Abstract
In this paper, we synthesized MC(BeA-co-MMA) copolymer microcapsules through suspension polymerization. The pendent n-behenyl group of BeA is highly crystalline, and it acts as the side-chain in the structure of BeA-co-MMA copolymer. The highly crystalline n-behenyl side-chain provides BeA-co-MMA copolymer thermal-energy-storage capacity. In order to investigate the correlation between the thermal properties and crystal structure of the BeA-co-MMA copolymer, the effects of monomer ratio, temperature changing and the changing rate, as well as synthesis method were discussed. The monomer ratio influenced crystal transition behavior and thermal properties greatly. The DSC results proved that when the monomer ratio of BeA and MMA was 3:1, MC(BeA-co-MMA)3 showed the highest average phase change enthalpy ΔH (105.1 J·g–1). It indicated that the n-behenyl side-chain formed a relatively perfect crystal region, which ensured a high energy storage capacity of the copolymer. All the DSC and SAXS results proved that the amount of BeA had a strong effect on the thermal-energy-storage capacity of the copolymer and the long spacing of crystals, but barely on the crystal lamella. It was found that MMA units worked like defects in the n-behenyl side-chain crystal structure of the BeA-co-MMA copolymer. Therefore, a lower fraction of MMA, that is, a higher fraction of BeA, contributed to a higher crystallinity of the BeA-co-MMA copolymer, providing a better energy storage capacity and thermoregulation property. ST(BeA-co-MMA) copolymer sheets with the same ingredients as microcapsules were also prepared through light-induced polymerization aiming at clarifying the effect of the synthesis method. The results proved that the synthesis method mainly influenced the copolymer chemical component, but lightly on the crystal packing of the n-behenyl side-chain.
Highlights
A latent heat storage system is a highly efficient and environmentally friendly means to use residual heat, recovering waste heat and to store/release thermal energy for saving energy
The behenyl acrylate (BeA) consisted of an n-behenyl chain with 22 methylene units and a vinyl group was used as the phase change monomer to synthesize P(BeA-co-MMA) copolymer microcapsules with methyl methacrylate (MMA) through suspension polymerization [18]
Using copolymer microcapsules and sheets with the same ingredients as samples, we investigated the effects of synthesis method on the thermal and crystallization performance of the copolymer materials
Summary
A latent heat storage system is a highly efficient and environmentally friendly means to use residual heat, recovering waste heat and to store/release thermal energy for saving energy. PCMs benefit from less phase segregation and good physical-chemical stability These features give them perfect thermal durability and cycling stability against thermal degradation required for a long-term service [10,11,12,13]. Comb-like polymers, with a crystalline long n-alkane side-chain attached to a main-chain, are known to pack into a layered structure with alternating side-chain crystal regions at room temperature [14,15,16,17]. Much of the work revolves about crystalline copolymer microcapsules and gels having a chemical structure with an n-alkane crystalline side-chain. The behenyl acrylate (BeA) consisted of an n-behenyl chain with 22 methylene units and a vinyl group was used as the phase change monomer to synthesize P(BeA-co-MMA) copolymer microcapsules with methyl methacrylate (MMA) through suspension polymerization [18]. We have confirmed that these copolymers can form crystal regions at room temperature to provide thermoregulation properties, and their application potential as form-stable solid–solid PCMs are greatly expected
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