Elsevier

Progress in Organic Coatings

Volume 126, January 2019, Pages 106-118
Progress in Organic Coatings

Robust alkyd/exfoliated graphene oxide nanocomposite as a surface coating

https://doi.org/10.1016/j.porgcoat.2018.09.032Get rights and content

Highlights

  • A robust alkyd/exfoliated graphene oxide nanocomposites was synthesized.

  • An eco-friendly nanocomposites was developed through guest–host chemistry.

  • Vegetable oil based alkyd is a modern stream for mechanical & anticorrosive coating.

  • Well-dispersed nanofillers in alkyd matrix exerted improved different properties.

  • The physico-mechanical and anticorrosive features of the alkyd matrix were enhanced.

Abstract

Design of advanced nanostructured coatings with ecofriendly character and highly branched structure has been given a particular attention. In this work, we developed a novel robust alkyd/exfoliated graphene oxide (GO) nanosheets composite coating via solution casting. Alkyd matrix with hyperbranched moiety was developed via polyesterification of sunflower oil and polyester. Hyperbranched polyester was facilely synthesized via A2 and B3 technique. Exfoliated GO with 0.5–2 nm sheet thickness was successfully prepared using a modified Hummer’s technique. Alkyd/GO composite paint was dried using auto-oxidative drying. Designing alkyd/exfoliated GO sheets with superior physico-mechanical properties exhibit high levels of durability and corrosion resistance for coating application. The influences of dispersing various GO nanosheet percentages in the synthesized alkyd were studied. Water contact angle measurements were used to assess the surface properties, while the salt spray test in 5% NaCl was performed to investigate the corrosion protection characteristics. The robustness of nanocoatings were investigated mechanically using impact, bending, crosshatch and abrasion experiments and thermally using the thermal gravimetric analysis. Well dispersed exfoliated GO nanofillers up to 0.5 wt. % achieved compatibility and superiority in reinforcing the mechanical and anti-corrosive properties of alkyd nanocoatings. The modeled coatings possess numerous advantages, such as simple preparation, cost-savings, ecofriendly construction, robustness, and durability.

Introduction

Employing green chemistry for eliminating harmful solvents from coating industry has attracted a global interest [1,2]. Polymeric alkyd coatings are the most extensively applied solution for metallic substrate protection because of their cost-effective, excellent durability and outstanding cohesion and anticorrosive properties [3,4]. Alkyd polymers represent 50% of the utilized resins in protective paint application [5]. Because of their various merits such as reduced viscosity, no entanglement, low molecular weight and large surface functionality, hyperbranched polymers represent an eco-friendly trend toward coatings with minimum VOC [6]. Hyperbranched polymers outperform other members in dendritic polymer group such as dendrimers because they are prepared in a single step protocol from commercially available monomers without the need for multi-purification steps [7].

Hyperbranched alkyd resins possess more progressed advantages as excellent colour retention, durable nature, weathering resistance, and high anticorrosive resistance [8]. Hyperbranched alkyd resins possess superior performance and drying properties as compared to high solid alkyds [9]. Alkyd paint resins are polyester-based materials modified vegetable-derived drying oils that contain many polyunsaturated fatty-acid chains [10]. A2 and B3 methodology represent the simplest technique to prepare hyperbranched polyester only by proper choice of the multifunctional monomers [11]. Vegetable oil, especially sunflower oil (SFO), based alkyd resins have a number of advantages, including versatility in structure and properties, overall low cost, ease of application with environmental sustainability benefits [12]. SFO belongs to Asteraceae family with large numbers of unsaturated fatty acid chains.

SFO based alkyd resins exhibit excellent color retention, weather resistance, durability in exterior finishes, and good anti-corrosive properties [13]. Sunflower acid oil had been used to prepare low cost alkyd resins for surface coating and as a binder for composite material [14]. Considerable efforts have been made to provide non-noble catalysts as a substitutional path to reduce costs to improve the marketing efficiency as well as improve their effectiveness; carbon-based materials have attracted considerable attention as a promising alternative to various applications [15,16].Introducing carbon nanomaterials into alkyd resins is a sophisticated method for designing advanced coatings since they feature lightweight, superior mechanical strength and flexibility [16a]. Studies into the anticorrosive and mechanical characteristics of graphene-based materials are currently at the research level [16b]. The large tortuous path caused by the GO sheets along with the chemical interactions with the polymer chains, stand as the main reasons for reporting many GO nanocomposites [17]. Chemically exfoliated two-dimensional (2D) graphene oxide (GO) nanosheets possess several advantages including excellent mechanical properties, high aspect ratio and large surface area, good processability, gram-scale production at very low cost, biocompatibility and straightforward chemical modification capability [18]. Nanosheets structure is another attractive building block to produce strong nanocomposites with improved chemical and thermal stability [19]. GO based nanocoatings have approved great potential for corrosion protection with non-toxic property and improved crosslinking ability [20]. They are suitable for functionalized organic and inorganic materials through guest–host chemistry due to the presence of oxygenated functional groups [21,22]. Nanostructured composite alkyd coating based on hyperbranched polymers exhibit minimum volatile organic content and durability features [23]. Investigating the effects of different nanofiller concentrations in the alkyd matrix is essential to determine the nanocomposite features [24,25]. Eco-friendly SFO-based alkyd/spherical ZnO nanocomposites was fabricated for mechanical and anticorrosive coatings [26]. Krishnamoorthy et al., [27,28] has demonstrated a cost-saving graphene based conductive alkyd paint via ball milling technique, which can be used in nanopainting of the conductive coating technology. Also, a multifunctional GO-based alkyd nanopaint with corrosion resistance, antibacterial and fouling inhibition properties has been developed.

This study introduces a cost-effective and environmental friendly alkyd coating via guest–host chemistry. A novel series of SFO alkyd/exfoliated GO nanosheets composites was fabricated via solution casting. The current work fabricated and the exfoliated GO based hyperbranched alkyd nanocomposite as a robust coating surface. Different GO nanosheet filler concentrations were dispersed and compared to investigate the structure-property relationship. The enhancement in physicochemical, surface, mechanical, and corrosion protection characteristics was studied. The outcomes from this study are promising include simplicity, eco-friendly, economic and long term durability.

Section snippets

Chemicals

Sebacic acid ((HOOC)(CH2)8(COOH), 99%), 1,1,1-tris(hydroxymethyl) propane (TMP, CH3CH2C(CH2OH)3, 98%), p-toluene sulfonic acid (P-TSA, CH3C6H4SO3H, 99%), synthetic graphite powder with particle size <20 μm and NaNO3 (99%) were supplied by Sigma–Aldrich. SFO as well as the drying agents (octoates of cobalt, calcium and zirconium with molecular formulas of C16H30CoO4, C16H30CaO4 and C32H60O8Zr, respectively) were obtained from Merck, India. Sulfuric acid (H2SO4, 95.0%), KMnO4 (99%), and H2O2

Structure characterization of SFO-alkyd

A simple A2+ B3 (between sebacic acid and TMP) preparation technique to prepare hyperbranched polyester and the prepared polyester undergoes further reaction with SFO to prepare hyperbranched alkyd resin as indicated in Scheme 1. SFO-alkyd 1HNMR spectrum was indicated in Fig. 1. The CH2OCOR protons and single bondCHdouble bondCH– protons of the alkyd's unsaturated fatty acids showed a chemical shifts at 4.035 and 5.36 ppm. The peaks at 1.2 - 0.86 ppm refer to the CH3 protons of fatty acid residues. The Peak at

Conclusions

Hyperbranched SFO-alkyd resin structure was facilely synthesized with high branching degree, low viscosity and abundant surface functional groups. The current study introduced for the first time a robust series of alkyd/GO nanosheet composites via a guest-host coating model. Exfoliated GO nanosheets were synthesized and controlled. Various percentages of GO nanosheets were loaded in the hyperbranched SFO-alkyd for designing robust nanocomposite coating material. A great emphasis was awarded to

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      Citation Excerpt :

      The biggest cause of concern for steel products, however, is the development of corrosion products in steel structures, which jeopardises the structure's safety and ability to be maintained. Steel materials utilized in a variety of sectors and pieces of machinery are less durable due to corrosion, which results in structural damage [1,2]. Steel substrates are frequently covered with polymer coatings to reduce corrosion.

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