Study Of Preparation And Properties Of New Mixed Cellulose Esters

The rapid increase of CO₂ content is the main cause of global warming.It is of strategic importance to achieve effective capture and utilization of CO₂ for mitigating the greenhouse effect.As the most abundant renewable resource on the earth,cellulose has the advantages of natural degradability,abundant reserves,wide distribution and excellent physical and chemical properties.It’s far-reaching significance for solving the energy crisis caused by the lack of petroleum-based energy to realize high value utilization of cellulose.This paper innovatively combines the use of CO₂ with the solubility modification of cellulose,and proposes a solution system of DBU/DMSO/CO₂,which can efficiently realize the homogeneous dissolution of cellulose and obtain high value-added cellulose derivatives.Among them,CO₂ not only participates in the dissolution of cellulose,but also reacts to the structure of cellulose chains,and successfully realizes the comprehensive utilization of biomass resources and CO₂,which is of great significance to alleviate the energy crisis and the greenhouse effect.（1）Homogeneous dissolution of cellulose was realized in DMSO/DBU/CO₂system.Bromohexane attacked the newly formed anionic intermediate of cellulose carbonate and acylated with anhydride to obtain cellulose derivatives with carbonate-carboxylic ester structure.A series of membranes were obtained by solvent evaporation method,the conditions of acylation time,acylation temperature,molar amount of reagent and different acylation reagents were studied.FT IR,¹H NMR,¹³C NMR,DSC,TG,GPC,SEM,AFM,contact angle and UV-visible spectrum,gas separation and dielectric constant were used to characterize the structure and performance of the material.It was found that by changing the reaction conditions,the microstructures of the materials could be controlled and the derivatives of the target substitution degree could be obtained.The lowest UV-visible absorbance of the membrane is 0.044.The permeability of CO₂,O₂ and H₂ were 179.72,30.25 and 89.86 Barrer,respectively,and the dielectric constant is 2.4.The prepared materials have potential applications in gas separation filed.（2）Homogeneous dissolution of cellulose was realized in DMSO/DBU/CO₂system.and Cellulose derivatives with carbonate-carbamate structure were obtained by in situ reaction with bromohexane and isocyanate reagent.The conditions of reaction time,temperature,molar amount of reagent and structure of isocyanate were explored.FT IR,¹H NMR,¹³C NMR,DSC,TG,GPC,SEM,AFM,contact angle and UV-visible spectrum,gas separation and dielectric constant were used to characterize the structure and performance of the material.It was found that by changing the reaction conditions,the microstructures of the materials could be controlled to obtain the derivatives of the target degree of substitution.The lowest UV-visible absorbance of the membrane is0.192.The permeability of CO₂,O₂ and H₂ is 41.28,7.52 and 40.22 Barrer,respectively,and the lowest dielectric constant is only 1.8.The prepared materials have potential applications in gas separation and microelectronic devices filed.（3）Homogeneous dissolution of cellulose was realized in DMSO/DBU/CO₂system.and a series of completely substituted pure cellulose carbamate and mixed cellulose carbamate derivatives were obtained by direct in situ reaction with isocyanate reagent.FT IR,¹H NMR,¹³C NMR,DSC and TG were used to study the structure and properties of the products.FT IR and ¹H ¹³C NMR results proved the accuracy of product structure.TG showed that pure cellulose butyl carbamate was thermal degraded at 151^oC,but the decomposition temperature of other pure cellulose was above 230 ^oC.DSC showed that the Tg of some derivatives was not obvious,and the maximum Tg was 206.7^oC of cellulose ethyl carbamate;GPC result showed that all the products had molecular weight,which is much larger than the original cellulose,the highest is 56.7KDa,but the product is more dispersible,and all the PDI indexes are above 2.0.