Spatially resolved indiffusion behavior of Cu2+ and Ni2+ in polypropylene

Abstract Microplastics and their effects on the environment and food chain have become increasingly important in recent years. These polymer particles, which are only few millimeters in size or smaller, accumulate in the environment and can enter the human food chain via animals that ingest them. Moreover, they can accumulate impurities such as heavy metals. Therefore, this study focuses on the indiffusion behavior of metal ions into semicrystalline polypropylene (PP) applying time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) at cryo‐conditions. Diffusion coefficients of Cu 2+ and Ni 2+ in PP are determined by classical SIMS depth profiling in frozen state ( T <−130°C) and subsequent data analysis according to Fick's second law of diffusion. The results show that diffusion of Cu 2+ ions in dry PP ( D PP,Cu = [2.21 ± 0.15]·10 −12 cm 2 /s) is faster compared to Ni 2+ ion diffusion of dry PP ( D PP,Ni = [4.43 ± 0.55]·10 −13 cm 2 /s). Interestingly, the diffusion of Cu 2+ ions in water‐saturated PP ( D PP,H2O,Cu = [1.91 ± 0.28]·10 −13 cm 2 /s) is slower compared to Cu 2+ ion diffusion in dry PP. Furthermore, high‐lateral resolution ToF‐SIMS analysis shows that metal ions only diffuse in certain areas of PP, which are most likely amorphous.