How to Increase Viscosity Index？
Time：
2026-01-28
How to Increase Viscosity Index?
In the world of high-performance lubricants, temperature is the ultimate adversary. For lubricant manufacturers and additive blenders, the goal is simple yet technically demanding: create a fluid that stays thick enough to protect components at high operating temperatures, yet remains fluid enough to ensure a smooth cold start.
This balance is defined by the Viscosity Index (VI). For B2B procurement managers and formulation chemists, understanding how to increase the viscosity index is not just about meeting technical specs—it is about optimizing cost-efficiency and product longevity.
Understanding the Viscosity Index (VI)
Before diving into the "how," we must address the "why." The Viscosity Index is a dimensionless number that describes the rate of change in viscosity of a fluid in relation to temperature. A high VI indicates that the fluid's viscosity changes very little as the temperature rises and falls. In contrast, a low VI suggests a fluid that thins out rapidly when heated and thickens significantly when cooled.
For industrial applications, high VI lubricants are essential. They provide a more consistent lubricating film, reduce wear, and improve energy efficiency across varying thermal environments.
1. Selecting High-Quality Base Oils
The foundation of any high-VI lubricant is the base oil itself. Not all base oils are created equal. The American Petroleum Institute (API) categorizes base oils into five groups, and your choice here dictates the "baseline" VI of your final product.
- Group II & III (Hydrocracked Oils): These mineral oils have undergone severe processing to remove impurities. Group III oils, in particular, offer a high natural VI (typically $>120$), making them an excellent starting point for synthetic-technology lubricants.
- Group IV (Polyalphaolefins - PAOs): As true synthetics, PAOs possess a naturally high VI, often ranging from 130 to 150. They offer exceptional thermal stability and are the go-to choice for premium automotive and industrial oils.
- Group V (Esters and others): Esters can be engineered to have incredibly high VIs and are often used as co-bases to improve the performance of Group III or IV formulations.
2. The Power of Viscosity Index Improvers (VIIs)
While base oil selection is critical, the most effective way to significantly increase the viscosity index is through the addition of Viscosity Index Improvers (VIIs). These are high-molecular-weight polymers that change their physical structure based on temperature.
The Mechanism of Action
At low temperatures, these polymer chains stay "coiled" up in a tight ball, which has a minimal effect on the oil's viscosity. As the oil heats up, these polymer chains "uncoil" or expand. This expansion increases the internal friction (viscosity) of the fluid, effectively countering the natural thinning of the base oil.
3. Choosing the Right Additive Chemistry
For a supplier like Chemost, offering the right chemistry is key. Different VII polymers offer different benefits:
- Olefin Copolymers (OCP): These are the most widely used VIIs in the industry. They are cost-effective and provide excellent thickening power. They are ideal for heavy-duty engine oils and general-purpose lubricants.
- Polymethacrylates (PMA): PMAs are often used in hydraulic fluids and gear oils. They not only increase the VI but also act as pour-point depressants, improving low-temperature fluidity.
- Hydrogenated Styrene-Diene (HSD): Known for their excellent shear stability, these are often found in high-end multi-grade engine oils where the lubricant must withstand intense mechanical stress without breaking down.
4. Balancing VI with Shear Stability
When increasing VI, manufacturers must consider Shear Stability. High-molecular-weight polymers are susceptible to "shearing"—literally being chopped into smaller pieces by the mechanical action of gears or pistons. Once a polymer shears, it loses its ability to increase the VI, leading to permanent viscosity loss.
In B2B formulations, the challenge is to find the "Sweet Spot": a polymer large enough to increase the VI significantly, but robust enough to resist mechanical shear over the entire service interval of the oil.
5. Synergy in Additive Packages
Increasing the viscosity index is rarely done in isolation. A professional additive package—the core business of Chemost—integrates VIIs with anti-wear agents, detergents, and antioxidants.
For instance, the interaction between a VI improver and a dispersant can affect the overall "thickening efficiency." By using a pre-formulated additive package, manufacturers ensure that the chemistry is balanced, preventing "additive dropout" and ensuring that the high VI remains stable throughout the lubricant's lifecycle.
The Economic Impact for B2B Clients
For lubricant wholesalers and manufacturers, increasing the VI of your product line offers a competitive edge:
- Reduced Energy Consumption: High VI oils reduce internal fluid friction during cold starts, saving energy.
- Extended Drain Intervals: Better thermal stability means the oil lasts longer before oxidizing.
- Market Positioning: Being able to market a "High VI" or "Multi-grade" lubricant allows for premium pricing and entry into the automotive and aerospace sectors.
Conclusion
Increasing the viscosity index is a sophisticated science of polymer selection and base oil synergy. Whether you are formulating a 5W-30 engine oil or a high-pressure hydraulic fluid, the choice of Viscosity Index Improver is the most critical decision in your formulation process.
At Chemost, we specialize in providing high-performance additive packages and VII solutions designed to meet the rigorous demands of modern machinery. By focusing on molecular stability and chemical synergy, we help you deliver lubricants that perform when the heat is on.
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