The interaction between vulcanized rubber and various solvents is of significant interest in environmental and materials analysis, particularly for microplastic storage, analysis, and recycling. In this study, the absorption and desorption kinetics of rubber specimens (composed of a typical car tire-tread material) when submerged in a solvent and during subsequent drying were examined by monitoring time-dependent mass changes. When submerged in water and dilute ethanol–water mixtures (≤50% ethanol), the rubber exhibits a small mass gain <1% due to absorption. In contrast, pure ethanol and isopropanol cause mass loss of up to 13.5%, indicating that leaching dominates under these conditions. In acetone, the mass initially increases rapidly by 3.5% due to absorption before leaching takes over, and it loses 7.4% of its original mass. These results highlight the dual processes of absorption and leaching in rubber-solvent systems and emphasize the need for careful solvent selection when handling suspended rubber-based microplastics. During drying, water and low-% ethanol–water mixtures remain within <1% of their initial weight, whereas solvent desorption results in up to a 20% mass decrease in the other samples. Analysis of the leachate by IR spectroscopy, TGA, and Mass spectrometry revealed that the processing oils, shorter-chain additives, and antioxidants are most susceptible to leaching.
To develop and validate new methodologies for evaluating water-soluble polymer (WSP) biodegradation, this research investigates non-radiolabeled dextrans with varying molecular weights (10 kDa-500 kDa) and radiolabeled [carboxyl-14C] dextrans ([carboxyl-14C] only on the reducing end of the dextran polymer molecules, 30 kDa and 200 kDa) in screening and simulation studies across different environmental compartments. In activated sludge and river water screening studies, all dextrans exhibited rapid and extensive mineralization to CO2 (>70%) in 28 d, indicating molecular weight and carboxyl functionalization do not significantly influence biodegradation for the materials tested. Radiolabeled [carboxyl-14C] dextrans were assessed under more environmentally realistic conditions to accurately quantify primary (loss of parent) and ultimate (mineralization) biodegradation rates and understand transformation pathways. To determine transformation pathways, analytical techniques were developed including thin layer chromatography (TLC) and radiochemical gel permeation chromatography coupled with solid scintillation counting (Rad-GPC-SSC). In an activated sludge simulation study, both radiolabeled materials rapidly and completely biodegraded reaching >50% mineralization in 8 h and >75% after 6 d, with an ultimate biodegradation half-life of 6.5 h and 7.5 h, respectively. Loss of parent polymer was rapid with a half-life of 0.2 h for both materials. In a river water simulation study investigating [carboxyl-14C] dextran 200k, primary and ultimate biodegradation remained fast with half-lives of 1 d and 14 d, respectively. Enzyme assays confirmed dextranase-mediated fragmentation as a dominant transformation pathway. Together, these data provide a valuable framework for assessing the biodegradation of other WSPs.
