By Jan H. Schut
Plastics made with genuinely new catalysts are hard to spot when resin companies don’t identify them in data sheets or only make them available to test partners. But several unusual new polypropylenes are in plain sight for the first time at the Polyolefins Conference on “The Polyolefin Renaissance” in Houston, February 23-26, hosted by the South Texas section of the Society of Plastics Engineers (www.spe-stx.org).
They’re made with three “new generation” catalysts. One is an unusual dual metallocene catalyst; the other two are “advanced” or “6th generation” Ziegler-Natta PP catalysts, though that isn’t easy to define. Ziegler-Natta catalyst generations are named for internal electron donors, which control the all-important orientation of monomers as they attach to the polymer chain, i.e. isotacticity and molecular weight distribution. (Generation 4 Ziegler-Natta is diethyl phthalate; generation 5 is diether or succinate.)
“Gen 6” catalysts claim higher activity (which benefits the resin company). They also claim to make PP with more stereo-selectivity, more controlled dispersion of monomers, higher purity, lower VOCs, and lower extractables. Some are also non-phthalate, but phthalate isn’t a clear criterion because “Gen 5” Ziegler-Natta catalysts like LyondellBasell Industries’ (www.lyondellbasell.com) diether or succinate have been non-phthalate for years. Phthalate internal donors are a hot button because of pending European regulations which could make PP with even minute phthalate traces a “controlled substance,” an obvious no-no for spunbonded or meltblown PP fibers for infant diapers. Here are the three “new catalyst” PPs.
FIRST PP COPOLYMERS FROM DOW’S ‘CHAIN-SHUTTLING’ DUAL CATALYST
Gary Marchand, research fellow at Dow Chemical Co. (www.dow.com), presents “PP-Based Olefin Block Copolymers as Compatibilizers for PE and PP.” It’s the first technical report on developmental “Intune” PP-based block copolymers made with Dow’s patent-applied-for CGC or chain-grafting catalyst technology (Patent Applic. # WO2005/090425, 26 and 27). Intune PP copolymers, announced at last year’s K Show in Germany, combine isotactic PP segments with crystalline PE segments (actually ethylene propylene copolymers) or with “PE, polyolefin elastomers and polar materials like EVOH and PA,” Dow says, “for blends and multilayer structures.” Intune PPs aren’t commercial yet, but are being tested as compatiblizers for PP/PE blends.
Dow’s chain-shuttling catalysts, introduced at ANTEC 2006, use two distinct catalysts and diethylzinc as the shuttling mechanism in one or more continuous solution reactor (s), Dow says. One metallocene catalyst produces hard blocks, a second hybrid metallocene catalyst produces soft blocks. Blocks form on the two catalysts, detach from them and park on diethylzinc particles before reattaching to new monomer blocks forming on the catalysts. The length of block segments is controlled by the ratio of diethylzinc to ethylene monomer, with a higher ratio making finer blocks, according to Dow presentations, while the overall hard-to-soft ratio is controlled by the relative amounts of the two catalysts.
Dow previously commercialized Infuse PE-based block copolymers, using its chain-shuttling catalyst technology to combine ethylene and octene monomers. Infuse PE block copolymers, introduced in 2008, allow high temperature and stiffness properties to be tuned independently for the first time. Infuse PE has temperature resistance up to the melting point of PE (about 138 °C) with low Tg. Intune PP could also have temperature resistance up to that of PP (potentially up to 163 °C), but Dow has only reported performance in blends. Dow’s CGC catalyst isn’t available for license.
PP COPOLYMERS FROM BOREALIS’S SIRIUS ZIEGLER-NATTA CATALYST
When Markus Gahleitner, senior group expert for PP at Borealis Polyolefine GmbH in Linz, Austria (www.borealisgroup.com), presents “A Brief History of High-Impact PP Copolymers,” he includes the most complex materials made so far with catalyst from Borealis’s Sirius emulsion process. These are certain BorSoft impact copolymers for medical films with higher purity, lower extractables, lower emissions, and better retention of mechanical and optical properties in steam sterilization, targeting PVC. They replace existing grades with higher property materials, but aren’t identified in data sheets.
The Sirius process was commercialized in 2006 and introduced at Polyolefins in 2009. Borealis uses it commercially to make advanced Ziegler-Natta catalyst for PP with higher activity and PP properties, but still with a phthalate internal donor (diethylhexyl phthalate). The Sirius process makes solid spherical Ziegler-Natta catalyst particles with magnesium chloride support formed in situ, not separately, for an active site structure that makes PP with relatively narrow MWD. “The replication is different even from other spherical catalysts,” Gahleitner notes. “Purity is higher, molecular weight distribution is slightly narrower, similar to diether catalysts, but with higher isotacticity.” Sirius technology is covered by over 60 patents (including U.S. Pat. # 7465775).
Interestingly, the Sirius emulsion process can also make metallocene catalysts for PP. Because emulsion distributes active sites evenly in round catalyst particles, Sirius metallocene catalysts would make heterogeneous PP copolymers with more uniform and evenly distributed soft domains than previous metallocene catalysts. Borealis invested 100 million Euros in a new semi-works Sirius catalyst production plant in Linz, Austria, which started in 2013, in addition to 50 million Euros for a new Innovation Center in Linz, which opened in 2009 for customer product R&D. Sirius Ziegler-Natta catalyst is also used by Borealis’s Borouge joint venture in Abu Dhabi, United Arab Emirates (www.borouge.com).
PP’S FROM W.R. GRACE’S ‘GEN 6’ CATALYST
John Kaarto, principal research scientist at W.R. Grace & Co., Columbia, MD (www.grace.com), presents “Investigations into Spinning Performance of PP from Developmental Catalysts,” describing fiber grades made from Grace’s non-phthalate Consista C601 catalyst. C601was developed by Dow and introduced in 2011 for Unipol gas phase processes. Dow called it the world’s first “Gen 6” Ziegler-Natta catalyst (substituted phenylene aromatic diester), referenced in some 70 patents (including U.S. Pat. # 8288585, WO # 2010078494, and U.S. Pat. Applic. # 20140012035). Grace licensed non-phthalate technology from Dow in 2011 and offered it as Grace’s HYamPP catalyst for isotactic PP. Then in 2013, Grace bought Dow’s Unipol PP catalyst technology and licensing business, including C601.
The non-phthalate catalyst reportedly makes PP with high isotacticity and broad MWD for a broad PP product line, not just fiber. Grades include homopolymer, random copolymer, impact copolymer and TPO for applications like BOPP, film, pipe, thermoforming, and injection molding including clear articles, Grace says. That’s a lot to make with one catalyst, but C601 can use up to three different external donors to tune products separately, according to Grace publications. Slovnaft a.s. in Bratislava, Slovak Republic, which started up in 2005, makes 100% of its PP production with C601 catalyst for a broad range of products.
C601 reportedly makes standard homopolymers 10%-20% stiffer than Dow’s 4th generation catalyst because of higher isotacticity, allowing down gauging in thermoforming and injection molding. Comonomer distribution is more uniform for better clarity (20% lower haze) in random copolymers. Higher catalyst response to hydrogen also reportedly makes PP impact copolymers with higher melt flow rates and up to 35% lower VOCs. (Hydrogen typically controls molecular weight and increases Ziegler-Natta catalyst activity by three-to-five times, but C601 reportedly requires less hydrogen for higher activity.) C601 has 40%-100% higher activity than Dow’s Gen 4 catalyst, so Grace says it’s cost neutral.