Effects of dehydration on the apolar surface energetics of inorganic paper fillers

The surface energies of various inorganic fillers including kaolin clay, titanium dioxide, and talc were examined using inverse gas chromatography (IGC). In an earlier investigation that examined calcium carbonate fillers, dehydration by heating under a dry nitrogen purge had a substantial influence on the apolar (γLWS) and polar (γABS) components of surface energy as measured using IGC. Using the same approach, the influence of such conditioning on several inorganic fillers used in papermaking were determined using preconditioning IGC from 100 to 300 °C, and sequential isothermal analysis at 100 °C. Results from IGC analysis of titanium dioxides (rutile and anatase) were similar to precipitated calcium carbonate (PCC) for temperatures up to 200 °C. PCC was significantly more energetic after preconditioning at 300 °C, which may indicate the onset of significant thermal decomposition that titanium dioxides will not exhibit. Kaolin clay samples had relatively high apolar surface energy similar to that of the chalk samples. Calcination gave lower γLWS values that could not be accounted for by changes in the microporous structure. More likely the differences resulted from contamination of highly energetic surface sites with adsorbates other than water. Talc samples exhibited relatively high apolar surface energies that increased with preconditioning temperature. The results provided insight into the significance of water on the final adhesion properties of fillers in the sheet structure or coating layer.