An Experimental Approach to Determining the Average Diffusion Coefficient of Volatile Components in Polymer Waste Materials

Abstract

One of the major challenges in recycling plastics is the removal of undesired volatile components from the polymeric phase, which may reduce process efficiency and negatively affect product quality. Accordingly, the recycling industry employs a broad range of degassing techniques, the efficiency of which often depends on the diffusion coefficient—a measure of the mass transport of volatile components in polymeric phases. The aim of this study was to develop a practically feasible experimental approach using thermogravimetric analysis (TGA) to determine the average diffusion coefficient of volatile components in polymer waste materials. First, the TGA method was validated with a pressure decay apparatus (PDA) using predefined binary material mixtures: Thin sheets were pressed from virgin high-density polyethylene (HDPE) and polypropylene (PP) and deliberately saturated with toluene in a sorption experiment. These saturated samples were then used in TGA and PDA desorption experiments at 60 °C, 80 °C and 100 °C, which yielded similar results with an average difference of 7.4% for the HDPE-toluene system and 14.7% for the PP-toluene system. When validated, TGA was employed to determine the diffusion coefficient of volatile components in post-industrial plastic waste melt at a temperature of 220 °C. The proposed method contributes to the understanding of diffusion-based mass transport in polymer waste materials and provides a key parameter for model-based process control and optimization. In practice, the diffusion coefficient results can be used to predict the degassing performance of an extrusion process in the mechanical recycling of plastic waste.

Assessment of property profile of post‐industrial polypropylene recyclates through a multivariable recycling process

“…These combined effects contribute to an enhanced degassing performance. 4,69 On the other hand, the results of the ATD-GC-MS measurements can be divided into qualitative and semiquantitative analyzes. The qualitative analysis aims to identify the prominent compounds present in the recyclates based on the mass spectroscopy spectra, while the semiquantitative analysis aims to compare the total VOC levels in the recyclates after being subjected to the various PSUs.…”

“…Plastic waste is fundamentally categorized based on its source, distinguishing between post-industrial and post-consumer waste. 4 Post-industrial waste originates from production residues and never reaches the end consumer (e.g., injection molding sprues), thus it is typically less contaminated making it readily recyclable, 1,[5][6][7] while post-consumer waste is generated after the use-phase and disposal. 5 The term "recovery" in the context of plastic wastes encompasses all methods of reclaiming plastic waste, including recycling, regardless of the waste type.…”

“…5 The term "recovery" in the context of plastic wastes encompasses all methods of reclaiming plastic waste, including recycling, regardless of the waste type. 4,8 Among the various approaches, mechanical recycling is widely regarded as one of the most efficient and effective practices. [9][10][11] Mechanical recycling typically involves techniques that transform plastic waste into secondary raw materials using physical processes such as shredding and extrusion.…”