From hydrophilic to hydrophobic wood using direct fluorination: A localized treatment

When controlled by the treatment duration or the quantity of reactive molecules, direct fluorination using F 2 gas is efficient to decrease the hydrophilicity of wood both in the form of massive piece and powder. To prove that silver fir pieces and wood flour (mix of spruce and silver fir species) were investigated as representative examples. In both the cases, hydroxyl groups are converted into C F bonds resulting in the decrease in affinity for water. Fluorination is mainly located in the outer parts of the wood cell, where the content of lignin is the highest, maintaining the inner ones nonmodified. Because the microstructure is maintained by this location of fluorination, the mechanical properties are conserved for silver fir pieces. The mechanical properties are even enhanced for composite containing fluorinated wood flour because of a better compatibility between the fluorinated fillers and the polyester matrix.