Nature as Resource. Characterization of natural and synthetic polymers: acid-base properties and sequestering ability towards bivalent metal cations

The polymer industry has shown exponential and continue growth; this phenomenon, in part, is due to the crisis which results from depletion of fossil fuels resources as raw materials. Environmental sustainability is one of the most important objective of the scientific community, therefore the employ of ecofriendly natural and synthetic polymers in different fields, as in pharmaceuticals, cosmetics, paints, industrial formulations and in medical applications is fundamental. The characterization of the acid-base properties and binding ability, and in general speciation studies, of the polymers is the first step to understand their potential use and application. The polyelectrolytes presented in this contribute are: polyethylene glycole (PEG), Acusol 445 (homopolymer of acrylic acid), carboxymethylcellulose (CMC) and Carrageenan. The speciation studies of the different polymers were performed by potentiometric technique in NaNO3 aqueous solutions, at I = 0.15 mol·dm-3 and T = 298.15 K. For the interpretation of the acid-base properties, a simplified approach called Diprotic-like model, was used. This model treats a polyelectrolyte like a simple low molecular weight ligand defining a minimum number of protonation sites required to extensively describe the system. The binding ability of the polyelectrolytes was studied towards three metal cations: Ca2+, Zn2+ and Sn2+. To complete the characterization of these polymers, their sequestering ability was evaluated by means the empirical parameter pL50.