Volcanic ash, coconut fiber debut in plastic automotive applications

Exotic materials are increasingly finding a home in automotive applications. Need the evidence? Check out the pillar trim in the 2011 Elantra and Rio vehicles. Engineers at Hyundai and Kia are now using a ground volcanic ash in a polypropylene and rubber composite to reduce costs and achieve a cloth-like appearance.

The goal of the project was to develop a pillar trim that looks better than non-painted injection molded pillars, which have a cheap, "plasticky" feel, says Joel Myers, senior engineer at Hyundai America Technical Center (Superior Township, MI). At the same time, the company wanted to avoid the high cost ($44 per part) of a cloth wrapping used in premium cars.

The new "cloth-looking" part costs $24 per part, just $2 more than the non-painted molded version. It also reduces component weight in the car from 2500 grams to 2250 grams. Scratch resistance is improved while odor and volatile organic compounds are reduced.

Compounding approach

The technology is an interesting combination of materials' and processing advances.

In the conventional process, talc (20% loading) is added at the beginning of the mixing process to a compound of polypropylene, rubber and additives. Then a fiber pile is added as a master batch at a 2% loading.

In the new approach, fiber pile is added early at a 0.5% level (no masterbatch) with volcanic filler, also at a 0.5% loading. Then talc is added through a second side feeder at just a 5% loading, with a 3% loading of glass bubbles. At the end of the mix cycle, a filler pile of 0.5% (again no masterbatch) is introduced to the compound, which still includes polypropylene, rubber and additives. Use of the glass bubbles to replace some of the talc reduces weight. Use of the direct compounding process to replace masterbatch cuts costs.

Myers says it's important to optimize the type, size and amount of glass bubble, fiber pile, and volcanic filler to keep a balance between mechanical properties and the cloth appearance. Two complementary colors are used in the fibers to boost the visual effect.

A marble effect of the volcanic filler contributes to the cloth appearance of the compound, says Myers. He also says the volcanic filler can emit negative ion and far-infrared radiation, further contributing to the allure of the pillar.

The material is produced by Hyundai Engineering Plastics Co. (Dangjin, Korea), which was spun off from Hyundai in 2000. The Tier supplier/moldmaker is Plakor (Hwaseong, Korea).

Coconut husks

Another interesting material now being used in cars is coconut husk fiber, also known as coir.

Ford is using coir to replace cotton shoddy in a polypropylene compound in the 2012 Focus Electric load floor, Elizabeth Johnston, advanced green engineer, told PlasticsToday in an interview. Ford calls the new material "cocofelt".

"Acoustic properties are the exact same as those with cotton shoddy," Johnston says.

The compound is a 50/50 mix of coir and polypropylene. Material from 1-2 coconut husks is used per part. Coir is a waste product that is not used for fuel because of its high ignition rate. It's abundant, says Johnston, and has "great inherent properties", including bending stiffness, ignition resistance, moisture resistance, microbial resistance and low odor.

The polypropylene acts as matrix glue, has a low density, and has an overall good performance-to-cost ratio.

She says that Ford's suppliers make sure that child labor is not used to collect the coconut husks, which are widely available in tropical areas. She also says Ford plans to expand applications for coir. It's slightly more expensive than cotton shoddy.

Johnston told PlasticsToday that the supply chain works like this: The coir fiber (from Natural Composites) and synthetic thermoplastic non-woven fabric is produced at Hobbs Bonded Fibers (Waco, TX) by carding and needle-punching a coconut fiber-based nonwoven material. The material is then run through a calender in-line to achieve a 6mm thickness. The finished non-woven material is sent to Aftech (Advanced Fabricating Technologies LLC; Rockford, MI) to die-cut into the shape for the part, and assembled with a hardboard layer and finishing carpet. Swiss automotive systems supplier Autoneum is the final supplier.

The volcanic ash and coir parts are both finalists in the 2011 Automotive Innovation Awards Program run by the Society of Plastics Engineers. Winners will be announced at a banquet Nov. 9 in Livonia, MI.