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The thickness of glue lines in 3-layer beech plywood was investigated. The plywood was manufactured in a laboratory using the phenol- formaldehyde and urea-formaldehyde resin. The thickness of the real glue lines between surfaces of adjacent veneers was measured using microscopy, and the thickness of the apparent glue lines including the real glue lines and the glue which penetrated into the wood was determined by means of a method worked out by the authors. It was found that the urea glue lines were thicker than the phenol ones and that the depth of glue penetration into veneers was the same for both glues.
The method for determination of the thickness of glue lines in plywood is proposed. This thickness, named the apparent thickness of the glue line, includes the real glue line between surfaces of adjacent veneers and the glue which penetrated into the wood. Application of the method for calculation of the apparent thickness of glue lines in beech 5-ply plywood manufactured in a laboratory using the phenol-formaldehyde resin is presented. Moreover, the real thickness of glue lines in plywood was determined using an optical microscope. The results of the microscopic measurements confirmed the proposed method.
Influence of veneer with knot holes on mechanical properties of densified wood laminate was tested. Tensile, compressive and parallel to veneer grain bending strength was tested. Percentage of veneers with knot holes, natural and made with hole saw was set on 10, 20, 30 and 50%. Test shows, after statistical verification, that even 50% veneers with knot holes does not significantly affect densified wood laminate strength.
During the tests 3-ply beech glued with fibrous polypropylene were made. 5 spread amounts were applied: 75, 100, 125, 150 and 175 g/m2. Shear strength, bending strength, modulus of elasticity, swell, absorbability after soaking, density and compression factor were tested. Presented results show certain possibility of production of proper plywood with waste fibrous polypropylene used as an adhesive. Polypropylene adhesive amount increase has different influence on various tested plywood parameters.
In this work they are shown possibilities of utilisation of adhesives for wood bonding, as: phenolic resins, resorcinol modified novolacs and m-Aminophenol modified novolacs.
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