CCI2014050734

-62-

For highly degraded leather, oiling and greasing or repla-cing water by less polar solvents do not suffice to prevent the partially detannized materiał from collapsing upon dry-ing. Instead, or in addition, a morę supporting medium is reąuired.

Impregnations with different polymers were tested. After a series of experiments, attention was focused on impregna-tion with polyethylene glycols, followed by freeze-drying. Freeze-drying (the transition of ice to water vapor) is a physically much less disruptive process than boiling (transition of liquid water to water vapor). Moreover, an object can keep its intended shape in a frozen condition during the elimination of the ice. However, freeze-drying reąuires a rigorous control of physical parameters, such as the temperaturę of the object and the cold trap, as well as the pressure in the lyophilization chamber. The resistance of materials to Iow temperatures and to strains due to the difference in specific volume of liquid and solid water should also be considered carefully.

Cleaning of Samples

After removal of earth and hard sticky deposits with brush and scaepel, the leather was soaked in 2% disodium EDTA (ethylenediaminetetraacetic acid salt) for 24 hours. It was then washed in running tap water for 8 to 16 hours.

Comparison of Different Impregnation Media

The basie media were water soluble silicone monemers for impregnation and in-situ polymerization. The monemers used were 3-aminopropyltriethoxysilane (Ta) and glycidoxypropyl-trimethoxysilane (Tg); both were purchased frem Aldrich Europę, Belgium. To reach a satisfactory rubbery state,

PEG 400 was added as a plasticizer. Since polymerization must be avoided during impregnation, the leather was first soaked in denatured ethanol for 72 hours. After 35 days, polymerization was initiated by the addition of water.

Other impregnation media tested are described in Table 1; in all mixtures but L/PEG400, ethanol was added to confirm to the silicone media.

The total duration of all impregnations was 46 days. After-wards, each sample was cut in two pieces: (a) and (b). The (a) pieces were packed airtight in plastic bags, frozen at -30°C for 1 hour, removed from the plastic and lyophilized. The diraensions were checked after conditioning at 55% relative humidity and 21 °C for two days. The (b) pieces were not lyophilized, but conditioned in a similar way.

They were checked for suppleness and, later on, dried in a vacuum dessicator over silicagel and NaOH to establish the moisture content.

Table 1: impregnations, other than silicone

L/PEG400: p/glycerin: PEG400: Blank:

4g Luviskol K30 (BASF) + 6.4g PEG400, diluted 80ml with water (4)

2g Polyviol 02/270 (Gelgolabo) + 32ml glycerine + 8ml ethanol, diluted to 88ml with water (6) 40ml Polydiol 400 (Huls) + 20ml water + 20ml ethanol references in (5)

40ml water + 40ml ethanol.

The results are compiled in Table 2. The sum of the sides of each sample, before and after treatment, allowed the calculation of % linear shrinkage (LS). MS is the % moisture content in the climatized samples.

Table 2: eyąluation of impregnation and freeze-drying and conditioning

Treatment	LS	MC	Evaluation
Ta/PEG400(40/4)	8	12	brown color, dry to the touch,
Ta/PEG400(40/6)	5	11	the ability to ply increases
Ta/PEG400(40/8)	6	11	with PEG content
Tg/PEG400(40/8)	3	7
L/PEG400	9	13	black, hard, not pliable
P/glycerin	8	18	black, humid touch, pliable over 180°
PEG400	3	15	black, supple, pliable over 90°
Blank	15	16	black, hard, brittle, curled

Impregnations with P/glycerin and with PEG400 gave the best results. The higher hygroscopicity of glycerin caused a higher moisture content and, hence, a morę or less humid touch. Except in cases where the leather was completely hardened, lyophilization improved its suppleness.