**3.1 Textile recycling techniques**

Recycling is the process of breaking down a product or material to make a material of a higher or equal value (upcycling) or of a lower value (downcycling), in which textiles are commonly mechanically or chemically broken down to their fiber constituents [41]. Biodegradation is another method used to recycle waste and to break down organic materials into compounds.

hand, are not designed to decompose and may release toxic substances into groundwater and the surrounding soil. If the average life of clothing could be extended by only 3 months, it would reduce waste generation as well as their carbon

apparent pressure on scarce natural resources. Circular economy, on the other hand, aims to move away from the unsustainable linear model by decoupling economic activity from the consumption of finite resources and designing waste out of the system. When the recycling component is included, it helps to absorb the residuals of industrial and consumer use [35–36]. Accordingly, circular economy's

• Put an end to waste generation and pollution during the design stage.

order to direct toward a more sustainable behavior (**Figure 1**) [37].

Reusing is the concept of using undamaged parts of used products for

The textile industry's linear model of "make, use, and dispose of" represents an

Within that concept, a five-step waste management hierarchy was introduced in

Waste generation prevention has the highest significance followed by reuse.

manufacturing activities. When textiles turn into waste and are disposed by their consumers, recycling offers the opportunity to save raw materials and energy as well as to reduce pollution. Product/material recovery includes the activities like repairing, refurbishing, and disassembling, performed to regain the product value at the end of its life cycle. To dispose generated waste is the last step of the

Textile recycling routes can be categorized in different ways as follows:

1.Mechanical, chemical, thermal, and biological based on the nature of the

and water footprints, by 5–10% [19, 31–34].

principles may be given as follows:

*Waste in Textile and Leather Sectors*

hierarchy [17, 38–41].

process.

**Figure 1.**

**64**

*Waste management hierarchy [38–39].*

• Keep products and materials in use.

• Restore and regenerate natural systems.

#### *3.1.1 Mechanical recycling*

The difference between mechanical and chemical recycling is that wet processing is eliminated or reduced in the mechanical recycling system [44]. Most of the current recycling systems for post-consumer waste textiles mainly include reuse and mechanical processes.

The method of mechanical recycling, which is categorized as a secondary recycling approach, is composed of two main processes: sorting of the waste material and the mechanical decomposition of the fabric. The material to be recycled is sorted according to fiber type, color, quality, etc. Sorting for post-industrial waste may be performed with a risk of uncertainty as the fiber content and properties of the fibers may not be always known. The in-house reprocessing of manufacturingrelated waste represents recycling on the primary level [39].

The disintegration of textile material to a fibrous form through mechanical recycling is referred to as shredding or garneting [38, 40–41]. In mechanical recycling machines, the fabrics are cut into small pieces of 1 to 8 cm strips with a rotary blade and separated into single fibers through a process known as "picking," "pulling," or "tearing" by needle-equipped cylinders which have progressively smaller spiked surfaces. On such machines waste is fed through a conveyor belt of the front roller to be transferred to the spiked roller. Spiked roller rotates clockwise, and bottom roller, located under the spiked one, rotates anticlockwise. The distance between the rollers can be varied according to the type of input material, and the waste is opened while passing through rollers.

Chemical recycling for polyester also includes glycolysis, hydrolysis, and

**Mechanical recycling Chemical recycling**

*Understanding Denim Recycling: A Quantitative Study with Lifecycle Assessment Methodology*

Categorized as a secondary recycling approach

*DOI: http://dx.doi.org/10.5772/intechopen.92793*

Mechanical recycling process is too aggressive to

Heterogeneity of post-consumer waste worsens

*Comparison of mechanical and chemical textile recycling techniques.*

Mechanical recycling has been efficiently adopted by industry for recycling of single fiber

It is not as energy-intensive as chemical

Wet processing is eliminated

recycling

materials

**Table 1.**

retain fiber quality

constant quality retention

and energy requirement for heating and scouring processes [42, 44].

Chemical recycling is a promising process since it allows the recovery of a more valuable product in comparison to the products recycled by mechanical processes [34, 38, 42, 44]. As it uses a selective degradation method, chemical recycling is expected to be more suitable for large-scale recycling of blended materials, while mechanical recycling has been efficiently adopted by industry for recycling of single fiber materials. In products of cotton and polyester, the fibers can be chemically separated and then reformed into new fibers [13]. On the other hand, although chemical textile recycling has broader use than do the mechanical method, chemical and water consumption (70% lower in case of mechanical processing) for wet processing is high. Barriers to the widespread adoption of chemical recycling also include high costs, multiple processing steps requiring high operational knowledge,

Categorized as a tertiary recycling approach

The biggest challenge is that chemical recycling is

Chemical recycling allows a more valuable product in comparison to the products recycled by

Chemical recycling depends on the quality of the

Chemical recycling is expected to be more suitable for large-scale recycling of blended materials

processed waste to a limited degree

Involves chemical processing

very energy-intensive

mechanical processes

A comparison of mechanical and chemical textile recycling techniques are given

Biodegradation can be featured as a method used by nature to recycle waste and to break down organic materials into compounds by microorganisms such as bacteria, fungi, insects, worms, and others. Through biodegradation processes, it is possible for nature to clean up wastes, to provide nutrients for the growth of new lives, and to produce the energy necessary for various biological processes [46]. Biochemical transformation via fermentation is an attractive way for utilizing recycling textile waste. Cotton is typically composed of 88–96% cellulose, and it is possible to hydrolyze waste cotton by enzymatic or chemical methods to obtain glucose and then ferment it into value-added products. Biogas production from textile waste via anaerobic digestion is an alternative route to utilize solid waste from textile industry. Organic compounds in solid waste can be used as a raw material to produce desired products via bioconversion processes. On the contrary, thermal and chemical processes can convert both organic and inorganic compounds

Conventional thermal processing refers to the combustion of solid waste and its conversion into energy. Since solid waste from the textile industry contains a high

metanolysis processes.

in **Table 1** [38, 44].

*3.1.3 Bioconversion processes*

to value-added products [47].

**67**

*3.1.4 Thermal and thermochemical conversion processes*

Mechanical recycling has some shortcomings since the process is too aggressive to retain fiber quality and can result in a 75% loss of value after the first cycle. The mechanical process breaks may cause a tremendous loss in fiber length and a significant decrease in the material quality. For the process, longer processing times are needed, and the production rate is lower. As a result, blending with virgin material (especially in the case of cotton and wool fibers) for spinning processes is inevitable [38, 42, 44]. Consistently, waste collected from the manufacturing supply chain produces higher-quality recycled fibers than those collected from postconsumer waste. The pre-consumer and post-industrial waste can be respun into yarns which are further woven or knitted into fabrics and then used in apparel, upholstery, etc. [13]. Heterogeneity of post-consumer waste worsens constant quality retention.

Nonetheless, despite the drawbacks of mechanical recycling, the technology has shown promising for the reprocessing of denim fabric and garments [45].

#### *3.1.2 Chemical recycling*

The method of chemical recycling, which is categorized as a tertiary recycling approach, involves chemical processing of the fiber polymers, e.g., depolymerizing or dissolving. Chemical recycling depends on the quality of the processed waste to a limited degree and decomposes fibers down to the polymeric level [39]. Various chemical recycling processes have been demonstrated and developed. Chemical recycling of synthetic polymers and feedstock recycling depolymerize waste plastics into base chemical molecule called monomers with high purity [38]. The presence of additives and chemicals used in the polymerization process affects the purity and quality of the monomers obtained after recycling. The thermochemical process used to decompose polymers is referred to as pyrolysis, sometimes thermolysis. Pyrolysis is conducted at various temperatures and pressure levels and with the presence of catalysts or reactive gases. Pyrolysis processes are only economically viable for certain manufactured fibers including polyesters, polyamides, and polyolefins [13, 40].

*Understanding Denim Recycling: A Quantitative Study with Lifecycle Assessment Methodology DOI: http://dx.doi.org/10.5772/intechopen.92793*


**Table 1.**

*3.1.1 Mechanical recycling*

reuse and mechanical processes.

*Waste in Textile and Leather Sectors*

The difference between mechanical and chemical recycling is that wet processing is eliminated or reduced in the mechanical recycling system [44]. Most of the current recycling systems for post-consumer waste textiles mainly include

The method of mechanical recycling, which is categorized as a secondary recycling approach, is composed of two main processes: sorting of the waste material and the mechanical decomposition of the fabric. The material to be recycled is sorted according to fiber type, color, quality, etc. Sorting for post-industrial waste may be performed with a risk of uncertainty as the fiber content and properties of the fibers may not be always known. The in-house reprocessing of manufacturing-

The disintegration of textile material to a fibrous form through mechanical recycling is referred to as shredding or garneting [38, 40–41]. In mechanical recycling machines, the fabrics are cut into small pieces of 1 to 8 cm strips with a rotary blade and separated into single fibers through a process known as "picking," "pulling," or "tearing" by needle-equipped cylinders which have progressively smaller spiked surfaces. On such machines waste is fed through a conveyor belt of the front roller to be transferred to the spiked roller. Spiked roller rotates clockwise, and bottom roller, located under the spiked one, rotates anticlockwise. The distance between the rollers can be varied according to the type of input material, and the

Mechanical recycling has some shortcomings since the process is too aggressive to retain fiber quality and can result in a 75% loss of value after the first cycle. The mechanical process breaks may cause a tremendous loss in fiber length and a significant decrease in the material quality. For the process, longer processing times are needed, and the production rate is lower. As a result, blending with virgin material (especially in the case of cotton and wool fibers) for spinning processes is inevitable [38, 42, 44]. Consistently, waste collected from the manufacturing supply chain produces higher-quality recycled fibers than those collected from postconsumer waste. The pre-consumer and post-industrial waste can be respun into yarns which are further woven or knitted into fabrics and then used in apparel, upholstery, etc. [13]. Heterogeneity of post-consumer waste worsens constant

Nonetheless, despite the drawbacks of mechanical recycling, the technology has

The method of chemical recycling, which is categorized as a tertiary recycling approach, involves chemical processing of the fiber polymers, e.g., depolymerizing or dissolving. Chemical recycling depends on the quality of the processed waste to a limited degree and decomposes fibers down to the polymeric level [39]. Various chemical recycling processes have been demonstrated and developed. Chemical recycling of synthetic polymers and feedstock recycling depolymerize waste plastics into base chemical molecule called monomers with high purity [38]. The presence of additives and chemicals used in the polymerization process affects the purity and quality of the monomers obtained after recycling. The thermochemical process used to decompose polymers is referred to as pyrolysis, sometimes thermolysis. Pyrolysis is conducted at various temperatures and pressure levels and with the presence of catalysts or reactive gases. Pyrolysis processes are only economically viable for certain manufactured fibers including polyesters, polyamides, and polyolefins [13, 40].

shown promising for the reprocessing of denim fabric and garments [45].

related waste represents recycling on the primary level [39].

waste is opened while passing through rollers.

quality retention.

**66**

*3.1.2 Chemical recycling*

*Comparison of mechanical and chemical textile recycling techniques.*

Chemical recycling for polyester also includes glycolysis, hydrolysis, and metanolysis processes.

Chemical recycling is a promising process since it allows the recovery of a more valuable product in comparison to the products recycled by mechanical processes [34, 38, 42, 44]. As it uses a selective degradation method, chemical recycling is expected to be more suitable for large-scale recycling of blended materials, while mechanical recycling has been efficiently adopted by industry for recycling of single fiber materials. In products of cotton and polyester, the fibers can be chemically separated and then reformed into new fibers [13]. On the other hand, although chemical textile recycling has broader use than do the mechanical method, chemical and water consumption (70% lower in case of mechanical processing) for wet processing is high. Barriers to the widespread adoption of chemical recycling also include high costs, multiple processing steps requiring high operational knowledge, and energy requirement for heating and scouring processes [42, 44].

A comparison of mechanical and chemical textile recycling techniques are given in **Table 1** [38, 44].
