Combining Experimental and Theoretical Tools to Probe Radio-Oxidation Products in Polyethylene

Area of Science:

• Polymer Science
• Computational Chemistry
• Spectroscopy

Background:

• Polyethylene is a widely used polymer across various industries.
• Infrared spectroscopy is a common method for assessing polymer aging, particularly oxidation.
• The carbonyl peak in infrared spectra is crucial for aging analysis but comprises multiple functional groups.

Purpose of the Study:

• To complement experimental infrared spectroscopy with density functional theory (DFT) calculations for polyethylene aging analysis.
• To investigate the contribution of various carbonyl groups to the overall carbonyl signature.
• To provide a theoretical basis for quantifying degradation products in aged polyethylene.

Main Methods:

• Utilized extended density functional theory (DFT) calculations to simulate infrared spectra of a polyethylene model.
• Developed a polyethylene model mimicking semicrystalline polymer features.
• Compared theoretical frequencies and intensities with literature data for deconvolution procedures.

Main Results:

• DFT calculations provide theoretical frequencies and intensities for carbonyl groups in polyethylene.
• A novel, theoretically-based method for estimating carbonyl group concentrations was developed.
• Comparison of deconvolution methods highlights uncertainties in contributions from conjugated ketones and ester/aldehyde ratios.

Conclusions:

• Density functional theory (DFT) is a valuable tool for analyzing and complementing experimental data in polymer aging studies.
• Theoretical calculations can aid in resolving complex carbonyl peaks and improving quantitative analysis.
• This study offers a new perspective on assessing polyethylene degradation through advanced computational methods.