Измельченные бумажно-смоляные пленки как реакционно-способные наполнители карбамидоформальдегидных смол

Abstract

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.