Brittle Cellulose Acetate Frames - Reasons?

[Bok]

Hi All,

working at compiling a list of reasons why a Cellulose Acetate frame becomes plasticized and goes brittle - apart from age, heat, alcohols etc.

[Chris Ryser]

Here is my full list of plastic materials breakdowns andhow to identify them:

Problem plastics, types of deterioration & where you find it:

Smells:

Vinegar: Ethanoic (acetic) acid produced by degrading cellulose acetate.

Mothballs: Camphor plasticiser in cellulose nitrate but not always an indication of degradation.

Sharp & acidic: Nitric acid or hydrochloric acid from cellulose nitrate or PVC respectively.

Sweaty & ‘plasticy’: Phthalate plasticisers in PVC and cellulose acetate have a characteristic smell, instantly recognisable as something ‘plastic’

Corrosion

Gradual acid release from PVC, cellulose nitrate and cellulose acetate can cause metal components to corrode. Corrosion can therefore be a warning sign that degradation has started.

Disintegrating tissue

Degrading PVC, cellulose acetate and cellulose nitrate release acidic vapours strong enough to attack cellulose on paperbased products. This will make them brittle and eventually they will crumble. As with corrosion this deterioration of wrappings might be the first sign that an object is deteriorating.

Heat

Celluloid (cellulose nitrate) film is highly combustible and requires a licence if you wish to store it. This material should not enter the museum. It should be copied onto another medium use specific storage (see NFA work).

Types of deterioration

Blistering Acidic vapours given off during deterioration create bubbles
Cellulose nitrate. Cellulose acetate

Bloom Additives migrating to the surface and becoming solid.
Cellulose nitrate, Cellulose acetate


Brittleness Chemical deterioration of the polymer chain or loss of plasticiser.Affects all plastics
Phenol formaldehyde starts off brittle

Cracking Physical damage of hard plastics and those thermoplastics which have lost plasticiser
Polystyrene PMMA Phenol formaldehyde Urea formaldehyde Cellulose. nitrate, Cellulose acetate

Crazing Random microscopic cracks at the surface or internally caused by internal stresses, uses of solvents, loss of plasticiser
Cellulose nitrate, PMMA, Casein

De-laminating Occurs when two different materials react differently to their environment, Could happen to most plastics but particularly seen with: Cellulose nitrate Cellulose acetate

Discolouration Acidic or alkali vapours and/or UV light.
PVC Epoxy resins Super glues Nylons Cellulose nitrate Cellulose acetate Phenol formaldehyde Early PMMA

Fraying Due to chemical break down of polymer chains.
Nylon Cellulose acetate Polypropylene

Weeping Plasticisers migrating to the surface, degradation products migrating to the surface. Linked to warping.
Cellulose nitrate Cellulose acetate PVC Polyurethane foam

[uncut]

Incorrect application of heat, either insufficient or excessive, can affect frame life span. Lens size, and dimension variation to the true shape can also accelerate frame deterioration.