Caractérisation des effets de la chaleur sur des cuirs de tannage végétal et développement d’une stratégie de restauration par voie enzymatique

Abstract : Heat, induced by fire, is particularly devastating for cultural heritage objects as it causes the destruction of all or part of these witnesses of the past. In this study, we focused on leather, a material largely present in heritage collections. Until now, no restoration method has been developed to treat the damaging effects of heat.The first aim of our study was to evaluate the effects of dry heat on leather samples through a systematic characterization. Model samples from a calf skin vegetable tanned in known conditions were used and the consequences of heat exposure was characterized at different structural scales using a range of physical, chemical and biochemical methods.Besides the visible browning and shrinkage of leather, heat induces many changes including a loss of mass, the melt of the crystalline regions, an increase in both hydrophobicity and rigidity. Some of these changes result from the protein aggregation induced by exposure to heat and evidenced by our research.Our second goal was to develop an innovative restoration method based on the use of biological molecules in order to respect the nature of the object. Enzymes such as proteases, able to hydrolyze protein aggregates, were used. One of the challenges was to provide the water necessary for the enzyme activity without wetting the leather surface in order to avoid further damage of the leather. Several enzyme supports were tested. The use of an enzymatic emulsion reveals neither darkening nor retraction and in some cases a flexibility gain is observed. Encouraging results were also obtained in the case of an ancient book cover made from calfskin and dated from the nineteenth century. Additional measurements lead to attribute its effect mainly to the emulsion itself, however longer-term measurements appear to show a positive effect of the enzyme on the flexibility gain. Although further characterizations on the long term are required, the treatment may constitute a new support for leather bio-restoration.Keywords: leather – thermal denaturation – protein aggregation – bio-restoration - proteases
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Eleonore Izquierdo. Caractérisation des effets de la chaleur sur des cuirs de tannage végétal et développement d’une stratégie de restauration par voie enzymatique. Biochimie, Biologie Moléculaire. Université de Cergy Pontoise, 2015. Français. ⟨NNT : 2015CERG0780⟩. ⟨tel-01347102⟩

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