Hot compaction of polyoxymethylene, part 1: Processing and mechanical evaluation

The hot‐compaction of polyoxymethylene powders in the solid state, otherwise pressure‐assisted sintering, is studied as an alternative way to the melt‐compression or injection molding processes. A native powder issued from suspension polymerization has been used, together with powders obtained from grinding of melt‐extruded pellets. The experimental conditions were optimized with regard to temperature, pressure, and time. Temperature is the most sensitive parameter of the process. Sintering at temperature close to the onset of the melting range turned out to be necessary for an efficient welding of the powder particles, as judged from mechanical properties. Despite a strong loss of ductility, the sintered samples have been easily machined out into strips for mechanical testing. A significant increase in crystallinity is observed for the sintered samples, as compared with the compression‐molded ones, accompanied with a nearly twofold increase of the Young's modulus. Scanning electron microscopy revealed that rupture of the sintered samples involves both inter‐ and intra‐granular fracture. Welding of the crystallites via molecular diffusion at the particle interface is suggested to be the mechanism of sintering. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1274–1284, 2006