Reversible Flocculation with Hydroxypropyl Guar−Borate, A Labile Anionic Polyelectrolyte

Cationic polystyrene latex was flocculated with mixtures of hydroxypropyl guar (HPG) and boric acid, which form an anionic polyelectrolyte HPG-borate. Flocculation could be reversed by either lowering pH or by adding fructoseboth procedures remove labile borate ions weakly bound to the HPG chains. Mixtures of phenyl boronic acid (PBA) and HPG also flocculate latex although the range of HPG-PBA concentrations, giving flocculation was much narrower than HPG-borate. The differences were explained by the tendency of borate ion to cross-link HPG chains, whereas PBA is monofunctional and cannot cross-link HPG.