Study on Properties of Modified Low Molar Ratio Urea-Formaldehyde Resins (I)

Abstract

For improving the performance of urea-formaldehyde (UF) resin, modified low molar ratio UF resins were developed to improve water resistance properties and reduce the formaldehyde emission of its bonded products. The effects of modifier feeding amount on the character of the cured resins were characterized by Fourier transform infrared spectroscopy (FTIR) measurement. The viscosity, pH value, solid content, free formaldehyde content, pot time, and curing time of the UF resins were also tested according to Chinese National Standards methods. The results show that the modified 1.00 molar ratio UF resins show lower free formaldehyde content and higher boiling-water-resistance comparing with unmodified ones. The boiling-water-resistant bonding strength of poplar plywood bonded with modified UF resin at 140 °C hot-press temperature can reach type I grade (100 °C water bath 3h) plywood requirement and the formaldehyde emission can meet the E0 grade plywood need.

Influence of Single/Collective Use of Curing Agents on the Curing Behavior and Bond Strength of Soy Protein-Melamine-Urea-Formaldehyde (SMUF) Resin for Plywood Assembly

“…Formaldehyde can react with NH 4 Cl to generate HCl, thereby promoting the curing of amino resin adhesives. However, when NH 4 Cl is added as a curing agent, the wood panel generates extremely toxic dioxin during combustion while low-molar ratio urea formaldehyde (UF) and MUF resins cannot be cured completely [27,28]. To overcome this issue, (NH 4 ) 2 SO 4 was used as a curing agent for amino resin adhesives such as UF and MUF.…”

Hydrolytic and thermal stability of urea‐formaldehyde resins based on tannin and betaine bio‐fillers

“…One of the approaches that gave significant results and proved to be very effective is the reduction of the molar ratio of formaldehyde and urea (FA/U) in the synthesis. 4,12,13 The problem with this method is that it affects the performance of the resin: it reduces adhesion, reactivity and prolongs the gelation time at the expense of reducing formaldehyde emission. Decreasing the molar ratio leads to obtaining resins with a crystalline structure which have worse adhesion than resins with an amorphous structure.…”

“…Therefore, in order to comply with strict legal regulations, and in order to improve the safety not only of the final use of UF resins but also of their production, numerous studies have been published with different approaches for reducing FA emissions. One of the approaches that gave significant results and proved to be very effective is the reduction of the molar ratio of formaldehyde and urea (FA/U) in the synthesis 4,12,13 . The problem with this method is that it affects the performance of the resin: it reduces adhesion, reactivity and prolongs the gelation time at the expense of reducing formaldehyde emission.…”