Effect of Time and Temperature on Stretch Wrap

Duration: Spring 2019

Students: Madison Reynolds and Jack Lumley

Faculty Advisors: Dr. Laszlo Horvath and Dr. John Bouldin

Palletized unit loads often depend on stretch wrapping to provide stability for products as they are transported all over the world. The containment force, or the combination of a film’s resistance to stretch and its compression of the load, is especially important to consider as it compresses and affects the ability of a unit load to resist movement. Linear low-density polyethylene (LLDPE) films are the most common throughout the industry in different gauges and production methods. There are also different films that may be marketed as high performance and contain additives to help improve mechanical properties. In addition, there are cast and blown films, which are manufactured using different methods that give properties such as better puncture resistance or gauge control.

Containment force is affected by the amount of pre-stretch and post-stretch applied to the film through different settings on the wrapping machine. Pre-stretch is the stretch a film experiences as it is going through the first two rollers of the wrapping machine; post-stretch is the elongation of the film as it exits the film carriage and contacts the load being wrapped. The pre- and post-stretch that a film experiences is the main component that manipulates containment forces applied to unit loads.

The effects of temperature on the containment force are not well explored, but it is speculated that if a wrapped unit load is heated up for a prolonged amount of time, containment force will decrease. This is already observable with standard temperatures as the film relaxes over time, but it is unknown if heat will cause a heightening of this phenomena. Failure of containment force on unit loads is already a hot topic issue that affects many companies financially because it causes many safety issues.

However, very few research investigations have been completed to specifically measure and observe films’ containment performance, stretch, and stabilization regarding temperature over time. This does not include how other variables impact the film itself and only includes its overall performance compared to a uniform and rigid unit load. Due to this lack of data, it is worthwhile to investigate these areas, especially considering how widely stretch film is used. If it is learned that a unit load is significantly affected by heat, research into how much it is affected can help in taking preventative maintenance for future situations.

The objective of the study was to investigate the change in containment force as a function of time and temperature. Multiple commonly used stretch film types and widely used containment forces were used.

These results conclude that heat and time do have a significant impact on the final containment force exerted on a unit load, more so at higher starting containment forces. The containment force decreased as much as 55% after 12 hours when greater containment force was used. There was no observable difference between the performance of films manufactured using different methods. The findings of the research can have a significant consequence to the way we design unit loads for stability. Thus, more investigation is needed to fully characterize the effect.