Developing polypropylene copolymer powder with a wide sintering window for laser powder bed fusion via extrusion and in-blend annealing

Abstract

Converting cheap resins like polypropylene (PP) copolymer into near-spherical powder materials with a wide sintering window (SW) is highly desired for broadening the feedstock palette for laser powder bed fusion (PBF-LB/P). Herein, a novel “melt extrusion-in blend annealing” strategy was proposed to achieve this aim, which involved dispersing the copolymer into a water-soluble matrix and then annealing the blend at temperatures near the melting point of the copolymer for a certain time. Spherical PP copolymer powders with largely widened SW (>30ºC) were obtained after removing the matrix. Two advantageous effects of in-blend annealing were identified. The first one was the elevation in the onset melting temperature due to crystal perfection. Another one was the decline in the onset crystallization temperature, which was suggested to relate to the migration of heterogeneous nuclei out of copolymer particles but required further verification. The obtained powder with optimized SW was fabricated into parts with low warpage at the cost of a slightly inferior mechanical performance possibly related to material degradation and changes in the crystal structure. The strategy proposed offers a promising prospect for developing new powders with optimized processing features for PBF-LB/P from commercially available resins.