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Chemistry and Industry of Forest Products ›› 2017, Vol. 37 ›› Issue (1): 101-108.doi: 10.3969/j.issn.0253-2417.2017.01.013

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Corrosion Inhibition of Steel in Glycolic Acid Solution by Cassava Starch Grafted Copolymer

LI Xianghong1, DENG Shuduan2, LI Yunxian1, LIU Jianxiang1   

  1. 1. Faculty of Science, Southwest Forestry University, Kunming 650224, China;
    2. Faculty of Materials Engineering, Southwest Forestry University, Kunming 650224, China
  • Received:2016-03-02 Online:2017-02-25 Published:2017-02-25

Abstract: Cassava starch grafted copolymer (CSGC) was synthesized via the chemical modification of cassava starch (CS) by grafting the monomer of acryl amide. The inhibition effect of CSGC on the corrosion of cold rolled steel (CRS) in glycolic acid was studied by weight loss method and electrochemical techniques. The results showed that CSGC could effectively retard the corrosion of cold rolled steel in glycolic acid solution. Inhibition efficiency was increased with the rise of dosage of CSGC. Meanwhile, it was decreased with the increasing of temperature and prolonging immersion time. The inhibition concentration, the maxima inhibition efficiency is found at 0.3 mol/L HOCH2COOH. The efficiency rose firstly. The inhibition efficiency was 92.1% as the steel were treated by 100 mg/L CSGC at 20℃ in 0.3 mol/L glycolic acid and it could also reach 89.1% even when the immersion time is prolonged to 72 h. The adsorption of CSGC on CRS surface in 0.3 mol/L glycolic acid at 20-50℃ obeyed the Langmuir isotherm with the adsorption enthalpy (ΔH) of -23.8 kJ/mol, the adsorption free energy (ΔG) was -28.3 kJ/mol to -28.9 kJ/mol and the adsorption entropy (ΔS) was about 15.4-16.8 J/(mol·K). The adsorption of CSGC on steel surface in glycolic acid was the mixed adsorption of physical and chemical adsorption. Also, it was an exothermic process accompanied with the increase of entropy. CSGC was considered as a mixed-type inhibitor via geometric blocking effect. Nyquist spectra exhibited one large capacitive loop followed by a small inductive loop at low frequencies. The charge transfer resistance significantly increased with the addition of CSGC, while interfacial double layer capacitance decreased.

Key words: cassava starch, graft copolymer, inhibitor, steel, glycolic acid

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