Coal char as an economical filler for phenolic composites

Abstract

This work introduces coal char prepared by pyrolysis of subbituminous coal as a filler for compression-molded phenolic resin composites to improve the physical properties along with reducing material costs. The effects of filler concentration, particle size, and blending method on mechanical and thermal properties as well as morphology were comprehensively studied in comparison to reference materials. When simply blending resin and char powders, the highest compressive strength of 246 MPa with a Young's modulus of 5.0 GPa was reached using 50 wt% coal char, outperforming an equal amount of wood fiber (sawdust) as a filler with 198 MPa compressive strength and 3.2 GPa Young's modulus. Subsequently, different solvents were employed as dispersants to improve particle dispersion allowing for higher filler loads. Tetrahydrofuran (THF) enabled the best dispersion and led to compressive/tensile strengths reaching 288 MPa/75 MPa for 60 wt% coal char and 307 MPa/37 MPa for 70 wt% coal char. In addition, the phenolic/coal char composites showed a significantly higher thermal stability over the sawdust composite as well as a commercial phenolic composite. Water absorption studies also illustrated improved performance of coal char with and without the THF dispersant over sawdust in reducing moisture absorption. The findings of this work suggest that coal char has significant potential to be used as a filler in novolac composites for applications such as load-bearing building materials where high compressive strength, stiffness, thermal stability, water resistance, and low cost are required.