Water-soluble binder with high flexural modulus for powder injection molding

A new binder system, containing ternary polymer blends of poly(methyl methacrylate) (PMMA), cellulose acetate butyrate (CAB) and polyethylene glycol (PEG), was introduced for the powder injection molding of stainless steel powders. The weight fraction of PEG in the binder was maintained to be 0.65. When the weight fraction of PMMA in the binder was 0.1–0.25 (thus the weight fraction of CAB was 0.1–0.25), the feedstocks with 56 vol% of steel powders were successfully injection molded without showing any jetting. Furthermore, the feedstocks have much higher flexural modulus compared with those prepared by a binder consisting only 35/65 (wt/wt) CAB/PEG blend. Three binary blends, PMMA/CAB, PMMA/PEG, and CAB/PEG, were completely miscible at an injection molding temperature of 130◦C. The extraction process employed in this study becomes environmentally favorable due to the major component (PEG) of the binder which is easily extracted by a solvent of water or ethanol. Also, the shape maintenance during the solvent extraction was excellent, and final sintered parts had excellent dimensional stability. Due to high flexural modulus of feedstocks, this binder system can be employed for preparing large sized injection-mold articles. C 2005 Springer Science + Business Media, Inc.