New high-I.V. PET resins target extrusion blown handleware.

New High-I.V. PET Resins Target Extrusion Blown Handleware

At least six resin companies are readying new extrusion blow molding bottle grades of PET for market in the first half of this year, some pegging commercial unveilings around Packpro, a major packaging show in Dusseldorf, Germany in late Mar, or the NPE show in Chicago two weeks later. Although the idea of creating PET resins for non-oriented handleware has suddenly attracted fresh interest, not all of these resins are new. Some of them sat quietly on product lists for months or even years, but their suppliers are running new trials and in some cases reformulating them.

Eastman Chemical Products, Inc. in Kingsport, Tenn.; Goodyear Tire & Rubber Co., Akron; ICI Americas Inc., Wilmington, Del.; Hoechst Celanese PET Resins Group, Spartanburg, S.C.; Du Pont Co., Wilmington, Del.; and Akzo nv, in Arnhem, the Netherlands, all have had high-I.V. extrusion blow molding grades in development for six months or longer. Eastman and Goodyear are said to have done the most extensive sampling with machinery companies and potential customers in the U.S., while Du Pont, Akzo and ICI have actually had material on the European market for some time in non-bottle applications.

"It's a major project," says ICI's senior technical account representative for PET, Paul Kaufman. "This is the first product since the 2-liter beverage bottle that's been strongly pushed by its end users. Everybody wants it."

THE RACE TO MARKET IN THE

U.S.

Hoechst Celanese will probably announce its new PET by the end of the first quarter. The resin still goes by its research name, Type 800. Du Pont, which has had two such PETs on the European market for months, may introduce them in the U.S. in the first or second quarter. Du Pont's resins, a copolymer and homopolymer, are made here and shipped to Europe for trials and one small bottle commercial application, says polyester development manager Linda Bateman.

ICI has had its Melinar 5922C (also made in the U.S.) on its European product list for four years, but it was aimed at tire cord and specialty fibers, not bottles. Now ICI is shipping it to Europe for bottle trials, says polyester business manager Roy Zemanovich. "There's a ground swell of new interest underway," he adds.

Similarly, Akzo's Arnite DO6-300, made in Holland, has been on the European market for at least four years for coextruding heavy-gauge barrier tubing. Akzo's resin first surfaced as an extrusion blown bottle grade in demonstrations by Bekum Maschinenfabriken GmbH of Germany at the Interplas exhibition in Birmingham, England, in November.

COST WILL BE THE BIG HURDLE

The problem with introducing extrusion blown PET to market will be economics, not technology, according to both resin and machinery producers. The technology involves raising PET's notoriously low melt strength by raising its molecular weight and thus its intrinsic viscosity (I.V.). Raising molecular weight usually translates into proportionately higher prices - e.g., a 10-15% higher I.V. costs slightly over 10-15% more than typical bottle grade.

The new PETs are made by either solid-state or melt-phase polymerization. Solid-sate, used by Goodyear, Hoechst, ICI and Akzo, requires holding the solid-state stage longer in the reactor to increase the length of molecular chains. This is what adds cost. Altering the polymer chemically with branching agents (trimellitic anhydride, for example) during melt-phase polymerization is another method of increasing melt strength. Branching is used by Du Pont and Eastman. It's also being pursued by Goodyear and by ICI in a forthcoming resin, likely to be announced in the first or second quarter. Melt-phase modification of the polymer, using a glycol or isophthalic acid (IPA), also lowers melting temperature and retards crystallization.

Industry sources say it's too early to tell how resin costs and prices will fall out. Du Pont is said to offer its resins in Europe "in the high 80s" ([cent]/lb) and ICI "in the low 80s," compared with 95 [cents]/lb for Eastman's PETG. But being companies "are all playing around now - no one can say for sure what they'll have, when, or what it will cost," says Martin Stark, v.p. and general manager of Bekum America Corp., in Williamston, Mich.

Another big cost unknown is the use of regrind in extrusion blown PETs. Regrind levels, degree of crystallinity in the regrind, and quality problems potentially created by use of regrind (like black specks) need a lot more study, machinery people say. One machinery company says it will be four to six months before a commercial application will have worked these issues through. Eastman senior technical representative James Mercer says trials with Eastman's X-resin (see PTJan.'91, p. 14) show that 30-50% regrind can be used in bottles. To be commercially accepted, says ICI's Kaufman, these resins must be able to use 50% regrind, since that's what the extrusion blow process typically produces.

Preliminary specs are available from some resin companies on these developmental grades. Surprisingly, the range of I.V.'s (compared with 0.72-0.84 for standard stretch-blown PET bottle resin) is not as uniform as might be expected (see table). [Tabular Data Omitted]

TARGETING PVC REPLACEMENT

The market for the new resins is expected to be mostly PVC replacement, both in the U.S. and Europe. In the U.S., PET may also appeal environmentally because of ready recycling markets in states where packaging faces mandatory recycling levels. "If a company now has four bottles in polyester and a couple of handled bottles in PVC, it would convenient to be able to say, 1All our bottles are PET and recyclable,'" says Du Pont's Bateman. Resin companies also expect new markets in converting opaque HDPE bottles that packagers may want to go clear, but not in PVC. Initial applications are likely to be smaller cosmetic and pharmaceutical bottles, but eventually water jugs are also a possibility. (CIRCLE 97)

HOW TO MODIFY MACHINERY

All these resins can run on existing extrusion blow machines used for PVC or HDPE, with modifications costing in the range of $30,000-50,000, the builders say. PVC equipment requires a change of screw to one with a shallower channel and without mixing pins, which create shear heat, says Eastman's Mercer. The screw must generate the possible shear because excessive heating beyond the melt point makes the resin less viscous, reducing parison strength. A screw with a lower compression ration of 2.5:1 to 3:1, vs. 4:1 for HDPE, is recommended by Eastman. ICI recommends 2:1 to 3.2:1, preferring ratios above 2.4:1.

PET also has to be totally dry to process well and give good bottle appearance, so a commercial dryer is needed on the hopper before the extruder to run hot desiccated air through the pellets before they enter the extruder. Extra temperature controls are also necessary because of PET's narrow processing window. Bekum's Stark notes that some older machines may not be practical to retrofit because of the difficulty or cost of adapting controls.

Blow molding machines for HDPE and PVC could need a head change, as well, to run these resins, machinery people say, though opinions differ. Bekum and Johnson Controls, Inc.'s Plastics Machinery Div. in Manchester, Mich., suggest that an HDPE head is more likely to need changing than a PVC head, which is more streamlined.

On the other hand, Battenfeld-Fischer Blowmolding Machines, Inc. finds that PVC heads, which have narrower melt channels, are more of a problem than HDPE heads, says Dane Belden, president of the U.S. branch in Waldwick, N.J. A PVD head is self-purging, since thermally sensitive PVC passes with high velocity through the narrow channels. Since PET isn't nearly as thermally sensitive, the same head doesn't require the high velocity; so backpressure builds up on the screw, which loses efficiency; output drops and the temperature rises. Belden says. In Germany, Battenfeld-Fischer reportedly "has had a lot of success" with 20:1 L/D, grooved-feed extruders. But in the U.S., the company is looking at PVC extruders, which aren't grooved. "We're trying a double-flighted barrier screw on a 24:1 smooth-bore extruder - that's known technology for PET film, but new to blow molders," Belden says.

Du Pont's resins are also said to require certain screw and barrel lengths, so a retrofit of either PVC or HDPE equipment with L/D of 20:1 or less would require changing not just the screw but the barrel as well. Du Pont's Bateman recommends an L/D of 24:1, compared with the 20:1 standard for PVC extruders, and 24:1 for HDPE. ICI's Kaufman says L/D for extrusion blown PET can be 20:1 to 28:1, but 24:1 is preferred. Bekum's Stark notes that 24:1 is standard for Bekum's PVC/PET extruders.

PHOTO : Recycling laws and concerns about replacing PVC are pushing development of extrusion blown bottle grades of PET. Gallon water-bottle samples were blown by Plastipak Packaging Co., Medina, Ohio, using a new Du Pont resin.