Reducing the carbon footprint of Hevea rubber carbon composites using surface-modified fly ash

CO2 intensive carbon black (CB) as filler material in natural Hevea rubber-based composites needs to be partially replaced by suitable fillers. In this study, a novel surface modified filler (SuMo FA) was made by encapsulating fly ash (FA) with a polysulphide coating. This SuMo FA was hydrophobic, minimized leaching, and was morphologically ideal as partial replacement filler of CB in Hevea rubber-based composites. This SuMO fly ash and unmodified FA was compounded from 5, 10 and 20 parts per hundred rubber (phr) accounting for partial substitution of CB at 5, 10, 20 and 40 (by weight (wt%)), respectively. The tensile properties and Shore A hardness were practically unchanged with unmodified FA at 5 wt% CB replacement. SuMo FA performed better, retaining tensile properties up to 20 wt% CB replacement. Major decreases were seen only at 40 wt% CB replacement. Chemical crosslink densities decreased somewhat with increasing ash content, while thermal stability remained constant. The encapsulation reduced the leachability of toxic heavy metals from SuMo FA to below United States-Environmental Protection Agency limits opening up the use of such composites in consumer markets in addition to industrial ones. Thus, SuMo FA is a promising waste-derived filler that can be used to partially replace carbon black in rubber composites without loss of mechanical properties or thermal stability.