Poly(butylene terephthalate)\nfor Laser Powder Bed\nFusion of Polymers: Feedstock Precipitation and Powder Characterization

Powder bed fusion of polymers with a laser beam (PBF-LB/P)\nis a\nlayer-based additive manufacturing method that excels in producing\nfunctional components of complex geometries. However, the limitation\nof commercially available materials to mostly polyamides reduces the\nrange of applications for PBF-LB/P-processed parts. Recently, liquid−liquid\nphase separation and crystallization have been reported as a suitable\nmethod to produce poly­(butylene terephthalate) (PBT) microparticles\nof good flowability as a PBF-LB/P feedstock. PBT is an interesting\nplastic feedstock as its properties allow for an extension of the\napplication of AM-built parts in the automotive and electronics sectors.\nStarting from PBT feed materials with different molar mass distributions,\nwe investigate the effect of the feed material used in the thermal\nprecipitation process under otherwise identical process parameters\non the resulting PBT powder properties. The thermal precipitation\nprocess is highly robust with respect to bulk solid properties, such\nas particle size distribution, particle shape, flowability, and intrinsic\nproperties (crystal structure and melting behavior). These product\ncharacteristics are virtually unaffected by the average molar mass\nof the PBT feed. Melt crystallization is accelerated, while the viscosity\ndecreases with decreasing molecular mass. Once favorable process conditions\nare defined, which lead to powders with suitable properties, the crystallization\nkinetics and melt viscosity can be adjusted accordingly without changing\nthe powder properties. Key parameters, which influence part porosity\n(through melt coalescence), layer adhesion, or the tendency of the\nmaterial to warp during the PBF-LB/P process, are adjustable to produce\na customized starting material.