Preparation And Properties Of Flame-retardant Cellulose Aerogels

Cellulose aerogels not only have the advantages of traditional aerogels such as low density,high specific surface area and high porosity,but also have natural,renewable and degradable advantages of the cellulose.Therefore,they have been used widely in furniture,architecture,aerospace,etc.and are one kind of great potential environmental protection materials.However,cellulose aerogels are extremely easy to burn in case of fire,which seriously threatens the safety of people's life and property.Therefore,it is particularly important to improve the flame retardancy of cellulose aerogels.In this thesis,two kinds of cellulose composite aerogels with flame retardancy were prepared by the simple freeze-drying method.Firstly,GO was used as the flame retardant of cellulose aerogels.The flame retardancy of the cellulose aerogels were improved due to barrier effects and the catalytic charring capacity of the GO.Then,on the basis of GO,Na-MMT was introduced as a synergistic flame retardant,and the flame retardancy of the cellulose aerogels were further improved by using the good barrier and high thermal stability of the Na-MMT.The structure and morphology of as-prepared cellulose aerogels were characterized by X ray powder diffractometer?XRD?,X-ray photoelectron spectroscopy?XPS?and scanning electron microscope?SEM?and so on.Then,the best preparation conditions were established.The thermal stability and flame retardancy of the cellulose composite aerogels were investigated by the combustion rate test,thermogravimetric analysis?TGA?and microconical calorimetry?MCC?.At last,the structure and morphology of char residue were analyzed by SEM,Raman spectroscopy and Fourier transform infrared spectroscopy?FTIR?to reveal the flame retardant mechanism.The main contents are as follows:1.Preparation and flame retardancy of cellulose/GO composite aerogelsCellulose/GO composite aerogels were prepared by a simple freeze-drying method.The results of XRD,Raman and SEM showed that the optimum dosage of GO in cellulose mucus was 5 wt%.Under this condition,GO was well dispersed in cellulose and could form ordered three-dimensional porous aerogels.The XPS results confirmed that the interaction between GO and cellulose was the hydrogen bonding.The TGA showed that the residual char increased significantly from 14.8%of pure cellulose aerogel to 18.5%of G5C95 aerogel under N₂ atmosphere.At the same time,compared with the GO aerogel,the G5C95aerogels had good compression performance.Under the optimum addition,after igniting the G5C95aerogel was always in the state of smoldering,and the combustion rate decreased from 5.67 mm s^-1 of pure cellulose aerogel to 0.57 mm s^-1 of G5C95 aerogel.The MCC results showed that compared with the pure cellulose aerogel,the peak heat release rate?PHRR?of the G5C95 aerogel decreased by 57.7%,and the total heat release?THR?decreased obviously,showing a better flame retardancy.SEM results of the char residue showed that char residue of the composite aerogel was denser than that of cellulose aerogel.The Raman result of char residue showed that GO increased the graphitization degree of residual char?the I_D:I_G value decreasing from 2.1 of pure cellulose aerogel to 1.3 of the flame-retardant cellulose aerogels?.In summary,due to the physical barrier effect and the ability of catalitic charring of GO,it can not only increase the amount of residual char,but also improve the density and the degree of graphitization of the residual char,thus the flame retardancy of the cellulose aerogels were improved effectively.2.Preparation and flame retardancy of cellulose/GO/MMT composite aerogelsIn order to further enhance the flame retardancy of cellulose aerogels,on the basis of GO,Na-MMT was introduced as a synergistic flame retardant to prepare cellulose/GO/Na-MMT composite aerogels.The results of XRD,Raman and SEM showed that with the addition of 20%Na-MMT and 5%GO?G5M20?,cellulose,Na-MMT and GO coexisted with each other and dispersed evenly,forming a dense and ordered porous structure.The TGA and DTG results showed that Na-MMT and GO improved the thermal stability of the cellulose/GO/Na-MMT composite aerogels,and the amount of residue increased from 2.8%of the pure cellulose aerogel to 14.7%of the G5M20 aerogel under air atmosphere.At the same time,the G5M20aerogels also had good compression performance.The results of the combustion rate showed that G5M20aerogel had the lowest combustion rate and there was no obvious flame and smoke release during the combustion process.Moreover,the aerogel was self-extinguishing after a few seconds.The results of MCC showed that compared with pure cellulose aerogels,the PHRR and THR of G5M20 reduced by about67.8%and 57.6%respectively,indicating that the introduction of Na-MMT further improved the flame retardancy of the composite aerogel.The SEM?FTIR and Raman results of the char residue showed that due to introduction of Na-MMT,char residue contained silicate and show denser.Simultoaneouly,char residue had a higher graphitization degree?the I_D:I_G value decreasing from 2.1 of the pure cellulose aerogel to 1.0 of the G5M20 aerogel?.In summary,with the addition of Na-MMT,the flame retardancy of GO can be further improved by using the barrier properties and high thermal stability of Na-MMT,which showed good flame retardancy for cellulose aerogels.