# Bio-Based Polyester Fiber Substitutes: From GWP to a More Comprehensive Environmental Analysis
## 4 Results and Discussion
### Climate Change Impact  
Climate change impact (CCI) has the highest weight in the single score results of the EF impact assessment method, reflecting its relevance in the overall environmental narrative of the EU. For this reason, the results of climate change impacts are presented and discussed in the first step of the assessment. Figure 2 shows the CCI results with the _Default_ and the _Modified EF_, the latter of which incorporates biogenic C uptake and emissions (as described in Materials and Methods). Since [PERSON] and [PERSON] [32] find that presenting only the CCI results obtained with carbon crediting in a cradle-to-gate study is misleading, we also take the opportunity to not only explore the relevance of the biogenic C but address the issue of carbon crediting on a solid example. When _Default_ EF is applied (i.e., darker bars in Figure 2), only three scenarios (2A, 2B, 7) are shown to perform within a \(\pm\)10% range of the conventional polyester, which is associated with 4.07 kg CO\({}_{2}\) eq./kg fiber. All other scenarios far surpass the baseline, rising up to 7.13 kg CO\({}_{2}\) eq./kg fiber for bio-based polyester derived from corn. Except in the case of PLA fiber, CCI is found to rise with the bio-content. Contrary to it, _Modified EF_ (i.e., lighter bars in Figure 2) leads to a completely different conclusion on the bio-based fibers as all perform notably better than the conventional polyester. Unlike 4.10 kg CO\({}_{2}\) eq./kg polyester, bio-based fibers are shown to have emissions as low as 1.54 kg CO\({}_{2}\) eq./kg fiber when crediting is applied. Furthermore, CCI decreases with the increasing bio-based content. Namely, when comparing the correspond  
Figure 2: Climate change impacts calculated with _Default_ EF (darker bars) and _Modified EF_ (lighter bars) methods. Note that the difference between the dark and light bars for each scenario reflects the biogenic carbon embedded in the fiber. The relative change between the two results is therefore calculated as (modified – default)/default result and illustrates the impact of carbon crediting on climate change results. ing partially and fully bio-based scenarios (1 vs. 3, 2A vs. 4A, 2B vs. 4B, 5 vs. 6), the latter display lower climate impacts; between these scenarios, we observe that CCI decreases from 32 to 41% by substituting not only MEG/PDO but PTA as well. Regardless of the method, we observe that Scenario 1 with a corn-derived MEG has a higher climate impact than the sugar-derived ones (2A, 2B). In comparison, such a conclusion is consistent with the finding of [PERSON] et al. ; in their cradle-to-grave study on GHG emissions, they identified that partially bio-based PET polymer from corn has higher climate results than the one from sugarcane ([PERSON] et al., 2016). Moreover, [PERSON] and [PERSON] ([PERSON] and [PERSON], 2019) had found that partially bio-based PTT polymer (here comparable to Scenario 5) has emissions of 4.1 kg CO\({}_{2}\) eq./kg polymer. Indeed, our _Default EF_ calculations point to a comparable level of emissions (4.71 kg CO\({}_{2}\) eq./kg fiber) for Scenario 5. Finally, [PERSON] et al. showed that NatureWorks' brand of PLA polymer emits 3.2 kg CO\({}_{2}\) eq./kg polymer without and 1.3 kg CO\({}_{2}\) eq./kg polymer with carbon crediting ([PERSON] et al., 2016). Their results are equally in the range of ours, as we add the melt spinning. Furthermore, on the topic of two impact methods, darker bars in Figure 2 reflect the fossil-based process emissions in the production chain of fibers. The difference between darker and corresponding lighter bars highlights the role of CO\({}_{2}\) sequestered from the atmosphere via crops' photosynthesis. The gap is thus displaying the carbon capture since the sequestered C eventually ends up embedded in fiber mass. The extent of this effect is portrayed by the relative change where we see the resulting decrease in emissions. The lighter bars hence represent net CO\({}_{2}\) eq. including all emissions and when this uptake is taken into account.