RESUMEN
Long-chain aliphatic polyesters are emerging sustainable materials that exhibit polyethylene-like properties while being amenable to chemical recycling and biodegradation. However, varying polyester chemical structures results in markedly different degradation rates, which cannot be predicted from commonly correlated bulk polyester properties, such as polymer melting temperature. To elucidate these structure-degradability relationships, long-chain polyesters varying in their monomer composition and crystallinity were subjected to enzymatic hydrolysis, the rates of which were quantified via detection of formed monomers. Copolymers with poorly water-soluble, long-chain diol monomers (e.g., 1,18-octadecanediol) demonstrated strongly reduced depolymerization rates compared to copolymers with shorter chain length diol monomers. This was illustrated by, e.g., the 20× faster hydrolysis of PE-4,18, consisting of 1,4-butanediol and 1,18-octadecanedicarboxylic acid monomers, relative to PE-18,4. The insoluble long-chain diol monomer released upon hydrolysis was proposed to remain attached to the bulk polymer surface, decreasing the accessibility of the remaining ester bonds to enzymes for further hydrolysis. Tuning of polyester crystallinity via the introduction of branched monomers led to variable hydrolysis rates, which increased by an order of magnitude when crystallinity decreased from 72% to 45%. The results reported enables the informed design of polyester structures with balanced material properties and amenability to depolymerization.
RESUMEN
The cross-linked nature of vulcanized rubbers as used in tire and many other applications prohibits an effective closed-loop mechanical or chemical recycling. Moreover, vulcanization significantly retards the material's biodegradation. Here, we report a recyclable and biodegradable rubber that is generated by the vulcanization of amorphous, unsaturated polyesters. The elastic material can be broken down via solvolysis into the underlying monomers. After removal of the vulcanized repeat units, the saturated monomers, constituting the major share of the material, can be recovered in overall recycling rates exceeding 90%. Respirometric biodegradation experiments by 13CO2 tracking under environmental conditions via the polyesters' diol monomer indicated depolymerization and partial mineralization of the vulcanized polyester rubbers.
RESUMEN
Polyethylene deconstruction to reusable smaller molecules is hindered by the chemical inertness of its hydrocarbon chains. Pyrolysis and related approaches commonly require high temperatures, are energy-intensive, and yield mixtures of multiple classes of compounds. Selective cleavage reactions under mild conditions (