Enhancing the Mechanical Properties of ElectrospunPoly(3-hydroxybutyrate-<i>co</i>-3-hydroxyvalerate) FiberMats Using Deep Eutectic Solvents

In this study, the use of deep eutectic solvents (DESs) was considered for the first time to improve the mechanical properties of electrospun poly­(3-hydroxybutyrate-<i>co</i>-3-hydroxyvalerate) (PHBV) fiber mats. For this, different DES formulations, namely, Choline Chloride (ChCl):Urea:Water, ChCl:Glycerol (Gly), and Gly:Sodium Citrate (NaCitrate), were selected and evaluated at a concentration of 10 wt %, and their efficacy enhancing mechanical properties was compared against traditional plasticizing additives glycerol and acetyl tributyl citrate (ATBC). The impact of these formulations on PHBV fiber mats was evaluated in terms of thermal, crystallinity, and mechanical properties, both as obtained and after aging. All samples produced macroscopically consistent, self-supporting, and handleable nonwoven material sheets. The DES-containing PHBV showed a thinner, bead-free surface morphology but a rugose surface morphology. DSC results indicated that glycerol, ATBC, and Gly:NaCitrate (DES) exhibited the highest reduction in melting temperatures, with a notable 5.6 °C decrease for the mat containing Gly:NaCitrate. Interestingly, electrospun PHBV fibers containing DES revealed a larger quantity of β-form planar zigzag chain conformations, so-called β-form crystals. Tensile test results revealed that depending on the additive formulation, the mechanical performance of the samples was fundamentally different from each other. Among DESs, PHBV fiber mats with ChCl-based DES were excessively brittle. Surprisingly and interestingly, PHBV fiber mats containing Gly:NaCitrate exhibited an unreported significant increase in all mechanical properties, including modulus, elongation at break, and toughness. Overall, this study highlights the potential of DESs as unique additives to tailor the mechanical properties of electrospun PHBV materials.