DD296216A5 - MOISTURE BUFFER FORMULATION - Google Patents

Abstract

The invention relates to a moisture buffer formulation characterized by a water-swellable, water-insoluble polymer and a mixture of (1) a non-volatile hydrophilic liquid and (2) water. By adjusting the relative proportions of (1) and (2) in the mixture, the relative humidity obtained by the moisture buffer formulation can be varied in the sealed container. The invention also relates to methods of maintaining relative humidity in a sealed container at a predicted height and to a container containing the moisture buffering formulation of the invention. In the preferred forms, the moisture buffer formulation contains a hydrophilic fibrous material which allows for the production of the moisture buffer as a free-flowing granule. In another preferred form, the moisture buffer formulation is prepared as a film.

Description

For this 1 page drawing

Subject of invention

The invention relates to a formulation for a moisturizer, a method for maintaining the relative humidity within narrow limits in a closed container in spite of temperature fluctuations and a container containing the moisture buffer formulation.

Background of the field

When air is trapped in a container at a given relative humidity and temperature, the relative humidity changes greatly as temperature changes. If z. B. air with 50% relative humidity at 25 ⁰ C enclosed in a container, so their relative humidity increases to 100% when the temperature at constant pressure to 14 ⁰ C is reduced. Below 14 ⁰ C, the moisture condenses in the container. Conversely, the relative humidity in the container drops when the temperature rises above 25 ^° C.

A number of materials which absorb large quantities of water are known in the art (see, for example, EP 0268498). A number of these compounds absorb from 200 to over 1000 grams of water per gram of material. Most of these superabsorbents are copolymers of acrylamide or acrylonitrile or salts of acrylic acid, which occur as parallel atomic chains at intervals cross-linked and form a staircase-like structure. The copolymer can also be reacted with starch to form graft copolymers of starch and acrylonitrile. Examples of such products are sold under the trade names Agrosoke, Igetagel, Teira-Sorb, Super-Sorb, Super Slurper and Alcosorb.

It has been found that by using such a water-swellable polymer it is possible to formulate a moisture buffer.

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Revelation of the invention

Thus, in a first aspect, the invention provides a moisture buffer formulation comprising a water-swellable, water-insoluble polymer and a mixture of (1) a nonvolatile, hydrophilic liquid and (2) water, the polymer becoming capable of being rendered to soak by the mixture and the relative proportions ( 1) and (2) are selected in the mixture so as to produce a pre-calculated relative humidity in a sealed container.

In a second aspect, the invention resides in a method of maintaining relative humidity in a sealed container at a predicted height to provide a moisture buffer formulation in the container comprising a water-swellable, water-insoluble polymer and a mixture of (I) a nonvolatile hydrophilic liquid and (2) water, wherein the polymer is swellable by the mixture and wherein the relative proportions of (1) and (2) are such as to maintain the relative humidity at the pre-calculated level.

In a third aspect, the invention resides in a sealed container in which the relative internal humidity is maintained at a pre-calculated level, wherein the predisposed container is characterized by providing a moisture buffer formulation in the container, and this moisture buffer formulation is a water-swellable, water-insoluble polymer and a mixture of (1) a nonvolatile hydrophilic liquid and (2) water, wherein the polymer becomes capable of being charged by the mixture and the relative proportions of (1) and (2) in the mixture are selected such that a predicted relative humidity in the closed container arises.

In the preferred embodiments of the invention, the moisture buffer formulation in the first, second and third aspects of the invention contains a hydrophilic fibrous material.

The hydrophilic fibrous material may be one of a number of compounds known in the art that can form a layer on the outside of the polymer as it swells through the mixture. A variety of natural and synthetic fibers, including cellulose and synthetic polymer fibers, can be used which are treated to have a hydrophilic surface. At present, polyethylene fiber QP 3850 from DuPont is preferred as the hydrophilic fiber material.

By Including Hydrophilic Fiber Material In the moisture buffer formulation, it becomes possible to prepare the moisture buffer formulation as free flowing granules. This also speeds and facilitates the preparation of the moisture buffer formulation. In addition, the effectiveness of the buffer effect of the moisture buffer formulation increases by the consequent increase in the ratio between the surface area of the moisture buffer formulation and its volume.

In a fourth aspect, the invention relates to a moisture buffer formulation in the form of a film comprising a solid support material and a water-swellable, water-insoluble polymer and a mixture of one (1) nonvolatile hydrophilic liquid and (2) water, wherein the polymer swells through the mixture and the reative shares of

(1) and (2) are selected in the mixture to give a predicted relative humidity in an enclosed air space, the formulation being fixed on the solid support material by applying a water soluble polymer to the solid support material which is compatible with the water swellable material , water-insoluble polymer and the mixture is coated.

The carrier material on which the moisture buffering film is formed or where it is located as an intermediate layer can be made of any fabric or gauze-like material. A range of natural or synthetic fibers can be used as a woven or nonwoven fabric. At present, DuPont Tyvec 1622 E polyethylene nonwoven fabric is preferred.

With the production of the moisture buffer as a film whose tensile strength and dimensions are not affected by water absorption or release, a more robust moisture buffer formulation results.

In the following, the expression "Predicted level of relative humidity" is intended to print the required level of relative humidity for any application As will be appreciated by those skilled in the art, the required level of relative humidity will vary from case to case For fresh vegetables or other products, a high relative humidity of more than 90% is required, while for the preservation of old metal objects, the required relative humidity may be in the range of 40-45%.

The water-swellable, water-insoluble polymer used in the moisture buffer formulation of the present invention can be derived from a variety of superabsorbent polymers known in the art, such as the trade names Terra-Sort, Agros-oke, Igetagel, Super-Sorb, Super Slurper 'and' Alcosorb 'known products.

However, at present, as the water-insoluble, water-swellable polymer, an acrylonitrile-sodium acrylate copolymer is preferred, and most preferable is the compound having the trade name 'Alcosorb AB3S'.

The nonvolatile hydrophilic liquid can be from any of a number of such compounds known in the art that can effect the swelling of the water-insoluble, water-swellable polymer. At present, however, a selection of this nonvolatile hydrophilic liquid from the group consisting of ethylene glycol, glycerol, digol, dimethylsulfoxide and dimethylformamide is preferred. Glycerol is particularly preferred as the nonvolatile hydrophilic liquid.

The relative humidity level obtained by the moisture buffer formulation of the invention can be regulated over a wide range by varying the proportions of water and the nonvolatile hydrophilic liquid used.

The essence of the invention and the manner in which the controllability can be achieved a better understanding, the following preferred forms of the invention with reference to the following examples will be explained.

example 1 Moisture buffer formulation for 30% relative humidity

Alcosorb AB3S (Allied Colloids Wyong NSW) is dried in a furnace at 110 ⁰ C to constant mass. To 26 g of this material are added 65.2 g of anhydrous glycerol and 8.8 g of distilled water. The ingredients are then quickly mixed into a smooth paste and placed in an airtight sealed pressure vessel. Thereafter, the vessel and contents are heated to 60 ° C for 24 hours. The vessel is then cooled slowly (usually over 24 hours) to the operating temperature of the moisture buffer, entering an insulated container.

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Botsplol 2

Moisture buffer formulation for 70% relative humidity

The same decomposition is carried out as in example 1 with the following exception regarding the masses of the constituents:

Polymer 26g

Glycerol 39.7 g,

Water 34.3g

Example 3 Foxtuck buffer formule for 80% relative humidity

The same procedure is carried out as in Example 1 with the following exception in respect of the masses of the constituents:

Polymer 26g

Glycerol 29.0g

Water 45.0g

The forming relatively solid gel can be crushed into particles and filled into bags of nonwoven fabric or other moisture vapor permeable material.

When a bag of a particular formulation is placed in a container whose humidity is to be regulated, the relative humidity of the trapped air in the range of 10% of the required relative humidity over a temperature range between 0 and 30 ° C can be obtained.

Example 4 Foil bottle buffer formulation for 50% relative humidity

Glycerol is diluted with water to a solution whose refractive index at 25 ⁰ C1.4365. 675 g of this solution are homogenized with 275 g of resin 'Alcosorb AB3S' (Allied Colloids Ltd.), which has a water content of 10% relative to dry matter.

The mixture is cured overnight at 70 ° C in a sealed container and then homogenized with 50 g of polyethylene pulp QP 3850 (DuPont). The resulting moisture buffer formulation consists of free-flowing white granules which buffer an enclosed air space to a relative humidity of 50%.

Example 5 Moisture buffer formulation for 90% relative humidity

Glycerol is diluted with water to a solution whose refractive index is at 25 ⁰ C 1.3643. 675 g of this solution are homogenized with 275 g resin 'Alcosorb AB3 S' (Allied Colloids Ltd.), which has a water content of 10% based on dry matter, and with 50 g polyethylene pulp QP 3850 (DuPont). The resulting moisture buffer consists of free-flowing white granules, which buffer an enclosed air space to a relative humidity of 90%.

The free-flowing granules can be filled in bags made of non-woven or other water-vapor-permeable material.

If such a bag placed in a container whose humidity is to be controlled, the relative humidity of the confined air space in the Boreich 10% of the geforderton relative humidity can be maintained over a temperature range between 0 and 3O ⁰ C.

Examples Moisture buffer In foil form for 60% relative humidity

Glycerol is diluted with water to a solution whose refractive index at 25 ⁰ C is 1.4562 (about 10% water). 530 g of this solution are mixed with 289 g of resin 'Alcosorb AB3 S' (Allied Colloids), which has a water content of 10% based on dry matter, until a smooth paste is formed. The paste is applied in a uniform layer on 2000 cm ² fibrous, hydrophilic polyethylene nonwoven (Tyvec 1622 E, DuPont) and covered with the same material. The moisture buffer sandwiched between the two layers of the nonwoven fabric is cured for 2 hours at 7O ⁰ C in a sealed vessel, to a flexible film is produced. A solution of polyvinyl alcohol (average molecular weight 14000, British Drug Houses) prepared by dissolving 27 g in 180 g of water is applied evenly on both sides of the film of the moisture buffer. The water is removed from the polyvinyl alcohol by the gel so that the gel particles are bonded to each other and to the Tyvec sandwich film by the polyvinyl alcohol. This process is carried out overnight by curing the film at room temperature in a sealed vessel. After curing, the moisture buffer film will feel dry and buffer a sealed room at 60% relative humidity.

Example 7

To demonstrate the effectiveness of a moisture buffer formulation of the invention, a number of formulations for a variety of relative humidities was prepared and the moisture generated in a sealed container with these formulations was assessed at 2O ⁰ C.

Eight formulations each containing 20.34g of Alcosorb AB3S at 10.5% water and 49.6g glycerol / water were prepared, varying the ratio of glycerol to water. The required relative humidity, the refractive index of the glycerol / water mixture and the percentage of water in the glycerol-water mixture are listed in Table 1.

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Table 1 refractive index percentage Required rela derGlycerol / water water tive moisture sermischung mass in the glycogen in% rol / water mixture 1.4660 4.3 20% 1.4579 9.2 30% 1.4484 6.4 40% 1.4368 23.3 50% 1.4230 32.0 60% 1.4064 43.9 70% 1.3868 58.3 80% 1.3646 72.4 90%

The results of these experiments are shown in the accompanying figure where the points reached the actual% relative humidity and the line show the ideal situation. The results clearly show that the moisture buffer produces a relative humidity within 5% of the required relative humidity.

Moisture buffer formulations for controlling the relative humidity between 10 and 5% relative humidity can be prepared in an analogous manner by increasing or decreasing the glycerol content in the formulation relative to the water, with the proportion of the water-swellable, water-insoluble polymer remaining constant. Like the o.g. Examples show that water-swellable, water-insoluble polymers can be used which have not been oven-dried, as well as non-anhydrous glycerol, but in these cases their water content must be determined and taken into account in the formulation.

Industrial applicability

The moisture buffer formulation of the invention is widely used in the industry, including:

1. When packaging fresh products in high humidity. The invention enables packaged flowers, fruits and vegetables to be kept at relatively high humidity (over 90%) without the risk of condensation upon temperature drop. This condensation can often lead to damage to these products.

2. Conservation of herbarium specimens. A relative humidity of 50 to 55% is required for showcases. This is difficult to achieve in many cases, but the formulation of the invention would allow it. In addition, when herbarium specimens are dried in the field, the formulation of the present invention enables them to be obtained under proper humidity under variable temperature conditions.

3. In horticulture. Root crops without soil, cuttings and grafting material can be mailed in packages containing cushions with the moisture buffer formulation of the present invention to maintain proper moisture.

4. Conservation of old metal objects. Old bronze objects can be stored with moisture buffer pads to maintain the ideal humidity between 40 and 45% relative humidity. Salt solutions such as lithium chloride have been used to control moisture in these cases, but with the risk of overflow and subsequent corrosion. The moisture buffer formulation according to the invention does not suffer from these disadvantages.

5. Conservation of wood, fabric and leather objects in museums. The problem of deviating from the ideal storage humidity of 50 to 60% relative humidity arises when moving from one museum or exhibition location to another or within showcases. If the humidity deviates, the objects swell or shrink. This burdens the object and eventually causes visible deterioration. The moisture buffer formulation of the invention is ideal for minimizing deterioration due to this cause.

6. Preservation of paintings, paper and textiles when these materials have to be stored at a relative humidity between 50 and 55%.

7. Biotechnological application, including breeding of microorganisms under specified conditions of water activity. For diagnostic purposes, bacteria and fungi are often isolated and grown on agar plates with fixed water activity. In order to keep water activity stable, the relative humidity over the agar plate must remain in equilibrium, i. H. at the same relative humidity to compensate for water activity in the agar plate. Depending on the application, this may vary between 70 and 95% relative humidity (0.7 to 0.95 water activity). Saturated salt solutions are often used for this purpose, but they are complicated to make and can easily overspray. The moisture buffer formulation of the present invention can be made to provide the required water activities in the atmosphere without these problems.

From the foregoing, it will be apparent that the invention is an advantageous improvement or alternative to the current state of the art. Furthermore, it will be understood that the invention may be embodied in other specific forms without altering its character or essential characteristics. Therefore, these embodiments are to be considered in all respects as an example and not as a limitation.

Claims (9)

-1- 295 Claims: A moisture buffer formulation characterized by a water-swellable, water-insoluble polymer and a mixture of (1) a nonvolatile hydrophilic liquid " _N and (2) water, whereby the polymer becomes swellable through the mixture and the relative proportions of (1) and (2) in the mixture are selected to give a predicted relative humidity in a sealed container. A moisture buffer formulation in the form of a film characterized by a solid support material, a water-swellable, water-insoluble polymer, and a mixture of (1) a non-volatile hydrophilic liquid and (2) water, which polymer is swellable by the mixture and the relative proportions of ( 1) and (2) are selected in the mixture to give a predicted relative humidity in a confined air space, the formulation being fixed on the solid support material by applying a water-soluble polymer to the solid support material which is compatible with the water-swellable, water-insoluble polymer and the mixture is coated. A moisture buffering formulation according to claim 1, characterized in that the moisture buffering formulation includes a hydrophilic fibrous material. 4. moisture buffer formulation according to claim 3, characterized in that the hydrophilic fiber material consists of Poyethylenpulpe. 5. moisture buffer formulation according to any one of claims 1 to 4, characterized in that the water-swellable, water-insoluble polymer consists of an acrylonitrile-sodium acrylate copolymer. A moisture buffering formulation according to any one of claims 1 to 5, characterized in that the non-volatile hydrophilic liquid is selected from the group consisting of ethylene glycol, glycerol, digol, dimethylsulfoxide and dimethylformamide. A moisture buffer formulation according to claim 6, characterized in that the nonvolatile hydrophilic liquid is glycerol. A method for maintaining relative humidity in a sealed container at a predicted height, characterized in that a moisture buffer formulation according to any one of claims 1 to 7 is provided within the container, the relative proportions of (1) and (2) be selected so that the relative humidity is maintained at a pre-calculated level. 9. A sealed container, characterized in that the relative internal humidity is maintained at a pre-calculated level, wherein the sealed container characterized in that a moisture buffer according to one of claims 1 to 7 is provided within the container.