Impact of Heat-Conductive Graphite Filler and Silicone Rubber on Thermal Energy Absorption and Flexibility of Polyethylene Glycol Phase Change Films

• A flexible PCM composite with PEG-functionalized graphite in a silicone rubber matrix was developed. • The PCM system reduced leakage to 5.9% after 40 cycles, maintaining 80% enthalpy efficiency. • Energy absorption increased by 180%, and specific heat capacity was enhanced by 179%. • The system demonstrated 1.2 × 10 –8 m 2 /s thermal diffusivity and 46 % energy absorption. • The PCM composite showed potential for efficient thermal management applications. Latent heat storage using solid–liquid phase change materials (PCMs) offers high energy storage capacity, adaptability across diverse temperature ranges, and minimal volume variation during phase transition. Nevertheless, conventional PCMs often suffer from low thermal conductivity, leakage during melting, and rigidity in the solid state, which hinder their practical use. In this study, a flexible and thermally enhanced PCM composite was developed by integrating polyethylene glycol (PEG, 2000 g/mol) with functionalized graphite (G) within a silicone rubber (SR) matrix. To improve interfacial compatibility between PEG and G, the graphite surface was chemically modified using toluene diisocyanate (TDI), ethylene glycol (EG), and PEG 600, introducing reactive functional groups capable of strong interfacial bonding with PEG chains. This modification effectively reduced PCM leakage to 5.9 % after 40 heating/cooling cycles, while maintaining 80 % enthalpy efficiency. Incorporating PEG PCM also enhanced the SR matrix’s thermal performance, increasing energy absorption by 180 % and the specific heat capacity by 179 %. The resulting phase change film exhibited a thermal diffusivity of 1.2 × 10 –8 m2/s, achieving 46 % thermal energy absorption. The combination of high conductivity, reduced leakage, and mechanical flexibility highlights this composite as a potential candidate for advanced thermal management and energy-storage applications.