Kuraray releases rubber for winter tire use

KASHIMA, Japan—Kuraray Co. Ltd. is broadening its approach with its liquid farnesene rubber line after several years of working with specific customers.

The first product from the line, LFR-107, could be used to improve grip in winter tire tread, said Ozzy Yoneji, elastomers business unit sales representative at Kuraray America Inc.

The new products come from the same source as a hydrogenated styrene farnesene copolymer created through a partnership with Amyris Inc., an industrial bioscience company located in Emeryville, Calif. Amyris used genetically engineered yeast cells to convert plant-sourced sugars such as sugarcane into target molecules. One of the target molecules is B-farnesene, a renewable monomer which was also used to create Kuraray's HSFC.

"Some of those molecules are used in biodiesel and fragrances. They're used in vitamins, and in a number of different applications," said Erich Klein, elastomers business unit marketing manager for Kuraray America. "They produce farnesene, which we then use to produce a grade of liquid rubber, which gives us very unique properties."

Because of LFR's branched structure, it shows some differentiation from conventional monomers like isoprene or butadiene, Yoneji said. Its viscosity also is completely different from those monomers because it has less entanglement.

"As a rubber compounder, that's important because lower viscosity means easier to process, and potentially no need for other plasticizers," Klein said.

Compared to liquid isoprene rubber and liquid butadiene rubber, LFR has a high reactivity, which could cut down on production time, Yoneji said.

"It has a very fast reactivity, so it's easier to vulcanize, which is cost-saving for the customer," he said.

LFR also could contribute to lower rolling resistance in a compound, as it has a low tan delta, Klein said.

In a natural rubber/carbon black compound, it also shows a lower Mooney viscosity and better plasticizing effect than treated distillate aromatic extracted oil, a conventional choice for tire compounds, Yoneji said. In a toluene extraction test, LFR above a molecular weight of 30,000 did not extract in the toluene, as opposed to TDAE. It also showed less migration, which also means a longer product life.

LFR could be used for applications as a replacement for resins and oils, such as soft bead filler, the under-cushion, under-tread and tread of the tire, because of the good plasticizing effect, less or no migration, and low tan delta, he said.

Kuraray tested the first product in the line, LFR-107, at low temperatures for softness and for suitability for use in winter tire tread. A polyfarnesene, LFR-107 has a molecular weight of 135,000, a Tg of -71°C and a specific gravity of 0.90.

Compared to TDAE, paraffinic oil and LBR-305 (polybutadiene), LFR-107 showed good softness at -20°, even though LBR-305 has a lower Tg at -95°, Yoneji said. The softness of the compound does not correlate with the Tg of the softener itself.

In a low-temperature friction test, Kuraray engineers introduced a machine with a rotating plate underneath a vertical disc that holds the rubber sample. The plate can be changed to simulate multiple conditions, such as asphalt, ice or snow, Yoneji said. With testing on ice, LFR-107 showed higher friction performance on ice, compared to TDAE, paraffinic oil and LBR-305.

LFR-107's performance in icy conditions also has been confirmed by other tire companies, Klein said.

"That's the reason why Sumitomo Rubber adopted our material, liquid farnesene rubber, for their winter tire tread part in winter tires," Yoneji said.

Kuraray currently is focusing on tire applications for the LFR line, but it could be used for other applications where a high reactivity is key, Klein said.

"We're thinking sealants, adhesives, potentially," he said. "But our primary focus at this point, and the natural fit, has been with tires."

Kuraray is in full production of LFR, and currently is increasing production at its Kashima, Japan, facility to meet demand, Klein said. The total overall liquid rubber capacity at the Kashima facility is 13 million metric tons, he said. Capacity only for LFR at the Kashima facility was not disclosed.

Kuraray has been working with companies in Europe, Japan and elsewhere in Asia, making tires using LFR. Samples are available to the market with a non-disclosure agreement and more potential products using LFR are on the way, Klein said.

"There's more development ongoing that we can't share at the moment," he said. "It fits well when you look at our overall product offering. We have new functionalized grades of liquid rubber that are coming out, so this is part of an ongoing effort to expand into different unique grades of liquid rubber that provide differentiated properties."