Nanofibers refer to linear materials with a diameter less than 100nm and a longer length. In practice, materials with a diameter less than 1000nm are usually also called nanofibers, and their specific surface area will be 100 times higher than micron-level fibers. The research and development of modified functional nanofibers and their membrane products will bring new thinking to fast, efficient, and environmentally friendly nonwoven products.
Melt extrusion phase separation method overcomes the difficulties of traditional electrospinning
Common methods for preparing nanofibers include melt-blowing, island spinning and electrospinning. The melt-blown method is mainly suitable for polypropylene materials with high melt index. The island technology can only prepare PET and PA66 fibers with diameters above 700nm. The production of nanofibers mainly relies on electrospinning. However, electrospinning still has production efficiency. Low, high processing costs and other issues. In addition, electrospinning requires the use of some organic solvents, which brings environmental problems and increases the cost of recycling equipment.
Based on this, while in the United States, the research team, together with their mentor Professor Sun Gang, developed a new high-output environmentally friendly thermoplastic nanofiber manufacturing process, namely the melt extrusion phase separation method, and used this to produce polyester and polyolefins. , polyamide, polyolefin copolymer and thermoplastic polyurethane and other nanofibers, the fiber diameter can be controlled in the range of 80nm ~ 500nm. This method successfully overcomes a series of technical problems in which it is difficult to prepare thermoplastic polymer nanofiber materials using traditional electrospinning technology, and fibers with diameters less than 700nm cannot be prepared using melt-blowing and melt electrospinning methods.
Series of axial fiber aggregates have good compatibility
The basic principle of the melt extrusion phase separation method is that two thermodynamically incompatible polymers are fully melt-blended and extruded in a twin-screw melt extruder. The blended polymer melt is heated in the extruder and The spinneret is elongated and deformed under the action of the shear and tensile composite force fields to form nanofiber bundles. Finally, the matrix polymer is removed to obtain the desired kind of thermoplastic nanofibers.
In the preparation process of thermoplastic nanofibers, we use cellulose ester as the polymer matrix. The big advantage of using cellulose ester is that it is incompatible with most thermoplastic polymers and can be easily and quickly removed from the mixed phase by acetone in subsequent processes. The removed cellulose ester can be recycled.
At present, using the incompatible system of cellulose esters and various thermoplastic polymers, the research group has successfully and efficiently prepared several thermoplastic nanofibers, including polyester, polyolefin and several functional copolymers.
The thermoplastic nanofibers prepared by this method are a series of axially arranged nanofiber aggregates, which have the characteristics of adjustable polymer structure and high compatibility with existing fiber production equipment. In addition, nanofiber membranes with different nonwoven matrix structures were successfully prepared by coating nanofibers on different matrix surfaces.
A variety of high-end application fields still need to be developed
By functionally modifying thermoplastic polymer nanofibers containing functional groups on their surfaces, their applications in a variety of fields can be realized. The research team has currently made progress in application research in the fields of biosensors, filtration separation, antibacterial and antifouling by modifying nanofibers.
Biosensors. Biosensor is an instrument that is sensitive to biologically active molecules and converts their concentration into electrical signals for detection. Polyethylene copolymerized glycidyl methacrylate (PE-co-GMA) nanofibers were successfully prepared by melt extrusion phase separation method. Since PE-co-GMA is a thermoplastic material with active epoxy groups, and this active epoxy group can be connected to amino acids in biologically active macromolecules such as proteins and enzymes through ring-opening reactions, it can be used This nanofiber has great potential for preparing biosensors.
Filtration and separation field. Due to the unique large specific surface area, good biocompatibility and low flow resistance of nanofibers, many scholars at home and abroad are committed to the application of nanofibers in improving filtration membrane efficiency. The filtration capacity of the nanofiber membrane prepared by the research team based on the calculation standard of TiO2 suspension rejection rate is as high as 99.6%. In addition, research shows that nanofiber membranes will have obvious advantages when applied in the field of filtration and separation.
In addition, the research team prepared hydrophilic PVA-co-PE nanofibers through a melt extrusion phase separation method, activated its surface with cyanuric chloride, and then grafted IDA to the surface of the nanofibers through a nucleophilic substitution reaction. , successfully prepared hydrophilic PVA-co-PE nanofibers with surface-cured IDA, and used the coating method to prepare the nanofibers into nanofiber membranes.
Anti-pollution field. Nanofibers with high specific surface areas have important application potential in the field of antibacterial fibers compared with traditional micron-sized fibers. The research team prepared a PVA-co-PE nanofiber membrane containing amphoteric sulfonamide ions on the surface through surface atom transfer radical polymerization (SI-ATRP) method to explore the antibacterial properties of this new anti-fouling nanofiber membrane. The study found that the number of colonies on the nanofiber membrane with amphoteric sulfonamide ions on the surface was much lower than that on the pure nanofiber. Through calculation, its antibacterial rate reaches 99.46%. Therefore, the nanofiber membrane with surface-grafted amphoteric sulfonamide ions also has excellent antibacterial properties.
In addition, polymer nanofibers�Materials have broader application potential yet to be developed in military, bioengineering, industrial protective clothing, enzyme catalysis, lithium battery separators, cosmetics, air and water filtration, etc. In future research, we should also pay attention to the economics, environmental friendliness, recycling and recyclability of the technology, as well as product safety certification and other issues.
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