Carbon Black–Enhanced Polyethylene Wax Phase Change Materials for Efficient Photothermal Energy Conversion and Storage in Mobile Heating Systems

Organic phase change materials (PCMs) have been used and studied for many years. In this work, we focus on an industrially available PCM—polyethylene waxes (PEW) modified with seven types of carbon black (CB) exhibiting different properties. Carbon black (CB) was selected as a more cost-effective modifier compared to carbon nanomaterials, as it is easier to implement industrially and capable of converting and storing thermal energy. The experiments were designed to evaluate the thermal properties and photothermal conversion efficiency of PCMs modified with different grades of carbon black. The influence of carbon black on selected PCM properties was investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TG), scanning electron microscopy (SEM), and laser flash analysis (LFA). Furthermore, the photothermal conversion capability was evaluated. The results indicate that modification with carbon black decreases the phase transition enthalpy for most formulations, with reductions ranging from 8 to 12% for 1 wt.% CB to 10–15% for 2.5 wt.% CB. At the same time, an improvement in the thermal conductivity of PCMs modified with carbon black was observed, with the best performance achieved for N234 carbon black, showing an increase of approximately 17–18% in the 25–55 °C temperature range. The ratio of the heat of solidification to the heat of melting (Qs/Qm) for most samples was approximately 0.90–0.98, indicating excellent thermal cycling stability. The highest photothermal conversion efficiency was observed for samples modified with N234 and N330; these materials exhibited the greatest temperature rise, reaching approximately 135 °C in about 15 min, due to enhanced light absorption of PCMs by carbon black. Overall, the results confirm that PEW/CB systems demonstrate a good balance between absorption, heat generation, and controlled phase-change behavior, making them promising candidates for solar–thermal energy storage and conversion applications.