# Bio-Based Polyester Fiber Substitutes: From GWP to a More Comprehensive Environmental Analysis
## 5 Conclusions  
The here summarized project performed a comparative LCA of fossil-based polyester (originating from fossil-based PET) and its bio-based substitutes--i.e., bio-polyester (drop-in), PTT fiber (smart drop-in), and PLA fiber (novel). All of the aforementioned fibers are produced here by melt spinning the homonymous polymers. Currently, all state-of-the-art production processes of these bio-based substitutes use first-generation feedstock, i.e., crops, predominantly corn and sugarcane. Production pathways of bio-based and fossil-based PET and PTT are found to have significant overlaps, which is a strong point for the use and retrofitting of the existing production capacities. As for the impact assessment, several common trends are observed across all presently examined fibers. Only three out of nine substitutes are found to be in the range of polyester, based on the overall scores (_Default EF_). The remainder offer no real environmental advantage since single scores are higher than for the incumbent. Moreover, the performance of bio-polyester and PTT fibers is shown to be strongly influenced by the profile of bio-PTA since this monomer accounts for a prevailing part of their C contents. More accurate modeling of PTA is therefore necessary for the future. We find that conclusions on climate results significantly depend on whether carbon crediting is applied or not. Climate impacts decrease for the same fiber up to 70% when biogenic carbon is accounted for. However, for this reduction to hold in the long(er) term, circular economy principles are mandatory. Otherwise, carbon crediting may end up as a method that artificially reduces the climate impacts of bio-based products as previously suggested. We also show that highly relevant impacts for all examined bio-based fibers are acidification, eutrophication (terrestrial, marine, freshwater), ecotoxicity, land and water use. Their impacts are found to rise with an increasing bio-content, while a sizeable part of the aforementioned impacts is directly linked to the used feedstock. Our study thus confirms that the adverse effects of bio-sourcing on non-climate impact categories are overlooked if not accounted for. Finally, the consumption of fossil resources is shown to drop only slightly relative to conventional polyester, by which we also show that the fossil-fuel dependency of the process chain does not decrease simply by a change to bio-based starting materials. In order to mitigate the adverse effects of bio-sourcing, we identify three major options--search for other functional substitutes of polyester, revert to feedstock diversification or improve the agricultural practices. In the first case, other bio-based fibers with favorable material properties should be considered, e.g., polyethylene furanoate. In the second case, the so-called second-generation feedstock should be considered and involves lingo-cellulosic waste and products such as wood mass, stalks, leaves, etc. As of yet, all the processes using such feedstock are only at the very beginning of development, and it will take significant time to catch up with present processes, based on first feedstock generation. In the last case, the environmental intensity of agriculture is to be mitigated by reducing the use and pollution of water and the use of pesticides and fertilizers, all of which are linked with acidification, eutrophication, and ecotoxicity. While the first strategy may have positive consequences on the plastic and textiles sectors, the mitigation of agricultural impacts should have a spill-over effect on all domains of the bio-based economy. In summary, taking into account the constraint of this research and the currently available technologies, this project identified important implications for bio-based textiles. Bio-based alternatives are found to be environmentally uncompetitive with conventional polyester. When European distance-to-target weights are applied, bio-based products are found to be counterproductive in mitigating environmental impacts.