Morphology and chemical elements detection of cured urea–formaldehyde resins

Abstract

As a part of understanding the hydrolysis of cured urea-formaldehyde (UF) resins that has been known as responsible for the formaldehyde emission, leading to sick building syndrome, this study attempted to investigate the morphology and to detect chemical elements of the cured UF resins of different formaldehyde/urea (F/ U) mole ratios and hardener (NH 4 Cl) levels, using field emission-scanning electron microscopy and energy-dispersive spectroscopy. Cured UF resins of low F/U mole ratio showed spherical structure whose diameter increased with an increase in the hardener level, whereas this was not observed for high F/U mole ratio UF resins regardless of the hardener levels. The energy-dispersive spectroscopy results showed five different chemical elements such as carbon, nitrogen, oxygen, chloride, and sodium in cured UF resins. The chloride distribution assumed as the presence of residual acid in the cured UF resins suggested that the hydrolysis of cured UF resins could initiate at the sites of chlorides on the surface of the spherical structures. As the hardener level increased, the quantities of both carbon and oxygen decreased, whereas those of nitrogen and chloride increased as expected. But the quantity of sodium was within measurement error.

Influence of starch addition on properties of methylolated urea/starch copolymer blends for application as a binder in the coating industry

“…Hydrolysis of cured urea resins has been known to be responsible for formaldehyde emission leading to sick building syndrome. It is therefore important to determine the formaldehyde emission from synthesized urea formaldehyde resin (Derkyi et al, 2008;Park et al, 2010). It is observed in figure 7 that the level of emission decreased with increase in the concentration of Cassava starch in the blend.…”

Tailoring of oxidized starch's adhesion using crosslinker and adhesion promotor for the recycling of fiberboards

“…This optimum level was obtained by comparing the mean values of density, internal bonding (IB) strength, modulus of rupture (MOR), modulus of elasticity (MOE), thickness swelling (TS), water absorption (WA), and formaldehyde emission (FE); the B‐pMDI/OS‐bonded MDF using statistical analysis. As a control, UF resins with formaldehyde/urea mole ratio of 1.0 were synthesized using an alkaline–acid two‐step reaction, as reported in the literature …”

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].…”

“…Thus, the information provided here adds new knowledge on the influence of F/U mole ratio on thermal curing kinetics of UF resins. We have described morphology and microstructure of cured UF resins in a solid film form [10,12]. Although liquid UF resins have been studied extensively, there is still an information gap in thermal curing behavior of partially cured solid UF resin.…”