| Cellulose aerogel has the advantages of excellent properties of traditional aerogel materials,and the naturally renewable of cellulose.In recent years,cellulose aerogel,as the third generation of aerogels,has gradually become a research hotspot in the field of aerogel.And it is a new environmental-friendly material with great development potential in the future.However,cellulose is high flammability,and the safety problems caused by the combustion of cellulose products have attracted much attention.Bio-based flame retardants are the focus of future research.The mechanical properties and dimensional stability of cellulose aerogel are poor,so how to solve this problem has practical significance for the application of cellulose aerogel.In this study,natural micron down fiber and flame retardants were used to prepare bio-based flame retardant reinforced cellulose aerogel,which provides a new way for the flame retardant and reinforcement of cellulose aerogel.The specific research contents of this study are as follows:(1)Natural down fiber reinforced cellulose aerogel: Two cellulose derivatives of carboxymethyl cellulose(CMC)and hydroxyethyl cellulose(HEC)were used as raw materials,and the cellulose composite aerogels were prepared using down feather fiber(DFF)as reinforcing material and glutaraldehyde(GA)as crosslinking agent to improve the mechanical properties.The basic physical and mechanical properties of cellulose composite aerogels were characterized,and the sound absorption and thermal insulation properties were studied.The results showed that the HEC/DFF composite aerogel had low density,high porosity,excellent sound absorption and good thermal insulation properties.The compression stress of the HEC/DFF composite aerogel was135% higher than that of the pure HEC aerogel.Its compression modulus increased from 46.37 k Pa to 128.65 k Pa,nearly three times higher than that of pure HEC aerogel.CMC/DFF aerogels also had low density and high porosity.The compression stress of CMC/DFF composite aerogels was 75% higher than that of pure CMC aerogels,and the compression modulus was about 5 times higher than that of pure CMC aerogels.Therefore,down fiber could significantly enhance the mechanical properties of cellulose aerogel,which could obtain good thermal insulation and sound absorption properties.(2)Preparation of cellulose/chitosan composite aerogels:Bio-based chitosan can be used as a nitrogen containing flame retardant component,which could combine with phosphorus containing flame retardant to obtain excellent flame retardancy.Based on this,cellulose/chitosan composite aerogels were prepared,and the effects of different crosslinking agents(glutaraldehyde,epichlorohydrin,polyethylene glycol diglycidyl ether,citric acid)on the properties of cellulose/chitosan composite aerogels were studied.Their basic physical and mechanical properties were characterized,and their sound absorption and thermal insulation properties were also studied.The results showed that the cellulose/chitosan composite aerogel prepared by GA had the best mechanical properties,and its compressive stress could reach 349.32 k Pa,which was significantly better than that of the other three crosslinking agents(15.31 k Pa,19.03 k Pa,16.30 k Pa,respectively).The sound absorption and thermal insulation tests showed that the sound absorption coefficient of the composite aerogel prepared by GA reached 0.854,and the thermal insulation coefficient reached 0.04900 W/m·k,which were also better than that of the other three crosslinking agents.Therefore,it was more ideal to use GA as crosslinking agent to prepare cellulose/chitosan composite aerogel.(3)Flame retardant cellulose composite aerogels: The effect of phytic acid and phytic acid/urea on the flame retardancy of cellulose aerogel was studied.The results showed that the introduction of phytic acid and phytic acid/urea could effectively improve the flame retardancy of cellulose aerogels.The limiting oxygen index(LOI)increased from 21% of pure cellulose aerogel to 25.7% and 32.5%,respectively.The epoxy group containing flame retardant was synthesized by phytic acid and ethylene glycol diglycidyl ether,which was used as the flame retardant and crosslinking agent simultaneous to prepare the flame retardant cellulose aerogel.The results showed that the strength of prepared composite cellulose aerogel was 153.65 k Pa,and its LOI value was34%,showing the excellent flame retardancy.The flame retardancy of the flame retardants on cellulose/chitosan composite aerogel were furhter studied.The addition of phytic acid and phytic acid /urea could increase the LOI value of cellulose/chitosan composite aerogel from 30% to 43.5% and 38%respectively.The flame retardancy of composite cellulose aerogel was significantly improved.At the same time,the synthetic epoxy group containing flame retardant was also used for cellulose/chitosan composite aerogel,which achieved a LOI value of higher than 50%.Therefore,the flame retardancy of cellulose aerogels could be effectively improved by using bio-based phytic acid and its derivatives flame retardants.(4)Preparation of cellulose aerogels using atmospheric pressure drying: This topic preliminarily investigated the possibility of preparing cellulose aerogels by atmospheric pressure drying.Cellulose aerogels were prepared based on solvent exchange method.Anhydrous ethanol,cyclohexane and ethyl acetate were selected as the exchanging solvent in research.Cellulose aerogels(CMCE)and cellulose/chitosan composite aerogels(CMC/CSE)were prepared using gradient temperature drying under atmospheric pressure,and their basic properties were characterized.The results showed that anhydrous ethanol as exchanging solvent could maintain the morphology of cellulose aerogel,and the cellulose aerogel prepared had the characteristics of low density(0.0516g/cm3)and high porosity(96.26%),Compared with the cellulose aerogels prepared by freeze-drying method,the density of the aerogels slightly increased while the porosity slightly decreased.The mechanical properties test showed that the compressive stress and modulus of cellulose aerogel prepared by atmospheric drying were 243.99 k Pa and298 k Pa,and its mechanical properties were slightly lower than those prepared by freeze-drying;The compression stress and compression modulus of cellulose/chitosan composite aerogel prepared by atmospheric pressure drying were 432.77 k Pa and7160 k Pa,which were better than those prepared by freeze-drying. |
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