Comparative curing kinetics of 1,4-bis (4-diaminobenzene-1-oxygen) n-butane and 4,4′-bis-(diaminodiphenyl) methane with tetraglycidyl methylene dianiline systems

Aromatic amine curing agent with flexible unit in backbone, 1,4-bis (4-diaminobenzene-1-oxygen) n-butane (DDBE), was synthesized, and the structure was confirmed by FT-IR and ¹H NMR. The curing kinetics of tetraglycidyl methylene dianiline (TGDDM, or AG80) using DDBE and 4,4′-bis-(diaminodiphenyl) methane (DDM) as curing agents, respectively, were comparatively studied by non-isothermal DSC with a model-fitting Málek approach and a model-free advanced isoconversional method of Vyazovkin. The dynamic mechanical properties and thermal stabilities of the cured materials were investigated by DMTA and TG, respectively. The results showed that the activation energy of AG80/DDBE system was slightly higher than that of AG80/DDM system. ?esták-Berggren model can generally simulate well the reaction rates of these two systems. DMTA measurements showed that the storage modulus of cured AG80/DDBE is similar to that of cured AG80/DDM at the temperature below glass transition temperature (T _g) and lower than that of cured AG80/DDM at the temperature above glass transition temperature, while T _g of cured AG80/DDBE is lower than that of cured AG80/DDM. TG showed that the thermal stabilities of these two cured systems are similar.     

Synthesis and properties of phosphorus-containing bio-based epoxy resin from itaconic acid

A phosphorus-containing bio-based epoxy resin (EADI) was synthesized from itaconic acid (IA) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO). As a matrix, its cured epoxy network with methyl hexahydrophthalic anhydride (MHHPA) as the curing agent showed comparable glass-transition temperature and mechanical properties to diglycidyl ether in a bisphenol A (DGEBA) system as well as good flame retardancy with UL94 V-0 grade during a vertical burning test. As a reactive flame retardant, its flame-resistant effect on DGEBA/MHHPA system as well as its influence on the curing behavior and the thermal and mechanical properties of the modified epoxy resin were investigated. Results showed that after the introduction of EADI, not only were the flame retardancy determined by vertical burning test, LOI measurement, and thermogravimetric analysis significantly improved, but also the curing reactivity, glass transition temperature (T _g), initial degradation temperature for 5% weight loss (T _d(5%)), and flexural modulus of the cured system improved as well. EADI has great potential to be used as a green flame retardant in epoxy resin systems.     

Benzoxazine-bismaleimide blends: Curing and thermal properties

A blend of bisphenol A based benzoxazine (Bz-A) and a bismaleimide (2,2-bis[4(4-maleimidophenoxy) phenyl] propane (BMI), was thermally polymerised in varying proportions and their cure and thermal characteristics were investigated. The differential scanning calorimetric analysis, supplemented by rheology confirmed a lowering of the cure temperature of BMI in the blend implying catalysis of the maleimide polymerisation by benzoxazine. FTIR studies provided evidences for the H-bonding between carbonyl group of BMI and -OH group of polybenzoxazine in the cured matrix. The cured matrix manifested a dual phase behaviour in SEM and DMTA with the minor phase constituted by polybenzoxazine dispersed in an interpenetrating polymer network (IPN) of polybenzoxazine and cured BMI. The IPN possessed improved thermal stability over the constituent polybenzoxazine. A benzoxazine monomer possessing allyl functional groups, 2,2′-bis(8-allyl-3-phenyl-3,4-dihydro-2H-1,3-benzoxazinyl) propane (Bz-allyl) was reactively blended with the same bismaleimide in varying stoichiometric ratios (Bz-allyl/BMI), where the curing involved mainly Alder-ene reaction between allyl- and maleimides groups and ring-opening polymerisation of benzoxazine. The rheological analysis showed the absence of catalytic polymerisation of BMI in this case. The overall processing temperature was lowered in the blend owing to the co-reaction of the two systems to form a single-phase matrix. The cured resins of both Bz-A/BMI and Bz-allyl/BMI blends exhibited better thermal stability than the respective polybenzoxazines. The T_g of the IPN was significantly improved over that of polybenzoxazine (Bz-A). However, the co-reaction resulted in a marginal decrease in the T_g of the system in comparison to the polybenzoxazine (Bz-allyl).     

Effect of the degree of cure on the viscoelastic properties of vinyl ester resins

Dynamic mechanical thermal analysis (DMTA) was performed on model vinyl ester resin (VER) samples prepared from bisGMA and styrene, partially cured using either benzoin ethyl ether (BEE) as a conventional photoinitiator or p-xylylene bis-(N,N-diethyldithiocarbamate) (XDT) as a photoiniferter, and on fully cured samples using benzoyl peroxide as a thermal initiator. Thermogravimetric studies showed that minimal styrene monomer was lost during the DMTA experiments. The DMTA experiments for the samples partially cured using BEE revealed two plateaus in the storage modulus and two peaks in the tan δ curves, attributed to trapped radicals gaining mobility and continuing polymerization after the samples were heated beyond their initial T_g. Only a single transition was observed for samples cured using XDT because this system did not contain trapped radicals. Performing photopolymerizations with XDT thus allowed us to probe the effect of cure conditions on the glass transition temperature, rubber modulus and relaxational behaviour of partially cured resins. The breadth of the glass transition was characterized in the temperature and frequency domains (obtained by time-temperature superposition). Partially cured bisGMA/styrene blends showed a narrowing of the transition in the frequency domain with increased cure but the bisGMA system showed no variation. When partially and fully cured bisGMA/styrene blends were studied, the breadths of the frequency domains showed opposite trends as the styrene concentration was varied. Thus, the breadth of the transition could not be interpreted as a simple measure of the network heterogeneity but is believed to be related to the distribution of mobilities in the network structure which determine the distribution of relaxation times. Time-temperature superposition yielded shift factors which, when fitted to the WLF equation, indicated that the free volume at the glass transition temperature (T_g) and the free volume expansion coefficient depended on both crosslink density and also the ability of the monomer units to pack into the network.     

Thermal properties of microcrystalline cellulose-filled PET–PTT blend polymer composites

Polymer composite materials were prepared from poly(ethylene terephthalate)–poly(trimethylene terephthalate) blends as the matrix and different microcrystalline cellulose (MCC) filler levels (0–40 wt%) using melt compounding followed by compression molding. The composites were analyzed using dynamic mechanical thermal analysis (DMTA), differential scanning calorimetry (DSC) and thermogravimetric analysis (TG). The DSC results indicated that there is no consistent or significant influence of the MCC addition on the glass transition (T _g), melting (T _m), and crystallization temperature of the composites. With increasing MCC content, dynamic mechanical properties improved because of the reinforcing effect of the MCC. The tan δ peak values from the DMTA were not significantly changed as the MCC content increased. TG indicated that the onset temperature of rapid thermal degradation decreased with increasing MCC content. It was also found that the thermal stability of the composites slightly decreased as the MCC content increased.     

The effect of water on the physicochemical and mechanical properties of gelatin

Strips of gelatin have been prepared by extrusion at different water contents varying from 20 to 50% H₂O (dry weight basis, d.w.b.). The processes of subsequent hydration or dehydration of these strips were followed by dynamic mechanical thermal analysis (DMTA), wide-angle X-ray diffraction and NMR relaxation measurements. A comparison of the calculated dependence of theT _g of gelatin (T _g anhydrous, 200?C) on water content (using the Ten Brinke and Karasz equation) with experimental results derived from DMTA showed that freshly extruded material followed the theoretical plot below 25% H₂O (d.w.b.), but at higher water contents, the7 _g deviated positively, probably due in part to the effect of delayed re-equilibration of water content after thawing of separated ice crystals. The experimental results determined after storage for one week fell on a different line, with aT _g of 145?C for anhydrous gelatin Possibly, theT _g is elevated by crystallization — a view supported by the WAXS spectra. The NMR relaxation results also showed a profound mobilization of the gelatin protons at water contents greater than 25% d.w.b.     

Viscoelastic properties and morphology of dicyanate ester/epoxy co-polymers modified with polysiloxane and butadiene–acrylonitrile rubbers

Dynamic mechanical analysis was conducted on specimens prepared from cyanate ester (CE) and epoxy (EP) resins cured together at various mass compositions. Increase of amount of epoxy resin in composition was shown to have a disadvantageous effect on glass transition temperature (T _g). It was shown that post-curing procedure was needed to produce a polymer matrix with a single glass transition relaxation, but increase in post-cure temperature up to 250 °C resulted in slight reduction in T _g for epoxy/cyanate copolymers. TG results proved that the presence of epoxy resin reduces thermal stability of the cyanate/epoxy materials. The neat CE and EP/CE systems containing 30 wt% of epoxy resin were modified using epoxy-terminated butadiene–acrylonitrile rubber (ETBN) and polysiloxane core–shell elastomer (PS). The scanning electron microscopy (SEM) results showed the existence of second phase of ETBN and PS modifiers. Only in the case of EP/CE composition modified with ETBN, well-dispersed second phase domains were observed. Analysis of SEM images for other CE- and EP/CE-modified systems revealed the formation of spherical aggregates.     

Cationic concentration effects on electron beam cured of carbon-epoxy composites

Electron beam (e-beam) curing is a technology that offers advantages over the thermal curing process, that usually requires high temperature and are time-consuming. E-beam curing is faster and occurs at low temperatures that help reduce residual mechanical stresses in a thermoset composite. The aim of the present study is to analyze the effects of cationic initiator (diaryliodonium hexafluoroantimonate) ranged from 1 to 3 wt% in DGEBA (diglycidyl ether of bisphenol A) epoxy resin when cured by a 1.5 MeV electron beam. The specimens were cured to a total dose of 200.4 kGy for 40 min. Analyses by dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC) show that the e-beam irradiated samples with 2 wt% cationic initiator were 96% cured obtained a glass transition temperature (tan δ) of 167 °C. The same epoxy resin, thermally cured for 16 h with an anhydride hardener, reached a T_g (tan δ) of 136 °C. So, the irradiated sample had its T_g increased approximately 20% and the curing process was much less time consuming.     

Thermal properties and kinetics of new-generation posterior bulk fill composite cured light-emitting diodes

In this study, the thermal behavior in terms of glass transition (T _g), degradation, and thermal stability of four commercial new-generation posterior bulk fill composites (Surefill SDR, Dentsply; Quixfill, Dentsply; Xtrabase, Voco; and Xtrafill, Voco) activated by light-emitting diodes (LEDs) was analyzed by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The activation energies (E _a) for the decomposition of the dental resins were calculated based on the Kissinger and Doyle kinetic models from the peaks of the endothermic curves obtained when the specimens were heated at four different temperatures (5, 10, 15, and 20 °C min^?1) during DSC. The results show that the Xtrabase composite displayed the highest T _g (120 °C at a 5 °C min^?1 heating rate) and E _a (157.64 kJ mol^?1) values associated with thermal degradation from the main chain of the polymer.     

Thermosetting epoxidized polybutadiene/low-molecular weight polyphenylene oxide compatible system with quite low-dielectric constant and loss prepared through co-curing reaction

Through the redistribution reaction of PPO, the hydroxyl-terminated low molecular weight PPO (PPO-OH) was prepared. Furthermore, after the reacting of PPO-OH with methacrylic anhydride, the double-bond-terminated low-molecular weight PPO (R-PPO) were synthesized, its M_n was 2631 g/mol. The R-PPO were co-cured with epoxidized polybutadiene (JP-100) to prepare JP-100/R-PPO cured systems. The JP-100/R-PPO cured systems showed single-phase morphology. The co-curing reaction with R-PPO could effectively improve the thermal performance of JP-100, the glass transition temperature (T_g) of cured JP-100/R-PPO systems raised greatly. For the cured JP-100/R-PPO (100/30) system, its T_g was 192°C. The dielectric constant and dissipation factor of cured JP-100/R-PPO systems were both decreased and showed good frequency stability. The dielectric constant and dissipation factor at 1 MHz of cured JP-100/R-PPO (100/30) system were 2.61 and 0.0038, respectively, were obviously lower than those of cured JP-100 system (which were 3.10 and 0.0099, respectively). The JP-100/R-PPO systems exhibited an excellent thermal stability. The 5% weight loss temperature (T_5%) of cured JP-100/R-PPO system was around 340°C.     

Mechanical properties and morphology of epoxy/poly(vinyl acetate)/poly(4-vinyl phenol) brominated system

Diglycidyl ether of bisfenol-A (DGEBA)/poly(vinyl acetate) (PVAc)/poly(4-vinyl phenol) brominated (PVPhBr) ternary blends cured with 4,4’-diaminodiphenylmethane (DDM) were investigated by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM). Homogeneous (DGEBA+DDM)/PVPhBr networks with a unique T _g are generated. Ternary blends (DGEBA+DDM)/PVAc/PVPhBr are initially miscible and phase separate upon curing arising two T _gs that correspond to a PVAc-rich phase and to epoxy network phase. Increasing the PVPhBr content the T _gof the PVAc phase move to higher temperatures as a consequence of the PVAc-PVPhBr interactions. Different morphologies are generated as a function of the blend composition.     

高性能环氧树脂/碳纳米管复合物的热分析研究

用差示扫描量热仪(DSC)、热失重分析仪(TGA)和动态力学热分析仪(DMTA)研究了多壁碳纳米管(MWNTs)/高性能4,4′-二氨基二苯甲烷四缩水甘油环氧树脂(TGDDM)/4,4′-二氨基二苯基砜(DDS)复合物的热性能.Kissinger和Flynn-Wall-Ozawa的非等温固化动力学研究发现,随着MWNTs含量的增加,复合物固化反应的活化能先减小后增大.TGA研究表明,MWNTs的添加对环氧树脂热稳定性影响很小.碳纳米管填充到TGDDM/DDS体系后,复合物的储存模量随着MWNTs含量的增加而增大,而玻璃化温度却随之减小.     

Further Study of Sub‐Tg Heat Flow Transition of a Cured Epoxy Resin

To further study the sub‐T_g heat flow transition of a cured epoxy resin, cured samples with different thermal history were investigated using torsion pendulum analysis (TPA) and thermal mechanical analysis (TMA). The results indicate that sub‐T_g heat flow transition could be related to the molecular relaxation from 20°C to the α‐peak, and that frozen‐in extra free volume is necessary for the appearance of sub‐T_g heat flow transition.     

Thermal analysis and gelation property of multifunctional epoxy resins used for pultruded composite ropes

Non-isothermal curing reactions of three different multifunctional epoxy resin systems were investigated by differential scanning calorimetry. The Kissinger equation was applied to calculate the apparent activation energy, and the Levenberg–Marquardt algorithm was used to fit the curing kinetic data. It was observed that the two-parameter model was in good match with the curing kinetics. In addition, dynamic mechanical thermal analysis was used to obtain the glass transition temperature (T _g). Furthermore, the thermal stabilities of the systems were studied by thermogravimetric (TG) analysis, the integral procedure decomposition temperature and temperature index T _s were used to characterize the thermal stability. Finally, the gelation time was measured by plate–knife method of a home-made device, and the relationship between gelation time and temperature was established, according to which the pultrusion process parameters were predicted.     

Synthesis and properties of Fe0.83V1.17O4

Thermal properties of the organic–inorganic bicontinuous nanocomposites prepared via in situ two-stage polymerization of various silanes, epoxy, and amine monomers are investigated, and the impact of filler content and its organic compatibility on thermal stability of these nanocomposites is studied. Two series of epoxy–silica nanocomposites, namely, EpSi-A and EpSi-B containing 0–20 wt% silica, are synthesized. An epoxy–silane coupling agent is employed to improve the organic compatibility of silica in EpSi–B nanocomposites. The composites synthesized via two-stage polymerization are characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric (TG) analysis. DSC and TG/differential thermogravimetric results reveal substantially high glass transition (T _g) and excellent thermal stability of the bicontinuous nanocomposites as compared with pristine epoxy polymer. Both T _g and thermal properties, however, considerably vary depending on the organic compatibility of the nanocomposites. Significantly higher decomposition temperatures are recorded in case of EpSi-B nanocomposites owing to the chemical links between the epoxy and silica phases. Kinetic studies also show relatively higher activation energies of pyrolysis for EpSi-B nanocomposites.     

Preparation and thermal properties of diglycidylether sulfone epoxy

A diglycidylether sulfone monomer (sulfone type epoxy monomer, SEP) was prepared from bis(4-hydroxyphenyl) sulfone (SDOL) and epichlorohydrin without any NaOH or KOH as basic catalyst. FT-IR, ¹H NMR, ¹³C NMR and mass spectroscopic instruments were utilized to determine the structure of the SEP monomer. The cured SEP epoxy material exhibited not only a higher T_g (163.81 °C) but also a higher T_g than pristine DGEBA (from 111.25 °C to 139.17 °C) when the SEP monomer moiety had been introduced into the DGEBA system. The thermal stability of cured epoxy herein was investigated by thermogravimetric analysis (TGA). The results demonstrated that the sulfone group of the cured SEP material decomposed at lower temperatures and formed thermally stable sulfate compounds, improving char yield and enhancing resistance against thermal oxidation. Additionally, the IPDT and char yield of the cured SEP epoxy (IPDT = 1455.75, char yield = 39.67%) exceeded those of conventional DGEBA epoxy (IPDT = 667.27, char yield = 16.25%).     

Thermal-oxidative aging of DGEBA/EPN/LMPA epoxy system: Chemical structure and thermal-mechanical properties

The evolvement of chemical structure and thermal-mechanical properties of diglycidyl ether of bisphenol-A and novolac epoxy resin blends cured with low molecular polyamide (DGEBA/EPN/LMPA system) during thermal-oxidative aging were investigated by Attenuated Total Reflectance Fourier Transform Infrared spectrometry (ATR-FTIR) and Dynamic Mechanical Thermal Analysis (DMTA). The results revealed that the chemical reactions during thermal-oxidative aging contained oxidation and chain scission. Some possible chemical reaction processes were given. There was a new compound formed during aging processes and the change of its glass transition temperature (T_g) with aging time followed an exponential law. In addition, the changes of dynamic mechanical behavior of this epoxy system aged at four different temperatures (110 °C, 130 °C, 150 °C, 170 °C) were compared. An empirical formula was obtained through kinetic analysis and this formula can be used to predict the oxidative degree of the surface at different aging temperature.     

Synergistic effects of layered double hydroxide with hyperfine magnesium hydroxide in halogen-free flame retardant EVA/HFMH/LDH nanocomposites

The synergistic effects of layered double hydroxide (LDH) with hyperfine magnesium hydroxide (HFMH) in halogen-free flame retardant ethylene-vinyl acetate (EVA)/HFMH/LDH nanocomposites have been studied by X-ray diffraction (XRD), transmission electron spectroscopy (TEM), thermogravimetric analysis (TGA), limiting oxygen index (LOI), mechanical properties' tests, and dynamic mechanical thermal analysis (DMTA). The XRD results show that the exfoliated EVA/HFMH/LDH can be obtained by controlling the LDH loading. The TEM images give the evidence that the organic-modified LDH (OM-LDH) can act as a disperser and help HFMH particles to disperse homogeneously in the EVA matrix. The TGA data demonstrate that the addition of LDH can raise 5-18 °C thermal degradation temperatures of EVA/HFMH/LDH nanocomposite samples with 5-15 phr OM-LDH compared with that of the control EVA/HFMH sample when 50% weight loss is selected as a point of comparison. The LOI and mechanical tests show that the LDH can act as flame retardant synergist and compatilizer to apparently increase the LOI and elongation at break values of EVA/HFMH/LDH nanocomposites. The DMTA data verify that the T_g value (−10 °C) of the EVA/HFMH/LDH nanocomposite sample with 15 phr LDH is much lower than that (T_g = −2 °C) of the control EVA/HFMH sample without LDH and approximates to the T_g value (−12 °C) of pure EVA, which indicates that the nanocomposites with LDH have more flexibility than that of the EVA/HFMH composites.     

Effect of iron-containing catalysts on thermal decomposition of cured GAP-AP propellants

The effects of various burning rate catalysts on thermal decomposition of cured glycidyl azide polymer (GAP)-ammonium perchlorate (AP) propellants have been studied by means of thermal analysis and a modified vacuum stability test (MVST). Four types of iron-containing catalysts examined in this paper are catocene, ferrocenecarboxaldehyde (FCA), ferrocene, and ferric oxide. Results of differential thermal analysis (DTA) and thermogravimetric analysis (TG) revealed that the catalysts play an important role in the decomposition of both AP and GAP. The peak decomposition temperature (T _m) of DTA curves and onset decomposition temperature (T _o) of TG patterns considerably shifted to a lower temperature as the concentration of catalysts increased in the propellants. The endothermic temperature of AP, however, is unaffected by the presence of burning rate catalysts in all cases. The activation energy of decomposition of the propellants in range of 80 to 120°C is determined, based on the MVST results.     

UV curable epoxy acrylate-clay nanocomposites

UV curable epoxy acrylates were reinforced with two different organically modified montmorillonites (MMTs) and an unmodified MMT. Conversion and rate of polymerization was monitored by real time infrared spectroscopy (RTIR) and photo-DSC. Microstructures were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and optical clarity. Optical clarity of the films containing clay was quite good as only a slight decrease was observed. Physical properties of the reinforced films were examined by differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), hardness and tensile testing. Enhancements in glass transition temperature (T_g), thermal stability and mechanical properties were observed. The films reinforced with the unmodified MMT exhibit the most significant enhancements in properties.