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New Vacuum Insulation Core Suits Temperature-Sensitive Products

Many high-value goods — from pharmaceuticals and blood products to flowers and foods — require tightly controlled temperature conditions throughout shipping and distribution. Manufacturers of such temperature-sensitive products are constantly searching for innovative insulated packaging solutions to assure safe transit while keeping costs down.

ISC Inc. is a Phoenix, AZ, developer of insulated packaging technology that exports a variety of products to locations throughout the world. The company specializes in molded polyurethane insulated shipping containers for temperature-sensitive products, offering custom design capabilities and an environmental test laboratory for thermal validation of the performance of container package configurations. When ISC recently learned of an insulation material from Dow Chemical Co. (Midland, MI) that could offer greater thermal performance than traditionally used materials, the company took notice, knowing that as the thermal efficiency of insulation material increases, so does the opportunity to lower overall distribution costs.

Greater Temperature Control
Dow's INSTILL vacuum insulation core is a patented, open-cell polystyrene foam for use in Vacuum Insulation Panels (VIPs). While VIP technology is not new, this thinner, more efficient insulation option has only recently become commercially viable. This is due in large part to the development of new materials such as INSTILL vacuum insulation core.

Compared to expanded polystyrene (EPS) "beadboard" and closed-cell rigid polyurethane (PU), which have provided adequate insulation performance in the past, VIPs using INSTILL core offer greater temperature-control assurance, leading to lower overall distribution costs. Reduced costs can be achieved through decreased package weight, use of less refrigerant and the use of less expensive shipping options (i.e., ground service instead of next day air). Or, if desired, payloads can be increased.

Unlike traditional insulating materials like closed-cell foams, foam beads or fiber blankets that attempt to trap gases to reduce the transfer of heat, vacuum insulation removes the gases within the insulating space. With the space evacuated or placed "under vacuum," the molecular presence and movement needed to transfer heat are greatly reduced. Table 1 shows the insulation performance of vacuum insulation panels vs. conventional insulation.

VIPs consist of a filler material, called a core, that is encapsulated by a thin, super-barrier film (Figure 1). The encapsulated system is then evacuated to a vacuum between 0.001 and 1.0 torr (0.0013 and 1.3 mbar) and sealed. The actual vacuum required depends on the specific core material used and the desired thermal resistance or "R-value" of the finished panel. The core, when under vacuum, serves to interrupt the "mean free path" of what few heat-transmitting molecules remain in the panel, while also withstanding external pressures that can be as high as 14.7 psi (101.4 kPa) due to the forces exerted on the VIP from atmospheric pressure. For a 1-sqft. panel, this equates to over 2,000 pounds of force (for a 1-sq.-meter panel, 10,000 kg). Being nearly impervious to outside gases, the barrier film sustains the required vacuum level (and thus, R-value) for the desired life of the panel.

To trap any molecules entering the panel or the modest outgassing that may occur from the VIP component materials, water and/or gas adsorbing materials are also placed inside the panel to maintain the vacuum for the intended life of the VIP. Adsorbents designed to attract water molecules are typically desiccants, whereas those designed to trap gases are called "getters."

Industrial Container Design
ISC worked with Dow Application Development Engineering (ADE) for more than a year in the development of an optimal VIP package design. Testing was conducted throughout the program in ISC's thermal distribution laboratory, which features multiple environmental chambers that can be programmed to simulate a range of ambient temperature profiles encountered during a product's transit or storage.

ISC ran comparison tests on three packages insulated with EPS, PU and VIPs incorporating INSTILL core. The three containers (each 13-3/8 in. long, 11 in. wide and 10 in. deep) all had 1-in. walls, identical payloads and the same amount of refrigerant. The product temperature was initially stabilized and then periodically measured and recorded via a thermocouple inserted into the payload. The container design is shown in Figure 2.

The three containers were tested at an ambient temperature of 22°C (72°F), and data from each thermocouple was read every 30 minutes. Since many temperature-sensitive pharmaceutical products must be stored between 2°C-8°C (36°F-46°F), the tests were cut off after the last probe reached 8°C (46°F).

The results showed a marked difference in insulating performance, with the VIP insulation incorporating INSTILL core maintaining product temperature below 8°C for an impressive 4.6 days. The more traditional polyurethane and EPS insulated containers maintained product temperature below 8°C for 1.7 days and 1.2 days, respectively. These results are shown in Figure 3.

1 Containers: Three identical containers were tested, one using EPS, one using PU and one using VIPs with INSTILL core as the insulating media. Each incorporated a corrugated sleeve to hold product and refrigerant.
Product: 1-L bottle filled with liquid water, stabilized at 4°C-6°C (39°F-43°F).
Refrigerant: Two 32-oz Polar Pack brick packs, which phase change at 0°C (32°F).

There are equally as impressive potential cost savings connected with the Figure 2 results. To ensure product protection, packages using EPS or PU insulation normally require shipping via next-day air, while a package using VIPs with INSTILL core could be shipped via more cost-effective methods that are less time-sensitive.

ISC is incorporating VIPs with INSTILL core into its shipping containers and temperature-controlled packaging. ISC's principle clients are in the biopharmaceutical and blood bank industries.