Surfactants: structure and sustainability

Surfactants are a vital component of many cellular polyurethane formulations. They control bubble formation and opening, keep mixtures of ingredients together, and speed up reactions. Simon Robinson looks at the trends affecting this class of additives.

There are many players in the surfactants business, but UTECH-polyurethane.com/ Urethanes Technology International was fortunate to be able to talk to three of the larger players: Dow Chemical, which recently took full ownership of Dow Corning; Evonik, which recently completed the purchase of Air Products’ catalyst business; and Momentive.

In foaming formulations, it appears there is a delicate balancing act between surfactant and catalyst. This is why both Dow and Evonik feel that recent business restructurings have given them expertise they previously lacked.

Dow Chemical took full ownership of Dow Corning, formerly a 50:50 joint venture with Corning, in 2016. The Dow Corning business now operates within Dow as its Performance Silicones business.

Integrate where you can

“This combination of silicones and polyurethanes is very exciting for us,” said Richard James, global segment leader for polyurethane additives at Dow Performance Silicones. "It brings together Dow Corning and Dow Chemical, which is very strong in the polyether and organic side of the molecule. In the surfactants sphere, we are the most back-integrated provider globally, second to none.

"We also have a clear line of communication from the silicone through the polyether to help us get closer to customers, and help them innovate," James says. "Dow is very strong on the polyol, isocyanates, and polyurethane systems side, and has the infrastructure, research and development and sales that Dow Corning lacked. Combining Dow and Dow Corning has created a business with novel surfactants that we can bring closer to the customer."

Integration at Evonik is much less advanced, as the purchase of Air Products’ catalyst business was only finalised early in January 2017; we will examine this in greater detail in a forthcoming issue of Urethanes Technology International. However, staff from both Evonik and Air Products sides of the company took part in a call about surfactants in early January, and the company is excited by the prospect of integrating of the two sides of the formulation coin.

As with so much polyurethane technology in recent years, the interior of the car's cockpit has been an important development space for surfactants, and polyurethane foam formulations in general. Because of its enclosed nature, the automotive cockpit can contain a much higher concentration of emissions from the components within it than a relatively well ventilated room.

Pressure in the cockpit

Tony Lanchak, vice president and general manager at Momentive said: “We have an advantage in the automotive area, with a strong global R&D footprint. This gives us opportunities to address regional needs, while having a clear global strategy.” The company claims to be the leader in stabilisers for automotive foams.

Annegret Terheiden, global technical director for moulded foam at Evonik, explained that there is more to a low VOC foam than simply the nature of the surfactants. “You have to consider the whole formulation,” she said. “It is difficult to discuss emissions purely from a surfactant point of view.”

Stephan Wendel, Evonik’s ADTS Manager Europe, agreed. "You need to find the right play between surfactants and amine catalysts and the silicone,” he said.

Pace of change

“The speed at which automotive regulations are being modified in the marketplace and the diversity of the standards by OEM and geographical region is a major challenge for us,” added Chris Clark, global moulded technical leader at Momentive. “We hope that this will eventually harmonise globally.”

Dow’s James believes that the OEMs are the real driving force behind regulation. “Automobiles are a hot confined space,” he said. “In that space, whatever is emitted, whether it's from the catalyst, polyol or surfactant, has to be minimised as much as possible."

Evonik’s Terheiden gave an indication of the balancing act facing automotive manufacturers. “Silicone surfactants generally only contribute to overall VOC,” she said. “In most OEM specifications, silicones are not specified. As a consequence, low VOC silicone surfactants are generally used when the seat cushion cannot pass the total VOCs. The amine emission quite often has to be reduced from the very beginning by using non-fugitive catalysts, especially when amines are part of the OEM´s specification.”

Susan Norris, regional marketing manager, flexible foam, North America at Momentive said that, as surfactants evolve towards lower emission products, it is natural for them to lose some of their performance characteristics. “Technical innovation is critical, especially in automotive moulded foams, so that while we reduce emissions, improve physical properties and widen processing latitude,” she said.

Dow’s James, speaking in early January 2017, explained that the company is looking at a whole new family of products for flexible moulded foams. “These will be in beta-testing with selected customers in Q3 or early Q4,” he said. “We hope to have a sales sheet out on these materials by the end of 2017. These are likely to be surfactants for HR moulded foam with lower emissions performance, which is a key driver for the automotive market."

For Dow, the primary markets will be in Europe and North America. However, he believes it is likely that many major orders will come from China, as Chinese automakers are quick to adopt Western standards. “They will also be available to regions such as Southeast Asia and India and the other developing economies if there is demand,” he added. “Tier 1 automotive suppliers are also very interested in Asia, so if we are working with the Tier 1 supplier in Europe or North America, information could quickly get passed around the world.”

Momentive is very active in automotive foam formulations. Its Niax silicone L-3558 can be considered for a wide variety of TDI or TDI/MDI-based moulded formulations, Clark said. “It has low emission characteristics, wide processing and good skin properties in TDI and TM formulations,” he explained. “It has also shown excellent foam flow performance in Europe, and good cell regulation in North American formulations.”

Fewer emissions

Evonik’s Terheiden said that surfactants can make a significant contribution to the overall VOC level when comparing a traditional seating formulation from several years ago using a traditional non-VOC-optimised silicone surfactant with a more modern formulation.

“In recent years, we have developed several low VOC alternatives while retaining performance, like Tegostab B 8734 LF2 and Dabco SI 1103 for MDI, or Tegostab B 8761 LF2 or B 8736 LF2 for TDI based foam,” she said.

“It's not easy to balance the competing demands of VOC reduction and performance maintenance. That's the game we are all in.”

Contradictory demands

Automotive light-weighting is a growing trend, and with the bulk of a car’s polyurethane foam being found in the vehicle’s seats, there is growing pressure on seat designers and makers to save weight, while retaining or increasing comfort levels. Increased comfort levels will be very important in the future, as driverless cars become more popular and there is less to distract the occupants.

“You can make the seat thinner and increase density,” said Evonik’s Wendel, outlining the conundrum facing seat makers, formulators and additive suppliers. “The problem is the OEMs are going in a different direction. They want to make the seats thinner and reduce, not increase, density. The big challenge for additive suppliers is to keep the performance and not compromise in seat comfort over time.” When lighter seats are required, he added, the biggest difficulty is retaining the physical properties specified by the OEM.

Terheiden, his colleague at Evonik, speculated about just how low it is possible for density to go. “With TDI, you can go lower in density than with MDI,” she said. “Formulating low-density MDI foams is more challenging. Here, you have to play with the right combination of surfactants to get the right level of stabilisation. While it is easier to reduce the density with TDI, it is often more challenging to retain physical properties, especially after heat humidity ageing, she said.

Away from cars, polyurethane foam mattresses and slabstock provide distinct challenges to surfactant manufacturers and their customers. In a business where margins are commonly very thin and there is only limited room for efficiency savings, surfactants can help block makers.

Rudiger Landers, technical manager for slabstock foam at Evonik, explained that in the domestic furniture market there is also a big segment that is driven by price. “There is pressure on prices in those applications, but the foam producer needs to be able to efficiently produce foam and be price competitive,” he said.

Fine tune for economy

Momentive’s, global marketing director for flexible foam additives, Alberto Melle, said, that raw materials account for about 80% of the cost of flexible slabstock foam, with other costs such as machinery accounting for the remaining 20%. “The foam formulation has to be fine-tuned to reduce scrap or waste,” he said. “Using surfactants that give wide processing latitude and good density distribution can contribute to lower scrap levels.” He added that silicone and process additives can play important roles in improving the process, and optimising foam yields.

Evonik’s Landers agreed. “Density profile and block geometry need to be accurate,” he said. “These two factors are strongly linked to the surfactant.” The right surfactant package can help foamers get the best foam yield, block geometry and the most constant density and porosity spread within the foam block, he believes. “The foam producers are able to improve the cost position.”

As Melle explained, “Gravity plays an important role, as when you make a bun between 1 and 1.3 m high, you can get increased density at the bottom. Niax L-595 reduces skin thickness and improves the density distribution, which can give you a higher block height. In most of the world, foam is sold by volume and foamers are interested in getting as much volume as possible out of the starting materials.”

Dow’s James added that surfactants help stabilise low-density foams and lower density high resilience foams. As the density of high resilience foam falls, he said, the performance of the surfactant and choice of surfactant become increasingly important. “There is a balance,” he said. “Foamers often increase the amount of surfactant to help stabilise the foam. But even if they get the desired effect, they may be using the wrong surfactant. There may be a more economical material with a different potency based upon its structure.”

At the other end of the furniture spectrum, demand for visco foam is increasing, said Emmanuelle Le Grand, market manager EMEA flexible foam, Evonik Industries. Visco foam may not necessarily be used as a whole mattress, but perhaps as a layer. “Customers are asking for very open visco foam,” she said. “As an additive supplier, we can help foam makers improve the breathability of the foam and the openness of the cells.”

As Momentive’s Melle said, viscoelastic foam is now a truly global product. “There’s a very sizeable viscoelastic foam market in China, based on TDI,” he said.

His colleague Lanchak agreed. “Quite a bit of viscoelastic foam is made in China, most of it intended for export,” he said. “This market has grown over the past few years. Other flexible segments have dropped off, but viscoelastic foam has held up. The viscoelastic foam market is growing in North America and Europe, and China’s viscoelastic foam production is tapping into that growth.”

Gabriel Kiss, global slab technical leader at Momentive, explained that the slabstock market has a demand for low emission products. “Demand is not at the same level of intensity as it is in the automotive market, but it is there,” he claimed. “We are developing new products that retain the performance levels customers expect while lowering foam emissions.”

Among the products Momentive plans to launch this year is L-594Plus, a new silicone surfactant for flexible slabstock foams, which the company claims offers good processing, fine cell structure and good density distribution.

Likely launches in 2017

The surfactants market is highly competitive, and each of the companies interviewed have quite different approaches to innovation.

Dow, for example, is excited about the integration with the former Dow Corning business, explained Richard James, global segment leader for polyurethane additives at Dow Performance Silicones. "Dow Corning is very good at manufacturing and developing new, novel surfactants. Dow Chemical has world-class application labs, a well-trusted salesforce and channel to market, and polyether technology.

“We sell 116 different surfactants into the polyethylene market,” he added. “These are all silicone polyethers. We sell similar molecules into the beauty care, agricultural and industrial markets. Overall, Dow has 262 such surfactants. We brought six silicone polyethers from these different marketing during the past year for use by polyurethane foam customers. If we don’t have the material, we can probably make it, because we are basic in polyether and we’re basic in silicone. If there’s a business case and if the customer really needs that innovation, we can make it happen,”

Evonik's headquarters are in Essen, Germany, and that is home to its main research and development effort. However, this is driven by requirements from markets around the world.

Evonik’s Emanuelle Le Grand, market manager for flexible foam in EMEA, believes that as OEMs and customers are located all over the world, it does not matter where research and development efforts take place; Evonik’s are predominantly located at its headquarters site in Essen, Germany, with support from teams in other regions. “As car makers are now so global, where we develop is less important,” she said.

Tony Lanchak believes that Momentive has an advantage in the automotive area, with a strong global R&D footprint. “This gives us opportunities to address regional needs, while having a clear global strategy,” he said.

Momentive will feature a number of new products at stand 600 in UTECH Las Americas. These will include Niax L-6745FL, which allows good foam properties to be achieved with better bond strength, and L-594Plus for flexible foams. The company will also be outlining its lower VOC products for MDI and TDI moulded foams.