Originally Published PMPN February 2005

Transportation Packaging

Phase-Change Materials Cut the Ice

Water-based gels are the workhorses of temperature control in the shipment of temperature-sensitive products. For esoteric applications, however, phase-change materials make it possible to hold a wider range of temperatures than ever before.

Jenevieve Blair Polin
Contributing Editor

TCP Reliable’s Phase 5 phase-change material is packaged using a thermal control panel that allows for a 72-hour shipping range with standard insulated shippers.

Giving Water a Run for the Money

The drawback of water-based gel as a refrigerant is the need to isolate it from product that requires a temperature range of 2°–8°C and that can’t tolerate freezing. “That meant a lot of design work,” laughs Sanford L. (“Sandy”) Cook, CPP, president of Thermal Packaging Solutions LLC (Ocean, NJ). “You had to put expanded polystyrene, urethane, bubble pack, or some other insulation between the gel packs and the payload. That made the package heavier and bigger and more expensive to ship.”

This problem prompted Cook’s firm to work with packaging manufacturers and suppliers and biopharmaceutical companies to develop high- and low-temperature PCMs, including those incorporating paraffin.

“If you put a match to a candle, it phases—liquefies—at a much higher temperature than water, and it solidifies at room temperature,” explains Cook. “So we took advantage of that characteristic to raise the phase point of a gel pack. Since the mean temperature for refrigerated biologics was 2º to 8ºC, we shot for 5ºC as the nominal. Now, you don’t need to insulate the gel packs from the precious biologics. You can wrap the product in gel packs and keep them at the right temperature. Hence the package is smaller and lighter weight.”

“Paraffins,” adds Larry Gordon, president of Cold Chain Technologies Inc. (Holliston, MA), “are composed of long carbon molecules that can be manipulated to alter their molecular weight. In doing so, one can create a paraffin solution to change phases at just about any temperature desired.”

Last fall, TechPak Solutions—now Life-Like Products, Northeast (Peabody, MA)—introduced the Guardian PCM 4C, which changes phase at 4ºC. Bruce Truesdale, general manager, explains the firm’s hybrid approach, which controls both cost and temperature. “We can use water-based gels for the bulk of the work of absorbing heat inside an insulated container, at about a 2:1 ratio of water-based gel packs to PCM 4C packs. The 4C acts to buffer the extreme cold of the frozen water-based packs, but it also has a second benefit in that it partially phases when it’s protecting against that very cold temperature. You get a kind of bonus at the end of the trip, when you still need BTU absorption (to keep it in that 2º to 8ºC range). The PCM 4C has, in a sense, become another gel pack, helping you get more hours out of your package,” Truesdale says.

The U-tek line of PCMs from SCA ThermoSafe incorporates hydrated salts, which helps control costs.

Cold Chain manufactures paraffin-based PCMs, but Gordon acknowledges that their biggest drawback is price. “They are an order of magnitude higher in price than a standard refrigerant gel. As a result, we have found that we are often able to meet the needs of our customers in a more effective and economical way without the use of paraffins.”

TCP Reliable Corp. (Edison, NJ) has a different view. “PCMs maintain narrow temperature ranges and generate multiple benefits to the end-user,” says president/CEO Maurice Barakat. “Our engineers had to rethink the package design, and they created Thermal Control Panels (TCPs) to allow customers to envelope the payload area and maximize the effectiveness of the PCMs. This design allowed us to extend the shipping range to 72 hours using standard insulated shippers, and they can be used for multiple temperature ranges.” This design won the Ameristar and Worldstar Packaging Awards in 2004.

Cold Ice Products (Oakland, CA) is another company investing in water-based PCMs. “We offer multiple phase-change refrigerants,” says Raymond Wilhelm, Cold Ice’s president. “We can custom formulate these products for different companies.” The Cold Ice product line includes PCMs for products requiring temperatures of 0° to –23°C.

Similarly, AcuTemp (Dayton, OH) offers a wide range of PCMs. “Water-based PCMs are the cheapest and easiest to use,” says Mike Sieron, the company’s sales and marketing manager. “We supply paraffin-based, nontoxic PCMs that can be blended to achieve the proper temperature. These are the best choices for use in closed shipping cycles where the product is returning.”

Sieron also adds that AcuTemp is aggressively targeting the pharmaceutical industry. “FDA is really starting to put some teeth into its transportation regulations,” he says. “Companies will need the proper shipping materials more than ever, and it’s a great opportunity for suppliers of PCMs.”

Polar Tech Industries (Genoa, IL) also manufactures temperature-sensitive packaging and shipping products, such as its Ice Brix line of gel refrigerant packs. “When it comes to surrounding your product effectively, you have to use ice,” says Don Santeler, the company’s president. “Phase-change materials can be an excellent solution, but they’re not for everyone. I’d say they’re good for only 1–2% of the pharmaceutical market.” Polar Tech’s Ice Brix line keeps products at a constant and desirable temperature for days at a time, according to Santeler.

Holding Heat

Laminar Medica’s new PCMs (right) offer multiple individual phase changes over a range of temperatures.

Much less expensive, and therefore of great interest, are PCMs that incorporate hydrated salts. SCA ThermoSafe Brands (Arlington Heights, IL) has been supplying PCMs using various hydrated salts under the U-tek brand name for more than 30 years. Recently, ThermoSafe began selling microencapsulated paraffin-like PCMs rated at 28°C and 35°C, as additions to its U-tek product line. The 35°C material has been particularly successful in a custom-designed configuration maintaining 36°C ± 3°C for a human cell–infused medical device in transit. This package replaced the customer’s own design that had used 25 or more units of warmed sterile saline to increase the thermal mass. According to SCA ThermoSafe, microencapsulation simplifies the packaging process for these materials and provides important flexibility for thermal engineering. It also brings to the market unconventional PCMs in a reliable pouch format that is more familiar to customers.

TCP Reliable also offers a broad range of PCMs, such as the Phase 5 and Phase 22. “We just completed a project with a large Canadian blood supply organization that had tried to maintain narrow temperature ranges [2°–8°C and 20°–24°C] in very demanding conditions,” explains Barakat. “Their final design—actually the only one that worked—is based on our PCMs, and we hope to implement it this spring.” This customer, Barakat explains, has developed and validated every step of the blood transit system from collection to the final destination in the hospital.

“We have supplied thousands of Thermal Control Panels for various temperature ranges without significant packaging performance issues,” continues Barakat. “PCMs require a formal quality assurance program to ensure that the containers are leakproof and reusable and that the phase change performance is repeatable. We are able to target very precisely most of the temperature ranges from –20° to 27°C and work with various chemical formulations, including eutectics and hydrocarbons. Our design approach allowed us to reduce the size and weight and simplify the conditioning of the packs and package qualification. This created a savings in freight and handling that will more than pay for the increased cost of the packaging.”

Life-Like’s Guardian PCM 28C—which holds temperature around 28ºC—was developed in response to a customer’s request. The customer, Organogenesis (Canton, MA), was shipping its Appligraf laboratory-grown living human skin in a custom-engineered package developed by Source Packaging of New England Inc. (Warwick, RI). (See the article “Smaller Boxes Spell Savings,” in the February 2003 issue of Pharmaceutical & Medical Packaging News, for details on the original package.) The company was limited to shipping in this package only via overnight air freight.

A blood shipper from SCA ThermoSafe features the company’s PCMs with hydrated salts.

“Their customers could schedule surgeries only Tuesday through Thursday, because Organogenesis couldn’t ship its product over the weekend. So they were really searching for a different kind of phase-change material, which would essentially grow their sales,” Truesdale explains. “They were looking for a 72-hour shipping window, and they couldn’t do that with standard phase-change materials. Now they actually get up into the low-80-hour window using the air-insulated box and this new PCM,” he adds.

Laminar Medica (Tring, Hertfordshire, UK) offers inorganic hydrated salt–based PCMs. The company is currently in the process of launching a completely new range of PCM solutions, based on these salts, called Medisorb and Mediphase.

The virtues of these new PCMs, says Laminar’s Katrina Bray, include storage and release of latent heat energy at nearly constant temperatures, making them similar to water. “Inorganic PCMs also store much denser values of latent heat energy in comparison with the organic variety, and therefore packaging performance with 0ºC systems is achievable,” says Bray.

Laminar claims that hydrated-salt PCMs can control temperatures ranging from –40º to 120°C. Laminar expects the new PCMs to impact package design for temperate product shipping. Given the changes in ambient temperatures when transporting platelets, for example, at 20°–24°C, a package may have to cope with significant periods of positive and negative temperature stress. “If a single-phase material were used,” Bray comments, “the package design would need to incorporate a combination of solid- and liquid-phase PCMs. The former prevents the payload from getting too warm and the latter from getting too cold. Sure, the necessary stability is achieved, but assembling the shipper becomes more complex and payload space is much reduced. With one of Laminar’s new-generation PCMs, however, multiple individual phase changes are offered over a range of temperatures using one preparation.”

One drawback of hydrated-salt solutions is their potential corrosiveness. “I’ve personally seen corrosive damage in testing a room-temperature PCM in our lab,” says Tom Pringle, acting technical director for ThermoSafe Brands. “The material leaked from the bags, and where it leaked, it actually removed the coating on the metal floor of our test chamber.”

Cold Chain’s Gordon reports a similar experience. “As a company, we have avoided hydrated salts, because they are such a mess. One customer gave us their hydrated salt and wanted us to test the package. The hydrated-salt solution leaked and dripped on the aluminum floor in our thermal chamber and corroded the surface. I just don’t want to introduce anything corrosive in my plant,” Gordon stresses.

Figure 1. Comparison of the phase-change time of low-temperature gels (–20°C and –50°C) with dry ice and water-based 0°C PCMs (phase-change materials). The test method involved using 1-lb PCMs frozen 10°C lower than their rated temperature and 1 lb of dry ice, all held at 30°C ambient temperature with no insulation. (10 lb of dry ice has a 24-hour sublimation rate.) The chart values should be viewed respective to the phase temperature of each of the PCMs (i.e., 0°C PCMs would not be used for a -20°C application). Insulations will extend phase time at variable rates based on their K value. Source: Thermal Packaging Solutions (Ocean, NJ) (click to enlarge).

Hydrated-salt-based PCMs are often available only in rigid bottles, for good reason. “In solid form, these are salt crystals,” Gordon points out. “They have very sharp edges that will rip right through a plastic pouch.”

With proper packaging, however, these PCMs may be manageable. “We have shipped a large number of units—probably 50,000 plus—to various customers without any leakage problem,” says TCP’s Barakat.

Laminar produces hydrated-salt PCMs in both rigid bottle packs and flexible, tough laminate materials. “Provided the proper control procedures are observed, disposal and spillage issues are, for all practical purposes nonexistent,” says Laminar’s Bray.

Another problem, though, according to Gordon, is that “hydrated salts tend to be unstable. If you run them through a phase change, they do not always perform the same way the second or third time around. This makes for some difficult reproducibility when considering qualification testing for pharmaceuticals. One reason is their tendency to precipitate, meaning that the solids of the salt reform and come out of solution.” Precipitation changes the molarity of the solution and thus alters the temperature at which phase change occurs.

Pringle points out another shortcoming of novel PCMs. “The staging of these materials above or below their phase point (solid or liquid phase) is inconvenient compared with using water-based gels that are staged in conventional refrigerators or freezers at refrigerated or frozen temperatures,” he explains.

This applies to both paraffins and hydrated salts. Explains Pringle: “Take, for example, a 4°C PCM. For summer shipments you have to stage it below its phase point to take advantage of its energy-absorbing characteristics. It goes from a solid to a liquid as it absorbs heat at 4°C. Conversely, in the winter you have to stage the 4ºC PCM above 4°C to gain the most benefit, as it gives off heat converting from a liquid to a solid at 4°C. There is no convenient staging equipment at constant 8°C or 2°C.”

Inefficiency is another negative aspect of PCMs. “Cost, hazard class, and convenience aside, the latent heat energy released as these materials solidify, or absorbed as they liquefy, is far less than that of plain water. Water solidifies in a unique way compared with most other materials,” Pringle points out. “As these other materials change from a liquid to a solid, their molecules stack up like cord wood. Water molecules actually form a crystalline structure that is the primary reason for their latent-heat advantage. Therefore, until new materials are identified and developed to overcome the disadvantages noted above, water-based gels used at various temperatures are still the temperature stabilizer of choice for shipping most temperature-sensitive pharmaceutical products.”

All components of a cold chain solution should be evaluated on an individual basis, adds Rod Derifield, CEO of EnviroCooler (Huntington Beach, CA). “EnviroCooler believes that the critical aspects of each component that affect performance should be characterized to understand why a particular solution performs in a certain way,” he says. “Specifically, this information is used for quality control and incoming inspection of each component, as well as component qualification (CQ) prior to qualifying or validating the entire process as part of operational and performance qualification. For gel packs, we believe such characteristics include the freezing point and melting point, rate of change, and total energy stored. In our view, understanding these product-impacting parameters is the foundation of a science-based approach to solving cold-chain problems in a consistent, repeatable, and controllable manner.”

Rivaling Dry Ice

At the other end of the temperature spectrum are PCMs that change phase at subzero temperatures. “We just finished a validation for a major healthcare products distributor in which we had to hold –20ºC as the high temperature and –40ºC as the low temperature,” Cook mentions. “So we worked with a company to develop a PCM that would hold it at –30ºC, and it was very successful.” The distributor has been using the low-temperature PCM since the middle of 2003 for many pharmaceutical shipments globally.

Since 1998, TCP Reliable has sold DICE products that hold –50ºC. “We have since developed custom formulations that maintain the internal temperature within the deep-freeze temperature range,” says Barakat.

Last year, SCA ThermoSafe Brands introduced a –50°C U-tek gel pack, the Model 760, which serves as an alternative to dry ice. Like its brethren, this PCM is not as efficient as its archetype. “No gel pack can match dry ice pound for pound,” explains Kevin Grogan, the company’s director of marketing and business development.

“The thing about dry ice is that it makes a double-phase change. It goes from a solid right to a gas, and skips liquid. As it sublimates, it releases a tremendous amount of energy. But what we’ve managed to do is offer something that gets down to within the desired temperature range, –50°C. It’s not –80°C, but it’s as close as we’ve been able to come while still offering a strong latent heat characteristic. In so doing, it can often eliminate dry ice altogether.”

What makes this option attractive? Some airlines now limit the amount of dry ice aboard each plane. “Because the cargo hold in most planes is sharing the same air with the cabin, if you had too much dry ice in the cargo hold, you can seriously degrade the air quality in the cabin,” Grogan explains.

Such a restriction on the use of dry ice in transport could cause a disastrous delay for a temperature-sensitive product. “The way you get around that if you’re in our industry is you make very efficient boxes that use a small amount of dry ice. We do that. Or you make dry-ice substitutes, like our –50° U-tek,” Grogan adds.

Copyright ©2005 Pharmaceutical & Medical Packaging News