Study On The Synthesis Of Starch-Silica Aerogels Via Ambient Pressure Drying Process

Silica aerogels have excellent physical and chemical properties because of their unique three-dimensional network structure,which have been applied in various fields such as medicine,catalysis,aerospace and building materials.And so the silica aerogels is great on scientific value.However,their unique structure also leads to the disadvantages of poor bulk formation and insufficient mechanical properties.To solve these defects of silica aerogels,we focused on enhancing the three-dimensional skeleton strength of SiO₂ aerogels.The effects of different alkaline catalysts systems,aging temperature and starch composite modification on the structure and properties of SiO₂ aerogels had been studied.Moreover,in order to maintain the unique structure of SiO₂ aerogels while improving its mechanical properties and formability,the preparation parameters of SiO₂ aerogels via the atmospheric pressure environment drying process had been optimized.The main research contents and conclusions are summarized as follows:A series of hydrophobic SiO₂ aerogels had been syntheiszed via the sol-gel method and ambient pressure drying process by using commercialized water glass with a modulus of 3.1as the silica source.The gel properties within four catalytic systems in terms of LiOH,KOH,NaOH and NH₃·H₂O were studied by changing different ratio of silicon to water and gel pH value,respectively.And the the optimum ratio of silicon to water is 1:4 and the pH of gel is about 5.2.In the optimal conditions of 1:4 for the ratio of silicon to water and 5.2 for the gel pH values at the aging temperature of 50°C,different catalytic systems on the structure and properties of silica aerogels had been investigated.It was shown that the specific surface area of SiO₂ aerogels synthesized with different alkaline catalyst was about 380-430m²/g.The pore volume was kept at 2.60-3.35cm³/g with a special double pore structure at 1.7nm and 32nm,respectively.And the thermal stability raised to about 400°C.The alkali metal ions from the alkaline catalyst may promote the dissolution between the nano-SiO₂ particles and enhance the connection area between the particles during the gel process.With different catalytic systems,effects of different aging temperatures on the structure and properties of SiO₂ aerogels had been examined.Used commercialized water glass with a modulus of 3.1 as the silicon source,a series of SiO₂ aerogels aged at 80?,120?were synthesized with LiOH,NaOH,KOH and NH₃·H₂O as different catalysts in the optimal conditions of 1:4 for the ratio of silicon to water and 5.2 for the gel pH values.It was found that increased the aging temperature was beneficial to increase the particle size of the skeleton particles of SiO₂ aerogels.However,it was not conducive to maintaining the large specific surface area of the aerogels when the aging temperature was too high.At the aging temperature of 80°C,the dissolution of alkali metal ions not only increases the particle size of the nano-SiO₂ particles,but also enhances the specific surface area of the SiO₂ aerogels while retaining the two-hole structure.Furthermore,based on the study of effects of different alkaline catalysts on the structure and properties of pure SiO₂ aerogels,starch was added as a modified material to synthysize starch-SiO₂ aerogels.And the influence of the molding method and the type of additives on the structure and properties of the starch-SiO₂ aerogels were analysed.The results showed that both one time forming method and post-foring method could successfully synthesize starch-SiO₂ aerogels.Sodium hexametaphosphate?SHMP?could crosslink starch in starch-SiO₂ aerogels,and formed a series network between starch and original skeleton of aerogels,which was beneficial to improving the stability of aerogels structure.And the introduction of silane coupler?KH570?could also enhance the degree of bonding between starch and SiO₂ skeleton,which could be used to improve the mechanical properties of the aerogels material.