ox‐CNFs), and shape‐memory thermoplastic polyurethane (TPU) were prepared in a chaotic mixer and their shape‐memory properties evaluated. The polymer was synthesized from 4,4′‐diphenylmethane diisocyanate, 1,4‐butanediol chain extender, and semicrystalline poly(ε‐caprolactone) diol soft segments. The shape‐memory action was triggered by both conductive and resistive heating. It was found that soft segment crystallinity and mechanical reinforcement by nanofibers produced competing effects on shape‐memory properties. A large reduction in soft segment crystallinity in the presence of CNF and stronger mechanical reinforcement by well‐dispersed ox‐CNF determined the shape‐memory properties of the respective composites. It was found that the maximum shape recovery force, respectively, 3 and 4 MPa, was obtained in the cases of 5 and 1 wt% CNF and ox‐CNF, respectively, compared with ～1.8 MPa for unfilled TPU. The degree of soft segment and hard segment phase separation and thermal stability of the composites were analyzed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers.     

Cure kinetics of epoxy resin and aromatic diamines

The kinetics of curing reaction of a diglycidyl ether of a bisphenol‐A based epoxy (DGEBA) with 4,4′‐diaminostillbene (DAS) and 4,4′‐diaminoazobenzene (DAAB) as curing agents are studied by differential scanning calorimetery (DSC) using the isothermal technique. The experimental data show that the cure reaction is autocatalytic in nature, and all kinetic parameters of the curing reaction are determined using a semiempirical equation. The reaction of DGEBA with DAS is faster than that with DAAB under the same conditions and the activation energies of both systems are higher than those reported for other aromatic diamines. With increasing isothermal temperature and concentration of curing agents the rate constants are increased by the increasing of probability collisions between epoxide and primary amine groups while the activation energies remain constant. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1049–1056, 2004     

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     

Kinetics and thermal characterization of epoxy‐amine systems

The curing behavior of epoxy resins was analyzed based on a simple kinetic model. We simulated the curing kinetics and found that it fits the experimental data well for both diglycidylether of bisphenol A–4,4′‐methylene dianiline and diglycidylether of bisphenol A–carboxyl‐terminated butadiene acrylonitrile–4,4′‐methylene dianiline systems. The kinetic results showed the curing of epoxy resins involves different reactive process and reaction stages, and the value of activation energy is dependent on the degree of conversion. By analyzing the effect of vitrification, at low curing temperature, we found the curing reaction at the later stage was practically diffusion‐controlled for unmodified resin, and the rubber component did not markedly decrease T_g at the early stage of reaction as would be expected. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2401–2408, 1999     

Cure kinetics of neat and carbon-fiber-reinforced TGDDM/DDS epoxy systems

The cure kinetics of neat and carbon fiber-reinforced commercial epoxy systems, based on Tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) and 4,4′-diaminodiphenylsulfone (DDS) were studied by means of differential scanning calorimetry (DSC). Analysis of DSC data indicated that the presence of the carbon fibers has a very small effect on the kinetics of cure. A kinetic model, arising from an autocatalyzed reaction mechanism, was applied to isothermal DSC data. The effect of diffusion control was incorporated into the reaction kinetics by modifying the overall rate constant, which is assumed to be a combination of the chemical rate constant and the diffusion rate constant. The chemical rate constant has the usual Arrhenius form, while the diffusion rate constant is described by a type of the Williams-Landel-Ferry (WLF) equation. The kinetic model, with parameters determined from isothermal DSC data, was successfully applied to dynamic DSC data over a broad temperature range that covers usual processing conditions. © 1996 John Wiley & Sons, Inc.     

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     

Influence of oxidation treatment of carbon powders on the cure kinetics of amine cured tetrafunctional epoxy resins

A tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) type tetrafunctional epoxy resin containing carbon powders was cured with the stoichiometric amount of a tetrafunctional curing agent, namely m-phenylenediamine (mPDA). Carbon powders were oxidised with air or nitric acid. The influence of carbon powders on curing of the resin was followed by dynamic mechanical analysis, Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Gelation and vitrification times were determined as a function of the variations of dynamic properties. The evolution of viscoelastic modulus during curing of the different mixtures showed that untreated carbon powder clearly accelerated the kinetics of curing whilst oxidation of carbon powders could remove their catalysing effect. These results were confirmed by monitoring the changes in conversion of epoxy and amine groups during cure using the FTIR technique. DSC experiments also showed the influence of carbon powder as a catalyst and the loss of the catalysing effect as a consequence of chemical treatment.     

Low-temperature fast curable behavior and properties of bio-based carbon fiber composites based on resveratrol

Environmentally friendly materials are an integral part of sustainable chemistry, and bio-based polymer composites are an important class of materials. The manufacture of composites is expected to reduce or even eliminate the use of adjuvants, considering the importance of reducing energy consumption and avoiding health and environmental risks. In this study, a phenyl-containing, polyfunctional, bio-based epoxy resin (TGER) was synthesized, and carbon fiber-reinforced, bio-based epoxy resin composites were fabricated by vacuum-assisted resin infusion using two aromatic amine curing agents, 4,4′-diaminodiphenylmethane (DDM) and 3,3′-diethyl-4,4′-diaminodiphenylmethane (DEDDM). Curing reactions and rheological behavior studies showed that TGER had higher curing reactivity toward DDM and DEDDM than to diglycidyl ether of bisphenol A (DGEBA) and possessed good processability. The results indicated that the resveratrol-based epoxy resin displayed low-temperature fast curing properties. The evaluation of the mechanical properties of the carbon fiber composites showed that the flexural strengths of CF/TGER/DDM and CF/TGER/DEDDM were 520 and 628 MPa, respectively. The initial decomposition temperature of CF/TGER composites is above 200°C. Furthermore, the carbon fiber–reinforced biopolymers possess excellent heat resistance. Therefore, carbon fiber-reinforced, resveratrol-based epoxy resin composites are promising candidates as alternatives to petroleum-based high-performance carbon fiber composites.     

Equivalent processing time analysis of glass transition development in epoxy/carbon fiber composite systems

The cure kinetics and glass transition development of a commercially available epoxy/carbon fiber prepreg system, DMS 2224 (Hexel F584), was investigated by isothermal and dynamic‐heating experiments. The curing kinetics of the model prepreg system exhibited a limited degree of cure as a function of isothermal curing temperatures seemingly due to the rate‐determining diffusion of growing polymer chains. Incorporating the obtained maximum degree of cure to the kinetic model development, the developed kinetic equation accurately described both isothermal and dynamic‐heating behavior of the model prepreg system. The glass transition temperature was also described by a modified DiBeneditto equation as a function of degree of cure. Finally, the equivalent processing time (EPT) was used to investigate the development of glass transition temperature for various curing conditions envisioning the internal stress buildup during curing and cooling stages of epoxy‐based composite processing. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 144–154, 2002; DOI 10.1002/app.10282     

Experimental modeling of the cure behavior of a formulated blend of DGEBA epoxy and C12‐C14 glycidyl ether as a reactive diluent

Microwave curing of polymer matrix composites has been suggested as an attractive substitute for conventional thermal curing. Formulations of epoxy and reactive diluents have the advantage of better wettability and uniform fiber impregnation. However, higher peak exotherms in large masses, and thus thermal overshoot, presents a challenge for cure cycle optimization. Therefore, building a reliable curing model will not only predict the behavior of these materials during actual processing, but also facilitate numerical modeling of the process and comparison of other resin formulations. In this study the effect of the reactive diluent on the isothermal cure kinetics of low viscosity epoxy was investigated using differential scanning calorimetry (DSC). A formulated blend of diglycidyl ether of bisphenol A (DGEBA) and C₁₂–C₁₄ aliphatic glycidyl was cured using diethylene triamine as the curing agent. Using a standardized procedure, ISO 113571‐5, the epoxy formulation was isothermally cured at several temperatures and the heat flow monitored and recorded. Using the heat flow data from DSC, the rate of cure was determined experimentally and a proper autocatalytic model with a total order of about 2.3 was fit to describe the process. Least‐square regression and isoconversion methods were used to find the model parameters and the activation energy, respectively. The accuracy of the model shows fine correlation with experimental data. By comparison to other epoxy resin without diluents, the analysis of the data shows that the reactive diluent increased the curing rate, while the values of activation energy and process parameters remained within the typical values of epoxy formulations. Based on these data, the future use of these types of resins in nonthermal curing of epoxy matrix composites is discussed. POLYM. COMPOS., 26:593–603, 2005. © 2005 Society of Plastics Engineers     

Cure kinetics of multifunctional epoxies with 2,2′‐dichloro‐4,4′‐diaminodiphenylmethane as hardener

The curing behavior of the epoxy resin N,N,N′,N′‐tetraglycidyldiaminodiphenyl methane (TGDDM) with triglycidyl p‐aminophenol as a reactive diluent was investigated using 2,2′‐dichloro‐4,4′‐diaminodiphenylmethane (DCDDM) as the curing agent. The effect of the curing agent on the kinetics of curing, shelf‐life, and thermal stability in comparison with a TGDDM‐diaminodiphenylsulfone (DDS) system was studied. The results showed a lesser activation energy at the lower level of conversion with a broader cure exotherm for the epoxy‐DCDDM system in comparison with the epoxy‐DDS system, although the overall activation energy for the two systems was comparable. TGA studies showed more stability in the epoxy‐DCDDM system than in the epoxy‐DDS system. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2097–2103, 2000     

Cure kinetics of ternary blends of epoxy resins studied by nonisothermal DSC data

The curing kinetics of blends of diglycidyl ether of bisphenol A (DGEBA), cycloaliphatic epoxy resins, and carboxyl‐terminated butadiene‐acrylonitrile random copolymer (CTBN) in presence of 4,4′‐diamino diphenyl sulfone (DDS) as the curing agent was studied by nonisothermal differential scanning calorimetry (DSC) technique at different heating rates. The kinetic parameters of the curing process were determined by isoconversional method given by Malek for the kinetic analysis of the data obtained by the thermal treatment. A two‐parameter (m, n) autocatalytic model (Sestak‐Berggren equation) was found to be the most adequate selected to describe the cure kinetics of the studied epoxy resins. The values of E_a were found to be 88.6 kJ mol^?1 and 61.6 kJ mol^?1, respectively, for the studied two sample series. Nonisothermal DSC curves obtained using the experimental data show a good agreement with that theoretically calculated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of polyaniline surface modification of carbon nanofibers on cure kinetics of epoxy resin

Polyaniline (PANI) “nanograss” was grown on carbon nanofibers (CNFs). The cure behavior of an epoxy resin with and without unmodified CNFs or PANI modified CNFs was studied by means of non‐isothermal and isothermal differential scanning calorimetry (DSC). CNFs accelerated the reaction of epoxy and diamine. PANI surface modification further increased the reaction rate and the extent of reaction. An autocatalytic cure kinetic model was used to fit the reaction curves. It was found that activation energies of the epoxy reaction decreased in the presence of CNFs and PANI modified CNFs. The observed catalytic effect of CNF and PANI surface coating can be very useful for low temperature cure of large epoxy composite products. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Cure kinetics of neat and graphite-fiber-reinforced epoxy formulations

An investigation was carried out into the cure kinetics of neat and graphite fiber-reinforced epoxy formulation, composed of tetraglycidyl 4,4′-diaminodiphenyl methane (TGDDM) resin and diaminodiphenyl sulfone (DDS) curing agent. Two experimental techniques were employed: isothermal differential scanning calorimetry (IDSC) and dynamic differential scanning calorimetry (DDSC). An autocatalytic mechanism with the overall reaction rate order of 2 was found to describe adequately the cure kinetics, of the neat resin and the composite. All kinetic parameters, including reaction rate constants, activation energies and preexponential factors, were calculated and reported. The presence of graphite fibers in the composite had only a very small initial effect on the kinetics of cure.     

Cure behaviour of epoxy resin matrices for carbon fibre composites

The cure behaviour of two resin formulations (with high and low curing agent content respectively) of an epoxy resin system, used as matrix for carbon fibre composites, was studied through calorimetric analysis. The aim of this work is to investigate the kinetics of this specific epoxy system in order to be able to choose a proper set of processing parameters which will give good composite material properties. The shape of the conversion curves gives evidence of the differences in the cure kinetics of the two systems. Furthermore, the values of the activation energies were determined both for formulation in the conversion range where vitrification occurs, following a phenomenological approach. These values give an indication of the differences in the curing mechanisms, when varying the content of curing agent. In particular, for both systems, the same reaction represents the onset of the cure process, ie the autocatalytic epoxy ring opening through addition reaction to the primary amine. This reaction dominates the entire cure process of the epoxy formulation at high curing agent content. Conversely, in the formulations with a low curing agent content, after depletion of the primary amines, different reactions may take place (with secondary amines and hydroxyl groups), depending on the cure temperature and the resin viscosity. © 1999 Society of Chemical Industry