Effect of processing variables on the durability of epoxy resins for composite systems

The Flory approach has been used to described the molecular characteristics of the non-linear polymerization of tetraglycidyl diamino diphenyl methane (TGDDM) cured with diphenyl sulfone (DDS). The cure behavior of commercial grade TGDDM-DDS mixtures was analyzed by means of differential scanning calorimetry (DSC), high-pressure liquid chromatography (HPLC), and steady and dynamic viscosity measurements. The gelation limits and molecular distribution measured in isothermal tests were in good agreement with experimental determinations. The gelation theory was further combined with the WLF treatment of the temperature dependency of the viscoelastic behavior for the reacting system in order to describe the viscosity profiles during complex cure cycles. Furthermore, this work relates moisture sorption and plasticization of two epoxy systems to hydrothermal and processing variables. A low cross-linked diglycidyl ether of bisphenol-A (DGEBA) cured with linear amines, such as ethylene diamine (EDA), diethylene triamine (DETA) and triethylene tetramine (TETA), and the highly cross-linked TGDDM-DDS system, have been studied. An increase in the equilibrium moisture content was observed as a result of thermal cycling in liquid environments. The hydrothermal interactions are shown to produce changes in the epoxy network structures and in the moisture sorption behavior.