Amid ongoing concern about plastic waste accumulating in municipal（市政的） landfills, and reliance on（依靠，信赖） imported oil to make plastics, scientists are reporting development of a new ultra-light biodegradable foam plastic material made from two unlikely ingredients（材料，作料） : The protein in milk and ordinary clay. The new substance could be used in furniture cushions, insulation（绝缘，隔离） , packaging, and other products, they report in the ACS' Biomacromolecules, a monthly journal. David Schiraldi and colleagues explain that 80 percent of the protein in cow milk is a substance called casein , which already finds uses in making adhesives（粘合剂） and paper coatings. But casein is not very strong, and water can wash it away. To beef up（加强，补充） casein, and boost its resistance to water, the scientists blended in a small amount of clay and a reactive molecule called glyceraldehyde（甘油醛） , which links casein's protein molecules together.

The scientists freeze-dried the resulting mixture, removing the water to produce a spongy（海绵状的） aerogel（气凝胶） , one of a family of substances so light and airy that they have been termed "solid smoke." To make the gossamer（轻飘飘的，薄弱的） foam stronger, they cured it in an oven, then tested its sturdiness（坚固，强健） . They concluded that it is strong enough for commercial uses, and biodegradable, with almost a third of the material breaking down within 30 days.