Enhancing thermal performance of low-temperature phase change materials based on tetradecane

Low-temperature phase change materials (PCMs) play a crucial role in mitigating ice and snow accumulation on asphalt pavements, thereby improving road safety and reducing maintenance costs. However, their practical implementation is hindered by the inherently low thermal conductivity and limited thermal stability. In this study, n-tetradecane (C14) with a phase change temperature of 5℃ was chosen as the phase change substrate. To improve its stability, polycaprolactone (PCL), a low-melting-point polymer was employed as a support matrix, while expanded graphite (EG) was incorporated as a thermal conductivity enhancer. Three different preparation methods including melt blending, vacuum adsorption, and directional freezing were explored to analyze their impact on the microstructural distribution of EG and the resultant thermal properties of the composite PCMs. A systematic analysis was then conducted to evaluate the influence of compaction density, EG content, and the microstructural arrangement of EG on the thermal conductivity of composite PCMs. The effectiveness of the three fabrication techniques in enhancing thermal conductivity was also compared. The experimental findings confirm that the integration of PCL successfully overcomes the compatibility limitations associated with conventional PCM support matrices, leading to the development of a functional low-temperature PCM with a phase change point at 5℃. The thermal conductivity of the composite PCM increased with higher compaction density and EG content. Among the three fabrication methods, the directional freezing technique proved to be the most effective in improving EG alignment, thereby optimizing heat transfer pathways. Specifically, when the EG content reached 15 % and the compaction density was 760 kg/m³, the axial thermal conductivity of the composite PCM with a directionally structured microstructure reached 4.482 W/(m·K), approximately 20 times higher than that of pure C14. The strategic selection of support matrices and the structured alignment of EG significantly enhance the thermal conductivity of PCMs. With the increase of PCMs content from 0 % to 8 %, the thermal conductivity decreased by up to 26.2 % at most. For every 2 % increase in the dosage of the composite PCM, the temperature of the test block can be regulated by approximately 1℃. After 100 cycles of the test block with an 8 % dosage, the winter heat storage time was prolonged by 3.2 h, and the stability of the test block was good after the phase change cycle. These findings offer valuable insights for improving the design, construction, and maintenance of asphalt pavements in cold environments, reducing reliance on de-icing chemicals and improving overall road durability.