Effect of extraction on the coatings produced from nanoparticle gels obtained from hardwood and softwood bark

Abstract

For coatings, non-extracted hardwood (birch) and softwood (pine) bark and that extracted in biorefinery were used. Lyophilic extractives (fats, waxes, etc.) were extracted with hexane and hydrophilic extractives (polyphenols, tannins, etc.) by means of successive extraction with solvents with increasing polarity, i.e. hexane, ethyl acetate, and ethanol water (1:1). The bark was destructed by the thermocatalytic destruction method and then dispersed in a water medium at a concentration of 8-10%. As a result, gel-like dispersions were obtained, which contained nanoparticles. It has been established that the coatings improve the Gurley air resistance and increase the mechanical properties (tensile strength, burst strength, stretch) of paper sheets. The coatings decrease the tensile strength in a wet state. The coatings made from extracted bark nanoparticle gels affect the properties of paper sheets to a greater extent. It is because extractive substances hinder the bond formation between the cellulose fibres and nanoparticles.