Abstract
Cellulose was premodified by short-chain fatty acid anhydrides, such as acetic anhydride (CA), propionic anhydride (CP), and butyric anhydride (CB), followed by grafting of polyoxyethylene (2) hexadecyl ether (E2C16) using toluene-2,4-diisocyanate as a coupling agent. The feeding molar ratio of E2C16 and the anhydroglucose unit (AGU) was fixed at 4:1, and then a series of CA-g-E2C16, CP-g-E2C16, and CB-g-E2C16 copolymers were successfully prepared. The structures and properties of the copolymers were characterized using FTIR (fourier transform infrared spectra), 1H-NMR (Proton nuclear magnetic resonance), DSC (Differential scanning calorimeter), POM (polarized light microscopy), TGA (thermogravimetric analysis) and WAXD (wide-angle X-ray diffraction). It was shown that with the anhydride/AGU ratio increasing, the degree of substitution (DS) value of E2C16 showed a trend of up first and then down. With the carbon chain length increasing, the DS value of E2C16 continuously increases. The phase transition temperature and thermal enthalpy of the copolymers increased with an increasing DS value of E2C16. When the ratio of CB/AGU was 1.5:1, the DS of E2C16 was up to the maximum value of 1.02, and the corresponding melting enthalpy and crystallization enthalpy were 32 J/g and 30 J/g, respectively. The copolymers showed solid–solid phase change behavior. The heat resistant temperature of cellulose-based solid–solid phase change materials was always higher than 270 °C. After the grafting reaction, the crystallinity of E2C16 decreased, while the crystal type was still hexagonal.
Highlights
Cellulose is a type of polysaccharide composed of repetitive D-glucose units linked through β(1→4) glycosidic bonds [1]
In the spectrum of cellulose, the wide peak at approximately 3200 cm− 1 is assigned to the absorption band of the hydroxyl groups on the anhydroglucose unit (AGU), whose intensity was significantly reduced in the spectra of copolymers
In the spectrum of E2 C16, the peaks at 2852 cm−1 and 2920 cm−1 are assigned to the characteristic absorption bands of the ethylene glycol repeat units and the saturated alkane group of E2 C16, respectively, which appeared in the spectra of cellulose acetate (CA)-g-E2 C16 (A3), CP-g-E2 C16 (P3), and CB-g-E2 C16 (B3) copolymers
Summary
Cellulose is a type of polysaccharide composed of repetitive D-glucose units linked through β(1→4) glycosidic bonds [1]. Cellulose is insoluble in common organic solvents and unable to be melt-processed before reaching its decomposition temperature [2,3]. Through modification [4,5,6,7,8,9], hydrogen bonding was weakened to a certain extent, while a grafted side chain increased molecular distance, which could further improve the solubility of cellulose. All the products possessed excellent solubility in common organic solvents (e.g., CHCl3 , acetone, ethyl acetate), and transparent films of cellulose esters were obtained by solution casting. These cellulose mixed esters exhibited thermoplastic behavior and could be processed by a traditional melt processing method. The effect of carbon chain length and usage amount of fatty acid anhydrides on structures and properties of cellulose-based solid–solid phase change materials were investigated in detail
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