Mitsubishi Heavy Industries Ltd. said Wednesday it has developed a recyclable polymer screw that “remembers” its original shape and becomes smooth when heated, allowing it to be easily removed from household electric appliances.

Mitsubishi said it plans to assist makers of household electric appliances to develop products that can be assembled with the shape-memory screws, with an eye to putting them on the market in 2004.

Shape-memory polymers are a type of plastic that change their configuration when heated to a certain temperature, assuming a different, predetermined shape.

When the shape-memory screw is heated to 120 C, the thread is absorbed into the body of the screw, allowing it to slide smoothly out of the appliance, the company said. Once the screw has cooled down, the thread reappears.

The strength of the polymer screw is only 10 percent that of a steel screw of the same size, but it is still strong enough for use in personal computers, mobile phones, television sets, air conditioners and other appliances.

Since the enactment in April 2001 of a law aimed at increasing the recycling of household electric appliance components, the issue of how to facilitate such efforts has come under closer scrutiny in industrial circles.

“Although our polymer screw is more costly than a steel screw, it provides higher cost-competitiveness if the smaller cost involved in disassembling appliances with such polymer screws is taken into account,” a Mitsubishi official said.

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