Preparation of Titanium Oxide/Epoxy Hybrid Anticorrosive Coating A

Preparation of Titanium oxide/Epoxy Hybrid Anticorrosive Coating

A Thesis

Presented to

The Graduate Faculty of The University of Akron

In Partial Fulfillment

of the Requirements for the Degree

Master of Science

August, 2016

Haoran Wang

Preparation of Titanium oxide/Epoxy Hybrid Anticorrosive Coating

Haoran Wang

Thesis

Approved: Accepted:

Advisor Dean of the College Dr. Mark D. Soucek Dr. Eric J. Amis

Committee MemberDean of the Graduate School Dr. Bryan Vogt Dr. Chand Midha

Committee MemberDate Dr. Nicole Zacharia

Department Chair Dr. Sadhan C. Jana

ABSTRACT

Using organic coating is an effective method to prevent metal from corrosion. The coating layer acts as barriers to impede the transport of aggressive molecules or ionics such as water, oxygen and chloride ion into the surface of the metal. By introducing inorganic phase into organic binders by sol-gel can improve the anticorrosion performance of organic coating due the formation of sol-gel layers which can passivate the steel surface, and block the corrosive molecular and ions in the surface of metal. In this dissertation, titanium alkoxide/epoxy hybrid coatings have been prepared by using titanium(IV) isopropoxide(TIIP) as inorganic sol –gel precursor. According to data obtained from DMTA, titanium alkoxide have the effect on improving the Tg and crosslink density of epoxy coating which can be attributed to the formation inorganic domains which can inhibit the movement of polymer chains. According to the data obtained from general coating test, coating film becomes more brittle by introducing titanium alkoxide into formulation. According to the results of electrical impedence spectroscopy(EIS), salt spray experiment and acid undercutting test, the anticorrosion performance is dramatically improved by adding titanium alkoxide into epoxy coating formulation which can be attributed to the formation of titanium alkoxide layers in the surface of steel substrate.

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ACKNOWLEDGEMENTS

I really feel grateful to my advisor, Dr. Mark D. Soucek. I would thank him for taking me in his research group and giving me valuable suggestions.

I would also like to thank all my group members. Thanks for their help and patience. I have got many experimental skill and knowledge from them.

Lastly, I would like to express my most special thanks and love to my parents, who has always been supporting me in my master study.

TABLE OF CONTENTS

Page

LIST OF FIGURES……………………………………………………………………...vii

LIST OF TABLES………………………………………………..………………………ix

CHAPTER

I. INTRODUCTION…………………………..……………...... ……...1

II. BACKGROUND…...…………………………………...... ……...3

2.1 Corrosion…………………………….……………………...….………………..…..3

2.1.1 Mechanism of wet corrosion...…………………...…………...……..……...... 3

2.1.2 Corrosion control methods….……………………...…...………...…………..5

2.2 Anticorrosive coatings……….…..…….…………..…....……………...... ………….7

2.2.1 Organic coating……………..…………………...…………...……..……...... 7

2.2.2Inorganic coating……………..…………………...…….…...……..……...... 8

2.2.3 Metallic coating…………………………………………………………...…..8

2.2.4 Organic/Inorganic hybrid coating …………………………………………....9

2.3Organic and inorganic hybrid coating……………………………………….……....9

2.3.1 Sol-gel process..……………………….…………….…..……...... 10

2.3.2 Blending method……………………...……….………………………….….13

2.3.3 Anticorrosive mechanism of organic/inorganic hybrid coating……….……..14

2.4BPA Epoxy coating ………………………………………………...….………..…17

2.5 Titanium(IV) isopropoxide…………………………….…………………………...20

2.5.1 The application of TIIP in anticorrosion…………………………………………...20

2.6 Electrical impedance spectroscopy(EIS)………………………...……………...22

III. EXPERIMENTAL SECTION …….………………………………………….……..23

3.1 Introduction…………………..…...………….…...... …….…...... 23

3.2 Experimental section…………………….……………………………..……...…...24

3.2.1

Materials ………………………………….…..…………..………...... 24

3.2.2 Epoxide equivalent weight determination……………………………….…...25

3.2.3 Preparation IPTES grafted epoxy……….…....…………..…..…..………...... 26

3.2.4 Formulation and film preparation TIIP/epoxy hybrid coating……………….28

3.2.5 Instrumentation………………………………………………………………30

3.3 Results and discussions…………………………...………………….……...…….33

3.3.1 Characterization of IPTES grafted epoxy……………………………………34

3.3.2 Viscoelastic property………………………………………………………...39

3.3.3 General coating properties………………………………………………...…43

3.3.4 Evaluating the anticorrosion performance by EIS………………………...…44

3.3.5 Evaluating the anticorrosion performance by salt spray……………………..52

3.3.6 Acid undercutting test……………………………………………………….54

IV. CONCLUSTIONS…...………...……………………………………………...……..57

REFERENCES…………………………………….………...…………………...... ……5

LIST OF FIGURES

Figure Page

2.1 Mechanism of wet corrosion………………..………………...... ….……....4

2.2 Representative sol-gel precursors …………………………………………………….9

2.3 Hydrolysis reaction mechansim under acid condition ……………...... 11

2.4 Hydrolysis reaction mechansim under basic condition……...... 11

2.5 Possible ways to fabricate inorganic/organic hybrid coatings…...... 13

2.6 Interactions between organic/inorganic hybrid coatings and the metallic substrate....15

2.7 Proposed mechanism of the interaction between organic/inorganic hybrid coating and steel substrate………….….……………………………………………………………...16

2.8 Proposed anticorrosive mechanism of barrier effect ...... 16

2.9 Molecular structure of BPA and

ECH…….………………………………………….17

2.10 Synthesis process of

DGEBA……………...... ………………..17

2.11 General formula of BPA epoxy resin……………………………………………….18

vii

2.12 Curing mechanism of BPA epoxy resin with deamine………………………………19

2.13 The impedance of ceramic coating and soybean oil coating…………………………21

3.1 Distillation setup and color change……………...... 27

3.2 Reaction between IPTES and BPA epoxy…….………………………..…...... 28

3.3FTIR spectroscopy for IPTES, EPON828 and IPTES grafted epoxy……….……….35

3.4 FTIR spectroscopy for the solution of blank reaction………………………………..35

3.5Liquid state 29Si NMR spectroscopy for

IPTES..……………………..………………36

viii

3.6Liquid state 29Si NMR spectroscopy for IPTESgrafted epoxy………………………37

3.7Mass spectroscopy for EPON-828…...... 38

3.8Mass spectroscopy for IPTES grafted EPON-828……………………………………38

3.9Storage Modulus for all coating films as a function with temperature……………….40

3.10Loss factor for all coating films as a function with temperature………………...... 41

3.11DSC curves for all coating films………………………………………..…………...42

3.12Bode plot and phase angle plot of EP0………………………………………..…….46

3.13Bode plot and phase angle plot of EP5………………………………………..…….47

3.14Bode plot and phase angle plot of

EP10………………………………………..……48

3.15Bode plot and phase angle plot of IPEP0………………………………………..…..49

3.16Bode plot and phase angle plot of IPEP5………………………………………..…..50

3.17Bode plot and phase angle plot of IPEP10……………………………………..…...51

3.18Impedence modulus at 1HZ as a function of immersion time……………………….52

3.19 Photograph of steel panel after 240h salt spray test………………………………….53

3.20Pitting and blistering area after 240h salt spray test…………………………..……..53

3.21Degree of undercutting at pH=2 AFTER 24h immersion……………………..……..54

3.22Delamination area of coating films as a function with time in

Ph=6…………..……..55

viii

3.23 Degree of undercutting at pH=6 after 72h immersion……………………………….56

LIST OF TABLES

TablePage

2.1 Characterization of commercial BPA epoxy resin…………………………………..18

3.1 Chemical’s nomenclature and structure………...…………………………………...24

3.2The formulation of titanium oxide/epoxy(EPON828) hybrid coating………………29

3.3The formulation of titanium oxide/epoxy(IPTES-EPON828) hybrid coating……...30

3.4Crosslink density, storage modulus, Tg and Loss factor……...... 43

3.5 General coating properties…………………………………………………………...44

CHAPTER I

INTRODUCTION

Corrosion can be seen everywhere which is bad for the economy. It is a chemical reaction related to the materials and the surrounding conditions. The materials discussed here are metals which are unstable in the natural environment.Many preferable methods have been developed for anticorrosion. Using coatings is one of the most effective methods to prevent material from the corrosion which acts as barriers to air, ions and water. There are two kinds of coatings: organic coatings and inorganic coatings. Both of them have their advantages and disadvantages. Compared to using one kind of coatings, organic-inorganic hybrid coatings could give the substrate a better protection and improve the anti-corrosion performance of the coatings. On the one hand, organic phase makes the coatings get excellent mechanical properties, such as strength, ductility, hardness, impact resistance, and fracture toughness. On the other hand, inorganic phase increases the adhesion and provides better anticorrosion properties. Many researches have been developed on alkoxyl silane-based hybrid coatings, but the influence of titanium isopropoxide on the anticorrosion performance of epoxy coating are never been studied.

In this dissertation, four kinds of the titanium alkoxide/epoxy hybrid coating havebeen prepared and characterized. In Chapter III, the standard liquid BPA epoxy resinwas modified by the 3-isocyanatopropyltrietoxysilane (IPTES). The structures were

confirmed by Fourier transform infrared spectroscopy (FT-IR) liquid state 29Si NMR and mass

spectrometry (MS).Two kinds of epoxy primer were used in formulation, the pure epoxy resin and coupling agent(IPTES) grafted epoxy resin. Six kinds of coating films were prepared by adding 0wt%, 5wt% and 10wt% to the pure xpoxy resin and IPTES grafted resin. And ethanol was selected as the solvent. The viscoelastic properties of coating films were tested by DMTA and DSC. General coating properties including pencil hardness, cross-hatch adhesion, pull-off adhesion, reverse impact resistance and MEK resistance were tested in aluminum panel according ASTM standards. Most importantly, the anticorrosion performance was evaluated by electrochemical spectroscopy (EIS) and

240h salt spray test in steel panel.

CHAPTER II

BACKGROUND

2.1 Corrosion

As a natural phenomenon, corrosion is defined as the degradation of the material caused by the chemical or electrochemical reaction between the materials and the surrounding environments.1,2The degradation process causes the deterioration of the properties of the materials. Metals such as aluminum and steel play a significant role in human society.The metal failure caused by corrosion has been seen as a serious safety and economic issue.The corrosion process of metals is inevitable, but can be controlled according to the mechanism of corrosion.

2.1.1 Mechanism of wet corrosion

Most of the common metals used in industry are thermodynamically unstable, which means that those metals tend to return to their thermodynamic stable state: metallic compounds.3 Those metallic compounds are the products of corrosion.

Two separate zones (anode and cathode) with different electric potentials, the electrolyte solution and the conductive metal between anode and cathode are the three basic conditions of the electrochemical reaction, and corrosion is the result of the electrochemical reaction. Figure 2.1 shows the mechanism of wet corrosion.4For

example,steel, a very commonmetal used in industry, the different areas with different electric potentials on steel

surface form the anode site and cathode site.4 At the anode site, the main reaction is the oxidation of iron element and the products are ferrous ions, as shown as reaction (1). At the cathode site, the reduction of oxygen by water is the main reaction, which generates hydroxyl ions, as shown as reaction (2). The oxidation of ferrous hydroxides generates the green hydrate magnetite, FeO·Fe2O3·H2O, and water, as shown as the reaction (3).

The green hydrate magnetite generates the black magnetite, FeO·Fe2O3, by losing the water, as shown as reaction (4). Then, the red-brown rust, hydrated hematite,

Fe2O3·H2O, is formed in the presence of oxygen and water, as shown as reaction (5).

The reaction (6) is the summary of reaction (1) - (5).

Fe ( s ) Fe2+ ( aq ) + 2e- ( 1 )

- - 2H2O ( l ) + O2 ( aq ) + 4e 4OH ( 2 )

6Fe(OH)2 ( aq ) + O2 ( aq ) 4H2O ( l ) + 2FeO·Fe2O3·H2O ( s ) ( 3 )

FeO·Fe2O3·H2O ( s ) FeO·Fe2O3 ( s ) + H2O ( l ) ( 4 )

· 2FeO·Fe2O3 ( s ) + O2 ( aq ) + 3H2O ( l ) 3Fe2O3 H2O ( s ) ( 5 )

6Fe ( s ) + 2O2 ( aq ) + 3H2O ( l ) 3Fe2O3·H2O ( s ) ( 6 )

Figure 2.1 Mechanism of wet corrosion

Reproduced with permission from ref 4

2.1.2 Corrosion control methods

Corrosion is inevitable, but can be controlled. Based on the mechanism of the corrosion, corrosion engineers and scientists have created several methods to protect the metals from corrosion, such as protective coating, corrosion-resistant alloy, corrosion inhibitors, cathodic protection and so on.5

Protective coating used for anticorrosion can be divided into: organic coating, inorganic nonmetallic coating, metallic coating and organic/inorganic hybrid coating.

Most of the protective coatings are based on those three mechanism: barrier effect, inhibitive effect and galvanic effect.4 Barrier effect is defined as impeding the transport of aggressive molecules6 or ionic7 such as water, oxygen and chloride ion into the surface of the metal. Inhibitive effect is defined as passivation of the metal surface to obtain a protective layer, such as conductive polymer coating or adding inhibitive factor into the coating formulation. Galvanic effect is defined as the protection mechanism is based on

sacrificing the electrochemically more active metals than the substrate, such as zinc-rich coating.

From the data of the US Census Bureau of Statistics, in 1977, the stainless steel, one of the most important alloy, was sold in US at a production cost of $5.5 billion.3 Also, the nickel-based, titanium-based alloy have been widely used in the severe environments.

Passivation in specificenvironment is the main anticorrosion mechanism for alloy. In general, the anticorrosive behavior of alloy is dependingon four kinds of factors: the specific chemical composition and metallurgical structure, the film on the surface, the surrounding environment, and the alloy/environment combination.5

Corrosion inhibitor have been defined as the chemical which is used to reduce the corrosion rate of the metal.3 Most of the corrosion inhibitors are reacting with the surface of the metal to form an inhibitive film. Corrosion inhibitor can be divided into three classes: passivators, organic inhibitors including slushing compounds and pickling inhibitors, and vapor phase inhibitors.5 Generally speaking, passivators are inorganic oxidizing chemical substance such as: chromates, nitrites, and molybdates. The mechanism of pickling inhibitor is forming an adsorbed layer on the surface of metal to block discharge of H+ and dissolution of metal ions.5 As for the slushing compound, it including oils, greases or waxes, which is used to protect steel surface from rusting temporarily. The last classes, vapor-phase inhibitor is defined as the vapor which has high vapor pressure and corrosion inhibiting properties.

Cathodic protection is the most effective corrosion control method because it almost can reduce the corrosion rate to zero by applying the external electric current. Impressed current cathodic protection( ICCP ) and sacrificial anode cathodic protection( SACA ) are

two types cathodic protection method. As for the mechanism of cathodic protection, it is working by eliminating the corrosion current flow. By adding the external current, the entire metal surface is polarized to the thermodynamic potential of anode.5 Cathodic protection have been wildly used in the bulk metal structure immersed in sea water or buried in soil.

2.2 Anticorrosive coatings

Anticorrosive coating used for anticorrosion can be divided into: organic coating, inorganic nonmetallic coating, metallic coating and organic/inorganic hybrid coating.

Most of the protective coatings are based on those three mechanism: barrier effect, inhibitive effect and galvanic effect.4 Barrier effect is defined as impeding the transport of aggressive molecules6 or ionic7 such as water, oxygen and chloride ion into the surface of the metal. Inhibitive effect is defined as passivation of the metal surface to obtained a protective layer, such as conductive polymer coating or adding inhibitive factor into the coating formulation. Galvanic effect is defined as the protection mechanism is based on sacrificing the electrochemically more active metals than the substrate, such as zinc-rich coating.

2.2.1 Organic coating

Organic binders, solvents, pigments, and additives are the four components of organic coatings.8 Organic binders are polymer resins, which including: acrylics, alkyds, amino resins, epoxies, polyesters, polyurethanes, polyurea and so on. Some of those binders have been widely used in industry as the anticorrosive coating. The specific

chemical structure gives those binders specific property to be used as anticorrosive coating. Such as, the excellent adhesion to the metal substrate, high impact strength, the barrier property to prevent moisture, oxygen and ions from metal substrate. Besides, some researchers find that the conducting polymer also can be used as anticorrosive coating.9

2.2.2 Inorganic nonmetallic coating

Generally speaking, there are three types inorganic nonmetallic coatings which are glass coating, portland cement coating and chemical-conversion coating.5 The powdered form glass is applied to the prepared metal, and then heat them to allow the soften glass bond to the surface of metal. Alkali borosilicates composed in glass coating can resist strong acids or mild alkalies. Portland cement coating can be applied by centrifugal casting, troweling and spraying. And cement coating has been widely used to protect steel water pipe. Chemical conversion coating is defined as the coating formed in situ by chemical reaction with the metal surface such as phosphate coating. Phosphate coating is hard and electrically non-conductive. This coating consists of insoluble phosphate which is contiguous and highlyadherent to metal surface. Also, this coating can cause the surface of the base metal tointegrate itself which will become a part of thecorrosion resistantfilm.

2.2.3 Metallic coating

According to anticorrosive mechanism, metallic coating can be divided into two types, noble coatings and sacrificial coatings. Nobel coatings are defined as the coatings

which only provide barrier protection property. Sacrificial coatings are defined are defined as the coatings which not only provide barrier protection property, but also provide cathodic protection property. In particular, there are several types metallic coatings that have been widely used in industry, such as nickel coating, tin coating, zinc coating, lead coating, cadmium coating, chromium coating, aluminum coating and so on.5

2.2.4 Organic/Inorganic hybrid Coating

The organic/inorganic hybrid material was raised in 1980s.10 Also, the organic/inorganic hybrid material is called creamer which is derived from ceramic and polymer. The organic/inorganic hybrid material not only combines the inorganic and organic characteristic, but also may own some unique properties. Generally speaking, the organic/inorganic hybrid coating can own the specific property from inorganic part such as: thermal stability, hardness and scratch resistance, and the specific property form organic phase such as: flexibility, toughness, impact resistance and adhesion. Also. The inorganic phase can improve the anticorrosive property of organic coating.

2.3 Organic/Inorganic hybrid coating

The interaction between organic phase and inorganic phase plays an important role in the final property of organic/inorganic hybrid coating. Typically, the interaction can be divided into two classes, weak interactions and strong interactions. Weak interactions include hydrogen bond, ionic bond, van der waals force and so on. The strong interaction is mainly provided by covalent bond. The organic/inorganic hybrid material not only combines the inorganic and organic characteristic, but also may own

some unique properties. Generally speaking, the organic/inorganic hybrid coating can own the specific property from inorganic part such as: thermal stability, hardness and scratch resistance, and the specific property form organic phase such as: flexibility, toughness, impact resistance and adhesion. Also. The inorganic phase can improve the anticorrosive property of organic coating. Basically, there are two methods to fabricate organic/inorganic hybrid coating, which are sol-gel process and blending method.11

2.3.1 Sol-gel process

Sol-gel process is define as the chemical reaction to fabricate ceramic material in situ by using sol-gel precursor. Sol-gel precursor is defined as the small molecule which can undergo hydrolysis and condensation reactions to form inorganic phase in organic/inorganic hybrid material. Usually, sol-gel precursors are metal or semimetal alkoxides, such as titanium, zirconium, aluminum and silicon. Figure 2.2 shows the most representative sol-gel precursors with name and chemical structure.

Figure 2.2 Representative sol-gel precursors

Sol-gel process starts with the hydrolysis reaction of sol-gel precursor. Sol-gel precursors react with water to form hydroxyl functional group, as shown as reaction ( 7 ).

OR OH

RO M OH RO M OR + H2O + ROH

OR OR ( 7 )

Then the condensation reaction happens between two partially hydrolyzed molecules with byproduct water, as shown as reaction ( 8 ), or with byproduct alcohol, as shown as reaction ( 9 ).

OH OH OH OH ( 8 ) RO M OH + RO M OH RO M O M OH + H2O

OR OR OR OR

OR OH OR OH

R O M O R + R O M O H R O M O M O H + R O H ( 9 )

OR OR OR OR

The overall sol-gel reaction is showed in reaction ( 10 ).

OH OR OR O M O M O M O OR OH OH O O O RO M OR + RO M OR +RO M OH O M O M O M O ( 10 ) OR OR OR O O O O M M M O OR OH OR

It is also worth mentioning that those sol-gel reactions are sensitive to whether the condition is acid or basic. Under acid condition, the linear structure is favored to form by hydrolysis reaction and the reaction mechanism is Sn2 mechanism, as shown as figure

2.3.12 Under basic condition, the dense three-demensional structure is favored to form

and the hydrolysis reaction is more slower than condensation reaction. The reaction is according to Sn1 mechanism, as shown as figure 2.4.12

Figure 2.3 Hydrolysis reaction mechansim under acid condition

Reproduced from reference 12

Figure 2.4 Hydrolysis reaction mechansim under basic condition

Reproduced with permission from reference 12

As an innovative and effective way to produce organic/inorganic hybrid material, sol-gel process have been widely used in fabricating coating. Dr. Mark D. Soucek’s research group have studied the organic/inorganic coating fabricated by sol-gel process in depth with different inorganic precursor such as tetraehyl orthosilicate, titanium(IV) isopropoxide and zirconium(IV) propoxide and with different organic polymer resin such as alkyd, polyureane and epoxy.13,14,15,16 And comparied with pure organic coating, adding inorganic phase into coating formulation can improve the antocorrosive

performance and adhension property significantly. In a particular organic/inorganic hybrid coating formulation, the suitable solvent is essential.

2.3.2 Blending method

Blending is another effective method to fabricate organic/inorganic hybrid material. Blending method is defined as using inorganic powders, rods, tubes or sheets to combine with organic phase directly. How to disperse the inorganic phase into organic phase well is the key point for blending method. Until now, material engineer and scientist have created several methods to disperse the inorganic phase in organic phase, such as, high shear rate mixing, bead milling, three-roll milling, ultrasonication and surface modification. Figure 2.5 shows the possible ways to fabricate organic/inorganic hybrid coating from nanopowders.17

Figure 2.5 Possible ways to fabricate inorganic/organic hybrid coatings

Reproduced with permission form reference 17

2.3.3 Anticorrosive mechanism of organic/inorganic hybrid coating

For the organic/inorganic hybrid coating prepared by sol-gel process, the interaction between inorganic precursor and metallic substrate is believed to be the reason that organic/inorganic hybrid coating have better anticorrosive performance than pure organic coating, as shown as figure 2.5.18 Dr. Mark D. Soucek research group has used tetraethyl orthosilicate ( TEOS ) to modify BPA epoxy. The modified BPA epoxy coating shows improved anticorrosive performance which is demonstrated by salt spray test. Dr.

Mark D. Soucek indicated that the mechanism of the excellent anticorrosive performance is the formation of sol-gel layer on the surface of steel substrate and the sol-gel layer can passivate the steel surface, and block the corrosive molecular and ions, as shown as figure

2.6.19

As for the organic/inorganic hybrid coating prepared by blending method, the main anticorrosive mechanism is believed to be barrier effect, which means that the by adding the impermeable inorganic particle or sheet into the coating formulation, the diffusion of corrosive species will be impeded, as shown as Figure 2.7.4 The most common inorganic phase is lamellar, such as micaceous iron oxide, aluminum sheet, clay sheet and so on.

Figure 2.6Interactions between organic/inorganic hybrid coatings and the metallic

substrate

Reproduce with permission from ref 18

Figure 2.7Proposed mechanism of the interaction between organic/inorganic hybrid

coating and steel substrate

Reproduced with permission from ref 19

Figure 2.8 Proposed anticorrosive mechanism of barrier effect

Reproduced with permission from ref 4

2.4 BPA epoxy coating

BPA epoxy resin is widely used as protective coating due to the excellent property such as excellent adhesion, chemical stability, and superior hardness. BPA epoxy resin is made from BPA and epichlorohydrin(ECH). Figure 2.8 shows the molecular structure of BPA and ECH. Figure 2.9 shows the synthesis process of DGEBA which is the monomer of BPA epoxy resin. BPA reacts with sodium hydroxide to generate BPA- and water which is the first step. Then, BPA- reacts with ECH to format sodium chloride and MGEBPA which have the oxirane ring. MGEBPA, as the initial product, will continue react with ECH to generate DGEBA Which is the monomer of

BPA epoxy resin.20

Figure 2.9 Molecular structure of BPA(left) and ECH(right)

Figure 2.10 Synthesis process of DGEBA

Reproduced with permission from ref 20

The epoxide of MGEBPA and DGEBPA can continue react with BPA- to generate BPA epoxy resin with hydroxyl group. Due to both BPA and ECH are difunctional, the final product is a kind of linear polymer. Figure 2.10 shows the general formula of BPA epoxy resin. It is worth to mention that by controlling the ratio of ECH to BPA, polymer with different molecular weight can be obtained, but the ECH is always excess. The difference of molecular weight is represented by the average n value. Table

2.1 shows the n value, epoxy equivalent weight(EEW) and melting point of the commercial BPA epoxy resins. With the increasing n value, the properties of BPA resins will change such as viscosity and melting point. The liquid BPA resin is the most widely using BPA epoxy resin.

Figure 2.11 General formula of BPA epoxy resin

Table 2.1 Characterization of commercial BPA epoxy resins

n value EEW MeltingPoint(°C)

～0.11-1.15 182-192 Liquid

～2 500-560 65-85

～5.5 875-950 90-110

～14.4 1600-2300 120-135

> 16 2500-5500 130-160

The curing mechanism of BPA epoxy resin is the ring opening reaction of the epoxide which is attacked by the active hydrogen atom, as shown as figure 2.11.4 A lot of

curing agents have been used to react with BPA epoxy resin which can be divided into

five classifications.21

• Aliphatic amines

• Aromatic amines

• Polyamides

• Anhydrides

• Polysulfides and mercaptans

Cycloaliphatic amines was the most common curing agent for BPA epoxy resin.

Recently, polyamides has been seen as the candidate to replace cycloaliphatic amines

which is highly toxic. The reaction between BPA epoxy resin and polyamides is very

slow which leading it be more maneuverable in formulation step. The coating properties

of polyamides cured epoxy coating are more moderately. And the flexibility, moisture

resistance and adhesion are higher than the BPA epoxy coating cured by amines agent.

Figure 2.12 Curing mechanism of BPA epoxy resin with diamine

Reproduced with permission from ref 4

2.5 Titanium(IV) isopropoxide

As mentioned above, Titanium(IV) isopropoxide(TIIP) is an important sol-gel precursor which has been used to prepare nanosized titanium dioxide22,23,24 and titanium oxide layer25,26,27.

2.5.1 The application of TIIP in anticorrosion

Titanium oxide film prepared from TIIP by sol-gel process have been proved that it is an excellent anticorrosive coating.28,29,30,31 The mechanism of the excellent anticorrosive performanceof the titanium oxide film are the passivating effect which means that it can passivate the metal surface, and barrier effect which means that it can block the transportation of corrosive molecular and ions. But it is always need very high temperature to prepare the inorganic titanium oxide film which limits the application in industry. And also, the titanium oxide film is very brittle.

2.5.2 Organic/inorganic hybrid coating prepared from TIIP

Several researches have used TIIP as sol-gel precursor to prepare organic/inorganic hybrid coating with improved properties. Mohammed Rafi Shaik32 prepared the castorOil based poly(urethane-esteramide)/TiO2 hybrid coating with excellent anticorrosion performance. Denize Maria Bechi33 prepared the organic/inorganic hybrid coatings based on epoxidized castor oil and APTES/TIP shows excellent anticorrosion performance, and he indicated that the coupling agent APTES plays the key role in keeping the flexibility of coating. Dr. Mark D. Soucek34 prepared the blown soybean oil creamer coating by using TIIP as sol-gel precursor. Compared with soy bean oil coating, the creamer coating shows the significantly improved adhesion and anticorrosive properties. Also, Dr. Mark D. Soucek indicated that the reason for the

improved anticorrosion performance is the formation of self assembling layer of titanium-oxide domains at the interface of coating and metal substrate. Figure 2.1234 shows the impedance modulus of ceramic coating and soybean oil coating. The impedance modulus 106 Ohm has been seen as the standard to evaluate if the coating has anticorrosion property which means that when the impedance modulus lower than 106

Ohm, the coating already lose the anticorrosion property. As we can, the soybean oil coating without adding TIIP failed within six weeks, and the ceramic coating still shows good anticorrosion performance after 14 weeks’ exposure.

Figure 2.13 The impedance modulus of ceramic coating(BLTIP) and soybean oil

coating(BL)

Reproduced with permission from ref 34

2.7 Electrical impedance spectroscopy(EIS)

EIS has been widely used to study the anticorrosion performance of organiccoatings.35EIS method can give a quantitative evaluation of the anticorrosion performance of coating and without damaging the organic coating.

Due to the insulating property of organic coating, a high electrical resistance is created by applying the coating layer on the surface of metal. With water and corrosive ions transport into the coating layer, the electrical resistance of coating will decrease. EIS can test the diffusion process of corrosive agents and corrosion process by measuring the electric parameters.

CHAPTER III

EXPERIMENTAL SECTION

3.1 Introduction

The organic/inorganic hybrid material was raised in 1980s.10 Also, the organic/inorganic hybrid material is called creamer which is derived from ceramic and polymer. The interaction between organic phase and inorganic phase plays an important role in the final property of organic/inorganic hybrid coating. Typically, the interaction can be divided into two classes, weak interactions and strong interactions. Weak interactions include hydrogen bond, ionic bond, van der waals force and so on. The strong interaction is mainly provided by covalent bond. The organic/inorganic hybrid material not only combines the inorganic and organic characteristic, but also may own some unique properties. Generally speaking, the organic/inorganic hybrid coating can own the specific property from inorganic part such as: thermal stability, hardness and scratch resistance, and the specific property form organic phase such as: flexibility, toughness, impact resistance and adhesion. Also. The inorganic phase can improve the anticorrosive property of organic coating.

coating, as shown as figure 2.5.18 Dr. Mark D. Soucek’s research group has used tetraethyl

orthosilicate ( TEOS ) to modify BPA epoxy. The modified BPA epoxy coating shows improved anticorrosive performance which is demonstrated by salt spay test. Dr. Mark D.

Soucek indicated that the mechanism of the excellent anticorrosive performance is the formation of sol-gel layer on the surface of steel substrate and the sol-gel layer can passivate the steel surface, and block the corrosive molecular and ions.

The objective of this chapter is to prepare and characterize the titanium oxide/epoxy hybrid coatings and to study the effects of the TIIP and coupling agent(IPTES) on the coating properties.

3.2 Experimental section

3.2.1 Materials

Bisphenol-A (BPA) based liquid epoxide (trade name: EPON828) and

EPIKURE™ Curing Agent 3192(modified polyamide)was bought from Hexion. 3-

(Triethoxysilyl)propyl isocyanate (IPTES) (95%), dibutyltin dilaurate(DBTDL) (95%), titanium (IV) isopropoxide (Sigma-Aldrich), tetrahydrofuran (THF),methylene chloride, tetraethyl ammonium bromide, glacial acetic acid, phenolphthalein, methanol and ethanol were purchased from Sigma Aldrich. Plain aluminum(bare) and steel(bare) substrate were purchased from the Q-Panel company.

Table 3.1 Chemical’s nomenclature and structure

Chemicals Nomenclature Structure

EPON 828 Bisphenol-A based epoxide resin liquid epoxide

Coupling 3-(Triethoxysilyl) agent propyl isocyanate

Solvent Toluene

solvent Ethanol

Catalyst Dibutyltin dilaurate

Sol-gel (Titanium(IV) precursors isopropoxide)

3.2.2 Epoxide equivalent weight(EEW) determination

EEW is determined by titration according to ASTM D1652-97. Weighing 0.4g

EPON 828 into a 250-mL Erlenmeyer flask. Then, adding30ml methylene chlorideto to dissolve the epoxy resin. At the same time, dissolving 3,75g tetraethyl ammonium bromide in 15ml glacial acetic acid.Mixing the epoxy solution and tetraethyl ammonium solution by using magnetic stirrer. Adding6 drops of phenolphthalein solution into the flask as the indicator. Using perchloric acid solution(0.1N in glacial acetic acid) to titrate until the color of solution changes from sharp blue to green.

(10)

According to equation (10), the EEW of EPON828 can be calculated as

189.88/equiv. W is the weight of the epoxy resin (g), V is the volume of perchloric acid solution (mL), and N is the normality of the perchloric acid solution which is 0.1N.

Based on the chemical structure of epoxy resin, the repeat unit n can be calculated according to EEW. For EPON828, n equals to 0.14 which means the hydroxyl number for EPON828 is 2712.57g/mol.

3.2.3 Preparation IPTES grafted epoxy

Using the reaction between hydroxyl group in EPON 828 and the isocyanategroup in IPTES, the alkoxysilane group has been grafted on the epoxide primer successfully by covalent bond. Due to the high activity of isocyanategroup which is sensitive to water and moisture, and the alkoxysilane group also can hydrolysis and condensation when water or moisture existence, how to avoid water and moisture is the main point for this reaction. The detailed synthesis protocol will be shown below.

Toluene is selected as the solvent for the reaction due to it is incompatibility with water. But most important, toluene can dissolve both EPON828 and IPTES. Although toluene is hydrophobic, but few water maybe dissolve in toluene. So, the sodium cube is selected to dry the toluene and benzophenone is selected as the indicator.35 When the toluene-sodium-benzophenone system is dry, the color will become dark blue, as shown as figure 3.1. After the solution become blue, toluene is distilled at 110 centigrade.

Figure 3.1 Distillation setup and color change

The reaction glassware is treated by trimethylchlorosilane toluene solution to remove react site in the glass ware. After treatment, the glassware is reinsed by methnol and then put in vacuum oven at 110 centigrade.

Adding 250g(0.092mol hydroxyl group) Epon 828 epoxide primer and magnetic stirrer into the schlenk flask taken out from vacuum oven. Then, using schlenk line to remove the water and moisure in the flask and epoxide primer at 80 centigrade. When there are no bubbles came out from the epoxide primer, transferring the distilled tolune to the flask by double-end tip. Then, close vacuum and let nitrogen flow into the flask. After the epoxide primer dissolve in toluene, adding 5 drops DBTDL as the catalyst by syringe.

Then, adding 18.18g(0.0736mol isocyanate group) IPTES by syringe drop by drop. After

4 hours, toluene was removed in vaccum.

Figure 3.2 Reaction between IPTES and BPA epoxy

3.2.4 Formulation and film preparation TIIP/epoxy hybrid coating

According to ASTM D1652-97, thee EEW of modified epoxy is 204.7g/equiv.

The EPKIURE 3192 is used as curing agent for both EPON828 epoxy resin and IPTES grated epoxy resin. TIIP is used as inorganic sol-gel precursor and ethanol is used as the solvent. In detail, adding epoxy resin and magnetic stirrer to flask. Then adding the solvent ethanol to the flask and trying dissolve the epoxy resin in ethanol. However, epoxy resin cannot dissolve well in ethanol, the color of the solution is white but not transparent. Then, adding the curing agent with a mole ratio of epoxy group to amine group 1:1.The amine equivalent weight of EPKIURE 3192 is 133 g/equiv.The solution become transparent gradually. This phenomenon is attributed to the much more hydroxyl group is generated from the reaction between epoxy resin and curing agent. After the

solution became transparent, adding theTIIP sol-gel precursor by syringe under the nitrogen atmosphere. Keeping stirring 1 h to make the TIIP mix well with the epoxy. In the film preparation step, both the aluminum and steel panels are cleaned with acetone by gently swiping. The wet films arecasted by 4 mil draw-down bar. The wet films is put in a dust free chamber 24h to make the film dry to touch. And then the films are thermal curing in 120OC, two hours. The final coating are obtained with around 50um thickness.Before all the coating tests, all the films are put in dust-free places one week.

The details of the formulation were shown in table 3.2 and table 3.3. EP standards for EPON 828 and IPEP standards for the IPTES grafted epoxy resin. And the digit after

EP and IPEP standards for the weight percent of TIIP based on the weight of epoxy resin.

Table 3.2 The formulation oftitanium oxide/epoxy(EPON828) hybrid coating

Table 3.3 The formulation of titanium oxide/epoxy(IPTES-EPON828) hybrid coating

3.2.5 Instrumentation

A variety of instruments were used to characterize the IPTES grafted epoxy resin and test the hybrid coatings such as: Fourier transform infraredspectroscopy, liquid-state

29Si nuclear magnetic resonance spectroscopy, mass spectrometry, differential scanning calorimetry,Dynamic mechanical thermal analysis and electrochemical impedance spectroscopy.

3.2.5.1 Fourier transform infrared (FT-IR) spectroscopy

Fourier transform infrared (FT-IR) spectroscopy was carried on Thermo Scientific

Nicolet 380 which is used to test the completion of the reactionand to characterize the chemical structure of IPTES grafted epoxy resin.

3.2.5.2 Liquid-state 29Si nuclear magnetic resonance(NMR) spectroscopy

Liquid-state29Si NMR spectroscopy was carried on Gemini-500 MHz spectrometer (Varian) which was used to characterizethe chemical structure of IPTES grafted epoxy resin.

3.2.5.3 Mass spectrometry

Mass spectrometrywascarried on a Bruker UltraFlex III MALDI tandem time-of- flight (TOF/TOF) mass spectrometer (Bruker Daltonics, Billerica, MA, USA) which was also used to characterizethe chemical structure of IPTES grafted epoxy resin.

3.2.5.4 Differential scanning calorimetry(DSC)

DSC was performed on TA DSC Q2000 which was used to test the glass-

o o transition Temperature(Tg) of hybrid coating. The first thermal cycle from -50 c to150 c was used to remove thermal history.

3.2.5.5 Dynamic mechanical thermal analysis(DMTA)

DMTA was carried on TA Instruments Q800 DMA which was to measure the viscoelastic property. A heating rate 3°C/min with a range from -20oc to150oc was used.

3.2.5.6 General coating properties

All of the general coating properties were tested according to ASTM standards on aluminum substrate such as: Pull-off adhesion(ASTM-D4541), cross-hatch adhesion(ASTM-D3359), reverse impact resistance(ASTM-D2794), pencil hardness(ASTM-D3363), MEK resistance(ASTM-D4752) and Pendulum hardness(ASTM-D4366).

3.2.5.7Electrochemical impedance spectroscopy(EIS)

EIS was used to evaluate the anticorrosion performance of hybrid coating. It was carried on a ZIVE SP1 system. The three electrodes(reference, working and counter) system with 3.5% NaCl solution was used. The open circuit potential with the frequency range from 100 KHZ to 10 MHZ with an alternating current voltage amplitude of 10mv was used to the measurements.

3.2.5.8 Salt-spray test

Salt spray test is operated on the Q-panel fog chamber according ASTM

B117.The steel panel coated by coatings are exposed in the sol-fog atmosphere made from 3.5wt% aqueous NaCl solution at 35 ±2oc for 240h. The region without coatings of panel are covered by adhesive tape. A cross scratch penetrated to the steel substrate is made in the coating.

3.2.5.9 Acid Undercutting

Acid undercutting test was operated in two types electrolytes solutions with pH=2 and pH=6. The solution with pH=2 was adjusted by acetic acid, and the solution with pH=6 was prepared by using monobasic and dibasic sodium phosphate. Theexposure part of steel panels without covering by coating films were protected with tape.An upwards cross-section scratch was made on the coating.

3.3 Results and discussions

According to the previous study from Dr. Mark D. Soucek research group34, the anticorrosion performance ofblown soybean oil coating was dramatically improved by adding TIIP into coating formulation. Also several studies19, have already proved that adding TEOS into epoxy resin can improve the anticorrosion performance. However, the effect of TIIP on epoxy coating is rarely studied. The objectives of this study are to study the influence of TIIP sol-gel precursor on the anticorrosion property and coating properties of BPA epoxy coating. Two types epoxy resin were used in formulation, one is the standard liquid BPA epoxy resin and the other one is the coupling agent grated liquid epoxy resin. The successful preparation of IPTES-Grafted epoxy was characterized by

FTIR, NMR and mass spectrometry. Eight kinds of coating films were prepared which were used to study the effect of TIIP and coupling agent(IPTES) on the performance of epoxy and hybrid epoxy coating. By using DSC and DMTA, Tg, crosslink density and storage modulus of those films were obtained. And the general coating properties were test according to ASTM standards. The last but the most important, anticorrosion performance was evaluated by EIS, salt spray and acid undercutting test.

3.3.1 Characterization of IPTES grafted epoxy

Figure 3.3 shows the FTIR spectroscopy for IPTES, EPON828 and IPTES grafted epoxy. For IPTES, the strong absorption band at 2270 cm-1 have been seen as the characteristic band forisocyanate group(-NCO).35,36,37 Figure 3.4 shows the FTIR spectroscopy for the solution of bank reaction. The blank reaction keeps the same conditions(temperature, solvent, catalyst, nitrogen atmosphere and reaction time) without epoxy resin. As we see, at both the beginning of blank reaction(t=0h) and the end of reaction(t=4h), the FTIR spectroscopy show the strong absorption band at 2270 cm-1. So, the conclusion can be obtained that IPTES cannot react with the solvent toluene, catalyst

DBTDL and itself at 60oc under nitrogen atmosphere and the preparation system is free of moisture, water and other chemical agents which is sensitive to isocyanate group.

For the FTIR spectroscopy of IPTES grated epoxy, there are no absorption band at 2270 cm-1 which indicates that IPTES have reacted with epoxy resin. And also compared with the FTIR spectroscopy of EPON828, IPTES grafted epoxy shows clear absorption band at 1725 cm-1 which has been seen as the characteristic band for –NH-

C=O-C- group.38And no absorption band shows at 1600-1700 cm-1 which has been seen as the characteristic band for –NH-C=O-NH- group38 which indicates that the epoxy resin is free of moisture and water after drying step. In collusion, by FTIR spectroscopy, the reaction between the –NCO group in IPTES and the –OH group in epoxy resin can be confirmed.

Figure 3.3 FTIR spectroscopy for IPTES, EPON828 and IPTES grafted epoxy

Figure 3.4 FTIR spectroscopy forthe solution of blank reaction

Based on FTIR spectroscopy, the reaction between the –NCO group in IPTES and the –OH group in epoxy resin can be confirmed. However the alkoxysilane group in

IPTES can hydrolysis and condensation when water or moisture existence. Figure 3.5 shows the liquid-state 29Si NMR spectroscopy for IPTES and figure 3.6 shows the liquid- state 29Si NMR spectroscopy for IPTES grafted epoxy. As we can, both IPTES and

IPTES grafted epoxy show the single resonance at 47.27 ppm and 45.74 pp, in T0 region which indicates that there are no hydrolysis or condensation reaction for alkoxysliane group in IPTES.

Figure 3.5 Liquid-state29Si NMR spectroscopy for IPTES

Figure 3.6 Liquid-state29Si NMR spectroscopy for IPTES grafted epoxy

Figure 3.7 and Figure 3.8 show the mass spectroscopy for EPON-828 and IPTES grafted EPON-828 respectively. As we can see, the main product is A1B0. Based on the analysis results of FTIR spectroscopy. liquid-state29Si NMR spectroscopy and mass spectroscopy, the successful preparation of IPTES grafted epoxy resin can be confirmed.

2 ug/mL in MeOH/THF w/ 2 uL addition of 5 ug/mL NaTFA 160429_EPON 828_160410A 91 (1.564) Cm (2:115) TOF MS ES+ 363.107 1.40e4 100 + [n0 + Na ] Sample: Epon 828 Concentration: 2 µg/mL in MeOH/THF 1:1 (v/v) w/ 3 µL addition of 5 µg/mL NaTFA Solvent background substracted

340 %

284

364.117 + 398.190 [n1 + Na ] 647.218

423.165 559.451 705.507 507.218 587.476 648.219 706.494 457.222 588.484 685.352

0 m/z 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 1050 1100 1150 1200

Figure 3.7 Mass spectroscopy for EPON-828

2 ug/mL in MeOH/THF w/ 2 uL addition of 5 ug/mL NaTFA 160429_EPON 828 - IPTES_160411A 36 (0.629) Cm (2:116) TOF MS ES+ MeOH/THF w/ 2 uL addition of 5 ug/mL NaTFA 363.115 8.33e3 100 + 160429_BACKGROUND_160411 57 (0.986) Cm (2:115) [ A0 + Na ] TOF MS ES+ 398.190 1.26e4 100 Sample: Epon 828 - IPTES Concentration: 2 µg/mL in MeOH/THF 1:1 (v/v) w/ 3 µL addition of 5 µg/mL NaTFA Solvent background substracted

+ [ A1B0 + H ] 670.251 875.314

+ [ A1B0 + Na ]

304.221 % 894.307 %

352.201 895.308 364.117 671.270

399.196

316.114 491.202 646.170 896.310 360.274 559.442 302.203 672.243 194.088 457.222 215.057 457.214 559.460 705.497 684.226 897.335 165.087 685.342 408.264 507.218 102.101 278.209 587.467 629.423 706.514 80.994 250.138 361.287 497.351 0541.391 m/z 200 300 400 500 600 907.234700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 0 m/z 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950

Figure 3.8 Mass spectroscopy for IPTES grafted EPON-828

3.3.2 Viscoelastic property

Vicoelastic properties of the coating films are investigated by DMTA with a heating rate 3°C/min with a range from -30oc to150oc.Figure 3.10 shows the storage modulus as a function with temperature and Figure 3.11 shows the loss factor Tanδ values for all coating films as a function with temperature. As we can see, for both pure epoxy resin and IPTES grafted epoxy resin, the storage modulus is increased in both glassy region and rubber region by adding TIIP precursor into coating formulations. And

IPEP0 shows lower storage modulus than EP0 in glassy region, but shows higher storage modulus than EP0 in rubber region. And the Tanδvalues decrease with increasing the amount TIPP precursor which can be attributed to the damping behavior of the inorganic phase. The temperature in the maximum value of Tanδhas been seen as the Tg of polymer related to αrelaxation, there are a clear increasing tendency for Tg with adding

TIIP precursor. The Tg measured by DSC shows the similar tendency with the Tg measured by DMTA, as shown as figure 3.12.The increase in Tg could be attributed to that the inorganic domain inhibit the movement of polymer chain. The crosslink density could be calculated according to equation (11).

νe=E’/3RT(11)

Where E’ is elastic modulus at rubber plateau, νeis the crosslink density, R is the gas constant and T is the temperature in Kelvin.

As shown as in table 3.3, the IPTES grafted epoxy coating with 10%wt TIIP shows highest crosslink, and all of the hybrid coatings show higher crosslink density and

Tg, storage modulus than the pure epoxy coating.

Figure 3.9 Storage Modulus for all coating films as a function with temperature

Figure 3.10 Tanδvalues for all coating films as a function with temperature

Figure 3.11 DSC curves for all coating films

Table 3.3 Crosslink density, storage modulus, Tg and Tanδ

SAMPL Crosslink E’ E25 Tg Tg Max Tanδ

E Density (mini (storage (DMTA) (DSC) Tanδ Breath

3 O O mol/m storage modulus / C / C /OC modulus) at 35oc)

/MPa /MPa

EP0 280.45 2.89 1462 71.51 53.08 0.780 20.5

EP5 562.85 5.8 1620 79.26 60.31 0.686 26.3

EP10 902.49 9.3 1757 82.61 64.45 0.553 31.5

IPEP0 458.04 4.72 987 75.09 59.32 0.728 22.1

IPEP5 882.12 8.76 1757 87.2 65.23 0.508 31.1

IPEP10 1775.87 18.3 1386 90.89 66.78 0.413 40.1

3.3.3 General coating properties

According to ASTM standards, general coating properties are tested in aluminum panel, including: pull-off adhesion, reverse impact resistance, pencil hardness, cross- hatch adhesion and MEK resistance. The results are summarized in Table 3.4.

As we can see, all the coating films show the excellent MEK resistance property of cross-hatch adhesion. Compared with the hybrid coatings with TIIP and pure epoxy coating, the pull-off adhesion and pencil hardness is improved and reverse impact resistance is decreased benefited from the adding of TIIP precursor.

Reverse impact resistance is an indicator for the flexibility of coating films. As we can see, the IPTES-grafted epoxy coating shows better impact resistance than pure epoxy coating. And epoxy coating films become more brittle by adding TIIP into formulation.

Table 3.4 General coating properties

Pull-off Reverse Pencil Cross-hatch MEK double

Adhesion impact hardness Adhesion rubs

(lb/in2) resistance

(kg/cm)

EP0 348 ± 8 70 ±2 4H 5B >200

EP5 427 ± 10 57 ± 2 5H 5B >200

EP10 370±15 44 ± 4 5H 5B >200

IPEP0 422 ±15 88 ± 2 5H 5B >200

IPEP5 463 ± 10 76 ± 4 5H 5B >200

IPEP10 460 ± 20 68 ± 2 5H 5B >200

3.3.4 Evaluating the anticorrosion performance by EIS

The anticorrosion performance of coating is evaluated in steel panel by EIS in 3.5%

NaCl solution. The exposure area is 3.8 cm2. Equivalent circuits are needed to fit the EIS measurements to evaluate the different anticorrosion behavior between hybrid coatings.

3.3.4.1 Results of EIS measurement.

The impedence modulus of the testing system can be obtained in different frequency ranging from 100KHZ to 10 mHZ. And the impedence at high frequency are

related to the resistance and capacitance of coating film, and the impedence at low frequency are related to the interlayer resistance and capacitance.40,41.42.43 Figure 3.12 to

3.17 show the Bode and phase angle plots measured at Day 1, Day 9, Day 35 and Day 70 for all the samples.

As we can see, at first, all of the coating films show an excellent protective ability with the impdedence modulus higher than 109 cm2.61The impedence modulus at low frequency for allhydrid coatings are higher than 109 cm2 until 70 days’ immersing. But the impedence modulus at low frequency for pure epoxy coating decreases obviously from 109 cm2 to 107 cm2 with the immersing time. Thisphenomenon indicates that the better protective ability of hybrid coatings than pure epoxy coating.

Also, the phase plot for EP0, EP10, IPEP0, IPEP10 show a clear decreasing trend from Day1 to Day 70. This decreasing trend of phase plot has been to the increasing of coating capacitance and decreasing of coating resistance caused by the permeating of electrolyte solution into coating film.42 However, the phase plot for EP5 and IPEP5 are more stable which indicates better barrier property.

Further, the impedance modulusas a function of immersion time at a specific frequency of 1HZ for all the coating films are shown in Figure 3.18. The coatings without

TIIP precursor shows a decreasing trend with the increasing immersion time, and the coatings with TIIP precursor are stable in 70 days immersion.

Figure 3.12Bode plot (top) and phase angle plot(bottom) of EP0 for steel substrate

Figure 3.13 Bode plot (top) and phase angle plot( bottom) of EP5 for steel substrate

Figure 3.14 Bode plot (top) and phase angle plot( bottom) of EP10 for steel substrate

Figure 3.15 Bode plot (top) and phase angle plot( bottom) of IPEP0 for steel substrate

Figure 3.16 Bode plot (top) and phase angle plot( bottom) of IPEP5 for steel substrate

Figure 3.17 Bode plot (top) and phase angle plot( bottom) of IPEP10 for steel substrate

Figure 3.18 Impedence modulus at 1HZ as a function of immersion time

3.3.5 Evaluating the anticorrosion performance by salt spray

The photographs of the steel panels after 240h exposureare shown in figure 3.21- figure 3.26. An inspection method by comparing the pitting and blistering after salt exposure have been widely to evaluate the coating anticorrosion performance.43 As we can see, there much more pitting and blistering in the panel coated by the coating without

TIIP precursor than the panel coated by the coating with TIIP precursor.

Figure 3.19 Photograph of steel panel after 240h salt spray test

600

2 500

400

300

200

Pitting and blistering area mm area blistering and Pitting 100

0 EP0 EP5 EP10 IPEP0 IPEP5 IPEP10 Sample name

Figure 3.20 Pitting and blistering area after 240h salt spray test

3.3.5 Acid undercutting test

The coating film will delamination from the scribe lines in acid condition due to the failure of bonding and the formation of corrosion products under the coating film.

Figure 3.24 and figure 3.25 shows the undercutting results. As we can, after 24h immersion in the solution with pH=2, all the coating films are delaminated from the scribe line. However, at pH=6 condition, the coating films with TIIP shows much less delamination area than the pure coating films after 72 h immersion.

Figure 3.21Degree of undercutting at pH=2 after 24h immersion

Figure 3.22 Delamination area of coating films as a function with time in pH=6

Figure 3.23 Degree of undercutting at pH=6 after 72h immersion

CHAPTER IV

CONCLUSION

Thisproject is based on organic/inorganic epoxy hybrid coatings for anticorrosion applications. IPTES grated epoxy resin is successfully prepared which is characterized by

FTIR, 29Si NMR and MS. Two kinds of epoxy primer were used in formulation, the pure epoxy resin and coupling agent(IPTES) grafted epoxy resin. Six kinds of coating films were prepared by adding 0wt%, 5wt% and 10wt% to the pure epoxy resin and IPTES grafted resin. And ethanol was selected as the solvent.The viscoelastic properties of coating films were tested by DMTA and DSC. General coating properties including pencil hardness, cross-hatch adhesion, pull-off adhesion, reverse impact resistance andMEKresistance were tested in aluminum panel according ASTM standards. Most importantly, the anticorrosion performance was evaluated by EIS and 240h salt spray test in steel panel.

By analyzing the results, a few conclusions related to the effects of TIIP and

IPTES on epoxy coating can be summarized. According to data obtained from DMTA and DSC, both TIIP and IPTES have the effect on improving the Tg and crosslink density of epoxy coating. According to the data obtained from general coating test, the IPTES grated epoxy coatings are more flexible than original epoxy coating. According to the results of EIS and salt test, the anticorrosion performance is dramatically improved by adding TIIP into epoxy coating formulation.

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