Development and performance evaluation of polypropylene composite reinforced with coal bottom ash modified via esterification and hydrothermal processes

Coal bottom ash (CBA) is one of the by-products of coal combustion from the power plant to generate electricity. However, due to its hygroscopic and porous structure, it has not been the interest of many researchers. Therefore, it is left unattended at the landfill and hence has now become the main dumping issue and environmental concern as it contains potential toxic elements such as As, Cd, Co, Cu, Cr, Mo, Ni, Pb, and Zn. Therefore, this study has modified this CBA to tackle the hygroscopic and porosity characteristics of CBA via esterification, mCBAE, and hydrothermal, mCBAH processes, respectively. The hygroscopic and porous structures of CBA have been minimized by both esterification and hydrothermal processes, respectively. These modified CBAs, mCBAE and mCBAH, were then used as fillers to develop green polypropylene (PP) and a PP composite. PP composites are materials made by combining a polymer matrix with fillers or reinforcements to enhance their mechanical, thermal, or other properties. In this case, the strength of the PP composite depends on the process conditions. It was found that the highest strength of the PP composite was obtained when CBA was modified via the esterification process at 40°C for 4hr using 75 g of palmitic acid as a surface modifier, PP/mCBAET40P75t4. Unfortunately, CBA modified via the hydrothermal process (mCBAH) was unable to form a smoother composite surface due to the decomposition of less thermally and mechanically stable minerals formed during the hydrothermal process when CBA reacts with a strong base. PP/mCBAET40P75t4 was further modified using maleic anhydride (MA) as a binder to enhance its strength. It was found that the addition of 1% MA binder was able to enhance the impact energy of PP/mCBAET40P75t4 from 3.75 J to 4.11 J, which is about a 10% increment. In addition, this 4 mm PP/mCBAET40P75t4 containing 1% MA was able to improve the impact energy of 6 mm neat PP (2.9 J) up to 40. Overall, the properties of this PP/mCBAET40P75t4 containing 1% MA were almost similar to the physical, chemical, mechanical, and electrical properties of pure PP, but with better strength. Therefore, for future work, it is recommended that this PP/mCBAET40P75t4 containing 1% MA be used to replace PP-based products across various applications, such as cable protection slabs, cable clips, and dashboards etc., to support sustainable, cost-efficient material development.