# Bio-Based Polyester Fiber Substitutes: From GWP to a More Comprehensive Environmental Analysis
## 4 Results and Discussion
### Further Midpoint Categories  
In addition to climate change, all 15 other impacts were examined in the impact assessment. Since carbon crediting affects only the emissions related to climate change, results for the remaining 15 categories are the same regardless of whether the applied EF method is modified or default. Here, 8 out of 15 most relevant categories are discussed in detail, while the remainder, which have low normalization results, can be found in Supporting information. Due to low relevance for the bio-based economy, the use of metal and mineral resources is, however, not elaborated here. Conversely, despite low normalization results, land use was still included due to its relevance in the bio-based economy in terms of agricultural surface needs. Note that any change in all the aforementioned impacts relative to Scenario 0 is still accounted for with upcoming single scores. The said results are found to largely depend on the bio-content and crop choice. As to the former, the gravity of acidification, all three eutrophication categories, ecotoxicity, water use, and land use generally increases with the bio-content, as attested by Figure 3. As to the latter, partially bio-based polyesters derived from sugarcane have the lowest results in acidification, eutrophication, ecotoxicity and water use and are largely comparable to those of polyester. Notably, the scenarios (2A, 2B) with MEG derived from sugarcane outperform those with MEG stemming from corn (3). To recall, scenarios 2A and 2B have or stem from a useful by-product in sugar/ethanol production (bagasse and molasses), which results in shared environmental burdens among the main and by-products. Moreover, out of all scenarios, fully bio-based scenarios have the worst impact results in acidification, eutrophication categories, ecotoxicity, water use as well as land use. Finally, the use of fossil resources does not decrease substantially, nor enough to balance out the increase in other impacts. For 8 out of 9 scenarios, fossil resource use is within 85% of the fossil consumption of conventional polyester. Conventional polyester is shown to have a better eutrophication profile than all bio-based fibers. It is identified that polyester causes eutrophication in the order of 0.17 g P  
Figure 3: Impact results for 8 chosen categories calculated with _Default EF_. Note that 100% of each impact category refers to the scenario with the highest results. eq./kg polyester (freshwater), 3 g N eq./kg polyester (marine) and 0.032 mol N eq./kg polyester (terrestrial). The said indicators increase with the bio-based content, up to 4.5, 4.7, and 5.3 times, respectively, as indicated in Figure 3. Limited comparison with previous studies is possible on this topic. An existing cradle-to-gate LCA has found that bio-based PET polymer, derived from sugarcane (comparable to Scenario 2B), has a eutrophication potential of 0.179 g P/kg polymer [24]. In our case, including melt spinning, the result for Scenario 2B amounts to 0.174 kg P eq./kg fiber. Furthermore, a recent study [25] found that freshwater and marine eutrophication increase 1.8 and 3.2 times, respectively, during manufacturing when switching from PET polymer to PLA. In our case, the increases amount to 3 times for freshwater and 2.2 times for marine eutrophication when comparing the PLA fiber (Scenario 7) to polyester (Scenario 0). The primary difference between our setups is that the said study [25] does not incorporate the transport and is elaborated on the polymer level for Europe only. Freshwater ecotoxicity impacts for bio-based fibers resemble those of freshwater eutrophication. Corn-based bio-polyester (Scenario 3) has the poorest ecotoxicity profile, its result being 4.9 times higher than Scenario 0. Corn agriculture is characterized by the notable use of pesticides such as glyphosate or atrazine, which contribute substantially to ecotoxicity profiles (high characterization factors).