title: Laser-Induced Breakdown Spectroscopy for the Characterization and Investigation of (Micro)Plastics and Their Weathering-Induced Oxidation Behavior
title: Laser-induzierte Plasmaspektroskopie zur Charakterisierung und Untersuchung von (Mikro-) Plastik und deren witterungsbedingtem Oxidationsverhalten
titleType: AlternativeTitle
Creators: name: Sommer, Caroline
Publisher: name: Philipps-Universität Marburg
Year: 2024
Subjects: heterogeneous plastic degradation
sediment samples
LIBS
Natural sciences &amp; mathematics
Naturwissenschaften
plastic identification
surface and depth profile analysis
Irgafos® 168,
Irgafos® 168
microplastics

description: This thesis deals with the characterization and investigation of (micro)plastic samples and their weathering-induced oxidation behavior using LIBS. Weathering-induced oxidation, or more specifically photo-oxidation induced by environmental factors, is the main mechanism for the degradation of PE, PP, and PS samples, which can lead to toxic by-products from the base polymer itself or additives or the uptake of pollutants. Therefore, its examination may provide information for assessing the hazards of (micro)plastics. In this context, LIBS is being explored as an alternative technique for the examination of (micro)plastics. A concept was developed to systematically separate plastics from natural materials, identify the polymer type, and determine the extent of oxidation on the surface and inside the sample. These investigations allow a more comprehensive characterization of plastic samples, often not achieved with conventional techniques. The ability of LIBS to detect the main constituents of plastics, as well as molecular signals in combination with depth profiling capabilities, opens up a wide range of new developments and opportunities in research and applications. The aim of this work is to demonstrate the problems of identifying microplastics using conventional methods and to prove that the new proposed method, LIBS, is an efficient alternative in these areas. In doing so, a more thorough explanation of the operation of the conventional methods is necessary to understand their possibilities and limitations. Chapter 1 introduces the topic by showing the relevance of (micro)plastic research. A rough overview of the state of research is presented, including an overview of the life circle of plastic debris. The relevance of a profound understanding of plastic identification and characterization, including the investigation of plastic degradation, is elaborated. Chapter 2 covers the background of this work in more detail. First, an overview of the materials under study is given, highlighting the chemical and physical differences between the various plastic types. Second, the experimental setups used in this study and the data processing are presented. Lastly, the different degradation processes involved in environmental plastic samples are discussed, with particular attention to photo-oxidation. At the end of the chapter, the common analytical techniques, i.e., microscopic, thermal, and spectroscopic methods, as well as their advantages and disadvantages, are discussed. The most common analytical challenges include long acquisition times, extensive sample pre-treatment, interference from color pigments, moisture, or organic matter, as well as the restriction to surface analysis. Chapter 3 presents LIBS for overcoming the analytical challenges of conventional methods. The chapter covers the physical principles of LIBS, specifically light-matter interaction and plasma formation, which serve as the theoretical foundation for the conducted experiments and their interpretation. The chapter ends with applying this experimental technique for surface and depth profile analysis. Chapter 4 summarizes the results of the attached publications. There is no question that the most effective way to combat plastic pollution is to prevent plastic from entering the environment. As this political goal is difficult to achieve, science is left with the task of detecting plastic and removing it from the environment. The difficulty of this task is demonstrated in this thesis.