| Chitin is the second most abundant natural polymer material in nature,and it has caused an academic upsurge in the fields of adsorption,catalysis,heat insulation,and biomedicine.Chitosan（CTS）is a derivative of chitin,with abundant raw material sources,non-toxic and harmless,biodegradable and high chemical activity（amine group,hydroxyl,etc.）and other excellent characteristics,CTS is used as a raw material to synthesize aerogel thermal insulation material will be highly compatible with the concept of building energy saving.However,the existing CTS aerogel has the scientific problems of weak mechanical strength and large-scale shrinkage in the preparation process,which seriously inhibit its market application.The profound research results are as follows:（1）The entanglement effect of nanofibrer cellulose（NFC）with different aspect ratios and the supramolecular force of linear polymer polyvinyl alcohol（PVA）on the shrinkage of CTS hybrid aerogels before and after drying process were studied,and its thermal insulation performance were tested.CTS hybrid aerogels with ultra-low shrinkage（radial:14.74%,axial:15.79%）before and after drying were successfully prepared using ethanol/water binary system as the solvent and after the processes of gelation,ageing,solvent exchange and drying.The effect of NFC with different aspect ratios on CTS hybrid aerogel was systematically analyzed,and the results showed that the optimum aspect ratio of NFC was 37.5.The CTS/PVA/NFC hybrid aerogel obtained after introducing the NFC with the best aspect ratio has a low thermal conductivity of 0.0224 W m-1 K-1 and excellent thermal insulation properties（at a hot surface temperature of 80.46℃,after 200 s,the cold surface temperature is maintained at 33.46℃）,the density is as low as 0.09 g cm-3 and the compressive strength as high as 0.51 MPa at strain of 10%.（2）The effects of introducing different proportions of silicon（Si）sol on the compression properties,shrinkage,thermal insulation and thermal insulation properties of CTS hybrid aerogels were explored.By adjusting the amount of Si sol,the problem of organic-inorganic interfacial bonding was successfully avoided and a completely homogeneous NFC/Si enhanced CTS hybrid aerogel was obtained.The research results show that the NFC/Si reinforced CTS hybrid aerogel can effectively control the overall shrinkage in axial and radial directions during the preparation process,and it was also found to have excellent thermal insulation properties at high temperatures（150℃）,and showed new characteristics of self-extinguishing.（3）A traditional method of constructing composite materials was studied in order to resolve the problem that the overall shrinkage of CTS aerogel was too high during the preparation process.The thermal insulation material-polyester（PET）foam with micron-scale hole structure was selected as the reinforcement to strengthen the CTS aerogel in situ,and the CTS sol was fully and uniformly filled in each hole of the PET foam in the vacuum environment,and the PET foam reinforced CTS aerogel composite material with near"zero"axial shrinkage was prepared.The obtained PET foam-reinforced CTS aerogel composites have excellent thermal stability,excellent thermal insulation properties and mechanical properties. |
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