| It is an important issue to protect human from the low temperature.Natural fiber materials,such as cotton,jute,silk,and wool,have been used to serve as warmth retention materials to reduce the heat loss of human body in the cold environment.However,the natural fibrous materials usually suffer from the drawbacks of large weight,moisture absorption,and ease of being damaged by worms,leading to the limited warmth retention performance.With the rapid development of technology,the synthetic fibers attracted extensive interests to be utilized as the fillings of the warm cloth due to their good mechanical property and low moisture regain,accounting for a large proportion of the fiber consumption.Unfortunately,the synthetic fibers obtained from the conventional spinning technique always exhibited relatively large diameter of>10μm,thereby restricting the further improvement of warmth retention performance and raising the urgent demands on the effective methods to fabricate ultrafine fibers.Electrospinning technology,as a unique method to fabricate ultrafine fibers,have attracted much attention.However,most present electrospun fibers were densely deposited into two-dimensional fibrous membranes,which cannot hold a lot of still air,leading to poor warmth retention performance.Recently,some three-dimensional fibrous materials were fabricated by electrospinning.Owing to the unstable fluffy structures and weak application performance,the obtained fluffy fibrous sponges showed unsatisfactory capacity to keep human body warm.Therefore,it is still a great challenge to prepare the ultralight fibrous materials with stable fluffy structures for effective warmth retention.In addition,the warmth retention materials easily suffer from the poor flame retardancy,resulting from the inflammable synthetic raw materials and fluffy structures filled with still air.Therewith,it is of great value to fabricate fluffy electrospun fibrous materials with lightweight,elasticity,flame-retardant property,and warmth retention performance.In this paper,PES and PU superfine fiber sponges with light weight,fluffy and high elasticity were prepared by electrospinning technology,and the effects of different ambient humidity on the microstructure and properties of fiber sponges were investigated.The results showed that the ultrafine fibrous sponges fabricated under relative humidity of 80%exhibited ultralight property with small fiber diameter of 3.0μm and volume density of 1.9mg cm-3.Moreover,after being compressed at a large strain of 60%,the sponge could rapidly recover to the original shape without plastic deformation;meanwhile,the maximum compression stress was only 194.3Pa,exhibiting excellent soft comfortability.The obtained fibrous sponge also presented outstanding warmth retention performance with low thermal conductivity of 21.9m W m-1 K-1.Ammonium polyphosphate（APP）,the friendly inorganic flame retardant,was introduce to endow the fibrous sponges with flame-retardancy.The effect of APP content on the microstructures and properties of fiber sponge was also researched.The results shown that the fibrous sponge could maintain its three-dimensional fluffy structure and stable mechanical property.The sponge could quickly recover to its original shape with maximum compression stress of 239.0Pa under a large compressive strain of 60%.The components of APP effectively improved the flame retardancy of the fiber sponge.With introducing APP with concentration of 16wt%,the LOI of the fiber sponge reached up to 25.2%,and the damage length in the vertical combustion test was only 111mm without melting drop,afterburning,and smoldering.The obtained Fibrous sponge could bear a large tensile deformation of 50%with tensile stress of 51.2k Pa.After 1000 cyclic compressive tests at strain of60%,the maximum compression stress and compression modulus can maintain more than 70%of the original state,suggesting remarkable compressive fatigue resistance.At a extreme low temperature of–50℃,the maximum compressive stress of fiber sponge under strain of 60%was130.9Pa,which demonstrated that our sponge still had excellent compression flexibility at low temperature.More importantly,the fibrous sponge still possessed a very low thermal conductivity(26.1m W m-1 K-1)in the environment with high relative humidity.After 1000 compression tests,the thermal conductivity of the fiber sponge did not increase significantly(26.5m W m-1 K-1).It demonstrated that the excellent and stable warmth retention performance in different conditions was achieved by the fibrous sponges.The microstructures,warmth retention performance,and flame retardancy of the fibrous sponges and other commercial warmth retention materials were also compared.Different from the conventional fibrous materials,the average fiber diameter（1.5μm）and average aperture（4.9μm）of our sponges were smaller than various commercial fibrous warmth retention materials.Benefiting from the unique characteristics,the thermal conductivity of the ultrafine fibrous sponge was only23.3m W m-1 K-1,which was much lower than the other fibrous materials.Compared with the conventional warmth retention materials,the ultrafine fibrous sponges also achieved remarkable flame retardant property with the best LOI（25.2%）and shortest damage length（111mm）,and there was no melting drop,afterburning,and smoldering.The successful preparation of FUFS enriched the types of ultralight electrospun fibrous warmth retention materials with flame retardancy,and provided a reference for the development of multi-functional electrospun fibrous materials for various applications... |
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