# Bio-Based Polyester Fiber Substitutes: From GWP to a More Comprehensive Environmental Analysis
## 4 Results and Discussion  
### Feedstock Requirements  
As evidenced by the production pathways, current bio-based strategies follow particular substitution approaches, all starting from first-generation feedstock. In the case of bio-polyester fibers, they displace the fossil-based intermediary products in established production pathways, namely ethylene and para-xylene, by homologous alternatives derived from bio-feedstock. In doing so, they add production steps to derive the two compounds through fermentation and chemical modification of an alcohol, while a substantial part of the chain follows without major modifications (e.g., Amoco process for PTA, ethylene-to-MEG, polymerization, melt spinning). In the case of PTT, an entirely new bio-basedpath for PDO was developed using bacterial fermentation; ethylene for fossil-based PDO is not substituted simply because its conversion into PDO is financially unattractive. In the case of PLA, its novelty does not permit a comparison with a pre-existing fossil-based counterpart, except that it too uses microbial fermentation. Under these conditions, modeled scenarios are shown to have vastly different feedstock requirements, as shown in Table 1. Namely, in order to produce 1 kg of the conventional polyester, 0.199 kg of ethylene and 0.585 kg of para-xylene are needed. The two compounds are regarded as primary inputs, while additional inputs such as oxygen or water not listed here do not fall under the bio-based innovation (no C to replace). When crops displace these petrochemical inputs, the requirements for primary inputs are shown to rise substantially due to feedstock and process modifications. Partially bio-based fibers require 1.089 to 3.043 kg crop/kg fiber in addition to the unchanged para-xylene quantities. Moreover, corn-derived MEG is observed to have higher feedstock efficiency than the sugarcane-derived versions since it requires less feedstock than the other two variations. MEG from directly fermented ethanol has a higher sugarcane requirement than the one stemming from molasses. The latter comes from a by-product of crystal sugar extraction, which means that other products are extracted from the sugarcane mass in parallel; in the former case, after fermentation, the mass is burned for energy recovery. The feedstock requirements rise for fully bio-based scenarios, where they range from 1.53 to 6.43 kg crops/kg fiber. It should be noted that the present LCA only partially accounts for whether the crop is of natural or genetically modified (GMO) origin. Namely, in accounting for the spatial and mass distribution of global corn production, part of this feedstock grown in the USA is presumed to be GMO. This question remains of great relevance to public opinion. At this point, the contribution of feedstock to the aggregate environmental impacts of the fiber is not addressed, only the crop quantities. The latter will depend on the environmental intensity of said crops, i.e., how they are grown. Since agriculture is an environmentally intense activity, we explore the contribution of bio-based feedstock to different impact categories in sub-chapter 4.3 (Further Midpoint Categories). \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Scenarios**} & \multicolumn{2}{c}{**Feedstock Requirements**} \\ \hline \multirow{2}{*}{**Name (Polymer)**} & **Bio-Based** & \multirow{2}{*}{**Primary Input**} & **Quantity** \\  & **C Content** & & **kg Input/kg Fiber** \\ \hline \multirow{2}{*}{Scenario 0 (PET)} & \multirow{2}{*}{0\%} & ethylene & 0.199 \\  & & para-xylene & 0.585 \\  & & corn & 1.089 \\  & & para-xylene & 0.585 \\  & & sugarcane & 3.043 \\  & & para-xylene & 0.585 \\  & & sugarcane & 2.235 \\  & 20\% & para-xylene & 0.585 \\  & 100\% & corn & 4.476 \\  & 100\% & sugarcane & 3.043 \\  & & corn & 3.387 \\  & 100\% & sugarcane & 2.235 \\  & & corn & 3.387 \\  & 100\% & corn & 0.862 \\  & 27\% & para-xylene & 0.545 \\  & 100\% & corn & 4.019 \\  & 100\% & corn & 1.530 \\ \hline \hline \end{tabular}
\end{table}