Sintering mechanisms involved in high-velocity compaction of nascent semicrystalline polymer powders

A new technique, high-velocity compaction (HVC), allows the processing of nascent semicrystalline polymer powders via sintering. For the two polymers studied, polyoxymethylene (POM) and ultra-high molecular weight polyethylene (UHMWPE), it has been observed that during HVC a fraction of the nascent polymer undergoes melting. After cooling, the material thus comprises both nascent polymer that has not undergone melting and melted–recrystallized polymer. First, the localization of the melted–recrystallized polymer is investigated by microscopic techniques and nanoindentation. This reveals that melting occurs first at particle interfaces. Then, it is demonstrated that welding of the particles occurs via chain diffusion and recrystallization during the cooling. The efficiency of these welding mechanisms is discussed in order to gain an insight into the possibilities of using HVC to process different types of polymers. In addition it is shown that for a given material the overall sintering quality is governed by the fraction of recrystallized material.