**Renewable Resources in Corrosion Resistance**

Eram Sharmin, Sharif Ahmad and Fahmina Zafar

*Department of Chemistry, Jamia Millia Islamia (A Central University), New Delhi, India* 

## **1. Introduction**

448 Corrosion Resistance

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Corrosion of metals or alloys occurs due to chemical or electrochemical reactions with their environment, which often results in drastic deterioration in the properties of metals or materials comprising thereof. Corrosion takes place on a steel surface, due to the development of anodic and cathodic areas, through oxidation and reduction reactions, forming of oxides of metals alloys. There are several corrosion causing agents or "corrodents" such as soot, sulphate salts, chloride ions, temperature, salinity, pH, dissolved gases, humidity, bacteria, sand, gravels, stones, mechanical stresses and also several protection methods employed for corrosion resistance such as the application of alloys, composites, inhibitors, cathodic and anodic protection, protective linings and coatings (Bierwagen, 1996; Ghali et al., 2007; Raja& Sethuraman, 2008; Sorensen et al.,2009). Notwithstanding, corrosion has become a gigantic problem today for every nation. The colossal detrimental impact of corrosion on the economy of a country can be manifested in billions of dollars spent annually to combat or control it.

In the past two decades, research and development efforts in the field have undergone vast changes globally, because of the everyday growing consumer expectations of good quality and performance coupled with lower cost, enormous hikes in the prices of petro-based chemicals out of fear of depleting stocks by the end of twenty first century, serious concerns pertaining to energy consumption and environmental contamination, regulations such as Clean Air Act Ammendments [CAAA, 1990], and above all the "cost of corrosion". These predictions, regulations and innovations have posed constant threats and challenges for anticorrosion industry forcing to change its gears worldwide. The corrosion chemists, researchers and engineers in industry and academics are actively engaged to explore and formulate new strategies to meet the mandatory limits of performance, cost and legislations. The ultimate solution is foreseen through the "excessive utilisation of our naturally available resources" primarily, to cut off the escalating prices of raw materials, to formulate environmentally benign materials, to expedite their post-service degradation, and to add value to a waste material. Consequently "environmentally friendly" or "green" coating technologies (waterborne [WB], powder, high-solid, hyperbranched and radiation-curable) have evolved, with special emphasis being laid on the excessive utilization of naturally available renewable resources thriving on acres of our agricultural lands. These may be formulated as corrosion resistant alloys, corrosion resistant composites, corrosion resistant pigments, corrosion resistant coatings, paints and corrosion inhibitors. Renewable resources provide cheaper and abundant biological feedstocks with numerous advantages, such as

Renewable Resources in Corrosion Resistance 451

Cellulose is the largest biopolymer obtained by photosynthesis. It is a crystalline polysaccharide. It is a linear long chain polymer of β(1→4) linked D-glucose units (5,000- 10,000), that condense through β(1→4)-glycosidic bonds (Fig. 2). It is mainly obtained from wood pulp and other plants but can also be extracted from algae and bacteria for industrial purposes. Cellulose and their derivativs are used in paper, paperboard, card stock, textiles, cellophane, smokeless gunpowder, pharmaceuticals, biofuels, foods, sponges, cosmetics,

Cellulose is crystalline in nature. In desirable quantities, it may be used as a modifier rendering toughness in fragile coatings. The primary hydroxyl groups present in the chain may further facilitate adhesion to the substrate. Hydrophoebically modified hydroxyethyl cellulose used in WB coatings and paints provided good gloss, levelling and sag resistance (Kroon 1993). Films obtained from regenerated cellulose (from cotton linter) by coating Castor oil polyurethane/benzyl konjac glucomannan semi-interpenetrating polymer networks were water resistant and biodegradable (Lu et al., 2004). Ethyl cellulose based aqueous dispersions and solvent based films were plasticized with *n*-alkenyl succinic anhydrides -2-octenyl succinic anhydride (OSA) and 2-dodecen-1-ylsuccinic anhydride to overcome the brittleness of cellulose films (Tarvainena et al., 2003). Films obtained showed excellent mechanical properties, low permeability, and good flexibility. Amoxicillin doped cellulose acetate films showed good corrosion resistance on AA2024-T3 substrate (Tamborim et al., 2011). Films doped with 2000ppm of the drug showed good anti-corrosion behavior as observed by Electrochemical Impedance Spectroscopy [EIS] results. These films showed lower current densities up to 3 days of immersion under anodic polarization. Scanning Vibrating Electrode Technique [SVET] results were found to be in close agreement with EIS and polarization results, also informing about the defects in coating. The results also showed a decrease of the electrochemical activity in the doped cellulose acetate films, relative to their undoped counterparts. Liu et al prepared cellulose acetate phthalate free films with diethyl phthalate/triethyl citrate as the plasticizer by spray method under heatonly (50°C for 24 h) and heat-humidity curing (50°C/75% RH for 24 h) conditions (Liu & Williams III, 2002). The latter (despite retaining higher content of plasticizer due to suppressed evaporation) provided increased mechanical strength and decreased water vapor permeability of the films. Triethyl acetate films showed increased % elongation, decreased tensile strength and elastic modulus relative to diethyl phthalate films, however,

reinforced plastics, water-soluble adhesives, binders and coatings.

**2.1 Cellulose** 

Fig. 2. Structure of cellulose.

**Use in corrosion resistance** 

the latter showed low permeability.

cost effectiveness, low toxicity, inherent biodegradability and environment friendliness They yield versatile materials through chemical transformations with plethora of applications, particularly in corrosion resistance against various corrodents [Fig. 1]. (Derksen et al., 1995, 1996; Gandini & Belgacem, 2002; Metzgr, 2001; Weiss, 1997; Ahmad, 2007).

Fig. 1. Renewable resource based materials provide corrosion resistance against various corrodents.
