Experimental and Theoretical Studies of α-Linolenic Acid as Green Corrosion Inhibitor for Carbon Steel in 0.5 M Sulfuric Acid.

A component of Salvia hispanica, α-linolenic acid, has been evaluated as a green corrosion inhibitor for 1018 carbon steel in 0.5 M sulfuric acid using weight loss tests, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) measurements. Theoretical calculations using Density Functional Theory (DFT) were used also. The results have shown that this compound is a good corrosion inhibitor, with an efficiency which increased with an increase in its concentration up to 600 ppm, but it decreased with a further increase in the concentration. α-linolenic acid formed protective corrosion products layer because it was chemically adsorbed onto the steel surface according to a Langmuir type of adsorption isotherms. Polarization curves have shown that α-linolenic acid is a good, mixed type of inhibitor with a predominant effect on the cathodic hydrogen evolution reactions. EIS measurements indicated a charge transfer-controlled corrosion process. DFT calculations indicated that α-linolenic acid was more efficient in an acidic environment than in a neutral one because has a high tendency to donate electrons and can be easily protonated. In addition to this, it had the highest EHUMO value, the best chemical reactivity, the greatest tendency to transfer electrons and a greater facility of modifying its electronic configuration in the presence of carbon steel specimens according to its chemical hardness value.

Elastomeric biodegradable starch/bentonite nanocomposites. Structure-thermo-mechanical correlation and degradation behavior.

We developed layered silicate nanocomposite films based on corn starch (CS) and bentonite nanoclay, plasticized with glycerol. The films were elastomeric with stretchability of ca. 60-90 % and Tg = -75 to -85 °C. The nanocomposites were exfoliated if cbentonite < 2 wt%, and intercalated if cbentonite > 3 wt%. The exfoliated morphology induced thermal stability as shown by TGA. Interestingly, bentonite induced a reduction of Tg while increasing the Young's modulus E and reducing the extensibility. The fracture energy was a decreasing function of cbentonite except at 2.9 wt%, where the nanocomposite exhibited maximum Young's modulus and toughness, as demonstrated by the Ashby-style plot. The nanocomposite films were biodegradable in anaerobic and aerobic conditions, and in anaerobic conditions the intercalated nanocomposite of cbentonite = 2.9 wt% exhibited slower rate of degradation. These results provide insights into the development of bio-degradable elastomeric food packaging and coatings suitable for sub-ambient conditions.