BONDING WOOD
FEICA Figure 50In woodwork, and in particular in the furniture-making industry, polyvinyl acetate dispersion adhesives have long superseded the carpentry adhesives based on animal proteins that were used thousand of years ago. Condensation resins (urea, melamine, phenolic and resorcinol-formaldehyde resins) have made possible the development of new wood-based materials such as plywood, chipboard and laminated composites (resorcinol/ phenol-formaldehyde resins) for building construction.
Melamine-formaldehyde resins are used in conjunction with special papers for manufacturing decorative boards for laminating wood for furniture manufacture. Polyurethane (PUR) adhesives that cure by exposure to moisture are currently of growing importance for the manufacture of chipboard, due to the fact that they represent formaldehyde-free alternatives to the aforementioned polycondensation resins. In addition, they are being increasingly used for bonding wooden construction elements. As with adhesives in many areas of technology, wood adhesives are also tending to become 100% systems -they combine simple application with rapid curing. Hot melts have proved particularly useful as adhesives for assembly work and for bonding decorative edging. The application of PUR hot melts, which cure via the influence of moisture, is very much on the increase for the structural bonding of wood and for joining wood with a host of other materials. This type of adhesive involves two different curing mechanisms: the solidification of the hotmelt on cooling means that the components are rapidly affixed. The chemical curing which then follows, involving the crosslinking of molecules, leads to high-strength bonds