Phase Change Paraffins Keep Blood Cool

A new bio-based, renewable phase change material is usedto keep blood and pharmaceuticals cool during shipping.

Called "Greenbox",the innovative technology received the top prize in the 22nd Annual DuPontAwards for Packaging Innovation.

Paraffin-based phase change materials have been used tocontrol temperatures in buildings for many years. But development of the new,more pure technology, combined with application to packaging, is new.

Entropy Solutions of Eden Prairie, MN, was awarded a U.S.patentin 2008 for use of the phase change materials in packaging.

According to Entropy Solutions, traditional methods ofshipping pharmaceuticals are energy intensive or may not work adequately.

"When pharmaceutical products are removed from arefrigeration storage unit and transported for use (e.g., to hospitals) theyare often transported in an insulated container overnight which may or may notcontain, for example, ice (i.e., frozen H₂O) or dry ice (i.e.,frozen CO₂)," says the patent. Ice, however, melts at 0C, which isnot adequate to maintain blood. Other approaches use electric power forrefrigeration.

"It is desired to have a lightweight, highly reliable,portable container that maintains the temperature of pharmaceutical products orother temperature sensitive materials over a relatively long or given period oftime," says the patent.

A material (paraffin or eutectic salt) may be designed tochange phase (melt or solidify) in a range around 4C, which is described as anideal temperature for storing bags of human blood.

In the Greenbox, phase change materials are placed withinopen areas of corrugated panels, which may be made of fiber or plastic. Anagent may also be injected to trigger temperature movements by the phase changematerial. For example, the agent may be used to initiate solidification when aliquid exists at a temperature that is lower than the normal solidificationtemperature.

The amount of heat needed to convert a kilogram of solidto a kilogram of liquid via melting is defined as the latent heat of melting.Entropy Solutions says that the magnitude of the latent heat of melting explainsthe effectiveness of melting as a cooling process. When a kilogram of ice melts,it absorbs about 330 kJ (kilojoules) of heat. To melt a kilogram of a typicalparaffin, about 232 kJ are needed.

Paraffins are highly engineered to achieve the exactheat-blocking required. Paraffins melt at a different temperature based on thenumber of carbon atoms. For example, the Astor brand of paraffinsproduced by Honeywell may be designed to store pharmaceutical products within aspecific temperature range around 8C.

Their sharp melting profiles allow controlled energyrelease and absorption. They are also stable and inert, making them suitablefor use in the Greenbox. Paraffins, which are relatively low in cost, can alsobe blended to achieve a specific temperature goal.

The DuPont judges lauded the Greenbox for dramaticallyreducing freight costs and packaging waste, in addition to its role in preservingtemperature-sensitive products. Companies such as Walmart Specialty Pharmacy,Abbott Laboratories, Amgen, American Red Cross and Medtronic use the system toship pharmaceuticals, biologics and blood supplies.

"PureTemp and its packaging applications likeGreenbox are changing the way life science companies do business, and we arehonored to receive this recognition from one of the world's pioneers insustainable packaging," Entropy CEO Eric Lindquist said.

Phase Change Paraffins Keep Blood Cool A

The Greenbox can be engineered to provide cooling at very specific temperatures.