HOUSTON — Polyethylene has outpaced polypropylene in the metallocene game so far, but a number of speakers and attendees at a recent industry conference said they believe metallocene PP still has a lot of untapped market potential.
``The initial promise [of metallocene PP] is still there,'' said Ken Sinclair, principal of STA Research in Sunnyvale, Calif. ``It's been limited by some performance problems, but solutions to these problems are out there in new patents.''
Metallocene PP production in 1999 is well short of the 1.5 billion pounds Sinclair had predicted in a presentation several years ago. Currently, only three producers — Exxon Chemical Co. of Houston, Fina Oil and Chemical Co. of Dallas and Targor GmbH of Mainz, Germany — are producing commercial amounts of metallocene PP. Sinclair estimates only 20-30 grades are available worldwide.
Sinclair pointed out that homopolymer metallocene PP can offer higher stiffness and strength, while the copolymer can provide increased impact resistance.
Metallocene PP could find a good niche in the fibers market, where it offers superior performance in spun-bound and nonwoven fibers used in diapers and other products.
Uses that combine both varieties of fibers have been troublesome, since bonding difficulties have created pinholes in fabric, making it unusable for medical applications.
In film uses, metallocene PP film to date has not shown enough stretch capacity to be practical. But PP makers say they have solutions to the problem in fibers applications.
Even though metallocene PP prices can be as much as 8 cents per pound higher than standard PP, Sinclair said long-term performance advantages justify the added cost.
``The trade-off strongly favors metallocene PP,'' said Sinclair, who added that metallocene PP could add as much as 1 percent growth per year to PP production during the course of the next decade.
Targor plant manager Franz Langhauser also is a believer in the future of metallocene PP. The firm, a 50-50 joint venture of Hoechst AG and BASF AG, is Western Europe's largest PP maker and has 600 million pounds of capacity dedicated to metallocene PP production.
Langhauser said metallocene PP has shown cycle-time and weight advantages when compared with conventional PP, polystyrene and polycarbonate in products including film, compact-disc cases and highlighting markers.
CD cases in particular have proved successful, as Targor has tested one-part cases with integrated hinges and a second model with a side-release mechanism. The cases are expected to be far more durable than traditional PS cases, while providing a 70 percent weight advantage and 10 percent cycle-time edge.
Chisso Petrochemical Corp. of Chiba, Japan, could be the next PP maker to go commercial with metallocene products. The company has developed new catalysts for metallocene PP use in injection molding, extrusion lamination and multilayer biaxially oriented PP film, according to Chisso supervisory research chemist Tsutomo Ushioda.
``The random copolymer PP we've made with our catalysts has been very promising in film because of its low levels of extractables,'' he said.
Ushioda said Chisso is moving toward commercial production, but has not announced a date when material might be available.
Because the PP molecule is more complex than the PE molecule, metallocene technology's ability to control performance finely may be more valuable in PP, said Doug Selman, Exxon's vice president of polymers technology.
``We can now create more flexible materials in polypropylene,'' Selman said.
``There are more variables to play with and manipulate in polypropylene. We're looking at a lot of opportunities there.''