A new two-step process to prepare microcellular epoxy foams based on kinetic analysis

Abstract

The foaming behavior of a diglycidyl ether of bisphenol-A (DGEBA) epoxy resin–anhydride hardener system at varying accelerator (tertiary amine) concentration, using chemical foaming agent (CFA), was investigated. The microstructure of foams revealed a smaller cell size, higher cell density, and more homogeneous distribution of cells at higher curing rate by varying accelerator contents, whereas not the same by varying foaming temperatures. The curing of epoxy system was studied by a differential scanning calorimetry, while the decomposition process of CFA was investigated by the foaming pressure measurement. Kinetics data showed that the addition of CFA in epoxy system produced obvious influence on the curing process of epoxy mixture; meanwhile, the decomposition reaction of CFA in epoxy system showed an autocatalytic behavior, which can be well predicted by Sestak–Berggren equation. Reaction rate constants of the curing of epoxy foaming system (k t ) and the degradation of CFA (k d ) were calculated, and the competition between these two simultaneously occurring reactions was expressed by the kinetic parameter k t /k d . The high specific value of k t /k d , which can be tuned by both accelerator concentration and foaming temperature, indicated that the curing rate was much higher than degradation rate of CFA. By further accelerating the curing rate in the foaming stage, a new two-step method was introduced to fabricate microcellular epoxy foam at relatively low viscosity.