Cure behavior and thermal stability analysis of multiwalled carbon nanotube/epoxy resin nanocomposites

As‐received multiwalled carbon nanotubes (MWCNTs) were first treated by a 3 : 1 (v/v) mixture of concentrated H₂SO₄/HNO₃ and further functionalized by ethylenediamine/dicyclohexylcarbodiimide/tetrahydrofuran solution. MWCNT/epoxy nanocomposites were prepared. Their cure behaviors were investigated by dynamic differential scanning calorimetry. Quantitative analysis of the activation energy as a function of the degree of curing was carried out by the Flynn‐Wall‐Ozawa method. The fitted multiple regression equations for values of the activation energy of different systems were obtained. MWCNTs have the retardation effect on the cure reaction of epoxy resin, while the functional groups on the surface of amine‐modified MWCNTs could accelerate the cure reactions. Thermal stability was studied by thermogravimetric analysis. The filling of amine‐modified MWCNTs is beneficial to lower the cure activation energy and improve thermal stability of the nanocomposite. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Cure kinetics of epoxy/anhydride nanocomposite systems with added reactive flame retardants

Montmorillonite nanocomposite systems obtained from epoxy cured using anhydride and the addition of a reacting flame retardant are studied in this paper. In particular, a thermokinetic analysis of the behavior of five different compounds was performed, using a differential scanning calorimeter. The isothermal tests showed double reaction peaks, due to the cure reactions of DGEBA/acid anhydride systems. The comparisons between dynamic thermograms (and between isothermal ones, too) for the different mixtures also showed that the addition of other active substances (such as a nanofiller or a flame retardant additive) does not change the mechanism of crosslinking from a qualitative point of view, but both the nanoreinforcement and the flame retardant seemed to exert an evident catalytic action on the cure reactions. A model describing the cure behavior of the aforementioned materials is proposed in this work. This model takes into account the fact that the reaction mechanism of each analyzed system is composed of a couple of parallel phenomena: the fast opening of anhydride ring (corresponding to a first exothermic peak and characterized by “n‐th order” kinetics) and resin networking (corresponding to a second exothermic peak and characterized by an “auto‐catalytic with zero initial velocity” behavior). The verification of the proposed model was performed by means of a comparison between experimental data (normalized curves derived from DSC thermograms) and theoretical data (derived from a numerical integration—using the second order Runge–Kutta method—of the model‐representative equation) and provided very good results. This allows one to apply such a model to any engineering process problem concerning the cure of DGEBA/acid anhydride/phyllosilicate nanocomposite systems. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1676–1689, 2004     

环氧树脂/酸酐固化剂体系的热性能研究

在使用传统酸酐固化剂Me-THPA(甲基四氢苯酐)的基础上,加入PA(邻苯二甲酸酐)或PMDA(均苯四甲酸酐),通过改变酸酐固化剂比例制备了高温固化EP(环氧树脂),并探讨了不同类型和比例的混合酸酐固化剂对EP固化产物耐热性的影响。研究结果表明:Me-THPA固化EP体系的耐热温度为116.99℃,Me-THPA/PA固化EP体系的耐热温度为134.63℃,Me-THPA/PMDA固化EP体系的耐热温度为283.73℃;Me-THPA/PMDA固化EP体系的耐热性相对最好,其耐热温度比Me-THPA固化EP体系提高了142.53%。     

Curing behavior and thermal properties of multifunctional epoxy resin with methylhexahydrophthalic anhydride

The curing behavior and thermal properties of bisphenol A type novolac epoxy resin (bisANER) with methylhexahydrophthalic anhydride (MHHPA) at an anhydride/epoxy group ratio of 0.85 was studied with Fourier‐transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and thermogravimetry. The results showed that the FTIR absorption intensity of anhydride and epoxide decreased during the curing reaction, and the absorption peak of ester appeared. The dynamic curing energies were determined as 48.5 and 54.1 kJ/mol with Kissinger and Flynn–Wall–Ozawa methods, respectively. DSC measurements showed that as higher is the curing temperature, higher is the glass transition. The thermal degradation of the cured bisANER/MHHPA network was identified as two steps: the breaking or detaching of ? OH, ? CH₂? , ? CH₃, OC? O and C? O? C, etc., taking place between 300 and 450°C; and the carbonizing or oxidating of aromatic rings occurring above 450°C. The kinetics of the degradation reaction was studied with Coats–Redfern method showing a first‐order process. In addition, vinyl cyclohexene dioxide (VCD) was employed as a reactive diluent for bisANER (VCD/bisANER = 1 : 2 w/w) and cured with MHHPA, and the obtained network had a higher T_g and a slight lower degradation temperature than the undiluted system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2041–2048, 2007     

环氧树脂上浆剂对PAN基碳纤维性能的影响

分别以KD-213,YD-128环氧树脂、复合环氧树脂及油酸酰胺改性的复合环氧树脂(改性环氧树脂)为主体的上浆剂对聚丙烯腈基碳纤维(PANCF)进行上浆,对上浆纤维的加工性能、表面形貌及其界面剪切强度(IFSS)进行了研究。结果表明:上浆剂改善了PANCF的耐磨性、毛丝量、耐水性及其复合材料的IFSS。其中改性环氧树脂上浆剂为最佳,可在PANCF表面形成一层完整的柔韧性光滑薄膜,上浆后的PANCF的耐磨次数为1887,毛丝量为0.14mg,吸水率小于等于0.005%,复合材料IFSS较未上浆纤维提高38.5%,达87.26GPa。     

Cure kinetics and thermal properties of tetramethylbiphenyl epoxy resin/phthalazinone‐containing diamine/hexa(phenoxy)cyclotriphophazene system

Inherently flame retardant epoxy resin is a kind of halogen‐free material for making high‐performance electronic materials. This work describes an inherently flame retardant epoxy system composed of 4,4′‐diglycidyl (3,3′,5,5′‐tetramethylbiphenyl) epoxy resin (TMBP), 1,2‐dihydro‐2‐(4‐aminophenyl)‐4‐(4‐(4‐aminophenoxy) phenyl) (2H) phthalazin‐1‐one (DAP), and hexa(phenoxy) cyclotriphophazene (HPCTP). The cure kinetics of TMBP/DAP in the presence or absence of HPCTP were investigated using isoconversional method by means of nonisothermal differential scanning calorimeter (DSC). Kinetic analysis results indicated that the effective activation energy (E_α) decreased with increasing the extent of conversion (α) for TMBP/DAP system because diffusion‐controlled reaction dominated the curing reaction gradually in the later cure stage. TMBP/DAP/HPCTP(10 wt %) system had higher E_α values than those of TMBP/DAP system in the early cure stage (α < 0.35), and an increase phenomenon of E_α ～ α dependence in the later cure stage (α ≥ 0.60) due to kinetic‐controlled reaction in the later cure stage. Such complex E_α ～ α dependence of TMBP/DAP/HPCTP(10 wt %) system might be associated with the change of the physical state (mainly viscosity) of the curing system due to the introduction of HPCTP. These cured epoxy resins had very high glass transition temperatures (202–235°C), excellent thermal stability with high 5 wt % decomposition temperatures (>340°C) and high char yields (>25.6 wt %). © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Curing kinetics and chemorheology of epoxy/anhydride system

The curing kinetics and chemorheology of a low‐viscosity laminating system, based on a bisphenol A epoxy resin, an anhydride curing agent, and a heterocyclic amine accelerator, are investigated. The curing kinetics are studied in both dynamic and isothermal conditions by means of differential scanning calorimetry. The steady shear and dynamic viscosity are measured throughout the epoxy/anhydride cure. The curing kinetics of the thermoset system is described by a modified Kamal kinetic model, accounting for the diffusion‐control effect. A chemorheological model that describes the system viscosity as a function of temperature and conversion is proposed. This model is a combination of the Williams–Landel–Ferry equation and a conversion term originally used by Castro and Macosko. A good agreement between the predicted and experimental results is obtained. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3012–3019, 2003     

Cure kinetics and properties of epoxy/dicyanate blends

The cure behavior and properties of epoxy/dicyanate blends containing a stoichiometric amount of an amine curing agent for epoxilde groups were investigated as a function of blend composition. Differential scanning calorimetry (DSC) was used to investigate the dynamic and isothermal cure behavior of the blends. The cure rate of the blend increased with increasing dicyanate content. A second order autocatalytic reaction mechanism described the cure kinetics of the blends. The kinetic parameters were determined by fitting the dynamic DSC data to the model kinetic equation. The k₁₀ and E₁ values were mainly affected by the change of dicyanate content. The glass transition temperature of the blend decreased with increasing dicyanate content. The thermal decomposition characteristics of the blends were investigated by thermogravimetric analysis (TGA). Dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA) were used to investigate the mechanical properties of the blends. With increasing dicyanate content, the cure rate increased but the thermal and mechanical properties of the cured blends were not improved.     

Multiscale thermal modeling of cured cycloaliphatic epoxy/carbon fiber composites

Cycloaliphatic epoxies (CEs) are commonly used for structural applications requiring improved resistance to elevated temperatures, UV radiation, and moisture relative to other epoxy materials. Accurate and efficient computational models can greatly facilitate the development of CE‐based composite materials for applications such as Aluminum Conductor Composite Core high‐voltage power lines. In this study, a new multiscale modeling method is developed for CE resins and composite materials to efficiently predict thermal properties (glass‐transition temperature, thermal expansion coefficient, and thermal conductivity). The predictions are compared to experimental data, and the results indicate that the multiscale modeling method can accurately predict thermal properties for CE‐based materials. For 85% crosslink densities, the predicted glass‐transition temperature, thermal expansion coefficient, and thermal conductivity are 279 °C, 109 ppm °C^?1, 0.24 W m^?1 K^?1, respectively. Thus, this multiscale modeling method can be used for the future development of improved CE composite materials for thermal applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46371.     

Epoxy/anhydride networks modified by epoxy/anhydride oligomers containing SiOH groups

Epoxy/anhydride oligomers containing variable amounts of trialkoxysilane groups were synthesized from phenyl glycidyl ether (PGE), 3‐glycidoxypropyl trimethoxysilane (GPMS), and methyl tetrahydrophthalic anhydride (MTHPA), using benzyldimethylamine (BDMA) as an initiator. They were hydrolyzed and partially condensed using diluted formic as a catalyst, with the last step carried out in a solution of diglycidyl ether of bisphenol A (DGEBA). By curing with a stoichiometric amount of MTHPA, in the presence of BDMA, plasticized epoxy/anhydride networks were obtained without any evidence of phase separation. These materials showed a better abrasion resistance than that of the neat matrix. The presence of free SiOH groups can be used to improve the adhesion to glass surfaces. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1365–1370, 2000     

环氧树脂／酸酐固化体系的固化动力学及耐热性研究

通过不同升温速率下的DSC研究了环氧树脂/酸酐固化体系的固化动力学.利用DSC、DMA和TGA研究了固化体系的耐热性能.通过分析确定了体系的固化工艺,采用Kissinger、Ozawa法计算出固化体系的表观活化能.其均值为62.00 kJ/mol,结合Crane公式求出反应级数为0.92.采用DSC法测得玻璃化转变温度Tg=183℃.采用DMA法测得玻璃化转变温度Tg=182℃.热失重曲线表明,固化体系的起始分解温度为350℃.     

Cure kinetics and conductivity of rigid rod epoxy with polyaniline as a curing agent

The samples of rigid rod epoxy resin (4,4′‐diglycidyl (3,3′,5,5′‐tetramethylbiphenyl) epoxy resin (TMBP)) with different weight contents of polyaniline (PANI) as a curing agent were prepared. The kinetics of curing reaction between TMBP and PANI was analyzed by dynamic differential scanning calorimetry in the temperature range of 25–300°C. The results showed that the heat of cure reaction of TMBP/PANI sample with 10 wt% PANI was larger than those of others. The active energies with different curing conversions of TMBP/PANI sample with 10 wt% PANI were calculated by iso‐conversional method using the Coats‐Redfern approximation. The results showed that the activation energy was dependent on the degree of conversion. The morphology of the cured samples was detected by scanning electron microscopy measurements. The relationship between morphology and conductivity of cured samples was researched. The conductivities increased from 2.7 × 10⁻⁴ to 9.5 × 10⁻⁴ S/cm with the increase of PANI from 5 to 20 wt% in cured samples. The thermal stabilities of cured TMBP/PANI samples were examined by thermogravimetric analysis. The results showed that the cured TMBP/PANI can be promising to use as a conducting adhesive. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Improved interfacial adhesion in carbon fiber/epoxy composites through a waterborne epoxy resin sizing agent

A series of self‐emulsified waterborne epoxy resin (WEP) emulsions were used as surface sizing for carbon fibers (CFs) to improve the interfacial adhesion between the CF and epoxy matrix. In this work, the hydrogenated bisphenol‐A epoxy resin (HBPAE) was modified by polyethylene glycol (PEG) with molecular weights of 400, 800, 1000, 1500, 2000, 4000, and 6000 g/mol. The properties of the WEP emulsion were examined by Fourier transform infrared spectroscopy, dynamic light scattering, and transmission electron microscopy. The surface characteristics of sized CFs were evaluated using scanning electron microscopy, atomic force microscopy, and X‐ray photoelectron spectroscopy. Afterwards, CF/EP composites were prepared and their fracture surface and interlaminar shear strength (ILSS) were examined. The results indicated that PEG2000 modified HBPAE sizing had the optimum emulsion stability and film‐forming ability. Meanwhile, the results also demonstrated that a continuous and uniform sizing layer was formed on the surface of CFs and the surface sizing was excellent in improving the chemical activity of CFs. Compared with unsized CFs, the O1s/C1s composition ratio was observed to increase from 11.51% to 33.17% and the ILSS of CF/EP composites increased from 81.2 to 89.7 MPa, exhibiting better mechanical property than that of commercial Takemoto S64 sized CFs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44757.     

Study on thermal stability of typical carbon fiber epoxy composites after airworthiness fire protection test

The thermal stability of the T700 carbon fiber epoxy composites, which had been tested under different conditions (nonvibration plus nonscrubbing airflow, vibration, scrubbing airflow, and vibration plus scrubbing airflow), were investigated according to the obtained weight loss behavior, integral program decomposition temperature (IPDF), and activation energies (E) by using thermogravietry-differential thermal analyzer. The results indicate that the weight loss ratio, IPDF, and E of T700 carbon fiber epoxy and its residues in the third and fourth layers are similar under the nonvibration plus nonscrubbing airflow and vibration, and the thermal stability under the vibration condition is slightly stronger. In addition, the weight loss ratio, IPDF, and E of the epoxy and its residues in materials are also similar under scrubbing airflow and vibration plus scrubbing airflow, and the thermal stability under vibration plus scrubbing airflow is better. However, it is significantly less than the thermal stability of materials under nonvibration plus nonscrubbing airflow and vibration. Therefore, it can be found that the vibration exacerbates the flame severity and the scrubbing airflow has a significant cooling effect on the material during the airworthiness fire protection test, which have guiding significance on the airworthiness fire prevention items formulation of carbon fiber composite.     

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.     

Cure kinetics and physical characterization of epoxy/modified boehmite nanocomposites

Nanocomposites based on a cross-linked epoxy matrix with the addition of a reinforcing organically modified boehmite nano-phase were realized and characterized with the aim to produce systems possessing enhanced properties over commercial epoxy systems. Different amounts of a commercially available organically modified boehmite were added to a diglycidyl ether of bisphenol A (DGEBA) epoxy matrix. The rheological characteristic and kinetic behavior of the liquid nano-filled mixtures were analyzed and compared to those displayed by the un-filled resin. A mathematical model was applied to the experimental rheological data in order to assess the aspect ratio of the nano-filler. A proper equation was employed to model the cure kinetics of the nano-filled epoxy systems. The nanocomposites were heat-cured in the presence of an aromatic amine hardener. They were, then, characterized by scanning electron microscopy with EDS analysis, dynamic mechanical thermal analysis, differential scanning calorimetry, and Flexural and Hardness tests. Significant increase in the glass transition temperature, Shore D hardness and maximum flexural strength was found. The experimental results demonstrated the effectiveness of the o-boehmite nano-filler to improve the physical and mechanical properties of the epoxy resin. Further studies are in progress to verify the protective efficiency of the epoxy-boehmite nanocomposite when applied on different substrates as adhesive or coating for construction materials, such as porous stones, concrete, wood, and metal.     

Super-crosslinked ionic liquid-intercalated montmorillonite/epoxy nanocomposites: Cure kinetics,viscoelastic behavior and thermal degradation mechanism

Super-crosslinked epoxy nanocomposites containing N-octadecyl-N′-octadecyl imidazolium iodide (IM)-functionalized montmorillonite (MMT-IM) nanoplatelets were developed and examined for cure kinetics, viscoelastic behavior and thermal degradation kinetics. The structure and morphology of MMT-IM were characterized by FTIR, XRD, TEM, and TGA. Synthesized MMT-IM revealed synergistic effects on the network formation, the glass transition temperature (T_g) and thermal stability of epoxy. Cure and viscoelastic behaviors of epoxy nanocomposites containing 0.1 wt% MMT and MMT-IM were compared based on DSC and DMA, respectively. Activation energy profile as a function of the extent of cure was obtained. DMA results indicated a strong interface between imidazole groups of MMT-IM and epoxy, which caused a significant improvement in storage modulus and the T_g of epoxy. Network degradation kinetics of epoxy containing 0.5, 2.0, and 5.0 wt% MMT and MMT-IM were compared by using Friedman, Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and the modified Coats-Redfern methods. Although addition of MMT to epoxy was detrimental to the T_g value, as featured by a fall from 94.1°C to 89.7°C detected by DMA method, and from 103.3°C to 97.9°C by DSC method, respectively. By contrast, meaningful increase in such values were observed in the same order from 94.1°C to 94.7°C and from 103.3°C to 104.7°C for super-crosslinked epoxy/MMT-IM systems.     

Improving the interlaminar shear strength and thermal conductivity of carbon fiber/epoxy laminates by utilizing the graphene-coated carbon fiber

The poor interlaminar properties restrict the application of carbon fiber reinforced polymer (CFRP) composites. In this work, a novel method for fabricating a graded interface structure is developed to improve the through-thickness thermal conductivity of CFRP composites. High-strength graphene nano-plates (GnP) and phenolic resin (PF) were selected to deposit on the surface of carbon fiber to design a novel CF/Epoxy laminates, where a simultaneous improvement of interlaminar shear strength (ILSS) and through-thickness thermal conductivity was observed. With addition of 1 wt % of GnP-PF in CF, 37.04% increase of the ILSS, and 16.67% enhancement of thermal conductivity compared to the original CFRP. The mechanism for improvement of both ILSS and thermal conductivity was studied by scanning electron microscopy and nano-indentation, where a better interface formed by GnP-PF has been clearly observed. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47061.     

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 kinetics of epoxy resins and aromatic diamines

An analysis of the cure kinetics of several different formulations composed of bifunctional epoxy resins and aromatic diamines was performed. A series of isothermal differential scanning calorimetry (DSC) runs (at higher temperature) and Fourier transform infrared spectroscopy (FT-IR) runs (at lower temperature) provided information about the kinetics of cure in the temperature range 18–160°C. All kinetic parameters of the curing reaction, including the reaction rate order, activation energy, and frequency factor were calculated and reported. Dynamic and isothermal DSC yielded different results. An explanation was offered in terms of different curing mechanisms which prevail under different curing conditions. A mechanism scheme was proposed to account for various possible reactions during cure.