High-density polyethylene (HDPE) is a popular choice for containment of paraffin- and plant-oil-based phase change material. But under some conditions, PCM-filled HDPE containers are vulnerable to leaching.
Inhance Technologies of Houston has developed a process called ColdShield™ to enhance HDPE's barrier properties. In an email interview, Prakash Iyer, senior vice president of business development and technology at Inhance, answered questions about the process.
Q: How does ColdShield work?
A: HDPE is not stable when exposed to organic solvents such as paraffins and plant oils. Many PCM formulations are organic in nature and will readily permeate through HDPE, causing contamination of the surroundings and irreversible damage to the contents being transported. Inhance, through the use of its proprietary barrier treatment process, developed ColdShield technology to specifically prevent permeation of paraffin and plant oil based phase change materials.
"ColdShield provides a double barrier layer by protecting the inside and outside wall of the PCM container. The technology converts the surface of ordinary HDPE into a high-performance barrier material which repels paraffins and plant oils. The surface of HDPE is converted into a ‘PTFE’ like material with excellent barrier properties. By keeping the PCM formulation in the bottle from permeating, Inhance’s ColdShield prevents temperature drifts of the packaging due to selective absorption of the PCM formulation into the bottle walls. In addition, due to its superior barrier protection, ColdShield allows reuse of the PCM containers for many years with minimal to no reconditioning."
Q: Inhance tested five PureTemp formulations in ColdShield-enhanced HDPE containers. Describe the results.
A: "Inhance tested PureTemp 4N, PureTemp 8N, PureTemp 18X, PureTemp 20X and PureTemp 23N to study how these PCM formulations permeated through HDPE containers. Testing for permeation was done at 50° over 28 days, which would roughly equate to a two-year shelf life. All PureTemp PCM formulations, except for PT20X, showed varying amounts of permeation (ranging from 0.25-3% weight loss) through HDPE. The same PCM formulations when tested in ColdShield-treated HDPE containers exhibited less than 0.1% permeation weight loss. In addition to PureTemp formulations, Inhance also tested hexadecane and tetradecane, which are commonly used in PCM formulations. The permeation rates of hexadecane and tetradecane without barrier protection is 3-5%, while ColdShield reduces this to 0.1%. The chart below reflects the data."
Q: How do you test ColdShield-treated containers for leaching?
A: "One of the simplest tests to evaluate for leaching is to do a weight-loss test on HDPE containers filled with these PCM formulations. Testing can be done at different temperatures for varying amounts of time. 49CFR.173 Appendix B, describes the commonly used test procedure to evaluate for permeation of liquids in plastic packaging, and is generally done at 18°C for 180 days, or 50°C for 28 days, or 60°C for 14 days. Per the U.S. Department of Transportation, the maximum permissible permeation rate for the above testing conditions should not be greater than 2% for nonpoisonous liquids."
Q: Describe the shape and dimensions of the containers tested with PureTemp, including wall thickness.
A: "The testing was done with 16-ounce round containers with a nominal wall thickness of 1mm. To give one perspective, the 16-ounce round container will be the best-case scenario for permeation since the surface area to volume of liquid is minimized, resulting in lower permeation numbers. In the case of HDPE PCM containers, they are generally flat and rectangular, increasing the surface area to volume ratio, which would result in worse permeation numbers."
Q: Is the ColdShield process patented?
A: "ColdShield technology has been developed by Inhance using proprietary process technologies. The technology itself is based on post-mold fluorination of HDPE containers, but Inhance has worked to understand the market needs and worked closely with its customers to come up with the optimum barrier required to eliminate permeation of PCM formulations."
Q: Are ColdShield-enhanced HDPE containers now being produced commercially for any PCM manufacturers?
A: "ColdShield-enhanced HDPE containers are being commercially used by some of the largest manufacturers of PCM formulations as well as OEMs involved in the cold chain logistics chain."
Q: On a percentage basis, how much does the ColdShield process add to the cost of an HDPE container?
A: "The cost of ColdShield is minimal compared to the value that it brings to the OEMs. The permeation of PCM into the package can result in costly recalls and contamination issues. Cold chain is used to often transport vaccines, biologics and organs across the globe and the loss/contamination of these contents can run into the millions. ColdShield provides the best barrier solution for HDPE rigid gel packs, thereby maintaining the PCM composition, while providing safe storage during transportation."
Q: Has research on ColdShield performance been published?
A: "ColdShield brochures are available on www.inhanceproducts.com. For further information contact firstname.lastname@example.org. Inhance is glad to partner with companies to educate them on the advantages of ColdShield and works closely with its customers to provide the optimum solution. Inhance also has test capabilities to carry our permeation testing as well as other fitness testing of different PCM formulations."
Q: Has the effect on heat transfer or other PCM performance characteristics been tested? How about the effect of, say, thousands of freeze/melt cycles on barrier properties?
A: "Inhance’s ColdShield technology has been tested and approved by OEMs and molders through stringent testing, including, but not limited to, permeation, freeze/melt cycles as well as mechanical testing. Since ColdShield is not a coating – ColdShield chemically transforms the surfaces of containers into a material that is resistant to solvents – there is no cracking or peeling of the barrier layer. In addition, since ColdShield does not change the bulk properties of the rigid gel pack, there is no change in the heat transfer profile. In addition, ColdShield provides a double layer of protection since the inside and the outside of the container is protected equally."
Q: Who are your competitors in this field, and how are your processes different?
A: "There are three or four options when it comes to how PCMs are packaged today. These include non-barrier HDPE containers, metal or barrier plastics such as nylon. In many cases, Inhance's ColdShield is the most economical and the best performing barrier solution in the market. As the market moves more towards better temperature control ranges, more paraffins and plant-oil based PCM formulations, ColdShield is the preferred barrier solution in the industry."
Q: What is the potential market size for ColdShield?
A: "Inhance currently treats millions of rigid PCM containers using its ColdShield technology. The market for these containers that need barrier protection from PCM formulations is growing significantly, due to some of the above stated reasons. The addressable market for Inhance’s ColdShield continues to grow with greater adoption of PCM formulations."
A company video illustrates some of Inhance Technologies' capabilities.