Synthesis and Fabrication of Betulin-Derived Polysulfide and Polysulfoxide Electrospun Fibers for Fruit Preservation

Plant-derived biocompounds play a crucial role in the field of renewable materials due to their sustainability as they can be converted into monomers for polymerization, comparable to numerous monomers obtained from petroleum. In this work, betulin, a triterpene derivative with antibacterial properties obtained from birch tree bark, was esterified to produce two varieties of α,ω-diene derivatives with different lengths of methylene spacers. These derivatives were then copolymerized with 2,2'-(ethylenedioxy)diethanethiol using thiol-ene photopolymerization. We optimized and confirmed the polymerization parameters such as solvents, catalysts, and monomer concentrations. These analyses allowed for the obtainment of polysulfides with a high molar mass of up to 38.9 kg/mol under the optimized conditions. Furthermore, the polysulfides were converted into polysulfoxides by using a dilute hydrogen peroxide solution. Thermal analysis of the obtained polymers revealed excellent thermal stability (up to 300 °C) and tunable glass transition temperatures depending on their molar mass and composition. We successfully produced fibers with a diameter of approximately 3.9 μm by using the electrospinning technique. The morphology and hydrophobicity of the fibers were analyzed by using scanning electron microscopy and water contact angle analysis. Plant-derived polymeric fibers exhibited good cellular biocompatibility and broad-spectrum antibacterial activity, making them promising candidates for applications in fruit preservation.