DUSSELDORF, GERMANY - Metallocene resins may be headed for automotive interiors. Sentinel Products Corp. of Hyannis, Mass., has developed foamed polypropylene sheet and bun products that it is targeting at auto interior applications, as an easy-to-recycle replacement for PVC, thermoplastic elastomers and polyurethane resins.
Sentinel developed the foamed PP products from Exxon Chemical Co. resins, using metallocene catalyst technology.
Scott Smith, Sentinel chief operating officer, revealed his company's development at AutoPlas '95, a conference on automotive plastic and rubber applications sponsored by Schotland Business Research Inc. of Skillman, N.J. AutoPlas took place Oct. 3-4 in Dusseldorf.
Smith claims PP foam has several advantages over various materials that are widely used in automotive interiors.
Automakers now use PVC, TPEs and PU resins as soft-touch, skin and cushioning components in combination with each other or in composite structures that combine them with wood, paper or glass reinforcements to produce instrument panels, door panels and seats. Combining the materials makes it difficult to recycle any of them, and automotive interior components typically are shredded as fluff and sent to a landfill.
Smith said varieties of metallocene PP foam could be used to make a soft-touch skin product and an underlying cushion that could be combined with conventional and reinforced PP components.
``Since 1990, polypropylene has gained rapid recognition as a viable materials choice for automotive interiors,'' Smith said.
``In five years, the use of PP for interiors, exteriors, under the hood and underbody applications has risen 23-27 percent. Much of this growth, especially with regard to interior applications, is attributed to improved temperature resistance, easier control for molded-in color and attractive material costs.''
Martin Hallam, European market development director for Montell Polyolefins, the largest PP producer in the world, confirmed Smith's remarks, claiming that PP offers opportunities to reduce weight and improve ecological performance by being easier to recycle than the PU and PVC materials now in use.
Smith said automakers also are attracted to PP because of its acoustic and sound-dampening characteristics.
However, Smith also noted that the use of PP has been limited by questions of flammability, processability and dimensional stability.
``The addition of metallocene resins into the PP matrix, or the tailoring of a PP molecular structure [through the use of metallocene catalyst technology] may address a number of these problems without sacrificing the other required performance criteria,'' Smith said.
``Preliminary research has shown that blends of metallocene and [conventional] polypropylene resins provide an excellent base for sheet foam, which is both flexible and processable,'' he said.
Smith said his company has produced metallocene polyolefin foams in continuous rolls and sheets as thin as 0.024 inches, and in buns as thick as 4 inches.
The thin sheets can be bonded in a single process with adhesives with the cushioning bun material, or they can be produced as an integral skin/foam composite with the buns. Either can be combined with conventional PP to make composite structures, Smith said.
Further, he said either composite structure can be thermoformed without diminishing its heat stability, while retaining embossed grains on the skin material.
Smith said metallocene PP materials can be stabilized to resist degradation caused by high heat and noxious chemicals for a long period, making them suitable for carmakers' demands that no signs of wear be evident in a 10-year period.