Polyol Esters: Born for Demanding Lubrications

Essential Facts About Polyol Esters You Need to Know​

 

What is a Synthetic Ester Base Oil?

Ester synthetic oils are produced by esterification and dehydration reactions using organic acids and organic alcohols as raw materials. They are classified into monoesters, diesters, polyol esters, complex esters, and aromatic esters.

 

 

The Emergence of Synthetic Esters?

In the 1930s, driven by the rapid development of Germany's aviation industry and supported by the country's advanced chemical industry foundation, Dr. Heinrich Zorn conducted systematic research that revealed the molecular mechanism behind the easy oxidation of natural esters, laying the scientific basis for modern ester lubricants and providing a theoretical foundation for the subsequent development of ester base stocks.

During World War II, due to the Allied blockade, Germany faced difficulties in obtaining reliable crude oil supplies. At the same time, because mineral lubricating oils back then had poor low-temperature performance, research and development of synthetic lubricants accelerated in response to the need for cold starts in aircraft and tanks under severe freezing conditions. Germany first synthesized diesters suitable for extreme cold and applied them in aero-engine oils.

Modern synthetic esters, especially neo-pentyl polyol esters, is used as lubricant base oils or additives, mainly applied in various types of high-end oil products. They has some performance characteristics that mineral base oils do not have.

Not all synthetic esters is naturally endowed with outstanding performance. Its molecular structure can be flexibly designed through the selection of different organic acids and polyols for esterification reactions. This customizability allows engineers to screening and optimize from a large number of possible molecular combinations to obtain ester structures with ideal properties.

 

It is this "designability" that makes polyol esters become one of the preferred materials in high-end industrial and specialty lubrication fields.

 

What is Polyol Ester?

Polyol ester (POE), is a kind of synthetic lubricant base oil that has excellent performances. It is synthesized by the esterification reaction between a polyol and fatty acids under the presence of a catalyst.

Among them, the neo-pentyl polyol esters (NPEs) is currently the absolute mainstream in high-performance synthetic ester base oils. Especially in applications where extreme demands on thermal stability and oxidative stability, it serves as a core component in many top-tier lubrication formulations.

 

Common polyols used for the synthesis of NPEs includes:

Neopentyl glycol (NPG)- 2 hydroxyl groups

Trimethylolpropane (TMP) or Trimethylolethane : - 3 hydroxyl groups

Pentaerythritol (PE) : - 4 hydroxyl groups

Dipentaerythritol (Di-PE) : - 6 hydroxyl groups

 

 

 

The Advantages of POEs

 

Excellent Low-Temperature Performance

POEs exhibit outstanding low-temperature performance, better than most mineral oils.

Superior Thermal-Oxidative Stability

POE oils with the help of antioxidants have excellent thermal-oxidative stability.

High Viscosity Index

They maintain stable viscosity across a wide temperature range, ensuring consistent lubrication performance.

Improves the Additives' Solubility

The high polarity of POEs helps improve the solubility of additives in formulations based on PAO or hydrogenated base stocks.

Excellent Lubricity

The ester molecules contain both polar ester groups and non-polar hydrocarbon chains. The polar groups adsorb easily onto metal surfaces to form lubricating films, while the hydrocarbon chains enhance oil solubility and reduce friction.

Seal Swell Agent for PAO-Based Formulations

POEs can help expand elastomeric seals in PAO-based lubricants to balance the seal material shrinkage caused by PAO.

Eco-friendly and Biodegradable

Most commercial polyol esters are biodegradable, making them an eco-friendly choice for environmentally sensitive applications.

 

Main Application Fields of Polyol Ester

• Aerospace Industry
• Refrigeration Compressor (Air Conditioning Compressor)
• Automotive engine oil (especially for high-end and racing engines)
• Industrial gear and bearing oils
• Hydraulic fluid (for high-end hydraulic system or special applications)
• Biodegradable lubricants (e.g., chain saw oils, outboard two-stroke engine oil)
• Metal processing fluid

 

What role does polyol ester play in the aerospace industry?

In the field of aerospace, synthetic ester lubricants were originally developed specifically for aviation engines and remains the core choice for aviation lubrication today. It is the extreme and harsh operating conditions of aircraft engines that has driven the continuous evolution and development of ester oils. Even though ester oils is now used in many industrial scenarios, due to its relatively high cost, it still mainly focus on the high-end lubrication market.

 

Why are polyol esters widely used in refrigeration compressors?

 

Refrigeration compressors widely use polyol esters primarily because they can "perfectly miscible" with eco-friendly refrigerants, e.g. HFC R134a, offering excellent miscibility. This ensures the lubricant can flow back to the compressor to provide effective lubrication.

It acts like an "all-purpose oil" that can bear the high temperatures inside the compressor while providing outstanding lubricity to reduce the metal part wear. It can also tolerate small amounts of moisture, helping to protect system stability. It is the most widely used commercial base oil for refrigeration compressor oils.

 

Chorus Lubricants offers high-grade polyol esters​​ specifically designed for extreme conditions. They are widely used in multiple industrial applications.

 

What are the disadvantages of polyol esters?

 

High cost

The biggest limitation of neopentyl polyol esters is their significantly higher price, exceeding that of mineral oil, PAO (polyalphaolefin), and even other synthetic esters.

 

Relatively poor hydrolytic stability

Although neopentyl POEs have good hydrolytic stability, they are still inferior to mineral oil and PAO. Although mineral oil and water can emulsify, hydrolysis is rarely observed.

 

Why is Acid Value a Key Indicator for Assessing Synthetic Ester Base Oil Quality?

 

The main sources of acid value in ester base oils are as follows:

Unreacted Free Fatty Acids

Ester base stocks should not contain residual free fatty acids during production, the lower the better for acid value.

Acid value reflects the precision of the production process. High-quality newly produced synthetic ester oils have very low initial acid values ​​(typically <0.05 mg KOH/g). This initial acid value is a key indicator of the quality of ester base oil.

Degradation

Synthetic ester oils will undergo degradation if they are not properly stored.

In high temperature, high humidity, direct sunlight, and unsealed containers, ester oils will deteriorate rapidly due to the hydrolysis and oxidation reactions.

In transportation and storage, we should pay more attention to ensure that the barrels are well sealed to prevent the ingress of air and moisture.

Once unsealed, the oil should be used within a short time. For daily storage, it should be stored in a cool and dry warehouse, avoiding high temperatures and humidity.

 

​​Chorus^® Lubricants Additive offers high-quality polyol esters with low acid value through a precision process, strict moisture control, and sealed storage.

 

TMP 3970 is a saturated polyol ester synthesized from trimethylolpropane and saturated fatty acids. It is widely used as a synthetic base stock and a lube additive in a wide range of applications.

Get in Touch for the cost-effective​ synthetic ester offers.