Water sorption isotherms of Kraft lignin and its composites

The water sorption properties of Kraft lignin before and after treatment with the enzyme laccase, and its composites with branched polyethylenimine and chitosan, respectively, have been studied. The experimental sorption isotherms were obtained by dynamic vapour sorption (DVS) method. The data were analysed using the Brunauer–Emmett–Teller (BET) and Guggenheim–Anderson–de Boer (GAB) models. Monolayer capacity and surface area of the samples were determined by the BET model, showing an increase in these values for the composites. Application of the GAB model over the whole range of humidities (0–95%) gave a perfect correlation between experimental and calculated sorption isotherms using the nonlinear least squares fitting (NLSF).