Chemical Foam Extension of Urea-Formaldehyde Glues

Fillers and extenders are used in resin adhesives to control certain properties and lower the cost per glue line. Shell flours help body the resin and reduce the danger of over-penetration and bleeding. However, the problem with shell flour is that only limited amounts can be used to obtain a workable mix and a satisfactory bond. The most serious problem is the spread; flour has no bonding properties and it interferes with the flow of the resin under heat and pressure. For these reasons, other methods of extension are needed. One method of foaming urea is by mechanical agitation. This creates a relatively unstable foam that must be used immediately. This, along with other short-comings, shows a need for a different foaming method. Chemical foaming using a high molecular weight resin formulation and a foaming catalyst offered the best method. The chemically foamed urea is much more stable. Experience has shown that the spread recommended for chemically foamed resin should be in the range of 15-25 pounds per thousand square feet of single glue line. Numerous field and control tests have shown that when properly applied, foamed resin, used under proper conditions, gives an excellent bond. In many cases, this foamed resin bond is superior to conventional resin bonds since the foamed resin contains no flour to interfere with the reaction on water which is absorbed by the wood.

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