Abstract: Parameters in resin manufacture to produce formaldehyde-urea(UF)resins capable of producing low formaldehyde emission particleboards and plywoods were presented and discussed.UF resins were produced through four stages of different reaction pH values(1.5,9.0,4.5,8.0).Free formaldehyde contents of UF resins were affected most significantly by the amount of the added urea in the last stage.During the weak acid stage,methylene linkages in the polymeric resin increased and dimethylene ether linkages decreased as formaldehyde/urea molar ratio and pH decreased.While in the alkaline pH stage,under similar formaldehyde/urea ratio,free formaldehyde content and formaldehyde emission decreased with increase of reaction pH.Addition of 2%-5%(mass ratio)crosslinking agent improved wood adhesion of UF resin of low molar ratio.Formaldehyde emission reached E1(<10 mg/100 g)standard requirement when particleboard and plywood were made with UF resin when formaldehyde/urea molar ratio was lowered to 1:1.

Key words: urea-formaldehyde resin, formaldehyde emission, crosslinking agent, particleboard, plywood