Modification of Properties of Composites Based on Ultra-High Molecular Weight Polyethylene by Creating Two-Layer Coatings with Low Molecular Weight Polyethylene on Filler Particles: Synthesis, Properties, and Application in 3D Printing by Selective Laser Sintering

Composites with a two-layer coating consisting of ultra-high molecular weight polyethylene and a lower molecular weight high-density polyethylene are synthesized by the sequential two-step polymerization of ethylene on the surface of catalyst-activated Al₂O₃ particles to modify the properties of composite materials with the ultra-high molecular weight polyethylene matrix. The pressed specimens of the composites with the two-layer coating are characterized by the uniform distribution of components. The effect of composition of polymer coating of Al₂O₃ particles on the thermophysical and rheological properties of composite reactor powders and the deformation–strength properties of pressed specimens is studied. In nascent composite particles with the two-layer coating, the morphology of outer polymer layers is different and depends on the polymer type. The creation of two-layer coatings with the outer layer of a lower molecular weight polyethylene on filler particles renders it possible to realize the melt flowability of the composites at certain component ratios, while preserving deformation–strength characteristics at a high level. The proposed polymerization technique shows promise for development of ultra-high molecular weight polyethylene composite powders with the desired morphology and rheological characteristics suitable for selective laser sintering 3D printing. All synthesized composite powders based on Al₂O₃ spherical particles with one- and two-layer polymer coatings have shape close to spherical, repeating the shape of filler particles. In terms of rheological characteristics, they meet the requirements of selective laser sintering 3D printing and have free flowability, and the material of parts printed by this technology does not suffer from warping and shrinkage.