DEGRADATION AND STABILIZATION OF CELLULOSE TRIACETATE BASE MOTION-PICTURE FILM

The artificial and natural degradation of cellulose triacetate base motion picture film material has been studied, using viscometry, moisture regain, acidity, infrared spectroscopy, and hydroperoxide analysis. Under both natural (archival) and accelerated aging conditions, there is a direct correlation between the moisture regain of the film material, acidity, and decrease in viscosity. From these results, two degradation processes are identified. The first is an acid-catalyzed hydrolytic deacetylation of the ester functionality; the second is an acid-catalyzed hydrolytic oxidative scission of the main cellulose chain. Oxidative degradation and deacetylation of the polymer are more significant in an open than a closed environment. Iron absorbed into the film from the metal container during storage acts as a powerful catalyst, accelerating the degradation and deacetylation processes; this is confirmed by doping the film with iron. The initiation process is shown to be associated with the iron-catalyzed decomposition of hydroperoxide groups. The average archival life of film in an iron container, determined by Arrhenius predictions, is 35 yr. Studies of the physical characteristics of the film indicate that the gelatin emulsion layer imparts some degree of stability to the film base through its ability to scavenge and neutralize the acetic acid and partially prevent the diffusion of oxygen into the film. The plasticizer also imparts stability through its ability to coordinate with the iron. Stabilization of the film material is achieved through the use of a tris combination of stabilizers in solution that can scavenge the acetic acid, react with the hydroperoxide groups, and deactivate transition metal ions. The implications of the underlying mechanistic behavior of these systems, together with that of its practical utilization in an archive, are discussed.