Atomic Scale Mechanisms Controlling the Oxidation of Polyethylene: A First Principles Study

Area of Science:

• Polymer Science
• Materials Chemistry
• Physical Chemistry

Background:

• Aliphatic polymers like polyethylene are crucial in various industries.
• Understanding thermal and radio-oxidation degradation is key to assessing material lifetime.
• Current kinetic models identify hydroperoxides as key transient species in degradation.

Purpose of the Study:

• To review and computationally assess mechanistic pathways for hydroperoxide formation and decomposition in polyethylene.
• To investigate the influence of the polymer's environment (crystalline vs. amorphous) on degradation reactions.
• To identify key radical species involved in polyethylene oxidation for improved kinetic modeling.

Main Methods:

• Literature review of mechanistic paths for hydroperoxide formation and decomposition.
• First principles calculations using Density Functional Theory (DFT).
• Analysis of reaction energies and environmental influences on chemical reactions.

Main Results:

• DFT calculations partially confirm existing literature data on reaction energies.
• Alternative, more favorable reaction pathways for hydroperoxide decomposition were identified.
• The influence of crystalline versus amorphous environments on reaction outcomes was highlighted.
• Hydroxyl radicals were found to play a significant role in hydroperoxide decomposition.

Conclusions:

• The study provides refined mechanistic insights into polyethylene oxidation.
• Computational findings suggest improvements for kinetic models used in polyethylene radio-oxidation simulations.
• Understanding the role of hydroxyl radicals can lead to more accurate lifetime predictions for polyethylene applications.