Sintering mechanisms of nascent semi-crystalline polymer powders by high velocity compaction
Résumé
A new technique, the High Velocity Compaction (HVC) allows the processing of nascent semicrystalline powders via sintering. It implies several controlled energy impacts on a powder-filled die. The die is heated up to a temperature below the melting temperature of the powder. Sintering occurs thanks to dissipation of a part of impacts energy which allows local heating and thus melting of a fraction of the powder. The aim of this paper is to evaluate the spatial localization of the part of powder which is melted during HVC process in order to estimate the quality of interparticular welding: "the sintering quality" and to deduce the most probable sintering mechanism. Two polymer powders are tested: PolyOxyMethylene and Ultra High Molecular Weight Poly Ethylene. This objective has been reached in particular thanks to local measurements of mechanical properties which have been performed by nanoidentation. It has been observed that a fraction of the nascent polymer undergoes melting-recrystallization during the process. Then, it is demonstrated that melting-recrystallization is needed to achieve sintering that would occurs by diffusion and intertwining of the chains at the melted state and also cocrystallization during the cooling. In light of these two mechanisms, the sintering quality is discussed in order to have an insight of HVC possibilities to process different type of polymers. © Springer/ESAFORM 2008.
Mots clés
Cocrystallization
Energy impact
High Velocity Compaction
Local heating
Local measurement
Melting temperatures
Nano-identation
Nascent powder
Polymer powders
Polyoxymethylene
Recrystallizations
Semi-cristalline polymer
Semi-crystalline polymer
Semicrystallines
Sintering mechanism
Spatial localization
Ultra-high molecular weight
Acetal resins
Compaction
Dies
Ethylene
Mechanical properties
Melting
Recrystallization (metallurgy)
Velocity
Sintering