WO2024153920A1

WO2024153920A1 - Phase change materials

Info

Publication number: WO2024153920A1
Application number: PCT/GB2024/050113
Authority: WO
Inventors: Ian Stuart Biggin; Rainer Busch
Original assignee: Individual
Current assignee: Individual
Priority date: 2023-01-16
Filing date: 2024-01-16
Publication date: 2024-07-25
Anticipated expiration: 2025-07-16
Also published as: GB202300637D0; GB2626197A

Abstract

Shape stable phase change compositions that comprise a foam member at least partially impregnated or containing phase change material, wherein said phase change material is a non-draining liquid or non-draining gel.

Description

Phase Change Materials

The present invention relates to an improved phase change material and shape or form stable materials in particular.

The following description refers to phase change materials for use as a thermal store to maintain a reduced or elevated temperature, relative to the ambient temperature, within containers, for example in transport of chilled medical goods such as vaccines. The skilled person will recognise that the present invention can be used to maintain the temperature of a variety of containers and the goods contained therein and is not limited to medicines, vaccines etc.

It is essential that when temperature sensitive items, including, but not limited to, vaccines and other pharmaceutical products, foods and beverages, human organs and other biological materials, are stored and/ or transported they are kept at a suitable temperature. Overheating or overcooling can damage these temperature sensitive materials. To reduce/prevent the spoilage/loss of efficacy of these materials, insulated storage/transport technology has been developed. In many instances this comprises the temperature sensitive materials, or payload (i.e. that part of the package from which revenue is derived), adjacent and/or abutting one or more packs of phase change material. The payload and one or more phase change material packs are then protected by insulation and finally exterior packaging.

The phase change temperature of the phase change material is selected to match the required storage temperature of the payload. Depending on the size of the payload, the final package could be a cardboard box, a pallet cover or larger. The packages are designed to protect their contents during transport and delivery to their final destination. Water is a common phase change material and it is often thickened to form a gel, in rigid plastic bottles or pouches.

It is also common to use organic phase change materials such as alkanes (n-tetradecane, n-hexadecane and n-octadecane), acids, alcohols or esters. Typical esters are described in U.S. Patent application No. 2018/0244971 , inventors Auerbach and Van Aken, which is incorporated herein by reference. These esters are reaction products of linear carboxylic acids, which have at least 4 carbon atoms and linear alcohols containing at least 4 carbon atoms, wherein the total number of carbon atoms in the ester is between 13 and 31. The use of other esters (e.g. methyl, ethyl and n-propyl) is also possible.

A problem can occur if one or more of the phase change material containers is damaged and the contents leak onto the temperature sensitive payload. This loss of integrity can lead to contamination of the payload and, potentially, a reduction in the ability of the phase change material to maintain constant temperature of the payload. Some phase change materials, such as n-tetradecane, can migrate through polyethylene bottles or affect the seals of multi-layered pouches. This can be alleviated by treating the HDPE bottles using fluorination to increase their resistance to the migration of phase change materials or by using pouches with more resistant seals.

The cost and weight of HDPE bottles provide a considerable contribution to the final costs of producing and distributing the temperature controlled packages. The use of plastic pouches, filled with phase change material, can significantly reduce both the weight and the cost. However, should a pouch become damaged then the danger of the loss of some, or all of the phase change material into the payload space, would be of major concern. This has been resolved, to an extent, by converting the phase change material into a shape stable form. This involves adding a gelling agent, such as a viscosifying polymer to the phase change material and heating it to either dissolve or partially dissolve the polymer. The resulting system is one which remains as a solid, even above the melting point of the phase change material, which reduces/ eliminates the danger of leakage should a pouch be damaged. A number of such systems currently exist on the market and some examples are covered in the following documents: US Patent application No. 2021292630 inventors Formato, Bakklas and Biswal; Patent No. W02014052409 inventors Formato and Bakklas, Patent No. DE102021005863 inventor Busch, Patent No. DE102020002843 inventor Busch, Patent No. DE102016013415 inventors Busch and Biggin. Shape stable, organic phase change materials may be prepared by various methods but linear styrene triblock polymers are often employed. These polymers comprise polystyrene end groups joined by a central hydrocarbon rubber section. This central section could comprise hydrocarbon monomers including but not limited to ethylene, propylene, butadiene, isoprene etc. The shape stable, or gelled, phase change material is prepared by mixing the phase change material and the polymer and heating the mixture until the polymer dissolves completely, or partially. It is then cooled to room temperature. Care must be taken to ensure that the heating temperature remains substantially below the flash point of the phase change material. The heated material can be poured into moulds and then cut to size, placed in a pouch and vacuum sealed, or it can be poured, whilst hot, directly into a pouch and vacuum sealed.

An alternative to the shape stable phase change materials for cold chain transport is the use of pouches containing a foam, impregnated with water or other phase change materials which are then sealed. These other phase change materials could be organic (alkanes, acids, alcohols or esters) or salt hydrates. Products based on this technology are sold by Temprecision International but tend to be based on phenol formaldehyde resins. These have a high absorptive capacity for water and phase change materials but are frangible, having low resistance to abrasion and pressure.

In US Patent No. 20020147242, inventors Salyer, Wynne and Swank, the authors claim a system based on a micropore, open cell foam, having an open cell content of >80% and an average pore size of 200 microns or less. Also claimed is the use of a polymeric thickening agent to viscosify the phase change material.

In EP1498680, inventors Vath, Moeck and Woerthwein, the authors claim a thermal storage unit which contains an open cell foam based on a melamine formaldehyde condensation product, the cell pores of which are completely or partially filled with a free flowing heat transfer medium, and its production.

It is therefore an aim of the present invention to provide an improved shape or form stable phase change material that addresses the abovementioned problems.

It is a further aim of the present invention to provide a method of manufacturing a phase change material that addresses the abovementioned problems.

It is a yet further aim of the present invention to provide a device containing a phase change material that addresses the abovementioned problems. In a first aspect of the invention there is provided a shape stable phase change composition comprising a foam member at least partially impregnated or containing phase change material, wherein said phase change material is a non-draining liquid or non-draining gel.

In a preferred embodiment the foam is an open cell foam. Typically the foam is melamine foam. Further typically the foam is melamine formaldehyde foam.

In a preferred embodiment the phase change material is a nondraining gel. Typically the gel is a viscosified phase change material. Further typically the phase change material gel includes a phase change material and at least one gelling agent or viscosifying polymer.

In one embodiment the gelling agent or polymer is preferably substantially < 15% by weight of the phase change material, more preferably at < 10% by weight and most preferably at 5% or less.

In one embodiment the phase change material is an alkane. Preferably the alkane is tetradecane (C14).

In one embodiment the phase change material is an ester. Typically the ester is octyl laurate (octyl dodecanoate) .

In one embodiment the phase change material is any one or any combination of; tetradecane, hexadecane, heptadecane, octadecane, eicosane, docosane (from Sasol Germany GmbH), esters including CrodaTherm 5, CrodaTherm 6.5, CrodaTherm 9.5, CrodaTherm 15, CrodaTherm 19, CrodaTherm 21, CrodaTherm 24W, CrodaTherm 29, CrodaTherm 32, CrodaTherm 37, CrodaTherm 53, CrodaTherm 60 and CrodaTherm 74 (from Croda Europe), stearyl alcohol and/or stearic acid.

In one embodiment the polymer or viscosifying polymer is a block copolymer. Typically the polymer is a styrene ethylene ethylene propylene styrene copolymer (SEEPS) .

In one embodiment the polymer is a thermoplastic copolymer. Typically the polymer is ethylene-butylene/ styrene thermoplastic copolymer.

In one embodiment the polymer is styrene- [ethylene- (ethylene- propylene)] -styrene block copolymer.

Typically polymer selection depends on the polarity of the phase change material. Non-polar phase change materials require a relatively low molecular weight polymer such as Septon 4033 a SEEPS block copolymer or ethylene-butylene/ styrene thermoplastic copolymer.

Further typically more polar phase change materials requires- a higher molecular weight polymer such as Septon 4077 a styrene- [ethylene- (ethylene-propylene)]-styrene block copolymer.

In one embodiment the polymer or viscosifying polymer is any one or any combination of; Septon HG-252, Septon 1020, Septon 4033, Septon 4055, Septon 4077, Septon 4099 (from Kuraray), Kraton 1654, Kraton 1651 , Kraton 1633 (from Kraton Polymers), Calprene H6120, Calprene H6144, Calprene H6174 and Calprene H6410X (from Dynasol Group) .

Preferably the composition is effective (absorbs energy at the phase transition) substantially at or between 2 °C — 8 °C. Typically the composition is effective to maintain a frozen temperature inside a container or the like at, or substantially around -20 °C.

Typically controlled room temperature or room temperature is defined as 15-25 °C.

In one embodiment the open cell foam is a phenolic foam.

In one embodiment the open cell foam is polyether — polyurethane foam and/ or polyester polyurethane foam.

In a second aspect of the invention there is provided a method of producing a phase change composition comprising an open cell foam impregnated with a phase change material gel or viscosified liquid wherein said gel or liquid is produced by heating a phase change material and a gelling agent or polymer to dissolve the gelling agent or polymer producing a substantially homogenous, low viscosity liquid.

Typically the heating temperature should be above room temperature, which is typically 15 °C to 30 °C, but below the flash point of the phase change material.

Further typically the hot liquid is then impregnated into the melamine formaldehyde foam and allowed to cool to room temperature.

In one embodiment the air within the foam is substantially replaced by the phase change material/polymer mixture. Typically the impregnation can be achieved by vacuum and/ or pressure impregnation. In a third aspect of the invention there is provided a phase change material device, said device comprising a pouch or housing containing a phase change composition comprising a foam member at least partially impregnated or containing phase change material, wherein said phase change material is a nondraining liquid or non-draining gel.

Specific embodiments of the invention are now described.

The present invention is an open cell, melamine formaldehyde foam which is impregnated with a viscosified phase change material at an elevated temperature and then allowed to cool to form a non-draining gel within the structure of the foam.

According to one aspect of the invention, a phase change material gel is produced by heating a phase change material and a gelling agent to dissolve the gelling agent and produce a homogenous, low viscosity liquid. The heating temperature should be above room temperature, which is typically 15°C to 30°C, but below the flash point of the phase change material. The hot liquid is then impregnated into the melamine formaldehyde foam and allowed to cool to room temperature. Ideally, the air within the foam should be replaced by the hot phase change material/polymer mixture. This can be achieved by either vacuum or pressure impregnation or other means such as dipping or spraying or any method known to those skilled in the art.

Traditional packs of phase change material, for cold chain packaging and transport are made from strong, rigid high density polyethylene, are self-supporting and can be used multiple times without fear of damage or leaks. However, they are heavy and expensive, particularly if they require fluorination to minimise/eliminate the migration of the phase change material through the container.

The present invention uses melamine formaldehyde foams which possess extremely high porosity/absorptive capacity, very low density (9 kg/ m³) and are both rigid and strong, to the extent that some of these are used as scouring pads to clean work surfaces etc. One disadvantage of these foams is that, due their open cell structure and inhomogeneous pore size (10 — 1000 microns) absorbed phase change materials, in their liquid phase, will not be retained and will drain out due to gravity or applied pressure. This invention overcomes this problem by increasing the viscosity of the phase change material by the use of viscosifying polymers.

The phase change material/polymer blend must be selected carefully to provide a suitable balance of performance, cost and ease of manufacture. The polymer should be selected such that it can be added preferably at < 15% by weight of the phase change material, more preferably at < 10% by weight and most preferably at 5% or less.

The polymer type and addition level should enable a low viscosity, homogenous phase change material/polymer solution to be produced at an elevated temperature, which is nevertheless below the flash point of the phase change material. This solution is then adsorbed into the foam using either vacuum or pressure and the temperature allowed to fall to room temperature.

Compatibility tests, were performed on a wide range of polymer and PCM blends. These involved mixing 5% by weight of viscosifying polymer with 95% by weight of PCM. The PCMs tested included alkanes such as tetradecane, hexadecane, heptadecane, octadecane, eicosane and docosane , from Sasol Germany GmbH and esters including CrodaTherm 5, CrodaTherm 6.5, CrodaTherm 9.5, CrodaTherm 15, CrodaTherm 19, CrodaTherm 21 , CrodaTherm 24W, CrodaTherm 29, CrodaTherm 32, CrodaTherm 37, CrodaTherm 53, CrodaTherm 60 and CrodaTherm 74 from Croda Europe. Also tested were stearyl alcohol and stearic acid.

The polymers tested included Septon HG-252, Septon 1020, Septon 4033, Septon 4055, Septon 4077, Septon 4099 from Kuraray; Kraton 1654, Kraton 1651, Kraton 1633 from Kraton Polymers, and Calprene H6120, Calprene H6144, Calprene H6174 and Calprene H6410X from Dynasol Group.

The tests involved heating the PCM/polymer mixture in a small, screw capped aluminium container until the mixture became a low viscosity liquid. It was then allowed to cool to a temperature above its crystallisation point and tested to determine whether it had formed a stable gel. The surface of the gel was contacted either with a finger, or a microscope slide to determine whether there was any free liquid on the surface of the gel or whether the gel was completely homogenous. This became known as the wet finger test. The examples below were based on PCM/polymer blends that passed the wet finger test and gave completely homogenous gels i.e. without free surface liquid.

The above tests had shown that both Septon 4033 and Calprene H6102 polymers gave satisfactory viscosity performance with tetradecane, i.e. they gave low viscosity liquids at 75 — 80°C but formed solid gels at lower temperatures (e.g. 40°C) which passed the wet finger test. Two samples of Basotect G+ were cut to size, 75 x 75 x 12.5mm, and their volumes calculated (— 70,300 mm³ or 70.3ml) . Due to the possibility of losses during processing, 80ml C14 was used for each sample, which weighed ~ 61g (80ml x 0.763g/ml) . Opting for 5% polymer addition level gave a polymer addition level of ~3.2g polymer/ 61g PCM. The two samples of tetradecane/polymer were placed in stainless steel beakers in an ~ 80°C oven for 1.25 hours and then poured into pouches containing the Basotect G+ foam, vacuum impregnated/ sealed and cooled to room temperature. The two impregnated foams were then removed from the pouches, any excess gel removed and the foam samples weighed. Both passed the wet finger test at room temperature. The tetradecane/polymer loading in the foam was calculated and shown below as a percentage of the maximum theoretical PCM/polymer loading:

1. Tetradecane/4033 - 98.8%

2. Tetradecane/H6120 - 98.7%

The samples were then placed in pouches and vacuum sealed and subjected to two hours in a 40°C water bath. The pouches were opened at 40°C and both passed the wet finger test i.e. there was no free liquid PCM present. Both samples withstood squeezing, between finger and thumb, at 40°C without any exudation from the foam.

A piece of Basotect G+ foam (75 x 75 x 12.5mm) was placed in a pouch and ~60g tetradecane added (no polymer) . After vacuum sealing, the PCM was not held tightly within the foam and gentle finger pressure, or gravity, was sufficient to cause the PCM to leak from the foam at room temperature.

Tests were also performed on a number of different open cell foams, with a sample of Basotect G+ (ex-BASF) used as a comparison. Apart from the Basotect G+ (melamineformaldehyde; density 0.009 g/ml), the other foams were Oasis Floral Foam (phenol-formaldehyde — density 0.025 g/ml), TFS 103 (polyether-polyurethane; density 0.025 g/ml), TFS 108 (polyether-polyurethane; density 0.065 g/ml), TFS 200 (polyester-polyurethane; density 0.032 g/ml) and TFS 407 (reticulated polyether-polyurethane; density 0.028 g/ml) . The Oasis foam was supplied by Smithers-Oasis UK. Ltd., whilst the other foams were supplied by Technical Foam Services Ltd. Apart from the Oasis foam, all the other samples would not retain all the PCM without the use of a viscosifying polymer. All samples measured 100mm x 100mm x supplied thickness. The thickness was as received from the supplier. The PCM/polymer solution comprised 5% by weight Septon 4077 and 95% by weight CrodaTherm 6.5. The solution was mixed and heated as above in Example 2. The required weight of solution was calculated and it was then weighed into a pouch, containing the foam under test, vacuum impregnated and heat sealed. All samples had been weighed and measured prior to impregnation and, once cool, the samples were removed from the pouches, any excess gel removed and the samples reweighed. The table below shows the estimated enthalpy of each foam sample based on the weight of impregnated PCM/polymer and an enthalpy of CrodaTherm 6.5 of 183 J/g (CrodaTherm 6.5 Technical Data Sheet). The weights of the foams and polymer were subtracted prior to the enthalpy calculation i.e. the values are based solely on the CrodaTherm 6.5 content.

TFS 108 25.5

Three samples (TFS 103, TFS 200 and TFS 407) showed similar performance to Basotect G + . However, Basotect G+ provided a stiffer, more resilient product which was extremely resistant to applied pressure. The Oasis foam was structurally weaker than the other samples and partially collapsed under vacuum.

T-History type tests — small, screw topped aluminium vials were weighed and fitted with K-type thermocouples in the centre of the vials. Two vials (1 and 2) had 15g tetradecane added.

A 95: 5 by weight blend of tetradecane:Calprene H6120 was added to a stainless steel beaker and heated for one hour at 80oC until all the polymer had dissolved. Two “plugs” of Basotect G+ foam, cut to be a tight fit within the vials, were placed in the beaker and reheated for 10 minutes. The beaker was then placed in a vacuum chamber and evacuated to impregnate the foam. The impregnated foam pieces were placed in vials 3 and 4 and reweighed. Sample 3 contained 15g PCM/polymer and sample 4 15.87g. After allowing for the weight of the foam and polymer, the PCM contents were as follows:

Sample 3 — 14g tetradecane

Sample 4 — 14.7g tetradecane

The vials were all heated for a further 30 minutes, to ensure good contact with the internal vial surface and then the thermocouples were fitted and the vials cooled to room temperature. All vials were placed in insulated foam jackets, to prevent too rapid temperature changes. The thermocouple data loggers were activated and the vials placed in a -18oC freezer. Once the samples had cooled to ~- 18oC they were removed from the freezer and allowed to warm to room temperature. This was repeated for a total of three freeze/melt cycles. The results are shown in figure 1 (for the 1 st cycle).

There were no major differences found between the four vials in any of the tests. This was unexpected due to the slightly lower tetradecane weights in samples 3 and 4. Hence, the shape stable PCM/ foam samples performed as well as the slightly increased quantities of liquid tetradecane in samples 1 and 2.

Claims

1. A shape stable phase change composition comprising a foam member at least partially impregnated or containing phase change material, wherein said phase change material is a nondraining liquid or non-draining gel.

2. A composition according to claim 1 wherein the foam is an open cell foam.

3. A composition according to claim 2 wherein the foam is melamine foam.

4. A composition according to claim 3 wherein the foam is melamine formaldehyde foam.

5. A composition according to any preceding claim wherein the gel is a viscosified phase change material.

6. A composition according to claim 5 wherein the phase change material gel includes a phase change material and at least one gelling agent or viscosifying polymer.

7. A composition according to claim 6 wherein the gelling agent or polymer is preferably substantially < 15% by weight of the phase change material, more preferably at < 10% by weight and most preferably at 5% or less.

8. A composition according to claim 7 wherein the phase change material is an alkane.

9. A composition according to claim 8 wherein the alkane is tetradecane (C14) .

10. A composition according to claim 7 wherein the phase change material is an ester.

11. A composition according to claim 10 wherein the ester is octyl laurate (octyl dodecanoate) .

12. A composition according to claim 8 wherein the phase change material is any one or any combination of; tetradecane, hexadecane, heptadecane, octadecane, eicosane, docosane (from Sasol Germany GmbH).

13. A composition according to claim 1 wherein the phase change material is any one or any combination of CrodaTherm 5, CrodaTherm 6.5, CrodaTherm 9.5, CrodaTherm 15, CrodaTherm 19, CrodaTherm 21, CrodaTherm 24W, CrodaTherm 29, CrodaTherm 32, CrodaTherm 37, CrodaTherm 53, CrodaTherm 60 and CrodaTherm 74 (from Croda Europe), stearyl alcohol and/ or stearic acid.

14. A composition according to claim 6 wherein the polymer or viscosifying polymer is a block copolymer.

15. A composition according to claim 14 wherein the polymer is a styrene ethylene ethylene propylene styrene copolymer (SEEPS) .

16. A composition according to claim 6 wherein the polymer is a thermoplastic copolymer.

17. A composition according to claim 16 wherein the polymer is ethylene-butylene/ styrene thermoplastic copolymer.

18. A composition according to claim 17 wherein the polymer is styrene - [ethylene - (ethylene -propylene)] - styrene block copolymer.

19. A composition according to any preceding claim wherein the polymer or viscosifying polymer is any one or any combination of; Septon HG-252, Septon 1020, Septon 4033, Septon 4055, Septon 4077, Septon 4099 (from Kuraray), Kraton 1654, Kraton 1651, Kraton 1633 (from Kraton Polymers), Calprene H6120, Calprene H6144, Calprene H6174 and Calprene H6410X (from Dynasol Group) .

20. A method of producing a phase change composition comprising an open cell foam impregnated with a phase change material gel or viscosified liquid wherein said gel or liquid is produced by heating a phase change material and a gelling agent or polymer to dissolve the gelling agent or polymer producing a substantially homogenous, low viscosity liquid.