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.     

Carbon-fibre epoxy prepreg (CFC) curing in an autoclave analogue process controlled by Dynamic Mechanical Analysis (DMA)

Carbon fibre prepregs have found widespread application in lightweight constructions. They are based on a carbon-fibre fabric impregnated with reactive epoxy resin. DMA measurements under temperature conditions similar to an autoclave programme were carried out using commercially available prepreg material with a high glass transition temperature. The characteristic of the temperature programme was a dynamic heating segment at 1.5 K/min followed by a longer isothermal segment at 180 °C. The courses of the storage modulus E′, loss modulus E″ and tanδ were recorded. The measuring frequency was varied between 1 Hz and 33.3 Hz. Gelation and vitrification are assigned. The influence of the measuring frequency on the time to vitrification and the correlation with DSC are discussed. The reaction does not end even after 10 h curing at 180 °C, which is interpreted as the slow cessation of the reaction caused by vitrification.     

Epoxy resins (DGEBA): The curing and physical aging process

Differential scanning calorimetry (DSC) and infrared spectroscopy (IR) were used to monitor the degree of cure of partially cured epoxy resin (Epon 828/MDA) samples. The extent of cure, as determined by residual heat of reaction, concurred with that determined by monitoring the infrared radiation absorbance of the epoxide group near 916 cm^?l. The fictive temperature T_{f, g} was found to increase with the degree of cure, increasing rapidly during cure until reaching a value near the cure temperature T_c of 130°C (approximately 80% cure) where the material vitrified. The greatly reduced reaction rate during the final 20% of cure was not only a consequence of vitrification but, as revealed by infrared spectroscopy, the result of the depletion in the number of reactive epoxide groups. The endothermic peak areas and peak temperatures evident during the DSC scans were used as a measure of the extent of “physical aging” which took place during the cure of this resin, and after, fully cured samples were aged 37°C below their ultimate glass temperature for various periods of time. The rate of physical aging slowed as the temperature increment (T_t,g ? T_c) increased. Although an endothermic peak was evident after only 1 h of cure (T_{f, g} = 138.3°C), such a peak did not appear until fully cured samples were aged for 16 h or more. Enthalpy data revealed that for partially cured material, the fictive temperature T_{f, a}, reflecting physical aging, increased with curing time. In contrast, the T_{f, a}, for fully cured samples decreased with sub-T_g aging time. The characteristic jump in the heat capacity ΔC_p which occurred at the T_{f, g} decreased as curing progressed. This decrease appears to be dependent upon the rotational and vibrational degrees of freedom of the glass. Finally, a graphical method of determining the fictive temperature T_{f, a}, of partially and fully cured epoxy material from measured endothermic peak areas was developed.     

Temperature modulation in PDSC for monitoring the curing under pressure

The use of pressure cell attached to a temperature modulated differential scanning calorimeter (TMDSC) is investigated to perform modulated DSC experiments at high pressures (TMPDSC). No previous reports were found on the use of TMPDSC. In this study, the proposed method is applied to the study of the pressure effect on the curing reaction of an epoxy system. Curing quasi-isothermal modulated experiments were performed at different pressures to evaluate the vitrification time. Linear heating modulated tests were also successfully performed at different pressures to separate the reversing glass transition effect from the residual exothermic cure reaction. The curing enthalpy, conversion versus temperature, and glass transition of the fully cured thermoset were also evaluated. All the studied parameters resulted to be affected by the pressure in the range from atmospheric pressure to 35 bar. It was observed that the curing enthalpy, the reaction rate and the conversion at any given time increase with any pressure increment. The usefulness of TMDSC to characterize the curing of thermosets is extended by PTMDSC to situations, i.e., aeronautics industry, where pressure curing is needed.     

Epoxy shape memory polymer (SMP): Material preparation,uniaxial tensile tests and dynamic mechanical analysis

The utilization of epoxy shape memory polymers (SMPs) as engineering materials for deployable structures has attracted considerable attention due to their excellent thermo-mechanical endurance and satisfactory processability. Knowledge of static and dynamic mechanical properties is essential for analyzing structural behavior and recovery, especially for new epoxy SMPs. In this paper, a new epoxy SMP was prepared with epoxy and aromatic amine curing agent. Uniaxial tensile tests and digital image correlation were used to obtain static mechanical properties. Dynamic mechanical analysis was carried out to evaluate glass transition temperatures that corresponded to the heat in the recovery process.It was found that elastic modulus, Poisson’s ratio and shear modulus are 1413 MPa, 0.35 and 591 MPa, respectively. The beginning of glass transition temperature of 37.4 °C could be effectively achieved by electrical heaters, validating the shape memory properties of epoxy SMPs. In general, this study could provide useful observations and basic mechanical properties of epoxy SMPs.     

Investigation of the curing behaviour of carbon fibre epoxy prepreg by Dynamic Mechanical Analysis DMA

Carbon fibre prepregs have found widespread application in lightweight constructions. They are based on a carbon fibre fabric impregnated with reactive epoxy resin. Measurements were carried out using commercially available prepreg material. For Dynamic Mechanical Analysis (DMA), a single cantilever measuring device was applied. The DMA results were refined by additional DSC measurements. The measurements were carried out with dynamic heating in the temperature range ?90 to 280 °C. The heating rates were 1 and 2 K/min, respectively. A glass transition of the uncured material (T_g0) near 1 °C, and crosslinking-induced vitrification and devitrification at the maximal glass transition temperature of the cured material (T_gmax) in the temperature range 220 to 230 °C were found. The activation energies for the glass transitions were determined using an Arrhenius plot. By detailed consideration of the influence of the frequency on the DMA data, indications for gelation were deduced.     

Thermomechanical characterization of BFRP and GFRP with different degree of conversion

Thermomechanical behavior of basalt fiber- and glass fiber-reinforced plastics (BFRP and GFRP) was characterized under the same conditions. The effect of an EDI binder formulation on Martens temperature was studied by varying the contents of a curing agent from 75 to 95 parts by weight (pbw) and of an accelerator from 1 to 2 pbw with respect to 100 pbw of an ED-22 resin. The Martens temperature was found to vary from 90 to 113 °С, depending on the component ratio. An optimum binder formulation was chosen, exhibiting stable results on heat resistance after curing at 150 °С for 2 and 10 h. To achieve different degree of conversion, BFRPs and GFRPs were fabricated using the chosen formulation and were cured at 100-110 °С for 30 min and then at 150 °С for 1 and 4 h. The said formulation can be recommended, with the maximum transition point of BFRPs and GFRPs reaching 137 °С.     

Dynamic mechanical analysis of ethylene tetrafluoroethylene (ETFE) foils in use for transparent membrane buildings

Glass transition temperature and tan delta (the ratio of loss modulus to storage modulus) are indispensable parameters for determining appropriate application range of ETFE foils. In this study, ETFE foils in terms of specimen number, material direction and thickness were investigated with dynamic mechanical analysis (DMA) over a temperature range of -70-100 °C at frequencies of 0.1, 1, and 10 Hz. Glass transition temperatures were obtained with storage modulus, loss modulus and tan delta curves. It is found that frequency effect on glass transition temperature was proportional and that frequency effect was more significant than material direction effect. Moreover, a comparison study showed that elastic modulus determined with quasi-static experiments was greater than storage modulus calculated with dynamic mechanical experiments. To propose suitable glass transition temperature ranges for engineering application, an approach to determine confidence interval based on statistical analysis was employed. The resulting intervals with confidence coefficient of 95% were 31.2–32.7 °C, 60.5–66.4 °C and 79.6–83.3 °C for storage modulus, loss modulus and tan delta, respectively. In general, this study could provide useful observations and values for evaluating dynamic mechanical properties of ETFE foils.     

Monitoring the glass transition temperature of polymeric composites with carbon nanotube buckypaper sensor

Carbon nanotube (CNT) Buckypapers can be infused with resin and easily incorporated into conventional fiber reinforced composites. In this paper, we propose to use Buckypaper (BP) as a new measuring method to determine the glass transition temperature of polymeric composites. The CNT-only BP was fabricated by spray-vacuum filtration method with monodispersion of multi-wall carbon nanotubes, and then co-cured with polymeric composites. After manufacturing, the glass transition temperature of polymeric composites could be obtained from the relationship between resistance and temperature of BP during the dynamic heating process. Experimental results show that the glass transition temperature of composite samples A and B monitored by BP sensors were 127 °C and 180 °C, while such temperatures obtained from a dynamical mechanical analyzer (DMA) were 128 °C and 184 °C respectively. This paper not only reveals the ability of BP as a sensor for monitoring the glass transition temperature of composite but also provides a new way to understand the glass transition phenomenon of composite.     

Cure kinetics of epoxy composite applied on stator bars insulation

Cure kinetics study of epoxy resin composite, employed as stator bars insulation system, was evaluated through differential scanning calorimetry using the dynamic methodology, different heating rates. These experiments provided some important information about the system as activation energy (E _a = 65.4 kJ mol⁻¹), glass transition (T _g) values on different curing stages including the final cured material information and, besides that, it enables the comparison of these data with new materials under development. The activation energy value allows the determination of different energy needs of the system under evaluation, specially temperature for the material cure, improving the possibility of comparison between different insulation systems in use in the high voltage insulation business. The composite conversion degree based on the cure enthalpy (ΔH _cure) at different time of cure was also subject of analysis and from that it was possible to comprehend the cure pattern which allows the cure state prediction of further samples of this type of material and the more accurate evaluation of similar samples acquired directly from stator bars.     

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.     

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     

Transparent Epoxy/Silica Nanocomposites with Increased Glass Transition Temperatures

Epoxy/silica nanocomposites were obtained by curing 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate in the presence of silica nanoparticles modified by (3-triethoxysilyl)propylsuccinic acid anhydride. Optimum conditions for the preparation of optically transparent polymer nanocomposites with increased glass transition temperatures are determined. The glass transition temperatures of the above nanocomposites are 30-40 °C higher than those of the neat epoxy resin synthesized under the same conditions (130 °C).     

Poly(urethane Methacrylate) Thermo-Setting Resins Studied by Thermogravimetry and Thermomechanical Analysis

Two different poly(urethane acrylate) resins (one with a trimer: PUA1, the second with a dimer: PUA2) prepared [1] by photo curing reaction are investigated by means of thermogravimetry and thermomechanical measurements. The lack of mass loss found up to 300°C for both systems shows their good thermal stability. Beyond this temperature, two mass losses occur consecutively. This mass loss already studied by TG-FTIR coupled measurements for PUA1 resin has been attributed to the degradation of carbonyl groups [1]. The extension to PUA2 and the comparison between the mass loss magnitude and the relative contain in acrylate of the resins leads to attribute the first degradation to the degradation of the acrylate fraction. The degradation of dimer based resin occurs earlier and with a faster kinetic than the trimer based resin. The variations of linear expansion and penetration coefficients measured by thermomechanical analysis (penetration probe) in the glassy state and in the glass transition temperature domain (the onset glass transition temperatures measured by DSC at 20°C min^–1 are respectively equal to 111 and 107°C for PUA1 and PUA2, the transitions, not well defined, extending over 30°C), show that despite of a weaker compactness, the trimer based resin is more rigid than the dimer one. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis and characterization of a novel polytriazole resin with low‐temperature curing character

A novel low‐temperature curing polytriazole resin was prepared from a triazide and a tetraalkyne and characterized. The resin can be cured at 70°C. The glass transition temperature T_g and thermal decomposition temperature T_d5 of the cured resin with the molar ratio of azide to alkyne group [A]/[B] = 1.0:1.0 reached 324 and 355°C, respectively. The study on the curing kinetics of the resin shows that the apparent activation energy of the curing reaction is 93 kJ mol^?1. The flexural strength of the cured resin reached 137.6 MPa at room temperature and 102.6 MPa at 185°C. Copyright © 2007 John Wiley & Sons, Ltd.     

Matching Cure Characteristics of Automotive Rubber Compound and Polyurethane Coating

The present investigation focuses on matching cure characteristics of EPDM rubber compound and polyurethane (PU) coating using temperature modulated and pressure differential scanning calorimetry (TMDSC, PDSC). TMDSC provides a detailed and better understanding of the curing process of model rubber system as well as complex automotive rubber compounds. The low level of unsaturation present in EPDM, results in the small heat of vulcanization (2–5 J g^–1), which is difficult to accurately measure using conventional differential scanning calorimetry (DSC). Thus, curing of highly filled EPDM compound was investigated using TMDSC. The kinetics of PU curing was monitored using pressure DSC (PDSC), and heat of curing was determined as 4.2 J g^–1 at 10°C min^–1 heating rate. It is found that complex automotive compounds and the PU coating are curing simultaneously. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of curing conditions and dibutyl phthalate concentration on the properties of cured epoxy resin

The influence of the curing conditions and dibutyl phthalate additions on the physicomechanical properties of cured polyepoxides based on ED-20 resin and 4,4'-diaminodiphenylmethane curing agent was examined. An increase in the curing temperature over 150°С does not noticeably influence the physicomechanical properties of the cured resin, and keeping of the reaction mixture at 180°С for 12 h leads to a considerable decrease in the glass transition temperature of the polymer. Addition of dibutyl phthalate in concentrations of up to 10 wt % decreases the glass transition teperature of the polymer by 44°C, but with increasing concentration of dibutyl phthalate the elastic modulus increases and the breaking strain slightly decreases. The dependence of the ultimate strength on the dibutyl phthalate concentration passes through a maximum at 3 wt % dibutyl phthalate.     

Study on improving the toughness of rapidly curing epoxy resin composite materials with a biobased microcrystalline cellulose

Rapid solidification molding is one of the main low-cost forming methods for composite materials, and the reasonable selection of the solidification molding process is the key to achieving material performance. The curing system used in this paper is the widely used, inexpensive, and readily available epoxy resin (WSR618) and the transparent, colorless, and less toxic 593 curing agent, which cures at room temperature. Through the study of various temperature formulations, a rapid curing system was determined that has a 10-min cure at 80°C. The results showed that when the mass ratio of epoxy (EP) resin to curing agent was 5:1, the curing system was selected at 80°C for 10 min, and the bending strength could reach 100.19 MPa, and the impact strength could reach 12.82 kJ/m². However, the difficulty caused by quick solidification was a reduction in mechanical characteristics, which required modification. Microcrystalline cellulose is cheap and readily available and widely available, so microcrystalline cellulose (MCC) was chosen for modification in this study. The experimental results showed that the addition of MCC reduced the fracture brittleness of EP composite materials. When 0.75% MCC was added, the bending and tensile strengths reached 116.88 and 52.53 MPa, respectively, which were 16.66% and 18.74% higher than unmodified EP. The elongation at break reached 11.57%, which is 14.13% higher than unmodified.     

Determination of the glass transition temperature in thin polymeric films used for microelectronic packaging by temperature-dependent spectroscopic ellipsometry

We characterized the glass transition temperature T_g of thin polyimide films by temperature-dependent spectroscopic ellipsometry and compared the results to DSC measurements of the bulk polymer. The effect of the curing temperature on T_g and the thermal expansion α(T) was analyzed. An improved ellipsometric data evaluation was used to get most precise and reliable T_g data. T_g increased with increasing curing temperature, while the bulk T_g was considerably lower than the thin film T_g. Both observations are attributed to the temperature sensitive release of the imidization by-product 2-hydroxyethyl methacrylate (HEMA) and crosslinker components as well as decomposition products from the material. Variation in the curing temperatures of 230–380 °C led to an increase in the T_g of 34 °C.     

Mixtures poly((<Emphasis Type="Italic">R</Emphasis>)-3-hydroxybutyrate) and poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactic acid) subjected to DSC

Blends of bacterial poly((R)-3-hydroxybutyrate) (PHB) and poly(l-lactic acid) (PLLA) synthesized by polycondensation of l-lactic acid or by ring-opening polymerization of l-lactide were studied. Miscibility was investigated through both conventional differential scanning calorimetry (DSC) and temperature-modulated DSC (TMDSC). PHB and low-molar mass PLLA were miscible in a whole concentration range, and a single glass transition temperature was observed. On the other hand, PHB/high-molar mass PLLA mixtures phase separate, giving rise to two glass transition temperatures corresponding to PHB and PLLA. A treatment of blends at 190 °C leads to formation of block/multiblock/random copolymers, and blends become miscible.