ADHESIVE QUALITIES OF CONSOLIDANTS FOR DETERIORATED WOOD
TOMOYASU SAKUNO, & ARNO P. SCHNIEWIND
THE STABILIZATION of deteriorated wooden artifacts of historical or archeological significance may require consolidation of the degraded wood material. To this end, the wood may be impregnated with a variety of natural and synthetic materials. The types of consolidants that might be used and their properties have been thoroughly discussed by Werner (1977). He particularly addressed the strengthening of deteriorated wood by impregnation with thermoplastic resins or other consolidants. Good adhesion between wood and consolidant is one of the most important factors for effective strengthening. Grattan (1980) listed good adhesive qualities as the first among 11 attributes of ideal consolidants. Consolidants should also perform well as adhesives so that loose fragments become reattached in the process of consolidation (Barclay 1981; Nakhla 1986).
Grattan (1980) investigated the consolidation of deteriorated wood using different types of thermoplastic resins and concluded that acrylics and polyvinyl butyrals were the most effective. Schniewind and Kronkright (1984) selected several consolidants of the acrylic, polyvinyl butyral, and polyvinyl acetate types to determine their effectiveness in strengthening deteriorated wood. An extensively degraded Indian canoe, a lumjawi, treated with a polyvinyl acetate resin was investigated. In addition systematic tests were made on material from Douglas-fir foundation piles that had been buried for about 70 years and had outer layers severely degraded by bacteria. An acrylic (Acryloid B72) and polyvinyl butyral (Butvar B98) were found to give the greatest improvement in bending strength.
Furthermore, Wang and Schniewind (1985) treated specimens from the severely degraded outer layer of piles from the same source with solutions of various combinations of consolidants and solvents. A detailed examination of the bending strength and stiffness of the treated wood was made. While the strengthening effect unquestionably depends in some measure on adhesive bonding strength, this relationship was not investigated directly. The use of the acrylic Acryloid B72 as an adhesive has been examined (Koob 1986), but the solution was prepared at 50% solids content w/w, appropriate as an adhesive formulation but much too viscous to be suitable for consolidation.
Accordingly, it appeared desirable to study adhesive bonding of thermoplastic resins in formulations suitable for consolidation. This study is important not only with respect to the reattachment of loose particles, as already pointed out, but also because the consolidant must be firmly bonded to the material that is being treated in order to obtain the most effective strengthening.