Ion exchange resins from phenol/formaldehyde resin-modified lignin

Phenol/formaldehyde resin, commonly sulfonated, is used as ion exchanger. Lignin, which is the phenolic polymer matrix in wood, was isolated from olive stone biomass by alkaline hydrolysis of weak ether bonds (Kraft lignin, KRL). It was then hydroxymethylated (KRLH) with an aqueous solution of formaldehyde. Novolac resin (N) was synthesized from phenol and formaldehyde under acidic conditions. KRL or KRLH was incorporated into phenol/formaldehyde during polymerization (N-KRL, N-KRLH). The products of polymerization (N, N-KRL and N-KRLH) were sulfonated with concentrated H2SO4 (1:3 w/w as typical proportion according to literature or 1:6 w/w as an excess of H2SO4) and then cross-linked with formaldehyde. The different products were characterized by IR spectroscopy, swelling in ethanol, acetone and in an aqueous solution of 1 N NaOH. The ion-exchange capacity, the moisture retention capacity and the titration curves of the sulfonated and cured products were determined. The ion-exchange capacity and the uptake of metal ions (mainly Co2+ and Cu2+) detected by atomic absorption spectroscopy, on the sulfonated materials, prepared in an excess of H2SO4, is higher for N-KRL and N-KRLH than for N and it takes place at the same rate or faster. The latter shows a medium acidic behaviour according to the titration curves, in contrast with the sulfonated N-KRLH and N-KRL, which show a strongly acidic behaviour. (C) 2001 Society of Chemical Industry.