Tech: Decaying plastic ?

Subject: Tech: Decaying plastic ?
From: GUEST,erbert
Date: 29 Mar 10 - 01:28 PM

I've just been clearing out a cupboard, and found a brand new telescopic umbrella,
totally unused and stored in its polythene retail bag for anything up to 10 years since purchase..

But as soon as I touched the plastic handle with just the slightest finger pressure it just crumbled into fragments..


Hows that then ?

Makes me concerned any other plastic objects that have been stored for a similar length of time,
might also have become just as brittle and useless.

That includes quite expensive music and photographic equipment
stored in similar relatively safe dry room temp conditions
in elderly relatives homes.

Subject: RE: Tech: Decaying plastic ?
From: Jack Campin
Date: 29 Mar 10 - 02:24 PM

Depends on *which* plastic. Some are much more stable than others and they all have different storage requirements - polycarbonate is resistant to most things but not to sunlight, for example. Ebonite (the greenish-black stuff used for clarinet mouthpieces) is susceptible to acids, gives off acid fumes as it decays, and so it undergoes accelerating deterioration if one decaying ebonite object is kept in the same case as a bunch of previously intact ones. Polyethylene is resistant to most chemicals and not much affected by light, but can embrittle over decades so it shatters like glass.

The worst is cellulose nitrate, used in prewar hard shiny objects (accordion cases, billiard balls, spectacle frames and the like). Not only does it crumble, it becomes a fire and explosion hazard. A typical old accordion has about as much stored energy as a stick of dynamite. It was used as the base for movie film until the 1930s, which makes movie archiving the sort of business you go into when the thrill of running a nuclear waste repository starts to seem too mundane.

Subject: RE: Tech: Decaying plastic ?
From: Little Robyn
Date: 29 Mar 10 - 02:33 PM

It's biodegradeable!
That's supposed to be a good thing.
It happens to my recycled plastic shopping bags sometimes.
I just hope it doesn't happen to my accordion - or umbrella.
Robyn

Subject: RE: Tech: Decaying plastic ?
From: Sandra in Sydney
Date: 29 Mar 10 - 06:27 PM

Some years back I found some strange flakes in my plastic bag storage bag.

They looked like soap flakes & it wasn't until I upended the bag & examined the flakes that I realised they were flakes of a very old biodegradable plastic bag cos some fragments were large enough to contain writing! Moral of the story - don't store biodegradable bags for future re-use! Re-use them immediately.

Some plastics are safe - clear plastic document sleeves & oven bags (normally used for cooking chickens etc so juices remain in the meat & don't splatter around your oven). Oven bags are perfect for photos, paper & textiles because they're not plastic - they're mylar, a conservation material.

I use oven bags to cover stuff that can get dusty cos I don't have enough glass-fronted cabinet, including white teddy bears, a doll's house full of small stuff that's a huge job to dust, textiles I have on display in frames that don't have glass or perspex,

Preserving your photographs at home


sandra

Subject: RE: Tech: Decaying plastic ?
From: Rowan
Date: 29 Mar 10 - 08:05 PM

And the foam plastics used in most camera (and some instrument) cases also degrades into powder after about 20 years. You can find out about the latest replacement types from your friendly museum staff, as they're having to deal with archival curation all the time.

Cheers, Rowan

Subject: RE: Tech: Decaying plastic ?
From: Tootler
Date: 30 Mar 10 - 06:04 PM

Polymers will degrade chemically over time. The mechanisms vary depending on the polymer, but common agents causing degradation include heat, light (especially UV), oxygen, acids and alkalis. The usual effect is in some way to shorten the polymer chain rendering the polymer to weaken and become brittle.

This Wikipedia article has a basic summary of the main mechanisms