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    Author(s): B.H. River; R.O. Ebewele; G.E. Myers
    Date: 1994
    Source: Holz als Roh- und Werkstoff. Vol. 52 (1994): Pages 179-184
    Publication Series: Miscellaneous Publication
    PDF: View PDF  (197 KB)

    Description

    Wood joints bonded with urea-formaldehyde (UF) are weakened by cyclic swelling and shrinking. To study the failure mechanisms in UF-bonded joints, specimens were bonded with unmodified, modified (amine), or phenol formaldehyde adhesive and subjected to accelerated aging. Modification of the adhesive properties increased the cleavage fracture toughness and shear strength of bonded joints and improved the resistance of joints to cyclic swell-shrink treatment and accelerated moist-heat aging. Joints bonded with some modified urea-formaldehyde adhesives were as resistant to these treatments as joints bonded with phenol formaldehyde. Physical and mechanical origins of the improved adhesive performance were determined by microscopic analysis. Cure-shrinkage stresses precracked unmodified adhesive layers and damaged the wood interphase. The damaged interphase was especially susceptible to the effects of cyclic swelling and shrinking stresses. Certain modifiers reduced or eliminated cure-shrinkage cracking and damage to the wood. Moist-heat aging caused molecular scission in the bulk unmodified adhesive layer as revealed by the onset of shear cracking in the adhesive layer and erosion of exposed surfaces. Certain modifiers reduced or eliminated molecular scission and erosion responsible for adhesive weakening in moist-heat aging. We conclude that incorporating flexible amines in the adhesive structure improves the durability and stability of UF-bonded joints.

    Publication Notes

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    • This article was written and prepared by U.S. Government employees on official time, and is therefore in the public domain.

    Citation

    River, B.H.; Ebewele, R.O.; Myers, G.E. 1994. Failure mechanisms in wood joints bonded with urea-formaldehyde adhesives. Holz als Roh- und Werkstoff. Vol. 52 (1994): Pages 179-184

    Keywords

    Wood joints, wood adhesives, urea-formaldehyde adhesives, failure

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