Powdered paper-resin films (PRF) composed of melamine-urea-formaldehyde resin and bleached pulp seem to be promising fillers for plywood glues as they increase the viscosity of the glue composition and interact chemically with the components of ureaformaldehyde resins. It is generally accepted that when 4–6 % PRF is mixed with ureaformaldehyde resin, the viscosity of the glue increases by 80–110 %, however the increase in viscosity is followed by an increase in the gelatinization time of the glue by 25–35 %. The reactivity of the films defined by the polycondensation rate of urea- and melamine-ureaformaldehyde oligomers was studied by determining the residual hydroxymethyl groups in the cured adhesive compositions. Our results show that when we add PRF into the resin, the content of unreacted hydroxymethyl groups increases from 1.0 % of a composition without any fillers to 2.5 % of a composition with 10 % of films in it. We found that the content of unreacted hydroxymethyl groups in the cured glue depends on the gelatinization time of the glue composition by 90 %. To speed up the glue curing, we replaced the ammonium chloride with a more effective curing agent МО-4СБ (Russian abbreviation), which helps to reduce the time of gelatinization time by 15 % for a mass fraction of 4–5 %. The content of hydroxymethyl groups in the cured glue with 4 % of PRF and 4–5 % of МО-4СБ was 0.6–0.7 %, which is 30–40 % less than in the resin without fillers. Samples of 3-layer plywood that contain 4 % of filler and 4 % of modifier-curing agent МО-4СБ had a glued seam that was 5 % stronger that of a control plywood sample which consisted of 8 % of kaolin and 1% of ammonium chloride. The increase in strength has reduced the rate of glue consumption by 15 % while meeting the requirements of the State Standard GOST 3916.1–2018 for the physical and mechanical parameters. As a result, using 4 % PRF as a filler for glue made from urea-formaldehyde resin helps to increase the viscosity of the glue on par with other mineral fillers. In addition, it increases the strength and the water resistance of the cured polymer. The growth of the physical and mechanical parameters occurs due to the polycondensation of urea- and melamine-urea-formaldehyde oligomers. However, an acceptable reaction rate requires the use of more effective curing agents than ammonium chloride.

Due to the high chemical activity of its filler, fiberboard is a unique material, it's formation can be ensured by chemical reactions of wood components. However, under hot pressing modes, typical for dry-process boards, chemical reactions do not have time to go through to the required extent, which requires the use of special modifiers that enhance the activity of the wood fiber. Bi- and polyfunctional compounds - sucrose, carbamide, and citric acid - were investigated as modifiers. The lowest efficiency was shown by sucrose, which is not able to ensure the compliance of the physical and mechanical parameters of the fiberboards with the requirements of standards; The use of urea and citric acid makes it possible to produce fiberboards that are not inferior in their properties to materials from urea-formaldehyde resin. Using the methods of chemical and instrumental analysis (IR spectroscopy, solid-state 13C NMR spectroscopy), it was found that during hot pressing, urea and citric acid react with components of the wood cell wall. Urea decomposes during pressing with the formation of ammonia and isocyanic acid, which, in turn, provides interfiber interaction. During hot pressing, citric acid reacts with hydroxyl groups of cell wall components by the esterification mechanism. Using the example of citric acid, it was found that plates that meet the requirements of the TSN-30 standart can be made only with a pressing time of 0.4 min / mm of the fiberboard thickness, which exceeds the technology requirements by more than two times. To ensure the competitiveness of the selected modifiers with respect to existing synthetic resins, it is necessary to find ways to reduce the pressing time.

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One of the urgent scientific and technical objectives in the technologies of plywood and wood boards is the search for ways to reduce of hot pressing time without increasing the formaldehyde emission from finished products. To solve this problem was developed the new modifier-curing agent MC-4SF, is mainly a product of interaction of citric acid with urea and ammonia. Compared to traditional ammonium salts, the modifier-curing agent combines the properties of both direct and latent catalysts. Determination of the composition of residual methylol groups in the aqueous extracts obtained by treating the resin cured at 100 °C showed that the modifier-curing agent provides relatively high hydrolytic stability of the UF-polymer during extraction. Spectra of solid-state 13C NMR showed that in resins cured with MC-4SF increased the compound of methylene bridges compared to resins cured with standard catalysts. It is possible that the amino groups of urea (or its derivatives) included in the modifier-curing agent, react with the methylol groups of UF oligomers, fitting urea into the structure of the resulting polymer. Thus explains the increased hydrolytic stability and reduced toxicity of the cured resin. Manufacturing tests of nine-layer plywood made with a modifier-curing agent showed that replacing ammonium sulfate with MC-4SF allows a significant reduction in pressing time at 110 °C without loss of quality of the finished product. With the same pressing time, it was possible to increase the line shear strength by 14% and to reduce formaldehyde emission by 45%.

Fiberboards are producing of vegetable raw materials and urea-formaldehyde glues. The necessity to bind formaldehyde led to the search for modifiers that are capable to reduce the toxicity of wood boards without impairment of their physico-mechanical properties. It was researched how guanylurea sulfate influences on some process, which are occur during the formation of wood boards. The salts were synthesized at molar ratios of cyanoguanidine : sulfuric acid from 1 : 0.1 to 1 : 0.5 and their effects on the technological parameters of the glue were investigated. It was found that in combination with the urea-formaldehyde resin guanylurea sulfate sworn GUS-0.5 synthesized at a 1 : 0.5 molar ratio is most suitable as it accelerates hardening of the resin without negative influence on other standard parameters. Physicochemical tests and 13C solid-state NMR spectroscopy have shown that upon injection into the glue GUS-0.5 reacts with the functional groups of the urea-formaldehyde oligomer while embedding into the structure of the curing resin. At temperatures of hot pressing of wood boards in case of injection into the composition separately from the glue GUS-0.5 is subject to thermal transformations with the formation of ammonia. It’s shown that the properties of fiberboards depend on the method of injection of the modifier into the composition. To effectively reduce toxicity without impairment of their physico-mechanical properties should be used a combined method of using the modifier when one half is injected into the glue and the other half separately.