题型：阅读理解 题类：常考题 难易度：普通
河南省中原名校2020届高三上学期英语第二次质量考评试卷（含小段音频）
Plastics remain one of the most - used materials for making many things. Things made of plastics can be very strong and last a long time. Plastics are also much lighter than metal and can easily be formed into different shapes. Plastics can take hundreds of years to break down on their own. And very few kinds are highly recyclable.
A team of researchers working at the US Department of Energy says it has created a kind of plastic that could lead to products that are 100 percent recyclable. It recently reported the discovery in a study in the journal Nature Chemistry.
The researchers say the new material is a plastic polymer (聚合体)called polydiketoenamine, or PDK. The team reports the material can be broken down in parts at the molecular (分子的)level. It can then be built up again to form plastics of different shapes, textures and colors. The researchers say this process can be repeated over and over again—without the plastic material losing any performance or quality.
"Most plastics were never made to be recycled," lead researcher Peter Christensen said in a statement. " But we have discovered a new way to assemble plastics that takes recycling into consideration from a molecular perspective. "
Many plastics have different chemicals added to them to make them more useful and powerful. The problem is that these chemicals attach to the monomers (单体), which remain in plastics even after the material gets processed at a recycling plant. The research team reported that, with the newly discovered PDK material, the monomers could be recovered and separated from any chemical additives.
Next, the researchers plan to develop PDK plastics "with a wide range of thermal and mechanical properties. These plastics could be used for many kinds of cloth, as well as things such as 3D printed materials and foams. In addition, the team is trying to include plant - based materials in the process.
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