| With the depletion of non-renewable resources and the deterioration of the environment,it is of great significance to explore environmentally-friendly and renewable biomass materials to solve the energy problems.Therefor,the renewable cellulose has attracted widespread attention from researchers.The research of this paper mainly has regenerated cellulose instead of traditional petroleum-based polymers as matrix and explores the dielectric properties of pure regenerated cellulose.Then,the regenerated cellulose was compounded with fly ash coated with polydopamine?FA@DA?and boron nitride nanosheet?BNNS?,respectively.Achieved the high energy density of the regenerated cellulose composite film by improving the dielectric constant and breakdown strength.The main results are as follows:?1?The sodium hydroxide/urea/water system as the solvent for cellulose.the regeneration baths used in this research including 5%sulfuric acid aqueous solution,5%aqueous sulfuric acid and 5%sodium sulfate aqueous solution,acetone and tert-butyl alcohol.The different regenerated cellulose films prepared by different regeneration baths and dried under different drying conditions?60°C;25°C;25°C,vacuum-pressure drying?.The films were placed under different humidity for 72 h and then tested for electrical properties.It was found that the regenerated cellulose films prepared by regeneration from inorganic solution have a high dielectric constant and a large dielectric loss,but less wear strength;The films dried at 25°C under vacuum-pressure conditions have a smaller dielectric constant and dielectric loss,while the breakdown strength is significantly improved.The films prepared by acetone and vacuum-compression conditions have the highest energy storage density of 1.23 J cm-3 at a breakdown strength of 205 MV m-1.As the humidity increases,the dielectric constant,dielectric loss and electrical conductivity of the films increase substantially at the same time,and the breakdown strength decreases sharply.?2?The fly ash?FA?and fly ash coated by polydopamine?FA@DA?were used as additives to compound with cellulose to prepare composite films.Simultaneously,the structure and dielectric energy storage properties of the composites were studied.Scanning electron microscope?SEM?images show that the FA@DA has better compatibility with regenerated cellulose than the unmodified fly ash.Thermogravimetric results show that the composite films have the favorable thermal stability.After adding FA@DA,the dielectric constant and the breakdown strength of the composite films were significantly improved.When the added amount was 50wt%,the dielectric constant was 11.9 at 100 Hz;when the FA@DA loading was 40wt%,the maximum breakdown strength and energy density reached 330 MV m-1 and3.47 J cm-3,respectively.The charge-discharge efficiency of the composite films is greater than 68%.?3?The boron nitride nanosheets were prepared by ultrasonic stripping of hexagonal boron nitride in a sodium hydroxide/urea/water solution,followed by dissolving cellulose in the same mixture to prepare the regenerated cellulose/boron nitride composite films?RC-BN?.SEM results show that the composite films have a regular 2D layered structure,and the thermogravimetric results show that the composite films have excellent thermal stability.When the BN loading is 30wt%,the thermal conductivity reaches 2.97 W m-1 K-1.The dielectric properties test showed that the dielectric constant and dielectric loss decreased with the addition of boron nitride while the breakdown strength was significantly improved.When the BN content was 10 wt%,the maximum breakdown strength of 370 MV m-1 and the highest energy density of 4.01 J cm-3 were achieved,while the charge and discharge efficiency are greater than 75%.The high temperature dielectric results show that the dielectric properties of RC-BN have good thermal stability compared to pure regenerated cellulose film. |
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