Problem plastics

The most likely plastics to degrade are cellulose acetate, cellulose nitrate, polyvinyl chloride and polyurethane.

Try to identify objects made of these materials before deterioration is visible and store them separately according to the guidelines given below. If degradation has begun you cannot reverse it or stop it. If however you move it into storage as outlined below you will slow down its progress.

Cellulose acetate

How deterioration happens:

Moisture causes the loss of acetate groups and the subsequent production of acetic acid. The presence of acetic acid accelerates the process of deterioration. As this happens a smell of vinegar is given off. Plasticisers can also migrate to the surface leaving a white powdery deposit and resulting in shrinkage which itself often causes distortion and further stress. As degradation proceeds, crazing and cracking may occur. The acetic acid fumes from deterioration corrodes metals.

Storage guidelines:

  • Temperature ideally 2- 5 centigrade.
  • RH ideally 20 to 30 %.
  • Do not wrap.
  • Keep away from absorbent materials.
  • Isolate from metals and other materials if possible.
  • Use air filtration or vapour scavengers.
  • Use indicators (for more information go to Useful material and products).

Cellulose nitrate

How deterioration happens:

Light and moisture cause the loss of nitrate as nitrogen oxides. Water and oxygen then turn this into acids, accelerating the process of deterioration and making the object brittle and prone to crazing and cracking, as well as forming sticky droplets on the surface. The emanations from deterioration corrode metals.

Storage guidelines:

  • Temperature 2- 5 centigrade.
  • RH 20 to 30 %.
  • Do not wrap.
  • Keep away from absorbent materials.
  • Isolate from metals and other materials if possible.
  • Use air filtration or vapour scavengers.
  • Good ventilation desirable.
  • Use indicators (for more information got to Useful material and products.

Polyvinyl chloride

How deterioration happens:

Light causes yellowing and darkening and can lead to the giving off of hydrochloric acid. Oxygen is also problematic. Plasticisers have a tendency to migrate to the surface causing bloom and tackiness which attracts dirt. The weeping is accompanied by a sweet smell. The loss of plasticiser causes the plastic to shrink and thus to warp and also to become more rigid.

Storage guidelines:

  • Temperature 5° centigrade.
  • RH 20 to 30%.
  • Enclose in non-absorbent material such as glass or polyester bags to prevent loss of plasticiser
  • Ideally oxygen free, using products such as oxygen scavengers.
  • Do not wrap.
  • Keep away from absorbent materials.
  • Store with future display requirements in mind.

Polyurethane foam

How deterioration happens:

Oxidation causes discolouration and loss of strength. The result can be catastrophic loss of structure leading to collapse.

Storage guidelines:

  • Temperature 20° centigrade
  • RH at the low end of 20 - 30%
  • Ideally oxygen free, using products such as oxygen scavengers.
  • Store with future display requirements in mind.