3D Printing of Sustainable Coal Polymer Composites: Study of Processing, Mechanical Performance, and Atomistic Matrix-Filler Interaction

Bituminous coal was utilized as a particulate filler in polymer-based composites to fabricate standard 1.75 mm coal-plastic composite filaments for material extrusion 3D printing. The composites were formulated by incorporating Pittsburgh No. 8 coal into polylactic acid, polyethylene terephthalate glycol, high-density polyethylene, and polyamide-12 resins with loadings ranging from 20 to 70 wt %. Coal-plastic composite filaments were extruded and printed by using the same processing parameters as the respective neat plastics. The introduction of coal ameliorated the warping problem of 3D printed high-density polyethylene, allowing for additive manufacturing of an inexpensive and widely available thermoplastic. The mechanical properties of the 3D printed composites were characterized and compared to those of composites fabricated using traditional compression molding. Microscopy of as-fractured samples revealed that particle pull-out and particle fracture were the predominant modes of composite failure. Tensile and flexural moduli as well as hardness had direct proportionality with increasing coal content, while flexural strength, tensile strength, and impact resistance decreased for most composite formulations. Interestingly, polyamide-based composites demonstrated greater maximum tensile and flexural strengths than unfilled plastic. Investigation of composite interfacial chemistry via molecular dynamics simulations and Fourier-transform spectroscopy revealed beneficial hydrogen bonding interactions between coal and polyamide-12, while no chemical reactions were evident for the other polymers investigated.

Automated summary

This article discusses the use of coal-plastic composite materials in 3D printing. By incorporating coal as a filler into different types of polymer resins, the researchers successfully fabricated composite filaments. The study found that the addition of coal improved printing issues with high-density polyethylene and that the mechanical properties of the composite materials were influenced by the amount of coal added.