Sustainable Textile Raw Materials: Review on Bioprocessing of Textile Waste via Electrospinning

Abstract

The fashion and textile industry in its current fast-rising business model has generated a huge amount of textile waste during and after the production process. The environmental impact of this waste is well documented as it poses serious threats to lives on earth. To confront the menace of this huge pollution problem, a number of research works were carried out to examine the possible re-utilization of these waste materials without further damaging the environment; for instance, reusing, generating valuable products, or regenerating fibrous materials to form a closed loop in the cotton textile waste lifecycle. This review covers different methodologies to transform cellulosic textile materials into various products with added value, such as cellulosic glucose, cellulase, etc., and finally, to regenerate the fibrous materials for re-application in textiles and fashion. This article presents an overall picture to researchers outlining the possible value addition of textile waste materials. Furthermore, the regeneration of cellulosic fibrous materials from textile waste will be brought into the limelight.

Full text

Citation: Suen, D.W.-S.; Chan,
E.M.-H.; Lau, Y.-Y.; Lee, R.H.-P.;
Tsang, P.W.-K.; Ouyang, S.; Tsang,
C.-W. Sustainable Textile Raw
Materials: Review on Bioprocessing
of Textile Waste via Electrospinning.
Sustainability 2023,15, 11638.
https://doi.org/10.3390/
su151511638
Academic Editor: Izabela
Luiza Ciesielska-Wróbel
Received: 31 May 2023
Revised: 6 July 2023
Accepted: 24 July 2023
Published: 27 July 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
sustainability
Review
Sustainable Textile Raw Materials: Review on Bioprocessing of
Textile Waste via Electrospinning
Dawson Wai-Shun Suen 1,† , Eve Man-Hin Chan 1, †, Yui-Yip Lau 2, Rachel Hiu-Pui Lee 1, Paul Wai-Kei Tsang 1,3,
Shaobo Ouyang 4, * and Chi-Wing Tsang 1, 3, *
1
Technological and Higher Education Institute of Hong Kong, 20A Tsing Yi Road, Tsing Yi, Hong Kong, China;
dawsonsuen@thei.edu.hk (D.W.-S.S.); evechan@thei.edu.hk (E.M.-H.C.); rachellee@thei.edu.hk (R.H.-P.L.);
paulwktsang@thei.edu.hk (P.W.-K.T.)
2Division of Business and Hospitality Management, College of Professional and Continuing Education, The
Hong Kong Polytechnic University, Hong Kong, China; yuiyip.lau@cpce-polyu.edu.hk
3Centre for Interdisciplinary Research on Food By-Products Utilization (CIFU), Hong Kong, China
4Faculty of Material Metallurgy and Chemistry, Jiangxi University of Science and Technology,
Ganzhou 341000, China
*Correspondence: ouyangshaobo2@163.com (S.O.); ctsang@thei.edu.hk (C.-W.T.)
†These authors contributed equally to this work.
Abstract:
The fashion and textile industry in its current fast-rising business model has generated a
huge amount of textile waste during and after the production process. The environmental impact of
this waste is well documented as it poses serious threats to lives on earth. To confront the menace of
this huge pollution problem, a number of research works were carried out to examine the possible re-
utilization of these waste materials without further damaging the environment; for instance, reusing,
generating valuable products, or regenerating fibrous materials to form a closed loop in the cotton
textile waste lifecycle. This review covers different methodologies to transform cellulosic textile
materials into various products with added value, such as cellulosic glucose, cellulase, etc., and finally,
to regenerate the fibrous materials for re-application in textiles and fashion. This article presents
an overall picture to researchers outlining the possible value addition of textile waste materials.
Furthermore, the regeneration of cellulosic fibrous materials from textile waste will be brought into
the limelight.
Keywords: electrospinning; regenerating fibers; bioprocessing; cellulose; textile wastes
1. Introduction and the Environmental Impact of the Textile and Apparel Industry
The textile industry is ranked the second largest polluting industry in the world
because of the creation of textile waste, ecosystem pollution, and the immense use of
chemicals and water [
1
]. The textile sector contributes to 3% of the total greenhouse gas
emissions [
2
]. Global apparel consumption is 400% in excess of the quantity consumed
20 years earlier [
3
]. The reducing life cycle of textile products, the rising living standards,
the expanding world population, and the increasing variety of textile materials driven by
worldwide fiber purchases all contribute to a considerable volume of post-consumer and
post-industrial fiber wastes [
4
]. Alongside the effect of globalization, the apparel industry
manufactures more clothing at lower costs due to the outsourced production to low-cost
countries as well as the anticipated trend of ‘fast fashion’, which commonly perceives
clothing as a ‘one-use’ product. Overall, ‘fast fashion’ embodied by cheapness, agility,
diversity, and mass production has prompted a rise in apparel consumption [1,5].
Consumers, to a certain extent, are still negligent of disposal approaches and sustain-
able consumption. The futile disposal of textiles is an emerging critical problem faced by
different parts of the globe [
4
]. At the global level, around 75% of textile waste was dumped
in landfill sites or burned; 25% was recycled or reused; and below 1% of the whole textile
Sustainability 2023,15, 11638. https://doi.org/10.3390/su151511638 https://www.mdpi.com/journal/sustainability

Sustainability 2023,15, 11638 2 of 18
was recycled as clothing. By the end of 2030, 92 million tons of textile waste will have been
created annually [
3
]. As such, making progress in recycling and reuse technologies for
transforming textile wastes from landfills is indispensable. There is a pressing need for
closed-loop recycling of fabrics. Different levels of international actions incorporating vari-
ous stakeholders have highlighted both environmental and economic difficulties that the
textile industry is encountering. For instance, Textile Exchange promised to decrease CO
2
emissions from material production and textile fibers by 30% before 2030 and to facilitate
the key role of circular economy, which are effective means for diminishing effects and
combating climate change. Textile recycling and reuse are crucial to attain such innovative
performance proclaimed by Textile Exchange [5].
Owing to the ever increasing amount of textile waste produced in the world, it is
essential to determine some environmentally friendly ways to deal with the waste, rather
than indiscriminately disposing of it in a landfill. Currently, there are two main sustainable
ways to process textile waste: reuse and recycle. Reusing textile waste extends the duration
of textiles to be in use, hence limiting the amount of new textiles to be produced for
the market. To speed up the process of adopting recycled materials, it is imperative to
investigate effective and economically viable ways to identify and classify textile materials
and to reprocess them [
6
]. Recycling, on the other hand, is to process textile wastes for other
purposes and is generally regarded as less beneficial than reuse, when suitably extending
the reusing stage. At present, the textile recycling rate remains low despite the numerous
recycling programs, investments, standards, and approaches that have been implemented.
The textile recycling rates in the European Union, the United States, and China are 25%,
15.2%, and 15%, respectively [2].
Textile waste comprises diverse materials, pertaining to synthetic non-cellulosic fibers
along with natural fibers, thus bringing the industry to a bioprocessing challenge [
6
]. One
way to recycle textile waste is via enzymatic decomposition. In this paper, recent advance-
ments in the bioprocesses of textile waste are first summarized and discussed, with a
specific focus on physicochemical and enzymatic methods, such as the modified pretreat-
ment methods, the production of cellulase-type enzymes from textile waste materials, and
the use of cellulase to recycle textile wastes. Second, recent advances on the electrospinning
technique, which is being used to produce nanofibers from a variety of materials, including
polymers, ceramics, and composites, will be discussed. In particular, the use of electro-
spinning to respin bioprocessed textile wastes is an emerging area of research that has the
potential to address the problem of textile waste and provide a sustainable alternative to
traditional textile production methods. One major research gap is the need for a systematic
evaluation of the properties of the electrospun nanofibers produced from bioprocessed
textile wastes, which include the studies on mechanical properties, surface morphology,
and the chemical composition of the nanofibers. These properties are crucial in determining
the potential applications of the nanofibers and optimizing the electrospinning process.
Another research gap could be the need to explore different methods for preparing bio-
processed textile waste for electrospinning. The electrospinning process typically requires
a solution of the material to be electrospun, and it is unclear how different methods of
bioprocessing could affect the properties of the resulting nanofibers. Challenges associated
with toxic solvents and large fiber diameters also exist within traditional electrospinning.
Additionally, there may be a need to investigate the scalability of the electrospinning pro-
cess for producing nanofibers from bioprocessed textile waste. While electrospinning has
been demonstrated at the laboratory scale, scaling up the process may require optimization
of the process parameters and equipment design.
The textile and apparel industry is a major global industry, accounting for about 2%
of the global GDP. Advanced production technologies have lowered costs, leading to a
‘fast fashion’ trend [
7
] where consumers buy and dispose of clothing at an increasing rate.
This trend has significant environmental impacts, including depletion of non-renewable
resources, greenhouse gas emissions, and excessive water and energy use, contributing to
irreversible climate change [
8
]. The disposal rate has made the industry the second largest

Sustainability 2023,15, 11638 3 of 18
polluter globally, with an estimated one garbage truck of textiles landfilled or burned every
second. If not addressed, the industry could use up a quarter of the world’s carbon quota
by 2050 [
9
]. For example, according to Monitoring of Solid Waste in Hong Kong—Waste
Statistics for 2018, a report from the Environmental Protection Department, Hong Kong,
approximately 392 tons of textile waste materials are produced daily, of which only 4.3%
are recycled locally (this percentage was comparable to the city’s market share in global
waste management, which is about 3% [
10
]), whereas the remaining textile waste ends up
in the landfills [11], thus posing environmental concerns.
In recent years, significant research has been carried out on the reuse and recycling
of textile materials. The reuse of textile materials requires various means to increase
the service span of textile products with or without prior modification in order to be
accepted by new owners [
12
]. On the other hand, textile recycling most often refers to
the reprocessing of pre- or post-consumer textile wastes for applications in new textile
or even non-textile products. Figure 1shows the reuse and recycling of different textile
materials. Post-consumer textile wastes contain yarns from processed cotton fibers, which
are woven or knitted into fabrics [
13
] and could be woven together with other natural or
synthetic fibers, such as nylon, polyester, polypropylene, and acrylic. This fiber mixture
in fabrics, along with additional treatments, results in the recycling and decomposition of
such materials becoming increasingly challenging.
Sustainability 2023, 15, x FOR PEER REVIEW 4 of 19
many parameters, such as enzyme type and concentration, reaction conditions, and sub-
strate characteristics, which can be challenging to optimize for a specific application. The
cost of enzymes used in bioprocessing can sometimes be very high, which may limit the
economic feasibility of the process. The yield of the product from bioprocessing can some-
times be relatively low, which may not be sufficient to meet commercial demands.
The methodology of this study is divided into seven sections. In Section 1, the re-
search background, seing, objectives, and the environmental impact of the textile and
apparel industry are provided. Next, the treating of textile waste using enzymatic treat-
ment to break down the fibers and remove any impurities or contaminants is elaborated
on in Section 2. The type of enzyme and treatment conditions can be optimized based on
the type of textile waste and the desired properties of the resulting nanofibers. Key textile
and clothing materials, namely cellulase and coon, are discussed in Sections 3 and 4,
respectively. The various pretreatments and enzymatic hydrolysis of cellulose are ex-
plained in Section 5. Fungal cellulase production from textile waste by solid–state fermen-
tation and the electrospinning and optimized conditions for defect-free nanofibers with
desired diameter are illustrated in Section 6. The conclusions and recommendations are
stated in Section 7.
Figure 1. The reuse and recycling of various textile materials.
Figure 1. The reuse and recycling of various textile materials.
Several review papers covered the reuse and recycling of textile materials [
14
–
19
].
They concluded that the current waste management methods for post-consumer textile
waste could be identified as waste prevention and minimization, reusing and recycling

Sustainability 2023,15, 11638 4 of 18
materials, and energy recovery and disposal of waste. Amongst them, recycling is one of the
best pollution control strategies. On the one hand, upcycling is defined as converting textile
wastes into higher value products, say new garments. On the other hand, down-cycling
is defined as converting textile wastes into raw materials of lower value. For example,
textile wastes can be used as additives in thermal insulation building materials [
20
,
21
], as
a binder in hydraulic lime [
22
], as well as in gypsum and cork composite materials [
23
].
Textile waste can also be synthesized into cellulose acetate [
24
]. Caprolactam can be
extracted from textile waste and repolymerized to produce Nylon 6 [
25
]. Ethanol can be
produced from such waste [
26
], while polyester and cotton raw materials can be obtained
after separation from textiles [
27
]. The cotton components can be bioconverted into other
materials with added value, such as biofuel [
26
], glucose syrup, and powder cellulose [
28
].
Due to the highly compact and crystalline nature of cotton, the challenge that remains with
the bioconversion of cotton components is to ensure a high conversion rate and product
yields. Chemical methods, such as first dissolving either cellulose or polyester followed
by depolymerizing via hydrolysis or alcoholysis, are commonly used processes. Non-
toxic and reusable solvents, such as N-methylmorpholine N-oxide, are frequently used for
dissolving cotton, while dimethyl terephthalate is used for dissolving polyester. However,
these recycling processes, such as methanolytic depolymerizations, are often carried out
under harsh conditions, which greatly complicate the recycling process [
29
]. In comparison,
bioprocessing can be performed to degrade textile wastes more selectively under much
milder conditions and it may reduce energy consumption and carbon emissions. This
process can also be more economically viable for industrial-scale production [
30
]. It is also
a highly selective process and allows for the targeted breakdown of specific components in
the textile waste and the production of high-quality products. Microbial hydrolases, such
as cellulase and ligninase, are particularly useful for degrading natural polymers under
enzymatic hydrolysis conditions. Recently, fungus has been used to produce cellulase from
cotton textile wastes, e.g., Aspergillus niger, which can then hydrolyze cotton wastes [
28
].
Silk can be degraded by using proteinase K from a fungus called Engyodontium album
to specifically cleave the site adjacent to the His, Phe, Trp, Ala, Ile, Leu, Pro, Val, and
Met amino acids [
31
]. However, one should bear in mind that bioprocessing may have
limited scalability, as the process may be slow and requires a large amount of space and
equipment to handle large quantities of textile waste. It involves many parameters, such as
enzyme type and concentration, reaction conditions, and substrate characteristics, which
can be challenging to optimize for a specific application. The cost of enzymes used in
bioprocessing can sometimes be very high, which may limit the economic feasibility of
the process. The yield of the product from bioprocessing can sometimes be relatively low,
which may not be sufficient to meet commercial demands.
The methodology of this study is divided into seven sections. In Section 1, the research
background, setting, objectives, and the environmental impact of the textile and apparel
industry are provided. Next, the treating of textile waste using enzymatic treatment to
break down the fibers and remove any impurities or contaminants is elaborated on in
Section 2. The type of enzyme and treatment conditions can be optimized based on the
type of textile waste and the desired properties of the resulting nanofibers. Key textile
and clothing materials, namely cellulase and cotton, are discussed in Sections 3and 4,
respectively. The various pretreatments and enzymatic hydrolysis of cellulose are explained
in Section 5. Fungal cellulase production from textile waste by solid–state fermentation
and the electrospinning and optimized conditions for defect-free nanofibers with desired
diameter are illustrated in Section 6. The conclusions and recommendations are stated in
Section 7.
2. Value Addition of Textile Waste Materials by Enzymatic Methods
Textile waste is a significant environmental problem, with large amounts of waste
generated by the textile industry and discarded by consumers every year. However,
textile waste can also be a valuable resource, with the potential for value addition through

Sustainability 2023,15, 11638 5 of 18
various processes such as recycling, upcycling, and bioprocessing. Recycling of textile waste
involves the conversion of waste textiles into new products, such as fibers, yarns, and fabrics.
This process can be accomplished through mechanical, chemical, or thermal methods.
Based on the IUPAC definition, biodegradation is the degradation caused by an
enzymatic process resulting from the action of cells, at least in part (IUPAC. Compendium
of Chemical Terminology). Textile-based polymers can be degraded, in the presence of
air and water, into smaller molecules by bacteria, fungi, and some other microorganisms
that biosynthesize relevant enzymes [
32
–
34
]. This kind of degradation is known as waste
recycling [
35
]. Most of the naturally existing and regenerated polymers (those purposefully
designed to resemble natural polymers) are biodegradable, but a few exceptions are also
available [
36
,
37
]. Among synthetic polymers, biodegradable aromatic polyesters, such
as polybutylene adipate-co-terephthalate, can be easily degraded and researchers have
designed enzymes to biodegrade polyethylene terephthalate or polyester-based textile
materials at a reasonable price [
38
–
40
]. For example, Li et al. [
28
] investigated the enzymatic
hydrolysis of cotton textile waste for the production of fermentable sugars, which can be
further processed into biofuels or bioproducts. Upcycling of textile waste involves the
transformation of waste textiles into higher-value products, such as fashion accessories
or home decor items. This process can be achieved through various methods, such as
cutting, sewing, and embroidery. For example, Gupta et al. [
41
] developed a method for the
upcycling of denim waste into fashionable bags and accessories. Bioprocessing of textile
waste involves the use of microorganisms or enzymes to break down the textile waste
into valuable products, such as biopolymers or biofuels. This process is environmentally
friendly and has the potential to produce high-value products from waste materials.
3. Cotton—A Cellulosic Material
The use of cotton, a type of natural cellulosic fiber, is widespread in the textile indus-
try [
42
]. The fibers are harvested from the cotton ball that grows on plants belonging to
the Gossypium hir-sutum family [
43
]. Cotton fibers are made up of long plant cells with a
multi-layered cell wall structure and a natural twist. The lumen, which is the innermost
part of the cell and originally the “living” part, is filled with liquid, and is protected by
primary and secondary walls. The outermost layer of the cotton fiber is called the cuticle,
which is made up of wax, proteins, and pectins, and is amorphous in nature. Microfibrils
form the primary and secondary walls, which have varying degrees of crystallinity and
molecular chain orientations [
43
]. Cotton fibers with well-developed cell walls are suitable
for use in textiles as they possess a dried cell in which the lumen becomes a hollow space
inside the collapsed cell wall [44].
Cotton fibers are composed of approximately 96% cellulose, which is the load-bearing
polymer in mature fibers. Cellulose comprises almost all of the secondary cell wall com-
ponents, with a high degree of polymerization (DP of 14,000), and 30% of the primary
wall, with a DP between 2000 and 6000 [
45
]. The remaining components of cotton fibers
are hemicelluloses and other trace elements [
46
]. The microfibrils that comprise the long
cellulose chains are arranged in different orders. In the crystalline zone, cellulose chains
are well-organized and linked through hydrogen bonds and van der Waals forces, while
an amorphous structure contains twisted or less ordered microfibrils [
47
]. The amorphous
cellulose is the weaker part of the cellulosic fibers and is susceptible to rapid hydrolysis by
enzymes [
48
]. Table 1lists the various textile production processes and the waste materials
generated during each process and after use.

Sustainability 2023,15, 11638 6 of 18
Table 1. Waste materials generated during the textile production processes and after use of textiles [49,50].
Material
Generation Process Solid Waste
Generation
Composition of
Waste Generated
Existing Methods
of Recycling
Material
Further
Applications
Cotton fibers Ginning Fiber waste Cellulose, protein,
sugar, wax
Mechanical
recycling Textile products
Yarn preparation Spinning Fiber lint, yarn
wastes
Cellulose, protein,
sugar
Re-spinning and
plying Carpet and clothes
Yarn preparation
for fabrics
Weaving
preparation
(warping, sizing)
Fibers, yarn wastes
Cellulose, protein,
starch, sugar
Re-spinning and
plying Carpet and clothes
Fabrics Weaving/knitting Yarn, fabrics Cellulose, starch,
sugar
Mechanical and
chemical recycling New fabrics
Fabric
pretreatment Desizing Fiber lint, yarn Cellulose Mechanical and
chemical recycling New fabrics
Fabric
pretreatment
Scouring and
bleaching
Few or very few
wastes -Mechanical and
chemical recycling New fabrics
Dyed and printed
fabrics
Dyeing and
printing
Few or very few
wastes -Mechanical and
chemical recycling New fabrics
Finishing Fabric finishing Torn fabrics Cellulose
After use Fabrics Cellulose
4. Cellulase
Cellulases are enzymes of great industrial interest due to their wide range of applica-
tions, including in the textile industry. They form a multi-enzyme system [
51
] that breaks
down the cellulosic materials into fermentable sugars. Cellulases are produced by various
types of bacteria and fungi, such as Cellulomonas fimi and Thermomonospora fusca [
52
], as well
as filamentous fungi belonging to the genera Trichoderma (i.e., T.viride,T.longibrachiatum,
T.reesei) and Aspergillus (A.niger N402, A.niger CKB) [
53
]. Among these, Trichoderma is the
most extensively studied fungal genus for the commercial production of cellulase [54–57].
The cellulase enzyme system that performs enzymatic hydrolysis of cellulose consists
of mainly three mono-enzymes,
β
-1,4-endoglucanases (EG),
β
-1,4-cellobiohydrolase (CBH),
and
β
-glucosidase [
58
]. These enzymes work together to break down
β
-1,4-glycosidic
bonds in amorphous cellulose, releasing fermentable sugars [
59
,
60
]. During this process,
endoglucanase hydrolyzes chains of cellulose to form new chain ends, which are further
broken down into soluble sugars (e.g., cellobiose) by exoglucanase. Cellobiose is then
converted to glucose with the help of
β
-glucosidase. The efficiency of enzymatic cellulose
hydrolysis is influenced by several factors, such as the cellulase preparation process [
61
],
the composition of cellulosic materials [
62
], and the pretreatment method. The reactivity
of cellulase and the properties of textile materials are also crucial factors in the hydrolysis
process [
63
]. Furthermore, the pH and temperature of the reaction vessel significantly affect
the hydrolysis process [64].
5. Pretreatment and Enzymatic Hydrolysis of Cellulose
5.1. Pretreatment
Pretreatment is the process to increase the sensitivity of textile materials, which can be
prone to further treatment [
61
,
65
]. The efficiency of any pretreatment method is decided by
the reactivity of cellulose and the increase in the yield of fermentable sugars from textile
materials [
66
,
67
]. The basic pretreatment approaches can be classified into four categories,
i.e., chemical (acid, alkali, and ionic liquid), biological, physical (milling and grinding), and
physico-chemical processes. The commonly used pretreatment methods for textile waste
are acid, alkali, ionic liquid, and supercritical fluid.

Sustainability 2023,15, 11638 7 of 18
5.2. Acid Pretreatment
Acid pretreatment can hydrolyze the polymeric bonds in the hemicellulose to form its
monomers, thus enhancing the availability of cellulose and increasing the biodegradability.
Although acid pretreatment gives large glucose yields, the main problems lie with the
formation of fermentation inhibitors (such as lignin-derived phenolic compounds), the
high costs of acid, and the need for corrosion-resistant equipment. Researchers, including
Chu et al. [
68
], Kuo et al. [
69
], Mahalakshmi et al. [
70
], Ouchi et al. [
71
], and Shen et al. [
72
],
have used either sulfuric acid or phosphoric acid at different concentrations and hydrolysis
conditions to treat the wasted cotton lint, yarns, cotton-based textiles, or blended fabrics.
The acid pretreatment method involves decomposing the microstructure of cellulose fibers
to expose the crystalline region with more reducing and non-reducing ends. This region
can then be hydrolyzed by enzymes, which helps to release sugars by facilitating the
enzymatic action. Additionally, the amorphous region of cellulose is hydrolyzed during
this process [73].
5.3. Alkali Pretreatment
Alkali pretreatment involves the use of bases, such as sodium, potassium, calcium,
and ammonium hydroxide, for waste textile materials [
74
–
76
]. The alkali pretreatment
increases cellulose digestibility through enhancing lignin solubilization and decreasing
cellulose crystallinity [
77
]. Another great advantage of alkali pretreatment is low inhibitor
formation [
66
]. Normally, alkali pretreatment is carried out at room temperature but it has
been tried at both lower and higher temperatures to improve the process. Jeihanipour and
Taherzadeh (2008) pretreated cotton lint and jeans with 12% NaOH at 0
◦
C for 180 min
for ethanol production. They observed that the pretreatment helped to achieve a more
than 89% glucose yield after enzymatic hydrolysis by S.cerevisiae. They also noted that
the alkali pretreatment gave a more than 30% better glucose yield than the phosphoric
acid pretreatment [
73
]. Gholamzad et al. pretreated polyester/cotton blended fabrics with
NaOH (7 wt%)/urea (12 wt%) at
−
20
◦
C, and claimed a 91% glucose yield after hydroly-
sis [
78
]. The NaOH/urea combination can be more useful in removing the hemicellulose
of cotton, which enhances the surface contact of cotton cellulose during the enzymatic
hydrolysis [79].
Studies have been carried out to examine when alkali pretreatment methods have
been modified further to improve the efficiency of the process. Lin et al. proposed a
new pretreatment method for treating cotton/PET textile waste to enhance the enzymatic
hydrolysis of cellulose to glucose [
80
]. The conversion yield of cotton to glucose could be
improved by over 98% and the residue PET fibers could be extracted for other applications.
The suggested pretreatment method is divided into three steps. Initially, the textile
waste is treated with the NaOH/urea solution at 0
◦
C for 6 h, followed by a regeneration
process in hot water, and finally, the substrate is digested by cellulase at 50
◦
C in acidic
pH 4.8 for 72 h. The main advantage of this pioneering method is the significant en-
hancement in digestibility (80% cotton cellulose digested within only 72 h) of the waste
textiles through the cellulose dissolution process, which is based on the cellulose dissoci-
ation theory suggested by Porro et al. [
17
]. Diluted NaOH treatment of cotton materials
causes swelling, leading to an increase in the internal pole size and a decrease in the
degree of polymerization and crystallinity. The addition of Na
+
to the crystalline lattice
leads to swelling of the native crystalline cellulose when it is in contact with a strong
alkaline solution.
Increasing the digestibility of textile waste relies on the regeneration of cotton fibers.
During the regeneration process, dissolved cellulose can shrink and form a new allomorph
structure known as cellulose II, resulting in a morphological change. Cellulose I is charac-
terized by parallel chains, while cellulose II is described as having an antiparallel structure
that is more accessible to enzymes. NaOH is effective at changing the cellulose structure
at lower temperatures due to the stronger binding of Na
+
and OH
−
to water, which en-
ables the breakage of hydrogen bonds within the cellulosic structure. Another feature

Sustainability 2023,15, 11638 8 of 18
of this process is that PET fibers become less complex after recycling, and the remaining
residue consists mainly of PET fibers that can be easily extracted. Finally, the low enzyme
loading of 5FPU/g glucan, compared with other pretreatment methods, means that it a
cost-effective option.
5.4. Ionic Liquid Pretreatment
The chemistry of the anion and cation can be tuned to generate a wide variety of
liquids, known as ionic liquids (IL) [
81
]. In recent years, pretreatment with ionic liquids has
gained popularity due to the tenability of the solvent chemistry. The main advantages of this
type of pretreatment are the ability to dissolve different types of biomasses, including cotton
cellulose, lignin, and hemicellulose hydrolysis, and the mild processing condition. Despite
these advantages, the main disadvantage of this process is the high cost of solvents. This is
the reason that solvent recovery and recycling are required for this kind of pretreatment.
The recovery of the IL depends on the vapor pressure; an IL with a low vapor pressure can
be recovered for more than 99%, thus reducing the cost of solvent usage [82].
Zhang et al. used AMIMCl to treat un-dyed 100% cotton t-shirts [
83
], and after 90 min
of pretreatment at 110
◦
C, a high sugar yield was achieved by using a reasonable amount
of cellulase. Turner et al. [
84
] observed that the presence of this IL in cellulosic materials
reduced the reactivity of cellulase enzymes during hydrolysis, which was reconfirmed by
Hong et al. [
85
]. To overcome this problem, he suggested washing the cellulose materials
with hot solvents before enzymatic treatment, which helped to achieve a very high sugar
yield of 94%. De Silva et al. directly treated cotton/polyester blended yarns with AMIMCl
at 120
◦
C for 6 h and dissolved the entire cotton portion, which was used for making
regenerated cellulosic fibers [
86
]. The polyester portion was completely recovered in
this process.
4-Methylmorpholine N-oxide (NMMO) is another solvent that can dissolve cellulose
with a reasonable yield [
87
,
88
]. This process involves treating cotton materials at 80
◦
C
with a low water content, which results in the dissolution of higher molecular weight
cotton fibers. However, like AMIMCl, the presence of NMMO in cellulosic materials has a
negative impact on enzymatic hydrolysis and fermentation [
88
,
89
]. Therefore, the treated
materials need to be washed before enzymatic hydrolysis to improve the process. Techno-
economic studies have shown that efficient recycling of NMMO is necessary to achieve an
economically viable pretreatment process for cotton materials using NMMO [90].
5.5. Supercritical Fluid Pretreatment
A supercritical fluid (SCF) is any substance at a temperature and pressure above its
critical point, where both gas and liquid phases coexist. Such fluids have the density of
liquids but can penetrate like gas inside the cellulosic materials. This is the reason these
liquids are used for pretreatment of cellulose-based biomasses [
91
]. The main advantages
of the SCF pretreatment process are the low degradation of sugar and low costs, but
high pressure is needed for this pretreatment and so special reactor vessels are required.
Supercritical CO
2
(SF-CO
2
) has been widely used as an extraction solvent [
88
]. In aqueous
solution, CO
2
forms carbonic acid and can improve the hydrolysis of polymers. Liu
et al. studied the performance of the enzymatic hydrolysis of cotton fibers pretreated
with supercritical CO
2
[
87
]. Saka and Ueno investigated the impact of supercritical water
(500
◦
C, 35 MPa) on glucose yields from various types of cellulosic fibers (such as cotton
linter, ramie, rayon, etc.) and found that the performance was similar to an acid treatment
with enzymatic hydrolysis [90].
6. Fungal Cellulase Production from Textile Waste by Solid–State Fermentation
At present, commercial cellulase is typically produced from soft rot fungi using solid–
state fermentation (SSF) and submerged fermentation (SmF) [
92
]. SSF is a fermentation
process that uses solid materials with low water activity as a substrate, providing a cost-
effective method for producing cellulases using natural polymers derived from agro-

Sustainability 2023,15, 11638 9 of 18
industrial residues [
93
,
94
]. In contrast, SmF occurs with a free-flowing suspension, is often
associated with low concentrations of the end product, requires additional downstream
processing steps, and consequently leads to high costs of cellulase production [95].
Cellulase contributes to approximately 40% of the total cost of the bioprocess; there-
fore, low-cost cellulase is highly desirable for an economically viable process. Aspergillus,
Trichoderma, and Thermoascus auranticus are well-known producers of cellulases and are com-
monly used in SSF on lignocellulosic substrates such as agricultural and plant biomasses [
94
,
96
,
97
].
Horticultural wastes and agricultural by-products, such as rice straw, have been adopted
as cost-effective substrates in cellulase production in the past decade [94,98].
Until recently, cotton-based textile waste has not been utilized as a substrate in SSF
for cellulase production. However, Lin and her colleagues developed a new approach
to use cotton-based textile waste for fungal cellulase production through SSF [
99
]. They
screened six fungal strains, including T.reesei,A.niger N402, A.niger CKB, Rhizomucor
variabilis,A.oryzae, and T.longibrachiatum, under different moisture conditions (65–85%) on
cotton fabrics. All strains were able to grow on cotton fabrics, and their cellulase activity
was evaluated after 7 days in terms of filter paper activity (FPase), which indicates the
degradation activities of the cellulase enzymes (see Table 2). Among the six fungal strains,
A.niger CKB yielded the highest cellulase activity (0.4 FPU/g).
Table 2. Cellulase activities of different fungal strains under various moisture conditions after 7 days [99].
Name of Strain Optimum Moisture Condition (%) Maximum Cellulase Activity (FPU/g)
A. niger CKB 70–75 0.43
A. niger N402 85 0.42
T. reesei 85 0.11
R. variabilis 65 0.20
A. oryzae 65–75 0.19
T. longibrachiatum 85 0.11
They applied different pretreatment methods, such as autoclaving, freezing alkali/urea
soaking, and milling, on six types of cotton and cotton/polyester-based textiles to explore
the effects on cellulase activity. Autoclaving was observed to be the optimal modification
strategy for pretreatment due to resultant cellulase activity at the highest level. It could
be attributed to the textile morphology modified by the mild hydrothermal treatment via
autoclaving (121
◦
C, 15 psi, 15 min), which partially removed the coating of the cellulosic
fibers and better exposed the cellulose to the fungus cellulase.
During the optimization process [
99
], it was observed that the highest cellulase activity
was obtained at 28
◦
C. Other important factors, including moisture content, inoculum size,
pH, and yeast extract concentration, were also optimized. Under the optimized SSF with a
moisture content of 78%, inoculum size of 3.10
×
10
7
spore/g, pH 7.29, and yeast extract of
2.24%, it was noticed that the cellulase activity improved by approximately 14%. When
this method was compared to other existing processes, it was observed that
β
-glucosidase
obtained in this study had the highest activity with a significant improvement against other
existing methods.
Utilization of Fungal Cellulase to Treat Textile Wastes
There have been limited studies on the use of cellulase enzymes to treat cellulosic
fabrics. In one study by Lin and coworkers (2019), commercial cellulase (Celluclast
1.5 L, Novozymes) and
β
-glucosidase were applied to pretreated cotton/polyester blended
fabrics [
28
,
97
]. The fabrics were pretreated using a mixture of 7% (w/v) NaOH and
12% (w/v) urea solution at 0
◦
C for 6 h and then washed thoroughly. Glucose yields
were measured after 0, 9, 12, 24, 48, 72, and 96 h. The pretreatment increased the glucose
yield by 30% compared to untreated textile materials. Additionally, the maximum glucose
yield was over 98% after 96 h of distillation at temperatures ranging from 45–55
◦
C, with a
cellulase dose of 40 FPU/g.

Sustainability 2023,15, 11638 10 of 18
Lin et al. (2019) also compared their different textile-based fungal cellulases against
commercially available cellulases (Novozyme, Cellulast 1.5 L) on a variety of textile fabrics;
100% cotton fabrics, denim fabrics, and different cotton/polyester blended fabrics [
28
]. The
result showed that fungal cellulose extracted from cotton fabrics gave a 7% higher glucose
yield compared to the commercial cellulose. The optimization of fermentation media
revealed that pretreated textiles and Mandels medium were the preferred substrates for
cellulase production. Using a cotton/PET (40/60 blended) based textile with 1% cellobiose
addition, T.reesei ATCC 24449 achieved the highest fungal cellulase activity of 18.75 FPU/g.
Fungal cellulase obtained from SmF resulted in similar hydrolysis yields as commercial
cellulase in the hydrolysis of textile waste. Figure 2shows the flow diagram for cellulase
production from textile waste and the utilization of produced cellulase for the valorization
of textile industrial waste.
Sustainability 2023, 15, x FOR PEER REVIEW 10 of 19
There have been limited studies on the use of cellulase enzymes to treat cellulosic
fabrics. In one study by Lin and coworkers (2019), commercial cellulase (Celluclast 1.5 L,
Novozymes) and β-glucosidase were applied to pretreated coon/polyester blended fab-
rics [28,97]. The fabrics were pretreated using a mixture of 7% (w/v) NaOH and 12% (w/v)
urea solution at 0 °C for 6 h and then washed thoroughly. Glucose yields were measured
after 0, 9, 12, 24, 48, 72, and 96 h. The pretreatment increased the glucose yield by 30%
compared to untreated textile materials. Additionally, the maximum glucose yield was
over 98% after 96 h of distillation at temperatures ranging from 45–55 °C, with a cellulase
dose of 40 FPU/g.
Lin et al. (2019) also compared their different textile-based fungal cellulases against
commercially available cellulases (Novozyme, Cellulast 1.5 L) on a variety of textile fab-
rics; 100% coon fabrics, denim fabrics, and different coon/polyester blended fabrics [28].
The result showed that fungal cellulose extracted from coon fabrics gave a 7% higher
glucose yield compared to the commercial cellulose. The optimization of fermentation
media revealed that pretreated textiles and Mandels medium were the preferred sub-
strates for cellulase production. Using a coon/PET (40/60 blended) based textile with 1%
cellobiose addition, T. reesei ATCC 24449 achieved the highest fungal cellulase activity of
18.75 FPU/g. Fungal cellulase obtained from SmF resulted in similar hydrolysis yields as
commercial cellulase in the hydrolysis of textile waste. Figure 2 shows the flow diagram
for cellulase production from textile waste and the utilization of produced cellulase for
the valorization of textile industrial waste.
Figure 2. A flow diagram depicting the lifecycle of coon textile waste. (The yellow highlighted
the starting point of the life cycle).
The above has reviewed sustainable strategies to recover coon from textile wastes
to identify new sources of materials for future textile application. Various pretreatments
of textile waste are introduced, followed by the enzymatic treatment of textile materials.
In addition, the utilization of coon textile materials for fungal cellulase production by
SSF is illustrated; fungal cellulases are used to treat textile wastes for the extraction of
glucose and to separate synthetic polymers, thus a biorecycling process is achieved.
7. Regenerated Fibers from Waste Materials via Electrospinning
The next step after obtaining recycled textile materials is to regenerate fibers from the
waste materials, and the focus of this paper is electrospinning. There are several methods
used to reprocess textile waste into fibers. Some of the most common methods include
Fermentation
Fungal Cellulase
Textile Waste
Hydrolysis
Glucose Rich
Hydrolysate
Bioconversion
New Textiles
Textile Wastes
Figure 2.
A flow diagram depicting the lifecycle of cotton textile waste. (The yellow highlighted the
starting point of the life cycle).
The above has reviewed sustainable strategies to recover cotton from textile wastes to
identify new sources of materials for future textile application. Various pretreatments of
textile waste are introduced, followed by the enzymatic treatment of textile materials. In
addition, the utilization of cotton textile materials for fungal cellulase production by SSF is
illustrated; fungal cellulases are used to treat textile wastes for the extraction of glucose
and to separate synthetic polymers, thus a biorecycling process is achieved.
7. Regenerated Fibers from Waste Materials via Electrospinning
The next step after obtaining recycled textile materials is to regenerate fibers from the
waste materials, and the focus of this paper is electrospinning. There are several methods
used to reprocess textile waste into fibers. Some of the most common methods include
mechanical, chemical, thermal, biological, and electrospinning. Mechanical recycling
involves shredding textile waste into smaller pieces and then using various mechanical
processes to transform them into fibers that can be used to produce new textiles. It has
the advantage of low energy consumption, minimal use of chemicals, and can be scaled
up efficiently. However, the resulting fibers may not be suitable for high-quality textiles.
During the process, fibers could be damaged, and their strength and durability are reduced.
Chemical recycling has the advantage of producing high-quality fibers and the process
is suitable for a wide range of textile waste; it can also be scaled up efficiently. However,
the process requires the use of chemicals that can be harmful to the environment and
results in the high consumption of energy. Thermal recycling is suitable for a wide range of

Sustainability 2023,15, 11638 11 of 18
textile waste to produce high-quality fibers; however, again, high energy could be required,
and it could produce harmful emissions. Now all types of textile waste could be suitable.
Biological recycling has the advantage of a lower energy demand and the chemical use
could be minimized. However, the process may take longer than other methods and may
not be suitable for various kinds of textile waste. Electrospinning is an efficient method
for synthesizing nanofibers with numerous desirable parameters, including fiber diameter,
specific surface area, interconnectivity, and rigidity [
100
], and is suitable for a wide range
of applications. Electrospun nanofibers have a high surface area-to-volume ratio, which
makes them highly suitable for various applications, such as filtration, tissue engineering,
and drug delivery. It allows for the production of nanofibers with a tunable diameter
and morphology, which can be tailored based on the specific application requirements. In
addition, it can be easily scaled up to produce large quantities of nanofibers, making it a
commercially viable technique. However, one should bear in mind that electrospinning
equipment can be expensive, which can limit its accessibility to some researchers and
industries. The electrospinning process has a relatively low throughput, which may not
be suitable for large-scale production. The process involves many parameters, such as
solution properties, process conditions, and collector type, which can be challenging to
optimize for a specific application and the spun fibers can sometimes have poor mechanical
properties, such as low tensile strength and poor durability, which may limit their use in
certain applications.
There are also different types of electrospinning, which should be carefully selected for
different purposes. Solution electrospinning is the most common type of electrospinning,
where a polymer solution is used as the spinning material. The solution is electrospun
into nanofibers, which are collected onto a substrate [
101
]. In the melt electrospinning
technique [
102
], the spinning material is a melted polymer, which is electrospun into
nanofibers. This method is used for thermoplastic polymers that can be melted and
solidified without undergoing chemical changes. Recently, coaxial electrospinning became
an emerging technique to produce nanofibers with core–shell structures [
103
]. It involves
the use of two or more concentrically arranged needles, where different materials are
electrospun from each needle. The emulsion electrospinning technique [
104
] involves the
use of an emulsion as the spinning material, where droplets of one material are dispersed
in another material. The emulsion is electrospun to produce nanofibers with a core–shell
structure. Electroblowing [
105
] is a modification of electrospinning, where compressed
air is used to assist in the electrospinning process. This results in the production of
nanofibers with a larger diameter than those produced by conventional electrospinning.
Needleless electrospinning [
106
] eliminates the use of needles and instead uses a high-
voltage electrode to generate a charged liquid jet, which is then collected onto a substrate
to produce nanofibers.
The simplest electrospinning system comprises three components: a method for the
influx of the polymer solution, a grounded metallic surface for the collection of ejected
electrospun fibers, and a high voltage source to induce an electric field (between the
spinneret and the grounded conductive collector) where these components together create
a straight liquid jet of polymer material that deposits on the surface of the collector [
107
].
Ultra-fine fibers can be produced due to the quick evaporation of solvents together with
the subsequent stretching and whipping processes [
108
]. Fiber parameters are closely
dependent on processing variables, such as voltage, distance between the emitter and
collector, humidity, and polymer solution properties, which have significant effects on the
outcome of the fiber characteristics [107].
Electrospinning essentially works by the interaction between the electric charges in
the polymer solution, the cellulose solution, and the external electric field. The external
electric field induces a charge on the surface of the solution and the increase in electric
field elongates the surface of the solution droplet and leads to the formation of threadlike
fibers [
107
]. The advantages of jet electrospinning over other spun methods are that the
small diameter of the jet enables rapid drying of the solvent and offers extreme confinement

Sustainability 2023,15, 11638 12 of 18
and alignment of polymer chains as well as nanocellulose, locking them rapidly to avoid
central relaxation of fibers of higher diameters to be synthesized by other methods [108].
Wet spinning is a blend of rheological and diffusional behaviors in which the orienta-
tion of fibers dictates the structural formation as well as the mechanical properties of fibers,
thus being the primary method for regenerating cellulose fibers. The rheologic portion,
or the viscoelastic property of the fibers, is responsible for the formation of a continuous
fiber without breakage and the elastic behavior of the polymer solution during spinning.
The diffusional portion consists of two parts: the diffusion of solvents from wet fibers into
the solution and the coagulant from the solution into the wet fibers. Under the combined
effects of the rheological and diffusional phenomena, the wet fibers precipitate out of the
solution upon contact with the coagulant [
109
]. However, wet spinning is not the focus
of this paper as the topic has already been covered by several previous literature reviews.
Moreover, electrospinning presents a multitude of advantages, with the best one being its
ability to cover items with nanofibers that are light in weight, hence displaying potential
suitability in futuristic applications.
Cellulose is the most common naturally occurring polymer in the world and is
structurally a linear polysaccharide with glucose being its monomer connected via
β
-1,4-
glycosidic bonds. Due to its notoriously low solubility, cellulose has remained a challenge
to dissolve or melt despite its abundancy. Numerous strategies have been employed to
increase its solubility, including the use of ionic liquids, the use of different solvent systems,
and the turning of cellulose into a more soluble form. This is crucial as cellulose can be
electrospun into nanofibers, but this requires cellulose to be dissolved into solution. Cellu-
lose derivatives, such as cellulose acetate, methyl and ethyl cellulose, and carboxymethyl
cellulose, have achieved better solubility than cellulose in both organic and inorganic
solvents [107].
A multitude of optimized solvents for dissolving cellulose for electrospinning
conditions have been developed by researchers, including a lithium chloride and
N,N-dimethylacetamide (LiCl/DMAc) as well as a trifluoroacetic acid and polyvinyl al-
cohol (TFA/PVA) solvent system [
100
]. It is believed that solvent properties, such as
semi-conductivity with moderate charge capacities and high volatilities, are ideal for effi-
cient electrospinning of cellulose fibers. However, the solubility of cellulose in these solvent
systems is still very dependent on the intrinsic factors of cellulose, notably its source, molec-
ular weight, and crystallinity. On the other hand, the dissolution of cellulose by TFA takes
place via the attack of the strong organofluorine acid at the glycosidic bonds, together with
the low boiling point and low viscosity, which allow quick evaporation of the solvent upon
deposition. In addition, experiments showed that the addition of PVA as the co-solvent
was crucial for the formation of continuous nanofibers instead of beaded particles; this was
attributed to the hydrogen bonding interactions between the PVA and cellulose materials.
One main advantage of using the TFA/PVA over LiCl/DMAc solvent system is that the
former produces fewer viscous solutions, which is important for continuous fibers via
electrospinning. It also demonstrates the ability to dissolve hemicellulose as well as lignin,
which is very common in both plants and recycled paper-derived materials [107].
Cellulose can be regenerated from cellulose derivatives upon electrospinning. In the
case of cellulose acetate, this was performed by first dissolving the cellulose acetate in an
optimized solvent system, which was then subsequently deacetylated back into the cellulose
as a post-electrospinning work up. These cellulose fibers derived from cellulose acetate
exhibit autonomous thread-like morphology, consistent diameters, a large surface area,
and an exceptional storage capacity, thereby demonstrating the practicality of regenerating
cellulose with the electrospinning method [107].
Electrospinning of cellulose is a process of much interest in recent decades and re-
search advancement has helped to overcome the limitation of its low solubility in common
solvents. This, together with dispersed instead of dissolved nanocellulose in various or-
ganic and inorganic solvents, allows the incorporation of nanocellulose into nanofibers
via electrospinning while maintaining the nanostructure and properties, such as the high

Sustainability 2023,15, 11638 13 of 18
mechanical strength, aspect ratio, as well as the biodegradability. The effects of various
electrospinning parameters on the fiber morphology of virgin cellulose have been studied
and can be summarized in Table 3below [
108
]. Recycled polymeric materials may have
different physical, chemical, and mechanical properties compared to virgin materials due
to the presence of impurities, additives, and degradation products. These impurities and
additives can affect the polymer’s molecular weight, crystallinity, and thermal stability,
which can influence the electrospinnability and properties of the resulting fibers. The
presence of impurities in recycled polymeric materials can also affect the fiber morphology,
diameter, and uniformity. For example, the presence of small particles or contaminants
may cause clogging of the spinneret or result in the formation of beads instead of fibers.
Therefore, to optimize the electrospinning process for recycled polymeric materials, it
may be necessary to modify the process parameters, such as the solvent system, spinning
conditions, and post-treatment methods, to account for the differences in the properties of
the recycled materials.
Table 3. Effects of electrospinning parameters on fiber morphology.
Electrospinning Parameters Effects on Fiber Morphology
Increased polymer concentration,
i.e., increasing viscosity Formation of longer fibers with increased fiber diameter
Increased conductivity Formation of beaded fibers with decreased fiber diameter
Increased surface tension Formation of beaded fibers
Increased flow rate Formation of continuous fibers with decreased fiber diameter
Increased voltage Formation of beaded fibers with increased fiber diameter
Increased distance between the spinneret and the collector
Decreased fiber diameter
Increased humidity Overall decreased fiber diameter and caused uneven diameter
distribution
Temperature Had no direct effect on fiber morphology
8. Conclusions and Recommendations
The advancements in textile recycling technology and the circular economy could
not only bring economic benefits, but also reduce many environmental problems caused
by high energy and water consumption and a high carbon footprint. Nonetheless, there
are still hurdles for these bioprocesses to be commercialized. Textile waste is always a
mixture of polymers, such as cotton, polyester, nylon; each of these polymers requires
specific treatment methods. Therefore, the sorting and separation of textile waste for
recycling should be a critical step before the bioprocessing treatment. Manual sorting
requires exhaustive labor and will lead to difficulties in identifying specific fabrics being
used for either generally lower grade applications, such as rags, or for higher grade
applications in which such materials could supplement the use of virgin fibers. Recent
sorting technology employs near-infrared (NIR) spectroscopy for sorting fibers according
to their composition and color. While this technology has been employed to the PET bottle
recycling procedure [
110
], it is highly recommended for the textile waste treatment process.
Another concern is the impurities, such as fiber-bonded dyestuff, that may be retained
after the bioprocessing treatment process. Non-environmentally friendly solvents, such
as dimethyl sulfoxide, are often used to decolorate the recycled fibers. Therefore, research
should also be focused on exploring more environmentally friendly decolorants.
With further research and technological advancements, bioprocessing and electrospin-
ning show promise for textile waste recycling. Adopting a circular economy approach and
integrating recycling with sustainable fiber production could help reduce environmental
impacts and resource depletion within the textile industry. However, government policies,
industrial symbiosis, and consumer awareness will also be crucial to enable a transition
towards a sustainable and circular future for the textile sector. Overall, this study has
highlighted the potential of using bioprocesses and electrospinning to generate value from
textile waste while regenerating sustainable cellulose fibers, as well as investigating a range

Sustainability 2023,15, 11638 14 of 18
of bioprocessing and electrospinning methods for recycling cotton from textile waste in a
sustainable manner. Pretreatments, including acid and alkali methods, can modify cotton
fibers for enzymatic hydrolysis using cellulases, while solid–state fermentation produces
fungal cellulases from textile waste that can hydrolyze cotton. Electrospinning regener-
ates cellulose nanofibers from waste cellulose that could be used in various applications.
Further optimization and innovations building on these methods could advance the more
environmentally friendly management and recycling of cotton textile waste. Finally, the
recycling procedure itself, when being scaled up, consumes a large amount of water and
energy and the lengthy procedural steps may involve the use of large-scale reactors, which
may incur extra costs to the total capital investment. Thus, the process itself may not
be as economical as the manufacturing process of the original fiber materials. This may
discourage the recycling industry to consider textile recycling; therefore, concepts such
as industrial symbiosis should be introduced in the process of plant design for the future
development of the industry [111].
Author Contributions:
Conceptualization, E.M.-H.C. and C.-W.T.; methodology, D.W.-S.S.; formal
analysis, D.W.-S.S., Y.-Y.L. and R.H.-P.L.; investigation, D.W.-S.S.; resources, P.W.-K.T.; data curation,
S.O.; writing—original draft preparation, E.M.-H.C. and C.-W.T.; writing—review and editing,
D.W.-S.S., Y.-Y.L. and R.H.-P.L.; visualization, R.H.-P.L.; supervision, C.-W.T.; project administration,
P.W.-K.T.; funding acquisition, P.W.-K.T. All authors have read and agreed to the published version of
the manuscript.
Funding:
This work described in this paper was fully supported by the Environment and Con-
servation Fund (Project No. ECF 54/2020), University Grants Committee—Research Matching
Grant Scheme (RMG024), and a grant from the Research Grants Council of the Hong Kong Special
Administrative Region, China (Project No. UGC/IDS(R)25/20).
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
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