FR2506292A1 - Reinforced cement prods. - contg. polyacrylonitrile fibre reinforcement - Google Patents

Abstract

Reinforced products with a hydraulic binder are made contg. acrylonitrile polymer fibres with 98-100 mol.% acrylonitrile units as reinforcing fibres and/or fillers. Pref. the fibres have a strength of 50 cN/tex and an elongation at break of at least 15%, a uniform length of 3-24 mm or a non-uniform length of up to 30 mm and a titer of 0.1-15 dtex. The polyacrylonitrile fibres are useful replacements for natural fibres such as asbestos in asbestos-cement type prods. such as sheets, corrugated sheets, pipes and moulded building parts. They can be processed by normal equipment used for making conventional asbestos cement sheets such as winding machine, rotary screen, flat screen, injection unit or filter press.

Description

 The present invention relates to products containing fibers made with hydraulic binders, characterized in that they use fibers of acrylonitrile polymers, in which the molar concentration of acrylonitrile units is from 98 to 100%, as fibers reinforcement ex or as charges.

 It further relates to a process for manufacturing these products, as defined in claim 9.

 Among the usual building materials, fiber-reinforced cement products, such as asbestos, have already been known for several decades. In the asbestos-cement industry, the methods of manufacturing building elements by winding according to the technique described in the Austrian patent 5,970 filed in the name of L. Hatschek, remain the most widespread today. The technology of this manufacturing process is described, for example, in detail in Harald Klos' book, "Asbestzement1 ,, Springer éditeur, 1967.

 These known processes for the manufacture, for example of pipes and asbestos-cement plates, are based on the use of cylindrical screen machines. In these methods, a diluted suspension of asbestos cement is sent in the form of a film on a felt via a machine tray and a cylindrical sieve and is then wound on a format cylinder or on a mandrel for the pipes until the desired thickness is reached hardening between oiled corrugated interlayers.

 In recent years, it has turned out that asbestos, which had worked well, would no longer be available in unlimited quantities and should be counted among the natural substances which could be predicted to run out the most. quickly. The exploitable asbestos deposits are also distributed over a small number of countries, which can also lead to undesirable dependence, which is manifested today by increasing prices.

 We therefore wish to use new fibers having reinforcing qualities and allowing feasibility via processing machines or traditional manufacturing machines for the asbestos-cement industry in order to obtain products having the mechanical characteristics. desired.

For simplicity, reference will be made in the present description to cement as a preferred binder. But we can use in place of cement all the other binders that set hydraulically. As binders hardening by hydration, non-exhaustive mention will be made of cement
Portland, molten aluminous cement, slag cement, trass cement, blast furnace cement, plaster, calcium silicates formed by autoclave treatment as well as combinations of the various binders.

 In addition, it is frequent to add to the binders the most diverse fillers and additives, capable of influencing favorably, for example on the porous structure of a hardened cement, or improving the behavior in ltripage of suspensions on filtering machines. As additives, it is possible in particular to consider materials such as fly ash, kieselgur, quartz flour, sandstone powder, kaolins, blast furnace slag, pozzolans, etc.

 There are already countless publications in the literature on the use of various natural, synthetic, organic and mineral fibers. For cement reinforcement, wool, cotton, silk, polyamide, polyester, polyacrylonitrile, polypropylene and polyvinyl alcohol fibers have already been studied. We know of mIPe works on glass fibers, steel, aramid and carbon. So far, none of these fibers has given good results in terms of reinforcing a cement matrix.

 The requirements for fibers used to reinforce cement and other binders that are hydraulically setting are extremely stringent.

 In terms of chemical characteristics, resistance to alkalis in hot saturated calcium hydroxide solutions is an absolute condition. The chemical constitution of a suitable fiber must therefore have as high a concentration as possible in polar functional groups, so that a sufficient affinity for the cement can be obtained.

 In terms of physical characteristics, the fibers must agree with those of hydraulic binders. In the case of cement, it is known that this material has a certain brittleness and can break for an elongation of only about 0.3%. It is therefore deduced therefrom that in cement, the reinforcing fibers which exhibit the best reinforcing action are those which oppose, for minimum elongation, the highest forces. However, it should be noted here that some fibers may change their properties when used in an aqueous suspension of cement, without anyone being able to predict to what extent such a change will occur. However, having good intrinsic properties may not exert the expected action in the cement, since the reinforcing properties change during the hydration processes of the cement.

 In addition to the above physical properties, it is also important that the fibers out of their transformation into fiber cement products by the draining process disperse well in a dilute aqueous suspension of cement, and remain evenly distributed even in the event of adding other additives. Good results have been obtained with fibers or mixtures of fibers in ranges of lengths up to 30 nm, it being understood that sections of fibers of uniform lengths can be used, for example in lengths from 3 to 24 mm, or in mixed lengths.

In certain cases, it has proved advantageous to subject the fibers to prior grinding having a cutting and / or fibrillation effect.

 As fibrous material, fibers having a titer of 0.1 to 15 dtex, in particular 0.5 to 15 dtex, can be considered.

 If we now study the fibers existing on the market according to the properties mentioned above, we can exclude all known textile types, such as polyester, polyacrylonitrile, polyamide, viscose, cotton and wool fibers, because their mechanical behavior is too different from that of hydraulic binders.

 High tenacity organic fibers based on polyester, polyvinyl alcohol or rayon, such as those used for example in the tire industry, it is true that their mechanical properties are superior to the known types of textile fibers. These favorable properties are however greatly reduced under the operating conditions (alkaline solution) of the manufacture of fiber-reinforced cement.

Other high performance fibers known in the art, such as glass fibers, carbon fibers and aramid fibers are either attacked by alkalies or are not very economical, and their affinity for the cement matrix moreover leaves something to be desired. They will therefore not preferably be used as reinforcement of the cement matrix.

 The object of the invention is therefore the use of a fibrous material already opposing for a low elongation a resistance force as high as possible, which is as little modified as possible by a suspension of cement and which communicates an increased mechanical resistance to cement-fiber composite after hardening.

 Polyacrylonitrile fibers are known to be among the fibers with the most common polar functional groups.

T
These fibers are produced in large quantities and are used mainly in the clothing sector. However, it has not been possible to obtain, with any of the types of polyacrylonitrile fibers existing on the market, a sufficient reinforcement action for hydraulic binders. The cause can be sought in the relatively low resistance and high elongation at break of these fibers. All the commercial polyacrylonitrile fibers contain, to improve their dyeability, their flexibility and to facilitate the spinning process, 4 to 15% of one or more comonomers such as vinyl acetate, methyl acrylate , methyl methacrylate and vinyl derivatives containing carboxy, sulfo or pyridine groups. It is true it is possible to improve to some extent the mechanical properties of these fibers, that is to say to reduce their elongation to breakage and increase their resistance by optimizing the fiber drawing processes after the filament formation operation behind the spinning nozzle. This technique is also well known to fiber manufacturers. However, the intrinsic properties of fibrous materials impose practical limits on this optimization. If a cement matrix is therefore reinforced with such optimized fibers, there is a certain improvement in the reinforcing effect with respect to a cement matrix compared to the conventional acrylic fibers mentioned, but this improvement is not not yet satisfactory.

 It has been found in the present invention that the aims pursued can be achieved by using polyacrylonitrile fibers made from a polymer having a molar concentration of acrylonitrile unit of at least 98%, and a relative viscosity, measured in 0.5% solution in dimethylformamide, of at least 2.60. These fibers are superior, when used in cement, to other high-tenacity polyacrylonitrile fibers having the conventional composition described above, in that they retain their initial properties in the alkaline aqueous suspension of cement.

 The invention therefore relates to solid products containing fibers and hydraulic binders, which are characterized in that they contain, as reinforcing fibers and / or as fillers, fibers of acrylonitrile polymers in which the molar concentration of acrylonitrile units is 98 to 100%.

 The fibers used are advantageously pretreated by the process in accordance with Swiss patent application no. 1297 / 79-0 (French patent 80/02733), which process is cited as forming part of the present description in its entirety.

 The fibers used in accordance with the invention and which can if necessary be used with other fibers, are advantageously added as reinforcement in an amount such that the total proportion of the fibers in the cured product is from 0.1 to 30 % by weight, preferably from 1 to 12% by weight and in particular from 1 to 8% by weight. They have lengths up to 30 mm, but sections of fibers can be used in mixed lengths. In specific cases, it has proved advantageous to pretreat the fibers by grinding having a cutting and / or fibrillation effect.

 As fibrous material, fibers having a titer of 0.1 to 15 dtex, in particular 0.5 to 15 dtex, can be considered.

 The transformation of these fibers into products in accordance with the invention is carried out in a known manner, for example on a Hatschek machine as indicated above, after mixing the binders with water and the usual adjuvants and additives, such as defined in claim 9.

The manufacture of fibers according to the invention does not fall within the scope of this patent application. It is carried out for example by a known method of dry spinning, or preferably in the wet. These high tenacity fibers having low elongation at break can for example be prepared as follows
1,700 g of a polymer consisting of 99.5% of acrylonitrile and 0.5% of methyl acrylate having a relative viscosity (measured in 0.5% solution in dimethylformamide (DMF)) of 2 are dissolved. , 85 in 8300 g of
DMF, to form a homogeneous spinning solution. After filtration, this solution is passed under pressure, at 16.2 ml / min., Through a 100-hole die (hole diameter 0.06 mm) in a precipitate bath. tation consisting of 50% DMF and 50% water, at 500 C.

 The filaments obtained are drawn, after an immersion length of 50 cm, at a speed of 5.5 m / min. They are stretched in two successive stretching baths, consisting of 60% DMF and 40% water, at a temperature of 99 ° C. at 29.3 m / min, they are washed and brightened with water in other baths, then they are dried on two heating rollers at surface temperatures of 140 or 1850C, allowing a shrinkage of 0.7 m / min. The residence time on the first roller at 140 ° C. is chosen so that the filament is shiny when it comes out of the roller, therefore no longer has vacuoles. The filament is drawn from the second roller at 33.3 m / min- and stretched through 4 heated plates which come into contact with the wire alternately from above and from below, at temperatures of 145, 145, 165 and 1800 C, at 95 m / min, using a unheated roll, then it is wound on coils. The effective total stretching ratio is 1: 17.3 the mechanical properties of the filaments thus obtained (type A) are collated in Table I.

 Particularly suitable types of fibers can also be obtained by an additional fixing treatment, for example with hot contact surfaces, hot air, hot water, steam, etc. after contact stretching (type B).

 For the fibers of type B used in the embodiment below, the fixing was carried out on two heated rollers without allowing removal. The surface temperatures of the rollers were 210 and 2300 C.

The textile and mechanical characteristics of these fibers are shown in Table I. Thanks to the fixing treatment, the shrinkage at the boil could be reduced from 9.5% to 2.0%.

 For the spinning process described above (variant A), another polymer which can be used in accordance with the invention has also been transformed into fibers, consisting of 99% of acrylonitrile units and 1% of methyl acrylate units having a relative viscosity. of 2.84 (type C), and on a comparison basis a conventional polymer with 96% of acrylonitrile units and 4 d of methyl acrylate units, having a relative viscosity of 2.78 (type D). By way of comparison, a commercial polyacrylonitrile fiber was also studied, intended for textile applications (type E), having the following composition: 93.5% of acrylonitrile units, 6% of methyl acrylate units and 0, 5% methallyl sulfonate.

 The mechanical properties of the fibers obtained are collated in Table I.

TABLE I Mechanical properties of high tenacity polyacrylonitrile fibers containing various molar concentrations of acrylonitrile (measured on isolated fibers)
TYPE A TYPE B TYPE C TYPE D TYPE E
TITLE (Dtex) 2.9 2.9 2.9 2.9 2.9
RESISTANCE CN / tex 83 74 82 85 35
ELONGATION AT 8.0 10.0 8.1 7.9 20
BREAK%
In the examples and comparative tests below and carried out under analogous conditions, the ability of these five types of fibers to reinforce the cement was brought out.

Preparation of mixtures for use on a Iiatschek machine
Pilot - Mixture 1 (control mixture).

 In a mill with wheels, one crushes during 30 minutes 153 kg of asbestos (NO 4 / NO 5 = 1/3) with 62 1 of water. The open asbestos is then introduced into a rapid vertical mixer in which there are 1.5 m3 of water. After having stirred for 10 minutes, the mixture is pumped in a horizontal mixer and 1 ton of cement with a specific surface of 3000 to 4000 square meters / g is added thereto. This suspension of asbestos-cement is then sent, yue of its subsequent implementation, to a vat of a pilot Hatschek machine.

Mixtures 2 to 4 according to the invention and other comparative mixtures 5 to 7
In a solvopulper, 80 kg of old paper (without glossy paper) and 15 kg of aluminum sulphate in 1 m3 of water are reduced to the pulp state for 10 minutes. This fiber suspension is diluted to 2.5 m3 and 20 kg of the polyacrylonitrile fiber samples to be tested are added, in 6 mm sections, after which mixing is continued for 5 minutes. Then 45 kg of powdered calcium hydroxide are added and stirring is continued for 12 minutes. After transfer to a cement mixer, 1000 kg of a cement having a specific surface of approximately 3000 to 4000 cm 2 / g are incorporated therein, for 15 minutes.

To improve the retention of the cement, 80 g of a polyacrylamide ("Separan NP - 10",
Dow Chemical Corp.) as a 0.2% aqueous solution. The mixture obtained is sent to the vat of a pilot Hatschek machine.

 Mix 7 was prepared without polyacrylonitrile fibers, from waste paper and cement only.

Preparation of test plates.

With mixtures 1 to 7 above, we prepare on a machine
Hatschek pilot with 7 format cylinder turns, 6 mm thick plates which are pressed between oiled sheets for 45 minutes in a stacking press, under a specific pressure of 250 KPa, until reaching a thickness 4.8 mm. The plates are tested after a maturation time of 28 days, after having been immersed in water for 3 days. The test results are collated in Table II.

TABLE II
Test results of cementitious plates reinforced with polyacrylon fibers sorted
RESISTANCE TO RESISTANCE DENSITY
MIXING NO BENDING ON PLATE SHOCK
SPECIAL
N / mm2 N / mm / mm2 g / cm 3
1) Asbestos (mixture
witness) 29, 2 1.8 1.76
2) PAN type A fibers
99.5% of patterns
acrylonitrile 26.3 2.7 1.76
3) PAN type A fibers
(called type B) to
99.5% acrylo patterns
nitrile, fixed 26.2 2.7 1.77
4) PAN fibers, type C
99.0% of patterns
acrylonitrile 25.9 2.6 1.74
5) PAN fibers, type D
(comparative mixture)
96.0% of patterns
acrylonitrile 21.8 2.7 1.76
6) PAN fibers, type E
(comparative mix) to
93.5% of patterns
acrylonitrile 20.2 2.6 1.75
7) Cellulose cement mixture
without PAN fibers (mixture
18.5 2.2 1.74
The flexural strengths of the fiber-reinforced cement slabs show this surprising fact that when using
PAN having% in acrylonitrile units close to or> 99% can make an important contribution to the strengthening of a cement matrix. The only initial values of the mechanical properties do not make it possible to interpret the importance of this reinforcement because it is found that between the fibers of Type ABC on the one hand and the fibers of Type D on the other hand the mechanical properties do not exhibit significant deviation.

The specific impact resistance is not influenced by the nature of the polyacrylonitrile fibers used. The specific impact resistance of asbestos-cement wafers is clearly surpassed by that of fiber-cement wafers. For practical use, in addition to impact resistance, bending resistance is of decisive importance. As shown in the table above, the fibers usable according to the invention give much higher values than the comparative fibers of types D and E.

In other test examples, it will be shown how the fibers used according to the invention behave in various cutting lengths and associated with usual loads. The tests were carried out as already described in the case of Examples 2 to 7, the additional fillers being added to the cement mixer after introduction of the cement. The fibers used in accordance with the invention were used as follows
MIX 8
Portland cement 81.5%
Filtrating silencer dust (5102 content = 98.8%, average particle size = 0.5 u 12.0%
Cellulose fibers (45 SR) 4.0%
PAN fibers, type B: 2.5%
These fibers were cut beforehand to 18 mm, then subjected to additional grinding in a knife mill ("Condux" type CS 500/600 - 4) .We obtained the distribution of the lengths of fibers
4.7 mm 10.2%
1.17 mm 19.6%
0.42 mm 33.2%
0.15 mm 26.9%
0.075 mm 9.7%
<0.075 mm 0.4%
MIX 9
Portland cement 82%
Blast furnace slag 8%
Rock wool 4%
PAN fibers / 6% cellulose blend
To obtain the premix of PAN fibers and of cellulose, 3 parts of PAN fibers, produced according to a variant of A, having a content of acrylonitrile motif content of 98 mol%, cut to a cutting length of 8 mm, are previously ground, with 2 parts of cellulose with sulphate, in a ball mill, so as to carry out a fibrillation. This premix is added at a rate of 6% in the aqueous suspension defined above.

 The two mixtures 8 and 9, as described above, are transformed into test plates on a pilot Hatschek machine, and tested after curing for 28 days. The results are collated in Table III.

TABLE III
Test results of wafers prepared from a cement reinforced with polyacrylonitrile fibers and containing fillers.

RESISTANCE TO RESISTANCE DENSITY
BENDING IN SHOCK
HELANGE NO SPECIAL PLATES
N / mm2 N / mm / mm2 g / cm3
8 26.4 2.3 1.76
9 26.6 2.4 1.85
The results of Table III show that the fibers used in accordance with the invention, even prepared in different ways and combined with various additives, give good resistance values.

The mixture 8 is particularly easy to implement. However, higher densities have been obtained with mixture 9.

Claims (17)

 1. Solid products containing fibers, made with hydraulic binders, characterized in that they use fibers of acrylonitrile polymers, in which the molar concentration of acrylonitrile units is 98 to 100%, as fibers reinforcement and / or as fillers.  2. Product according to claim 1, characterized in that the fibers have a resistance of at least 50 CN / tex and an elongation at break of 15 ss minimum.  3. Product according to any one of claims 1 and 2, characterized in that the fibers have a uniform length of 3 to 24 mm.  4. Product according to any one of claims 1 and 2, characterized in that the fibers have a non-uniform length distribution up to 30 mm.  5. Product according to any one of claims 3 or 4, characterized in that the fibers have undergone a fibrous grinding treatment.  6. Product according to any one of the preceding claims, characterized in that the fibers have a titre of 0.1 to 15 dtex.  7. Product according to any one of the preceding claims, characterized in that it is prepared by a draining process, using for example winding machines with cylindrical screen and endless cloth, injection facilities, press filters, press belt filters, wringer belt filters and / or vacuum suction filters.  8. Product according to any one of the preceding claims in the form of flat plates, profiled plates, pipes and special parts, in particular for building and public works.  9. A method of manufacturing the products according to claim 1, characterized in that hydraulic binders are mixed with water, the usual adjuvants and additives and fibers of acrylonitrile polymers having a molar concentration of acrylonitrile units of 98 to 100% as reinforcing fibers and / or as fillers, in that the mixture is drained, if necessary partially, in this cotton brings it into the desired form and in that it is allowed to harden. .  10. Method according to claim 9, characterized in that the fibers have a resistance of at least 50 CN / tex and an elongation at break of 15% at most.  11. Method according to any one of claims 9 or 10, characterized in that the fibers have a uniform length of 3 to 24 mm.  12. Method according to any one of claims 9 or 10 characterized in that the fibers have a non-uniform length distribution, up to 30 mm.  13. Method according to any one of claims 11 or 12 characterized in that the fibers have been treated by fibrous grinding.  14. Method according to any one of claims 10 to 13, characterized in that the fibers have a titre of 0.1 to 15 dtex.  15. Method according to any one of claims 10 to 14, characterized in that the mixture is partially drained before shaping, for example using winding machines with cylindrical sieves and endless fabric, of installations injection, filter presses, press belt filters, wringer belt filters and or vacuum suction filters.  16. Method according to any one of claims 10 to 15, characterized in that the mixture is shaped into flat plates, profiled plates, pipes or special parts, in particular for building or public works.  17. Use of the products according to claim 1, as a building element.