Research of Bioproof Materials at Superficial Modification of Wood

Abstract

The mechanism and conditions of surface modification of wood by phosphorous-containing and siliceous organic compounds have been studied. Wood has the ability to absorb moisture from the air, and the moisture content of wood produces a significant effect on the physical and mechanical properties of wood. Traditional water-repellent agents of lignocellulosic materials are Organic Silicon Compounds (OSC). Our research is aimed at developing a “soft” silylation technology, in which the degree of chemical modification is negligible, and the content of chemically bound Si amounts to ~ 1%. As silylating agents, alkylhydride siloxanes, alkoxysilanes were used. From alkylhydride siloxanes, polyethylhydride siloxane (PEHS) and polymethylhydride siloxane (PMS) with different n-polymerization degrees were used. Activating hydrophilic additives were ammonium fluoride, potassium fluoride and titanates. The treatment of wood with salts, with the subsequent treatment with OSCs facilitated the penetration of OSCs into the wood while the processes of “soft” silylation proceeded. “Soft” silylation of wood with polyalkylhydride siloxanes proceeds in the presence of catalyst additives, the degree of silylation is low and depends on the nature of the additives. The dependence of distribution of OSCs in the wood on the nature of the additives is evidenced by the method of scanning electron microscopy. Phosphorous-containing organic compounds (FOC) have a high penetrating ability, while completely filling the intercellular structure of the wood. With the sequential impregnation of the wood with FOCs and OSCs, organic silicon compounds enter the intercellular space of the wood, with dense spongy OSC deposits, which in some places completely fill the internal cavities of cellular tubes of the wood. As FOC, for example, a 40% solution of trichloroethylphosphate (TCEP) was used. Decaying of wood over time starts from the surface, since there are no diffusive limitations in the sorption process. Surface modification of wood can increase its durability due to increased biological stability and hydrophobic behaviour, which will ensure a long-lasting protection. Long-lasting protection is due to the formation of covalent bonds of wood (cellulose) with a modifier. Wood samples after surface “soft” modification with FOCs and OSCs were tested for hydrophobic behaviour and biological stability. The samples were tested in the climate chamber with irrigation of the samples with water in a mode of -30°C to +40°C. To determine the hydrophobic behaviour, the limiting wetting angle was determined. The biological stability was determined by the growth of testing cultures of the fungi Aspergillus, Penicillium, Trihoderma and some others according to GOST 9.048-89. The amount of the data obtained allows to make a conclusion about the nondurable decrease in water absorption capacity during surface modification of wood with OSCs. Long-lasting biological and water resistance is achieved only in cases when surface application of OSCs is carried out on the pre-phosphorylated wood. Phosphorylation thus leads to the formation of covalent bonds. The compounds developed were successfully used for 10-15 years to preserve the monuments both of wooden architecture and the buildings and structures made of stone, bricks, and concrete.