MXPA00003257A - Shaped fibre cement products and reinforcing fibres for same - Google Patents

Abstract

The invention concerns polypropylene fibres for reinforcing fibre cement products and the method for treating said fibres and the fibre cement products reinforced with such fibres. The fibres comprise, at the surface, an organic polymer deposit containing olefinic monomers and containing polar groups;said deposit is obtained by surface treatment using an aqueous dispersion of said polymers. Said fibre cement products have enhanced properties of breaking strength under stress and better resistance to cracking.

Description

PRODUCTS FORMED WITH FIBROCEMENT AND REINFORCEMENT FIBERS FOR SUCH PRODUCTS The present invention relates to a new reinforcing fiber for products formed with f ibr or c ** eme n t o, to a process of treatment of this fiber, as well as to the products of f ibrocement? reinforced with this fiber Fiber cement is used to produce solid products formed of the most diverse forms, such as, among others, roofing elements and facades such as tiles, plan or corrugated plates, pipes and storage tanks. These solid products formed are based on an aqueous hydraulic suspension comprising hydraulic binders, reinforcing fibers and, possibly, fillers. This aqueous suspension is mixed for the purpose of obtaining a uniform substance distribution of the components. The suspension is then drained. The fresh product thus obtained can then be shaped, for example in the form of a flat plate, corrugated plate or in the form of a tube. It is then allowed to "harden the fresh product formed under atmospheric conditions or under conditions of pressure, under specific temperature and humidity." The most widespread fairing procedure is the Hatschek process, whose technology, originally applied to asbestos-cement, It has been extensively described in the work "Asbeskement" by Harald Klos (Springe Verlag, 1967). Other manufacturing procedures are, for example, the Magnani, Mazza, Flo -on, extrusion and injection procedures. Hatschek is based on the use of cyclical sieving machines, in this process, a mat coming from a diluted suspension of asbestos and cement contained in a tank, is transferred to a felt, by means of a cylindrical funnel. , and then rolled up to the required thickness with the help of easy forming for the manufacture of corrugated sheets, the asbestos-cement sheet for On the forming cylinder is cut and detached from this cylinder after reaching the desired thickness. This sheet is then shaped and allowed to harden into three forms of oiled corrugated metal.

For some applications, "it proved useful to com - prize the fresh product after shaping it, but before hardening it (by buying it)." In this way, a distinction is made between the products formed with non - squeezed fiber cement and the products The products formed with compressed fibrocement were compressed between their formation and their hardening, under a pressure equal or superior to 4, 9 MPa (50 kgf / cm2) .These products are usually formed with compressed fiber cement. It should be in the fresh state at pressures between 9.8 MPa and 24.5 MPa (between 100 and 250 kgf / cm2) .Asbestos has both reinforcing properties due to its own tensile strength, and qualities of use in in relation to the excellent aptitude for dispersion in an aqueous suspension * of cement.In the runoff stage, due to its good filtration properties and good affinity for cement or, the asbestos fibers can retain the fine particles in suspension of the composite mixture in the course of the configuration. In the hydrated final product, the high tensile strength, combined with the high modulus of elasticity and the weak elongation at rupture, contribute to confer to the products manufactured with asbestos-cement, its high resistance to the known bending. However, asbestos has become an undesirable compound for reasons related to the environment and health and important efforts have been devoted to attempts to replicate it. It is therefore convenient to use new fibers as reinforcement agents and also as implementation aids for use as hydraulic agiomers before, for example to reinforce the cement. No natural or synthetic fiber that manifests all the properties of asbestos fibers has been discovered. Alkali resistance in saturated calcium hydroxide solutions is a particular criterion to which reinforcing fibers must respond. It is also important that the fibers can easily be dispersed in an * p * et?; * "diluted aqueous cement and which may also remain uniformly dispersed when the contribution is made- of other additives when said fibers are to be used in runoff techniques for the production of fiber cement products.At the same time, good dispersion is important. of the fibers so that they do not form agglomerates and so that the density of the fibers is homogeneous in the finished fiber cement product, but also so that the fibers are not oriented in one direction. The preferential direction, the fiber cement product would have a different resistance according to the direction of the breaking force, The literature already contains innumerable publications on the use of various organic and inorganic fibers * "natural or synthetic. The fibers constituted by cellulose, polyamide, polyester, polyacrylonitrile, polypropylene and polyvinyl alcohol, among others have been the object of research related to cement reinforcement. Also, works on the fibers formed with glass, steel, * aramid and carbon are known. Among all of them, all of the properties required, especially for cement, are still present.

For example, glass has low chemical stability, steel shows corrosion and has a too high density, carbon is too brittle, adheres poorly and has a high price, cellulose has insufficient durability, and common polyethylene and polypropylene they have insufficient tensile strength. Among the reinforcing fibers currently used, polyacrylonitrile (PAN) and polyvinyl alcohol (PVA) fibers are generally preferred. In isolation or in combination, these fibers allow a fibrocement shaped product having a resistance ** ** to *** high traction, in combination with an acceptable ductility. of PVA are expensive and considerably increase the total cost of the fiber cement products that contain them.Polypropylene fibers have an excellent resistance to alkalis, even at temperatures that can go up to 110 ° C. They are durable and inexpensive fibers. However, it is generally stated that polypropylene fibers are technically insufficient when it comes to reinforcing materials whose cement-based matrix is relatively brittle.

It has been previously treated to improve the polypropylene fibers, especially by * the incorporation of additives in the mass of the fibers. JP 6-219797 to Daiwabo Créate discloses bicomponent polypropylene fibers which contain, in their peripheral part, calcium carbonate. In British Patent 2,030,891, uneven particles are introduced into the thermoplastic fibers by bombardment. The documents GB-2.021552, WO 9 ~ 4/20654, EP-A-0 240,167, and WO 87/04144 describe hydraulic taking products whose reinforcing fibers are made from modified polymer. The fibers are, therefore, modified each time in the mass, which implies numerous disadvantages. This incorporation of additives in the dough, even of polypropylene fibers, increases the manufacturing cost and implies a modification of the mechanical characteristics of the reinforcing fiber, especially because it decreases its tenacity. EP310.100 also discloses polyolefin fibers containing inorganic p a * r t i c u 1 s included in the mass of the fibers, none of the particles remaining on the surface of the fiber. These fibers are manufactured from a film that may have been subjected to certain surface treatments. The mentioned surface treatments consist of chemical, electrical or mechanical modifications of the fiber. This document also mentions the application of surfactants on the surface of the fiber. It is also known to use polypropylene esters which have a high tensile strength (EP 0.525.737 Dai abo). "In European patent EP-AO 537.129, run s ** pondi e ~ n Patent No. 250,524, granted on April 18, 1997, describes manufactured products made of cement solids reinforced with this type of polypropylene fibers. A problem that still arises in the fiber cement products in the plates reinforced with this type of fibers is the appearance of cracks in the edges of the plate in particular in the course of the long-term aging of these products. On the other hand, rupture work is of considerable importance for the use of fiber cement products. A high value is sought (product of high ductility). In addition, a high ductility is important in order to be able, if the case * arises, to machine the pieces of fiber cement: drill, nail, saw ^ etc. Finally, safety also increases in the course of the use of products, such as ceilings, because too rapid or too violent ruptures are avoided under load * ". *" In uncompressed, fiber-reinforced fiber cement products Polypropylene, the work of rupture has generally a very weak value. In view of the reasons listed above, in particular due to their low resistance to cracking and their weak rupture work, the use of the products of compressed and non-compressed products, whose reinforcing fibers are polypropylene fibers, remains to the present very limited. It can be observed that certain polypropylene fibers are used, in small quantities, in asphalt products, to reduce cracking of the asphalt. For example, fibers marketed under the name -Crackstop® are known.

This type of fiber has insufficient mechanical properties and therefore is totally inadequate to reinforce fiber cement products such as roofing or façade elements. In fact, fiber cement products are characterized by a very large ratio of sf e f f e c e e e sp e s. The cracking problem of such products is therefore completely different from that of solid asphalt products. In fiber cement products, the fibers must actually fulfill a reinforcing function, while in the asphalt products, the amount of fibers is significantly less important and does not really fulfill this reinforcing function. In addition, the proportions of the different constituents, especially cement, are very different in asbestos products and asphalt products. Also, the conditions of implementation and the conditions of use are actually very different. It has been discovered, however, unexpectedly and surprisingly that polypropylene fibers, even common ones, but which have been subjected to a simple surface treatment with the aid of an aqueous dispersion of polymers, give good results, that is to say that it is possible to produce a product configured of fiber cement having a high breaking work and a good resistance to cracking, by means of polypropylene fibers that have been subjected to this surface treatment. The object of the invention is to provide shaped products of fiber cement that avoid the drawbacks that are typical of the known state of the art. One of the objects of the invention is especially that of procuring a product configured of fiber cement having good mechanical properties, such as a high breaking work and a good resistance to cracking, with low total cost price. The present invention aims at a polypropylene fiber for reinforcing products configured with fiber cement, manufactured by means of a hydraulic intake composition comprising especially water, hydraulic binders and reinforcing fibers. The fibers according to the invention comprise an organic polymer deposit comprising olefinic monomers and comprising polar groups, having been applied by surface treatment with the aid of an aqueous dispersion of this polymer. According to one embodiment, said aqueous dispersion comprises, alone or as a mixture, an organic polymer selected from the homopolymers and copolymers of olefinic monomers modified after synthesis (for example by grafting) with polar groups. Said polar groups are, for example, selected from maleic anhydride, acrylic acid or methacrylic acid. Said aqueous dispersion may also comprise, alone or as a mixture, an organic polymer chosen from the homopolymers and copolymers of olefinic monomers modified by oxidation. Said aqueous dispersion may also comprise, alone or in admixture, an organic polymer selected from the copolymers of an olefinic monomer and a polar monomer, such as, for example, methacrylic acid and acrylic acid optionally neutralized by ions. ** ** In an advantageous manner, the polypropylene fibers that have been subjected to said treatment, comprise from 0.05 to 5% by weight and preferably from 0.15 to 1.5% by weight of said organic polymer deposit that crrrrp rren of polar groups, in relation to the weight of the fiber. The polypropylene fibers according to the invention preferably have a denier (d) comprised between 0.5 and 10, and even more preferably between 0.5 and 2. The fibers can advantageously be cut at a length which may be between 2 to 20 mm; preferably the length of the fibers is staggered between 5 to 10 mm. The section of the fibers may be circular or may have an irregular shape, for example X or Y shape. The fibers may be in crepe form during the time they are stretched or thereafter. The technique of crepe formation of the fibers can include operations such as false twisting, the entanglement treatment by air current (comprising the TASLAN treatment) or the compression treatment (namely in the press-tow). The fibers according to the invention can also be obtained by fibrillating an extruded polypropylene film. The fibers can then have a ribbon shape.

The reinforcing fibers can be obtained from resin of any type of polypropylene commonly used. The polypropylene fibers, or a part of the polypropylene fibers, may optionally comprise fillers. They may additionally comprise, in addition, a hydrophilizing agent such as an alkali metal salt of alkyl phosphate, such as a sodium or potassium salt, advantageously comprising 8 to 18 carbon atoms. According to a variant embodiment, the fibers according to the invention or a part of the fibers according to the invention can be constituted by highly crystalline polypropylene which, for example, has a breaking strength - in the state of fibers greater than 490 N / mm2, a ratio of mass average molecular weight to number average molecular weight (Q) < to 4.5, a content of insoluble constituents (Hl) comprised between 97 and 100 and a fraction of isotactic pentades in moles (IPF) comprised between 94 and 100. According to another embodiment of the invention, the reinforcing fibers, or A p art of the reinforcing fibers can be bi-composite polypropylene fibers, consisting, for example, of a core and an outer cape, the outer layer of which contains carbonate particles of inert metals. , such as for example calcium carbonate, magnesium carbonate or their mixtures. The present invention also aims, a method of surface treatment of polypropylene fibers for the reinforcement of fiber cement products; this method consists in placing the polypropylene fibers in contact with an aqueous dispersion of organic polymers comprising olefinic monomers and comprising polar groups. Preferably, the concentration of the aqueous dispersion is from 0.5 to 40% of the organic polymers. In a particularly advantageous manner, said surface treatment is carried out by contacting the fibers with an applicator roller which is immersed in a treatment bath comprising said aqueous dispersion. All other forms of treatment such as immersion, spray, or curtain applications can be considered.

According to the technique used for the treatment of surfaces, the concentration of the dispersion must be adjusted. For bath treatments, the aqueous dispersion preferably has a concentration of organic polymers comprised between 0.5 and 10% dry material. For spray surface treatments, the preferred concentrations of the d i s p e r * s ion are for example comprised between 10 and 40% dry matter. * _ _ _ Said surface treatment is loyalized, at choice, before, during or after the stretch stage of the fibers. Depending on the case, the treatment is carried out on hot or cold fibers. Various surface treatments can possibly be provided in the manufacture of the reinforcing fibers. Generally, the treatment bath can be regulated between 20 and 80 ° C. The present invention also has as objective, shaped products of fiber cement comprising reinforcing fibers such as those described above and reinforcing fibers treated by the method described above.

Preferably, the fiber cement products comprise from 0.3 to 4% and even more preferably from 0.5 to 2.5% by weight in relation to the initial total dry mix of polypropylene fibers according to the invention. The fiber cement products according to the invention may further comprise inorganic fibers or organic fibers other than the polypropylene fibers according to the invention. ** Examples of organic fibers that can be used in combination with the treated polypropylene fibers are polyacrylonitrile, polyvinyl alcohol, polyamide, polyester, aramid, carbon and polyolefin fibers. Examples of inorganic fibers that can be used in combination with the treated polypropylene fibers are glass fibers, the rock wool, the wool of grout, the fibers of wo 1 s t oni t a, ceramic fibers and the like. For reasons of simplification, reference is made to cement as a preferred binder in the present disclosure. However, all other hydraulic tap binders can be used, instead of cement. Appropriate hydraulic fillers are considered to be the materials that contain ~ u * n inorganic cement and / or an inorganic binder or adhesive that hardens by hydration. Particularly suitable binders are those which harden by **** hydration, especially, for example, Portland cement, high alumina cement, iron Portland cement, trass cement, grout cement, gypsum, Calcium silicates formed by autoclaving and particulate binder combinations. Frequently additive loads are added to the binders, which can improve, for example, the runoff behavior of the suspensions on the machines of the conveyor belt. Possible additives are materials such as fly ash, amorphous silica, ground quartz, ground rock, clays, blast furnace slurries, carbonates, puzzolanos * etc. The total amount of fillers is ** preferably less than 50% in p is or in relation to the initial total weight in the dry state of the product. The product according to the invention may further comprise fibers for use, preferably in an amount equal to or less than 10% by weight relative to the initial total weight in the dry state of the product. The product according to the invention can be, for example, a roofing or façade element, such as a flat plate, a corrugated plate or another accessory element of various shapes. The invention is described in more detail in more detail with the help of specific embodiments.

EXAMPLES In the following examples, fiber cement products reinforced with polypropylene fibers treated according to the invention, were c * omp * araton with fiber cement products made with the same untreated polypropylene fibers. ~~ Baths' of treatment used _ __ _ Bath 1): Composition MICHEM® emulsion 94340-E by Michelman Int'l & Co., diluted with water, to a concentration of 4% dry material. This is an aqueous dispersion which comprises polypropylene grafted with maleic anhydride of the Epolene® E-43 type from Eastman Chemical. The dispersion has the following characteristics: emulsifying agents: no ionices **** - average particle size: 40 nm -pH: 7.5-9.0 Bath 2): same composition as in bath 1), diluted to 4%, to which 0.1% surfactant of the type Silwet® L-77 of OSI Specialties (alpha-1, 1, 1, 3, 5.5, 5-Heptamethyl-trisiloxanilpropyl-omega methoxy-poly (ethylene oxide).

Bath 3): composition n_ ° M 5984 of Michelman Int'l & Co., diluted with water to a concentration of 4% dry material, to which was added 0.1% surfactant of the Silwet® L-77 type from OSI Specialties. Composition No. M 5984 is an aqueous dispersion comprising an ethylene-propylene copolymer grafted to maleic anhydride of type * A-C® X 597 from Allied Signal.

Bath 4): composition No. M 93935 of Michelman Int 'L & Co., diluted with water to a concentration of 4% dry material, to which 0.1% surfactant of the Silwet® L-77 type from OSI Specialties was added.

Composition M 93935 is an aqueous dispersion comprising a high density polyethylene (HDPE) oxidised type AC® 392 HDPE from Allied Signal. The dispersion has the following characteristics: - emulsifying agents: non-ionic - average particle size: 40 nm - pH: 9.0 - 10.5 Bath 5): Aquacer 524 Composition of B-Wax, diluted with water up to one with "4% dry material centrio" This is an aqueous dispersion_ comprising polypropylene grafted with maleic anhydride of the Epolene® E-43 type from Eastman Chemical The dispersion comprises anionic emulsifying agents.

Bath 6): Composition Aquacer 841 by Byk-Wax, diluted with water to a concentration of 4% dry material. This is an aqueous dispersion comprising polypropylene grafted with macular anhydride of the Epolene® E-43 type from Eastman Chemical. The dispersion comprises c a t ionic emulsifying agents.

Bath 7): same composition as bath _1) but diluted to a dry material concentration (grafted polypropylene) of 0.2%.

Bath 8): same composition as bath 1) but diluted to a concentration of grafted polypropylene dry material) of 1.0 Bathroom 9) Aquaseal 1127 composition of Paramelt B.V. diluted to a dry material concentration of i ± so-. - This composition is an aqueous dispersion of a copolymer of ethylene and of methacrylic acid.

Bath 10): same composition as bailo _ ^ 9) but diluted to a concentration of dry material (ethylene and methacrylic acid copolymer) of 4 Bath 11) Aquaseal 1088 composition of Paramelt B.V. diluted to a dry material concentration of 1%. This composition is an aqueous dispersion of a copolymer of ethylene and methacrylic acid neutralized with the Na + ions (ionomer).

Bath 12): same composition as for the bath 11) but diluted to a concentration of dry materials (ethylene and methacrylic acid copolymer neutralized with Na + ions) of 4%. Likewise, several blank tests were carried out to demonstrate the difference between the fibers treated according to the invention and the fibers of the state of the art treated with the known surfactants. These agents do not fall within the definition of polymers comprising olefinic monomers and comprising polar groups: White A: Composition comprising 4 __% _ of modified siloxane-based wetting agent (used to convert polypropylene fibers into hydrophilic fibers) of the company SCHILL UND SEILACHER.

White B: Composition comprising 4% Lurol PP-5030 - 3-0% (emulsifier, lubricant and antistatic mixture) from the company GOULSTON TECHNOLOGIES.

White C: Composition that_ comprises 4% _ of hexanol (commonly used as a wetting agent).

Preparation of polypropylene fibers Standard polypropylene resin granules (melting point 165 ° C, melt flow index (MFI9 of 25) were heated in an extruder (varying the temperature at the point of the extruder between 240 ° C and 280 ° C) and were spun in a classical manner, the fibers were then stretched with conventional equipment. According to a first preparation procedure, the spinning and stretching of the fibers was carried out discontinuously. preparation procedure, spinning and stretching were carried out continuously.The fibers then have the following characteristics: - title: 1,18 dtex - tenacity: 730 N / mm2 - initial modulus: 7460 n / mm2 - rupture extension : 19,0 After stretching, the fibers were impregnated in one of the treatment baths described above, by contact with an applicator roller immersed in the treatment bath. The treatment bath applied to the fibers by this treatment is about 0.15% to 1.5% by weight in relation to the weight of the fiber. This concentration is measured by nuclear magnetic resonance (NMR) with the aid of a commercial device OXFORD RMN QP 20+. This equipment is used in a standard way to quantify the endings of surfaces applied to the fibers, especially in textile technology. This apparatus is designed to determine the concentration of a given component that contains the protons in its molecular structure. Comparative tests were also carried out: Io without impregnation in the treatment bath, 2o with impregnation in the compositions of colored agents (White A, White B and White C) The fibers were then conventionally cut to a length of 8 mm before _ to be used in construction materials mixtures. In the examples 1 to 6 given below, the impregnation with the treatment bath was carried out after the stretching of the fibers, but it is also possible to carry out this treatment during the stretch stage or directly after the spinning, before of the stretching of the fibers. In the following example 1 bis, the treatments were carried out between the spinning stage and the stretching stage of the fibers.

EXAMPLES 1 TO 6 and 1 bis _ _ Preparation of the mixes and putting into operation in the maquina ** at Hatschek. ___ "___ The following compounds were mixed with water: - 77.2% cement, - 1.8% polypropylene fibers treated on the surface with one of the baths described above, - 3.0% amorphous silica, and - 15% flying ash.

The concentrations given are the concentrations of solids in relation to the total dry matter. This suspension is diluted with water to a concentration of 30 g per liter and then transferred to the tank of a Hatschek machine. Shortly before the introduction of the suspension in the tank, 200 ppm of a flocculating agent of the polyacrylamide type is added to improve the retention of the cement. Plates are produced with the help of the machine with 22 turns of the forming cylinder. The plates are then pressed between two oiled steel molds in a press under a specific applied pressure of 18 D bar (17.7 MPa) m, until an average thickness of 5.5 mm is reached. The leaves are made to harden under cover of plastic material for 28 hours under a relative humidity of 100% at 20 ° C.

Mechanical tests of resistance to bending and cracking Mechanical tests are carried out in the dry state, - in the air. In principle, the flexural strength of the samples is determined in a mechanical test machine in the curve of a classic three-point bending test. The apparatus records the stress-strain curve. The work of breaking under maximum load (IMOR) expressed in joules per m2 (J / m2) is integral to the stress-strain function until the loading of r up t u r a. The resistance to cracking is also determined by a severe rancebide test to cause cracking along the edges of the fiber cement products (cracking test). The cracks were obtained by artificially creating a moisture gradient between the edges of the central part of the plates by differential drying between the outer and inner areas of the product. For this purpose, a series of fiber cement sheets manufactured in a Hatschek machine, compressed and allowed to harden under a humid atmosphere for 28 days as described above, were cut into 30 cm x 30 cm sections and stacked one on top of the other, inserting an interleaver every 10 pieces.

The upper part and the bottom, the pile (about 40 plates) are provided with two appropriate cover plates not ab ssent of a material such as steel or polyester. The battery is placed in a ventilated oven at 60 ° C for 24 h. . The cracks then appear on the edges of the plates. The plates are examined one by one and the lengths of the cracks visible to the naked eye are measured. The lengths of the cracks of each plate are aggregated and totalized with 5 plates. The results are given in table I below.

TABLE I It can be deduced from Table I -previous, that the compressed fiber cement products reinforced with polypropylene fibers treated on the surface with one of the 6 baths described, present a more important rupture work (increase of 19 to 75%) than that of the fiber cement product using the same polypropylene fibers but without treatment. This improvement of the rupture work is also observed in relation to fiber cement products whose polypropylene fibers have been treated with a surfactant (White A, B or C). Likewise, the products according to the invention, present in the cracking test a significant decrease in the total length of the average cracks (from 39 to 84% depending on the case), either in relation to the product that compi * e ** n of the fibers that have not been subjected to treatment or * in relation to the products comprising the fibers that have undergone treatment with the help of one of the targets A to C.

EXAMPLES 7 TO 12 Preparation of the mixtures and commissioning on a Hatschek machine The same preparation procedure as described for examples 1 to 6 was used here, leaving aside the fact that the products were not compressed. The plates produced with the help of the Hatschek machine were therefore allowed to harden directly without intermediate pressing stage. The results were gathered in the following table II.

TABLE II As with the compressed fiber cement products, for the non-compressed products, it can be deduced from the preceding Table II, that the surface treatment of the ordinary polypropylene fibers with one of the baths 7 to 12 described above, provides in the product finished an important increase of the work of rupture (increase of 202 to 403% in re 1 ac t to the product whose fibers have not undergone the treatment). This improvement of the rupture work is equally remarkable in relation to fiber cement products whose polypropylene fibers have been treated with the surfactant (White A, B or C). Likewise, the measured values of the total length of the cracks for the non-compressed products according to the invention show a decrease of 19 to 24% in relation to the product whose fibers have not been subjected to treatment. This improvement in cracking is also observed in relation to the products whose fibers have been treated with one of the Targets A to C. The invention therefore allows a simple and inexpensive surface treatment of the polypropylene fibers, an increase of breaking work and an improvement in the crack resistance of fiber cement products reinforced with these fibers. This treatment can be applied to any type of polypropylene fiber.

The effects of this treatment are particularly unexpected. Despite the very short contact time ** of the fibers with the composition of the treatment bath, the adhesion of the particles on the fiber seems to be important.These effects are much more unexpected because, in spite of the mixture of the fibers and cement in a large amount of water and under significant agitation, in the manufacture of fiber cement products, will retain "the effect of the treatment of the fibers. It should also be noted that these results are obtained when the übrocemento products are subjected to tests under very unfavorable conditions for medix-the rupture work, that is, in the dry state, in the air. Having thus specially described and claimed the nature of the present invention and the manner in which it is to be put into practice, it is claimed to claim exclusive property and right:

Claims (14)

1. Polypropylene fiber for the reinforcement of fiber cement products, characterized in that it comprises on the surface an organic polymer deposit comprising ethylenic and / or propylenic monomers and because it comprises polar groups, with the exclusion of the vinyl acetate-ethylene copolymer, by applying this deposit by treating the surface with the aid of an aqueous dispersion of this polymer.

2. Fiber according to the rei indication 1, characterized in that the organic polymer is chosen from the homopolymers and copolymers of ethylenic and / or propylenic monomers modified after polar group synthesis.

3. Fiber according to any of the preceding claims, characterized in that the polar groups are chosen from maleic anhydride, acrylic acid or methacrylic acid.

4. Fiber according to any of the preceding claims, characterized in that the organic polymer is chosen from the homopolymers and copolymers of ethylenic and / or propylenic monomers modified by oxidation.

5. Fiber according to any of the preceding claims, characterized in that "the organic polymer is selected from among the copolymers of an ethylenic and / or propylene monomer and of a polar monomer, optionally neutralized by ions, to the exclusion of vinyl acetate-ethylene.

6. Fiber according to any of the preceding claims, characterized in that the denier (d) of the polypropylene fibers is not between 0.5 and 10.

7. Fiber according to any of the above indications characterized because the length of the polypropylene fibers is between 2 _ and 20 mm.

8. Fiber according to any of the previous claims, characterized in that said deposit represents from 0.05 to 5% by weight of dry matter in relation to the dry matter of the fiber.

9. Surface treatment process of polypropylene fibers for the reinforcement of fiber cement products, characterized in that the fibers are contacted with an aqueous dispersion of organic polymers "comprising ethylenic and / or propylenic monomers and comprising polar groups, with the exclusion of the dispersions comprising the vinyl acetate or ethylene copolymer.

10. Process according to the preceding claim, characterized in that the aqueous dispersion comprises from 0.5 to 40%, of organic polymers comprising ethylenic and / or propylenic monomers and polar groups.

11. Product _ formed with fiber cement manufactured by a hydraulic taking composition comprising water, hydraulic binders and reinforcing fibers according to any of claims 1 to 8.

12. Product formed with fiber cement manufactured by a hydraulic intake composition comprising water, hydraulic binders and reinforcing fibers treated with the treatment process according to any of claims 9 and 10.

13. Product according to any of claims 11 and 12, characterized in that it comprises from 1 to 5% by weight in relation to the initial total dry mix of reinforcing fibers.

14. Product according to any of the rei indications 11 to 13, characterized in that c o n s i s "t e in a corrugated or flat plate.