Curing characteristics of carboxyl functionalized glucose resin and epoxy resin

The curing characteristics of carboxylic functionalized glucose resin (glucose maleic acid ester vinyl resin: GMAEV) and epoxy resin have been studied using DSC and FTIR methods. Exothermic reactions attributed to esterification and etherification reactions of the hydroxyl and carboxyl functionalities of GMAEV with the epoxy groups were identified. Exothermic reactions showed very different patterns according to the degree of carboxyl group substituent of GMAEV. The results showed that esterification reaction occurs in the early stage of cure and then etherification followed after completion of the esterification. A cured matrix containing epoxy resin and 50 wt.% of GMAEV was prepared and characterized. The cured matrix showed thermal stability up to 300 °C. The average glass transition temperature and storage modulus of the matrix were as high as 95 °C and 2700 MPa, respectively. The cured matrix of epoxy resin and GMAEV with higher degree of carboxyl group was found to have a lower density due to the formation of bulky groups in the crosslinks.     

Curing characteristics of o-cresol novolac epoxy resin modified by bismaleimide

Curing characteristics of o-cresol novolac epoxy resin modified by 4,4-diaminodiphenylmethane bismaleimide (DDM-BMI) using FTIR were investigated and the glass transition temperature was measured. With the addition of DDM as hardener, the relative curing reaction conversion of DDM-BMI increased with equivalent weight ratio [R₁ = (equiv wt summation of epoxy and DDM-BMI)/equiv wt of DDM] and weight ratio of epoxy and DDM-BMI (R₂ = wt of epoxy resin/wt of DDM-BMI). Using phenol novolac resin (PN) as hardener, the curing reaction conversion of DDM-BMI was hardly changed, but the variation of that in the epoxy resin was observed with R₂ change. © 1996 John Wiley & Sons, Inc.     

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。     

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.     

Water absorption effects on hydrophilic polymer matrix of carboxyl functionalized glucose resin and epoxy resin

The effects of water absorption on hydrophilic polymer matrices based on carboxylic functionalized glucose (glucose maleic acid ester vinyl resin) and epoxy resins were studied as a function of curing temperature. The matrix cured at higher temperature shows compact crosslinks due to the higher concentration of ether bonds comparing to the matrix cured at the lower temperature. The polymer matrices cured at different temperatures were immersed in water at room temperature for 1000 h and the thermomechanical properties of the cured polymers were characterized using DMA and TGA. Two types of sorbed water were identified. Type I sorbed water contributed mainly to increasing the weight and to the decrease in T_g due to a plasticizer effect. Type II sorbed water was not removed after heating the polymer to 110 °C for an hour. Type II sorbed water causes changes in the mechanical properties of the polymers cured at different temperatures depending on the crosslinks of the matrix. The cured matrix at the higher temperature has the comparatively tight crosslinks in the network structure and the sorbed water molecule disturbed the polymer network resulting in the degradation of the matrix such as microcracks.     

Graft interpenetrating polymer networks composed of epoxy resin and urethane acrylate resin

For enhancing the interpenetratoin and/or compatibility of the simultaneous interpenetrating networks (SINs) composed of epoxy resin (epoxy) and urethane acrylate resin (UAR), the graft epoxy consisting of different lengths of poly(oxypropylene) (PO) side chains were synthesized and characterized. It was found that the graft epoxy composed of short PO side chains [MW 480, epoxy-g-PO(480)] showed a compatible system while if consisting of longer PO grafts [MW 950, epoxy-g-PO(950)] exhibited a partial microphase separation morphology. DSC measurements as well as the SEM or TEM observation indicated that the interpenetration between the two phases for epoxy/UAR SINs including epoxy-g-PO(480) was improved appreciably due to the excellent miscibility between the PO grafts and PO segments existing in the graft epoxy and the UAR network, respectively. In this case, for SIN(80/20) containing 10 wt % of epoxy-g-PO(480) the tensile strength increases by a factor of 2.70 compared with that of pure epoxy network. However, the improvement of interpenetration and/or compatibility between the two networks as well as the mechanical properties for SINs composed of epoxy-g-PO(950) are limited resulting in the partial microphase separation of epoxy-g-PO(950) network's own self. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3568–3574, 1999     

Synthesis and properties of isosorbide based epoxy resin

Isosorbide based epoxy resin (IS-EPO) of epoxy number: 0.44 mol/100 g was synthesised in the one step reaction from 1,4:3,6-dianhydro-d-glucitol (isosorbide) and epichlorohydrin in the presence of concentrated aqueous NaOH. The product obtained was characterised by means of NMR, FT-IR and ESI MS spectroscopy. Compositions with typical hardeners were prepared and cured. The thermal and mechanical properties of the resulting materials were evaluated. Comparison with commercially available epoxy resin Epidian 5 shows relatively good mechanical performance of IS-EPO which makes isosorbide a promising candidate to replace bisphenol A (BPA).     

Application of isoconversional and multivariate non-linear regression methods for evaluation of the degradation mechanism and kinetic parameters of an epoxy resin

The thermo-oxidative degradation of an epoxy resin obtained by curing of an industrially produced DGEBA mixture with 4,4′-methylene-dianiline (MDA) and used as electric insulator has been investigated by TG + DTG + DSC simultaneous analyses performed in static air atmosphere, at five heating rates. TG, DTG and DSC curves showed that, in the temperature range 25-900 °C, a glass transition followed by three thermo-oxidative processes occur. The processing of the non-isothermal data corresponding to the first process of thermo-oxidation was performed by using Netzsch Thermokinetics - A Software Module for Kinetic Analysis. The dependence of the activation energy, evaluated by isoconversional methods, on the conversion degree and the relative high standard deviations of this quantity show that the investigated process is a complex one. The mechanism and the corresponding kinetic parameters were determined by multivariate non-linear regression program and checked for quasi-isothermal data. It was pointed out that the first process of thermo-oxidation of the investigated resin consists in four steps, each step having a specific kinetic triplet. The obtained results were used for prediction of the thermal lifetime of the material corresponding to some temperatures of use and the end point criterion 5% and 10% mass loss.     

基于松香酸酐的环氧树脂体系固化动力学及TTT图绘制

研制了基于松香酸酐固化剂的生物质环氧树脂体系,采用全动态DSC法研究了树脂体系的固化反应动力学,通过半经验的唯象模型拟合得到了固化反应参数,活化能Ea为59.68 kJ/g,指前因子A0为1.28×1015s-1,反应级数n为2.483,由此建立了体系固化温度/时间/固化度间的关系;采用恒温DSC及DMA方法测试玻璃化转变温度,应用DiBenedetto经验方程拟合得到了玻璃化转变温度与固化度间的关系.应用锥板旋转黏度计测试了树脂体系不同温度下的凝胶时间,通过线性回归分析得到了凝胶时间与温度之间的关系.由唯象模型和DiBenedetto方程分别计算得到凝胶时的固化度为0.386,玻璃化转变温度为26.22°C.由上述工作绘制了基于松香酸酐生物质树脂体系的TTT(time-temperature-transition diagram)固化图,可确定树脂体系在不同温度任意时间下的状态.     

Curing studies of epoxy resin with nadic endcapped phosphorylated amines

Polyimides have aromatic moieties in the backbone structure which are responsible for their increased thermal stability. If phosphorus is introduced in the main chain structure of polyimides, there is further improvement in the thermal stability. This has been proved by the work carried out in our group. The polyimide having amine termination can be used for crosslinking of epoxy resins.In the present study amine terminated phosphorus containing nadicimide were taken as curing agent for DGEBA resins. The curing characteristics of DGEBA resin were studied by DSC using different amounts of nadic endcapped phosphorylated amines. DSC thermogram showed the heat of polymerization was lower as compared to system cured with aromatic amines.     

Thermal properties of epoxy resin nanocomposites based on hydrotalcites

Epoxy resin nanocomposites containing home-made hydrotalcites (HTlc) have been prepared and their properties have been studied and compared with those of montmorillonite (MMT)-type layered silicates-based nanocomposites. Nanofiller dispersion in the polymer matrix has been evaluated by transmission (TEM) electron microscopy and wide angle X-ray diffraction (WAXD), while nanocomposite thermal properties have been studied in detail by thermogravimetric analysis (TGA/DTG) and cone calorimeter tests.The morphological studies have shown that the compatibilisation of the above two type of nanofillers allowed us to obtain nanostructured materials. As far as thermal properties are concerned, nanocomposites based on HTlc are found to decompose, both in air and nitrogen, following a trend similar to that of the neat polymer matrix, while in the case of the nanocomposite based on the organophilic MMT a slight improvement was found in air. Conversely, cone calorimetric tests have demonstrated that only the organophilic hydrotalcite was capable of decreasing the peak of the heat release rate in a relevant way.     

Synthesis of novel epoxy-group modified phosphazene-containing nanotube and its reinforcing effect in epoxy resin

In this work, novel epoxy-group modified phosphazene-containing nanotubes (EPPZTs) were successfully synthesized through the reaction between epichlorohydrin and phosphazene-containing nanotubes with active hydroxyl groups. The structure was characterized by Fourier transform infrared spectroscopy (FTIR) and the morphology was investigated by scanning electron microscopy (SEM). EPPZTs/epoxy resin composites were prepared by introducing EPPZTs into epoxy resin matrix (EP618). Impact strength and tensile strength of the composites with different content of EPPZTs were tested and SEM was used to study the dispersion of EPPZTs in polymer matrix. The best effect in reinforcing the matrix was observed when the content of EPPZTs was 0.1%. The thermal stability of the composites was studied by thermo gravimetric analysis (TGA) and it was found that the addition of EPPZTs effectively increased the residue and decreased the weight loss rate.     

Effects of organo-montmorillonite dispersion on thermal stability of epoxy resin nanocomposites

Montmorillonite (MMT) was modified with the acidified cocamidopropyl betaine (CAB) and the resulting organo-montmorillonite (O-MMT) was dispersed in an epoxy/methyl tetrahydrophthalic anhydride system to form epoxy nanocomposites. The dispersion state of the MMT in the matrix was investigated by X-ray diffraction and scanning electronic microscopy. The thermal stability of the epoxy nanocomposites was examined by TGA. Thermal stability of the epoxy nanocomposite is dependent upon the dispersion state of the OMMT in the epoxy matrix although all the epoxy nanocomposites had enhanced thermal stability compared with the neat epoxy resin. The thermal stability of the epoxy resin nanocomposites was correlated with the dispersion state of the MMT in the epoxy resin matrix.     

Curing behavior and properties of high biosourced epoxy resin blends based on a triepoxy monomer and a tricarboxylic acid hardener from 10-undecenoic acid

Renewable propane-1,2,3-triyl tris(9-(oxiran-2-yl) nonanoate) (EGU, 100 wt% biogenic) and a tricarboxylic acid triglyceride (CGTU) hardener (85.7 wt% biogenic) were synthesized from 10-undecenoic acid (10-UDA) and used to produce epoxy resins with 52–92 wt% biobased carbon. CGTU was prepared by thermally activated thiol-ene coupling of thioglycolic acid onto propane-1,2,3-triyl tris(undec-10-enoate), (GUD) in the absence of solvent. The characterized CGTU was used as a green hardener of blends based on EGU and a conventional bisphenol A-based epoxy pre-polymer (DGEBA) at various mass percentages (0–100 wt%) with an stoichiometric epoxy/acid equivalent ratio. Calorimetric studies revealed higher peak temperature, lower reaction heats, and longer gelation times in resins with high EGU proportion, evidencing the lower reactivity of aliphatic EGU compared with aromatic DGEBA. Cured resins were yellowish transparent rubber-like materials with glass transition temperatures (Tg) varying from −14 °C to −42 °C and tensile strength in the range of 1750 kPa–790 kPa, for 0 and 100 wt % EGU, respectively. The soluble fraction of all resins was less than 4.3%, reflecting a high level of crosslinking. Thermosets with high biobased content showed both UV-light protection and visible light transparency.     

A novel fluorescent epoxy resin for organophosphate pesticide detection

In this work,a novel bisbenzimidazolylpyridine-functionalized fluorescent epoxy resin was synthesized for organophosphate pesticide detection.The epoxy resin was characterized by Fourier-transform infrared spectroscopy(FT-IR),proton nuclear magnetic resonance spectroscopy(~1H NMR),gel permeation chromatography(CPC),differential scanning calorimetry(DSC) and fluorescence spectroscopy.After loading with Eu(Ⅲ) ions,the epoxy resin showed a strong fluorescence emission.The fluorescence emission was observed to be instantaneously quenched when exposed to trace amount of diethyl chlorophosphate in solution.The Stern-Volmer quenching constants K_(sv) for quenching at617 nm was determined to be 0.377 × 10~3 L/mol.This sensitive emission-quenching function and easy processing nature of the polymeric support enable the resin to be a promising chemosensor candidate for the detection of organophosphates.     

Studies on the synthesis and curing of epoxidized novolac vinyl ester resin from renewable resource material

Cardanol-based epoxidized novolac vinyl ester resin (CNEVER) was synthesized by reacting cardanol-based epoxidized novolac (CNE) resin and methacrylic acid (MA) (CNE:MA molar ratio 1:0.9) in presence of triphenylphosphine as catalyst at 90 °C. The CNE resin was prepared by the reaction of cardanol-based novolac-type phenolic (CFN) resin and epichlorohydrin, in basic medium, at 120 °C. The CFN resin was synthesized by reacting cardanol (C) and formaldehyde (F) (C/F ratio = 1:0.7) with p-toluene sulphonic acid (PTSA) as catalyst (0.5 wt.%) at 120 °C for 7 h. The resin products were analyzed by Fourier-transform infra-red (FTIR) and nuclear magnetic resonance (NMR) spectroscopic analysis. The number-average molecular weight of the prepared CNEVER was found to be 859 gmol⁻¹ as determined by gel permeation chromatographic (GPC) analysis. The resin was cured by using the mixture of resin, benzoyl peroxide, and styrene at 120 °C. The CNEVER resin was found to be cured in 60 min at 120 °C. Differential scanning calorimetric (DSC) technique was used to investigate the curing behaviour. Single step mass loss in dynamic thermogravimetric (TG) trace of CNEVER was observed. Thermal stability of the vinyl ester sample containing 40 wt.% styrene was the highest amongst all other prepared systems.     

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.     

Curing reaction of biphenyl epoxy resin with different phenolic functional hardeners

The investigation of cure kinetics and relationships between glass transition temperature and conversion of biphenyl epoxy resin (4,4′-diglycidyloxy-3,3′,5,5′-tetramethyl biphenyl) with different phenolic hardeners was performed by differential scanning calorimeter using an isothermal approach over the temperature range 120–150°C. All kinetic parameters of the curing reaction including the reaction order, activation energy, and rate constant were calculated and reported. The results indicate that the curing reaction of formulations using xylok and dicyclopentadiene type phenolic resins (DCPDP) as hardeners proceeds through a first-order kinetic mechanism, whereas the curing reaction of formulations using phenol novolac as a hardener goes through an autocatalytic kinetic mechanism. The differences of curing reaction with the change of hardener in biphenyl epoxy resin systems were explained with the relationships between T_g and reaction conversion using the DiBenedetto equation. A detailed cure mechanism in biphenyl-type epoxy resin with the different hardeners has been suggested. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 773–783, 1998     

Synthesis of phosphorus-based flame retardant systems and their use in an epoxy resin

Methods are proposed to synthesize efficient organophosphorous compounds and combine them with montmorillonite nanoparticles. The chemical-physical structure and mechanism of action of the new systems were studied in epoxy resin. Best results were achieved using the fully phosphorylated calixresorcinarene derivative: the heat release rate peak could be decreased by 61% and the LOI value was increased from 21 to 28. The salt form of additives in case of phosphorylated phloroglucine derivatives was not advantageous in epoxy resin, because the additives could not participate in the crosslinking process effectively due to their inhomogenous distribution in the matrix. The incorporation of the nanoparticles did not create the desired flame retardant effect which can be explained by the increased heat conductivity and lower mobility of the nanoparticles due to the crosslinked structure.     

Reaction-induced phase separation in rubber-modified epoxy resin

The phase separation mechanism,and structure development during curing of epoxy with a novel liquid rubber-ZR were investigated by time-resolved light scattering,optical microscope and differential scanning calonmetry (DSC) The mixture loaded with curing agent was a single-phase system in the early stage of curing.When the cure reaction proceeded,phase separation took place via the spinodal decomposition induced by polymerization of epoxy resin.This was supported by the characteristic change of light scattering profile with curing time.Cure reaction plays an important role in the progress of phase separation.The bigger the cure reaction rate is,the longer periodic distance will be.The overall two-phase structure was basically locked in when the conversion approached 80% estimated by DSC,and finally the co-continuous two-phase structure was successfully obtained.