Preparation And Characterizations Of Chitosan/Phenolic Aldehyde Aerogels And Composites By Ambient Pressure Drying Method

The huge energy consumption of the country puts forward new requirements for the comprehensive performance of exterior wall insulation materials.Chitosan aerogel has the advantages of abundant raw materials,low environmental load and excellent thermal insulation performance.However,there are some problems such as high preparation cost,easy combustion and weak mechanical properties,which limit its application potential in the field of building exterior wall insulation.In order to solve the above problems,this paper proposes to optimize the traditional preparation strategy of chitosan aerogels.The preparation strategy of chitosan/phenolic hybrid aerogels that can be dried at atmospheric pressure is prepared by using the original cross-linking agent-free preparation strategy,which solves the dependence of chitosan aerogels on supercritical drying.The problem of high preparation cost and the initial improvement of its mechanical properties.On this basis,the silicon source was introduced to continue to enhance the chitosan/phenolic hybrid aerogel,and the chitosan hybrid aerogel network structure was constructed at the nanoscale.Finally,the silicon source enhanced chitosan/phenolic hybrid aerogel material with controllable morphology was successfully prepared,which reduced the heat release rate.Finally,for the first time,chitosan/phenolic hybrid aerogels and their composite materials with excellent compression performance,good thermal insulation performance and excellent thermal stability were prepared by using solvent-free replacement preparation process optimization,which solved the problems of high preparation cost,easy combustion and weak mechanical properties of chitosan aerogels for a long time.The main results are as follows:（1）The preparation and properties of chitosan/phenolic hybrid aerogels by atmospheric pressure drying were studied.The results showed that the preparation of chitosan/phenolic hybrid that could be dried at atmospheric pressure was completed under the preparation strategy without crosslinking agent.On this basis,the preparation strategy without crosslinking agent was determined,and the thermal insulation performance,mechanical properties and heat release rate of CTS/PF-As prepared by this strategy were tested.The results show that CTS/PF-As has moderate mechanical properties.When the strain is 10%,the compressive strength is as high as 0.31 MPa.It has a moderate thermal conductivity of 0.0334 W m^-1 K^-1 and good thermal insulation performance.The density is as low as 0.165 g cm^-3.（2）The preparation and properties of chitosan/phenolic/silica hybrid aerogels by ambient pressure drying were studied.By adjusting the amount of silica sol and fumed silica,the controllable preparation of chitosan/phenolic microstructure was successfully achieved.The results showed that the density of CTS-PF-LS-2.5 was reduced to 0.112 g cm^-3,the thermal conductivity was as low as0.0296 W m^-1K^-1,and the peak heat release rate was also reduced to 29.556 W g^-1.（3）The preparation and properties of chitosan/phenolic aerogel composites by solvent-free displacement atmospheric pressure drying method were studied.Compared with CTS/PF-As,the mechanical properties of CTS/PF-As are more than three times higher.When the strain is 10%,the compressive strength is as high as 1.04 MPa,the heat release rate is reduced to 40.277 W g^-1,and the thermal conductivity is slightly increased,the value is 0.0342 W m^-1K^-1.The CTS/PF series composites with and without solvent replacement were studied and compared.Both of them showed extremely high heat release rate at about 400°C.The CTS/PF-PU-E and CTS/PF-PU-NE were94.828 W g^-1 and 90.038 W g^-1,respectively.