Development of Novel Plastics from Soybean and Corn Oils

Grant# 01-03
Principal Investigator: Valerie V. Sheares (Ashby)
Organization: Iowa State University
Technical Area: Renewable Energy

Project Final Report

I. Introduction
In the United States, oil is used more than any other form of energy, supplying approximately 40 of all the energy that the country consumes. In fact, the U.S. uses approximately 25 of the oil used in the world per year. The uses include fuels, lubricants, fertilizers and plastics. Today, only about half of the oil consumed in the U.S. is actually produced here. The continuous, required importation of petroleum comes at a significant cost to the country. Since fossil fuels require considerable processing before they can be used to make the final commercial products, the petroleum-based plastics industry in quite energy intensive. Therefore, new bioplastics that can be prepared from readily available, inexpensive soybean and corn oils should cut the overall energy consumption used to produce these new consumer plastics. Given the state of this major source of energy, we have sought to conduct research that would develop an alternative to petroleum for one of its major and increasing uses, plastics.

During the two-years of funding on this project, the overall goal has been to produce materials ranging from viscous oils to engineering plastics from soybean and corn oils using simple, inexpensive, commercially viable chemistry. Moreover, by partially replacing petroleum products like styrene with soybean and corn oils using well-established industrial processes, the Larock/Ashby technology should help stretch the supply of petroleum feedstocks and facilitate industrial acceptance and introduction of these plant-based plastics. The work that we have accomplished and will do in the future should have the long-term broader impact of decreasing the dependence on imported fuels and the reliance on energy production from nonrenewable, resource-depleting fuels. With the tremendous commercial importance of the plastics industry, it is obvious that even the partial replacement of petroleum-based materials with useful, new bioplastics from renewable, agricultural materials, like soybean and corn oils, will have an impact not only energy-wise, but also economically and environmentally.

Objectives

The specific objectives for the originally proposed three-year project were the following:

1) to optimize the reaction conditions, procedures and processes for a variety of soybean oils, corn oil and comonomers to produce useful materials ranging from oils to plastics and composites;

2) to determine the thermophysical and mechanical properties of the polymers and composites;

3) to correlate the oil structures, reaction formulations and processing techniques utilized with the resulting properties, including damping and shape memory properties;

4) to compare the properties with commercial polymers using standard industrial techniques in order to determine where these new polymers may find commercial utility;

5) to transfer the project results to appropriate audiences through presentations at conferences, journal publications and presentations to industrial parties and to transfer the technology with the help of CATD (the Center for Advanced Technology Development at Iowa State University), and the Iowa
Soybean Promotion Board to potential industrial partners.

III. Research Accomplishments

Year 1 objectives
In Year 1, the following questions were addressed. (1) What are the optimum cationic polymerization conditions necessary to obtain promising materials? (2) How do the changes in the polymerization conditions affect the polymer’s thermophysical and mechanical properties, particularly their damping and shape memory behavior?

Year 1 results
In Year 1, we systematically investigated the cationic copolymerization of soybean oil, low saturation soybean oil (LoSatSoy oil) and conjugated LoSatSoy oil with divinylbenzene comonomer or mixtures of styrene and divinylbenzene. By varying the stoichiometry, the type of soybean oils and comonomers, and reaction times and temperatures, we obtained a variety of promising polymeric materials ranging from elastomers to ductile plastics to rigid and relatively brittle plastics. We investigated the cationic copolymerization process and found that soybean oil not only participates in the copolymerization, but its triglyceride also contributes significantly to crosslinking. A full paper entitled “New Soybean Oil – Styrene – Divinylbenzene Thermosetting Copolymers: VI. Time-temperature-transformation cure diagram and the effect of curing conditions on the Thermosets Properties” was published in the journal Polymer International.

Thermogravimetric analysis (TGA) results showed that these new polymers are thermally stable under 200 °C, and exhibit maximum thermal decomposition at around 450 °C. In other words, our bioplastics have better thermal stability than polyethylene and polystyrene. Dynamic mechanical analysis indicated that these new materials possess glass transition temperatures ranging from 0 °C to 115 °C. The mechanical properties of the soy plastics have also been characterized, including tensile, compressive, flexural, and Izod impact strength according to ASTM standards. The mechanical properties of the soy plastics are comparable to those of commercially available conventional plastics (polyethylene, polystyrene), and close to the lower limit of some commercial engineering plastics, such as unsaturated polyester resins. Two reviews of this work entitled “”Novel Polymeric Materials from Biological Oils” were published in the Journal of Polymers and the Environment, and Polymers and Material Science Engineering.

Our soy bioplastics possess excellent shape memory properties. Those properties were measured and that work was published in a full paper entitled “New Soybean Oil – Styrene – Divinylbenzene Thermosetting Polymers. V. Shape Memory Effect” in the Journal of Applied Polymer Science. We have also measured the excellent damping properties of these materials and determined the damping ratio of a typical soy plastic at a high frequency (1700 Hz). A paper entitled “New Soybean Oil – Styrene – Divinylbenzene Thermosetting Polymers. IV. Good Damping Properties” was published in Polymers and Advanced Technologies.

Finally, in the first year of funding, we experimented with some potential alternatives to relatively expensive divinylbenzene. Two different unsaturated polyester prepolymers were examined. The prepolymers are prepared by the condensation polymerization of maleic anhydride and ethylene glycol. Thus, the prepolymers contain more than three reactive C=C bonds. However, the prepolymers did not mix well with soybean oil before reaction due to their high inherent viscosities. Several series of new soybean oil polymer samples were also synthesized to test the damping ratios at different temperatures and frequencies. A temperature-controlled chamber was designed to do the damping ratio tests. Some experiments also were performed on the fabrication of soybean oil polymer – natural fiber composites, in collaboration with Iowa-based Creative Composites, Inc.

Year 2 Objectives
In Year 2, work was continued on the above-mentioned aspects of this project, while research on the following questions was begun. (1) What correlations can be made between the structure of the oils and the properties of the resulting oils? (2) How do these properties compare to those of present commercial polymers and where might these new polymers find commercial utility? In Year 2, we also examined what other comonomers could be employed in these copolymerization reactions.

Year 2 Results
A variety of new polymers ranging from rubbery materials to tough and rigid plastics were prepared during the second year by the cationic copolymerization of soy oil, styrene and divinylbenzene. The following additional properties were measured on these new materials: modulus of elasticity in tension, ultimate tensile strength, elongation at break, compressive strength, flexural strength and Izod impact strength. We have also carried out more work on the damping properties of the soy oil plastics at higher frequencies.

During this period, various comonomers were examined in the soy oil plastic formulations. Divinylbenzene (DVB) proved to be a good crosslinking agent in soy oil and corn oil polymers. We tried to find other crosslinking agents to replace the relatively expensive DVB. We have found that dicyclopentadiene (DCP), which is as cheap as soybean oil or cheaper, is a good crosslinking agent for natural oil polymers. The resulting polymers are hard solids. However, at room temperature, the polymerization progresses only very slowly. In order to generate hard solid polymers, heat was needed during the curing process. While this leads to nice hard solid polymers in small vials, in the larger molds we use to prepare materials for testing, we were getting much different materials. After running a number of tests, we have found that the manner in which we seal the larger molds is critical to getting good materials and using thicker molds also helps a great deal. We are now ready to actively explore these new DCP-crosslinked materials. We have also tried other monomers, such as vinyl acetate (VA) and butyl vinyl ether (BVE). It was assumed that VA could be used to produce solid materials, but the resulting polymers were weak solids. When BVE was used, the polymerization reaction was very fast, but the resulting polymer was not solid. Because we were looking for strong solid materials, only DCP polymers are being further examined at this stage.

During the second year of this grant, new thermosetting polymeric materials were prepared from the cationic copolymerization of corn oil or conjugated corn oil with styrene and divinylbenzene initiated by boron trifluoride diethyl etherate or related modified initiators. The gel times ranged from a few minutes to hours or even days, depending on the stoichiometry and curing temperatures employed. These polymeric materials possess crosslink densities of 5.0 x 10 – 1.5 x 104 mol/m3 and glass transition temperatures ofTg = 30-99 °C. The materials range from soft rubbers to tough and rigid plastics. The Young’s moduli of these materials vary from 0.6 to 474 MPa; the ultimate tensile strengths vary from 0.5 to 17.6 MPa; the percent elongations at break vary from 2 to 198; the flexural strengths vary from 0.2 to 36 MPa; and the compressive strengths vary from 4.8 to 63.8 MPa. In addition to commercially viable thermophysical and mechanical properties, these new materials also possess good damping and shape memory properties, suggesting numerous, promising applications for these novel corn oil-based polymeric materials. A full paper entitled “Synthesis, Structure, Thermophysical and mMechanical Properties of New Polymers Prepared by the Cationic Copolymerization of Corn Oil, Styrene and Divinylbenzene” will appear shortly in the Journal of Applied Polymer Science.

In the second year of the grant, we also began testing the cationic polymerization of various additional natural oils [peanut, sesame, sunflower, safflower, walnut, linseed and tung oils] with styrene and divinylbenzene to determine the properties of these new plastics. As expected, there appears to be a very good correlation with the number of carbon-carbon double bonds in the oil and the resulting properties. The more double bonds there are, the more crosslinking that takes place and the stronger the resulting materials. We anticipate that we should be able to fine tune the properties of our plastics by adding various amounts of other oils that are either more or less unsaturated than soybean and corn oils and predict the properties of the resulting mixed vegetable oil plastics.

IV. Technology Transfer
The process of transferring this technology to industry has already begun in earnest. Besides publication of our work in appropriate technical journals these last two years, our technology received excellent publicity through an Iowa State University press release, which resulted in articles mentioning our research in the following publications: Alchemist, Farm World, Inform (the magazine of the American Oil Chemist’s Society, which featured us in an article entitled “Bioplastics: A Burgeoning Industry”), Machine Design, ISU Center for Crops Utilization Research (twice). Radio Iowa, the Iowa State University Daily, Industrial Bioprocessing, Wallaces Farmer, and the ISU College of Liberal Arts and Sciences newsletter. During the period 2001-2003, Dr. Larock has also made presentations at Archer Daniels Midland, the American Oil Chemist’s Society national meetings in Minnesota and Kansas City (where his talks both received awards for the outstanding paper in the symposium), DuPont Central Research, a Gordon Conference on biodegradable polymers in England, the Iowa Legislature (a poster), American Chemical Society National Meeting – Division of Polymeric Materials: Science and Engineering – Symposium on Polymers from Renewable Resources, Corn Utilization and Technology Conference in Kansas City (first place poster), Federal University of Rio Grande Do Sul in Porto Alegre, Brazil, Dow Chemical, a conference in Kansas City entitled “Creating Value for Biobased Resources: Moving Beyond Petroleum”, a group of Iowa companies interested in collaborative efforts on bioplastics at the Iowa State University Center for Advanced Technology Development, and Cortec Corp., Minnesota Mining and Manufacturing, and Cargill in the Twin Cities.

We have also been contacted by Atrium Medical in New England about testing some of our new bioplastic materials. They are a major producer of medical stents and were attracted by the mechanical and thermophysical properties of our materials and the fact that they are made from a biorenewable and presumably non-toxic material, soybean oil. Those samples are going to be tested for their toxicity first, before considering potential medical applications.