Determination of the hydrothermal stability of leather and parchment: The significance of heating rate and shrinkage intervals (original) (raw)
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Heritage Science
The aim of this study was to advance the current understanding on the mechanism of deterioration of historical vegetable tanned leathers and establish new criteria for quantifying their deterioration using micro differential scanning calorimetry (micro DSC) and micro hot table (MHT) method. Ten historical leather objects were investigated to this purpose. The calorimetric indices of macromolecular change identified for fibrous collagen provided quantitative results on the bulk material and deconvolution of DSC denaturation peaks revealed the dynamics of deterioration in historical leather. The results brought clear evidence that long-term natural ageing of leather induces the destabilization of chemically modified collagen thereby promoting its partial de-tanning and allowing micro-unfolding of chemically unmodified collagen. As deterioration continues toward the extreme, collagen molecules become highly unstable allowing for gelatinisation and irreversible denaturation. It is thus explained the coexistence of collagen populations with distinct thermal stability in historical leather. They are grouped in three main structural domains, namely "leather-like", "parchment-like" and "gelatine-like", whose mass percentages determines leather stability against further natural ageing and deterioration. As a result of the MHT and micro DSC parameters correlation, a more comprehensive set of criteria, including T f and T l values, as well ∆C and ∆T intervals' lengths, was introduced for better interpreting the shrinking activity of collagen in historical vegetable-tanned leathers and open thus the way for the highly sought in situ evaluation of leather artefacts.
Thermal characterization of new, artificially aged and historical leather and parchment
Journal of Analytical and Applied Pyrolysis, 2015
The aging mechanism of leather and parchment was studied by thermoanalytical methods to understand the effect of the environment on the historical manuscripts and the heritage of libraries and archives. Alkaline and acidic treatments followed by thermal dehydration were applied to achieve chemical changes in the structure of new leather and parchment similar to the slow natural aging of historical samples. Chemical and structural changes during both natural and artificial aging processes were characterized by thermoanalytical techniques. The thermal stability and the evolution profile of the decomposition products under slow heating were studied by thermogravimetry/mass spectrometry (TG/MS). The distribution of the decomposition products of these collagenbased materials under fast pyrolysis was characterized by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). It was found that the maximal rate of the thermal decomposition (DTG max) significantly decreases by aging in case of both leather and parchment samples indicating the degree of deterioration. Py-GC/MS has been found to be a suitable technique to sensitively monitor the degradation of the polyphenolic components of the vegetable tannins under natural or artificial aging. It was established that the tannin content of leather is more significantly affected by natural aging and alkaline treatment than the main structure of the polypeptide chains. Principal component analysis (PCA) has been used to find statistical correlations between the experimental data for leather samples. The results of the PCA confirmed that the alkaline treatment and the natural aging processes similarly modify the tannin content of the vegetable tanned leather.
Indonesian Journal of Chemical Studies
The shrinkage of leather becomes a problem when leather is used in the form of leather shoes or other products and is heated at a high temperature. This technical study addressed shrinkage occurring in most leather shoes used in Pakistan during the shoe manufacturing process. The chemical testing results revealed fat content (4.0-4.5%), chromic oxide (2.3-2.5%), ash content (1.3-1.6%), and pH (3.5-3.7) under significant limits. The effects of hydrothermal and dry heat shrinkage were investigated in selected shoe-upper leathers. The leather samples showed (18-41%) shrinkage in all 03 samples. The results revealed that an extensive change in various physical tests, such as tensile strength, % elongation, tear strength, had been found with heat induction. The temperature and time of heat contact significantly affect the destruction of bonding in shoe upper leather after being converted into shoes.
Thermal analysis on parchments I: DSC and TGA combined approach for heat damage assessment
Thermochimica Acta, 2006
Ancient, new and artificially aged parchments were investigated with both differential scanning calorimetry (DSC) and thermogravimetry (TGA). Criteria to define a quantitative ranking of the damage experienced by the bulk collagen of historical parchments were assessed. A damage-related correlation was found between the collagen denaturation temperature and the moisture content of the parchment. Qualitative rules for the evaluation of the damage at the nano-and mesoscopic level were achieved on the basis of peculiarities of the shape and width of the DSC signals and confirmed by small angle X-ray scattering patterns.
Characterization of New and Artificially Aged Parchments
Leather and Footwear Journal
This study aims to characterize new and artificially aged parchments. Parchment samples of calf, sheep, goat and pig were exposed to artificial ageing at 70°C in 3 cycles: first cycle for 7 days, second cycle for 14 days and 21 days for the 3 rd cycle. Thus, a treatment temperature of 70°C was selected to avoid sudden structural changes and rapid collagen denaturation. To evaluate the deterioration degree of parchments, the samples exposed to the first cycle were subjected to physical-mechanical, chemical tests and shrinkage temperature while the samples exposed to the second and 3 rd cycle to physical-mechanical test. Depending on the ageing cycles significant changes were reported. The accelerated ageing of parchments degraded the physical-mechanical properties and lowered the shrinkage temperature. The behavior of sheep and goat parchment samples to accelerated ageing suggests a rather high deterioration in the hydrothermal stability. KEYWORDS: physical-mechanical properties, shrinkage temperature, parchment, collagen, accelerated ageing CARACTERIZAREA PERGAMENTELOR NOI ŞI ÎMBĂTRÂNITE ARTIFICIAL REZUMAT. Acest studiu își propune să caracterizeze pergamentele noi și îmbătrânite artificial. Probe de pergament de vițel, oaie, capră și porc au fost expuse la îmbătrânire artificială la 70°C în 3 cicluri: primul ciclu timp de 7 zile, al doilea ciclu timp de 14 zile și 21 de zile pentru al 3-lea ciclu. A fost selectată astfel o temperatură de tratare de 70°C pentru a evita schimbările bruște structurale și denaturarea rapidă a colagenului. Pentru a evalua gradul de deteriorare a pergamentelor probele expuse la primul ciclu de îmbătrânire au fost testate prin analize fizico-mecanice, chimice și temperatura de contracție, iar probele expuse la ciclurile II și III la analize fizico-mecanice. În funcție de ciclurile de îmbătrânire au fost raportate modificări semnificative. Îmbătrânirea accelerată a pergamentelor a produs degradări ale proprietăților fizicomecanice și ale temperaturii de contracție. Comportamentul probelor de pergament de ovine și caprine la îmbătrânirea accelerată sugerează o deteriorare destul de mare a stabilității hidrotermice. CUVINTE CHEIE: proprietăți fizico-mecanice, temperatura de contracție, pergament, colagen, îmbătrânire accelerată CARACTÉRISATION DES PARCHEMINS NOUVEAUX ET ÂGÉS ARTIFICIELLEMENT RÉSUMÉ. Cette étude vise à caractériser les parchemins nouveaux et artificiellement âgés. Des échantillons de parchemin de veau, mouton, chèvre et porc ont été exposés au vieillissement artificiel à 70°C en 3 cycles : premier cycle pendant 7 jours, deuxième cycle pendant 14 jours et 21 jours pour le 3 e cycle. Ainsi on a choisi une température de traitement de 70°C pour éviter les changements structurels soudains et dénaturation rapide du collagène. Des tests physico-mécaniques, chimiques et de température de retrait ont été utilisés pour évaluer le degré de détérioration des parchemins. Selon les cycles de vieillissement, des changements importants ont été signalés. Le vieillissement accéléré des parchemins a provoqué des dégradations des propriétés physico-mécaniques et de la température de retrait. Le comportement des échantillons de parchemins de mouton et de chèvre au vieillissement accéléré suggère une détérioration assez élevée de la stabilité hydrothermale. MOTS CLÉS : propriétés physico-mécaniques, température de retrait, parchemin, collagène, vieillissement accéléré
Polymer Degradation and Stability, 2020
In this paper we aimed at the characterization of heat-induced changes on molecular organization of collagen within parchment in very low relative humidity conditions. Collagenous materials are intrinsically heat-sensitive and hygroscopic. Parchment documents and artefacts are heterogenous materials made from a matrix of collagen fibres whose surface is often interfaced with gelatine layers. Thus, as they age and deteriorate, parchments become even less thermally stable and more hygroscopic. Getting insight into the subtler structural alterations of collagen is critical to establishing appropriate temperature and relative humidity conditions for the preservation of parchment artefacts. To this purpose, we monitored the molecular changes induced by exposing parchment prepared according to traditional recipes to increasing temperature (e.g. 50 °C, 80 °C, 100 °C, 120 °C, 150 °C, 180 °C and 200 °C) and low relative humidity (10%) by vibrational spectroscopy (Infrared spectroscopy in ATR acquisition mode and Raman spectroscopy) whereas the macroscopic changes in collagen fibers stability were evaluated through Micro Hot Table (MHT) method. Colorimetric measurements were also performed and related to parchment deterioration processes. Artificial ageing confirmed the pattern of collagen thermally induced deterioration consisting of triple helix conversion into intermediate conformations (neither native, nor properly heat-denaturated) followed by denaturation at 120 °C and progressive gelatinisation at T ≥ 150 °C. The shrinkage behaviour of collagen fibers was detailed at molecular level by FTIR-ATR and Raman analyses through the multiple changes that occur in the position and intensities of the amide I, amide II and amide III components. Besides, significant changes were detected in the ν(C-C) region associated with proline and hydroxyproline residues and protein backbone in the Raman spectra. Moreover, a set of spectral biomarkers was unequivocally assigned to collagen gelatinization. The results of this study can therefore serve as important tools towards a better understanding of ancient parchment condition.
Journal of Thermal Analysis and Calorimetry, 2011
Our recent developments concerning the assessment of parchments deterioration using DSC are reported. Measurements performed on samples in excess water conditions, in static air and gas flow provided qualitative and quantitative information on parchment ageing and deterioration at microscopic and mesoscopic level, when assembly of fibres/fibrils is weakened, partially and eventually completely lost, and at molecular level, when triple helix uncoiling occurs. A damage ranking scale based on a large collection of DSC parameters obtained by investigating artificially aged samples was set up. Deconvolution of the DSC thermal denaturation peaks in excess water enabled evaluating and discriminating stability of parchments with similar damage levels. Further experimental evidences such as softening of the crystalline fraction of collagen, thermal-oxidation and collagen gelatinisation were detected by DSC measurements in gas flow and static air, and related to specific deterioration patterns. DSC measurement of wet samples provided an objective and reliable method for evaluating parchment shrinkage temperature overcoming the limitations of conventional methods.
Mechanical and Thermomechanical Characterization of Different Leathers
Springer eBooks, 2018
Leather materials are able to undergo various strain and stress states during their elaboration process and their use in numerous applications. Although the experimental mechanical response in tension of leathers has been studied in the literature for decades, scarce information is available on the nature of their elasticity and more generally on their thermomechanical behaviors. In the present study, two leathers were tested under uniaxial cyclic loading while temperature changes were measured at the specimens' surface by infrared thermography. The heat power at the origin of the temperature changes was then determined by using an adequate version of heat diffusion equation which is applicable to homogeneous tests. Results enabled us to discuss on the physical nature of the thermoelastic coupling in leathers. Intrinsic dissipation caused by the mechanical irreversibility was also detected. Distinct behaviors are evidenced as a function of the type of leathers.
Assessment of thermal stability of collagen in parchment by DSC in excess water
Deterioration of parchment is a complex process that is greatly determined by changes in the environment in which they have been stored, often for very many years. Damage assessment and diagnosis, along with monitoring and modelling of the impact of the environment on parchment, thus demand a detailed knowledge of the deterioration mechanisms and pathways associated with all levels of its structure. This paper briefly describes ageing and deterioration pathways of historical parchments achieved by non-invasive or invasive, non-destructive or micro-destructive techniques that target its molecular, nanoscopic and mesoscopic properties, namely IR spectroscopy, unilateral NMR, DSC, and SEM, respectively.