A major problem in the manufacture of three-dimensional laminated veneer products is damage due to stretching and/or buckling of the veneer. To reduce or eliminate this problem a modification of the veneer could be a solution, but the modification may also lower the quality of the adhesive bond. The purpose of this study was to investigate how different modifications influence the adhesive bond strength between the veneers. Three different modifications were studied: 1) surface veneer pre-bonded with paper and hot melt adhesive under a surface pressure of 1.8 MPa at a temperature of 130°C; 2) veneer pre-bonded with polypropylene fabric glued to the veneer with an urea formaldehyde (UF) adhesive system under a surface pressure of 1.0 MPa at a temperature of 80°C; 3) densified veneer. An unmodified veneer was tested as a reference. The modified veneers were bonded to an unmodified veneer with an UF adhesive system under a surface pressure of 1.5 MPa at a temperature of 90°C. Determination of tensile shear strength was performed in an ABES testing machine as a single lap joint test directly after bonding and after climate cycling. The results showed that veneer pre-bonded with polypropylene fabric and UF adhesive gave a weak glue-line, indicating that the pre-bonded veneer with polypropylene fabric and UF adhesive impairs the bonding. The other groups showed no significant difference from the reference veneer in tests before climatic cycling. The climate cycling deteriorated the adhesive bonds slightly for specimens pre-bonded with both paper and polypropylene fabric.
Keywords: densification, pre-bonding, open system, THM processing, veneer, wood adhesive bonds
Authors
Blomqvist L.
Department of Forestry and Wood Technology, Linnӕus University, Växjö
Sterley M.
SP Wood technology, SP Technical Research Institute of Sweden, Stockholm, Sweden
Sandberg D.
Division of Wood Science and Engineering, Department of Engineering Sciences and Mathematics, Luleå University of Technology, Skellefteå
Johansson J.
Department of Forestry and Wood Technology, Linnӕus University, Växjö
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