Plastic materials are among the most common sources of microplastics in the environment due to their widespread use. Despite their chemical stability and durability, microplastic particles are generated through mechanical abrasion, UV-induced degradation, and thermal stress, releasing fragments of various sizes and chemical properties. Understanding the thermal behaviour of plastics is therefore essential for assessing their stability, degradation mechanisms, and the formation of volatile products relevant to environmental and health impacts.
In this master's thesis, the thermal properties of three plastic-derived materials: high-density polyethylene (HDPE), cellulose acetate (CA), and tyre rubber (NR/SBR/BR composite), were studied using a combination of thermal analysis techniques. These materials were selected as representative sources of microplastics originating from bottle caps, cigarette filters, and tyre wear particles. Thermogravimetry (TGA) was used to determine decomposition temperature ranges and to evaluate the influence of heating rate, sample mass, and particle size on degradation behaviour. Microplastic particles were found to decompose slightly differently from larger fragments, confirming the effect of specific surface area on the degradation process. Differential scanning calorimetry (DSC) complemented TGA by providing insight into the enthalpy changes associated with decomposition in inert and oxidative atmospheres.
Activation energies (Ea) were determined using the isoconversional Kissinger–Akahira–Sunose (KAS) and Ozawa–Flynn–Wall (OFW) methods. HDPE exhibited nearly constant Ea values throughout decomposition, whereas CA and rubber showed more complex kinetic behaviour consistent with their chemical composition.
Volatile degradation products were identified using TGA-FTIR and TGA-IST16-GC-MS. TGA-FTIR enabled the detection of functional groups in the evolving gases, while TGA-IST16-GC-MS provided detailed identification of individual compounds. TGA-FTIR was used to analyse all three samples, while TGA-IST16-GC-MS was used to analyse HDPE and cigarette filters. The most prominent signals corresponded to aliphatic hydrocarbons for HDPE and acetic acid for CA, in agreement with their known degradation pathways. The combined use of these techniques proved effective in providing insight into the chemical processes occurring during the thermal decomposition of polymers.
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