Surface chemistry and moisture sorption properties of wood coated with multifunctional alkoxysilanes by sol‐gel process

Abstract

Sol-gel surface deposition of a hydrophobic polysiloxane coating on wood was accomplished by using a mixture of a low molecular weight multifunctional alkoxysilane, methyltrimethoxysilane (MTMOS), and a high molecular weight multifunctional alkoxysilane, hexadecyltrimethoxysilane (HDTMOS). Investigation of the surface chemistry and morphology of the wood specimens by means of ATR-FTIR, energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, SEM, and atomic force microscopy indicated that the sol-gel process results in deposition of polysiloxane networks that are bonded to the wood by polycondensation with surface hydroxyl groups. The surface hydroxyl groups involved in the bonds appear to be located predominantly on the cellulose component of the wood. The sol-gel deposit on the wood substrates lowered the rates of water and water vapor sorption. The low molecular weight MTMOS apparently penetrated the outer surface layers of the wood and condensed with hydroxyls that may not be readily accessible to the high molecular weight HDTMOS. Once attached to such sites, it is reasonable to assume that some of these surface derivatives of MTMOS condensed with other molecules of MTMOS and HDTMOS with a long hydrocarbon chain to form a polysiloxane network that is hydrophobic. The ultimate effect of the sol-gel deposit can therefore be regarded as not only to decrease the surface concentration of hydrogen-bonding sites, but also to stereochemically hinder the formation of hydrogen bonds between such sites and water molecules.

Modification of hemp shiv properties using water-repellent sol–gel coatings

“…A single layer of sol-gel coating on the shiv resulted in 30% overall mass gain. This is in agreement with sol-gel coatings on wood resulting in 25-35% mass gain due to the absorption of coatings within the cell wall [27,34]. Further coatings on the same piece of shiv showed that the mass gain followed a linear trend.…”

Potassium methyl siliconate‐treated pulp fibers and their effects on wood plastic composites: Water sorption and dimensional stability

“…Hydrogen bonds formed between polysilanols and hydroxyls on fibers permit the polysilanol network to be anchored to the fibers. 22 Figure 1 exhibits the FTIR spectra of both PMS-treated anduntreated bleached pulp fiber. The absorbance peaks at 1271, 1104, 1019, and 768 cm À1 correspond to the molecular vibrations of siloxane components on the PMS-treated fibers.…”

“…The absorbance peaks at 1271, 1104, 1019, and 768 cm À1 correspond to the molecular vibrations of siloxane components on the PMS-treated fibers. The peak at 1271 cm À1 of the PMS-treated fibers resulted from stretching vibrations of the SiACH 3 bonds, 20,22,23 whereas the peak at 768 cm À1 corresponds to the vibrations of a collection of bonds, including SiAO, SiAC, and/or SiAOAC. 22,24 The peak at 1019 cm À1 is typically attributed to stretching of SiAOASi bonds 23,25 developed among the silanols.…”

“…The peak at 1271 cm À1 of the PMS-treated fibers resulted from stretching vibrations of the SiACH 3 bonds, 20,22,23 whereas the peak at 768 cm À1 corresponds to the vibrations of a collection of bonds, including SiAO, SiAC, and/or SiAOAC. 22,24 The peak at 1019 cm À1 is typically attributed to stretching of SiAOASi bonds 23,25 developed among the silanols. The sharp peak at 1104 cm À1 is due to asymmetric vibrations of the SiAOAC bonds, 26,27 which emerge when silanols and polysilanols are anchored chemically to cellulosic fibers.…”

Preventive action of organosilicon treatments against disfigurement of wood under laboratory and outdoor conditions

“…Their suitability to protect wood was suggested and aspects like durability, moisture stability etc. have been investigated (Hager 1995;Tshabalala et al 2003;Mai and Militz 2004;De Vetter and Van Acker 2005). However, most studies found that treatment of wood with organosilicons can only lead to a significant improvement of the investigated property when applied at (very) high concentrations (Hill et al 2004;Weigenand et al 2007;De Vetter et al 2009a).…”