A guide to epoxidized soybean oil — what it is, how it stabilizes and plasticizes PVC, and how it compares with phthalate plasticizers — from a US-based distributor.
Epoxidized soybean oil (ESBO) is a bio-based plasticizer and heat stabilizer made by epoxidizing soybean oil. Its epoxide groups absorb the hydrochloric acid that PVC releases as it degrades, improving heat and light stability, flexibility, and plasticizer permanence. Stratus Chemical supplies ESBO in drums and totes, with COA and SDS.
| Chemical name | Epoxidized soybean oil |
|---|---|
| CAS number | 8013-07-8 |
| Synonyms | ESBO, ESO, epoxidized soya oil, soybean oil epoxidized |
| Type | Bio-based plasticizer, heat stabilizer, acid scavenger |
| Grade supplied | Oxirane oxygen >6.8% |
| Packaging | 455 lb drums, 2,274 lb totes |
Epoxidized soybean oil is refined soybean oil whose carbon–carbon double bonds have been converted to epoxide (oxirane) rings, usually by reaction with hydrogen peroxide and an organic acid. The result is a pale yellow, low-odor liquid that is compatible with PVC and many other polymers.
The epoxide rings are what make it useful. When PVC is heated during processing, or exposed to light in service, it releases hydrochloric acid, which accelerates further breakdown and causes yellowing and brittleness. ESBO’s epoxide groups react with that acid and remove it, which is why ESBO works as a co-stabilizer alongside calcium-zinc and other metal-soap stabilizers. At the same time, its long fatty-acid chains soften the polymer, so one additive does two jobs.
| Appearance | Pale yellow liquid |
|---|---|
| Odor | Mild, oily |
| Oxirane oxygen | >6.8% |
| Iodine value | <2.5 mg/g |
| Acid value | <1.0 mg/g |
| Water | <0.10 wt% |
| Color, APHA | <150 |
| Specific gravity at 25 °C | 0.9280–1.0020 |
| Refractive index at 25 °C | 1.4690–1.4730 |
| Viscosity, Brookfield at 25 °C | 320–340 cP |
| Pour point | 32 °F |
| Volatile loss, 160 °C / 2 h | <0.02% |
Typical values. The Certificate of Analysis for each lot governs. Oxirane oxygen and iodine value are the two numbers to check: high oxirane oxygen means more acid-scavenging capacity, and a low iodine value confirms the double bonds were fully epoxidized.
This is the dominant use. ESBO goes into flexible PVC film, sheet, hose, wire and cable jacketing, flooring, and gaskets, and into semi-rigid and rigid compounds. It is typically dosed at a few phr as a co-stabilizer with calcium-zinc stabilizers, and higher when it is also doing plasticizer work; the right level is established by trial. Its very low volatility (<0.02% loss at 160 °C over two hours) helps the finished part keep its flexibility over time.
ESBO is used as a grinding liquid for pigment dispersions and color concentrates for PVC, where it wets pigment and adds stabilizer to the compound at the same time.
The same acid-absorbing chemistry protects chlorinated hydrocarbons and chlorinated resins, soy-based printing inks, lubricants, and metalworking and cutting oils from acid build-up.
ESBO plasticizes PVC and PVA emulsions, chlorinated rubber, nitrocellulose, and neoprene.
The epoxide rings can be opened to make bio-based polyols for polyurethanes and to build polyester resins, giving formulators a renewable feedstock.
| ESBO | Primary plasticizers (DINP, DOTP) | |
|---|---|---|
| Source | Bio-based (soybean oil) | Petrochemical |
| Main role | Co-stabilizer plus secondary plasticizer | Primary plasticizer |
| Heat and light stabilization | Yes — scavenges HCl | No |
| Volatility | Very low | Low |
| Compatibility at high loading | Limited — can exude | Good |
| Low-temperature flexibility | Weaker | Better |
| Phthalate-free | Yes | DINP: no; DOTP: yes |
How to choose: ESBO rarely replaces a primary plasticizer outright. Its strength is doing two jobs — stabilizing and plasticizing — in a small dose, and lowering the phthalate content and carbon footprint of a compound. At high loadings it can migrate to the surface and it gives less low-temperature flexibility than DINP or DOTP, so most flexible PVC formulas use ESBO alongside a primary plasticizer rather than instead of one.
Cold weather. ESBO has a pour point of about 32 °F, so it thickens sharply in cold storage. Keep drums and totes indoors above freezing, or warm them before pumping.
Keep it dry and away from acids. Water and strong acids open the epoxide rings and reduce oxirane oxygen — the property you are paying for. Keep containers closed and store in a cool, dry, well-ventilated area away from incompatible materials.
Wear appropriate personal protective equipment and wash after handling. COA and SDS are provided with every shipment.
Epoxidized soybean oil (ESBO) is used mainly as a plasticizer and heat stabilizer in flexible, semi-rigid, and rigid PVC compounds, where it scavenges the hydrochloric acid released as PVC degrades. It is also used as an acid scavenger in chlorinated hydrocarbons, soy-based inks, lubricants, and cutting oils, as a plasticizer for chlorinated rubber, nitrocellulose, and neoprene, and as an intermediate for polyols and polyesters. Stratus Chemical supplies ESBO in drums and totes.
The CAS number for epoxidized soybean oil is 8013-07-8. It is also known as ESBO, ESO, or epoxidized soya oil.
ESO and ESBO are two abbreviations for the same material, epoxidized soybean oil (CAS 8013-07-8). ESBO is more common in PVC and packaging, while ESO is used more often in coatings and chemical-intermediate markets.
Oxirane oxygen is the percentage of epoxide oxygen in epoxidized soybean oil and is the main measure of its quality. The epoxide groups are what react with hydrochloric acid to stabilize PVC, so higher oxirane oxygen means more acid-scavenging capacity. Stratus Chemical’s ESBO is typically above 6.8% oxirane oxygen, with an iodine value below 2.5 showing near-complete epoxidation.
Yes. Epoxidized soybean oil is a bio-based, phthalate-free plasticizer made from soybean oil. It is usually used alongside a primary plasticizer such as DOTP or DINP rather than as the only plasticizer, because it improves heat stability and lowers volatility but has limited compatibility with PVC at very high loadings.
Epoxidized soybean oil is typically used at a few parts per hundred resin (phr) in PVC as a co-stabilizer with calcium-zinc or other metal-soap stabilizers, and at higher levels when it also serves as a secondary plasticizer. The right level depends on the compound and is established by trial, watching heat stability and any surface exudation.
Store epoxidized soybean oil in closed containers in a cool, dry, well-ventilated area away from strong acids and other incompatible materials. Its pour point is about 32 °F, so it thickens in cold weather and may need warming before pumping. Keep containers sealed to protect the low water content.
Stratus Chemical supplies epoxidized soybean oil in 455 lb drums and 2,274 lb totes, with a Certificate of Analysis and Safety Data Sheet on every shipment. To get pricing, send Stratus Chemical the volume and delivery location through the quote form and you will receive a response within one business day.
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