Chinese scientists have found that polyurethane is strengthened by the addition of a small amount of melanin, the molecule in animals’ skin and hair that gives them color and helps protect against ultraviolet light.

From durable foam seating and insulation to glossy coatings and stretchy textiles, polyurethane is used in a number of products. As such, scientists have taken an interest in making it more durable.

Many products requiring durability are made from polyurethane.Researchers have experimented with adding fillers, such as silica, carbon nanotubes, and graphene oxide. But these efforts have typically led to the enhancement of only one physical property at a time, for example, tensile strength—how hard a material can be pulled before it snaps—or toughness, that is, how much energy it can absorb without breaking.

Researchers led by Mingqing Chen and Weifu Dong, of the School of Chemical and Material Engineering at Jiangnan University, have found that polyurethane containing 2% melanin, extracted from the ink sacs of cuttlefish, improved both the material's tensile strength and toughness. These properties were enhanced approximately tenfold, increasing from, respectively, 5.6 megapascals (MPa) and 33 megajoules per cubic meter (MJ/m3) in plain polyurethane to 51.5 MPa and 413 MJ/m3 after melanin was added.

Polyurethane's stretchability was also boosted considerably, the researchers found. In its original state, it could stretch 770% before breaking. The melanin-infused version was able to expand by 1,880% before rupturing.