Saturday, July 4, 2009

Plastic is not forever

Well, well, well. Who'da thunk it?

Works of art and historical pieces held in galleries and museums around the world are degenerating and disintegrating.

Priceless historical pieces, for example, the first plastic toothbrush, are crumbling.

A handful of unstable, "malignant" plastics are responsible for most of the carnage. Cellulose nitrate was the first widely used plastic (it dates to the early 1830s); it was used to make the film in reel-to-reels. It's remembered today for being a notorious fire hazard: Billiard balls made of cellulose nitrate would occasionally explode on contact, and the plastic was responsible for the destruction of many early movie theaters, as hot projection booths caused the film to catch fire. For safety reasons, cellulose acetate, the material Gabo used, began to replace cellulose nitrate in many applications in the 1930s, though it wasn't any more durable. Because both plastics were based on readily available plant matter (cellulose is the main component of a plant's cell walls), they found widespread use until the 1970s, despite their flaws.

More recently, manufacturers and artists have turned to latex and wholly synthetic plastics like PVC or polyurethane. But these plastics have also proved feeble over the long term. At a molecular level, plastics are long chains of a single molecule repeated over and over. Such long chains would be uselessly brittle on their own, but chemists realized they could add chemicals, called "plasticizers," whose molecules work their way between the chains and soften the plastics up. This greatly increased malleability, and virtually all plastics today employ plasticizers. Unfortunately, plastics will squeeze the plasticizers out over time. This process pushes the chemicals to the surface of the object, leaving the underlying plastic fragile. Different plastics deteriorate in different ways under different conditions, depending on what plasticizers or dyes were added. But the end result tends to be forms of matter rarely seen outside the reject piles of industrial chemistry labs. You can recognize "bleeding" or "weeping" plastics by the slimy plasticizers pooling on their surfaces. Other plastics push powder to their surfaces and feel sugary to the touch.
Myself, I'm quite taken with the exploding billiard balls, it would sure make a game of pool at the pub interesting!

It gets worse:

Worst of all, when plastics weep and bleed they can corrupt everything around them. Chemicals evaporate from their surface and acidify any moisture inside a display case. This causes mini bouts of acid rain that in turn eat away at the plastic in nearby objects—as well as any cloth, metal, or paper in those objects. Curators can lay down special carbon cloths beneath a plastic object to absorb some acid, but some plastics have to be quarantined immediately. Museums have also used plastics to coat nonplastic objects like silver (to prevent tarnishing) and paintings (to prevent flaking). But plastic coatings often "bloom" and turn opaque or "crizzle" (i.e., wrinkle) like dried rubber cement, changes that can damage the very object the coating was meant to preserve.
Read more.

I bet those enviro bags have a half life much longer than the crumbly, cracky plastics self destructing in the museums and art galleries of the worl.

Thanks to Minicapt!

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