Influence of alkali and Si-based treatments on the physical and chemical characteristics of miscanthus stem fragments

⿢Reduced hydrophilicity of miscanthus by silane treatment in aqueous media.⿢Silica condensation rate is generally improved in the presence of miscanthus.⿢Morphology of the silica coating depended on pH and plant pre-treatment.⿢Alkali treatment changes noticeably the composition and morphology of miscanthus.⿢Mild alkali media changes miscanthus structure with a least effect on crystallinity.

Lignocellulosic materials in the form of miscanthus stem fragments were treated in order to limit their drawbacks (hydrophilicity, degradability, compatibility) when willing to use them as fillers for new bio-based concrete composites. This included a pre-alkaline soaking of the stem fragments followed by sol-gel tetraethoxysilane treatments in aqueous solutions. Since a modification of miscanthus using these methods has not been previously reported, the efficiency of the reactions was investigated at different pH conditions. The hydrolysis and condensation reactions of silane were monitored through the colorimetric silicomolybdenum method; the miscanthus structural changes, surface topography and the evidence of silica deposition on the fragments⿿ surface were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, electron microscopy and infrared spectroscopy. Results showed that the highest hydrophobicity, calculated by the water absorption of the stem fragments, was obtained for silane treatments in acidic and basic media. However, silica condensation followed different kinetics for each media conditions and headed to different morphology of the miscanthus coating. The alkali pre-treatment led to more hydrophilic products but with a more fibrillated surface, which may be potentially useful for its application in concrete.

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