Stretch Your Imagination

March 1, 2010
Material handlers can improve end-of-line packaging sustainability by reducing stretch film consumption.

The sustainability of packaging is less about the physical package and more about lowering the social, environmental and economic impacts of packaging across the supply chain. Reducing stretch film consumption is essential for improving the sustainability of transporting pallet loads.

If, at first glance, conserving a packaging material as insubstantial as stretch film seems trivial, consider that in 2006, the year the Freedonia Group used as a base for an analysis of U.S. stretch film consumption, organizations spent $1.5 billion on this material. Freedonia analysts predict that the U.S. market for stretch film used in pallet wrapping will increase 4.7% annually from 2006 through 2011. At that time, more than 1.9 billion pounds of petroleum-based resin will be consumed in the manufacture of stretch film for the U.S. market. With the cost of a barrel of oil at unheard-of highs, companies must effectively reduce usage of all petroleum-based materials, including stretch film, to contain costs.

Another look at the impact of stretch film comes from Dow Chemical. Dow reports that advances in chemistry and enhanced products, processes and services have allowed it to down-gauge stretch film by more than 25% in the last decade. The company calculates that this reduction saves, on a global basis, 1 billion pounds of polyethylene resin a year. This is the equivalent energy savings of 293 million gallons of gasoline or heating and cooling for 643,000 homes for one year. As Freedonia and Dow indicate, there is nothing insubstantial about stretch film.

Application Techniques

Stretch film is a highly engineered material, and every film is designed to be pre-stretched within a specified range to bring out the material's maximum strength characteristics. This range is usually between 200% to 300%.

There are two ways to apply stretch wrap: by hand and by machine. Hand wrapping is labor intensive and slow. Manual effort cannot effectively stretch the film greater than 10% to 20% on average. This has negative consequences on holding strength and unit stabilization. To increase stabilization, personnel often overwrap the pallet and consume more material than necessary.

Stretch wrap machines are the preferred means of obtaining high performance from the material and eliminating the negatives of hand wrapping. The more the material is stretched, the lower the usage and the greater the savings. Other advantages include lower labor costs, greater load stabilization and less damage to pallet loads during transportation.

Stretch wrap machines are typically justified on a return-on-investment basis by calculating material and labor savings. For example, companies A, B and C wrap identical pallet loads per day using the same type of stretch film that costs $45 per roll. Company A's machine achieves 25% stretch, while company B achieves 150% stretch, and company C achieves 250% stretch. Annual film costs for the three companies are shown below:

Company 90 pallets/day 250 pallets/day 500 pallets/day A-25% stretch $15,376 $42,712 $85,425 B-150% stretch $8,491 $23,587 $47,175 C-250% stretch $5,967 $16,575 $33,150

Material savings add up quickly and justify the investment in a high-performance pallet-wrapping machine.

In terms of improving the sustainability of the operation, company C at 250% stretch and 500 pallets a day will consume about 1,135 fewer rolls than company A and 285 fewer rolls than company B on an annual basis.

Company C not only lowers operating costs, it improves the sustainability of its end-of-line packaging operation. The reason is that company C decreases the number of deliveries of rolls of film into its plant and also the weight of every pallet leaving the facility. These efficiencies in transportation result in reduced energy consumption and carbon dioxide emissions.

Look for pallet-wrapping machines that achieve at least 250% stretch, which is optimum for today's high-performance films.

Film Stretch and Load Stabilization

To achieve 250% stretch, the film must undergo powered pre-stretch before being wrapped around the pallet. The pallet wrapper's film carriage uses an electric motor to turn two specially surfaced rollers, each rotating at a different speed. The speed differential stretches the film. When investigating the powered pre-stretch capabilities of a machine, look for:

  • Precision-machined pre-stretch rollers for ultimate consistency;

  • State-of-the-art polyurethane roller surface with lifetime warranty;

  • Full speed range (stop to full speed) motor speed control;

  • Drop-in threading for easier and safer film threading.

If you take a rubber band and stretch it to its limit, you will see the band become thinner as it loses width. The same thing happens to stretch film during powered pre-stretch. Equipment manufacturers minimize the loss in width by making sure the two pre-stretch rollers are relatively close to one another. Look for this feature when considering a pallet-wrapping machine because the film should lose the least amount of width possible.

As the stretch wrap machine applies film over sides and corners of pallet loads, payout speed must constantly change for uniform hold strength and unit stabilization. The reason for this is that the film must be played out faster around a corner. The film carriage's response time at corners should be virtually instantaneous, or the lag in speed-up will increase the drag on the film and promote tearing.

Operations personnel may compensate for frequent tears by buying higher-gauge wrap, which costs more and, in effect, wastes material. They do not understand that the root cause of the problem is not the thickness of the film but the application around corners. Specify a machine with state-of-the-art corner compensation/motion control technology. Operations personnel will find they can actually use a thinner gauge film with this equipment.

Also look for advanced force-to-load control. Heavier, more rugged pallet loads — for example, manufactured concrete products — require more force to load than lighter and more easily crushed loads (e.g., PET bottles). The pallet-wrapping machine must have easy-to-use, automatic force-to-load settings. Power pre-stretch, corner compensation and force-to-load settings all impact the consistency and quality of the stretch wrapping process. These capabilities also mean operations personnel can use lightweight material for the application and improve sustainability.

While recovery and reuse of material is preferable, recycling stretch film is not economically feasible for most companies. The more effective means of conserving this material is to use less by stretching the film at least 250% to 300%. Knowing what to look for in stretch films and pallet-wrapping machines helps ensure improvements in economic, social and environmental sustainability.

Mark Collins is vice president of sales with Orion Packaging, a supplier of stretch wrapping systems.

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