Effects of Fatty Acid Anhydride on the Structure and Thermal Properties of Cellulose-g-Polyoxyethylene (2) Hexadecyl Ether

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.