Poplar wood (Populus euramericana cv. “I-214”) has been impregnated by pulse dipping at 0.7–0.8 MPa for 30 min with a mixture of methylolurea and sodium silicate, and the sol modifier has been cured within the wood micropores by in situ gel polymerization by kiln drying, so that a Si-O-Si framework was formed. The treated wood acquired higher mechanical strength and its hygroscopicity was lowered. It was demonstrated by X-ray diffraction that sodium silicate crystallized within the interfibrillar region of the cell wall. Fourier transform infrared spectra showed that reactions occurred between the wood-OH, Si-OH, and N-CH2-OH from methylolurea to form C-O-Si and C-O-C bonds. As visible by scanning electron microscopy (SEM), the Si-O-Si framework was embedded in the pretreated wood. Moreover, SEM-energy-dispersive X-ray spectroscopy analysis revealed that the modifier formed layers from various thicknesses ranging from a thin layer on the cell walls up to big amounts filling the lumen.
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Chen et al. (2013) studied this question.