Lubricating greases and engineering polymers are fundamental in this scenario, but their intrinsic performance is rarely sufficient for demanding modern conditions. This is where additives come in: precision chemical components designed to transform a base lubricant or polymer into a high-performance solution.
This technical article explores the world of additives for greases and polymers, detailing their functions, types, and the impact they have on overcoming the most severe tribological challenges, from extreme pressure (EP) to thermal stability.
A lubricating grease is a semi-solid system composed of three elements: a base oil (which provides lubrication), a thickener (which holds the oil in place), and an additive package. Additives, generally making up 0% to 15% of the formulation, are chemical substances introduced to impart new properties or reinforce existing ones. Their primary functions include:
In the polymer sector (plastics, rubbers), additives perform similar functions, such as reducing wear on moving components (nylon gears) or acting as internal lubricants to facilitate processing.
The additive package is a complex mixture. Solid lubricants are a crucial category for high-load applications where the base oil film cannot maintain surface separation.
MoS2 has been the benchmark solid lubricant for decades. Its lamellar structure (similar to graphite) allows it to shear easily under load, creating a low-friction lubricating film.
Advantages of Molybdenum Disulfide
Its main advantage is its proven ability to reduce wear and provide excellent EP performance. It is a robust and well-known additive in the industry.
Common Applications of MoS2
It is widely used in automotive greases, especially in constant velocity (CV) joints, and in industrial applications with heavy, sliding loads, such as in mining or construction.
Synthetic metal sulfides, such as tin sulfide (SnS2) and bismuth sulfide (Bi2S3), have emerged as advanced alternatives to MoS2, offering specialized performance and overcoming some of its limitations.
Advantages of Synthetic Sulfides
They offer exceptional thermal stability, which is crucial in high-temperature applications where MoS2 can oxidize. Furthermore, their synthetic production allows for precise control over particle size and morphology, and their prices tend to be more stable than that of molybdenum.
Common Applications of Synthetic Sulfides
They are ideal for high-temperature greases, lubrication of polymers during processing, and as components in friction materials (brake pads).
Innovamat’s BI Series is a high-purity synthetic bismuth sulfide (Bi2S3) designed as a high-performance solid lubricant.
Advantages of the BI Series
It works by forming a tenacious protective film on metal surfaces. Test data (ASTM D2596 4-Ball EP Test) shows that greases formulated with Innovamat’s BI Series can achieve a Weld Point greater than 3000 N, exceeding the performance of standard MoS2 formulations (approx. 2450 N). Additionally, bismuth offers a cost-stability advantage.
See the Synthetic Metal Sulfide BI10
Common Applications of the BI Series
Formulations for heavy-duty industrial greases, open gear lubrication, metal forming applications, and bearings subjected to shock loads.
This category includes extreme-performance solid lubricants, such as tungsten disulfide (WS2), offered by Innovamat.
Advantages of the WS Series
WS2 offers one of the lowest coefficients of friction among solid lubricants, superior thermal stability, and an extremely high load-carrying capacity. It generally outperforms MoS2 in severe conditions.
Common Applications of the WS Series
Aerospace applications, vacuum systems, ultra-high-performance bearings, and wherever temperature or load exceeds the capabilities of MoS2.
Innovamat’s SN Series is a synthetic tin sulfide (SnS2) engineered for superior thermal stability.
Advantages of the SN Series
Its main advantage is its high-temperature performance. In comparative 4-Ball tests, formulations with the SN Series not only achieve weld points exceeding 3000 N, but also demonstrate a significant reduction in wear scarring compared to MoS2.
Common Applications of the SN Series
High-temperature chain lubricants, greases for polymer extrusion, and as a key component in friction materials requiring high-temperature stability.
Innovamat’s ZN Series is based on ultrafine zinc sulfide (ZnS).
Advantages of the ZN Series
ZnS acts as a white solid lubricant and an EP/AW agent. It is particularly effective in reducing wear in plastics and elastomers and offers good thermal stability.
Common Applications of the ZN Series
Anti-wear additive for polymer compounds (nylon, acetal), light-colored greases, and applications requiring a non-dark solid lubricant.
Combining different solid lubricants can create a synergistic effect, where the blend’s performance surpasses that of the individual components. Innovamat has capitalized on this synergy in its MX, MS, and WL series.
Innovamat’s MX Series is designed for maximum performance, leveraging synergies between advanced chemical compounds.
Advantages of the MX Series
These blends are engineered to offer unparalleled EP/AW performance. 4-Ball test data show exceptionally high Weld Points (exceeding 3900 N) and excellent wear protection, without causing copper corrosion (1b Classification in ASTM D4048).
Common Applications of the MX Series
Top-tier (Tier 1) greases for the automotive industry and critical industrial applications where failure is not an option (e.g., wind turbine bearings, heavy machinery).
Innovamat’s MS Series is designed to offer the best cost-to-performance ratio, positioning itself as a direct, high-performance replacement for MoS2.
Advantages of the MS Series
MS formulations match or improve upon the wear protection of MoS2, but dramatically surpass it in extreme pressure capability (Weld Points > 3900 N vs. ~2450 N for MoS2). This allows formulators to improve EP performance without increasing costs.
Common Applications of the MS Series
Direct replacement for MoS2 in existing formulations, general-purpose EP greases, chassis lubrication, and construction equipment.
For applications where the dark color of MoS2 or graphite is a problem, white solid lubricants are required.
Innovamat’s WL Series is a synergistic blend of white solid lubricants.
Advantages of the WL Series
It offers extreme EP performance, surpassing all other additives in testing (Weld Point > 6000 N) and providing the lowest wear scar (0.42 mm). Being white, it is ideal for clean applications.
Common applications of the WL Series
Food-grade greases (potential H1/H2 registration), textile industry lubrication, paper processing, plastic bearings, and cleanroom applications.
Anti-Wear (AW) additives and Friction Modifiers (FM) create protective films (tribofilms) on metal surfaces. This prevents direct contact between asperities, drastically reducing adhesive wear and the coefficient of friction.
Extreme Pressure (EP) additives, like the synthetic sulfides in Innovamat’s BI, SN, and MX series, are thermally activated under high loads. They react chemically with the metal surface to form a sacrificial layer (e.g., iron sulfide) that is easier to shear than the metal itself, thus preventing welding and component seizure.
In polymers, lubricant additives (like ZnS or SnS2) act as internal lubricants, improving the melt flow of the polymer. This reduces friction in the mold, facilitates demolding, decreases processing equipment wear, and can improve the mechanical and wear-resistance properties of the final product.
A distinct but critical area for polymer additives is flame retardants. Non-halogenated flame retardants are essential for meeting fire safety regulations, an area of specialization for Innovamat.
Unlike brominated or chlorinated systems, non-halogenated flame retardants (such as those based on phosphorus, nitrogen, or metal hydroxides) do not release toxic and corrosive halogen gases when burned. They comply with strict environmental regulations (e.g., RoHS) and offer a safer solution for applications in electronics, construction, and transportation.
Used in bearings, open gears, guides, and chains in industries such as steel, paper, mining, and power generation (e.g., wind turbines). These applications demand high EP resistance (MS, MX series) and often resistance to water and high temperatures (SN series).
Incorporated into nylon, acetal (POM), or PTFE compounds to create “self-lubricating plastics.” They reduce wear in plastic gears, bushings, and seals. White additives (WL series) are preferred to avoid altering the product’s color.
Solid lubricants (MoS2, WS2, WL Series) are dispersed in resins to create dry-film coatings or “Anti-Friction Coatings” (AFC). These coatings provide lifetime lubrication for inaccessible components, such as screw threads or internal mechanisms.
Additives are not optional; they are the technology that enables greases and polymers to withstand modern industrial conditions. While MoS2 has been a mainstay, today’s challenges of higher temperatures, heavier loads, and greater efficiency demand advanced solutions.
Innovamat’s solutions, such as synthetic sulfides (Bismuth, Tin) and synergistic blends (MX, MS, WL Series), are proving to deliver superior performance in Extreme Pressure and thermal stability, providing engineers and formulators with the tools needed to design the next generation of high-performance lubricants and materials.
What factors should be considered when choosing an additive for industrial greases?
The complete “Tribosystem” must be considered:
How do additives affect energy efficiency in industrial systems?
Friction modifiers and solid lubricants (MoS2, WS2) reduce the coefficient of friction between surfaces. A lower coefficient of friction means less energy is lost as heat due to friction. This translates directly into lower energy demand (electricity, fuel) to operate the machinery, improving overall energy efficiency.
What is the difference between organic and metallic additives in tribological applications?
How do additives for polymers improve the properties of plastics and rubbers?They improve properties in two ways:
What is the importance of synergistic additives in grease and polymer formulation?
Synergy occurs when the combination of two or more additives produces an effect greater than the sum of its parts. This is vital because a single additive can rarely solve all problems. For example, an EP additive might protect against welding but slightly increase wear; by combining it with an AW agent, you get both EP protection and low wear. Innovamat’s MX and MS series are examples of how synergy between different sulfides and lubricants creates a product with superior EP and AW performance compared to any single component alone.
Why are formulators looking for alternatives to Molybdenum Disulfide (MoS2)?
Mainly for three reasons: cost, specific performance, and compatibility.
Are there regulatory or environmental concerns about the future of MoS2?
Yes. Molybdenum is a heavy metal, and there is growing global regulatory pressure (similar to REACH) to monitor and limit the use of heavy metals due to their potential for bioaccumulation in the environment. While its use is not banned, this regulatory uncertainty drives formulators to seek more sustainable alternatives with a more favorable environmental profile, such as synthetic bismuth sulfides (BI Series) or optimized blends, to “future-proof” their formulations and align with corporate sustainability goals.
