The last few years have been tough on ABS (acrylonitrile butadiene styrene) thermoplastics. In just about every application, it seems ABS has been losing ground to arch-rival polypropylene (PPO), which appears poised to deliver a knockout punch at any time.

Most recently, ABS was pummeled by the University of Michigan's Office for the Study of Automotive Transportation's Delphi IX report. In the report, panelists gave ABS the equivalent of a standing eight count when it came time to predict future applications.

The numbers don't look good. The study forecasts the amount of ABS interior trim panels will drop from a current 44% of the market to 20% by 2008, with polypropylene jumping from 50% of the market to 75%. Likewise, ABS door trim panels are expected to drop from 45% to 20%, while polypropylene surges from 35% to 65%.

The '99 Ford Cougar is a typical example. Its highly sculpted interior door panels are made from a new high-melt flow engineered polypropylene produced by Mytex Polymers, a partnership between Exxon Chemical and Mitsubishi Chemical Corp. They are manufactured with a new low-pressure molding process especially suited for polypropylene.

Mytex worked closely with Visteon, Ford's parts-making subsidiary, on the process, which combines a vinyl skin olefin foam laminate with a polypropylene substrate that is molded in one fast cycle. Because the olefin foam and polypropylene are similar chemically, they bond together easily without adhesives, plus the higher flow resin allows for thinner walls - which translates into a lighter part - without sacrificing performance. Besides eliminating the cost of adhesives, the process also chops a vacuum-forming operation usually needed.

The situation for ABS is worse when it comes to instrument panel retainers. In fact, panelists forecast ABS to disappear from IP retainers by 2008, compared with an estimated 10% penetration today.

For the near future, polypropylene is expected to continue to make inroads in various applications. Japan was the first market to make major use of the material, followed by Europe and, more recently, North America, says Bill Windscheif, director of marketing at Montell North Americas Automotive Business Group. Montell is the largest supplier of polypropylene materials worldwide.

In North America, the polypropylene content per vehicle now is about 55 to 60 lbs. (25-27 kg) Mr. Windscheif says. That's up more than 10 lbs. (4.5 kg) per vehicle from three years ago. "We expect it to continue to grow at this rate for the next few years," he adds.

Polypropylene is lighter than most competitive materials and more durable, proponents argue.

Polypropylene also claims to offer OEMs and Tier 1 suppliers greater design flexibility for large-part moldings.

In Europe, more than 90% of the rigid dashboards on A class vehicles use polypropylene, Montell says. This trend is expected to spread to North America in the future, Mr. Windscheif adds, as are applications in bumper systems, wheel flares, trim panels, seat backs and washer reservoirs.

There's no question that ABS is losing ground versus polypropylene, says Jim Best, president of Market Search Inc. But it's not as dire as some predict, he emphasizes.

There are a number of places where ABS has a clear advantage.

Even the U of M study recognizes this, noting that polypropylene will be used in all simple interior trim applications, but ABS may be used when it comes to more high-end applications that are covered with carpeting or cloth. ABS also has demonstrated that it has the strength to meet new government-mandated FMVSS 201 head-impact standards for upper vehicle interior components. That means ABS may be able to retain structural A-, B-, and C-pillar cover applications, which may have otherwise migrated to polypropylene and other olefin materials if not for the new standard. However, polypropylene makers also are showing off designs they say can do the job.

The 1998 Chrysler Concorde and Dodge Intrepid use a one-piece ABS upper interior pillar system with molded-in-ribs designed to meet FMVSS 201's head-impact criteria. The one-piece design, made from Dow Automotive's Magnum impact-modified ABS resin, also saves money by reducing molding time, and it eliminates the need for additional assembly steps and costs associated with multiple-piece systems, explains John Zessin, Dow's commercial director for North America.

Overall, Dow says the program saved $1.75 million compared with a traditional two-piece thermoplastic pillar and energy absorbing foam design; and it saved $3.25 million compared with a painted PC/ABS pillar design.

At the end of the day, people will distinguish between applications that are primarily aesthetic and those that are more functional, Mr. Zessin explains.

Polypropylene has become the primary material for aesthetics. Whereas in applications where function is important, whether it's in terms of heat or impact, ABS still is doing very well.

Dow Automotive also scored a major coup when it was announced that it will supply 100% of the PC/ABS resin (a polycarbonate/ABS blend) in North America to Ford Motor Co.s Visteon Automotive Systems. The company's Pulse 2000 PC/ABS recently was chosen by Visteon to replace polycarbonate on IPs and other interior applications on Ford trucks.

Compared with polycarbonate, PC/ABS provides an improved melt flow rate allowing for faster cycle times and enhanced chemical resistance. The material also is being evaluated for unpainted, molded-in-color IP applications, according to Dow, on Ford's F-Super Duty trucks in South America.

PC/ABS, a polycarbonate/ABS blend, also is playing a big part in Bayer Corp. 's future plans. For example, Bayer's Bayblend PC/ABS was used on the 1998 Ford Mondeo's instrument panel cluster, says Cary Riggs, account manager for Bayer's Polymers Div. Using Bayblend with a polycarbonate film-insert molding helped

Ford shaved 10% off the cost of the part, Mr. Riggs says.

The use of thermoplastic olefins (TPOs), another group of plastics, also is forecasted to grow in coming years. In fact, TPOs could become one of the preferred materials in vehicle interiors as automakers work to eliminate paint and reduce weight, explains Dow's Mr. Zessin.

"We see this as an ongoing evolution. OEMs may switch over in the next year or so to TPOs, starting with structural pillars, then migrating to IPs and other areas that require some area of impact and eliminate color."

What about the use of a single material - for recycling and design harmonization purposes - throughout an interior system such as the overhead unit or door? While panelists in the U of M study say there is increasing interest in designing components from similar plastic families, the industry as a whole is reacting cautiously.

Commonizing materials is a good thought as we look at recycling and harmonizing, Mr. Zessin says. But it's a stretch to get to one material. "I dont think people will make the wrong engineering decisions to get to one material. That's not our goal," he says. - with Drew Winter