Fabrication and characterization of a new enhanced hybrid shell microPCM for thermal energy storage

MicroPCMs (microencapsulated phase-change materials) were successfully synthesized using PMMA (poly(methyl methacrylate)) and UF (urea-formaldehyde) as raw materials for hybrid shells, and n-tetradecane as core materials. NMA (n-methylol acrylamide) with two functional groups of double-bond and hydroxymethyl was used as a crosslinking agent. The morphologies and chemical structures of microPCMs were characterized using scanning electron microscopy (SEM) and Fourier transformed infrared (FTIR) spectroscopy. The agglomerations of the UF/PMMA hybrid samples might be influenced by two factors: cross linking action of NMA and PMMA/UF ratio in shell materials. The phase change properties and thermal durability were investigated by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA), respectively. The UF/NMA/PMMA hybrid shell microcapsules has an enthalpy of 175.5 J/g which is higher than the single-layer shell samples of PMMA and UF, and a better leakproofness than the UF/PMMA hybrid samples without NMA owing to the semi-IPN microstructure. Likewise, the UF/NMA/PMMA hybrid samples have higher thermal durability than the single layer shell samples of PMMA and UF and the UF/PMMA hybrid samples without NMA. Moreover, the thermal cycling test of the UF/PMMA hybrid samples with NMA was carried out for 100 heating/cooling cycles and indicated that the developed hybrid shell microPCMs have good chemical stability and thermal reliability. The heating-up experiment revealed that the foam treated by microcapsules had a better thermoregulatory property than the raw foam. Based on the results obtained, it can be concluded that n-tetradecane/UF/PMMA microPCMs have potential thermal energy storage applications.