reading

Chapter 2: Deposition of Environmentally Compliant Cerium-Containing Coatings and Primers on Copper-Containing Aluminium Aircraft Alloys

Chapter 3: Ferrites as Non-Toxic Pigments for Eco-Friendly Corrosion Protection Coatings

3.2 Crystalline Structure, Physicochemical Properties, and Inhibition Mechanism of Ferrites

Chapter 5: Development of Novel Biobased Epoxy Films with Aliphatic and Aromatic Amine Hardeners for the Partial Replacement of Bisphenol A in Primer Coatings

5.4 Spectroscopy Characterization of Epoxidized Linseed Oil Cured with Amine Hardeners

Chapter 6: Silica-Based Sol–Gel Coatings: A Critical Perspective from a Practical Viewpoint

Chapter 9: Low-Temperature Aqueous Coatings for Solar Thermal Absorber Applications

9.3 Structural and Morphological Investigations of α-Cr₂O₃ Monodispersed Meso-spherical Particles

Chapter 10: Eco-Friendly Recycled Pharmaceutical Inhibitor/Waste Particle Containing Hybrid Coatings for Corrosion Protection

Chapter 11: Chemical Interaction of Modified Zinc–Phosphate Green Pigment on Waterborne Coatings in Steel

Chapter 12: Development of Soybean Oil-Based Polyols and Their Applications in Urethane and Melamine-Cured Thermoset Coatings

13.3 The Use of Materials from Renewable Resources in Powder Coating Applications

13.5 Powder Coatings from the Combined Chemical Recycle of Polymers and the Use of Renewable Resources

Chapter 14: The Synthesis and Applications of Non-isocyanate Based Polyurethanes as Environmentally Friendly “Green” Coatings

Studies and investigations on materials failure are critical aspects of science and engineering. The failure analysis of existing materials and the development of new materials demands in-depth understanding of the concepts and principles involved in the deterioration of materials The Material’s Degradation and Failure series encourages the publication of titles that are centered on understanding the failure in materials. Topics treating the kinetics and mechanism of degradation of materials is of particular interest. Similarly, characterization techniques that record macroscopic (e.g., tensile testing), microscopic (e.g., in-situ observation) and nanoscopic (e.g., nanoindentation) damages in materials will be of interest. Modeling studies that cover failure in materials will also be included in this series.

Series Editors: Atul Tiwari and Baldev Raj
Dr. Atul Tiwari, CChem
Director, R&D, Pantheon Chemicals
225 W. Deer Valley Road #4
Phoenix, AZ 85027 USA
Email: atulmrc@yahoo.com, atiwari@pantheonchemical.com

Dr. Baldev Raj, FTWAS, FNAE, FNA, FASc, FNASc
Director, National Institute of Advanced Studies
Indian Institute of Science Campus
Bangalore 560 012, India
Email: baldev.dr@gmail.com, baldev_dr@nias.iisc.ernet.in

Publishers at Scrivener
Martin Scrivener(martin@scrivenerpublishing.com)
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Co-published by John Wiley & Sons, Inc. Hoboken, New Jersey, and Scrivener Publishing LLC, Salem, Massachusetts.
Published simultaneously in Canada.

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Library of Congress Cataloging-in-Publication Data:
Names: Tiwari, Atul, editor. | Galanis, Anthony, editor. | Soucek, Mark D., editor.
Title: Biobased and environmental benign coatings / edited by Atul Tiwari, Anthony Galanis, and Mark D. Soucek.
Description: Salem, Massachusetts : Scrivener Publishing ; Hoboken, New Jersey : John Wiley & Sons, 2016. |
Includes bibliographical references and index.
Identifiers: LCCN 2015049858| ISBN 9781119184928 (cloth) |
ISBN 9781119185116 (Adobe PDF) |
ISBN 9781119185109 (epub)
Subjects: LCSH: Coatings. | Coatings--Environmental aspects.
Classification: LCC TA418.9.C57 B56 2016 | DDC 667/.9--dc23 LC record available at http://lccn.loc.gov/2015049858

An enormous volume of petrochemicals is being consumed in the preparation of coatings for a wide variety of applications. The ever-growing demand and competitive edge in industry has compelled scientists to develop new materials that are high performance and cost-effective. The global sale in the coating industry is estimated to be approximately $127 billion that includes areas such as industrial, architectural, decorative, protective, and energy related etc. An exceedingly large volume of petrochemicals used to manufacture coatings has led to severe environmental damage from volatile organic compounds that continuously outgas throughout the lifespan of the products.

Due to the vast amounts of chemical ingredients being used around human, plant, and other animal life forms, it becomes imperative that ingredients used in preparing such compounds are environmentally and human friendly. The biobased chemicals are increasingly being utilized in making new coatings; however, such formulations do not always meet the stringent properties demanded by industry compared with their synthetic counterparts. Inferior thermal and environmental stability along with the increased competitive cost often pose challenges on the reaction mechanistic routes adopted by scientists.

A major portion of such biobased ingredients is that these are derived from our live feedstocks and that poses additional burdens on the growers. Agricultural scientists are working tirelessly on devising new genetically engineered crops that can be used to create protective materials consumed by an exponentially expanding human population. For example, genetically modified soybean and linseed oils are the new ingredients for biobased coatings. Development of biobased coatings is in its infancy and toxicologists are concerned of possible negative implications on human health after prolong usage as the new genetically modified crops have not yet been tested for long term stability. It is a common misperception that cheapest is easiest to make although the reverse is true with coatings and paints. It is worth noting that more than sixty variable parameters need to be tested and verified on coatings before any product can achieve a commercial success.

New raw materials, relatively untested compositions, elevated cost and inferior properties compared to the petroleum-based competitors constantly pose immediate threats to utilization of new biobased or benign coating materials. An extended knowledge of chemical and physical science along with engineering technology is needed for such a demanding product development. Although numerous open and patented literatures are flooded with compounds that claim lucrative properties from relatively new formulas, it is crucial to educate students and researchers who are involved in such technological developments. This book is a collection of articles written on various process parameters involved in the development of complex environmental benign high performance coatings. The first few chapters of this book describe the state-of-the-art technologies presently available. The conversion of soybean oil to polyvinyl ether and use of cerium and ferrite compounds in coatings are described in these chapters. Similarly, there is a dedicated chapter on the use of coatings and films on fruits and vegetables. The next few chapters of this book are meant for the developers who will learn the new concepts helping those formulating innovative products for commercial success. For example, the use of biobased epoxy to replace bis-phenol A-based epoxy resin in coating is discussed in a separate chapter followed by a chapter on silica-based sol-gel coatings. The use of fatty acid for the manufacturing of waterborne coatings is also discussed. Finally, the book focuses on the various testing and evaluation parameters followed by new conceptual methods. The utilization of pharmaceutical inhibitors or recycled polymers in coatings is reviewed in detail along with nonisocyanate cured polyurethane coatings.

We are confident that this book will be of interest to the readers from diverse backgrounds in chemistry, physics, biology, materials science, and chemical engineering. It can serve as a reference book for students and research scholars and as a unique guide for the industrial technologists.

Chapter 1

Novel Biobased Polymers for Coating Applications

Harjoyti Kalita^1,2, Deep Kalita³, Samim Alam³, Andrey Chernykh¹, Ihor Tarnavchyk^1,3, James Bahr¹, Satyabrata Samanta¹, Anurad Jayasooriyama¹, Shashi Fernando¹, Sermadurai Selvakumar⁴, Dona Suranga Wickramaratne¹, Mukund Sibi⁴, and Bret J. Chisholm^1,2,3*

¹Center for Nanoscale Science and Engineering, North Dakota State University, Fargo, ND, USA

²Materials and Nanotechnology Program, North Dakota State University, Fargo, ND, USA

³Department of Coatings and Polymeric Materials, North Dakota State University, Fargo, ND, USA

⁴Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND, USA

Abstract

Linear, soluble polymers were produced from unsaturated biobased compounds using a carbocationic polymerization process. The unsaturated biobased compounds that were first converted to vinyl ether monomers and subsequently polymerized were plant oil triglycerides, cardanol, and eugenol. As a result of the much higher reactivity of the vinyl ether group compared to the unsaturation derived from the biobased compounds and the ability to tailor the cationic polymerization process, polymerization was exclusively limited to vinyl ether groups. By preserving the unsaturation derived from the biobased compounds, the polymers could be cross-linked into insoluble coatings by autoxidation. In addition, the unsaturation can be converted to other functional groups, such as epoxy groups, which enable other cross-linking mechanisms. This document describes some of the polymers and coatings that have been produced with the technology.

Keywords: Plant oil, soybean oil, poly(vinyl ether), coating, autoxidation, biobased, cardanol, eugenol, cationic polymerization

1.1 Introduction

Prior to the ample supply of petrochemicals, coatings were largely derived from renewable resources such as plant oils, fats, plant proteins, polysaccharides, terpenes, and minerals [1]. As a result of the low cost and tremendous diversity of petrochemicals, development of new coating components based on renewable/biobased resources was largely abandoned. Due to concerns with the finite supply of fossil resources, geo-political events, the environment, and human health, the use of biobased materials in the coatings industry is making a resurgence.

In general, technology innovation within the coatings industry has been largely driven by regulations aimed at protecting both the environment and human health. These regulations have historically been focused on the reduction of the volatile organic compound (VOC) content of coatings. However, due to growing consumer demand for more environmentally friendly products, the chemical and materials industries have been placing more emphasis on the complete environmental impact of products. The total environmental impact of a product or material is typically assessed by conducting a life cycle analysis.

Of the coating resin technologies utilized today, alkyd resin technology uses a significant fraction of biobased materials. Alkyd resins were developed in the mid-1920s primarily as a means to reduce the drying time of coatings based on drying oils such as linseed oil, tung oil, walnut oil, perilla oil, and poppy seed oil [2]. Plant oil triglycerides are highly flexible molecules and, as a result, a significant degree of crosslinking is required for a drying oil-based coating to become dry to the touch. With the availability of petrochemicals, aromatic monomers, such as phthalic anhydride and isophthalic acid, were used to produce polyesters modified with fatty acid esters chains derived from a plant oil. The higher glass transition temperature (T_g) of these polyesters, referred to as alkyds, enabled films to become dry to the touch shortly after solvent evaporation from the film. Chemical resistance and film hardness were developed over time due to cross-linking by autoxidation.

The mechanism of the oxidative process, commonly referred to as autoxidation, is a free-radical process that possesses initiation, propagation, and termination steps [3–7]. As shown in Figure 1.1, initiation occurs by abstraction of a bis-allylic hydrogen by singlet oxygen to produce a carbon-centered radical (I). This radical is delocalized over the pentadiene structure and reacts with oxygen to produce the peroxy radical and conjugation in the fatty acid ester chain (II). The peroxy radical can participate in a number of reactions including hydrogen abstraction to produce the hydroperoxide (III). The hydroperoxide is thermally unstable and can undergo homolytic cleavage to produce an ether radical and a hydroxyl radical (IV). Cross-links are formed primarily by radical coupling reactions that result in a variety of cross-links including ether bonds, peroxide bonds, and carbon–carbon bonds.

Figure 1.1 A schematic illustrating the process of autoxidation.

The general classes of resins/polymers currently used in the coatings industry include epoxies, polyurethanes, alkyds, acrylics, polyesters, and amino resins. Of these, acrylic resins represent the highest volume resins used in the coatings industry. The utility of acrylic resins can be largely attributed to the tremendous diversity in thermal and physiochemical properties that can be achieved through copolymerization. Most coating films derived from acrylic resins are thermoplastic and thus possess limited chemical and stain resistance. It has long been recognized that the incorporation of fatty acid ester chains into the pendent groups of acrylic resins would be a useful method for introducing cross-links into coating films to provide enhanced properties [8–13]. However, acrylate or methacrylate monomers possessing the linoleic and linolenic fatty acid ester pendent groups needed for effective oxidative cross-linking would be expected to be problematic due to the presence of the readily abstractable bis-allylic hydrogen atoms. These bis-allylic hydrogen atoms would be expected to lead to extensive chain transfer and perhaps gelation during the polymerization.

In the past few decades, tremendous progress has been made in the carbocationic polymerization of vinyl monomers [14]. Although carbocations are generally very reactive species, processes have been developed that enable very controlled polymerization. In fact, living carbocationic polymerization systems have been developed for a number of monomers including vinyl ethers [15], isobutylene [16], and styrene [17]. The controlled reactivity of the propagation step with these living polymerization systems is generally believed to be the result of a propagation step that involves an equilibrium between dormant and active species [18, 19]. A number of polymerization variables can be used to tailor the nature of a carbocationic polymerization including temperature, initiator composition, Lewis acid co-initiator composition, Lewis acid co-initiator concentration, addition of a Lewis base, Lewis base composition, Lewis base concentration, and solvent composition.

1.2 Polymers Based on Plant Oils

Using simple base-catalyzed transesterification of a vinyl ether alcohol with either a plant oil triglyceride or fatty alkyl ester, a novel vinyl ether monomer was produced [13]. Figure 1.2 shows the synthetic process using 2-(vinyloxy)ethanol as the vinyl ether alcohol and methyl soyate as the fatty alkyl ester. As illustrated in the figure, this monomer, 2-(vinyloxy)ethyl soyate (2-VOES), is a mixture based on the fatty acid ester composition of methyl soyate. As illustrated in Figure 1.3, the polymerization system developed for these plant oil-based vinyl ether monomers involves the use of the addition product of isobutyl vinyl ether and acetic acid as the initiator, ethylaluminum sesquichloride as the co-initiator, and toluene as the solvent. Using this system, a living polymerization was achieved [20].

Figure 1.2 The synthetic scheme used to produce a novel soybean oil-based vinyl ether monomer, i.e. 2-VOES.

Figure 1.3 An illustration of the polymerization system utilized for the production of plant oil-based poly(vinyl ether)s.

For most carbocationic polymerizations of a vinyl ether produced using a Lewis acid co-initiator, such as ethylaluminum sesquichloride, an appropriate concentration of a Lewis base is needed to obtain a living polymerization. The mechanism of ‘Lewis-base assisted living cationic polymerization’ is believed to involve an equilibrium between dormant and active chain ends with the concentration of active chain ends being much lower than that of the dormant chain ends. The Lewis base is believed to reduce both the concentration of active chain ends and the reactivity of active chain ends. As described by Kanazawa et al. [18, 19, 21], the Lewis base: (1) complexes with the Lewis acid co-initiator resulting in the formation of monomeric Lewis acid species and an adjustment of acidity; (2) stabilizes active chains through direct interaction; and (3) stabilizes the counteranion generated upon initiation. For the polymerization of 2-VOES, it is believed that the ester group present in the monomer serves the role of a Lewis base additive typically utilized in a ‘Lewis base-assisted’ living carbocationic polymerization. The obtainment of a living polymerization enabled control of polymer molecule weight, narrow molecular weight distribution polymers, and the production of block copolymers [22].

1.2.1 Properties of Homopolymers and Their Surface Coatings

To date, plant oil-based poly(vinyl ether) homopolymers have been produced using soybean oil (SBO), hydrogenated SBO (HSBO), corn oil (CO), and palm oil (PO) as the parent plant oil. As expected, the thermal properties of these novel polymers varied as a function of the oil or fatty methyl ester used to produce the monomer. For example, polymers based on SBO and CO were amorphous liquids at room temperature, while the polymer based on HSBO was a waxy solid. The solid nature of the latter can be attributed to the high chain packing efficiency of the saturated fatty acid ester pendent chains. While the polymers based on SBO and CO were liquids at room temperature, side chain crystallization was observed using differential scanning calorimetry (DSC). For example, as shown in Figure 1.4a, the DSC for the SBO-based polymer, poly(2-VOES), displays a weak, broad endotherm with a peak maximum at –25 °C and a T_g at –92 °C [13, 22]. Compared to the parent oil, i.e. SBO, the heat of fusion for the SBO-based polymer was much lower indicating that the higher viscosity and polymeric nature of the latter significantly inhibited fatty acid ester chain crystallization. As shown in Figure 1.4b, the polymer based on PO, poly[2-(vinyloxy)ethyl palmitate] [poly(2-VOEP)], showed a melting temperature just below room temperature, which is consistent with the relative content of saturated fatty acid ester chains compared to the polymer based on SBO [23].

Figure 1.4 DSC thermograms for poly(2-VOES) and SBO (a) as well as poly(2-VOEP) and PO (b).

Reproduced with permission from the American Coatings Association [13].

As a result of the polymeric nature of the plant oil-based polymers, the number of bis-allylic protons, allylic protons, and double bonds per molecule is much higher than that of the parent oil. As a result, the degree of autoxidation needed to produce a cross-linked network is significantly reduced compared to the parent oil. In fact, it was demonstrated that a coating produced by simply blending titanium dioxide with poly(2-VOES) became tack free in less than one-tenth the time required for an analogous coating based on linseed oil to become tack free [24]. Thus, by converting a semi-drying oil, such as SBO, to a polymer, drying properties can be achieved that are far superior to that of a drying oil. This feature of the plant oil-based polymer technology also translates to other curing chemistries. For example, the double bonds in poly(2-VOES) were converted to epoxide groups using peracetic acid and cross-linked networks produced using an anhydride curing agent. To illustrate the relative difference in the time required to reach the gel point for this network as compared to an analogous network based on epoxidized SBO (ESBO), rheological measurements were made as a function of time at 100 °C. For the epoxidized poly(2-VOES)/anhydride mixture, viscosity began to rise after just 20 min, while 2 h was required for the ESBO/anhydride mixture [22].

A similar trend was also observed for a comparison between polyurethane networks based on a polyol derived from poly(2-VOEP) to analogous networks based on a polyol derived from PO. Hydroxy groups were incorporated into poly(2-VOEP) and PO by first epoxidizing the double bonds in the materials and then ring-opening the epoxide groups with methanol [25]. In addition to providing a lower degree of functional group conversion to produce a cross-linked network, the molecular architecture of a plant oil-based polymer enables a significantly higher cross-link density compared to the triglyceride analog. This feature can be attributed to the methine carbon atoms present in the polymer backbone that function as additional cross-links in the network when the material is cured [22]. Further, cure shrinkage for cross-linked networks derived from a plant oil-based polymer would be expected to be lower than that for an a analogous network based on the parent triglyceride simply because of the molecular weight difference between the two materials.

Another attribute of the plant oil-based polymer technology is the ability to produce polymers that are essentially colorless. In general, plant oils possess some degree of color which is related to its composition. The common drying oil used in paints and coatings is linseed oil. As shown in Figure 1.5a, linseed oil is quite yellow in color. The yellowness of linseed is problematic for the production of white and pale colored paints. Figure 1.5b shows a coating film produced by simply blending rutile titanium dioxide with linseed oil, casting the coating onto a substrate, and allowing the coating to cure at ambient conditions. As shown in Figure 1.5b, the cured coating is “off-white” due to the yellowness of the linseed oil. Since the vinyl ether monomers produced from a plant oil are significantly lower molecular weight, they can be vacuum distilled to remove color. It was found that the colorless vinyl ether monomer can be polymerized by cationic polymerization to produce a colorless polymer. Figure 1.6a provides an image of poly(2-VOES) produced from vacuum-distilled 2-VOES, while Figure 1.6b shows an image of a white paint produced from the poly(2-VOES) and rutile titanium dioxide in analogous fashion as that described for the linseed oil paint shown in Figure 1.5b. A comparison of Figure 1.6b to Figure 1.5b shows that the poly(2-VOES) derived from vacuum-distilled 2-VOES provides a white paint that does not possess the yellowness that is obtained when linseed oil is used as the binder.

Figure 1.5 Images showing the color of linseed oil (a) and a paint produced by blending linseed oil with rutile titanium dioxide (b).

Figure 1.6 Images showing the color of poly(2-VOES) derived from vacuum-distilled 2-VOES (a) and a paint produced by blending the poly(2-VOES) with rutile titanium dioxide (b).

1.2.2 Properties of Copolymers and Their Surface Coatings

Probably, the most useful aspect of the plant oil-based polymer technology is the ability to widely tailor properties through copolymerization. This was demonstrated using a number of co-monomers including cyclohexyl vinyl ether (CHVE), menthol vinyl ether (MVE), and pentaethylene glycol ethyl vinyl ether (PEGEVE). Since homopolymers of the plant oil-based vinyl ethers possess a very low T_g, it was of interest to increase polymer T_g by copolymerization. As illustrated in Figure 1.7, both CHVE and MVE possess the cyclohexyl ring attached to the vinyl ether oxygen atom with MVE possessing a substituted ring. CHVE is commercially available, while MVE was synthesized in-house. MVE represents a potentially biobased monomer since menthol is a naturally occurring terpene that can be obtained from the peppermint plant, Mentha x pipertia (Lamiaceae) [26]. As expected, copolymerization of 2-VOES with these cycloaliphatic vinyl ether monomers enabled the formation of cross-linked films with increased T_g‘s compared to the control film based on the homopolymer of 2-VOES (i.e. poly(2-VOES)). Figure 1.8 shows the variation in T_g as a function of comonomer content for films cured at room temperature by autoxidation [27, 28].

Figure 1.7 Chemical structures for vinyl ether monomers that were copolymerized with 2-VOES.

Figure 1.8 The variation in T_g with comonomer content for 2-VOES-based copolymer films cured at room temperature by autoxidation.

Copolymerization of 2-VOES with PEGEVE was utilized as a means to provide dispersability of the polymer in water without the need for surfactant. The amphiphilic copolymers produced were shown to be surface active as determined by measuring critical micelle concentration [29]. Three different copolymers were produced that varied with respect to PEGEVE repeat unit content. From these copolymers, aqueous dispersions were produced that also contained a water-based drier package. The solids content of the dispersions was 30 wt.% and all three copolymers gave stable dispersions. Figure 1.9a shows the variation in drying time with copolymer composition, while Figure 1.9b provides an image of a coating cast and cured at ambient conditions on a glass panel. As shown in Figure 1.9a, coatings cured relatively fast with the tack-free time decreasing with increasing 2-VOES repeat unit content. From Figure 1.9b, it can be seen that cured films had excellent optical clarity, which can be attributed to the lack of surfactant in the films.

Figure 1.9 Tack-free time as a function of PEGEVE repeat unit content (a) and an image of a coated glass panel partially laid over the NDSU logo (b).

1.3 Polymers Based on Cardanol

Cardanol is derived from cashew nut liquid, which is a byproduct of cashew nut processing [30]. The primary component of cashew nut liquid is anacardic acid, which can be converted to cardanol by thermal decarboxylation. Cardanol is a mixture of four different meta-alkyl phenols that differ with respect to the degree of unsaturation in the alkyl side chain, as shown in Figure 1.10 [31]. As a result of the success obtained with the plant oil-based poly(vinyl ether)s described earlier, it was of interest to produce and characterize poly(vinyl ether)s containing cardanol units in the pendent chains of the repeat units. A novel vinyl ether monomer of cardanol, i.e. cardanol ethyl vinyl ether, was produced using the Williamson ether synthesis reaction shown in Figure 1.11. This monomer was successfully polymerized using the same polymerization system used for the production of the plant oil-based vinyl ethers. With this polymerization system, a soluble, tacky polymer was produced.

Figure 1.10 The chemical structure of cardanol.

Figure 1.11 A schematic illustrating the synthesis of cardanol ethyl vinyl ether.

A solution of the polymer was combined with a drier package and films were cast on steel panels. Three different curing conditions were investigated. Curing at room temperature was done over a period of two weeks, while curing at 120 °C and 150 °C was done for 1 h. For elevated temperature curing, coated panels were placed into the oven shortly after the solvent had evaporated from the film. In addition to coated steel panels, free films specimens were prepared by casting films over Teflon™-laminated glass panels. Table 1.1 displays the properties of the coatings and free films prepared. In general, the coatings produced were relatively flexible and possessed sub-ambient T_g’s. Although the coatings possessed sub-ambient T_g’s, they exhibited good solvent resistance as expressed by the number methyl ethyl ketone (MEK) double rubs.

Table 1.1 Data obtained for cured films of poly(cardanol ethyl vinyl ether).

1.4 Polymers Based on Eugenol

Eugenol is a major component of Ocimum, Cinnamon, and Clove oils [32]. Eugenol is primarily obtained from the clove buds of Eugenia aromatic and Eugenia caryophyllata belonging to the family Mytraceae indigenous to the Molluca Islands. It is also cultivated in other parts of Indonesia, Zanzibar, Madagascar, and Ceylon. Eugenol is also a potential product from the breakdown of lignin, and approximately 50 million tons of lignin is produced annually from the pulp and paper industries worldwide [33].

Analogous to the monomer based on cardanol, eugenol ethyl vinyl ether (EEVE) was produced from eugenol and 2-chloroethyl vinyl ether. This monomer was readily polymerized by cationic polymerization to produce a soluble polymer that was a viscose, tacky liquid at room temperature with a T_g of approximately 2 °C. Using proton nuclear magnetic resonance spectroscopy, preservation of the allyl group derived from eugenol was confirmed.

As illustrated in Figure 1.12, the methylene hydrogen atoms between the vinyl group and the phenyl group should be very labile to abstraction by singlet oxygen since the radical can be resonance stabilized by both the adjacent double bond and the phenyl ring. As a result, it was of interest to determine if poly(EEVE) could be cured into a cross-linked film by autoxidation. A poly(EEVE) sample with a number-average molecular weight of 17,900 g/mol was dissolved in toluene at 35 wt.%. To this solution, a drier package containing cobalt 2-ethylhexanoate, zirconium 2-ethylhexanoate, and zinc carboxylate was added. With this system, a cast film became dry-to-the-touch in 10 min. Coating specimens were produced using three different curing conditions, i.e. curing at room temperature for 3 weeks, 120 °C for 1 h, and 150 °C for 1 h. In addition to films cast on steel substrates, free films were produced and used to determine film mechanical and viscoelastic properties. Table 1.2 shows the properties obtained for the coatings and films produced.

Figure 1.12 Illustration of resonance stabilization of a radical generated by hydrogen abstraction by singlet oxygen.

As shown in Figure 1.13, the presence of the vinyl groups in poly(EEVE) enables the production of polyepoxide resins by simple oxidation using, for example, m-chloroperoxybenzoic acid as the oxidant. An epoxidized version of poly(EEVE) was produced and cross-linked films generated using diethylenetriamine (DETA) as the cross-linking agent and a 1/1 epoxy/NH mole/mole ratio. For comparison purposes, cross-linked films of the diglycidyl ether of bisphenol-A (DGEBPA) were also produced using DETA. Figure 1.14 displays the viscoelastic properties of the network derived from epoxidized poly(EEVE) and DETA. From the tangent delta data, a T_g of 130 °C was determined. It was very interesting to observe this high of a T_g considering the relatively high molecular mobility of the poly(vinyl ether) polymer backbone. Obviously the very high cross-link density derived from the high number of epoxy groups per polymer molecule enables such a high T_g.

Figure 1.13 The synthetic scheme used to produce an epoxidized version of poly(EEVE).

Figure 1.14 The viscoelastic properties of the network derived from epoxidized poly(EEVE) and DETA.

Table 1.3 provides a comparison of the properties of coatings cast and cured on steel substrates. As shown in the table, the hardness, flexibility, and adhesion of the coating based on epoxidized poly(EEVE) was similar to that of the analogous coating based on DGEBPA. The primary difference between these two coatings involved the chemical resistance and impact resistance. The chemical resistance, as expressed using the MEK double rub test, was dramatically better for the coatings based on epoxidized poly(EEVE). After 1,000 MEK double rubs, no visible damage to the coating was observed. In contrast, the coating based on DGEBPA failed after 310 double rubs. With regard to impact resistance, the coating based on the epoxidized poly(EEVE) showed a lower impact resistance than the coating based on DGEBPA. The higher MEK resistance and lower impact resistance associated with the epoxidized poly(EEVE) are consistent with a higher cross-link density for this coating.

Table 1.3 Data obtained for coatings based on epoxidized poly(EEVE) and DGEBPA that were cast and cured on steel substrates.

1.5 Conclusion

The results presented in this document demonstrate the utility of a carbocationic polymerization system for producing novel biobased polymers that retain the unsaturation derived from the biobased component. The high reactivity of the vinyl ether functional group and the appropriate choice of the polymerization system enabled linear polymers to be produced with relatively narrow molecular weight distributions. The ability to retain unsaturation from the biobased component enabled the production of cross-linked coatings using autoxidation. The high number of allylic hydrogens and double bonds per molecule associated with these unsaturated poly(vinyl ether)s results in relatively fast curing by autoxidation due to the gel point being reached at relatively low extents of reaction. Another important aspect of this polymer technology is the ability to utilize copolymerization to tailor polymer and coating properties. The unsaturation present in the polymer produced can also be easily converted to other functional groups, such as the epoxy group, to enable other cross-linking mechanisms.

Acknowledgments

The authors thank the Department of Energy (grant DE-FG36-08GO088160), United States Department of Agriculture/National Institute of Food and Agriculture (grant 2012-38202-19283), United Soybean Board, National Science Foundation (grants IIA-1330840, IIA-1355466, and IIP-1401801), and North Dakota Soybean Council for financial support.

Disclaimer

This report was prepared as an account of work sponsored by an agency of the US Government. Neither the US Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the US Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the US Government or any agency thereof.

References

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Chapter 2

Deposition of Environmentally Compliant Cerium-Containing Coatings and Primers on Copper-Containing Aluminium Aircraft Alloys

Abstract

This chapter describes the basic concepts related to the application of cerium compounds as a main alternative to the already restricted approaches of the use of toxic and environmentally unacceptable compounds. The chapter begins with a brief description of the importance of aluminium alloys for the aircraft industry and the basic corrosion forms and damages typical for these alloys. Besides the indispensability of the coating procedures for providing long-term corrosion protection, the basic multilayered coatings systems are also discussed. Following this, the basic stages and factors of deposition of cerium conversion coatings (CeCCs) as primer coating layers are described. Subsequently, various methods that involve cerium compounds as active components in upper and finishing coating layers are proposed based on the literature analysis. Furthermore, some alternatives of the cerium compounds as environmentally friendly active coating ingredients, such as organic corrosion inhibitors, are also proposed. The chapter finishes with the recent and the most actual directions for further improvement of coatings. Finally, the development of dense, self-healing, sun-light-protected, hydrophobic coatings are described.

Keywords: Aircraft alloys, corrosion protection, cerium conversion coatings, technological aspects, hybrid and nanocomposite materials, corrosion inhibitors, multifunctionality

Epoxy resin	DGEBPA	Epoxidized poly(EEVE)
König pendulum hardness (s) ASTM D4366	225 ± 2	205 ± 1
Crosshatch adhesion ASTM D3359	5B ± 0	5B ± 0
Conical mandrel bend test ASTM D522	>30% elong.	>30% elong.
Reverse impact (in lb) ASTM D2794	43	8
MEK double rubs ASTM D5402	310	>1,000

Chapter 1

Novel Biobased Polymers for Coating Applications

Abstract

1.1 Introduction

1.2 Polymers Based on Plant Oils

1.2.1 Properties of Homopolymers and Their Surface Coatings

1.2.2 Properties of Copolymers and Their Surface Coatings

1.3 Polymers Based on Cardanol

1.4 Polymers Based on Eugenol

1.5 Conclusion

Acknowledgments

Disclaimer

References

Chapter 2

Deposition of Environmentally Compliant Cerium-Containing Coatings and Primers on Copper-Containing Aluminium Aircraft Alloys

Abstract

2.1 Importance and Indispensability of the Corrosion-Protective Coating Layers

2.1.1 Employment of Reliable Materials for the Aircraft Industry