This process occurs quickly under uncontrolled storage conditions, particularly unventilated environments showing high temperature and humidity (temperature above 10 ☌ and a relative humidity above 50% ). 2), photocatalytic and hydrolytic loss of nitro substitutive groups of the CN base.
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Mainly, degradation starts with the thermal (Fig. The complex pathways of degradation of CN bases have been recently summarized by Neves et al. Ĭellulose nitrate photographic and cinematographic materials are known to be intrinsically unstable. Thanks to its low cost, CN was initially widely employed for producing film bases, but due to its high flammability, its use of was progressively reduced and then definitely abandoned in 1951. Since 1889, flexible polymeric films made of CN with a degree of substitution (DS) of around 2 were used as support for the first examples of cinematographic film. Graphical abstractĬN is a cellulose derivate where hydroxyl groups in the glucopyranose ring have been substituted by nitrate groups O-NO 2. In particular, the tested DES formulations showed superior cleaning power compared to isopropyl alcohol and, at the selected application times, resulted capable to remove the gelatin residues without affecting the CN film supports. Selected areas over the frames of a real deteriorated CN cinematographic film were cleaned comparing the DES performances with the ones obtained using isopropyl alcohol as an example of a traditional method. These solvents are inexpensive (when compared to traditional solvents), easy to prepare, green (non volatile, safe towards the operators and the environment, and potentially recyclable), non flammable and have been previously proposed for the extraction of proteinaceous materials, but their use for the restoration of photographic negatives or cinematographic films has not been reported yet. To overcome these drawbacks, we have evaluated the performance of three choline chloride and betaine-based Deep Eutectic Solvent (DES) formulations as alternative for the removal of gelatine residues from CN supports. However, these methods are either slow and ineffective or could potentially damage the degraded CN supports. Traditional approaches to clean gelatin residues from the surface of CN bases include the mechanical removal with scalpels and the use of organic solvents (such as isopropyl alcohol). This causes the formation of gelatin residues which stick on the back of the superimposed frames inside the reels creating a deposit. The decrease in pH, for instance, lowers the viscosity of gelatin, which becomes softer. However, CN bases degradation may prevent the scanning of the films.
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Thus, to prevent the disappearance of the movies, their scanning and digitalization become a priority. This material is particularly unstable and can undergoes severe degradation due to thermal, photocatalytic and hydrolytic loss of nitro groups from the lateral chain. Cellulose nitrate (CN) has been used in the past as support for photographic negatives and cinematographic films.