Abstract:
Urea is a low cost material with thermal and mechanical properties suitable for use in investment
casting pattern molding compounds. Conventional compounds are made by a “cooking” process
wherein the urea is added to and dissolved in an aqueous solution of a water soluble polymer
followed by evaporation of the water. Here we describe novel formulations based on either
polyvinyl alcohol (PVOH) plasticized by glycerol or ethylene vinyl acetate (EVA) resins together
with wax that can be prepared by a facile twin-screw compounding process. The thermo-mechanical
properties of these compounds were characterized using differential scanning calorimetry (DSC),
thermo gravimetric analysis (TGA), dynamic mechanical analysis (DMA) and three bend point
tests. The PVOH-based molding compounds featured better mechanical properties than those based
on EVA. Increasing the polymer content produced weaker but tougher molding compounds.
Increasing wax content improved stiffness but resulted in a loss of toughness. The TG results
showed that both compounds decomposed readily at elevated temperatures and left less than 3 wt.
% ash at 800°C.
