Abstract:
The application of coal fly ash as mineral filler in polymers is hampered by the aggregation of the ash particles and
a lack of interaction between the ash and polymer. Therefore surface treatment is usually performed on mineral
fillers to enhance workability and compatibility between the polymer and filler. In this study, a commercially
available South African coal fly ash sample was surface modified under a variety of conditions with an anionic
surfactant, sodium lauryl sulphate (SLS), with the aim to alter the surface properties of the ash. The properties
of 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 transform
infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF). A small
shift of the S\O stretch vibration in FTIR spectra of SLS treated fly ash is indicative of interaction between fly
ash and SLS. Although the overall chemical composition of the SLS modified coal fly ash sample was not altered
extensively, significant changes could be observed in its physical properties. Contact angle measurements indicated
that the hydrophilic surface of untreated fly ash was rendered hydrophobic after SLS treatment. SEM and
TEM results showed agglomerates on the surface of most of the fly ash spheres. Feasibility tests of using fly ash
samples as filler in PVC indicated that SLS treated fly ash can successfully replace CaCO3 as filler in PVC under conditions
of low filler loadings.
