Plastic Rot! What causes it?

[Ratch]

I have been collecting HO/OO scale Blue Edge Box figures for some considerable time now.  I find that occasionally, figures still stored sealed in their boxes in mint condition have started to crumble, whereas their immediate neighbours stored in exactly the same way remain as fresh and new as the day they left the factory.

What causes this random situation to occur? Sunlight has not played a factor (As I was led to believe) and storage has been consistent. Is it to do with the consistency of the Polypropylene or Polyethylene batch used on the day of manufacture? Just as Celluloid decays and becomes unstable with prolonged exposure to the atmosphere, is it just a natural process for these little plastic soldiers to eventually "Fade Away" as do their real life counterparts (allegedly). 

There is surely no cure, but are there any means of delaying, postponing or even stopping this process from continuing? I do not treat my collection as an investment, that would be far too speculative with very little reward, they are just one of life's pleasures.

It would be nice to know if there is a way to stop them from turning into dust, if only for a little while longer.

[Ratch]

 Not sure what you mean by Blue Edge Box

http://airfixtributeforum.myfastforum.org/viewtopic.php?f=393&t=31593

[Sailorman]

Interesting. 

My first guess would have been sunlight.  There is no doubt that sunlight does this and yet you say sunlight is not a factor.  

I wouldn't know enough about the material and I think this is a question for any

chemists on the site.......

[jopres57]

This is one thing that I’ve wondered about for years; how long does modelling plastic last before it starts to deteriorate?  I’ve been bungling together plastic kits for over fifty years now and still have some built forty odd year specimens stored in boxes, along with an Airfix King Richard that has been stood on various shelves since about 1966!  I am quite pleased that I have not observed signs of any plastic beginning to crumble so far, so I’m hoping they’ll last me a good few years yet.

I also have in my stash some older kits from the sixties and seventies that I purchased on E-bay. Despite the fact that some boxes show signs of excessive wear and tear and/or damp, the kits themselves show no visible signs of damage. These are kits from various manufacturers apart from Airfix, so it seems that the plastic is probably a lot tougher than most people think. Sensor ( above ) may just be having some bad luck, but I would also be interested in the subject of model preservation.

[Ratch]

 I think Sensor must be talking about the polythene figures. My Guards Band had turned almost cheese-like

http://pic100.picturetrail.com/VOL761/13303934/24761111/413331959.jpg

Kits tend to be moulded from polystyrene rather than polythene, though I suspect that formulations for the plastics used may have changed over the 60-odd years since they were first produced.

[Braille Dave]

I wouldn't be surprised if it isn't different batches of materials- There are so many factors that affect materials, it is almost impossible to guarantee an absolutely consistent product from batch to batch with the same manufacturer. Even within the production process there will be varying factors, from the time of day, the temperature, humidity, etc, within the factory; how long the plastic has been held before its used.

 

If you multiply those factors across the suppliers of the constituent parts of the plastic, through the plastic supplier to the moulders.