Differential scanning calorimetry of urea–formaldehyde adhesive resins, synthesized under different pH conditions

Abstract

ABSTRACT:The purpose of this study was to investigate the effects of reaction pH conditions on thermal behavior of urea-formaldehyde (UF) resins, for the possible reduction of formaldehyde emission of particleboard bonded with them. Thermal curing properties of UF resins, synthesized at three different reaction pH conditions, such as alkaline (pH 7.5), weak acid (pH 4.5), and strong acid (pH 1.0), were characterized with multiheating rate method of differential scanning calorimetry. As heating rate increased, the onset and peak temperatures increased for all three UF resins. By contrast, the heat of reaction (⌬H) was not much changed with increasing heating rates. The activation energy (E a ) increased as the reaction pH decreased from alkaline to strong acid condition. The formaldehyde emission of particleboard was the lowest for the UF resins prepared under strong acid, whereas it showed the poorest bond strength. These results indicated that thermal curing behavior was related to chemical species, affecting the formaldehyde emission, while the poor bond strength was believed to be related to the molecular mobility of the resin used.

Effect of different acids during the synthesis of urea‐formaldehyde adhesives and the mechanical properties of medium‐density fiberboards bonded with them

“…Several di‐ and trimethylolureas, for example 10 – 12 , are produced from 8 and 9 . Tetramethylolurea has never been observed . These results are confirmed by previous studies on the competitive formation of comparable condensed structures (Figure ) …”

“…Tetramethylolurea has never been observed. 5,6 These results are confirmed by previous studies on the competitive formation of comparable condensed structures ( Figure 1). 7 It is accepted that, at alkaline pH, the polycondensation of methylolureas does not form methylene bridges but leads to the formation of low-molecular-weight oligomers linked by methylene ether bridges, and no methylene bridges are created.…”

“…15 Differential scanning calorimetry (DSC) is a widely used technique in polymer research as it provides an easy and fast kinetic evaluation of the curing reaction of thermosetting polymers. 6 A number of studies have used DSC to characterize the thermal curing behavior of liquid and solid UF adhesives as affected by different molar ratios. 19,20 Little information can be found in the literature about various effects of different catalysts on UF resin synthesis.…”

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].…”

Synthesis, Characterization and Glass Reinforcement of Urea-Formaldehyde-Phenol Resins

“…Bonding with UF adhesive is cheaper than with PF adhesive and it permits the formation of strong bonds under a wide variety of conditions. The study of urea-formaldehyde resinification and characterizations are well established [1][2][3][4][5][6][7][8]. UF resins offer technical advantages in many applications such as adhesives, binders, resin glue and anticorrosive coatings [9][10][11][12][13][14][15].…”