Controllable Preparation And Properties Of Diacetate Aerogels And Their Hybrid Materials

The deterioration of fresh commodities such as meat,fruits and vegetables,and aquatic products has become increasingly serious,resulting in a huge waste of resources.The emergence of cold chain insulation box has solved the above problems to a great extent.However,there are still some deficiencies in the current commercial insulation box of insulation materials,such as the toxic gas released in combusting for polyurethane foam,the easy combustion for polystyrene foam,and the insufficient mechanical properties for vacuum insulation panels.Cellulose aerogel is a new type of green and eco-friendly material with high porosity,high specific surface area,and extremely low density.Meanwhile,comparing with traditional inorganic aerogels and polymer aerogels,cellulose aerogel has better biocompatibility,higher compressive strength,and better biodegradability.Therefore,using cellulose diacetate as raw material,and cellulose diacetate aerogels were prepared by supercritical fluid drying of carbon dioxide in this paper.The effects of the amount of 2,4-toluene diisocyanate and pyridine on their microstructure,compressive properties,thermal insulation properties,and thermal stability were investigated.On this basis,introducing polybenzoxazine to cellulose diacetate aerogels,and the polybenzoxazine/cellulose acetate hybrid aerogels were prepared by atmospheric drying method.Studying the effect of raw material（benzoxazine and 2,4-toluenediol）dosage on their microstructure,compression properties,thermal insulation properties,thermal stability,and flame retardant properties.The main research contents and results are as follows:（1）Studying the effect of the amount of 2,4-toluene diisocyanate on cellulose diacetate aerogels.According to the characteristics that the hydroxyl groups on cellulose diacetate molecules can react with 2,4-toluene diisocyanate,the cellulose diacetate aerogels were prepared by carbon dioxide supercritical fluid drying.The results show that the interior of the aerogel is similar to a pearl chain network structure,the pore size distribution is mainly 1-50nm,the lowest density is 0.073 g cm^-3,the lowest shrinkage rate is 11.2%,and the thermal conductivity is as low as 0.021 W m^-1 K^-1,the temperature used theoretically（theoretical working temperature）can reach 230^oC.This is due to the uniform nano-network structure and pearl-like skeleton.Meanwhile,the compressive strength corresponding to 3%strain is up to1.78 MPa.This is attributed to the chemically cross-linked structure and strong hydrogen bonding.（2）Studying the effect of the amount of pyridine on cellulose diacetate aerogels.To further optimize the network structure of cellulose diacetate aerogel,the network structure was regulated by adjusting the amount of pyridine,and the cellulose diacetate aerogel was prepared by drying with carbon dioxide supercritical fluid.The results show that the inner pore size distribution of the aerogel is mainly 1-50 nm,the lowest density is 0.069 g cm^-3,and the lowest shrinkage rate is 7.1%.At the same time,the maximum compressive strength corresponding to3%strain is 0.22 MPa,the compressive strength after 2 h of low-temperature treatment is 0.12MPa（3%strain）,and the thermal conductivity is as low as 0.021 W m^-1 K^-1,and the theoretical working temperature is up to 230^oC.By adjusting the amount of pyridine,the pore structure is further optimized,the size of the network skeleton becomes larger,the density and shrinkage rate is reduced,and the compression performance is improved to a certain extent.（3）Studying the effect of raw material dosage on polybenzoxazine/cellulose diacetate hybrid aerogels.To endow the cellulose diacetate aerogels with flame retardancy and further improve their compression performance.By introducing polybenzoxazine network,and the polybenzoxazine/cellulose diacetate hybrid aerogels were prepared by atmospheric drying method.The results show that the aerogel has a three-dimensional cross-linked nano-network structure,the pore size is mainly distributed in 1-100 nm,the lowest density is 0.11 g cm^-3,and the lowest shrinkage rate is 8.2%.Meanwhile,the maximum compressive strength corresponding to 3%strain is 0.73 MPa,the compressive strength after low-temperature treatment for 2 h is 0.32 MPa（3%strain）,and the minimum thermal conductivity is 0.033 W m^-1 K^-1,the theoretical working temperature is up to 251^oC,and the self-extinguishing time from the fire is 0.34 s.It can be seen that the introduction of the polybenzoxazine network builds a multiple network structure inside the aerogel and forms a strong hydrogen bond,which ensures low density and low shrinkage rate,greatly improves the compressive properties of cellulose diacetate aerogel and gives their flame retardant properties.