Study On Synthetic Processing And Catalyst System Of Environmental-Friendly Modified Urea-formaldehyde Resins

Urea-formaldehyde resin (UF) accounts for80%of the amino resin and is widelyused as a kind of wood adhesive, but the problem of high formaldehyde emission exists in the process of its application. Therefore, the development of low content of free formaldehyde resin has been the goal of the timber industry.The main objective of this paper is to study the influence of catalyst systems to the performance of UF resin and the content of free formaldehyde in alkaline-acid process, as well as the performance of UF resin modified by phenol in strongly base process.Single variable method is used to study the process parameters on the properties of the resin. The ammonium chloride method is used for determining the variation of the content of free formaldehyde in UF resin. The viscosity, solid content and other properties are tested too. The modern analytical methods such as nuclear magnetic resonance and infrared spectroscopy are used for analyzing the molecular structure and curing behavior of UF resin.The appropriate reaction conditions of the alkaline-acid process:molar ratio of F/U is1.3:1, the reaction temperature is80℃, the reaction time is3h. The content of free formaldehyde of the resin is0.4221%. The suitable reaction conditions of strongly base process:phenol adds in the early reaction and accounts for0.8%of the overall weight, and sodium hydroxide accounts for14%, the content of free formaldehyde of the resin is0.1%.Drawn by the study of catalyst systems in alkaline-acid process:In traditional catalysts, catalytic effect from excellent to poor of alkali in addition stage:(HOCH2CH2)3N、Ba(OH)2、NaOH、Na2CO3, the content of free formaldehyde is:0.3072%、0.3857%、0.4255%、0.5562%; that of acid in polycondensation stage:CF3SO3H、HCOOH、 CH2COOH, the content of free formaldehyde is:0.3246%、0.4255%、0.6087%.In the new catalysts,8‰cation exchange resin is used as acid catalyst in polycondensation stage, the content of free formaldehyde is0.3286%, so it plays a good catalytic effect. D301anion exchange resin is used as base catalyst in addition stage, the content of free formaldehyde is more than0.75%, the catalytic effect is poor;4%D201anion exchange resin is used too, the content of free formaldehyde is0.3211%, it plays a good catalytic effect, and the overall performance of the finished resin are better.