Carbon nanotube-reinforced crosslinked polyethylene pipes for geothermal applications: From synthesis to decomposition using analytical pyrolysis-GC/MS and thermogravimetric analysis

Carbon nanotube reinforced crosslinked high density polyethylene (PEX) nanocomposites were synthesized for geothermal applications requiring higher polymer thermal conductivity and a comprehensive thermal decomposition study was performed. The prepared nanocomposites were investigated by laser flash analysis and temperature modulated differential scanning calorimetry revealing a great enhancement on the specific heat capacity along with a further enhancement on the thermal diffusivity, resulting in some cases in an overall thermal conductivity increase of more than 200%. For the thermal decomposition or recycling process of the produced nanocomposites, a thorough examination of the decomposition process and its kinetics was performed by using thermogravimetry and analytical pyrolysis-gas chromatography-mass spectroscopy. From this systematic study, two possible decomposition mechanisms for PEX were proposed for the first time in literature and the decomposition kinetics results, which were conducted using isoconversional and model-fitting methods, were in agreement with the proposed mechanisms. From the complementary use of analytical pyrolysis and thermal analysis techniques study it was revealed that the presence of carbon nanotubes hinders the diffusion of the primary scission products of PEX and enhances its thermal stability.