Adapting gravimetric sorption analyzer to estimate water vapor diffusivity in micrometric size cellulose particles

This study aims at developing a reliable and simple-to-implement methodology for the estimation of apparent water vapor diffusivity at the scale of micrometric size cellulose particles based on gravimetric measurements. The water vapor apparent diffusivity value was evaluated by using a quartz crystal microbalance (QCM) on a cellulose sample of 1 µg was 4 × 10⁻¹² m² s⁻¹. Water vapor sorption kinetics at successive relative humidity (RH) steps were measured using a dynamic vapor sorption (DVS) microbalance by testing two types of sample preparation, i.e. either a powder bed or a compressed tablet. Water vapor apparent diffusivity was identified at each RH step by employing an analytic solution corresponding to the sample type: plane sheet for both powder bed and tablet considered as porous media and finite cylinder for a population of particles. The impact of the initial cellulose sample mass was also investigated. Water vapor diffusivity values varied from 6 × 10⁻¹⁵ to 4 × 10⁻¹⁰ m² s⁻¹ depending on the sample mass, sample preparation mode, analytic solution and/or sample porosity. The DVS-based methodology was compared to the value obtained from QCM measurements.