Castor Oil PP: A Technical Deep Dive into Polyurethane Grade Castor Oil

1. Technical Overview

Castor Oil PP (Polyurethane Polyol) Grade is a high-purity, refined triglyceride specifically engineered for the polyurethane (PU) industry. Unlike standard industrial grades, the PP grade is strictly monitored for its hydroxyl value consistency and ultra-low moisture content. In the chemistry of polyurethanes, castor oil acts as a natural, bio-based trifunctional polyol.¹ The secondary hydroxyl group located on the 12th carbon of the ricinoleic acid chain reacts with isocyanates to form urethane linkages. Castor Oil PP is essential for manufacturers seeking to produce elastomers, coatings, and sealants with high hydrolytic stability and excellent electrical insulation properties.

2. Chemical Structure & Composition

The molecular profile of Castor Oil PP is dominated by the triglyceride of Ricinoleic acid (²$C_{18}H_{34}O_3$).³

• Ricinoleic Acid (~90%): Provides the three-armed (trifunctional) structure necessary for cross-linking.

• Secondary Hydroxyl Groups: The placement of the -OH group in the middle of the fatty acid chain provides steric hindrance, resulting in a controlled reaction rate with isocyanates compared to primary polyols.

• Saturated Fatty Acids: Minimal presence of stearic and palmitic acids ensures the polyol remains a clear liquid for uniform blending.

3. Physical & Chemical Properties

• Appearance: Pale yellow, clear, and bright liquid.⁴

• Viscosity: 6.5 – 8.5 Stokes at 25°C, providing a manageable viscosity for RIM (Reaction Injection Molding) or manual mixing.

• Hydroxyl Value: 160 – 168 mg KOH/g, a critical parameter for stoichiometric calculations in PU formulations.⁵

• Moisture Content: Strictly limited to <0.10% (often lower) to prevent side reactions with isocyanates.

• Acid Value: Low (<1.0) to prevent interference with catalysts.

4. Reaction Chemistry

In PU synthesis, Castor Oil PP reacts with diisocyanates (such as MDI or TDI):

1. Stoichiometric Balance: The Hydroxyl (OH) value of the PP grade allows chemists to calculate the exact Isocyanate Index.

2. Cross-linking: The trifunctionality leads to a network structure, providing better heat resistance and mechanical strength than difunctional linear polyols.

3. Hydrolytic Stability: Due to the hydrophobic nature of the long hydrocarbon chains, PU resins made with Castor Oil PP exhibit superior resistance to water and humidity.

5. When to Use vs. When NOT to Use

Use Castor Oil PP when:

• Manufacturing potting compounds for electronics where high dielectric strength is required.

• Producing high-performance floor coatings (PU Screeds) and waterproof membranes.

• Formulating bio-based PU foams or elastomers to increase “Green” carbon content.

Do NOT use Castor Oil PP when:

• The application requires a rigid, high-density foam that needs a high-functionality synthetic polyol (functionality > 4).

• The formulation is a water-based system where a specialized water-dispersible polyol is needed instead of a pure oil.

6. Compatibility Profile

Castor Oil PP exhibits excellent synergy with:

• Synthetic Polyols: Can be blended with polyether or polyester polyols to adjust flexibility and cost.

• Catalysts: Highly compatible with organometallic catalysts (Dabco, DBTDL).

• Fillers: Excellent wetting properties for calcium carbonate, silica, and barium sulfate.

7. Manufacturing Process (Product Focus)

The production of PP Grade involves advanced refining:

1. Double Filtration: To remove all suspended solids that could act as nucleating agents in foams.

2. Chemical Neutralization: To achieve an ultra-low Acid Value, preventing catalyst deactivation.

3. Vacuum Dehydration: The oil is subjected to intensive vacuum drying at elevated temperatures to strip moisture to levels below 0.05% – 0.10%.

4. Batch-to-Batch Standardization: Each lot is tested specifically for Hydroxyl value to ensure the customer doesn’t need to change their Isocyanate ratio.

8. Technical Specifications Table

Parameter	Specification (PP Grade)
Appearance	Pale Yellow, Clear & Bright
Hydroxyl Value (mg KOH/g)	160 – 168
Moisture Content (Karl Fischer)	0.10% Max (Target 0.05%)
Acid Value (mg KOH/g)	1.0 Max
Iodine Value (Wijs)	82 – 90
Saponification Value	176 – 187
Specific Gravity (at 30°C)6	0.954 – 0.9607
Color (Gardner)	2.0 Max

9. Quality Grade Analysis

The hallmark of Castor Oil PP is its Moisture Control. While “First Special Grade” (FSG) allows for up to 0.25% moisture, the PP grade is strictly controlled. In polyurethane chemistry, moisture reacts with isocyanates to produce ⁸$CO_2$ gas.⁹ Excessive moisture in the polyol leads to unwanted pinholes, bubbles, and “foaming” in what should be a solid elastomer or coating.

10. Impact of Impurities

• Moisture: Causes brittle films and surface defects due to $CO_2$ gas evolution.

• High Acid Value: Neutralizes the amine catalysts used in PU reactions, leading to slow or incomplete curing.

• Particulates: Can cause electrical failure in potting compounds.

11. Industry-Wise Application 1: Electrical Encapsulation

Castor Oil PP is widely used in potting and encapsulation of transformers and capacitors. Its low moisture and high purity provide excellent insulation and protect sensitive components from vibration and moisture.

12. Industry-Wise Application 2: Industrial Flooring

In PU-Concrete and self-leveling floors, the PP grade acts as the binder. It provides the necessary toughness to withstand heavy machinery and the chemical resistance needed for food processing plants.

13. Industry-Wise Application 3: Coatings & Adhesives

Used in the production of solvent-free adhesives and high-solids coatings. The resulting films are flexible, show excellent adhesion to various substrates, and do not become brittle over time.

14. Industry-Wise Application 4: Bio-Lubricants

Though primarily a PU grade, its low moisture and acid value make it a premium choice for high-performance biodegradable lubricants where oxidative stability is enhanced by the removal of impurities.

15. Formulation Guide

• Dewatering: Even though Castor Oil PP is low-moisture, if the user adds fillers (like pigments), it is recommended to degas the entire polyol-filler blend under vacuum before adding the isocyanate.

• Catalyst Dosage: Start with 0.02% to 0.1% DBTDL based on the total polyol weight to achieve the desired pot life.

16. Sustainability Data

Castor Oil PP is a 100% bio-based polyol. It allows PU manufacturers to replace petroleum-derived polyols with a renewable resource, contributing to a lower Carbon Footprint for the finished product.

17. Packaging & Logistics (Technical)

• Standard: 200kg Epoxy-lined MS Drums (to prevent metal ions from leaching into the polyol).

• Bulk: ISO Tanks with nitrogen padding.

• Seal Integrity: Once opened, drums should be used immediately or re-sealed with a nitrogen blanket to prevent atmospheric moisture absorption.

18. Storage Science

Castor Oil PP is hygroscopic (it attracts moisture). It must be stored in a dry, temperature-controlled environment. If stored in bulk, the use of desiccant breathers on storage tanks is mandatory to ensure the oil remains “dry” for PU reactions.

19. Troubleshooting Guide

• Problem: Bubbles in the cured elastomer. Solution: The polyol has likely absorbed moisture; check the moisture content via Karl Fischer titration.

• Problem: Tacky surface after cure. Solution: Check the Isocyanate Index; if the Hydroxyl value of the polyol lot has changed, the isocyanate dosage may need adjustment.

20. Regulatory Compliance

Our Castor Oil PP is REACH Compliant and produced under strict quality management systems (ISO 9001:2015), ensuring it meets the rigorous demands of the global chemical industry.

21. Safety (SDS Summary)

• Handling: Wear protective eyewear and gloves. Non-toxic.

• Fire: High flash point (>280°C). Use foam or dry chemical.

• Disposal: Dispose of according to local environmental regulations; do not allow large quantities to enter water systems.

22. Sample Validation Process

For PU manufacturers, we recommend a “Gel Time” test using your standard isocyanate and catalyst package. This confirms the reactivity profile of the Castor Oil PP batch in your specific system.

23. Commercial Efficiency

Using Nova Industries’ Castor Oil PP reduces the need for in-house vacuum dewatering, saving time and energy costs for the end-user. The high batch-to-batch consistency ensures a 99% first-time-right production rate.

24. Technical FAQs

1. Can I use FSG instead of PP grade? Only if your application is moisture-insensitive. For elastomers and coatings, the higher moisture in FSG will likely cause defects.

2. Is this oil compatible with MDI and TDI? Yes, it reacts efficiently with all common aromatic and aliphatic isocyanates.

3. Does it require heating before use? Generally no, but if stored below 15°C, warming to 25°C will ensure consistent viscosity for metering pumps.

25. Contact CTA

For technical data sheets, Isocyanate Index calculation support, or to request a sample of our PP Grade, please contact our technical export team at: export@novaind.in