Wood composite materials based on glycoluril-modified urea-formaldehyde resins

Urea-formaldehyde oligomers are urea and formaldehyde polycondensation products and are used as adhesives for wood composite materials. Currently, urea-formaldehyde resins are cheaper and more available than other binders. Composite materials on their base are easily exposed to mechanical processing. These materials also have acceptable parameters of mechanical strength and hardness. It is known that the main disadvantage of urea-formaldehyde resins is high concentration of free formaldehyde and its emission during the formation and subsequent application of wood composite materials. According to the International Agency for Research on Cancer data, formaldehyde is a carcinogen of the first category. It is known that an easy way to reduce toxicity is to decrease the urea / formaldehyde molar ratio. However, the extremely low molar ratio leads to the reduction of the reactivity of oligomers. It also has a negative effect on the physical and mechanical properties of wood materials based on thereof. The technology to synthesize melamine-urea-formaldehyde resins has a wide application. Structural materials based on these types of resins have low toxicity, high water resistance and high strength performance. However, a high content of melamine in resin (about 30-40 %) is required to achieve such high performance. This significantly increases the costs of materials based on melamine-urea-formaldehyde resins. Thus, one can conclude that both the modifier and modification method are effective in case they do not influence drastically the technological processes used to manufacture the resins and resin-based materials, and simultaneously are able to reduce the toxicity of both resins and panels without changing their basic technical characteristics and improving the physical and mechanical properties of wood composite materials. In the present work the results of the influence of a modifying additive for urea-formaldehyde resins on physical and mechanical properties and toxicity of wood materials are presented. It is established that the increase of glycoluril quantity in urea-formaldehyde resin allows reducing the emission of formaldehyde from the particle board. It is shown that optimal quantity of glycoluril as a modifier of urea-formaldehyde resin, which does not allow a decrease of the physical mechanical properties, is two percent. Production experiments established toxicity reducing by 40 % of particle boards based on glycoluril-modified urea-formaldehyde resins in comparison with particle boards based on unmodified binders.

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