Corrosion Inhibition Of Cassava Starch Grafted Copolymer On Cold Rolled Steel In Citric Acid

In the past few decades,chemical modification method of starch attracted the interest of the scientists in the field of fundamental research and industrial applied research due to strong reactivity and intermolecular force of starch and good mechanical properties and other excellent performance of polymer.Currently,the grafted copolymer of starch is the hotspot in the research of starch chemical modification.Introduction of the olefins into starch chemical modification,preparation and development of"environmentally-friendly" corrosion inhibitor plays great scientific significance in the field of metal protection.In this thesis,three kinds of grafted copolymers were prepared through oxidization reduction reaction and then were used as the corrosion inhibitors for cold rolled steel in citric acid(C6H8O7).The main contents included the following four parts:Part1:Cassava starch-acryl amide grafted copolymer(CSGC)was prepared by grafting acryl amide(AA)onto cassava starch(CS)with oxidization reduction reaction.Infrared spectroscopy(IR),weight loss,potentiodynamic polarization curves,electrochemical impedance spectroscopy(EIS),atomic force microscope(AFM),scanning electron microscope(SEM)and X-ray diffraction(XRD)were used to research the corrosion inhibition of CSGC for cold rolled steel in 0.2 mol·L-1 C6H8O7 The results showed that the inhibition efficiency was higher than 70%with the inhibitor concentration dosage of 100 mg·L-1 at 50 ? obtainted by weight loss method,electrochemical polarization curves and EIS.The adsorption of CSGC on the steel surface was in accordance with langmuir adsorption isotherm.The polarization curve shows that CSGC was a mixed type inhibitor.AFM,SEM and XRD confirm that the corrosion of cold rolled steel was retarded by adding CSGC to the C6H8O7 solution.Part2:Cassava starch-phenylethylene-methylmethacrylate grafted copolymer(CS-PE-MMA)was prepared by oxidization reduction reaction.The CS-PE-MMA corrosion film was prepared on the surface of cold-rolled steel by self-assemble technique.The morphology and composition of CS-PE-MMA corrosion film were studied by SEM and IR.The corrosion inhibition of CS-PE-MMA self-assembled film on cold rolled steel in 0.2 mol·L-1 C6H8O7 solution was studied by means of potentiodynamic polarization curves and EIS.The results showed that the CS-PE-MMA can be adsorbed on cold rolled steel surface to form a stable and orderly ball patchy dense corrosion film.The polarization curves and electrochemical impedance spectroscopy showed that the self-assembled molecular monolayerhas the highest inhibition rate of 73.0%in 0.2 mol·L-1 citric acid solution,which was a mixed type inhibitor.Part 3:Cassava starch-sodium allyl sulfonate-acrylamide grafted copolymer(CS-SAS-AA)was prepared by oxidization reduction reaction.The corrosion inhibition of CS-SAS-AA for cold rolled steel in 1.0 mol/L C6H8O7 solution was studied by IR,weight loss method,potentiodynamic polarization curve and EIS.The results showed that the corrosion inhibition performance of CS-SAS-AA increases from 6 h to 24 h,and then decreases from 24 h to 96 h,the corrosion time of the best corrosion resistance was 24 h.The corrosion inhibition of CS-SAS-AA increaseds from 0.2 mol·L-1 to 1.0 mol·L-1 of citric acid,and then decreaseds with the further increased of C6H8O7 concentration.When the concentration of C6H8O7 was 1.0 mol-L'1,the CS-SAS-AA has the best corrosion inhibition.The adsorption of CS-SAS-AA on the steel surface obeys Langmuir adsorption isotherm and the high degree of corrosion rate coincidence calculated by the weight loss method,electrochemical polarization curve method and EIS.The CS-SAS-AA was a kind of mixed inhibition.The sustained-release rate of CS-SAS-AA for cold rolled steel in 1.0 mol·L-1 C6H8O7 solution was 63.0%when the concentration of CS-SAS-AA at 400 mg·L-1.Part4:Selecting the methoxyl and glucopyranose molecules as the basic unit of starch molecule,the grafted copolymerization reaction mechanism of starch was calculated by using the density functional theory(DFT)method.The model molecules,reaction species,transition states,and products were optimized and frequencies were calculated by B3LYP/6-31G(d,p)method of Gaussian 09 program.The single point energies of all the stationgary points were calculated by the M06-2X/def2TZVP method.The transition state was found via the TS method and verified via IRC.The difference between the energy of transition state and the energy of the reactants were considered as the activation energy.Simultaneously,we obtained the zero calibration data of the optimized structures and the thermodynamic data of reaction at 298.15 K.The results indicated that:(1)the frequency of all the optimized structures were all real stable structures.The transition state has a unique imaginary frequency.IRC demonstrated that these transition state structures were the first order saddle point of the potential energy surface.The reactants and the products linked with each other via transition state.(2)The calculation simulation study indicated that the three contents as follows via of free radical polymerization:a.In the copolymerization reaction route of CSGC,the oxygen radical reacted with the ?-site C atom of AA with priority.The oxygen radical transferred to the a-site C atom of AA to forming the C radical,b.In the copolymerization reaction route of CS-PE-MMA,the oxygen radical reacted with the?-site C atom of MMA with priority.The oxygen radical transferred to the a-site C atom of MMA to forming the C radical.After the reaction consumed of MMA,the PE was grafted on the MMA by polymerization.c.In the copolymerization reaction route of CS-SAS-AA,the oxygen radical reacted with the ?-site C atom of SAS with priority.The oxygen radical transferred to the ?-site C atom of SAS to forming the C radical.After the reaction consumed of SAS,the AA was grafted on the SAS by polymerization.