The Structural Conservation of Panel Paintings

on the relatively low concentration used. When polar solvents were used—

acetone for Acryloid B72, and ethanol for AYAT and B98—all three resins

performed about the same. For B98 no pure nonpolar solvent could be

located, but the adhesive qualities of Acryloid B72 and AYAT in the nonpo-

lar toluene were only a fraction of what was found with polar solvents.

Solvent volatility is another consideration. Solvents may be

retained for a period, as shown in Table 3, for cast films of Acryloid B72

and Butvar B98. Missing values ofTgindicate values too low to measure.

The more volatile solvents with low boiling points, such as acetone, can be

removed more readily following treatment. This relative ease of removal

reduces problems with objectionable residual vapors as well as with sol-

vents retained by the consolidant resin. Retained solvents will lower the

Tgof the resin and tend to make it less effective (Carlson and Schniewind

1990), but this result can be minimized by the use of solvents with low

boiling points. However, less volatile solvents may prove superior in cases

when consolidant is applied by brushing, since they would allow more

time for deeper penetration.

Schniewind examined the effect of aging on consolidated wood

samples (Schniewind 1990b). Bending tests made two weeks, one year, and

three and a halfyears after treatment of deteriorated wood with B98 in

ethanol or a mixture of ethanol and toluene, and Acryloid B72 in acetone

or toluene, showed no overall aging effect. The sole exception was

C  W P 99

N

Jo

int

sh

ea

rs

tre

ng

th

(M

Pa

)

AYAT     B72     B98     White glue

7 .0

6 .0

5 .0

4.0

3.0

2 .0

1 .0

0 .0

P

+

N

P P P

N

Table 3 Glass-transition temperatures (Tg) and retained-solvent concentrations of cast films of Acryloid B72 and Butvar B98. The asterisk denotes
the azeotrope boiling point of toluene-ethanol-water.

Drying condition
1 day, 20 °C 30 days, 20 °C 50 days, 20 °C
Solvent
Boiling Residual Residual Residual
Polymer Type point (°C) Tg(° C) solvent (%) Tg(° C) solvent (%) Tg(° C) solvent (%)

B72 Acetone 56 — 5.8 39 0.3 40 0.0

B72 Ethyl acetate 77 — 6.3 — 2.2 40 0.2

B98 Methanol 65 — 19.7 54 3.2 75 0.3

B98 Ethanol-toluene 74 * — 12.3 49 4.8 66 1.5

Figure 2
Static shear strength values for adhesive joints
in deteriorated Douglas-fir made with AYAT,
Acryloid B72, Butvar B98, and PVA emulsion
white glue. P 5 polar solvent; N 5 nonpolar
solvent.