Synthesis of functionalized polyurethane foam using BES chain extender for lead ion removal from aqueous solutions

Abstract

Polyurethane foams functionalized with sulphonic acid groups have been found to be strong cation exchangers. This novel property of the foam was used to exchange lead (Pb2+) ions from aqueous solutions. Polyurethane foam synthesis is based on addition polymerization of an isocyanate (–NCO) with a polyol. The primary reaction is due to the reaction of the highly reactive –NCO groups of the isocyanate with the hydroxyl (–OH) groups of the polyol to form the urethane species. Toluene-2,4-diisocyanate,2,6-diisocyanate (CAS: 584-84-9) was reacted with polypropylene glycol 1200 (CAS 25322-69-4) in 2:1 molar ratio to form a linear pre polymer. The linear pre-polymer was further polymerized using N,N-bis(2-hydorxyethyl)-2-aminoethane-sulfonic acid (CAS 10191-18-1) chain extender. An organotin catalyst was used to accelerate the reaction and distilled water was used as a foaming agent to synthesize the functionalized polyurethane foam. The synthesized foam has an open cell content ranging from 70% to 91% and the density ranges from 160 to 432 kg/m3 depending on the foam formulation. The foam was exposed to Pb2+ solutions of known concentrations by batch process. The amount of remaining Pb2+ in the solution in parts per billion (ppb) was determined using an inductively coupled plasma mass spectrometer. The maximum Pb2+ ions exchanged per gram of the foam was measured to be 50–54 ppb from a 100 ppb Pb2+ solution over a period of 90 min. In this paper, we present the foam synthesis procedure with the design of experiments to study the effect of processing variables on the performance of this material.