Advanced Analytical Framework for Pyrolysis Product Characterization and Emission Profiling in Mixed Plastic Waste:...

Area of Science:

• Polymer Chemistry
• Analytical Chemistry
• Environmental Science

Background:

• Chemical recycling of mixed plastic waste aims to recover valuable hydrocarbon products.
• Additive-derived non-intentionally added substances (NIASs) and other residues can compromise product quality and safety.
• Understanding the composition of recycled hydrocarbon streams is crucial for their safe application.

Purpose of the Study:

• To characterize volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), and water migrants in polyolefin-rich waste streams.
• To identify and quantify NIASs originating from plastic additives and degradation.
• To assess the impact of feedstock composition and oxidation on the quality of recycled hydrocarbon products.

Main Methods:

• Analytical pyrolysis coupled with comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry (Py-GC×GC-TOF-MS) for six polyolefin waste streams.
• Headspace/solvent-extraction GC-MS and aqueous migration testing for three consumer-grade plastics.
• Rapid pyrolysis at 650 °C to analyze condensable products.

Main Results:

• Condensable pyrolysis products were primarily C5-C30 aliphatic hydrocarbons.
• Polyethylene (PE)-rich streams yielded n-paraffins and α-olefins; polypropylene (PP)-rich streams produced branched olefins and aromatics.
• Additive-derived NIASs (e.g., hindered phenols, spiro-diones) and oxidation products were detected at low levels, particularly in weathered HDPE.

Conclusions:

• Relatively clean polyolefin streams can produce hydrocarbon-rich pyrolysates suitable for recycling.
• Oxidized polyethylene and additive-derived NIASs represent key targets for quality control in chemical recycling.
• GC-based methods effectively characterize the volatile and extractable fractions, informing process optimization and safety assessments.