【Frontiers in HaiChuan Chemical Technology】Researchers from Fudan University achieved efficient depolymerization of polyamides through alcoholysis under mild conditions

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Researchers at Fudan University have achieved efficient depolymerization of polyamides through alcoholysis under mild conditions. 2025-10-10 14:46:53 The continuous increase in global plastic consumption has led to serious environmental problems, particularly the worsening of \"white pollution\". Due to improper disposal and insufficient recycling of plastic waste, nearly 91% of plastic is burned or landfilled, which not only increases greenhouse gas emissions but also leads to the release of microplastics into the environment. To achieve an environment-friendly economy, plastic recycling has become a focus of attention, among which chemical recycling is highly regarded for its ability to break down polymers into monomers and enable a closed-loop cycle. As one of the five major engineering plastics, polyamide (commonly known as nylon) has an annual market volume of over 8.5 million tons. However, its amide bonds are chemically stable due to resonance stabilization and strong hydrogen bonding, making it difficult to decompose under mild conditions; traditional methods require high temperature and pressure, which limits its sustainable recycling. Recently, Professor Tu Tao from Fudan University, in collaboration with Xu Bing, proposed an innovative method: using methyl tolsulfonate as an activator to achieve efficient depolymerization of polyamides through hydrolysis under mild conditions. This strategy can convert various polyamides into high-value monomers such as ε-caprolactam, amino acid esters, or diamines/diesters, with yields approaching quantitative levels and excellent selectivity. Experimental and theoretical mechanism studies indicate that p-toluenesulfonic acid plays a key role in the alcoholysis process; by facilitating the nucleophilic attack of alcohols on amide groups, it enables the formation of tetrahedral intermediates, providing a viable pathway for the cyclic recovery of polyamides. The related paper, titled “Sustainable recycling of polyamides via C–N bond cleavage facilitated by methyl tosylate under mild conditions,” was published in Nature Communications; Yang Jitong is the first author of the paper. At the beginning of the research, the team used PA6 as a model to systematically screen for hydrolysis additives. The results show that methyl tosylate can be rapidly converted to p-toluenesulfonic acid in methanol, effectively promoting the degradation of PA6, and its hydrolysis selectivity is superior to that of other Brønsted or Lewis acids. By monitoring the reaction process using nuclear magnetic resonance, the researchers observed a gradual weakening of the signals associated with amide bonds, while the signals of ester groups and protonated amino groups increased, confirming the efficiency of the hydrolysis. Dynamic analysis showed that the reaction followed first-order kinetics, and there was a positive correlation between p-toluenesulfonic acid concentration and the reaction rate. Upon further exploring the range of substrates, the research team found that this strategy exhibited good applicability to various alcohols and polyamides. Aliphatic primary alcohols can react efficiently with PA6 to achieve high conversion rates and selectivity ； Aromatic alcohols are suitable, but their selectivity is slightly lower. For other polyamides such as PA66, PA11, and PA12, this method can also depolymerize them into diamine tolsulfonates and diesters, and the products can be separated and purified through solvent extraction and recrystallization. It is worth noting that even for industrial nylon products containing glass fiber reinforcement, this method can fully recover the reinforcement materials while degrading the polyamide, demonstrating excellent practical application potential. To achieve closed-loop recycling, the team also carried out further treatment on the degradation products. Amino acid methyl esters can be converted into the corresponding amino acid esters through a neutralization reaction, and serve as monomers for the synthesis of PA11 and PA12 ； The recovery of ε-caprolactam is achieved through intramolecular cyclization of the amide, yielding a high-purity product in high yield under alkaline conditions. Furthermore, methyl tosylate can be recovered in the form of potassium tosylate after use and regenerated as an activator, reflecting the sustainability of this process. When verifying the feasibility of actual waste plastic recycling, researchers selected post-consumer PA products such as fishing lines, cable ties, gears, and screws. The results showed that all samples achieved a conversion rate of up to 99% under mild conditions, with a monomer recovery rate of up to 94%. It is particularly encouraging that this method can also handle mixtures of PA6 with other polymers such as PE, PP, PS, and PET, where the degradation of PA6 is hardly affected by the co-existing polymers, and the products can be efficiently separated based on differences in solubility. Theoretical calculations further revealed the reaction mechanism: p-toluenesulfonic acid activates the amide bond and neutralizes the amino group through concerted proton transfer, thereby driving the alcoholysis process ； The cyclization reaction involves an intramolecular nucleophilic attack by the amino group on the ester group, forming a tetrahedral intermediate, which ultimately closes to form ε-caprolactam. These findings provide important evidence for understanding the degradation pathways of polyamides under mild conditions. In summary, this study developed a new method for the efficient depolymerization of polyamides under mild conditions, which not only achieves high yield recovery of the monomers but also proves effective in complex mixed waste plastic systems, demonstrating good scalability and practicality. This work provides innovative ideas and technical support for reducing white pollution and promoting the development of a circular plastic economy, and is expected to play an important role in future sustainable polymer recycling strategies.