Recycling of cotton textile waste: Technological process,applications,and sustainability within a circular economy

Sorting

Textiles are meticulously sorted based on crucial factors such as fiber content, color, and condition, a step acknowledged as fundamental for ensuring efficient downstream processing and minimizing contamination within recycled materials. While this initial categorization is essential, our analysis suggests that the accuracy and efficiency of current sorting techniques, particularly when relying heavily on manual labor, present significant limitations. The inherent variability in human judgment can lead to inconsistencies, impacting the quality of the recycled output. Furthermore, the increasing complexity of textile blends poses a considerable challenge for rapid and precise identification. In our opinion, future advancements in automated sorting technologies, incorporating spectroscopic analysis and artificial intelligence, hold the key to overcoming these limitations and significantly enhancing the efficacy of textile waste recycling. The two main categories of sorting techniques for textile waste, while providing a foundational framework, highlight the need for continuous innovation in this critical initial stage. ⁴⁶

Cleaning

Textile recycling facilities sort used textiles by fiber type, quality, and intended use. After sorting, cleaning is the next critical stage. This cleaning process removes dirt, debris, and contaminants from the textiles. ⁶⁹ There are several reasons why cleaning is essential. Firstly, clean textiles are easier to process further. Whether the textiles are destined for a second life as used clothing or are broken down into fibers for new products, cleanliness improves quality. Dirt and debris can damage fibers, reducing their value. Additionally, cleaning ensures the hygiene of recycled textiles, particularly those intended for reuse. Finally, clean textiles can be more efficiently sorted by color and may require less water or chemicals during the actual recycling process. ⁷⁰ Contamination by dirt, oils, and dyes needs to be removed. Techniques like mechanical cleaning (using de-dusting machines) and wet cleaning (with water and mild detergents) are employed. However, wet cleaning should be approached judiciously and avoided in certain scenarios. For instance, textiles known to be highly degraded or prone to excessive shrinkage or color bleeding during washing are often better candidates for mechanical cleaning methods alone. Similarly, for certain high-value or delicate vintage textiles intended for direct reuse, specialized dry cleaning or minimal intervention may be preferable to prevent damage. Furthermore, the water and energy consumption associated with wet cleaning must be carefully considered, especially when dealing with large volumes of textiles or in regions with water scarcity. In such cases, optimizing mechanical cleaning or exploring alternative low-water cleaning technologies may be more sustainable options.

Mechanical recycling

After preparation, non-fibrous materials like buttons, zippers, and trims are removed. The sorted cotton materials might be cut into smaller pieces for easier processing. ⁷¹ Figure 3 shows the general conversion process of textiles, such as cotton waste, into recycled yarn. Following the removal of non-fibrous components and potential cutting of sorted cotton materials, the shredding stage is a critical step in mechanical recycling, directly influencing the sustainability and environmental footprint of the process. This involves the use of tearing machines, which employ robust rotating cylinders with aggressive teeth or wires to mechanically disrupt the fabric structure and liberate the fibers. The energy consumption and efficiency of these machines are key considerations from an environmental perspective. Subsequently, the material is often processed by a garnet machine, which further refines the fiber separation using a series of rollers with finer wire teeth operating at varying speeds. This more delicate action aims to improve fiber alignment and remove smaller impurities, ultimately impacting the quality and yield of the recycled fibers. Optimizing the operational parameters of both tearing and garnet machines, such as rotor speed, tooth configuration, and processing time, is crucial not only for achieving desired fiber characteristics but also for minimizing energy usage and waste generation within the mechanical recycling pathway, thus contributing to its overall sustainability.OPEN IN VIEWER

Shredding and opening

Cotton waste gets a new lease of life through a two-step process: shredding and opening. First, specialized machinery tears the material into smaller fibers, and this process is called shredding. ⁷² This stage is crucial, as it aims to maximize the length of the resulting fibers for better reusability. The second step, opening, further refines the shredded cotton. Here, carding machines take over, separating and aligning the individual fibers. ⁷³ This well-established method relies solely on physical processes to transform cotton waste into a valuable resource. As shown in the schematic workflow diagram for the mechanical recovery of cotton fibers Figure 4(a), the textile shredding process starts by sorting the scraps by color. This ensures that the resulting fibers are pure and have minimal contamination from other colors. The scraps are then perforated to reduce their size and make it easier to shred. Through several shredding stages, the fibers are gradually separated from the scraps. Finally, the shredded fibers are compressed into bales and packaged in bags. ⁷⁴ OPEN IN VIEWER

Figure 4.

(A) Schematic workflow for the mechanical recovery of cotton fibers; (B) Physical Mechanical recycling process (a) material feeding to shredding machine, (b) shredding in several zones, (c) material delivery after shredding, (d) final bale making, (C) Pre-consumer textile wastes: (a) spinning hard waste, (C-b) woven cut clips and (c) knit cut clips, (d) garments cut clips (D) After shredding, pre-consumer recycled fiber obtained from (a) spinning hard waste & woven cut clip, and (b) knit cut clip. Post-consumer recycled fibers obtained from (c) second-hand garments cut clips ⁹ .

Cotton fiber waste recycling is a multi-step process. As it is seen in Figure 4(b), First, the raw cotton fiber waste is fed into a shredding machine (Figure 4(b-a)). Then, the material is shredded in multiple zones to ensure complete fragmentation and then transported to the next stage, as illustrated in Figure 4(b-b). The materials then delivered for baling after shredding (Figure 4(b-c)). The final step of the process is bale making. It is the stage where the shredded fiber is compressed into bales for storage or further processing, as depicted in Figure 4(b-d). The recycled cotton fiber obtained from this process can be used in various textile applications. For example, Figure 4(d-a and b) illustrates the spinning of hard waste and woven cut clips, which are then used to create new fabrics. whereas Figure 4(d-c and d) demonstrates the knitting of cut clips of the post-consumer textile waste and garment cut clips procured from second-hand clothing shop, both are another method of utilizing recycled cotton fiber. The pre-and post-consumer recycled fibers obtained after shredding are shown in Figure 4(d-a, b and c). This illustrates how post-consumers recycle fibers, made from used clothing and fabric scraps, and could be used in new textile products to promote a more sustainable and circular economy.

The length and strength of shredded fibers affect the reliability of the material, as seen in Table 1. Reliability is calculated using formula (1). ⁷³

SCI = − 322.98 + ( 2.89 × STR ) − ( 9.02 × MIC ) + ( 43.53 × ( UHML ) ) + ( 4.29 × UI )

(1)

where: SCI (Spinning Consistency Index), STR (Strength), MIC (Micronaire), UHML (Upper Half Mean Length), UI (Uniformity Index).

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Table 1.

Reliability index.

Fiber type	UHML (Inch)	Micronair (-)	STR (gf/Tex)	UI	SCI
Cotton lint	1.2	4.32	31.55	81.14	130
Shredded cotton	0.83	4.47	27.84	58.74	5

SCI measures the reliability of fiber. A higher SCI indicates better material quality and manufacturing performance. STR is the fiber’s resistance to breakage. It’s measured in grams per tex, where tex is a unit of linear density. MIC measures fiber fineness by assessing its linear density based on maturity. UHML is the average length of the longest 50% of fibers, measured in inches. UI measures the consistency of fiber length. It’s calculated as the percentage difference between the mean length (ML) and the mean length of the longest 50% of fibers (UHML). It is important to note that the constant term in the SCI formula, −322.98, is an empirically derived baseline value, likely originating from the statistical regression analysis used to establish the relationship between fiber properties and spinning consistency.

A researcher shredded different pre-consumer cotton scraps (loose vs tight-knit, dyed vs undyed) to see how it affects recycled fiber quality. They analyzed for fiber yield, length, spinnability, and final yarn strength. Shredding loose, undyed knits resulted in better-quality recycled fibers with higher yarn strength and less waste. Dyed fabrics overall produced lower-quality recycled fibers. ⁷⁴ Recycled denim was used to create a textile reinforcement for epoxy resin composites. The denim, made entirely of cotton, was shredded into small pieces and blended to simulate the industrial tearing process. These recycled cotton scraps were then incorporated into epoxy resin composites. The addition of 30% recycled denim significantly improved the composite’s tensile strength and stiffness compared to pure resin. ⁷⁵

Blending and spinning

Mechanically recycled cotton fibers are generally shorter than their virgin counterparts. This length difference can be accommodated at both the fiber and yarn stages of production. Common textile machinery like blow rooms, carding machines, draw frames, and spinning frames can be used to blend recycled and virgin cotton fibers into a uniform yarn, as illustrated in Figure 5. Simplex performs mainly attuning the silver that comes from the drawing frame and making it ready for the next process, which is spinning. There are different spinning techniques. Even though ring spinning is the common one after the simplex process, an open-end spinning is also practiced in the recycling fiber production as it is capable of processing shorter and more irregular fibers, which are plentiful in recycled fiber. Open-end spinning is specifically preferred in the production of coarse and medium-count yarns utilized in the manufacturing of denim fabrics, towels, socks, upholstery fabrics, and industrial fabrics. It possesses high efficiency, lower power requirement, and tolerance to variation in fibers, thus making it a good method to utilize post-consumer and post-industrial textile waste in producing new yarns. Once the thin yarn is produced in the spinning machine, the autoconer machine changes the coped yarns into a big form of the cone for the best suitability of the next process. They might be blended with virgin cotton or other fibers to achieve desired properties in the final yarn. Finally, the blended fibers are spun into new yarns for use in textile production. The recovered fibers are then spun into new yarn for various applications. The final spinning can be performed using ring spinning, compact spinning, rotor spinning, and others.

A study investigated the potential of using recycled cotton from pre-consumer fabric waste in the production of elastic core-spun yarns for stretch denim. Recycled cotton fibers were blended with virgin cotton Figure 6(a) in varying proportions (10%–60%) and spun into 16 Ne (36.9 Tex) yarns. The addition of recycled cotton improved fiber control during the drafting process, allowing for a higher incorporation of recycled material (up to 60%) into the yarn (Figure 6(b)). The elastic yarn was then used as a core in the spinning process (Figure 6(c)). The yarns we produced were of very high quality. They were much smoother, had fewer flaws, and were stronger than regular yarns. They were among the top 5% to 50% best yarns according to the Uster Statistics 2023. Even the yarn made with 60% recycled material (as shown in Figure 6(d)) was strong enough to be used on a fast air-jet loom that runs at 950 rpm. ⁷⁶ Another research project explored the possibility of making denim fabric with dual-core elastic yarn from recycled cotton waste. A modified ring spinning process was employed to create these yarns, incorporating various elastomeric components such as T400®, PBT, PES, Lycra®, and both virgin and recycled cotton. The resulting Ne 18/1 yarns were assessed for strength, imperfection index, elongation, unevenness, and hairiness. As shown in Figure 6(e), compared to dual-core yarn made entirely from virgin cotton, the recycled cotton version exhibited lower strength and elongation, as well as higher imperfection index, unevenness, and hairiness values. This is because recycled cotton fibers may have undergone degradation due to factors such as exposure to sunlight, chemicals, or mechanical stress during their previous use. This degradation can result in weaker, shorter, and more damaged fibers, leading to lower overall yarn quality. ⁷⁵ OPEN IN VIEWER

Figure 6.

(a) Virgin cotton; (b) recycled cotton; (c) spandex filament; (d) elastic core-spun melange yarn consisting of an elastane filament at the core, surrounded by a sheath made from a blend of recycled and virgin cotton fibers. ⁷⁵ ; (e) yarn tensile strength, yarn elongation, and unevenness of 100% cotton and recycled yarn ²⁷⁴ .

The summarized data on recycled textile products through different techniques are shown in Table 2. It is a comprehensive overview of various cotton waste recycling techniques, and the resulting products are reported from various literature.

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Table 2.

Cotton waste recycling for value-added textiles.

Type of waste	Recycling techniques	Final product	Application	Ref.
Cotton fabric	Shredding	Fibers for cloth	Commercial production	75
Cotton, polyester fibers	Mechanical recycling and ring-spinning	Produced (10–20 Ne) yarn and then successfully produced fabric	Denim, towels, and home furnishing clothes	73
Cotton, polyesters, cellulose	Shredding	Fibers and yarns	Covering blankets, waddings, absorbing blankets & new textile product	74
Cotton, wool fibers	Cutting, picking, tearing	Fibers and yarn	Non-woven & woven fabric	75
Cotton fibers	Cutting, shredding, carding	Fibers for cloth	Upholstery product, lower quality	274

Chemical recycling

Chemical recycling is combined with mechanical recycling to improve the quality of recycled materials, especially for uses like food contact. This process transforms waste into high-value raw materials that would otherwise be discarded. This solution supports the circular economy, which promotes the use of waste as a valuable resource.^77,78 Solvent-based technologies can recycle both natural and synthetic fibers. Cotton, lyocell, viscose, polyester, and other cellulose or plastic-based fibers can be processed using these techniques. While chemical recycling of cotton has achieved commercial scale, technologies for blended fabrics are still under development, progressing from research to pilot and industrial stages. To accelerate the adoption of chemical recycling, transparency in material composition and collaborative innovation are crucial. By deconstructing cotton at the molecular level, this innovative approach unlocks the potential to create entirely new materials.^79,80 Current chemical polymer recycling processes convert pure cotton into cellulose pulp, a precursor for other regenerated cellulose fibers. While theoretically recyclable multiple times, the polymer chains within the cellulose degrade with each cycle. Additionally, research indicates that fiber quality deteriorates with each use, limiting the number of times the material can be recycled for apparel applications. ⁸¹ Further research is necessary to fully understand the potential for repeated recycling of this process, including effective methods for identifying and treating low-quality fibers. While several examples exist for recycling pure cellulose-based fiber streams, such as Lenzing’s Refibra lyocell fiber made from cotton scraps and wood, the industry is still in its early stages. Innovative companies are developing technologies to turn used clothing into new fabric. Renewcell, Infinited Fibre Company, and Evrnu are examples of this, with Evrnu even creating prototype jeans and T-shirts from recycled cotton in partnership with Levi’s and Target. ¹⁴ Chemical recycling presents a promising avenue for transforming cotton waste into high-quality recycled fibers or even innovative new materials. While these technologies offer substantial potential, their widespread adoption and optimization are essential to fully realizing their environmental and economic benefits. Several techniques have been developed for chemically recycling textile waste. The following section discusses the common chemical recycling methods.

Enzymatic/biological degradation, gasification and hydrothermal

This environmentally friendly approach uses enzymes specifically designed to break down certain types of fibers. ⁸⁹ For example, cellulase enzymes can be used to break down cellulose in cotton waste. The enzymes act as catalysts, accelerating the natural degradation process. This method utilizes enzymes and biological catalysts to break down specific components of textiles. It’s particularly effective for natural fibers like cotton, where enzymes like cellulase can degrade cellulose polymers. The resulting breakdown products can be used for various applications, including biofuels or regenerated cellulose materials. Microorganisms or their enzymes can break down polymers into smaller pieces called monomers. These monomers can be used to make new products. This process can work with both bioplastics and traditional plastics. It might also help clean up pollution. ⁵² Besides, gasification uses high temperatures in an oxygen-limited environment to convert textile waste into combustible gas (syngas). The syngas can then be used for energy generation or further processed into fuels. Gasification doesn’t directly create new fibers, but it offers a way to utilize waste for energy production.^90,91 Hydrothermal is considered an emerging technique that uses high-pressure hot water (typically above 180°C) to break down textile waste into valuable chemicals or precursors for new. ⁹² This process uses high-pressure and hot water (not necessarily boiling) to break down complex molecules in the textile waste. It can be used alone or combined with other methods like enzymatic treatment. Depending on the conditions and textile composition, hydrothermal treatment can achieve various outcomes, like breaking down dyes, weakening fiber bonds for easier mechanical recycling, or even converting biomass into usable chemicals. ⁹³

Table 3 shows a comparison of different techniques of chemical recycling.

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Table 3.

Comparison of different techniques of chemical recycling.

Technique	Short description	Advantages	Disadvantages
Pyrolysis	Break down textiles using high heat in an oxygen-limited environment.	- Can handle mixed blends	- High energy consumption
		- Produces valuable byproducts like syngas	- Potential for harmful emissions
			- Lower quality recycled fibers
Hydrolysis	Breaks down textiles using water and heat/acid/enzymes.	- Works for various fibers (polyester, nylon)	- May require pre-sorting
		- Can be energy-efficient with optimization	- Potential for corrosive waste streams
Enzymatic	Uses enzymes to break down specific fibers (e.g., cellulose in cotton).	- Environmentally friendly	- Slower process
		- Potentially low energy consumption	- Limited fiber types processed
			- High enzyme cost
Gasification	Convert textiles into combustible gas using high heat.	- Can handle mixed waste	- Complex technology
		- Produces syngas for energy	- Requires additional cleaning for syngas
Hydrothermal	It uses high-pressure hot water to break down textiles.	- Promising for various fibers	- Technology under development
		- Potential for lower energy use	- Limited commercial availability

Plasma technology and microwave-assisted recycling

The plasma technology method utilizes high-temperature ionized gas (plasma) to break down textile waste into valuable components. ⁴⁶ It’s still under development, but researchers see the potential for depolymerization into usable monomers or even conversion into valuable chemicals. ⁹² However, the microwave-assisted approach uses microwave radiation to break down or modify textile materials. It’s being explored for various applications, such as separating blended fabrics or enhancing the digestibility of natural fibers for enzymatic recycling. ⁹⁴ Considering the potential for both plasma and microwave technologies to offer novel pathways for textile waste valorization, particularly for complex waste streams, we recommend increased research and development efforts to optimize their efficiency and assess their overall environmental and economic feasibility compared to more established methods.

Needle punching

This method involves punching carded cotton waste fibers with barbed needles. The barbs interlock the fibers, creating a strong and dimensionally stable nonwoven fabric. In research, shredded 100% cotton waste is used to create nonwoven mats. The waste is first cut into fibers (see Figure 9(a)) and turned into mats using carding and needle punching (see Figure 9(b)). ⁹⁷ OPEN IN VIEWER

Dry, wet and air-laid

The dry-laid method involves opening and cleaning of the cotton waste, followed by a carding process that orients the fibers predominantly in one or two directions. In contrast, the air-laid method involves spreading the fibers into a uniform layer using air currents, resulting in a more random fiber orientation. A bonding agent, often a resin or heat, is applied to create a web-like structure. This technique is known for its simplicity and is good for lower-strength applications. ⁹⁸ On the contrary, in the wet-laid process, a dilute slurry of cotton waste fibers is deposited onto a forming screen. Water is then drained, and the remaining web is bonded using heat, pressure, or a chemical binder. ⁹⁹ Like wet-laid, but instead of a water slurry, air is used to transport the cotton waste fibers onto a forming screen. Binders are then applied to create the final nonwoven structure. Cotton/Polyester garment waste was recycled for thermal and acoustic functions using the Air-Laid process. Waste materials from “cut and sew” knitwear production are used as raw input. Post-consumer knitwear scraps were collected from garment manufacturing facilities and sorted by color before recycling. These materials were processed in a reused fabric opener machine to yield recycled fibers. Subsequently, a carding machine was employed to convert the recycled fibers into air-laid webs of varying densities. Carding system of recycled fiber differs from conventional systems in that it handles short, irregular, and contaminated fibers from shredded fabrics in more powerful machinery (e.g., Garnett machines) and includes multiple opening steps, intensive cleaning, and waste removal units to recover usable fibers, whereas conventional systems handle longer, cleaner virgin fibers in weaker, single-stage processing. Polyvinyl acetate (PVA), as depicted in Figure 10(a), served as the binding agent for these webs. It is noteworthy that the binder primarily adheres to the surface layers and exhibits limited penetration into the relatively thick structure. Spray adhesive bonding ensures precise binder application, even distribution, and a soft fabric finish. Adhesive application is strictly controlled at a 20% add-on rate. Careful monitoring prevents excessive or insufficient adhesive flow from the sprayer. Finally, the nonwoven fabrics are obtained, as shown in Figure 10(b) and (c). ¹⁰⁰ OPEN IN VIEWER

Resin and thermal bonding

Cotton waste fibers are mixed with a resin binder and then spread onto a forming screen. Heat and pressure are applied to activate the resin and create a strong, nonwoven sheet. ¹⁰¹ In thermal bonding, the nonwovens are produced by utilizing heat to melt synthetic fibers within the cotton waste blend, creating a web structure. This method is often used with a blend of cotton and polyester fibers (Table 4). ¹⁰²

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Table 4.

Comparison of different techniques for bio-based nonwovens from cotton waste.

Method	Advantages	Disadvantages	Applications
Needle punching	- Excellent for creating strong, thick nonwovens	- Requires additional processing steps for waste cotton (cleaning, shredding)	- Geotextiles, carpet underlays, upholstery padding, industrial mats
	- Good for bulky materials like waste cotton	- May not achieve a very smooth surface
	- Fibers mechanically locked in good durability	- Limited control over fiber orientation
	- Can incorporate different fiber types
Dry Laid	- Simple and fast process	- Lower strength compared to other methods	- Filters, disposable medical textiles, insulation layers, packaging materials
	- Good for low-density nonwovens	- Requires strong bonding agent for waste cotton
	- Can handle a variety of fiber lengths	- Limited control over fiber distribution
	- Waste cotton readily available
Wet-laid	- Creates good uniformity and drape	- High water consumption	- Tea/coffee filters, wipes, medical dressings, tablecloths
	- Suitable for applications requiring absorbency	- Requires drying stage, adding energy use
	- Can use a water-based bonding agent (more eco-friendly)	- Waste cotton may need additional cleaning due to water processing
Air Laid	- Excellent for lightweight, breathable nonwovens	- Lower strength compared to other methods	- Hygiene products (diapers, feminine pads), insulation materials, breathable agricultural covers
	- Good for insulation applications	- Requires precise control of airflow
	- Can incorporate different fiber types easily	- Waste cotton may require additional processing for size consistency
Resin bonding	- Creates strong, durable nonwovens	- Use chemical adhesives, raising environmental concerns	- Automotive interiors, protective clothing, water-resistant packaging, furniture linings
	- Offers good water resistance	- Resin bonding can be more expensive
	- Can create a smooth surface finish	- Waste cotton may require pre-treatment for optimal adhesion
Thermal bonding	- Fast and efficient process	- Requires specific fiber types that melt well or polymer	- Disposable face masks, shopping bags, lightweight packaging, book covers
	- No harsh chemicals involved	- Strength may be lower compared to other methods
	- Good for simple, nonwoven structures	- Limited control over fiber orientation

Hand lay-up

In this manual method, cotton fibers are arranged in a mold and then saturated with a bio-based resin. This process is repeated to build up multiple layers of the material Figure 11(a). To ensure a smooth, even finish, a vacuum bag is used to eliminate air pockets and compress the laminate. Hand lay-up is a versatile method suitable for producing complex shapes, but it is labor-intensive and has lower production rates compared to other methods. Researchers discovered that discarded woven fabrics can be used directly as reinforcing materials in composites without needing to separate individual fibers. The fabric’s consistent alignment ensures that the resulting composites have uniform properties. By using soybean-based bio-resins to reinforce cotton fabric, researchers created biocomposites with impressive strength and durability. Without any additional fiber treatments, these composites achieved a tensile strength of over 100 MPa and a modulus of over 10 MPa. Additionally, they exhibited an impact strength of over 70 kJ/m². ¹⁰³ As shown in Figure 11(b), researchers employed cotton waste fabric as reinforcement and sawdust as filler with pp matrix using a hot press technique. Single cotton fabric fiber was sandwiched between layers of polypropylene and wood sawdust particles. The composites exhibited improved tensile and flexural properties when cotton fabric was incorporated. ¹⁰⁴ OPEN IN VIEWER

The composite was prepared using the hand lay-up method, using recycled cotton fibers (CFRC) with epoxy resin. As shown in Figure 11(c), the composite reinforced with 30% recycled cotton fiber had better flexural strength. ¹⁰⁵ The composite tensile strength was significantly boosted by incorporating varying amounts of cotton fibers, as depicted in Figure 11(d). The flexural result was also high at 25 wt% cotton fiber. In another study, composites were prepared from recycled grey cotton fabric reinforced with polyester matrix in various configurations. All composites demonstrated good thermal stability up to 305°C, followed by a gradual mass loss (310°C–405°C), significant degradation (>405°C), and residual char at 655°C. Free vibration analysis revealed superior energy absorption properties in cotton-wool fiber composites compared to the other configurations. ¹

Compression molding

Compression molding involves placing a pre-measured mixture of bio-based resin (e.g., epoxy) and cotton fiber preform into a heated mold cavity. The mold is closed under high pressure (typically 5–20 MPa) using hydraulic or mechanical presses (Figure 12(b)), and heat (100°C–200°C) is applied to cure the resin. This process is cost-effective for small-to-medium production runs due to low tooling costs, though cycle times increase with part thickness. Researchers utilized recycled cotton fibers blended with epoxy resin, varying fiber weight fractions (0.1–0.4), to produce 3 mm-thick thermoset composites. Cotton/epoxy composites exhibited superior mechanical strength compared to polyester/epoxy due to enhanced fiber-matrix adhesion (Figure 12(c)). Key advantages include simplicity, compatibility with natural fibers, and suitability for flat or moderately complex geometries (e.g., automotive panels, industrial mats). Limitations include slower cycle times for thick sections and challenges in achieving uniform fiber distribution. ¹¹⁶ OPEN IN VIEWER

Extrusion molding

In this method, the bio-based resin and cotton fibers are continuously fed into an extruder. The extruder mixes and heats the materials, forcing the molten composite through a die to create a desired shape (Figure 13(a)). Extrusion is a high-volume production process suitable for producing long, continuous profiles like pipes, boards, and films. Researchers studied composite materials made from silk fiber and cotton waste. These materials were shaped into various sizes and combined in different proportions with a plastic called polypropylene (PP). The materials were then processed using a double-screw extruder. The study found that adding more cotton waste to the composite improved its heat resistance and softening point. This was confirmed by Vicat softening tests and heat deflection temperature. Additionally, the cotton waste addition had a similar effect on the composite’s thermal properties as adding silk fiber. Finally, the impact strength and elongation of the composite increased when 6% cotton waste was added. This suggests that cotton waste can enhance the composite’s toughness and flexibility. As shown in Figure 13(b), the composite is made from 3% cotton waste, and 97% PP has a smooth surface, which indicates that the fiber and matrix are well harmonized. Some fibers were shown on the surface of the composite at higher magnification (Figure 13(c)). When cotton waste percentage increased to 6%, the SEM results showed a slightly rough surface compared to 3% cotton waste (Figure 13(d)). This result is clearly shown at a 750X magnification level (Figure 13(e)). This surface change may be because of the use of large sizes of recycled waste fiber. ¹¹⁷ OPEN IN VIEWER

Injection molding

Injection molding is a high-pressure manufacturing process where molten composite material is forced into a closed mold (70–150 MPa) and rapidly cooled to solidify into precise, complex shapes. To integrate cotton waste into this method, preprocessing is essential. First, raw cotton fibers undergo cleaning to remove impurities, followed by chopping or milling into short fibers (0.5–5 mm) to ensure uniform dispersion. Due to cotton’s hydrophilic nature, thorough drying (e.g., 80°C–100°C for 4–6 h) is critical to reduce moisture content below 1%, preventing voids and interfacial defects during molding. To address compatibility issues between hydrophilic cotton and hydrophobic polymer matrices (e.g., PLA or recycled PET), coupling agents like maleic anhydride-grafted PLA (MA-g-PLA) are often incorporated to enhance adhesion. The prepared cotton fibers are blended with a thermoplastic matrix, such as biodegradable PLA or recycled plastics, using a twin-screw extruder. The mixture is melted at controlled temperatures (160°C–200°C, depending on the polymer) to avoid thermal degradation of cotton fibers, which can occur above 180°C. The molten composite is injected into a steel or aluminum mold equipped with cooling channels to ensure rapid solidification, with cycle times ranging from 30 to 120 s. After cooling, the finished part is ejected and trimmed. Research demonstrates that cotton fiber-reinforced PLA composites exhibit significant improvements in mechanical properties, including up to 25% higher stiffness and 15% greater tensile strength compared to pure PLA, as shown in Figure 14(c). ¹¹⁸ While injection molding enables high-volume production of intricate parts like biodegradable food containers, agricultural tools, and automotive components, challenges persist. Cotton’s low flowability can lead to fiber clumping, necessitating optimized screw designs for even distribution. Additionally, the process is limited to thermoplastic matrices, excluding thermosets, and narrow processing windows due to cotton’s moisture sensitivity and thermal instability. Despite these constraints, advancements in material compatibility and process control continue to expand applications in sustainable consumer goods and packaging.OPEN IN VIEWER

The composite, made from recycled denim fibers and polypropylene (PP), showed improved tensile strength compared to the unreinforced PP. The denim fibers were first bound with polyvinyl acetate and then pelletized with PP before being extruded into the composite. This new manufacturing process helped to preserve the beneficial properties of the recycled denim fibers. ¹¹⁹ Researchers have created eco-friendly and affordable composite materials using recycled cotton waste. By breaking down textile scraps into short fibers, they combined these fibers with a partially plant-based plastic (bio-PET). This new material is stronger, stiffer, and more resistant to heat than the original plastic alone. With the right amount of recycled cotton fibers, these composite pieces could be ideal for packaging food and other products. ¹²⁰ Injection molding excels at creating intricate, three-dimensional forms with remarkable precision.^121,122 This is due to it cast molten material into precision molds under controlled pressure and temperature. Such a high-pressure process forcing the material into every nook and cranny of the mold and helps to produce complex geometries, fine details, and uniform dimensions among high volumes of parts with ease, which makes it suitable for producing detailed and repeatable parts at high efficiency. Furthermore, injection molding offers precise control over fiber orientation within the part through mold design and how the process is run. This intricate control over both shape and fiber alignment makes injection molding ideal for creating complex parts with a smooth surface finish and minimal material waste.

Solution casting and resin transfer molding

To make a bio-based polymer composite, we first dissolve the polymer in a liquid to form a thick mixture. Then, we add cotton fibers to this mixture and spread it out on a flat surface. As the liquid dries, the polymer and cotton fibers stick together to form a solid film. This method is ideal for creating thin, flat materials (Figure 15).OPEN IN VIEWER

The composite panels in Figure 16 were made by placing 100% cotton fabric on a nonwoven mat and covering it with perforated film and peel-ply. A vacuum pump was then used to eradicate air from the system and ensure that the resin fully infiltrated the fabric. After vacuum sealing, the resin was cured to create a composite panel. Although composite properties are generally different from those of virgin fibers, the chemical modifications in this process improved fiber-matrix adhesion, resulting in panels with promising characteristics. These lightweight panels with excellent mechanical properties showed substantial applications in different industries, including automotive and construction. ¹²³ Resin transfer molding (RTM) involves placing a dry cotton fiber preform into a closed mold, then injecting low-viscosity bio-based resin (e.g., epoxy, soy-based resins) under moderate pressure (0.3–1 MPa) until the preform is fully impregnated. The resin cures at elevated temperatures (80°C–120°C), forming a high-strength composite. Key considerations include resin viscosity (<500 cP) to ensure proper flow through the fiber bed and mold design with strategic inlet/outlet ports to minimize voids. RTM excels in producing large, intricate parts with consistent fiber alignment (e.g., automotive body panels, wind turbine blades). For cotton waste, studies show that surface treatments (alkali or silane) improve resin wettability, reducing porosity. Compared to compression molding, RTM offers better control over fiber placement and resin distribution but requires higher initial tooling costs.OPEN IN VIEWER

Vacuum infusion

Vacuum infusion is a manufacturing process used to create composite materials by drawing resin through dry reinforcement materials using vacuum pressure. This method (Figure 17(a) involves placing dry reinforcement materials in a mold, sealing the mold with a vacuum bag, and introducing resin into the mold. A vacuum pump is then activated to draw air out of the mold, forcing the resin to flow through the reinforcement materials. Once the resin has completely infiltrated the materials, the part is cured, solidifying the composite. Vacuum infusion offers several benefits, including high-quality parts, controlled resin-to-fiber ratio, reduced waste, versatility, and suitability for large-part production. By using recycled nonwoven materials like cotton, polyester, and cotton/polyester blends mixed into epoxy resin, this technique is widely applied in various industries, including aerospace, automotive, marine, wind energy, and sports equipment. As shown in Figure 17(b), the composite panels are made using a vacuum infusion process. Mechanical, thermal, and acoustic tests show that both the nonwoven fabrics and composite panels have good properties. These panels are promising for reducing noise and offer advantages over pure epoxy products. ¹²⁴ OPEN IN VIEWER

Table 5 shows the different bio-based composite materials reinforced by recycled cotton, their methods, and the main findings from various literature. To summarize, LDPE, especially with MA-LDPE and processed via extrusion, is a highly effective matrix for cost-efficient, high-strength recycled cotton composites. Studies show significant improvements in mechanical properties with specific formulations. Epoxy resin, particularly when combined with rGO or hemp fibers and processed by compression molding, excels in high-performance structural applications, yielding substantial increases in strength and impact resistance. For recyclable and cost-effective solutions, recycled PP processed through injection molding offers durability for complex parts, as demonstrated by its performance under cyclic stress with cotton waste. Extrusion is optimal for thermoplastics like LDPE and PP, while compression molding suits thermosets like epoxy. The choice of matrix and method depends on the application’s priorities, balancing strength, cost, recyclability, and complexity.

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Table 5.

Bio-based composite materials reinforced by recycled cotton.

Type of waste/reinforcement	Polymer	Method used	Findings	Ref.
Waste cotton fabric (15 mm × 15 mm, 2.5% and 25%)	LDPE	Extrusion	Cotton waste reinforcement at a 25% concentration significantly increased both tensile strength and Young’s modulus.	115
Cotton waste fiber (10% and 15%)	Recycled polypropylene	Extrusion	As the amount of cotton waste increases, the mechanical properties of the material, particularly its elasticity, also improve.	116
Cotton waste fiber (20% and 30%)	Virgin LPDE (v-LDPE) and r-LDPE	Extrusion	The material with the highest tensile strength (TS), Young’s modulus (YM), flexural strength, and flexural modulus was a composite containing 30% cotton fiber, 65% low-density polyethylene (LDPE) matrix, and 5% maleic anhydride-grafted LDPE (MA-LDPE) interfacial bonding agent.	276
Cotton flocks from end-of-life jeans fabric (16 wt.%)	PP	Injection molding	Composites underwent morphological, tensile, and fatigue testing, with stress levels ranging from 50 to 90% of their ultimate tensile strength.	118
Shredded cotton fabric waste (0.3%), graphene oxide (rGO) nanoparticles, and enzyme-treated hemp fiber (HF) microparticles as a filler	Epoxy resin	Compression molding	The addition of 0.3 wt% of rGO to a cotton/epoxy composite resulted in a 10% increase in tensile strength, a 20% increase in flexural strength, and a 30% increase in impact strength. When 3 wt% of HF particles were added to the cotton/epoxy composite, tensile strength increased by 20%, flexural strength increased by 14%, and impact strength increased by 116%.	120
Cotton waste shoddy (carded web: 0.1, 0.2, 0.3, and 0.4 wt%)	Epoxy resin	Compression molding	The composite’s mechanical properties were on par with commercial wood. They could be used to make a dashboard panel.	119
Waste cotton fabric layer (10, 15, 20%) and wood-saw-dust	PP	Hot pressing	The addition of cotton fabric enhanced the tensile and flexural strength of the composites.	113
Cotton fabric	Unsaturated polyester	Compression molding	The composite ceiling made from a mix of 33% cotton fabric waste and 67% unsaturated polyester had impressive strength. It could withstand a maximum tensile force of 198 MPa, a flexural force of 30.1 megapascals, and a compressive force of 1105.3 MPa.	121
Cotton burr and stem fibers (10-30 Wt.%)	PLA	Compression molding	Flexural modulus rose 42% with 30% weight addition.	122
Cotton fiber	PLA	Solution casting	The addition of short cotton fibers significantly enhanced the mechanical properties of the composite material. Tensile modules increased by a substantial 18.6 times, while tensile strength rose from 2.07 MPa to 4.38 MPa. Additionally, composite elongation improved from 104.56% to 8.82%, and impact strength increased by a notable 28.4%.	123

Recycled cotton biocomposites in automotive industry

The global automobile market’s growing demand and the need for sustainability have led to a growing demand for natural fiber-based materials for automotives. The researcher discussed the fabrication of small automobile components using natural fibers, including textile waste (cotton waste), as shown in Figure 28. These composite materials can be recycled regularly to reduce textile waste and promote sustainable transportation.^197–205 Furthermore, biocomposites are transforming the composite sector for the automotive industry by promoting a circular economy from fiber extraction to final disposal, as indicated in Figure 28(a). This approach is safer and more environmentally friendly than synthetic and plastic materials. ²⁰⁶ This indicates that recycling and working in this area in the automotive industry can improve the economic cycle and reduce environmental pollution. Additionally, the incorporation of textile and cotton fabric solid waste materials can contribute to a zero-waste environment, ²⁰⁷ as shown in Figure 28(b). In addition to their biodegradability, natural fibers (recycled cotton) offer superior sound absorption owing to their porous structure, making them increasingly popular in automotive composites (Figure 28(c) and (d)). ²⁰⁸ OPEN IN VIEWER

Owing to its advantages and properties, the utilization of recycled cotton waste fibers in composite materials for automotive applications is an emerging area of interest, and numerous researchers have contributed their work in this area by adopting the concept of other fibers. Meng et al. ²¹¹ highlighted the potential for recycled carbon fiber components to achieve lower life cycle environmental impacts in automotive applications, suggesting that similar benefits could be realized with recycled cotton fibers when used in composites. Research emphasized the automotive sector’s focus on lightweight materials to meet CO₂ emission limits, indicating that fiber-reinforced composites, potentially including those with recycled cotton, could contribute to this goal. ²⁰⁹ But there are challenges related to the use of recycled fibers including milled fibers, which could include cotton, are often relegated to low-value applications owing to performance concerns after the reclamation process. ²¹⁰ This necessitates rigorous testing and qualification to ensure confidence in their performance. Additionally, researchers have used the blending of waste cotton with virgin cotton and other fibers to mitigate the performance issue of recycled cotton fiber composites for automotive applications. Researchers also discussed the use of recycled cotton fibers blended with virgin cotton in the textile sector, which could inform similar blending strategies in automotive composites to achieve desired properties. ²⁴² Another research work also highlighted the use of recycled e-glass/cotton reinforced with epoxy resin composite felt in the automotive industry, emphasizing the positive effect of natural fibers on improving the flammability behavior of fabrics, which is crucial for safety in automotive applications. ²¹¹ The use of waste cotton fibers as a filler for polylactide (PLA) composites, noting improvements in thermal and mechanical properties, albeit with a slight reduction in thermal stability further supported by other research work. In contrast, study pointed out that although the reuse of construction and demolition waste in composites has been studied, the specific application of recycled cotton from such sources in automotive composites has not been thoroughly examined. ²¹² It also cautions that recycled materials can result in lower mechanical properties than virgin materials and highlights the need for careful consideration of potential contamination. Another research discussed mechanical and physical property improvements in composites using silk and cotton fibers, suggesting their potential use in automotive parts to achieve lighter vehicles and reduce environmental impact. Another researcher also provided insights into the recycling process of textile waste and the advantages of natural fibers, including cotton, as reinforcing materials in composites, which align with the automotive industry’s goals for lightweight and eco-friendly materials.^213,247 Further reinforced the suitability of composite materials with recycled cotton for automotive applications, ²¹⁴ discussing the classification of composites in automotive parts and presenting mechanical testing of hybrid bio-composites, including cotton, for potential automotive use. In general, the literature suggests that recycled cotton waste fibers have significant potential for use in automotive composites, offering benefits such as improved flammability, mechanical properties, and environmental sustainability. Another work also outlined the benefits of implementing waste recycling in four main organizations: cotton producers, textile industry, garment factories, waste recyclers, and automotive industry as shown in Figure 29. ²⁰⁸ This approach promotes a circular economy, pollution-free environment, and zero-waste production system, ultimately fostering a cleaner environment. However, challenges such as potential contamination and weaker mechanical properties compared to those of virgin materials must be addressed. Further research into the practicality and economics of production, as well as comprehensive mechanical testing, is necessary to fully realize the potential of recycled cotton fiber composites in automotive applications.OPEN IN VIEWER

Recycled cotton waste biocomposite materials in construction industry

The clothing and textile industries have significant environmental impacts and consume substantial raw materials. ²⁶³ To tackle these challenges, there is a need for sustainable solutions that balance environmental, economic, and performance factors. Potential applications include eco-friendly thermal and acoustic insulation, innovative concrete, asphalt concrete, and composite materials manufacturing, which could help reduce waste in the rapidly expanding textile sector. ²¹⁶ Processing cotton waste fibers for reinforcement offers notable environmental and economic advantages, especially in construction applications. ²¹⁷ In concrete, waste cotton fibers serve as reinforcements without pozzolanic properties, enhancing composite volume more than weight and improving resistance to flexural and compressive stress. ²¹⁸ For example, incorporating 1% gamma-irradiated cotton fibers from discarded blue jeans into polyester concrete boosts flexural strain by 40% and flexural strength by 7%. ²¹⁹ Research indicates that mixing cotton with polyester enhances their mechanical properties ²²⁰ and combining cotton waste with limestone powder waste and concrete can yield lightweight bricks. ²²¹ Textile waste, including fabrics and fibers, is also integrated into modern construction. Fiber-based composites emerging as viable alternatives to traditional building materials in residential construction. ²⁶⁴ Recent studies have investigated hybrids that use textile fibers as reinforcements, resulting in lighter composites made from fabric scraps, epoxy resin, and foundry gravel. While textile fibers do not significantly improve the bending and compressive strengths of polymeric materials, they can mitigate brittleness. ²⁴⁸ The use of recycled cotton waste fibers in construction composites is gaining interest due to its environmental and economic benefits. One study examined hybrid composites reinforced with cotton fibers from waste textiles, revealing significant improvements in mechanical properties when combined with glass and jute fibers. These thermally stable composites have the potential to replace timber in various construction applications. ²²³ Additionally, research emphasizes the importance of waste utilization in sustainable composites, noting that the properties of waste materials and their intended use within the composite matrix are critical for successful structural applications. ²²³ However, challenges remain, such as variability in the physical and mechanical properties of waste cotton fibers, which can impact composite performance. ²²³ Figure 30 illustrates the sustainable properties of cotton fiber composites, showcasing their effective applications. Research has indicated that using waste cotton in construction can enhance bending and compressive properties. Studies have developed composite materials from cotton waste for building insulation, improving compressive strength, stiffness, and durability while enhancing energy absorption and flexural stiffness. ²²⁴ Another investigation into fly ash-based geopolymer reinforcement with cotton fiber found that increasing cotton fiber content enhanced porosity and flexural strength, attributed to good adhesion within matrix. ²²⁵ Recycled cotton waste has also been used as a filler in reinforced structures, expanding its application in geopolymer reinforcements. Research has explored recycled cotton fibers as reinforcement in composites with recycled polyethylene and polypropylene matrices, indicating their potential for sustainable insulation panels and nonwoven composites in housing systems. Furthermore, studies have developed bio-composites from cotton carpel, kenaf, flax, cotton stalks, and southern yellow pine, showing improved mechanical properties compared to unblended composites. The strength of these bio-composites is influenced by the physical and mechanical properties of the cotton fibers, fiber orientation, and composite composition. ²²⁶ OPEN IN VIEWER

The acoustic, thermal, and physical properties of composites made from waste cotton and pigeon pea stalk fibers were also studied (Figure 31(a) and (b)) and the result reveals high sound absorption coefficients and insulation properties, which are desirable characteristics for construction materials (Figure 31(d)). ²⁵⁷ The acoustic absorption values for the waste cotton and pea stalk-blended samples indicate that the sound absorption coefficient increases with frequency across all samples (S1C, S2P, S3C/P, S4C/P, S5C/P, and S6C/P). Examination of the waste composite samples after tensile testing revealed that fiber pull-out was significant in blends containing 6% fiber with a length of 4 mm. In contrast, composites with 20% fiber content and a length of 14 mm demonstrated the best matrix/fiber adhesion quality, as illustrated in Figure 31(c).OPEN IN VIEWER

A study highlighted the significance of recycling waste fibers for cement-based composites (CBCs), which can improve the mechanical behaviors and durability of construction materials with minimum environmental impacts. Additionally, Do et al. developed cellulose-based aerogel composites from pineapple leaf (PF) and cotton waste fibers (CF), which demonstrated high mechanical strength and low thermal conductivity, that lead them to be suitable for building thermal insulation. The PF/CF aerogel composites exhibited excellent thermal conductivity, ranging from 0.039 to 0.043 W m⁻¹ K^-1, as shown in Figure 32, indicating their effectiveness as thermal insulators. As the total fiber content increased, thermal conductivity rose from 0.041 to 0.043 W m⁻¹ K^-1 (Figure 32(a)). However, variations in the fiber ratio did not significantly influence the thermal conductivity due to minimal changes in porosity (Figure 32(b)). Similarly, Piekarska et al. investigated the use of waste cotton fibers as fillers in polylactide (PLA) composites, which showed enhanced thermal and mechanical properties, indicating their potential for construction applications.OPEN IN VIEWER

Taşdemır et al. investigated fiber-reinforced composite structures against their mechanical and thermal properties, made form waste silk and cotton fibers for improved construction. This research conclusion indicated that recycled cotton waste fibers can be effectively utilized in various composite materials for construction applications. These composites offer enhanced mechanical and thermal properties, sound and moisture insulation, and sustainability. The integration of such materials into the construction industry could contribute to more environmentally friendly practices and efficient waste management.^{206–209,223}

Recycled cotton fiber biocomposite in agriculture and furniture

The use of recycled cotton waste fibers in composites is gaining traction, especially for applications in agriculture and furniture. These composites bring sustainable replacement to traditional materials by leveraging the inherent properties of cotton waste to increase the performance and environmental footprint of the resulting products.^{123,169–172} Wang and his colleagues developed a method to turn short cotton fibers into a strong, eco-friendly paper material. This new paper could be used for many different purposes, including colorful papers and smart packaging. ²⁶⁵ This CCP demonstrates significant strength and water resistance, suggesting its utility in agricultural applications, where durability and resistance to moisture are crucial. Piekarska et al. didn’t directly address agricultural applications, but they did highlight the potential of waste cotton fibers as fillers for polylactide (PLA) composites, which could be extrapolated to agricultural uses such as biodegradable plant pots or mulch films. The improved thermal and mechanical properties of these composites indicate their suitability for such applications. Sakthivel et al. ²¹² further explored the use of recycled cotton and polyester fibers reinforced with recycled polypropylene (PP) for nonwoven composites, which could be utilized as construction materials for housing systems, potentially including agricultural structures. Some researchers also discussed the development of composites using waste cotton and other agricultural residues, such as pigeon pea stalks, for applications that require sound absorption, thermal insulation, and moisture resistance. ²²⁷ These properties are beneficial for agricultural applications, such as in controlled environment agriculture or storage facilities. On the contrary, other studies did not directly focus on agricultural applications provided insights into the mechanical and physical properties of waste cotton fiber composites, which could inform their use in agricultural contexts, such as in the development of responsive materials for sensing applications. In turn, this research indicates that recycled cotton waste fibers can be effectively utilized in composites for various agricultural applications. These applications range from packaging and mulching materials to construction elements for agricultural buildings and responsive materials for agricultural technologies. These studies collectively demonstrate the potential of these materials to contribute to sustainability in agriculture by repurposing textile waste and enhancing the performance of agricultural products. ²³⁶

In the context of furniture applications, Dhir highlighted the advantages of natural fiber composites (NFCs), including cotton fibers, for use in various industries, including furniture. NFCs are appreciated for their mechanical and physical properties, which make them suitable for molded materials that require moderate strength. Kucukali-Ozturk et al. ²⁰¹ discussed the use of recycled cotton fibers and polyethylene in composites designed for sustainable insulation panels, which could be applied in furniture or building applications, providing thermal and physical benefits. Baccouch et al. ¹¹⁴ focused on enhancing the fiber-matrix interface in cotton-waste-reinforced composite panels, which could be used in furniture construction, as shown in Figure 33(a). Chemical treatment of cotton fibers significantly improved the mechanical properties of the composites, highlighting their suitability for furniture applications. In a similar vein, Bodur et al. ²³² found that alkaline treatment of waste cotton fabric enhances the mechanical properties of low-density polyethylene composites. The optimal treatment conditions were identified as 1 M concentration and a soaking time of 5 h, leading to notable increases in tensile strength and Young’s modulus. This improvement is attributed to the roughened surface of the treated cotton fibers, as shown in Figure 33(b). These properties make the waste cotton fiber composite better suited for outdoor applications, especially in the agricultural sector. However, the mechanical properties deteriorated with increasing soaking time and concentration. In summary, the incorporation of recycled cotton waste fibers into composites presents a promising avenue for the development of sustainable materials in the agricultural and furniture sectors. These composites capitalize on the advantageous properties of cotton waste, such as biodegradability and mechanical strength, to create products that are both environmentally friendly and functionally superior. Research in this field supports the broader objectives of cleaner production and resource efficiency, contributing to the achievement of Sustainable Development Goals^123,169.OPEN IN VIEWER

Recycled cotton waste biocomposite materials in the sport industry

Utilization of recycled cotton fibers in composites for sports applications is an emerging area of interest as it corresponds with the sustainability and resource efficiency principles. While the provided papers do not explicitly discuss the application of such composites in sports, they offer insights into the properties and potential uses of recycled cotton fiber composites that could be relevant to the sports industry. Recycled cotton fibers have been shown to enhance the mechanical properties of various composites. For example, the incorporation of cotton waste fibers into polyethylene matrices has been shown to improve the elongation characteristics of the resulting composites. This suggests that such materials could be beneficial in sports applications where flexibility and impact resistance are important, such as in protective gears or flexible components of sports equipment. The enhancement of the engineering properties of concrete through the incorporation of recycled textiles could be extrapolated to sports infrastructure, where improved durability and energy absorption are desirable features on surfaces such as running tracks or courts. Additionally, the thermal insulation properties of cotton-waste fiber composites can be explored for sportswear or outdoor sports equipment. ¹⁸⁰ Sezgin et al. ¹⁸¹ developed high-value composite materials by integrating textile and packaging waste from two different sectors. They tested the acoustic insulation properties of the composite panels, finding that the sound absorption analysis revealed the composites acted like porous materials, with improved performance across the frequency range. In summary, while the direct application of recycled cotton waste fiber composites in sports has not been extensively covered in the literature, the properties of these materials suggest potential benefits for sports applications. The improved mechanical properties, such as enhanced elongation, tensile strength, and durability, indicate that recycled cotton fiber composites can be used in the development of sports equipment and infrastructure that are both environmentally friendly and performance-oriented. ²⁶⁵ Further research and development are needed to tailor these materials for specific sporting applications and fully understand their performance in such contexts.

Recycled cotton waste biocomposite materials in packaging industry

Innovative waste management strategies are spread in the technology and engineering sectors to bring environmental sustainability, particularly through waste engineering and effective technological solutions to address cotton waste issues. The bioeconomy concept has revolutionized the sustainable processing of cotton waste into bioproducts for packaging applications. Leal et al. ²³⁵ proposed that circular design can significantly minimize the use of additives and chemicals when recycling cotton waste for packaging materials. Reichert et al. explored the potential of utilizing cellulose from biobased materials for bio-packaging applications, emphasizing the opportunities for creating a bioeconomy through the processing of cotton waste for sustainable packaging. They highlighted the promising prospects of circular design in bio-packaging, as illustrated Figure 34. Additionally, bio-cellulose composites derived from cellulose offer a promising structural solution for sheet coating and binders, owing to their high degree of polymerization, modulus, and tensile strength, making them suitable for bio-composite production. ²²⁰ Reddy ²²¹ suggested that polymer composites made of cotton could be combined with fillers and additives and then reprocessed into various forms. Ramamoorthy et al. ²⁶⁴ suggested that cotton waste can be combined with feather fibers to create handspun yarns for packaging purposes. Montava-Jordà and colleagues ²⁶³ discovered that cotton fibers measuring between 10 and 30 μm in diameter and having a long, thin shape improved the strength and durability of a polymer composite material used for non-food packaging. This enhanced composite exhibited high tensile strength and desirable mechanical properties, making it well-suited for its intended purpose.OPEN IN VIEWER

Specifically, Wang et al. ⁸³ presented a novel approach for creating a renewable cellulose fiber self-reinforcing composite paper (CCP) from short cotton fibers, which demonstrates superior tensile strength and water resistance compared with commercial A4 paper. This CCP, with its potential for a wide range of applications, including colored and intelligent packaging papers, exemplifies the innovative use of cotton waste in packaging materials, as shown in Figure 35. ²⁶⁵ In contrast, while Wang et al. ²⁶⁵ focused on the creation of paper-like composites, other studies have explored the use of cotton waste fibers in combination with thermoplastics. Some researchers discussed the reinforcement of polyethylene with recycled cotton fibers to produce sustainable composite materials that are potentially applicable in packaging owing to their improved physical and thermal properties. ²⁶⁴ Similarly, others investigated the use of recycled cotton and polyester fibers in polypropylene composites, which could be tailored for packaging applications owing to their enhanced mechanical characteristics. ²¹² Do et al. ⁸³ introduced an innovative cellulose-based aerogel composite using cotton waste fibers, which exhibited excellent thermal insulation properties and mechanical strength, making it suitable for packaging applications that require thermal management.OPEN IN VIEWER

Furthermore, Srivastava et al. ²⁴⁰ discussed the development of biodegradable packaging films using lignocellulosic biomass, which includes cotton waste, in combination with biodegradable polymers, such as polyvinyl alcohol, highlighting the role of cotton waste in reducing plastic pollution. Jamshaid et al. investigated the creation of knitted hollow composites using recycled cotton fibers (RCF) and glass fibers (GF). These composites are suitable for packaging heavy-weight products across various industries, including aerospace, marine, automotive, civil infrastructure, medical prosthetics, and sports equipment, as illustrated in Figure 36. The flexural strength of RCF-reinforced hollow composites surpassed that of double-layered cardboard packaging material, highlighting their enhanced stiffness. The impact energy absorption of GF and RCF composites, as well as cardboard material, was also assessed. GF-reinforced composites consistently exhibited higher impact energy absorption than RCF-based samples. Furthermore, specimens with thicker tube walls, regardless of reinforcing fiber type, demonstrated improved impact energy absorption. The utilization of recycled fiber represents a significant stride towards environmentally friendly materials and waste reduction. Their performance, when compared to commercial packaging materials, suggests potential applications as replacements, contributing to a reduction in environmental burdens. Therefore, this research indicates that recycled cotton waste fibers can be effectively utilized in various composite materials for packaging applications. These composites not only help in managing textile waste but also contribute to the development of sustainable packaging solutions. ²⁴¹ These studies demonstrate the flexibility of cotton waste as a reinforcement material, which can improve the mechanical properties, thermal insulation, and environmental sustainability of packaging products.OPEN IN VIEWER

Automobile applications

Nonwoven fabrics, which are engineered fabrics created by mechanical, thermal, or chemical bonding or interlocking fibers, are increasingly being considered for use in the automotive industry owing to their versatility and cost-effectiveness.^{185–212,261} However, there are challenges associated with the use of recycled cotton fibers in nonwoven materials, particularly in terms of maintaining the quality and performance of end products. Mechanical recycling methods, such as shredding, can shorten the fiber length and reduce the fiber quality, which may limit the application of recycled textiles in demanding environments such as those found in automobiles. ²¹⁶ Despite these challenges, research has shown that nonwoven fabrics made from recycled cotton and other fibers possess desirable properties such as abrasion resistance, thermal resistance, and air permeability, which are important for automotive applications.^236–244 For instance, loop-bonded nonwoven fabrics created from recycled cotton and acrylic-blended fibers have shown desirable properties, such as abrasion resistance and water penetration resistance, which are beneficial for automotive applications where durability and resistance to elements are crucial.^245,246 Nonwoven materials made from recycled cotton fibers can be used for interior components, such as car seat covers, headliners, and insulation materials. These components benefit from the natural properties of cotton, such as breathability and absorbency, while also contributing to sustainability goals by reducing waste and consumption of virgin materials. ²⁴⁷ Additionally, the incorporation of recycled cotton fibers into nonwoven composites has been shown to improve sound absorption, which is a critical factor for acoustic comfort in vehicle interiors. ²¹³ The research examined the acoustic properties of nonwoven fibrous materials created from coffee husk and cotton waste, revealing that sound absorption is influenced by both the thickness of the materials and the ratio of coffee husk to cotton fibers. The study also showed that these materials were most effective at absorbing low-frequency noise, which is more harmful to human health than high-frequency noise (Figure 38). These advancements support the industry’s move towards greater sustainability without compromising performance or comfort. ²⁴⁸ OPEN IN VIEWER

Moreover, in cotton weaving, false self-edge formation results in waste in weft and warp yarns.^249–251 The extra weft yarn can account for 9%–10% of the waste, with the extra yarn length accounting for 7–9 cm on each side. Interestingly, researchers have analyzed the economic benefits and key technologies for overcoming weaving waste selvage, finding that efficient and reasonable use of bio-based materials offers better economic and environmental benefits.^249–251 Fera et al. ²⁰⁸ created stitch-bonded non-woven samples by recycling woven fabric selvage waste, as shown in Figure 39. The air permeability of the developed sample decreased its sound absorption performance. The test results highlight the importance of the sound absorption properties of sound-absorbing materials for automotive applications. ²⁰⁸ OPEN IN VIEWER

Medical and hygienic applications

Biopolymers, such as cotton, are utilized in biomedical packaging, antimicrobial materials, biosensing, and tissue engineering applications; cotton is a prime example of a natural fiber with over 95% cellulose content.^250,251 Therefore, the utilization of recycled cotton waste fibers as nonwoven materials for medical applications is an area of growing interest. Nonwoven fabrics are increasingly used in medical settings because of their cost-effectiveness and functional properties such as disposability, absorbency, and barrier protection. ²⁵² Interestingly, although nonwoven materials are advantageous for medical applications, the incorporation of recycled cotton fibers enhances these benefits. Recycled cotton, derived from garment waste or other textile by-products, offers a sustainable alternative to virgin cotton, reducing the environmental impacts associated with cotton cultivation and processing. ²⁵³ Moreover, the inherent properties of cotton, such as breathability, softness, and high absorbency, are preserved during the recycling process, making it suitable for medical textiles. ²⁵⁴ However, maintaining the performance standards required for medical applications is a challenge. Research shows that nonwoven fabrics made from recycled cotton can meet industry demands. For example, loop-bonded nonwoven fabrics combining recycled cotton and acrylic fibers demonstrate excellent durability, comfort, and moisture management, making them suitable for medical textiles. ²⁵⁵ Additionally, the abrasion resistance and water repellency of these fabrics can be optimized, which is crucial for protective medical garments. ²⁵⁶ Moreover, nonwovens made from recycled cotton fibers offer a sustainable alternative to traditional materials, aligning with the increasing demand for environmentally friendly and biodegradable products. ²³⁸ These nonwoven materials are suitable for single-use medical products, such as hygiene items, wipes, and other disposables because of their natural properties, including absorbency and comfort. ²³⁸ However, the mechanical recycling of cotton can lead to a reduction in fiber length and quality, which may limit the application of recycled textiles in certain contexts. ²¹⁶ Despite this, the development of nonwoven fabrics from recycled cotton has been shown to possess desirable properties, such as adequate moisture resistance, which is crucial for medical applications, without compromising insulation and acoustic properties. Furthermore, research has explored the link between cotton fiber classification and the physical and functional characteristics of nonwoven fabrics. This suggests that fibers can be selectively sourced based on quality for specific applications, which could improve the performance of medical nonwoven fabrics. ²³⁸ However, further study can lead to the wider adoption of recycled cotton nonwovens in healthcare, contributing to both environmental conservation and the advancement of medical textiles. ²¹⁴ Additionally, nonwoven fabrics made from recycled cotton and other fibers exhibit beneficial properties, including excellent absorbency, low electrostatic charge, comfort, disposability, and sanitation value, making them ideal for hygienic applications. ²⁶³ These fabrics can be designed for faster drying, enhanced durability, and a luxurious soft feel, making them ideal for hygiene applications. However, there are challenges associated with the use of recycled cotton, such as a reduction in fiber quality, which may limit the application of the resulting textiles. ²¹⁶ Despite these challenges, research has demonstrated that non-woven materials made from recycled cotton can be designed with specific properties such as thermal resistance, air permeability, and moisture vapor transmission, which are beneficial for hygienic applications.^216,236 Additionally, recycling cotton-based non-woven fabrics are being explored for their potential use in various hygienic products such as diapers, wipes, and medical textiles.^237,238,258 These materials are valued for their absorbency, softness, and disposability, which are critical for hygiene applications. The research has demonstrated that even lower-quality cotton fibers, often sold at discounted prices, can be effectively used in nonwoven applications, enhancing moisture management and fluid handling performance. ²³⁷ This suggests that the non-woven fabric industry could provide an alternative market for these fibers, which are less suitable for conventional textile manufacturing.

Packaging applications

Nonwoven fabrics composed of recycled cotton and polyester fibers can be utilized in various forms, including filling fibers and recycled yarn, making them suitable for packaging applications. ²³⁹ These non-woven fabrics can be engineered to possess desirable properties, such as uniform thickness, softness, and low rigidity, which are beneficial for protective packaging materials. However, there are challenges associated with the recycling of cotton waste, as the process can shorten the fiber length and reduce the fiber quality, potentially limiting the application of the resulting textiles. ²¹⁶ Despite these challenges, research has shown that nonwoven preforms made from a combination of polypropylene and cotton can exhibit satisfactory mechanical and thermal behavior, making them suitable for use in composite materials that could be applied in packaging. ²¹⁶ In the context of sustainability, the incorporation of textile waste nonwoven fabric as reinforcement in cement-based matrices has demonstrated improved toughness and stress-bearing capacity, indicating its potential for use in nonstructural packaging applications. Moreover, the selection of appropriate cotton waste, such as loosely knitted greige cotton fabrics, can lead to better quality recycled fibers and, consequently, higher-quality non-woven materials for packaging. ¹⁶⁷ Rodrigues et al. ²⁵⁵ studied the use of small cotton pieces for the production of wet-laid nonwoven fabrics. These pieces were shrunk to obtain recycled fibers, which were then refined using a process. The results showed that replacing bleached eucalyptus kraft pulp (BEKP) with 70% cotton waste fibers in wet-laid nonwovens reduced the use of virgin raw materials and improved the mechanical properties of the structures by 80% and 14%, respectively. The study also found that refining small cotton pieces was more promising than refining recycled fibers because fewer steps were required. This approach can be explored for various products and end applications, such as lampshades and flower packaging. Moreover, several studies have demonstrated that recycled cotton and polyester fibers can be effectively used to create non-woven mats with desirable properties, such as sound absorption, moisture resistance, and thermal insulation. These are achieved through various blending ratios and bonding methods, with a focus on maintaining the performance under high humidity conditions.^242,253 In addition, this research highlights the importance of physical properties, such as density, thickness, porosity, and air permeability, for packaging applications. These characteristics are crucial for packaging materials that require a balance between protection and breathability. Moreover, the creation of loop-bonded nonwoven fabrics from a blend of recycled cotton and acrylic fibers demonstrates potential for applications that demand abrasion resistance, water penetration resistance, and air permeability. ¹⁸² However, further research is needed to tailor these non-woven materials to specific packaging requirements and to evaluate their performance in packaging applications.