Rapid oxidative fragmentation of polypropylene with pH control in seawater for preparation of realistic reference microplastics

Various tiny plastic particles were retrieved from the sea and studied using scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) analysis to prepare realistic reference microplastics (MP). Most of the MP exhibited a diameter of < 20 x 10(-6) m and 0.1-0.2 molar ratios of oxygen to carbon atoms (O/C), indicating that they primarily comprised polyethylene (PE), polypropylene (PP), and polystyrene (PS). It took a long time to reproduce such O/C ratios in standard laboratory weathering methods. For example, degrading of 30 x 30 x 0.060 mm PP film required 75 days for the 0.1 ratio, even with an advanced oxidation process (AOP) using a sulfate radical anion (SO4 center dot(-)) initiator in distilled water at 65 degrees C. However, seawater drastically improved the PP degradation performance of AOP under a weak acid condition to achieve the 0.1 ratio of PP film in only 15 days. The combination of seawater and the SO4 center dot(-) initiator accelerated the degradation process and showed that the MP's size could be controlled according to the degradation time.

Automated summary

Various tiny plastic particles were studied using SEM/EDX analysis to prepare reference microplastics. Most of the particles were composed of polyethylene, polypropylene, and polystyrene. Standard laboratory weathering methods took a long time to reproduce the composition, but seawater significantly improved the degradation process.