Influence of Grinded Dust as a Filler of Carbamideoformaldehyde Adhesives on Their Technological Properties

Abstract

One of the main indicators of the quality of plywood is its environmental friendliness, which is characterized by the content of free formaldehyde. To produce plywood with formaldehyde emission class E0, E1, low-toxic urea-formaldehyde resins should be used. These resins have low final viscosity, which can lead to a decrease in the strength properties of plywood due to excessive penetration of glue into the wood. The viscosity of the working solution of the glue can be changed by the use of fillers (wood flour, rye flour, kaolin, etc.). The results of the research have showed that wood flour has high adsorption capacity and 2-5 m. shares of wood flour increase the viscosity of the adhesive from 60 to 180 s by the VZ-4 viscometer. At the same time, a large amount of grinding dust accumulates in the woodworking shops. To assess the possibility of using grinding dust as a filler of urea-formaldehyde resins, a comparative analysis of the properties of grinding dust obtained by grinding various materials and wood flour in accordance with State Standard 16362-86 has been carried out. The results have showed that grinding dust is comparable to wood flour in moisture, bulk density. The fractional composition of the grinding dust is larger, but most of it corresponds to the necessary fractions of 0.25; 0.18; 0.125 after sorting. The article studies the effect of the fraction and the amount of grinding dust on the strength properties of plywood, as well as on the technological properties of the adhesive (dynamic viscosity, pH, gel time). The maximum increase in the strength of plywood has been 63% when using grinding dust of 0.125 fractions in the amount of 1 m.sh. Adding grinding dust to the adhesive solution leads to an increase in its dynamic viscosity and the larger the particle, the more the viscosity changes. Filling of urea-formaldehyde resins with grinding dust shifts the pH of the adhesive solution towards the neutral and slightly acidic medium and reduces the gelatin time to 55-60 sec. The conducted studies show that the use of grinding dust as a filler of urea-formaldehyde adhesives leads to a decrease in internal stresses in the cured adhesive and an increase in the strength of the gluing of plywood