Behaviour of films of regenerated cellulose in strongly alkaline environments. Estimation of non-homogeneity from ionic conductance

Abstract

Membrane conductance and other data have been analysed to evaluate the tortuosity factor, θ, from considerations of anionic mobilities within a regenerated cellulose film immersed in KOH solutions. Application of the equation θ=(1 +Vp)/(1 –Vp), where Vp is the volume fraction occupied by the gel framework in an homogeneous gel, indicated mobilities which were too high by 30–40%. It is proposed that these discrepancies arose from heterogeneity in the film due to the presence of a fraction x of non-ionically conducting, crystalline particles of cellulose. In the range of 0–3 mol dm–3 KOH x was approximately 0.32 in good agreement with the value of 0.36 determined from equilibrium ion-exchange measurements. x decreased to ca. 0.1 in 5.3 mol dm–3 KOH owing to ionisation and swelling of initially crystalline regions. Between 5.3 and 7 mol dm–3 KOH x showed an increase to ca. 0.35: this deduction is consistent with the formation of a new crystalline phase, potassium cellulose II. At KOH concentrations above 7 mol dm–3 there was an apparent decrease in x, probably related to the ionisation of secondary alcohol groups.