Hergesell Adrian H, Popp Stephan, Meena Raghavendra, Ospina Guarin Viviana M, Seitzinger Claire L, Sievers Carsten, Li Guanna, Vollmer Ina
Inorganic Chemistry and Catalysis Group, Institute for Sustainable and Circular Chemistry, Utrecht University The Netherlands
Biobased Chemistry and Technology, Wageningen University The Netherlands.
Chem Sci. 2025 Aug 15. doi: 10.1039/d5sc03348a.
Mechano-chemistry can depolymerize plastics to their monomers. The conversion of polyolefins, however, suffers from low chain cleavage rates and the low stability of radical intermediates. Therefore, insights into the degradation mechanism are crucial to obtain higher yields. Herein, we promote the mechano-chemical degradation of polypropylene by milling with sand as an additive, which increases depolymerization yields by a factor of 25. Fracture of sand crystals causes homolytic cleavage of Si-O bonds resulting in unpaired surface electrons, which possess radical reactivity and can initiate degradation reactions of polypropylene, ultimately resulting in smaller hydrocarbons. We show that this mechanism based on surface radicals dominates over alternative pathways based on locally increased temperature or surface roughening of grinding spheres. While inorganic materials, such as glass fiber in composites, are typically unwanted in (chemical) recycling scenarios, we show that they can be exploited to drive mechano-chemical depolymerization. Our study illustrates that control over the radical-based degradation mechanism during the mechano-chemical conversion of polyolefins is key to increase yields and technological viability.
机械化学可以将塑料解聚为单体。然而，聚烯烃的转化存在链裂解速率低和自由基中间体稳定性差的问题。因此，深入了解降解机理对于获得更高的产率至关重要。在此，我们通过添加沙子进行研磨来促进聚丙烯的机械化学降解，这使解聚产率提高了25倍。沙晶的破裂导致Si-O键的均裂，产生未成对的表面电子，这些电子具有自由基反应性，可以引发聚丙烯的降解反应，最终生成较小的碳氢化合物。我们表明，这种基于表面自由基的机制比基于局部温度升高或研磨球表面粗糙度增加的替代途径更为重要。虽然在（化学）回收场景中，复合材料中的无机材料（如玻璃纤维）通常是不需要的，但我们表明它们可以被用来驱动机械化学解聚。我们的研究表明，在聚烯烃的机械化学转化过程中，控制基于自由基的降解机制是提高产率和技术可行性的关键。
