Physicochemical and microscopic properties of wood polymer modified with silane compounds

Impregnation of wood with monomers is one of the methods to improve biological and mechanical properties of wood. Methymetacrylate (MMA) is a common kind of vinyl monomers that applied broadly in wood polymer composite manufacturing. But vinyl monomers are non-polar and exclusively fill cell lumens and other void spaces, without significant effect on hydroxyl groups of wood. Therefore, despite reducing water absorption rate, the resultant wood polymer still remains hydrophil. Bonding formation between non-polar monomers and hydroxyl groups of wood through incorporated modification, probably will improve physical and mechanical properties of wood. This research performed with the purpose of investigation the effect of cell wall modification with tetraethoxy silane (TEOS) and vinyltriethoxy silan (VTEOS) on physical properties, chemical and microscopic structure of methymetacrylate wood polymer.

Modification of poplar wood was performed by a double process vacuum/pressure, initially with TEOS and subsequently with VTEOS/MMA at presence of benzoyl peroxide as initiator. At first, samples were impregnated with TEOS, and cell wall modification performed at 120 C. Then cell wall modified samples were impregnated with MMA. In combined level, modified samples with TEOS, were impregnated simultaneously with MMA/VTEOS. Water absorption and dimensional change, chemical and microscopic structure of result wood polymer, were respectively investigated by immersing samples in water, Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM).

Changes in FTIR spectra confirmed wood cell wall modification with silane compounds. Modification with TEOS/VTEOS/MMA induced the highest intensity of carbonyl peak. Presence of MMA in cell lumen and increase of its presence in structure of cell wall modified wood confirmed by SEM. Modification with silane compounds enhanced monomer to polymer conversion rate which was more significant in vinyl silane compound. Vinyltriethoxy silane containing level, in spite of lower reactivity, indicated higher weight gain due to possibility of polymerization and bound formation with MMA. Water repellent efficiency of MMA containing samples were reduced with increasing immersion time in water, which cell wall modification with silane compounds decreased this reduction. The highest anti-swelling efficiency were observed in TEOS/VTEOS/MMA modification level.

Incorporation of cell wall modification with silane compounds and impregnation of lumens with MMA, increased compatibility of polymer with cell wall, and also cell lumens occupied with polymer. Modification with both two silane compounds and MMA had highest enhancement in physical properties of wood polymer composite. VTEOS in comparison to TEOS, induced significant enhancement in properties of result wood polymer composite.