Fibre-containing products manufactured with hydraulic binders

(74) Prosecutor Civil Service. Jan E. Hetgerud,

Bryns Patentkontor A / S, Oslo.

(30) Priority requested 20.03.81, Switzerland, No 1919/81.

(54) DESCRIPTION OF THE INVENTION FIBEROUS PRODUCTS MANUFACTURED WITH HYDRAULIC BINDING AGENTS AND THE METHOD OF PRODUCING THEREOF.

(57) Summary

For the reinforcement of products made of acrylonitrile 98%.

hydraulic binders use fibers of polymerisates with a molar concentration of the acrylonitrile unit of at least

The fibers advantageously exhibit one

15%.

strength of at least 50 cN / tex and a breaking extension of at most

These fibers, after bonding, provide products with good flexural strength and excellent impact resistance.

(56) Published publications None.

BACKGROUND OF THE INVENTION Field of the Invention This invention relates to fiber-containing products and, in particular, to fibrous solid products made from hydraulic binders.

The invention also relates to a process for the manufacture of such products.

Among the usual building materials are fiber-reinforced cement products made from asbestos and cement, already known for decades. In the asbestos cement industry, manufacturing processes for building elements according to Wickelverfahren after L Hatschek (AT-PS 5970) are still widely used. The technology for this production process is e.g. described in detail in a book by Harald Klos, entitled Asbestos Cement, published by Springer Verlag in 1967.

This known process for the preparation of e.g. asbestos cement pipes and plates are based on the use of circular screening machines. Thereby, a diluted asbestos cement suspension is wound up via a fabric box and a screen cylinder in the form of a web, by means of format rollers and tube cores up to the desired thickness. For the manufacture of corrugated sheets, the asbestos cement floor can be cut after rolling to the desired thickness and placed between oiled corrugated sheets for curing.

In recent years, it has now been found that the frequently used asbestos is no longer available in unlimited quantities, and must be counted towards those natural substances whose supplies are likely to be used up most quickly. Storage sites for commercially viable asbestos are only distributed in a few countries, which in turn leads to unwanted dependence, which is already reflected in rising prices.

Thus, it is desirable to use new fibers as reinforcing fibers and as fillers for hydraulic binders, e.g. for cement reinforcement, fibers suitable for use in the processing industry, e.g. the asbestos cement industry, and widespread fiber-based product manufacturing facilities where the products have the desired mechanical properties.

For the sake of simplicity, the present disclosure refers to cement as the preferred binder. However, all other hydraulically bonding binders can be used instead of cement. Suitable hydraulically bonding binders include a material containing an inorganic cement and / or an inorganic binder or adhesive that is cured by hydration. Particularly suitable binders which can be cured by hydration include e.g. portland cement, alumina melt cement, iron portland cement, trace cement, blast furnace cement, plaster, the calcium silicates arising from autoclave treatment and combination of some of these binders.

To the binders are also frequently added the various fillers and additives, such as e.g. positively affects the pore structure of a cement stone, or e.g. can improve the dewatering behavior of the slurry on the dewatering machine. Such additives include fly ash, silica dust, quartz flour, stone flour, kaolin, blast furnace slag, puzzolan etc.

In the literature there are already numerous publications for the use of the various natural, synthetic, inorganic and organic fibers. For reinforcement for cement, wool, cotton, silk, polyamide, polyester, polyacrylonitrile, polypropylene and polyvinyl alcohol fibers have already been investigated. Likewise, works are known on glass, steel, aramid and carbon fibers. Of all these fibers it has hitherto been found that none has proved particularly suitable.

The requirements for fibers to be used for the reinforcement of cement and other hydraulic bonding binders are very strict:

In the chemical requirements, above all, the alkali resistance in saturated calcium hydroxide solution at elevated temperatures is an absolute prerequisite. In view of the chemical structure of a suitable fiber, it can be said that the highest possible concentration of polar functional groups must be present, so that a satisfactory affinity for cement can be obtained.

Furthermore, the physical fiber data must match the physical data of the hydraulic binders for some special properties. With cement it is known that this material exhibits some brittleness and e.g. it can be broken up by an expansion of about 0.3%. For cement reinforcing fibers, such fibers exhibit the best reinforcing effect, the effect that puts the greatest forces towards minimal expansion. Thereby, however, it is to be noted that fibers treated with a regular cement slurry can change their properties, whereby it is not foreseeable on what scale such a change can occur. This means that despite good mechanical starting values ​​for a fiber, it is possible that this does not produce the desired effect in the cement as the fiber properties change during hydration.

In addition to these aforementioned physical properties of fibers, it is equally important that the fibers be dispersed well in a dilute aqueous cement slurry, and also remain homogeneously distributed by the addition of additional additives when these fibers are to be further processed into fiber cement products by dewatering methods. It has been found advantageous to use fibers or fiber blends in the length range up to 30 mm, whereby the fiber cuts are uniform, e.g. in lengths from 3-24 mm, or in mixtures of lengths. In special cases, it has been found advantageous to pre-treat the fibers by an up-cutting or fibrillating paint. Especially as fibers are used with a titer of 0.1-15 dtex, especially 0.5-15 dtex.

If the commercially available fibers are now being examined for the above-mentioned properties, all known textile fiber types, such as polyester, polyacrylonitrile, polyamide, viscose, cotton and wool fibers, must be peeled out as their mechanical behavior differs too much from those for the hydraulic binder.

High-strength organic fibers based on polyester, polyvinyl alcohol or rayon, such as e.g. used in the automotive tire industry, although textile fiber types are superior in terms of mechanical properties, these valuable properties are, however, greatly reduced under the wet alkaline process conditions in the manufacture of fiber cement. Other high-performance fibers known in the art, such as glass fibers, carbon fibers and aramid fibers, are either not alkali resistant or not economical, and sometimes the affinity for the cement matrix is ​​too poor. Therefore, for use as cement reinforcing fibers, they are not considered.

The object of the present invention is therefore to use a fiber material which already exhibits, at a low expansion, the highest possible resistance, which is changed as little as possible by a cement slurry, and which gives cement-fiber composite material increased mechanical strength after curing.

It is known that polyacrylonitrile fibers are among the most widely used fibers with polar functional groups. These fibers are produced in large quantities and are used above all in the clothing sector. However, until now no sufficient reinforcing effects could be achieved for hydraulically bonding binders available on the market obtainable polyacrylonitrile fiber types. The reason may well lie in the relatively low strength and high fracture extensions for these fibers. All commercially available polyacrylonitrile fibers contain, for improving the staining ability, the textile grip, and the ease of thread forming process 4 - 15% of one or more comonomers, such as vinyl acetate, methyl acrylate, methyl methacrylate, and carboxy, sulfo or pyridine group-containing vinyl derivatives. Admittedly, it is possible to improve the mechanical properties of these fibers to a certain extent, i.e., to reduce fracture expansion and to increase the strength. This can be done by the well-known optimization of the tensile process of the fibers after the fiber formation after the spinning nozzle among the fiber producers. However, this optimization has certain practical limits due to. the inherent properties of the fiber materials. If a cement matrix is ​​reinforced with such fibers, it also turns out to be a certain, but not entirely satisfactory improvement in the reinforcing effect over a cement matrix with the conventional acrylic fibers mentioned.

It has now surprisingly been found that it is possible to use polyacrylonitrile films for the desired purposes, in which a polymer having a molar concentration of at least 98% acrylonitrile units and a relative viscosity of at least 2.60 (measured as 0.5%) is used. in solution in dimethylformamide). Such fibers are superior to other high-strength polyacrylonitrile fibers of the above-described conventional compositions in cement use, retaining their original properties in the aqueous-alkaline cement slurry, in particular retaining their strength properties such as e.g. a high A module e.g. in the range 1000 cN / tex - 2000 cN / tex.

According to this invention, the present invention relates to fibrous products of the prior art and are characterized in accordance with claim 1.

The invention further relates to a process for the production of fibrous products of the preamble mentioned and characterized in that according to claim 11.

Advantageously, the fibers used can be pretreated according to the invention. frem6

152002 once small teas described in DE-OS 30 02 484.

The fibers used in accordance with the invention which may be used in combination with other fibers are advantageously mixed in such an amount that the total fiber content of the cured product is from 0.1 to 30% by weight, and preferably from 1 to 12% by weight, as pure reinforcing fibers especially from 1-8% by weight. The fibers are generally used in the length range up to 30 mm, whereby the fiber cuts may be uniform, e.g. within the range of 3-24 mm, or they can be used in mixtures of lengths. In particular fibers, it has been found advantageous to pre-treat the fibers by a cutting and / or fibrillating grinding.

In particular, fibers having a titer of 0.1-15 dtex, especially 0.5 - 15 dtex, are used as fiber material.

The processing of such fibers into products according to the invention takes place in a known manner by mixing the binder of water and the usual adjuvants and additives, as defined in claim 10, e.g. on a Hatschek machine as mentioned above.

The production of the fibers according to the invention is not subject to the application; by a known dry or preferably wet-spinning method. These high-strength fibers with a low fracture extension can e.g. prepared as follows:

1700 g of a polymer of 99.5% acrylonitrile and 0.5% acrylic acid methyl ester having a relative viscosity of 2.85 (measured as 0.5% solution in dimethylformamide, DMF), dissolves in 8300 g DMF to a homogeneous spin solution . After filtration, the solution is pressurized at a rate of 16.2 ml / min through a 100-hole nozzle diameter of 0.06 mm into a precipitation bath consisting of 50% DMF and 50% water and exhibiting a temperature of 50 ° C.

The obtained threads are pulled off after a dip of 50 cm at a speed of 5.5 m / min. In two consecutive tensile baths, consisting of 60% DMF and 40% water, they are stretched at a temperature of 99 ° C to 29.3 m / min, in additional baths in water they are washed and stripped, and finally dried in two heated duo drums with heating temperatures of 140 and 140 respectively. 185 ° C while allowing a shrinkage of 0.7 m / min. The residence time of the first duo with a temperature of 140 ° C was chosen so that the threads were shiny when leaving the duo, ie they did not exhibit any more vacuoles. From the second duo, the wires were pulled off at 33.3 m / min and stretched over four heated plates, which touched the wires alternating from top to bottom at temperatures of 145, 145, 165 and 180 ° C, at 95 m / min. a non-heated duo, and then wound on coils. The effective overall tensile ratio was 1: 17.3, and the mechanical properties of the strands thus obtained (type A) are summarized in Table 1.

Particularly suitable fiber types can also be obtained by a further fixation treatment, e.g. for hot contact surfaces, hot air, hot water, water vapor etc. according to contact pull method.

For the fibers of type B used in the following example, the fixation was performed on two heated duos without allowing shrinkage. The surface temperature of these dues was 210 and 230 ° C. The textile mechanical data for these fibers is given in Table 1. At the fixation treatment, the boiling shrinkage could be lowered from 9.5 - 2.0%.

Ih. the above described spin method (variant A), a polymer of 99% acrylonitrile units and 1% acrylic acid methyl ester units having a relative viscosity of 2.84 (type C) and a conventional polymer with 96% acrylonitrile units and 4% was also prepared. acrylic acid methyl ester units having a relative viscosity of 2.78 (type D). For comparison, a commercially available polyacrylonitrile fiber for textile purposes (type E) was also tested with the following composition:

93.5% acrylonitrile units, 6% acrylic acid methyl ester units and 0.5% metalyl sulfonate.

The mechanical properties of the resulting fibers are summarized in Table 1.

Fibers of acrylonitrile polymeric materials having a molar concentration of at least 98% acrylonitrile units, as used in the present invention, exhibit a sufficient alkali resistance, even at elevated temperatures, to meet the requirements mentioned above.

Table 1

Mechanical properties of high-strength polyacrylonitrile fibers with different molar concentrations of acrylonitrile (measured as single fibers)

<td></td><td>Type A 99.5% AN</td><td>Type B 99.5% AN</td><td>Type C 99.0% AN</td><td>Type D 96.0% AN</td><td>Type E 93.5% AN</td>

<td>Try to*</td><td></td><td></td><td></td><td></td><td></td>

<td>Titer dtex</td><td> 2,9</td><td> 2,9</td><td> 2,9</td><td> 2,9</td><td> 2,9</td>

<td>Firmness cN / tex</td><td> 83</td><td> 74</td><td> 82</td><td> 85</td><td> 35</td>

<td>A module cN / tex</td><td> 1490</td><td> 1420</td><td> 1510</td><td> 1410</td><td> 1100</td>

<td>at break</td><td> % 8,0</td><td> 10,0</td><td> 8,1</td><td> 7,9</td><td> 20</td>

<td>Sample B **</td><td></td><td></td><td></td><td></td><td></td>

<td>Firmness cN / tex</td><td> 81</td><td> 74</td><td> 80</td><td> 70</td><td> 23</td>

<td>A module cN / tex</td><td> 1400</td><td> 1350</td><td> 1490</td><td> 810</td><td> 630</td>

<td>at break</td><td> % 9,1</td><td> 10,8</td><td> 8,3</td><td> 12,0</td><td> 35</td>

Sample A *: Single fiber test under normal conditions, 20 ° C, 65% relative humidity.

Sample B * *; The fibers were used for testing the cement ambient resistance prior to the usual test in accordance with A by dipping for 24 hours at 80 ° C in an aqueous slurry of so-called Portland cement in 1 liter of water, and then conditioned for Sample A.

For the assessment of these five fiber types for their ability as cement reinforcing fibers, the following examples and comparative experiments are described under analogous conditions.

Preparation of the mixture for processing on a Hatschek machine

Mixture 1 ____ (Comparative Example)

In a collision course 153 kg of asbestos was treated (quality 4:!

quality 5 = 1: 3) with 62 liters of water for 30 min. The digestive | tede was then introduced into a fast-running vertical blank

3i there, containing 1.5 m of water. After stirring for 10i

In mine, it was pumped into a horizontal mixer and mixed in

2i tonnes of cement with a specific surface area of ​​3000 - 4000 cm / |

g. This asbestos cement slurry was then transferred | to a Hatschek machine for further processing.I i

Mixtures 2 to 4 and Comparative Examples 5 to 7

In a solvokoker, 80 kg of old paper was cooked (without glossy;

paper) and 15 kg of aluminum sulfate for 1 m³ water for 10 min. This fiber suspension was diluted to 2.5 m³and, kg of the polyacrylonitrile fiber samples to be examined were added, in these having a cut length of 6 mm, after which it was further cooked for 5 minutes. Then, 45 kg of powdered calcium hydroxide was added and boiled for a further 12 minutes. After re-pumping in a cement mixer, 1000 kg of cement with a specific surface area of ​​about 3000 - 4000 cm / g were mixed in;

my.;

In order to improve the cement retention capacity, it was in fiber.

the cement slurry also mixed 80 g of a polyacrylamide (Separan NP-10) in the form of

0.2% aqueous solution. The present composition was transferred by means of ordinary apparatus in a Hatschek machine.

Mixture 7 was prepared without polyacrylonitrile fibers, only of old paper and cement.

Preparation of the test plates

With the above compositions 1-7, on a Hatschek machine with 7 turns of the format roller, plates of 6 mm thickness were prepared which were pressed between oiled tin plates for 45 minutes in a stack press with a specific press pressure of 250 bar to a thickness of 4.8 mm. The plates were tested after a set time of 28 days, after the plates were watered for 3 days. The test results are listed in Table 2.

Table II

Test results for cement slabs reinforced with polyacrylonitrile fibers.

<td>Blandingsnr.</td><td>Bending tensile strength N / mm 2</td><td>Specific impact toughness 2 N / mm / mm</td><td>Platedensitet , ³g / cm</td>

<td>1) Asbestos (comparative example)</td><td> 29,2</td><td>OE OE 1.1</td><td> 1,76</td>

<td>2) PAN fibers Type A with 99.5% acrylonitrile units</td><td> 26,3</td><td> 2,7</td><td> 1,76</td>

<td>3) PAN fibers Type A with 99.5% acrylic nitrile units, fixed</td><td> 26,2</td><td> '2,7</td><td> 1,77</td>

<td>4) PAN C Type fibers with 99% acrylic nitrile units</td><td> 25,9</td><td> 2,6</td><td> 1,74</td>

<td>5) PAN fibers Type D (Comparison six pads) with 96% acrylic nitrate units</td><td> 21,8</td><td> 2,7</td><td> 1,76</td>

<td colspan="2">6) PAN fibers Type E (comparative example) with 93.5% acrylonitrile units 20.2</td><td> 2,6</td><td> 1,75</td>

continue, next page

7) Cellulose cement blend without PAN fibers (Comparative Example) 18.5 2.2 1.74

The flexural strength of the fiber reinforced cement sheets shows that when using polyacrylonitrile fibers having substantially the same mechanical starting values, very surprisingly only the polyacrylonitrile groups type A and type B used, with 99.5% acrylonitrile units, and type C with 99% acrylonitrile units, are in capable of providing substantial reinforcement in a cement matrix. The specific impact strength is not affected by the type of polyacrylonitrile fiber used. The specific impact toughness of the asbestos cement slabs is greatly exceeded by that of the fiber cement slabs. For the practical application, besides the impact toughness, the bending tensile strength is also of decisive importance. As can be seen from the above table, the fibers used according to the invention give substantially higher values ​​than the type D and type E. comparative fibers. In further comparative examples, it will be shown how the fibers used in the invention also prove useful in different fiber dimensions and in combination with ordinary fillers. The tests were carried out as before with mixtures 2-7, whereby the additional fillers were added to the cement mixer after introduction of the cement. The fibers used according to the invention were used as follows:

Mixture 8

Portland cement 81.5%

Silicon dioxide filter dust (SiC 2 content = 98.8% average particle sizes = 0.5 µm) 12.0%

Cellulose fibers (45 ° SR) 4.0%

Type B PAN fibers 2.5%

These fibers were pre-cut to 18 mm and then ground on a cutting mill (Condux type CS 500 / 600-4).

This resulted in the following fiber length distribution:

<td colspan="2">4 mesh</td><td> 10,2%</td>

<td> 14</td><td>II</td><td> 19,6%</td>

<td> 35</td><td>it</td><td> 33,2%</td>

<td> 100</td><td>II</td><td> 26,9%</td>

<td> 200</td><td> 11</td><td> 9,7%</td>

<td> &gt;200</td><td> 11</td><td> 0,4%</td>

(mesh means here; masks / 2.54 cm)

Mixture 9

Portland cement 82%

Blast furnace slag 8%

Mineral wool 4%

PAN fibers / cellulose mixture 6% share PAN fibers made according to variant A having a content of 98 mole% of acrylonitrile units and having a cut length of 8 mm was pre-fibril milled together with 2 parts of sulfate cellulose in a boiler refiner. This mixture was added in an amount of 6%.

The two blends 8 and 9 were prepared as described above on a Hatschek sample plate machine and tested after 28 days curing. The results are summarized in Table III.

Table III

Test results for cement slabs reinforced with polyacrylonitrile fibers and fillers.

<td>Blandingsnr.</td><td>flexural</td><td>specific</td><td>Platedensi-</td>

<td></td><td>strength</td><td>impact resistance</td><td>tet</td>

<td></td><td>N / ram³</td><td>2 N / mm / mm</td><td>g / cm³</td>

<td> 8)</td><td> 26,4</td><td> 2,3</td><td> 1,76</td>

<td> 9)</td><td> 26,6</td><td> 2,4</td><td> 1,85</td>

<td>results</td><td colspan="3">Table III shows that in accordance with the invention,</td>

<td>turned fibers</td><td>also processed</td><td>on different</td><td>way and in the coming</td>

bination with different additives exhibits good firming values. While blend 8 is particularly easy to process, higher densities with blend 9 could be obtained.