by Pan Demetrakakes, Editor

Sustainability is a smart strategy, but in many cases, it goes only from the neck down.

Closures have often been an afterthought in sustainability strategies -if thought of at all--for several reasons. The amount of plastic or metal involved is relatively small, which reduces the potential for material savings, or so the thinking goes. Lightweighting them has the potential to adversely affect performance. And they usually are made of resins other than polyethylene, which often is the only one a recycling center will accept.

But end users who are committed to sustainability can find a lot of potential in closures, especially when they’re considered as part of an overall strategy.

Some of the most high-profile lightweighting projects, such as extra-light water bottles for Nestlé and others, have included short-skirt closures. These save on plastic for the bottle finish as well as the closure. They also have the potential to be used on both single- and multi-serve bottle sizes, making capping more efficient. Capper conversion kits are available from some manufacturers to make the adjustments necessary for handling the shorter closures.

Shortening the skirt is one of the major strategies for making closures more sustainable. (Graphic courtesy Weatherchem Corp.)

Skirting the issue

The two major skirt types are 400 and 485, meaning the depth in inches (0.4 and 0.485 inches, respectively) between the inner surface that contacts the lip of the bottle and the bottom of the skirt. A shorter skirt means a shorter bottle finish, for a savings of plastic that can add up in a high-volume operation. When Kraft Foods made its much-lauded switch to a lighter bottle for salad dressing in 2008, moving to a 400 closure was part of the strategy.

“With some of our newer projects, we’re really encouraging people to go with the 400 skirt finish,” says Whitney Swamy, product manager for Weatherchem Corp. “It’s much shorter, and those caps themselves are very light as well.”

Another material-saving alternative is switching from screw-on to snap-on closures, says Craig Sawicki, executive vice president with TricorBraun. Snap-on closures don’t need threads, allowing for reduced plastic in both the closure and the container finish. A major orange juice producer recently made the switch from screw-on to snap-on closures for its carafe-like polyethylene terephthalate (PET) bottles, Sawicki says.

As closure skirts get shorter, they raise the issue of product security, because there are fewer threads to engage the closure and hold it in place.

“As you shorten the finish, you also decrease the thread engagement,” Sawicki says. “It’s possible that you have sealing issues just because of the minimal engagement of a 400 versus a 410 or taller finish. So we’ll frequently adjust the sealing characteristics of the cap to make up for that difference in thread engagement.” Induction liners and valve seals are two options that offer extra security, he says.

Custom applications allow for even better coordination between closures and containers, which yields more potential for lightweighting, says Jason Stull, sales and marketing director of Stull Technologies.

“In many cases, we will develop custom closures that will coordinate with a custom bottleneck,” Stull says. “That allows us to offer unique functionality and advantages that you couldn’t achieve if you were just looking at the closure. We look at the package as a system, so in some cases we’re able to reduce the material in the container as well as the closure, through the closure design, by focusing on the entire package.”

Other aspects of sustainability with closures are invisible to the consumer, and often to the closures’ end user, but can make a difference nonetheless. One of these has to do with what goes within the manufacturer’s plant.

When closures are lightweighted, it not only takes less material to mold them, but less energy. The energy savings carry over into shipping. Other manufacturing aspects can be “greened” as well. Weatherchem, for instance, has instituted zero-waste manufacturing practices in its production plant, with the goal of sending nothing to landfills in a few years-no scrap, corrugated, paper or other waste.Resin restrictionsOne aspect of sustainability that hasn’t taken hold very well with closures is resin choice. The major sustainable strategies here are to choose a resin that is easily recyclable (which almost always means some form of polyethylene), has completely or partially recycled content, or is biodegradable and/or renewable bioresins like polylactic acid.

However, when it comes to closures, all those strategies are problematic. Polypropylene (PP) is the most popular choice for closures because of its rigidity and durability, which polyethylene usually can’t match. Swamy says Weatherchem looked into bioresins, but they didn’t perform well. As for recycled resins, regulations regarding their use for food-contact applications make them hard to use for closures.

Stull says that to comply with FDA food-contact regulations, a closure manufacturer that wants to use recycled plastic would have to specify resin with a strictly enforced supply chain, from the post-consumer or post-industrial source onward. That gets expensive.

“To achieve that [desired] quality level with post-industrial or post-consumer material, the feedstock has to be tightly controlled,” he says. “Because of the control of that feedstock, it’s either difficult or more costly to obtain. For customers who truly have a commitment to it, they’re going to do that. But a lot of time, the cost outweighs the benefits.”

 There is one bright spot, however: a growing movement to get recycling centers to accept PP. Whole Foods Market stores, for example, have instituted a program called “Gimme 5” to encourage consumers to turn in PP packaging (PP is No. 5 in the recycling codes that appear on the bottoms of containers). The program is oriented toward containers like yogurt or cottage cheese tubs, but Swamy notes it can also encompass PP closures.

Closures may not be the most likely packaging component to change for sustainability’s sake. But end users who are scrutinizing their packaging with a green eye would do well to start at the top.F&BP

For More Information

Stull Technologies


Weatherchem Corp.