The Future is Modified
These days, selecting additives for engine oils requires careful consideration, as the search for better fuel economy continues. Philip Reeve peers into the formulators cauldron to examine the role viscosity modifiers play.
New lubricant requirements for internal combustion engines continue to be driven by environmental regulations, particularly fuel economy and emissions control. These regulations aim to reduce carbon dioxide, a greenhouse gas, oxides of sulfur and nitrogen and particulates in an effort to improve air quality and play a part in mitigating climate change.
Original equipment manufacturers continually make changes to vehicle hardware to meet these new regulations. New lubricant quality specifications from industry bodies and OEMs then follow to provide protection for the latest passenger car, motorcycle and commercial vehicle engines.
As new lubricant requirements for ICE crankcases emerge, this will drive formulation changes. Viscosity modifiers, or viscosity index improvers, have a key role to play in future lubricant formulations. How will the market change to meet these challenges and how will the product options develop?
Finding a Purpose
Lubricant base oil viscosity drops rapidly as the temperature rises. VMs are added to a lubricant formulation to better control the rate of change of viscosity with temperature. They are used to make multigrade oils as defined in the SAE J300 Viscosity Grade Classification.
Multigrade oils have good low-temperature properties, allowing the engine to turn over and pump the oil when cold. This is combined with acceptable viscosity/oil film thickness under high-temperature conditions to give operational protection. The vast majority of engine oils used worldwide contain VMs and they are a key part of the lubricant formulators chemistry options.
VMs used in crankcase oils are oil-soluble polymers and have a high molecular weight. There is a range of chemistry types available, including polymethacrylates, olefin copolymers and hydrogenated styrene/diene. The polymer architecture can be linear or based on a star shape.
Additionally, the molecular weight of the polymer can be varied. Higher molecular weight tends to reduce the polymer treat rate. However, it makes the lubricant more susceptible to viscosity loss due to polymer shearing. A further variant is the addition of dispersancy onto the polymer making a dispersant VM.
Lubricants are continuing along a trend toward lighter viscosity grades to support improved fuel economy. But as oil viscosity decreases, this creates a greater challenge to formulators to ensure satisfactory durability. For lighter viscosity grades, higher-quality API Group II and Group III base stocks are needed. They have better volatility, viscosity and temperature characteristics than Group I base stocks. Greater use of Group II and Group III tends to reduce demand for VMs.
The emerging growth in very low-viscosity oils, such as SAE 0W-16 or 0W-20, is expected to result in reduced demand for VMs. The treat rate of VMs in these formulations is very low (or zero) compared with wider viscosity grades such as 5W-30 or 10W-40.
On the other hand, residual lower-quality monograde oils in emerging markets are slowly moving to multigrades, which increases VM demand.
Erika Vela, the global VM portfolio manager for United Kingdom-based additive company Infineum, told LubesnGreases that the overall size of the VM market will continue to grow for several years.
The increased demand through switches from monogrades to multigrades is expected to overwhelm any reductions from greater use of Group II and III base stocks. Additionally, there are benefits to using VMs in very low-viscosity oils. The temporary viscosity loss arising from the VM enables or can lead to improved fuel economy, she said.
Supply Chain Complexity
Lubricant blending plants are often under operational pressure to manage both the number of materials held and the quantity of inventory. Adding a new component to the portfolio requires extra tankage and drum storage space, as well as possibly additional investment. VMs are typically supplied in a dissolved form, as a polymer concentrate in a base oil. These products require storage or heating typically to around 100 degrees Celsius in order for them to be pumped into blend vessels. In some cases, the polymer is supplied in solid form and lubricant blend plants can dissolve the polymer themselves into their own base oil. Although this creates a dissolved VM in situ, it does however require an initial capital outlay and incurs higher operational costs.
The major additive companies will usually run engine test programs with their own VM. This is understandable from an economic perspective, allowing product volumes from a program to be maximized through sales of both the additive package and associated VM. This helps offset the program investment versus supporting sales of a competitive VM.
For the lubricant blender though, it adds to complexity. Ideally, blenders look for two or three VMs that they can use across a range of product types and applications, rather than stock multiple VMs that marry up with each suppliers additive package.
Stocking more additives at a manufacturing site increases complexity, so is not a preferred solution for lubricant blenders, Rolfe Hartley, an independent chemicals consultant, told LubesnGreases.
Testing can be conducted for VM interchange between different suppliers, but this incurs additional engine testing expense as an extension of the original core engine test program. VM interchange is not always possible and can add even further expense when OEM-approved products are in question, becoming an impractical and costly solution.
Looking to the future, polymer suppliers continue to explore newer chemistry variants. These can be incremental improvements of existing products, for example, to improve specific properties such as treat rate or in-service shear stability.
Other new products are primarily looking to improve fuel economy. In some specific OEM applications at very low viscosity, newer polymethacrylate VMs have been used to support fuel economy improvements. Other new products have also been introduced specifically for low-viscosity oils in response to the implementation of new fuel economy driving cycles. They are designed to contract at critical operating temperatures to reduce viscosity contribution.
There is also scope for greater use of dispersant VMs. The dispersant is a component of the additive package and usually makes a substantial contribution to viscosity.
A dispersant VM can or may create a different balance between viscosity and wear protection, Vela said, while Hartley added, The viscometric debits due to the dispersant can be minimized by using a dispersant VM. However, the potential benefits have not yet been fully demonstrated.
The outlook for the VM market is complicated, but fundamentally total demand is anticipated to continue growing in the short term. The key driver of this growth is the ongoing move away from monograde oils in emerging markets, despite lower demand for VMs, as higher-quality base stocks are more prevalent.
Lube oil marketers will continue to seek simplification in the blend plants. However, the wide variety of VM suppliers and product options, high VM interchange test costs, the lack of OEM flexibility and an economic drive for additive companies to sell their own VMs combine to make simplification a significant hurdle. Vela also sees the continued need for different chemistry options in order to meet OEM requirements, as the type of VM can significantly influence an engines performance.
The challenge for new VM technology is to create products that have improved formulation viscometrics to support fuel economy benefits. Technically advanced VMs for fuel economy are available and they have been tested in very low-viscosity grade products. There is potential for dispersant VMs, but this remains to be fulfilled through new products.
The market drivers for improved fuel economy and OEM-approved products are in place. If the commercial return on the lubricants are strong enough then lube blenders should be willing to accept the increased operational complexity.