New insights into the degradation mechanism of cellulose nitrate in cinematographic films by Raman microscopy

Abstract

The degradation of cellulose nitrate cinematographic films stored inside an aluminum can was studied by infrared spectroscopy and Raman microscopy. Cellulose nitrate image heritage is strongly susceptible to degradation, being a major conservation challenge. Infrared spectroscopy has been the traditional technique in the assessment of the polymer degradation, but new in situ diagnostic tools to monitor the initial stages of degradation are needed. In this work, cellulose nitrate films were produced and irradiated as aging references to understand how chemical changes were observed in Raman spectroscopy. In comparison with infrared spectroscopy, this technique confirmed the mechanisms proposed in the literature and, at advanced stages of degradation, provided new relevant information detecting an intense peak at 1046 cm −1 associated to nitric acid. Comparing these results with the cinematographic films, it was observed that the plasticizers, which identification was more straightforward using Raman microscopy, have contributions in the regions were chemical changes occur, making it difficult to draw conclusions. Nevertheless, nitric acid and silver nitrate peaks were found in Raman spectra confirming the unstable and noxious environment inside de aluminum can and proving that Raman microscopy can be a valuable complementary in situ technique for cellulose nitrate degradation studies.

A diagnostic tool for assessing the conservation condition of cellulose nitrate and acetate in heritage collections: quantifying the degree of substitution by infrared spectroscopy

“…The films present inside are in an advanced stage of degradation, with tacky emulsion, loss of image and intense noxious smell. These films have already been studied in a published work by infrared and Raman spectroscopies [31].…”

“…1. At time 0, both spectra are characterized by the stretching of the CH and CH 2 bonds between 2900 and 3000 cm −1 ; the strong nitrate vibration bands (μFTIR: 1653, 1280 and 840 cm −1 ; ATR-FTIR: 1636, 1274 and 827 cm −1 ); the cellulosic vibrational envelope between 1200 and 900 cm −1 [31]. A decrease in DS leads to a decrease of the nitrate groups absorbance and an increase of the hydroxyl band (3700 -3000 cm −1 ), evolving towards the spectrum of cellulose, Fig.…”

Plasticiser loss in heritage collections: its prevalence, cause, effect, and methods for analysis

“…In situ identification of additives within historic polymeric objects has been most successfully demonstrated using Raman spectroscopy; including the use of a portable dispersive instrument (excitation at 785 nm) and laboratory-based FT-Raman instruments (excitation at 1064 nm) [111][112][113]. Using a portable spectrometer to survey historic aviation glasses, Madden et al identified camphor in CN, alongside dimethyl phthalate, diethyl phthalate and TPP in CA.…”

Cellulose and its derivatives: towards biomedical applications

“…7). Cellulose nitrate is the polynitrate ester of cellulose with a typical 2.2-2.8 nitrate groups per glucose unit within the structure (Neves et al 2019). Cellulose nitrate properties and applications depend on the degree of nitration.…”