ACID-BASE SURFACE-ENERGY CHARACTERIZATION OF MICROCRYSTALLINE CELLULOSE AND 2 WOOD PULP FIBER TYPES USING INVERSE GAS-CHROMATOGRAPHY

The surface energetics of three cellulosic solids are characterized in terms of their propensity to enter into Lifshitz-van der Waals and Lewis acid-base interactions with carefully-selected monofunctionally acidic and basic probes. The interactions are examined by vapor adsorption measurements, using the technique of inverse gas chromatography (IGC). Adsorption characteristics are studied beyond the region of infinite dilution along the adsorption isotherm, i.e., full adsorption isotherms are developed for the probes on the solid surfaces, from which the relative distributions of solid surface site energetics are determined. The differential distributions are uniquely expressed in terms of the potential for entering into acid-base interactions. The three surfaces exhibit both acidic and basic character but are predominantly acidic in nature. Probe molar areas are determined from a fit of the BET model of adsorption to the isotherms develop for one of the fiber surface types. These areas are then used in all computations of the work of adhesion from the Gibbs free energy change upon adsorption. Finally, from the thermodynamic functions evaluated at 2% coverage of the solid surfaces, descriptors of the acid-base nature of the three cellulosic materials are determined using models of the enthalpy of acid-base adduct formation within the framework of Fowkes' model of the acid-base contribution to the work of adhesion. Values of modified Fowkes-Gutmann parameters are reported, which suggest that the solid surfaces are predominantly acidic.