Controlled degradation of PET mediated by its crystallinity differences via ionic liquids catalysis for the preparation of high-performance hydrogel sensors

The high-value recycling of post-consumer PET requires breakthroughs in directed depolymerization and carbon chain topology regulation technologies. However, the long-range uniformity of the internal structure of PET, combined with the inability of existing catalysts to differentiate between disordered amorphous regions and ordered crystalline regions, renders the controlled degradation of PET a challenging area of research. In this study, we utilized metal-free phosphate diester ionic liquids (PDILs) to achieve the controlled glycolysis of PET (1500 to 1800 g·mol −1 ) for the first time. By exploiting the difference in degradation difficulty between the amorphous and crystalline regions, a two-stage degradation model “amorphous degradation-crystallization degradation” was employed to achieve controlled glycolysis of PET. Under the catalysis of PDILs, the molecular weight of PET particles decreased overall through the permeation of ethylene glycol and the sequential degradation of PET's amorphous and crystalline regions. The “crystallization protection” effect of the crystalline regions enabled the achievement of a high yield (>70 %) while maintaining controlled molecular weight equilibrium. In addition, this study presented a utilization strategy for oligomer by developing a conductive hydrogel sensor with enhanced mechanical properties. This approach established a novel upgrade pathway of “waste PET - oligomer - advanced materials” providing new insights into the controlled degradation of PET and the subsequent utilization of its degradation products. • Controlled degradation of PET using metal-free ionic liquids catalyst to obtain high-yield oligomers product. • Oligomers can be separated by simple centrifugation. • Controlled degradation follows the two-stage mechanism of “amorphous degradation - crystallization degradation” • A double network hydrogel is supplemented with glycolysis products of waste PET catalyzed by metal-free ionic liquids. • Application of oligomers to tough conductive hydrogel sensors by one-pot method.