Apparatus for gravimetric measurement of moisture sorption isotherms for 1-100 g samples in parallel

This article presents a new apparatus for collecting water vapor sorption isotherms in parallel with example data from acetylated and thermally modified loblolly pine. The experimental setup consists of an enclosure that is continuously flushed with a carrier gas of known RH supplied by an RH generator and a balance with precision of 0.1 mg. All samples are placed on the balance and the mass is monitored as a function of time. At a given RH, the measurements are stopped when the change in the total mass of all samples are less than or equal to a change in MC of 0.1 μg g-1 min-1 (0.000 01%) per minute over a 24 h window. The sorption isotherms effectively differentiated the wood modifications; isotherm models fit the data extremely well (R2 ≥ 0.95 for all treatments). A comparison of the data with measurements on the same specimens conditioned over saturated salt solutions shows that the method is comparable with isotherms acquired over saturated salts. When compared with the saturated salt solution method for collecting isotherms, this method requires less labor. Furthermore, unlike traditional dynamic vapor sorption methods, this apparatus easily allows multiple macroscopic samples to be run in parallel.