Preparation Of TiO₂ Hollow Multishell Structures/polyurethane Composite And Its Thermal Insulation Application

The heat transfer characteristics of materials are dominated by their physical structure and chemical composition.Hollow structural materials have strong advantages in the field of thermal management,such as light weight,high porosity and low thermal conductivity.Hollow Multishell Structures(HoMSs)is a kind of novel hollow structural materials,which has multiple shells and independent closed cavities separated by the shells,and shows unique temporal and spatial order in mass and energy transmission.HoMSs materials have been proved to bring new breakthroughs in the fields of sequential drug release and sequential absorption of electromagnetic waves.However,there are few reports on the research of HoMSs in the field of thermal energy transfer,especially in the composite system of HoMSs and polymer materials.In order to explore the heat transfer characteristics of HoMSs materials,this paper firstly compounded TiO₂ HoMSs prepared by sequential template method with thermal-responsive polyurethane.The thermal aggregation effect of HoMSs was found,and it was revealed that the thermal aggregation effect was closely related to the number of HoMSs shells,which provided a new method for studying the heat transfer process in multistage hollow structures.This novel HoMSs composite functional material has both thermal aggregation effect and thermal responsiveness,so it has the potential as an intelligent thermal insulation material.Finally,this paper also studied the thermal insulation performance,heat radiation shielding performance and low temperature insulation performance of HoMSs composite materials,and obtained the following important achievements:Firstly,carbonaceous microspheres were obtained by dehydration polycondensation of sucrose under hydrothermal conditions,and then used as hard template to absorb cheap titanium tetrachloride aqueous solution.Nanosized TiO₂hollow spheres,double-and triple-shelled TiO₂ HoMSs were synthesized by controlling hydrothermal temperature,adsorption time and calcination rate of removing hard template.Since the surface of the TiO₂ HoMSs was rich in-OH groups,the surface of TiO₂ HoMSs can be chemically modified with the silane coupling agent 3-aminopropyltriethoxysilane.In this way,the stability of the composite of the HoMSs and polymer substrate can be maintained well.In addition,as the number of shell increased,the specific surface area of the TiO₂ HoMSs gradually increased.This mean that TiO₂ HoMSs had an increased air-solid phase interfaces,thereby increasing the overall thermal resistance.Secondly,using tetrahydrofuran as the solvent,4,4-dimethyldiisocyanate as the hard segment,polyethylene glycol as the soft segment,and neopentyl glycol as the chain extender,the temperature sensitive polyurethane(TSPU)was successfully synthesized by a two-step method.The structural properties,phase change behavior,and thermal properties of the synthesized TSPU were characterized and analyzed.The phase transition temperature of TSPU was about 60?when the reaction temperature was 60?,the reaction time was 4 h,and the ratio of hard and soft segments was 1.0.This kind of phase change material had temperature response ability.The soft segment inside the polyurethane underwent phase change and became soft when the temperature was higher than the phase change temperature,making the thermal conductivity better.The soft molecular chains freezed when the temperature was lower than the phase transition temperature.The movement of the molecular chain inside the polyurethane was hindered,which made the thermal insulation performance better.Thirdly,TiO₂ HoMSs whose surfaces had been chemically modified were compounded with TSPU to obtain three TSPU/TiO₂ HoMSs composite.The thermal aggregation effect of HoMSs was found by comparing DSC results.With the increase of the number of HoMSs shells,the thermal accumulation effect of HoMSs materials became more obvious.In addition,in terms of heat conduction,with the increase of the number of HoMSs shells,the temperature rise curve of HoMSs composites can be slower and slower,exhibiting enhanced thermal insulation performance.However,when the HoMSs composite material reached the phase transition temperature,its thermal insulation performance weakened and it had certain heat dissipation performance,which showed an intelligent temperature response performance.When the doping amount of the triple-shelled TiO₂ HoMSs was 2 wt%,the composite can achieve a temperature difference of 6.6?under a temperature field of 50?.However,the sample box coated with the above composite material can keep 8.5?when the heat preservation test was carried out at 4?.Finally,the thermal radiation shielding characteristics of HoMSs composites were explored.The results showed that the triple-shelled TiO₂ HoMSs composite had lower light transmittance,which can greatly reduce the thermal gain caused by solar thermal radiation.Finally,based on the solid heat transfer module in COMSOL Multiphysics software,the polymer/HoMSs geometric model was established.By simulating the heat transfer process of composite materials with different number of shells of HoMSs,the calculation results showed that the heat accumulation effect becomes more obvious with the increase of the number of shells.Triple-shelled HoMSs composites showed better thermal insulation performance.