Hydrophobisation of tannin-based foams by covalent grafting of silanes

• Tannin-based foams were hydrophobised by chemical grafting of three kinds of moieties.
• The two treated foam formulations presented quite high water repellence.
• Water vapour sorption, however, could never be completely prevented.
• Increase of thermal conductivity with relative humidity was limited for treated foams.

Thermally insulating foams based on Mimosa bark extracts (Acacia Meansii) were hydrophobised with the aim of decreasing their sensitivity to moisture. Two different formulations leading to rigid foams presenting similar porosity were prepared, and were covalently grafted with three kinds of organosilanes. Non-treated and hydrophobised samples were all thoroughly characterised by FTIR spectroscopy, contact angle measurements and corresponding surface energy calculations, water sorption and thermal conductivity studies. Hydrophobisation produced a significant repellence towards liquid water but did not prevent water vapour sorption. Water uptake, however, was limited compared to the non-treated materials. As a result, the increase of thermal conductivity at high relative humidity was lower after hydrophobisation.