Fluorination/Torrefaction Combination to Further Improve the Hydrophobicity of Wood

Following recent works on gas/solid fluorination applied to massive wood that sustainably increased its hydrophobicity thanks to the substitution of -OH groups by covalent fluorine atoms, the present paper demonstrates that torrefaction may replace the step of the removal of HF. Because of the strength of covalent C-F bonds, torrefaction does not result in defluorination. The fluorination/torrefaction combination acts at two scales: the surface develops hydrophobicity thanks to the presence of fluorine atoms whereas torrefaction enhances the water molecules barrier. Such improvements are achieved whatever the initial hydrophilicity of the wood species contrary to the fluorination or torrefaction alone.