Defect formation during binder removal in ethylene vinyl acetate filled system

This paper focuses on determining the criteria for defect formation during the early stages of thermal binder removal within an ethylene vinyl acetate (EVA) polymer filled with submicron SiC ceramic powder. The only product of the early stage thermal degradation reaction of EVA within an inert atmosphere is acetic acid. This single component and well characterized organic reaction product has allowed the defect forming criteria to be definitively examined. It will be shown that bloating occurs in the early stages of binder removal as a result of pressure build-up in the specimen resulting from acetic acid formed from the thermal elimination reaction of EVA. The first part of this paper examines defect formation occurring in the pure polymer within a hot-stage optical microscope. Bubble formation is observed in the pure polymer. Next, bloating occurring in the molded system is examined. The affect of mineral oil on bloating is also discussed as well as the effect that molding pressure has on bloating. It was found that molding pressure effects defect formation. Finally, this paper presents binder removal maps that were developed for specimens up to 8 mm thick. These bloating maps indicate the existence of two primary bloating regimes.