Sophorolipid‐Derived Unsaturated and Epoxy Fatty Acid Estolides as Plasticizers for Poly(3‐Hydroxybutyrate)

Unsaturated and epoxy fatty acid estolides were synthesized from the ω and ω‐1 hydroxy fatty acids derived from sophorolipids (SL). These estolides were utilized as additives in solution‐cast poly(3‐hydroxybutyrate) (P3HB) films and their plasticizing effects reported. Estolides in the P3HB film matrix resulted in slight reductions of melting and glass transition temperatures while the crystallinity remained relatively constant (±2.0 %). Scanning electron microscopy revealed irregular film surfaces in the presence of both estolides and the formation of pores within the P3HB film matrix. These irregularities influenced the tensile properties of the films by incrementally decreasing the tensile strength and moduli of the P3HB films and increasing their elongation. Curing the films for 3 months in the presence of estolide triggered an enhanced tensile strength and modulus when compared to the initial films. Irradiation was implemented in an attempt to crosslink the estolides. Results showed that radiation did not result in crosslinking but rather instigated chain scission and reduced the molecular weights by up to 81 % which further reduced the tensile strength, elongation and modulus of the P3HB films. These tensile property variations showed that while the tensile strength of the P3HB films declined in the presence of both estolides, the plasticity and elongation improved validating that these unique SL‐derived estolides can be effectively used as plasticizers in P3HB films.