Polyethylene-based and polypropylene-based composites, incorporating silica nanoparticles and geopolymers, were prepared by melt compounding. Scanning electron microscope (SEM) images indicate that the silica nanoparticles do not distribute uniformly as fine particles in the matrix, but are unevenly distributed as clusters. As a result, the tensile properties of those composites are inferior to those of the matrix polymer. A novel concept of in situ formation of a reinforcing phase has been investigated as a method of resolving that problem. The reinforcing elements are microcrystalline phases developed during melt processing of mixtures of geopolymer precursors with polyethylene or polypropylene. Preliminary tensile test data on injection moulded specimens show some improvement in mechanical properties of both geopolymer–polyethylene and geopolymer–polypropylene composites relative to the matrix polymers. Scanning electron micrographs clearly show the presence in the composites of a nanoscale acicular crystalline structure that is thought to act as a fibre-like reinforcement.
