In this article, Kevin Valentine, Chief Technical Officer at TP3 Global Limited, discusses why performance indicators such as R-values are only part of the story. Pharmaceutical companies and their logistics partners are enjoying more availability and a wider range of temperature-controlled distribution lanes within pharmaceutical supply chains than ever before. This means more choice when specifying thermal protection solutions that are both cost-effective and fit-for-purpose.
This has led to a current trend of moving away from temperature-controlled packaging solutions, particularly as well-controlled distribution lanes and effective thermal covers become the norm. Although designed to provide a greater level of protection in uncontrolled distribution lanes and general cargo facilities, temperature-controlled packaging solutions can also be costly and offer very low payload efficiency. In controlled distribution lanes, for example, they are often over-engineered and can provide a greater level of protection than is actually required.
As a result, thermal protection solutions are becoming increasingly popular within controlled distribution lanes. This is, however, bringing its own set of challenges, including the lack of a consistent approach to product performance assessment.
Setting the standard
The design, qualification and implementation of temperature-controlled packaging solutions within the pharmaceutical supply chain has long been supported by well-established and accepted industry standards, such as ISTA 7D and, more recently, ISTA 7E and its supporting testing procedure, Standard 20. The same, unfortunately, cannot be said of thermal protection solutions such as thermal pallet covers, PMC covers or container liners, which are less well served by a common approach to performance assessment and qualification.
Take cover
Thermal covers protect against three sources of heat exchange: conduction, convection and radiation. A common measure of performance, which is also the most likely to be requested by customers, is the material’s R-value. This measures the material’s ability to resist heat transfer by conduction, with the higher number indicating a higher resistance. The problem is that this only tells part of the story!
R-values do not take into consideration the importance of either convection or radiation, which has a particular relevance for breaks within a controlled distribution lane. This is because exposure to direct sunlight is a major source of radiated heat transfer. It is not uncommon for the temperature in direct sunlight to be 15–20 °C hotter than the ambient temperature in the shade. A break in a controlled lane on a warm summer’s day could, therefore, see a pallet exposed to direct sunlight temperatures of 50–60 °C, even in temperate regions. For this reason, a thermal cover’s ability to reflect radiated heat is of paramount importance; yet, it is not wholly represented within a material’s R-value.
Madness in the method
In addition to this, there are a number of discrepancies regarding the measurement of R-values. There is potential for incorrect comparisons of a material’s thermal performance when using R-values, owing to a confusion between International Standards of Units (SI) and Imperial Units (US). The US R-value unit, which is measured as BTU/(h x ft x °F), is 5.68 times greater than the SI R-value unit, which is measured as (m2 x k)/W. Both can be referred to as a measure of an R-value, but they are often quoted without their corresponding unit of measurement, which can make comparisons between different values difficult and often misleading.
R-values will also differ based on the test method adopted. A material tested with a 25 mm air gap between both its surface layers and the testing device, for example, will show a higher R-value than the same material tested with no air gaps. It is therefore important to understand which test method has been used to derive the R-value. This includes consideration of the material’s thickness, as well as the temperature at which it is tested. The thermal conductivity of a material can change at different temperatures, with the R-value differing by as much as 10% when tested at hot (>25 °C) or cold (<0 °C) temperatures.
Keeping things consistent
The importance of understanding how a material’s R-value has been derived cannot be underestimated. Yet, with no accepted industry standard in place, it remains difficult to gather coherent and comparable data from which an informed decision can be made.
The use of standard methods for testing and reporting the thermal properties of a material that is used for the manufacture of thermal protection solutions would, of course, help pharmaceutical companies and their logistics partners to compare alternative materials and reduce any risks when adopting a solution.
In the absence of such a standard, however, specifiers and quality personnel should assess the foundations of the thermal protection solution’s testing and qualifications, by ensuring that the equipment, methodologies and procedures are conducted in an appropriate and consistent manner.
Temperature-controlled distribution lanes will continue to develop, as will the adoption of thermal protection solutions to mitigate against the risks from inevitable breaks within these lanes. It will therefore become increasingly important for specifiers and end users to understand the performance data and their origins as part of the qualification and implementation of such products.
Ultimately, a level of standardisation within this process will be required to reduce risk, improve quality and reduce costs within the distribution of temperature-sensitive pharmaceutical products. TP3 Global uses ASTM C518-17 Standard test method for steady-state thermal transmission properties by means of the heat flow meter apparatus. Figures for TP3 materials are quoted in SI units.
