Harnessing the Potential of Biobased Furandicarboxylate Polyesters in Manufacturing Sustainable Films, Fibers and Nanofibers

Poly(alkylene furanoate)s (PAF) are the most credible bioderived alternative to oil-based poly(alkylene terephthalate)s, as they show superior thermomechanical and functional properties and are therefore attractive for applications in the packaging, textile, and biomedical fields. This work summarizes some of the most recent and promising developments in the processing and characterization of PAFs with variable alkyl chain length and PAF/polylactide (PLA) blends and nanocomposites, highlighting the advantages and challenges of each processing technique and the main thermomechanical and functional properties of the resulting films, fibers, and nanofibrous mats.<br/><br/>Solvent mixing and casting have been used to prepare PLA/PAF films, and their microstructural and thermomechanical properties were evaluated as a function of PAF concentration (5–30 wt%) and type (4–10 carbon atoms in the alkyl subunit). For neat PAFs, an increase in the alkyl chain length promotes a decrease in T_g and T_m and an increasing tendency to crystallize. However, the latter is true only for PAFs with an even number of methylene groups in the alkyl subunit, while crystallization is generally hindered for the odd-numbered ones. For PLA/PAF blends, the added PAFs are effective in mitigating one of the most important drawbacks of PLA, i.e., its brittleness, as the strain at break of the resulting blends is up to 30 times higher than that of neat PLA. Adding PAFs to PLA also increases its gas- and UV-shielding properties while keeping good transparency in the visible range, which is very desirable for packaging applications. The permeability and diffusivity to N₂, O₂, and CO₂ further decreases with the addition of reduced graphene oxide (rGO), which also promotes blend compatibilization and microstructural refinement [1-3].<br/><br/>The same PLA/PAF blends were also processed to produce fibers, both through solutions spinning and through melt spinning, and a detailed statistical analysis was performed to establish the optimal drawing conditions for each composition. Also in this case, the addition of a small (5-10 wt%) fraction of PAFs (with either short- or long alkyl subunits) promotes a remarkable increase in the strain at break compared to neat PLA [4] and, in some cases, also a simultaneous enhancement in the mechanical strength and elastic modulus. Following SEM observations, this effect has been attributed to the orientation and possible crystallization of the PAF phase and a plastic-rubber transition of PAF domains in the strain-hardening phase of the stress-strain curve.<br/><br/>Finally, we explored, for the first time, the production of nanofibrous mats made of poly(butylene 2,5-furanoate) (PBF) and poly(pentamethylene 2,5-furanoate) (PPeF), which have very similar chemical structures but remarkably different physical and mechanical properties [5]. A detailed morphological analysis of the resulting non-woven mats, carried out through SEM analysis, allowed the screening of the best processing conditions for PBF and PPeF. The resulting mats are not cytotoxic, promote cell adhesion without any surface treatment, and allow the retainment and controlled release of model drugs (e.g., dexamethasone), thus being promising for biomedical applications, for example as patches for transdermal drug delivery.<br/><br/>[1] Fredi, G.; Rigotti, D.; Bikiaris, D. N.; Dorigato, A., <i>Polymer </i><b>2021,</b> <i>218</i>, 123527.<br/>[2] Rigotti, D.; Soccio, M.; Dorigato, A.; Gazzano, M.; Siracusa, V.; Fredi, G.; Lotti, N., <i>ACS Sustainable Chemistry and Engineering </i><b>2021,</b> <i>9</i> (41), 13742-13750.<br/>[3] Fredi, G.; Dorigato, A.; Dussin, A.; Xanthopoulou, E.; Bikiaris, D. N.; Botta, L.; Fiore, V.; Pegoretti, A., <i>Molecules </i><b>2022,</b> <i>27</i>, 6371.<br/>[4] Perin, D.; Rigotti, D.; Fredi, G.; Papageorgiou, G. Z.; Bikiaris, D. N.; Dorigato, A., <i>Journal of polymers and the environment </i><b>2021,</b> <i>29</i>, 3948–3963.<br/>[5] Santi, S.; Soccio, M.; Fredi, G. (corr).; Lotti, N.; Dorigato, A.,. <i>Polymer </i><b>2023,</b> <i>279</i>, 126021.