Abstract: A series of urea-modified phenol formaldehyde(PUF) resin systems with different urea contents were prepared and used in the preparation of plywood(when the dosages of urea(U) were 0, 25%, 43% and 66% of the mass of phenol(P), the obtained samples were recorded as PF, PUF-1, PUF-2 and PUF-3). The resins were used for preparing plywood and the change of resins during plywood processing was studied. The results showed that the contact angles of the PUF-3 resin with eucalyptus and poplar were 79.6ånd 81.1°, and the compatibility of PUF to eucalyptus wood was better than that of poplar wood. And the curing processes of four kinds of resins were obtained by DSC analysis. The temperatures of maximum curing rate of PF, PUF-1, PUF-2 and PUF-3 were 146.8, 171.4, 171.8 and 171.8℃. The rheological behavior of the complex system formed by mixing PUF-3 with flour was studied by means of rotating rheometer, and the curing reaction began to occur at 110℃, and the suitable hot-pressing temperature was (130±5)℃. The thermogravimetric analysis of PF and PUF-3 before and after hot pressing showed that the high temperature resistance of PUF was better than that of PF, and the heat resistance of structure formed by hot pressing was better. The properties of plywood produced with the four resins were qualified and reached E₀ level, the formaldehyde emission of eucalyptus plywood was less than 0.5mg/L, and the bonding strengths of plywood were 1.42, 1.11, 0.98 and 0.92MPa, respectively.

Key words: urea-modified phenol formaldehyde resin, wood adhesive, artificial board, processing technology