Synthesis of novel porous tannin-phenol-formaldehyde cation exchange resin from Terminalia arjuna (Kumbuk)

Abstract

Natural tannins have a high affinity to absorb metal ions, proteins and some other biomolecules. In this study, tannins extracted from Terminalia arjuna (Kumbuk) were used to synthesise renewable tannin-phenol-formaldehyde resin systems and a porous modified resin system. A series of resin systems was synthesised by varying the incorporated phenol content. The ion exchange capacities of the resins produced were studied and the resin with the highest ion exchange capacity was selected. It was sulfonated to increase the properties further. A monovalent cation, Na+ was used to estimate the adsorption properties of both sulfonated and unsulfonated resin systems. Solubility and swelling properties of the resins were measured to check their applicability as an ion exchanger in aqueous media at different pH values. Fourier transform infrared spectroscopy (FTIR) analysis was carried out to characterise the synthesised resins. Scanning electronic microscopic (SEM) images were obtained to study the morphology of the resins produced. Sulfonated tannin-phenolformaldehyde resin with the tannin/phenol ratio of 1:1 showed the highest adsorption capacity for the metal ion used (Na+), which was 1.552 meq/g. To increase the surface area and to gain an efficient flow rate, a porous tannin-phenol-formaldehyde resin system was prepared. Synthesis was carried out using hexamethylenetetramine as both the cross linker and the catalyst. Coconut oil was used as the porogenic agent to create the porous structure through emulsion templating process. Synthesised porous resin contains μm and nm scale porous structures.