Toward the Direct Synthesis of HDPE Powders for Powder Bed Fusion Based Additive Manufacturing

Abstract

AbstractPowder bed fusion (PBF) suitable polyethylene particles are targeted by means of a direct synthesis, using a bisimino pyridine iron catalyst (BIP FeCl2) supported on microsized silica particles. An active support is generated by treating spray dried silica microparticles with a methyl aluminoxane activated BIP FeCl2 catalyst in toluene. Semibatch ethylene polymerization is mapped with respect to pressure, temperature, and reaction time to find optimal reaction parameters. The optimized synthesis leads to round polyethylene particles with a median size of ≈50 µm which have a sinter window of 8–15 °C and an unconfined yield stress (ffc) of 1.5 in a ring shear tester. The Young modulus of injection molded samples is in the range of 150–250 Pa with an elongation at break of about 30%. The powder flowability is improved by coating with nanosilica powder to an ffc of 3.8. Additivitation with carbon black allows to laser sinter the powder to solid parts in a small scale adapted setup for selective laser sintering (PBF/laser beam (LB)/P). Severe caking is preventing the preparation of CAD model conform parts. Commercial HDPE powder for PBF is additivated the same way to give substantially solid built parts, but with similar caking.