Preparation And Modification Of Heat-insulating And Flame-retardant Nano-cellulose/clay Aerogel

In this work,aerogels based on biocompatible and biodegradable cellulose nano fibril(CNF)were prepared through an environmentally-friendly freeze-drying method.Then a facile strategy was adopt to construct low-flammability CNF-based aerogels with improved mechanical properties by incorporating sodium montmorillonite(MMT),melamine-formaldehyde(MF)resins and boric acid(BA).The structures and properties of prepared CNF-based aerogels were characterized by Fourier transform infrared spectroscopy(FTIR),scanning electron microscope(SEM),compression test,thermal conductivity,thermogravimetric analysis(TGA),limiting oxygen index test(LOT),vertical burning test(UL-94)and cone calorimetry.Regarding CNF/MMT composite aerogels,the addition of MMT has changed the micro structure of the aero gels.For example,when the content o f MMT in the aero ge ls was not less than 0.75 g,a three-dimensional network structure appeared.In addition,the introduction of MMT not only enhanced the mechanical properties of CNF aerogels but also improved the thermal stability.However,excessive MMT would have a negative impact on the performance of the aerogels.In addition,according to the LOI test results,the addition of MMT did not significantly improve the flame retardancy of CNF-based aerogels.The chemical cro ss-linking was realized between CNF and MF after post-heating.SEM images indicated that MF cross-linking did not significantly change the micro structures.However,the cross-linking improved the materials mechanical properties of the aerogels.By adding 50 wt%of MF,the compressive modulus and compressive stress of the CNF aerogels increased by 316%and 114%,respectively.The successful cross-linking of MF and CNFs also made the CNF-based aerogels with an excellent thermal stability and flame retardancy.Especially,under due to the synergistic flame retardant effect of MMT and MF,the LOI values of CNF/MMT/MF composite aerogels were higher than 50%,and the UL-94 grade were V-0.Among them,the LOI value of the sample CNF1MMT1MF1 reached up to 57%,and the corresponding peak of heat release rate(PHRR)and total heat release(THR)were also reduced to 5.99 kW/m2 and 0.72 MJ/m2,respectively.BA was introduced to the aforementioned composite aerogels.BA cross-linking reduced the interspacing of layered of aerogels,further introduction of MF formed polymeric fibrils that connected the layer.These changes on microstructures further improved the mechanical and flame properties of aerogels.The compression test results showed that the modified aerogels had excellent mechanical properties,and 1.125 g was the optimum addition amount of BA.Further addition of MF brought more excellent thermal stability and flame retardant properties to the composite aerogels.When the amount of BA was more than 1.125 g,the LOI value of the samples was greater than 40%,and the UL-94 grade was V-0.On this basis,1.5%MF incorporation made aerogels' LOI value higher than 85%.These results indicated that BA and MF had a synergistic effect on the mechanical performance and flame retardant properties of the CNF/MMT aerogels.