Phenolic resin/PEO-PPO block copolymer composite materials as phase change materials (PCM) for latent heat thermal energy storage (LHTES)

Abstract

Many block copolymers can be used in the soft-template synthesis procedures of OMC (ordered mesoporous carbon). Some of the most common are block copolymers composed of PEO [poly (ethylene oxide)] and PPO [poly(propylene oxide)], like the triblock copolymer Pluronic F127 (PEO106PPO70PEO106). DSC analysis of Pluronic F127 shows endothermic and exothermic peaks (at 54 and 30°C) due to the melting and crystallization of the PEO blocks. This indicates that this commercially available block copolymer could be used as a phase change material (PCM).Nanostructured polymer blends like the phenolic resin/PEO-PPO block copolymer composite materials prepared using some soft-template synthesis procedures of OMC could be useful as a solid-solid PCMs if the crystallization of the PEO blocks of the block copolymer is possible within the material.DSC analysis of particles of a phenolic resin/F127 composite material (material P9) prepared using one soft-template synthesis procedure of OMC in solution in basic media (thermal treatment of an alkaline (pH around 9) aqueous solution of F127 and a phenol-formaldehyde resin, followed by centrifugation) shows no evidence of an endothermic or exothermic process. A reduction of the pH of the phenol-formaldehyde resin aqueous solution (from about 9 to 8.5) before the thermal treatment has an effect in the phase separation, that in this case leads to the formation of two layers; a polymer rich phase in the bottom of the reactor and above a layer composed mainly by water. Thermal treatment of the polymer rich phase at 100°C for 24h yields a solid composite material (material P8.5). DSC analysis shows an endothermic peak (35°C) in every cycle, attributable to the fusion of PEO crystalline domains. This indicates that the crystallization of the PEO blocks is possible in this material; but there is not an obvious exothermic peak.The material P8.5 has a higher F127 content (around 60%; estimated by TGA) than the material P9 (around 40%); this indicates that in these composite materials the final block copolymer content has an effect on the crystallization of the PEO blocks.Other synthesis procedures of OMC like EISA (evaporation induced self-assembly) provide a better control of some characteristics, like the block copolymer content. Materials with a high F127 content (60% m/m) were prepared by EISA (controlled evaporation of the solvent of an ethanolic solution of F127 and a phenol-formaldehyde resin, followed by a thermopolymerization process at 100°C for 24h). The DSC analysis shows an endothermic peak (38°C) and an exothermic peak at a low temperature (–20°C).These results indicate that the synthesis procedures of OMC using a phenolic resin and a PEO block copolymer could be a suitable alternative for the production of solid-solid PCMs.