Preparation Of Soft Silica Nanofibrous Membranes For Thermal Insulation

As an important way of energy saving and thermal protection, thermal insulation has anextensive applications and needs in the field of buildings, ships, furnaces, pipelines, aerospace,thermal battery and fire-protection clothing. The material used itself is the core of thermal insulation.Ceramic fiber thermal insulation material, with the advantages of light weight, high temperatureresistance, excellent thermal insulation, good mechanical vibration-resistant and non-toxic, isincreasingly becoming the most promising materials used in the thermal protection system.However, although ceramic fiber has many good properties, its application has been limited by itsbrittleness and low strength. Therefore, researching and developing flexible and high-strengthceramic fiber is of great significance while striving to retain its outstanding intrinsical performance.The emergence of nanotechnology brings hope and ideas to develop ceramic fiber with goodflexibility and high strength used as thermal insulation materials. Among the technologies toprepared nanofibers, electrospinning, which can produce continuous and controllable nanofibers atlow production costs, is currently the most potential method to realize the industrial-scaleproduction of nanofibrous materials. In the researches of silica nanofibers prepared byelectrospinning, there exist the problems of spinning difficulty, membrane defects and lowproduction efficiency, on the other hand, the study about its own flexibility and mechanicalproperties of silica nanofiber is rarely mentioned, which in fact is closely related to its practicalapplication.Aiming at resolving these problems, in this paper, the poly(vinyl alcohol) with lower molecularweight is selected as electrospun polymer template and the hydrolysis process of tetraethylorthosilicate is regulated at the same time to get superior spinning liquid formulations. Using theoptimized electrospinning process, defect-free silica nanofibrious membranes are prepared. What ismore, the production efficiency is increased by more than5times compared with the existingresearch. In order to obtain silica nanofiber membranes with higher strength and better flexibility,this research study the influence of calcination temperature and sodium chloride contents on themorphology structure of silica nanofibrious membrane by setting different calcination temperaturesand different concentration of sodium chloride in the precursor solution, and how the microstructure of silica nanofibrious membrane determines its flexibility and tensile properties is also discussed.The results show that the impact of calcination temperature and sodium chloride concentration onthe microstructure of silica nanofibrous membrane is different. By increasing calcinationtemperature, a global adhesion structure is formed in the membrane so that the fiber inside loses theability to adjust its shape and the relative position，which deteriorated the mechanical properties ofthe membrane. By adding appropriate concentration of sodium chloride in the precursor solution,not only a finer fiber diameter silica nanofiber but also a special dispersed and localized adhesivestructure is obtained due to the sodium chloride existed in the hybrid membrane. This microstructurecan ensure adequate internal fibers to deform and produce relative sliding when the membrane iscompelled by an external force and then deformed. Meanwhile the presence of adhesion points inthe membrane also increases the number of fibers that bear the stress when the membrane is ruptured.It increase the tensile strength of the membrane while ensure its good flexibility. Therefore, in thisproject not only the strength of flexible silica nanofibrous membrane is further reinforced byregulating its micro-structure, but also the industrialization process of electrospinning silicananofibers has been promoted, which laid a good foundation for its practical applications.With the advantages of lightweight, soft, seismic, acoustic, wearable property andenvironment-friendly prepared process, the obtained silica nanofibrous membrane has an ultra-lowthermal conductivity at room temperature in the insulation test, and also exhibits excellent thermalinsulation properties in practical application. Therefore, the silica nanofibrous membrane is an ideathermal insulation material which will play an important role in the field of thermal insulation.