Electrospun capric acid/polyethylene terephthalate composite nanofibres for storage and retrieval of thermal energy

Abstract

Composite nanofibres based on capric acid (CA) and polyethylene terephthalate (PET) with different mass ratios of CA/PET ranging from 0·5∶1, 1∶1, 1·5∶1, 2∶1 to 2·5∶1 were fabricated by electrospinning as innovative form-stable phase change materials for storage and retrieval of thermal energy. The morphological structures, thermal energy storage properties and thermal stability of electrospun CA/PET composite nanofibres were characterised by field emission scanning electron microscopy (FE-SEM), transmission electronic microscopy (TEM), differential scanning calorimetry (DSC) and thermogravimetric analyses (TGA) respectively. The FE-SEM images revealed that the electrospun CA/PET composite nanofibres had a cylindrical morphology with average fibre diameters in the range of about 145–192 nm. Additionally, the FE-SEM and TEM images indicated that the CA distributed on the surface and within the core of the composite nanofibres. The results acquired from DSC analyses indicated that the mass ratio of CA versus PET played an important role on the enthalpy values of melting and crystallisation of the composite nanofibres, while it had no appreciable effect on the temperatures of phase transitions. Moreover, the results of DSC thermal cycling suggested that the thermal energy storage properties of the CA in the composite nanofibres had hardly been influenced during thermal cycling, indicating that the electrospun CA/PET composite nanofibres had good thermal reliability. The TGA results showed that both the onset thermal degradation temperature and the charred residue at 700°C of the composite nanofibres were lower than those of pure PET nanofibres as a result of the thermal instability of the CA molecular chains.