WO2007128679A1

WO2007128679A1 - Fibre-cement product compositions and shaped products obtained therefrom

Info

Publication number: WO2007128679A1
Application number: PCT/EP2007/053952
Authority: WO
Inventors: Benoît de Lhoneux; M. Lieven Alderweireldt
Original assignee: Redco S.A.
Priority date: 2006-05-09
Filing date: 2007-04-23
Publication date: 2007-11-15
Also published as: EP1854770A1; PT1854770E; BRPI0711389A2; MX2008014174A; ES2385392T3; EP1854770B1; SI1854770T1; ATE556036T1; BRPI0711389B1; DK1854770T3

Abstract

The invention concerns a composition of fibre-cement products comprising reinforcing fibres comprising at least fibres containing poly(vinylalcohol) (A) and of synthetic organic fibres (B). The fibres containing poly(vinylalcohol) (A) have a titre of at least 4,0 dtex and lower than 15,0 dtex. The synthetic organic fibres (B) are selected among fibres made of poly(vinylalcohol) characterized by a titre of at least 1,5 dtex and lower than 3,0 dtex, or made of polymers or copolymers of propylene characterized by a titre of at least 0,7 dtex and lower than 3,0 dtex, or their blends. The invention is also related to shaped products, particularly flat or corrugated fibre-cement sheets obtained from such a composition.

Description

FIBRE-CEMENT PRODUCT COMPOSITIONS AND SHAPED PRODUCTS OBTAINED THEREFROM

Field of the invention

The invention concerns a fibre-cement product composition comprising reinforcing fibres comprising at least polyvinylalcohol fibres (A) and synthetic organic fibres (B) .

The invention is also related to shaped fibre-cement products manufactured from said composition. Roof and fagade elements, flat and corrugated sheets, slates, tubes and storage tanks can be cited amongst others as examples of shaped fibre-cement products.

State of the art

Shaped fibre-cement products are manufactured starting from an aqueous suspension comprising hydraulic binders, reinforcing and processing fibres, and possibly fillers. This aqueous suspension is mixed in order to obtain a uniform distribution of the components. This suspension is then dewatered. The so obtained green fresh product can be shaped as a flat sheet, a corrugated sheet or a tube. The green shaped product is then hardened under atmospheric conditions or under specific pressure, temperature and humidity conditions.

The Hatschek process is most widely known for the manufacturing of fibre-cement products. This process, initially applied to the asbestos-cement, is exhaustively described in the book "Asbestzement" by Harald Klos (Springer Verlag, 1967). Other manufacturing processes known by the man skilled in the art which can be cited are Magnani, Mazza, Flow-on, extrusion and injection. The Hatschek process, particularly suited for the manufacture of flat sheets, corrugated sheets and tubes, is based on the use of a dewatering cylindrical sieve. In this way, a layer originating from a diluted suspension of fibres, cement, fillers and additives contained in a vat is transferred to a felt, through a cylindrical sieve; this layer is then enrolled on a forming drum until the required thickness of the sheet is obtained.

The fibre-cement sheet shaped on the forming drum is cut and removed from the drum, once the desired thickness is obtained. This sheet is then subjected to a forming step, which in the case of corrugated sheets consists of putting it between corrugated sheets, for instance metal corrugated sheets which have been oiled. Afterwards, it is submitted to a hardening stage.

For certain applications it seems to be useful to compress the green product between the forming and the curing (post- compression) . We call these pressed fibre-cement products opposed to non-pressed fibre-cement products. The pressed fibre-cement products are compressed between the forming and the curing stage at pressures equal to or higher than 4,9 MPa. Usually, the applied pressures are comprised between 9,8 MPa and 24,5 MPa.

Until recently, many fibre-cement products were manufactured from asbestos-cement. As asbestos is dangerous for the environment and the health, it was recommended not to use it anymore. Other reinforcing and processing fibres have since then been used for the manufacturing of fibre- cement products.

The fibres used instead of asbestos fibres must have the same characteristics as the asbestos fibres. They have to be alkali-resistant (e.g. to saturated calciumhydroxide solutions) . They also have to be easily dispersable in an aqueous diluted cement dispersion. They have to remain uniformly dispersed upon the addition of other additives as well. The good dispersion of fibres is important on the one hand to make sure that these fibres do not form agglomerates, and on the other hand to ensure the homogeneous concentration of the fibres in the finished fibre-cement product. The fibres used as reinforcing agents must also have good mechanical properties. The literature contains publications related to the use of natural or synthetic organic and inorganic fibres. Thus fibres of cellulose, polyamide, polyester, polyacrylonitrile (PAN) , polypropylene (PP) and poly (vinylalcohol) (PVA) were used for the reinforcement. In the same way, work has been done with glass, steel, aramide and carbon fibres. Unfortunately, no natural or synthetic fibre has all the previously mentioned properties. Besides, it is important to manufacture shaped fibre-cement products with good mechanical properties and at an interesting cost price. Accordingly, it is known to use hydraulic setting compositions comprising synthetic reinforcing fibres. Among reinforcement fibres currently used, fibres of polyacrylonitrile (PAN) and poly (vinylalcohol vinyl) (PVA) are generally preferred. Separately or in combination, these fibres make it possible to manufacture shaped fibre- cement products which have a high tensile strength and flexural resistance. Unfortunately, PVA and PAN fibres do not confer to the shaped products a sufficient impact resistance, especially after ageing during exterior exposure . The polypropylene (PP) fibres have an excellent resistance to alkalis, even at temperatures close to 110° C. These fibres are durable and inexpensive. However, used only, the PP fibres are in general technically insufficient to reinforce cement containing materials.

The document JP2003-267768 discloses hydraulic panels obtained by wet process comprising PVA reinforcing fibres having a titre from 6 to 30 dtex. However, the fibre-cement plates obtained from such compositions have an insufficient impact resistance when they are used for example for roofing applications, and more particularly after natural ageing during exposure to carbon dioxide present in the air . Patent application EP-A 0 155 520 describes hydraulic setting compositions comprising a mixture of PVA and PAN fibres having a titre from 0,5 to 10 dtex. However, the products manufactured from these compositions have a impact resistance which is too low.

Summary of the invention

It is a purpose of the invention to propose a composition of fibre-cement products comprising reinforcing fibres comprising at least fibres containing poly (vinylalcohol) (A) and synthetic organic fibres (B) which discards the disadvantages of the existing compositions.

It is a purpose of the invention to propose a composition of fibre-cement products easy to implement comprising inexpensive reinforcing fibres which resist alkalis, and which present a homogeneous and stable dispersion as well as a high reinforcement capacity. Moreover, it is a question of proposing a composition of fibre-cement products presenting an excellent processability, a good flexural resistance and a high and durable impact resistance, even after ageing during external exposure, and whose cost is not prohibitory.

To this end, the composition according to the invention is characterized in that:

- the poly (vinylalcohol) fibres (A) have a titre of at least 4,0 dtex and lower than 15,0 dtex; and the synthetic organic fibres (B) are selected among fibres made of poly (vinylalcohol) presenting a titre of at least 1,5 dtex and lower than 3,0 dtex, or of polymers or copolymers of propylene having a titre of at least 0,7 dtex and lower than 3,0 dtex or their blends.

The composition according to the present invention comprises fibres (A) of poly (vinylalcohol) (PVA) characterized by a titre of at least 4,0 dtex and lower than 15,0 dtex. Products comprising fibres (A) of PVA having a titre lower than 4,0 dtex have an insufficient impact resistance. Products comprising fibres (A) of PVA having a titre of at least 15,0 dtex have a flexural resistance which is too low. The composition according to the present invention comprises synthetic organic fibres (B) selected among fibres made of poly (vinylalcohol) characterized by a titre of at least 1,5 dtex and lower than 3,0 dtex or of polymers or copolymers of propylene characterized by a titre of at least 0,7 dtex and lower than 3,0 dtex or their blends. Fibre-cement products comprising fibres (B) made of polymers or copolymers of propylene having a titre lower than 0,7 dtex suffer from a bad processability, whereas products comprising fibres (B) made of polymers or copolymers of propylene having a titre of at least 3,0 dtex do not have the required mechanical properties. Fibre-cement products comprising fibres (B) made of poly (vinylalcohol) with a titre lower than 1,5 dtex suffer from a bad processability, whereas products comprising fibres (B) made of poly (vinylalcohol) with a titre of at least 3,0 dtex do not have the required mechanical properties. Advantageously, the composition according to the present invention comprises poly (vinylalcohol) fibres (A) having a titre of at least 5,0 dtex and lower than 7,5 dtex. According to a particular embodiment, the composition according to the invention is characterized in that it comprises fibres (A) and fibres (B) having a tenacity of at least 8 cN/dtex.

The products comprising fibres (A) and (B) whose tenacity is lower than 8 cN/dtex do not have the required mechanical properties . According to an advantageous embodiment, the composition according to the invention is characterized in that it comprises from 0,1 to 5 weight % of fibres (A) and from 0,1 to 5 weight % of fibres (B) with respect to the total initial dry weight of the composition. In order to make reading easier and for clarity, the expression "weight percentage of fibre" used in the following description must be understood as related to fibres in a composition, like "weight percentage of fibre weight compared to the initial dry total weight of the composition" .

Indeed, the fibre-cement products manufactured using compositions comprising less than 0,lweight % of fibre (A) weight suffer from a impact resistance which is too low. In addition, products manufactured from compositions comprising more than 5 weight% of fibre (A) have insufficient mechanical properties due to a bad dispersion of fibres in the cement matrix. Products manufactured using compositions comprising less than 0,1 weight % of fibre (B) suffer from a impact resistance which is too low and/or from a insufficient flexural resistance. Compositions comprising more than 5 weight % of fibre (B) give fibre-cement products having insufficient mechanical properties due to a bad dispersion of fibres in the cement matrix.

Advantageously, the composition according to the present invention comprises from 0,5 to 2,5 weight % of fibre (A) . A composition comprising from 0,3 to 2,5 weight % of fibre (B) gives good results.

The synthetic organic fibres (B) are selected among fibres made of poly (vinylalcohol) , of polymers or copolymers of propylene, or their blends. Fibres (B) comprising a blend of fibres made of poly (vinylalcohol) and of polymers or copolymers of propylene are particularly preferred.

According to another embodiment of the invention, the composition is characterized in that it comprises fibres

(B) comprising a blend of fibres made of poly (vinylalcohol) having a titre of at least 1,5 dtex and lower than 2,5 dtex and of fibres made of polymers or copolymers of propylene having a titre of at least 0,7 dtex and lower than 1,5 dtex . According to a particular embodiment, the composition according to the invention is characterized in that it comprises fibres (B) comprising from 0,3 to 1,5 weight % of fibres made of poly (vinylalcohol) (PVA) and from 0,3 to 1,5 weight % of fibres made of polymers or copolymers of propylene (PP) . According to a particular embodiment, the composition according to the invention is characterized in that it comprises, besides the fibres (A) and the fibres (B) , from 0,1 to 5 weight % of polyolefinic fibrils. By fibrils, one understands here an entanglement of polyolefinic microfibres which can, for example, be obtained by flash spinning, i.e. by instantaneous evaporation of the solvent of a concentrated solution of fibres by decompression when it passes through an orifice. The polyolefinic fibrils act in particular like reinforcing and processing agents. The composition according to the invention comprises preferably from 0,5 to 2 weight % of polyolefinic fibrils. The compositions according to the invention comprising from 0,5 to 2,5weight % of PVA fibres (A), from 0,3 to 1,5 weight % of PP fibres (B), from 0,3 to 1,5 weight % of PVA fibres (B) and from 0,5 to 2 weight % of polyolefinic fibrils, give particularly good results. The composition according to the invention advantageously comprises polyolefinic fibrils made of polymers or copolymers of propylene or ethylene. One prefers particularly the polyolefinic fibrils made of high density polyethylene

(HDPE) .

According to a particular embodiment, the fibres (A) and the fibres (B) of the composition according to the invention can advantageously be cut to a length ranging from 2 to 20 mm; preferably the length of fibres ranges from 3 to 11 mm. The section of fibres can be circular or of irregular form, for example in form of X or Y. The fibres can be textured while they are stretched or afterwards. According to a particular embodiment, the fibres (B) made of polymers or copolymers of propylene (PP) can also be obtained starting from an extruded polypropylene film. The fibres can then present the shape of ribbon. The fibres (B) made of PP can be obtained from resin of any type of polypropylene usually used. At least a part of the fibres (B) can possibly comprise fillers. They can moreover possibly comprise a hydrophilizing agent such as an alkaline metal salt of an alkylphosphate, such as a potassium or sodium salt, comprising advantageously from 8 to 18 carbon atoms. According to an alternative of execution, the fibres (B) made of PP can consist of high isotacticity polypropylene with a narrow molecular weight distribution. According to another form of execution of the invention, the fibres (B) made of PP, can comprise coextruded bicomponent fibres, consisting for example, of a core and an external layer, whose external layer contains alkaline earth metal carbonate particles, such as for example, calcium carbonate, magnesium carbonate or their blends. According to an advantageous procedure of this invention, the fibres (B) containing PP have been submitted to a surface oxidation treatment, such as corona discharge or plasma, in order to improve their affinity to the cement matrix. According to a particularly advantageous alternative of this invention, PP fibres (B) can have undergone a surface oxidation treatment, followed by a treatment using wetting agents, which are applied by sprinkling or by immersion in a hydrophilic avivage or hydrophilic lubricant composition or an aqueous dispersion of polar organic polymers or a dispersion of olefinic homopolymers and copolymers of olefinic monomers modified after synthesis by polar groups chosen preferably among maleic anhydride, acrylic acid, or the methacrylic acid, and obtained for example by grafting. According to a particular embodiment, the composition according to the invention is characterized in that it comprises besides the fibres (A) and the fibres (B) , other reinforcing fibres chosen among inorganic or organic fibres. Preferably, the organic fibres are selected among fibres of polyacrylonitrile, polyamide, polyester, aramide, carbon and polyolefins. Advantageously, the inorganic fibres are selected among glass fibres, rockwool, slag wool, wollastonite fibres, ceramic fibres and similars. According to a particular embodiment, the composition according to the invention is characterized in that it comprises cement as hydraulic binder. Advantageously, cement is selected among Portland cement, cement with high alumina content, Portland cement of iron, the trass-cement, slag cement, plaster, calcium silicates formed by autoclave treatment and combinations of particular binders. Portland cement is particularly well suited.

According to a particular embodiment, the composition according to the invention is characterized in that the cement comprises fillers and additives, particularly to improve the dewatering behaviour of the suspensions. The additives are preferably selected among the dispersants, plasticizers and the flocculants. The fillers are advantageously selected among the fly-ashes, amorphous silica, ground quartz, the ground rock, clays, blast furnace slag, carbonates, pozzolanas, etc. The total quantity of fillers is, preferably, lower than 50 weight % compared to the total initial dry weight of the composition .

Advantageously, the composition according to the invention preferably comprises processing fibres, in a quantity equal or lower than 10 weight % with respect to the total initial dry weight of the composition. Cellulose fibres are particularly well suited for the filtration of the cement particles . It is an object of the invention to offer fibre-cement products having a good flexural resistance combined with an excellent impact resistance, even after ageing. For this reason, the fibre-cement product according to the invention is characterized in that it is manufactured starting from a composition according to the present invention. The product according to the invention has a good impact Charpy resistance, measured according to standard ASTM D- 256-81 (method B) , even after ageing during exposure to carbon dioxide. In addition, the product according to the present invention has a high flexural modulus. According to a particular embodiment, the product according to the invention is preferably a roofing or fagade element, a flat or corrugated sheet. The composition according to the invention is particularly suited to the manufacture of corrugated sheets. According to another particular embodiment, the product has the shape of a pipe, of a tank storage element or of all other accessories of various shapes.

Detailed description of particular embodiments

It will be obvious for the man skilled in the art that the present invention is not limited to what was disclosed and described particularly above. All new characteristics and each combination of these characteristics belong to the scope of the invention. The numerical references in the claims do not limit the scope of their protection. The use of the verbs "to comprise or to include" and their conjugated forms does not exclude the presence of other elements than those cited in the claims. The use of the article "a or an" in front of an element, does not exclude the presence of a plurality of such elements. The invention is described hereafter in a detailed way using particular examples of embodiment.

EXAMPLES Characteristics of the used reinforcing fibres

Table I

(*) SWP: "Synthetic Wood Pulp": synthetic paste made of HDPE microfibres (fibrils) .

The (PP) fibres (B) Daiwabo E12-C were submitted to a

10 corona treatment.

Preparation of the blends and production on Mini-Hatschek machine

15 Cementitious products were manufactured by the Hatschek technique, according to a pilot method reproducing rather accurately the main characteristics of the products obtained by industrial methods. The compositions which have been used after strong dilution 0 with water, are mentioned in tables II and III

(concentrations in solids expressed in weight % with respect to the total dry matter) and in which the processing fibres SUKP refer to an unbleached paste of coniferous trees refined to 65° SR (Schopper-Riegler) and P30 indicates Portland cement.

The sheets were hardened during one night at 50⁰C, and afterwards under plastic cover sheet during 7 days at room temperature.

Sampling

The sheets are sawn in order to obtain the desired dimensions. The mechanical properties are measured after ageing in an oven of 600 L at 60⁰C and 90 % of relative humidity, with injection of 1,5 1 CC>2/min during 24 hours; the CO₂ concentration ranges thus from 7 % at the beginning of conditioning to 12 % at the end of the conditioning.

Measurement of the Charpy impact resistance

The Charpy impact resistance is measured according to standard ASTM D-256-81, method B, using an apparatus Zwick DIN 5102.100/00 on air-dry samples of 15*120 mm and a span of 100 mm. Ten samples are measured in the two directions (direction machine and direction perpendicular to this) . The results (average of 20 measurements) are expressed in % compared to a reference corresponding to the comparative example 1 in table II.

Measurement of flexural resistance

The flexural_resistance is determined by a classic flexural test on three points using an apparatus UTS, a span of 146 mm and a test speed of 20 mm/minute. Ten samples saturated with water are measured in the two directions (direction machine and direction perpendicular to this) . The apparatus records the curve stress/strain and the modulus of rupture (MOR) can be determined. The results (average of 20 measurements) are expressed in % compared to a reference corresponding to the comparative example 1 of table II.

Table II - Comparative examples

The comparative examples 1 to 4 in table II show that compositions comprising only fibres (A) or fibres (B) have an insufficient impact resistance and/or a flexural modulus of resistance which is too low. An increase in the concentration of fibres (A) (as shown in comparative example 5) or of fibres (B) (as shown in comparative example 6) does not give a sufficient impact resistance combined with a sufficient flexural modulus. The use of a blend of PVA having a titre of 2,0 dtex and PP having a titre of 0,9 dtex as in comparative example 7 results into a modulus of rupture which is too low. Table III - Examples according to the invention

The comparison of example 2 of table III with the comparative example 5 of table II shows that by replacing a part of the PVA fibres (A) by PVA fibres (B) , the flexural resistance is improved while maintaining a good impact resistance . The examples 3 and 5 of table III show that the best results are obtained with fibres (B) comprising PVA and PP fibres .

Also, the comparison of examples 3 with example 6 of table III shows that by replacing part of the cellulose fibres by HDPE fibrils, the impact resistance is still improved. The present invention was described in specific terms of execution which are an illustration of the invention and which should not be considered as restrictive.

Claims

1. Composition of fibre-cement products comprising reinforcing fibres comprising at least fibres containing poly (vinylalcohol) (A) and of synthetic organic fibres (B), characterized in that: - the fibres containing poly (vinylalcohol) (A) have a titre of at least 4,0 dtex and lower than 15,0 dtex; and

-synthetic organic fibres (B) selected among fibres made of poly (vinylalcohol) having a a titre of at least 1,5 dtex and lower than 3,0 dtex, or made of polymers or copolymers of propylene having a titre of at least 0,7 dtex and lower than 3,0 dtex or their blends.

2. Composition according to claim 1, characterized in that the fibres (A) have a titre of at least 5,0 dtex and lower than 7, 5 dtex .

3. Composition according to one of the preceding claims, characterized in that the fibres (A) and (B) have a tenacity of at least 8 cN/dtex.

4. Composition according to one of the preceding claims, characterized in that the fibres (A) and (B) have a length of 3 to 11 mm.

5. Composition according to one of the preceding claims, characterized in that it comprises from 0,1 to 5 weight % of fibre (A) with respect to the total initial dry weight of the composition.

6. Composition according to one of the preceding claims, characterized in that it comprises from 0,1 to 5 weight % of fibre (B) with respect to the total initial dry weight of the composition.

7. Composition according to claim 5, characterized in that it comprises from 0,5 to 2,5 weight % of fibre (A) .

8. Composition according to claim 6, characterized in that it comprises from 0,3 to 2,5 weight % of fibres (B) .

9. Composition according to any of claims 1 to 6, characterized in that the fibres (B) comprise from 0,3 to 1,5 weight % of fibres made poly (vinylalcohol) and from 0,3 to 1,5 weight % of fibres made of polypropylene with respect to the total initial dry weight of the composition.

10. Composition according to any of the preceding claims, characterized in that the fibres (B) comprise fibres made of poly (vinylalcohol) having a titre of at least 1,5 dtex and lower than 2,5 dtex.

11. Composition according to any of the preceding claims, characterized in that the fibres (B) comprise fibres made of polymers or copolymers of propylene having a titre of at least 0,7 dtex and lower than 1,5 dtex.

12. Composition according to any of the preceding claims, characterized in that it comprises, besides the fibres (A) and the fibres (B), from 0,1 to 5 weight % of polyolefinic fibrils with respect to the total initial dry weight of the composition .

13. Composition according to claim 12, characterized in that it comprises from 0,5 to 2 weight % of polyolefinic fibrils with respect to the total initial dry weight of the composition.

14. Composition according to one of the claims 12 or 13, characterized in that the polyolefinic fibrils are selected among fibrils made of polymers or copolymers of propylene or ethylene or their blends.

15. Composition according to any of the preceding claims, characterized in that synthetic organic fibres (B) are made of polymers or copolymers of propylene which were subjected to an oxidation surface treatment.

16. Fibre-cement product manufactured by means of a composition according to any of claims 1 to 15.

17. Fibre-cement product according to claim 16, characterized in that it is a flat or corrugated sheet.