| Aerogel are a kind of nano-porous material with many excellent properties,such as huge specific surface area,extremely low density,high porosity and so on.These characteristics make aerogels have good applications in adsorption,energy storage,heat insulation,catalysis and other fields.However,because the aerogel skeleton is bonded by nanoparticles,this structural feature makes aerogels have high brittleness,which leads to the monotonous product form.At present,aerogel products in the market and in literature reports are usually in the form of aerogel powder,aerogel felt and aerogel block,but there are few reports on aerogel fiber which has a wider application field.This is because fibrous materials put forward higher requirements for the mechanical properties of aerogels.Therefore,it is of great theoretical and practical significance to improve the mechanical properties of aerogel materials and prepare aerogel fibers.In order to solve the above problems,this study carried out the following three parts of experiments:(1)Silica-bacterial cellulose composite aerogel fibers were prepared by using tetraethoxysilane as silicon source.The effects of the concentration of tetraethoxysilane on the thermal insulation and mechanical properties of composite aerogel fibers were investigated.Effect of secondary molding process on mechanical properties of composite aerogel fibers.The concrete implementation steps are as follows:firstly,the bacterial cellulose with macroscopic form of fibrous was prepared by laser cutting machine,which was used as the matrix for network enhancement.Then,the silica sol prepared by tetraethoxysilane was diffused into the linear matrix,and the composite wet sol was moulded twice through the mold to form the composite wet gel fiber with nanoscale interpenetrating network structure composed of silica gel framework and bacterial cellulose matrix.Finally,hydrophobic silica-bacterial cellulose composite aerogel fibers were obtained by modifying the composite wet gel fiber and drying at atmospheric pressure.The composite aerogel fiber samples were analyzed by electron microscope,mechanical properties,hydrophobicity,thermal insulation,specific surface area and pore size,density and porosity,and the content of silica in aerogel.The porosity of the composite aerogel fiber prepared from tetraethyl orthosilicate was as high as 93.6%,the lowest density was only0.110 g/cm~3,and the pore size range was 13.7-15.5 nm,which belongs to mesoporous material.The lowest content of silicon dioxide in aerogel was 27%W/W.The tensile strength of aerogel fiber was as high as 5.4 MPa.When the dosage of tetraethyl orthosilicate was 2.55m L,the aerogel fiber has high specific surface area(606.9 m~2/g),and the thermal insulation performance of the product is the best:when the heat source temperature was 210?,the surface temperature of the sample was only 132?.This process provides a new method for preparing aerogel fibers with excellent properties,which meets the mechanical properties requirements of wearable applications for aerogel fibers.(2)Compared with tetraethyl orthosilicate as silicon source,inorganic silicon source sodium metasilicate as silicon source is cheaper to prepare silica-bacterial cellulose composite aerogel fiber.In order to solve the problem of small time window of gel,some technological improvements were made,which makes the experimental operation more flexible.The specific experimental steps are as follows:the linear bacterial cellulose obtained by laser cutting was combined with the silica sol prepared by sodium metasilicate as silicon source to form bacterial cellulose containing sodium metasilicate.The composite wet sol fiber was remolded by mold,and the silica-bacterial cellulose composite aerogel fiber was formed by hydrochloric acid fumigation process.The thermal insulation properties,mechanical properties,specific surface area and electron microscope analysis of the samples were analyzed.The effects of the concentration of sodium metasilicate on the mechanical properties and thermal insulation properties of composite aerogel fibers were investigated.The silica-bacterial cellulose composite aerogel fiber has a tensile strength up to 4.5 MPa,and a specific surface area up to 128.3m2/g.When the concentration of sodium metasilicate is 20 wt%,the thermal insulation effect of the corresponding aerogel fiber is the best.When the heat source temperature is 150?,the surface temperature of the corresponding aerogel fiber is only 103?.The composite aerogel fiber prepared by this process has excellent thermal insulation and mechanical properties and can be well used in thermal insulation field.(3)In order to get rid of the restriction of the matrix morphology of bacterial cellulose on the length of aerogel fiber,and to make the aerogel raw material more green and environmentally friendly,the composite aerogel fiber was successfully prepared by using natural polymer materials chitosan and bacterial cellulose in this chapter.Firstly,different concentrations of oxidized bacterial cellulose slurry were prepared.Through the wet spinning process,the bacterial cellulose slurry was injected into the ethanol coagulation bath,and then the extruded linear bacterial cellulose was soaked in chitosan solution and low concentration formaldehyde solution to form chitosan-bacterial cellulose composite wet gel fiber,and finally,chitosan-bacterial cellulose composite aerogel fiber was prepared by freeze-drying.The specific surface area,thermal insulation and electron microscope analysis of the samples were carried out.The effect of the concentration of bacterial cellulose on the thermal insulation of the composite aerogel fiber was investigated.The maximum specific surface area of the prepared sample is 100.6 m~2/g.When the concentration of bacterial cellulose is 0.02 g/m L,the thermal insulation effect of the corresponding sample is the best.When the heat source temperature is 210?,the surface temperature of the sample is only158?.And the mechanical strength of the sample is good,up to 5.9 MPa.The preparation process is easy to operate,and the product is a natural polymer material,which is expected to be used as textile thermal insulation material.To sum up,aerogel fibers with good thermal insulation properties were successfully prepared,which enriched the morphology of aerogels and expanded the application field of aerogels.Without destroying the overall structure of the microbial cellulose network,it can significantly improve the mechanical properties of silica aerogel as a toughened substrate,especially after secondary shaping to regulate the spatial distribution of the fiber. |
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