Hydrolytic stability of cured urea‐formaldehyde resins modified by additives

Abstract

Urea-formaldehyde (UF) resins are prone to hydrolysis that results in low-moisture resistance and subsequent formaldehyde emission from UF resin-bonded wood panels. This study was conducted to investigate hydrolytic stability of modified UF resins as a way of lowering the formaldehyde emission of cured UF resin. Neat UF resins with three different formaldehyde/urea (F/U) mole ratios (1.4, 1.2, and 1.0) were modified, after resin synthesis, by adding four additives such as sodium hydrosulfite, sodium bisulfite, acrylamide, and polymeric 4,4 0 -diphenylmethane diisocyanate (pMDI). All additives were added to UF resins with three different F/U mole ratios before curing the resin. The hydrolytic stability of UF resins was determined by measuring the mass loss and liberated formaldehyde concentration of cured and modified UF resins after acid hydrolysis. Modified UF resins of lower F/U mole ratios of 1.0 and 1.2 showed better hydrolytic stability than the one of higher F/U mole ratio of 1.4, except the modified UF resins with pMDI. The hydrolytic stability of modified UF resins by sulfur compounds (sodium bisulfate and sodium hydrosulfite) decreased with an increase in their level. However, both acrylamide and pMDI were much more effective than two sulfur compounds in terms of hydrolytic stability of modified UF resins. These results indicated that modified UF resin of the F/U mole ratio of 1.2 by adding acrylamide was the most effective in improving the hydrolytic stability of UF resin.

Influence of acrylamide copolymerization of urea–formaldehyde resin adhesives to their chemical structure and performance

“…In addition, the UF resin modification by a simple mixing of acrylamide showed that the acrylamide did improve the hydrolytic stability of modified UF resin compared to that of other additives. 15 However, there are limited studies on UF resin modification by the acrylamide copolymerization to lower the formaldehyde emissions of UF resin bonded-wood panels. So, this study investigated the chemical structure of modified UF resins by the copolymerization of acrylamide at different levels.…”

Comparison of thermal curing behavior of liquid and solid urea–formaldehyde resins with different formaldehyde/urea mole ratios

“…Our group has been characterizing various features of UF resins, such as hydrolytic stability, morphology, crystallinity, and microstructure [10][11][12][13][14][15][16][17]. Moreover, this work is an extension of our works that have been focused on understanding the impact of F/U mole ratio to properties of liquid [15] or/and cured UF resins [11].…”

Micro-Morphological Features of Cured Urea-Formaldehyde Adhesives Detected by Transmission Electron Microscopy

“…Further, as a binder, UF resin adhesives penetrated not only in cell lumens but also into tracheid walls [5]; thus interaction between wood and UF adhesives occurs continuously. Many studies have investigated the hydrolysis of UF resin adhesives to understand the mechanism of formaldehyde release, not only from pure cured UF resin adhesives [2,[6][7][8][9][10][11][12] but also from UF resin adhesive-bonded wood panel products [13][14][15][16]. The tendency toward hydrolytic degradation of a cured UF resin adhesives depends on its chemical structure and the degree of crosslinking and could be accelerated by high temperatures and strong acidic conditions [15].…”