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additives feature | Coupling agents

Xiameter are among the additives used or evaluated for this application. “Increasing silica levels and effectively reducing the amount of carbon black [in a tyre] reduces rolling resistance and improves fuel effi ciency,” Hein says. The silane is also necessary because although silica improves tread stock properties, the chemical has low compatibility with elastomers, weakens the rubber matrix and can thus reduce tread life. Loadings of Xiameter silanes for this and other

applications can be as low as 0.1% by weight to 10%, though Hein says general levels are in the 0.5% to 3% by weight range. Another additive supplier working on formulations

Titanate and zirconate additives from Kenrich react with inorganic and organic materials including graphene, a model of which is shown here

formulators a powerful platform on which to add functionality. As a result, silanes are often the “go to” additives when properties enhancement is required in a various applications. “Some of the trends in silanes follow the larger

Coupling agents are used to

improve silica dispersion in

tread stock as tyre manufac- turers comply with rolling resistance label rules (Photo: Michelin)

mega-trends in the marketplace,” says Travis Hein, technical account specialist for Xiameter silanes at Dow Corning. For example, “People are looking to silanes to help them make ‘green’ materials.” Applications here include solar cells, where organic coatings are used to treat the polysilicon cells. “The silanes help ensure good adhesion and long-term durability of the coat- ings,” he notes. “I think the trends you will see in silane coupling agents will involve adding multiple functionalities to provide a combination of benefi ts such as improved dispersion and water repellency,” Hein adds. One new area in which silanes fi nd increasing use is tyre manufacturing, where they couple silica with tyre rubber. There are several benefi ts to this, but a major advantage is reducing “rolling resistance” in cars and trucks as part of a regulatory effort to minimize fuel consumption. The idea is that decreasing the amount of energy absorbed by tyres will reduce vehicle fuel use. Europe recently started a tyre-labelling program to inform consumers about the rolling resistance of tyres prior to purchase, and the US is expected to eventually implement a similar program.

Sulfi do-brand silanes from 18 COMPOUNDING WORLD | January 2013

that reduce rolling resistance is Cray Valley. The company uses two basic chemistries: low glass-transi- tion-temperature (Tg) polybutadiene (PBD) oligomers (tradename Ricon) and high-Tg-temperature styrene maleic anhydride (SMA) copolymers (tradename SMA). These materials — “our starting points,” says Jeremy Austin, business development manager — permit the company to graft appropriate chemistries onto the molecular backbone of each and start building functionality. The choice as to whether to use low-Tg-temperature PBD or high-Tg-temperature SMA in a formulation is usually determined by the resin or fi ller it will interact with. Elastomeric polymers generally work better with the low-Tg backbone, while engineering thermoplastics such as PA and polyester function well with a high-Tg backbone. The approach is paying off in rolling resistance. “We have seen up to a 30% improvement,” says Todd Speece, Cray Valley’s marketing director. He believes this reduction in rolling resistance will contribute fuel savings of 3 to 5% in a vehicle.

The additives that Cray Valley is working on with several undisclosed customers are in testing, though Speece expects one or two grades to be commercial later this year. The company is not only looking to reduce rolling resistance but improve tyre grip and handling as well.

“Historically, you could only improve one property at the expense of the other two,” he remarks. “But in the past several years we’ve learned enough about properties enhance- ment to improve [rolling resistance and grip] without affecting [han- dling].”

Speece says the technology is applicable to all vehicles including trucks. The program could be a

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