Research On Polyurethane Solid-solid Phase Change Heat Storage Material

In this paper, a novel solid-solid phase change heat storage polyurethane (PUPCM) with various molecular weight PEG-based soft segment and MDI-BDO-based hard segments was synthesized by two-step solution polymerization. FT-IR,DSC,WAXD,TG,SEM were used to study the structural characteristics,phase change behavior, heat storage characteristics, aggregation structure and phase change mechanism.The result indicates that the PUPCM has good thermal properties: great transition enthalpy; suitable phase transition temperature; good thermal stability; no liquid leakage in the phase transition process; great phase transition reversibility, the enthalpy of positive process and reverse process is almost the same, and the direction is decided by the temperature; reasonably good stability throughout the cycling process. It can be considered as promising PCMs.Polarization Microscope (POM), Wide Angle X-ray Diffraction(WAXD) investigations indicate that the soft segments of PUPCM are crystalline and the crystal structures are spherulites, but the spherulites size is much smaller than that of PEG because of the soft segment PEG's crystallization in PUPCM confined by the hard segment. The heat storage is caused by the transition of the soft segments of PUPCM from crystalline state to amorphous. The energy is mainly obtained from the heat caused by entropy change between the low-entropy crystal state and high-entropy amorphous state. The hard segments have no contribution to the phase change heat storage, but it acts as"physical cross-linkers", restricting PEG's segmental movement, when it is heated to the temperature 30-40℃above PEG's melting point, PUPCM still doesn't move freely and keep its solid state.Polyurethane with solid-solid phase change heat storage properties has two essential conditions: Firstly, the soft domain is crystalline with high melting enthalpy(ΔH) and suitable melting temperature; secondly, the hard segments can bind themselves together via hydrogen bonding and forming crystallite,becoming the"cross-linkers"to keep PUPCM in solid state above phase change temperature. The result indicates that the soft segments are not able to crystallize until its average...