Re­searchers de­velop new skin-cool­ing syn­thetic tex­tile

China Daily (USA) - - ACROSS AMERICA - By LIA ZHU in San Fran­cisco li­azhu@chi­nadai­lyusa.com

Chi­nese re­searchers at Stan­ford Univer­sity have de­vel­oped a plas­tic-based tex­tile that can cool the hu­man body and maybe some­day re­duce the de­mand for air con­di­tion­ing.

The ma­te­rial cools by not only tak­ing away sweat like or­di­nary fab­rics do, but also al­low­ing heat that the body emits as in­frared ra­di­a­tion to pass through, which makes the wearer feel al­most 4 de­grees Fahren­heit cooler than when wear­ing cot­ton clothes, ac­cord­ing to the re­searchers’ study, re­cently pub­lished by Sci­ence.

By cool­ing the per­son rather than the en­tire build­ing, a sub­stan­tial im­pact could be made on global en­ergy use, ac­cord­ing to Yi Cui, an as­so­ciate pro­fes­sor of ma­te­ri­als sci­ence and en­gi­neer­ing at Stan­ford and lead au­thor of the study.

At the nor­mal skin tem­per­a­ture of 93 de­grees Fahren­heit, the hu­man body emits mid-in­frared ra­di­a­tion, an in­vis­i­ble and be­nign wave­length of light, which con­trib­utes to more than 50 per­cent of the to­tal body-heat loss in a typ­i­cal in­door sce­nario like an of­fice.

By cool­ing the per­son rather than the en­tire build­ing, a sub­stan­tial im­pact could be made on global en­ergy use.

Yi Cui, an as­so­ciate pro­fes­sor of ma­te­ri­als sci­ence and en­gi­neer­ing at Stan­ford and lead au­thor of the study

How­ever, tra­di­tional textiles are not de­signed for in­frared ra­di­a­tion con­trol.

To en­hance ra­dia­tive dis­si­pa­tion in hot weather, the re­searchers found nanoporous poly­eth­yl­ene (nanoPE), a vari­ant of poly­eth­yl­ene widely used in bat­tery-mak­ing, which al­lows in­frared ra­di­a­tion to pass through it while be­ing opaque to vis­i­ble light.

There are also other chal­lenges that the re­searchers need to ad­dress be­sides en­sur­ing the cool­ing ef­fect, such as wick­ing, me­chan­i­cal strength and air per­me­abil­ity, which are im­por­tant for a tex­tile to be wear­able.

The re­searchers al­tered nanoPE with a num­ber of pro­cesses in or­der to make it a suit­able hu­man cloth.

They first cre­ated mi­cro­holes as small as hu­man hair with com­monly used mi­cronee­dle punch­ing, re­sem­bling the spac­ing be­tween the yarns in wo­ven cot­ton tex­tile.

Be­cause the hole is so small, the visual opac­ity is not af­fected. The wick­ing rate and the me­chan­i­cal strength of the new ma­te­rial also are com­pa­ra­ble with cot­ton, ac­cord­ing to the study.

To make the thin ma­te­rial more fab­ric-like, the re­searchers cre­ated a three­layer ma­te­rial with two sheets of treated poly­eth­yl­ene sand­wich­ing a cot­ton mesh for strength and thick­ness.

They then tested the cool­ing ef­fect of nanoPE with a de­vice that sim­u­lated the heat out­put of skin. It was 3.6 de­grees Fahren­heit less than the cot­ton ma­te­rial.

Though the tem­per­a­ture dif­fer­ence is small, it can be the air con­di­tioner set­point dif­fer­ence, said the re­searchers.

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