Catalytic Degradation of Polylactic Acid over Al2O3@SiO2 Core–Shell Catalysts

Abstract

Al2O3@SiO2 core–shell catalysts were synthesized by sol–gel method. The core size’control was provided by using of polyethylene glycol (PEG) and glycerol. The shell thickness was optimized by using the different amount of tetraethylorthosilicate (TEOS). The formation of core and shell structures in catalysts was seen in high resolution transmission electron microscopy (HRTEM) images. In some catalysts, the use of PEG caused to formation of a more monodisperse core structure. The particle size of catalysts was observed in the range of 8–12 nm. The BET (Brunauer–Emmett–Teller) surface area and total pore volume of catalysts ranged 440–1014 m2/g and 1.28–2.57 cm3/g, respectively. In addition, pore diameter reached up to 25 nm. The use of PEG and glycerol improved textural properties. While BET surface area and total pore volume values decreased by the increase of TEOS amount, shell thickness increased a little. Fourier transform infrared (FTIR) spectrums of the pyridine adsorbed catalysts revealed the presence of Lewis and Bronsted acid sites in the catalysts. The catalysts were tested in the degradation of polylactic acid (PLA) by using thermogravimetric analysis (TGA) technique. TGA results showed the degradation temperature of PLA decreased from 353 to 321 °C in the presence of catalysts. Activation energy values were calculated using Flynn–Wall–Ozawa method. The activation energy was reduced from 337 to 199 kJ/mol. Pore structure, particle size and acidity of catalysts significantly affected the degradation performance.