Prospective Evaluation of Polyolefin-Derived Pyrolysis Wax as a Phase-Change Material: Thermophysical Characterization and Life Cycle Assessment

Abstract Climate change is projected to intensify across global regions, raising demand for energy-intensive heating and cooling systems and further contributing to greenhouse gas (GHG) emissions. Phase-change materials (PCMs) offer a means of attenuating this demand by absorbing and releasing heat during phase transitions, thereby improving building energy efficiency. However, their production can be environmentally intensive due to the use of fossil-derived or resource-demanding feedstocks. This study examines waxes recovered from the pyrolysis of common polyolefin waste streams, including high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP), as alternative PCM feedstocks. The thermophysical properties of the waxes were characterized using differential scanning calorimetry (DSC), while Fourier-transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) were used to further characterize the treated HDPE-derived wax (tHDPE wax). Following posttreatment, tHDPE wax exhibited promising thermal properties, with melting and crystallization peaks at 38.2 ± 0.7 and 34.5 ± 0.5 °C, respectively, a latent heat of fusion of 171.4 ± 4.2 J/g, and a crystallization enthalpy of 154.3 ± 2.7 J/g, comparable to commercial paraffin PCMs. FTIR showed no detectable change in chemical functional groups following fractionation, while XRD indicated increased crystallinity relative to the untreated HDPE wax. A cradle-to-gate life cycle assessment (LCA), based on a functional unit of 100 MJ m–3 of latent thermal storage, was performed for the tHDPE wax and compared to paraffin, capric acid, polyethylene glycol, and sodium sulfate decahydrate. Results indicate that using tHDPE wax as PCM feedstock can reduce global warming impact, human toxicity, land use, and fossil resource use by over 90% each compared with conventional organic PCMs. Overall, the combined thermophysical characterization and environmental assessment suggest that converting polyolefin waste, specifically HDPE, into PCMs represents a viable circular-economy pathway that can reduce waste burdens and enhance the sustainability of construction materials.