Evaluation of Coupling Agents in Poly(propylene)/Fly Ash Composites: Effect on Processing and Mechanical Properties

Composites containing 50 wt.-% fly ash in a PP homopolymer were prepared via batch mixing and compression moulding. The following coupling agents were evaluated: Lubrizol Solplus C800, N,N'-(1,3-phenylene)dimaleimide, gamma-methacryloxypropyltrimethoxysilane and maleic-anhydride-grafted PP. At the filler level investigated, C800 gave the best balance of composite strength and toughness. In the latter case filler-matrix adhesion appeared weaker relative to gamma-MPS, BMI and m-PP, all of which gave excessively strong filler-matrix adhesion leading to a reduction in composite toughness. The unexpected weakness of the C800/fly ash interaction may be related to removal of surface calcium ions from the fly ash via reaction of a single calcium ion with two C800 molecules.