Characterisation of the surface of a cellulosic multi-purpose office paper by inverse gas chromatography

The surface of multi-purpose cellulosic office paper has been analysed by inverse gas chromatography (IGC). The parameters determined were the dispersive component of the surface free energy, the enthalpy of adsorption and the entropy of adsorption of polar and apolar probes, the Lewis acidity constant, K-a and the Lewis basicity constant, K-b. It can be concluded that the dispersive component of the surface free energy, gamma (d)(s) decreases with temperature, in the range 50-90 degreesC. The temperature coefficient of gamma (d)(s), d gamma (d)(s)/dT, is -0.35 mJm(-2)K(-1). The values of K-a and K-b were determined to be 0.11 +/- 0.011 and 0.94 +/- 0.211, respectively. The predominant surface basicity agrees with expectation, bearing in mind the presence of calcium carbonate, and of a styrene-acrylic copolymer, in the surface sizing formulation. It is thought that during the drying stages following the surface sizing treatment, the starch used as the binder migrates to the interior of the surface sizing layer and then to the paper bulk itself. This migration contributes to a decrease in the hydrophilicity of the surface, and also results in the surface showing only slight Lewis acidity.