Nano-, meso- and macro-swelling characterization of impregnated compression wood cell walls

Wood cell walls when contacted with humid atmosphere or an aqueous solution containing electrolytes or polymers undergo the phenomenon of swelling. In this work, experimental data were produced to quantify the effects of the adsorption water and solutes, which were introduced in the material by equilibration with a solution used as osmotic reservoir. For this reason, different environmental setups have been developed, allowing the control of temperature, water chemical potential, and ionic strength during the sorption process. The aim of this paper is to describe three experimental setups, focused on different levels: at the nanometric scale, small-angle scattering at controlled humidity; at the mesoscopic scale, environmental scanning electron microscopy; and at the macroscopic scale, tensile stage involving immersion of samples in solutions. Applicability and efficiency of the three setups are described. Moreover, it was shown how the combination of the results obtained via the three methodologies can be compared to expectations from a general Equation of State (EOS approach), where wood swelling with water and salt solutions is presented as the dependence of the distance between adjacent cellulose fibrils on the osmotic pressure. The total pressure calculated takes into account chemical, colloidal and mechanical terms in the force balance of the wood cell wall.