No abstract

Conventional polymer processes, such as injection and extrusion, require the melting of the polymer. High-velocity compaction (HVC) allows the processing of polymer powders via sintering without the need of a melting stage. It opens up a new horizon for polymers that have processing issues linked to the melting stage. Because of chemical degradation above the melting point and significant shrinkage, the injection of semicrystalline polymer polyoxymethylene (POM) is often problematic. Nascent, highly crystalline POM powder has been successfully processed by HVC, and this process appears to be an interesting alternative to injection for certain applications. POM processed by HVC has a remarkably high stiffness but is brittle. A microstructural investigation, involving differential scanning calorimetry experiments and scanning electron microscopy, has been conducted to explain these unusual mechanical properties. It appears that in POM processed by HVC, the stiffness is due to particularly high crystallinity, and brittleness is intrinsic to nascent POM powder.