SYNOPSISThe objective of this study was to improve the durability and stability of urea-formaldehydebonded 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 diand triamines offers promise for improving the durability and stability of urea-formaldehydebonded wood products.

synopsisThe performance of adhesive bonded joints depends on many factors, one of which is the adhesive formulation. The effects of organic and inorganic fillers upon the fracture toughness of phenol-resorcinol-formaldehyde adhesive in hard maple joints were explored in this study. Analytical techniques (DSC, IR, SEM, and GPC), and solubility studies were employed to relate physical effects to chemical effects of the fillers. The resin showed two distinct stages of cure: (1) a low temperature exotherm associated with resorcinol and paraformaldehyde and (2) a high temperature endotherm associated with the base resin. Filler was found not to affect the cure. Fillers did have a profound effect on the morphology of the wood-adhesive interphase and upon the bulk adhesive properties. These effects, revealed in both SEM and fracture toughness studies, are discussed at length.

SYNOPSISMangrove bark tannin adhesives are based on a renewable resource. They are potential substitutes or supplements for phenol-formaldehyde (PF) wood-bonding adhesives which are derived from petroleum, a finite natural resource. However, mangrove tannin adhesives exhibit poor adhesive properties including poor wet strength, brittleness, and poor wood penetration. These problems were addressed by treating tannin extract with acetic anhydride and then sodium hydroxide followed by modification with 20% resole-type P F resin. Significant structural changes occurred after the chemical treatment. Heat of reaction of tannin with formaldehyde was increased while the activation energy was drastically reduced. Premature cure was also reduced. The fortified formulations had good plywood adhesive properties.

SYNOPSISThe objective of this study was to improve the durability and stability of urea-formaldehydebonded wood products by decreasing the internal stress developed during the resin cure and by improving the ability of the cured system to withstand cyclic stresses. Urea-formaldehyde resins were modified either by incorporating urea-capped di-and trifunctional amines into the resin structure or by using the hydrochloride derivatives of some of these amines as the curing agent, or by both methods. This study supplements ourprevious work by examining the effects of additional amines and subjecting bonded products to additional testing. Solid wood joints bonded with a variety ( 7 of 15) of modified adhesives had resistance to cyclic stress superior compared to that of joints bonded with unmodified urea-formaldehyde adhesive; at least three of the modified adhesives approached the behavior of phenolformaldehyde-bonded joints. Resistance to moist heat aging, although still inferior to that of phenol-formaldehyde-bonded joints, was significantly improved for joints bonded with modified adhesives over joints made with unmodified resins. The fracture behavior of joints made with modified adhesives was different from that of joints made with unmodified resins. The fracture energy was greater for joints made with three of four modified adhesives than for joints made with unmodified resins. Modified adhesives produced particleboards with enhanced cyclic stress resistance. Formaldehyde emission from particleboards made with resins modified with urea-terminated amines was less than emission from boards made with unmodified resins. However, emissions from particleboards made with amine hydrochlorides were not improved compared to those from boards made with an ammonium chloride curing agent. 0 1993 John Wiley & Sons, 1nc.t

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