Morphology Control Of Core-shell Micro-nanofibrous Membranes And Its Phase Change Temperature-regulating Performance

Generally speaking,the average temperature of human skin is 33℃,and the deep blood temperature is the most comfortable at 38℃.The human body can passively regulate its own temperature through metabolism.By combining solid and liquid phase change materials with high latent heat and fiber or textile,the phase change temperature adjusting textile can actively adjust the temperature of human internal microenvironment according to the change of environment and human body temperature,realize the function of heat storage and temperature regulation,and improve human comfort.Electrospinning is a simple and effective new processing technology of micro and nano fibers.It plays a great role in biomedical materials,filtration and protection,catalysis,energy,optoelectronics,food engineering,cosmetics and other fields.It has the advantages of diversified fiber components and fine control of structure.The prepared fibers have large specific surface area,high porosity and good flexibility,which can meet the requirements of human comfort.By coaxial electrostatic spinning and using phase change material as core layer,the unstable and easy leakage problems of solid and liquid phase change materials can be solved.Firstly,polyethylene glycol（PEG）with different molecular weight was compounded.Through the calculation and test of Schroeder formula,it was determined that the mass ratio of PEG1000-2 to PEG1500 was 6:1,and the phase transition temperature of mixed peg was 36.4℃.The core-shell polyacrylonitrile/polyethylene glycol（PAN/PEG）fiber membranes were prepared by coaxial electrospinning.The effects of core layer pushing speed from 0.005 mm/min to 0.025 mm/min on the morphology and thermal properties of the membranes were investigated.The results showed that the PAN/PEG fiber films had smooth surface and regular morphology,the fiber diameter was 300±25 nm,and the enthalpy value reached 92.69 J·g^-1when the shell and core are pushed at 0.08 mm/min and 0.015mm/min respectively.In order to further improve the heat transfer efficiency of the fiber membrane,the boron nitride/polyacrylonitrile/polyethylene glycol（BN/PAN/PEG）core-shell phase change temperature regulating fiber membrane was prepared by adding the sheet thermal conductive material boron nitride（BN）into the PAN spinning solution in the shell.The effects of BN concentration in Pan spinning solution at 1%,3%,5%,7%and 9%on the morphology and thermal properties of BN/PAN/PEG fiber were discussed.When the mass fraction of BN was 9%,the average diameter of BN/PAN/PEG fiber was 153 nm,the fiber diameter was uniform,the surface of BN was densely distributed,and the enthalpy value reached 52.3 J·g^-1.The thermal imaging results showed that the average temperature difference of9%BN/PAN/PEG fiber membrane was 2.2℃,and the heat transfer rate was faster than that of PAN/PEG fiber membrane.The breaking strength of 9%BN/PAN/PEG fiber membrane was 979 k Pa,30.4%higher than that of PAN/PEG fiber membrane.Due to the obvious thickening effect of sheet thermal conductive material BN and limited filling amount,spherical Al₂O₃was used in this study for comparison.Al₂O₃/PAN/PEG core-shell phase change temperature regulating fiber membrane was prepared by adding spherical Al₂O₃/PAN/PEG into PAN shell.The effects of Al₂O₃concentration in Pan spinning solution of 1%,3%,5%,7%and 9%on the morphology and thermal properties of Al₂O₃/PAN/PEG fiber were discussed.The diameter of Al₂O₃/PAN/PEG fiber was 528±175 nm and the enthalpy value of Al₂O₃/PAN/PEG fiber membrane was 85.54 J·g^-1when the Al₂O₃content was 5%.Thermal imaging tests showed that the surface temperature of 5%Al₂O₃/PAN/PEG sample was 34.0℃,3.4℃ lower than that of PAN/PEG at 45 s of heating time.The average temperature difference between 5%Al₂O₃/PAN/PEG and PAN/PEG was2.98℃,indicating that the addition of Al₂O₃,the heat conduction efficiency of Al₂O₃/PAN/PEG fiber membrane was improved,which made it have better thermal regulation performance.On the basis of previous work,PAN/PEG fiber membranes with porous shell structure were prepared by using PEG as core layer and PAN as shell layer.The results showed that when the relative molecular weight of pan was 45000 and the amount of water in the shell was 7%,the pan/PEG fiber shell had microporous structure.The sustained release properties of porous PAN/PEG fiber membrane were studied by UV spectrophotometer by adding reactive red X-3B into the core layer.The sustained-release performance of porous pan/PEG fiber membrane was studied by adding active red X-3B into the core layer and using UV spectrophotometer.When the test temperature increased from room temperature to 30℃,PAN/PEG fiber membrane and porous PAN/PEG fiber membrane had similar dye release rate.When the test temperature increased from 30℃to 35℃,the absorbance of porous PAN/PEG fiber membrane in the solution changed from 0.076 to 0.086.The concentration of dye increased from 0.407 mg·m L^-1to 0.457 mg·m L^-1.These results indicate that porous PAN/PEG fiber membrane has the properties of phase modulation and controlled drug release,and can be used as a functional medical dressing,not only effectively regulate the skin temperature around the wound,but also can rapidly release drugs and promote wound healing.