Symbol of modern life faces own mortality
It was California suburbia, 1967. Drowning in mass-production prosperity, Benjamin Braddock, Dustin Hoffman's character in "The Graduate," was searching for solidity. A well-meaning grownup offered one word for his future: Plastics.
But as it turns out, those plastics wouldn't have had much of a future. Tupperware, Barbie Dolls, Naugahyde and other plastic emblems of the 20th century are in jeopardy. Even untouched, these cultural symbols will inevitably grow brittle, warp and crack.
For most people, old plastics are easily replaced. But for museums, deterioration of plastics and other synthetic polymers is hampering efforts to preserve the essence of modern life.
"The problem of polymer materials in museums is getting to be bigger and bigger," said Mary Baker, a museum conservator and consultant to the Smithsonian Institution.
"Ten to 20 years ago, preserving the '70s may not have seemed like a priority," she said. "The farther you get away, you start recognizing that yes, indeed, the first Tupperware bowls are important."
Scientists and museum conservators discussed decay of plastics and other treasured polymers in Washington, D.C., at a recent meeting of the American Chemical Society.
The problem came as a surprise to many museum curators, who assumed plastics were sturdy enough that they didn't need special care. Now museums realize that plastics are slipping away.
The National Air and Space Museum is working to preserve the yellowed and
cracking suits that protected U.S. astronauts in outer space.
Other researchers are developing methods to measure how badly deteriorated a plastic is. And polymers other than plastics--for instance, in the oil paints used by masters as far back as Rembrandt--are also under scrutiny. Scientists are discovering some harmful chemical reactions that well-meaning conservators can trigger with techniques meant to preserve oil paintings.
Because oil paints and plastics are both polymers, they're susceptible to a particular kind of chemical damage. Polymers are made mostly of carbon, hydrogen and oxygen atoms. The bonds between those atoms are particularly susceptible to ultraviolet light, physical damage and even room heat, Baker said.
Also, polymers can be made in the first place because they're composed of chemicals that react readily. "Once you put them together, you can't say `OK, don't react,"' Baker said.
One of polymers' biggest enemies is inescapable. An oxygen molecule, split into a pair of atoms by an energy source like UV light, is voracious.
"It just attacks everything in sight," Baker said. Without oxygen, a polymer can still decay, but not as quickly.
Some plastic figurines kept in ordinary storage conditions at museums have simply shattered on their own, Baker said.
Polymers aren't the only component of plastics that deteriorates. Softeners, known as plasticizers, are added to the polymers to make them moldable. A plasticizer known as dioctyl phthalate added to PVC (polyvinyl chloride) seeps out of objects like bowls, dashboards and other materials, says Yvonne Shashoua of the National Museum of Denmark.
"What I'm finding is that PVC is not going to last for future generations," Shashoua said. "Once the plasticizer is lost, the object shrinks and gets sticky."
One of the objects Shashoua studies is tubing found inside the spacesuits from the Apollo missions. Life-support hoses that supplied the astronauts with moist air and removed carbon dioxide were made of PVC. So were the tubes sewn into the liquid-cooled garments. The hoses and tubes are deteriorating, Shashoua said.
Almost two dozen layers of polymer materials--like nylon, Dacron and Mylar--in the spacesuit fabric are also starting to age, said Lisa Young, a conservator at the National Air and Space Museum.
"To the visible eye, they're not that bad," Young said. "But we have samples, and there's definitely things happening inside."
Deterioration of the suits came as something of a surprise.
"They were subjected to such harsh conditions in space, people expected them to survive anything," Young said.
The air and space museum, as part of the Saving America's Treasures program, is amid a two-year project to recommend how best to preserve the spacesuits, while still being able exhibit them.
"Our goal is another 100 years," Young said. "Some of these materials are just going to degrade."
Museum conservators are not the only people who need to worry about plastic decay. Even people who store time capsules for future generations should be cautious.
Several years ago, researchers at the Smithsonian came up with recommendations for homemade time capsules. The most convenient container, it turns out, is the plastic used in soda bottles and peanut-butter jars--polyethylene terephthalate. Although it's a plastic itself, it has the advantage of keeping out oxygen, said Baker.
Plastic keepsakes are not good bets for posterity, but acid-free paper and wood, as well as noncorrosive metals, are.
And for good measure, Baker said, it wouldn't hurt to throw in an oxygen absorber, commonly used for preserving edible dry goods.
"Then you close it up and put it away for 50 years," she said. Away from oxygen and light, "things should come out pretty much how you put them in."