Strategies for Polyester Packaging

It has been a wild ride since 1977 when polyester bottles of Pepsi-Cola appeared in Western Michigan. Coca-Cola altered its distribution systems to accommodate the new “unbreakable” PET bottles with the moderate carbon dioxide barrier. P&G boldly dared to fill its Scope mouthwash into plastic bottles. Salad dressings, peanut butter, barbecue sauce, juice, water, and, now, jam and beer followed.

The Packaging Strategies™ PET Strategies 2000 Conference attempted to provide an analysis of PET bottles and jars today and tomorrow. This column will summarize the key food and beverage related elements of the conference.

End Users. A panel of food and beverage industry food packaging and engineering experts provided a perspective on the effect of polyester bottles and jars on their companies’ products and operations: Tim Garnett of Coca-Cola, John Collier of Vlasic, Ed Lerner of Welch’s, and Xaviar Sabas of Danone. All packages were critiqued: metal cans corrode and leak, glass is heavy and breakable, and plastic loses carbonation, permits oxygen ingress, and has temperature limitations. Thus, shelf life may not be as long as desired in PET bottles and jars. The basic PET homopolymer used to fabricate bottles and jars is approaching the top of its development curve in terms of functional barrier ability.

Recognizing the boundaries of polyester’s gas and moisture barrier properties, Coca-Cola joined with partners such as Krones to develop BESTPET, a glass-coated polyester bottle capable of providing five or more times the shelf life, i.e., oxygen barrier, of 500-mL and smaller packages compared to uncoated. The BESTPET process uses anodic arc with elemental silicon in a vacuum chamber with continuous bottle infeed and output. The silicon is subsequently coated to protect against scuffing.

Vlasic has just introduced dill pickles in a wide-mouth polyester jar capable of withstanding “normal” pasteurization temperature (about 170°F internal). Dill pickles are packaged primarily during the summer but are consumed throughout the year. Ambient-temperature shelf life is “adequate,” admittedly not as long as attained with glass jars, but what shelf life ever is as good as in glass?

Welch’s recently introduced juice in 16-oz polyester bottles and bread spread in 32-oz polyester jars. The former are achieved by applying external coatings (thermoset epoxy amines?). The latter requires a high-temperature-resistant structure for hot filling. Distribution channels have been shortened to accommodate the barrier limitations of PET packages. Both packages are direct responses to consumer requests for lighter-weight and easier-to-handle packaging.

Beer in Polyester Bottles. Most major and many minor brewers are at least dabbling in plastic packaging for beer. If, as indicated above, monolayer homopolymer polyester is not satisfactory for 500-mL bottles of juice, then 12 oz (333 mL) of beer certainly cannot be held. The answer might lie in the alternative barrier enhancement technologies being tested. There are three types of multilayer plastics: sequential injection (Continental PET Technologies and DPL); simultaneous injection (American National Can, Schmalbach Lubeca, and Kortec multigate coinjection); and -I-O-I (Exxi-Pak and Tetra Pak’s Sealica).

There are two main kinds of coatings: chemical deposition barriers and plasma discharge deposition barriers. Among the former are PPG’s Bairocade™ thermoset epoxy amine, an excellent O₂ and CO₂ barrier, and DuPont’s Edge. There are two types of plasma discharge deposition barriers: silicon dioxide, such as BESTPET and Tetra Pak’s Glaskin; and amorphous carbon, such as Sidel’s Actis and Kirin, which is an excellent O₂ and CO₂ barrier. Actis, Kirin, and Glaskin are internal coatings, and BESTPET is external.

Gas-barrier materials being evaluated include the passive ethylene vinyl alcohol (EVOH), nylon MXD6, nanocomposites, and Blox™. Active barrier package materials include oxygen scavengers such as ferrous iron, ascorbic acid, Crown’s Oxbar™ within a coinjection multilayer, Chevron’s emcm (claimed odor free), and EVOH/scavenger in both the bottle wall and the closure liner. With the exception of Oxbar, these do not necessarily encompass CO₂ barrier.

Crown Cork & Seal’s Dan Abramowicz said that silica coatings provide excellent barrier but tend to be brittle, leading to pathways for permeation when bottles are stressed. The scavenging technologies offer better oxygen barrier than passive structures, with performance not unlike that of glass.

The array of alternatives offered is daunting; just to assess each of the options represents a major task for a brewer, and more technologies are appearing periodically, each claiming to be the ideal.

Manufacturing costs of barrier-enhanced polyester bottles for beer, according to Gordon Bockner and Bob Miller, are $0.068–0.078/bottle premium over glass for multilayer PET and about $0.072/bottle for chemical coating. All polyester beer bottles to date have been filled with flash-pasteurized or cold-filtered beer. Polyester bottles are not yet capable of withstanding the temperatures of post-fill pasteurization that is used by more than 70% of all beer in the United States. A weight and therefore a cost premium of up to $0.003/bottle is required for tunnel pasteurization, translating into a nearly $0.003/bottle net product advantage for cold filling, not a highly significant difference. Variable cost therefore is not a major driver for cold-fill vs post-fill pasteurization, but product characteristics, capital equipment, etc., are still in the picture.

And then there is the issue of recycling: if a significant fraction of beer bottles convert to plastic, the U.S. and other countries will be faced with developing an infrastructure that can remove not merely homopolymer polyester, as it does now with carbonated beverage bottles, but polyester admixed with something that may or may not recycle into carpet fiber or new bottles.

And don’t forget regulatory issues linked with food-contact flavor challenges. Just because a few of the technologies have received letters of no objection from the Food and Drug Administration does not necessarily signal a clean path.

Aseptic Packaging. Tom Szemplenski discussed the growth of plastic-bottle aseptic and hot-filling installations in North America and Europe. Today, 14 manufacturers of aseptic packaging machines are offering 18 different models installed in more than 200 sites around the world. Products being filled include fruit beverages, water, tea, coffee, sauces, and dairy products. The packages emanating from these systems are displacing the classical paperboard cartons because of their transparency and reclosability.

Aseptic packaging is growing because of its cost advantage over heavier-weight heat-set polyester required for hot filling. At present, all but two U.S. installations are engineered for high-acid products; i.e., only two are known to be packaging low-acid liquids for ambient temperature distribution. Many are applied, however, for low-acid aseptic packaging to permit refrigerated distribution.

Market Size. Hot-filled juices and juice drinks represented the first major application for heat-set polyester bottles. The major sizes today are 32, 48, and 64 oz, but several smaller sizes using enhanced barrier polyester have entered the U.S. marketplace. The current market volume for the larger sizes is about 1.5 billion units, growing at about 5–6% annually.

Growth of single-serve, i.e., 20-oz and below, PET bottles for fruit beverages has been relatively slow because of the paucity of barrier and the cost to enhance barrier. In 1999, fewer than 200 million such bottles were produced. However, volume should be as high as 2 billion bottles in 2002.

Isotonic beverages in plastic bottles represent a market of more than 1.2 billion units, growing at 5% annually. Ready-to-drink tea has been filled into some 2 billion bottles. Pasta sauce has been hot-filled into PET jars, of which about 10–15 million were produced last year. Even more recent are jams and jellies, also using hot filling. And how can we forget ketchup, whose 500 million bottles are converting into polyester rather rapidly? The product that launched barrier plastic food bottles during the 1980s using coextrusion blow-molded polypropylene/EVOH/polypropylene technology is defecting from its historic roots.

Can enough PET bottle research be generated to drive the development that is obviously falling short of the ideal because of relatively low temperature resistance and marginal gas and moisture barrier resistance unless enhanced at added cost? Is it essential that we match the properties of glass bottles and jars to succeed in this ever-changing packaging scene? And who will conduct the tedious objective evaluations of polyester—and other barrier plastic structures—to determine the advantages and limitations each of the many developments in this area?

by AARON L. BRODY
Contributing Editor