Selection of appropriate polyoxymethylene based binder for feedstock material used in powder injection moulding

Abstract

Polyoxymethylene (POM) has found applications as a binder material in Powder Injection Moulding (PIM) due to its ability to depolymerize rapidly under acidic conditions. Such ability represents an advantage during the binder removal step of PIM. However, currently available POM has high viscosity that can complicate the injection moulding process of parts with complex geometry. For this reason it is necessary to investigate methods of lowering the viscosity of POM-based binders, but without affecting their solid mechanical properties (i.e. creep compliance). In this investigation, the addition of a low molecular weight polymer, and the reduction of the average molecular weight of POM were investigated as possible ways of decreasing the viscosity of PIM binders. The addition of the low molecular weight additive (WAX) caused a small decrease in the viscosity of the POM-based binder and a small increase in its solid creep compliance. On the other hand, lowering the average molecular weight of POM caused a large decrease in viscosity, but also an acceptable increase in creep compliance. Therefore, by selecting an appropriate molecular weight of POM, it is possible to improve the performance of POM-based binders for PIM.