Preparation Of PVDF/keratin Electret Nanofiber Membrane And Its Application In Air Filtration

For the protection of the health of global community and environment,it has become an immediate concern to exploit high-efficient and eco-friendly air filter with stable charge to capture atmospheric particulate matter.Due to the influence of processing method and external environment,traditional air filtration materials are not easy to possess the advantages of high efficiency,low resistance and stable charge storage at the same time.Nevertheless,electrospinning provides a novel direction for solving the above problems through in-situ injection of stable charges and remarkable fibrous controllability.In addition,abundant and biodegradable natural protein resources also show great potential in bio-based filtration materials.In this paper,keratin was extracted from natural wool and introduced into polyvinylidene fluoride(PVDF)nanofibers with electrospinning,and PVDF/keratin electret nanofiber filter with high removal efficiency and excellent charge stability was prepared to realize the application in filtration materials such as masks and air purifiers,and the filter was finished with water and oil repellent by impregnation method to prolong its service life.The primary contents and conclusions are as follows:(1)The effects of solution properties and spinning conditions on the fibrous forming were investigated using PVDF as raw material.Among them,the solution concentration,solvent system and spinning voltage had a marked impact on the morphology and diameter of PVDF nanofibers,the receiving distance changed the fibrous diameter,the drum speed only affected the fibrous order,and the flow rate influenced the stability of the spinning process.The optimal spinning parameters were determined as follows:the polymer concentration was 12 wt%,the ratio of N,N-dimethylformamide and acetone in solvent was 6/4,the spinning voltage was 20 k V,the receiving distance was 17 cm,the drum speed was 600 r/min,and the flow rate was 1 m L/h.Nanofibers with various surface morphology(smooth,wrinkled,porous)were prepared by controlling solvent composition and relative humidity.The stretching of electric field transformed?-phase into?-phase in PVDF nanofibers,and the supreme?-phase content reached 83.96%.Additionally,PVDF nanofibers had high heat resistance and hydrophobicity.(2)Keratin was extracted from wool by _L-cysteine reduction method.It was observed from the image of scanning electron microscope that the keratin showed broken and flaky shape.The results of infrared spectrum and x-ray diffraction tests proved that there were amide structures in the molecular structure of keratin.(3)The PVDF/keratin composite nanofiber membrane was prepared by blending spinning under the optimal parameters.The results illustrated that the average diameter and pore size of PVDF/keratin nanofiber mat diminished with the growing keratin content.In the infrared spectrum of PVDF/keratin nanofibers,the characteristic peaks of?and?phase crystals of PVDF and the absorption peaks of amide band of keratin were observed simultaneously,which certified that keratin was successfully introduced into PVDF nanofibers.The addition of keratin weakened the tensile strength of electrospun nanofiber mat from 1.899 MPa to 0.976 MPa.As the content of keratin enlarged,the fibrous structure became compact and the tensile stress of PFK-30 nanofibers recovered to 1.815 MPa.The initial surface potential and charge stability of PVDF/keratin nanofibers increased and then decreased with the increase of keratin content,but the hydrophobicity was not affected.By the way,the surface of PFK-30 nanofiber had the highest initial potential of-4.93 k V and the best charge stability.Based on the dual effects of fibrous structure and electret performance,keratin improved the filtration efficiency of nanofiber mats.Most importantly,the PFK-30 composite membrane exhibited a high PM_0.3 removal efficiency of99.731%,a low pressure drop of 127 Pa and a maximum quality factor of 0.04662 Pa^-1.Normally,various applications of filters could be achieved by adjusting the basis weight of the filtration material and the air flow.(4)In order to obtain water-repellence and oil-repellence fibers,impregnation method was used to attach the three-proof finishing agent to the surface of PFK-30 nanofiber with basis weight of 8.64 g/m~2.The results displayed that the diameter of PFK-30 nanofiber increased and the pore size decreased with the enhancement of finishing liquor concentration.After finishing,PFK-30nanofibers changed from oleophilic to oleophobic,and the hydrophobicity did not change significantly.Since water molecules could act as carriers of charge,the initial surface potential of the finished PFK-30 nanofiber mats quickly decayed.The decrease of electret performance reduced the filtration efficiency of PFK-30 nanofiber membrane.However,the pore size was lessened with the increase of the concentration of finishing liquid,which leaded to the gradual improvement of filtration efficiency and linear increase of pressure drop.Considering the cost of raw materials,the PFK-30 nanofiber membrane was treated with 10 g/L finishing liquor.Consequently,the finished PFK-30 nanofiber mat had strong resistance to water and oil,and its filtration efficiency reached 98.464%and pressure drop was only 208 Pa.