Take a look at PP now.

You may already think of polypropylene as one of the most versatile polymers. Yet the up-and-coming crop exceeds the reach of today's PP resins in almost every performance category. New polymerization technologies are expanding its boundaries in existing markets and pushing it into areas where it has had either marginal or no presence.

Though metallocene catalysts are the latest tool for making super-PPs, they are still in their toddler, if not infant, stages. Meanwhile, several new generations of high-activity Ziegler-Natta catalysts are responsible for most of the new high-performance PPs that have been appearing on the market.

Among the recent arrivals are PPs with improved melt flow, higher crystallinity and stiffness, higher impact, greater flexibility, and enhanced heat resistance. Grades with improved barrier properties, heat sealability, and clarity are also emerging.

METALLOCENES: WHAT IMPACT?

Kenneth Sinclair, senior consultant at SRI International in Menlo Park, Calif., predicts that the use of conventional PPs will peak in 2000 and that by 2010, 60-70% of PP will be metallocene catalyzed. Some industry observers project that by the year 2000 nearly all PP suppliers will have converted 10-25% of their PP production to metallocene catalysts.

Cost will greatly determine mPPs' rate of market penetration. Initially, mPP homopolymer will carry a premium of up to 7-8c/lb, Sinclair predicts, but that differential will decline as more suppliers enter the market. "By 2010, metallocene PPs are likely to be selling at the same prices as conventional PPs would have if metallocenes had not come about," Sinclair states.

Last fall, Exxon launched the first commercial metallocene-catalyzed propylene polymers under the trade name Achieve. The initial three grades are for spun-bond textiles used in diapers, personal hygiene products, hospital gowns and face masks, and filtration articles.

Due to their narrow molecular-weight distribution, these resins crystallize very fast while gaining fiber strength. They are said to offer significant improvements in nonwoven fiber properties that could provide fabrics with softer, cloth-like feel. These fabrics could be stronger and lighter and have reduced odor and extractable content. Manufacturers would enjoy reduced scrap rates and improved yields.

David Anderson, marketing development manager for Achieve polymers, says customers are reporting 10-20% finer denier capability, lower oil and wax extraction, and increased output rates. Extrusion and spinning equipment will develop increased throughput capacity to take advantage of these new polymers, says Anderson.

Exxon next plans to commercialize Achieve grades for melt-blown nonwovens. In the longer run, Exxon plans to develop grades for heat-seal films and molded products.

Besides Exxon, the only North American producer with much experience in mPP is Fina Oil & Chemical. Fina has focused on syndiotactic PP (sPP), a new molecular form of the resin, which the company has produced on commercial-scale equipment (PT, Nov. '93, p. 27,' Aug. '94, p. 21; Dec. '94, p. 14). Market development manager Joe Schardl says sPP is one to two years from commercialization.

Because of its high cost, Fina is aiming sPP at specialty films, where it reportedly offers unusually high clarity, gloss, toughness, and tear resistance, as well as lower seal temperatures. Injection molding is another target.

Syndiotactic PP processes differently from standard isotactic PP (iPP) because it crystallizes much slower, so significant equipment modification will be needed to run this material optimally, Shardl concedes. Fina has experimented with blending sPP and iPP to overcome the loss in production rates. Output reportedly returns to normal with blends of 75-90% iPP.

Fina is also seeking to solve the processability problem with new sPP grades that have broader molecular-weight distribution. Fina's manager of polymer R&D Edwar Shamshoum says one such grade, EOD 95-07, shows improved shear thinning and a 50% higher crystallization rate than narrow-MWD sPP. He says it has the potential to process as well as a conventional random copolymer. Energy required to extrude this material is 20-30% lower than for narrow-MWD sPP. This improved flowability is expected to open up opportunities in injection molding and blow molding.

Clear impact sPP is another recent development. "The aim is to get improved low-temperature impact, clarity, and processability with minor change in stiffness," says Shamshoum. The first grade reportedly has better toughness at -25 C and better clarity than either a standard random copolymer or high-impact PP. Its only deficiency has been slow injection molding cycles. Fina has since come up with grades that show 25% faster cycles than a conventional 3% random copolymer.

Metallocene iPP is also in the works at Fina, which has successfully completed commercial-scale trial runs of both homopolymers and copolymers.

Amoco Chemical is also making its first foray into metallocene technology that it has licensed from Stanford University. Amoco is still at the laboratory stage in development of elastomeric homopolymer PP (EHPP) that combines isotactic and atactic PP in the same polymer chain. The proportions can be varied to provide controlled elastomeric character (PT, Oct. '95, p. 65). Specialty product manager Charles Damianides says the first grade is a truly elastomeric fiber resin that will be aimed at medical nonwovens.

Other producers are also exploring metallocene catalysts for PP. For example, both Dow and Union Carbide say they have metallocene technology that can be adapted to PP. There's also activity in metallocenes at Montell Polyolefins. "Montell is an active player with significant development programs in place," says Robert Sperati, director of business development for Montell corporate strategy. "We expect this technology to provide the most benefits to PP copolymers and specialty homopolymers. Applications served by basic homopolymers will be less affected by metallocene technologies."

MORE NEW-TECH PPs

Several suppliers are using improved versions of conventional Ziegler-Natta catalysts to broaden their product slates with enhanced homopolymers, impact copolymers, and random copolymers. "Processors are getting a wider variety of products - a bit higher priced, but far better in performance," says Michael Kimmins, marketing manager at Phillips Sumika.

The company will use Sumitomo's gas-phase process and catalyst to make impact and random copolymers and homopolymers in a new 270-million-lb/yr plant due for start-up in third quarter. Kimmins says the major focus will be on impact copolymers, a market that Phillips Chemical Co. did not serve before forming the joint venture with Sumitomo. Initial customer trials next month will focus on automotive applications.

Sperati from Montell says the company has aimed its Catalloy copolymer process at developing materials with the potential to create new markets - those not traditionally served by PP or where PP has a small presence. "This technology has allowed us to produce materials ranging from soft to stiff and which are also much easier to process," Sperati states. Lighter packaging materials, materials that can be steam sterilized for medical applications, and grades for geomembranes that can withstand outdoor light exposure are some recent commercial successes.

PERMEABILITY OF METALIZED COEX BOPP FILMS (20 MICRON)(a)

Cefor Butene Random Copolymer Vs. Conventional Ethylene RCP

                                Metalized Permeability
Coex Coating            Gas Transmission            Water Vapor
(1 micron)            cc/100 [in.sup.2]/day       g/[m.sup.2]/day

5.5% [C.sub.2]                  8.2                    0.188
4.0% [C.sub.4]                  0.3                    0.022

a Data from Shell Polypropylene Co.

One example is in calendering, where Montell has developed what it says are "drop-in replacements" for flexible PVC. "We can come up with sheet that looks and feels like PVC but has better properties," Sperati claims. Other PVC alternatives are being aimed at siding and shingles. Still another Catalloy resin is designed for air-quenched blown film lines traditionally used for LDPE and LLDPE bag production.

SOFTER & STIFFER THAN EVER

Thanks to new polymerization technologies, PP has been made both stiffer and more flexible. Higher stiffness, as well as improved moisture barrier and heat resistance, have given newer "high-crystallinity" (HCPP) homopolymers an edge in packaging films and injection molding. Amoco is using new technology jointly developed with Chisso of Japan to make the family of Accpro HCCP materials. One example is Accpro 9117, a 2.0 MFR resin for OPP films that require improved strength and HDT, lower WVTR, and high modulus. Its higher melt strength also allows for thermoforming.

Another recent development is Accpro 9346, a 5.0 MFR injection grade for appliances. It's used for the spin basket of the new GE washing machine. Still developmental, but available in large trial quantities, is a high-flow (35 MFR) homopolymer that's said to have interesting possibilities in TPOs.

Fina has also entered the HCPP arena with its newly commercial EOD-94-08 homopolymer, said to offer high heat resistance and stiffness (PT, Dec. '95, p. 17). It's geared toward moisture-barrier films, injection molding, and TPOs.

Rexene has gone in the other direction with its new-technology Rexflex FPO (flexible polyolefin) materials, which were introduced at NPE '94 (PT, May '94, p. 15). They're expected to become fully commercial in the third quarter when a 60-million-lb/yr dedicated line is brought on stream. Rexene developed a proprietary in-reactor process and catalyst that control the level of crystallinity and yield unusual balances of high melting point (295-320 F), flexibility (25-52 Shore A), and elasticity (700% to over 1000% ultimate elongation).

"By controlling crystallinity as opposed to adding comonomer, we can obtain flexibility and softness without sacrificing temperature performance," says marketing manager Joseph Bonk. "Another characteristic of Rexflex is high melt strength, making it suitable for foaming." The first three grades - FPO 100, 2300, and 1700 - are homopolymers with tensile moduli of 10,000 psi, 20,000 psi, and 55,000 psi, respectively (typical PP homopolymer ranges from 150,000 to 200,000 psi). They can be used in injection molding, blown and cast film, and thermoforming. FPO materials reportedly compete with PVC, high-VA EVAs, and rubber, and make a great base material for TPOs, Bonk says.

Phillips Sumika is heading in another direction with new stiff/tough homopolymers. "We have technology that allows us to vary the stiffness/impact balance," says Mike Kimmins. Instead of an impact copolymer, processors will soon be able to choose a straight homopolymer offering 10-20% higher impact strength without significantly affecting stiffness or cost. The company is gearing up to launch these "enhanced homopolymers" for injection molded packaging, though Kimmins also sees potential in films and fibers.

BALANCING ACT

Newer impact PP copolymers are more than just tough: They show better balances of stiffness, impact, and processability, as well as fewer extractables.

Quantum Chemical has new high-impact in-reactor copolymers for injection molding. They have narrow MWD and extremely good color and balance of physical properties, according to marketing manager John Denzer. FDA extractables are below 2.6% by weight for retort and other cook-in-package applications. These new copolymers reportedly also offer a good balance of flow, stiffness, and toughness - e.g., up to 30 MFR, flexural moduli from 50,000 to over 200,000 psi, and "No-Break" Izod impact at room temperature.

Quantum also has a new high-crystallinity impact copolymer, PP8835 HW, with a flex modulus over 200,000 psi and notched Izod value of 1.2-1.5 ft-lb/in. It's intended to replace filled PP and engineering resins in auto-interior moldings.

Another development from Quantum is an in-reactor impact copolymer for rotomolding. It reportedly can compete with impact-modified PP and HDPE. This 20-MFR resin is aimed at medical parts. Good chemical resistance, toughness, ductility at low temperatures, and high service temperatures are claimed.

For sheet extrusion and blow molding, Quantum has introduced a high-melt-strength impact copolymer, PP1415HC, with 0.8 MFR, flex modulus over 200,000 psi, and notched Izod impact of 13-15 ft-lb/in.

Montell has a new high-flow (19 MFR) impact copolymer with increased impact and stiffness for auto interior trim. It has a flex modulus of 150,000 psi and notched Izod impact of 3.4 ft-lb/in.

High flow (above 30 MFR) is one reason why Amoco's relatively new Acctuf copolymers are gaining acceptance in auto interior trim. A recent addition to the line is Acctuf 3950, said to have excellent balance of impact and stiffness. Another new Acctuf entry is a 0.4-0.5 MFR grade for sheet extrusion and blow molding that is making inroads in tank liners.

Epsilon Products recently launched a higher-flow (37 MFR) impact copolymer for auto interior and under-hood uses. Grade 2235 has a notched Izod value of 1.5 ft-lb/in. and flex modulus of 180,000 psi.

RANDOM COPOLYMERS

Even without metallocenes, random copolymers (RCPs) are achieving better sealability, higher stiffness, and higher barrier.

Fina has developed improved RCPs for heat-seal applications. "Super-Z" resin has a melting point of 248 F, versus a more typical 260 F. Versions with even lower melting points are expected this year.

Shell Polypropylene Co. (just purchased by Union Carbide) is finding new applications for its Cefor butene PP copolymers. Cefor products were initially targeted to replace ethylene RCPs in OPP seal coatings and cast film (PT, Dec. '94, p. 14). Now, Shell is aiming to penetrate the shrink-film market with Cefor grades having higher butene content (above 15%) and exhibiting 50% or greater shrinkage at low temperature (212 F). Shell has also shown that at lower butene contents (8% or less), Cefor can significantly enhance properties of metalized OPP films. Besides good low-temperature performance, better stiffness, better opticals, and improved adhesion, metalized coextrusions of Cefor over homopolymer OPP offer six- to tenfold improvement in both oxygen and moisture barrier over conventional ethylene RCP, says marketing manager Malcolm Schard.

Rexene plans to offer copolymers of Rexflex FPO for use as impact and flexibility modifiers in compounding. For example, when blended with standard homopolymer, Rexflex FPO reportedly can yield properties similar to a random copolymer.

RELATED ARTICLE: WHAT DO METALLOCENES OFFER?

* For Fibers: Improved flow, drawability, and purity; controlled melting temperature; greater softness, resilience, and elasticity.

* For Film: Higher stiffness; higher or lower [O.sub.2] transmission; improved clarity, sealability, and crease resistance.

* For Injection Molding: Higher stiffness; better impact/stiffness balance and low-temperature impact; improve TPOs; better flow.

* For Raffia: Increased stiffness, resilience, recovery, dimensional stability, and purity.

* For Blow Molding: Higher clarity and melt strength; controlled stiffness.

* For Sheet & Other Uses: Better processability, clarity, cross-linkability, thermoformability, and calenderability.

Source: Kenneth Sinclair, SRI International