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.
Online monitoring of water pollutants is of great importance for the early detection of contaminants and improving the quality of drinking water. We showcase a smart design of a miniaturized, low-cost, versatile, and handheld optofluidic chip for characterizing microplastics (MPs) in water, which are a potential threat to our environment. The chip encompasses all the required optics for guiding the light to/from the microfluidics, all sandwiched together as a unique miniaturized system. Size and concentration of MPs are characterized by measuring the static light scattering (SLS) signal at two different angles: 0 and 40 degrees. In fact, the concentration of MPs is obtained by observing the SLS signal only at one angle, while for the size of MPs one needs to calculate the variation of signal at two concentrations. In a next step, the performance of the optofluidic chip is benchmarked against a commercial bulky system. The latter works based on a technique called “Goniophotometry”, capable of measuring the SLS signal at a broad range of scattering angles between - 90 and +90 degrees. Chemometric algorithms like Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA) are used to extract the size and concentration of MPs in water using the bulky system. The different sizes and concentrations of MPs are prepared using commercial Polystyrene (PS) beads. It is shown that the developed optofluidic microsystem provides a comparable performance to the commercial bulky machine and is thus a significant step towards the online monitoring of water pollutants, like MPs, in drinking water.
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