Cellulose nitrate deterioration

Cellulose nitrate is very easily ignited and bums very rapidly or explosively, depending on the degree of confinement, degree of nitration and state of subdivision. Unless very pure and stabilised, it deteriorates in storage and may ignite... 

A survey of plastics-containing objects in the British Museum and the National Museum of Denmark showed that 1% of objects were actively deteriorating and were in immediate need of conservation, while 12% exhibited deterioration and required cleaning, stabilising and repair. All the acute objects contained cellulose nitrate, cellulose acetate, plasticised PVC or polyurethane foam. Most objects (60%) were defined as being of low conservation priority, that is, they were in a stable condition but needed some treatment such as cleaning. Only just over one quarter required no conservation treatment. In general, deterioration of plastic objects in museums is visible within 5-25 years of collection. 

It should be remembered that most museum objects have been used or displayed before they are collected. They have an unknown past, usually, which contributes greatly to the rate and type of deterioration. Instability of the earliest plastics, cellulose nitrate and acetate is expected due to their poorly stabilised formulations and because they are the oldest man-made plastics in museums. However, PVC was first developed in 1926 and is still in use, so its deterioration is rather unexpected. 

Metal ions. Copper ions act as catalysts to accelerate deterioration reactions of many polymers, particularly synthetic rubbers. Spectacle frames constructed from cellulose nitrate are often more degraded in the area around copper-containing screws and around the wires in the arms, than... 

Cellulose nitrate poses two major health risks. First, old film made of cellulose nitrate has a tendency to deteriorate and decompose. That process results in the release of oxides of nitrogen, which may be toxic to a greater or lesser degree. This problem is of special concern to people who have occasion to work with old films, but not usually to the general public. Second, cellulose nitrate is a very flammable material that ignites when exposed to even minimal flames or sparks. Most products that contain cellulose nitrate today have been treated to minimize that risk. However, products that were made many years ago do not have the same protection and may pose safety risks to people who come into contact with them. 

The majority of investigations on the degradation of cellulose acetate have been conducted on photographic film (cellulose triacetate) rather than moulded material. like cellulose nitrate, cellulose acetate (CA) is deteriorated by both physical and chemical factors and the physical cause of degradation is plasticizer loss. Three-dimensional objects moulded from cellulose acetate comprise 20-40 per cent by weight plasticizer. Typical plasticizers include triphenyl... 

Derrick, M., Stulik, D. and Ornendez, E. (1993). Deterioration of cellulose nitrate sculptures made by Gabo and Pevsner. In Postprints of Saving the Twentieth Century The Conservation of Modern Materials Ottawa, 15-20 September 1991 (D. Grattan, ed.) pp. 169-182, Canadian Conservation Institute. 

Edge, M., Allen, N. S., Hayes, M., Riley, P. N. K., et al. (1990). Mechanisms of deterioration in cellulose nitrate base archival cinematograph film. European Polymer Journal, 26(6), 623-630. 

Military Grades of NC The product produced by the above nitration purification process is of max stability. It is generally v si alk and contains less than 0.01% cellulose sulfate, which is unstable to heat moisture. The great care taken in the purification of NC is necessary since propellants made from NC contg even small amts of unstable impurities deteriorate rapidly. The US military grades of NC ate as... 

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