Automation of carbonyl index calculations for fast evaluation of microplastics degradation

Abstract: The broad use of plastics has resulted in the increase in both production and consequent plastic pollution in the environment. Microplastics, defined as particles < 5 mm, is of special interest because of its wide existence in environment and potential hazards to our ecosystem. The degradation of microplastics can be studied using Fourier Transform Infrared spectroscopy (FTIR), where the optical absorption of different functional groups in a molecule can be detected and used for identification. By studying the change in intensity or peak area of certain functional groups (such as carbonyl, hydroxyl, or vinyl) in the spectrum, the degradation of microplastics can be quantified. In the past decades, carbonyl index (intensity or area change of carbonyl group in FTIR spectra), has been applied as a quantitative probe to monitor the extent of plastics degradation. However, the analysis of FTIR spectra requires expertise and comparison between different reports are often difficult due to non-standardized methods. Therefore, an automated method is urgently needed to ease the difficulty. This project has developed a program that automates and standardizes the analysis of the spectrum. The program calculates an index by using specified area under the band corresponding to a functional group peak and a reference peak. By comparing the indexes over time, degradation can be quantified. Additionally, poly(vinyl chloride) (PVC) particles were subjected to a heterogeneous photo-Fenton process for 116 hours to obtain data of microplastics degradation. Both optical imaging and FTIR were used to characterize the degradation of PVC, on aspects of size reduction and band changes, respectively. The obtained FTIR data were fed into the developed program to calculate carbonyl index, and the result suggests a degradation of the PVC particles. This implies that the program can effectively reduce the time of analysis for researchers and evaluate and/or calculate the degradation of plastics.