Youdaoplaceholder0 Index Improver introduction
Youdaoplaceholder0 Index Improver, usually translated into Chinese as Viscosity Index Improver or viscosity enhancer, is a high-molecular polymer additive added to lubricating oil (mainly engine oil, hydraulic oil and gear oil, etc.). Its core function is to improve the viscosity-temperature performance of lubricating oil, that is, to reduce the fluctuation range of lubricating oil viscosity with temperature changes.

1. Core concept: Viscosity Index and the Challenges Faced by Lubricating Oil
To understand its function, one must first grasp two key points:

The viscosity of lubricating oil: It is an indicator for measuring the internal flow resistance of lubricating oil and directly affects the formation and thickness of the oil film. Viscosity is one of the most important properties of lubricating oil.

Viscosity-temperature characteristics: The viscosity of almost all lubricating oils changes with temperature - as the temperature rises, the viscosity decreases. When the temperature drops, the viscosity increases.

What problems will this change bring?

At high temperatures: If the viscosity becomes too low, an oil film of sufficient strength cannot be formed, causing direct contact between metal parts and accelerating wear.

At low temperatures: If the viscosity is too high, the lubricating oil will become as thick as syrup, causing difficulty in starting the engine, high pumping resistance, resulting in starting wear and insufficient fuel supply.

The viscosity index is a quantitative indicator that measures the degree to which the viscosity of lubricating oil changes with temperature. The higher the VI value, the less the viscosity of the lubricating oil changes with temperature, and the better its viscosity-temperature performance.

Viscosity index improvers were developed precisely to enhance the VI value of lubricating oil.

2. Functions and Benefits
By increasing the viscosity index, the improver can bring the following key benefits:

Realizing multi-grade oil: This is its most revolutionary contribution. It enables a single type of lubricating oil to simultaneously meet the viscosity requirements at both high and low temperatures, such as the common 5W-30, 10W-40, etc.

The number before "W" (such as 5W) indicates low-temperature viscosity. The smaller the number, the better the low-temperature fluidity.

The number after "W" (such as 30) indicates high-temperature viscosity. The larger the number, the higher the strength of the oil film at high temperatures.

Offer a wider operating temperature range: Enable the lubricating oil to provide effective protection in both extremely cold and hot environments, making it an all-weather oil.

Reduce engine starting wear: Excellent low-temperature fluidity ensures that the lubricating oil can quickly reach all lubrication points during cold starts.

Enhance high-temperature protection: Ensure that sufficient oil film strength is maintained even when the engine is under high load operation.

Potential fuel economy: By optimizing friction and reducing resistance during cold starts, it helps to lower fuel consumption.

3. Mechanism of Action
Viscosity index improver is an oil-soluble high-molecular polymer. Its physical form in oil changes with temperature, thereby ingeniously regulating viscosity.

At low temperatures: The polymer molecular chains in the oil are tightly curled into small balls, causing little hindrance to the flow between lubricating oil molecules. Therefore, it basically does not increase the viscosity of the lubricating oil at low temperatures, ensuring good low-temperature fluidity.

At high temperatures: The polymer molecular chains stretch out due to thermal motion, expand in volume, and form huge, loose linear structures. These stretched macromolecules will greatly increase the flow resistance between lubricating oil molecules, thereby effectively preventing the excessive decrease in the viscosity of the lubricating oil at high temperatures.

A vivid metaphor: Just like a bowl of clear soup and a bowl of soup with starch added.

Clear soup (without improvers) : It becomes very thick when cold and becomes thin when hot, with a significant change in viscosity.

Soup (with improvers) : It won't be overly thick when cold and won't become too thin when hot, maintaining a more stable state.
Viscosity index improvers are like "smart thickeners" in lubricating oil. They "expand" in hot weather to maintain viscosity and "contract" in cold weather to reduce resistance.

4. Main chemical components
The commonly used viscosity index improvers are usually the following types of high-molecular polymers

Polymethacrylate

Olefin copolymer

Hydrogenated styrene-diene copolymer

Polyisobutylene

5. An important challenge: Shear stability
Viscosity index improvers are not flawless; they face a major challenge: mechanical shear.

The source of the problem: In components with high shear stress such as high-speed gears and engine bearings, the huge mechanical force will cut these long polymer molecular chains.

Consequence: Once the polymer molecules are cut, their viscosity-increasing capacity (especially at high temperatures) will permanently decline, resulting in a reduction in the actual viscosity of the lubricating oil, which may no longer meet the design requirements.

Solution: Therefore, developing viscosity index improvers with high shear stability is one of the core technologies. Molecular structure design (such as the introduction of long-chain alkyl side chains) helps to enhance its shear resistance.