Additive manufacturing of microplastic reference materials through microextrusion provides monodisperse and exactly counted particles

Reference materials play a fundamental role in standardizing and validating analytical and technical processes in research and industry. This also applies for the analysis of microplastic pollution, which should allow for both particle count and weight assessment. Here, we showcase a novel production method for monodisperse and count-accurate microplastic reference materials (MRM) using microextrusion via adapted nozzles in commercially available 3D-printers. The method is highly reliable and produces approximately 1,000 particles h^{- 1} with defined size and shape. We explored different thermoplastics such as LDPE, PA, PLA, PCL, and PMMA and size classes (224 -1,349 μm in diameter) concerning size and shape accuracy and reproducibility. The resulting particles showed low variability in size with a standard deviation between 3 and 30%. Particle size was adjusted using different nozzle diameters. Our approach provides a wide range of possible MRM readily available for analysis, process validation and environmental monitoring of microplastics. These reference materials may significantly contribute to the understanding of behaviour and dynamics of microplastics as novel entities with potentially detrimental effects on environment and human health.