Castor oil (ricinoleic acid triglyceride)
A plant oil that is a polyol straight from nature: castor oil’s built-in hydroxyl groups make it a classic bio-based ingredient in moisture-tolerant polyurethanes.
Castor oil is pressed from the seeds of Ricinus communis. About 90% of its fatty acid content is ricinoleic acid, which carries a hydroxyl group on its chain. That gives castor oil an OH number around 160–168 mg KOH/g and an average functionality of roughly 2.7.
Castor oil and its derivatives are used in polyurethane coatings, potting and encapsulating compounds, sealants and elastomers. It adds flexibility, water resistance and hydrophobicity, and its long fatty chains help formulations tolerate damp conditions better than many polyether systems.
From an OH number of about 164, the equivalent weight is roughly 342 g/eq. The secondary hydroxyl groups are less reactive than primary ones, so catalysts are commonly used. Its fatty-acid structure yields hydrophobic, flexible networks with good electrical insulating properties.
Castor oil itself is low in hazard. Use dehydrated, low-moisture grades for isocyanate systems and keep containers sealed.
Yes. It comes directly from castor beans and is one of the few plant oils that naturally carries hydroxyl groups, so it can be used as a polyol with little modification.
Its long hydrophobic fatty-acid chains repel water, which helps castor-based polyurethanes resist moisture during and after cure.
