Modeling microplastic with polyethylene (PE) spherical particles: a differential scanning calorimetry approach for quantification

Abstract

Detection, identification, and quantification of microplastics have become increasingly relevant for determining their contribution and role in environmental pollution. Thermal analysis is positioned as one of the alternative techniques employed to quantify microplastics. However, a deeper investigation that explores its capabilities is required, since in techniques such as difference scanning calorimetry (DSC), the result of the melting curve is potentially affected by the size of the micro particles. Therefore, to use this technique in the field of quantitative analysis of microplastics, it is necessary to make an evaluation of how the micro particle size affects the signal obtained. We use spherical polyethylene (PE) particles of different sizes (75-710 μm) as a microplastic model to study the effect of particle size and the mixtures of different particle sizes on the melting curve. The effect of possible interferences on the DSC signal was studied and real microplastics isolated from wastewater were tested. It was found that the DSC signal (both melting temperature and peak shape) is affected by the size of the particles, even in the case of mixtures of particles of different sizes. However, through an appropriate sample preparation, it is possible to identify the signals corresponding to microplastics of different sizes and thus quantify their contribution to the mass of the sample. It was evidenced that factors such as the presence of inorganic materials tend to modify the melting temperature. Also, removal of interferences of organic origin is feasible. In addition, the presence of PP, HDPE and LDPE was evidenced in wastewater samples. Our results represent an important advance in the use of the DSC technique in the field of microplastics, since the existence of particles of different sizes can be evidenced in the same sample allowing for an estimation of the number of microplastic particles. Finally, we show the applicability of DSC study on microplastics in environmental matrices.

Keywords: Differential scanning calorimetry; Microplastics; Polymer; Quantification.