Preparation And Properties Of Cellulose Ester In Ionic Liquid Cosolvent System By Transesterification

With the increase of the environmental awareness,cellulose has been popular in the application of making kinds of materials due to its economic advantages.As the most abundant natural polymer,it has many attractive properties such as renewability,biodegradability and biocompatibility.However,there are some drawbacks which would limit its application because cellulose can not be dissolved in water or common organic solvents due to its strong inter-and intra-hydrogen bonds.The lack of thermal plasticity also makes it hardly to be melted for compression molding.Through chemical modification,the physicochemical properties of cellulose can be significantly changed and the application can be easier.In the present study,cellulose esters were prepared by transesterification in ionic liquid cosolvent system.The results were as follows:Recently,IL/cosolvent system has generated a lot of interest in dissolving cellulose and being the reaction media for kinds of cellulose modification.In the present study,both 1-allyl-3-methylimidazolium chloride(AmimCl)/ dimethyl sulfoxide(DMSO)and AmimCl/ N,N-dimethylformamide(DMF)systems were employed to synthesized cellulose acetate by transesterification.Microcrystalline cellulose,1,8-Diazabicyclo[5.4.0]undec-7-ene(DBU)and isopropenyl acetate were chosen as the raw material,catalyst and acetylation reagent,respectively.The results revealed that DMSO was a fine cosolvent for the transesterification in homogeneous solution.Moreover,DMSO had better effect on the reaction as the cosolovent under the given conditions and the degree of the substitution(DS)of cellulose acetate were significantly enhanced through increasing the molar ratio of DMSO.The synthesized products were characterized by Fourier transform infrared(FT-IR)spectroscopy,1H-nuclear magnetic resonance(NMR),13C-NMR,correlation spectroscopy(COSY),heteronuclear single quantum correlation(HSQC),and X-ray diffraction(XRD)to confirm the structure of cellulose acetate.The improved thermal properties of cellulose acetate were also evaluated using thermogravimetric analysis(TGA)/derivative thermogravimetry(DTG).The preparation of cellulose laurate was investigated through transesterification in AmimCl/DMSO cosolvent system by using vinyl laurate as an acylation reagent and DBU as an effective catalyst.The effects of reaction temperature,reaction time and the molar ratio of vinyl laurate to anhydride glucose unit(AGU)were investigated.DS ranged from 1.47 to 2.74 under the selected conditions and the reaction order of three hydroxyl groups was C-6 >C-3 >C-2.The chemical structure of cellulose laurate were explored by FT-IR spectroscopy,1H-NMR,13C-NMR,HSQC and XRD to confirm the occurrence of transesterification.The improved thermal stability of cellulose laurate was proved by TGA.The tensile analysis and the contact angle measurement confirmed the ductile behavior and the hydrophobicity of the films made from cellulose laurate.Cellulose laurate/Nano TiO2 films were prepared by ultrasound blending.The effect of amount of TiO2 on the properties of the films was investigated.The result showed that tensile strength of the composite film was improved and the water vapour permeability(WVP)were decreased with proper amount of TiO2.The lowest WVP achieved to 2.15×10-11 g s-1 m-1 Pa-1 with 1% TiO2.Although the addition of TiO2 would decrease the water contact angle,the composite films remained hydrophobic with the amount of 4% when the water contact angle was 94.1o.Also the composite film presented UV light shielding property.