**3. An overview of denim-related life cycle assessment (LCA) studies**

The global denim jeans market is expected to reach almost \$60 billion in 2023. Besides, it is well known that the entire lifecycle of one pair of denim jeans has a significant environmental impact so far as the world's ecological balance is concerned. As a result, with the effect of increasing consumer awareness, denim industry has shifted toward adopting more sustainable manufacturing processes, which in turn makes it necessary more than ever for the industry to systematically evaluate the environmental impacts of denim fabric production from a life cycle perspective in an attempt to effectively handle consumer related activities.

Despite the sizeable consumption of denim garments, there are very limited studies regarding LCA of such products. Levi Strauss and Co. was one of the first brands conducting an LCA to analyze the environmental impact of a pair of Levi jeans for its entire life span. Their study indicated that about 3781 L of freshwater was consumed and 33.4 kg CO2 eq of greenhouse gas (GHG) was emitted throughout the entire lifespan of a pair of cotton jeans. Moreover, it showed that consumer care had the largest impact (37%) on climate change over the life cycle, which was followed by the fabric product (27%) [29].

Hackett et al. studied the cradle-to-gate phases of the life cycle assessment of a pair of denim jeans and a T-shirt utilizing ReCiPe 2008 methodology. The study demonstrated that cotton fiber cultivation and harvesting most significantly contributed to the overall environmental impacts, and that the use of fertilizers, pesticides, and irrigation water had a direct influence on this very impact [30].

Karthik and Murugan studied carbon foot print (CF) values for all activities involved in manufacturing denim and identified the relevant processes and technologies contributing most to greenhouse gases (GHG) emissions [31].

Vos performed a water footprint (WF) assessment on a pair of blue jeans using a hybrid approach of the LCA and water footprint assessment (WFA) methods. The results revealed that raw materials (64%) and consumer washing (32%) dominated the blue WF [32].

Morita et al. in their study, investigated the environmental (climate changes [CC]) and energy performance (primary energy demand [PED]) of jeans manufacture in Brazil using LCA method. They found that CC and PED impacts associated with the production of one pair of jeans were 7.86 kg CO2 eq and 124 MJ, respectively. Moreover, they proposed scenarios based on cotton and yarn imports as well as jeans themselves from the United States, in addition to the replacement of natural gas for wood. They demonstrated that the decreased impact of CC (4.44 kg CO2 eq/FU) belongs to the production of jeans in Brazil using wood for heating [33].

Akı et al. conducted an experimental work regarding the life cycle assessment of a denim fabric with and without recycled fiber content using SimaPro software as assessment tool and the inventory based on denim production figures of a denim company in Turkey. They concluded that global warming potential decreases by 5%, eutrophication drops by 8% and abiotic resource depletion by 3% with each addition of 10% recycled content in the fiber blend used for denim production. In their following study, the authors mapped and discussed the environmental impact of recycled and bio-based polymeric fibers in a denim fabric using LCA as a framework. In doing so, the methodology given in the authors' previous study was employed and all of the calculations were performed from cradle to denim factory gate. Furthermore, the inventory was based on the 2020 denim production figures of a denim company in Turkey. The results indicated that Tencel and Refibra scored the lowest in every impact category analyzed, except for the land use. They also showed that PLA appeared to have better values in every environmental impact category, when compared to PET, though recycled PET performed better than PLA for Global Warming Potential, Eutrophication and Abiotic Depletion impacts [34, 35].

Zhao et al. analyzed the virtual carbon and water flows in the global denimproduct trade using the footprint methods. The findings of the study indicated that virtual carbon in the global denim trade increased from 14.8 Mt. CO2e in 2001 to 16.0 Mt. CO2e in 2018 whereas the virtual water consumption decreased from 5.6 billion m3 in 2001 to 4.7 billion m3 in 2018. Moreover, the results revealed that both the denim fabric and cotton fiber production contributed the most of the carbon emissions and

#### *Life-Cycle Assessment as a Next Level of Transparency in Denim Manufacturing DOI: http://dx.doi.org/10.5772/intechopen.110763*

water consumption, and that polyester blended denim had 5% greater carbon footprint and 72% lower water footprint than its cotton counterpart [36].

Fidan et al. performed an integrated sustainability assessment of denim fabric made from mechanically recycled cotton fiber by applying combined heat and power plant (CHP) for fabric production. In that study, global warming potential (GWP), acidification potential (AP), eutrophication potential (EP), water use, and cumulative energy demand (CED) were taken as environmental impact categories, and accordingly, the LCA results revealed that the highest environmental impact improvements were obtained as 98% water use, 90%EP, 74% AP, 63% CED, and 54% GWP when 100% recycled cotton and CHP plant were used in the production [37]. Fidan et al., in another study did investigate the benefits of organic cotton fiber use in denim production with the help of life cycle assessment methodology based on four different scenarios. The environmental impact categories of global warming potential, eutrophication, terrestrial ecotoxicity, acidification, and freshwater ecotoxicity potential were analyzed using CML-IA method. The results showed that the lowest environmental impacts were obtained when 100% organic cotton fiber (scenario 4) was employed as raw material, such that it improved terrestrial ecotoxicity and freshwater ecotoxicity potential by 87% and 59%, respectively [38].

Luo et al. extended the LCA research boundary to the entire life cycle of textile products by adopting the process-level modular water footprint (WF) assessment method proposed by Li et al. [39] into both carbon and water footprints assessment of textile products. In doing so, the key issues such as module decomposition based on complex process flows and technology options, together with assembly methodology of process modules in varying product life cycle stages, were taken into account. They accordingly utilized a case study of a pair of cotton jeans to verify the feasibility as well as flexibility of the method. The results of the study revealed that the greenhouse (GHG) emissions, water consumption, water eutrophication and water eco toxicity impacts for the life cycle of one pair of jeans from cotton cultivation to product disposal were 90.37 kg CO2 eq, 13.74 m3 H2O eq, 1.67 × 10−2 kg PO4 3− eq and 112.41 m3 H2O eq, respectively, and that finishing, cotton cultivation and laundering processes were major contributors to the environmental impacts under discussion. Finally, the study proposed 12 scenarios based on the Chinese consumers' care patterns, which pointed out that the washing with top loader washing machine, line drying, and no ironing once a month in 2-year lifetime of jeans was the best combination by contributing 1.86%, 4.86%, 19.00%, and 1.08% to the total CF, WSF, water eutrophication footprint, and water ecotoxicity footprint, in turn [40].

The existing studies on LCA analysis of denim products (fabrics, garments), majority of which focuses on cotton based denim, imply that the scope of researches may be broadened toward the works on both renewable resources and recycling of materials to see the sustainability rate of a product.
