What is Nanofiber?
Nanofibres are extremely small; they vary in size from 1 micron to approximately 0.5 nanometres. Figure 1 shows how much smaller nanofibers are compared to a human hair, which is 50-150 µm. They were pioneered by the aerospace industry, which places quite a premium on weight and space when planning space missions. Non-woven sheets can be produced via an electro spinning process that can draw on a variety of raw materials, such as carbon and ceramics. Tiny fibers are collected as non-woven sheets that can cover well, and they are combined with lightweight materials. Amazingly, a piece of fabric the size of a football pitch can be folded so that it is the size of a sugar lump! Also, Nanofibres can be incorporated onto the surface of fabrics or added to yarns. Nanofibers are very fine and this influences the mechanical and reflective properties of the fabric.
Nanofibers are fibers with diameters of 100 nm or less, which have characteristic features such as extremely small pore dimensions, large surface-area-to-volume ratio and superior mechanical properties. Therefore, nanofibers have a wide range of applications in areas such as high-performance filtration, tissue engineering, wound dressing, vascular grafts, energy storage, battery separators, enzyme immobilization, electrochemical sensing, composite materials, reinforcements and blood vessel engineering.
The fabrication of nanofibers has been given much attention by many researchers in the last three decades. Electrospinning or electrostatic spinning is the most common method used to fabricate nanofibers. The existing fiber spinning technologies for synthetic fibrous materials cannot produce robust fibres with diameters lower than 2 μm due to technical limitations. Electrospinning is the process widely used for the fabrication of nanofibers, as it is simple and suitable for a variety of polymers. Other processes that can be used for nanofiber fabrication include melt blowing, flash spinning, bi-component spinning, force spinning, phase separation and drawing.
The market of nanofibres are about 176 US million dollars in 2012 and it grows to 825 million US dollars in 2017. The nanofiber market is projected to reach USD 4.16 billion by 2030.
Properties of Nanofibers:
Nanofibers have unique chemical and physical properties, heat, and electrical conductivity, strength, elongation. Many other chemicals and properties may be different from the same materials in bulk size. Nanofibers have high surface to volume ratio, low density, improve mechanical properties, high surface energy.
Summarized properties of nanofibers:
- Extremely Lightweight and Strong
- Fine, Smooth and Delicate
- Versatile—can incorporate different fibers and be engineered to suit various end uses
- Good covering power
- Large areas of fabric reduced to a small size
- Many nanofibers are safe and eco-friendly.
- Nanofibers are highly porous, allowing easy air and liquid flow.
Electrospun nanofibres possess noticeable differences in their thermal, mechanical and electrical properties when compared with normal fibres.
a) Thermal Properties:
The thermal properties of nanofibers can be analyzed by differential scanning calorimetry (DSC). Electrospun nanofibers of Poly- L-Lactide Acid (PLLA) possess lower crystallinity, melting temperature (Tm) and glass transition temperature (Tg) than semi-crystalline PLLA resins. The low crystallinity can be attributed to the high rate of evaporation and rapid solidification before their collection onto the collector. The decrease in Tg and Tm is due to the large surface area to volume ratio of nanofibres with air as plasticizer. The lower heat of fusion and melting temperature of PEO nanofibres when compared with the PEO powder was attributed to the decreased crystallinity after electrospinning.
b) Mechanical Properties:
The mechanical properties of nanofibers such as tensile strength, elongation and modulus are affected by the surface morphology, pore size and its distribution. The tensile strength of PVA fibre aggregate was found to increase with the increasing weight percentage of glyoxal to PVA while the elongation decreased.
c) Electrical Properties:
The electrospun nanofibres containing carbon nanotubes (CNTs) have superior electrical properties (high energy densities and low driving voltages). The nanocomposites of ether/clay (organically modified) exhibit ionic conductivity, which is several orders of magnitude higher than that of the corresponding clay. The intercalation of electroactive polymers into clay minerals can further improve the conductivity.
Application of Nanofibers:
Due to unique properties, area of application of nanofibers are widespread. It can used in filtration of air, water, and oil separation, in energy conservation used in batteries, medical textiles, self-cleaning textiles, electronics field, smart textiles, sports tech, etc.
The nanofibres with high surface area and numerous pores have enormous applications in tissue scaffolds, nanocomposites, protective clothing, filtration, and electronics. Nanofibers are used in seamless spray products, breathable membranes for clothing (e.g. sportswear), filters for industrial purposes, space mission fabrics. Nanotechnology fibres have endless uses in our fast-growing, technological world; they are developed specially for performance and function.
Besides, nanofibers are widely used in biomedical, electronic, sensors, filter application, protective textile materials etc. Explain these applications below:
a) Biomedical Applications:
Nanofibers are widely used in medical applications, which include, drug and gene delivery, artificial blood vessels, artificial organs, and medical facemasks. For example, carbon fiber hollow nano tubes, smaller than blood cells, have potential to carry drugs in to blood cells.
- Tissue Engineering: Nanofibers serve as scaffolds for cell growth, mimicking the extracellular matrix to support tissue regeneration. Supports mineralized tissue formation and may be used for the treatment of bone defects.
- Drug Delivery: They can be used to create controlled drug release systems, allowing for targeted and sustained delivery of pharmaceuticals.
- Wound Dressing: Nanofiber mats can be used as advanced wound dressings that promote healing by providing a moist environment, absorbing exudates, and protecting against infections. The degummed silk fibroin nanofibre non-wovens were applied for wound dressing and found to be favourable for cell attachment, growth and proliferation. Besides, nanofibres and non-woven fabrics that have potential application in wound healing, tissue engineering and as haemostatic agents.
b) Electronic Applications
- Energy Storage: Nanofibers are used in batteries and supercapacitors to enhance energy storage capacity and improve charging rates due to their high surface area. The performance of the capacitors produced by carbonization of electrospun PAN fibre can be improved by controlling the activation temperature, the pore density and the structure. Conducting nanofibres with the potential for applications in micro and optoelectronics such as nanowires, LEDs, photocells etc.
- Flexible Electronics: Their use in flexible substrates for displays, sensors, and wearable devices allows for the development of lightweight and bendable electronic gadgets.
c) Nanofiber Sensors:
- Chemical Sensors: Nanofibers can detect chemical changes due to their high sensitivity, making them ideal for gas sensors and environmental monitoring. The improvement in sensitivity of the sensors produced from nanosurfaces for humidity sensing, hydrogen peroxide and glucose sensing. The CNT-based sensors demonstrated 35 times increase in the strain-sensing ability for only 0.05 wt.% of the nanotube.
- Biosensors: They are employed in biosensors for the detection of biomolecules, enabling applications in medical diagnostics and food safety.
d) Filter Applications:
Nanofibers have significant applications in the area of filtration since their surface area is substantially greater and have smaller micropores than melt blown (MB) webs. High porous structure with high surface area makes them ideally suited for many filtration applications. Nanofibers are ideally suited for filtering submicron particles from air or water.
The electrospun nanosurfaces are well known in the filtration industry for their high filtration efficiency for small particles because of the nanoscale fibre diameter and high specific area to volume ratio.
- Air and Water Filtration: Nanofibers are used to create highly efficient filters that can remove fine particles, bacteria, and viruses from air and water due to their small pore size. The application of electrospun nanofibres in pulse-clean cartridges for dust collection and cabin air filtration of mining vehicles.
- Oil-Water Separation: In environmental protection, nanofiber filters are used to separate oil from water, particularly in cleaning up oil spills.
e) Protective Textile Materials:
For protective clothing applications, the nanofibre webs could be directly applied to garment systems.
- Personal Protective Equipment (PPE): Nanofibers are integrated into PPE like masks, gloves, and gowns to provide enhanced protection against biological agents, chemicals, and particulate matter. Protective clothing for agricultural workers was developed using the electrospun PP webs and laminates produced via melt-electrospinning The layered composite material was incorporated with electrospun nanofibres and utilized as protective clothing.
- Bulletproof Vests: Due to their strength and light weight, nanofibers are used in the development of body armor and other protective clothing.
Challenges in Nanofibers:
The production process for nanofibers can be expensive compared to conventional fibers due to low production rate and high cost of technology. In addition the vapors emitting from electrospinning solution while forming the web need to be recovered or disposed of in an environmental friendly manner. This involves additional equipment and cost. Producing nanofibers in large quantities while maintaining consistent quality is difficult. The fineness of fiber and evaporated vapor also raises much concern over possible health hazard due to inhalation of fibers. Achieving uniform fiber diameter and distribution across large areas is challenging. Thus the challenges faced can be summarized as:
- Economics
- Health hazards
- Solvent vapor
- Packaging shipping handling
Because of its exceptional qualities there is an ongoing effort to strike a balance between the advantages and the cost. The disposal and degradation of synthetic nanofibers can pose environmental risks.
You may also like: Electrospinning and Electrospun Nanofibers: Process, Properties and Uses
References:
- Fibres to Smart Textiles: Advances in Manufacturing, Technologies, and Applications Edited by Asis Patnaik and Sweta Patnaik
- Nanofibers and Nanotechnology in Textiles Edited by P. J. Brown and K. Stevens
- Fibers for Technical Textiles edited by Sheraz Ahmad • Abher Rasheed • Yasir Nawab
- Fibres to Fabrics by Bev Ashford
Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.
