Synthesis and characterization of epoxidized palm oil hydrogel

Abstract

A bio-based hydrogel (HPEPO) was synthesized from epoxidized palm oil (EPO) by using ring opening polymerization (ROP) in the presence of a fluoroantimonic acid hexahydrate (HSbF6·6H2O) catalyst, followed by a chemical hydrolysis catalyzed with sodium hydroxide (NaOH). A response surface methodology (RSM) was adopted to optimize the reaction parameters, namely, concentration of NaOH solution, NaOH solution loading and reaction time used during the chemical hydrolysis. The successful ring opening of EPO was confirmed by the disappearance of the epoxy functional group at 833 cm-1 of the Fourier transform infrared and at 2.8 to 3.0 ppm of nuclear magnetic resonance spectra. The increase of melting points of HPEPO was observed in the temperature range between 45 °C to 60 °C, corresponded to the increase of crystalline phase in hydrogel as determined by differential scanning calorimetry. The thermal stability of hydrogel was improved up to 200 °C, as shown by thermogravimetric analysis. Apart from that, the swelling behavior that was largely influenced by the hydrophilic carboxyl group and the hydrophobic alkyl group of hydrogel showed some sensitiveness towards the temperature changes, ranging from 15 °C to 40 °C. Meanwhile, the RSM analysis showed that the optimum conditions for all reaction parameters were achieved at 0.33 M concentration of NaOH solution, 73 mL of NaOH solution loading and 25 hours of reaction time.