Characterization of Photo-Cross-Linked Polyethylene Pipes for Geothermal Energy Storage.

Area of Science:

• Materials Science
• Polymer Chemistry
• Energy Storage

Background:

• Cross-linked polyethylene (PEX) is a candidate for high-temperature applications.
• Novel photoinitiated cross-linking (PEX-e) offers potential advantages.
• Understanding PEX-e properties is crucial for borehole thermal energy storage systems.

Purpose of the Study:

• To investigate the morphology and thermo-mechanical properties of novel PEX-e pipes.
• To compare PEX-e formulations with conventional PEX-a and PE100 pipes.
• To assess the suitability of PEX-e for high-temperature borehole thermal energy storage.

Main Methods:

• Gel content for cross-linking degree.
• Dynamic Mechanical Analysis (DMA) for cross-link density and molecular weight.
• ¹H static Nuclear Magnetic Resonance (NMR) for phase composition and molecular mobility.
• Differential Scanning Calorimetry (DSC) for thermal behavior.
• Fourier Transform Infrared (FTIR) spectroscopy, Oxidation Induction Time (OIT), and Thermogravimetric Analysis (TGA) for oxidative stability.

Main Results:

• Both PEX-e formulations achieved adequate cross-linking and high OIT values.
• PEX-e2 displayed non-uniform cross-link distribution, leading to a reduced storage modulus.
• FTIR detected oxidation byproducts in PEX-e1 during the cross-linking process.

Conclusions:

• PEX-e pipes demonstrate potential for high-temperature energy storage applications.
• Cross-link distribution significantly influences the thermo-mechanical performance of PEX-e.
• Further optimization of PEX-e formulation and processing is necessary to mitigate oxidation and improve properties.