Structurally Tuned Citric Acid–Based Polyester Thermoset with Balanced Barrier, Durability, and Biodegradation Performance

Conventional thermoset polymers play a vital role in high-performance applications. However, their reliance on nonrenewable resources and irreversible cross-linked structures hinders recycling, presenting significant sustainability and end-of-life challenges. In this study, a thermosetting polyester derived from citric acid, 1,4-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedimethanol was developed to overcome both the ecological and recyclability limitations of its predecessor. This material exhibits high tensile strength (93 ± 1.2 MPa) and maintains optical transparency (98.9 ± 0.6%). Additionally, it has barrier properties, with oxygen and water vapor transmission rates of 0.2 cc m–2 d–1 and 2.9 g m–2 d–1, respectively. The network is also recyclable via hot-press induced transesterification as supported by consistent mechanical performance and preserved film integrity after reprocessing. Moreover, it is fully degradable under composting conditions, with over 90% degradation achieved within 6 weeks. By integrating renewable monomers into a robust yet degradable architecture, the synthesized polyester thermoset reduces its reliance on petroleum resources and carbon footprint. These findings demonstrate the potential of PCCC as a multifunctional thermoset for next-generation sustainable applications.