Mineral fibre undergoing degradation in physiological environment

The present invention relates to mineral fibers capable of degrading in a physiological environment, more precisely fibers having a composition that allows their decomposition in contact with the physiological environment.

Thermal or sound insulation of buildings is often made of materials mainly made of mineral wool, such as basalt wool, the special shape of insulated places often forces people involved in laying these materials to cut them in place. This operation causes the fibers to break and possibly scatter some of them in the air. The result may be accidental fiber entry into the airways. Although the harmful effects of inhaled fibers were not shown, it was considered necessary to calm the users by offering them a product capable of easily dissolving in a physiological environment.

The object of the invention is to propose mineral fibers with a composition that allows their rapid degradation in contact with the physiological environment.

The invention relates in particular to fibers obtainable by conventional external centrifugation techniques. These techniques are used to make fibers from glass obtained by melting raw materials such as basalts or blast furnace slags. Some of these techniques, also known as free spinning, involve pouring a stream of molten glass onto the outer surface of a rotating drum rotating at a high speed around an axis perpendicular to the direction of the glass stream. Under the centrifugal force, part of the glass' transforms into fibers, and the rest is directed to another drum where the same phenomenon occurs; three or four drums can be placed in the path of molten glass.

The object of the invention was achieved by modifying the compositions of known glasses used in free centrifugation techniques. When testing such glass compositions, mainly containing silica, alumina, alkaline earth oxides, it was found that the addition of phosphorus pentoxide allows obtaining glasses which, in the form of fibers, decompose quickly into

167 825 physiological environment. Furthermore, the properties of the most important glasses according to the invention are similar to those of known glasses. Therefore, they can be formed into fibers using classic rotating drums.

The mineral fibers of the invention include the following ingredients in weight ratios defined within the following limits:

SiO₂ 337 to 58%

Al₂O3 3 to 14%

CaO 7 dd 40%

MgO 4 to 146%

P₂ ABOUT₅ 1 to 10%

fe₂O3 0 to 148% with the sum of CaO + MgO + Fe₂O3 is higher than 28%, just like the sum of Na2O and K2O shares is lower than about 7%. All iron contained in the fiber composition of the invention is expressed in the form of ferric oxide.

The fibers thus defined can be made from pure ingredients, but are usually obtained by melting a mixture of raw materials capable of forming glass with the possible addition of other oxides, such as titanium oxide and manganese oxide, referred to as impurities within the invention. The total content of these impurities is less than or equal to about 3% by weight.

To enable the use of external centrifugation techniques, compositions of the invention preferably exhibit proper viscosity at a relatively low temperature. It depends to a large extent on the total sum of SiO2 and AhO3 oxides. Within the invention, the sum of these oxides is usually equal to or greater than about 80% by weight. Fiber production is also conditioned by the greater or smaller ability of glass to grow crystals in its mass. This phenomenon, called glazing, is characterized by several temperatures, one at which the crystal growth rate is the highest and the other at which this velocity becomes zero (liquidus).

This phenomenon depends largely on the total sum of alkaline earth oxides. Within the invention, the sum is less than about 00% by weight.

To ensure good heat resistance of the fibers, it is desirable that the sum of CaO + MgO + Fe2O3 be greater than about 28% by weight.

The range of preferred compositions having the composition according to the invention is limited by the following weight ratios:

up to d8% to 6%

22) up to 33% to 146%

0, 1 to 40% to o%

04 to 58% <3%

SiO2 Al2O3 CaO MgO Fe2O3 P2 O5

Na 2 O + K₂For pollution

Another weight range of compositions according to the invention is determined by the following weight ratios:

<td>SiO2</td><td>33 to d0%</td>

<td>Al2 O3</td><td>7 to 14%</td>

<td>CaO</td><td>22 to 330%</td>

<td>MgO</td><td>6 to 146%</td>

<td>Fe2O3</td><td>0, and up to 4%</td>

<td>P2 O5</td><td>3 3 oo%</td>

<td>Na 2 O + K 2 O</td><td>0.1 to 58%</td>

impurities &lt;3%

The advantages of the invention are illustrated in the following examples.

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Measurements of the degree of degradation in the physiological environment were carried out on fibers with a constant diameter of about 10 microns. These fibers were immersed in a solution simulating the extracellular fluid of the following composition (expressed in g / liter):

<td>MgCl</td><td> 0,212</td>

<td>NaCl</td><td> 6,415</td>

<td>Na2HPO4</td><td> 0,148</td>

<td>Na2SO4.2H2O</td><td> 0,179</td>

<td>CaCl2.4H20</td><td> 0,318</td>

<td>NaHCO3</td><td> 2,703</td>

<td>Disodium tartrate. 2H2O</td><td> 0,180</td>

<td>Trisodium citrate. 5,5Κ2&gt; 0</td><td> 0,186</td>

<td>Sodium lactate</td><td> 0,175</td>

<td>Sodium pyruvate</td><td> 0,172</td>

<td>glycine</td><td> 0,118</td>

<td colspan="2">The following were selected to determine the degree of fiberglass distribution in this solution</td>

experimental conditions: two hundred milligrams of fibers were placed between two perforated discs separated by a circular ring. Both discs, 4.3 cm in diameter, were covered with a polycarbonate filter. The whole was a measuring cell through which a solution flowed, controlled by a peristaltic pump. The flow rate was 40 milliliters per day and the test duration was 20 days. The cell and bottle containing said solution was kept at 37 ° C. After passing through the cell, this solution was collected into bottles for later analysis. The analysis consists in measuring the amount of silica that has gone into solution; the ratio of the weight of dissolved silica to the weight of silica initially contained in the fiber gives a percentage result, which is a good indicator of the ability of the tested fiber to degrade in a physiological environment. Tables 1 and 2 give the compositions tested and the results obtained. Table 1 contains the compositions explaining the invention and two known compositions serving as a reference (glass No. 1 and 4).

The presence of phosphorus pentoxide in the fibers of the invention always results in an increase in the amount of silica dissolved in the solution acting on the fibers of the abovementioned compositions as compared to the fibers in which phosphorus is practically not present. Table 2 summarizes several experimental results in support of this claim. A comparison between glasses No. 1 and 3 and glasses No. 4 and 6 shows that reducing the proportion of alumina in favor of silica promotes the decomposition of the tested fibers. A comparison between glasses No. 2 and 3 and between glasses No. 5 and 6 shows that in glasses where the degree of decomposition is not very small, the replacement of phosphorus pentoxide by silica causes a significant increase in the degree of decomposition of the tested fibers. The effect of phosphorus pentoxide on the degree of fiber degradation remains significant in glass with a high content of alumina, as shown in glasses 4 and 7. Phosphorus is introduced into a mixture capable of forming glass in the form of, for example, disodium phosphate or calcium phosphate. When the amount of phosphate introduced into this mixture is relatively large, it can sometimes make it difficult to melt. For this reason, the phosphorus pentoxide content of the compositions remains equal to or less than about 10% by weight. Compositions according to the invention, which at the same time exhibit viscosity and glazing characteristics, adapted to the process of obtaining fibers by external centrifugation and in the form of fibers, a high decomposition rate in a physiological environment, contain approximately less than 7% by weight of alkali oxides. The mineral fibers of the invention shown in Table 1 are completely resistant to temperatures up to about 700 ° C. It was found that cubic samples of these fibers (100 kg / m³) heated in an oven for 30 minutes at 700 ° C show less settling than 10%.

The glasses of the invention can be formed into fibers using known external centrifugation devices as described, for example, in US Pat. No. 2,663,051, European Pat. No. EP-A-0 167 508 or FR-A -2 609 708. The fibers thus obtained provide excellent quality fibrous materials suitable for numerous applications. For example, the fibers of the invention are preferably used in the form of panels of certain geometrical shapes, stiffened with polymerized binder or in the form of tubular products for insulation of pipelines. The fibers of the invention are also used in the form of mattresses sewn to cardboard or a metal mesh, in the form of rollers and loose for filling.

Table 1

Compositions in percentage by weight

<td>Ingredients</td><td colspan="8">Glass No.</td>

<td></td><td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td><td> 7</td><td> 8</td>

<td>SiO2</td><td> 47,1</td><td> 49,9</td><td> 56,4</td><td> 45,7</td><td> 49,7</td><td> 52,7</td><td> 39,7</td><td> 44,9</td>

<td>Fe2O3</td><td> 12,9</td><td> 12,9</td><td> 12,9</td><td> 2,1</td><td> 2,1</td><td> 2,1</td><td> 2,1</td><td> 10</td>

<td>Al2O3</td><td> 13,8</td><td> 4,5</td><td> 4,5</td><td> 11,5</td><td> 4,5</td><td> 4,5</td><td> 11,5</td><td> 4,5</td>

<td>CaO</td><td> 10,3</td><td> 10,3</td><td> 10,3</td><td> 29,5</td><td> 29,5</td><td> 29,5</td><td> 29,5</td><td> 29,5</td>

<td>MgO</td><td> 9,1</td><td> 9,1</td><td> 9,1</td><td> 7,4</td><td> 7,4</td><td> 7,4</td><td> 7,4</td><td> 7,4</td>

<td>Na 2 O</td><td> 2,7</td><td> 2,7</td><td> 2,7</td><td> 1,4</td><td> 1,4</td><td> 1,4</td><td> 1,4</td><td> 1,4</td>

<td>K2O</td><td> 1,2</td><td> 1,2</td><td> 1,2</td><td> 1,3</td><td> 1,3</td><td> 1,3</td><td> 1,3</td><td> 1,3</td>

<td>P2O5</td><td> 0,3</td><td> 6,5</td><td> 0,3</td><td> 0,1</td><td> 3</td><td> 0,2</td><td> 6</td><td> 3</td>

<td>contamination connection</td><td> 2,6</td><td> 2,9</td><td> 2,6</td><td> 1</td><td> 1,1</td><td> 0,9</td><td> 1,1</td><td> 0,7</td>

Table 2

Chemical resistance in physiological environment. Amount of dissolved SiO2 (in percent)

<td rowspan="2">Time actions</td><td colspan="8">Glass No.</td>

<td> 1</td><td> 2</td><td> 3</td><td> 4</td><td> 5</td><td> 6</td><td> 7</td><td> 8</td>

<td>20 days</td><td> 0,7</td><td> 5,1</td><td> 2,5</td><td> 0,9</td><td> 11,4</td><td> 5,2</td><td> 2,6</td><td> 5,3</td>

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