Amid ongoing¹ 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 foam² 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, insulation³（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 adhesives⁶（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 molecule⁴ called glyceraldehyde（甘油醛） , which links casein's protein molecules⁵ 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 gossamer⁷（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.