Lightweight And Washable Micro/Nanofiber Aerogel For Effective Warmth Retention

People who have been exposed to the cold environment for a long time have slow blood circulation and vasoconstriction.They are vulnerable to hypothermia and cardiovascular diseases,resulting in limb frostbite and even death.Wearing warm clothing can effectively reduce the heat transfer of human body to the outside world and maintain the body temperature stability,so it is an important method to resist severe cold.After the long-term development of warmth retention clothing,fiber materials stand out from many warmth retention materials due to easy acquisition,simple processing,and close-fitting,and are widely used in clothing to keep warm.In recent years,fiber aerogels have attracted much attention because of their low volume density,low thermal conductivity,and controllable preparation.However,the problems of the three-dimensional fluffy structure of warmth retention fiber aerogel materials are easy to collapse and the materials can not be washed,which affects the warmth retention performance in actual application.This topic combines the electrospinning technology and freeze-drying method to prepare lightweight,washable warmth retention polyethylene terephthalate（PET）microfiber/polyacrylonitrile（PAN）nanofiber aerogel,which provides a new idea for the design and development of fiber warmth retention materials.Specific research results include the following parts:1.PAN nanofibers with great morphology and a uniform diameter（average diameter is 226 nm）are prepared by the one-step electrospinning.The effects of PET microfiber/PAN nanofiber ratio on morphology,mechanical properties,and warmth retention performances of warmth retention fiber aerogel are studied.It is found that with the increase of PET microfiber content,the appearance and structural integrity of warmth retention fiber aerogel material are affected,and the warmth retention performances and compressive stress of the material increase firstly and then decrease.When the ratio of PET microfiber to PAN nanofiber content is 2/2,the mechanical properties and warmth retention properties are the best.Select this fiber content ratio to further study,it is found that with the increase of volume density,the thermal conductivity and plastic deformation decrease firstly and then increase after 100 compression cycles（60%strain）.When the fiber content ratio is 2/2 and the design volume density is 5 mg/cm~3,the best properties of the material are as follows:thermal conductivity of 26.3m W/m K at 25℃and stress 817 Pa at 60%strain.2.To improve the mechanical properties of warmth retention fiber aerogel,trifunctional group aziridine（TTMA）and aqueous acrylate（WA）emulsion are added to the composite fiber dispersion as a crosslinking agent,and the fiber aerogel is thermally crosslinked and self-assembled.The effects of both contents on the morphology,mechanical properties,and warmth retention properties of warmth retention fiber aerogel are studied.Mechanical properties and warmth retention properties of the material would decrease with the increase of the content.When the content of TTMA is 10 wt%and WA is 5 wt%,the affective bond between fibers is generated,and the mechanical properties and warmth retention are the best.The maximum stress of the first 60%strain compression cycle is 1265Pa,the maximum stress of the 500th compression cycle is 988 Pa,and the plastic deformation is about2.6%.The thermal conductivity is 26.4 m W/m K at 25℃,and 26.8 m W/m K after 500 cycles of compression with 60%strain.3.To achieve the purpose of aerogel washable,water-based fluorocarbon resin（WF）emulsion is added to the composite fiber dispersion to reduce the surface energy and endow the material with hydrophobic properties.The effects of WF content on the morphology,washable properties,and warmth retention properties of materials are studied.It is found that WF is evenly distributed and has no obvious effect on the material structure.The static water contact angle of the material increases with the increase of WF content,but when the WF content is more than 15 wt%,the static water contact angle remains at about 150°and almost doesn’t increase.At this time,the volume density of the material is 7.1 mg/cm~3,and the thermal conductivity at 25℃is 26.3 m W/m K.The sizes,static water contact angle,and thermal conductivity remain stable after 5 times of washing and 500 times of compression cycle with 60%strain.