Method for preparing a viscoelastic coolant gel

Abstract

A method for preparing a viscoelastic gel comprising providing first and second mixers, providing a water stream to the first mixer, adding a dry aluminum sulfate powder and a dry carboxymethyl cellulose powder to the water stream, mixing the aluminum sulfate powder, carboxymethyl cellulose powder, and water in the first mixer to create an agglomerate rich gel mixture, transferring the agglomerate rich gel mixture to the second mixer, mixing the gel mixture in the second mixer to create a viscoelastic gel, removing the viscoelastic gel, wherein the second mixer is downstream from the first mixer.

Description

[0001] METHOD FOR PREPARING A VISCOELASTIC COOLANT GEL Field of the Invention The invention is related to a method for making a cold pack to keep items cold, such as for use in cold chain packaging, where the temperature of an item being shipped is important. Background Viscoelastic gels are a unique class of materials composed of multi-dimensional networks of hydrophilic (bio)polymers that have the property to retain a significant amount of water. These versatile materials have gained substantial attention due to their remarkable properties, such as their property to absorb and retain high content of liquid and their readily biodegradable characteristics. Viscoelastic gels are applied in a wide array of applications, including medical devices, drug delivery systems, wound care products, and coolants. Viscoelastic gels prepared by crosslinking carboxymethyl cellulose (CMC) with metal ions result in a plant-based-gel which are highly absorbent and have excellent physical properties and dynamic viscoelasticities. These jelly-like materials offer a high performing solution for innovative cooling applications, providing efficient and sustainable alternatives to traditional coolants. The use of viscoelastic gels as a coolant leverages their high liquid content and thermal properties when used as a cooling system in shipping packages. Current processes for producing viscoelastic gels include mixing water and carboxymethyl cellulose (CMC) to create a cellulose gel, separately mixing aluminum sulfate with water to form an aqueous solution, then adding the aqueous solution to the cellulose gel. Other known ways of producing viscoelastic gels include either adding aluminum sulfate powder to the cellulose gel or adding CMC powder to an aluminum sulfate solution. Summary The inventors found optimal results when a dry aluminum sulfate powder and a dry carboxymethyl cellulose powder are simultaneously added to a water stream and processed successively by an inline single pass high-shear mixer and a high shear batch mixer in the second step. The percentage ratio for the different components was gradually optimized to the point of optimal crosslinking and water retention. This resulted in a viscoelastic and jelly-like gel with firm and flexible structure. The additional property to retain high water content results in the gel remaining in the packaging in the event of a puncture or tear in the packaging material. An exemplary method for preparing a viscoelastic gel includes providing first and second stage mixers, providing a water stream to the inline single pass high-shear mixer, adding a dry aluminum sulfate powder and a dry carboxymethyl cellulose powder to the water stream. The method includes mixing the aluminum sulfate powder, carboxymethyl cellulose powder, and water in the inline single pass high-shear mixer to create an agglomerate rich gel mixture. Then, transferring the gel mixture to the mixing vessel, mixing the agglomerate rich gel mixture in the high shear batch mixer to create a smooth viscoelastic gel. In the method, the high shear batch mixer is downstream from the inline single pass high-shear mixer. The method can include providing the first mixer as an inline single pass high- shear mixer. The method can include providing the second mixer as a static high shear mixer. The method can include providing the first mixer as a high shear batch mixer. The method can include providing the first mixer as a high shear dynamic mixer. The method can include providing the second mixer as a high shear batch mixer. The method can include providing the second mixer as a high shear dynamic mixer. The method can include adding the dry aluminum sulfate powder and the dry carboxymethyl cellulose powder simultaneously to the water stream. The method can include adding the dry carboxymethyl cellulose powder and dry aluminum sulfate powder in a ratio of 6:1 to 4:1. Brief Description of the Drawings FIG.1 is a schematic diagram of an exemplary process for forming a viscoelastic gel, FIGS.2-4 are schematic diagrams of exemplary high shear mixing methods, FIG.5 is a graph of the viscosity of an exemplary gel over time, and FIG.6 is a flowchart of an exemplary process. Detailed Description The disclosure relates to a method or process to produce a viscoelastic gel. More specifically, the disclosure relates to producing a carboxymethyl cellulose (CMC) aluminum sulfate gel that retains structure and firmness over time and shows desirable freezing and thawing properties that are beneficial to use in coolant packs for shipping. Aluminum sulfate has been found to increase the stability and firmness over time of gel packs. The aluminum ions of the aluminum sulfate create a crosslinked polymer network, which results in a significantly firmer structure. Viscoelastic gels can be used as part of a cooling system for shipping parcels. A known method of producing viscoelastic gels includes creating two liquid or viscous compositions: (1) mixing water and cellulose to create a cellulose gel, (2) separately mixing aluminum sulfate (Al2(SO4)3) with water to form an aqueous solution. Finally, the aluminum sulfate solution is added to the cellulose gel. Viscoelastic gels can also be made by adding aluminum sulfate powder to the cellulose gel or adding carboxymethyl cellulose powder to an aluminum sulfate solution. An exemplary process for preparing a viscoelastic gel is shown in FIG.1. A water stream is processed to an inline single pass high-shear mixer 110. Both carboxymethyl cellulose (CMC) powder and aluminum sulfate powder are simultaneously processed to the mixer 110. After mixing in the inline single pass high-shear mixer 110, the combined water-CMC-aluminum sulfate mixture, which can be referred to as the “agglomerate rich gel mixture” are fed downstream to a high shear batch mixer 112 for further mixing to produce a smooth viscoelastic gel. The mixture can optionally be fed to a stirred buffer tank 114, with internal mixer. Next, the mixture is fed to a filling or storage tank 116, where it is stored until it is processed and packed as coolant packs to ship temperature sensitive products. Mixing methods with low to medium shear, as shown in FIGS.2 and 3, are not suitable. In an exemplary embodiment, the mixer is a high shear mixer as shown in FIG. 4. Preferably, a high shear vortex is made prior to adding the carboxymethyl cellulose powder and aluminum sulfate powder as shown in FIG.4. The inventors have found that coolant packs that use a high viscosity gel exhibit improved cooling and binding properties compared to water or low viscosity cooling products. The inventors experimented with numerous different formulations and mixing methods. The inventors varied the percentage ratio for the different components looking to optimize to the point of optimal crosslinking for water retention. The compositions and mixing methods for the different gel formulations are set out in Tables 1 – 3 below. The tables recite “tap water” to indicate that the water, used in the formulations, had no pretreatment. For the experiments a sodium carboxymethyl cellulose is used, but any carboxymethyl cellulose can be used.

[0002] Table 1 Table 2

[0003] Table 3 Table 3 shows that formulations R2A and R2P each contain a similar amount of aluminum sulfate, carboxymethyl cellulose, and water. The difference was that formulation R2P included mixing the components simultaneously, whereas formulation R2A first created two mixtures: an aluminum sulfate solution and a cellulose gel and then combined the mixtures. Table 3 also shows that the R2P formulation exhibited significantly higher viscosity (35,000 cps) than the R2A formulation (17,500 cps). The inventors then experimented with varying the concentrations to further improve the viscosity. As shown in Table 3, formulation R2M had the highest viscosity and appeared as a firm gel. The ratio of CMC to aluminum sulfate is around 5:1. The inventors found optimal results when a dry aluminum sulfate powder and a dry carboxymethyl cellulose powder are simultaneously processed to a water stream and successively mixed by an inline single pass high-shear mixer followed by a high shear batch mixer in the second step. Table 1 shows that formulation G1 has a maximum viscosity of 36,000 cps while using significantly higher aluminum sulfate and carboxymethyl cellulose concentrations compared to formulation R2M, Table 3. Formulation R2M has a maximum viscosity of 43,000 cps. This results in a more effective product for a significant lower materials cost. The preferred R2M formulation showed a viscoelastic and jelly-like gel substance with firm, tight, compact, flexible structure and has high water retention properties. The property to retain high water content and the tight compact structure provides a gel remaining in the packaging when punctures or tears occur in the packaging material. All biodegradable gels eventually deteriorate due to natural degradability and their viscosity will decrease slightly over time. The R2M formulation exhibited high viscosity stability, that is, the viscosity deteriorated very slowly as compared to typical biodegradable coolants. As shown in FIG.5, the R2M formulation has a higher viscosity than other coolants, and maintains a high, and mostly constant, viscosity for numerous months. FIG.6 shows an exemplary method 1000 for preparing a viscoelastic gel and includes the following steps: (i) providing first and second mixers 1010, (ii) providing a water stream to the first mixer 1020, (iii) adding a dry aluminum sulfate powder and a dry carboxymethyl cellulose powder to the water stream 1030, (iv) mixing the aluminum sulfate powder, carboxymethyl cellulose powder, and water in the first mixer to create an agglomerate rich gel mixture 1040, (v) transferring the agglomerate rich gel mixture to the second mixer 1050, (vi) mixing the gel mixture in the second mixer to create a viscoelastic gel 1060, (vii) removing the viscoelastic gel 1070, and (viii) storing the viscoelastic gel 1080. Although the invention has been shown and described with respect to certain embodiments, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described integers (components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such integers are intended to correspond, unless otherwise indicated, to any integer which performs the specified function of the described integer (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment of the invention.

Claims

Claims What is claimed is:

1. A method for preparing a viscoelastic gel comprising: providing first and second mixers, providing a water stream to the first mixer, adding a dry aluminum sulfate powder and a dry carboxymethyl cellulose powder to the water stream, mixing the aluminum sulfate powder, carboxymethyl cellulose powder, and water in the first mixer to create an agglomerate rich gel mixture, transferring the agglomerate rich gel mixture to the second mixer, mixing the gel mixture in the second mixer to create a viscoelastic gel, removing the viscoelastic gel, wherein the second mixer is downstream from the first mixer.

2. The method as set forth in claim 1, wherein the first mixer is an inline single pass high-shear mixer.

3. The method as set forth in claim 1 or claim 2, wherein the second mixer is a static high shear mixer.

4. The method as set forth in claim 1 or any of claims 1 to 3, wherein the first mixer is a high shear batch mixer.

5. The method as set forth in claim 1 or any of claims 1 to 3, wherein the first mixer is a high shear dynamic mixer.

6. The method as set forth in claim 1 or any of claims 1 to 5, wherein the second mixer is a high shear batch mixer.

7. The method as set forth in claim 1 or any of claims 1 to 5, wherein the second mixer is a high shear dynamic mixer.

8. The method as set forth in claim 1 or any of claims 1 to 7, wherein the dry aluminum sulfate powder and the dry carboxymethyl cellulose powder are added simultaneously to the water stream.

9. The method as set forth in claim 1 or any of claims 1 to 8, wherein the ratio of dry carboxymethyl cellulose powder to dry aluminum sulfate powder is 4:

1.

10. The method as set forth in claim 1 or any of claims 1 to 8, wherein the ratio of dry carboxymethyl cellulose powder to dry aluminum sulfate powder is 5:

1.

11. The method as set forth in claim 1 or any of claims 1 to 8, wherein the ratio of dry carboxymethyl cellulose powder to dry aluminum sulfate powder is 6:1.

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