Preparation And Thermal Insulation Performance Of Hollow Microspheres-based Composites

With the advancement of science and technology and the rapid development of the economy,mankind's demand for energy is increasing,and the problem of energy shortage is becoming increasingly serious.At the same time,the trend of global warming has been exacerbated Thermal insulation,as one of the effective ways to save energy and reduce emissions,has a wide range of applications in the fields of construction,ships,furnaces,pipes,aerospace,thermal batteries and fire protection clothing.Although traditional insulation materials have good properties,they can't achieve the demands of social development.In this study,hollow glass microspheres(HGM)were selected as barrier fillers,and water-based polyurethane(WPU)was used as a binder.The coating method was used to combine water-based polyurethane with glass fiber fabric to prepare lightweight thermal insulating composites.It founds that as the content of hollow glass microspheres increased,the bulk densities and the thermal conductivities of the composites gradually decreased,and the thermal insulation effect was gradually improved.The volume content of glass fiber fabric in the composite is 35%.The bulk density of the composite is 0.54 g/cm3,and the thermal conductivity is 0.1154 W/(m·K),which decreased 45.2%compared with the material without hollow glass microspheres,when the volume ratio of HGM and WPU is 0.8.At 70?,the composite with a thickness of 2 mm can achieve a thermal insulation effect with a temperature difference of 17.74?.In order to solve the problems of large hollow glass microspheres and low compressive strength,smaller hollow SiO2 microspheres with better size uniformity were successfully prepared via hydrothermal and sol-gel methods.Hydrothermal carbon spheres were used as templates,and tetraethylsilicate(TEOS)was used as the precursor.The surface of the carbon spheres is coated with a layer of silicon dioxide(SiO2).Then,the carbon template was removed via the calcination.In addition,hollow SiO2 microspheres having different sizes can be obtained by adjusting the glucose concentration and the TEOS concentration.The specific surface area of the hollow SiO2 microspheres is 13.27 m2/g.The morphological observation and pore size analysis show that the hollow SiO2 microspheres are completely and have a high closed porosity,which is suitable as a thermal insulation filler.It created conditions to further optimize the thermal insulation performance of the composites.Furthermore,in order to prepare thermal insulation materials with super-low thermal conductivity,the hollow SiO2/PAN composite fibrous membrane was prepared by using the electrospinning technology.Hollow SiO2 microspheres were used as the filler and polyacrylonitrile(PAN)was used as the matrix.This composite fibrous membranes have excellent thermal insulation properties and flexibility.The thermal conductivity of the composite fiber membrane is 0.01639 W/(m·K),which is 69.7%lower than that of PAN fibrous membrane,when the content of hollow SiO2 microspheres is 15 wt%.At 70?,a 15 wt%hollow SiO2/PAN composite fibrous membrane with a thickness of 0.5 mm can achieve a thermal insulation effect with a temperature difference of 15.7?.The composite fibrous membrane can reach a thermal insulation effect with a temperature difference of 26.84?,when the thickness is 2 mm.Also the material is flexible.The hydrophobicity of the composite fibrous membrane can be improved through pre-oxidation and hydrophobic treatment,which is beneficial to stabilize the excellent thermal insulation performance of the composite fibrous membrane.In addition,combining silver nanowires with the composite fibrous membrane can improve the infrared reflection capability of the composite and effectively reduce the heat loss caused by thermal radiation.This thesis shows that hollow microspheres can enhance the thermal insulation properties of composites to a certain extent,and the composites have the advantages of light weight and low thermal conductivity.Then,compounded with silver nanowires to further improve the infrared radiation reflection of the composite.Finally,flexible composite materials with light weight and low thermal conductivity were prepared through reasonable structural design,using porous structure and low thermal conductivity of still air in this work.