The Preparation And Thermal Behavior Of Flame Retardant Carbon Nanotubes Modified Phase Change Material Microcapsules

Solid-liquid organic phase change material（PCM）shows great application potential in the field of building insulation materials due to the unique heat storage and release properties.However,liquid PCM will flow and result in leakage phenomenon.Therefore,it is necessary to encapsulate PCM into PCM microcapsules with stable form through microencapsulation technology.At present,the organic polymer material shell commonly used in the preparation of PCM microcapsules exhibits the advantages of excellent encapsulation performance and high compatibility with the organic substrate.But the low thermal conductivity will reduce the heat transfer efficiency of PCM microcapsules,thus leading to the decrease of temperature control effect.At the same time,the flammability of polymer materials will increase the fire risk of PCM microcapsules during the application.In order to solve these two problems,carbon nanotubes（CNT）with high thermal conductivity were selected as the filler,and Fe₃O₄,3-aminopropyl-triethoxysilane（APTES）and 4,4’-methylene diphenyl diisocyanate（MDI）were used to modify CNT to prepare three kinds of flame-retardant CNT（Fe-CNT,Si-CNT and N-CNT）.Then flame-retardant CNT modified PCM microcapsules were synthesized,and PCM microcapsules were added into rigid polyurethane foam to prepare composite insulation materials.In addition,the effects of the above three flame-retardant CNT on the thermal behavior of PCM microcapsules and composite insulation materials were analyzed and compared.The main research contents and conclusions are as follows:1.Fe-CNT was prepared by the synthesis of Fe₃O₄pellets on the CNT surface through a pot of hydrothermal method,and then the modified PCM microcapsules（Fe-C-PCM）were produced by embedding Fe-CNT into PCM microcapsules.Finally,the composite insulation material（RPUF-Fe-C-PCM）with Fe-C-PCM was prepared.The results showed that the particle size of Fe₃O₄pellets was mostly about 200 nm,and the Fe₃O₄pellets on the surface of Fe-CNT presented a monodisperse state.Fe-C-PCM was polymerized around Fe₃O₄spheres after coating CNT,and the particle size of PCM microcapsules was about 130 nm.Fe-CNT improved the thermal stability of PCM microcapsules while maintaining excellent thermal conductivity,so that RPUF-Fe-C-PCM showed better temperature control ability.In addition,the p HRR,THR and TSP of RPUF-Fe-C-PCM were 8.68%,6.85%and 10.94%lower than RPUF-C-PCM,respectively.In conclusion,Fe-CNT enhanced the thermal stability of PCM microcapsules and the flame retardancy and temperature regulation performance of composite insulation materials while ensuring excellent thermal conductivity.2.Si-CNT was prepared by introducing APTES on the surface of CNT through chemical grafting method,and then the modified PCM microcapsules（Si-C-PCM）were produced by embedding Si-CNT into PCM microcapsules.Finally,the composite insulation material（RPUF-Si-C-PCM）with Si-C-PCM was prepared.The results showed that APTES formed a rough thin layer on the surface of CNT,and the diameter of Si-CNT increased from 20 nm（pure CNT）to about 25 nm.The Si-C-PCM was about 300 nm in diameter,and the Si-CNT could be clearly seen passing through it.Si-CNT improved the thermal stability of PCM microcapsules while maintaining excellent thermal conductivity,so that RPUF-Si-C-PCM showed better temperature control ability.In addition,the p HRR and TSP of RPUF-Si-C-PCM were 20.02%and18.7%lower than RPUF-C-PCM,respectively.In conclusion,Si-CNT enhanced the thermal stability of PCM microcapsules and the flame retardancy and temperature regulation performance of composite insulation materials while ensuring excellent thermal conductivity.3.N-CNT was prepared by introducing MDI on the surface of CNT through chemical grafting method,and then the modified PCM microcapsules（N-C-PCM）were produced by embedding N-CNT into PCM microcapsules.Finally,the composite insulation material（RPUF-N-C-PCM）with N-C-PCM was prepared.The results showed that MDI formed a thin layer with particle protrusions on the surface of CNT,and the diameter of the N-CNT increased to about 35 nm.The N-C-PCM exhibited a relatively standard spherical shape with a diameter of about 160 nm,and N-CNT could be clearly seen through it.N-CNT improved the thermal stability of PCM microcapsules while maintaining excellent thermal conductivity,so that RPUF-N-C-PCM showed better temperature control ability.In addition,the p HRR,THR and TSP of RPUF-N-C-PCM were 12.73%,12.51%and 11%lower than RPUF-C-PCM,respectively.In conclusion,N-CNT enhanced the thermal stability of PCM microcapsules and the flame retardancy and temperature regulation performance of composite insulation materials while ensuring excellent thermal conductivity.4.The effects of Fe-CNT,Si-CNT and N-CNT on the morphology,thermal conductivity,thermal stability of PCM microcapsules,flame retardancy and temperature regulation performance of composite insulation materials were compared and analyzed.The following rules are obtained after analysis:The influence of Fe₃O₄on the morphology of CNT is local,while APTES and MDI cover the entire surface of CNT.Due to better compatibility with PMMA,the thermal conductivity of organic modified CNT is improved compared with inorganic modified CNT.Accordingly,RPUF-N-C-PCM and RPUF-Si-C-PCM also show better temperature regulation performance.Fe-CNT plays a more positive role in enhancing the thermal stability of PCM microcapsules.The synergistic flame-retardant effect of Si element and CNT can significantly reduce the p HRR and TSP values of composite insulation materials,but it shows no effect on reducing THR.Fe-CNT and N-CNT can simultaneously reduce p HRR,THR and TSP values of composite insulation materials,but the decrease degree is not as good as Si-CNT.Among them,N element and CNT produced better flame-retardant effect.