Characterization of the surface and physical properties of South African coal fly ash modified by sodium lauryl sulphate (SLS) for applications in PVC composites

摘要

The application of coal fly ash as mineral filler in polymers is hampered by the aggregation of the ash particles anda lack of interaction between the ash and polymer. Therefore surface treatment is usually performed on mineralfillers to enhance workability and compatibility between the polymer and filler. In this study, a commerciallyavailable South African coal fly ash sample was surface modified under a variety of conditions with an anionicsurfactant, sodium lauryl sulphate (SLS), with the aim to alter the surface properties of the ash. The propertiesof the modified products were compared to those of the untreated samples by means of scanning electron microscopy(SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA-IR), Fourier transforminfrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF). A smallshift of the S\O stretch vibration in FTIR spectra of SLS treated fly ash is indicative of interaction between flyash and SLS. Although the overall chemical composition of the SLS modified coal fly ash sample was not alteredextensively, significant changes could be observed in its physical properties. Contact angle measurements indicatedthat the hydrophilic surface of untreated fly ash was rendered hydrophobic after SLS treatment. SEM andTEM results showed agglomerates on the surface of most of the fly ash spheres. Feasibility tests of using fly ashsamples as filler in PVC indicated that SLS treated fly ash can successfully replace CaCO3 as filler in PVC under conditionsof low filler loadings.