Flame-retardant and fire-resistant polymer compositions made from lime

Abstract

A mineral filler in a flame-retardant organic polymer composition comprising a calcium compound for a fire-resistant effect characterized in that said calcium compound comprises at least calcium hydroxide, use of same and the combustion residue obtained therefrom, and polymer sheaths for electrical cables containing the mineral filler in the flame-retardant polymer composition.

Claims

1. A mineral filler in a flame retardant and fire resistant organic polymer composition comprising a calcium compound containing at least calcium hydroxide particles as a fire resistant additive of the polymer composition, wherein the calcium hydroxide particles have a particle size d.sub.10 comprised between 0.9 μm and 1.1 μm and d.sub.90 comprised between 6.2 μm and 9.8 μm, said particle sizes being measured by means of laser granulometry after dispersion in methanol and after deagglomeration of the filler by means of ultrasound.

2. A mineral filler according to claim 1, wherein the said calcium hydroxide is hydrated lime also known as slaked lime, in powdery form.

3. A mineral filler according to claim 1, comprising at least one magnesium compound, in the form of a magnesium hydroxide as a flame retardant additive.

4. A mineral filler according to claim 3, wherein the calcium compound and the magnesium compound are two separate compounds in a mixture.

5. A mineral filler according to claim 3, wherein the calcium compound and the magnesium compound of the said mineral filler of the flame retardant polymer composition are tightly bound and derived from a slaking of quicklime with a suspension of magnesium hydroxide.

6. A mineral filler according to claim 3 wherein the calcium compound and magnesium compound are tightly bound and derived from a total or partial slaking of dolomite lime.

7. A mineral filler according to claim 6, wherein the said calcium compound and the said magnesium compound that are tightly bound form a semi hydrated dolomite having the general formula aCaCO.sub.3.bCa(OH).sub.2.cMg(OH).sub.2.dMgO.eCaO, a,b,c,d and e being mole fractions with (a+b+e)/(c+d) being comprised between 0.8 and 1.2, and having values such that : b represents the mole fraction corresponding to a proportion by weight that is greater than or equal to 15% and less than or equal to 69%, c represents the mole fraction corresponding to a proportion by weight that is greater than or equal to 1%, d represents the mole fraction corresponding to a proportion by weight that is greater than or equal to 1% and generally less than 41%, a represents the mole fraction corresponding to a proportion by weight that is greater than or equal to 0%, e represents the mole fraction corresponding to a proportion by weight that is greater than or equal to 0%.

8. A mineral filler according to claim 7, wherein the said semi-hydrated dolomite comprises agglomerates of aggregates of particles.

9. A mineral filler according to claim 6, wherein the said calcium compound and the said magnesium compound that are tightly bound form a fully hydrated dolomite having the general formula aCaCO.sub.3.bCa(OH).sub.2.cMg(OH).sub.2.dMgO.eCaO, a,b,c,d and e being mole fractions with (a+b+e)/(c+d) being comprised between 0.8 and 1.2, and having values such that : b represents the mole fraction corresponding to a proportion by weight of 45% to 57%, c represents the mole fraction corresponding to a proportion by weight of 35% to 42% d represents the mole fraction corresponding to a proportion by weight of 0% to 2%, a represents the mole fraction corresponding to a proportion by weight that is greater than or equal to 0%, e represents the mole fraction corresponding to a proportion by weight of 0% to 3%.

10. A mineral filler according to claim 9, wherein the said fully hydrated dolomite comprises agglomerates of aggregates of particles.

11. A mineral filler according to claim 9 wherein the said hydrated dolomite is in powdery form and have particles whereof the size is less than 1 mm.

12. A method for manufacturing a flame retardant polymer composition comprising the following steps of: a) mixing of at least two granular polymers in order to form a first mixture of granular polymers, in the dry state in a first mixing vessel ; b) feeding of the said granular mixture into a blending vessel ; e) feeding of at least one mineral filler according to claim 1, into the said blending vessel accompanied by the formation of a second mixture ; d) melting of the said second mixture in order to form the said flame retardant polymer composition in the molten state, and feeding of the said flame retardant polymer composition in the molten state through an extrusion die in order to form wires of extrudated flame retardant polymer composition; and e) cutting of the said wires of extrudated flame retardant polymer composition according to a predetermined size in order to form solid granules of flame retardant polymer composition.

13. A manufacturing method according to claim 12, wherein at least one of the said at least two polymers is selected from the group consisting of polyethylenes, polypropylenes, polystyrenes, copolymers of ethylene and propylene (EPR), terpolymers of ethylene-propylene-diene-monomer (EPDM), copolymers of ethylene and vinyl acetate (EVA) having low/medium acetate content, copolymers of ethylene and methyl acrylate (EMA) having low/medium acrylate content, copolymers of ethylene and ethyl acrylate (EEA) having low acrylate content, copolymers of ethylene and butyl acrylate (ESA) having low acrylate content, copolymers of ethylene and octane, ethylene based polymers, polypropylene based polymers, polystyrene based polymers, halogenated polymers, or any mixture of these compounds.

14. A method according to claim 12, wherein the mineral filler is incorporated into the flame retardant polymer composition in an amount of 1% to 80% by weight, advantageously from 40% to 75% by weight, in relation to the total weight of the said flame retardant polymer composition.

15. A polymer sheath for electrical cables characterised in that it contains as a fire resistance additive the mineral filler of claim 1.

16. A polymer sheath according to claim 15, wherein the said flame retardant organic polymer composition comprises a thermoplastic, thermosetting or elastomer type of polymer of natural or synthetic origin.

17. A polymer sheath according to claim 16, wherein the said organic polymer is selected from the group consisting of polyethylenes, polypropylenes, polystyrenes, copolymers of ethylene and propylene (EPR), terpolymers of ethylene-propylene-diene-monomer (EPDM), copolymers of ethylene and vinyl acetate (EVA) having low/medium acetate content, copolymers of ethylene and methyl acrylate (EMA) having low/medium acrylate content, copolymers of ethylene and ethyl acrylate (EEA) having low acrylate content, copolymers of ethylene and butyl acrylate (ESA) having low acrylate content, copolymers of ethylene and octane, ethylene based polymers, polypropylene based polymers, polystyrene based polymers, halogenated polymers, or any mixture of these compounds.

Description

(1) FIG. 1 is a schematic illustration of the measurement device for measuring the compressive mechanical strength of the combustion residues.

(2) FIG. 2 is a graph illustrating the results of the fire test by means of cone calorimetry of the flame retardant polymer compositions according to the Examples 1 to 3.

(3) FIGS. 3A and 3B are photographs of the combustion residue of the flame retardant polymer composition according to the Example 1.

(4) FIGS. 4A and 4B are photographs of the combustion residue of the flame retardant polymer composition according to the Example 2.

(5) FIGS. 5A and 5B are photographs of the combustion residue of the flame retardant polymer composition according to the Example 3.

(6) FIG. 6 is a graph illustrating the results of the fire test by means of cone calorimetry of the flame retardant polymer composition according to the Example 4.

(7) FIGS. 7A and 7B are photographs of the combustion residue of the flame retardant polymer composition according to the Example 4.

(8) FIG. 8 is a graph illustrating the results of the fire test by means of cone calorimetry of the flame retardant polymer compositions according to the Examples 5 to 7.

(9) FIGS. 9A and 9B are photographs of the combustion residue of the flame retardant polymer composition according to the Example 5.

(10) FIG. 10 is a photograph of the combustion residue of the flame retardant polymer composition according to the Example 6.

(11) FIG. 11 is a photograph of the combustion residue of the flame retardant polymer composition according to the Example 7.

(12) FIG. 12 is a graph illustrating the results of the fire test by means of cone calorimetry of the flame retardant polymer compositions according to the Examples 8 to 10.

(13) FIGS. 13A and 13B are photographs of the combustion residue of the flame retardant polymer composition according to the Example 8.

(14) FIGS. 14A and 14B are photographs of the combustion residue of the flame retardant polymer composition according to the Example 9.

(15) FIGS. 15A and 15B are photographs of the combustion residue of the flame retardant polymer composition according to the Example 10.

(16) FIGS. 16A and 16B are photographs of the combustion residue of the flame retardant polymer composition according to the Comparative Example 1.

(17) FIGS. 17A and 17B are photographs of the combustion residue of the flame retardant polymer composition according to the Comparative Example 2.

(18) FIGS. 18A and 18B are photographs of the combustion residue of the flame retardant polymer composition according to the Comparative Example 3.

(19) FIGS. 19A and 19B are photographs of the combustion residue of the flame retardant polymer composition according to the Comparative Example 4.

(20) FIGS. 20A and 20B are photographs of the residue of combustion of the flame retardant polymer composition according to the Comparative Example 5.

(21) FIGS. 21A and 21B are photographs of the combustion residue of the flame retardant polymer composition according to the Comparative Example 6.

(22) In the figures, elements that are identical or similar bear the same reference numerals.

(23) The present invention therefore relates to a flame retardant and fire resistant polymer composition comprising a polymer and a mineral filler which contains at least one calcium compound in the form of calcium hydroxide.

(24) The mineral filler may also include a magnesium compound. This magnesium compound may be added into the admixture or be tightly bound to the calcium compound by carrying out a partial or total slaking of the dolomite lime.

(25) These flame retardant polymer compositions have the extremely advantageous characteristic of providing at the conclusion of the combustion a cohesive residue that, in addition to a flame retarding effect (“flame retardant” as per the English terminology) confers the filler with an effect of resistance to fire (“fire resistant” as per the English terminology), sometimes also referred to as “ceramising” effect.

(26) At the current time no standard tests are available for the measurement of cohesion of the combustion residues of the polymer compositions. At the initial stage, the cohesion of the residue can be assessed qualitatively by means of simple observation of a residue obtained at the end of the cone calorimetry test. During this observation, however, some quantitative data may be estimated: i) the number of cracks passing across the residue (transverse cracks), ii) the depth of these cracks (that is to say only whether the cracks are only present at the surface or if they pass through the entire thickness of the combustion residue), iii) the cohesiveness may also be represented by the maximum size of the sample (the sample making up the entire thickness of the residue and whose cross section is similar to a square) which may be taken without being broken in the residue obtained at the conclusion of the cone calorimeter test (which has a square cross section with sides measuring 100 mm).

(27) Pursuant to the scope and meaning of the invention, the term “transverse crack” refers to a crack that passes across from one side of the combustion residue to the other which is obtained at the conclusion of the cone calorimetry test and which is present in the form of a sample having a square cross section with sides measuring 100 mm.

(28) In order to ensure the cohesion of the residue, as well as being present in limited numbers, these transverse cracks must also be quite shallow, that is to say, that they should not be passing through the entire thickness of the residue.

(29) Any residue having 1 to 10 deep crack(s) is considered to be moderately cohesive.

(30) Any residue having more than 10 deep cracks is considered not to be cohesive.

(31) Any combustion residue will be considered to be cohesive where it has only a very limited number of cracks passing across it, which is less than or equal to 3, preferably less than or equal to 2, or even to 1, and in a particularly preferable manner zero, after combustion in accordance with the standardised method of the cone calorimetry test as per ISO 5660-1 or ASTM E 1354.

(32) Now considering the maximum size of the sample (side of the sample making up the entire thickness of the residue and whose cross section is similar to a square), which can be taken without being broken in the said residue obtained after conclusion of the cone calorimetry test (which itself has a square cross section with sides measuring 100 mm), the residue is said to be cohesive if this said size is greater than or equal to 10 mm, preferably greater than or equal to 30 mm, preferably greater than or equal to 50 mm.

(33) Furthermore, a quantitative method has been developed in the context of this invention in order to determine the mechanical strength of the combustion residues. This method is only applicable for combustion residues in which it is possible to take a sample whereof the cross section is similar to a square with sides measuring at least 100 mm, that is to say, whereof the cross section is at least as large as the surface of the movable platen used for this measurement.

(34) It consists of performing a measurement of the compressive strength by means of using a texturometer-Chatillon digital force gauge (DFGS 50 model), on three samples of a combustion residue. These three samples are taken from different locations in the residue having a square cross section with sides measuring 100 mm obtained upon completion of cone calorimetry measurements. The principle of this method is illustrated in FIG. 1. Each sample 2 is placed at the centre of a fixed rectangular metal plate 1 measuring approximately 100 mm×200 mm. Manually, a second metal plate 3, this time very considerably smaller and circular (12 mm in diameter) is brought by means of a lever 6 that makes it possible to manually cause the lowering of the movable platen, to be in contact with the sample 2. This second plate 3 being connected to a force gauge 4, the force applied, arrow 5, on the sample by the movable platen at the time of complete rupture of the sample can be determined. The useful value is the average of the breaking strength values measured for the three samples of a combustion residue. The measured strength is expressed in Newtons (N), but may be normalised by the surface of the circular movable platen in order to determine the compressive mechanical strength of the residue in Pascal (Pa). Quite obviously, the samples used for this measurement should have a cross section that is at least as large as the surface of the circular movable platen, such that the force is applied over the entire surface of this platen.

(35) This method does not allow for the determination of a single criterion and its outcome depends on antagonistic effects. Indeed, the higher the porosity of the residue, for example as a result of phenomena similar to intumescence, the lower its compressive strength will be, although its cohesiveness could be very good. Conversely, a residue with low porosity may exhibit poor cohesiveness and a high degree of cracking, while each sample of this residue may have a high mechanical strength.

EXAMPLES

Example 1

Use as a Flame Retardant Filler for a Hydrated Lime with Fine Particle Size Grade in an EVA Polymer Composition

(36) A hydrated lime was obtained in an industrial process by means of calcination of a natural limestone, and followed by hydration (slaking) via a dry process, in an industrial hydrator, of the quicklime obtained after calcination. The slaked lime produced thus has a moisture content lower than 2% by weight and is in powdery form. It is then subjected to an industrial particle size (granulometric) separation step that is used so as to remove the coarser particles. At the conclusion of this industrial manufacturing process, the slaked lime is once again separated by means of various different steps of separation by air flotation, this time using laboratory scale means and processes, in order to obtain a fine particle size grade, called particle size (granulometric) grade A. The properties of this grade A hydrated lime are summarised together in the Table 1.

(37) This filler is incorporated in an amount representing up to 60% by weight in a matrix of co-polymer of ethylene and vinyl acetate containing 28% of vinyl acetate (EVA 328, Escorene UL328, produced by ExxonMobil Chemical). The mixing between the polymer matrix and the mineral filler is performed by making use of a twin-screw extruder. Plates, prepared with a hydraulic press, measuring 100×100×4 mm.sup.3 were then subjected to the fire test by cone calorimetry. The residues obtained at the conclusion of the cone calorimeter test (combustion residues) are at the initial stage observed and photographed in order to assess the degree of cohesion thereof, and then the compressive mechanical strength thereof is characterised by carrying out the method previously described above in the text and illustrated in FIG. 1.

(38) The results of the fire tests by cone calorimetry are shown in FIG. 2. They are compared to those obtained for the host polymer that is unfilled (EVA) and for the same polymer, filled under the same conditions and with the same proportions of ATH (Martinal OL 107 LEO-Albemarle, described in Table 2) and MDH (Magnin H10-Albemarle, described in Table 2).

(39) The cone calorimetry tests carried out for this composition show clearly that the incorporation of 60% of this grade A hydrated lime in the EVA matrix significantly reduces the energy released during the combustion of the polymer (the maximum of the HRR curve is significantly lower in comparison to the unfilled EVA). This reduction is comparable to that measured for the EVA composition containing ATH. It is moreover also more significant than that measured for the EVA composition containing MDH. On the other hand, the release of heat is spread out over a longer period of time than for the unfilled EVA, which makes it possible to avoid the hot spots which are the root cause of the propagation of the fire spreading from one room to the other.

(40) The observation of combustion residues shown in the FIGS. 3A and 3B and characterised in the Table 3 makes it possible to conclude that following conclusion of the combustion thereof, the composition of this example led to the formation of a cohesive residue this residue is composed of a single layer and not a powder, ash or any other divided material. This residue therefore has an appearance that is totally different from that of the residues obtained for the ATH based or MDH based compositions, which are in the form of powder or ash (FIGS. 16A and 16B in the case of MDH and FIGS. 17A and 17B in the case of ATH). The layer of the residue of this example is ‘swollen’ (FIG. 3B). The residue does not contain any transverse cracks, but rather, only cracks that are shorter and which are not deep cracks, but only surface cracks. The measurement of the compressive strength of the residue resulted in an average value (based on 3 measurements performed with the equipment shown in FIG. 1 on the samples taken from different locations in the combustion residue) of 125 kPa, with the three measured values being 111 kPa, 122 kPa and 143 kPa (Table 3).

Example 2

Use as a Flame Retardant Filler for a Hydrated Lime with Coarser Particle Size Grade in an EVA Composition

(41) The mineral filler used in Example 2 has the same origin as the hydrated lime used in Example 1 and it is therefore similar thereto, with the only difference being the size of its particles. Indeed, the steps of separation by air flotation implemented using laboratory scale means and processes for the grade A hydrated lime of Example 1 were carried out under different conditions, with a coarser cut size, in order to obtain hydrated lime having grade B particle size which is coarser than the grade A size. The properties of the grade B hydrated lime are summarised in Table 1. The particle size involved here corresponds to the measurement of the particle size shown in Table 1 here below, that is to say the measurement performed by means of laser granulometry on the powder dispersed in methanol and not deagglomerated and representating the size of the agglomerates. The polymer matrix is once again EVA 328.

(42) The results of the fire test by cone calorimetry recorded for this composition are shown in FIG. 2, and indicate a level of flame retardancy effect that is very much similar to that obtained for the particle size (granulometric) grade A hydrated lime of Example 1, despite there however, being a shorter duration of effectiveness.

(43) The residues obtained at the conclusion of the cone calorimeter test (combustion residues), have been characterised in the same manner as in the Example 1. The observation of these residues shown in the FIGS. 4A and 4B and characterised in Table 3 provides the data to conclude that upon conclusion of combustion thereof, the composition used in this example led to the formation of a cohesive residue comparable to that obtained from the composition used in Example 1. The measurement of the mechanical strength of the residue resulted in an average value (based on measurements performed on three samples taken from different locations in the combustion residue) of 134 kPa, the three measured values being 120 kPa, 125 kPa and 157 kPa,

Example 3

Use as a Flame Retardant Filler for a Hydrated Lime with Low Specific Surface Area in an EVA Polymer Composition

(44) This example is similar to Example 2, with the only exception that the standard hydrated lime in Example 2 has been replaced by a hydrated lime having a lower specific surface area. This hydrated lime having a low specific surface area is industrially synthesised with a process similar to the method used for the production of standard hydrated lime, but by adding during the course of the synthesis an additive that accelerates the kinetics of hydration of the quicklime, resulting in the closure of porosity and thus preventing the development of the specific surface area of the hydrated lime. The main characteristics of the hydrated lime used in this example are summarised in the Table 1.

(45) The results of the fire tests by cone calorimetry are shown in FIG. 2 and are very much comparable to those obtained for the composition used in Example 2. The residues obtained upon conclusion of combustion of the composition of this example are presented in the FIGS. 5A and 5B. These photographs provide evidence of the formation of a cohesive residue upon conclusion of combustion of the composition used in this example, this residue containing no transverse cracks and no deep cracks. The compressive strength measured as in the previous examples is 26, 33 and 37 kPa respectively over the three samples taken from the cohesive residue, which is an average of 32 kPa.

Example 4

Use as a Flame Retardant Filler for a Fine Particle Size Grade of Hydrated Lime in a Polystyrene Polymer Composition

(46) Example 4 is similar to Example 1 in that the mineral filler is still for the grade A particle size hydrated lime presented in Table 1, but the polymer matrix this time is of polystyrene (PS, Polystyrol VPT0013 GR2). The level of filler content in the matrix is 50% by weight.

(47) The results of the fire tests by cone calorimetry recorded for this composition are shown in FIG. 6. They have been compared to the results obtained for the unfilled polymer B (PS) and indicate, once again, a very significant level of flame retardancy for the hydrated lime. The residues at the conclusion of the cone calorimeter test (combustion residues), have been characterised in the same manner as in the Example 1.

(48) The observation of these combustion residues shown in the FIGS. 7A and 7B and characterised in Table 3 provides the data to conclude that upon conclusion of combustion thereof, the composition used in this example led to the formation of a moderately cohesive residue: unlike the residues obtained from the polystyrene compositions filled with ATH or MDH, which are presented in the form of powder or ash (FIGS. 20A and 20B in the case of MDH and FIGS. 21 A and 21 B in the case of ATH), the residue obtained with the composition in this example is composed of a cohesive layer even if this layer is cracked in several places. The residue includes 2 deep transverse cracks. Despite this cracking, a sample of the cross section similar to a square with sides measuring about 30 mm can be withdrawn from the entire thickness of this residue. Moreover, the measurement of the mechanical strength of the residue resulted in an average value (based on measurements performed on three samples taken from different locations in the combustion residue) of 98 kPa, the three measured values being 67 kPa, 105 kPa and 123 kPa. If the cohesion of the combustion residue is not as good for this composition than for the composition used in Example 1 detailed above and composed of the same mineral filler but a different polymer matrix, the mechanical strength is however entirely satisfactory for the residue of the composition of this example.

Example 5

Use as a Flame Retardant Filler for a Fine Particle Size Grade Hydrated Lime, that has been Surface Treated, in a Polymer Composition of MDPE

(49) The flame retardant filler used in the composition of this example is obtained by surface treating calcium stearate with a standard hydrated lime. For this, a hydrated lime that is very much comparable to the one used in Example 1 (of the same origin and the same particle size grade) is selected, then 2 kg of lime are placed in a Lodige brand horizontal blade mixer with a total capacity of 20 L (M20), preheated to 60° C. Calcium stearate is then added to this mixer in an amount of up to 4% by weight of the hydrated lime (that is 80 g of calcium stearate). The stirring in the mixer is started and then the mixture is heated to 200° C. (it takes about 17 minutes of heating so as to raise the temperature of the mixture from 60° C. to 200° C.). When this temperature of 200° C. is reached, the mixing is continued for 10 minutes at 200° C., before being stopped, then the product is allowed to stand until it is completely cooled.

(50) This surface treated filler is then incorporated in an amount representing up to 50% by weight in a matrix of medium density polyethylene (MDPE 3802, cable grade produced by Total). The incorporation of the filler in this matrix is carried out with a Brabender type mixer. The plates measuring 100×100×4 mm.sup.3 that are used for the fire test by cone calorimetry were prepared with a hydraulic press.

(51) Again, the combustion residues obtained at the conclusion of the cone calorimeter test of the samples of the composition used in this Example were characterised.

(52) The results recorded during measurements performed with the cone calorimeter are compared in FIG. 8 with those obtained for the host polymer that is unfilled (MDPE) and for the same polymer, filled under the same conditions and with the same proportions of MDH (whose main properties are provided in Table 2).

(53) Once again, these results clearly indicate a net flame retardant effect for the hydrated lime in comparison to the unfilled polymer, an effect that is indeed very much comparable to that obtained with the MDH, in spite however, of there being a shorter ignition time period.

(54) The observation of these combustion residues shown in the FIGS. 9A and 9B and characterised in Table 3 provides the data to conclude that upon conclusion of combustion thereof, the composition used in this example led to the formation of a cohesive residue: this residue is composed of a cohesive layer, unlike the residue obtained for a comparable composition of MDPE and MDH whereof the residue is similar to a powder or ash (FIGS. 18A and 18B). The residue includes one transverse crack and the crack is not deep. Despite this cracking, a sample of the cross section similar to a square with sides measuring about 30 mm can be withdrawn from the entire thickness of this residue. Moreover, the measurement of the mechanical strength of the residue resulted in an average value (based on measurements performed on three samples taken from different locations in the combustion residue) of 17 kPa, the three measured values being 11 kPa, 19 kPa and 20 kPa.

Example 6

Use as a Flame Retardant Filler of a Mineral Filler Consisting of Ca(OH)2 and Mg(OH)2 Tightly Bound in a MDPE Polymer Composition

(55) In this example, the polymer matrix is MDPE as was the case in Example 5. However, unlike in the previous examples, the mineral filler was synthesised in the laboratory. The synthesis is carried out in a pilot hydrator, wherein quick lime is hydrated in the presence of Mg(OH).sub.2 that was obtained commercially in the form of an aqueous suspension containing 53% by weight of Mg(OH).sub.2. The flow rates for quicklime and for the suspension of Mg(OH).sub.2 are calculated in a manner so as to obtain, at the output of the hydrator, a product containing about 22% by weight of Mg(OH).sub.2 and the rest of the hydrated lime (about 73% Ca(OH).sub.2) with impurities and unburnt remnants. The suspension of Mg(OH).sub.2 is diluted, with the water introduced by the suspension into the hydrator being adjusted in a manner so as to have during the hydration reaction a moisture content of the product at the output of the hydrator of less than 4%. The hydration is carried out on a continuous basis. Given its low moisture content, the product that comes out of the hydrator does not require any drying step. However, its particle size is controlled. In order to do this, it goes through the same steps of particle size separation as those undergone by the grade A hydrated lime presented in the Example 1, in order to obtain a fine particle size grade that is suitable for the preparation of compositions as described in the invention. This filler presents a d.sub.50 of 5.1 μm, a d.sub.90 of 30.1 μm and a d.sub.97 of 111.0 μm, as measured in accordance with the granulometry or particle size analysis method 1 described in the text and used for the determination of the values for the fillers presented in the Tables 1 and 2.

(56) During the synthesis process, the Mg(OH).sub.2 does not undergo any change. As the Mg(OH).sub.2 is incorporated continuously over the course of the hydration reaction of the quicklime, this method provides the possibility of obtaining an intimate admixture of Mg(OH).sub.2 and Ca(OH).sub.2.

(57) In the same manner as in Example 5, this filler is incorporated into the MDPE in an amount of up to 50% by weight and the compositions thus prepared are characterised, just as with the combustion residues.

(58) The results of the fire tests by cone calorimetry are represented in FIG. 8 and is very much comparable to those obtained for the composition used in Example 5.

(59) The observation of the combustion residue shown in FIG. 10 and characterised in Table 3 provides the data allowing it to be said that, upon conclusion of combustion thereof, the composition used in this example led to the formation of a cohesive residue in comparison to the residue obtained for a comparable composition based on MDPE and MDH (FIGS. 18A and 18B). This residue does not have any transverse cracks and nor any deep cracks.

Example 7

Use as a Flame Retardant Filler of a Mineral Filler, Consisting of Ca(OH)2 and Mg(OH)2 that are Tightly Bound, Surface-Treated in a MDPE Polymer Composition of

(60) Example 7 is very much similar to Example 6, with the only real difference being that the laboratory filler no 1 is replaced by a laboratory filler no 2. This new laboratory filler is obtained by the same method as that described in Example 6, with the exception being that this time around, the calcium stearate is added into the suspension of Mg(OH).sub.2 which is used for hydration of the quicklime. The ratio of Ca/Mg is kept equivalent to that used in Example 6 (about 22% of Mg(OH).sub.2 in the final product, the remainder being Ca(OH).sub.2, CaCO.sub.3 and impurities). The quantity of stearate is added in a manner so as to have about 4% of calcium stearate in relation to the weight of the mixed mineral filler based on Ca and Mg obtained at the conclusion of the synthesis. This filler presents a d.sub.50 of 6.0 μm, a d.sub.90 of 69.6 μm and a d.sub.97 of 146.8 μm, as measured in accordance with the granulometry or particle size analysis method 1 described in the text and used for the determination of the values presented for the fillers in the Tables 1 and 2.

(61) The addition of calcium stearate in situ during the reaction for the preparation of mixed Ca—Mg filler is aimed at promoting contact of the filler thus synthesised with the polymer matrices. As in Example 6, this filler is incorporated in a MDPE matrix.

(62) The cone calorimetry results for this composition are illustrated in FIG. 8. Logically, the addition of calcium stearate to the filler does not in any way modify its fire retardant properties. The mechanical properties of the composition (breaking elongation, resilience), not shown here, have been improved in comparison with those of the composition used in Example 6, due to the addition of calcium stearate.

(63) The combustion residue is presented in FIG. 11. It is very much similar to that shown for the Example 6 in FIG. 10.

Example 8

Use as a Flame Retardant Filler of a Semi-Hydrated Dolomite of Fine Particle Size Grade in an EVA Polymer Composition

(64) The composition used in this example is comparable to that used in Example 1, but this time around, the mineral filler is not a hydrated lime, but a semi-hydrated dolomite. This dolomite filler is of a particle size grade that is comparable to the fine particle size grade, known as grade A, of the hydrated lime, or even finer still. The semi-hydrated dolomite of the composition of this example is presented in Table 1. The polymer matrix is EVA 328 as in the Example 1 and the content of filler in this matrix is 60% by weight.

(65) The results of the fire tests by cone calorimetry are shown in FIG. 12 and are comparable to the results obtained for the composition used in Example 1.

(66) The observation of the combustion residues shown in the FIGS. 13A and 13B and characterised in Table 3 provides the data allowing it to be said that, upon conclusion of combustion thereof, the composition used in this example led to the formation of a cohesive residue in comparison to the residue obtained for the MDH based or ATH based compositions whereof the residues are similar to a powder or ash (FIGS. 16A and 16B in the case of MDH and FIGS. 17A and 17B in the case of ATH). The residue is in fact present in the form of a single layer and with no cracks, not even on the surface. Moreover, the measurement of the mechanical strength of the residue resulted in a high average value (based on measurements performed on three samples taken from different locations in the combustion residue) of 206 kPa, with the three measured values being 162 kPa, 195 kPa and 260 kPa. These results indicate that the presence of Mg in the mineral filler does not impair the fire resistance effect thereof.

Example 9

Use as a Flame Retardant Filler of a Mineral Filler Consisting of Hydrated Lime of Fine Particle Size Grade and MDH in an Admixture in an EVA Polymer Composition

(67) The composition used in this example is an EVA 328 based composition as in the Examples 1 to 3 and 8 here above, in which the mineral filler is a mixture of two powders. As in the previous examples based on EVA, the mineral filler is incorporated in an amount representing up to 60% of the total weight of the composition, but this filler is an admixture of 40% by weight of MDH (Magnifin H10-Albemarle described in Table 2) and 20% by weight of hydrated lime of particle size grade A as used in the majority of the examples provided here above and whose properties are detailed in Table 1, these percentages being expressed relative to the total weight of the composition. The mixing of these powders is carried out manually, prior to the introduction thereof into the gravimetric dosing device that provides the ability to control the level of mineral filler content in the composition at the time of preparation of the composition, which is done by following the method described in Example 1.

(68) The results of the fire tests are compared to those obtained for the host polymer that is unfilled (EVA) and for the same polymer, filled under the same conditions and with 60% of MDH as in FIG. 12.

(69) The results obtained in the cone calorimetry tests for this composition indicate that the mixture of 40% MDH+20% hydrated lime is a flame retardant that is very considerably better in EVA than the MDH alone. The HRR curve as a function of time is very significantly lower and spread out over time. This improvement is probably linked to the fact that Mg(OH).sub.2 and therefore the MDH is soluble in the acetic acid which is released during the combustion of the EVA of this composition, unlike the Ca(OH).sub.2 which is not soluble.

(70) The observation of the combustion residues shown in the FIGS. 14A and 14B and characterised in the Table 3 makes it possible to conclude that following conclusion of the combustion thereof, the composition of this example led to the formation of a cohesive residue that is very different from the residue obtained for the EVA filled only with MDH (FIGS. 16A and 16B). In fact, the residue obtained for the composition of this example is not black and is presented in the form of a cohesive and inflated crust. Appearing on this residue are 1 to 2 transverse cracks which however, are not deep. The measurement of the mechanical strength of the residue resulted in an average value (based on measurements performed on three samples taken from different locations in the combustion residue) of 33 kPa, with the three measured values being 14 kPa, 33 kPa and 53 kPa. Whereas this value is not really high, it however, is quite significantly higher than in the case of a composition of EVA 328 based on 60% of MDH alone, for which it is not even possible to perform the measurement of the mechanical strength of the combustion residue, given that it is not possible to take any samples of a suitable size that would be sufficient for carrying out this measurement.

Example 10

Use as a Flame Retardant Filler of a Mineral Filler Consisting of Fine Particle Size Grade Hydrated Lime and ATH in an Admixture in an EVA Polymer Composition

(71) This example is similar to the Example 9 provided here above, the mineral filler incorporated into the EVA 328 still being a mixture of fillers. However, this time around, the MDH is replaced by ATH (Martinal OL 107 LEO-Albemarle), with the composition containing as a consequence thereof 40% by weight of ATH and 20% by weight of hydrated lime of particle size grade A, these percentages being as usual expressed in relation to the total weight of the composition. The main properties of the fillers that make up this mixture are given in Table 1 for the grade A hydrated lime and in Table 2 for the ATH.

(72) As in Example 9, this mixture of fillers is incorporated into the EVA 328 and the compositions thus prepared are characterised, just as with the combustion residues.

(73) FIG. 12 shows that this composition has a better flame retardant effect than that of the ATH alone.

(74) The observation of the combustion residues shown in the FIGS. 15A and 15B and characterised in the Table 3 makes it possible to conclude that following conclusion of the combustion thereof, the composition of this example led to the formation of a cohesive residue, unlike a composition of EVA 328 containing 60% of ATH only and which results in the formation of a powdery residue (FIGS. 17A and 17B). This cohesive residue is coloured a significantly darker black that most of the residues obtained for the compositions used in the other examples. The measurement of the mechanical strength of the residue resulted in an average value (based on measurements performed on three samples taken from different locations in the combustion residue) of 29 kPa, with the three measured values being 17 kPa, 34 kPa and 37 kPa.

Comparative Example 1

Use as a Flame Retardant Filler of MDH in an EVA 328 Polymer Composition

(75) In this comparative example, the polymer matrix is EVA 328, as is also the case in the Examples 1 to 3 and 8 to 10 provided here above. This time around, the matrix is filled, by following the method described in the Example 1, with 60% by weight of MDH (Magnifin H 10-Albemarle) whose main properties are presented in Table 2.

(76) The residue obtained with this composition after conclusion of the cone calorimetry test is completely black and has no cohesiveness as is shown in the FIGS. 16A and 16B. It is presented in the form of an ash. In addition, it is not possible to apply the measurement of mechanical strength as described in the text and in the FIG. 1, to this residue, given that it is not possible to take any samples of a suitable size that would be sufficient for carrying out this measurement.

Comparative Example 2

Use as a Flame Retardant Filler of ATH in an EVA 328 Polymer Composition

(77) This comparative example is similar to Comparative Example 1, however with the replacement of the 60% of MDH by 60% of ATH (Martinal OL 107 LEO-Albemarle, Table 2) in the EVA 328 matrix.

(78) As in the Comparative Example 1, the residue obtained with this composition after conclusion of the cone calorimetry test has no cohesiveness as is shown in the FIGS. 17A and 17B. It is presented in the form of an ash. In addition, it is not possible to apply the measurement of mechanical strength as described in the text and in the FIG. 1, to this residue, given that it is not possible to take any samples of a suitable size that would be sufficient for carrying out this measurement.

Comparative Example 3

Use as Flame Retardant Filler of MDH in a Polymer Composition of MDPE

(79) In this comparative example, the polymer matrix is the same MDPE (medium density polyethylene) as in Example 5 provided here above. This time around, this matrix is filled, by following the method described in Example 5, with 50% by weight of MDH (Magnifin H10-Albemarle) whose main properties are presented in Table 2.

(80) The residue obtained with this composition after conclusion of the cone calorimetry test is shown in the FIGS. 18A and 18B. It has no has no cohesiveness and is presented in the form of an ash. In addition, it is not possible to apply the measurement of mechanical strength as described in the text and in the FIG. 1, to this residue, given that it is not possible to take any samples of a suitable size that would be sufficient for carrying out this measurement.

Comparative Example 4

Use as Flame Retardant Filler of MDH in a Polymer Composition of MDPE, in the Presence of a Ceramising Agent

(81) This comparative example is similar to Comparative Example 3, but this time around, the 50% of MDH is replaced by a mixture composed of 45% of MDH and 5% of a clay, more precisely, modified montmorillonite clay (Cloisite 30B, Rockwood Specialties Inc), these percentages being expressed in relation to the total weight of the composition. Nanoclays, in particular this Cloisite, are known to allow for the formation of a cohesive residue by means of a synergistic effect between these fillers and the flame retardant additives (here MDH). This ceramising effect is validated in EVA 328, or a composition of EVA 328 containing 55% of MDH and 5% of Cloisite resulting following conclusion of the combustion in a very cohesive residue (not illustrated here). In contrast, in the MDPE, the substitution of a part of the MDH by Cloisite appears to be without any effect, the combustion residue presented in the FIGS. 19A and 19B and corresponding to the composition with the Cloisite being completely identical to the combustion residue obtained for the same matrix filled with the same MDH but without Cloisite (FIGS. 18A and 18B).

Comparative Example 5

Use as a Flame Retardant Filler of MDH in a Polystyrene Polymer Composition

(82) In this comparative example, the polymer matrix is the same polystyrene as in the Example 4 provided here above. This time around, the matrix is filled with 50% by weight of MDH (Magnifin H10-Albemarle) whose main properties are presented in Table 2.

(83) The residue obtained with this composition after conclusion of the cone calorimetry test is shown in the FIGS. 20A and 20B. It has no cohesiveness and is presented in the form of an ash. In addition, it is not possible to apply the measurement of mechanical strength as described in the text and in the FIG. 1, to this residue, given that it is not possible to take any samples of a suitable size that would be sufficient for carrying out this measurement.

Comparative Example 6

Use as a Flame Retardant Filler of ATH in a Polystyrene Polymer Composition

(84) This comparative example is similar to the Comparative Example 5, however with the replacement of the 50% of MDH by 50% of ATH (Martinal OL 107 LEO-Albemarle, Table 2) in the PS matrix.

(85) As in the Comparative Example 1, the residue obtained with this composition after conclusion of the cone calorimetry test has no cohesiveness as is shown in the FIGS. 21A and 21B. It is presented in the form of an ash. In addition, it is not possible to apply the measurement of mechanical strength as described in the text and in the FIG. 1, to this residue, given that it is not possible to take any samples of a suitable size that would be sufficient for carrying out this measurement.

(86) TABLE-US-00001 TABLE 1 Standard Grade A Standard Hydrated Lime Semi Hydrated Lime Grade B having low Hydrated (Ex 1, 4, 9 Hydrated specific surface area Dolomite and 10) Lime (Ex 2) (Ex 3) (Ex 8) Ca(OH).sub.2 (% by weight) 92.8 94.3 96.4 55.3 CaCO.sub.3 (% by weight) 5.9 4.2 1.5 4.8 Mg(OH).sub.2.sup.(1) (% by weight) — — — 11.1 MgO.sup.(1) (% by weight) — — — 24.6 CaO (% by weight) 0.02 0.13 0.20 1.8 Ca/Mg (mol) — — — Sum of impurities.sup.(2) (% by weight) 1.26 1.37 1.68 2.45 Fe.sub.2O.sub.3 (% by weight) 0.13 0.19 0.24 0.45 Moisture 150° C. (% by weight) 50 0.7 1.1 0.5 0.8 Surface BET (m.sup.2/g) 14.8 15.8 7.5 11.3 Particle size (Granulometry) 1.sup.(3) d.sub.3 (μm) 0.8 0.8 0.8 0.6 d.sub.10 (μm) 1.2 1.5 1.7 1.1 d.sub.50 (μm) 2.9 5.1 7.4 3.2 d.sub.90 (μm) 6.2 39.8 99.7 7.4 d.sub.97 (μm) 33.0 92.1 161.2 9.8 d.sub.100 (μm) 309.6 309.6 309.6 76.4 Particle size (Granulometry) 2.sup.(4) d.sub.3 (μm) 0.7 0.7 0.7 0.5 d.sub.10 (μm) 1.1 1.3 1.1 0.9 d.sub.50 (μm) 3.2 3.9 3.5 2.7 d.sub.90 (μm) 8.9 9.8 8.9 6.2 d.sub.97 (μm) 14.3 17.2 11.2 7.4 d.sub.100 (μm) 39.8 43.7 43.7 11.8 Temp of decomposition Mg(OH).sub.2 (° C.).sup.(1) — — — 250-420 Temp of decomposition Ca(OH).sub.2 (° C.) 400-550 400-580 400-610 420-580 T 95% (° C.) 455 470 477 443 .sup.(1)Applicable only for dolomites .sup.(2)MgO + SiO.sub.2 + Al.sub.2O.sub.3 + Fe.sub.2O.sub.3 + MnO + P.sub.2O.sub.5 + K.sub.2O + SO.sub.3 for the limes, SiO.sub.2+ Al.sub.2O.sub.3 + Fe.sub.2O.sub.3 + MnO + P.sub.2O.sub.5+ K.sub.2O + SO.sub.3 in the case of dolomites .sup.(3)Measurement of the size of the agglomerates by means of laser granulometry on the non disagglomerated powder .sup.(4)Measurement of the size of the aggregates by means of laser granulometry on the disagglomerated powder by ultrasound

(87) TABLE-US-00002 TABLE 2 ATH MDH (Example (Example 10, and 9, and Comparative Comparative Examples 2 Examples 1 and 6) and 3 to 5) Al(OH).sub.3 (% by weight) 99.8 — Mg(OH).sub.2 .sup.(1) (% by weight) — 100.0 Sum of impurities .sup.(1) (% by weight) 0.19 0.03 Surface BET (m.sup.2/g) 5.3 9.5 Porous Volume (cm.sup.3/g) 0.017 0.029 Particle size (Granulometry) 1 .sup.(2) d.sub.3 (μm) 0.6 0.5 d.sub.10 (μm) 0.9 0.7 d.sub.50 (μm) 1.8 1.7 d.sub.90 (μm) 3.5 25.0 d.sub.97 (μm) 4.4 52.6 d.sub.100 (μm) 7.4 83.9 Particle size (Granulometry) 2 .sup.(3) d.sub.3 (μm) 0.7 0.4 d.sub.10 (μm) 1.0 0.6 d.sub.50 (μm) 2.0 1.1 d.sub.90 (μm) 3.5 1.7 d.sub.97 (μm) 4.2 2.0 d.sub.100 (μm) 6.8 2.9 Temp of decomposition hydroxide (° C.) 210-550 340-550 T 95% (° C.) 301 413 .sup.(1) SiO.sub.2 + CaO + Fe.sub.2O.sub.3 + Na.sub.2O + SO.sub.3 + Cl .sup.(2) Measurement of the size of the agglomerates by means of laser granulometry on the non disagglomerated powder .sup.(3) Measurement of the size of the aggregates by means of laser granulometry on the disagglomerated powder by ultrasound

(88) TABLE-US-00003 TABLE 3 Example No 1 2 3 4 5 6 7 8 9 10 Number of transverse 0 0 0 2 1 0 0 0 1-2 0 cracks Deep Cracks — — — yes no — — — no — Maximum size of a — — — 30 30 — — — — — sample (mm) .sup.(1) Average Mechanical 125 134 32 98 17 NA NA 206 33 29 Strength kPa) Minimum Mechanical 111 120 26 87 11 NA NA 162 14 17 Strength kPa) Maximum Mechanical 143 157 37 123 20 NA NA 280 53 37 Strength kPa) .sup.(1) Maximum size of the sample (the sample making up the entire thickness of the residue and whose cross section is similar to a square) which may be taken without being broken in the residue obtained at the conclusion of the cone calorimeter test, which has sides measuring 100 mm. NA: The compressive mechanical strength of the combustion residues was not measured (not available)