In this research problems related to the swelling and water adsorption of particle boards were examined. Wood panels are composite material made from wood chips and chemical components, and have different properties when compared to solid wood. Numerous important investigations have been carried out until nowadays in this field, but the relationship and dependence between the mentioned factors have changed and are still changing because of the continuous decline in raw wood quality, application of new carbamide-formaldehyde resins (influenced by the reduction in formaldehyde emission), and introduction of new hydrophobic materials. Swelling and water adsorption were investigated in experimental three-layer V20 type particle boards made in the laboratory, using different wood species with a high share of hardwoods as a material with poorer properties for boards production. Carbamide-formaldehyde resins with very low molarity ratio carbamide-formaldehyde (1 to 1,2) and with a minimal share of free formaldehyde were used. Paraffin emulsions of 33% and 66% concentration were used as a hydrophobic material (one produced in a particle boards factory and the other in the petrochemical industry). Nine series of particle boards were produced: boards without paraffin emulsion, with addition of 0.3; 0.6; 0.9 and 1.2 % of 33% paraffin emulsion, and with addition of 0.3; 0.6; 0.9 and 1.2 of 66% paraffin emulsion. 30 samples were sawn from each series, and they were used for the determination of density, swelling and water adsorption. All the samples were made of the same mixture of wood chips, so that the density differences were caused by a higher or lower porosity of the test boards (low precision of dosing and mat formation). The aim and purpose of the particle board samples testing were to determine the correlation between swelling and density, water adsorption and density, swelling and water adsorption for the nine series of samples having a different share of the paraffin emulsion. The correlation between the swelling and particle board density (boards without paraffin) has a positive linear regression trend, and the correlation of water adsorption and density has a negative linear regression trend. There was no linear regression determined between the swelling and water adsorption. Particle boards having 33% paraffin emulsion concentration did not show any correlation between the swelling and density, but the correlation between the water adsorption and density was determined to be linear with a negative inclination and a linear regression trend. The correlation coefficient was small until an optimal additive quantity was added, and after that point the correlation coefficient become higher. The particle board having paraffin emulsion of 66% concentration, showed negative linear regression trend with a steep slope of regression straight line and a changing coefficient of correlation. The particle board having paraffin emulsion of 33 % concentration exhibited a low correlation between the swelling and water adsorption when the additive share was 0.6 %, with the additive proportion of 0.9% the correlation was obvious, and with 1.2%. The correlation was very good. Particle board having paraffin emulsion of 66% concentration had a low correlation between the swelling and water adsorption when 0.3 % of the emulsion was added, but at a higher share there was no correlation between these parameters. The average values of all boardseries show a positive linear regression between the swelling and water adsorption.
