首页|Thermo-oxidative ageing of photo-crosslinked polyethylene pipes for thermal energy storage

Thermo-oxidative ageing of photo-crosslinked polyethylene pipes for thermal energy storage

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  • NETL
  • NSTL
  • Elsevier
This study presents a comprehensive evaluation of the thermo-oxidative stability of crosslinked polyethylene (PEX) pipes designed for borehole thermal energy storage (BTES) systems, with a particular focus on a novel PEX type produced via a photo-initiated crosslinking process (PEX-e). Two formulations, PEX-el and PEX-e2, were assessed and compared to commercial peroxide-crosslinked polyethylene (PEX-a) and bimodal polyethylene (PE100) pipes. The pipes were aged in distilled water at the intended BTES service temperature for 210 days, with periodic analyses conducted to monitor antioxidant (AO) depletion and the formation of degradation products. Advanced analytical techniques were employed, including Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy, gel content analysis, colorimetry, differential scanning calorimetry (DSC), oxidation induction time (OIT), and dynamic mechanical analysis (DMA). FTIR analysis revealed the presence of degradation-related peaks on the pipe surfaces, while the formation of oxidation products in the bulk material was limited. Phase composition analysis showed that physical ageing dominated during the first 30 days, leading to increased crystallinity and enhanced lamellar thickness. Over time, chain scission emerged as the primary degradation mechanism, resulting in molecular weight reductions, with PEX-a being the most severely affected. No abrupt changes in phase composition or mechanical properties were observed after 210 days of ageing, indicating that the pipes remained in the induction phase of degradation. Interestingly, despite their high OIT levels, both PEX-e formulations exhibited accelerated AO depletion during prolonged exposure, suggesting the need for further optimization of PEX-e formulations to ensure long-term stability under demanding BTES conditions.

UV-cured polyethylenePolyethylene degradationSolid state NMRMagic spinning angle NMR1H static NMRCrosslinking density

Giulia Simao de Sousa、Andrew Root、Ivo Heinmaa、Adib Kalantar Mehrjerdi、Jose Roberto Moraes d'Almeida、Mikael Skrifvars

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Swedish Centre for Resource Recovery, Faculty of Textiles, Engineering and Business, University of Bords, Sweden||Department of Chemical and Materials Engineering, Pontifical Catholic University of Rio de Janeiro, Brazil

MagSol, Finland

National Institute of Chemical Physics and Biophysics, Estonia

Swedish Centre for Resource Recovery, Faculty of Textiles, Engineering and Business, University of Bords, Sweden||MuoviTech AB, Sweden

Department of Chemical and Materials Engineering, Pontifical Catholic University of Rio de Janeiro, Brazil

Swedish Centre for Resource Recovery, Faculty of Textiles, Engineering and Business, University of Bords, Sweden

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2025

10.1016/j.polymdegradstab.2025.111365

Polymer degradation and stability

Polymer degradation and stability

SCI
ISSN：0141-3910
年,卷(期)：2025.239(Sep.)
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