CCI2014050736

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be lcwer than its melting temperature-in or out of the lyophilization chamber during the fuli freeze-drying treat-ment. We determined freezing points of PEG/water mixtures by recording the cooling ratę of samples put in a dewar filled with liąuid air. For all the grades tested (PEG400, -600, -1000 from Huls Chemie, Belgium; PEG1500 from Union Carbide, London, Great Britain), an Et of at least -40°C may be expected.

Influence of PEG Grade and Concentration

A piece of sole leather from a 16th century shoe, excavated in Brussels, was cleaned and cut in equal parts. Each piece was impregnated in either 30% or 50% (c/v) PEG of the grades 400, 600, 1000 and 1500, for six weeks at room temperaturę. Two samples were put in distilled water and were further treated in a similar way. After impregnation, the pieces were blotted, measured, and frożen at -80°C for 3 hours. Lyophilization was performed over 15 hours, where-by an end pressure of 30m Torr was reached; the lyophilized samples were weighed immediately and were conditioned in a controlled atmosphere (55% RH and 21°C) until they reached a constant weight. Frcm Table 3, it follows that the dimen-sional change of each sample under either treatment is negligible. The rehydration was less effective for a higher polymerization grade or a higher concentration, except with PEG400.

Table 3: eyaluation of the condition of leather, in functions of the impregnation medium

impregnation

medium

30%PEG400 50%PEG400 30%PEG600 50%PEG600 30%PEG1000 50%PEG1000 30%PEG1500 50%PEG1500 H₂0

h₂o

dimensional change (%)

+2

0

0

+1

-2

+1

0

0

-15

-12

water

content (%)

13.1

14.0

13.4 12.6 12.9 11 .5

12.1

11.5

16.4

16.5

Suppleness and visual aspect were very gocd for all treated samples. Impregnations with 50%PEG of any grade tended to make the leather darker and stiffer, expect for PEG400, where no difference was noticed. The untreated samples were hard, almost non-pliable, but lighter in color. Impregnation with 50% PEG caused the samples to feel moist to the touch under the atmospheric conditions described above. Shrinkage was minimized by both higher PEG concentrations and lower prefreezing temperatures. In 50% PEG400, it did not seem necessary to prefreeze the sample at all.

Influence of PEG Concentration and Prefreezing Conditions

Samples of a sole from a 16th century shoe from the same excavation in Brussels were cut and impregnated in either 20%-, 35%-, or 50% PEG400 in water (v/v) for 6 weeks at room temperaturę. Before lyophilization, the pieces were kept at either room temperaturę, -20°C, or 80°C for 15 hours. Freeze-drying and climatization were performed as previously described. The results are given in Table 4.

Table 4: ęyaluation of the condition ofleather, in function of PEG400 concentration and prefreezing temperaturę

impregnation	prefreezing	dimensional	water
medium	temperaturę	(°C) change (%)	uptake (%)
H20	RT	-12.7	13.7
20% PEG400	RT	- 7.3	12.7
35% PEG400	RT	- 3.3	12.1
50% PEG400	RT	- 1 .4	12.0
H20	-20	-10.1	14.2
20% PEG400	-20	- 4.7	13.0
35% PEG400	-20	- 1 .7	10.8
50% PEG400	-20	- 0.5	9.5
H20	-80	-10.6	14.5
20% PEG400	-80	- 5.2	13.0
35% PEG400	-80	- 1 .1	12.3
50% PEG400	-80	- 0.2	9.5