GB2167398A

GB2167398A - Supplemented polymeric substance for use in growing media

Info

Publication number: GB2167398A
Application number: GB08527107A
Authority: GB
Inventors: Allan Cooke
Original assignee: Chemical Discoveries SA
Current assignee: Chemical Discoveries SA
Priority date: 1984-11-08
Filing date: 1985-11-04
Publication date: 1986-05-29
Also published as: GB8527107D0; CA1283555C; GB2167398B

Abstract

A highly water-absorbent polymeric substance is supplemented with an additive. The additive is applied in aqueous medium to particles of the polymeric substance so that the medium is absorbed. Water is then removed by drying to give loose particles of supplemented polymeric substance which can be moved with a growing medium such as soil or sand. The polymeric substance may be an acrylamide polymer cross-linked with N,N'-methylene bisacrylamide. The additive may be a colouring agent for identification purposes or a plant nutrient or a bacterial strain for soil conditioning. <IMAGE>

Description

SPECIFICATION Supplemented polymeric substance for use in growing media This invention relates to polymeric substances in loose, particulate form for use in growing media.

British Patent Application 2127005 describes a highly water-absorbent polymeric substance which can be mixed with a growing material such as soil or sand so as to produce a growing medium having improved properties particularly with regard to water retention and physical stability.

More specifically, the Application describes a method of producing a growing medium comprising steps of polymerizing an acrylamide monomer with N,N'-methylene bisacrylamide cross-linking agent in the presence of water and an initiator, said cross-linking agent amounting to up to 5% by weight of the monomer, and the reaction conditions of said polymerization being selected, so that a polymeric substance is formed which is capable of absorbing at least 30 times its own volume of water to form a firm gel which is of a sticky or tacky consistency sufficient to adhere to the roots of a plant and to permit free migration of water from the gel into the plant roots; dividing the polymeric substance into particles; and mixing a minor proportion of said particles with a major proportion of a particulate growing material.

The above described polymeric substance has special, advantageous properties. However, these properties may not be readily apparent from the raw material as supplied to the end user in so far as such material comprises a mass of whitish crystalline particles which may not be clearly distinguishable in appearance and feel from other polymeric substances, or indeed other non-polymeric substances such as inorganic fertilisers, which are supplied for use for soil conditioning or other agricultural or horticultural purposes.

There is therefore the possibility that mistakes can readily be made in the conditioning of a growing material (i.e. by incorporation of the wrong conditioning substance) and such mistakes can be costly in so far as they may result in ultimate failure or poor performance of a crop.

One object of the present invention is to provide a simple yet effective means of identifying a polymeric substance whereby inadvertent use of a wrong or undesired material can be avoided or at least minimised.

According to one aspect of the invention therefore there is provided a mass of loose, particulate polymeric substance which is identified by colouration thereof, characterised in that the said substance is highly water-absorbent and a proportion of the particles thereof have absorbed thereon or incorporated therein a colouring agent having a different colour or shade from the remaining proportion of the particles.

In this way a distinctive "speckled" appearance can be achieved which is capable of clearly identifying the polymeric substance thereby to distinguish this from other substances generally of similar particulate form.

The arrangement may be such that a minor proportion of the particles is coloured and the remaining major proportion is in its natural uncoloured state e.g. whitish or transparent or translucent. Alternatively the minor proportion may be deeply coloured and the major portion may be the same colour but of a much lighter shade. Other arrangements are also possible including, for example, the use of a major portion of coloured particles, and the use of two or more different colours.

In each case however it will be understood that a distinctive variegated effect can be achieved which is not readily confused with other materials even coloured materials.

The desired colouration may be achieved in any suitable manner and using any suitable colouring agent. Preferably, however, and in accordance with a second aspect of the present invention there is provided a method of identifying a mass of loose, particulate polymeric substance which is of a highly waterabsorbent nature, wherein a body of the said polymeric substance containing absorbed water is exposed to a water-miscible or -soluble colouring agent in an aqueous medium so that the colouring agent is absorbed in a nonhomogeneous manner with regard to the said body.

The colouring agent may be applied to the polymeric substance in any suitable manner. In one embodiment, polymeric substance in the form of a dry loose material is spread from a feed hopper onto a conveyor belt to form an even layer of a depth of about 1cm to 5cm.

The conveyor belt may be moving at the rate of about 610 to 1525cm per minute. The substance is sprayed with a solution of a water-soluble dyestuff using jets (e.g. six jets) on an arm supported by brackets attached to the conveyor frame. The jets are supplied from containers holding coloured dyes. Droplets of the solution contact the polymer granules or particles and are absorbed. The resulting material has a minor proportion of particles, on the top surface of the layer, which are strongly coloured, the remaining particles may be weakly coloured (possibly in different shades) immediately below the surface, and particles at the bottom of the layer are not coloured. The particles are conveyed to blending apparatus (after drying) and the particles of different shades are blended so that the strongly coloured particles are relatively evenly distributed.A multi-colour effect can be attained by submitting the polymeric material to two or more successive exposures to differ ently coloured dyestuffs.

Highly water-absorbent polymeric substances, such as that referred to above and described on British Application 2127005, can also be advantageously impregnated with substances other than or additional to colouring agents. Thus in accordance with a further aspect of the present invention, highly waterabsorbent polymeric substance in loose particulate form is supplemented by absorbing one or more nutrient substances into or on the particles. The procedure may be effected in like manner to that described above with reference to the absorption of colouring material.

Thus the nutrient substance may be a watermiscible or -soluble substance incorporated in an aqueous medium, additionally or alternatively to colouring material, which medium is sprayed on some or all of the particles, the particles then being dried. More specifically, all aspects of the above described procedure relating to the incorporation of colouring material may be applied to the incorporation of nutrients with the nutrient or nutrients substituted for or used in conjunction with the colouring material.

by way of example the nutrients may comprise one or more of: urea; nutrient salts; materials derived from seaweed; chelates e.g. of cobalt, zinc, boron, nickel, calcium, ureic nitrogen, phosphorous pentoxide, potassium oxide, magnesium oxide, iron, manganese, copper, molybdenum and other chelated elements and micronutrients in various proportions and formulations to suit requirements for individual species of plants.

Moreover, in accordance with a further aspect of the present invention, highly waterabsorbent polymeric substance in loose particulate form, such as that referred to above and described in the abovementioned Application 2127005, is supplemented by absorbing one or more bacterial strains into or on the particles.

The bacterial strain may be of the Rhizobium species which is useful in conditioning soil. In particular one or more of the following Rhizobium strains may be used: Rh. meliloti CC 2551, Rh. leguminosarum 3740, Rh. japonicum USDA 110 and 191 and the Cicer arietinum (chickpea) specific strains 3889 and CP44a.

The polymeric particles may be impregnated with the bacterial strain in an aqueous medium and the water may then be removed by drying e.g. in a vacuum dessicator chamber. The impregnated particles may then be stored in sealed sterile containers prior to use.

The polymeric particles are preferably sterilised (e.g. by autoclaving at 121"C and 15 psi) before being impregnated.

Suitably the particles may be impregnated with the bacterial strain grown in an aqueous mannitol-yeast extract broth at a culture density of at least 108 cells per ml. 1ml of this culture may be added to 0.25 gms polymeric substance.

The particles may be contacted with the aqueous medium containing the bacterial strain simply by immersing the particles in the medium. Alternatively a spraying technique may be used as described above with reference to the absorption of colouring material and/or nutrients. More specifically, all aspects of the above described procedure relating to the incorporation of colouring material and/or nutrients may be applied to the incorporation of bacterial strains with the bacterial strain or strains substituted for or used in conjunction with the colouring material and/or the nutrient or nutrients.

A principal aspect of the present invention consists of a method of making a supplemented highly water-absorbent polymeric substance for use in a growing medium characterised in that an aqueous medium containing one or more additive substances is absorbed by a mass of particles of said polymeric substance and water is removed by drying to give loose additive-supplemented particles of said polymeric substance. This principal aspect may embody any or all of the details of the above described various aspects of the invention.

With regard to the nature of the polymeric substance used in any of the foregoing aspects of the invention, this is preferably an acrylamide polymer cross-linked with up to 5% N,N'-methylene bisacrylamide which absorbs at least 30 times its own volume of water to form a sticky gel as referred to above and which is described in U.K. Application 2127005. Particularly with this polymeric substance the additive material is absorbed into the substance i.e. so as to penetrate the three dimensional polymeric structure thereof.

The resulting supplemented (e.g. identified and/or nutrient incorporating and/or bacterial strain incorporating) material of the invention may be used to improve the properties of a particulate growing material, as described in U.K. Application 2127005 by mixing a minor proportion of the identified material with a major proportion of the growing material.

Claims

1. A method of making a supplemented highly water-absorbent polymeric substance for use in a growing medium, characterised in that an aqueous medium containing one or more additive substances is absorbed by a mass of particles of said polymeric substance and water is removed by drying to give loose additive-supplemented particles of said polymeric substance.

2. A method according to claim 1, characterised in that the aqueous medium is sprayed onto the mass of particles of polymeric substance.

3. A method according to claim 1 or 2, characterised in that the aqueous medium is absorbed by only a portion of the mass of particles.

4. A method according to any one of claims 1 to 3, characterised in that the additive substance or substances comprises one or more plant nutrients.

5. A method according to any one of claims 1 to 4, characterised in that the additive substance or substances comprise one or more bacterial strains.

6. A method acording to any one of claims 1 to 5, characterised in that the additive substance or substances comprise one or more colouring agents or dyestuffs.

7. Loose particles of supplemented polymeric substance when made by the method of any one of claims 1 to 6.

8. A mass of loose particulate polymeric substance which is identified by colouration thereof, characterised in that the said substance is highly water-absorbent and a proportion of the particles thereof have absorbed thereon or incorporated therein a colouring agent having a different colour or shade from the remaining proportion of the particles.

9. A mass of particles according to claim 8, characterised in that only a proportion of the particles is coloured.

10. A method of identifying a mass of loose particulate polymeric substance which is of a highly water-absorbent nature, wherein a body of the said polymeric substance containing absorbed water is exposed to a watermiscible or -soluble colouring agent in an aqueous medium so that the colouring agent is absorbed in a non-homogeneous manner with regard to the said body.

11. A method according to claim 10, characterised in that polymeric substance in the form of a dry loose material is spread from a feed hopper onto a moving conveyor belt to form a layer, this layer is sprayed with a solution of a water-soluble dyestuff so that the particles in the top surface of the layer absorb the dyestuff and become coloured, and the particles are dried and blended.

12. Loose particles of identified polymeric substance when made by the method of claim 11.

13. Loose particles according to claim 7 or 8 or 12, wherein the polymeric substance comprises an acrylamide polymer cross-linked with up to 5% N,N'-methylene bisacrylamide which absorbs at least 30 times its own volume of water to form a sticky gel.

14. A growing medium comprising a mixture of a minor proportion of loose particles according to claim 7 or 8 or 12 or 13 with a major proportion of a growing material.