# Bio-Based Polyester Fiber Substitutes: From GWP to a More Comprehensive Environmental Analysis
## 2 Materials and Methods  
This study performs a comparative LCA of polyester and three types of its substitutes with varying levels of bio-based content. It aims to identify the environmental advantages and disadvantages of the bio-sourcing of polyester and point to the most influential parameters for the environmental performance of bio-based alternatives (in the context of the European bio-based economy). The functional unit of comparison is 1 kg of fiber, finished, at factory gate, while the scope of the study is cradle-to-gate, i.e., from the primary inputs (crop or fossil-based compounds) to the finished fiber, at factory gate. Life cycle inventories were modeled based on state-of-the-art production processes (see chapter Production Pathways and Scenarios) for every fiber. Background data for this modeling were retrieved from the ecoinvent database, version 3.6 (recycled-content system model). The entire modeling was conducted in the software tool Simapro, version 9.1.1.1. For the life cycle impact assessment (LCIA), the Environmental Footprint (EF) method as implemented in Simapro (i.e., _\"EF 3.0 Method (adapted), version 1.00\"_)--with its default characterization, normalization, and weighting factors--was applied in the first step (referred here as _Default EF_). However, the implementation of this method in Simapro does not account for biogenic CO\({}_{2}\) uptake and emissions during the life cycle; therefore, a modified version of the said impact assessment method was applied to account for carbon sequestered from the atmosphere during crop growth. Modifications in characterization factors for climate change impacts for the uptake of CO\({}_{2}\) from the air (factor -1 instead of 0), for biogenic emissions of CO\({}_{2}\) (factor of 1 instead of 0), and for biogenic carbon monoxide emissions (factor of 1.57 instead of 0) were added. No other characterization factors, normalization or weighting parameters were modified. This _Modified EF_ method, therefore, allowed us to determine the relevance of biogenic C net emissions in the production process of the fiber. Additionally, two more modified EF methods are produced by replacing the default weighting factors with distance-to-policy-target weights reported in [PERSON] et al. [36], which reflect the gap between the EU's current and the desired state in environmental impacts. Amongst others, the importance of climate change decreases with these alternative target weights, while the relevance of factors such as ecotoxicity, eutrophication, and acidification increases [36]. These modified methods allowed us to assess whether bio-based innovation was indeed aligned with the European environmental policy targets (binding and non-binding) as well as to perform a sensitivity analysis of our results. The impact assessment method where only these weights are changed is referred to as _Default Castellani_. Finally, the method where both elements, i.e., the characterization (same as in _Modified EF_) and the weighting factors, are modified is referred to as _Modified Castellani_. The characterization results are calculated for all 16 EF default impact categories included in this method. The single score results represent the aggregate scores after normalization and corresponding weighting and are expressed in points (Pt). Production pathways are represented in Figure 1, while LCIA results are summarized in Table 1 and Figures 2-6. In order to facilitate the interpretation of the results, the same color-coding is applied throughout the paper, where grey stands for fossil-based products, orange for partially bio-based, and green for fully bio-based products. In LCIA, a darker shade of bars refers to results of _Default EF_ and lighter to _Modified EF_. The production of fossil-based MEG and PTA is globally well-established. The traditional production of MEG starts with ethylene derived from natural gas. Ethylene is oxidized into ethylene oxide and subject to hydrolysis to arrive to MEG [28]. All the production steps are enchaned on the same production site.