Microencapsulation of stearic acid with polymethylmethacrylate using iron (III) chloride as photo-initiator for thermal energy storage

A Rapid Method for Low Temperature Microencapsulation of Phase Change Materials (PCMs) Using a Coiled Tube Ultraviolet Reactor

Microencapsulation of phase change materials (PCMs) remain a suitable option within building materials, as they contribute to the thermal mass and provide an energy buffer, an added benefit. This paper presents a novel method for the rapid fabrication of microencapsulated phase change materials (PCMs) at ambient conditions in a perfluoroalkoxy (PFA) coiled tube ultraviolet (UV) reactor. The objective of this study was to optimize key parameters such as the product yield and quality of the as-prepared microcapsules. Rubitherm® RT-21™ PCM was microencapsulated within shells of poly-methyl-methacrylate (PMMA) through a suspension emulsion polymerization approach, where the crosslinking of polymers was driven by UV radiations with an appropriate photoinitiator. The characteristics of the resulting PCM microcapsules were found to be affected by the volumetric flow rate of the emulsion inside the coiled tube reactor. Higher volumetric flow rates led to higher PCM contents and higher microencapsulation efficiency, resulting in an average particle size of 6.5 µm. Furthermore, the effect of curing time on the PCM microcapsule properties was investigated. The optimum encapsulation yield, conversion, efficiency and PCM content were observed after 10 min of polymerization time. The thermal analysis indicated that the developed process had an efficiency of 85.8%, and the capsules were characterized with excellent thermal properties. Compared to the conventional thermal microencapsulation processes, the use of a coiled tube UV reactor with an appropriate photoinitiator enables the encapsulation of heat-sensitive PCMs at ambient conditions, and reduces the microencapsulation time dramatically. As a result, this novel microencapsulation approach can lead to a wider scope of PCM encapsulation and enable rapid, continuous and potentially large-scale industrial production of PCM microcapsules with low energy consumption.

Cryogenic conditioning of microencapsulated phase change material for thermal energy storage

Microencapsulation is a viable technique to protect and retain the properties of phase change materials (PCMs) that are used in thermal energy storage (TES) applications. In this study, an organic ester as a phase change material was microencapsulated using melamine-formaldehyde as the shell material. This microencapsulated PCM (MPCM) was examined with cyclic cryogenic treatment and combined cyclic cryogenic heat treatment processes. The surface morphology studies showed that the shell surfaces had no distortions or roughness after cryogenic treatment. The cryogenically conditioned microcapsules exhibited diffraction peak intensity shifts and crystal structure changes. The onset of melting for the nonconditioned and conditioned microcapsules were measured to be 8.56-9.56 °C, respectively. Furthermore, after undergoing the cryogenic and heat treatment processes, the PCM microcapsules had appreciable latent heat capacities of 39.8 kJ/kg and 60.7 kJ/kg, respectively. Additionally, the microcapsules were found to have good chemical stability after the cryogenic treatment. In addition, the cryogenically conditioned microcapsules were found to be thermally stable up to 128.9 °C, whereas the nonconditioned microcapsules were stable up to 101.9 °C. Based on the test results, it is obvious that the cryogenically conditioned microcapsules exhibited good thermal properties and are very desirable for cool thermal energy storage applications.

A Novel Encapsulation Method for Phase Change Materials with a AgBr Shell as a Thermal Energy Storage Material

Micro/nanoencapsulated phase change materials, used typically as energy storage materials, are frequently applied in energy-saving and energy-efficient processes. In this work, we proposed a novel method for the micro/nanoencapsulation of phase change materials (PCMs), which has the advantage of simple operation and can be suitable for encapsulation of more than one PCM. Fatty acid PCMs, such as steric acid and palmitic acid, and non-fatty acid PCMs, like beeswax, have both been successfully micro/nanoencapsulated by a silver bromide (AgBr) shell with this method. The obtained fatty acid/AgBr micro/nanocapsules, with diameters of less than 1 µm, show good thermal storage capacities over 150 J/g with their encapsulation ratios as high as 92.4%. Similarly, the prepared beeswax/AgBr micro/nanocapsules show a high encapsulation ratio. In addition, all the micro/nanocapsules exhibit good thermal stability. Therefore, the method developed by this work is highly-efficient for the encapsulation of PCMs, which is beneficial for PCMs in various applications as energy storage materials.