Wood has been used as a construction material for small objects, furniture, and large-scale buildings since antiquity. The protection of wooden objects and wooden buildings of significant cultural heritage from water-induced decay processes is of great importance. In the present work, hybrid coatings consisting of Sivo 121 and nanolignin were produced and deposited onto chestnut (Castanea sativa) and oak (Quercus frainetto) specimens. Sivo 121 is an aqueous siloxane-based product which is used for wood protection, whereas nanolignin was extracted from beechwood.
The effects of the nanolignin concentration on the wetting properties and surface structures of the hybrid coatings were investigated and an optimal Sivo/nanolignin mass ratio was found for each wood species. This optimal ratio provided enhanced hydrophobicity, as demonstrated by the elevated contact angles (CAs) of water drops. The maximum CA of 145° was measured for coated oak, which is approaching the threshold of superhydrophobicity. However, the rose-petal effect was evident, with water drops remaining pinned even when the coated samples were tilted to a perpendicular position. Notably, the drops rolled off the coatings' surfaces when the coated wood samples were agitated.
The performance of the hybrid coating with the optimal Sivo/nanolignin mass ratio was evaluated through a series of tests. The coating caused only minor alterations to the natural colour of the two untreated woods (ΔE<5) and offered very good protection against water absorption through capillarity. The results of the graveyard durability test highlighted the treatment's protective efficacy. Furthermore, the coating exhibited excellent chemical and mechanical stability, as confirmed by applying drops of various pHs and conducting the tape peeling test. Finally, the CAs of the coated chestnut and oak were monitored over time after placing the samples outdoors and within an artificially accelerated aging chamber. The results showed that the CAs remained stable over time, confirming the coating's durability.
