Self-regulating thermal energy storage device

This work introduces a self-regulating device for the repeated temperature-controlled release of heat from sodium acetate trihydrate used as switchable phase change material (sPCM). Benefiting from the two-way shape changes of an actuating shape memory polymer (SMP), contact of the sPCM’s crystal nuclei with the sPCM was established upon cooling to release thermal energy and inhibited upon heating to regenerate the system. To identify the most suitable SMP, five types of phase-segregated polyester urethanes (PEUs) were synthesized. For this purpose, polyester diols were first produced and then brought to reaction with 4,4’-diphenylmethane diisocyanate and 1,4-butanediol. Adjacently, the thermal, mechanical and two-way shape memory properties of the PEUs were characterized. As expected, the molecular structure had an influence on the thermal and mechanical properties and thus on the actuation. Under a constant external load, the thermomechanically pretreated PEUs exhibited thermoreversible strain changes between 28% and 36% in cycle 20. By exploiting this behaviour in conjunction with the sPCM, ‘programmed heat release’ became possible. In the future, such systems could be used to prevent the ambient temperature in residential buildings, greenhouses and transport processes from falling below a threshold value specified by the lower actuation temperature of the SMP.