HDPE@UHMWPE Powders for Power Bed Fusion Based Additive Manufacturing

• Published in: Macromolecular materials and engineering Vol. 307; no. 7
• Main Authors: Wencke, Yannick L., Proes, Friedrich, Imgrund, Phillip, Luinstra, Gerrit A.
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 01-07-2022
• Subjects: Caking; Carbon black; catalyst support; Embossing; in situ ethylene polymerization; Laser beam welding; Laser sintering; Manufacturing; mechanical properties; powder bed fusion; Powder beds; Ring shear tests; Silicon dioxide; Sintering (powder metallurgy); thermal sintering; Toluene; UHMWPE; Ultra high molecular weight polyethylene
• ISSN: 1438-7492; 1439-2054
• DOI: 10.1002/mame.202100964

Commercial UHMWPE powder of 60 µm size (d50) embossed with 2–5 wt% of nanosilica is used as a support for the preparation of core–shell HDPE@silica@UHMWPE particles. The HDPE shell is generated by polymerization of ethylene in toluene slurry after treatment of the silica@UHMWPE with a methyl aluminoxane activated bisimine pyridine iron complex. Heat pressing the powder gives a solid material with identifiable original UHMWPE particles and a layer from fusion of UHMWPE and the surrounding HDPE shell; the properties match those of the UHMWPE base material. The powder flow properties of the HDPE@silica@UHMWPE are insufficient for a powder bed fusion process, a value for the flow function between 2 and 3 is measured in a ring shear tester. Additivation with nanosilica helps to overcome the insufficient flowability and allows the material to be recoated in a power bed fusion system. Laser sintering gives evidence for a substantial mixing and welding of the HDPE shells and UHMWPE. Caking at the surface of the built parts hinders the manufacturing of isolated parts. Further additivation with carbon black reduces the caking; however, the welding within the HDPE@silica@UHMWPE material is much less strong.
UHMWPE powder is imprinted with nanosilica powder in a high energy mixing procedure. Methyl aluminoxane activated iron bisimine pyridine catalyst is fixated onto the particles and ethylene is polymerized onto the surface. The resulting HDPE@silica@UHMWPE particles are sintered thermally and by laser energy. The material properties of build parts and flow properties of powders (after additivation with nanosilica) are reported.