Prospects for the use of shungite as a formaldehyde sorbent in composite materials

Abstract

During the production of modern wood-based construction materials, synthetic adhesives are used, the toxicity of which is determined by the presence of free formaldehyde. The release of free formaldehyde from products can continue for an extended indefinite period. The development of methods for the reduction of the emission of formaldehyde during the production and the use of composite wood materials is undoubtedly an urgent task. The purpose of the study was the optimization of the method for increasing the adsorption-structural characteristics of a filler based on natural schungite, the study of the effect of the porous structure of carbon-containing adsorbents used as fillers on the emission of formaldehyde in wood glued composite materials. Schungite, BAU-7 activated carbon, nanodispersed carbon material Sibunit and PM-75 soot were studied as fillers. For the development of a porous structure and an increase in the dispersion of schungite, the following methods of modifying schungite were used: dry mechanical activation, activation by electromagnetic fields in the range of 150 ÷ 800W microwave (microwave EMF), steam-gas activation in various temperature and time modes and chemical activation with sulphuric acid. Chemical activation was carried out in a solution of 2M H₂SO₄ with constant stirring at a temperature of 97^oC for 7.5 hours with a Heidolph LABOROTA 4000 rotary evaporator. The analysis of the texture and state of the surface of materials was carried out by equilibrium adsorption, vibrational spectroscopy, X-ray microanalysis (EDAX method). The emission of free formaldehyde was studied by the chamber method. It is shown that mechanical and thermal activation allowed increasing the schungite surface by a factor of 10-35 and obtain samples with high dispersion (in the range from 90 nm to 40 μm). The most effective as an adsorptive filler of the adhesive composition was the use of nanodispersed mechanically activated schungite and Sibunit. The use of nanodispersed mechanically activated schungite reduced the emission of formaldehyde from wood composite materials to 0.040 mg/m³, which is two times lower than the normal value 0.124 mg/m³ of formaldehyde in the air.