Polyamine‐modified urea–formaldehyde‐bonded wood joints. III. Fracture toughness and cyclic stress and hydrolysis resistance

Abstract

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

Influence of acrylamide copolymerization of urea–formaldehyde resin adhesives to their chemical structure and performance

“…13 Modified UF resin with urea-terminated hexamethylenediamine, bishexametylenetriamine, and poly (propylene oxide) resulted in an excellent stability of the UF resin. 13,14 These studies also reported that the resistance of UF resin bonded joints to cyclic stress was substantially improved by modifying the resins. In addition, the UF resin modification by a simple mixing of acrylamide showed that the acrylamide did improve the hydrolytic stability of modified UF resin compared to that of other additives.…”

Enthalpies and entropies of fusion of ten alkane-α, ω-diamines H2 N– (CH 2)n– NH2 where 3⩽n⩽12

“…Alkane-α, ω-diamines are an industrially important class of monomers employed in the synthesis and preparation of a number of polymers. (1,2) Their solvation (3)(4)(5) and protonation (6)(7)(8) in aqueous solution have also been the subject of calorimetric studies since they are thought to act as biochemical model compounds.…”

Tensile shear strength of UF- and MUF-bonded veneer related to data of adhesives and cell walls measured by nanoindentation

“…However, UF bonded particleboards are not suited for moist environments, primarily because of their susceptibility to hydrolytic degradation of adhesive bonds. By contrast, only a few studies were devoted to micromechanical behaviour and bond performance of UF and MUF (Bolton and Irle 1987;Bolton 1988, 1991;Ebewele et al 1991Ebewele et al , 1993River et al 1994). Several improvements can be achieved by increasing the melamine content, such as better bond strength and decrease of formaldehyde emission, decreased water absorption and thickness swelling (No and Kim 2007;Hse et al 2008).…”