Inverse gas chromatography, IGC, has been used to investigate the surface properties of calcined kaolins and the effect of the mechanical properties of a Nylon-6 composite containing the clay. Modification of the kaolin with an aminosilane coupling agent lowered its surface energy so that it was comparable with that of the polymer matrix and changed the surface from being acidic to being predominantly basic. The surface of the nylon was also found to be basic but susceptible to hydrogen bonding. Incorporation of the kaolin into nylon changed the mechanical properties, raised the modulus and toughness of the materials. Better results were achieved for the coated kaolin than the uncoated material and this correlated with the surface energy measurements.

Inverse gas chromatography, IGC, has been used to investigate the surface properties of two calcined kaolins and of polyethylene composites containing calcined kaolin. The results reveal differences in the two kaolins that were not found in XPS spectra nor in their influence on the melting behaviour of the polymer. The kaolin that had a markedly higher surface energy and stronger Lewis acid behaviour was found to shower greater photooxidative degradation in accelerated weathering tests. This novel application of IGC derived surface characterisation of solids further extends the usefulness of the method in this type of work.

Inverse gas chromatography (IGC) has been used to characterize the surfaces of a pure calcitic calcium carbonate as well as samples that had been treated with sodium polyacrylate and/or stearic acid. The dispersive components of the surface free energy for the pure material agreed well with related literature data. Polar contributions to the surface interactions with a range of probes were determined. The results show that the surface treatments reduced the polarities of the surfaces and that modification with stearic acid produced a non-polar, low-energy surface. Some mechanical properties of the polypropylene composites containing the modified calcium carbonates were found to correlate well with the filler surface energies.