Assessing the potential of quartz crystal microbalance to estimate water vapor transfer in micrometric size cellulose particles

Abstract

This study aims at assessing the use of a quartz crystal microbalance (QCM) coupled with an adsorption system to measure water vapor transfer properties in micrometric size cellulose particles. This apparatus allows measuring successfully water vapor sorption kinetics at successive relative humidity (RH) steps on a dispersion of individual micrometric size cellulose particles (1 μg) with a total acquisition duration of the order of one hour. Apparent diffusivity and water uptake at equilibrium were estimated at each step of RH by considering two different particle geometries in mass transfer modeling, i.e. sphere or finite cylinder, based on the results obtained from image analysis. Water vapor diffusivity values varied from 2.4 × 10 m s to 4.2 × 10 m s over the tested RH range (0-80%) whatever the model used. A finite cylinder or spherical geometry could be used equally for diffusivity identification for a particle size aspect ratio lower than 2.

Impact of Two-Dimensional Particle Size Distribution on Estimation of Water Vapor Diffusivity in Micrometric Size Cellulose Particles

“…Water vapor diffusivity was calculated at different steps of relative humidity (RH) by fitting sorption kinetic curves ( Figure 5 ) with Equation (5) or Equation (10), depending on whether particle size distribution or a global indicator was used. As previously observed [ 23 ], the RH steps were difficult to adjust. That is why RH step was not incremented by constant steps.…”

“…The initial mass of cellulose ranged from 1 to 1.5 µg. A more detailed description of this preparation was given in the study of Thoury-Monbrun et al [ 23 ]. Knowing the total mass of deposited cellulose and that the mass of one particle of cellulose was around 5.7 × 10 −4 µg (value estimated from the true density of cellulose particles and the volume of one particle), it was calculated that around 2000 particles were deposited on each quartz substrate.…”

“…Equation (5) presents the product of the solutions for the radial part and the axial part of the diffusion to obtain the analytical solution for a finite cylinder where and are, respectively, the mass of water vapor sorbed in the cylinder at time t and at infinite time and positive roots of Equation (6) where is the Bessel function of the first kind of order 0. Details on this analytical solution can be found in Thoury-Monbrun et al [ 23 ]. …”

“…Diffusivity was also estimated from associated fibers, such as films or papers [ 5 ], or samples of raw biomasses, such as wheat straw, raffia, or wood [ 7 , 21 , 22 ]. Only one paper has been recently published on the estimation of water vapor diffusivity in micrometric size cellulose particles [ 23 ]. However, global descriptors of particle morphology have been used to estimate diffusivity, without considering the impact of the whole size distribution.…”

“…As regards to the dimensions that have to be used as input parameters in models, authors usually consider global descriptors for the size distribution e.g., median or mean, which implies to assume a homogeneous population of identical particles. Dealing with the estimation of water vapor diffusivity in particles with shape close to spheres or short cylinders, previous studies either considered the mean particle diameter in surface to assess water diffusion in maltodextrin powder [ 24 ], used the weight average radius that was evaluated by optical microscopy observations in the case of agave fibers [ 19 ] or used medians average in volume of diameter and length assessed by image analysis in the case of cylindrical cellulose particles [ 23 ]. Some authors demonstrated the importance of considering a dimensional particle size distribution (PSD) instead of a global descriptor to evaluate mass transfer properties in heterogeneous size particles [ 25 , 26 ].…”