Performance and structures of urea-formaldehyde resins prepared with different formaldehyde solutions

Two types of urea–formaldehyde (UF) resin adhesives were synthesized with standard formaldehyde solution with 37% concentration and concentrated formaldehyde solution with 45% concentration. For 37% formaldehyde, 10% methanol was used as an inhibitor. For 45% formaldehyde, no more methanol was added. The chemical structure and changes during the resin preparation were analyzed. The performance of particleboards prepared with these resins was evaluated. The results indicated that the main difference between the concentrated formaldehyde and the standard formaldehyde was the higher content of methanol in the latter. Methanol affected the reaction during the preparation of UF resins and the final performance of the resins. Samples of the UF resin with standard formaldehyde taken at different stages during its preparation showed different contents of methylol groups, methylene ether bonds, uron structure, methylene bonds, and other groups compared to the resin prepared from concentrated formaldehyde. The performance concerning water resistance, mechanical performance, and formaldehyde emission of the particleboards prepared with the UF resin with concentrated formaldehyde was better than that with the resin with standard formaldehyde.