Advances in Polyvinyl Acetate Glues for Woodworking

A discussion is presented of the development and use of vinyl acetate resins and vinyl acetate copolymers for the woodworking field. Polyvinyl acetates were examined as possible adhesives beginning in 1937 when they were used for bonding absorbent surfaces such as paper, leather, building materials, and wood. The first practical adhesives based on emulsions of polyvinyl acetate were produced in 1939. With the introduction of polyvinyl acetate in an emulsion form, the use of this adhesive was greatly accelerated. An emulsion of a resin consists of tiny particles of the resin suspended or dispersed in water and kept in uniform size and degree of distribution by means of carefully selected emulsifying agents. When the emulsion is placed on an absorbing surface, the aqueous phase is drawn by capillary action into the structure of the absorbing surface, leaving behind the tiny particles of resin which fuse together with great rapidity to form the adhesive film. The setting speed of the emulsions depends upon two factors, nature of the emulsion and the absorbing capacity of the surface. Polyvinyl emulsions were first introduced to fill the need for high-speed packaging materials. With a war-time shortage of protein and starch glues, the furniture industry began exploring the possibilities of using vinyl acetate emulsions for the bonding of wood. The use of these resins was first employed about 1943, but many technical problems surrounding the correct use of this resin had to be resolved. Rapid setting speeds are a distinct feature of the polyvinyl acetate emulsions. Comparisons in block shear strengths between animal glue and polyvinyl glue are given after various elapsed periods of assembly. The same comparisons are made with different clamping pressures. One of the early difficulties experienced with polyvinyl acetate emulsion appears to have been caused by the inability of the adhesive to withstand continuous loading. Research continued in an effort to correct this tendency and a copolymer was introduced which minimized the tendency of this resin to creep. Another problem was low temperature sensitivity. Below 40?F. polyvinyl acetate emulsions had a tendency to coagulate. Further research on this problem led to the development of an improved copolymer which was not damaged by repeated freezing or thawing.

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