Chemistry of removal of ethylene vinyl acetate binders

The research presented herein has focused on debinding of an ethylene copol ymer from a SiC based moulded ceramic green body within an inert atmosphere . Upon heating, the pure polymer undergoes a two-stage thermal degradation process. In the first stage, acetic acid is the only degradation product fo rmed. The effect of the introduction of high surface area powder on the che mistry and kinetics of this first stage reaction was examined. The effluent s were captured and analysed in a gas chromatograph/mass spectrometer. The product of the reaction was not altered by introduction of the ceramic powd er. However, the kinetics of the reaction were altered. The kinetics of the reaction were determined with the use of thermogravimetric analysis (TGA). The mechanism of mass transport during binder removal was determined by mo nitoring dimensional changes during binder removal. It was found that one u nit volume of shrinkage corresponded with one unit volume of binder removed , indicating that no porosity developed. The escaping acetic acid effluents must diffuse through the liquid polymer filled pores to escape. Bloating w as observed in certain conditions and was attributed to the concentration o f acetic acid exceeding a critical value, resulting in bubbling. (C) 1998 K luwer Academic Publishers.