The thermal degradation of an epoxy system consisting of a diglycidyl ether of bisphenol A (DGEBA, n=0) and m-xylylenediamine (m-XDA) was studied by both thermogravimetric analysis (TG) and dielectric analysis (DEA). It has been checked a deviation of the typical behaviour in the Arrhenius plot expected for this kind of systems, owing to the thermal degradation. Both, structural relaxation time and conductivity values, were represented as a function of the mass loss, that allow a relationship to be obtained between characteristic relaxation time and the degree of degradation at the beginning of the degradation process.
Introduction Highly cross-linked epoxy thermosets are widely used as adhesives and matrices for fibre-composite materials because they possess good combination of thermal and mechanical properties, high glass transition
Thermal analysis characterization of isosorbide-containing thermosets
Isosorbide epoxy as BPA replacement for thermosets industry
thermosets and thermoplastics. BPA-based epoxies are manufactured for plastic lining of cans used for food, polycarbonate baby bottles, and tableware; white dental fillings; and sealants [ 14 ]. The growing global production of BPA not only puts the burden on
Synthesis and curing activity of latent ring-opening metathesis polymerization (ROMP)-based catalytic systems are reported using polydicyclopentadiene (pDCPD) as a model system. Differential scanning calorimetry (DSC) is used to monitor the ROMP reactions and to characterize the cured networks. These systems are either slow or completely inactive at ambient temperatures, yet at high temperatures the superior curing activity of other ROMP catalysts are retained. The resulting thermosets show glass transition temperatures from 10 to 25 °C higher than when cured with other ROMP catalysts.
high network or cross-link density, thermosets do not posses the chain mobility of the thermoplastics so widely used in self-healing concepts. Therefore, the self-healing of thermosets has followed distinctly different approaches. The hollow fibre
The glass transition temperature of thermosets is determined by alternating differential scanning calorimetry (ADSC), which is a temperature modulated DSC technique. The different values of the glass transition obtained from heat flow measurements (total and reversible) and heat capacity (modulus of the complex heat capacity) are analysed and compared with the values obtained by conventional DSC. The effect of the sample mass on the values of T g, heat capacity and phase angle has been analysed. The effect of the thermal contact between sample and pan has been studied using samples cured directly inside the pan and disc-shaped samples of different thickness. The results obtained for the thermal properties and the phase angle are compared and analysed. The modulus of the complex heat capacity enables the determination of the dynamic glass transition, T g , which is frequency dependent. The apparent activation energy ofthe relaxation process associated with the glass transition has been evaluated from the dependence of T g on the period of the modulation.
In the present work, gelation and vitrification experimental data are obtained by TMA and DMTA techniques using the same thermoset based on an epoxy-amine system. The results show that the times obtained are not equivalent and depend on the technique used. An attempt has been made to compare both determinations using the degree of cure obtained by means of DSC technique. The principal conclusion that we want to emphasize is that it is the conversion degree and not the time of the phenomenological changes that take place during cure, that is the link to connect and interrelate the results obtained with different techniques. A method is also described for constructing the TTT diagram with only DSC and TMA or DMTA data.
Introduction Thermoset polymer composites are preferred for many applications because of their strength, dimensional stability, resistance to heat, solvents and corrosive environments. They usually have a high glass transition
Vitrification during the isothermal cure of thermosets
Part I. An investigation using TOPEM, a new temperature modulated technique
The process of vitrification that occurs during the isothermal cure of a cross-linking system at temperatures below T g∞, the glass transition temperature of the fully cured resin, has been studied by TOPEM, a new temperature modulated DSC (TMDSC) technique based upon the use of stochastic temperature pulses. A comparison is made between TOPEM and another TMDSC technique, and some advantages of TOPEM are considered. The TOPEM technique is used to show that the mobility factor is not always a reliable approach to predicting the cure rate during vitrification, in view of its frequency dependence. Also, the dependence of the apparent vitrification time on frequency is examined. There appears to be a non-linear relationship between the apparent vitrification time and log(frequency), which is further discussed in the second part of this series.