Processability and Mechanical Properties of Polyoxymethylene in Powder Injection Molding

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Polyoxymethylene (POM) is considered a high performance engineering polymer with many applications primarily in the automotive industry. Currently, POM has also found uses in powder injection molding (PIM) technology, where it acts as a carrier medium for metal or ceramic powders during the injection molding process, it is later removed and a metallic or ceramic piece is obtained after sintering. The main advantage of using POM in PIM technology is the faster debinding process compare to polyolefin-based feedstock, since POM sublimates into its monomer directly when exposed to an acid vapor. During the process of PIM, the binder has two contradictory requirements: viscosity should be as low as possible when in the molten state, but mechanical properties in the solid state, like toughness, should be as high as possible. One way to lower the viscosity is to use POM with lower molecular weights. In this work it has been observed that the viscosity follows a power law function as with other linear polymers, while the fracture toughness follows an exponential function of the average molecular weight. Therefore, a molecular weight can be chosen in a way that a compromise between low enough viscosity and sufficient fracture toughness can be reached.