Perparration Of Nanoscale Cellulose Aerogels And Their Thermal Insulation Properties

Nanocellulose is a kind of renewable material with a wide range of sources,mainly from cotton,hemp,trees and other plant materials.Nanoscale cellulose aerogels have high specific surface area,high porosity and low thermal conductivity,and make up for the shortcomings of silica aerogels being fragile and easy to be powdered.As a new material,nanoscale aerogels have great applications in medical and health,aerospace,building insulation materials and military industries.The research on thermal insulation aerogels is still mainly based on silica aerogels,but the good flexibility and easy graft modification of nanoscale aerogels make it very important to study heat insulation.The aim of this study is to prepare nanofibers aerogels and study their thermal insulation.In order to prepare nanofibers aerogel insulation materials with excellent properties,two different ratios of silane coupling agents,TERT butyl alcohol replacement and coupling agent / TERT butanol / nano Si O2 system were prepared under three systems.And thermal insulation analysis.Firstly,the nano aerogels and M-CNF aerogels were prepared by blending siloxane with amino propyl triethoxy silane(KH550)and methyl three methyl silane(MTMS)mass fraction of3:1,2:1,1:1,1:2 and 1:3 respectively.With the increase of KH550 addition,the thermal stability and compression strength of K-CNF aerogels gradually increased.When the KH550 ratio was 1:1,the K-CNF aerogels had the best performance density.With the increase of MTMS addition,the thermal stability of M-CNF aerogels increased gradually,and the hydrophobic angle reached 156 degrees,and the compression strength and thermal conductivity increased first and then decreased.The best density is 14.59 mg/cm3,the surface hole is small and dense,the maximum compressive strength is 7.25 KPa,and the thermal conductivity is 0.0386 W/Mk.The properties of the modified K-CNF aerogels and M-CNF aerogels were better than those of the unmodified CNF aerogels,but the properties of the M-CNF aerogels were better than those of the K-CNF aerogels with the best addition ratio of 1:1 when the addition ratio was 1:2.Secondly,MTMS was added to the 1:2 ratio,and then MD-CNF aerogels were obtained after freeze-drying by TERT butyl alcohol solution.TERT butyl alcohol was used as a solvent to replace the original aerogel in water.After being freeze-dried,it was extracted as a solvent without changing the composition of silane modified aerogel.Although the MD-CNF aerogel decreased the crystallinity compared with CNF aerogel,it did not change the crystalline structure of nanofibers,but still maintained the structure of cellulose I.The increase of terbutanol sublimationresulted in an increase in the internal porosity of the aerogels and a decrease in the skeleton support system.The maximum compressive strength of MD-CNF aerogels was 4.24 KPa,lower than that of M-CNF aerogels.The mass loss law of MD-CNF aerogels and M-CNF aerogels is basically the same,but the thermal stability of MD-CNF aerogels is slightly improved.MD-CNF aerogel is a good hydrophobic material as well as M-CNF aerogels,and also has a certain oil absorption.In MD-CNF aqueous aerogels,the oil absorption rate is higher than that in air.MD-CNF aerogels show coexistence of holes and cobweb structures,indicating that TERT butyl alcohol can improve the porosity of aerogels.Therefore,the thermal conductivity of MD-CNF aerogels is significantly reduced to 0.03493 W/Mk compared with M-CNF aerogels.In general,TERT butyl alcohol replacement can maintain the thermal stability of M-CNF aerogels to a certain extent and reduce its thermal conductivity.Finally,on the basis of the best MTMS modification in Chapter 1,0.3 g nanoscale silica powder was added to prepare MS-CNF aerogels and MDS-CNF aerogels based on TERT butyl alcohol substitution.The addition of nano Si O2 powder changed the intensity of Si peak in aerogels.After the substitution of TERT butyl alcohol,the degree of crystallinity of MDS-CNF aerogels decreased to 45.08%,but the two kinds of Nano-cellulose aerogels still maintained cellulose type I crystal structure.The N2-adsorption and desorption of MS-CNF aerogels and MDS-CNF aerogels are all IV adsorption isotherms.The pore size distribution curves of aerogels are consistent.The pore sizes are mainly mesopores between 2-50 nm.However,there are still a few pores in the MDS-CNF aerogels between 0-2 nm,the specific surface product of MDS-CNF aerogels,and that of Kong Rong are 2 times higher than that of MS-CNF aerogels,while the average pore size is 3.057 nm below that of MS-CNF aerogels.It indicates that the substitution of TERT butyl alcohol can effectively improve the porosity of aerogels.The addition of nano Si O2 powder makes the aerogels have higher compression recovery.The thermal stability is higher than that of M-CNF aerogel,and its thermal insulation performance is much better than that of MD-CNF aerogel.The thermal conductivity of MDS-CNF aerogel replaced by TERT butanol is0.02687 W/Mk,and it can reach 0.03610 W/Mk after two compression.It is a good thermal insulation material.