FR2611725A1 - Friable, aerated substrate based on polyurethane, applicable in horticulture and process for obtaining it - Google Patents

Abstract

This substrate, of fibrous structure, exhibits a water absorption ratio of at least 90 % of its volume in a very short lapse of time, while discharging at least 90 % of the absorbed water in the same lapse of time, once placed outside the water, is obtained by a process consisting in reacting a polyol with a polyisocyanate in the presence of a catalyst and of a blowing agent and in increasing the exothermic nature of this reaction by causing "core smouldering" while avoiding autoinflammation. Application in the field of horticulture.

Description

 The present invention relates to a friable aerated substrate based on polyurethane applicable in particular in horticulture and its production process.

 We know that polyurethane finds multiple applications. It is generally in the form of foams and these can be either rigid.

either semi-rigid or still flexible.

 According to the internal structure. these foams are respectively of the closed cell type, with distributed cells, one open and the other closed, and finally, with open cells.

 One of the possible applications of rigid open cell mosses is to use them as carriers for fresh cut flowers, because of their ability to absorb and store water.

 These foams have a structure with a regular homogeneous network in the three axes of space. giving them a certain elasticity, thus making a relatively malleable product. Such foams can also be used in the particulate state. once crushed. mixed with potting soil, in the horticulture sector.

 The present invention relates to a new type of polyurethane foam "characterized by an aerated heterogeneous structure of the fibrous type and by the fact that it is crumbly to the point of crumbling under simple manual pressure.

 Another important characteristic of the product of the invention lies in the fact that it absorbs at least 90 Z of its volume of water in a very short period of time and that it rejects at least 90 Z of the water absorbed in the same amount of time. once put out of the water.

 The invention also relates to a process for obtaining such foams.

We know how to make "polyurethane foams thanne" by exploiting the well-known classic reaction:
polyol + polyisocyanate ---> polyurethane, in the presence of a catalyst. a blowing agent and possibly a surfactant.

 It is well known to those skilled in the art that this reaction is eminently exothermic. It is therefore necessary, in order to obtain a valid product, that part of the calories can be evacuated during the reaction, failing which, one can witness the auto-ignition of the foam formed.

Thus, up to now, the exploitation of the above-mentioned reaction is carried out under conditions such as
1. either that the expansion evolves slowly, which allows the production of large volumes of foam
2. or that the expansion evolves rapidly, which allows the production of coating foams, for example by the projection technique.

 In both cases, it is avoided that the temperature at the heart of the foam formed exceeds 100 -10O'C.

By doing so. the phenomenon well known in the art is avoided under the name of "core cramage", a phenomenon due to an excessive rise in temperature. We therefore obtain products with a homogeneous network structure, with open, closed cells, or open and closed cells.

 However, the present invention makes use of this hitherto undesirable "cramage à coeur" phenomenon, which makes it possible to obtain the product according to the invention, which differs from the products currently known in the sense that it has no regular network structure. On the other hand, obtaining this "cramage à coeur" allows the formation of an eminently non-coherent fibrous structure, not malleable but on the contrary brittle.

 The raw materials used to obtain the product according to the invention are those which are commonly used in the field of the manufacture of polyurethane foams of the rigid type, namely polyols having a hydroxyl number of between 500 and 700 Among these polyols, mention will be made in particular of those derived from sucrose as well as those derived from sorbitol.

 As regards isocyanates, mention will be made in particular of 4,4'-diphenylmethanediisocyanate, with an NCO content of between 27 and 29%, which is the most commonly used.

 As regards blowing agents, agents of the "Freon 11" type are generally used, methylene chloride and water. As for the catalysts, these are generally chosen from aliphatic tertiary amines.

 Those skilled in the art also know how to use surfactants, if necessary, of the silicone type, chosen from siloxanes (polyether base or polyester base).

 These surfactants are generally assigned a rule for homogenizing the reaction mixture.

 Those skilled in the art also know that by varying the nature and the proportion of the catalyst used and / or the blowing agent. it can act on the speed of expansion, therefore on the more or less rapid exothermicity of the reaction and, consequently, avoid the phenomena of "cramage in heart and auto-ignition of the product. Given that, according to l he invention is sought for the manifestation or the appearance of the phenomenon of "core cramage" controlled, the blowing agent used will preferably be water. Indeed, it is known that the reaction between the polyisocyanate and l water is itself exothermic, which goes in the desired direction, namely to promote an intake of additional calories.

 In the manufacture of a polyurethane according to the usual technique, the proportions between the polyol used and the polyisocyanate are substantially stoichiometric with a slight excess of polyisocyanate in the case where the blowing agent is water.

 In accordance with the invention and to further promote an exothermic reaction, the blowing agent used being water, the proportion of polyisocyanate will still be in excess. Advantageously, a weight ratio of polyisocyanatelpolyol of between 140,100 and 160/100 will be cited.

 The interest and the scope of the invention will emerge more clearly from the example which follows, given simply by way of illustration and in no way limiting.

Example
We start with a premix of the following composition
- polyol derived from sucrose,
hydroxyl number 700) 84.9 Z by weight,
- catalyst (dimethyl
ethanolamine) 3.0 Z by weight,
- silicone (siloxane modi
(polyether base) 0.1 Z by weight,
- blowing agent (water) 12.0 7. by weight,
Once this premix has been formed, polyisocyanate (4,4-diphenylmethanediisocyanate) is added to it in a ratio of 140/100.

 The mixture is poured into a mold of about 2 m3 with a height of 50 cm. The foam expands freely. When the core temperature reaches 120-C (determined by a thermal probe or by any other appropriate means), the phenomenon of "core burn-in" is stopped by cooling. This can be achieved by quickly cutting the foam block into sheets 3.5 to 5 cm thick, for example.

 Examination of such plates under the microscope reveals a non-definable structure and in particular the absence of cells. On the other hand, a structure analogous to a fibrous structure is observed, the fibers of which are generally long and oriented in the direction of expansion.

When cutting out of these plates, parallelepipeds in the form of bricks with a
3 volume of 2 dm3 and we immerse these bricks in water, we see that they absorb 90 X of their volume of water in less than a minute and that once out of the water, they reject the latter at a rate of 90% relative to the amount absorbed, also in less than a minute.

 When dry, these plates are eminently friable by simple manual crushing without significant effort, giving a fine dust.

 The product according to the invention can find numerous applications, in particular in the field of horticulture. This is how we can achieve volumes in which seeds, plants, cuttings and plants can be easily inserted into the mass. Because of the great ability of the product according to the invention to absorb and reject water, it will thus be possible to promote humidification and successive aeration of the roots of the plant. Given the friability and relative fragility of this product, the roots can easily pass through and pre-destroy it as it grows.

 Because of its mechanically degradable nature and when it is in the soil after transplantation, it will be easy to return the soil by any appropriate means. without any discomfort due to residual products (dust). It should also be noted that this dust can contribute to the enrichment of the earth.

 Otherwise. the chemical inertness and the thermal resistance below 100 ° C. allows sterilization in an autoclave of the product of the invention, allowing its use in the laboratory for in vitro tests.

 Of course, the product according to the invention may include in its structure various additives such as fertilizers, fungicidal agents, long-term fertilizers, activated carbon, dyes, thus conferring on the basic polyurethane various complementary functions adding to the hydrophilic character, such as for example nourishing, fungicidal, growth inhibiting functions.

 It goes without saying that the present invention has been described for purely explanatory and in no way limitative and that any modification, in particular in terms of technical equivalences, may be made therein, without going beyond its ambit.

Claims (11)

 1. Substrate based on polyurethane, characterized in that it is brittle, airy; with a fibrous structure and that it has a water absorption rate of at least 90 Z of its volume in a very short period of time, while rejecting at least 90 Z of the water absorbed in the same lapse of time. once put out of the water.  2. Substrate according to claim 1, characterized in that said absorption of at least 90% of its volume takes place in less than a minute.  3. Substrate according to claim 1 or 2, characterized in that it is eminently friable by simple manual crushing, without significant effort.  4. Substrate according to any one of claims 1 to 3, characterized in that it has a structure analogous to a fibrous structure whose fibers are generally long and oriented.  5. A method of manufacturing the substrate according to any one of claims 1 to 4. characterized in that it consists in reacting a polyol on a polyisocyanate in the presence of a catalyst and a blowing agent and in enhancing the character exothermic of this reaction by causing "heart burn", while avoiding self-ignition.  6. Method according to claim 5, characterized in that the reaction is stopped when the core temperature reaches 100-120-C  7. Method according to claim 5 or 6, characterized in that a polyol having a hydroxyl number between 500 and 700 is used, an isocyanate chosen from the family of 4,4'-diphenylmethane-diisocyanate, an NCO content of between 27 and 29% and an expanding agent chosen from agents of the "Freon" type, methylene chloride and water, and a catalyst chosen from aliphatic tertiary amines.  8. Method according to claim 7, characterized in that the polyol is a derivative of sucrose or sorbitol.  9. Method according to any one of claims 1 to 8, characterized in that the reaction medium contains a surfactant of the silicone type chosen from siloxanes.  10. Method according to any one of claims 1 to 9, characterized in that the blowing agent is water and that the weight ratio between the polyisocyanate and the polyol is between 140/100 and 160/100 .  11. Application of the substrate according to any one of claims 1 to 4 in the field of horticulture.