Polyurethanes are an important class of polymers because of their wide industrial applications in automobiles, construction, household appliances, medicine, packaging, furniture, thermal, and electrical/vibration insulations. There is a global effort to replace petrochemicals with compounds from renewable resources. We propose to use soybean oil for the preparation of non-isocyanate polyurethanes using a cost-effective method that can be used for consumer as well as industrial applications. We plan to synthesize non-isocyanate polyurethanes using soybean oil-based compounds as a substitute for petrochemical-based polyols. Soybean oil-based non-isocyanate polyurethanes will be used for foams, coatings, and adhesives industries.

Traditional polyurethane synthesis stems from the polyaddition reaction of diisocyanates and diols, both of which are largely derived from fossil fuel sources. The isocyanates are produced from hazardous and toxic phosgene gas by the phosgenation process. Phosgene is an extremely toxic gas. Additionally, the isocyanates are toxic and moisture-sensitive and cannot be prepared without sophisticated safety devices, thus posing serious environmental and human health risks. Consequently, a strong thrust has been directed to polyurethanes that avoid diisocyanates and have a reduced carbon footprint.
This proposal provides a solution to both problems. We propose to synthesize non-isocyanate polyurethanes using soybean oil-based compounds as a substitute for petrochemical-based polyols. We will also use carbon dioxide during the synthesis of non-isocyanate polyurethanes which is a global warming gas. The conversion of carbon dioxide into value-added and safe chemicals is very attractive to industries and environmental protection agencies. Non-isocyanate polyurethane-based foams, coatings, and adhesives will be developed for industrial applications.

There has been increased demand for the utilization of renewable materials for industrial applications. Soybean oil will be applied for value-added applications in polyurethanes, coating, and adhesive industries. The global polyurethane market size was estimated at over $72 billion in 2021, exhibiting a CAGR of 4.3% over the forecast period of 2022-2030. The market is driven by the presence of stringent environmental regulations designed by various regulatory bodies. Environmental concerns are likely to continue playing a key role in the formulation and use of these materials. The proposed research on soybean oil-based value-added materials will provide new pathways to utilize a large quantity of soybean oil providing greater value for the soybean farmers. The initial seed money from the Kansas Soybean Commission will help us to develop technology for commercialization. The societal impact of this project is significant as this proposal provides an opportunity for students to be involved in research, education, and product development. The outcome of this research will be used for business development, which will provide economic development to the State of Kansas. We expect to have a patent, two graduate thesis, and three peer-reviewed publications. The outcome of the project will be presented in seminars at Pittsburg State University and at conferences (after protecting intellectual properties). These seminars will be opened to the public to enhance community involvement in science and education. This will be a great platform to create public awareness regarding the value-added applications of soybean oil.

Updated January 9, 2025:
We started by creating a special type of soybean oil called carbonated soybean oil (CSBO) from regular soybean oil (SBO). This involved two steps and some testing to ensure it worked. We checked the results with tools like FT-IR (a way to analyze chemical bonds) and measured how thick the liquid was at room temperature. Later, we used a method called 1H NMR to confirm that the CSBO was successfully made. Once we had the CSBO, we experimented with adding certain chemicals called diamines and triamines to see how they affected its ability to act as an adhesive. These included isophorone diamine (IPDA), meta-xylylenediamine (m-XDA), and tris(2-aminoethyl)amine (TAA). We wanted to understand how reaction time, temperature, and the amount of these chemicals would influence the adhesive’s strength.

Initially, we mixed CSBO with IPDA in a 1:3.5 ratio and tested it at various temperatures—room temperature, 30°C, 50°C, 70°C, and 80°C—for 24 hours. We used FT-IR to monitor how the chemical reaction progressed, which showed a decrease in a particular bond (carbonate carbonyl peak) as the temperature went up. We then tested how strong the adhesive was on wood and found that curing it at 70°C gave better strength than curing it at 50°C. However, even at 70°C, some of the original chemical bonds didn’t fully react. Next, we changed the ratio of CSBO to IPDA to 1:4 and 1:2.5, trying different curing temperatures again (50°C, 70°C, and 90°C). We found that at a 1:4 ratio and 70°C, the chemical bonds completely reacted. But when we increased the temperature to 90°C, some bonds reappeared, and the adhesive became weaker. This suggested that too high a temperature might reverse part of the reaction. We also studied the adhesive's thermal properties. Using a method called DSC, we found that the material changed from rigid to soft at around 31°C (its glass transition temperature). We also used TGA to see how it reacted to heat in an oxygen-free environment.

To explore how reducing the amount of IPDA would affect the adhesive, we tested a 1:2.5 ratio at various temperatures. The results showed that the best adhesive strength occurred with a ratio of 3.5–4.0 parts IPDA to 1 part CSBO, cured at 70°C for 24 hours. This was consistent with our earlier findings. We then repeated similar tests with another chemical, m-XDA. Using a 1:2.5 and 1:3.0 ratio of CSBO to m-XDA, we monitored the reactions at 50°C, 70°C, and 90°C, over different times ranging from 1 to 24 hours. We discovered that at 70°C, the 1:2.5 mixture needed about 20 hours to mostly complete the reaction, while the 1:3.0 mixture needed only 16 hours. Both ratios showed good progress in reducing the carbonate carbonyl peak.

Afterward, we increased the m-XDA ratio to 1:3.5 and tested the adhesive strength at 70°C for 12, 16, and 24 hours. We found that curing for 16 hours gave the highest strength, at nearly 5 MPa (a measure of pressure or strength). Interestingly, increasing the curing time to 24 hours didn’t make much difference, and raising the m-XDA ratio further to 1:4 actually reduced the adhesive's strength. We studied the thermal properties of the adhesive made with the 1:3.5 ratio of m-XDA. It softened at around 19°C and showed stability at higher temperatures when tested in an oxygen-free environment. However, when we increased the m-XDA ratio to 1:4, the adhesive became weaker, likely because of incomplete reactions or disruptions in the structure. Finally, we tried a third chemical, TAA, combining it with CSBO in ratios of 1:2.0, 1:2.5, and 1:3.0. We tested these mixtures at 50°C, 70°C, and 90°C, for times ranging from 1 to 5 hours. The FT-IR analysis showed that a 1:2.5 ratio cured at 70°C for 3 hours was the most effective. Unfortunately, when we tested the adhesive on wood, it failed, likely because of poor bonding or improper curing conditions.

In summary, we found that the best adhesive results were achieved using specific conditions: for IPDA, a 1:3.5–4.0 ratio of CSBO to diamine cured at 70°C for 24 hours, and for m-XDA, a 1:3.5 ratio cured at 70°C for 16 hours. The attempts with TAA were less successful, and further work is needed to improve those results. Throughout, we used careful monitoring and testing to optimize the reactions and understand how each factor affected the final adhesive properties.

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Polyurethanes are used in the production of flexible foams (39%), rigid foams (26%), coatings (13%), binders (4%), elastomers, and adhesives. The global polyurethane market size was valued at USD 72.82 billion in 2021 and is expected to expand at a compound annual growth rate (CAGR) of 4.3% from 2022 to 2030. Over 24 million metric tons of polyurethane were used globally in 2021. Utilizing soybean oil for such a huge industry will generate a demand of ~ 15 million metric tons of soybean oil (over 3 billion soybean bushels) per year. Kansas ranked 10th in soybean production among US states. Soybeans will provide a good source of raw material for the polyurethane industry. Creating advanced materials and technologies using soybean oil will provide financial benefits to soybean growers.