Identification and characterisation of microplastics released from plastic-coated paper cups using micro-Raman spectroscopy

Abstract

Microplastics (MPs) are contaminants of emerging concern in food and the food supply chain because they may cause adverse effects to human health. Furthermore, food contact material (FCM) may introduce a huge amount of different MPs into food in the process of using. Micro-Raman spectroscopy is a widely used qualitative technology for MPs determination and analysis due to its high resolution (down to 1 μm). In this study, five brands of plastic (polyethylene, PE)-coated paper cups from different manufacturers were collected and the scenario of using them to drink hot water was simulated, and the water extracts were tested by micro-Raman spectroscopy for MPs determination. Optical images and Raman spectra of particles detected were collected, while their concentration in water extract and size distribution were summarised. The average concentration of MPs found in water extracts from 5 paper cups is 12.93 ± 11.69 × 105 item/L, with particle sizes between 1 and 60 μm (in length). Three types of microplastic particles were characterised by Raman spectra based on polymer spectral library, which are PE, polyamide (PA) and uncertain MP. The morphology of PE films before and after exposure to hot water were observed by SEM imaging. The results indicated the inner coating of virgin film of plastic-coated paper cups had a high surface roughness, which lead to breakages and peeling that produced microplastic particles when exposure to hot water.