Sorbic Acid–Tung Oil–Sulfur Terpolymer Prepared via Inverse Vulcanization and Its Application as Antibacterial and Toughness Modifier for Polylactide

Biopolymers as abundant, sustainable, and environment-friendly renewable material have been regarded as the best alternative to nondegradable fossil products. However, these biopolymers are often confronted with problems such as high prices, poor mechanical properties, and susceptibility to bacterial erosion. In the current study, inverse vulcanization was adopted to synthesize polymers with multisulfur segments cross-linked by plant-based sorbic acid and non-edible tung oil. The synthesized copolymer exhibited tailorable glass transition temperatures (0.3–24.8 °C) and rheological behaviors with modulus alterable within an order of magnitude. The addition of transesterification catalyst Zn(acac)2 lowered the activation energy of stress relaxation by ∼20 kJ/mol. Thanks to the dynamic reversible S–S bonds, this networked polymer also exhibited regulatable thermal self-healing behaviors. Moreover, in the blending with polylactide (PLA), the reversible dissociation of S–S bonds at high temperature facilitates the dispersion of polysulfides in the PLA matrix, which can be further improved by adding catalyst, adjusting monomer ratios, etc. As a result, the polysulfides not only toughen the PLA but also endow the blends with excellent antibacterial activities attributed to the intrinsic bacteriostatic sorbic acid and sulfur. Used as a modifer for bioplastics to adjust their mechanical properties and functions, polysulfides are expected to have potential applications in medical materials or food packaging fields.