The study investigated the extent to which the properties of MDF boards change with changes in the moisture of fibers forming mats from 4.5 to 10.5%. MDF panels were produced in the laboratory with an assumed density of 660kg/m3 and a thickness of 12 mm. It has been found that it is possible to produce boards without their delamination in the whole range of humidity of fibers. The increased amount of water vapor in the mats when they are pressed is likely to influence better plasticization of the fibers, which translates to improved properties of the boards. Increasing moisture content from 6.5 to 10.5% increases the modulus of rupture by approx. 9%, the modulus of elasticity by approx. 7%, intemal bonds by approx.30% and reduces swelling by approx. 22%.
Industrially produced HDFs were subjected to heating or the boards have been covered with a layer of vegetable oil, and then the boards were heated at 150° C for 1.5-2.5 h These operations aimed at increasing the tensile properties and reduce swelling to the extent that these boards may be used in wet conditions outdoors. Properties of produced boards were examined, which concluded that boards thermal treatment leads to a significant improvement of their properties (MOR and MOE increase and decrease of TS) and oil saturation of boards can be useful to reduce the swelling of boards.
The paper proposes the production of a three-layer MDF instead one layer boards. Three-layer panels have been made from fibers of varying dimensions for the outer and the core layers. The outer layers were produced from standard fibers, while the core layer from longer and thicker fibers (of lower pulp freeness). In order to determine the optimal technological parameters in the production of three layer boards, the experimental plan was used in the study. Three factors at two levels were tested. Analysis of variance (ANOVA) was used to analyze the significance of factors. Regression coefficients and 3D contour plots were used to quantify the relationship between panel properties and test factors. Properties of obtained boards were tested according to the standard EN 622-5/2010. All selected factors within the examined range of settings had influence on MDF properties. It has been found that the best properties of the plates were 25x50x25 involving layers, the content of the glue in the outer layers of 10% and the core layer of 12% at the time of overheating of the mats 90s.