Determination of changes in the mechanical and color properties of some wood species treated with shellac

The properties of wood, which is a natural and sustainable substance, change under biotic and abiotic factors. Different methods along with chemical/natural substances are used to extend the service life of wood and increase its performance under different conditions. Shellac is a natural product secreted by insects onto host trees. It is used extensively as a coating, especially in the food and pharmaceutical industries. Its natural properties and biocompatibility increase the areas where it is used. This study investigated the effects on the physical and mechanical properties of pine, beech, and fir species impregnated with shellac solutions at different concentrations (1%, 3%, and 5%) and sodium hydroxide (NaOH). The study found that 10% NaOH solution caused significant decreases in the bending strength values. The highest bending strength values were obtained for the Scots pine and fir woods at 5% shellac concentration and for the beech wood at 1% concentration. The highest modulus of elasticity (MOE) values were reached at 1% shellac concentration in all three tree species. Although the lightness (L*) of the wood samples decreased with shellac impregnation, the chromatic coordinate (a* and b*) values increased. According to the Fourier-transform infrared (FTIR) spectroscopy results, changes were determined in the chemical structures of the wood samples impregnated with NaOH, whereas the shellac did not cause a change in the chemical structure of the wood samples.