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GM develops plastic battery pack for Chevy Volt

A green revolution in automotive engineering is apparent in the 26 finalists in this year's Innovation Awards Program sponsored by the Society of Plastics Engineers Automotive Division. Two of the three finalists in the power transmission category are for plastic packages for batteries used in electric or hybrid cars and there are four finalists for materials using renewable feedstocks. Virtually every entry emphasizes weight savings over previously used materials or more efficient processes that use less energy.

Ron Daul, director of manufacturing engineering-plastics at General Motors, said GM has developed a battery pack for the Chevy Volt injection molded in glass-reinforced polyamide 6/6 from BASF. "This is the first global high-volume lithium-ion battery pack integrating large-sized prismatic (pouch)-based battery cells," he told 25 judges in a presentation held in Auburn Hills, MI.

There are 135 repeating frames in a Volt battery pack, which weighs 37 pounds. The parts are manufactured and assembled in a clean room operated by Mann+Hummel USA. Multi cavity tooling was built by Omega Tool Corp. Synventive provided hot runners for the tools. Daul declined to disclose the upper temperature requirement for the application.

A competing finalist is a Sanyo module for a 228-volt battery used in the Volkswagen Touareg Hybrid. The part has 10 separate modules with 24 batteries each. They are molded with an unfilled blend of polyphenylene ether resin and polystyrene. Use of the Noryl blend from Sabic Innovative Plastics cut weight 48% compared to a comparable structure made from die cast aluminum.

PTT breaks out

Rick Bell, a global development manager for renewable materials, presented two DuPont environmental innovations. One is the first use of biobased poly trimethylene terephthalate (PTT) in an automotive application. The Toyota Prius is using the material for vent louver vanes.  "PTT is unique and has excellent surface appearance with high glass loadings and may eliminate the need for painting with strength structural plastics," Bell said. He compared the material's mechanical properties to PBT-type polyester or polyamide 6. Corn feedstock represents 37% of the polymer portion of the compound's composition. The remainder comes from oil-based feedstocks. The final compound is 45% glass filled.

Another DuPont innovation is a castor oil-based polyamide 1010 used in biodiesel fuel lines on several Fiat and other unidentified car platforms in Europe. The part is a thermoformed diesel feed line from filter to engine. Bell said the biobased polyamide has excellent chemical resistance to biobased diesel fuel, which he said is more aggressive than diesel fuel based on petroleum. In the United States, multilayer constructions using a fluoropolymer are typically used to deal with biodiesel fuel. The monolayer structure is less expensive.

Other interesting materials innovations included development of a castor-based foaming material by Ford for use in instrument panels and doors, use of recycled oil booms in a Chevy Volt component, and development of a Ford load floor that uses fiber from coconut husks.

Castor oil foam

Development of the castor-based foam by Ford is particularly interesting because Ford has been the global leader in using foam made in part from soybean oil, a project supported by American farmers.

Bari Brown, Ford advanced product development engineer, said the company's strategy is to use the castor oil-based foam in applications currently not penetrated by the soy version. He's referring to instrument panels and doors. Castor oil is derived from the Ricinus Communis flowering spurge plant, which grows in tropical regions.

The new castor oil-based foam is described as significantly more durable than the previously used oil-based material, with a 36% better tensile strength, which measures the foam's ability to hold shape over time. Tear strength is better by 5%, while elongation -- stretch under temperature or impact stress -- is reduced by almost 12%.

Another big deal-the castor oil foam cures 43% faster than the oil-based foam. Ford worked with BASF Polyurethane Systems to develop the new polyol, which is partially based on the castor oil feedstock. First application is an instrument panel in the 2012 Ford Focus. Category winners and the Grand Award winner will be announced Nov. 9 at a banquet in Livonia, MI, near Detroit.

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