Chemical Structure and Properties

Epoxidized soybean oil (ESO) is produced by reacting soybean oil with epichlorohydrin under alkaline conditions. This process causes the double bonds in the unsaturated fatty acids in soybean oil to undergo epoxidation, introducing oxygen-containing epoxy groups into the fatty acid chains. The chemical structure of ESO consists of epoxy rings attached to esters of oleic, linoleic, and linolenic acids, the main fatty acids present in soybean oil.

The epoxy groups introduce new physical and chemical properties compared to regular soybean oil Epoxidized Soybean Oil is a viscous yellowish liquid at room temperature with low volatility. It is insoluble in water but soluble in many organic solvents. The presence of epoxy groups makes ESO reactive and able to crosslink and polymerize when combined with other chemicals and under certain conditions. Its reactivity allows it to function as a plasticizer, polymer additive, or resin.

Epoxidized Soybean Oil Uses as a Plasticizer

One of the major uses of ESO is as a plasticizer, especially as a replacement for phthalate plasticizers which are considered toxic. As a plasticizer, ESO is added to polymers like polyvinyl chloride (PVC) to make them softer and more flexible. The epoxy groups in ESO can react with hydrogen atoms on the polymer chains during processing, forming covalent bonds that mechanically entangle the polymer molecules. This plasticizing effect increases the workability and flexibility of rigid polymers.

ESO has excellent plasticizing efficiency compared to phthalates. It allows polymers to maintain good properties even at lower plasticizer concentrations. Studies have shown PVC formulations plasticized with ESO to be fully compatible, with equal or improved properties in terms of processability, strength, and long-term performance. ESO does not have the potential toxicity issues associated with phthalate plasticizers and it enhances the eco-friendliness of plasticized products. For these reasons, it has gained widespread adoption as a sustainably-sourced replacement for phthalates in applications like films, cable jacketing, flooring, toys, and medical devices.

Epoxidized Soybean Oil Uses in Coatings and Adhesives

Another major market for ESO is in coatings and adhesives. The epoxy functionality of ESO allows it to react and polymerize as part of coating or adhesive formulations. In coatings, it serves as a reactive diluent or co-polymerizer that improves the film properties of paints, varnishes, and lacquers. ESO provides flexibility, hardness, abrasion resistance, corrosion protection, and adhesion when used in these applications.

In structural and multi-purpose adhesives, ESO functions as a crosslinking agent that reacts with other components to strengthen the bond between substrates. Its low volatility also helps prevent bubbles in bonded joints. ESO is especially useful in epoxy-based wood flooring adhesives and metal or fiberglass laminating resins where high bond strength is required. The natural sourcing and renewable nature of ESO makes it preferable to petroleum-derived equivalents in terms of sustainability.

Other Applications

Beyond plastics and coatings/adhesives, ESO has found use in a number of other applications due to its unique chemical structure and reactivity. It is used as a stabilizer or emulsifier in agriculture applications like fertilizers and pesticides. In construction materials, it improves water resistance in stucco, plaster, and tile adhesives.

ESO functions as a reactive diluent or precursor in epoxy resins that are used to manufacture laminates, printed circuit boards, composites, and molds. Due to its low polarity, ESO is also added as a co-monomer in latex paints to enhance water resistance and block staining. In personal care products, it functions as a thickening agent and stabilizer particularly for mineral-based sunscreens and foundations.

Potential Drawbacks and Alternatives

While ESO clearly has sustainability advantages over petroleum-derived alternatives, it does have some disadvantages to be aware of. Its high viscosity can pose processability challenges. Furthermore, the oxirane groups in ESO impart reactivity that requires control during processing and storage to prevent premature reactions. Excessive heat exposure could cause it to discolor or degrade. Its solubility in organic solvents also raises disposal considerations compared to water-soluble products.

For applications where the reactivity or cost of ESO is not ideal, other bio-based alternatives exist. Examples include polyol esters from vegetable oils which function similarly to phthalates as non-reactive plasticizers. Glycerol esters are also effective plasticizers with better clarity but lower functionality than ESO. Epoxidized Castor Oil is a drop-in replacement with higher oxirane content but greater expense than ESO. Overall, ESO remains one of the leading green chemistry substitutions for petrochemical plasticizers and polymer additives due to its favorable properties and value.

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