2 SYNTHETIC RESINS AS CONSOLIDANTS

THERMOSETTING SYNTHETIC resins such as epoxy, polyester, and methyl acrylate are chemically or radiation curing synthetic polymers. This category of synthetic resins has been commercially applied in the manufacture of wood-plastic composites, and is known to impart strength as well as improve other physical properties of undegraded wood. Thermosetting synthetic resins such as epoxy and methyl methacrylate have also been used as consolidants for deteriorated wood (Schaffer, 1971, 1974; and Munnikendam, 1969). However, thermosetting resins are definitely not reversible. Also, epoxy treated wood may have an aesthetically unsatisfactory appearance (Schaffer, 1971), and the heat developed in curing may lead to out-of-control rapid cure and damage to an object (Munnikendam, 1978; Grattan, 1980).

Soluble thermoplastic resins are able to impart strength to deteriorated wood and to meet the requirement of reversibility. Grattan (1980) examined a number of commercially available thermoplastic resins, and found polyvinyl butyral and acrylics to be the most promising consolidants. Subsequently, Barclay (1981) used polyvinyl butyral to consolidate an eighteenth-century English fire engine.

In connection with the conservation of a canoe, Schniewind and Kronkright (1984) did a series of tests using different resins. Tests on bacterially degraded wood showed that polyvinyl butyral (Butvar) gave the most improvement in strength, followed by an acrylic (Acryloid B72) and then polyvinyl acetates (AYAT, AYAF, AYAA and AYAC). Moreover, they found that the relative improvement in strength was proportional to the degree of deterioration.

Many researchers (Munnikendam, 1978; Schaffer 1971; and Werner 1977) have criticized the use of this group of polymers, because large quantities of solvent are involved. Once conservators think about reversibility of treatment, however, impregnation with soluble thermoplastic polymers becomes the most promising method.