Preparation And Properties Of Insitu Flame Retardant Cellulose Aerogels

As a kind of natural polymer,cellulose has many advantages such as wide source of raw materials,good biodegradability and biocompatibility.It has been researched and developed into a variety of materials and widely used in many fields.Cellulose based aerogel has outstanding thermal insulation properties,but the flammability of cellulose limits its application in this field.Therefore,it is of great significance to improve its flame retardancy.In this dissertation,an in-situ preparation method of flame retardant based on NaOH/ZnO/Urea dissolution system was developed,and the NaOH/ZnO/Urea dissolution system was transformed into flame retardant system through in-situ reaction.High performance flame-retardant cellulose aerogel was prepared successfully,and its properties and mechanism were studied.The main content of this dissertation is as follows:（1）Determination of NaOH/ZnO dissolution system and preparation and characterization of cellulose aerogel.The component ratio was determined as NaOH:ZnO=6%:0.3%,and the solubility of cellulose was 66.22%.Cellulose aerogel was prepared by conventional freeze-drying and gradient freeze-drying methods.The freeze-drying methods on the pore structure and properties of the aerogel were analyzed by SEM,BET methods.Cellulose aerogels with network structure and lamellar structure were obtained by conventional freeze-drying and gradient freeze-drying,respectively.The former has higher specific surface area,adsorbability and smaller pore volume.The crystal from of cellulose after aerogel molding is cellulose II.ZnO and NaOH are loaded with the form of Na₂O-ZnO₂-2H₂O,and the aerogels do not have flame retardant properties.（2）Preparation and characterization of in-situ flame-retardant cellulose aerogel based on NaOH/ZnO solution system.The effect of temperature,boric acid concentration and reaction time on the in-situ reaction of cellulose aerogel was investigated.The morphology,distribution and properties of the flame retardants were analyzed by SEM,EDS,FTIR,XRD and XPS.Temperature 80℃,boric acid concentration 9%and reaction time 24 h were the ideal conditions for in-situ reaction.Compared with cellulose aerogel,the thermal release mode of in-situ flame-retardant aerogel changed from single peak to double peak,and its HRC,THR and PHRR decreased by 76%,28%and 43%,respectively,and its LOI value was higher than80%,and its flame-retardant grade could reach V-0 level.In addition,the compressive strength of the aerogel is increased by about two times.（3）Preparation,characterization and mechanism analysis of Urea synergistic flame retardant cellulose aeroge based on NaOH/ZnO/Urea dissolution system.Urea synergistic flame retardant cellulose aeroge was prepared by adding urea into the solution system.After the addition of urea,the solubility of cellulose was 71.50%,the heat release mode changed into three peaks,and the HRC,THR,and PHRR decreased by 48%,46%and 35.5%.The LOI value of the aerogel was higher than 80%,and the flame-retardant grade was V-0,and the residual burning time decreased by about 90%.Compared with the in-situ flame-retardant aerogel without urea,it showed outstanding self-extinguishing performance,and the mechanical strength of cellulose aerogel was further improved.Through carbon residue analysis and TG-FTIR analysis,the flame retardant mechanism can be explained by zinc borate and boric acid promoting carbon formation on the surface of aerogel,heat absorption by volatilization of internal crystalline water and film formation by melting of borate.The self-extinguishing flame retardant mechanism can be explained by CO₂,NH₃and other flame retardant gases released from water vapor and urea.