Renewable Polyurethane Microcapsules with Isosorbide Derivatives

Oct 28, 2013 - Renewable polyurethane microcapsules containing isosorbide derivatives for self-repairing anticorrosion coatings were easily manufactur...
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Renewable Polyurethane Microcapsules with Isosorbide Derivatives for Self-Healing Anticorrosion Coatings Eunjoo Koh,† Sangjun Lee,†,‡ Jihoon Shin,† and Young-Wun Kim*,†,‡ †

Research Center for Biobased Chemistry, Korea Research Institute of Chemical Technology, 141 Gajeong-ro, Yuseong−gu, Daejeon 305-600, Republic of Korea ‡ Department of Green Chemistry and Environmental Biotechnology, University of Science & Technology, 113, Gwahak-ro, Yuseong−gu, Daejeon 305-350, Republic of Korea S Supporting Information *

ABSTRACT: Renewable polyurethane microcapsules containing isosorbide derivatives for self-repairing anticorrosion coatings were easily manufactured by interfacial polymerization of a dimer ester−diisocyanate (DE−TDI) prepolymer derived from waste vegetable oil and 1,4-butanediol (BD) as a chain extender using ultrasonication. Two kinds of corrosion inhibitors were also synthesized by the ring-opening reaction of succinic anhydride (SA) or maleic anhydride (MA). Microcapsules having 11−38 μm in diameter were obtained, and the typical core content of microcapsules was around 40−45 wt %. Salt spray tests used for evaluating self-healing anticorrosion coating systems showed significant rust retardancy, depending on the content of the isosorbide derivatives for corrosion control.

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have been reported;22 however, there have been few studies about PU capsules with corrosion inhibitors. Herein, we report the following: (a) synthesis of dimer alcohol based on dimer acid, derived from a waste vegetable oil,23−28 as an alternative resource of renewable polyol, which was reacted with diisocyanate to form PU microcapsule shell; (b) preparation of corrosion inhibitors from isosorbide oleic ester derivatives for core materials; (c) interfacial polymerization using ultrasonication to form corrosion-inhibiting microcapsules; and (d) corrosion inhibitor testing from accelerated corrosion spray tests of the PU capsules that showed an excellent anticorrosion performance with a rusting degree in the range of 0−0.47% on low inhibitor loading.

INTRODUCTION Corrosion of metal substrates is generally caused by physical or chemical attacks, such as salinity, oxidation, and repetitive freeze−thaw cycles, that finally result in its life span decreasing.1,2 Several corrosion protection methods such as coating and films have been developed using active,3 passive,4 permanent,5 and temporary corrosion protections6 for a wide range of industrial applications. The delivery method of corrosion inhibitors creates some problems in maintaining their initial efficiency around damaged surfaces.7−9 The use of functional microcapsules containing healing agents to act as a corrosion inhibitor can offer a positive solution for the short durability or deterioration of anticorrosion properties.10−12 Microencapsulation is one of the methods used for storing and protecting core materials from the external environment; these microcapsules can be dispersed into various paint systems to release corrosion inhibiting or self-healing constituent when mechanically ruptured. This occurs when the coating is damaged by physical scratching.13−15 Microcapsules are manufactured by physical flow, separation, and interfacial polymerization of shell materials around core particles16,17 using agitation, such as mechanical stirring, homogenization, and ultrasonication. The sonication method for preparing microcapsules has the desirable advantages of a large interfacial area between oil-in-water phases and the generation of more homogeneous dispersion that provides high encapsulation efficiency.18,19 Although melamine formaldehyde and poly(vinyl chloride) (PVC) can be used as the shell wall material of microcapsules,20 polyurethane (PU) has been used with favorable results17,21 since PU is economical in industrial applications and has robust physical properties, high thermal stability, and clear transparency. Recently, PU microcapsules containing healants and coating repairing compounds to prevent corrosion on scratches of coated metal substrates © 2013 American Chemical Society

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RESULTS AND DISCUSSION Synthesis of Isosorbide Derivatives for Anticorrosion Materials. Oleic acid−isosorbide (OA−IS) was prepared via esterification of isosorbide and oleic acid (Scheme 1). 1H NMR spectroscopy analysis revealed the appearance of the methylene protons at 2.32 ppm adjacent to the ester linkage between oleic acid and isosorbide, with 53% isolated yield (Supporting Information Figure S1). Subsequent reactions of OA−IS with succinic anhydride (SA) or maleic anhydride (MA) were also confirmed by 1H NMR spectra (Supporting Information Figures S2 and S3). Upon completion of the reaction, new signals for the methylene protons of monosuccinic ester and two protons at the double bond of monomaleic ester in the isosorbide derivatives appeared at 2.71 and 6.48 ppm, with reaction yields of 62 and 54%, respectively. Received: Revised: Accepted: Published: 15541

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for a secondary amine group of urethane, an isocyanate (N CO) group, and an amide carbonyl group, respectively (Figure 1b). The reaction completion for the DE−TDI prepolymer was determined through reducing the intensity of the vibration band at 2277 cm−1, corresponding to an NCO stretch. There were IR peaks of the PU microcapsules at v = 3480 and 1699 cm−1 for secondary amine and amide carbonyl of the capsule urethane, and no single peak at 2277 cm−1 for the isocyanate group was observed, indicating that a urethane linkage with BD was formed in the microcapsule shell wall (Figure 1c). The decrease of intensity at 2277 cm−1 of the NCO vibration band was only observed at a higher temperature, over 40 °C, for 6 h. The FT-IR spectroscopy proved polymerization for encapsulation using a DE−TDI prepolymer derived from DA. Encapsulated isosorbide derivatives (ID) as anticorrosion chemicals in PU capsules were characterized using FT-IR (Figure 1). Small amounts of capsules frozen in liquid nitrogen were crushed and washed with n-hexane to collect the core materials. As the core materials were composed of oil for emulsion polymerization and a corrosion inhibitor (OA−IS−MA or OA−IS−SA), the FT-IR spectra of the collected materials showed stretching and bending vibrations at 2930 and 1450 cm−1 for a long alkyl chain’s methylene groups of the oil and at 1735 cm−1 for carbonyl groups of ID (Figure 1d extended), indicating that ID had been encapsulated and released even with small amounts. Microcapsule Size Distribution. There are several factors that determine the size of microcapsules, such as the geometry of the mixing device, blade hydrodynamics, viscosity, interfacial tension of the media, shear/agitation rate,13,17,20 temperature, and surfactant effects. The microcapsule size distributions were measured with different content (25−200 ppm) of two corrosion inhibitors (OA−IS−MA and OA−IS−SA) in PU capsules while all the other factors were kept constant (Table 1). The ultrasound amplitude vibration was fixed at 70%. Because there was no chemical reaction between the hydroxyl group and isocyanate below 40 °C, the temperature of the suspended solution was kept at 50 °C. The PU microcapsules

Scheme 1. Synthesis of Isosorbide Derivatives (OA−IS−MA and OA−IS−SA) for Corrosion Inhibitors and Core Materials in Polyurethane Microcapsules

Synthesis of Renewable PU Microcapsules. As shown in Scheme 2 and Supporting Information Figure S4, dimer alcohol (DA−OH) as a polyol was prepared by condensation of dimer acid (DA) and 1,4-butanediol (BD). Thereafter, dimer ester−diisocyanate (DE−TDI), as a prepolymer for PU microcapsules, was synthesized with DA−OH and toluene1,4-diisocyanate (TDI) (Scheme 2). Microcapsules containing isosorbide derivatives for anticorrosion were prepared by interfacial polymerization in an oil-in-water emulsion. DE− TDI prepolymer with about 20 wt % of NCO content was dissolved in chlorobenzene. Water-soluble 1,4-butanediol (BD) served as a chain extender for the polyurethane (PU) capsule shell because the relative reaction rate of the diol/NCO is ten times as fast as that of water/NCO.17 Eight PU microcapsule formulations were prepared with 25, 50, 100, and 200 ppm of two core corrosion inhibitors in oil used for the emulsion (Table 1). The chemical structures of the resultant microcapsules and the prepolymer were characterized by Fourier transform infrared spectroscopy (FT-IR) (Figure 1). IR bands of the prepolymers appeared at v = 3315, 2277, and 1705 cm−1

Scheme 2. Synthesis of PU Microcapsules Using BD as a Chain Extender and DE−TDI as Prepolymer from DA−OH on the Basis of DA

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Table 1. Characterization Data for the PU Microcapsules Synthesized with Different Concentrations of a Core Corrosion Inhibitora PU capsule control sampleb SMC 1c SMC 2c SMC 3c SMC 4c SMC 5d SMC 6d SMC 7d SMC 8d

weight loss of PU capsules (%)e

diameter in the PU capsules (μm)

theoretical weight loss of PU capsules (%)f

rusting degree (%) (1/21/40 weeks)

0

47

15 ± 8

48

2.55/3.23/5.13

200 100 50 25 200 100 50 25

40 43 44 44 41 45 42 45

20 ± 15 12 ± 8 29 ± 16 38 ± 11 18 ± 11 11 ± 4 14 ± 8 14 ± 7

43 49 44 45 43 46 45 45

0/0/0.05 0/0/0.03 0.01/0.01/0.01 0.02/0.04/0.14 0/0/0.03 0.02/0.02/0.05 0/0.02/0.10 0.17/0.32/0.47

conc. of core materials (ppm)

a See the Experimental Section for details. bThe controlled PU capsule has only oil without anticorrosion material. cThese PU microcapsules have OA−IS−MA in oil as a core material. dThese PU microcapsules have OA−IS−SA in oil as a core material. eMeasured on the weight of ruptured PU capsules after heating at 180 °C for 48 h. fCalculated using the equations supported by ref 29.

approximately 40−45 wt % of weight loss after heating, which meant that the ID core materials, including oil and corrosion inhibitors, were mostly decomposed (Table 1).30 These experimental values for the weight loss are in close agreement with the theoretical values of the core content in the PU capsules calculated by the PU capsule’s diameter, PU shell thickness, the density of the oil, and the PU capsule wall (Table 1).29 Surface Morphology. The surface and shell morphology of the microcapsules, prepared using different ultrasonic amplitude vibrations (60, 70, and 80%), was investigated using scanning electron microscopy (SEM) (Figure 3). Figures 3a and b showed that the mean diameters of PU microcapsules and standard deviations were 70 ± 23 and 16 ± 6.5 μm by 60 and 70% amplitude rates, the size of the capsules prepared by 80% of amplitude (6.6 ± 2.3 μm) was relatively smaller and uniform (Figure 3c). When 60, 70, and 80% of amplitude rates were applied for PU microcapsule synthesis, 49, 43, and 38% of core contents in the capsules, respecvitely, were measured. With increasing amplitude vibration strength in the ultrasonic process, the size of the prepared microcapsules gradually decreased, and the content of the core materials also decreased. Fluid shear force by amplitude vibration controlled the size and the core content of the capsules. It was observed that larger capsules prepared with a relatively low amplitude rate had thicker shell walls. However, the ratio of shell wall thickness to capsule diameter was kept constant at about 0.05. Micromoire patterns were found on the outer surface of the capsules prepared using 80% of amplitude vibration (Figure 3c).

Figure 1. FT-IR spectra of (a) toluene-1,4-diisocyanate (TDI), (b) DE−TDI prepolymer, (c) PU microcapsule wall, (d) released capsule core (OA−IS−MA), and (e) pure corrosion inhibitor (OA−IS−MA).

with a prepolymer from polyols, based on renewable dimer acid, and two biobased anticorrosion reagents, showed narrow capsule size distributions caused by the constant amplitude of the ultrasound (Figure 2). It was observed that the capsule size (12−38 μm) having OA−IS−MA was slightly larger than the microcapsule size (11−18 μm) containing OA−IS−SA. In general, PU microcapsules had 11−38 μm of average diameter, 4−15 μm of standard deviation, and 1−4 μm of PU capsule wall thickness. In addition, ruptured capsules with ID material and oil were heated at 180 °C for 48 h to investigate weight loss of PU capsules. It was observed that all the capsules had

Figure 2. The size distributions of PU microcapsules filled with OA−IS−MA (a) and OA−IS−SA (b) as a corrosion inhibitor according to the concentration of corrosion inhibitor (25−200 ppm). 15543

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Figure 3. Surface and shell morphology of microcapsules obtained at various ultrasonic amplitudes.

Figure 4. (a) TGA weight loss curves of synthesized PU microcapsules (SMC 1 and 8) along with authentic traces for OA−IS−MA, DE−TDI (prepolymer), and PU microcapsule shell wall. (b) Derivatives of TGA data of OA−IS−MA, DE−TDI (prepolymer), microcapsule shell wall, and the filled capsules (SMA 1 and 8). All the experiments were conducted at a heating rate of 20 °C/min in a N2 environment.

Scheme 3. Schematic of the Corrosion Protection Process: (a) Self-Healing Coating Containing a Microencapsulated Corrosion Inhibitor, (b) Damage to the Coating Layer Releases an Anticorrosion Agent, and (c) Crack Protected by Anticorrosion Protection Barriers.

Thermal Properties. The thermal properties of the anticorrosion core material (OA−IS−MA), DE−TDI prepolymer, microcapsule shell wall, and the filled microcapsules (SMC 1 and SMC 8) were characterized by thermogravimetric analysis (TGA). The weight loss of TGA curves and derivatives for each material are given in Figure 4. The decomposition of OA−IS−MA as a core material began at 160 °C and was completed at 320 °C. The prepolymer gradually started to decompose at 100 °C and was completely fragmented at 470 °C. The TGA curve of the DE−TDI prepolymer consisted of two weight loss stages corresponding to the polyol soft segments at 250−350 °C and the isocyanate hard parts at 350− 470 °C, respectively. There was about 5% weight loss for the synthesized microcapsules at 100 °C due to the water

remaining in the capsules after interfacial polymerization. Two distinct weight loss stages for the prepared microcapsules were revealed above 100 °C in the TGA curves. The first weight loss was attributed to the decomposition of polyol soft segments for the capsules at 270−360 °C, which was significantly overlapped with the degradation temperature of OA−IS−MA as core materials, and the second weight loss was at 370−500 °C from the breakup of isocyanate hard domains for the microcapsules composed of the DE−TDI prepolymer. Compared with the above breakup temperature of isocyanate hard segments for the prepolymer, the decomposition temperature might be a little elevated, owing to closely connected with hard segments via PU microcapsule synthesis. The storage capacity for the core inhibitor in the filled PU capsules was 15544

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Figure 5. Morphological evaluation of self-healing anticorrosion coatings after 40 weeks. SEM images of (a) the scratched region of the control panel and (b) the self-healing anticorrosion coating after healing (SMC 2).

measured by the weight loss of the core materials, which approached 40−45 wt %. Anticorrosion Study. The corrosion protection property can be illustrated using the concept of self-healing microcapsules in a coating system, visualizing an inner cross section where microcapsules were evenly scattered in the primer layer (Scheme 3). When the paint layer (top-surface and 15−35 μm of thickness) and the primer layer (bottom and 30−40 μm of thickness) (Scheme 3a) were cracked by physical force, the corrosion inhibiting microcapsules also burst and the core material was subsequently released around the ruptured microcapsules (Scheme 3b). Protection barriers for the steel panel were finally built in the damaged area (Scheme 3c). Scanning electron microscopy (SEM) images of the scratched region in the control panel and SMC 2 revealed the morphology of the self-healing anticorrosion coating (Figure 5a and b). Even though the flow of the corrosion inhibitor and oil was not observed on the metal substrate, corrosion protection of the substrate was readily apparent even after 40 weeks. There was hardly any corroded trace in the inhibitorcoated cross-sectioned sample (SMC 2), whereas a large quantity of rust was found in the damaged area of the control panel. Microcapsules filled with an isosorbide inhibitor were integrated into a hydrophilic primer layer and water-born paint was subsequently outer-coated to create a self-repairing coating. A preliminary test was carried out to evaluate self-healing and anticorrosion performance using OA−IS−MA or OA−IS−SA as a corrosion inhibiting agent. The self-corrosion protection efficiencies had been observed for forty weeks. The results from the accelerated corrosion spray test using salt solution clearly proved that, compared with the blank specimen that had severe corrosion, the steel plate coated with 200, 100, and 50 ppm of OA−IS−MA or OA−IS−SA in the microcapsules displayed significant corrosion protection (Figure 6 and Supporting Information Figure S5). Corrosion resistance was reduced by decreasing the content of the corrosion inhibitor. The steel panel with 25 ppm of OA−IS−MA showed incipient corrosion after one week and had no more serious rust even after forty weeks (Supporting Information Figure S5e and j). However, the corrosion protection efficiency was slightly less on the steel plate with 25 ppm of OA−IS−SA, where rusting areas expanded within forty weeks (Supporting Information Figure S5o and t). A rusting degree analysis revealed that the rusting area of the control specimen grew from 2.55 to 5.13% of the panel area, whereas the worst value of rust degree obtained

Figure 6. Corrosion test results for a PU coating loaded with and without microcapsules filled with anticorrosion agents (OA−IS−MA and OA−IS−SA) after 1 week and 40 weeks.

from SMC 8 with OA−IS−MA increased from 0.17 to 0.47% after forty weeks (Figure 7 and Table 1). The other samples showed negligible rusting degree values, except for SMC 6, which deteriorated to 0.05% (Supporting Information Figure S5m and r). In addition, OA−IS−MA had better anticorrosion efficiency than OA−IS−SA (Figure 7 and Table 1). It could be explained by our previous work that the π orbital of the double bond at OA−IS−MA, which is the only difference between OA−IS−MA and OA−IS−SA, can more effectively interact with the metal surface than OA−IS−SA, so that OA−IS−MA showed better anticorrosion efficiency than OA−IS−SA (Figure 7 and Table 1).31 It is also believed that the carboxylic acid groups in the synthesized isosorbide oleic ester acid can afford effective corrosion protection. This implies that the corrosion inhibition property is generated by attachment of the carboxylic acid on the metal surface; it is also believed that the degree of rusting on the substrate is related with the 15545

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Coatings Co. Ltd., and the primer (XKB014) and diluent (KSM-6060) were obtained from Chokwang Paint Co. Ltd. Measurements. An 1H NMR spectrometer (Bruker DPX300) was employed at room temperature to confirm successful reaction and determine the molar mass of the products. Qualitative analyses by FT-IR (Bio-RAD FTS165), LC−MS (Agilent Technologies 7890A GC system), and HPLC (Agilent Technologies 1260 infinity series) for the products were carried out. The molar mass (Mn and Mw) was determined by SEC in tetrahydrofuran (1.0 mL/min) at 40 °C versus polystyrene standards using a Waters high-pressure liquid chromatography system equipped with a UV Waters 2690 using three columns (PL, Mixed-B × 2 and 500 Å × 1 pore size) and a Waters 2414 differential refractometer. The hydroxyl value (OH) was determined by the ASTM D1957 method (Metrohm, 888 Titrando). The NCO content in the DE−TDI prepolymer was calculated via titration. The synthesized prepolymer (1 g) was completely dissolved with toluene (50 mL). Di-n-butyl amine solution (15 mL, 0.1 N) was added using a pipet. After swirling for 15 min, isopropyl alcohol (50 mL) and bromophenol blue indicator solution (4−6 drops) were added. Two titrations were performed with hydrochloric acid (0.1 N) to a yellow end point. The NCO content was calculated as follows: NCO, % = [(B − V)N × 0.0420]/(W × 100), where B and V (both in mL) are the volumes of HCl for titration of the blank and the prepolymer, respectively, N is the normality of HCl, and W is the grams of prepolymer.17,33,34 The microcapsule size and distribution were measured using a Mastersizer particle size analyzer (Microtrac S3000) in the range of 0.2−1500 μm. The mean diameter was determined from data sets of at least 10 measurements before recording their size. The surface morphology and capsule shell thickness were observed by a scanning electron microscopy (SEM) system (XL-30S FEG, Philips). The microcapsules were mounted on a conductive stage and ruptured with a razor blade to facilitate membrane thickness measurement. Samples were sputtered with a thin layer (∼10 nm) of gold−palladium to reduce charging. Thermogravimetric analysis (TA Instruments Inc. TA3 11/ SD T2960) was used to study the thermal stability and core content of the prepared capsules. Small amounts of microcapsule (10−20 mg) were heated from 25 to 800 °C at a rate 20 °C/min in a nitrogen atmosphere. Evaluation of Self-Healing Anticorrosion Properties. Scheme 3 shows a schematic of a cross section image where the primer (bottom layer) and paint layer (surface) are applied to a carbon steel plate as an anticorrosion coating. Microcapsules were added into the primer layer at 15 wt %. Water-based paint and hydrophilic primer were diluted with water in a ratio of 6 to 4 and 4 to 1, respectively. The coatings were applied using control bar coaters (Sheen Instruments). The thickness of the primer layer was about 35 ± 5 μm, and that of the paint layer was around 25 ± 10 μm. After curing, cross scratches were applied manually on the coating by a razor blade and were left for 24 h in a thermo-hygrostat for release of the core material. Tests were performed according to the ASTM C 1624−0535 for the scratch test and ASTM B 117−7336 for the salt spray test. Observation by an optical microscope (Olympus, BX51) equipped with a device camera (IMT i-Solution TM Inc.) revealed the anticorrosion efficiency for surface rusting and evaluated the percentage of rusting on the painted steel surface on the basis of ASTM D 610−08.37 This test was useful for quantifying the amount and distribution of visible surface rust (Figure 6).

Figure 7. Rusting degree analysis between the control sample (CS) and the corrosion inhibitor microcapsules.

concentration of the corrosion inhibitors. In this work, the corrosion protection property is stabilized at 100−200 ppm of anticorrosion contents rather than 25 ppm.32 Therefore, we concluded that the renewable polyurethane microcapsule containing the isosorbide corrosion inhibitor afforded outstanding anticorrosion properties even at 25 ppm of core material content on steel plates evaluated with the accelerated corrosion test.

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CONCLUSIONS Isosorbide-derivative-filled polyurethane (PU) microcapsules for self-healing anticorrosion coatings were synthesized by an interfacial polymerization of DE−TDI prepolymer and 1,4butanediol. A dimer ester−diisocyanate (DE−TDI) prepolymer was also prepared with ester polyols based on dimer acid from waste vegetable oil and toluene diisocyanate. Encapsulation of the corrosion inhibitor within a polyurethane shell wall was confirmed by FT-IR. Spherical microcapsules with diameters in the range of 11−38 μm and shell wall thicknesses in the range of 1−4 μm were prepared under ultrasound sonication. The isosorbide derivatives content of the resultant capsules was approximately 40−45 wt %. The polyurethane microcapsules also exhibited good storage and chemical stability below 200 °C. The efficiency of the PU microcapsules containing the selfhealing corrosion inhibitor was investigated in a painting system. The results under an accelerated corrosion testing indicated that the microcapsules provided noteworthy corrosion resistance with rusting degree in the range of 0− 0.47% with inhibitors loading from 25 ppm to 200 ppm. These findings showed that isosorbide derivatives will afford new selfrepairing chemistries for anticorrosion-filled capsules.

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EXPERIMENTAL SECTION Materials. Isosorbide, oleic acid, succinic anhydride, maleic anhydride, and p-toluenesulfonic acid monohydrate for corrosion inhibitors synthesis and dimer acid, 1,4-butanediol, toluene-2,4-diisocyanate, cyclohexanone, chlorobenzene, and gum arabic surfactant for the synthesis of prepolymer and microcapsules were of commercial grade and used without further purification unless otherwise specified. Oil (P-31) for interfacial polymerization was purchased from S-OIL Corporation. The car paint (model No. DHDC-2740) and diluent (DHDC-2740) were purchased from NOROO Paint & 15546

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Synthesis of Prepolymer (DE−TDI). Dimer ester−toluene diisocyanate prepolymer (DE−TDI) prepolymer was prepared as a constituent for the PU microcapsule shell wall as shown in Scheme 2. The mixture of toluene-2,4-diisocyanate (2.53 g) and cyclohexanone (25 mL) was agitated using a magnetic stirrer at 80 °C. DA−OH (7.04 g) was slowly added to the above TDI solution and allowed to react for 24 h. The resulting mixture was then distilled at 100 °C under 15 Torr for 5 h to remove cyclohexanone, water, and excess TDI, leaving a yellowish and viscous prepolymer in the flask. In addition, the molar mass was determined by SEC as a Mn value of 2,206 and a Mw value of 5,294 (D = 2.4). Synthesis of Microcapsules Containing Corrosion Inhibitor. After DE−TDI (6 g) was completely dissolved into chlorobenzene (3 g) at 30 °C, the solution was slowly poured into the gum arabic solution (59.9 g of a deionized water containing 10 wt % gum arabic as surfactant). Oil (6 g) containing a corrosion inhibitor for the core material was added to the solution. After preagitation (Matsushita Electric Industrial Co. Ltd.) for 5 min at 4000 rpm, the emulsion solution was encapsulated using a probe sonicator (Bransonic 2510 Sonicator, Branson Ultrasonics Corporation) at 500 W (20 kHz) for 25 min at 50 °C. BD (6 g) as a chain extender was slowly added to the emulsion to initiate the interfacial polymerization at the oil-in-water interface. The reaction was stopped after 2 h, and the resulting microcapsules were washed with deionized water several times and filtered in a vacuum. The isolated microcapsules were air-dried for 24 h. The yield of microcapsules was about 70 wt %.

Synthesis of Isosorbide Monooleic Ester (OA−IS). Isosorbide (14.0 g, 96 mmol) and oleic acid (20 g, 63.7 mmol, 90%) were dissolved in 200 mL of methylene chloride with pTSA (0.121 g, 0.637 mmol), then heated at 120 °C for 24 h using a Dean−Stark trap connected with a reflux condenser. The reaction mixture was cooled to room temperature, neutralized with saturated sodium bicarbonate solution, and washed with deionized water three times. The organic layer was dried over anhydrous magnesium sulfate and evaporated to dryness to afford an amorphous solid. The product was purified by column chromatography on silica gel with ethyl acetate/ hexane (1:3, v/v) to obtain a white solid (OA−IS; 13.9 g; yield, 53.0%). 1H NMR (CDCl3): δ 5.35 (m, 2H), 5.23 (s, 1H), 4.63 (t, 1H), 4.48 (d, 1H), 4.32 (m, 1H), 4.02 (d, 2H), 3.89 (q, 1H), 3.58 (q, 1H), 2.32 (t, 2H), 2.02 (m, 4H), 1.59 (m, 2H), 1.30 (m, 20H), 0.88 (m, 3H). Synthesis of Isosorbide Monooleic Ester Succinic Acid (OA−IS−SA). OA−IS (3.0 g, 7.3 mmol) and succinic anhydride (0.80 g, 8.0 mmol) were dissolved in 4 mL of toluene and heated at 120 °C for 24 h. The reaction mixture was cooled to room temperature, filtered, and dried in vacuum. The residue was purified by column chromatography on silica gel with ethyl acetate/hexane (1:3, v/v) to give yellow oil (OA−IS−SA; 2.3 g; yield, 62.0%). 1H NMR (CDCl3): δ 5.35 (m, 2H), 5.20−5.15 (m, 2H), 4.84 (t, 1H), 4.46 (d, 1H), 4.11 (t, 1H), 3.97−3.92 (m, 2H), 3.84 (m, 1H), 2.71 (m, 4H), 2.31 (t, 2H), 2.02 (m, 4H), 1.61 (t, 2H), 1.26 (m, 20H), 0.88 (m, 3H). Synthesis of Isosorbide Monooleic Ester Maleic Acid (OA−IS−MA). OA−IS (2.0 g, 4.9 mmol) and maleic anhydride (0.53 g, 5.4 mmol) were dissolved in 4 mL of toluene and heated at 120 °C for 24 h. The reaction mixture was cooled to room temperature, filtered, and dried in vacuum. The residue was purified by column chromatography on silica gel with ethyl acetate/hexane (1:3, v/v) to give yellow oil (OA−IS−MA; 1.34 g; yield, 54.0%). 1H NMR (CDCl3): δ 6.48 (q, 2H), 5.36−5.27 (m, 3H), 5.22 (s, 1H), 4.91 (t, 1H), 4.51 (d, 1H), 3.97−3.95 (m, 4H), 2.32 (t, 2H), 2.02 (m, 4H), 1.61 (t, 2H), 1.30 (m, 20H), 0.88 (m, 3H). Synthesis of Dimer Alcohol (DA−OH). Toluene (200 mL) was added to a mixture of dimer acid (23.4 g, 41.7 mmol), 1,4-butanediol (37.6 g, 417 mmol), and p-toluenesulfonic acid (0.718g, 4.17 mmol) in a 250 mL 4-neck round-bottom flask connected with Dean−Stark apparatus to remove the water from the byproduct. The stirred mixture was heated progressively to reflux temperature for esterification and kept for 6 h. After the complete reaction, it was cooled to room temperature and evaporated to remove the solvent. The product was neutralized with saturated NaHCO3 solution and washed three times with chloroform/water (1:4, v/v). The collected organic phase was dried over anhydrous NaHSO3, filtered, and evaporated in a vacuum. The resulting viscous liquid was dried in a vacuum oven at 50 °C for 15 h (28.2 g recovered; 96% isolated yield of DAEs−OH; an Mn value of 704 g mol−1 determined by SEC). The hydroxyl value was 146.0 mg KOH g−1. 1H NMR (CDCl3): δ 4.11 (t, 4H), 3.68 (t, 4H), 2.53 (m, 1H), 2.29 (t, 4H), 1.96 (m, 3H), 1.75−1.59 (m, 15H), 1.26 (m, 33H), 0.88 (t, 6H). 13C {1H} NMR (CDCl3): δ 173.7, 137.4, 128.8, 128.0, 125.1, 63.9, 61.5, 34.1, 31.8, 29.6− 28.8, 25.0−24.8, 22.6, 21.2, 14.0. FT-IR ν (cm−1): 3461 (O H), 2925−2854 (CH stretch), 1737 (CO), 1175 (ester CO). LS−MS (m/z) calcd. for [M− + K+], MS (LC/MS): 742.5. Found: 741.

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ASSOCIATED CONTENT

* Supporting Information S

1 H NMR spectra for OA−IS, OA−IS−SA, OA−IS−MA, DA, and DA−OH, and results of corrosion protection test for a PU coating with and without microcapsule filled with anticorrosion agents (OA−IS−MA and OA−IS−SA) after 1 week and 40 weeks. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*Y.-W. Kim. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This study was supported by the R&D Center for Valuable Recycling (GlobalTop Environmental Technology Development Program) through a grant from the Ministry of Environment (GT-11-C-01-270-0).

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REFERENCES

(1) Kalendová, A.; Veselý, D.; Sapurina, I.; Stejskal, J. Anticorrosion efficiency of organic coatings depending on the pigment volume concentration of polyaniline phosphate. Prog. Org. Coat. 2008, 63, 228. (2) Morcillo, M.; Chico, B.; Mariaca, L.; Otero, E. Salinity in marine atmospheric corrosion: its dependence on the wind regime existing in the site. Corros. Sci. 2000, 42, 91. (3) Shchukin, D. G.; Zheludkevich, M.; Yasakau, K.; Lamaka, S.; Ferreira, M. G. S.; Möhwald, H. Layer-by-Layer Assembled Nanocontainers for Self-Healing Corrosion Protection. Adv. Mater. 2006, 18, 1672.

15547

dx.doi.org/10.1021/ie402505s | Ind. Eng. Chem. Res. 2013, 52, 15541−15548

Industrial & Engineering Chemistry Research

Article

(4) Tan, C. K.; Blackwood, D. J. Corrosion protection by multilayered conducting polymer coatings. Corros. Sci. 2003, 45, 545. (5) Zheludkevich, M. L.; Yasakau, K. A.; Bastos, A. C.; Karavai, O. V.; Ferreira, M. G. S. On the application of electrochemical impedance spectroscopy to study the self-healing properties of protective coatings. Electrochem. Commun. 2007, 9, 2622. (6) Motte, C.; Maury, N.; Olivier, M.-G.; Petitjean, J.-P.; Willem, J.-F. Cerium treatments for temporary protection of electroplated steel. Surf. Coat. Technol. 2005, 200, 2366. (7) Brown, E. N.; White, S. R.; Sottos, N. R. Microcapsule induced toughening in a self-healing polymer composite. J. Mater. Sci. 2004, 39, 1703. (8) Kessler, M. R.; Sottos, N. R.; White, S. R. Self-healing structural composite materials. Composites, Part A 2003, 34, 743. (9) Hager, M. D.; Greil, P.; Leyens, C.; Zwaag, S. van der; Schubert, U. S. Self-Healing Materials. Adv. Mater. 2010, 22, 5424. (10) Yuan, Y. C.; Rong, M. Z.; Zhang, M. Q.; Chen, J.; Yang, G. C.; Li, X. M. Self-Healig Polymeric Materials Using Epoxy/Mercaptan as the Healant. Macromolecules 2008, 41, 5197. (11) Porter, R.; Miale, J. B. Extended Control of Marine Fouling. Appl. Biochem. Biotechnol. 1984, 9, 439. (12) Kuang, F.; Shi, T.; Wang, J.; Jia, F. Microencapsulation technology for thiourea corrosion inhibitor. J. Solid State Electrochem. 2009, 13, 1729. (13) Yeom, C. K.; Oh, S. B.; Rhim, J. W.; Lee, J. M. Microencapsulation of Water-Soluble Herbicide by Interfacial Reaction. I. Characterization of Microencapsulation. J. Appl. Polym. Sci. 2000, 78, 1645. (14) Yamaguchi, M.; Ono, S.; Okamoto, K. Interdiffusion of dangling chains in weak gel and its application to self-repairing material. Mater. Sci. Eng., B 2009, 162, 189. (15) García, S. J.; Fischer, H. R.; Zwaag, S. van der. A critical appraisal of the potential of self healing polymeric coatings. Prog. Org. Coat. 2011, 72, 211. (16) Scher, H. B.; Rodson, M.; Lee, K.-S. Microencapsulation of Pesticides by Interfacial Polymerization Utilizing Isocyanate or Aminoplast Chemistry. Pestic. Sci. 1998, 54, 394. (17) Yang, J.; Keller, M. W.; Moore, J. S.; White, S. R.; Sottos, N. R. Microencapsulation of Isocyanates for Self-Healing Polymers. Macromolecules 2008, 41, 9650. (18) Yan, C.; Resau, J. H.; Hewetson, J.; West, M.; Rill, W. L.; Kende, M. Characterization and morphological analysis of protein-loaded poly(lactide-co-glycolide) microparticles prepared by water-in-oil-inwater emulsion technique. J. Controlled Release 1994, 32, 231. (19) Jafari, S. M.; He, Y.; Bhandari, B. Production of sub-micro emulsions by ultrasound and microfluidization techniques. J. Food Eng. 2007, 82, 478. (20) Bachtsi, A. R.; Kiparissides, C. Synthesis and release studies of oil-containing poly(vinyl alcohol) microcapsules prepared by coacervation. J. Controlled Release 1996, 38, 49. (21) Hong, K.; Park, S. Preparation of polyurea microcapsules with different composition ratios: Structures and thermal properties. Mater. Sci. Eng., A 1999, 272, 418. (22) Tatiya, P. D.; Hedaoo, R. K.; Mahulikar, P. P.; Gite, V. V. Novel Polyurea Microcapsules Using Dendritic Functional Monomer: Synthesis, Characterization, and Its Use in Self-healing and Anticorrosive Polyurethane Coatings. Ind. Eng. Chem. Res. 2013, 52, 1562. (23) Hojabri, L.; Kong, X.; Narine, S. S. Functional Thermoplastics from Linear Diols and Diisocyanates Produced Entirely from Renewable Lipid Sources. Biomacromolecules 2010, 11, 911. (24) Hu, Y. H.; Gao, Y.; Wang, D. N.; Hu, C. P.; Zu, S.; Vanoverloop, L.; Randall, D. Rigid Polyurethane Foam Prepared from a Rape Seed Oil Based Polyol. J. Appl. Polym. Sci. 2002, 84, 591. (25) Sharma, V.; Kundu, P. P. Condensation polymers from natural oils. Prog. Polym. Sci. 2008, 33, 1199. (26) Hill, K. Fats and oils as oleochemical raw materials. Pure Appl. Chem. 2000, 72, 1255.

(27) Hablot, E.; Matadi, R.; Ahzi, S.; Vaudemond, R.; Ruch, D.; Avérous, L. Yield behaviour of renewable biocomposites of dimer fatty acid-based polyamides with cellulose fibres. Compos. Sci. Technol. 2010, 70, 525. (28) Lu, Y.; Larock, R. C. Soybean-Oil-Based Waterborne Polyurethane Dispersions: Effects of Polyol Functionality and Hard Segment Content on Properties. Biomacromolecules 2008, 9, 3332. (29) Li, W.; Wang, J.; Wang, X.; Wu, S.; Zhang, X. Effects of ammonium chloride and heat treatment on residual formaldehyde contents of melamine-formaldehyde microcapsules. Colloid Polym. Sci. 2007, 285, 1691. (30) Liu, X.; Zhang, H.; Wang, J.; Wang, Z.; Wang, S. Preparation of epoxy microcapsule based self-healing coatings and their behavior. Surf. Coat. Technol. 2012, 206, 4976. (31) Yoo, S. H.; Kim, Y. W.; Chung, K. W.; Baik, S. Y.; Kim, J. S. Synthesis and corrosion inhibition behavior of imidazoline derivatives based on vegetable oil. Corros. Sci. 2012, 59, 42. (32) Baek, S−Y.; Kim, Y−W.; Chung, K.; Yoo, S−H.; Kim, N. K.; Kim, Y−J. Synthesis of Succinic Acid Alkyl Half-Ester Derivatives with Improved Lubricity Characteristics. Ind. Eng. Chem Res. 2012, 51, 3564. (33) Wu, Q.; Yoshino, T.; Sakabe, H.; Zhang, H.; Isobe, S. Chemical modification of zein by bifunctional polycaprolactone (PCL). Polymer 2003, 44, 3909. (34) Kweon, D.-K.; Cha, D.-S.; Park, H.-J.; Lim, S.-T. Starch-gPolycaprolactone Copolymerization Using Diisocyanate Intermediates and Thermal Characteristics of the Copolymers. J. Appl. Polym. Sci. 2000, 78, 986. (35) ASTM. ASTM C 1624−05. Standard test method for adhesion strength and mechanical failure modes of ceramic coatings by quantitative single point scratch testing. In Annual book of ASTM standard. American Society for Testing and Materials, International: West Conshohocken, PA, 2005. (36) ASTM. ASTM B 117−73. Standard method of salt spray (fog) testing. In Annual book of ASTM standard. American Society for Testing and Materials, International: West Conshohocken, PA, 1973. (37) ASTM. ASTM D 610−08. Standard test method for evaluating degree of rusting on painted steel surfaces. In Annual book of ASTM standard. American Society for Testing and Materials, International: West Conshohocken, PA, 2008.

15548

dx.doi.org/10.1021/ie402505s | Ind. Eng. Chem. Res. 2013, 52, 15541−15548