Insights into the synthesis of PEF from FDCA: steps toward environmental and food safety excellence in packaging applications

Poly(ethylene 2,5-furandicarboxylate) (PEF) is considered today as a very promising biobased polymer for packaging applications. The main reason lies in its extraordinary barrier properties: oxygen permeability in PEF is reduced by a factor of about 10 with respect to poly(ethylene terephthalate) (PET) (1). In terms of the synthesis of PEF, scientific literature describes synthetic procedures based on the transesterification of the dimethylester of the 2,5-furandicarboxylic acid (2,3,4). This research, instead, aims at studying the possibility of a practical and profitable synthetic route of PEF starting from the 2,5-furandicarboxylic acid. In this respect two catalysts, zinc acetate (ZnAcO) and aluminum acetylacetonate (Al(acac)3), chosen for their compatibility with food contact applications and for featuring a potentially reduced environmental impact, were investigated. The synthesis was performed by using tight reaction conditions: low excess of diol and short reaction time. Indeed, the use of high amount of glycol could lead to the ether-bridges (DEG) formation, which significantly reduces the extremely valuable barrier performances of PEF; high polymerization times lead to material yellowing, indicating the occurrence of by-side reactions. Different catalyst amounts and addition times were tested and the obtained polymers were characterized in terms of inherent viscosity, color (absorbance at 400 nm), and diethylene glycol content, as summarized in Table 1. Since titanium (IV) butoxide (TBT) is the most used catalyst in the PEF syntheses, PEF samples prepared with it were reported as a reference for the present study. Results show that ZnAcO and Al(acac)3 are very promising catalysts for the PEF polymerization from FDCA, because the use of ZnAcO allows them to reach relatively high inherent viscosity in the usual polymerization procedure, while the use of Al(acac)3 leads to materials characterized by very low yellowing. In this case, the moderate molecular weight obtained for aluminum-based PEF was overcome by a final step of solid state polymerization (SSP), which increases the viscosity from 0.25 to 0.39 dL/g in just 3 days. Finally, the obtained amorphous PEF samples result filmable and therefore suitable for the manufacturing of various packaging articles.