Análise da eficiência do uso de biopolímeros a base de carboidratos como inibidores de corrosão do aço do concreto armado

Abstract

Due to increasing environmental awareness and strict legislation, in recent years there has been an increasing tendency to use green approaches characterized by a minimal environmental load. Green corrosion inhibitors have attracted more attention in recent years as an effective and environmentally friendly technique. Carbohydrate-based biopolymers are available in nature, renewable and an ecological alternative to organic inhibitors with toxic potential. The main polysaccharides of commercial interest are cellulose and starch, especially more complex carbohydrates, as these polymers are formed by basic glucose units, linked as rings of acetal groups and, therefore, have high hydrophilicity. Within this context, the present work carried out exploratory tests to select potential candidates among the tested compounds, based on dissolution, for evaluation in simulated concrete pore solution (SPC), composed of cement and vacuum filtered water, in addition to simulation corrosive environment with the use of sodium chloride (NaCl). The additive that showed the best potential for use as a corrosion inhibitor was hydroxypropylmethylcellulose (HPMC). To optimize the experiment, an experimental design was used to determine the best concentrations of HPMC as a corrosion inhibitor in an environment contaminated by chlorides. For this analysis, the following experiments were carried out in an electrochemical cell: open potential circuit (OCP), electrochemical impedance spectroscopy (EIS) and linear scanning voltammetry (LSV), in addition to measuring pH and conductivity. The experimental design adopted was a central composite rotational design (DCCR), with variables being the amount of HPMC and NaCl, and the responses being corrosion potential (Ecor), polarization resistance (Rp), and conductivity. The statistical evaluation of the planning showed that for Ecor, Rp and conductivity, the HPMC and NaCl variables were significant (p<0.10), and the statistical model showed a correlation greater than 90% with the experimental data. OCP and polarization curve analyzes indicate the formation of a passive film on steel immersed in a solution containing HPMC. Tafel polarization demonstrates promising anticorrosive performance of HPMC. Statistical analysis, through DCCR, confirmed that the medium containing HPMC has better passivating properties, showing that this biopolymer can be used as a corrosion inhibitor for reinforced concrete in civil construction. The EIS results revealed an increase in the charge transfer resistance of the samples in the presence of HPMC, compared to the reference system. HPMC had greater efficiency as a corrosion inhibitor in samples contaminated with 17.5 g/L of NaCl, from 75% to 98%. In solutions containing 35.1 g/L of NaCl, only the maximum dosage of HPMC (1.2 g/L) was successful as a corrosion inhibitor, with an efficiency of 58%