Preparation And Properties Of Microencapsulated Phase Change Materials With Acrylic-based Polymer Shells

Phase change materials (PCMs) is promising for use in thermal energy storage andthermal regulation due to their characteristic of storing thermal energy at a constanttemperature via phase transition and their ability to provide high energy storagedensities. Microencapsulated phase change materials (MicroPCMs) are PCMs inliquid/solid form enveloped within a polymer or inorganic shell, the size of which is inthe range of1-1000μm. There are many advantages of MicroPCMs, such as preventingthe interior PCMs from leakage, withstanding the change in the storage material volumeduring phase transition, reducing reactivity of PCMs toward the outside environmentand increasing heat transfer area. Acrylic resins are very attractive shell materialsbecause of their good impact strength, excellent dimensional stability, weatherresistance, non-toxic, ease of fabrication and commercial availability at reasonable cost.In this paper, microcapsules containing n-alkane with different acrylic-based polymershells were fabricated by a suspension-like polymerization. The as-preparedMicroPCMs were characterized and analyzed.Firstly, MicroPCMs with the crosslinked methylmethacrylate (MMA)-basedpolymer as shells were prepared.1,4-butylene glycol diacrylate (BDDA),divinylbenzene (DVB), trimethylolpropanetriacrylate (TMPTA) and pentaerythritoltetraacrylate (PETRA) were employed as crosslinking agents. Increasing crosslinkablefunctional moieties of the crosslinking agents and amount of crosslinking agent led toan increase in the shell mechanical strength, the heat storage capacities and the thermalstabilities of the MicroPCMs. Both shell mechanical strength and heat capacity ofMicroPCMs with DVB were higher than those of MicroPCMs prepared with BDDAdue to the two-vinyl group in DVB connecting with rigid phenyl group. Pilot-scalechemical reaction was carried out based on the above synthetic process, and a yield ofmore than1kg can be obtained per time.Secondly, MicroPCMs with different methylmethacrylate (MMA)-basedcopolymer shells were fabricated. Butyl acrylate (BA), butyl methacrylate (BMA),lauryl methacrylate (LMA) and stearyl methacrylate (SMA) were employed asmonomers to copolymerize with MMA. Heat capacities of MicroPCMs decreased withthe increase in the length of the side chains of the monomer, which is BMA<LMA<SMA. Thermal resistant temperatures of both uncrosslinked andcrosslinked MicroPCMs had the same sequence of changes, i.e., MicroPCMs withP(MMA-co-SMA)> MicroPCMs with P(MMA-co-BMA)> MicroPCMs withP(MMA-co-BA)> MicroPCMs with P(MMA-co-LMA).Thirdly, MicroPCMs with crosslinked PBMA, PBA, PLMA and PSMA shellswere fabricated. DVB and pentaerythritol triacrylate (PETA) were employed ascrosslinking agents. The MicroPCMs prepared by using DVB show greater heatcapacities and thermal stabilities compared with the MicroPCMs prepared by usingPETA. Heat capacities of both the MicroPCMs with PBMA and PBA were higher thanthose of MicroPCMs with PLMA and PSMA. The MicroPCMs with PBMA has thehighest thermal resistant temperature when prepared by DVB, while the MicroPCMswith PSMA exhibits the greatest thermal stability when prepared by PETA.Finally, MicroPCMs with different BMA-based copolymer shells were synthesized.Methacrylic acid (MAA) and acrylic acid (AA) were employed as monomers tocopolymerize with BMA. The performances of MicroPCMs have been improved whenMAA or AA was introduced to the polymer shells. Furthermore, heat capacity andthermal stability enhanced with the increasing of MAA content in the acryliccomposition of the shell. Thermal images showed that the gypsum board withincorporated P(BMA-co-MAA)/n-octadecane microcapsules possessedtemperature-regulated property.