THE INCREASE OF FIRE-RESISTANCE OF VENEER-BASED COMPOSITES
Influence of different types of fire-retardants, methods and regimes of veneer impregnation, regimes of plywood pressing, which it made using impregnated veneer, on the fire-resistance, physical and mechanical properties of plywood was studied. Compounding of fire-retardants and regimes of veneer impregnation and plywood pressing are offered, that provides the I-st group of heat-resistance and transfers the plywood from the group of increase combustibility materials (G4) into the group of hardness combustible materials (G2). It was found, that diffusive method of wet veneer impregnation is characterized by less salting-out of fire-retardants on the veneer surface and its more homogeneous distribution in the middle of veneer compared to capillary method of dry veneer impregnation. The part of ammonium sulfate is substituted for ammonium bromide for reduction of corrosive ability of the DC fire-retardant and the next compounding of fire-retardant - diammonium phosphate : ammonium sulfate : ammonium bromide (1:0,625:0,375) was recommended. It is investigated that dependence of fire-retardant content on the temperature of impregnation solution is linear, and on the duration of impregnation it is logarithmic. Maximum fire-retardant content is observed for the temperature of impregnation solution 60 <sup>о</sup>C, concentration of impregnation solution 50%, duration of impregnation 75 min. The plywood heat-resistance gets better with the increase of fire-retardant content. Taking into account fireproof and mechanical plywood properties and the economic aspect of plywood production it is recommended to carry out wet veneer impregnation by the diffusive method for the concentration of impregnation solution 30%, temperature of impregnation solution 22 <sup>о</sup>C and duration of impregnation 8 min. The recommended technological parameters of heat-resistant plywood pressing are: temperature of press plates - 115ºC, duration - 8 min, glue spread - 120 g/m <sup>2</sup>.