Fast molecular rearrangements hold key to plastic's... (reaking apart. Polymer glasses are used...)

Fast molecular rearrangements hold key to plastic's toughness

Date:12/1/2008

reaking apart.

"Polymer glasses are used in many, many different applications," including polycarbonate, which is found in popular reusable water bottles, Ediger says. Aircraft windows are also often made of polycarbonate. "One of the reasons polymer glasses are used is that they don't break when you drop them or fly into a bird at 600 miles per hour."

However, their properties can change dramatically under different physical conditions such as pressure, temperature, and humidity. For example, many polymer glasses become brittle at low temperatures, as anyone knows who has ever dropped a plastic container from the freezer or tried to work on vinyl house siding in cold weather.

As plastics become more and more prevalent in everything from electronics to airplanes, scientists and engineers face questions about the fundamental properties and long-term stability of these materials over a range of conditions.

For example, next-generation commercial aircraft are trending toward including less metal in favor of higher proportions of lightweight polymer materials - roughly 50 percent in the new Boeing 787 compared to only 10 percent in the Boeing 777 - and engineers need to know how these materials will respond to different stresses: a hard landing, strong winds, or changes in temperature or humidity.

"How is it going to respond 20 years from now when it gets twisted, or stretched, or compressed? Is it going to respond by absorbing that energy and staying intact, or is it going to respond by breaking bonds and flying apart into pieces?" asks Ediger.

The Wisconsin team examined the mechanics of a common plastic called polymethylmethacrylate also known as Plexiglas or acrylic - and found that a pulling force had a pronounced effect on the molecules within the material, speeding up their individual movements by more than a factor of 1,000. The team observed internal molecular rearrangements within 50 seconds that would have taken a full day witho
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Contact: Mark Ediger
ediger@chem.wisc.edu
608-262-7273
University of Wisconsin-Madison
Source:Eurekalert

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Fast molecular rearrangements hold key to plastic's...(reaking apart. Polymer glasses are used...)