Towards a quantitative approach for the accurate analysis of blended microplastics based on 3-D micro-Raman spectroscopy

The huge demand of the market for plastic products together with inappropriate management of plastics waste endanger the environment with microplastics (MPs) pollution. MPs, commonly known as tiny plastic particles between 1 μm – 5 mm, do not always release to the environment with a simple structure made of a single-type polymer. Rather, MPs may release from bulky blended polymers that have enormous industrial applications. In the latter case, the structure of MPs can be very complicated and composed of various types of polymers, thus making their analysis very challenging. Accurate investigation of MPs requires a meticulous analysis approach that provides information about many parameters such as size, type, concentration, number, etc. among others. In this work, we showcase the application of 3-D micro-Raman spectroscopy as a promising approach for the accurate analysis of blended microplastics (B-MPs). Polypropylene (PP) and Low-Density Polyethylene (LDPE), as two widely used polymers, are blended at various weight ratios including 25/75, 50/50, and 75/25, and are thoroughly investigated. Thanks to the high precision of 3-D Raman mapping, not only the types of polymers are distinguished in complex B-MPs but also the morphology of the distribution of polymers as well as their quantitative concentrations are accurately estimated. Subsequently, a parameter defined as the Concentration Estimate Error (CEE) is used to evaluate the performance of the adopted approaches. In the last step, the application of a line-shaped laser line focus is demonstrated for shortening the measurement time of 3-D Raman mapping from 56 to 2 hours, still acquiring valuable information about the morphology and concentration of polymers in B-MPs.