Characterization Of The Mechanical Properties Of Microencapsulated Phase Change Materials And Gypsum-based Composite

In the fields of solar energy utilization,energy recycle and energy-efficient building,the technology of phase change for heat storage was widely used in order to conserve resources and protect the environment.Microencapsulation technology was used for packaging phase change materials to solve the leakage of phase change material,and the problem of the compatibility with substrate material.In this paper,the MF/paraffin microcapsules were prepared by in-situ polymerization,and mixed into the gypsum materials.The phase change microcapsules were easily deformation and destruction lead to the phase change materials leakage during used,it would be affected the stability and durability of the microcapsules.So it was very important to characterization mechanical properties of a single microcapsule.In the present work,the physical and mechanical properties of melamine resin/paraffin microcapsules were characterized.The size distribution of the microcapsules was measured by a laser particle size analyzer.A laser scanning confocal microscope(LSCM)was used to measure and record the shape and size of the microcapsules which were selected for micro-compression tests.The failure load of each microcapsule monomer was measured by instrumented nanoindentation with a flat-ended indenter.Based on the hypotheses that the deformation of the microcapsule is symmetric and the volume of the microcapsule keeps unchanged,a method for estimating the failure limit of a single microcapsule was proposed.The experimental results show that the failure loads of the microcapsules increase linearly with the increasing of microcapsule size,while the compression failure strain(34.5%±3.0%)and circumferential failure strain(34.2%±5.1%)are independent of the microcapsule size.It thus demonstrates that the compressive failure strain and the circumferential failure strain can be used to characterize the failure limit of a single microcapsule.Gypsum-based composites were manufactured by adding different kinds of phase change microcapsules in order to develop building materials with high thermal energy storage.The different addition(5wt%;10wt%;15wt% and 20wt%)of MF/paraffin microcapsules and PMMA/paraffin microcapsules were mixed into the gypsum materials.The mechanical properties of the gypsum-based composite materials were measured by universal testing machine to explore that the influence of the microcapsule wall materials and particle size.The experimental results show that the compression strength of the PMMA/paraffin microcapsules composite materials decreases linearly with the increase of microcapsules content,the compression strength of the MF/paraffin microcapsules composite materials decreases sharply with the increase of microcapsules content more than 5wt%.The addition of phase change microcapsules to gypsum decreases their compression strength,when the addition of 15wt% of the MF/paraffin microcapsules and the addition of 15wt% of PMMA/paraffin microcapsules,theirs compression strength respectively were 4.20 Mpa and 7.96 Mpa satisfied the mechanical standard for gypsum as building materials.In this paper,a method for estimating the failure limit of a single microcapsule was proposed,the compressive failure strain and the circumferential failure strain can be used to characterize the failure limit of a single microcapsule.The compression strength of the phase change microcapsules composite materials decreases with the increase of microcapsules content.