Polylactic acid is an aliphatic polyester material derived from biomass, which has good biocompatibility and biodegradability, as well as advantages such as high mechanical strength, good transparency, and easy processing and molding. It is the largest synthetic degradable plastic in industrialization. Polylactic acid can be prepared by direct dehydration polymerization of lactic acid and ring opening polymerization of lactide.
Polylactic acid is aliphatic polyester made from lactic acid through processes such as oligomerization, cyclization, and polymerization. The conversion process of polylactic acid is as follows - starch extracted from crops such as corn is hydrolyzed and fermented by microorganisms to produce lactic acid, which is further converted into polylactic acid through condensation polymerization or ring opening polymerization. Due to the presence of both hydroxyl (- OH) and carboxyl (- COOH) groups in lactic acid monomers, they can undergo condensation reactions with the carboxyl and hydroxyl groups of another lactic acid monomer, respectively.
Microplastics (MPs), as carriers of pollutants, have received widespread attention due to their environmental impact. However, the adsorption behavior and antibacterial mechanism of MPs exposed to the environment are limited. Here, the adsorption of tetracycline (TC) by polylactic acid (PLA), polyvinyl chloride (PVC), and polyethylene (PE) MPs exposed to soil indicates that the adsorption capacity of MPs for TC increases after soil exposure, with PLA showing the strongest increase.
The isothermal adsorption results of PE and PLA exposed to soil indicate that the adsorption of TC on heterogeneous surfaces is influenced by physical and chemical adsorption processes. After soil exposure, the equilibrium absorption capacity of MPs for TC increased by 88% (PLA), 26% (PVC), and 15% (PE).
The dissolved organic matter in soil promotes the desorption of TC from the surface of MPs, and the morphology of TC changes with pH. Without the addition of biological pollutants, the affected MPs in the soil have the potential to promote the degradation of TC in the solution. Density functional theory (DFT) calculations confirm that PE and PVC mainly adsorb TC through physical interactions, while PLA can adsorb TC through hydrogen bonding with TC. These results elucidate the adsorption behavior and mechanism of TC on MPs in the original and soil, which helps to assess the risk of combined pollution of MPs and antibiotics.
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Reference
- Insights into behavior and mechanism of tetracycline adsorption on virgin and soil-exposed microplastics.
Journal of Hazardous Materials 440 (2022): 129770.
