Epoxy systems for low temperature applications
Epoxy-based formulated products are finding increased utility in a wide variety of structural and electrical applications that are required to operate in low temperature environments. Cryogenic technology is accelerating the growth in these fields. This versatile thermosetting polymer offers many attractive features such as high mechanical strength, outstanding dielectric characteristics, excellent adhesive properties, very good chemical resistance and excellent thermal endurance. Such features make them materials of choice for high and medium voltage electrical apparatus that operate in below zero Celsius environments. At lower operating temperatures, many factors come into play affecting overall performance. Among these factors are: speed and effectiveness of cure, fracture toughness characteristics, and thermal expansion properties.
Factors influencing the glass transition of DGEBA-anhydride epoxy resins
Abstract A number of chemical and physical factors influence the glass transition behaviour of anhydride-cured diglycidyl ether of bisphenol A (DGEBA) type epoxy resins. Several of these were investigated using differential scanning calorimetry to assess the nature of the glass transition, the transition temperature and the glass- and liquid-phase specific heats. The influence of molecular weight and chemical functionality, cooling rate and silica fillers were investigated for unreacted epoxy prepolymers. Two anhydride-cured systems were also considered and the influence of cure with and without silica fillers and the effect of phase separation and cooling rate were investigated.
Cure kinetics of a high epoxide/hydroxyl group‐ratio bisphenol a epoxy resin—anhydride system by infrared absorption spectroscopy
An infrared absorption spectroscopy study of the curing kinetics of a low (1.12) epoxide/hydroxyl-group ratio bisphenol A epoxy resin—phthalic anhydride system is reported. A full infrared peak assignment to molecular vibrational modes is given for the range 400 to 4000 cm−1, and the optical density behavior of all peaks during reaction is discussed in detail. Proposed rival reaction mechanisms are considered and their respective kinetic behavior discussed. The reaction was found to follow consecutive-step addition esterification and simultaneous addition etherification, and epoxide—hydroxyl group and carboxylic acid dimer hydrogen bonding was found to occur. The reaction behavior supports a proposed hydroxyl group-limited inhomogeneous bulk reaction mechanism of a colloid type.