3D Printing of sustainable coal polymer composites: Thermophysical characteristics

Recently, there has been a growing interest in enlisting polymer-based additive manufacturing in high-volume structural applications such as wind turbine blade tooling and additive housing construction. However, the availability of sustainable and environmentally friendly 3D printable materials could present a serious challenge, precluding the technology expansion to such applications. This research was focused on developing sustainable and environmentally friendly coal-plastic composites for use in high-volume applications. Polylactic acid, polyethylene terephthalate glycol, high-density polyethylene, and polyamide-12 resins were melt-mixed with bituminous Pittsburgh No. 8 coal at loadings varying from 20 wt % to 70 wt % coal. Thermoplastic composite filaments were extruded and processed with commercial 3D printers. Important thermophysical properties including coefficients of thermal expansion, heat deflection temperatures, glass transition and melt temperatures, specific heat capacities, thermal conductivities, and thermal stabilities of the coal-plastic composites were investigated. Coefficient of thermal expansion values for the composites had an inverse relationship with coal content lending to decreased print warping and consistent 3D printing of high-density polyethylene materials. Coal increased the heat deflection temperature of high-density polyethylene composites while little to no effect was observed for the other plastics. All composites maintained comparable melt temperatures, allowing for processing with commercial equipment. Specific heat capacity and thermal conductivity decreased with coal loading for all composite materials. Thermogravimetric analysis under air showed that the introduction of coal improved the thermal stability of all plastics by increasing the decomposition temperatures at 5 % and 50 % weight loss and by reducing the maximum decomposition rates.