On the mechanisms of action and methods of evaluation efficiency acceptors of formaldehyde in wood boards
The efficiency of formaldehyde acceptors were studied on the example of urea and cyanoguanidine. The nature of the conversion of cyanoguanidine was researched at the temperatures of inner and outer layers of the wood boards. Medium density fiberboards, which have thickness of 4 mm were making for modeling the temperature conditions. The model of inner layer were making at the temperature of hot press plates 130 °С, and model of outer layers at 220 °С. Samples of medium density fiberboards were investigated using the methods of NMR-spectroscopy, improved photo colorimetric method of definition of formaldehyde and standards physic-mechanical tests. It was established that at the temperature of outer layers decomposition of cyanoguanidine with ammonia formations prevails, and at the temperature of inner layer the addition reaction of formaldehyde to aminogroups prevails. Acceptor, which was introduced into the board separately from glue in quantity 1.5% of the mass of the board can bind more than 50% of the emitted formaldehyde at 220 °C and only 15% at 130 °C. Photos of the horizontal incisions of medium density fiberboard samples are shown. They demonstrate that samples, which were made at temperature of inner layer have in its structure acceptor, which retains its aggregate state and is observed in the form of a coarse powder, and the samples, which were made at temperature of outer layer don’t have any inclusions in it is structure. Functional evaluation of the acceptor was given through relation of quantity tied formaldehyde towards maximum quantity of formaldehyde, which in theory can react with acceptor. Results were expressed as degree of interaction completeness. For cyanoguanidine in samples, modeling the temperature of inner layer it is 0.48%, and to samples, which modeling the temperature of outer layers it is 0.89%. Comparing the results with other acceptors it was defined, that degree of interaction completeness is similar and very low. It was established that conditions of manufacturing wood boards are poorly suitable for chemical reaction because of diffusion and kinetic limitations. To estimate the effectiveness of acceptors according to equimolar reaction is not enough, and the technical evaluation through efficiency coefficient is required.