The use of polyolefins-based hot melts for wood bonding

The shear strength of three-layer birch veneer/polyolefin/birch veneer lap joints has been investigated. It was found that the optimum technological parameters for producing three-layer laminated systems (plywood) at 180°C were a pressure time of 1-3 min (plus 3-min preheating) and pressure of 5-10 MPa. All the systems investigated exhibited relatively high values of shear strength, which were higher than those of the industrially produced plywood based on phenol-formaldehyde glues (3.5-5 MPa). It is shown that the use of interfacial modifiers can increase the shear strength by 50% compared with its initial values. The high shear resistance is explained by the high mechanical adhesion between the hot melts and the wood substrate. After a prolonged moisture influence (70 days at relative air humidity of 80%), all the systems investigated showed a considerable (up to 25%) increase in the shear strength. This can be explained by swelling of birch veneer, which gives rise to additional resistance forces between the hot melt and the substrate.