GB2343962A - Liquid absorption and weighing - Google Patents

Abstract

To weigh a small quantity of liquid it is absorbed into a foam material which is weighed before and after the absorption. The foam material is of open-celled polyvinyl alcohol and is such that it does not significantly wet a surface on which it rests. The foam material may alternatively be used as a filter paper substitute, as an absorbent for urine or menstrual fluid, as a carrier member for nicotine or a therapeutic agent, e,g, hormones for hormone replacement therapy, or as an encapsulant for an agricultural or horticultural medium.

Description

LIQUID ABSORPTION The invention relates to liquid absorption.

Many materials are capable of absorbing liquids such as water and different materials are used in different situations. Natural and artificial sponges are used in household cleaning tasks for mopping up spilled liquids; filter papers are used to collect liquids for weighing in scientific and materials testing laboratories ; super-absorbing gels are used as moisture retainers for horticultural purposes, and so forth.

One particular foam material, open-cell polyvinyl alcohol foam, has high absorbency but the unappealing property of becoming hard when dry; though flexibility is completely recoverable on re-wetting, this property has militated against its widespread application outside, seemingly ; of the field of household use as a chamois leather.

The present invention provides new uses for such a material, which may described generally as an open-cell foam material which behaves in water as a negatively charged colloid.

The invention, in one aspect, comprises a method for collecting e. g. for weighing small quantities of a liquid comprising absorbing the liquid into a foam material which is a good absorber for the liquid and which will hold significant quantities of the liquid without release or without significant release so that it does not wet or significantly wet a surface on which it rests.

In another aspect, the invention comprises a method for collecting e. g. for weighing small quantities of a liquid comprising absorbing the liquid into a foam material which is a good absorber for the liquid by virtue of its open cell foam structure but which is noter se an absorbent material.

In yet another aspect, the invention comprises a method for collecting e. g. for weighing small quantities of a liquid comprising absorbing the liquid into a compressed foam material, especially one which is a high-density foam with low open cell area on the surface.

The foam material may be weighed before and after absorbing a quantity of liquid whose weight is to be determined. The foam material may be used for incremental weighing measurements-as compared to filter paper, normally used in such measurements as of retentivity and expression of water under pressure from absorbers in diapers and incontinence control garments, the foam material retains considerably more water, and can be used several times without intervening drying. It is also much longer lasting than filter paper (normally used for one measurement only) being usable for three thousand measurements before showing any significant deterioration. This is possible with a sheet or disc of foam having substantially the same dimensions as filter paper, though usually somewhat thicker, depending on the requirements of any particular operation.

In multiple weighings, the foam may be precisely returned to a given state by applied pressure to remove liquid absorbed for the previous weighing.

A foam material is preferred which is open-cell and of a material which behaves in water as a negatively charged colloid, such as polyvinyl alcohol aforementioned.

Such a foam can absorb up to twelve times its dry weight of water, and the wet volume is about 20% greater than the dry volume.

A disc of 75 mm diameter in the dry state will measure for example 90 mm in diameter when hydrated.

Pore shape and size can be precisely specified by manufacturing conditions.

Such a foam can also be used as a metallic cation absorber, according to another aspect of the invention, in odour and/or incontinence control products.

The same foam, according to another aspect of the invention, can be used as a slow release treatment substance carrying medium, such as an agricultural or horticultural fertiliser or plant treatment medium, or as a carrying medium for human or animal therapeutic substances. Plants may draw fluid from the material at a rate appropriate to their metabolism. A PVA foam is, moreover, bio-degradable, unlike other polymers currently used for a like purpose. It is also resistant to ultra-violet radiation, so, while being eventually bio-degradable, is nevertheless sufficiently durable in strong sunlight, good growing conditions.

The invention also comprises a clamp used in combination with a filter paper substitute or slow release substance carrying medium according to other aspects of the invention, adapted to apply pressure thereto to adjust the liquid content thereof to a predetermined level (which can be zero or substantially zero).

Foam material artefacts according to the invention and methods for using them will now be described with reference to the accompanying drawings, in which: Figure 1 is a filter paper substitute used in a test of absorbent properties of an absorbent material used e. g. in diapers; Figure 2 is a diagram showing a clamp arrangement cooperating with a filter paper substitute; Figure 3 is a diagram showing a soil nutrient carrying liner for a hanging basket or a planter; and Figure 4 is a diagram of a bandage or plaster incorporating a carrying member for a therapeutic agent for treatment of the human or animal body.

The drawings illustrate various novel configurations and uses of the new absorbent foam material polyvinyl alcohol foam.

Figure 1 illustrates a filter paper substitute 11 for testing absorbent properties of an absorbent material 12 of the kind used, for example, in baby diapers, feminine hygiene, and incontinence devices. The material 12 is placed on a test surface and is loaded with a pre-set volume of fluid or, more usually perhaps, common salt solution or a solution approximating to urine or menstrual fluid. The quantity loaded may depend upon the absorbent and wicking properties of the material 12.

After a lapse of time, which may be determined by electrical measurement of the quantity of water or solution absorbed by the material 12, pressure is brought to bear on it by a weight or driven platen 14. The filter paper substitute 11 lies directly on the test product 12, fluid is pressed out of the test product 12 through the pressure of 14 and is collected by 11.

Water or solution flowing on to the filter paper substitute 11 as a result of being expressed from the material 12 is absorbed thereby.

The amount of water or solution absorbed as a result of a predetermined testing procedure is measured by weighing the filter paper substitute 11 when it has absorbed the water or solution, and comparing its wet weight with its dry weight.

Unlike regular filter paper, the substitute 11 made of polyvinyl alcohol can absorb many times-perhaps 10 to 15 times-its own weight, yet remains dry in appearance and does not wet the surface of the support 15. This ensures that all the water absorbed is measured in the weighing procedure and, indeed, depending of course on the circumstances, can be used again and again without any intervening drying out right up until it becomes saturated, for successive tests, the incremental weight between tests indicating the amount of water absorbed at each test.

Ordinarily, a filter paper would be used for but a single test and thrown away. Using the filter paper substitute 11, not only can it be used and re-used without drying out up to its capacity, it can then be dried out and used over again. Current indications suggest that in this way it can be used for thousands of tests.

As the polyvinyl alcohol foam hardens on complete drying out, it may be desirable for multiple tests, where the capacity of the foam is likely to be reached, to reduce the liquid content of the foam in a standard or predetermined way to an extent where it has reached absorption capacity but is not yet completely dry and brittle. A clamp or press arrangement as seen in Figure 2 with a perforate platen 21 and press member 22 precisely weighted or otherwise loaded, possibly, for foams of a prescribed dry thickness, with stop members 23 to allow compression to a predetermined wet (or, perhaps more accurately, moist) thickness, can be used so to reduce the liquid content.

While use of a filter paper substitute 11 as an absorber-a common enough use for filter paper-has been described above, it also turns out, once the concept of presenting the foam material as a filter paper substitute has been suggested, that it actually has unexpected properties as a filtration medium.

Of course, open-cell foam plastics have been widely used in filtration, as air filters in automobiles, air conditioning systems and in water filtration as in pond filters. But filters made of polyvinyl alcohol have substantial advantages as regards durability, chemical resistance, abrasion resistance, UV resistance and linting as compared to conventional cellulose or polyurethane sponges.

However, not only the brittle dry state, but also other factors would appear to militate against the use of polyvinyl alcohol as a filtration medium, especially for filtration of aqueous media.

It is, in fact, precisely the very high water absorption capacity-as well as the speed at which absorbtion takes places-that would seem to be a deterrent to use as a conventional filter, it being, on the face of it, required of a filter that it separates the filtrate from the solids filtered out, so retention of filtrate would appear to be conter- indicated. However, it turns out, again, on experimentation, that any filtrate retained in the filter can be recovered without any contamination by retained solids, by pressureas by a clamp as described with references to Figure 2.

This suggests an inventive method of filtration in which a polyvinyl alcohol (or like material) foam is allowed to fill to capacity the filtrate then being pressed out. Of course, once filled to capacity, it is possible simply to stream the liquid therethrough at whatever rate the foam will permit, as in normal filtering, but to press out retained filtrate at the end of the filtration process or as required at intervals during it.

Retained filtered-out solids can be washed out at the end of the process or, if desired, by dissolving the polyvinyl alcohol in a solvent that does not also dissolve the solids desired to be recovered, or, conversely, by using a solvent for the solids that does not also attack the polyvinyl alcohol.

The rate of passage of liquid through a polyvinyl alcohol foam filter will depend inter alia on cell size and shape which may be precisely specified during manufacture to suit different purposes.

The foam material, behaving, as it does, as a negatively charged colloid in water, can be used to recover dissolved material from a water, particularly metallic ions and ammonium ions responsible for odours e. g. from urine, so that the water absorption and cation retention characteristics render the polyvinyl alcohol foam material effective in diaper and incontinence garment usage. AS before, the tendency to hardness or brittleness on drying out would tend to militate against such use. This can, however, be effectively countered by, for example, pelletising or granulating the foam material (perhaps as by ergogenic grinding) and encapsulating it in a permeable or semipermeable membrane.

Another application for the foam is as a slow release material. Figure 3 illustrates a shaped foam lining 31 for a hanging basket or planter 32 which may be sold in the dry state having been impregnated with nutrients or fertiliser for plant growth and/or with pest control agents, or in the flexible, moist state in a moisture-seal bag.

Figure 4 illustrates in cross-section a bandage or plaster 41 containing a foam material of polyvinyl alcohol 42 contained in a permeable envelope 43 attached to a backing 44.

The foam can contain therapeutic agents for slow release onto or in through the skin such for example as hormones for hormone replacement therapy (HRT) or nicotine for controlled reduction in nicotine dependence. The foam structure-cell size and shape-can be adapted for control, taken together with encapsulation permeability, concentration and consistency of the absorbed substance in its liquid medium, of the release rate.

As, moreover, release rate may be affected by pressure, a bandage or plaster may be so constructed as to deliver more therapeutic agent on demand, for example of painkiller.

Claims (16)

1. CLAIMS 1. A method for collecting e. g. for weighing small quantities of a liquid comprising absorbing the liquid into a foam material which is a good absorber for the liquid and which will hold significant quantities of the liquid without release or without significant release so that it does not wet or significantly wet a surface on which it rests.
2. 2. A method according to claim 1, in which the foam material is weighed before and after absorbing a quantity of liquid whose weight is to be determined.
3. 3. A method according to claim 2, in which the foam material is used for incremental weighing measurements.
4. 4. A method according to any one of claims 1 to 3, in which the foam material is in the form of a filter paper.
5. 5. A method according to any one of claims 1 to 4, in which the foam is an open-cell foam of a material which behaves in water as a negatively charged colloid.
6. 6. A method according to claim 5, in which the foam is of polyvinyl alcohol.
7. 7. A foam material when used in a method according to any one of claims 1 to 4.
8. 8. A filter paper substitute comprising an open-cell foam material of a type which behaves in water as a negatively charged colloid.
9. 9. A filter paper substitute according to claim 8, comprising a polyvinyl alcohol foam.
10. 10. A metallic cation absorber in odour and/or incontinence control products comprising an open-cell foam material of a type which behaves in water as a negatively charged colloid.
11. 11. An absorber according to claim 10, comprising a polyvinyl alcohol foam.
12. 12. A slow release treatment substance carrying medium comprising an opencell foam material which behaves in water as a negatively charged colloid.
13. 13. A medium according to claim 12, comprising polyvinyl alcohol.
14. 14. A medium according to claim 12 or claim 13, used as an agricultural or horticultural fertilise or plant treatment medium.
15. 15. A medium according to claim 12 or claim 13, used as a carrying medium for human or animal therapeutic substances.
16. 16. A clamp in combination with a filter paper substitute or slow release substance carrying medium adapted to apply pressure thereto to adjust the liquid content thereof to a predetermined level.