FIELD OF THE INVENTION

The present invention relates to a cooling element according to the preamble of claim 1. Additionally, the invention relates to a shipping box comprising one or more cooling elements. Moreover, the invention relates to a method for temperature stabilization. Also, the invention relates to a use of such a method or cooling element or shipping box.

BACKGROUND

Low-temperature product shipments are often done using dry ice (frozen or solid carbon dioxide) as a refrigerant. In equilibrium, under atmospheric conditions, the sublimation temperature of dry ice is around -78.5°C. These shipments consist of a thermally insulated shipping box containing dry ice pellets, the product to be shipped and a temperature logger. The product and logger are fully covered by dry ice on all sides.

After the transport, the shipping box is unpacked and the product and logger recovered. Temperature readings are downloaded from the logger. The temperature logs sometimes show that the internal temperature of the box reached temperatures much lower than the expected -78.5°C. Temperature readings as low as -94°C have been observed. Such unexpected temperature excursions can be problematic for some products. For example, rubber-stoppered vials can lose their sealing integrity below approx. -85°C, which can result in a higher risk of product contamination or stability issues of the product.

To circumvent the issue, shipments are sometimes done at higher temperatures, such as -20°C. Such shipments require the use of packs of selected phase-change material(s) as a refrigerant material. However, this approach is more complex and costly than the use of dry ice as refrigerant. Additionally, not all products are compatible with shipments at these elevated temperatures.

The issue of the temperature excursions has reportedly been noticed several times in the past. Testing by global specialist courier BioCair showed that tipping of a shipping box filled with dry ice can produce temperature excursions within the box: see the web page https://www.biocair.com/latest/news/what-causes-some-dry-ice -shipments-to-reach-90-c. Due to tipping of the box the concentration of carbon dioxide gas in the box is reduced and ambient gases such as oxygen and nitrogen may be let in, which affects the sublimation conditions.

Although reports and attempted explanations of the phenomenon exist, no solution to the phenomenon have been provided. There is still a need to solve to the above-mentioned temperature excursion issue, while maintaining the use of dry ice as a refrigerant in shipping boxes.

It is an object of the present invention to overcome or mitigate the above detrimental effects.

SUMMARY

The above object is achieved by a cooling element comprising a container, the container defining a volume within one or more walls of the container; the volume being airtight sealed, wherein the container contains dry ice (solid carbon dioxide) and is configured for releasing carbon dioxide gas from the volume and blocking ingress of ambient gas into the volume.

The cooling element as defined above overcomes the temperature excursion issue by providing that in the container filled with dry ice the gas volume is consisting of carbon dioxide is maintained at a constant composition without disturbance from ambient gases, i.e., by mixing with variable amounts of ambient gases. Additionally, the provision for the release of carbon dioxide gas allows the internal pressure to remain constant and equal or near ambient pressure. As a result, the equilibrium between the solid phase and the gas phase of carbon dioxide (CO2) remains constant by maintaining the CO2 partial pressure at a constant level. A constant CO2 partial pressure prevents excessive sublimation of carbon dioxide relative to the ‘normal’ sublimation required for remaining at the sublimation point. Since the sublimation reaction is endothermic, excessive sublimation would be accompanied by strong cooling below the equilibrium temperature, which is -78.5°C at atmospheric pressure (1 atm, -1013 hPa).

According to an aspect, the invention provides a cooling element as described above wherein the material of the container walls is selectively permeable for carbon dioxide gas.

Advantageously, carbon dioxide can be released from the container by diffusion through the wall(s) of the container. The container material allows that the internal pressure can be regulated in this manner, while preventing entry of ambient gas into the internal volume, which would alter the equilibrium conditions between CO2 gas and dry ice.

According to an aspect, the invention provides a cooling element as described above wherein the container comprises a one-way valve for releasing gas from the internal volume.

The one-way valve allows the release of carbon dioxide gas from the container, while preventing entry of ambient gas into the internal volume.

According to an aspect, the invention provides a cooling element as described above wherein the one-way valve is an overpressure release valve. By using an overpressure release valve, the release pressure can be predetermined which allows to control the pressure of CO2 in contact with the dry ice and thus the sublimation temperature. In a further embodiment, the one-way valve is configured to release carbon dioxide gas from the internal volume at an internal overpressure relative to ambient pressure.

According to an aspect, the invention provides a cooling element as described above wherein the material of the container is a flexible material.

By providing that the container material is flexible, a receptacle (an object with an internal volume) for holding a product can be surrounded by/wrapped in the cooling element, improving the thermal contact such that better cooling of the product can be obtained.

According to an aspect, the invention provides a cooling element as described above wherein the volume of the container is configured for containing between about 50 grams and about 20 kilograms of carbon dioxide dry ice.

According to an aspect, the invention provides a cooling element as described above wherein the carbon dioxide dry ice is provided in the form of dry ice pellets. By using pellets, the dry ice has a relative large surface which allows that an equilibrium between gas and solid carbon dioxide can be obtained at relatively high rate.

Also, the present invention relates to a shipping box comprising a thermally insulated volume therein, and configured for holding a product or a receptacle holding a product and one or more cooling elements as described above, wherein the one or more cooling elements are arranged to enclose the product or the receptacle holding the product.

According to an aspect, the invention relates to a shipping box comprising a thermally insulated volume therein, and configured for holding at least one receptacle and one or more cooling elements as described above, wherein the one or more cooling elements are arranged to enclose the receptacle. By using cooling elements as described above, the shipping box is configured to maintain its temperature at carbon dioxide sublimation temperature (-78.5°C at 1 atm) without the risk of temperature changes to lower temperatures of about -85°C.

According to an aspect, the invention provides a shipping box as described above wherein the shipping box is configured with thermally insulating walls and cover surrounding the thermally insulated volume.

According to an aspect, the invention provides a shipping box as described above wherein the thermally insulated volume is configured to have an internal pressure equal to external air pressure.

The shipping box is arranged to have a same internal pressure as the ambient which is useful in environments where expected pressure changes are relatively small.

According to an aspect, the invention provides a shipping box as described above wherein the thermally insulated volume is an air-tight volume and the shipping box comprises a pressure relief valve for releasing gas from the thermally insulated volume.

By providing a predetermined pressure in the shipping box, the release pressure for carbon dioxide from the cooling element and the internal pressure of the cooling element can be pre-set which provides that a better control of the temperature in the cooling element.

According to an aspect, the invention provides a shipping box as described above wherein a temperature logger is placed in the thermally insulated volume adjoining the receptacle for holding a product, and the one or more cooling elements are arranged to enclose both the receptacle and the temperature logger.

According to an aspect, the invention provides a shipping box as described above, wherein the receptacle comprises a vial containing a (bio)pharmaceutical substance or advanced therapy medicinal product, and the vial is provided with a rubber stopper.

According to an aspect, the invention provides a shipping box as described above, wherein the (bio)pharmaceutical substance or advanced therapy medicinal product comprise one or more substances selected from a group comprising small molecules, oligonucleotides, nucleic acids, peptides, proteins, antibodies, protein or antibody-drug conjugates, gene therapy, cell therapy, vaccines, blood or blood-derived components and microbiota derived products.

The present invention also relates to a method for temperature stabilisation of a product contained in one or more receptacles, during shipment in dry ice, comprising: providing a shipping box comprising a thermally insulated volume therein; placing one or more cooling elements and a receptacle holding a product in the thermally insulated volume, while arranging the one or more cooling elements to enclose the one or more receptacles, in which each cooling element comprises a container, the container defining an internal volume within one or more walls of the container; the internal volume being air-tight sealed and filled with dry ice, wherein the container is configured for releasing carbon dioxide gas from the volume and for blocking ingress of ambient gas into the volume; the method further comprising: releasing carbon dioxide gas from the internal volume of the container at a predetermined overpressure of the carbon dioxide gas relative to ambient pressure.

The present invention also relates to a method for temperature stabilisation of one or more receptacles during shipment in dry ice, comprising: providing a shipping box comprising a thermally insulated volume therein; placing one or more cooling elements and a receptacle holding a product in the thermally insulated volume, while arranging the one or more cooling elements to enclose the one or more receptacles, in which each cooling element comprises a container, the container defining an internal volume within one or more walls of the container; the internal volume being air-tight sealed and filled with dry ice, wherein the container is configured for releasing carbon dioxide gas from the volume and for blocking ingress of ambient gas into the volume; the method further comprising: releasing carbon dioxide gas from the internal volume of the container at a predetermined overpressure of the carbon dioxide gas relative to ambient pressure.

The effect of the method steps is that the equilibrium between gas and solid is better maintained, which results in a better control of the cooling temperature.

According to an aspect, the invention provides a method as described above wherein the material of the container walls is selectively permeable for carbon dioxide gas.

According to an aspect, the invention provides a method as described above wherein the method comprises providing the container with a one-way valve for releasing carbon dioxide gas from the internal volume.

According to an aspect, the invention provides a method as described above wherein the one-way valve is configured as an overpressure valve. According to an aspect, the invention provides a method as described above wherein the method comprises maintaining a pressure in the thermally insulated volume at ambient pressure.

According to an aspect, the invention provides a method as described above wherein the method comprises: providing the thermally insulated volume as an air-tight volume and providing the shipping box with a pressure relief valve for releasing gas from the thermally insulated volume for maintaining a constant pressure in the thermally insulated volume.

According to an aspect, the invention provides a method as described above wherein the method comprises: arranging a temperature logger in the thermally insulated volume adjoining the receptacle for holding the product, and the temperature logger is also enclosed by the one or more cooling elements.

According to an aspect, the invention provides a method as described above wherein the method further comprises: maintaining a temperature in the thermally insulated volume at the sublimation temperature of carbon dioxide, while dry ice is present in the one or more cooling elements.

According to an aspect, the invention provides a method as described above wherein the method comprises: preceding the placement of one or more cooling elements and a product in the thermally insulated volume of the shipping box: providing the container of the cooling elements with an opening to access the internal volume of the cooling elements; filling the internal volume of the cooling elements with dry ice through the opening; air-tight sealing the opening after filling the internal volume with dry ice; and providing the container of the cooling elements with a pressure regulation means.

According to an aspect, the invention provides a method as described above wherein the method comprises: preceding the placement of one or more cooling elements and one or more receptacles in the thermally insulated volume of the shipping box: providing the container of the cooling elements with an opening to access the internal volume of the cooling elements; filling the internal volume of the cooling elements with dry ice through the opening; air-tight sealing the opening after filling the internal volume with dry ice; and providing the container of the cooling elements with a pressure regulation means.

According to an aspect, the invention provides a method as described above wherein the method comprises: preceding the placement of one or more cooling elements and a product in the thermally insulated volume of the shipping box: providing the container of the cooling elements with an opening to access the internal volume of the cooling elements; filling the internal volume of the cooling elements with dry ice through the opening; air-tight sealing the opening after filling the internal volume with dry ice; and maintaining a small opening in the air-tight sealing for releasing carbon dioxide gas from the internal volume and for blocking ingress of ambient gas into the volume.

According to an aspect, the invention provides a method as described above wherein the method comprises: preceding the placement of one or more cooling elements and one or more receptacles in the thermally insulated volume of the shipping box: providing the container of the cooling elements with an opening to access the internal volume of the cooling elements; filling the internal volume of the cooling elements with dry ice through the opening; air-tight sealing the opening after filling the internal volume with dry ice; and maintaining a small opening in the air-tight sealing for releasing carbon dioxide gas from the internal volume and for blocking ingress of ambient gas into the volume.

According to an aspect, the invention provides for the use of a cooling element as defined above for the shipment in dry ice of at least one receptacle holding a product comprising a (bio)pharmaceutical substance or advanced therapy medicinal product. The invention also provides for the use of a cooling element as defined above for the shipment in dry ice of at least one receptacle holding a product comprising a (bio)pharmaceutical substance or advanced therapy medicinal product, wherein during the shipment in dry ice there is a temperature stabilization of the product contained in said at least one receptacle; wherein there is a shipping box comprising a thermally insulated volume therein; wherein there is one or more cooling elements as defined above and at least one receptacle in the thermally insulated volume; and wherein the one or more cooling elements are arranged to enclose the one or more receptacles. Additionally or alternatively, the invention provides for the use of a shipping box as defined above for the shipment of at least one receptacle holding a product comprising a (bio)pharmaceutical substance or advanced therapy medicinal product. Additionally or alternatively, the invention provides for the use of a method for temperature stabilisation as defined above for the shipment of at least one receptacle holding a product comprising a (bio)pharmaceutical substance or advanced therapy medicinal product(s).

Advantageous embodiments are further defined by the dependent claims. BRIEF DESCRIPTION OF DRAWINGS

The invention will be explained in more detail below with reference to drawings in which illustrative embodiments thereof are shown. They are intended exclusively for illustrative purposes and not to restrict the inventive concept, which is defined by the appended claims.

Figure 1 schematically shows a cooling element according to an embodiment of the invention.

Figures 2 and 3 schematically show a cooling element according to an embodiment of the invention.

Figure 4 schematically shows a shipping box according to an embodiment of the invention. Figure 5 shows the carbon dioxide phase diagram.

Figure 6. Carbon dioxide phase diagram of the region of interest (a) and change of CO2 concentration occurring when another gas enters the shipment box (b).

Figure 7: Representation of a standard CB-EPS-24 transportation box.

Figure 8: Schematic representation of the conventional approach (Fig. 8 A) and new approach tested in the exploratory study described in the example (Fig. 8B).

Figure 9: Sealed CO2 valve bag for packing entire dry-ice content during shipment. One-way valve let CO2 gas out and prevents temperature drop in the box.

Figure 10 A: Two pouches filled with dry ice and the thermocouples in a CBS-EPS-24 box. B: Full 6 pouches filled with dry ice placed in a CBS-EPS-24 box.

C: CB-EPS-24 box filled directly with dry-ice with thermocouple placement.

Figure 11. A: The freezer bags used for the experiment. Note the partially closed sealing zipper for CO2 venting.

B: Shipping box filled with 16 freezer bags filled with dry ice.

Figure 12: This experiment compared the temperature in a shipping box filled with dry ice (Fig. 12A) to the temperature in a box filled with dry ice-containing sealed “coffee bean” bags (Fig. 12B). During the first two hours of the experiment the shipping box was closed. After two hours, two air holes (15mm diameter) were punched diagonally across from each other in the sides (walls) of each of the boxes, allowing an airflow to circulate through the boxes.

Figure 13: This experiment compared the temperature in a shipping box filled with dry ice (Fig. 13 A) to the temperature in a box filled with dry ice-containing sealable freezer bags (Fig. 13B). During the first hour and 20 minutes of the experiment the shipping box was closed. After approx, one hour and 20 minutes, two air holes (15mm diameter) were punched diagonally across from each other in the sides (walls) of each of the boxes, allowing an airflow to circulate through the boxes.

DETAILED DESCRIPTION OF EMBODIMENTS

Figure 1 schematically shows a cooling element 10 according to an embodiment of the invention.

The cooling element 10 of the invention comprises a container 20 which is configured to hold carbon dioxide in an internal volume 30 of the container. The internal volume is defined by the walls of the container and is configured to be air-tight sealable. The container is provided with a pressure regulation means 25 to provide that an internal pressure in the internal volume 30 can be regulated, i.e., kept substantially constant. The internal volume can be filled with solid carbon dioxide (dry ice) as refrigerant. In this manner a cooling element is constructed that enables that in the internal volume 30 an equilibrium between dry ice and carbon dioxide gas can be maintained since the gas remains at a constant composition and constant pressure and ingress of ambient gases is substantially blocked. As a result, an excessive sublimation of carbon dioxide due to a change of the gas composition above the dry ice and the temperature drop caused by such excessive sublimation are prevented.

The pressure regulation 25 of the cooling element provides that the pressure of the carbon dioxide gas is maintained at a substantially constant pressure to avoid an overpressure that can deform or damage the container of the cooling element.

According to an embodiment, the walls 20 of the container are or comprise selectively permeable membranes 25 for carbon dioxide gas which allow that carbon dioxide gas can diffuse from the internal volume to the outside of the container (for example the ambient).

Alternatively or additionally a one-way gas release valve 25 can be arranged in a wall of the container to release gas from the internal volume at a predetermined internal pressure. The one-way valve can be an overpressure release valve.

The cooling element can be embodied in various manners as explained below in more detail. Figure 2 schematically show a cooling element 10 according to an embodiment of the invention. According to an embodiment, the container is a pouch made from flexible material such as a plastic that is filled with dry ice and carbon dioxide gas.

According to an embodiment the pouch comprises a one-way gas release valve 25 as described above.

Such a pouch is a member of a plurality of similar or identical pouches that are designed to be placed adjacent to a receptacle for a product (not shown) such as a vial, bottle or box. To obtain cooling, the receptacle is surrounded by a plurality of the pouches which thermally isolate the receptacle and its contents from the environment.

Figure 3 schematically shows a cooling element 12 according to an embodiment of the invention.

According to an embodiment, the cooling element comprises a flexible or deformable pouch capable of containing dry ice and carbon dioxide gas and which is designed to be wrapped or folded around a receptacle 40. In this manner cooling of the receptacle can be done by means of a single cooling element. In a further embodiment, the cooling element is designed as a sleeve in which the product can be inserted. The internal volume 30 of the cooling element 12 is formed in between the inner and outer walls 22, 24 of the sleeve.

The cooling element can have various sizes and shapes depending on the application: the internal volume can be configured to contain between about 50 grams and about 20 kilograms of dry ice. In a preferred embodiment, the dry ice is provided in the form of dry ice pellets. The internal volume 30 of the cooling element 10; 12 is filled with dry ice and subsequently air-tight sealed.

Figure 4 schematically shows a shipping box 50 according to an embodiment of the invention. The shipping box is arranged for transport of receptacle(s) (40) for holding product(s) that require cooling to avoid exposure to varying and/or relatively high temperature. The shipping box comprises bottom, top and side walls 52, 54, 56 that form an enclosure which defines a shipping volume 58 for holding the receptacle(s) 40. In an embodiment, the top wall of the shipping box is a removable cover to provide access to a top opening of the shipping volume.

Typically, the walls 52, 54, 56 are constructed from or comprise thermal insulating material to provide thermal insulation of the shipping volume. Within the shipping volume, one or more cooling elements 10; 12 as described above can be arranged. The receptacle(s) 40 is (are) placed in the shipping volume 58 in a manner that the receptacle is enveloped or surrounded by the one or more cooling elements.

For example, the receptacle can be wrapped in a foldable cooling element and then placed in the shipping box. Alternatively, the receptacle and cooling elements are stacked in the shipping volume in a manner that the receptacle is surrounded on substantially all sides by the cooling elements.

In addition, a temperature logging device 60 may be included with the receptacle(s) 40. For example, the receptacle(s) and the logger device are in a package that is surrounded by the cooling element(s) 10; 12.

The shipping box 50 as shown in Figure 4 is oriented in upright position.

During use, the dry ice absorbs heat, sublimation of CO2 takes place within the internal volume of the cooling element(s) 10; 12 and the amount of carbon dioxide gas in the internal volume 30 increases. The pressure in the internal volume 30 is regulated and excess carbon dioxide gas is released into the shipping volume 58 which is separated from the internal volume 30 of the cooling element(s). Most of the released carbon dioxide gas is accumulating in the shipping volume. However due to the separation the carbon dioxide gas in the shipping volume is not included in the equilibrium reaction of the carbon dioxide gas and the dry ice in the cooling elements. The reaction between the carbon dioxide gas and the dry ice is contained in the cooling elements and isolated from the ambient.

The shipping box 50 may be an air-tight sealable box. In order to prevent overpressure in the shipping volume, the shipping box is provided with an overpressure valve (not shown) to release carbon dioxide gas from the shipping volume. Alternatively, the shipping box may comprise one or more through-holes (not shown) in the walls to reduce the overpressure relative to the ambient pressure.

In a tipped orientation, the top opening of the shipping box is not horizontally levelled, and in this orientation, carbon dioxide gas can flow out from the shipping box into the ambient. At the same time, ambient gas can enter the shipping volume. However, due to the confinement of the dry ice and carbon dioxide gas in the internal volume 30 of the cooling element(s) 10; 12, the ambient gas will not enter the internal volume 30.

Consequently, the equilibrium of the dry ice and carbon dioxide gas and the sublimation reaction is not disturbed by inflow of ambient gas. The temperature in the shipping box will not change significantly if some ambient gas enters the shipping volume.

According to an embodiment, the shipping box is used for transport or shipment of receptacles 40 such as vials 42 containing a (bio)pharmaceutical substance that requires cooling to prevent deterioration.

Such (bio)pharmaceuticals, including advanced therapy medicinal products (ATMPs), may comprise one or more substances selected from a group comprising small molecules, oligonucleotides, nucleic acids, peptides, proteins, antibodies, protein or antibody-drug conjugates, gene therapy, cell therapy, vaccines, blood or blood-derived components and microbiota derived products.

According to an embodiment, the invention relates to a method for temperature stabilisation of one or more receptacles 40 during shipment in dry ice, which comprises

— providing a shipping box 50 that comprises a thermally insulated volume 58 therein;

— placing one or more cooling elements 10; 12 and the one or more receptacles 40 in the thermally insulated volume, while arranging the one or more cooling elements to enclose the product, in which each cooling element comprises a container 20, the container defining an internal volume 30 within one or more walls of the container; the internal volume 30 is airtight sealed and filled with dry ice, and the container is configured for releasing carbon dioxide gas from the volume and for blocking ingress of ambient gas into the volume.

The method further comprises releasing carbon dioxide gas from the internal volume of the container at a predetermined overpressure of the carbon dioxide gas relative to ambient pressure.

The method above can be used for the transportation or shipment of receptacles such as vials containing (bio)pharmaceuticals as described above.

Figure 5 shows the carbon dioxide phase diagram. The phase diagram shows the phases (solid 100, liquid 105, gas 110) of carbon dioxide as a function of temperature and pressure. The phases are separated by binary phase lines: carbon dioxide gas and solid are separated by a sublimation line 120, gas and liquid by a saturation line 130 and solid and liquid by a melting line 140. The sublimation line, saturation line and melting line meet at a triple point 150.

From the diagram, it is evident that the sublimation temperature of CO2 at atmospheric pressure is around -78.5°C. At this temperature, both gaseous and solid CO2 are present in equilibrium. CO2 will naturally sublimate or freeze (and absorb or release heat, respectively) as necessary while maintaining this temperature. If the pressure changes, so will this equilibrium temperature: as indicated by the solid-gas binary phase line 130, the equilibrium temperature drops as the pressure drops. This is well known, and often cited as the cause of temperature variations. However, it is important to note that the pressure shown on a phase diagram is in regard to the partial pressure of the species of interest (CO2, in our case). It is possible that the partial pressure of CO2 drops, while maintaining a constant absolute pressure of e.g. 1 atm. This can be the case when ambient gases (mainly N2 and O2) are mixed with the gaseous CO2 phase.

In short, the sublimation temperature of dry ice at 1 atm is only -78.5°C when considering a 100% CO2 atmosphere in equilibrium with dry ice.

So, the temperature of a gaseous/solid CO2 system can drop below -78.5°C in two situations: when the absolute pressure drops below 1 atm, while maintaining a 100% CO2 concentration (i.e. during air transport), or when the relative concentration of CO2 drops below 100% while maintaining an absolute pressure of 1 atm (i.e. during mixing with other gases).

The present invention prevents relatively large temperature excursions below the atmospheric sublimation point of carbon dioxide at -78.5°C by application of the cooling element as described above. As the temperature remains substantially constant in the cooling element, the temperature of a receptacle and product (i.e., a rubber stopped vial 42, 44 and substance in the vial) enclosed by one or more cooling elements will not significantly vary. As a result, the risk of an impaired sealing integrity of rubber stopped 44 vials 42 is reduced.

The invention also provides for the use of a cooling element as defined above for the shipment in dry ice of at least one receptacle holding a product comprising a (bio)pharmaceutical substance or advanced therapy medicinal product, wherein during the shipment in dry ice there is a temperature stabilization of the product contained in said at least one receptacle (40); wherein there is a shipping box (50) comprising a thermally insulated volume (58) therein; wherein there is one or more cooling elements (10, 12) as defined above and at least one receptacle (40) in the thermally insulated volume (58); and wherein the one or more cooling elements (10, 12) are arranged to enclose the at least one receptacle (40). The present invention may be embodied in other specific forms without departing from its essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive to the inventive concept. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. It will be apparent to the person skilled in the art that alternative and equivalent embodiments of the invention can be conceived and reduced to practice. In addition, many modifications may be made to adapt a particular configuration or material to the teachings of the invention without departing from the essential scope thereof.

EXAMPLES

Optimization of shipments in dry ice.

There are two most common types of transportation packages: a CB-EPS-24 box and a GDI 80L box. Dry ice (solid carbon dioxide, CO2) is used as a cooling agent to support transportation and storage of a variety of products at temperatures below -70°C (e.g. at -78.5°C). In a shipment box, dry ice is usually surrounded by 100% gaseous CO2, at an ambient pressure of 1 bar. However, if the CO2 is replaced by another gas, the partial pressure drops (Figure 6) and therefore also the temperature of the cooling agent. During shipment, an imperfect sealing of a shipment box can causeCO2 gas from dry ice to escape from the box and to be substituted by air which comes in contact with dry ice inside the box. The consequential fluctuations in CO2 concentration cause corresponding uncontrolled temperature fluctuations that could harm the quality of the shipped product. Instead of the expected temperature of -78.5 °C, excursions to temperatures below -90 °C have been measured lately during shipments. In this exploratory experimental study, we have tested new configurations of shipment, amongst others, using one-way vented dry ice bags, and compared this with conventional ways of dry ice shipment, wherein a product is directly placed in contact with dry ice in a shipment box.

Experimental design

The experiment consisted of two parts. In the first part the conventional shipment approach was tested. An inner insulating Styrofoam box (Figure 7) with two holes (radius of each hole was 15mm, see Figure 8 for more details) was used as a transportation box. The holes enabled cross-airflow within the box and were made for mimicking imperfections of the sealing in standard transportation boxes that can occur before or during a shipment.

In order to measure temperature excursions, a set of thermocouples and a datalogger were used. A plastic rod (16mm PVC pipe) with 4 thermocouples attached on an even distance from each other was placed in the centre of the box allowing temperature monitoring along one axis (see Figure 8 A for more details). The box was then filled with dry ice (volume/mass = 20L) and closed tightly, allowing only thermocouple wires to stretch out from the box (Fig. 10C).

In the second part of the experiment, instead of putting dry ice directly into the transportation box, sealed bags, like the one depicted on Fig. 9, were used. Dry ice was first put into sealed, one-way vented bags, which were then placed into the transportation box (Figures 8B, 10A and 10B). During the experiment, the temperature was logged by the thermocouples that were connected to a Graphtec GL240 datalogger that saved temperature data onto CSV files. The lid of the box was closed during the entire test. Data analysis was performed on a written Python program to plot the temperature excursion curves and determine the relevant temperatures for each part of the experiment (conventional and new approach). To reduce measurement time, two CB-EPS-24 boxes were measured simultaneously, with one box containing dry ice-containing pouches and the other box being filled directly with dry ice.

The boxes were closed and first allowed to equilibrate in the absence of any air leaks for a period of one to two hours, with the thermocouple datalogger running. After that initial period, two air holes (15mm diameter) were punched diagonally across from each other in the sides (walls) of each of the boxes, allowing an airflow to circulate through the boxes. The boxes were left in this state overnight.

The one-way vented (coffee bean) bags were relatively large in view of the interior of the shipping box, making it difficult to completely fill the box with these bags. Gaps between the bags were large so the box with bags contained significantly less dry ice than the box that was filled with dry ice directly (estimated to be less than half the amount of dry ice, by weight). Also, some areas of the box (upper edges) did not fit an additional bag and thus contained air gaps (FIG. 10). Because of this sub-optimal configuration, the experiment was repeated using standard sealable 1.5L plastic freezer bags (Fig. 11). These bags were smaller and made of a thinner, more flexible material (e.g. low density Polyethylene (LDPE)), allowing a better filling of the box. 16 of the plastic freezer bags were used to fill a shipping box. The required venting of the bags was achieved by only partially closing the seal strip, leaving an opening of 2 cm in length.

RESULTS

COFFEE BEAN POUCH

The result of the “coffee bean pouch” experiment is shown in Error! Reference source not found.12. The control experiments, which took place the first two hours of the experiment, during which the shipping box was closed (no air leak) show that the temperature in both box interiors were ranging between -70 and -80 deg C, where the box filled directly with dry ice had a more uniform temperature, and closer to the expected temperature of - 78.8°C (Fig. 12A). In the second box, the temperature varied more, due to the reduced surface area and increased thermal resistance caused by the coffee bean bags. In both cases, the topmost thermocouple was not covered in dry ice, therefore it shows a much higher temperature than the other thermocouples.

After introducing an artificial air leak, after approx. 2 hours, the box containing unprotected dry ice, showed a temperature drop, slowly reaching equilibrium temperatures that were between 7-14 degrees lower. The lowest temperature that was reached was -92 °C, which would qualify as a “low-temperature excursion” (Fig. 12 A). The box with dry icecontaining coffee bean bags also showed a slight drop in temperature, but only about 3 deg C. The minimum temperature that was reached in that experiment was -78 °C, which would not be classified as a temperature excursion (Fig. 12B). Interestingly, the observed temperature drop appeared to occur much faster in the box containing coffee bean bags than in the box containing unprotected dry ice.

FREEZER BAGS

Repeating the same experiment with the sealable freezer bags (Fig. 11 A) gave similar results. In this experiment, the temperature drop in the box with unprotected dry ice was even larger, reaching a minimum temperature of -96 °C (Fig. 13 A).

The temperature change in the box containing partly sealed dry ice bags was smaller, showing a very low temperature drop measured by the thermocouple at 8cm, while the thermocouples at 2cm and 14 cm measured a small rise in temperature (Fig. 13B). The temperature profile looked slightly more stable for the freezer bags than for the coffee pouches. Again, the top thermocouple (20cm) in both boxes showed a much higher temperature because it was located above the level of the dry ice. The warming of the temperature due to the incoming air caused by the leak can clearly be seen in the upper thermocouple.

SUMMARY

By packaging dry ice in vented pouches before placing them in shipping boxes, ambient air is prevented from mixing with the CO2 generated by dry ice, which has proved to be the cause of temperature excursions.

The results of this study demonstrate that a significant reduction in temperature variation can be obtained when dry ice is kept into sealed pouches instead of placed directly into a shipping box. Two different types of pouches were used:

• heat sealable and vented coffee bean bags

• standard 1 ,5L sealable plastic freezer bags

Both types of pouches have showed to provide the desired protection against temperature excursions. “Unprotected” dry ice led to temperature excursions down to -96 °C, while dry ice contained in pouches caused only small temperature variations, but never going below -78 °C, and therefore not causing a “low-temperature excursion”.

The second type of pouch (freezer bags) was tested after encountering several practical issues with the available coffee bean bags (size, seal, surface area, material thickness, thermal conductance, packing efficiency). Indeed, a slightly more stable interior temperature was achieved using the smaller and thinner freezer bags.

The experiments have also shown that a one-way valve is not strictly necessary and may be replaced by a small vent hole or opening in the pouch. As long as the vent hole or opening is small, CO2 that escapes through the hole or opening will prevent the ingress of ambient air into the pouch, thus providing a functionality similar to the one-way valve. The important features of the present invention are thus 1) the non-permeable pouch, combined with 2) a feature that allows the escape of gaseous CO2.