WO1981002968A1

WO1981002968A1 - An inert growth medium and method for its preparation

Info

Publication number: WO1981002968A1
Application number: PCT/DK1981/000034
Authority: WO
Inventors: H Kronborg
Original assignee: Metzeler As; H Kronborg
Priority date: 1980-04-16
Filing date: 1981-04-13
Publication date: 1981-10-29
Also published as: ES8206143A1; GB2084981A; NO814288L; AU7152781A; ES502079A0; NL8120117A; JPS57500451A; EP0050140A1; SE8002860L

Abstract

An inert growth medium based on resilient polyurethane foam prepared of hydrophobic polyurethane foam, whereby natural fibres, preferably in an amount of 10-70% by weight calculated on the end product, are admixed to obtain an optimal water retentiveness. The hydrophobic polyurethane foam may be recombined, and the natural fibres may be present in the form of granulated paper or in the form of disintegrated pulp (fluff).

Description

An Inert Growth Medium and Method for Its Preparation

Technical Field

The present invention deals with an inert growth medium based on resilient polyurethane foam.

Background Art

Soil as growth medium is encumbered with several draw¬ backs. It may for instance be difficult to perform a con¬ trolled supply of nutritives to plants growing in soil. Furthermore, it may be difficult to influence the bac- terial environment in the soil without -simultaneously detrimentally influencing the growing conditions of the plants .

During recent years growth of plants without using soil, the so-called hydroculture, has therefore been employed, whereby a plurality of inert growth media have been used, to which nutritives may be added for the plants under controlled conditions. However, when using the inert growth media, it turned out to be difficult to obtain an appropriate balance between firstly the requirement of a sufficient air content in the growth medium, secondly the requirement of a sufficient water retentiveness, and thirdly the requirement of absence of substances irritat¬ ing the skin.

During tests for developing synthetic growth media, va- rious types of plastics have inter alia been used, e.g. polyurethane foam and polyacrylonitrile grafted upon pulpwood fibres in connection with in situ polymerisa¬ tion, ion exchangers saturated with fertilizers, species of clay, and ground peat. Such media are for instance described in SΞ-PS No. 349,225, the DE-AS No. 1,221,484 and No . 1, 227 , 724 , and FR-PS No . 2 , 065 , 215 .

However, none of these tests turned out to be completel satisfactory. When admixing for instance peat, the medi will no longer remain inert because a plurality of va- rious organic and inorganic nutritives as well as patho genie germs and other bacteria detrimental to the grow sometimes exist in pea .

The above SE-PS discloses a growth medium comprising a felt-like mass of natural cellulosic fibres, an acrylo= nitrile polymer being chemically bonded thereto through in situ polymerisation. The growth medium is composed of the resulting polymer-grafted pulpwood fibres, and a predetermined weight ratio of the polymer portion to the cellulosic portion of the fibres is stated for thes pulpwood fibres, said weight ratio being determined by the amount of polymer used for the polymer-grafting of the pulpwood fibres .

Moreover DE-OS No. 2,054,823 discloses a method of pre¬ paring plant substrates based on polyurethane foam sub- stances.

By the method dealt with in the DE-OS storage-stable, compressed plant substrates are prepared in finally di¬ mensioned plastic film wrappings, said plant substrates being based on hydrophilic, resilient polyurethane foam substances. These polyurethane foam substances must be capable of swelling in order to absorb the water supply to such an extent that they fill out the plastic film wrappings completely.

In connection with the hydrophilic polyurethane foam it may be advantageous to use hydrophobic polyurethane foa since the use of the hydrophilic polyurethane foam in- volves considerable problems. Thus it is known to the person skilled in the art that rockwool ^ products are encumbered with the essential drawback that sufficient ventilation is difficult to obtain, whereby it is almost impossible to avoid root rot, said rockwool ^ products to a great extent being used as plant culture substrates and exactly characterised by being highly hydrophilic .

The use of hydrophobic polyurethane foam overcomes the above drawbacks concerning root rot arising when using the hydrophilic polyurethane foam. This is due to the fact that the material upon moistening contains the necessary amount of air. Moreover the material is pleas¬ ant to work with and does not irritate the skin. Fur¬ thermore it can be stored in compressed condition be- fore the use. However, the hydrophobic polyurethane foam presents the problem that as a consequence of its hydrophobic nature it is difficult to moisten and it does not provide the capillarity sufficient for obtain¬ ing the necessary water retentiveness. An admixture of hydrophilic polyurethane foam into a hydrophobic poly= urethane foam can no more ensure an appropriate moisten¬ ing and water retentiveness than an admixture of hydro= phobic polyurethane foam into hydrophilic polyurethane foam can, because it has turned out that the amount of water being bonded to the hydrophilic polyurethane foam is bonded so strongly thereto that the water is not available for the plant roots in such a manner that the roots are capable of absorbing the water.

Disclosure of Invention

The object of the present is to provide an inert growth medium based on resilient polyurethane foam, which meets the above requirements concerning sufficient content of air, sufficient water retentiveness, and absence of sub- stances irritating the skin.

For this purpose the growth medium according to the in¬ vention is characterised in that the polyurethane foam is hydrophobic, and that it contains natural fibres, preferably in an amount of 10-70% by weight calculated on the end product, in order to obtain an optimal water retentiveness.

As natural fibres it is preferred to use granulated paper, preferably in an amount of 40-60% by weight, or disintegrated pulp (fluff) , preferably in an amount of 25-35% by weight.

It turned out surprisingly that by varying the amount o natural fibres it is possible to provide an optimal wat retentiveness. Thus it turned out to be possible to adjust an appropriate hydrophobic/hydrophilic balance b varying the amount of hydrophobic polyurethane and hydr philic natural fibres within the above limits.

As a contributory factor for a correct adjustment of th hydrophobic/hydrophilic balance it is according to an e bodiment of the invention preferred to use a moistening agent, preferably a non-ionic active moistening agent a the preparation of the growth medium.

It is according to the invention preferred to use poly= urethane foam in the form of recombined foam, which is provided by cut residues from the preparation of greate objects of resilient foam plastics being granulated and upon admixing of binding agent being formed under suppl of heat.

The growth medium dealt with may for instance advanta- geously be used as growth medium for plants on root, which are to be exported or imported, as growth medium for ornamental plants on root for use in hospitals, and as growth medium for plants for energy forests.

Brief Description of Drawing and Mode for Carrying Out the Invention

The invention will be described more detailed in the following example with reference to the accompanying drawing illustrating the results of comparison tests.

Example

For measuring the effect of admixing pulp into recombined polyurethane foam, the following samples were prepared:

I Recombined foam without pulp.

II Recombined foam containing 15% by weight of pulp.

III Recombined foam containing 30% by weight of pulp. IV Recombined foam containing 43.5% by weight of pulp,

3

All samples had a density of 50 kg/ and were prepared in accordance with the following table:

I II III IV

Granulated polyurethane 174 g 144 g 114 g 87 g Cellulosic fluff 30 g 60 g 87 g Prepolymer 26 g 26 g 26 g 26 g

"Berol" 087.10% in water 40 g 40 g 40 g 40 g Steam for 2 minutes + + + +

The granulated polyurethane contained resilient polyure= thane foam granulated into small bits of 2 to 30 mm, pre¬ ferably 5 to 10 mm. The cellulosic fluff used contained disintegrated pulp of the same type that is used in nap¬ pies. The prepolymer was a binding agent comprising 100 parts of polyetherpolyol with an OH-value of 43 togethe with 20 parts of toluene diisocyanate. Prior to the use the mixture had been prereacted for 48 hours at room temperature.

"Berol" 087 is a non-ionic active moistening agent from Berol Kemi AB.

Granulated polyurethane and cellulosic fluff were mixed in a mixer. During the stirring a solution of "Berol" 087 was supplied by means of a spray gun, and finally diluted prepolymer was supplied by means of a spray gun. The dilution was performed by Freon 11, which later on evaporated upon the spraying.

The mixture was transferred into a 8 liter mould, and superheated steam was supplied for 2 minutes, whereupon the completed sample was removed after further 5 minutes

For comparing testing 7 roundels were punched out of the samples I-IV. The roundels had a diameter of 77 mm and a thickness of 10 mm. The 7 roundels of each material were piled on a degreased plastic plate, which was subsequent ly submerged into water in order to ensure that the pile was completely saturated with water in connection with pressing out all the air. The piles were subsequently removed from the water and after standing for 10 minutes the weight increase of each roundel was measured. Based on these measurements, the absorbed amount of water was calculated in percentage by volume as function of the height of the roundel in question in the pile. The re¬ maining amount of water appears from the drawing.

Subsequently the samples were placed in such a manner that the lowest roundel was submerged in water . Upon 24 hours, the remaininσ amount of v/ater was estimated. Hereby the samples I and II turned out to be dried-up in the uppermost roundels, whereas the samples III and IV had also maintained their moistness in the uppermost roundels. An essential improvement of the water reten- tiveness is thus obtained by a content of cellulosic fibres of 30% or more.

Claims

Claims :

1. An inert growth medium based on resilient poly= urethane foam, c h a r a c t e r i s e d in that the polyurethane foam is hydrophobic, and that it contains natural fibres, preferably in an amount of 10-70% by weight calculated on the end product, in order to obtai an optimal water retentiveness.

2. A growth medium as claimed in claim 1, c h a r a c t e r i s e d by the hydrophobic polyurethane foam being recombined polyurethane foam.

3. A growth medium as claimed in claim 1 or 2, c h a r a c t e r i s e d by the natural fibres being present in the form of granulated paper in an amount of 40-60% by weight.

4. A growth medium as claimed in claim 1 ox 2, c h a r a c t e r i s e d by the natural fibres being present in the form of disintegrated pulp (fluff) in an amount of 25-35% by weight.

5. A growth medium as claimed in any one of the pre ceding claims 1 to 4, c h a r a c t e r i s e d by sai medium. at the preparation being treated with a non-ioni active moistening agent.

6. A method of preparing an inert growth medium based on polyurethane foam, c h a r a c t e r i s e d by hydrophobic polyurethane foam being mixed with natu¬ ral fibres in an amount of 10-70% by weight calculated on the end product.

7. A method as claimed in claim 6, c h a r a c ¬ t e r i s e d by using recombined polyurethane foam as hydrophobic polyurethane foam.

8. A method as claimed in claim 6 or 7, c ha r a c - t e r i s e d by using granulated paper in an amount of 40-60% by weight as natural fibres.

9. A method as claimed in claim 6 or 7, c h a r ¬ a c t e r i s e d by using disintegrated pulp (fluff) in an amount of 25-35% by weight as natural fibres.

10. A method as claimed in any one of the preceding claims 6 to 9, c h a r a c t e r i s e d by the poly= urethane foam and the fibre material being treated with a non-ionic active moistening agent in connection with the preparation of the growth medium.