Performance enhancing oligomeric amide additives for epoxy resins

Abstract

Additives that enhance the mechanical properties of epoxy resins, by reducing the free volume and thereby restricting the molecular motions, are known as antiplasticizers. Antiplasticizers usually increase the modulus and strength but can decrease the glass transition temperature of the material. A series of oligomeric amide additives were synthesised, that would, when mixed with TGDDM and DDS, react to form strong hydrogen bonds and reduce the free volume in the system. The effect of end group functionality was tested by synthesising both amine terminated and acid terminated additives. The ability of these additives to enhance the mechanical properties of the cured resin was examined by conducting fracture toughness and tensile testing. Results obtained for compact tension specimens and tensile testing specimens were inconclusive due to unavoidable imperfections incurred during specimen preparation. The cure kinetics of the resin was studied using Differential Scanning Calorimetry or DSC. Dynamic temperature scanning DSC indicated that the cure reaction was not affected significantly by these additives. At higher heating rates, as expected, the degree of cure and rate of cure shifted to higher temperatures. Arrhenius type activation energy calculations showed that incorporating amine terminated additive did not significantly increase the activation energy of cure (Ea). However, a significant increase in Ea was observed when the resin was cured with acid terminated additive. DMA and TMA data indicated that the glass transition temperature of the matrix did not show a significant reduction upon addition of the additives to the resin. Thermal degradation of the resin was studied using Thermo Gravimetric Analysis or TGA. Results indicated that the presence of an additive does not affect the thermal stability of the resin.