Respirometry and Cell Viability Studies for Sustainable Polyesters and Their Hydrolysis Products

Significant research effort has been directed toward the development of sustainable plastics that are high-performance, bioderived, and/or degrade into nontoxic byproducts in natural or engineered environments (i.e., industrial composting facilities). We report the low cytotoxicity of poly(γ-methyl-ϵ-caprolactone) (PMCL)-based materials and the hydrolysis product of PMCL, sodium 6-hydroxy-4-methylcaproate. The concentration of sodium 6-hydroxy-4-methylcaproate that leads to 50% cell death (TD50) is 179 mM, a value that is similar to that of the hydrolysis product of polycaprolactone and higher than that of the hydrolysis product of polylactide. We also report the degradability of two PMCL materials with different architectures (cross-linked and linear triblock polymers) under simulated industrial composting conditions. These materials reached high degrees of carbon mineralization (>85%) over the course of 120 days as monitored by CO2 evolution. Finally, we examined the industrial compostability of a new aromatic polyester, poly(salicylic methyl glycolide). This material reached 89% carbon mineralization after 120 days, an important finding given the recalcitrance toward degradation of ubiquitous aromatic polyesters.