Sustainable Debinding and Recovery of CO2-Soluble Binders

Abstract

Metal and ceramic forming applications using conventional binders are associated with a number of environmental problems such as toxic emissions and carcinogenic wastes released from conventional binder removal processes. Here, we examine several materials as possible binder candidates for a sustainable technology wherein the binder can be recovered and recycled by supercritical carbon dioxide. The candidates include an acetylated sugar, β-d-galactose pentaacetate, and two tert-butyl aromatics, 1,3,5-tri-tert-butylbenzene and 2,4,6-tri-tert-butylphenol, which have significantly high solubility in supercritical carbon dioxide. We have demonstrated high-pressure carbon dioxide debinding of sand molds, each bound with candidate binders, at moderate temperatures and pressures. Practical operating conditions are suggested from the complementary binder–carbon dioxide phase behavior studies. Compared to solvent debinding, these novel binders exhibit rapid dissolution into supercritical CO2 due to enhanced transport properties. With high supercritical CO2 debinding efficiency, these materials are promising for developing more sustainable material forming processes, where toxic emissions and hazardous wastes of conventional debinding techniques can be eliminated, and materials recycling and reuse can be achieved.