Waste derived polysulphide coating on fly ash as fillers in plastic composite

Abstract

Modifying fly ash (FA) for filler application can facilitate a cleaner, high volume and high value-application of FA. One of the major hurdles of utilizing unencapsulated FA as fillers is due to its hydrophilicity and tendency to leach out metals. The current study aims to develop a surface-modified FA (SuMo FA) as a suitable filler by coating it with a cross-linked polysulfide polymer from waste sulphur and oil derivatives. A Class F FA was coated with an in-house developed polysulfide polymer and was followed by a series of physicochemical analysis and 24-h batch leaching tests. This SuMo FA was compounded within PP and PE matrix and its thermo-mechanical properties were evaluated. The novel SuMo FA was ideal for filler application as it exhibited suitable spherical shape and size, hydrophobicity (contact angle ≅120°), and reduced leaching potential. Major contaminants (B, Cr, Pb, and Sr) in leachate of SuMo FA decreased by more than one order. Compounding the SuMo FA in polypropylene (PP) and polyethylene (PE) at 20 % (by weight) increased the onset temperature as compared to virgin polymers as well as filler-based polymers (with uncoated FA and CaCO3). Similarly, the SuMo FA filled polymers exhibited the best overall mechanical properties (under flexural and tensile loading) as well as notch impact strength. The Shore D hardness implies that SuMo FA filled polymers were almost identical to the conventionally used CaCO3 filled polymers. The leachate concentration of final PP composites with FA and SuMo FA fillers were lower than the regulatory limit for B, Ba, Cr and Sr. The developed filler material from the SuMo FA can potentially reduce dependence on relatively costly CaCO3 fillers in polymer production thus adhering to United Nation sustainable development goals (6 and 12).