Summary
Scalability and commercial-scale production have been and continue to be unresolved engineering problems for most of the successfully produced bench-top “green” chemicals, particularly products derived from soybean byproducts. In this project, the research team will build upon the success they realized from prior synthesis method using soybean-derived gallic acid (GA) create a critically important epoxy resin for food packaging applications.
The team aims to synthesize new thermoset materials in this project using bio-based building blocks extracted from soybean byproducts. The new bio-based epoxy resins will be constructed by incorporating Gallic Acid (GA), Phytic Acid (PA), and 1,3-Propanediol (PD), with a focus on applications related to internal can coatings intended for food packaging. GA from soybean milk residue was once again selected as a building block due to its bio-based availability, multifunctionality, rigidity, and antioxidant and non-toxic properties. This rigid aromatic unit can be substituted for the harmful fossil fuel-based aromatic monomers commonly used in food and beverage can coatings. PA, a well-known non-toxic compound, can also be extracted from soybeans in high quantities during the soymilk and biofuel production processes. This compound forms stable complexes by chelating to minerals, making it beneficial for anticorrosion applications; therefore, PA will be used for its anti-corrosive characteristics and as a soybean-derived epoxy hardener. PD, a safe bio-based compound, will also be utilized to further modify the resin’s thermal and mechanical properties by imparting additional flexibility into the crosslinked network.

Goals
Upon successful completion of this project, a novel bio-based epoxy resins derived from soybean processing byproducts for food and beverage can coatings will be produced. The obtained materials will replace the harmful fossil fuel-based thermosets frequently employed in metal food packaging.

Benefit to Consumers, Manufacturers, and Soybean Farmers
The globally increasing demand for soybean products, including soymilk and tofu, has prompted a reconsideration of several production byproducts previously considered as waste. These products are now considered valuable raw materials that offer alternative solutions to harmful fossil oil-based counterparts. Consequently, soybean producers have an opportunity to diversify their product offerings and help them overcome challenges related to growing and trade fluctuations, especially in ND, where the annual revenues from soybean production averaged $2.3 billion between 2018 and 20204. This project will directly benefit ND soybean farmers by adding value to soybeans as a crop and agricultural byproduct.

Research hypothesis
To date, food industries have been heavily dependent upon use pf petro-based monomers to produce crosslinked thermosets that can be used effectively as an anti-corrosive layer between the food and the metal container. Toxic monomeric building block and degraded polymer products can leach into preserved food, causing severe health effects. Hence, it is hypothesized in this project that a new and viable alternative can coating epoxies can be produced using gallic acid from soybean processing.

Project Justification and Rationale
The global production of bio-based polymers from agricultural residues has increased remarkably since 2013. The global bio-based polymer market is forecasted to increase at a CAGR of 5.50% between 2022 and 2029, reaching a value of USD 12.16 billion by 20296. Developing safe, bio-based materials from non-food renewable resources adds value to agricultural byproducts due to this anticipated growing demand for sustainable products. Recent advancements in agro-industrial byproduct extraction methods have resulted in several valuable aromatic and aliphatic compounds that can replace their petro-based counterparts, especially in the production of bio-based polymers for food packaging. Effective food preservation and extended shelf life are crucial factors that food production industries must consider, especially in the canned food production sector. Manufacturers have relied heavily on the use of petro-based epoxy resins as lining materials for food and beverage cans to prevent metal corrosion and food contamination since the 1960s. Several recent research studies, however, have revealed that petro-based epoxy resins can leach into food, causing adverse health effects, especially in women and children. Accordingly, using petro-based epoxy resins, particularly bisphenol-A (BPA), in infant feeding bottles and children's food manufacturing has been banned in several EU countries, and five states in the USA. Investments in alternative bio-based epoxy resins from agro-industrial byproducts are very much needed and they align strongly with growing trends in the industrial landscape as they move toward green, responsible, and safe goods, along with the expected changes in BPA-based epoxy safety classifications. This work aims to produced alternative from readily accessible building units via well-established synthetic approaches and scaled up to industrial levels.

Methods
The aims of this project will be accomplished by conducted five primary tasks: 1) synthesizing the GA-based Tetraglycidyl ether of gallic acid (TEGA) monomeric building block, 2) synthesizing the diglycidyl ether of 1,3-propanediol (DEPD) precursor, 3) producing the bio-based epoxy resin, 4) thermally treating and characterizing the synthesized monomeric building blocks, and 5) mechanically test and optimize the physical properties, along with the anticorrosion performance of the obtained coatings. These five tasks should be completed within the 12-month duration of the research grant.

Potential Barriers to Achieving Anticipated Results
Challenges related to phytic acid thermal stability are expected during the thermal curing process; therefore, we will test thermal curing at temperatures ranging from 50 to 140°C. A previous study has reported that the gradual increase in thermal curing temperature, up to 200 °C, does not promote phytic acid instability11 due to the partial incorporation of phytic acid into the material structure during the curing process. The monomers synthesized via the one-step approach have produced low-yield pure products, less than 60%12. Accordingly, we propose testing the two-step synthetic method as an alternative strategy to achieve the target monomers at higher yields. A comparative analysis of both methods will be conducted to determine the most cost-effective approach, considering costs and percentage yields.

The primary objective of this project is designing and producing new thermosets as alternative materials to fossil fuel-based resins for canned food coating applications at the University of North Dakota’s (UND’s) Chemical Engineering Department. These polymers contain non-toxic building blocks and can be substituted for the potentially carcinogenic fossil fuel-materials in food packaging applications. These designed materials are composed of naturally occurring components that may pose a low risk to human health in the event of resin degradation and monomer release.

The expected deliverables from this project include a new, cost-effective, and safe bio-based epoxy resins derived from soybean processing byproducts for food and beverage can coatings. The produced materials will replace the BPA-based thermosets frequently employed in metal food packaging.

Updated November 28, 2024:
Research Overview and Objectives
With this work, the PI aims to synthesize new thermoset materials in this project using bio-based building blocks extracted from soybean byproducts. The new bio-based epoxy resins will be constructed by incorporating Gallic Acid (GA), Phytic Acid (PA), and 1,3-Propanediol (PD), with a focus on applications related to internal can coatings intended for food packaging. GA from soybean milk residue was once again selected as a building block due to its bio-based availability, multifunctionality, rigidity, and antioxidant and non-toxic properties. This rigid aromatic unit can be substituted for the harmful fossil fuel-based aromatic monomers commonly used in food and beverage can coatings, such as Bisphenol A (BPA). PA, a well-known non-toxic compound, can also be extracted from soybeans in high quantities during the soymilk and biofuel production processes. This compound forms stable complexes by chelating to minerals, making it beneficial for anticorrosion applications; therefore, PA will be used for its anti-corrosive characteristics and as a soybean-derived epoxy hardener. PD, a safe bio-based compound, will also be utilized to further modify the resin’s thermal and mechanical properties by imparting additional flexibility into the crosslinked network.

The PI aims to design new thermosets as alternative materials to fossil fuel-based resins for canned food coating applications at the University of North Dakota’s (UND’s) Chemical Engineering Department. These polymers contain non-toxic building blocks and can be substituted for the potentially carcinogenic BPA materials in food packaging applications. These designed materials are composed of naturally occurring components that may pose a low risk to human health in the event of resin degradation and monomer release. The project objectives are encapsulated in discrete tasks below.

Task 1 – Tetraglycidyl ether of gallic acid (TEGA) synthesis
GA-based monomer synthesis will be tested using two well-established synthetic approaches (Figure 1). The synthetic routes will be compared in terms of the monomer’s production cost, yield, and purity. Approach 1: GA will be reacted with an excess of epichlorohydrin in the presence of a catalytic amount of tetrabutylammonium bromide (TBAB) using a one-step synthetic approach9. Afterward, a sodium hydroxide solution (20%, w/w) will be added to the reaction mixture under vigorous stirring to obtain the target monomer. Approach 2: A GA- based monomer will be reacted with allyl bromide in the two-step synthetic method10. The allylated product will then be transformed into its tetraglycidyl ether using m-chloroperbenzoic acid and triethyl amine as a catalyst.

Task 2 – Diglycidyl ether of 1,3-propanediol (DEPD) synthesis
Similarly to Task 1, diglycidyl ether of 1,3-propanediol will be synthesized via one- and two-step synthetic approaches. Both approaches will be tested to compare the monomer’s production cost, purity, and percentage yield (Figure 2).

Task 3 – Soybean-derived epoxy resin synthesis
The bio-based epoxy resin will be synthesized by mixing different ratios of TEGA and DEPD with PA. The molar ratio of the PA to epoxy groups will be varied, and the thermal curing step will be tested at temperatures ranging from 50 to 140°C (Figure 3).

Task 4 – Thermal behavior and spectral characterization
The synthesized monomers will be characterized using nuclear magnetic resonance (1H and 13C NMR) and infrared (IR) spectroscopy. The new epoxy resins will be characterized using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and infrared (IR) spectroscopy. The resin’s thermal properties will be tuned by varying the TEGA/DEPD ratios. Additionally, the influence of the curing conditions (time, temperature, humidity) on the material’s thermal stability will be explored.
Task 5 – Mechanical properties and anticorrosion behavior
Dynamic Mechanical Analysis will be used to study the thermosets' stress relaxation behavior, and a mechanical testing machine will be used to measure the tensile properties. Similarly to the previous task, the influence of the monomers' molar ratio and curing conditions on the mechanical properties will be investigated. Additionally, the anticorrosion behavior of the developed coating materials will be investigated using salt spray testing and adhesion testing.


Completed Work: Deliverables and/or Milestones
For Task 1, tetra-allylated gallic acid (AGA) was synthesized at high yield of 82% in preparation as a feedstock to synthesize tetraglycidyl ether gallic acid (TEGA).

Gallic acid glycidylation was achieved through a two-step chemical synthesis process. First, the hydroxyl groups of gallic acid were allylated with the assistance of an alkaline catalyst, resulting in tetra-allylated gallic acid (AGA). In the second step, the double bonds in AGA were epoxidized to produce a mixture of glycidylated gallic acid derivatives. The allylation was carried out using various synthetic reagents and optimized reaction conditions to achieve a high yield of the tetra-allylated AGA monomer. Several reaction protocols from the literature were tested and refined to optimize the yield (Table 1). The choice of solvent, reaction temperature, and the molar ratios of reagents were carefully varied and controlled to determine the optimal conditions for the allylation step.

TEGA was then synthesized and, among the mono- di-, and tri- byproducts, the desired tetraglycidyl ether gallic acid synthesis was achieved with a yield of 80% (Figure 4)


Progress of Work and Results to Date
As this is the first progress report, the completed work listed above is also the progress/results to date.

Work to be Completed
The next steps are applying lessons learned in Task 1 to start Task 2. In the meantime, we will finish scaling up the reaction to increase the yield of the tetraallylated product, followed by the epoxidation step using mCPBA to obtain allyl 3,4,5-tris(allyloxy)benzoate. The ratio of tetra-, tri-, di-, and mono-allylated products will again be characterized using GC-MS analysis.

Other Relevant Information
Unforeseen blockers prevented the estimated completion of Task 1 on time. Primarily, the low yield of AGA from the initial synthesis routes prompted additional tests for confirmation before varying the experimental conditions to improve the yield. This variance included more time consulting the literature and cross-examining experimental conditions and results of multiple studies. However, now that the correct conditions have been realized, further progress into the project can proceed. The silver lining here is that the same solutions that were found in Task 1 will also be applied to Task 2 since it uses the same synthesis route. We can therefore say with confidence that Task 2 will take significantly less time than Task 1.

Barring other unforeseen blockers, the potential blocker listed in the proposal submission remains on the horizon: the thermal stability of phytic acid for Task 4. However, the mitigation strategy of using temperatures ranging from 50 to 140°C should prove sufficient as a previous study has reported that the gradual increase in thermal curing temperature, up to 200 °C, does not promote phytic acid instability due to the partial incorporation of phytic acid into the material structure during the curing process. Additionally, the time to test these temperatures is also baked into the project schedule.

Summary
The PI aims to synthesize new thermoset materials in this project, with a focus on applications related to internal can coatings intended for food packaging, using bio-based building blocks extracted from soybean byproducts: Gallic Acid (GA), Phytic Acid (PA), and 1,3-Propanediol (PD). GA can be substituted for the harmful fossil fuel-based aromatic monomers commonly used in food and beverage can coatings, such as Bisphenol A (BPA). PA forms stable complexes by chelating to minerals, making it beneficial for anticorrosion applications; therefore, PA will be used for its anti-corrosive characteristics and as a soybean-derived epoxy hardener. PD will further modify the resin’s thermal and mechanical properties by imparting additional flexibility into the crosslinked network. The project objectives encompass five tasks throughout the period of performance. Task 1 was delayed due to low yields of the tetra-allylated gallic acid (AGA) feedstock stemming from the reaction conditions outlined in the literature. These low yields have since been improved, and the AGA used to synthesize the target tetraglycidyl ether gallic (TEGA) with a yield amongst other byproducts of 80%. Further improvements will be made to the yield of AGA, but Task 2 is set to start and take full advantage of the lessons learned in Task 1, significantly reducing the risk of further delays.

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The globally increasing demand for soybean products, including soymilk and tofu, has prompted a reconsideration of several production byproducts previously considered as waste. These products are now considered valuable raw materials that offer alternative solutions to harmful fossil oil-based counterparts. Consequently, soybean producers have an opportunity to diversify their product offerings and help them overcome challenges related to growing and trade fluctuations, especially in ND, where the annual revenues from soybean production averaged $2.3 billion between 2018 and 20204. This project will directly benefit ND soybean farmers by adding value to soybeans as a crop and agricultural byproduct.