Stable Preparation Of Electrospun SF/PHBV Composite Nanofiber And Its Structure And Properties

In modern society,air quality has been seriously damaged with the continuous advancement of industrialization and urbanization,threatening human health at all times.The morbidity and mortality of various respiratory diseases are increasing year by year.In addition,airborne droplets,aerosols and particulate matters can carry bacteria,viruses,spores and other pathogens that contribute to the spread of disease.Especially since the outbreak of the COVID-19,due to the highly contagious nature of the new crown virus,it has now spread around the world.Therefore,it is particularly necessary to develop medical protective materials with high-efficiency filtering and protective properties to block the spread of the epidemic and protect public health and safety.However,traditional medical protective materials have poor wearing comfort and are prone to feel stuffy,and due to the non-degradability of these materials,they will cause secondary pollution after being discarded.In order to improve the wearing comfort of medical protective materials and protect the ecological environment,it is of great practical significance and social value to study and prepare highly protective,degradable and comfortable bio-based medical protective materials.Aiming at the deficiencies and defects of the current traditional medical protective materials,starting from the concept of green environmental protection,this study selected a natural polymer material with good human affinity-silk fibroin(SF)and multifunctional bio-based polymer-poly(3-hydroxybutyrate-3-hydroxyvalerate)(PHBV)two green degradable materials as the main raw materials,using PHBV to improve the crystallization ability of electrospun fibers,thereby improving their mechanical properties,and using SF to improve the moisture absorption ability of fibers,thereby improving the comfort of its use.First,the preparation method and formation mechanism of SF/PHBV composite spinning solutions with uniform,stable and good spinnability were studied,and then SF/PHBV composite nanofibers were obtained by electrospinning.The effects of the composition of the composite spinning solutions on the stable preparation and fiber morphology of SF/PHBV nanofibers were systematically studied and analyzed.The microstructure and properties of SF/PHBV composite nanofiber membranes were explored.On this basis,the SF/PHBV/PLA micro-nano composite materials were developed with polylactic acid(PLA)non-woven fabric as the base fabric.Based on the national standards for disposable medical protective clothing fabrics and protective masks,the filtration performance,hydrophilicity and hydrophobicity,moisture permeability,static decay properties and other protective and wearing properties of the composite materials were systematically measured and analyzed in order to explore the feasibility of their application in the field of medical protective materials.The main research results include the following aspects:(1)The effect of solvent systems on the stability of SF/PHBV composite spinning solutions.The SF/PHBV composite spinning solutions were prepared by using two solvents,in which SF was dissolved with 98%pure FA,and PHBV was dissolved in three systems:TCM,TCM/DMF,and TCM/DCE.The solubility and solution stability of PHBV,as well as the stability and rheological properties of SF/PHBV composite spinning solutions with different PHBV contents were studied.The research results showed that when PHBV was dissolved in TCM and SF was dissolved in 98%pure FA,a relatively stable SF/PHBV composite spinning solution could be prepared.The precipitate in the SF/PHBV composite spinning solution was formed by the aggregation of SF macromolecules,which was mainly due to the increase of the electrostatic interaction between protein molecules by organic solvents such as TCM,and the deformic acid effect,which eventually led to a decrease in the stability of SF and precipitation occurred.According to the difference of the organic solvent content in the composite spinning solutions,the SF/PHBV composite spinning solutions had three states:a solution that had precipitates and could not be spun normally;solution without precipitation but easy to phase separation and a homogeneous and stable solution.(2)The electrostatic spinnability of LP-SF/PHBV composite spinning solution.When the solute mass ratio of SF to PHBV in the composite spinning solution was 10/1,under the conditions of a voltage of 15 kV,a flow rate of 0.3 mL/h,and a spinning distance of 13 cm,the spinning stability and fiber-forming effect of LP-SF/PHBV composite nanofibers were better.The spinning process was continuous and stable,and the fiber surface was smooth and uniform,no beaded structure.The fiber diameter was 171.10 ±40.38 nm.However,due to the low content of PHBV,the infrared characteristic peaks,crystalline diffraction peaks and thermal decomposition peaks of PHBV were not observed in the LP-SF/PHBV composite nanofibers.The structure and properties of the fibers were similar to those of pure SF nanofibers.(3)Effects of the composition of the composite spinning solutions on the stable preparation and fiber morphology of SF/PHBV nanofibers.With the increase of PHBV content in the composite spinning solutions,the composite spinning solutions would become unstable,but by reducing the mass fraction of SF solution and correspondingly increasing the mass fraction of PHBV solution,the stability of the composite spinning solutions could be maintained,and could increase the content of PHBV in the composite spinning solutions.The viscosity of SF/PHBV composite spinning solutions decreased with the increase of shear rate,and the solutions had the characteristics of non-Newtonian fluid.When the mass fraction of SF and PHBV solution was unchanged,the viscosity of composite spinning solutions increased with the increase of PHBV content.When the content of PHBV in the composite spinning solutions was unchanged,decreasing the mass fraction of SF solution and increasing the mass fraction of PHBV solution could reduce the viscosity of the composite spinning solutions.When the mass fraction of SF solution and PHBV solution were both 8 wt.%,a composite spinning solution(S8P8(1/1))with PHBV content of 50%and spinnability could be obtained.When the voltage was 22 kV,the flow rate was 0.3 mL/h,and the spinning distance was 13 cm,the fiber formation effect of S8P8(1/1)composite nanofibers was better,and the fiber diameter was 93.45±14.68 nm,but the spinning solution could not be spun stably for a long time.Keeping the mass fraction of SF and PHBV solution at 8 wt.%,under the same spinning conditions,S8P8(4/1),S8P8(3/1),and S8P8(2/1)composite spinning solutions could be spun stably for a long time.The fiber diameters were 75.93 ± 21.83 nm,69.35 ± 21.55 nm and 61.40 ±12.31 nm,respectively,thus the stable preparation of SF/PHBV composite nanofibers with a PHBV content of more than 30%and a diameter of less than 100 nm was realized..(4)Structure and properties of electrospun SF/PHBV composite nanofiber membranes.The infrared characteristic peaks,crystal diffraction peaks and thermal decomposition peaks of PHBV could be clearly observed in the composite fibers because the content of PHBV increased.The mechanical properties of pure SF nanofiber membranes were poor.The addition of PHBV could significantly improve the mechanical properties of SF/PHBV composite nanofiber membranes.With the increase of PHBV content,the breaking strength of the composite nanofiber membranes increased significantly,while the elongation at break decreased.Keeping the content of PHBV unchanged,with the increase of spinning time,the breaking strength and breaking elongation of the composite nanofiber membrane both increased simultaneously.The pore size of the electrospun SF/PHBV composite nanofiber membranes was small,with an average pore size between 500 and 800 nm.With the increase of spinning time,the average pore size of the composite nanofiber membranes showed a decreasing trend as a whole.(5)Protection and wearability performance of SF/PHBV/PLA composite materials.The SF/PHBV composite nanofibers were directly spun onto the PLA base fabric to obtain SF/PHBV/PLA composite materials.The average pore size of the composite materials was 1-2 μm.When the spinning time was 1.0 h,the filtration protection performance of SF/PHBV/PLA composite materials was the best,which met the technical requirements of medical protective masks and disposable medical protective clothing.The electrospun SF/PHBV/PLA composite materials had the characteristics of hydrophilic inside and hydrophobic outside,which made the composite materials could play a good role in moisture absorption and moisture conduction.The average moisture permeability of SF/PHBV/PLA composite materials was 3500-4000 g/(m2·d).The air filtration performance,moisture permeability and static decay properties of the SF/PHBV/PLA composite materials met the requirements of national standards for medical disposable protective clothing and medical protective masks,and at the same time had good moisture absorption and moisture conductivity,which was conducive to improving the wearing comfort of medical protective clothing and improving the performance of medical protective masks.