Siloxane–PMMA hybrid anti-corrosion coatings reinforced by lignin

Abstract

a b s t r a c t a r t i c l e i n f o Available online xxxx Keywords: Lignin Siloxane-PMMA hybrid Sol-gel process Anti-corrosion coatingsNovel organic-inorganic hybrid coatings prepared using siloxane-poly(methyl methacrylate) (PMMA) were synthesized using the sol-gel process, with incorporation of lignin to improve mechanical strength, thermal stability and hydrophobicity, while maintaining the high anti-corrosive protection of siloxane-PMMA coatings. Dispersion of lignin in the siloxane-PMMA hybrid was analyzed by optical microscopy. Structural, morphological and wettability analysis of the about 2.5 μm thick coatings, deposited on carbon steel by dip-coating, was performed by X-ray photoelectron spectroscopy, atomic force microscopy and contact angle measurements. Thermal stability was investigated by thermogravimetry and the mechanical properties were studied by microhardness and microscratch measurements. Electrochemical impedance spectroscopy was used to evaluate corrosion resistance in saline aqueous environments. All coatings showed good dispersion of lignin in the hybrid matrix and low surface roughness between 0.3 and 0.4 nm. Incorporation of lignin increased hydrophobicity, microhardness and scratch resistance, in addition to shifting thermal degradation events to higher temperatures. The electrochemical tests showed that the hybrids act as efficient diffusion barriers, with corrosion resistance in the range of 10 8 Ωcm 2 after exposure to 3.5% NaCl aqueous solution. The hybrid containing a intermediate lignin content of 0.10 wt.% presented the best result, exhibiting the most hydrophobic surface (87.9°water drop contact angle), the highest hardness value (31.5 HV), high scratch resistance (up to 80.7 mN) and elevated impedance modulus (10 8 Ωcm 2 ) after 50 days exposure.

Organic-Inorganic Hybrid Coatings for Corrosion Protection of Metallic Surfaces

“…Properties of PMMA-silica hybrids containing lignin, CNT or GO: film thickness (optical interferometry); limit of thermal stability T 0 in N 2 atmosphere (TGA); critical load for delamination (microscrach test); impedance modulus |Z|, after 1 day exposure to 3.5% NaCl solution (EIS); and coating lifetime in 3.5% NaCl (EIS). , remaining almost unchanged after 50 days of exposure to aggressive environment [20].…”

“…Properties, such as low density, low abrasive character, hydrophobicity, and low cost, make lignin ideal to use as filler in polymeric and organic-inorganic hybrid matrices [20].…”

“…In addition, the thermal degradation events, obtained by thermogravimetric analysis (TGA) under nitrogen atmosphere, were shifted to higher temperatures with lignin addition, due to its phenolic structure which has the ability to trap radicals formed during the depolymerisation. Besides increasing the thermal stability of the polymeric phase, it acts also as UV stabilizer [20].…”

“…The resulting substantial lifetime increase is attributed to the formation of insoluble oxides and hydroxides in the corroded zones [3,11,[14][15][16][17]. On the other hand, significant improvements of thermal and mechanical properties have been achieved by incorporation of clays, lignin, carbon nanotubes, graphene oxide, and graphene into polymeric or organic-inorganic matrices [18][19][20].…”

From Waste to Valuable Resource: Lignin as a Sustainable Anti-Corrosion Coating

“…Consequently, it is necessary to follow the principles of circular economy in the development of sustainable industrial ecosystems, and, from this perspective, it is surprising how underutilized some of the side-streams of the biorefinery (pulp and paper) industries are. In particular lignin, which is a very abundant natural polymer that provides the structural strength of plants [1,2] and has an annual production of approximately 100 million tons globally. Nevertheless, despite this high level of output, currently only 2% is utilized in value-added products, and the rest is predominantly burnt as a heat source in the integral processes of pulp/papermaking [3].…”