**8. Discussion**

This study mapped and discussed the environmental impact of recycled and bio-based polymeric fibers in a denim fabric. LCA was used as a framework since it is mostly recognized as a tool to quantify the overall impact from a systems perspective.

The data suggested that based on generic data, categorizing fibers as good or bad for the environment is incomplete. The production methodologies used for fibers and their influence on the subsequent product lifecycle are as equally important as fibers' direct environmental impact. A doubled life span of a garment decreases the average garment's climate impact by 52% considering the consumer will buy less garments in a given duration [103, 104]. Therefore, PET, and Recycled PET fibers in this study provided a longer lifetime to a product considering their fiber properties as stated in **Table 3**. On the other hand, fossil fuel and energy use related environmental impact categories such as Global Warming Potential and Abiotic Depletion were calculated as the highest for Article 02 where virgin PET was used. It should be noted that the energy system with which the fibers are produced here may change this data in either positive or negative direction. Once virgin PET is replaced with recycled PET, as in Article 03, these impacts reduce since fossil fuel usage is eliminated. The addition of Recycled PET content reflected the least amount of global warming potential impact. Both PET and Recycled PET presented the best impact for water use and land use categories. Since non renewable resources are already consumed for the virgin material production and post consumer PET remains as a waste for thousands of years in the system if not recycled, one should consider post consumer PET recycled materials (e.g. plastics from oceans) as a solution. On the other hand, the issue with microplastics shedding from synthetic/man-made based textiles which appears to be an important environmental problem, is not discussed in the LCA methodology.

Bio-based man-made polymers, such as Tencel, Refibra and PLA can be stated as the second group to increase the life span of a garment. Especially, Tencel and Refibra scored the lowest in every impact category analyzed in the study, except for the land use. In land use, the value is still lower than cotton. PLA, however, appears to have better values in every environmental impact category, when compared to PET. Although, the study shows that for Global Warming Potential, Eutrophication and Abiotic Depletion impacts, recycled PET is recorded better than PLA, it should be stated here that this result may change with the energy system used for the production of fibers. Besides, PLA is compostable and biodegradable in freshwater, marine and soil conditions.

To conclude, it is unlikely to state that one fiber can be the leader of sustainability alone as there is not one metric that is sufficiently broad enough to incorporate all the fields of sustainability. However, the key point for decreasing footprint of a denim fabric is to use both renewable resources and energy. Therefore, recycled and bio-based materials appear to be an effective solution for a lower environmental footprint in the life of a denim garment. Nevertheless, by bearing the fact that today's waste can be tomorrow's raw material in mind, sources of recycled PET (post or pre consumer) as well as recyclability of garments should be discussed in more detail, which are the topics of further studies.
