RESUMEN
The impregnation process of Scots pine and beech samples with tannin solutions was investigated. The two materials involved in the process (impregnation solution and wood samples) are studied in depth. Viscosity of mimosa tannin solutions and the anatomical aspect of beech and Scots pine were analysed and correlated. The viscosity of tannin solutions presents a non-newtonian behaviour when its pH level increases, and in the case of addition of hexamine as a hardener, the crosslinking of the flavonoids turns out to be of great importance. During the impregnation of Scots pine (Pinus sylvestris L.) and beech (Fagus sylvatica L.), the liquid and solid uptakes were monitored while taking into consideration the different conditions of the impregnation process. This method allowed to identify the best conditions needed in order to get a successful preservative uptake for each wooden substrate. The penetration mechanism within the wood of both species was revealed with the aid of a microscopic analysis. Scots pine is impregnated through the tracheids in the longitudinal direction and through parenchyma rays in the radial direction, whereas in beech, the penetration occurs almost completely through longitudinal vessels.
RESUMEN
Tannin-based rigid foams of different bulk densities and their carbonized counterparts were investigated for the first time by X-ray microtomography. This method allowed acquisition of three-dimensional pictures of such highly porous materials. Through mathematical treatment of the images, extremely useful physical characteristics such as porosity, fraction of open cells, connectivity, tortuosity, and pore-size distribution were determined as a function of the foam's density. The obtained information was compared with independent data derived from pycnometry measurements and scanning electron microscope image analysis. The agreement was shown to be acceptable in the limit of the accuracy of the laboratory microtomograph (4 microm). Moreover, recalculating properties like permeability were shown to be quite possible based on the results of standard microtomography data.
RESUMEN
Tannin-based rigid foams, prepared from 95% natural material, are suggested for replacing synthetic phenol-formaldehyde foams in various applications. For that purpose, a few physical properties were measured and reported here: resistance to fire and chemicals, absorption of various liquids, permeability, thermal conductivity and mechanical (compressive and tensile) strength. Modifying the composition through the use of boric and/or phosphoric acid allowed substantial increase of fire resistance. The materials were also found to present good resistance to strong acid and bases, and to solvents. High affinity for water, but limited one for organic liquids, was also evidenced. Finally, slightly anisotropic mechanical properties were measured. The materials present a brittle behaviour, whether tested in compression or traction; nevertheless, their strengths, as well as their thermal conductivities, are fully comparable with those of their phenolic counterparts. We show that such materials of vegetable origins can compete with synthetic ones for most of traditional applications.
