Using the information

Now we know more or less what happens when storing film.

• Storing it in contact with iron isn’t good.
• The emulsion is beneficial, but it will be lost as a consequence of base degradation.
• Humidity is more important than temperature in controlling film stability.

Having gained this information, what do we do about all these things? One option is to utilize this information to help decide when to copy the material that is degrading: we can use the chemical information about how degraded the film is to produce stability tests so that, at least, we can prioritize copying. Alternatively, we can stabilize the material itself, though to stabilize an individual polymer requires a recognition of the fact that it is contributing to its own instability.

Bearing in mind the major features that contribute to the instability of the film, if we are to stabilize the material, we must introduce something that can block the effects of all those particular factors: oxygen, the presence of any metal ions, the presence of elevated temperatures and moisture - all of which help to produce radicals or acetic acid that break the system down.

The particular combination that we have looked at is a tris-stabilizer, which is a combination of:

• a hindered piperidine stabilizer, Tinuvin 770, which acts as a mop for radicals and also, because it is basic, as a mop for any acid products,
• a metal de-activator, Irganox MD 1024, which complexes the metal ions so that they cannot accelerate the break down of peroxides to radical species,
• an anti-oxidant to counteract the effects of any radicals or any oxygen.

Comparing the property retention, the viscosity retention, of a controlled material with no stabilizer and a material with this tris-stabilizer system, you can see that the retention of properties is much superior with the stabilizer present (Figure 6).

Our Arrhenius testing predicted that in a metal can, stored at 50% RH, with no stabilizer the film would last 35 years. We believe that the stabilizer will give a six-fold increase in life to around 215 years (Figure 7).