Preparation of cured urea–formaldehyde resins of low formaldehyde emission

Several polymers containing amino or amido groups and biuret were tested as additives to ureaformaldehyde (UF) resin in order to neutralize its inherent acidity and combine free formaldehyde released upon hydrolysis of cured UF polycondensate. Each modifier was incorporated to liquid methylolureas at weight ratios of 1:100, 2:100, and 3:100 prior to curing with the aid of acetic acid. Over 10 days of maintaining aqueous suspensions of the ground-up resultant solid resins at ambient temperature, a neutralizing effect was exhibited most visibly by polyacrylamide, polymethacrylamide, and biuret, the test with chitosan and casein giving results slightly different from those obtained for the control nonmodified cured UF polymer. Polyacrylamide, biuret, and casein proved to be excellent inhibitors of formaldehyde release from the hardened resins which were suspended in water at ambient temperature. On the other hand, chitosan did not reduce the evolution of HCHO but, instead, augmented it when its content was 1 g/100 g of the original liquid resin before cure.