Engineering Green Packaging

Food, beverage and consumer product packaging will soon get a whole lot greener. And much of the credit goes to Wal-Mart.

The retailing giant, last November, announced it would implement a new Sustainable Packing Scorecard as part of a goal to reduce its packaging consumption 5 percent by 2013. Starting in February, the company will look to the scorecard's sustainability metrics as a way to evaluate the packaging used by its 60,000-plus suppliers.

Wal-Mart based the scorecard on what are called the "Seven R's of Packaging" — remove, reduce, reuse, recycle, renew, revenue and read. From a technology standpoint, the scorecard favors packaging methods that reduce greenhouse gas production, result in more efficient package designs, cost less to transport and offer end-of-life options other than the landfill (see sidebar for the full list).

Given Wal-Mart's clout, the scorecard has already started to sharpen the packaging in-dustry's focus on sustainability. "The scorecard hasn't even gone into effect yet, but it's become a powerful catalyst in sustainability efforts," says Anne Johnson, director of the Sustainable Packaging Coalition. Some companies have already started to introduce new packages designed to earn a good score. J&J Packaging, to take one example, in May, filed for a patent on a new kind of scorecard-friendly standup blister pack.

It may be tempting to dismiss the scorecard as a corporate green-washing attempt or to ask whether a 5 percent reduction in packaging goes far enough. But Wal-Mart has come up with a sustainability initiative that does look at the environmental footprint of packaging through its full life cycle.

And Wal-Mart isn't alone in taking this life cycle approach. The Sustainable Packaging Coalition likewise has a broad view of sustainability, which isn't surprising given the organization is part of GreenBlue, a non-profit institute founded to promote the adoption of cradle-to-cradle design principles. Developed by McDonough Braungart Design Chemistry, these principles look at the full environmental impact of products — their raw materials, their end of life "and everything in between," says Johnson. As applied to packaging, the cradle-to-cradle approach also takes performance, economic and social goals into account. "Sustainable technologies won't do much good without the acceptance of consumers and the packaging industry," she says.

The packaging industry hasn't always looked at sustainability through such a broad lens. "Even a few years ago there was a tendency to look at sustainability in the context of just the package itself rather than its cradle-to-cradle impact," says Johnson.

This life cycle approach to sustainability promises to bring about sweeping changes in packaging design and materials. And those changes will create new challenges for the engineers who design packaging machines. "Packaging materials, package design and machinery have to be compatible. So, there's a lot that machine builders can do to help with sustainability," says Jeff Wooster, who is responsible for food and specialty packaging technology at the Dow Plastics.

Machine builders, for example, will need to adapt equipment to run the new biodegradable materials. They'll also have to support efforts to make better use of existing materials. And because packaging's life cycle includes all the production steps, machine builders will be called upon for innovations that can improve the efficiency of manufacturing lines, reducing the energy consumption and greenhouse gas emissions associated with production.

Here Come the Bioplastics

One the biggest changes associated with sustainability involves the addition of biopolymers to the portfolio of packaging plastics. Though very different in their chemistry, these biopolymers tend to have a few things in common. Most come entirely from sustainable feedstocks such as corn or sugar cane. Most are biodegradable in the right composting environments.

The biopolymer that has made the most commercial progress in North America so far is polylactic acid (PLA) supplied by Cargill's NatureWorks LLC. The company has commercial applications in flexible packaging for relatively short-lived products like fresh-cut produce and baked goods. "The perimeter of the supermarket has been our sweet spot," says David Stanton, NatureWork's brand manager. NatureWorks PLA, which is derived from fermented corn starch, has also seen use in thermoformed trays and blow-molded bottles. Stanton says "millions of pounds per year" of the NatureWorks PLA already go into packaging applications and he adds the company is currently expanding its production facility to its nameplate capacity of 300 million lb/year.

Another up-and-coming biopolymer comes from Telles, a joint venture of Metabolix and Archer Daniels Midland. The venture plans, next year, to open a commercial biorefinery capable of polyhydroxyalkanoates. These Mirel PHAs are already available in smaller quantities from an ADM facility. The first Mirel grade has been for injection molding and it has been molded into caps and closures on a developmental basis, according to Dan Gilliland, business development director for Metabolix. In the coming months, new grades suitable for film, sheet and thermoforming will be rolled out. Gilliland says he expects a blow molding grade, for bottles, to be available sometime next year.

A very different family of compostable packaging materials has been introduced by Innovia Films, the big producer of cellophane and other speciality films. Called Nature-Flex, these films are based on wood pulp. "They're a derivative of cellophane, the original packaging film," says Malcolm Cohn, the company's North American marketing director. Some NatureFlex materials also have a coating to allow heat sealing. Cohn says the most promising applications in North America include overwrap for fresh produce packaged on biodegradable trays — an increasingly popular alternative to traditional "pick-and-pay" packaging. The NatureFlex films can be heat sealed on form-fill and seal lines. "It gives quite a strong seal on its own, about 400 grams per inch" says Cohn. The coated version says the weld strengths make the bags suitable for packages with contents up to 1 lb.

A different twist on sustainable polymers comes from Dow. The company, last month, announced it would partner with Brazilian ethanol producer Crystalsev to produce polyethylene using sugar cane rather than petroleum feedstocks. According to Tony Kingsbury, Dow's sustainability leader, the new cane-based plastics will act just like their fossil-fuel-based cousins. "They're molecularly identical," he says. In fact, when asked how users would be able to tell the two versions apart, Kingsbury quips, "I think you'd have to do some carbon dating."

Other biopolymers — some compostable, some not — are available from new and established plastic suppliers with the latter list including BASF, DuPont and Novamont.

At first glance, biopolymers do seem to have an inherent sustainability advantage. Since packaging biopolymers rely on agricultural feedstocks, they do offer a big reduction in fossil fuel use. A life cycle analyst would remind us that growing, harvesting and transporting the feedstocks still requires fossil fuels. But not nearly as much as a plastic based on fossil fuel. Metabolix's Gilliland claims just 80 to 90 percent of the fossil fuel usage of a traditional polymer comes from the feedstocks. "So our fossil fuel usage is that much less," he says.

Biology Issues

With those kind of advantages, a lot of environmental hype surrounds biopolymers right now. Yet, these advantages also make it easy to overlook the fact these bio-based materials have a long way to go before they can truly compete with traditional plastics.

Part of their problem comes down to capacity. "There's not enough infrastructure in the world to replace polyethylene alone. One big biopolymer application from a company like McDonald's and there wouldn't be enough resin for anything else," says Mark Kitzis, vice president of R&D for Alcan Packaging.

Then there's the price of these emerging materials. Conservative estimates have biopolymers costing at least two to three times more than petroleum-based plastics, though the magnitude of the difference varies depending on which plastic you use as a point of comparison. Cohn, for example, acknowledges NatureFlex costs about two times as much as commodity polypropylene. Gilliland says Mirel will cost about three times as much as polyethylene.

Price isn't everything, however. Suppliers of bioplastics believe consumers and brand owners will eventually exert enough pressure on brand owners to increase the value of biopolymer packaging. As Cohn points out, the incremental cost of using a NatureFlex biopolymer might add up to just a half-cent per package. "For a product that costs three or four dollars, a half a cent won't seem like much to the consumer," he says.

Packaging suppliers, though, tend to have a different take on price. "For a package that costs two cents, which is pretty typical, a half cent is a lot," says Jeff Schuetz, staff vice president for global technology Sonoco Products Co. He adds that Sonoco has identified some niche applications where biopolymers make sense, but the company's customers have so far taken a pass, citing the price premium.

The end-of-life options for bioplastics may not be all they're cracked up to be, either. Each biopolymer composts at different rates under different conditions, but the real issue is whether they'll get to a compost heap at all. "When's the last time you ran across an industrial-sized composting facility with the ability to collect used packaging?" Kitzis asks. And in a country where we don't even have an adequate recycling infrastructure, he has a good point.

Without a composting infrastructure, biopolymer packages — rigid or flexible — stand a good chance of ending up as solid waste. "The materials need specific environmental conditions to break down. If you put them in a landfill, they're not going anywhere," Kitzis says.

And while it's true biopolymers can be recycled rather than composted, they can pose problems in a recycling stream, too. PLA bottles, for example, can be tough to distinguish from PET bottles. And if more than a few percent of PLA gets in the PET recycling stream, the quality of the PET recyclate degrades. NatureWorks' Stanton says his company recognizes this problem and is already at work on better sortation technology and other ways to create a separate PLA recycling stream.

Bioplastics present technical difficulties, too. Kitzis can rattle off a long list of ways in which these new materials don't measure up to petroleum-based materials in use now. His list of deficiencies includes barrier properties, coefficient of friction (COF), tensile properties, stiffness and sealability. For packages requiring a long shelf life, "barrier properties are one of the biggest hurdles," Kitzis says.

And for the sake of "machinability" on existing packaging machines, COF and stiffness differences can be a deal breaker. "Biopolymers tend to be stiffer and have higher coefficients of friction," says Kitzis. "They tend not to machine as fast."

Sonoco's Schuetz agrees. "Coefficient of friction is a big deal through the entire supply chain. It matters to the guy stacking the shelves even if he doesn't know what it is," he says. And it matters a whole lot more to a packaging house that has to slow down its form-fill and seal lines to accommodate a biopolymer.

Neither Kitzis and Schuetz have written off biopolymers. In fact, they both oversee R&D labs that evaluate and develop these materials every day. Both of these engineers simply argue it will take work before biopolymers can offer the performance and productivity offered by incumbent packaging materials.

Engineering to the Rescue

And that's where design engineers come in. With the possible exception of the barrier properties, the deficiencies associated with biopolymers can be lessened by tweaking plastics processing and packaging machines. In fact, some of the changes are analogous to the changes that would have to be made to switch purpose-built packaging lines between different fossil-fuel based polymers. "Our materials are not drop-in replacements for anything, just as polystyrene is not a drop-in for polypropylene," says Metabolix's Gilliland.

Some machine builders have already started this process. Norland International supplies turnkey bottle-making and packaging systems, mostly to the bottled water industry. Earlier this year, the company rolled out a blow-molding machine specifically designed to make PLA bottles. Bruce Kucera, Norland's vice president, says his engineers had to put "a lot of time and effort" into understanding how PLA processes before they could build this new Freedom Series PLA machine. "The most important thing was getting a handle on temperature," he says, explaining PLA processes at lower temperatures than PET and has a narrower processing window. "The processing window in our experience is about 25 percent smaller than PET," Kucera says. Accommodating that smaller window required the company to upgrade its temperature controls for the machine and mold cooling system.

ULMA Packaging is another machine builder that has had to tweak form-fill and seal equipment to work with biopolymers. "We're beginning to get requests for machines that handle biopolymers," says Bill Chastain, the company's North American vice president and managing director.

"Biopolymers basically run on the standard types of machines, but they do require modifications to the sealing systems. The materials have a sealing range that's not quite as wide as the polymers we normally run," Chastain says. Among the modifications are constant-temperature sealing bars coated with Teflon, additional temperate sensors on the sealing system and tighter temperature controls. While not difficult from a technical standpoint, the changes do constitute what Chastain describes as a "major retrofit" to an existing machine.

Chastain believes biopolymers will usher in another type of machinery change, at least for new equipment orders. "I think you'll see more machines that can switch between biopolymers and standard polymers," he says. The reason is that volumes for biopolymer packaging are still small enough that utilization would suffer if the machine made only biopolymer runs.

ULMA has, for years, been making packaging machines that can run more than one type of material. For instance, it has machines with two seal rollers — each optimized for a different type of plastic. Chastain sees a similar arrangement emerging to accommodate biopolymers.

More machine builders will likely follow Norland and ULMA's example as biopolymers become more common. And there's little doubt they will become more common over the coming years, especially in light of Wal-Mart's influence.

Even though the scorecard doesn't specifically favor biopolymers, Wal-Mart seems to be going down a path that will help its adoption. The company declined to be interviewed about biopolymers, but it did e-mail a statement that encourages their use and calls them "more sustainable than other synthetic materials used in packaging."

Use Less, Waste Less

Even without biopolymers, there's another route to sustainability, one that involves making more efficient use of fossil-fuel-based materials. While it doesn't get the attention that biopolymers do, this route to sustainability arguably has a much greater and more immediate impact. "There's a lot of hype around biopolymers and I'm concerned that hype can overshadow the sustainability improvements we can make now," says Schuetz.

Some of those improvements involve package design. Maximizing the contents-to-package ratio to reduce the amount of packaging, improving cube utilization to minimize the environmental costs of transporting goods and eliminating unnecessary layers of packaging are three strategies Kitzis cites. They're also strategies that figure into Wal-Mart's scorecard.

Another important strategy involves the downgauging of packages — essentially making them thinner and lighter. "This is something we can do right now," says Kitzis. "Go from 1.5 mils down to 1 mil and right off the bat you've reduced materials usage by 33 percent," he says, adding the fossil fuels and greenhouse gases associated with the manufacturing and transportation of the raw material and the package itself likewise drop.

Schuetz, too, likes downgauging as a sustainability strategy and he points out that upgrading to materials with better mechanical and physical properties can make it possible. Dow, for one, has been supporting this approach with a variety of premium packaging materials for blow molding, thermoforming and film.

In flexible packaging, Wooster says the key properties to maintain in downgauged structure are often COF and barrier properties, both of which can be preserved with resin additives.

Rigid packages can benefit from better tensile and impact properties, allowing them to deal with higher forces from top loads or screw-on closures. As a rule-of-thumb, Wooster says, the replacement resin should offer enough of a property bump to offer a 10 percent reduction in package gauge or weight. For less of a reduction, it might not make sense to re-qualify a new material. "Ten percent seems to be the magic number," he says. The corresponding property changes would typically have to be higher. For example, making a rigid package with a wall that's 10 percent thinner might require a stiffness improvement of 20 to 25 percent — because load properties equal modulus times the thickness cubed.

While some of the downgauging opportunities rest on resin development, machine builders can play a role here, too. Wooster gives one example from film packaging. "Winder speed is often the limiting factor in these lines," he says. So, let's say Dow designs a resin that lets a film producer reduce thickness from 2 mils to 1 mil while maintaining the same barrier performance. Packaging film is usually sold by surface area, so this kind of downgauging is an attractive proposition for a film producers. "That's half the resin for the same amount of film," Wooster says. But winder technology would need to improve to produce quality rolls of the thinner film.

Kitzis also touches on sustainability through design engineering. For example, he imagines new systems that help the contents of bags settle more quickly, a development that could make it possible to eliminate more head space from some dry goods packages. Citing the need to look at packaging from a life cycle perspective, he says machines that reduce waste and improve energy utilization in packaging plants will also help boost sustainability. "The machinery guys will be a big part of the sustainability solution," he says.