Overview of Cold Chain Packaging Systems
Packaging Systems (Insulated shippers) for use in the cold chain industry are categorized as Active, Passive, or Hybrid systems, and sometimes include the use of thermal covers. Passive shippers are the simplest and most cost-effective shipping system design among the three. Passive shippers do not rely on an external power source to help maintain the payload temperature. Passive packaging relies on thermal insulation of various materials, which slows the conduction of heat, which can affect the interior payload. They can be designed for single or multiple use and usually consist of an outer shipper (single/multiwalled corrugated paper shippers, corrugated plastic containers, and durable molded plastic shippers), thermal insulation (EPS foam, PUR/PU foam, VIPs, bioplastics), a refrigerant (gel pack, dry ice), thermal buffer (PCM), and dunnage to fill voids. Corrugated paper-based shippers are the most popular and most affordable for single-use shippers. Outer plastic shells increase durability over paper, resist moisture, and are easily cleanable. Molded polymer shippers are similar to totes and outdoor coolers, have long-term reusability, and protect against mechanical hazards. The shell materials can affect the thermal performance of the shipper, but minimally. It is the insulation which is the primary line of defense against both heat and cold.
Material Selection in Passive Shippers
The choice of materials used to make the shipper is affected by the type of shipment, temperature, time to ship to delivery, ambient conditions, and delivery mode. The choice of thermal insulation is a prime consideration of a passive shipper’s design. Thermal insulation must have a high R-value (resistance to heat transfer by conduction) to slow heat transfer. Key factors to consider when selecting thermal insulation include cost, durability, and reusability of the insulation. VIP panels have the best R-value, but are heavier than foam, and are subject to puncture, which will render the VIP panel ineffective. EPS foam must be 10 times thicker than a VIP to have the same thermal performance. It is much cheaper. PUR foam falls in between the two in cost and R-value. More environmentally sustainable options to EPS and PUR are insulation materials made from starch, wood, and paper. PLA is a bioplastic (non-petroleum).
Thermal Design and Assembly Considerations
The quality of design of the shipper needs to be taken into consideration. Thermal insulation can be designed to minimize gaps (thermal bridging), or weak points where heat can transfer in/out of the shipper through conduction, which will cause the payload to heat up or cool down more quickly. Two-part, or “C shaped” insulation can be fitted together with fewer gaps and is faster to assemble than when several individual panels of insulation are fitted together inside the shipper, especially due to shifting of the insulation during movement during shipment.
Use of Refrigerants in Passive Shippers
Passive shippers can also utilize refrigerants (dry ice, gel packs) to increase the temperature range the payload is exposed to during transit, while extending the timeframe the payload can be shipped without an excursion. Both product types have their benefits and challenges, with gel packs being the simplest, most cost-effective solution. The gel packs need to be preconditioned in a flat shape in order to prevent thermal bridging. Gel packs come in mats to form a “C shape” pack out which helps to mitigate this by better surrounding the payload. Dry ice can be utilized but can present its own conditions and hazards (See Frontiers blog: “Dry Ice and Its Use in Cold Chain Packaging Industry Today”). Dry ice will require a liner/thermal buffer, with special panels to help prevent its shifting during transit, compensate for shrinkage in volume during sublimation, and to help prevent thermal bridging as a consequence of this. In addition, the CO2 sublimate needs to escape under specified conditions, or it can not only become a hazard, but can risk supercooling of the payload itself.
Qualification and Testing Standards
Passive Packaging Shippers can be qualified through rigorous testing protocols to meet ISTA testing standards. These standards (i.e., Standard 20; 7E, 7D) can be used to certify the shipper’s payload will remain safe when the package is exposed to a range of conditions the package may endure in a variety of shipping lanes. These conditions include specific atmospheric changes (temperature, humidity, pressure) over a variety of time frames, shocks (drops and impact), vehicle vibration, and compression (static, dynamic, and machine).
