- René Larsen, Experiments and observations in the study of environmental impact on historical vegetable tanned leathers, pp.85-99
doi:10.1016/S0040-6031(00)00616-X
(restricted access)
Abstract:
The hydrothermal stability in the form of the shrinkage temperature (Ts) is a fine measure of the deterioration of vegetable tanned leathers. Previously, it has been demonstrated that the Ts can be predicted by multiple regression modelling based on parameters for the chemical breakdown of the collagen and tannin structures, the sulphate content and acidity of the leather as well as the interaction of these four parameters. In the present paper, several deterioration profiles are suggested for both the natural and artificial aged leathers based on significant regression analyses of the grouped data. The possible existence of several deterioration profiles is supported by more than 100 years of observational and experimental studies of natural and artificial ageing, and is probably mainly due to difference in tannin type and storage conditions. On this basis the problems in using simple standard artificial ageing systems are discussed, and improvement of more complex systems suggested. The latter based on continuation of combined observational and experimental studies using the multiple regression modelling of the Ts as an instrument for adjusting and developing the ageing system.
Abstract:
The hydrothermal stability in the form of the shrinkage temperature (Ts) is a fine measure of the deterioration of vegetable tanned leathers. Previously, it has been demonstrated that the Ts can be predicted by multiple regression modelling based on parameters for the chemical breakdown of the collagen and tannin structures, the sulphate content and acidity of the leather as well as the interaction of these four parameters. In the present paper, several deterioration profiles are suggested for both the natural and artificial aged leathers based on significant regression analyses of the grouped data. The possible existence of several deterioration profiles is supported by more than 100 years of observational and experimental studies of natural and artificial ageing, and is probably mainly due to difference in tannin type and storage conditions. On this basis the problems in using simple standard artificial ageing systems are discussed, and improvement of more complex systems suggested. The latter based on continuation of combined observational and experimental studies using the multiple regression modelling of the Ts as an instrument for adjusting and developing the ageing system.
- Claire Chahine, Changes in hydrothermal stability of leather and parchment with
deterioration: a DSC study, pp.101-110
doi:10.1016/S0040-6031(00)00617-1
(restricted access)
Abstract:
Differential scanning calorimetry (DSC) allows to study the enthalpy changes which are associated with the denaturation of collagen, of which shrinkage is the macroscopic manifestation. Damage to skin, leather or parchment may be expected to manifest as a decrease of either the temperature of denaturation and/or the enthalpy changes. These modifications are associated with those of other chemical and mechanical characteristics. DSC is a very fine tool to follow in an easy way the reaction of leather or parchment to an ageing or a conservation treatment. While for leather ΔH seems to have less than Td, for parchment, it must be looked at very carefully since an unchanged Td value can be accompanied by a fall of ΔH. The case of archeological waterlogged leather is particular since the state of deterioration is apparently not correlated with the hydrothermal stability.
Differential scanning calorimetry (DSC) allows to study the enthalpy changes which are associated with the denaturation of collagen, of which shrinkage is the macroscopic manifestation. Damage to skin, leather or parchment may be expected to manifest as a decrease of either the temperature of denaturation and/or the enthalpy changes. These modifications are associated with those of other chemical and mechanical characteristics. DSC is a very fine tool to follow in an easy way the reaction of leather or parchment to an ageing or a conservation treatment. While for leather ΔH seems to have less than Td, for parchment, it must be looked at very carefully since an unchanged Td value can be accompanied by a fall of ΔH. The case of archeological waterlogged leather is particular since the state of deterioration is apparently not correlated with the hydrothermal stability.
-Neil S. Cohen, M. Odlyha and G. M.
Foster, Measurement of shrinkage behaviour in leather and parchment by
dynamic mechanical thermal analysis, pp. 111-117
doi:10.1016/S0040-6031(00)00618-3 (restricted access)
doi:10.1016/S0040-6031(00)00618-3 (restricted access)
Abstract:
The mechanical behaviour of modern and historic parchment and leather samples through their shrinkage temperature is described. The measurements are made possible by the novel modification of a standard dynamic mechanical thermal analyser (Rheometric Scientific DMTA Mk3) to enable experiments to be conducted on samples immersed in water. A sample of parchment was clamped in tensile mode under a small static applied force. The temperature of the water could be controlled and thus it was possible to heat the sample and monitor the change in its displacement as it passed through the shrinkage temperature. Information could therefore be obtained on the percentage shrinkage and the temperature range over which it occurred. Furthermore, the method also provided useful information on the expansion or contraction of the samples on initial immersion in water, which relates to ease of sample wettability, and on the changes during drying process and rehydration.
-Tim J. Wess and Joseph P. Orgel, Changes
in collagen structure: drying, dehydrothermal treatment and relation to long
term deterioration, pp.119-128
doi:10.1016/S0040-6031(00)00619-5 (restricted access)
doi:10.1016/S0040-6031(00)00619-5 (restricted access)
Abstract:
Collagen is the major component of most connective tissues in animals. The structure of the helix and axial molecular packing within fibrils is well documented. Less is known about the structural alterations that occur on drying and the compounded changes that occur on dehydrothermal treatment. The structural properties of collagen and its supramolecular architecture are of importance in these states, since many of the industrial applications of collagen-based materials involve dried collagen or dehydrothermally treated collagen. The effects of drying and thermal treatment of collagen can be observed by X-ray diffraction, the changes in the diffraction pattern relate to changes in the axial packing of collagen molecules as dehydration occurs. The meridional diffraction series becomes truncated indicating induced structural disorder, the spreading of diffraction features indicate that the molecular orientation is altered for some of the collagen chains or portions of collagen chains within a fibril. Dehydrothermal treatment of parchment collagen for up to 24 h reduces the axial periodicity of the collagen fibril from 64.5 to 60.0 nm. Analysis of the X-ray diffraction data shows the possible alterations in molecular packing that may explain the structural changes.