Nanostructured Poly(methyl Methacrylate)–Silica Coatings for Corrosion Protection of Reinforcing Steel

Abstract

In the absence of preventive maintenance, corrosion of structural steel by the deterioration of the passive layer due to exposure to aggressive environments is the main failure factor of reinforced concrete. To overcome economic, safety, and environmental implications, present research efforts focus on eco-friendly organic–inorganic hybrid coatings to achieve effective protection of reinforcing steel. Nanostructured PMMA (poly­(methyl methacrylate))–silica coatings developed by combining reactions of the polymerization of methyl methacrylate and 3-[(methacryloxy)­propyl]­trimethoxysilane with the sol–gel hydrolytic condensation of tetraethyl orthosilicate using isopropanol as a solvent represent a promising approach to accomplish this goal. The nanoscale dispersion of silica nodes covalently conjugated with PMMA chains led to transparent, homogeneous, and pore-free coatings deposited with a thickness of 15 μm on 2D and 3D reinforcing steel. Mechanical, thermal, and surface analyses showed a strong adhesion of the coating to the substrate surface (15.9 MPa), a thermal stability of up to 256 °C, and a contact angle of about 75°. Electrochemical assays in standard 3.5 wt % NaCl solution, simulated carbonated, and alkaline concrete pore solutions confirmed effective corrosion protection, with an impedance modulus of up to 100 GΩ cm2 (at 4 mHz) and a lifetime of more than 670 days. Hence, PMMA–silica hybrid coatings are an eco-friendly and efficient alternative to protect reinforcing steel against corrosion, helping to prevent structural failures and fatal accidents.

Green-High-Performance PMMA–Silica–Li Barrier Coatings

“…For exposure times of more than one year for all samples, except for Li4, the coatings show excellent barrier properties, highlighting the long-term stability of the Li2 sample maintaining a high impedance in aggressive solution over more than two years without failure (Figure 7d). This performance, confirmed in Figure S4 for the second set of samples, is comparable to the best anti-corrosion coatings reported to date [4,14,23]. The coating with the highest lithium concentration (4000 ppm) showed an initial impedance modulus of about one order of magnitude lower and then a continuous decrease over longer exposure periods, suggesting that the integrity of the hybrid network was impaired by Li 2 O 3 incorporation.…”

“…Figure 4f displays a representative image of the Li2 coating on AA7075, showing a homogeneous layer obtained by dip-coating. Samples containing low Li concentrations are transparent and colorless, as reported in [14], while for higher lithium concentrations, a slightly yellowish layer was formed.…”

“…Electrochemical, thermal, barrier, and mechanical properties of PMMA-silica coatings reported so far are compared with those found in the present work in Table 2. Excellent barrier properties have been reported for PMMA-silica and acrylic-silica coatings synthesized at similar conditions even when tested under harsh conditions such as acidic [9] and alkaline [14] solutions. Nonetheless, despite their high performance, most formulations use toxic solvents such as tetrahydrofuran, butyl acetate, and xylene.…”

“…A number of recent studies have investigated the effects of the inclusion of different corrosion inhibitors in hybrid coatings based on cerium, lithium, and molybdenum salts and organic inhibitors, such as 2-mercaptobenzimidazole, that are capable of significantly prolonging the service life of metallic components by retarding the progression of corrosion and the self-healing ability [7,[13][14][15][16][17]. In the event of corrosive or mechanical damage, ionic species are released from the bulk into corrosion-affected zones and act as a cathodic inhibitor by reacting with hydroxyls from the oxygen reduction reaction, forming an insoluble layer that prevents the progress of corrosive action [13,14,18]. Despite the high performance of these coating systems, most formulations used for the preparation involve harmful solvents, making their use on the industrial scale problematic.…”

Eco-Friendly Sustainable and Responsive High-Performance Benzotriazole-Metal Organic Frameworks/Silica Composite Coating with Active/Passive Corrosion Protection on Copper

“…Inorganic coatings have been widely used for corrosion protection on metals due to their excellent chemical stability, 1,2 environmentally friendly process, 3 and simple construction due to their excellent wear resistance and high hardness. 4−6 However, the intrinsic hydrophilicity 7 of silica weaken the corrosion resistance against corrosive medium.…”