Traditional flame retardants often contain halogens and produce toxic gases when burned. Hence, in this study, low-cost, environmentally friendly compounds that act as fire retardants are investigated. These materials often contain nanoparticles, from which TiO₂ and SiO₂ are the most promising. In this work, pedunculate oak wood specimens were modified with sodium silicate (Na₂SiO₃, i.e., water glass) and TiO₂, SiO₂, and ZnO nanoparticles using the vacuum-pressure technique. Changes in the samples and fire characteristics of modified wood were studied via thermal analysis (TA), infrared spectroscopy (FTIR), and scanning electron microscopy, coupled with energy-dispersive X-ray spectroscopy (SEM-EDX). The results of TA showed the most significant wood decomposition at a temperature of 350 °C, with a non-significant influence of the nanoparticles. A dominant effect of sodium silicate was observed in the main weight-loss step, resulting in a drop in decomposition temperature within the temperature range of 36–44 °C. More intensive decomposition of wood treated with water glass and nanoparticles led to a faster release of non-combustible gases, which slowed down the combustion process. The results demonstrated that wood modifications using sodium silicate and nanoparticle systems have potentially enhanced flame retardant properties.

Thermal modification improves the properties of wood, especially its stability and durability. We thermally treated spruce wood with the Thermowood process at three temperatures (160 °C, 180 °C, and 210 °C) and subjected it to accelerated aging in wet mode. We evaluated the chemical composition (wet chemistry, infrared spectroscopy), color, surface morphology, and wetting of the wood surface with water. Thermal treatment caused a significant decrease in hemicelluloses (up to 72.39% at a temperature of 210 °C), which initiated an increase in the content of more resistant wood components—cellulose and lignin. With accelerated aging, the hemicellulose content decreased by another 5%. The most significant differences between the infrared spectra of thermally modified wood before and after exposure to accelerated aging were in the absorption bands of lignin (1509 and 1596 cm⁻¹) and in the region of carbonyl groups between 1800 and 1630 cm⁻¹. Thermal treatment also caused a change in the color of the wood to dark brown; the overall color difference ΔE increased several times. The thermal-induced shortening of polysaccharide fibers and reduction in their width were even more manifested during accelerated aging. This work contains new knowledge about the properties critical for the reuse of thermally modified wood after accelerated aging, simulating the end of its life cycle.

One of the strategies to improve the fire resistance of wood is to use flame retardants. It would be best to find an ecological, nonhalogenated flame retardant to improve the fire protection properties. In this work, oak wood (Quercus robur L.) samples were treated with an aqueous solution of sodium silicate and expandable graphite flakes, which were applied to different parts of the samples: only on the top, on the sides and together on the top and sides of samples. The fire characteristics of samples were studied by a non-standard test method—a radiant heat source test which is used to determine the mass loss and ignition time of the tested samples (50 mm × 40 mm × 10 mm), and the measurement was carried out using a visual recording of a thermal camera. The results of the laboratory test method showed a significant positive effect of the application of the retardant treated only on the top and together on the top and the sides of the samples in terms of decreasing the mass loss and the course of temperature. When we treated only the sides of the sample, the results were closer to the untreated samples, so there was more than 80% weight loss and a significant temperature increase. The results demonstrated that the appropriate modification of the wood using sodium silicate and expandable graphite flakes has the potential to reduce the loss of mass by 79% and reduce the rise in temperature on the surface of the sample.

In order to not limit the possibilities of using wood due to its flammability, the implementation of fire protection is an essential requirement. An integral part of the research on the fire protection of wood is the determination of the effectiveness of the applied protective means and their effect on changing its behavior under fire conditions. In this work, samples of spruce wood (Picea abies (L.) H. Karst) (50 mm × 40 mm × 10 mm) were treated with an aqueous solution of sodium silicate and different types of expandable graphite flakes that were applied to the surface of the samples. The fire characteristics of the samples were studied using a non-standard test method, the radiant heat source test, which was used to determine the mass loss, burning rate, and ignition time of the test samples, and the measurement was carried out via visual recording with a thermal camera. The results of the laboratory test method showed a significant positive effect of the application of all types of expandable graphite flakes. The main insight is that a suitable wood modification using expandable graphite flakes in combination with water glass has the potential to reduce mass loss by at least 73 ± 3% and reduce the temperature rise on the surface of the sample. The lower temperature of the surface of the burning material reduces the possibility of heat transfer to the surrounding materials and thus reduces the rate of fire spread.

Thermal modification is an environmentally friendly process that does not utilize chemical agents to enhance the stability and durability of wood. The use of thermally modified wood results in a significantly extended lifespan compared with untreated wood, with minimal maintenance requirements, thereby reducing the carbon footprint. This study examines the impact of varying modification temperatures (160, 180, and 210 °C) on the lignin of spruce wood using the ThermoWood process and following the accelerated aging of thermally modified wood. Wet chemistry methods, including nitrobenzene oxidation (NBO), size exclusion chromatography (SEC), thermogravimetry (TG), differential thermogravimetry (DTG), and Fourier transform infrared spectroscopy (FTIR), were employed to investigate the alterations in lignin. At lower modification temperatures, the predominant reaction is the degradation of lignin, which results in a reduction in the molecular weight and an enhanced yield of NBO (vanillin and vanillic acid) products. At elevated temperatures, condensation and repolymerization reactions become the dominant processes, increasing these traits. The lignin content of aged wood is higher than that of thermally modified wood, which has a lower molecular weight and a lower decomposition temperature. The results demonstrate that lignin isolated from thermally modified wood at the end of its life cycle is a promising feedstock for carbon-based materials and the production of a variety of aromatic monomers, including phenols, aromatic aldehydes and acids, and benzene derivatives.

Wood, one of the materials predominantly employed in construction, possesses various advantageous properties alongside certain drawbacks, such as susceptibility to thermal degradation. To enhance wood fire resistance, one approach involves the application of flame retardants. This study compared the fire-retardant effectiveness of expandable graphite, bonded with water glass, as a coating for spruce wood against commercially available fire-retardant treatments. Spruce wood samples (Picea abies (L.) H. Karst) underwent treatment with three distinct retardants: expandable graphite in combination with water glass, Bochemit Antiflash, and Bochemit Pyro. The fire-technical characteristics of the samples were examined by a non-standard test method—a test with a radiant heat source. The experiment evaluated the fire-retardant properties by recording changes in sample mass, burning rate, and temperature difference. The best results among all flame retardants were achieved by expandable graphite in combination with water glass, in all evaluation criteria. Among all the flame retardants used, expandable graphite in combination with water glass achieved the best results in all evaluation criteria.