URON resins for the manufacture of E1 formaldehyde emission class plywood

Urea-formaldehyde (UF) resin is a common binder used in the production of interior grade plywood. Uron resin is also a kind of UF resin formed by cross linking Urea and formaldehyde at appropriate pH and temperature during which the dimethylol ureas are shifted to form cyclic urons. In this study, the uron resins for bonding wood veneers to transform into low formaldehyde emission plywood were prepared. The uron resins prepared were also modified by blending the uron and the conventional UF resin. This study revealed that introducing the uron structure in the resin drastically minimized the free formaldehyde content in the resin and also reduced the emission of formaldehyde from the plywood bonded with uron resins and combination of uron with UF resins by 85% and 90% respectively. This study established the uron resin synthesis condensation time of 50 min at 92ºc, alkaline pH of 7.2 to 7.5 and 20 min at acidic pH of 4.5 to 4.8. The total reaction time required was less than that of conventional UF resin. The results of the bond quality of the plywood, free formaldehyde content and the formaldehyde emission levels indicated that the plywood made with the uron resins synthesized for 20 min condensation time in second stage blended with equal proportion of conventional UF resin (Formaldehyde/Urea molar ratio of 1:1.7) yielded excellent bond quality (Moisture Resistance grade) as per IS 848:2006 and conformed to the E1 formaldehyde emission class as per EN 13,986. Equally blending the uron resin with UF resin yielded greater bond strength with lower formaldehyde emission than a simple conventional UF resin.