AU2947192A - Glass fibres used as a substrate for soilless cultivation - Google Patents

Description

1 GLASS FIBERS USED AS A SUBSTRATE FOR SOILLESS CULTIVATION The invention concerns glass fibers to be used in .5 agricultural applications. The invention more particularly concerns fibers to be used as the essential elements of a substrate for soil-free cultivation. Generally speaking, a soil-free cultivation 10 substrate needs to have sufficient mechanical resistance so as to avoid subsidence under the effect of both a root development and a mechanical stressing due to a wettening effect and a circulation of the nutritive solution in the substrate. Furthermore, it 15 needs to allow for availability of the nutritive solution for the plant and ensure good aeration of the roots. Obviously, an effort is currently made to find the lowest possible cost and density. Indoor cultivation substrates are generally 20 produced from mineral wool. These substrates possess advantageous properties. However, the mineral wool is obtained from fibers produced by a method known as the external hydro-extraction or centrifugal method. These methods normally result in obtaining a relatively large 25 proportion of infibrated particles present in the substrate and also products with a relatively low density of approximately between 60 and 80 kg/m3. Indoor cultivation substrates formed of glass wool has also been proposed. This glass wool is obtained 30 from fibers produced by a method known as the internal hydro-extraction or centrifugal method which appears in full details in the following description. The density 2 of these substrates may be significantly much lower and is most often between 15 and 50 kg/m3. There now follows descriptions of glass fiber compositions satisfying the characteristics required 5 for a use of the substrate for soil-free cultivation. The patent EP 201 426 describes a glass composition for fibers to be used as a substrate for soil-free cultivation which clearly satisfies the hydric and mechanical requirements as regards soil-free 10 cultivation. However, some of these constituents released on contact of the nutritive solution may be unfavourable to certain cultivation systems. The aim of the present invention is to provide 15 fibers whose glass composition possesses characteristics so that they are able to contain fibers according to the internal hydro-extraction method, said fibers being intended for the constitution of substrates for soil-free cultivation. 20 The aim of the present invention is to provide a substrate for low density soil-free cultivation and acting as a root support which easily is impregnated with the nutritive solution and does not adversely affect the growth of the plants. 25 These aims of the invention may be attained by using fibers having the following glass composition: SiCE 55 - 70% A120 1 - 8% CaO 5 - 9% 30 MgO 1.5 - 4% Na 2 0 13 - 18.5% K 20 0.5 - 10% Fe 203 3 ZnO 0 - 4% MnO 0 - 4% TiO2 0 - 4% P2 0 5 0 - 4% 5 Impurities < 1% the sum of the contents of B 2 0 3 , Li 2 0 and F being less than or equal to 1%. The impurities include all the compounds not 10 featured in the preceding list and which are introduced by the natural raw materials used to produce these glass compositions. These impurities also include certain constituents originating from refining agents, such as sulfates added into the mixture of vitrifiable 15 raw materials. The glass fibers on the invention are able to be obtained from the internal hydro-extraction method. This method makes it possible to obtain and reproduce fibers virtually free from infibrated particles. 20 Moreover, these techniques make it possible to produce low density substrates. This type of fiber production technique is detailed in a large number of publications. For more details, reference may be made in particular to the patent FR 1 25 382 917 and FR 2 443 436. According to these techniques, the molten glass is introduced inside the centrifugal machine and, under the effect of centrifugal force, is projected onto its peripheral strip. A large number of orifices is provided on this 30 strip. The glass is projected horizontally through these orifices. The resultant glass nets are advantageously stretched by gaseous currents so as to transform them into fibers.

4 The glass fibers of the invention are obtained from portions of glass having physical characteristics making it possible to fibrate them according to this method. These characteristics are defined hereafter. In 5 particular, they have a viscosity of 1000 poises at a temperature of generally lower than 1200' C and preferably less than 1150'C. Another significant physical characteristic for the production of fibers concerns the devitrification 10 temperatures, that is the temperatures corresponding to the formation of crystals in the vitreous mass. In fact, these crystals are likely to seal off the orifices of the centrifugal machine. Several temperatures enable this devitrification to 15 be characterized : - the temperature at which the growing rate of crystals is nil, currently known as liquidus, - the temperature at which the growing rate of crystals is maximum. 20 Generally speaking, the difference between the temperature corresponding to a viscosity of 1000 poises and the temperature of the liquidus is preferably greater than or equal to 50'C. It is desirable to obtain a minimum growth rate of 25 the crystals, namely less than 3 microns per minute. Another important characteristic to be taken into consideration is the hydrolytic resistance of the composition, particularly when it is intended to be used as a substrate for soil-free cultivation. This 30 resistance is measured according to the standard method of the Deutsche Glastechnische Gesellschaft (DGG). The DGG constituting the fibers of the invention is preferably less than or equal to 30 millgrams.

5 The composition of the glass fibers of the invention is characterized by a low percentage of boron oxide. In fact, it has been observed that when the sum of the weight contents of B 2 03 ' Li 2 0 and F exceed 1%, the quantities of these elements freed by the glass fibers in the nutritive solution exceed the tolerance thresholds of certain plants. The compositions of glass fibers traditionally used 10 contain about 5% in weight of B 20 3 and up to between 2 and 3% of Li20 and F. These elements play an important role with regard to the various properties of the glass. In particular, they make it possible to reduce viscosity and the risks of devitrification and improve 15 hydrolytic resistance. Despite the high reduction of the proportion of these compositions and indeed their suppression, they are nevertheless able to retain correct chemical and physical properties. 20 Thus, an increase of the percentages of alkaline oxides makes it possible to maintain viscosity within acceptable limits yet without provoking any accentuation of devitrification, the sodium oxide content still being at least equal to 13%. 25 The Na 2 0 content must not exceed about 18.5% beyond this value, the DGG of the glass is too high which would adversely affect the mechanical properties of the fibers. Other alkaline oxides may be introduced into the 30 composition of the fibers of the invention. Thus, K2 0 and Li 2 0 lower viscosity without resulting in causing a significant reduction of the DOG. The viscosity and devitrification are also kept 6 within acceptable limits by virtue of the CaO and MgO earthy alkaline oxides. In particular, the CaO content must be equal at least to 5% in weight so as to avoid any too siginificant increase of viscosity. Beyond 9%, 5 CaO results in a significant increasing of the risks of devitrification. Al 2 0 3 is introduced into the composition of the glass fibers of the invention at the rate of at least 1% in weight. This mainly has the effect of keeping the 10 DGG with values of less than 30 milligrams despite the high proportion of alkaline oxides. The proportion of Al 2 , 0 3 in the compositions of the invention does not exceed 8% ; beyond this value, the viscosity and risks of devitrification increase considerably. 15 Other oxides, such as ZnO, MnO and Fe Og, TiO and 2 0-2 P 2 o 5 , may be introduced into, the composition of the fibers of the invention. These oxides have the effect of fluidizing the glass without affecting the devitrification of the 20 glass whilst improving the DGG. Series of tests as listed in the annexed table show the influence of the compounds present in a glass composition on the physical characteristics defined below. 25 The preferred glass compositions of the invention include the following compounds in the following limits expressed as weight percentages SiO 2 58 67% Al2 0 3 4.5 7.5% 30 CaO 5 9% MgO 1.5 4% Na2 0 17 18.5% K 20 0.5 4% 7 Fe2 03 0 3% ZnO 0 3% MnO 0 3% TiO 2 0 3% 5 P2 05 0 3% Impurities < 1% the sum of the contents of B 2 0 , Li 2 0 and F being less than or equal to 1%. Another family of preferred glass compositions of 10 the invention is described below. These compositions differ by virtue of one portion of soda being replaced by potassium making it possible to limit the freeing of sodium by those fibers in contact with the nutritive solution. The limits are expressed as weight 15 percentages SiO 2 55 65% Al 203 4.5 7.5% CaO 5 8% MgO 1.5 4% 20 Na 20 13 17.5% K 2 0 4 10% Fe 2 0 3 0 3% ZnO 0 3% MnO 0 3% 25 TiO 2 0 3%

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2 0 5 0 3% Impurities < 1% the sum of the contents of B o Li 0 and F being less 2 21 2 than or equal to 1%. 30 The invention also concerns substrates for soil free cultivation and constituted by fibers obtained from a glass composition according to the invention. These substrates produced by the internal 8 centrifugal method advantageously have a low density and are easily impregnated by the nutritive solution. These substrates of the invention do not play any nutritional role with regard to the plant and do not 5 impede the growth of plants : in contact with the nutritive solution, no harmful element is likely to be released with a content able to impede the growth of the plants. In particular, the inventors have shown that a 10 percentage of boron, lithium and fluorine released in contact with the nutritive solution and greater than 0.5 mg/l is harmful to certain cultivation systems. Similarly, excessive releasings of lithium and fluorine have negative effects on certain cultivation systems. 15 When in contact with the nutritive solution, the substrates of the invention release a boron, lithium and fluorine content less than or equal to 0.5 mg/i. The absence of harmful effects on plants is tested via an attentive observation of the behaviour of the 20 cultivated plants and an observation of their growth. According to the invention, the substrates advantageously have a particular structure so as to improve their mechanical resistance. The substrates of the invention may possess a 25 structure as defined in the patent application FR 89 03372 in which the fibers are orientated along random directions providing the material with isotropic properties, especially an improved mechanical resistance. 30 The unpublished patent application FR 90 158909 describes another structure for improving the mechanical resistance of the substrate. This substrate is formed of a mixture of fine fibers and thicker 9 fibers. The thicker fibers provide the substrate with improved mechanical resistance. The advantages of the invention are revealed by experimental tests described in the following detailed 5 description. The releasing of boron, lithium and fluorine of a substrate in contact with the nutritive solution is tested. Two samples of substrates, A and B, with identical dimensions and conforming to the invention 10 (respectively compositions 4 and 11 in the table) are separately saturation-immersed for 6 weeks in a nutritive solution bath with an identical composition and a pH of 5.9. The quantities of boron, lithium and fluorine 15 released at the end of 6 weeks by the two tested substrates are entered on the following table (in mg per litre of nutritive solution) Substrate A B 20 Fluorine 0.06 0.03 Boron 0.07 0.09 Lithium 0.018 0.040 TOTAL 0.148 0.160 25 These tests show the influence of the composition of the glass fibers constituting a substrate on the boron, lithium and fluorine contents released by said fibers in the nutritive solution and make it possible to produce glass wool substrates compatible with all 30 cultivation systems.

10 TABLE Composition 1 2 3 4 5 6 7 Si02 65,21 63,9 62,82 64,98 64,21 64,21 64,21 A1203 4,55 4,55 4,45 4,53 4,55 4,55 4,55 CaO 7,65 7,85 7,75 7,62 7,65 7,65 7,65 MgO 2,8 2,7 2,65 2,79 2,8 2,8 2,8 Na20 18,2 18,4 18,45 18,14 18,2 18,2 18,2 K20 1,05 1,05 1 1,05 1,05 1,05 1,05 Fe203 0,105 1,05 2,4 0,105 0,105 0,105 MnO 1 ZnO 1 B203 0,35 Ti02 Li20 1 P205 Impurities 0,435 0,5 0,48 0,54 0,435 0,435 0,435 Properties Temperature with a visco sity of 1000 poises

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0 C) (1) 1120 1117 1103 1113 1076 1109 1110 Liquidus (*C) -2 960 970 990 958 940 972 (1)-(2) (*C) 160 147 113 155 136 137 max cristalli sation rate (,"m/mn) 1,8 1,41 1,58 1,7 1,88 1,76 DGG (mg) 29,2 26,5 29,2 30 29 11 TABLE (continued) Composition 8 9 10 11 12 13 14 15 Si02 63,21 63,15 63,25 60,95 59,7 57,4 59,9 61,2 A1203 4,55 4,7 4,7 6,7 6,5 6,5 6,6 4,5 Ca0 7,65 7,65 7,65 7,65 7,4 7,4 5,1 7,6 MgO 2,8 2,8 2,8 2,8 2,6 2,5 2,5 2,8 Na20 18,2 17,7 17,7 17,7 15,2 17,5 17,5 17,7 K20 1,05 0,9 0,9 1,2 5,8 5,8 5,8 1,2 Fe203 0,105 0,22 0,2 0,2 0,2 0,2 0,2 0,2 MnO 2 ZnO 2 B203 0,4 0,4 0,4 0,35 0,3 0,5 0,4 Ti02 0,18 2,1 2,1 1,7 1,8 1,8 2,5 Li20 P205 1,8 Impurities 0,435 0,3 0,3 0,3 0,55 0,6 0,1 0,3 Properties Temperature with a visco sity of 1000 poises

(

0 C) (1) 1100 1118 1116 1119 1115 1066 1103 1100 Liquidus (*C) -2 (1)-(2) (*C) max cristalli sation rate (/A m/mn) 1,72 DGG (mg) 28 22,6 21,7 17,5 21

Claims (2)

1. Glass fibers to be used as constituents for a soil-free cultivation substrate, wherein their 5 composition mainly includes the following compounds whose proportions are expressed as w eight percentages SiO 2 55 70 ; Al 2 03 1 8% q7 CaO 5 9% It- Y 10 MgO 1.5 4% Na 2 0 13

18.5% K 2 0 0.5 10% Fe 2 0 3 0 4% ZnO 0 4% 15 MnO 0 4 TiO 2 0 4% 2 05 0 4% Impurities 1% the sum of the contents of B 2 0 3 , Li 2 0 and F being 20 less than or equal to 1%. L">0 3 2. Glass fibers according to claim 1, wherein their composition mainly includes the following compounds whose proportions are expressed as weight percentages : 25 SiO 2 58 67% Al 203 4.5 7.5% CaO 5 9% MgO 1.5 4% Na 0 17 18.5% 2 30 K 2 0 0.5 4% Fe 20 3 0 3% ZnO 0 3% MnO 0 3% 13 TiO 2 0 4% P 205 0 4% Impurities < 1% the sum of the contents of B 2 03 , Li 2 0 and F being 5 less than or equal to 1%. 3. Glass fibers according to claim 1, wherein their composition mainly includes the following compounds whose proportions are expressed as weight percentages : 10 SiO 2 55 65% Al 2 0 3 4.5 7.5% CaO 5 8% MgO 1.5 4% Na 2 0 13 17.5% 15 K 2 0 4 10% ' Fe20 3 0 3% ZnO 0 3% MnO 0 3% TiO 2 0 3% 20 p 2 0 5 0 3% Impurities < 1% the sum of the contents of B 0 , Li 0 and F being less than or equal to 1%. 4. Substrate for soil-free cultivation and 25 constituted by glass fibers whose composition mainly includes the following compounds, the proportions of the latter being expressed as weight percentages Si0 2 55 70% A1 2 0 3 1 8% 30 CaO 5 9% MgO 1.5 4% Na2 0 13 18.5% K 2 0 0.5 10% 14 Fe 0 0 4% 2 3 ZnO 0 4% MnO 0 4% TiO2 0 4% 5 P2 054% Impurities < 1% the sum of the contents of B2 0 3 ,Li2 0 and F being less than or equal to 1%. 5. Substrate for soil-free cultivation according 10 to claim 4 and constituted by glass fibers whose composition mainly includes the following compounds, the proportions of the latter being expressed as weight percentages : SiO2 58 67% 15 A1 2 0 3 4.5 7.5% CaO 5 9% MgO 1.5 4% Na 2 0 17 18.5% K 20 0.5 4% 20 Fe 20 3 0 3% ZnO 0 3% MnO 0 3% TiO 2 0 3% P2 05 0 3% 25 Impurities < 1% the sum of the contents of B 0 , Li 0 and F being less than or equal to 1%. 3 6. Substrate for soil-free cultivation according to claim 4 and constituted by glass fibers whose 30 composition mainly includes the following compounds, the proportions of the latter being expressed as weight percentages SiO 2 55 65% 15 Al 0 4.5 7.5% 2 3 CaO 5 8% MgO 1.5 4% Na 2 0 13 17.5% K 2 0 4 10% Fe20 0 3% ZnO 0 3% MnO 0 3% TiO2 0 3% 10 P 20 5 0 3% Impurities < 1% the sum of the contents of B 2 0 3 , Li 2 0 and F being less than or equal to 1%. 7 Substrate for soil-free cultivation according 15 toaAfecfaims 4, 5 and 6, wherein said substrate is formed of fibers which, when in contact with a nutritive solution, only release elements whose nature and concentration in the nutritive solution are without any effects likely to impede the growth of plants. 20 8. Substrate for soil-free cultivation according to claim 7, wherein, when the substrate is 75% volume saturated by a nutritive solution, the content of boron, lithium or fluorine released into the latter is less than or equal to 0.5 mg/l.