Poly(styrene-butadiene) (SBR) rubber compounds have wide applications for conveyor belts for various harvesting equipment due to its excellent mechanical and wear properties and relatively low price. The disadvantage of SBR rubber is the high coefficient of friction (COF) resulting in overheating of moving conveyor parts with the resulting thermal damage of the belt. The use of externally applied surface lubricants provides only a temporary solution. The currently available fatty acid-derived slip additives (FASA) reduce COF but have limited application due to uncontrolled migration to the surface (bloom).
In this project, we will develop new soybean oil (SBO)-based additives for low-friction rubber. Our previous research has shown that chemically modified SBO has good compatibility with SBR and can replace petroleum-based processing oils in SBR rubber formulations. The further modification of SBO with polar functional groups will provide the required properties for SBO based additives, such as the controlled migration to the surface of the rubber and lubricating effect. Our preliminary experiments showed that SBO modified with polar functionalities when added to the SBR compound in an amount of 3% reduces the friction of steel on SBR rubber by 45%. The properties of modified SBO such as the number of functional groups and molecular weight can be tuned in order to control the migration and provide optimal lubrication.
In this project, a new soy-based product for the rubber industry will be developed which will improve the performance of rubber used in belting for harvesting equipment applications and also increase the use of soybean oil.

In this project, we will develop a new soybean oil-based additive for low-friction rubber. We will be looking for the new compounds synthesized from soybean oil that will be compatible with poly(styrene-butadiene) (SBR) rubber, but also possess the functional groups that will drive the additive to the surface of rubber constantly providing a thin “slip” layer. The new additive will reduce the coefficient of friction (COF) of SBR rubber providing the lubricating effect. The lowfriction SBR rubber formulated with the soy-based additive will be used for the manufacturing of conveyor belts and rubber belts for harvesting equipment with improved properties such as reduced friction and friction heat and increased wearing resistance.

The project deliverable will be the identification of the chemical structure of additive for SBR rubber synthesized from soybean oil that will reduce a COF for SBR rubber with controlled migration to the surface of the rubber. The concentration of the soy-based additive in the SBR compound will be optimized. Other project deliverables will include project final report and the possibility of publication of results in a scientific journal and/or submitting a patent application.

Updated November 25, 2020:

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Updated June 29, 2021:

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The objective of this project was to evaluate the potential of modified soybean oils (SBO) as additives for poly(styrene-butadiene) (SBR) rubber compounds for reduction of coefficient of surface friction of the rubber. SBR rubber is widely used for the manufacturing of conveyor belts and rubber belts for various agriculture harvesting equipment. SBR rubber has good mechanical strength and durability but has a high coefficient of friction (COF) which leads to overheating and damaging of the rubber belt. Chemically modified soybean oils were studied as additives to SBR rubber compounds. The compounds were vulcanized and tested for surface friction after different periods of time. Two modified SBOs were selected as additives that reduce surface friction. One additive is partially hydrogenated soybean oil (PHSO) which is an inexpensive commercial product having wide application in the food industry, cosmetics, and household products. The second additive named SOFA was synthesized by chemical modification of SBO with polystyrene and a fluoroacrylate. Both modified SBOs demonstrated reduction of surface friction of rubber compared to the reference rubber (see figure).
The SBR compounds were formulated with carbon black, petroleum-based aromatic oil, and different amounts of the modified soy-based additives. For some compounds, the petroleum-based oil was completely replaced with soy-based additives. Compounds were vulcanized and tested for mechanical properties. The results demonstrated that PHSO improves the mechanical properties of rubber such as tensile strength and hardness. SOFA slightly reduces the tensile strength of rubber but provides a stable reduction of surface friction. Both PHSO and SOFA can be used as additives for SBR compounds with enhanced mechanical and improved surface properties.
This project has identified a new potential use for soybean oil in industrial applications: for the modification of the surface friction properties of rubber compounds.

The development of soy-based additive for low-friction rubber will benefit North Dakota soybean farmers in two direct ways. First, the use of soybean oil for new material for agriculture equipment applications will be increased. According to Future Market Insight, the market for agriculture and food grade conveyor belt in the USA is forecasted to rich $3 Billion in 2020. The company WCCO Belting Inc. in Wahpeton, ND, provided us with the numbers for the estimation of the amount of soybean oil that can be used by WCCO alone. The amount of rubber that the company will use for 0.039” thick cover for tube conveyor slider back applications is approximately 290,000 lbs per year. The estimated amount of soy-based additive for this amount of rubber will be 11,600 lbs/year. To produce this amount of additive, 12,900 lbs/year of soybean oil or 1,102/year bushels of soybeans will be needed. If the low friction additive will work, WCCO can use the additive for many other rubber compounds for industrial belts requiring a low COF, so the required amount of soybean oil will grow to higher volumes if other companies also start using the soy-based additive for their compounds.
The second benefit for soybean farmers will be the improved performance of their harvesting equipment, longer service life, and lower maintenance cost.