Chelating agents in aqueous, partially-hydrolyzed, poly(vinyl acetate) dispersions crosslinked with borax. Physicochemical characterization and an application

Abstract

The physico-chemical properties of two chelating agents, trisodium citrate (TSC) and ethylenediamine tetraacetic acid (EDTA), have been studied in highly viscous polymeric dispersions (HVPDs), obtained by crosslinking partially hydrolyzed (ca. 80 or 87% with 3% of the monomer units with carboxylate groups) poly(vinyl acetate)s (xPVA, where × = 80 or 87, respectively) with borax in water. Small angle X-ray scattering (SAXS), 11B NMR and rheology data for the systems are reported as a function of the concentration of the chelators. The SAXS data show that addition of TSC or EDTA increases the dimensions of the xPVA-based network as well as the affinity between the polymer chains and the aqueous continuous phase. 11B NMR spectra indicate that less than 15% of the borate ions were esterified by the hydroxyl groups of the xPVA and that the degree of boron crosslinking was not affected significantly by the addition of TSC or EDTA. Oscillating rheological tests, conducted in the linear viscoelastic region, show that both these chelators have a structuring effect on the 80PVA and 87PVA crosslinked networks. Furthermore, calculated continuous mechanical relaxation spectra H(τ) show the presence of a single peak whose width increases upon increasing the concentration of either of the chelators, indicating a broadening of the distribution of the relaxation modes. In addition, the structural effects of the addition of metal ions into the HVPDs were investigated by means of SAXS and 11B NMR. Finally, the efficiency of the HVPDs for the removal of surface degradation patinas on an artificially prepared copper specimen and on a XIII century reliquary box was tested. The amount of altered copper removed from the copper plates was assessed by ICP analyses.