desirable, but this characteristic also means that little strength can be
added to the much stiffer material that is being consolidated.Influence of solvents used for thermoplastic resins
The choice of solvents for thermoplastic resins can influence the ease of
penetration, either by the degree of solvent polarity or by the resulting
solution viscosity. The property of a given polymer deposited from solu-
tion may depend on the dynamic quality of the solvent used. Hansen and
coworkers f ound significantly different mechanical properties offilms of
AYAT cast from acetone and from toluene, with toluene giving the lower
values (Hansen et al. 1991). Wang and Schniewind found evidence that the
use of polar rather than nonpolar solvents tended to result in somewhat
gr eater levels of strengthening (Wang and Schniewind 1985). The distribu-
tion of consolidant, however, was not significantly affected by solvent
polarity (Schniewind and Eastman 1994).
Solvent polarity was also found to be an important factor in the
study of the incidental adhesive qualities of soluble resin consolidants
(Sakuno and Schniewind 1990). It should be noted that adhesives and con-
solidants differ fundamentally in their formulation, regardless of the simi-
larities discussed. Consolidants are formulated at low viscosity to achieve
maximum penetration; adhesives for a porous material like wood must be
formulated to have relatively high viscosity in order to limit penetration,
since most of the adhesive should remain on the surfaces to be joined.
Thus Koob used Acryloid B72 in acetone as an adhesive at a concentration
of 50% (weight basis), as compared to the 10–15% concentration used for
consolidation (Koob 1986). Sakuno and Schniewind used 15% solutions
(weight basis) of AYAT, Acryloid B72, and Butvar B98, each in two different
solvents, to study the incidental adhesive qualities of consolidant solutions
(Sakuno and Schniewind 1990). These incidental adhesive qualities of con-
solidants relate to their ability to reattach loose fragments in the process of
consolidation treatment. The results are summarized in Figure 2. Not unex-
pectedly, none of the consolidant solutions performed as well as the com-
monlyused PVA “white glue” adhesive, the explanation for which is based98 Schniewind
Table 2 Properties of resins and their strengthening capability, or improvement factor, calcu-
lated as the ratio of bending strength of treated deteriorated Douglas-fir samples to
that of untreated controls. The asterisk denotes a value that is not practical to measure.Tensile Improve-
Molecular strength Tg ment
Resin weight (MPa) (°C) factor Reference
Butvar B90 45,000 46 68 1.14 Wang and Schniewind 1985
Butvar B98 34,000 46 68 1.19 Wang and Schniewind 1985
Butvar B98 34,000 46 68 1.20 Schniewind and Kronkright 1984
Acryloid B72 — — 40 1.16 Schniewind and Kronkright 1984
AYAT 167,000 29 28 1.13 Schniewind and Kronkright 1984
AYAF 113,000 18 24 1.10 Schniewind and Kronkright 1984
AYAA 83,000 10 21 1.03 Schniewind and Kronkright 1984
AYAC 12,800 * 16 1.11 Schniewind and Kronkright 1984