In situ formation of a glassy MgO/Na2O–SiO2 solid in Scots pine (Pinus sylvestris L.) sapwood through a wet-chemistry approach

Abstract

The demand for safe and durable modified-wood products is increasing in the construction sector. In this work, the in situ wet-chemistry synthesis of a glassy MgO/Na₂O–SiO₂ solid in Scots pine (Pinus sylvestris L.) sapwood via a two-stage impregnation process using an industrial timber-impregnation autoclave is reported. Magnesium sulphate heptahydrate (MgSO₄·7H₂O), a historic fire retardant, and silica-rich sodium silicate (Na₂O·3.3SiO₂) solutions were used as the precursors. The degree of wood matrix saturation was controlled by adjusting the Na₂O·3.3SiO₂ concentration (0.06 M, 0.3 M and 0.6 M). Wood saturation and density at various stages of the treatment were assessed by X-ray computed tomography (CT), which showed that the internal regions of the wood blocks remained saturated with the solution up to 24 hours post-impregnation. Phase analysis of the coprecipitated powders revealed the formation of amorphous silicates in the MgO/Na₂O–SiO₂ system. Thermal analysis showed that the wood treated using a low Na₂O·3.3SiO₂ concentration exhibited a behaviour similar to that of the untreated wood and indicated that the thermal stability of Scots pine sapwood can be improved through the incorporation of silicates. This work demonstrates the potential for fabricating hybrid bio-based building materials using water-insoluble solid additives, thereby advancing sustainable construction practices.