Study On Synthetic Technique Of Low Cost And Low Toxic Urea-formaldehyde Resins

Urea-formaldehyde (UF) resins has many advantages such as abundant raw materials, low cost, good agglutinative performance and so on,are most widely used adhesives. However UF resins and their products will release formaldehyde which seriously affect healthy in mind and body of people in the process of production and their application. The adhesive industry has focused on the research to produce UF resins with low free formaldehyde content (FFC) and with high agglutinative strength.The effect of several factors on UF resin properties were firstly studied on the basis of"mild base-mild acid-mild base"synthetic technique, which included adding urea in three portions respectively. The factors are the molar ratio of formaldehyde to urea, the pH value, the temperature and time of reaction in every stage, and there is no modifying agent used during the synthetic technique.According to the above experiments, the synthetic conditions are determined as follows. The molar ratios of formaldehyde to urea are r1=2.4, r2=1.8 and r3=1.2; the pH values are: pH1=8.0, pH2=5.0 and pH3=8.5, the temperature are T1=60℃, T2=91℃and T3=70℃; the reaction time are t1=60min, and t3=40min. The UF resins produced by the process meet the requests of national standard for low free formaldehyde. The viscosity is 65.2mPa.S, the curing time is 42.0s, the solid content is 49.93%, the free formaldehyde content is 0.44%, for the UF resin. Especially the agglutinative strength of cold pressing board is as high as 1.52 MPa, exceeding that of the national standard for hot pressing board (>0.8MPa). The cold pressing method is superior to the hot pressing method, not only for easy operation but also for more energy savings.when oxidative starch join in urea formaldehyde resin, the free formaldehyde content is decreased, the solid content is improved, agglutinative strength is increased, store time is elongated. At one time, produce cost is increased.