Preparation And Properties Of Cellulose Ester-based Solid-solid Phase Change Materials

Cellulose,as a kind of green renewable resources,is non-toxic,biodegradable,cheap and has a good biocompatibility.Moreover,it is an abundant resource.However,the decomposition temperature of cellulose is lower than its melting temperature due to the intramolecular and intermolecular hydrogen bonding.Therefore,it can not be melt processed,and is insoluble in common organic solvents.In this paper,the microcrystalline cellulose,as the raw material,was dissolved in1-allyl-3-methylimidazolium chloride([Amim]Cl)ionic liquid or 1-ethyl-3-methylimidazolium acetate/N,N-dimethyl acetamide,then benzoyl chloride(BC)was grafted to cellulose.The properties of cellulose benzoate(CB)synthesed in different feed molar ratios of BC,different reaction temperatures in certain time were explored by fourier transform infrared(FTIR),nuclear magnetic resonance spectroscopy(1H-NMR),differential scanning calorimetry(DSC),thermogravimetric analysis(TG),thermogravimetry(POM)and solubility test as well as characterization methods.Cellulose benzoate-g-diethylene glycol hexadecyl ether(CB-g-E2C16)solid-solid phase change material was prepared by using cellulose as monomer and diethylene glycol n-hexadecyl ether(E2C 16)as functional monomer.The effect of different reaction parameters including feeding molar ratios(E2C16:AGU = 2:1-8:1 mol%)and different reaction temperature(70℃-110℃)on the structure and properties of the product was investigated.CB has poor thermoplasticity when CB(DS = 0.12)has a low degree of substitution.The glass transition temperature(143.2℃-182.1℃)of CB begins to appear with the increase of substitution degree.The larger the DS is,the lower the glass transition temperature is.The thermal stability of CB(DS = 0.13-1.05)is lower than that of microcrystalline cellulose,but the thermodynamic stability of CB is higher than that of cellulose when the substitution degree is higher than 2.80.The CB(DS = 0.13-2.98)could be dissolved in polar solvents such as DMSO and DMF.Higher substituted CB(DS = 2.80-2.98)not only could be dissolved in polar solvents DMSO and DMF but also could be dissolved in acetone.CB(DS = 1.05)shows signs of melting under a hot stage microscope.CB-g-E2C16 solid-solid phase change material has a phase transition enthalpy of 7 J/g-24 J/g and excellent thermal stability when the DS were 0.68-1.24.The initial decomposition temperatures were 280℃-300℃,and the peak value decomposition temperatures were 320℃-340℃.Furthermore,CB-g-E2C16 can be dissolved in DMSO and DMF and other polar solvents.The CB-g-E2C16 copolymer prepared at the reaction temperature of 70℃-110℃ were not melted at the temperatures of 30℃-250℃,and the solid-solid phase transformation was observed under the hot stage microscope.