High-strength adhesive derived from sustainable components

Abstract

(i) Epoxidized oil, (ii) a nucleophile, and (iii) a high-strength adhesive composition containing components such as phenolic compounds derived from large-scale, sustainably supplied, low-cost biological materials, its use, and a method of manufacturing the same.

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims priority to U.S. Provisional Patent Application No. 63 / 338,465, filed on May 5, 2022, which is hereby incorporated by reference in its entirety.

[0002] Statement of Government Support This invention was made with government support under Navy Research Office grant N00014 - 19 - 1 - 2342. The government has certain rights in this invention.

[0003] The present disclosure relates to high - strength adhesives manufactured using sustainable components. In particular, the present disclosure relates to high - strength adhesives that include bio - based materials that promote recycling and enable a sustainable materials ecosystem.

Background Art

[0004] This section presents aspects that may be useful in promoting a better understanding of the present disclosure. Accordingly, these descriptions should be read from this perspective and should not be construed as an admission as to what is prior art or what is not prior art.

[0005] From electronic devices to furniture, most consumer products are joined with adhesives. High performance, versatility, and low cost are the characteristics of modern glues. However, these characteristics also give rise to some environmental drawbacks. Since these materials are derived from petroleum, they create permanent bonds, lack chemical decomposability, and are toxic. Because adhesives are supplied in such unnatural ways, most components cannot be separated for recycling. Since the bonds cannot be broken down, the substrates cannot be separated, recycling is hindered, and products are driven to landfills. These discarded adhesive resins further exacerbate the problem of marine microplastics. For example, the toxicity of plywood binders that emit carcinogenic formaldehyde can also be a concern. Society is awash with disposable products and packaging. Biomimetic chemistry inspired by the adhesive substances of shellfish provides the required cross-linking. Biologically supplied adhesives can provide the necessary path towards a sustainable material ecosystem.

[0006] When compared with modern materials, cost and performance are persistent issues with bio-based alternative adhesives. With regard to bioadhesives, availability is a further barrier to sustainability. The components of bio-based materials are not easily manufactured on a large scale. Therefore, they are not adopted in the industry.

[0007] Therefore, there is an unmet need for a high-strength adhesive that is easy to recycle, safe for the ecosystem, low-cost, manufactured using bio-based materials, and readily available on a large scale. The objective of the present disclosure is to provide such an adhesive. This objective and other objectives and advantages, as well as the features of the invention, will be apparent from the detailed description provided herein. Summary of the Invention

[0008] An adhesive composition is provided that comprises (i) epoxidized oil (EO), (ii) a nucleophile, and (iii) a phenolic compound.

[0009] The epoxidized oil may be any suitable epoxidized oil obtained from a sustainable source. In some embodiments, the sustainable source may be a plant or vegetable. In some embodiments, the epoxidized oil is epoxidized soybean oil.

[0010] The nucleophile may be a compound containing a moiety selected from the group consisting of acids, alcohols, amines, and thiols. In some embodiments, the nucleophile may be selected from fumaric acid, glycerol, malic acid, succinic acid, or combinations thereof. In some embodiments, the nucleophile is malic acid.

[0011] The phenolic compound may be selected from catechol, gallic acid, gallol, lignin, tannic acid, or combinations thereof. In some embodiments, the phenolic compound is tannic acid.

[0012] In some embodiments, the adhesive composition may optionally further comprise a solvent. Examples of solvents include, but are not limited to, alcohols, water, chloroform, dichloromethane, dimethyl sulfoxide, and dimethylformamide. In some embodiments, the solvent may be an alcohol such as ethanol or methanol.

[0013] In some embodiments, EO, the nucleophile, and the phenolic compound may be present in a mass ratio of about 1:0.1:0.1 to about 1:10:10.

[0014] In some embodiments, an adhesive composition consisting essentially of (i) epoxidized soybean oil (ESO), (ii) malic acid, (iii) tannic acid, and (iv) ethanol. ESO, malic acid, and tannic acid are present in a mass ratio of about 1:0.1:0.1 to about 1:10:10.

[0015] A method of making an adhesive composition, i) heating an epoxidized oil (EO), ii) A step of mixing a phenolic compound with the epoxidized oil of step (i) to obtain a solution, wherein the phenolic compound is optionally in the form of a solution in a solvent. iii) A step of adding a nucleophile to the solution of step (ii) and heating the solution, and iv) A step of cooling the solution to room temperature A method is provided that includes the above steps, and then an adhesive composition is obtained.

[0016] EO may be heated at a temperature of about 70 °C to about 90 °C to obtain a desired viscosity. The solution of step (iii) may be heated at a temperature of about 70 °C to about 90 °C. The solution can be heated overnight and cooled to room temperature to obtain an adhesive composition.

[0017] The adhesive composition can be used to adhere a substrate. The substrate may be exposed to dry, wet, humid or underwater conditions. The substrate may be selected from metal substrates such as steel or aluminum, wood, plastics such as polyvinyl chloride (PVC) or polytetrafluoroethylene (Teflon), ceramics, or combinations thereof. In some embodiments, the metal substrate may be steel or aluminum.

[0018] A method of using the adhesive composition is provided, which includes a step of applying the adhesive composition to at least a first substrate adhered to at least a second substrate, and a step of adhering at least the first substrate and at least the second substrate to each other. The method further includes a step of applying the adhesive composition to at least the second substrate before adhering at least the first substrate and at least the second substrate. At least one of the substrates is exposed to dry, humid, wet or underwater conditions.

[0019] The present disclosure is more easily understood from the following detailed description of the embodiments presented in conjunction with the accompanying drawings.

Brief Description of the Drawings

[0020]

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Best Mode for Carrying Out the Invention

[0021] For the purpose of facilitating understanding of the principles of the present disclosure, embodiments shown in the drawings are hereby referred to and described using specific language. It is not intended to limit the scope by the description of these embodiments. On the contrary, the present disclosure is intended to embrace alternatives, modifications, and equivalents that may be included within the spirit and scope of the present application as defined by the appended claims.

[0022] The terms "adhesive" and "adhesive composition" are used interchangeably.

[0023] The term "phenolic compound" refers to a compound having a chemical structure with at least one aromatic ring to which one or more hydroxyl groups are bonded to the aromatic ring. "Phenolic compounds" may also include polyphenols, which may have multiple aromatic rings to which one or more hydroxyl groups are bonded to the multiple aromatic rings.

[0024] It is well known that epoxy paste is formed by the reaction of a polyfunctional epoxy-containing compound such as bisphenol A diglycidyl ether with a polyamine containing triethylenetetramine. The nucleophilic amine opens the 3-membered epoxy ring to form a C-N bond and forms a widely cross-linked matrix. Soybean oil, one of the most widely available sources of renewable organic matter, is an alternative to epoxy. Epoxidized soybean oil is obtained by a simple reaction of soybean oil with an acid and hydrogen peroxide. Epoxidized soybean oil is a low-cost bio-based material that is easily available on a large scale. However, epoxidized soybean oil reacted with polyamine only results in a highly viscous oil that is not suitable for adhesion, so it cannot be a direct substitute for bisphenol A diglycidyl ether.

[0025] Marine mussels attach to rocks by proteins containing 3,4-dihydroxyphenylalanine (DOPA). These DOPA groups enable the protein to bind to the surface via hydrogen bonding and metal chelation among several interactions. Furthermore, the oxidation of these pendant dihydroxyphenyl (i.e., catechol) groups results in cross-links that cause cohesive interactions. Thus, when catechol-like chemicals are included in an adhesive formulation, epoxidized soybean oil can be transformed into a strong adhesive.

[0026] From the above perspectives, the present disclosure provides an adhesive composition comprising (i) epoxidized oil (EO), (ii) a nucleophile, and (iii) a phenolic compound. In its embodiments, the adhesive composition consists essentially of or consists of (i) to (iii).

[0027] This adhesive composition may be a high-strength adhesive containing components derived from sustainable biological sources. The biological source may be an agricultural feedstock that is low-cost, readily available on a large scale, and easily recyclable.

[0028] The epoxidized oil may be any suitable epoxidized oil obtained from a sustainable source. The sustainable source may be a plant or a vegetable. In some embodiments, the epoxidized oil is epoxidized soybean oil (ESO).

[0029] ESO may be made from soybean oil. The soybean oil may be obtained from soybean plants, while the nucleophile and the phenolic compound may be obtained from other sustainable natural sources. Thus, the adhesive may be non-toxic and peelable.

[0030] The nucleophile is any suitable polyfunctional bio-based nucleophile capable of opening an epoxy ring. Examples of nucleophiles include, but are not limited to, compounds containing moieties selected from the group consisting of acids, alcohols, amines, and thiols. In some embodiments, the nucleophile is selected from malic acid, glycerol, malic acid, succinic acid, or combinations thereof. In an exemplary embodiment, the nucleophile is malic acid.

[0031] The phenolic compound may be selected from catechol, gallic acid, gallol, lignin, tannic acid, or combinations thereof. Phenolic compounds, such as tannic acid, contain abundant reactive terminal phenolic hydroxyl groups with a highly branched aromatic / alicyclic polyester core, which can form a highly crosslinked network with ESO having highly active epoxy groups. In an exemplary embodiment, the phenolic compound is tannic acid.

[0032] The adhesive composition may further contain a solvent. In some embodiments, when the phenolic compound used is tannic acid, the adhesive composition may contain a solvent. Thus, the use of a solvent in the adhesive composition may be optional. In that embodiment, the adhesive composition may consist essentially of (or alternatively consist of) a solvent.

[0033] Any suitable solvent for solubilizing tannic acid can be used. Examples of solvents include, but are not limited to, alcohols such as ethanol or methanol, water, chloroform, dichloromethane, dimethyl sulfoxide, and dimethylformamide. In some embodiments, the solvent is ethanol.

[0034] In some embodiments, EO, the nucleophile, and the phenolic compound may be present in a mass ratio of about 1:0.1:0.1 to about 1:10:10 (e.g., about 1:0.1:0.1 to 1:10:10, 1:0.1:0.1 to about 1:10:10, or 1:0.1:0.1 to 1:10:10). In some embodiments, EO, the nucleophile, and the phenolic compound may be present in a mass ratio of about 1:0.3:0.3 to about 1:0.6:0.6 (e.g., about 1:0.3:0.3 to 1:0.6:0.6, 1:0.3:0.3 to about 1:0.6:0.6, or 1:0.3:0.3 to 1:0.6:0.6). Desirably, EO, the nucleophile, and the phenolic compound may be present in a mass ratio of about 1:0.4:0.5 (e.g., 1:0.4:0.5).

[0035] In some embodiments, a highest-strength adhesive composition (the "soy-mal-tan") containing (i) ESO (ii) malic acid, and (iii) tannic acid is provided. ESO, malic acid, and tannic acid may be present in a mass ratio of about 1:0.1:0.1 to about 1:10:10 (e.g., about 1:0.1:0.1 to 1:10:10, 1:0.1:0.1 to about 1:10:10, or 1:0.1:0.1 to 1:10:10). In some embodiments, ESO, malic acid, and tannic acid may be present in a mass ratio of about 1:0.3:0.3 to about 1:0.6:0.6 (e.g., about 1:0.3:0.3 to 1:0.6:0.6, 1:0.3:0.3 to about 1:0.6:0.6, or 1:0.3:0.3 to 1:0.6:0.6). Desirably, ESO, malic acid, and tannic acid may be present in a mass ratio of about 1:0.4:0.5 (e.g., 1:0.4:0.5). The adhesive composition can further contain an organic solvent such as alcohol. In some embodiments, the alcohol is ethanol or methanol. The amount of the organic solvent such as ethanol present is about 0.4 g (e.g., 0.4 g) per 1 gram of soy-mal-tan. In that embodiment, the adhesive composition consists essentially of, or consists of, soy-mal-tan and ethanol.

[0036] Epoxidized oil, a nucleophile, and a phenolic compound can form covalent bonds and a highly cross-linked matrix, which contributes to high-strength adhesion.

[0037] The adhesive composition may be produced by reacting EO, a nucleophile, and a phenolic compound. ESO, a nucleophile (e.g., malic acid), and a phenolic compound (e.g., tannic acid) can be reacted together to obtain an adhesive composition (e.g., soy-mal-tan). ESO, malic acid, and tannic acid may be represented by the structures shown below. In some embodiments, reacting the three components together can result in an adhesive that is supplied with high strength and sustainability.

[0038] [Chemical formula]

[0039] A method for preparing an adhesive composition, i) heating an epoxidized oil (EO); ii) mixing a phenolic compound with the epoxidized oil of step (i) to obtain a solution, where the phenolic compound is optionally in the form of a solution in a solvent; iii) adding a nucleophile to the solution of step (ii) and heating the solution; and iv) cooling the solution to room temperature is provided, whereby an adhesive composition is obtained.

[0040] The reaction may be carried out at about 20°C to about 90°C, such as about 20°C to 90°C, 20°C to about 90°C, or 20°C to 90°C. Desirably, the reaction is carried out at about 20°C to about 70°C, such as about 20°C to 70°C, 20°C to about 70°C, or 20°C to 70°C. The reaction may be carried out for about 6 hours to about 24 hours, such as about 6 hours to 24 hours, 6 hours to about 24 hours, or 6 hours to 24 hours. This simple mixing and heating process can be easily implemented on a large scale.

[0041] Any suitable solvent that solubilizes tannic acid can be used. Examples of solvents include, but are not limited to, alcohols such as ethanol or methanol, water, chloroform, dichloromethane, dimethyl sulfoxide, and dimethylformamide. In some embodiments, the solvent is ethanol.

[0042] In some embodiments, the EO can be heated at a temperature of about 70°C to about 90°C to reduce the viscosity. Reacting at 70°C for 24 hours gives an amber-colored, flowable gel adhesive composition for application between substrates. The heated material can be placed between the substrates and cured to form the final adhesive. The adhesive can be cured at about 20°C to about 180°C, such as about 20°C - 180°C, 20°C - 180°C, 20°C - about 180°C, or 20°C - 180°C for about 1 hour to about 24 hours, such as about 1 hour - 24 hours, 1 hour - about 24 hours, or 1 hour - 24 hours. The high bond strength of the adhesive can be achieved when cured at about 180°C for about 24 hours. After curing (180°C, 24 hours), the adhesive may become a hard, blackish solid.

[0043] A method of using the adhesive composition is further provided, comprising the steps of applying the adhesive composition to at least a first substrate that is adhered to at least a second substrate, and adhering at least the first substrate and at least the second substrate to each other. The method further comprises the step of applying the adhesive composition to at least the second substrate before adhering at least the first substrate and at least the second substrate to each other.

[0044] The adhesive composition can be used when the first substrate and / or the second substrate are exposed to dry, humid, wet, or underwater conditions.

[0045] The substrate to be used next may be selected from metals such as steel or aluminum, wood, plastics such as polyvinyl chloride (PVC) or polytetrafluoroethylene (Teflon), ceramics, or any combination thereof. The metal substrate may be polished or sandblasted. In some embodiments, the metal substrate may be steel or aluminum.

[0046] Figure 3 shows the curing of an adhesive placed between two steel pieces and cured at 180 °C for 1, 3, 6, 18, or 24 hours. The bond strength was significantly stronger at 180 °C than at 70 °C or room temperature (Table 1). A 24-hour cure time resulted in the strongest bond, but a 6-hour cure was equivalent and produced less carbon dioxide emissions upon heating.

[0047]

Table 1

[0048] The bonding properties of the adhesive were investigated using aluminum and steel substrates. Figures 4A and 4B show that the bonds often fully reached the structural strength (e.g., >1 MPa), ranging from 10 ± 1 MPa for sandblasted aluminum to 16 ± 1 MPa for polished steel. The structural strength of polished aluminum and sandblasted steel was approximately 13 MPa. The adhesive control containing only two components was significantly weaker or did not bond at all. Epoxidized soybean oil containing malic acid (without tannic acid) bonded at 1.9 ± 0.4 MPa. Malic acid containing tannic acid (without epoxidized soybean oil) formed a hard solid with no bonding ability. Epoxidized soybean oil and tannic acid (without malic acid) did not cure to a solid.

[0049] To ensure that the product remains intact when facing difficult conditions, a certain degree of water resistance is required. However, the water resistance of current industrial adhesives hinders peeling, component recycling, and decomposition in landfills. To confirm the peeling of the adhesive, a water resistance test was conducted. The water used in the underwater environmental test was seawater. The substrate can be immersed in water during or after adhesive application. In the water resistance test, when the substrate was immersed for one week, gradual peeling was shown over time. Figure 10 shows that when the substrate was immersed in water for 24 hours, soy-mal-tan maintained approximately 75 - 100% of the initial dry bonding strength. After one week in water, approximately 26 - 78% of the bond persisted.

[0050] The adhesive composition can be used as a high-strength adhesive for automotive, construction, and electronic applications. The adhesive composition may be useful for bonding vehicle parts, and the vehicle may be an automobile.

[0051] The lightweighting of automobiles and trucks is an example where adhesives can offer additional environmental benefits. The change from heavy rivets and welding to adhesive bonding can reduce vehicle weight and improve fuel efficiency. Figure 10 shows how the rocker panel of a pickup truck can be riveted to the cross-section of a steel bar representing the vehicle frame, demonstrating the performance of the soy-mal-tan adhesive for joining substrates. The adhesive was cured with a heat gun for 5 minutes. By replacing 36.9 grams of steel rivets with 0.9 grams of glue, the mass of the binder in these assemblies was reduced by approximately 97%.

[0052] The goal of material sustainability may include both having bio-based starting components and low levels of energy input. Soy-mal-tan was cured at 180°C for 6 hours. For comparison, epoxy is cured using a wide range of conditions. It was observed that epoxy does not achieve complete curing by just maintaining at room temperature. Automotive, construction, and electronic applications account for a large proportion of epoxy consumption and may be used at 120 - 180°C for 30 minutes under general conditions.

Examples

[0053] Material 450 lb of epoxidized soybean oil (ESO) was purchased from a chemical company. DL-Malic acid, fumaric acid, succinic acid, glycerol, tannic acid, gallic acid, and lignin were all purchased from Sigma-Aldrich and used without modification. Pyrocatechol was purchased from Acros and used without modification.

[0054] [Example 1] Synthesis of Epoxidized Soybean Oil - Malic Acid - Tannic Acid (Soy - Mal - Tan) 1.0 g of ESO was added to a 20 mL glass vial with a magnetic stir bar and heated at 70 °C in a water bath. After sufficient heating to lower the viscosity, 1 mL of a 0.5 g / mL tannic acid / EtOH solution was added to the ESO and mixed for about 5 minutes. Then, 0.4 g of malic acid was slowly added to the solution until it was completely dissolved. The reaction mixture was heated overnight, removed from the water bath, and cooled to room temperature. At this point, the adhesive was amber in color, free - flowing while still warm, and gradually solidified to room temperature.

[0055] [Example 2] Synthesis of Epoxidized Soybean Oil - Glycerol - Tannic Acid (Soy - Gly - Tan) Epoxidized soybean oil, glycerol, and tannic acid were used to prepare Soy - Gal - Tan using the procedure of Example 1.

[0056] Preparation of the adherend Metal The steel used was low - carbon and conformed to ASTM A109 standards. The aluminum was 6061 alloy and conformed to ASTM B209 standards.

[0057] Abrasive substrate Adherends (12 mm × 3.175 mm × 89 mm) of ground ASTM aluminum and stainless steel were polished using various metal polishing bars and polishing wheels. The stainless-steel adherends were successively polished with black emery bars and then common blue bars. Since aluminum is soft, the ground aluminum was prepared using only brown tripoli bars. After polishing, excess grease was wiped off, and all substrates were cleaned using a stepwise solvent system consisting of hexane, acetone, MeOH, and finally DI water. The substrates were dried overnight before use.

[0058] Sandblasted substrates ASTM aluminum and stainless-steel adherends were placed in a sandblasting cabinet and prepared using an abrasive composed of fine glass bead media. To directly compare the manner in which soy-mal-tan acts on smooth or rough interfaces, the glass beads were used to create a rough surface on the substrates.

[0059] Low-energy plastics Polyvinyl chloride (PVC) and polytetrafluoroethylene (Teflon) substrates were cut into pieces (12 mm × 12 mm × 89 mm). Neither material required special preparation before use in the adhesive tests.

[0060] Wood Pine pieces were cut to dimensions of 12 mm × 12 mm × 89 mm. The surface of the pine substrates was simply treated with 60-grit sandpaper.

[0061] Application of adhesives to substrates 50 mg of soy-mal-tan was added to each lap-shear pair of substrates. The material was applied while warm for ease of viscosity. The second adherend was placed on top of the first adherend to form an overlap area of approximately 12 mm × ~12 mm. The lap-shear joints were clamped together and the soy-mal-tan was spread between the substrates. After cooling to room temperature, the material solidified between the substrates. These joints were placed in an oven at 180 °C for 6 hours for high-energy substrates and 24 hours for Teflon. The PVC samples were placed in an oven at 110 °C for 24 hours due to the melting point of this plastic. After curing at 180 °C, the soy-mal-tan presented a dark brown / black color and became harder than after the initial reaction.

[0062] Adhesion test The adhesive strength was first determined using an Instron 5544 equipped with a 2 kN load cell. Samples exceeding the capacity of the load cell were measured using an MTS Insight materials testing instrument equipped with a 10 kN load cell or an Instron 34TM-30 instrument equipped with a 30 kN load cell. For both Instron and MTS, the samples were placed in the instrument using two steel crossbars (e.g., drill bit blanks) to fix each adherend. The crossbars were pulled apart and stress was applied to the joint at a tensile speed of 2 mm / min. The maximum force applied to the joint before failure was recorded in Newtons (N). The obtained adhesive strength in megapascals (MPa) was calculated by dividing this maximum force (N) by the overlap area of the joint (m2). The reported adhesion data is the average of at least 10 samples, and the error bars represent the 90% confidence interval. One exception here was the water resistance test of EMT where n = 5. If the joint separated immediately after being lifted, these samples were given a value of 0 when calculating the average.

[0063] Artificial seawater Artificial seawater was prepared using an Aquacraft Marine Environment Salt mixture. The salt was dissolved in reverse osmosis purified water to a final salinity concentration of 28 - 30 ppt as measured by a refractometer. The water was aerated for at least 7 days before use.

[0064] Characteristic evaluation IR spectroscopy The infrared spectrum was obtained using a Thermo Nicolet Nexus FT-IR equipped with diamond and ZnSe ATR. Data from solid samples were collected from 800 to 4500 cm -1 using an MCT detector. These data were analyzed to determine the disappearance of functional groups.

[0065] Infrared (IR) spectroscopy suggested a similar bonding scheme with a potential shift from acid to ester (about 1680 - about 1720 cm -1 ) when malic acid was reacted with epoxidized soybean oil both in the presence and absence of tannic acid (Figure 9). The carboxylic acid CO-OH bands (1408, 1278 cm -1 ) of malic acid were also less observable after combination with epoxidized soybean oil.

[0066] NMR spectroscopy Samples for NMR studies were prepared using DMSO-d6 solvent and run using an Oxford 300 MHz magnet. 1 1H-NMR and 13 13C-NMR were performed on each sample and then analyzed using Mestrenova software. Peaks of individual spectra were separated to observe the appearance or disappearance of specific groups.

[0067] According to proton nuclear magnetic resonance ( 1 1H NMR) spectroscopy, the starting epoxy groups in epoxidized soybean oil disappeared due to reaction with malic acid, or to a lesser extent with tannic acid (Figure 9). The consumption of epoxy groups by reaction with both malic acid and tannic acid was further confirmed by acid titration. Also, 1 in the 1H NMR spectrum, the appearance of alcohol (3.38 ppm) was observed, which is a characteristic result of epoxy ring-opening after reaction with a nucleophile. The 1The resonance of the alcohol in the 1H NMR did not change, indicating that it was from malic acid where the acid group had reacted with the epoxy. Epoxidized soil oil + malic acid + tannic acid (at approximately 172.2 ppm) or epoxidized soil oil + malic acid (at approximately 172.5 ppm) (Figure 9B) showed aliphatic ester formation. 13 A small shift in the 13C NMR spectrum was observed, supporting the coupling of the acid + epoxy. The presence of multiple broad peaks indicated the formation of a crosslinked heterogeneous system.

[0068] Differential scanning calorimetry (DSC) Differential scanning calorimetry was performed using a Perkin Elmer equipped with a 2P Intracooler and nitrogen gas purge. Each scan was programmed to run from -10 °C to 200 °C at 10 °C / min and cool from 200 °C to -10 °C at 40 °C / min. Individual thermograms were used to calculate the glass transition temperature of each material.

[0069] Differential scanning calorimetry (DSC) showed that the thermal events of epoxidized soybean oil, which is an oil at room temperature, may shift to higher temperatures by reaction with malic acid and, in some cases, tannic acid. In the complete system of epoxidized soil oil + malic acid + tannic acid, there were distinct high-temperature thermal events that did not correlate with epoxidized soil oil (below room temperature), tannic acid (alone >200 °C), or malic acid.

[0070] Epoxy titration The determination of the epoxy groups remaining after the reaction was carried out using a previously published ASTM method. The sample was titrated from a HBr stock solution until the color changed to the same color as the control. The epoxy concentration was calculated using the volume until the color change was reached.

[0071] Temperature A standard T-type thermocouple was used to determine the approximate output temperatures of a household hair dryer and a laboratory heat gun.

[0072] Microscopy Scanning electron microscope images were collected using a FEI Quanta 3D FEG instrument equipped with a gallium ion beam, an Everhart-Thornley detector, and a typical acceleration voltage of 5 kV.

[0073] The bonded joints were separated and investigated by a scanning electron microscope (SEM, Figure 7). A mixture of adhesive failure mechanisms and cohesive failure mechanisms was found in both the epoxy and the soy-mal-tan samples, but the differences were clear. The epoxy showed a single clean fracture typical of brittleness. The SEM images of soy-mal-tan were more complex, with some stress lines indicating that mechanical forces were distributed throughout the bulk material. Here too, soy-mal-tan did not seem to be as brittle as the epoxy.

[0074] Similar data for soy-mal-tan adhesives cured at room temperature, 70 °C, and 180 °C showed a somewhat softer fracture, indicating a more ductile material than brittle commercial equivalents. When the bonded joints were separated and investigated by a scanning electron microscope (SEM, Figure 7), a similar situation was seen. A mixture of adhesive failure mechanisms and cohesive failure mechanisms was found in both the epoxy and the soy-mal-tan samples, but the differences were clear. The epoxy showed a single clean fracture typical of brittleness. The SEM images of soy-mal-tan were more complex, with some stress lines indicating that mechanical forces were distributed throughout the bulk material. Soy-mal-tan did not seem to be as brittle as the epoxy.

[0075] These analytical methods indicate that soy-mal-tan is a widely cross-linked matrix in which all three components are involved in covalent bond formation. Epoxidized soybean oil and malic acid were coupled via aliphatic ester bonds. Malic acid also reacted directly with tannic acid via aromatic ester bonds. Perhaps less prominent are the formed esters composed of tannic acid coupled to epoxidized soybean oil.

[0076] Double shear test The adhesive composition was placed between two steel sheets and cured at 180 °C for 3, 18, or 24 hours. A curing time of 24 hours yielded the most promising results. After cooling, the joint was pulled until it broke, and the adhesion was quantified by dividing the maximum force at breakage by the overlapping area of the substrates.

[0077] Double-shear bonding provides a practical means for obtaining large amounts of data with high reproducibility. The adhesion was quantified by dividing the maximum force at breakage by the overlapping area of the substrates when the joint was pulled apart. Different component ratios were investigated for epoxidized soybean oil and tannic acid with either glycerol or malic acid (Figures 1 and 2). Ultimately, the strongest system was epoxidized soybean oil:malic acid:tannic acid (「soy-mal-tan」) at a mass ratio of 1:0.4:0.5. One gram of soy-mal-tan contained approximately 0.4 grams of ethanol to solubilize the tannic acid.

[0078] Bond strength To quantify the performance of soy-mal-tan, its bonding to aluminum and steel, polished or sandblasted respectively, was investigated. Figures 4A and 4B show that this new adhesive system bonded well to each substrate up to structural strengths of 10 ± MPa for sanded aluminum and up to 16 ± 1 MPa for polished steel. Both polished aluminum and sandblasted steel were intermediate at approximately 13 MPa. Controls with only two components were substantially weaker or did not bond at all. Epoxidized soybean oil and malic acid (without tannic acid) bonded at 1.9 ± 0.4 MPa. Malic acid and tannic acid (without epoxidized soybean oil) formed a hard solid with no ability to bond. Epoxidized soybean oil and tannic acid (without malic acid) did not cure to a solid.

[0079] Benchmark evaluations against commercial products are also shown in Figure 6. Each paste was cured according to the manufacturer's instructions (e.g., time, temperature, use of clamps) and applied between substrates in the same amount (about 50 mg) as soy-mal-tan. The two most widely available bio-based adhesives are starch paste and glue. Figure 6A using sandblasted steel substrates shows that the bio-based products bonded at about 0.7 - 1.5 MPa, about one order of magnitude lower than soy-mal-tan. Among the petroleum-derived products, Elmer’s Glue-All (polyvinyl acetate) and Gorilla Glue (polyurethane) were also weak against sandblasted steel at about 1.0 - 1.2 MPa. Here, the bonds of Super Glue (cyanoacrylate, 10 ± 2 MPa) and epoxy (13 ± 2 MPa) were similar to that of soy-mal-tan (13 ± 2 MPa). When used on polished aluminum substrates, soy-mal-tan (13 ± 1 MPa) outperformed all benchmarks including Super Glue (9 ± 4 MPa) and epoxy (7 ± 1 MPa), which are generally considered the two strongest types of structural adhesives (Figure 6B). Figure 6C shows data for polytetrafluoroethylene (Teflon), an exemplary low surface energy substrate. Here, the petroleum-based paste was the strongest (about 0.7 - 1 MPa), but soy-mal-tan (0.3 ± 0.1 MPa) outperformed the commercial bio-based products (about 0 - 0.05 MPa). Similar adhesion data for polished steel, sandblasted aluminum, and polyvinyl chloride (PVC) substrates are also shown in Figures 4A, 4B, and 5.

[0080] Wood is particularly sustainable, and plywood is one of the most widely used building materials. The reaction (70 °C, 5 days) and curing (120 °C, 3 days) conditions were changed for wood. Both soy-mal-tan and most commercial systems achieved bonds that exceeded the strength of the wood (Figure 6D). In Figure 6E, intact adhesive joints and broken wood can be seen. The conditions used for bonding the wood were somewhat extreme, but the fact that substrate failure was observed indicates that parameters that are not as severe may be appropriate for actual use.

[0081] To explore the range of potential usage conditions, soy-mal-tan (1:0.4:0.5 ratio) was applied between polished steel substrates and cured at room temperature for 24 hours. The bond strength of 0.7 ± 0.1 MPa was lower than the bond strength of 16 ± 1 MPa for curing at 180 °C for 6 hours. Alternative curing using a household hair dryer (about 65 °C) for 5 minutes might increase the bond to 1.2 ± 0.5 MPa. For a 5-minute exposure to a higher-temperature laboratory heat gun (about 200 °C), 4.1 ± 0.4 MPa was generated. Table 1 shows similar data for polished aluminum, sandblasted aluminum, and sandblasted steel.

[0082] Some degree of water resistance is necessary to ensure that the product remains intact when faced with difficult conditions. However, the water resistance of current industrial adhesives hinders peeling, recycling of components, and decomposition in landfills. The water resistance of the adhesive was tested. Pairs of bonded polished aluminum substrates were subjected to harsher conditions than many consumer products experience. Joints with a 1.2 × 1.2 cm overlap were cured in air (70 °C, 24 hours or 180 °C, 6 hours), immersed in deionized water for various times, and then the bond strength was measured. Figure 10 shows that soy-mal-tan maintained about 75 - 100% of the initial dry bond strength when in water for 24 hours. Even after 1 week in water, about 26 - 78% of the bond persisted. Similar experiments were conducted in artificial seawater, showing generally similar results, although the loss of bond over time was slightly faster (Figure 10). These two extremes from deionized water to artificial seawater span most aqueous conditions and indicate that the potential role of salts in peeling is small.

[0083] In the control experiment, it was shown that the performance of the epoxy was also affected by salt water. Over a week in water, the average strength of the joints did not change significantly, but the error bars increased dramatically. Epoxy is known to swell in water. Here, it is shown that exposure to water made the epoxy more flexible, and bubbles began to form, and water had penetrated the material. Ground aluminum substrates bonded with soy-mal-tan and cured at 180 °C for 24 hours were subjected to the severe condition of immersion in boiling deionized water for 4 hours (Figure 11). The adhesion of these samples was 3 ± 2 MPa, compared to 15 ± 1 MPa for the control samples left on the table.

[0084] The need for industrial strength with respect to adhesive performance extends over a wide range. For example, packaging is not particularly difficult at 0.5 - 4 MPa. At the other extreme, there are high requirements for the structures of automobiles and aircraft spacecraft at 5 - 30 MPa. It can be difficult to directly compare the numbers, with variables including changes in joint configuration, substrate, environment, and service conditions. Nevertheless, soy-mal tan bonds to metals at about 10 - 16 MPa and may be within the range of requirements for the most demanding applications.

[0085] The lightweighting of automobiles and trucks is an example where new materials can offer further environmental benefits. The change from heavy rivets and welding to adhesive bonding can reduce vehicle weight and improve fuel efficiency. Figure 4B shows how the rocker panel of a pickup truck can be riveted to a cross-section of a steel bar representing the vehicle frame. Also shown is an alternative form using soy-mal-tan for bonding the substrate. Here, the adhesive was cured with a heat gun for 5 minutes. By replacing 36.9 grams of steel rivets with 0.9 grams of glue, the mass of the binder for these assemblies was reduced by approximately 97%.

[0086] CO2 emission data When 1 ton of epoxy is produced and cured, it is estimated that about 5.8 tons of CO2 emissions will occur. In the production of 1 ton of soy-mal-tan, about 11 tons of CO2 are consumed, and in the curing of 1 ton of soy-mal-tan, about 6.6 tons of CO2 are emitted. Therefore, the estimated production and use of 1 ton of soy-mal-tan may absorb approximately 4.4 tons of CO2.

[0087] Furthermore, any of the embodiments described in the following list of clauses are considered to be part of the present invention. A. An adhesive composition comprising (i) an epoxidized oil (EO), (ii) a nucleophile, and (iii) a phenolic compound. B. The adhesive composition according to clause A, wherein the epoxidized oil is epoxidized soybean oil. C. The adhesive composition according to clause A, wherein the nucleophile is a compound comprising a moiety selected from the group consisting of acids, alcohols, amines, and thiols. D. The adhesive composition according to clause C, wherein the nucleophile is selected from fumaric acid, glycerol, malic acid, succinic acid, or a combination thereof. E. The adhesive composition according to clause D, wherein the nucleophile is malic acid. F. The adhesive composition according to clause A, wherein the phenolic compound is selected from catechol, gallic acid, gallol, lignin, tannic acid, or a combination thereof. G. The adhesive composition according to clause F, wherein the phenolic compound is tannic acid. H. The adhesive composition according to clause A or G, wherein the composition further comprises a solvent. I. The adhesive composition according to clause H, wherein the solvent is selected from alcohols, water, chloroform, dichloromethane, dimethyl sulfoxide, and dimethylformamide. J. The adhesive composition according to clause I, wherein the solvent is ethanol or methanol. K. The adhesive composition according to clause A, wherein the EO, nucleophile, and phenolic compound are present in a mass ratio of about 1:0.1:0.1 to about 1:10:10. An adhesive composition consisting essentially of (i) epoxidized soybean oil (ESO), (ii) malic acid, (iii) tannic acid, and (iv) ethanol. M. The adhesive composition according to clause L, wherein ESO, malic acid, and tannic acid are present in a mass ratio of about 1:0.1:0.1 to about 1:10:10. N. An adhered substrate comprising the adhesive composition according to any one of clauses A to M. O. The adhered substrate according to clause N, wherein the substrate is exposed to dry, wet, humid, or underwater conditions. P. The adhered substrate according to clause O, wherein the substrate is metal, wood, plastic, ceramic, or any combination thereof. Q. The adhered substrate according to clause P, wherein the metal substrate is steel or aluminum. R. A method for producing the adhesive composition according to clause A or L, comprising: i) heating an epoxidized oil (EO); ii) mixing a phenolic compound with the epoxidized oil of step (i) to obtain a solution, wherein the phenolic compound is optionally in the form of a solution in a solvent; iii) adding a nucleophile to the solution of step (ii) and heating the solution; and iv) cooling the solution to room temperature whereby an adhesive composition is obtained. S. The method according to clause R, wherein EO is epoxidized soybean oil. T. The method according to clause R, wherein EO and the solution of step (iii) are heated at a temperature of about 70°C to about 90°C. U. The method according to clause R, wherein the solvent is selected from alcohol, water, chloroform, dichloromethane, dimethyl sulfoxide, and dimethylformamide. V. The method according to clause R, wherein the nucleophile is a compound comprising a moiety selected from the group consisting of acids, alcohols, amines, and thiols. W. The method according to clause V, wherein the nucleophile is selected from fumaric acid, glycerol, malic acid, succinic acid, or a combination thereof. X. The method according to clause W, wherein the nucleating agent is malic acid. Y. The method according to clause R, wherein the phenolic compound is selected from catechol, gallic acid, gallol, lignin, tannic acid, or a combination thereof. Z. The method according to clause Y, wherein the phenolic compound is tannic acid. A’. A method of using the adhesive composition according to any one of clauses A to M, comprising the steps of applying the adhesive composition to at least a first substrate adhered to at least a second substrate, and adhering at least the first substrate and at least the second substrate to each other. B’. The method according to clause A’, further comprising the step of applying the adhesive composition to at least the second substrate before adhering at least the first substrate and at least the second substrate to each other. C’. The method according to clause A’ or B’, wherein at least the first substrate and / or at least the second substrate are exposed to dry, humid, wet, or underwater conditions. D’. The method according to clause A’ or B’, wherein at least the first substrate and / or at least the second substrate are metal, wood, plastic, ceramic, or any combination thereof. E’. The method according to clause D’, wherein the metal is steel or aluminum.

[0088] As used herein, the following terms and phrases shall have the meanings defined below. Unless otherwise defined, all technical and scientific terms used herein shall have the same meaning as commonly understood by one of ordinary skill in the art.

[0089] The term "about" can tolerate variations in values or ranges within, for example, 10%, 5%, or 1% of the limits of the recited value or recited range.

[0090] The term "substantially" can tolerate variations in values or ranges within, for example, 90%, 95%, or 99% of the limits of the recited value or recited range.

[0091] The terms "a", "an", or "the" are used to include one or more unless the context clearly dictates otherwise. The term "or" is used to refer to a non-exclusive "or" unless otherwise indicated. Further, phrases or terms utilized herein and not otherwise defined are for illustrative purposes only and not for purposes of limitation. The use of section headings is for assisting in the reading of the document and is not to be construed as limiting. Further, information related to a particular section may appear inside or outside of that particular section. The terms "including" and "having" are defined as comprising (i.e., open language).

[0092] Furthermore, all publications, patents, and patent documents referred to in this document are hereby incorporated by reference in their entirety as if each were individually incorporated by reference. In the event of a conflict in usage between this document and those documents so incorporated by reference, the usage of the incorporated reference shall be considered supplementary to the usage of this document. For irreconcilable conflicts, the usage in this document shall prevail.

[0093] One of ordinary skill in the art will recognize that numerous modifications can be made to the specific implementations described above. The implementations should not be limited to the specific limitations described. Other implementations may be possible.

[0094] The scope of the method and apparatus is intended to be defined by the following claims. However, it should be understood that the present disclosure may be practiced otherwise than as specifically described and illustrated without departing from its spirit or scope. One of ordinary skill in the art should understand that various alternatives to the embodiments described herein may be utilized in practicing the claims without departing from the spirit and scope defined by the following claims.

Claims

1. An adhesive composition comprising (i) an epoxidized oil (EO), (ii) a nucleophile, and (iii) a phenolic compound.

2. The adhesive composition according to claim 1, wherein the epoxidized oil is epoxidized soybean oil.

3. The adhesive composition according to claim 1, wherein the nucleophile is a compound containing a moiety selected from the group consisting of an acid, an alcohol, an amine, and a thiol.

4. The adhesive composition according to claim 3, wherein the nucleophile is selected from fumaric acid, glycerol, malic acid, succinic acid, or a combination thereof.

5. The adhesive composition according to claim 4, wherein the nucleophile is malic acid.

6. The adhesive composition according to claim 1, wherein the phenolic compound is selected from catechol, gallic acid, gallol, lignin, tannic acid, or a combination thereof.

7. The adhesive composition according to claim 6, wherein the phenolic compound is tannic acid.

8. The adhesive composition according to claim 1 or 7, wherein the composition further comprises a solvent.

9. The adhesive composition according to claim 8, wherein the solvent is selected from alcohol, water, chloroform, dichloromethane, dimethyl sulfoxide, and dimethylformamide.

10. The adhesive composition according to claim 9, wherein the solvent is ethanol or methanol.

11. The adhesive composition according to claim 1, wherein the EO, nucleophile, and phenolic compound are present in a mass ratio of about 1:0.1:0.1 to about 1:10:

10.

12. An adhesive composition consisting essentially of (i) epoxidized soybean oil (ESO), (ii) malic acid, (iii) tannic acid, and (iv) ethanol.

13. The adhesive composition according to claim 12, wherein the ESO, malic acid, and tannic acid are present in a mass ratio of about 1:0.1:0.1 to about 1:10:

10.

14. An adhered substrate comprising the adhesive composition according to any one of claims 1 to 13.

15. The adhered substrate according to claim 14, wherein the substrate is exposed to dry, wet, humid, or underwater conditions.

16. The adhered substrate according to claim 14, wherein the substrate is metal, wood, plastic, ceramic, or any combination thereof.

17. The adhered substrate according to claim 16, wherein the metal substrate is steel or aluminum.

18. A method for producing the adhesive composition according to claim 1 or 12, comprising: i) heating an epoxidized oil (EO); ii) mixing a phenolic compound with the epoxidized oil of step (i) to obtain a solution, wherein the phenolic compound is optionally in the form of a solution in a solvent; iii) adding a nucleophile to the solution of step (ii) and heating the solution; and iv) cooling the solution to room temperature thereafter obtaining the adhesive composition.

19. The method according to claim 18, wherein the EO is epoxidized soybean oil.

20. The method according to claim 18, wherein the EO and the solution of step (iii) are heated at a temperature of about 70°C to about 90°C.

21. The method according to claim 18, wherein the solvent is selected from alcohol, water, chloroform, dichloromethane, dimethyl sulfoxide, and dimethylformamide.

22. The method according to claim 18, wherein the nucleophile is a compound containing a moiety selected from the group consisting of acids, alcohols, amines, and thiols.

23. The method according to claim 22, wherein the nucleophile is selected from fumaric acid, glycerol, malic acid, succinic acid, or a combination thereof.

24. The method according to claim 23, wherein the nucleophile is malic acid.

25. The method according to claim 18, wherein the phenolic compound is selected from catechol, gallic acid, gallol, lignin, tannic acid, or a combination thereof.

26. The method according to claim 25, wherein the phenolic compound is tannic acid.

27. A method of using the adhesive composition according to any one of claims 1 to 13, comprising applying the adhesive composition to at least a first substrate to be adhered to at least a second substrate, and adhering the at least first substrate and the at least second substrate to each other.

28. The method according to claim 27, further comprising applying the adhesive composition to the at least second substrate before adhering the at least first substrate and the at least second substrate to each other.

29. The method according to claim 27 or 28, wherein the at least first substrate and / or the at least second substrate are exposed to dry, humid, wet, or underwater conditions.

30. The method according to claim 27 or 28, wherein the at least first substrate and / or the at least second substrate is metal, wood, plastic, ceramic, or any combination thereof.

31. The method according to claim 30, wherein the metal is steel or aluminum.

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