Study On Preparation And Heat Radiation Performance Of Micro/nano Fibrous Thermal Insulation Materials

Thermal insulation materials are widely used in various applications for reducing heat transfer between a medium and its environment. Among the various insulating materials, such as vacuum insulation panels, foam insulation and powder insulation etc, electrospun nanofibrous materials have advantages in terms of high thermal insulation, because of their extremely high porosity. Within the porous fibrous materials, the mechanism of heat transfer mainly consists of three parts, conduction through the solid material of the fibres, conduction through the intervening air and thermal radiation through electromagnetic. Lots of research on fibrous insulation have shown that radiative heat transfer within these highly porous media could be a significant contribution to the total heat transfer.The radiative heat flux through fibrous insulations could be reduced by decreasing fibre fractional volume, by increasing fibre emissivity as well as by reducing fibre radius. Therefore, developing superfine fibres has been found to be one of the most efficient ways to reduce radiative heat flux within fibrous insulations and hereby improve the thermal insulating performance.Electrospinning is a simple and effective method for producing polymeric nanofibrous membranes with high surface-to-volume ratio under the driving force of an external electric field on melts or polymer solutions. Coating nanofibers can create materials of exceptional quality for radiation shielding, catalysis, antimicrobial and reinforcement, as nanofibers have very large surface area to mass ratios and mechanical integrity. Titanium dioxide?TiO₂? is one of the most studied metal oxides for its many applications, and has been particularly extensively studied as a photocatalyst and as opacifier et al. For different applications, TiO₂ has been coated onto various substrates via different deposition techniques, e.g. sol–gel processing, evaporation- deposition, dip-coating, and spin-coating. In the present work, we introduced Lb L self-assembling method to coat TiO₂ nanoparticles onto electrospun PVDF fibrous membrane, using two assembling raw materials of polyacrylic acid?PAA? and TiO₂ nanoparticles which are easy to obtain from the market. This route is very feasible with fewer steps,cheaper material and more efficient.Therefore, in this paper, electrospun micro/nano fibers and TiO₂@electrospun micro/nano fibers were prepared via electrospinning technology and self-assembly technology, using SEM, TEM and FTIR to determine microstructure and thermal radiation properties of materials. The results showed that, the finest fibers of 449 mn could be obtained when the conditions are 29 wt.%, 1ml/h, 15.5kv, 15 cm. In the infrared wavelength range of 2.5-25mm, with the fiber diameter increasing, Rosseland mean the extinction coefficient of electrospun micro/nano fibers increased and radiation heat conductivity decreased; under the temperature of 300 K, radiant heat conductivity of PVDF fibers respectively decreased from 0.095(10^-3W/m K) to 0.037(10^-3W/mK). After assembling 4 layer of TiO₂, infrared transmittance of PVDF fibers were significantly reduced, Rosseland mean the extinction coefficient increased from 31.9 cm-1 to 325 cm-1; under the temperature of 230 K and 420 K, radiant heat conductivity of PVDF fibers respectively decreased to 0.011(10^-3W/mK) and 0.066(10^-3W/mK) respectively, indicating that the shielding properties of the fiber material for heat radiation had been improved effectively.