Debinding behaviour of a water soluble PEG/PMMA binder for Ti metal injection moulding

Polyethylene glycol (PEG) has been becoming a common component in the design of water soluble binder systems for metal injection moulding. Similar to solvent debinding, PEG can be leached out by water and the mechanism of debinding was proposed in the literature with somehow misleading information about the debinding mechanism, particularly about the formation of PEG gel. This work investigates the debinding behaviours of a PEG-based binder in titanium compacts. Titanium powder is formulated with PEG, poly(methyl methacrylate) (PMMA) and stearic acid (SA) to formulate titanium feedstock. To determine the debinding kinetics, the PEG removal percentages are measured at three different temperatures and for various specimen thicknesses. A mathematic model based on diffusion-controlled debinding process is established. The evolution of porous microstructure during the water debinding process is observed using scanning electron microscopy. Based on these observations, a water debinding mechanism for titanium alloy compacts formulated with PEG-based binders is proposed.

► The water-debinding behaviours of the PEG binder system were investigated.
► PEG dissolution and transportation, and the pore structure development.
► A water debinding mechanism of PEG-based binders is proposed.
► Incorrect explanation of PEG gelling in the literature is corrected.
► Correction/modification made as per the reviewers' comments and suggestions.