Biomass Electrospinning: Recycling Materials for Green Economy Applications

Abstract

The development and advancement of electrospinning (ES) presents a unique material technology of the future achieved by fabricating novel nanofibrous materials with multifunctional physical (three-dimensional [3D] structure, nanoscalable sizes) and chemical characteristics (functional groups). Advancing the possibility of preparing various classes of novel organic and inorganic electrospun fiber composites with unique features such as polymer alloys, nanoparticles (NPs), active agents, and devices. This feature gives provision for internal access of the setup parameters such as polymer precursor material, polymer concentration, solvent, and the method of fiber collection that consequentially improves the intrinsic control of the construction mechanism of the final nanofibrous architecture. In synthetic electrospinning, the nanofibrous material processing allows for internal control of the electrospinning mechanism and foster chemical crosslinking to generate covalent connections between polymeric fibers. Comparing technologies according to materials of the future revealed that electrospinning supports the formation of micro-scale and in some cases nano-scale fibers while the formation of thin films is facilitated by the electrospraying system. Recent innovations point to various biomass waste streams that may be used as an alternative source of polymeric materials for application in electrospinning to produce materials for the future.

1. Introduction

Electrospinning (ES), as a nanotechnology, exhibits strong evolution of materials used across a broad spectrum from bioactive (microorganisms-infused for biomedical applications) to manufacturing (adhesion, proliferation, and differentiation of the mimetic for mechanical, chemical and electrochemical applications) nanofibers [1]. The advent of bioeconomy and innovation technological development presented opportunities for remarkable progress in the expansion of methods and multiple applicability for the electrospun nanofibers. Waste biomass and other recyclable materials are also finding use in ES as an adaptable and sustainable innovative approach for making ultrathin fibers [2]. Valorization of biomass waste materials such as plant biomass, waste plastic, industrial effluent and other waste biomass streams have been processed through various technologies to produce a wide range of higher hierarchical recycled fibrous products. These including biodegradable bio plastic, filtration membranes, nanofibers as macro, micro and nanomaterials. Advancement in innovative ES techniques allows for intrinsic control of the physicochemical factors, including physical (morphology, diameter, orientation); surface (volumetric dispersion, porosity and thickness) and chemical (functional groups) characteristics of the final product [2].

Electrospinning method entails the utilization of voltage to create an electric field, polymer solution of specific concentration and electrospinning pump to introduce the spinneret onto collector plate. The resulting products are electrospun nanofibers characterized by their fibrous morphology, three-dimensional (3D) porous framework, nanoscale and chemical character that enable unique capabilities across multiple fields; which are difficult to create using conventional methods. Thermally induced phase separation nanofibers, and electrospun nanofiber scaffolds, for example, are being developed and are widely regarded as an emerging technology and a potential strategy for biosensing, drug delivery, soft tissue regeneration, hard tissue regeneration, and wound healing. The capacity to alter numerous control aspects of the functional scaffold, such as fiber geometrical features and alignment, architecture, and subsequent material performance, is the technique’s most prominent feature [1]. More importantly, electrospinning allows for the creation of a wide range of novel materials, including polymer alloys, nanoparticles, and active agents.

Nanofiber preparation employing the ES method has proved to be a future-proof materials technology, with numerous appealing characteristics such as outstanding mechanical properties and large specific surface areas. Due to the versatility, utility, and simplicity of the ES technology, the fibers produced are particularly appealing for numerous applications from a simple process capable of producing diverse morphologies [3]. The use of metal organic frameworks (MOFs) due to its flexible and functionalized molecular structures, nanofibers composites were fabricated as a novel molecular system with highly engineered structures for tailored applications. The usage of MOFs/carbon nanofibers (CNFs) as good electrode materials in energy transformation and storage technologies that include supercapacitors, sensors, and electrocatalysts is one of the most basic applications [4].

Electrospinning for materials technology of the future have seen a wide range of innovations of the technology including home-made re-designing of the technology to improve the ES apparatus reproducibility. Thus hybrid electrospun structures on different types of polymers have been developed and optimized to create products for various applications [5]. This chapter explores electrospinning innovation technology and the materials of the future, their properties and characteristics and applications. The focus materials of the future will be products fabricated from recyclable waste biomass materials as a way of valorization for higher hierarchical bioeconomic products.

2. Advances in electrospinning technology

The ability to tailor structural and morphological aspects of electrospun materials, such as the surface topography of nanofibers, and their porosity that allows enhanced mimicking of the manufactured material matrix, has sparked interest in the ES technology. This is accomplished by the ability to modify the electrospinning assembly in numerous ways in order to combine polymers with a wide range of materials (incorporate active materials such as drugs, inorganic catalysts, growth factors, functional groups and DNA/RNA as necessary in the various applications of the fabricated nanofibers [6]. Figure 1 is a schematic diagram showing a simple set up of the electrospinning system.

Figure 1.

Schematic illustration of vertical electrospinning setup [6].

Mokhtari et al. compared the technical assembly of the electrospraying and the electrospinning systems. This is because the two systems have different mechanisms of performing the fabrication of carbon materials they produce in unique distinct ways as shown in Figure 2. Electrospinning (Figure 2a) supports the formation of micro-scale and in some cases nano-scale fibers while the formation of thin films is facilitated by the electrospraying system (Figure 2b) aids in the formation of thin films [7]. As a result of insufficient polymer-chain entanglements in the polymer chains network, it was discovered that applying a high voltage below the minimum concentration causes electrospraying rather than electrospinning.

Figure 2.

(a) Schematic drawing of a typical electrospray setup. (b) Schematic drawing of a typical electrospinning setup.

It was observed that varying the ratio of the polymer solution and the electrospinning potential difference results in the formation of unique materials ranging from beaded carbon deposits, heterogeneous fibers, uniform fibers, and entangled fibers [7]. Advanced efforts to improve electrospinning performance and the quality of the nanofibers while increasing cost-effective productivity of electrospinning and other nanofiber assembly technologies include integration of key concepts of conventional fiber production methods with nanotechnology. Electro-blowing, gas-jet/gas-assisted electrospinning, and solution blowing, which advanced from melt blowing, combined with electro-centrifugal processing, centrifugal spinning, near field electrospinning with dip-pen nanolithography, and XanoShear, which combines shearing with wet spinning, are among the merged electrospinning conceptual technologies [8].

A look into a study of electrospinning as a versatile technique for fibrous material manufacturing in advanced fabrication of the electrospun biopolymer-based biomaterials compared the conventional needle-based and an innovative needless-based electrospinning processes. Figure 3 presents the unique feature of the needless-based ES process is that the polymer solution is positioned in a bath and a high voltage polarized spinning mandrill is immersed into the bath.

Figure 3.

Electrospinning setups needle-based (left) and needleless (right) [2].

When the rotating mandrill comes into contact with the grounded collection electrode, it collects a thin layer of polymer solution, which is subsequently subjected to an electric field. The electrostatic forces of the field at the needle’s tip, or the thin layer of polymer solution at the rotating mandrill, overcome the solution’s surface tension, pushing it to form several or a single Taylor cone, as illustrated in Figure 4. On its way to the collector, the charged polymer jet from the cones is ejected and extended. The solvent evaporates from the solution, weakening the continuous jet of pure polymer and depositing it in a fibrous form on the collector [2].

Figure 4.

Needleless roller for electrospinning of polymer solutions.

A needleless mechanism performs the electrospinning of the polymer solution from the surface of a revolving roller. The roller is partially immersed in a tank containing material to be electrospun, as shown in Figure 4. On the roller’s surface, a layer of consistently new material is generated by a rotating roller. When compared to needle electrospinning, the technique produces a large number of Taylor cones on the roller’s surface, resulting in the technology’s industrial applicability in mass manufacture of nanofibers materials [9].

Complex fibrous nanostructures have been prepared through manipulation of many experimental parameters of a multifluid electrospinning process. This is an innovative shift from the traditional single-fluid blending electrospinning process. However, there are difficulties in using multifluid processes, such as compatibility concerns of set up parameters including fluids, rate of stock feed and average proportions, interfacial tensions, and electrospinning sustainability [10]. Mass production of nanofibers using electrospinning was determined through the development of the macromolecular ES principle. The molecular flow in the spinning process, as well as the molecular direction in nanofibers, can be tailored to advance the electronic, and physico-chemical properties of nanofibrous materials, which influence their applications, molecular orientation in nanofibers, and structural hierarchical significance [11]. Several recent methods were developed to manufacture nanofibers using macromolecular ES processes. For example, industrial yarn production processes were only applicable for solution electrospinning via the innovative conceptualized gas-assisted melt ES. (GAME) as shown in Figure 5.

Figure 5.

Macromolecular electrospinning equipment showing a possible laminar flow in the suction tube [12].

The unique characteristic of the innovative technique is the observed occurrence that turbulent air applies a pulling force, subsequently leading to an increase in output and a 10% reduction in melt jet width, with an additional 20-fold thinning when the air jet temperature is increased [12].

Multi-temperature control electrospinning (MTCES) is a practical way to spin molten polymers on a submicron level fiber than the conventional molten/solution ES. The molten precursor polymer was treated to quad-heating regions in the proposed MTCES design: needle, nozzle, rotating area, and collector to augment and regulate fiber size and morphology. The nozzle, spinning thermal parameters and dimensions, electric field, and flow rate of the MTCES are all adjusted to change the fiber diameter [13]. The MTCES setup is depicted in Figure 6. The technical mechanism demonstrates that the jet propagation begins to bend significantly near the collector at 25°C, and at 80°C, a strong melt jet propagation increases the dwelling time of the jet in the rotary region, demonstrating a distinct multi-control ES scheme, which was characterized by extensive preliminary work and models that used the same or similar setup schemes.

Figure 6.

The multi-temperature control electrospinning setup showing the multi-heating zone melt electrospinning [13].

Energy materials have been fabricated by ES techniques as an alternative to fossil fuels and environmental mitigation initiatives. The nanofibrous materials produced by ES are extensively used in electrochemical energy storage devices. This is because the materials have inherent excellent properties, including an increased surface area, high dimensional ratio, good flexibility, high permeability, with several functionalities. A shift from the conventional ES methods saw the development of innovative enhanced ES techniques that produce nanofibers with novel special hierarchical nanostructures [14].

The core-shell structure was chosen because of its distinctive features, which can help to improve the preferred properties. Co-electrospinning creates core-shell fibers by filling two distinct precursor solutions into the double nozzles, as shown in Figure 7 [14].

Figure 7.

Scheme for coaxial electrospinning [15].

The simplicity of setup and low cost, together with the ability to fabricate nanofibers with a wide range of compositions and morphologies, has aided ES technology’s innovative advancement. Electrospinning-created nanofibrous structures provide appealing extracellular matrix conditions for the fixing, migration, and variation of materials matrix, including those giving rise to hard structure regeneration. The creation of structural materials regenerating nanofibers has been utilized by ES technology developments, which include material simulating composite/hybrid configurations and surface functionalization such as mineralization [16].

A special trifluid electrospinning technology was also developed as an innovation to the co-electrospinning process. This advancement provided for complex multi-chamber nanostructures for designing novel functional nanomaterials. The complex structure consisted of a collective shell and two independent openings of a multi-chamber nanostructure, with each having its own unique complex property, and these compartments form a total composite assembly within a region limited by nanofiber diameter. The sheath-separate-core fused nanostructure synchronized the functionalities of the three ES monolithic nanocomposites to afford a smart regulated release profile of a multi-chamber nanostructure, with each chamber characterized by distinct intrinsic complex property, and the structural compartments constituting a whole fused structure inside a section restricted by the diameter of nanofiber as shown in Figure 8 [17].

Figure 8.

Designs of the complex spinneret for implementing trifluid electrospinning: (a) a digital image showing a full view of the spinneret; (b) front view; (c) side view; and (d) a diagram about the organization of a structural outlet from three inlets [17].

Precision electrospinning, enabled by recent improvements in ES technology, is being envisioned as a viable option for fabricating 3D nanofibrous materials with a desired microstructure. Internal access to setup parameters such as solvent and fiber collecting method has increased intrinsic control of final nanofibrous architecture creation mechanism, as shown in Figure 9 [18].

Figure 9.

Setup used to form 3D nanofibrous scaffold using a negatively charged electrode or negative ion generator [18].

Plastic and other waste materials from industrial, domestic and agricultural activities, are the modern scourge on the face of the planet. The global call for re-use and recycle is gaining tremendous recognition with scientist scrambling for innovative ways of using waste materials in the circular economy. Waste biomass has been explored as an alternative source of polymers that may be used in wide range of ES processes targeting specific valorized products. As new materials use emerge and novel materials are electrospun into nanofibers, it is becoming increasingly critical to grasp current breakthroughs in biomass conversion into polymer sources for nanofibrous structures in order to fully exploit their potential. Advancements in waste biomass conversion technologies such as bio digestion, pyrolysis of plastic, and waste agricultural plant biomass wastes into bio oils and other polymers have preceded this.

3. Waste biomass feedstock for electrospinning nanofibers

Biomass is organic substances that is renewable and comprises plants and animals matter and may be combusted for heat or treated into renewable polymeric materials or fuels using a range of technologies. Most of the biomass end up as environmental waste materials that contaminate the land, rivers and oceans. Waste biomass include waste plant materials from crops, animal waste (dung and sewage), industrial waste in the form of effluent coming from industries such as petrochemical, food processing, textile dye effluent, pharmaceutical, and solid waste biomass including plastics, plant residues, (bagasse and other dregs), timber offcuts and sawdust, pulp and paper processing waste etc. These various biomass waste streams may be used as an alternative source of polymeric materials that may be used in electrospinning to produce materials for the future. Three classes of the waste biomass will be discussed namely synthetic waste biomass, natural flora waste biomass and natural fauna-based waste biomass.

3.1 Synthetic waste biomass

Plastic is the largest solid waste biomass on the face of the earth’s surface while textile and pharmaceutical effluent are major synthetic liquid waste biomass. Unless great strides are made to valorize these waste streams and find hierarchical bioeconomic applications of these materials, they will persist in the environment as contaminants. Due to its tunable features, including wettability, surface charge, transparency, elasticity, porosity, and surface to volume proportion, various polymeric fibrous nano materials have been developed as simulated extracellular matrix. Using ES nanofibers of natural polymers (NPs) and synthetic polymers (SPs) as simulated extracellular matrix for tissue regeneration, a comprehensive investigation identified five basic kinds of nanofibrous polymers. NP–NP composites, NP–SP composites, SP–SP composites, cross-linked, and modified polymers with mineral materials are some of the polymers available [19]. Polycaprolactone (PCL), polylactic acid (PLA), poly(lactic-co-glycolic acid) (PLGA), and polyethylene terephthalate (PET) are some of prevalent well-known synthetic polymers [20, 21].

In recent years, a variety of processing technologies have been utilized in the manufacture of polymeric fibrous nano materials, including drawing, 3D printing, template synthesis, phase separation, self-assembly, ES, and so on. Synthetic ES nanofibrous materials processing allows for internal control of the electrospinning mechanism and foster chemical crosslinking to generate covalent connections between polymeric fibers. In either in situ electrospinning or post-spinning crosslinking, this manipulation is done to target qualities of the material of application in which the fibers will be used. Highly porous electrospun nanofibrous membranes, for example, have sparked a lot of interest in water filtering applications. Figure 10 presents some of the common synthetic biomass materials used in ES of nanofibers. The creation of a reduced pore size and its distribution is highly favored by a thicker membrane with a lower mean fiber diameter, albeit the influence of membrane thickness is rather restricted. A high flux microfiltration (MF) sheath was fabricated based on efficient control of the total composite structure containing the electrospun layer thickness of 200 ± 10 m and a mean fiber diameter of 100 ± 20 nm [22].

Figure 10.

Synthetic polymers used in electrospinning of nanofibrous materials.

A previous study looked at the spinnibility of various polymers, such as aqueous poly(ethylene oxide) (PEO) dispersed in alcohol-to-water mixtures. Fiber production was found to be possible with viscosities ranging from 1 to 20 poises and superficial tensions of 35−55 dynes/cm. Electrospinning, however, was not feasible at viscosities more than 20 poises due to flow instability produced by the solution’s high cohesiveness [23].

3.1.1 Natural flora waste biomass for electrospinning: material technology of the future

Spongy pomelo peels, rice husk, rice straw, sugar cane bagasse, coffee beans, coconut shells, and peanut shells have all been investigated as alternative sources of carbonaceous materials from biomass. In comparison to other carbonaceous precursors, these and other natural plant/floral biomass resources have grown increasingly appealing due to their availability, low cost, easy accessibility, and environmental friendliness. As a result, floral biomass has gotten a lot of attention in the electrospinning, biomedical, and energy storage fields [24]. Okara, soy pulp, or tofu dregs, for example, is a pulp made up of insoluble components of the soybean that remain after pureed soybeans are filtered for soy milk and tofu manufacture. Recent reviews have reported on the feasibility of ES fibrous nano materials made from a variety of decomposable and biocompatible matter, including natural proteins like floral and faunal collagen, gelatin, silk, chitosan, and alginate [25].

The preparation of the waste floral/plant biomass for ES of nanofibrous materials involves a number of steps that extract plant proteins in the insoluble parts of the waste biomass. Silk fibroin (SF), for example, is made by degumming raw silk fibers twice with a 0.5% (W/W) NaHCO₃ base medium at 100°C, over half an hour period followed by rinsing with warm dH₂O. At 70°C for 6 h, degummed silk (SF) is dispersed in a ternary aqueous medium of calcium chloride-ethanol-water (1:2:8 in molar ratio). The SF was filtered and lyophilized after 3 days of dialysis using cellulose hollow sheath (250-7u; Sigma) in dH₂O to get the regenerated SF sponges. Dispersing the SF sponges in 98% methanoic acid (Aldrich) for 3 h makes SF solutions. The molar quantities of SF solutions for electrospinning range from 3% to 15% by weight [26].

Extracted silk fibroin was used to prepare silk electrospinning as presented in Figure 11. Electrospun SF nanofibers with varied silicon fibroin concentrations of 3%, 6%, 9%, and 12% are shown in SEM micrographs. The most prevalent natural polymers used as ES nanofiber materials include chitosan, collagen, gelatin and silk [20, 21]. Natural polymer nanofibers present distinguished features like biodegradability and biocompatibility, a phenomenon that makes them suitable materials in biological environments. Figure 12 presents some of the abundant natural polymers adapted for ES nanofibers production. Chitin and its over 50% deacetylated derivative, chitosan, for example, are commonly used natural polysaccharides as scaffolds. Blending with other materials are thus required to tailor-make materials with a set of acceptable features and attributes in order to achieve a stronger composite. Chitin/silk fibroin (chitin/SF) nanofibers, for example, were used to make novel ECM scaffolds [27].

Figure 11.

SEM micrographs of electrospun SF nanofibers with concentration of (a) 3%, (b) 6%, (c) 9%, and (d) 12% [26].

Figure 12.

Natural polymers used in electrospinning of nanofibrous materials.

Biocompatibility and biological activity are two characteristics of natural polymers. However, these polymers have some drawbacks, such as engineering and processing difficulties due to poor mechanical strength, restricted processing and manufacturing capacities, batch-to-batch variability, and the possibility of pathogen transmission [20]. Collagen and proteoglycans, for example, make up the majority of the body’s natural extracellular matrices (ECMs), which vary in composition depending on tissue type. Nanofibrous scaffolds made of collagen fused with glycosaminoglycans (GAGs), the major constituent of proteoglycans like condroitin sulfates and hyaluronic acid, are suitable for creating a perfect scaffold that mimics the natural ECM. Collagen and GAGs’ utility, on the other hand, has been limited because of their exorbitant price and poor mechanical qualities. In biomedical applications, this phenomenon can be addressed by fusing natural polymers such as proteins polymeric strands and polysaccharides fibrous materials, which can improve biotic transformation of cells and accelerate tissue development [27].

Most of the insoluble floral biomass is in the form of lignocellulosic and chitin material. The success of tapping into the floral biomass as a resource for ES of nanofibrous material depends on the ability to depolymerize the lignin and chitin long polymer chains. It is these polymers that will be used for ES processes to produce electrospun nanofibers. Recently, there has been renewed interest in producing carbon fibers from sustainable cellulosic precursors [28]. The abundance and cost effectiveness of cellulose as a material generator, as well as the relatively ecologically friendly fiber production methods used preceded this interest. Recent research on regenerated cellulose fibers from a fluid crystalline fabrication route as a carbon fiber precursor generated strands with a modulus of 140 GPa for the shell area and 40 GPa for the core area, indicating that CNFs resulting from nano-sized cellulosic precursors are even more competent as physical reinforcement than micron-sized fibers; because of their reduced diameters, providing a greater surface area for bonding and stress transfer [29].

3.1.2 Natural fauna waste biomass for electrospinning: material technology of the future

Animal manure, agricultural residues, organic portion of municipal solid garbage, industrial waste biomass, and natural vegetation cycle waste are all examples of enormous amounts of organic waste produced by many sectors. Similarly, fauna waste biomass, primarily in the form of keratin, a durable, fibrous protein found in advanced vertebrates (mammals, birds, and reptiles) and human epithelial cells, has been widely employed in ES for the creation of nanofibrous materials. Millions of tons of keratin-containing biomass are produced by the food business, particularly the meat market, slaughterhouses, and wool manufacturers. These sectors are rapidly expanding, with the United States, Brazil, and China accounting for more than 40 million tons of fauna-based biomass annually [30]. Inadequate management of these organic wastes can harm the environment by polluting water and air, lowering people’s quality of life [31].

If controlled with scientific interventions, organic waste no longer persists as garbage, but instead becomes a rich source of substrate, polymers, and molecules for the production of a variety of value ES nanofibrous products [32]. Detailed studies explored potential applications of the fauna generated organic waste in the production of biogas for energy production. Human waste is disposed of as sewage in the form of biological wastewater. Technological advances unravelled biological wastewater treatment plants (WWTP) as an approach to converting biomass into rich materials for precursor molecules for polymerization in ES nanofibrous material fabrication or for energy production [33]. Fauna waste biomass in the form of dung (Figure 13), piggery or fowl wastewater treatment with purple phototrophic bacteria was explored as a promising platform for electrospinning biomass resource recovery process under optimized operational conditions [34].

Figure 13.

Fauna biomass: cow dung is co-digested with sewage for production of gas in an anaerobic bio digester.

It is important to note that fauna waste biomass is a natural phenomenal bio digestive process of converting lignocellulosic and chitin organic biomass and transform it into shorter chains of polysaccharides and other polymeric substrates for ES nanofibrous materials production. Anaerobic bio digestion followed by catalytic polymerization of biogas molecules such as methane, ethane and propane, will produce tailor-made polymeric materials that may be used in electrospinning production of carbon nanofibrous materials. Figure 14 is an advanced industrial scale bio digestion plant for production of biogas.

Figure 14.

Sewage treatment plant for gas production.

Bio digestion of fauna waste biomass is a significant alternative supply of materials for electrospinning of nanofibrous materials when modern methods are used. Previous research on bio digestion of fauna waste biomass for methane production found that the influence of pre-treatment results in a substantial increase in gas production of up to 67%, with a 52% methane content in the biogas. As a result, it was determined that pretreatment of both feed and biomass improves biogas output but not methane content [35]. According to recent studies, the valorization of bio or organic waste is being prioritized in order to tackle the rapid accumulation of waste generated from food production activities, as well as to create sustainable feedstock for industrial materials and chemicals in place of fossils and synthetic materials (see Section 3.1). Biogas, compost, and small platform molecules are currently produced from biowaste via anaerobic bio digestion, fermentation, and thermo-chemical methods as shown in Figure 15. There are currently no commercial low-temperature chemical methods for valorizing organic lignin fractions as feedstock for modified compounds. Thus, research has been conducted to fill this technological gap, demonstrating that moderate thermal hydrolysis of municipal bio-waste manure reserve is a safe, environmentally sustainable, and affordable process for transforming lignin-like material from compost into value-added specialty chemicals for the production of ES nanofibrous materials (Figure 15) [37].

Figure 15.

Auger/screw pyrolysis reactor concept using heat carrier [36].

Biomass is a readily available and long-lasting ES material that may be turned into carbon based smart energy storage device and other uses. For carbon nanofiber manufacture, many strategies were used to meet various goals, including an increased productivity, easy dimensional parameters manipulation, energy efficient, and a high turnover. Nonetheless, several critical features of biomass-based fibrous carbon nano materials are yet to be extensively studied, thus information gaps still exist for each process to be supplied. As a result, more research is needed to expand our knowledge of the essential characteristics of various processes in order to generate highly desirable precursor materials for ES fibrous carbon nano materials manufacture from organic matter for sustainable materials manufacturing and energy smart storage applications [38].

An example of fauna waste biomass material rich in extractable materials for ES nanofibers materials is feathers from the poultry industry. Chicken feathers, comprises 90% raw keratin protein and 70% amino acids, can be employed as one of the primary sources for extracting keratin. Keratin is used in a variety of industries, including biotechnology, waste management, cosmetics, and medicine [39]. Waste feathers can be converted into keratin in a cost-effective and environmentally beneficial manner. Keratin is an insoluble protein of the cytoskeletal element with a size of 8–10 nm that belongs to a group known as intermediate filaments (IFs). Keratin is a fibrous protein with a helical structure, as seen in Figure 16, and is the ecosystem’s third most prevalent natural biomass polymer after chitin and cellulose [41].

Figure 16.

An α-helix and β-pleated sheet keratin and the molecular structure [40].

4. Innovative waste biomass-sourced electrospun products

Electrospun fibers fabricated from waste biomass sources has resulted in manufacturability of bioactive electrospun nanofibers and has been reported as potential drug delivery agents [42], wound dressing with antibacterial activity, filtration, cosmetics, protective clothing, electrical applications [43] catalysis [44], food industry [44], facial mask [45], and smart energy storage devices, such as supercapacitors as illustrated in Figure 17.

Figure 17.

Applications of nanofibers in different fields for day to day activities.

Natural biopolymer electrospun products are made up of ultrafine fibers that are reusable, nontoxic, biocompatible, biodegradable and antibacterial properties. The fibers have been reported to possess excellent physical and chemical characteristics such as high degrees of crystallinity, aspect ratio, large specific surface area, number of surface hydroxyl groups, thermal resistance and excellent mechanical properties [45, 46]. However, the substantial chemical and energy consumption associated with the isolation of macro-sized fibers to nano-sized fibers creates manufacturing hurdles for waste bioactive electrospun nanofibers [46]. As a result, findings on waste bioactive electrospun nanofibers are still in their infancy in the literature [46].

4.1 Biomedical product

In the biomedical field, literature reports on manufactured products made from biomass electrospun fibers range from medication delivery agents to biomaterials [42], wound dressing with antibacterial activity, facial mask [45], and tissue regenerative biomedical applications as presented in Figure 18.

Figure 18.

Illustration of various applications of bioactive electrospun fibers in the biomedical field [43].

The ultrafine fibers have been previously reported to result in high-performance filters and applicability in facial masks [45, 47]. Various ultrafine fiber filters have been created that can filter particles larger than 10 nm with excellent efficiency. Spider-web network filters are described in the literature as having a combination of extremely efficient, long-range electrostatic property, low air resistance, and great transparency [45, 47]. Viruses can be blocked by ultrafine fiber filters [47]. Irrespective of the challenges associated with the fabrication of bioactive electrospun fibers products. The choice of polymer used aid in fabricating fibers with antimicrobial activities [45].

Figure 19a presents a typical electrospinning technology. Choice of polymer, concentration, flow rate, needle, and tip-to-collector distance all affect fiber quality. Figure 19b shows various types of electrospun fibers. The structure of a hybrid filter that works as both a filter and a hydrophobic layer is shown in Figure 19c and d.

Figure 19.

(a) Scheme of electrospinning technology. (b) Various SEM images of electrospun nanofibers. (c) Scheme of generally utilized masks. (d) The proposed structure of electrospun ultrafine fibrous masks.

Facial masks constructed from electrospun biomass possess key characteristic performance features that has the potential to outcompete with the masks in the market. Advantages of biomass electrospun masks vary from the transparent, reusability, antiviral, degradable smart masks that possess filtration, thermal stability, and water resistance [45]. The facial mask technique has a wide range of possible uses, including filtration systems in water treatment, protective garments, and cosmetics [45].

As a result of the structure and bioactivity of loaded pharmaceuticals remaining unaltered during the spinning process, electrospun drug-delivery agents drew interest. They also reduced in vitro drug burst release and can contain a range of biomolecules [48]. Drug delivery agents fabricated from all forms of cellulose polymer results in drug delivery systems that are hydrophilic, eco-friendly, bio-degradable, and biocompatible [42].

4.2 Renewable energy products

Incorporation of NPs, natural biomass onto the polymer through the electrostatic interaction between their functional groups has a stabilizing effect on NPs [44, 49]. These electrospun catalyst found application in catalysis, supercapacitors, corrosion inhibition, and within the food industry natural polymers [44, 49].

Carbon-based supercapacitors with a large interactive surface and high permeability have sparked interest in natural floral and faunal waste materials, owing to the growing ecological consciousness. Electrospun cellulose-based supercapacitors are still in the laboratory stage, despite their rich carbon abundance of roughly 44%, great stability, and exceptional permeability linked with its hierarchical conformation and exceedingly efficient rigid lateral chains in cellulose [49]. The energy density of cellulose-based supercapacitors is low [49]. Hence the poor electrical performance and cell voltage. Another limitation is time consumption associated with economic factor in the optimization stage of cellulose electrospun mats.

As an alternate technique for increasing the electrochemical properties of lignin/cellulose nanofiber electrodes, creating compound electrode materials with a lignin/cellulose backbone can be used to address these constraints [49, 50]. Literature presented flexibility, wide surface area, outstanding mechanical flexibility, and particularly good electrical conductivity, composite nanofibers and ES activated carbon fiber network (ACFN) as attributes to improved performance. When employed as supercapacitor electrodes, they have a high electrical performance, a phenomenon attributed to their pseudo-capacitance [51, 52]. As a result, ACFNs lignin/cellulose nanofiber composites could be an attractive electrode material for biomass-based flexible supercapacitors [49]. Furthermore, when the electrolyte penetrates the micropores of the electrospun mats, as shown in Figure 20, the characteristics of the electrospun biomass composites can be adjusted, allowing for the wettability feasible with the preferred electrolyte [53].

Figure 20.

Supercapacitive cell with thin film-coated carbon powder-based electrodes and free-standing and flexible flexible carbon nanofiber electrodes in conjunction with a polymer electrolyte [50].

In aqueous electrolytes, heteroatoms have been reported to enhance wettability of carbonaceous surfaces [54]. Lignin has a lot of oxygen functional groups and a lot of active hydrophilic surface. However, biomass-derived ECNF p-doped performed worse relative to the commercial CF. The lower performance could be attributable to the starting material’s higher number of oxygen functional groups. P-doping has been reported to block micro/mesopores, reduce conductivity and electron transport [50]. Jet viscosity of the polymer was not measured, as such further research still has to be done.

As a result, environmentally friendly biomass electrospun fibers with improved performance in working electrochemical devices have demonstrated that the fabrication of future smart energy storage materials will be ecologically viable, providing a completely green alternative to the powering of transportation and conventional storage [50].

4.3 Electrical products

The versatility of waste biomass electrospun fibers, as well as their controllable physical and chemical properties, make them a model technique for electrode fabricating and flow media for a variable of smart energy devices, with the ability to reduce mass transport and activate overpotentials, thereby increasing competence [50]. Natural biomass is being used as a polymer of choice because of its capacity to infuse sustainable principles in electrochemical device materials. This also contributes to their capacity to increase the use of renewable electricity through their application [50]. Lignin is a waste by-product derived from natural flora that has been documented to exist in three different types: Different molecular weights and mechanical and thermal stabilities of kraft (KL), ethanol organosolvents (EOL), and phosphoric acid lignin (PL) [50]. For vanadium redox couples, electrospun carbon nanofibers produced from PL and KL at 9 kV demonstrated excellent cyclic voltammetry electrochemical performance. Figure 20 clearly illustrates potential electrical products that can be fabricated from waste biomass electrospun fibers. Redox flow batteries (RFBs), fuel cells, and metal air batteries are some of the potential products shown in Figure 20 [50]. The use of electrospun material in RFBs is still in its infancy and requires further development. Nonetheless, the improved redox couple’s catalytic activity of waste biomass electrospun fibers provides an alternate solution to commercial electrodes’ high overpotential when discharge current density is large [50].

Electrospun fibers made from waste biomass have the potential to be used in redox flow batteries because they form microstructures with large surface areas and mass transport qualities in the electrodes. Similarly, improved biomass electrospun fiber applicability in fuel cells and metal air batteries offers a conductive-advanced structure for the gas diffusion layers that can dope and/or support catalytic nanoparticles, as well as electrochemically active fibers [50].

5. Conclusion and future works

The advancement of electrospinning (ES) technologies and the industrial production of ES fibrous carbon nano materials to suit or facilitate different bioeconomic uses was aided by technical innovation. It may be inferred that the capacity to change the electrospinning assembly in various ways, in order to combine different materials with a wide variety of properties as well as incorporate active elements, will have a substantial impact on the production of materials in the future. By combining essential concepts from traditional fiber manufacturing techniques with nanotechnology, the performance of electrospinning technology and the quality of nanofibers can be increased. In comparison to other carbonaceous precursors, natural flora and fauna waste biomass for future electrospinning material technology has become increasingly appealing due to its abundance, low cost, easy accessibility, and environmental friendliness. Most of the insoluble floral biomass is in the form of lignocellulosic and chitin material while the soluble biomass is in the form of proteins and polysaccharides. Fauna waste biomass is mainly in the form of keratin. Millions of tons of keratin biomass are produced by industry, particularly the meat market, slaughterhouses, and wool manufacturers. The determination of marketable low thermal chemical procedures to valorize bio and organic waste lignin fractions as feedstock for commercial chemicals will be the focus of future work aimed at advancing electrospinning materials.