Surface modification of birch and acetylated birch wood by silicone nanofilaments

Sammanfattning: The increasing awareness of sustainability motivates the development of building materials from renewable resources. The requirements of wood-based products with improved durability, for example, enhanced liquid repellence and UV and biological resistance, are still a challenge. Surface modification of wood by a superhydrophobic layer is one approach for counteracting the challenge. In this thesis, wood veneers of untreated and acetylated birch were surface-modified with fluorinated or non-fluorinated silicone nanofilaments in gas phase. Results demonstrated that the fluorine surface-modified birch (F-SMB) samples showed superamphiphobicity, i.e. a surface that repelled water, ethylene glycol and hexadecane with contact angles (CAs) greater than 150° and roll-off angles (ROAs) of less than 10°. Fluorine-free surface-modified birch and acetylated birch (SMB and SMAB) showed superhydrophobicity with static CA greater than 160° towards water and low ROA even for samples prepared with the shortest reaction time of 1 h.The surface-modified wood showed good wetting resistance analyzed by the multicycle Wilhelmy plate method. The SMB showed a lower water uptake than the acetylated wood while the SMAB showed the lowest water uptake, i.e. a pronounced increased water resistance, due to a combined effect of acetylation and surface modification. The silicone nanofilaments were not degraded after UV irradiation. Both the UV-irradiated SMB and SMAB still showed good wetting resistance with high static CAs and low water uptake. The UV-irradiated SMAB showed the lowest water uptake. The SMB and F-SMB showed good mold resistance with mold appearing later or with less intensity than those on the untreated birch due to the improved water resistance. All acetylated birch showed an even better mold resistance since the acetylation reduces the moisture absorption in the wood substance; whereas the surface modifications on acetylated birch played a slightly negative effect due to side effects from the surface modifications. All birch samples showed high blue stain coverage but almost no blue stain fungi were observed on the acetylated birch. The preconditioned and UV-irradiated acetylated wood samples showed good mold resistance as well. However, more outdoor tests need to be performed to further understand the resistance to mold and blue stain fungal growth on acetylated wood.The surface modifications of both untreated and acetylated birch give excellent water repellence and resistance, which shows the potential of such surface-modified wood in outdoor applications.