POLYAMINE-MODIFIED UREA-FORMALDEHYDE RESINS .1. SYNTHESIS, STRUCTURE, AND PROPERTIES

The objective of this study was to improve the durability and stability of urea-formaldehyde-bonded wood products by decreasing the internal stress developed during resin cure and by improving the ability of the cured resin to withstand cyclic stresses. This paper presents initial results from modifying a urea-formaldehyde resin by incorporating di- and trifunctional amines. The amines were incorporated by adding them as amines during resin synthesis, by adding urea-capped amines during resin synthesis, and by using amine hydrochlorides as acidic curing agents. Addition of amines during resin synthesis produced uncurable resins. However, modification with urea-capped amines or curing with amine hydrochlorides provided cure rates comparable to that of unmodified resin cured with ammonium chloride. These modifications also reduced the tendency of the resin to crack and fracture and substantially improved the resistance of bonded joints to cyclic stress imposed by cyclic wet-dry exposures. Resins cured with amine hydrochlorides had lower formaldehyde liberation than those cured with ammonium chloride. Thus, incorporation of flexible di-and triamines offers promise for improving the durability and stability of urea-formaldehyde-bonded wood products.