Clearly Tough New PE Film Resins Also Scroe High on Processability.
New families of polyethylene resins for blown and cast film are reshaping the conventional hierarchy. This is particularly true in LLDPE, where the old ranking of copolymer types (octene, hexene, butene) by strength and other mechanical properties is no longer strictly valid.
LLDPE film grades based on metallocene catalysts (mLLDPE) have already made their mark, but it's evident that they are not the last word in performance. Other new polymerization processes and catalyst technologies show the promise of setting new benchmarks for film clarity and/or strength.
For example, newer Ziegler-Natta processes yield octene LLDPE that reportedly can go head to head with mLLDPE, as well as "super-hexenes" that can compete with Z-N octenes and mLLDPEs. There is now even a "super butene" that bridges the gap between conventional butene and hexene copolymers. Further, new non-metallocene, single-site catalysts are challenging conventional metallocenes in performance plus processability.
Since the commercial introduction of this resin category by Exxon (now Exxon-Mobil) in 1995, mLLDPE film resins have found niches in four market areas--food packaging, stretch film (mainly cast), heavy-duty sacks, and diaper sheet. The domestic players in this league are ExxonMobil, Dow, and Phillips Chemical. Their materials are used primarily in multilayer structures where they are said to permit down-gauging by up to 20% while retaining toughness.
ExxonMobil will introduce two groups of products this year. One is a major extension of its Exceed hexene mLLDPE, which now comprises five grades for blown film and three for cast film. New blown-film resins will offer improved processability, better optics, and lower gels, primarily the result of new additives, according to Exceed market manager George Panagopoulos. Four new Exceed grades with 0.7 to 1.5 MI and 0.917 to 0.922 density will be introduced, along with four slip and antiblock versions.
A totally new and so-far unnamed mLLDPE family will also debut in 2000. ExxonMobil says only that they will be made with Unipol gas-phase polymerization and will have a different melt-index and density range from current grades. Developed for food packaging and personal-care applications, they are expected to offer enhanced sealabiity and clarity and vastly improved toughness--e.g., 25-50% higher dart impact than existing mLLDPE.
Dow Plastics has added four new grades to its line of Elite octene copolymers produced with its solution process and Insite metallocene technology. The Elite line now includes six grades for blown and two for cast film. Like the initial Elite 5105 blown-film grade, newer Elite 5101 (0.85 MI, 0.920 g/cc) displays extremely high dart impact ([greater than]850 g), good heat-seal and hot-tack performance, plus the added benefits of an optimized slip and antiblock formula. It is suited to heavyduty bags, food packaging, and agricultural films.
New Elite 5401 (1 MI, 0.916 g/cc) also has an optimized slip/antiblock package. Like the earlier Elite 5400 blown-film grade, it has very high dart impact ([greater than]850 g) at low temperatures, making it suitable for frozen-food and specialty packaging such as ice bags.
New Elite 5410 for blown film (1.3 MI, 0.918 g/cc) is said to offer good sealability and dart impact for lamination films such as sealant webs. New Elite 5230 for cast stretch film (4.0 MI, 0.916 density) boasts high impact strength and good puncture resistance at moderate stretch levels on irregularly shaped loads. On regular loads, it reportedly can provide excellent extensability for higher yields.
Meanwhile, Dow has formed an R&D venture and cross-licensing deal with Mitsui Chemicals to develop metallocene catalysts that will reportedly allow incorporation of polar comonomers such as methyl methacrylate and vinyl acetate, whose use has been limited as they tend to "kill" earlier Z-N and metallocene catalysts. Such catalysts could provide properties characteristic of costlier polymers, such as adhesion, gas barrier, and oil resistance. However, ability to incorporate polar comonomers is also claimed for some of the emerging non-metallocene single-site technologies discussed below.
Meanwhile, Dow and BP Amoco have completed a successful, extended run of Dow's Insite metallocene catalyst technology in a commercial PE plant in Indonesia using BP Amoco's low-pressure, gas-phase Innovene process. At last fall's Polyolefins and Elastomers Conference in Houston (hometown of the ponsor, PlastiChem Consultants), researchers from the two companies reported breaking the usual tradeoff between mechanical properties and processability in two new product families.
One is an LLDPE for film that's said to be superior to top-end Z-N products in both performance and processability. The other is described as a "true" competitor for LDPE with similar processability and superior performance. Plans to license the process have been delayed by Dow's pending acquisition of Union Carbide.
Phillips Chemical will soon add a fifth grade to its mPact line of mLLDPE blown-film resins that emerged in the last three years. Phillips has gradually moved up the density scale with these products, which are produced with its loop-slurry process. It started with grades of 0.916 and 0.918 g/cc and later added 0.928 and 0.933 g/cc. The latest addition, mPact D449, has 1 MI and 0.942 density, along with low haze (7%) and high gloss (66). According to films manager Dan Gray, higher-density mLLDPE with low haze is a new market niche. Whereas other mLLDPEs above 0.925 density typically show 10-15% haze, Phillips has achieved haze values in the 4-7% range. Phillips plans to expand its portfolio within the next two years with other higher-density (0.930-0.940) mLLDPEs.
Although a number of firms are working on metallocene-catalyzed HDPE, Asahi Chemical Industry Co., Ltd. in Tokyo appears to be the first to bring a commercial product to market. Its new Creolex is made with Dow Chemical's Insite technology in a slurry process. It contains a very small amount of butene-1 comonomer, though Asahi says it can make homopolymer, too. The material is capable of high gloss and clarity and it boasts excellent processability, having a shear-rate/viscosity curve very similar to standard HDPE. Easy processing is attributed to broader molecular-weight distribution than other metallocene resins.
Creolex reportedly offers twice the impact strength and three times the ESCR of conventional HDPE. Creep resistance is also said to be improved. Because mHDPE is more thermally stable, it better with-stands reprocessing, Asahi claims. Creolex is offered for film, pipe, and blow molding, but is not marketed in North America.
Z-N has more tricks left
When it comes to polyethylene innovation, metallocenes are far from the only game in town. New film resins from "enhanced" Ziegler-Natta processes are also helping to shake up the traditional resin hierarchies, and more extensions of this decade-sold technology are on the way.
Around mid-year, Nova Chemicals will start-up a 770-million-lb/yr plant in Joffre, Alberta, that will utilize its new-generation Z-N "Advanced Sclairtech" process. Based on solution-phase Sclair technology acquired from DuPont Canada in 1994, this process will make octene copolymers that reportedly combine the processability of standard LLDPE with metallocenes' flexibility to vary the molecular-weight distribution. Nova says the process can also use hexene and butene comonomers and even metallocene catalysts.
Nova will launch an entire product slate within the first 18 months of start-up, including 10 blown- and cast-film resins with 0.5 to 4 MI and densities of 0.905 to 0.936. Marketing manager Debra Van Holst says the focus is on blown film, including multi-layer food, frozen-food, and liquid packaging and heavy-duty bags.
Says Sclairtech R&D manager John Fischer, "We have seen incredibly high melt strength--about double that of our existing Sclair octene LLDPE. Similar results have also been observed when compared with competitors' octene LLDPE, as well as super hexenes and mLLDPE grades." He says the process allows considerable tailoring of optical properties, toughness, and dart impact.
Another "next-generation" Z-N catalyst is being used in a Unipol gas-phase reactor by Equistar Chemicals to introduce the Petrothene Select series of high-performance hexene LLDPEs for blown film. They reportedely produce films with better processability and tear strength than mLLDPE. They also boast better melt strength and dart impact than other super-hexenes and are positioned as substitutes for octene LLDPE and mLLDPE. With a density of 0.916 g/cc, the two basic grades (each with a slip/antiblock version) have MIs of 0.7 and 1.0. They are aimed at heavy-duty films, commercial and industrial packaging, and frozen foods.
Since early last year, Huntsman Corp. has been in full production of its new Rexell family of "enhanced" octene LLDPE film resins. They are made with a solution process licensed from DSM of the Netherlands plus a new-generation Z-N catalyst. Of the current 25 grades, about half are for blown film, 30% are for cast film, and 20% are for injection molding. The film resins are said to offer high dart impact, high tear strength, and excellent clarity and gloss.
Examples include two new 1-MI blownfilm grades. Rexell L8408 (0.917 g/cc) boasts an excellent combination of sealability, mechanical strength, optics, and very low gel levels. It's recommended as a sealing layer in coextruded food packaging. Film properties (1.5mil) include 9% haze, 66 gloss rating, 290-g dart impact, and 460-g MD Elmendorf tear.
Ultra-low-density Rexell V8403 (0.914 glcc) reportedly has excellent resistance to impact, puncture, tearing, and flex cracking, plus good seal strength, hot tack, and sealability through contaminants. It is intended to be a sealing layer for bag-in-box films, coextrusion, and laminating films. Film properties (1 mil) include 6% haze, 73 gloss, 400-g dart impact, and 400-g MD Elmendorf tear.
Since Montell Polyolefins entered the PE business in the mid-90s, it has launched film-resin families that were claimed to set new benchmarks for LLDPE processability and performance. All are produced with its Spherilene multi-reactor Z-N polymerization process, which is capable of adding multiple comonomers in each reactor.
From the initial offerings, two families of ethylene terpolymers remain: "Super Butenes" (12301 series) and clarity grades (12001 series). "Super Butene" grades (1 MI and 0.912 density) boast 33% higher dart impact, 66% better tear resistance, and more bubble stability than typical butene LLDPE. They are used in liners, trash bags, and other thin films where hexeneLLDPE properties are not needed. The 12001 clarity blown-film series (0.95 MI, 0.912 g/cc) boasts optics comparable to LDPE-4-6% haze and 70-80 gloss, plus dart impact strength between those of butene and hexene LLDPEs.
More recent additions are socalled "Quattropolymers," made from ethylene and three comonomers, which are positioned to compete with octene and super-hexene LLDPE. One commercial grade is XY022 (0.65 MI, 0.911 g/cc), a general-purpose blown-film resin with high dart impact for heavy-duty bags and industrial packaging. Also commercial is XYO2O (2.25 MI, 0.910 g/cc), designed for the core of cast coextruded stretch film. It is said to have properties comparable to conventional hexene grades but also allows for higher stretch (300-350% prestretch vs. the usual 250-300%), owing to very low gel levels.
Soon to be launched XY024 and XY026 (0.35 and 0.55 MI, respectively, both 0.9 18 g/cc) are for blown shrink film. Their TD shrink performance is said to be comparable to conventional fractional-melt LDPEs. Yet, their physical properties are so much better that a 2-intl LDPE film can be replaced with 1.25 mils of XY024 or XY026 and maintain the same overall performance, Montell claims. The TD shrink properties of these Quattropolymers reportedly will also allow processors to replace LDPE/LLDPE blends with a single resin without sacrificing performance.
XY024 and XY026 also are said to compare favorably with conventional 0.925-0.930 g/cc octene and super-hexene LLDPEs in applications requiring high stiffness or tensile strength. XY024 reportedly works well in very thin-gauge liners where high TD break strength is important. XY026 has secondary applications in produce tear-off bags, where a combination of good optics and bag openability are important. It also makes a tough heavy-duty industrial bag.
'Single-site' breaks out
Another category of new film resins comes from an emerging class of "single-site" catalysts that are not metallocenes. "Single-site" refers to these catalysts' ability to produce highly homogeneous resins of narrow MWD, similar to metallocenes.
Resins made with the new single-site technologies are said to combine the enhanced processability of conventional Z-N catalysis along with the narrow MWD and higher performance properties of metallocene resins. Also, the new catalysts reportedly offer more flexibility in design of the catalyst molecule. Says Dr. Mark Mack, Equistar's director of catalyst and process R&D, "They allow for different comonomers, including polar comonomers, to be incorporated into low-pressure systems, which could allow for making new polymers with enhanced functionalities."
Equistar has discovered a single-site technology with which it has made developmental grades of both high-strength and easy-processing HDPE film resins. The new "Star" single-site technology can produce material said to overcome many of the deficiencies of previous mHDPE attempts, along with processing characteristics comparable to those of conventional loop-slurry, chromium-catalyst HDPE. Equistar is looking for processors interested in sampling this demonstration technology in the first quarter of this year.
According to Mack, Equistar uses a small amount of an undisclosed alpha-olefin comonomer to produce 1-MI HDPE film grades with very narrow MWD. The high-strength version yields 1-mil film with twice the puncture resistance of conventional HDPE, plus 50% higher MD tear and equivalent tensile strength. Since bubble stability is lower, Equistar sees this grade as suitable mainly for blending or coextrusion with mLLDPE to add puncture or tear resistance.
The easy-processing variant of Equistar's new HDPE produces a 1-mil film that matches the bubble stability of a chromium-catalyst, loop-slurry HDPE. Although puncture, impact, and tear strengths are only slightly improved, MD tear is still over 50% higher than conventional levels. It can be used as a neat resin in typical HDPE blown films.
Both higher strength and improved processability can be achieved with the new catalyst, but only by going to lower densities notes Mack. He says Equistar is aiming for a whole range of Star single-site products, from HDPE to LLDPE for pipe and rotomolding, as well as high-clarity, high-performance LLDPE films.
Nova Chemicals has a new family of non-metallocene single-site catalysts that are very compatible with the Advanced Sclairtech process and make easy transitions from Z-N catalysts. The initial focus is on octene LLDPEs of 0.905-0.915 g/cc that can replace VLDPE, LLDPE of 0.925 density, and mLLDPE of 0.935 density. An early developmental grade of 0.918 g/cc has very high clarity (less than 4% haze) and is aimed at specialty food packaging like liquid pouches and fresh-cut produce bags. Opportunities in MDPE and HDPE will also be pursued.
Over the last three years, Eastman Chemical has introduced a string of new hexene-LLDPE film-resin families made with the BP gas-phase process and Eastman's proprietary Energx catalyst technology. Although Eastman will not characterize the catalyst, it appears to offer ome single-site-like performance properties.
Eastman started in 1997 with Tenite Hifor high-toughness grades (0.917-0.918 g/cc) and Mxsten lower density resins (0.905-0.914 g/cc) for cast and blown film. They were followed a year later with Hifor Clear blown-film grades (0.85 MI, 0.917 g/cc) that combine high clarity (4.2% haze, 83 gloss) with high toughness (dart impact of 350 g) and good MD tear strength (375 g/mil). Arriving about the same time was the Mxsite family of high-cling blown and cast grades for stretch film (0.7 to 2.3 MI, 0.907 to 0.915 g/cc). They boast 25% better puncture resistance than competing LLDPE/ULDPE blends.
Just a year old is Eastman's Mxsten CV family of hexene-LLDPE "plastomers" made with the BP process and Eastman's proprietary catalyst. Nine grades for blown and cast films boast a better balance of strength properties than mLLDPEs. They have MIs of 0.5 to 3.2 and densities of 0.905 to 0.914. They compete with ULDPE, metallocene plastomers, and blends of LLDPE with high-comonomer (6-10%) EVA.
The newest family, Hifor Xtreme, boasts exceptionally low seal-initiation temperature combined with high stiffness, high clarity, and high MD tear resistance. It is marketed for high-performance food packaging and hygienic films, as well as uses ranging from industrial packaging and merchandise bags to cross-laminated and agricultural films. Customer trials show it beats competitive materials' dart-impact strength even at 25% thinner gauge. It has 7% haze and a 70 gloss reading. Various blown- and cast-film formulations come in densities of 0.917 and 0.926 g/cc and MIs of 0.5-0.85.
Still more to come...
In 1996, DuPont announced that it had developed a new generation of cost-effective, non-metallocene single-site catalysts that produce narrow-MWD polyolefins ranging from linear, high-crystalline, high-density polymers to highly branched amorphous resins. This new Versipol technology involves two types of non-Ziegler-Natta single-site catalysts.
One type is a family of nickel/palladium di-imine catalysts that can produce LLDPE for films and molding. A second family of Versipol catalysts are iron/cobalt (Fe/Co) types that are said to produce highly linear polymers with high crystallinity and unusual combinations of density, stiffness, and moisture barrier.
Versipol catalysts are potentially useful in gas-phase, solution, and slurry-loop processes. Development is under way in all three. Some members of the Fe/Co catalyst family produce linear alpha-olefins (LAO) directly from ethylene.
The uniqueness of the Versipol family, according to technology director David A. Holmes, is the wide spectrum of polymers they can produce from ethylene alone, among which are unique structures that are expected to display advantageous rheological and property profiles. "We believe the Versipol technology can go beyond the metallocene polymers in their property/performance profiles," says Holmes.
Due to the breadth of this technology, DuPont has been looking for appropriate partners in the polyolefins industry. A number of independent licensing agreements are now under consideration, says business manager James E. Smith.
Properties of Montell's Spherilene Quattropolymer (1-Mil [Film.sup.a]) Montell Octene Hexene Montell Montell Film Property XY022 LLDPE LLDPE XY026 XY024 Features High Dart Blend of High Impact Stiffness, Stiffness, Tensile Str., Tensile Str. Dart Impact Dart Drop, g 221 149 162 115 100 Elmendorf Tear, g MD 333 344 306 394 490 TD 535 612 555 620 718 Tensile Yield Str., MD 1771 1671 1732 1823 1850 psi TD 1698 1675 1709 1946 1975 Ultimate Tensile MD 8783 7813 8977 9180 9615 Str., psi TD 6151 6227 7243 6715 7347 Elongation, % MD 600 650 670 490 TD 800 800 890 800 2% Secant Mod,, MD 29 28.5 26.5 33.2 33.3 kpsi TD 29 30 31 36.7 38.7 Haze, % 12 13 11 Status Commercial Commercial Commercial 1st Qtr '00 1st Qtr '00 (Est.)
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30 Dow Plastics, Midland, Mich.
31 DuPont Co., Wilmington, Del.
32 Eastman Chemical Co., Kingsport, Tenn.
33 Equistar Chemicals, LP, Houston
34 ExxonMobil Chemical Co., Houston
35 Huntsman Corp., Houston
36 Montell Polyolefins, Wilmington, Del.
37 Nova Chemicals, Ltd., Calgary, Alberta
38 Phillips Chemical Co., Bartlesville, Okla,
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|Comment:||Clearly Tough New PE Film Resins Also Scroe High on Processability.|
|Date:||Jan 1, 2000|
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