Solution Blow Spinning: Introduction and Application

Introduction

Nanofiber materials have the advantages of large specific surface area, high porosity, low density, good mechanical flexibility and so on, which show broad application prospects in many fields. There are various methods for preparing nanofiber materials, including electrospinning, solution blow spinning (SBS), the centrifugal spinning, the melt-blown Spinning, etc. SBS combines the advantages of electrospinning and melt-blown spinning, the process is simple and safe, spinning efficiency is high, suitable for a wider range of solution system, can choose more diverse raw materials, can control the structure and diameter of nanofibers. Since its development in 2009, SBS has received extensive attention from many fields and has become an efficient and versatile method for fabricating nanofiber materials with controllable microstructure and morphology.

In recent years, the number of papers on the topic of SBS has remained high (see Table 1). Tianjin Polytechnic University, Suzhou University, Beijing Institute of Fashion Technology, Jiangnan University, Donghua University, Dalian Polytechnic University and other universities are committed to using SBS to spinning nanofibers, so as to study the practicality of nanomaterials in various fields.The research enthusiasm of universities on SBS shows that blow spinning technology has great potential in the preparation of nanomaterials. With the deepening of research, spinning technology is becoming increasingly mature.This paper introduces the basic principle of solution blow spinning and its applicable raw materials, focusing on the influence of process parameters on solution blow spinning, and expounds the practical application of solution blow spinning nanofibers.

Solution blow spinning process

Blown spinning classification

Blown spinning is divided into solution method and melt method.
The solution method is to dissolve the polymer in volatile solvent to make spinning solution, spinning out of the spinneret hole at the same time by the high speed hot gas around the spray, so that the solution stream is stretched, and the solvent evaporation and curing, trapping on the net to form short fibers or non-woven fabric or collection of long filament bundles. This spinning method is called Solution blow spinning (SBS).
Melt method is used to melt polymer slices with spinning screw extruder and quantitatively extrude them. When melt is extruded out of the spinnblow hole, it is sprayed by the surrounding high-speed thermal flow and made into fibers, also known as melt-blown Spinning.

Principle of solution blow spinning

Medeiros et al. ^[1] first proposed the technology of preparing nanofibers by solution blow spinning, which combined the characteristics of melt blowing technology and dry spinning technology. The basic principle of this technology is that the small flow of solution is subjected to ultra-fine stretching under the action of high-speed airflow, and at the same time the solvent is evaporated and solidified into nanofibers. The schematic diagram of the principle is shown in the picture^[2-3].The core components of solution blow spinning equipment include injection pump, nozzle, compressed air, collector. During the spinning process, the spinning solution is transported to the spinneret hole of the spinneret head at a steady flow rate under the pressure of the syringe pump. At the same time, high pressure air flow around the blow hole to form stable ring, drive the solution trickle speeding stretching, uniform stability of solution formed trickle solution in the process of rapid evaporation of solvent and under the action of a housing complex aura are intertwined, curly eventually formed in the shade on this network structure stable, random three-dimensional crimp nanofiber felt.

Process factors of solution blow spinning

1.Polymer solution: polymer solution viscosity, polymer solution advance rate

Li Lei et al. ^[4] used solution blow spinning to prepare alumina fiber, and found that the influence of polymer solution viscosity on fiber morphology and diameter was different from that in general cases. When the viscosity was too small, the fiber diameter was coarser, possibly because there was too much solvent and it did not evaporate completely when it reached the receiver.The nanofiber is compact and its properties are improved. When Kasiri et al. ^[5] used low concentration (8%) polystyrene polymer solution for blow spinning, the blow was unstable and beaded microstructures were formed on the collector. As the concentration reached 10%, the viscosity of the solution increased, and the fiber was smoother and larger in diameter. The research results of Rotta et al. ^[6] showed that the average diameter of fibers increased with the acceleration of injection speed.

2.Nozzle design

3.The air flow field

Kasiri et al. ^[5] observed the fiber morphology of solution blow-spun polystyrene material (PS) under high-speed air flow with different air pressures, and found that the average diameter and diameter distribution of the prepared fibers increased slightly when the air pressure increased at a lower value. When the air pressure was higher, the optimal fiber orientation was narrower and more fibers could be collected by the collector.

4.Receiving distance

Studies have shown that the solvent evaporation rate in the process of solution blow spinning will affect the final morphological characteristics of the fibers, and the distance between the nozzle and the receiver will affect the solvent evaporation rate, which largely determines whether the fibers will eventually form films or intertwine with each other ^[10].

Solution blow spinning raw materials

Many materials can be used to produce nanofiber materials by SBS technology. Polymers are the most commonly used materials for fabricating fibers via SBS. SBS has no special requirement on the dielectric constant of the spinning solution, so it is suitable for a wider range of spinning ^[11].

 In the laboratory of Jia Chao et al. ^[11], they used SBS to study the spinnability of many polymer materials, polyacrylonitrile (PAN), polyvinylpyrrolidone (PVP), poly(methyl methacrylate)(PMMA), polyamide (PA), polylactic acid (PLA), polyimide (PI), poly(ethylene oxide) (PEO), poly(imide dioxime) (PIDO), SiO2 fibers, TiO2 fibers, ZrO2 fibers, BaTiO3 fibers, SnO2 fibers, SiO2− Al2O3 composite fibers，ZrO2−Al2O3 composite fibers, YSZ fibers, carbon fibers, metal fibers, polymer-based composite fibers，PAN-based carbon fibers，AgNF fibers，PLA-SiO2 composite fibers, PLA-TiO2 composite fibers, PLA-CeO2 composite fibers.

In addition to synthetic polymers, natural polymers, such as cellulose, zein, and gelatin, have also been successfully blown and spun into fibrous materials. For some non-spinnable natural polymers, mixing them with spinnable synthetic polymers is an effective strategy to obtain spinnable SBS solutions. 

Glebert et al. ^[12] studied synthetic polymers and composites,including Poly (acrylonitrile), Poly (vinylidene fluoride), Poly (vinylpyrrolidone), Poly (methyl methacrylate), Poly (vinyl chloride),Sulfonated poly (ether ether ketone) and Sulfonated poly (ether sulfone), Polyimide, Poly (lactic acid), Poly (lactic acid-co-glycolic acid), Poly (ethylene oxide), Cellulose, Lignin, Nylon, Polyurethane, Poly (vinyl acetate), Poly (vinyl alcohol), and Poly(ethyl-co-vinyl acetate), Poly (styrene), Poly (caprolactone).

Application of solution blow spinning nanofibers

Thermal insulation material

Lightweight thermal insulation materials with low thermal conductivity are urgently needed in aerospace, thermal power, battery thermal protection and other fields. Ceramic fibrous spongy materials are ideal for thermal insulation because of their low density and thermal conductivity. However, producing such insulation materials efficiently and cheaply remains a challenge ^[11].

Biomedical

Nanofibers have unique application advantages in biomedicine, and related products have entered the market. As a new nanofiber processing technology, solution blow spinning can directly deposit the fiber on the specified target, even on the surface of biological tissues, which further expands the application of nanofibers in the biomedical field ^[13].

Flexible Electronic Devices

Metal materials have good electrical conductivity, but bulk metals have poor flexibility and are difficult to be used in flexible electronic devices. Processing metals into fibers significantly increases their flexibility while retaining their inherent electrical conductivity. Metal fibers have excellent flexibility and electrical conductivity, which can meet the application requirements of flexible electronic devices ^[11].

Environmental protection

The nanomaterials prepared by SBS technology can be used for air filtration and pollutant adsorption. KHALID et al. ^[14] coated the window screen with nanofibers on a large scale to protect the room from suspended matter pollution, and prepared a transparent air filter with light transmittance of more than 80%, and the efficiency level of PM2.5 removal could reach more than 99%. KOLBASOV et al. ^[15] successfully prepared PA6-based nanofiber membrane containing bio-based polymer by solution blow spinning method (bio-based polymer was made of lignin, oats, chitosan, sodium alginate and soybean protein as raw materials), and studied the adsorption effect of this membrane on heavy metal pollutant lead (Pb).

Solution blow spinning machine

• Spinning solution thin flow is three-dimensional curled and entangled by the turbulent shear action of high-speed airflow field inside the spinning box. The process is short, the process is simple, the conditions are easy to control, and it can be large-scale production.
• The average diameter of nanofibers of the prepared nonwovens ranges from 0.01-3μm, which is smaller than that of conventional polypropylene melt-blown nonwovens, and has excellent performance.

Taking unlimited polymer solution as the processing object, it can overcome the requirements of the existing melt blowout technology on the thermoplasticity and high melt fluidity of raw materials, and has universal applicability.

Technical specification

Model	Compatibility	Sample size（mm2）	Nozzle number
L1.0	Standalone, lab scale	300*400	1-6
M1.0	Benchtop, lab scale	300*400	1-6
P10	Pilot scale	300*cont 600*cont	1-32

Number of spinneret capillary tubes	80~140
Angle between the spinneret capillary and the horizontal plane	45°
Temperature of dissolution kettle	40℃
High pressure air flow temperature	45℃
Spinning speed	207ml/h（15% PAN was dissolved in N, N-dimethyl acetamide） 267 ml/h（20% PAN was dissolved in N, N-dimethyl acetamide）
Traction wind pressure	2.6~3.0MPa
Suction air pressure	4kpa

References

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