Sustainability Approach of Recycled Denim Fabrics with a Life Cycle Assessment

Denim is one of the most common fabrics worldwide. The volume of jeans produced by textile manufacturers and used by consumers is substantial. For this reason, environmental degradation associated with denim fabric production is extremely dangerous. Studies in the literature on recycling in the denim industry are increasing day by day. Denim textile wastes are generated during the production process in textile factories or after consumer consumption. It is defined as any clothing or household items made of textile material that the consumer no longer needs and decides to discard [1].

The use of recycled materials (fiber, yarn, and fabric) in the production of denim products has become even more critical to increase the recycling potential of cotton to meet the current and future market demands of the textile and ready-made clothing industry. The decision to use recycled materials in products occurs at the design and product development stage and continues throughout the production [2]. Recycling is the process of transforming waste materials into new materials and objects. The recyclability of a material depends on its ability to regain the properties it had in its original state. The main components of recycling are reduction, reuse, and recycling, and it has progressed to the stages of rebuy as the 4th component and recovery as the 5th in the textile industry. These recycling processes are generally divided into two methods: mechanical or chemical recycling of fibers [3]. The main difference between mechanical and chemical recycling is the eliminating or reducing of wet processing in the mechanical recycling system [2].

In general, the recycled textile material production cycle is shown in Figure 1 [4]. Mechanical recycling is the process of making textile waste reusable through physical processes. It consists of two main processes: separation of waste material and mechanical separation of the fabric. In mechanical recycling, recycled materials are classified accordingly depending on fiber type, color, quality, etc. This process includes the sorting, cleaning, and re-fibering of textile waste. This fiber can then be used in new textile products [5].

Fig. 1.

The textile denim industry in our country is turning to sustainable and environmentally friendly production methods [6]. At this point, sustainable denim must include a life cycle at all stages to minimize the environmental harm. For this reason, designing life cycle analysis is more important than product design [7]. Life cycle assessment enables the calculation of wastes and emissions resulting from all inputs, such as energy, raw materials, chemicals, and water used to produce or deliver a product, process, or service. Accordingly, it is a scientific analysis method that creates opportunities for making necessary improvements and reducing natural resource consumption [8]. The life cycle of denim fabrics begins with the production of raw materials such as fiber and chemicals. In addition to raw materials, energy and water are also used in fabric production, which causes air and water emissions and production waste [2].

Alp et al. conducted a comparative study of yarns produced using the rotor spinning method with recycled cotton (r-COT) and a cotton (COT) blend used in different proportions. They examined the results of the properties of these yarns (volume irregularity, Uster hairiness, defect index, breaking strength, and elongation at break). All analysis results of the fabrics produced were examined, and it was determined that as the recycled cotton composition increased, the weft strength, warp and weft tear strength, relative water vapor permeability, thermal conductivity, and thermal absorption values decreased and thickness values increased [9].

In the study by Okandan et al. (2023), open-ended rotor (OE) yarns were spun from a 50/50 blend of recycled cotton (r-CO) and virgin cotton (C) fibers from pre-consumer cotton products. The effect of production parameters (rotor type, core type, and torque type) on yarn properties was investigated. It was concluded that 50/50 r-CO/C open-end rotor yarn samples produced with the narrowest rotor type, spiral, and green torque type caused lower hairiness and IPI, and higher elongation [10].

Alexander, E. S. (2023) measured the effect of using recycled cotton in denim fabrics on fabric strength quality and performance characteristics compared to minimum standards. As a result of the performance tests performed on denim fabrics, it was measured that the warp tear strength decreased; but all fabrics exceeded the minimum performance standards [11].

İvedi et al. (2019) ensured the collection of post-user denim waste. The cotton fiber was recycled and blended with virgin polyester for good tensile strength. Indigo-dyed fabric denim fabric was produced for pockets and compared with traditional pocket fabric. No significant effect on strength properties was observed between recycled yarn and conventional yarn. These results showed that fabric-containing materials could be used as pocket-recycled fabric for denim fabrics [12].

In Doba Kadem and Özdemir's study, some comfort features of denim fabric produced using recycled fibers after consumer use (PC denim) and original denim fabric of the same construction (REF denim) were determined and compared. In the study, air permeability, stiffness, and determination of dimensional change during the washing and drying of post-consumer denim fabrics were determined according to the standards. According to the results, this recycling process can be used effectively in denim production [13].

In the study by Erayman Yüksel and Korkmaz, LCA determination was made for recycled cotton products for sustainable textile designs. It was shown that the use of cotton has a lower environmental impact than that of recycled BCI cotton in all environmental impact categories [7].

In another experimental study, the life cycle analysis (LCA) of finished fabrics produced as denim and sportswear products of soy protein fiber, an innovative natural fiber, was performed. In the study, eight different blends consisting of cotton, soybean fiber and cotton/soybean blend yarns were used in the weft of woven fabrics selected from the denim and sportswear product group. It was observed that soy fiber content does not adversely affect the fastness and performance of woven fabrics. All fabric samples in the study underwent life cycle analysis (LCA) separately for denim and sportswear lines. The best result was in the life cycle analysis study of soybean fiber; it was obtained in fabrics using 90% cotton – 10% soy fiber in the weft for denim fabric and 50% cotton - 50% soy fiber yarn in sportswear fabric production [14].

In another paper, within the framework of increasing the contributions to sustainable development goals and reducing the water footprint, the sustainable production potential of a factory producing denim fabrics was studied in association with the sustainable development goals. As a result of the evaluations, it emerged as a more dominant view that the factory's contribution to sustainable development goals should be evaluated according to the total production capacity. The sustainability evaluation made according to the total production capacity determined that the factory contributed approximately 12% to Sustainable Development Goal 12 in the period examined, according to both the life cycle assessment and material input per service methods. Although there is inconsistency in the life cycle assessment and material input per service method results, it was predicted that there are economic and environmental gain potentials related to Sustainable Development Goals 13, 14, and 15, and the sustainable production potential of the factory can be increased [15].

With another study, the tensile strength, tear strength and softness values of re-cyled denim produced by partial recycling of cotton waste and denim fabrics produced from 100% cotton in a denim enterprise that had had a significant share in the sector in recent years were determined according to standards and the results were interpreted. As a result, it was determined that the recycling process in the denim production process can be used beneficially in denim production [16].

Another study investigated the contribution of the use of organic cotton fiber to the environmental impact of denim fabric, instead of conventional cotton fiber. The CML-IA method was applied to investigate the result of substituting organic cotton instead of conventional cotton. As life cycle inventory, primary production data were used during denim production as well as secondary data from the Ecoinvent Database. LCA application from the cradle to the gate was implemented using Simapro 8.5.2 software. As a result of that LCA study, all environmental impacts of denim fabric decreased with the use of organic cotton. A significant reduction in fresh aquatic ecotoxicity by 96% was achieved compared to the use of conventional cotton. Moreover, in terrestrial ecotoxicity and photochemical oxidation potentials, quite remarkable improvements were made, 90% and 57%, respectively [17].

In this study, denim fabrics were produced using weft yarns obtained from mechanically recycled fibers after consumer use, and the breaking strength, tearing strength, thermal resistance, water vapor permeability, air permeability, and fabric stiffness of those fabrics were determined according to the standards. The results obtained indicate that this recycling process can be used effectively in denim production. A life cycle analysis of the recycled denim fabrics was made using the SimaPro software program, and the environmental effects of the production were also revealed.

Weft yarns with an ayarn count of Ne 13/1 were used in the study. Six different raw materials were used to produce different denim woven fabrics, one of which is reference denim with a 3/1 Z twill weave structure. The warp thread of all fabrics was Ne 6,5/1 Open End 30% Recycled / 70% Cotton.

Warp and weft properties are given in Table 1 [18]. In this study, various recycled fibers (cotton, polyester, elastane) and different recycled cotton compositions (80-70-60-50-40%) were used. Yarns were produced with a new modified ring spinning method and the conventional ring spinning method, and denim fabrics were obtained from those yarns. The yarns used in the study are post-consumer recycled yarns.

Unevenness test results of the recycled blended yarns used in the study are shown in Table 2 [18], and the strength test results are given in Table 3.

When the unevenness measurements were examined, it was determined that the unevenness was higher with an increase in the rate of recycled cotton.

The hairiness of yarns containing recycled cotton is much higher than for yarns produced from conventional cotton. The lowest hairiness value belongs to the reference yarns, as expected. In yarns using recycled cotton, the excess of short and unproductive fibers attached to the yarn increases the hairiness value of the yarns. If the table is evaluated in general, it can be said that the yarn unevenness and some yarn properties (thin places, thick places, neps) increase with an increase in the recycling rate.

As can be seen in Table 2, it was observed that after the reference yarn, the sample with the highest strength values and the lowest recycle rate was number D2. It can be said that the strength (Rkm) decreases as the sample goes from D2 to D6, and in this case, the specific strength (Rkm) value decreases as the recycle rate increases in the mixture. As the recycling rate increased, the yarn strength values decreased up to 36.65% compared to the reference fabric. Tests and standards applied to denim fabrics with 5 different recycling rates are given in Table 3.

Within the scope of this study, denim fabrics with a high recycling rate were produced using yarns produced from the recycling of cotton, one of the most important raw material sources for the textile industry, and the performance properties and thermal comfort properties of these fabrics were examined. For denim fabrics, yarns were obtained using polyester and elastane, and recycled cotton was used at various rates as weft yarn. Denim fabrics with a 3/1 Z twill weave structure were produced using cotton (70% conventional cotton, 30% recycled cotton) yarn as the warp yarn. Tests of the breaking strength, tear strength, elasticity, thermal resistance, water vapor permeability, stiffness, and air permeability of the denim fabrics were made, and the change in the recycling rate was evaluated in terms of fabric usage performance. Within the scope of the study, it was observed that the structural properties of the fabrics produced and the composition of recycled cotton used affect the performance and comfort properties of the fabric. The effect of the cotton recycling rate on recycled denim fabrics was evaluated by LCA (life cycle analysis).

As a result of the LCA evaluation, with the use of cotton with a high percentage of recycling additives instead of the conventional cotton, as in the reference fabric, resource depletion (fossil fuels), global warming, depletion of the ozone layer, the toxic effect on human, freshwater, and terrestrial life, total water use, and other categories were observed to undergo a significant improvement.

In addition, since the process flow is the same for all samples during production, the rate of improvement in environmental impacts only comes from the effect of recycling.

Essentially, in this study, fiber was obtained by recycling from fiber and yarn wastes generated during the yarn production phase in a denim enterprise, where pre-consumer yarn was produced by mixing recycled fibers at different rates, and denim fabrics were obtained at different recycling rates. All production was made in the same denim facility.

With this study, it was aimed to reveal the importance of more environmentally friendly denim fabric production by increasing the recycled fiber ratio, and the impact of denim fabrics on the life cycle in terms of sustainability was evaluated with LCA. It was also stated that consumers can choose sustainable denim and that these fabrics are suitable for use in terms of performance properties.