Structure–property interface correlation of fly ash–isotactic polypropylene composites

Composites of isotactic semicrystalline polypropylene (PP) reinforced with fly ash (FA) particles (particle size 5–60 μm) were prepared by injection moulding at 210 °C incorporating 20, 45 and 60% by weight of fly ash. Tensile tests were carried out at 25, 50 and 70 °C. WAXRD, DSC and SEM studies were also undertaken. Modulus of elasticity of all composites at all temperatures was higher than that of the corresponding PP samples—the gain ranged between 10 and 60%. The strength of the composites had a mixed trend. At 25 °C, the composites suffered significant loss in strength, as much as 47%, whereas, at 50 and 70 °C, there was up to 15% gain in strength. Strain to failure of the composite samples ranged from as low as 6% at 25 °C to over 50% at 70 °C, coinciding with increase of Pukanszky parameter from 1.5 to 4.1. WAXRD and DSC tests confirm that FA is nucleator of β-crystalline phase the amount of which increases to a maximum of 11% with increasing FA. SEM studies indicated that the polymer had a distinctly high lamellar ductility and showed interfacial interaction with FA in 20% FA composites at 50 and 70 °C. The –OH group on the surface of FA appears responsible for the formation of interfacial interaction with PP chain. Notched Charpy tests showed a maximum gain of 58% impact energy for the composite with 45% FA, tested at 70 °C over that of pure PP at 25 °C.