Nucleation and impact modification of polypropylene laser sintered parts

Abstract

Selective laser sintering (SLS) is a manufacturing technology whereby parts are built through layerwise application and selective consolidation of a polymer powder by a laser. With this additive manufacturing technology, polymer parts can be built with nearly no limits to complexity and nearly without geometrical constraints. Recently, a handful of polypropylene (PP) materials has been added to the rather limited portfolio of laser sintering powders. In conventional extrusion, the use of nucleating agents to increase clarity and impact resistance of PP is widespread. The current investigation focusses on the use of a nucleating agent in the SLS process to improve the mechanical properties of PP parts. Using a nucleating agent is not without challenges. It must be assured that addition of the agent does not change the thermal properties of the polymer in such a way, that the requirements of the SLS process cannot be met. On the other hand, it must be assured that the nucleating agent becomes effective, even without the intensive mixing of conventional extrusion. In this study, a polypropylene laser sintering material was dry blended with the sorbitol-based 1,2,3-trideoxy-4,6:5,7-bis-O-[(4-propylphenyl)methylene]-nonitol soluble nucleating agent and processed on an SLS machine with various process parameters. Effectiveness of the nucleating agent was confirmed with DSC, and a significant increase of impact resistance could be achieved, without compromising the processability of the material.