Modification of wood with silicon compounds. inorganic silicon compounds and sol-gel systems: a review

This review describes the treatment of wood with various inorganic silicon compounds. Among these compounds silicofluorides represent one of the long-known classes of wood preservatives based on silicon. Data on an organic fluorosilicon compound (silafluofen) are additionally presented. The mode of action of these fluorides is based on their biocidal action. Water glass, an alkali silicate, was able to enhance the durability of wood but showed some important drawbacks. Because of its high hygroscopicity and its high pH values, increased moisture absorption and strength loss of wood was frequently observed. Wood treated with tetraalkoxysilanes showed an enhanced dimensional stability, especially when the hydrolysis and the condensation of the silanes was controlled to react within the cell wall. Durability and fire resistance were improved to a certain degree and could be significantly enhanced by addition of boron compounds.Abbreviations ASE antishrink efficiency - CCA (preservatives based on) copper, chromium, arsenic - CSAS colloidal silicic acid solution - EDX energy dispersive X-ray analysis - EPMA electron probe X-ray microanalysis - HFOETMOS 2-heptadecafluorooctylethyltrimethoxysilane - MEE moisture-excluding efficiency - MoE modulus of elasticity - r.h. relative humidity - SAMS silicic acid monomer solution - SEM scanning electron microscopy - TEOS tetraethoxysilane/triethyl orthosilicate - TEP triethylphosphite - TGA thermogravimetric analysis - TMB trimethylborate - TMOS tetramethoxysilane - TMP trimethylphosphite - TPOS tetrapropoxysilane - WPG weight percent gain