Ukrainian museum and monasteries preserve a large number of parchment and leather documents dated from the 14 th to the 19 th centuries. As any organic structure, these materials are subjected to the destructive processes due to physico-chemical (light, humidity, temperature, pollutants, etc

Lucretia Miu

Maria Giurginca

Mihaela Vilsan

Petru Budrugeac

Victorya Plavan

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REV. CHIM. (Bucharest) ♦ 61♦ Nr. 7 ♦ 2010 http://www.revistadechimie.ro 627
Evaluation of the Physico – chemical Characteristics of Leather
Samples of Some Historical Objects from Kiev
VICTORYA PLAVAN1, MARIA GIURGINCA2*, PETRU BUDRUGEAC3, MIHAELA VILSAN4, LUCRETIA MIU4
1Kiev National University of Technologies & Design, 2, Nemirovich-Danchensko Str., Kiev, 02011, Ukraine
2 University Politechnica of Bucharest, 011061, 1 Polizu, Bucharest, Romania
3National Institute for Research and Development in Electrical Engineering ICPE-CA, Splaiul Unirii 313, 030138, Bucharest,
Romania
4National Research and Development Institute for Textile and Leather, 93 Ion Minulescu, 031215 Bucharest, Romania
Ukrainian museum and monasteries preserve a large number of parchment and leather documents dated
from the 14th to the 19th centuries. As any organic structure, these materials are subjected to the destructive
processes due to physico-chemical (light, humidity, temperature, pollutants, etc), biological and
microbiological factors that lead to change in the polypeptide chain structure. The change resulting from the
oxidation, hydrolysis and gelatinization processes in the collagen, can be identified in the IR (middle and
NIR), UV-VIS spectra based on some characteristic bands, thermal analysis (DSC) and MHT techniques.
These techniques were applied to point out the different kinds of degradation at the microsopic, mesoscopic
and molecular levels of the collagen materials.
Keywords: leather, DSC, FTIR and UV-VIS-NIR spectra
Ukrainian museums and monasteries preserve a large
number of parchment and leather documents dated from
the 14th to the 19th centuries, whose deterioration must be
evaluated for selection of the suitable treatment for
preservation and restoration.
As any organic structure, these materials are subjected
to the destructive processes due to physico-chemical (light,
humidity, temperature, pollutants, etc.), biological and
microbiological factors that lead to changes in the
polypeptide chain structure. The change resulting from the
oxidation, hydrolysis and gelatinization processes in the
collagen can be identified in the IR (middle and NIR), UV-
VIS spectra based on some characteristic bands, thermal
analysis (DSC) and shrinkage temperature by MHT method
(Micro Hot Table) [1 – 4].
Based on experience gathered by analyzing the collagen
support (leather and parchment) by varied investigation
techniques [5 – 10], our paper presents data regarding the
study of leather samples coming from Ukrainian patrimony
objects.
Experimental part
Devices
- FT-IR 100 Spectrometer, Perkin-Elmer with vertical ATR,
with diamond head;
- UV-VIS-NIR-V670 Spectrometer, Jasco with diffuse
reflectance accessory ILN-725; both techniques are non-
destructive;
 - The DSC curves were recorded using DSC 204 F1
Phoenix apparatus produced by Netzsch – Germany. The
following kind of DSC measurements were performed:
· DSC analysis of the sample (1.12-1.71 mg) in nitrogen
flow (purity of gas is higher than 99.999%; 20 mL.min-1), in
an open aluminium pan, at the heating rate of 10 K.min-1,
and in the temperature range 250C … 2800C;
·DSC analysis of the sample (0.93-2.50 mg) immersed
in water (35μL deionised water), hermetically sealed in
an aluminium pan and stocked for 24 h. Each sample was
heated from 250C to 1100C, at a heating rate of 10 K.min-1;
- MHT with Caloric equipment (Stereomicroscope
Leica), hot table, webcam, computer and software to
acquire the image correlated with the shrinkage
temperature.
Materials
- P1 book leather, Lvov;
- P2 book leather, Lvov;
- P3 archaeological leather (XV century);
- P4 carriage leather – Historical Museum (Kiev).
- P5 calf leather tanned with quebracho (ICPI, Bucharest)
Results and discussions
Spectral characteristics
In order to identify the degradation types, we selected
some IR spectral characteristics:
3450 – 3200 cm-1 for νOH + νNH
1660 – 1630 cm-1 for νC=O (amide I)
1550 – 1530 cm-1 for δNH (amide II)
1750 – 1700 cm-1 for νC=O (oxygenated structures)
We have computed:
- AI/AII for information regarding the hydrolysis degree of
the collagen support;
- Δν = ν1 - ν2 for information on the denaturation of the
polypeptide chain [4, 9, 11].
The main spectral characteristics of the investigated
samples are presented in table 1.
In comparison with the standard – calf leather tanned
with quebracho – all the historical leathers present a 10 –
30% higher degree of hydrolysis and oxidation groups
coming from the tanning agent (at P5) as well as from
oxidative processes taking place in time (P1 - P4) proved
by the presence of the free acids (ν 1730 cm-1) and the
ketones (ν 1750 cm-1) (fig. 1) [8].
For the UV-VIS-NIR domain, the main bands are:
- bands from the 250 – 500 nm domain, attributed to the
π→π* and n→π* like the extended conjugation structure
from the tannants;
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REV. CHIM. (Bucharest) ♦ 61♦ Nr.7 ♦ 2010http://www.revistadechimie.ro628
- the 1470 – 1510 nm band given by the valence harmonic
vibrations of the hydroxyl groups (νOH) from the water
absorbed into the collagen structure and which allows the
identification of the types and the strength of the hydrogen
bond from the peptide chain;
- the 1900 – 1920 nm bands are given by the valence
and deformation vibrations (νOH + δOH) of the hydroxyl
groups from the peptide chain.
In the UV-VIS domain, all the samples present a wide
band at 250 – 500 nm due to the – CONH – group and the
tanning agent color. In the NIR domain, the bands from
1480 – 1500 and 1900 – 1920 nm point to the presence of
Table 1
CHARACTERISTICS OF THE LEATHERS
Fig. 1. FT-IR spectra of the
samples
the hydroxyl structures associated inter/intra molecular by
hydrogen bonds (fig. 2) [12, 13].
The absorbance of the 1480 – 1500 nm band is partially
correlated with the shrinkage temperature (ST) pointing
to changes in the hydrogen bonds structure.
The main chromatic characteristics are the luminosity
(L*) and chroma (C*), while for the differentiation of the
samples, we selected the value  ΔL* = L*st - L
*
s (st – standard,
s – sample).
The change in luminosity varies between 21 – 35%,
suggesting an increase of the luminosity but the nuance
angle remains in the same domain (50 – 70%).
REV. CHIM. (Bucharest) ♦ 61♦ Nr. 7 ♦ 2010 http://www.revistadechimie.ro 629
Thermal characteristics
DSC analysis in N2 flow
Figure 3 shows the DSC curves obtained by analysis in
N2 flow for the investigated samples; similar DSC curves
were obtained for many new and old collagen-based
materials [5,14]. At a relative low temperature, each
investigated material has exhibited an endothermic peak,
denoted by I, corresponding to the loss of material humidity.
For the samples P1, P2 and P5, this process is followed by
one or two endothermic processes, denoted by II.  This
process, earlier detected by Okamoto and Saeki [15, 16],
and recently [5, 14] put in evidence for pure collagen and
collagen-based materials, could be explained by the
biphasic amorphous-crystalline structure of collagen-
based materials according to which the crystalline triple-
helix is embedded into a amorphous matrix [5]. Very
recently [14], the data from Proton solid-state NMR,
obtained for pure collagen, parchments and leathers, have
lead to a three-phase model (rigid, inter-face, and mobile
phase). Consequently, the process II might be related to
softening (melting) of the rigid (crystalline) part of
parchment.
The characteristic parameters put in evidence in the
DSC curves –N2 flow are listed in table 2.
According to the curves shown in figure 4 the data listed
in table 2:
(a) the standard sample exhibit a single melting process
having the parameters in the ranges previously reported
[14] for many new leathers manufactured by vegetable
tanning (2400C≤ Tm≤ 252
0C; 0.9 J.g-1≤−ΔH≤  2.2 J.g-1);
(b) the samples P1 and P2 exhibit melting points in the
temperature range 1130C … 1210C;
(c) the sample P1 exhibits two melting processes;
(d) in the temperature range  in which the analyses were
performed, the sample P4 has not a melting process.
The statement (b) could be explained by the results
obtained in our previous DSC study of the thermal behavior
of leathers and parchments [14]. It was observed that at
the heating in both O2 and synthetic air flows, all
investigated new leathers manufactured by vegetable
tanning and old leathers exhibit a softening process at lower
temperatures (1180C … 1350C). This means that a thermo-
oxidation of new and old leathers occurs when these
materials are heated in oxidative atmosphere. It was also
Fig. 2.UV-VIS-NIR spectra of the samples P1 (1),
P2 (2) and P3 (3)1
2
3
Fig. 3. DSC curves obtained by analysis for samples in N2 flow
REV. CHIM. (Bucharest) ♦ 61♦ Nr.7 ♦ 2010http://www.revistadechimie.ro630
Table 2
THE CHARACTERISTIC PARAMETERS OF THE PROCESSES PUT IN EVIDENCE IN DSC CURVES
noted that at the heating in N2 flow, some sorts of old leathers
have also exhibited a softening process around 1330 C.
This means that the thermo-oxidation process also has
taken place during the naturally ageing of leathers. Our
results show that such a process occurred at the natural
aging of leathers P1 and P2.
The statement (c) could be explained by heterogeneity
of the sample P1, while the statement (d) shows that the
leather P3 looses its crystalline part by natural ageing [15].
DSC analysis of the sample immersed in water
Figure 4 shows the DSC curves obtained by analysis of
the investigated samples immersed in water.
The DSC analysis of the samples immersed in waters
show that in the temperature range 200C…950C only the
recent manufactured leather exhibit a single endothermic
peak. The characteristic parameters put in evidence in the
DSC curves –water are listed in table 2.
It was pointed out by several authors [16] that the value
of the shrinkage temperature determined by classical or
MHT methods for a given collagen based material is closed
to the extrapolated onset temperature (Tonset in table 2)
corresponding to the main process of denaturation put in
evidence in DSC curve recorded for the sample immersed
in water. The existence of many peaks in the DSC curve
Fig. 4.DSC curves for the investigated leathers immersed in water
REV. CHIM. (Bucharest) ♦ 61♦ Nr. 7 ♦ 2010 http://www.revistadechimie.ro
(fig. 5 and table 2) indicates a high degree of material
heterogeneity. On the other hand, the DSC investigation of
many collagen based materials [5] leads to the following
values of Tonset: 77.1±8.0
0C for recent leathers manufactured
by vegetal tanning, 67.0±12.00C for  middle age leathers,
58.0±7.00C for new and old (middle age) parchments, and
40.1±2.20C for fresh collagen extracted from animal skins.
The data listed in table 2 allow making some similarities
between the hydrothermal stabilities of the investigated
leathers and the above mentioned collagen based
materials. The low values of Tonset and/or the existence of
many DSC peaks indicate a high degree of deterioration of
all investigated leathers.
Shrinkage temperature
By using the MHT method (Micro Hot Table) the results
obtained are shown in the table 3.
The samples P1 – P4 have 30 % lower shrinkage
temperature in comparison with the standard (P5).
Conclusion
The samples from Ukraine present a moderate degree
of degradation, 20 – 35% losses in the initial luminosity
and, on average, a 23% diminishing in the contraction
temperature. The shrinkage temperature is semi-
quantitatively correlated with the absorbance of the 1480
– 1500 nm bands, pointing to changes in the hydroxyl
structures associated by hydrogen bonds.
The DSC analyses of some patrimony leathers were
performed in the following conditions: samples immersed
in water, hermetically sealed in an aluminum pan and
stocked for 24 h; samples in open crucible, under N2 flow.
The DSC plots recorded in gas flow show two different
processes occurring, namely, the loss of water
(dehydration) and the softening (melting). Focusing on the
second process observed when the analysis is performed
in N2 flow, it was pointed out that unlike the new leathers,
and the naturally aged ones exhibit an advanced degree of
oxidation.
Table 3
THE VALUES OF SHRINKAGE TEMPERATURE
The results obtained by DSC analyses of sample
immersed in water show a high heterogeneity of the old
leathers, which could be assigned as a mixture of untanned
collagen and sorts of leathers with different degree of cross-
linking.
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Manuscript received: 10.11.2009
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