The curing kinetics and mechanical properties of epoxy resin composites reinforced by PEEK microparticles

In this paper, a polyether-ether-ketone (PEEK)/epoxy composite was prepared by using PEEK microparticles as the reinforcement. The nonisothermal differential scanning calorimetry (DSC) test was used to evaluate the curing reaction of PEEK/epoxy resin system. The curing kinetics of this system were examined utilizing nonisothermal kinetic analyses (Kissinger and Ozawa), isoconversional methods (Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose) and an autocatalytic reaction model. During these analyses, the kinetic parameters and models were obtained, the curing behavior of PEEK/epoxy resin system under dynamic conditions was predicted. The results show that isoconversional methods can adequately interpret the curing behavior of PEEK/epoxy resin system and that the theoretical DSC curves calculated by the autocatalytic reaction model are in good agreement with experimental data. Furthermore, the tensile elongation at break, tensile strength, flexural strength, compression strength and compression modulus increased by 81.6%, 33.66%, 36.53%, 10.98% and 15.14%, respectively, when PEEK microparticles were added in epoxy resin composites.     

Investigation of curing kinetics of various cycloaliphatic epoxy resins using dynamic thermal analysis

Curing reactions of three cycloaliphatic epoxy resins with methyltetrahydrophthalic anhydride (MTHPA) was investigated by differential scanning calorimetry at different heating rates. Activation energy was calculated based on Kissinger method and varied in the range of 67-72 kJ/mol depending on sample. The curing kinetic behavior was well described by Sestak-Berggren (SB) model and the order of the curing reaction is observed to be from 0.02 to 2.11 according to sample.     

Mechanical properties of polymer composites based on commercial epoxy vinyl ester resin and glass fiber

The effect of the addition of methyl ethyl ketone peroxide (MEKP) and cobalt naphthenate (CoNaph) on the mechanical behavior of epoxy vinyl ester resin (EVER) laminates has been investigated by using a factorial experimental design, in which the MEKP and NaphCo contents were varied. Previous results showed that there is an interaction effect between the process variables analysed on the mechanical properties evaluated. It was also observed that the MEKP/CoNaph ratio affected the tensile behavior of the EVER/glass fiber composites.     

Effect of new nonionic curing agent on curing kinetics and mechanical properties of epoxy resin

The current research work presents a novel nonionic curing agent (AEDA) synthesized by utilizing ethylene glycol diglycidyl ether (EGDE), 3,4-dimethoxyaniline (DI), and triethylenetetramine (TETA). Infrared spectroscopy and nuclear magnetic resonance spectroscopy were used to characterize the structure of AEDA curing agent. Non-isothermal scanning calorimetry was used to determine the activation energy and curing conditions of epoxy resin in the curing process. An impact testing machine, a tensile testing machine and a scanning electron microscope (SEM) were used to analyze the impact strength, tensile strength, bending strength, and micromorphology of the AEDA/E-51 system with different mass ratios. The results show that AEDA is an effective high-temperature curing agent. For the AEDA/E-51 system with the optimal mass ratio of 10:100, the best curing temperature is 92.15°C, and the post-curing temperature is 135.65°C. Furthermore, the apparent activation energy (E_a) of 1670 J/mol, the pre-exponential factor (A) of 3.7 × 10^?4, and the reaction series (n) value of 0.76 are obtained for the AEDA/E-51 system. The impact strength of AEDA/E-51 epoxy resin polymer is 7.82 kJ/m², tensile strength is 14.2 MPa, and bending strength is 18.92 MPa. The micromorphological results of the AEDA/E-51 system are consistent with the results of DSC test and mechanical properties test. Hence, this study provides theoretical support for the practical applications of AEDA as curing agent.     

聚醚链段长度对氨基聚醚-环氧树脂力学性能的影响

以柔性端氨基聚醚(BATPE)和双酚A环氧树脂(DGEBA)为原料, 制备了无微相分离结构的无定型AB交联热固性树脂. 测试了3种不同聚乙二醇(PEG)链段长度(M_PE)的BATPE-DGEBA环氧树脂固化产物的应力-应变曲线、动态力学温度谱和冲击断面形貌. 结果表明, 在环氧树脂交联网络中引入两端与DGEBA化学连接的PEG链段能避免微相分离结构的生成, 有利于提高DGEBA链段的应变松弛速率. 增加M_PE, 一方面能降低环氧树脂固化产物的玻璃化转变温度和室温下的刚度和拉伸强度, 增加韧性(包括冲击强度和拉伸韧性)、断裂应变和模量损耗因子; 另一方面也能提高固化产物在低温下的储存模量. 优化M_PE可制备出在中低温下同时具有优异的拉伸强度、模量、断裂应变和冲击性能的BATPE-DGEBA环氧树脂.     

用FTIR定量研究环氧树脂固化反应动力学制样方法的确定

利用FTIR进行环氧树脂固化反应的动力学研究需要精确的样品制备方法,摸索到一套合适的样品制备方法。将KBr研成细粉,通过孔径为0.074mm筛子使粒子均匀,在120~150℃下加热24h后,取0.25g,放入红外压片模具,在压力为800MPa条件下加压时间5~10min,压制成厚度为0.08mm的透明均匀KBr盐片。将环氧树脂均匀涂在这种KBr盐片上,放入微型反应器中反应,之后一同放入FTIR仪中进行扫描,实验证明这种制样方法可以保证红外定量分析的可靠性。     

Thermal cured epoxy resins using certain calixarenes and their esterified derivatives as curing agents

The acetyl esterified calixarene (CA) derivatives were prepared from calix[4]resorcinarene (CRA), and p‐tert‐butylcalixarene (BCA[n], n = 4, 6, 8), respectively. Using these CA derivatives as curing agents, the thermal curing reactions of two multifunctional epoxy resins (jER 828, 186 g/equiv., and ESCN, 193.7 g/equiv.) were investigated. The temperatures of glass transition (T_g) and decomposition (T) were measured by DSC and TGA, respectively. Based on the yields, T_gs, and T_ds of the thermal cured jER 828 epoxy resin with CRA‐E100, the curing conditions were optimized to be tetrabutylphosphonium bromide (TBPB) as catalyst in NMP at 160 °C for 15 h. Under this curing condition, the cured materials of jER 828 or ESCN using various CA derivatives as curing agents were prepared. Except for BCA4 derivatives, the yields of thermal curing reaction were higher than 90%. T_gs and Ts of the resultant cured materials were in the range of 113–248 °C and 363–404 °C, respectively. These results mean that the cured epoxy resins with excellent T_gs were successfully formed by using CA derivatives as curing agents. It was also found that the T_gs of cured epoxy resins were strongly affected by the degree of esterification of CA derivatives. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1931–1942, 2010     

Curing reaction characteristics and phase behaviors of biphenol type epoxy resins with phenol novolac resins

Diglycidyl ether of 4,4′-dihydroxybiphenol (BPDGE) is a liquid crystalline epoxy. The biphenyl epoxy (diglycidyl ether of 3,3′,5,5′-tetramethyl-4,4′-biphenyl, TMBPDGE) has found great applications in plastic encapsulated semiconductor packaging. Phenol novolac (PN) was used as curing agent. The reaction kinetics of BPDGE/PN and TMBPDGE/PN systems in the presence of triphenylphosphine (TPP) were characterized by an isoconversional method under dynamic conditions using differential scanning calorimetry (DSC) measurements. The results showed that the curing of epoxy resins involves different reaction stages and the values of activation energy are dependent on the degree of conversion. The effects of curing temperature on their phase structure have been investigated with polarized optical microscopy and Wide-angle X-ray diffraction. With proper curing process, BPDGE showed a nematic phase when cured with PN.     

Thermal and photochemical ageing of epoxy resin - Influence of curing agents

The thermal and photochemical ageing of epoxy resin was studied using photoacoustic-FTIR spectroscopy. This technique was satisfactory for both unfilled resin and glass fibre filled epoxy composite. The influence of the curing agent (anhydride or amine) was significant for ageing. The durability of anhydride-epoxy system was the best for both thermal and photoageing.     

Comparative studies on the curing kinetics and thermal stability of tetrafunctional epoxy resins using various amines as curing agents

The curing reactions of the epoxy resins tetraglycidyl diaminodiphenyl methane (TGDDM) and tetraglycidyl methylenebis (o-toluidine) (TGMBT) using diaminodiphenyl sulfone (DDS), diaminodiphenyl methane (DDM) and diethylenetriamine (DETA) as curing agents were studied kinetically by differential scanning calorimetry. The dynamic scans in the temperature range 20°–300°C were analyzed to estimate the activation energy and the order of reaction for the curing process using some empirical relations. The activation energy for the various epoxy systems is observed in the range 71.9–110.2 kJ·mol^–1. The cured epoxy resins were studied for kinetics of thermal degradation by thermogravimetry in a static air atmosphere at a heating rate of 10 deg·min^–1. The thermal degradation reactions were found to proceed in a single step having an activation energy in the range 27.6–51.4 kJ·mol^–1.

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Zusammenfassung Die Vernetzungsreaktionen der Epoxidharze Tetraglycidyl-diamino-diphenyl-methan (TGDDM) und Tetraglycidyl-methylen-bis(o-toluidin) (TGMBT) unter Verwendung von Diaminodiphenylsulfon (DDS), Diaminodiphenylmethan (DDM) und Diethylentriamin (DETA) als Vernetzungsmittel wurden kinetisch mittels DSC untersucht. Die dynamischen Scans im Temperaturbereich 20°–300°C wurden analysiert, um unter Anwendung einiger empirischer Gleichungen die Aktivierungsenergie und die Reaktionsordnung des Vernetzungsprozesses zu ermitteln. Die Aktivierungsenergie der einzelnen Epoxy-Systeme liegt im Bereich 71.9–110.2 kJ·mol^–1. An der ausgehärteten Harze wurde mittels TG in einer statischen Luftatmosphäre un deiner Aufheizgeschwindigkeit von 10 Grad/min die Kinetik des termischen Abbaues untersucht. Man fand, daß die thermiscehn Abbaureaktionen in einem Schritt ablaufen und ihre Aktivierungsenergie im Intervall 27.6–51.4 kJ·mol^–1 liegt.

     

Luminescence spectroscopy as a tool for testing of cure kinetics of epoxy resins

In this paper, steady-state luminescence spectroscopy is used for the analysis of curing of epoxy resin. The advantage of this method is its rapidity, simplicity and sensitivity. Moreover, this method is contactless, and thus non-invasive. The aim is to analyze epoxy resin, mathematically describe its curing kinetics and determine its storage temperature. Using the photoluminescence method, a rapid procedure for obtaining the necessary technological data is achieved. This method is suitable for continuous measurement in production because there is no contact with the material, and the measurement itself can be performed very quickly. The elaborated mathematical model can serve as a basis for creating algorithms for automated data processing in case of fully robotic workplaces.     

Cationic polymerization and physicochemical properties of a biobased epoxy resin initiated by thermally latent catalysts

The cationic polymerization and physicochemical properties of a biobased epoxy resin, epoxidized castor oil (ECO), initiated by N-benzylpyrazinium hexafluoroantimonate (BPH) and N-benzylquinoxalinium hexafluoroantimonate (BQH) as thermally latent catalysts were studied. As a result, BPH and BQH show an activity at different temperatures in the present systems. The cured ECO/BPH system showed a higher glass transition temperature, a lower coefficient of thermal expansion, and higher thermal stability factors than those of the ECO/BQH system. On the other hand, the mechanical properties of the ECO/BQH system were higher than those of the ECO/BPH system. These have been attributed to the differences in crosslinking level of cured resins, which were induced by the different activity of the latent catalysts.     

Synthesis, curing kinetics and thermal properties of bisphenol-AP-based benzoxazine

A novel bisphenol-AP-aniline-based benzoxazine monomer (B-AP-a) was synthesized from the reaction of 4,4′-(1-phenylethylidene) bisphenol (bisphenol-AP) with formaldehyde and aniline. The chemical structures were identified by FT-IR, ¹H and ¹³C NMR analyses. The polymerization behavior of the monomer and the types of hydrogen bonding species were monitored by differential scanning calorimetry (DSC) and FT-IR. The curing kinetics was studied by isothermal DSC and the isothermal kinetic parameters were determined. The thermal properties of cured benzoxazine were measured by DSC and thermogravimetric analysis (TGA). The bisphenol-AP-aniline-based polybenzoxazine (poly(B-AP-a)) exhibited higher glass transition temperature (T_g) and better thermal stability than corresponding bisphenol A-aniline-based polybenzoxazines (poly(BA-a)). The T_g value of poly(B-AP-a) is 171 °C. The temperatures corresponding to 5% and 10% weight loss is 317 and 347 °C, respectively, and the char yield is 42.2% at 800 °C. The isothermal curing behavior of B-AP-a displayed autocatalysis and diffusion control characteristics. The modified autocatalytic model showed good agreement with experimental results.     

Improvement in fracture behaviors of epoxy resins toughened with sulfonated poly(ether sulfone)

The sulfonated poly(ether sulfone) (SPES) was successfully prepared using chlorosulfonic acid as a sulfonating agent. Diglycidylether of bisphenol-A (DGEBA) epoxy resins were modified with different contents of SPES, and the thermal and mechanical interfacial properties of DGEBA/SPES blends were investigated. As a result, the surface free energy of the blends was increased by the addition of SPES. DSC measurements revealed that the curing reaction was delayed with the increase of SPES content. Whereas, the thermal stabilities of the blends were slightly decreased as the SPES content increased. Meanwhile, the glass transition temperature and fracture toughness of the blends were increased with increasing SPES content, due to the improved intermolecular interactions, such as hydrogen bonding, between the hydroxyl group of DGEBA and the sulfonic group of SPES in the blends. The agreement could be observed by SEM which revealed phase separated morphology of DGEBA/SPES blends.     

Curing behavior and kinetics of epoxy resins cured with liquid crystalline curing agent

This article describes the synthesis of a liquid crystalline curing agent 4,4′-bis-(4-amine-butyloxy)-biphenyl (BABB), and its application as a curing agent for the epoxy resin (DGEBA) in comparison with normal curing agent, 4,4′-diaminobiphenyl (DABP). BABB was investigated with polarized optical microscopy, differential scanning calorimetry, and small-angle X-ray scatting, and the results showed that BABB displayed smectic liquid crystalline phase. The curing behaviors of DGEBA cured with BABB and DABP were studied by using differential scanning calorimetry (DSC), polarized optical microscopy (POM), and dynamic mechanical analysis (DMA). The results indicated that BABB showed a higher chemical reactivity than DABP. The kinetics was studied under isothermal conditions using an isoconversional method, and the isothermal DSC data can be fitted reasonably by an autocatalytic curing model. The nematic droplet texture was observed for the resulting polymer network of DGEBA/BABB system, while the DGEBA/DABP system showed an isotropic state. The storage modulus of DGEBA/BABB system was enhanced in comparison with DGEBA/DABP system because of the formation of LC phase, whereas the glass transition temperatures decreased because of the introduction of flexible spacer group.     

The reinforcing effect of polydopamine functionalized graphene nanoplatelets on the mechanical properties of epoxy resins at cryogenic temperature

In order to obtain epoxy nanocomposites with excellent mechanical properties at cryogenic temperature, an efficient method to functionalize graphene nanoplatelets (GNPs) is proposed. Through a simple dip-coating procedure, the GNPs were first functionalized with deposition of polydopamine coating (PDA@GNPs). Then, using polydopamine as a bridge, the PDA@GNPs were modified with amine groups after polyetheramine T403 grafting (T403-PDA@GNPs). Fourier transform infrared spectroscopy, thermogravimetric analysis and X-ray photoelectron spectroscopy analyses proved the successful functionalization of PDA and polyetheramine T403 on the surface of GNPs. Adding 0.1 wt% T403-PDA@GNPs significantly improved the cryogenic tensile strength and impact strength of the epoxy nanocomposites by 34.5% and 64.5%, which showed greater reinforcing effect than the pristine GNPs (12.6% and 19.1%) and PDA@GNPs (26.3% and 50.1%). The results of dynamic mechanical analysis and scanning electron microscopy observations indicated that the PDA and further polyetheramine T403 functionalization improved the interfacial interactions between GNPs and matrix, which ensured the much improved mechanical properties.     

Mechanical properties degradation of polyimide films irradiated by atomic oxygen

Mechanical properties of polyimide films are degraded by exposure to a low earth orbit environment. The main environmental factor for that degradation is atomic oxygen (AO). Using tensile tests, AO-irradiated surface topography observations, and fracture surface analyses, this study investigated the degradation behavior of polyimide films’ mechanical properties by increased AO fluence and its accompanying degradation mechanisms. Tensile strength and elongation of polyimide films were reduced concomitantly with increased AO fluence. Furthermore, AO-irradiated polyimide films fractured from the AO-irradiated surfaces, of which roughness became marked as AO fluence increased. These results reflect that reduction of mechanical properties is attributable to the roughness increase in AO-irradiated surfaces. Polyimide films coated with indium tin oxide (ITO) were also evaluated to confirm the degradation behavior of AO protective films. Surfaces of ITO-coated polyimide films remained smooth even after AO irradiation. However, undercut cavities were formed at ITO coating defect sites. Rupture of ITO-coated polyimide films initiates from the undercut cavities, engendering large reduction of tensile strength and elongation. The degradation of the mechanical properties of ITO-coated polyimide films increased substantially until the undercut cavities fully penetrated the film.     

Chemorheological study of the curing kinetics of a phenolic resol resin gelled

The changes in the resin viscosity, conductivity, mass, and enthalpy during curing reactions have been studied to obtain kinetic parameters that allow modeling of the resin behavior throughout its industrial application. In this work, isothermal rheological tests of a phenolic resol resin were performed in order to study its complex viscosity during crosslinking reactions. Samples were prepared by a precuring treatment in a heated plate press to reach gel point of the resin. Rheological analyses of resol resin curing were carried out at five different temperatures (80-100 °C), and the kinetic models of Arrhenius and Kiuna were applied. The resol resin curing presented an activation energy of 72.1 kJ/mol according to the Arrhenius model. The Kiuna model was proposed to fit the non-linear evolution of the resin’s complex viscosity at the highest temperatures. This kinetic model was suitable for predicting the changes in the complex viscosity of the resol resin after its gelation, and the process activation energy obtained for the second order polynomial applied in this model was 88.1 kJ/mol. In addition, the profile for the degree of curing of resol resin was determined from measurements of the material’s elastic modulus.     

Dilute solution properties of epoxy resins

Number-average molecular weights of fractions of epoxy resins were estimated by vapor-pressure osmometry and size exclusion chromatography coupled with multiple-angle light scattering. Potential reasons for differences between the two sets of data are examined. The molecular weight dependences of the intrinsic viscosity in tetrahydrofuran and chloroform are discussed in terms of theories which take into account the low-molecular weight character of poly(hydroxy ether) chains. The polymer-solvent interaction parameter is estimated. The impact of the presence of branched chains on the results of size exclusion chromatography is examined. It is shown that the universal calibration of size exclusion chromatographic columns by polystyrene is reliable at molecular weights above 2000 only.     

Investigation of the curing reactions of some multifunctional epoxy resins using differential scanning calorimetry

Curing reaction of three tetrafunctional epoxy resins in the presence of tetraethylene tetramine was examined by differential scanning calorimetry at different heating rates. The kinetic parameters of the curing reaction were determined using various computational methods (Barrett, Borchardt–Daniels and Kissinger). The heating rate shows a great influence on the curing process. The activation energy varied in the range 43–80 kJ/mol, and the order of the curing reaction is observed to be ≈1.0 with slight variations.