Strain-induced consolidation of partially disentangled polypropylene

Abstract

The role of entanglement of polymer chains in the merging and consolidation of polypropylene (PP) powder grains was elucidated. The entanglement density was varied by the dissolution of PP and precipitation. The differently entangled powders were sintered, without melting, applying severe plastic deformation by equal channel multiangular extrusion (ECMAE). Compaction by ECMAE resulted in healing of the interparticle pores, as well as the formation of a fibrillar structure, more significant in the case of disentangled PP. Lower entanglement density also led to the formation of thicker interfaces and to new crystals due to the strain-induced crystallization of slacks between entanglement knots. The consolidation of disentangled powder was drastically better than entangled PP powder: the yielding in compression occurred via crystallographic slips in the sintered disentangled powder while in the entangled PP powder through a series of weak elements and defects, due to much poorer compactness and cohesion. It was suggested that better consolidation of disentangled PP powder is due to reptation of longer slacks between entanglement knots and also due to sideway motions of their loops.

Keywords

• processing technologies
• polypropylene
• disentanglement
• sintering
• solid state extrusion