Upcycling Postconsumer High-Density Polyethylene (PC-HDPE): Thermal Stability and Kinetics Study of the Filaments Extruded from PC-HDPE

Abstract

Thermal stability and kinetics of thermolysis of postconsumer milk containers made of high-density polyethylene (PC-HDPE) and filament rods extruded from them (HDPE-F) were examined by thermogravimetric analysis (TGA) with six linear temperature programs under a stream of nitrogen. The total weightloss of each sample took place in a one-step decomposition to volatiles at the heating rates, β = 1, 10, 25, 50, 70, and 100 Kmin^-1. The values of initial decomposition temperature, the temperature at the maximum thermal degradation rate, and the maximum rate of decomposition were increased by increasing the heating rate as was the expectation. The isoconversional method was used to evaluate the fundamental kinetic parameters, the activation energy barrier (E_a), the Arrhenius pre-exponential factor (A), and the mechanism of the reaction, f(α). The values of E_a were independent of the model and heating rate, as was expected. However, the values of A depended on the model and the extent of reaction (α). The values of the E_a of PC-HDPE initiated at 171 kJ/mol at α = 0.05 and it increased to 207 kJ/mole at α = 0.95. The values of E_a of the HDPE-F rod were relatively constant for all α values, being 227 ± 3 kJ/mol. It was justified by the absence of easily volatilized substances in the HDPE-F. Knowledge of the thermal stability and decomposition kinetics of the starting materials (PC-HDPE) and the product (HDPE-F) is important in the context of thermochemical conversion processes aimed at the use of PC-HDPE as raw materials for recycling, upcycling, and down-cycling for objects used under room conditions.

Keywords:

• activation energy
• filaments
• high-density polyethylene (HDPE)
• isoconversional degradation
• kinetics
• postconsumer polyethylene (PC-PE)
• pyrolysis
• rods
• thermal decomposition
• thermal degradation
• waste plastics

Acknowledgments

The author declares no competing financial interest. In addition, he is grateful for the supports of Dr. Judith Sally and Dr. Louis Whitesides; and recognizes the participation of the undergraduate students Josiah Henderson, Nurranahaar Abussalam, and Bradon Galloway during the sample preparation and measurements. Any opinions, findings, and conclusions, or recommendations expressed in this material are those of the author and do not necessarily reflect those of the Funding Agencies.

Additional information

Funding

This work was supported by the U.S. Department of Agriculture, National Institute of Food and Agriculture, Evans-Allen project number SCX-311-21-17 and SCX-311-29-21.