Scanning Electron Microscopy of Plywood Glue Lines<sup>1</sup>
Abstract
Douglas-fir plywood panels made under specific conditions to represent dried-out, undercured, high-moisture, and rough-veneer glue bonds were tested in shear, and the failure surfaces were evaluated by light and scanning electron microscopy.
Results showed low shear strength and low percentages of wood failure in all above panels. Wood failure occurred both by intrawall failure and transwall failure parallel with the grain direction in wood. Scanning electron microscopy made it possible to distinguish between glue-coated areas versus uncoated wood fracture and clearly showed glue distribution and the physical form of glue on the failure surface.
Dried-out bonds are characterized by the lack of a continuous glue line, little or no transfer of glue onto the face veneer, and mostly by adhesive failure. The most important features of high-moisture joints are the formation of numerous steam bubbles in the glue line and the lack of a continuous glue bond. These are due to the excessive squeeze-out of glue in the press and the overpenetration of glue into the wood. Both rough-veneer and low-pressure joints provide discontinuous glue lines because of the lack of continuous contacts between the adjacent veneers.
All results show that examination of shear specimens by SEM is an effective method for determining the cause of glue-line failure.
References
Côté, W. A., and R. C. Vasishth. 1970. Light and electron microscopic studies of wood/wood coating systems. 10th Fatipec Congress. Verlag Chemie 6mbH, Weinheim/Bergstr. p. 57-65.nKoran, Z. 1968. Electron microscopy of tangential tracheid surfaces of black spruce produced by tensile failure at various temperatures. Sven. Paperstidn. 71(17): 567-576.nQuirk, J. T. 1968. Fluorescence microscopy for detecting adhesives on fracture surfaces. USDA Forest Serv. Forest Prod. Lab. Res. Note FPL-0191.n
Downloads
Published
Issue
Section
License
The copyright of an article published in Wood and Fiber Science is transferred to the Society of Wood Science and Technology (for U. S. Government employees: to the extent transferable), effective if and when the article is accepted for publication. This transfer grants the Society of Wood Science and Technology permission to republish all or any part of the article in any form, e.g., reprints for sale, microfiche, proceedings, etc. However, the authors reserve the following as set forth in the Copyright Law:
1. All proprietary rights other than copyright, such as patent rights.
2. The right to grant or refuse permission to third parties to republish all or part of the article or translations thereof. In the case of whole articles, such third parties must obtain Society of Wood Science and Technology written permission as well. However, the Society may grant rights with respect to Journal issues as a whole.
3. The right to use all or part of this article in future works of their own, such as lectures, press releases, reviews, text books, or reprint books.
