Phenol and Resorcinol Adhesives

Urea formaldehyde, acid-curing, phenolic, phenol-resorcinol, resorcinol formaldehyde, and melamine formaldehyde are the available adhesives suitable for assembly gluing. Among these, phenol-resorcinol and resorcinol formaldehyde are the most durable waterproof adhesives. Modification of urea formaldehyde adhesives with benzyl and furfuryl alcohol produces adhesives with better bonding quality and craze resistance. They are not, however, as durable as bonds developed in the hot press using phenolic or melamine adhesives. Acid-curing phenolic adhesives are capable of setting at room temperature or at mildly elevated temperatures. They are also capable of curing by radio frequency and are relatively free from arcing. Their limited shelf life, however, presents a serious handicap. Melamine formaldehyde adhesives for low-temperature or intermediate-temperature gluing all require some addition of acidogenic materials. There has been little acceptance of melamine adhesives in assembly work. Straight resorcinol formaldehyde and phenol-resorcinol adhesives are capable of curing at room temperature to provide bonds equal in durability to those produced by hot-press phenolic adhesives. The capability of these adhesives of setting at a neutral pH and on the mildly alkaline side provides freedom from catalyst attack on wood fibers. The disadvantages of this class of adhesives are the high cost of resorcinol and the inherent wine-red color.

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