Weather-resistant wood products, phenolic adhesives

The most prominent wood adhesives used over the last quarter of a century have been aminoplast and polyphenolic types (2). In the United States, polyphenolic adhesives continue to be predominantly used for production of weather-resistant wood products, such as structural plywoods and flake boards (3). Phenolic resin prices have increased over the past decade, generally paralleling phenol prices. This increase has occurred in part due to a continuing erosion of United States phenol manufacturing capacity and the corresponding increase in availability of phenol from other countries. Any significant increase in the price of oil (the source of phenol) itself or interruption in supply will only compound the problem and raise phenol prices even higher. 

Phenolic adhesives continue to be the most significant adhesives for the production of weather-resistant wood products. The energy crisis of the seventies, the cost of phenol, and the inevitable decline in petroleum reserves have caused the wood industry to focus attention on obtaining adhesive self-sufficiency (1). This concern arises primarily from the questionable longterm availability of resins and secondarily from the economics of adhesive resin use. Ready availability of adhesive resins is critical to the manufacture of bonded wood products. In practical terms, this means that new adhesive systems are needed in which part, or perhaps all, of the petroleum-derived phenolic component is replaced... 

The wood panels industry heavily relies on the use of synthetic resins and adhesives, as adhesively bonded products of one kind or another constitute about 80% of the wood products on the market today. In short, without adhesives and resins this industry would not exist [1,2]. Among these products a certain proportion of wood panels are manufactured for exterior, weather resistant application. Phenol-formaldehyde (PF) resins, and more recently, phenol-urea-formaldehyde (PUF) resins [3-8] are the most commonly used resins among the leading adhesives for exterior grade wood panels. 

The main advantage of all types of phenolic resin adhesives for wood is their remarkable weather and water resistance. Their main use is then for the manufacture of exterior- and marine-grade wood products, structural or otherwise. 

Resorcinol-formaldehyde resins are cold-setting adhesives for wood structures. Urea-formaldehyde adhesives, commonly modified with melamine formaldehyde, are used in the production of plywood and in wood veneering for interior applications. Phenol-form-aldehyde and resorcinol-formaldehyde adhesive systems have the best heat and weather resistance. 

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