RU2145368C1 - Method of producing cellulose fibers, rubber articles and tire - Google Patents

Abstract

FIELD: methods of production of cellulose extrudates from optically anizotropic solutions. SUBSTANCE: cellulose extrudates are produced from optically anizotropic solution containing 94-100 wt.% of the following components: cellulose, phosphoric acid and/or its anhydrates and water. Extrudates are produced by solution extrusion and coagulation of formed extrudates. They are additionally treated to obtain their degree of acidity equalling at least 7, strength preservation efficiency of 80% or above, and content of phosphorous combined with cellulose of 0.02-3.00 wt.%. EFFECT: higher heat resistance of fibers and their efficient use as reinforcing material. 5 cl, 1 tbl, 3 ex

Description

This invention relates to a method for producing cellulose extrudates from an optically anisotropic solution containing 94-100 wt.% Of the following components:
- cellulose,
- phosphoric acid and / or its anhydrides,
- water,
by extrusion of the solution and subsequent coagulation of the resulting extrudates.

 Such a method is disclosed in a pending application of the same applicant, which is based on Dutch patent application NL 9401351.

It was found that the fibers obtained by extrusion and coagulation of the solution mentioned above are particularly sensitive to heat treatment. For example, it was found that heat treatment for 5 minutes at 175 ^o C can lead to a decrease in the tensile strength of the fibers by about 80% compared with the initial tensile strength.

 The sensitivity of the extrudates to heat treatment can be reduced by additional processing of the extrudates. The essence of the invention lies in the fact that in such a method as mentioned above, the extrudates are further processed so that after this additional processing, the degree of acidity of the extrudates is at least 7.

 In the present description, a solvent consists, by definition, of added phosphoric acid and / or its anhydrides and of all water present in the solution, which is not chemically bound. For this reason, water released from cellulose, which is usually added last, in this description is considered part of the solvent, as is water from substances that belong to the "other components", and these substances can be added at any time during the preparation of the solution.

The term "phosphoric acid" in this application means all inorganic acids of phosphorus, including mixtures thereof. Phosphoric acid is an acid with pentavalent phosphorus, i.e. H ₃ PO ₄ . Its anhydrous equivalent, i.e. anhydride, also known as phosphorus pentoxide (P ₂ O ₅ ). Depending on the amount of water in the system, in addition to phosphoric acid and phosphorus pentoxide, there are a number of pentavalent phosphorus acids that have the ability to bind water, which occupy an intermediate position between phosphorus pentoxide and phosphoric acid. Alternatively, you can use solvents containing, say, phosphoric acid, with a concentration of phosphoric acid less than 100%.

 Due to the reaction between phosphoric acid and cellulose, the solution may contain phosphoric derivatives of cellulose. It is believed that these cellulose derivatives also relate to components constituting a 94-100 wt.% Solution. Where the weight percentages of cellulose in solution described in this description relate to phosphorus derivatives of cellulose, they refer to values calculated on the basis of cellulose. The same is true for the amounts of phosphorus mentioned in this description.

Anisotropic solution
Even at a cellulose concentration of 8% in an phosphoric acid solution, anisotropy is observed and anisotropic solutions are still obtained at cellulose concentrations of 40% or higher. Such high concentrations are preferably obtained at elevated temperatures. Selecting a cellulose concentration of more than 8% gives a significantly more economical way to obtain products from solutions. Such anisotropic solutions can be obtained by choosing a cellulose concentration in the range of about 8 to 40%. It was found that the optimal technology for processing these solutions into fibers is achieved at concentrations in the range from 10 to 30%, preferably from 12.5 to 25%. Most preferably from 15 to 23%. For other applications of the solutions, the optimal concentration ranges may be different.

In order to obtain a solvent system with which anisotropic solutions can be prepared, the phosphorus content is determined by converting the weighted amounts of phosphoric acid in the solvent into equivalent weighted amounts of the corresponding anhydride. When recalculated in this way, phosphoric acid contains 72.4% of phosphorus pentoxide and the rest is water, and polyphosphoric acid H ₆ P ₄ O ₁₃ contains 84% of phosphorus pentoxide, and the rest is water.

The concentration of P ₂ O ₅ in the solvent is calculated first based on the total amount of inorganic acids of phosphorus and their anhydrides and the total amount of water in the solvent, recalculating the acids to water and P ₂ O ₅ and calculating what percentage of the indicated total weight amount is P ₂ O ₅ . If other phosphoric acids are used, the conversion to the corresponding anhydrides is carried out similarly.

 If the phosphorus-containing system contains pentavalent phosphorus acids, the solvent for the preparation of the anisotropic solution will contain 65-89 wt.% Phosphorus pentoxide, preferably from 70 to 80 wt.%. In a most preferred embodiment of the present invention, a solvent containing from 71 to 75 wt.% Phosphorus pentoxide is used to prepare anisotropic solutions containing from 8 to 15 wt.% Cellulose, and a solvent containing from 72 to 79 wt.% Phosphorus pentoxide, used for the preparation of anisotropic solutions containing from 15 to 40 wt.% cellulose.

 In addition to water, phosphoric acid and / or its anhydrides, cellulose and / or reaction products of phosphoric acid with cellulose, other substances may be present in the solution.

 For example, solutions can be obtained by mixing the components, which can be divided into four groups: cellulose, water, inorganic acids of phosphorus and their anhydrides, and other components. "Other components" may be substances that improve the processability of the cellulose solution, solvents other than phosphoric acid, or additives, for example, to counteract cellulose destruction to the fullest extent possible, or dyes, etc.

 In accordance with this, the solution consists of 94-100 wt.% Cellulose, phosphoric acid and / or its anhydrides and water. Preferably, the solution contains 96-100 wt.% Cellulose, phosphoric acid and / or its anhydrides, and water.

 Preferably, additives or additives are present only in an amount of 0 to 4 weight. %, based on the total weight of the solution. However, even more preferred is a solution containing the smallest possible amount of other substances besides cellulose, phosphoric acid and / or its anhydrides and water, i.e. from 0 to 1 wt.% additives.

Preparation of anisotropic solution
In a. from. USSR SU 1348396 and SU 1397456 give several examples of the preparation of solutions of cellulose in phosphoric acid. The total time required to obtain a homogeneous solution is from 2 to 400 hours. In addition, it was found that during the preparation of the solution there is a sharp and uncontrolled decrease in the degree of polymerization.

 When preparing solutions on an industrial scale, it is undesirable when long periods of time are required for dissolution, since in this case large sizes of reservoirs are required for dissolving and storing the solutions. Moreover, the continuous preparation of such solutions is difficult due to the long periods of time required for dissolution. In addition, a sharp, uncontrolled decrease in the degree of polymerization (SP) of cellulose may be unfavorable for subsequent use of the solution, for example, when the solution is used to make cellulose fibers. An uncontrolled decrease in SP during the preparation of the solution will also make it difficult to prepare a solution of sufficiently constant quality, especially when various types of cellulose are used to prepare the solution.

 From the above documents it is clearly seen that the dissolution of cellulose in a solvent containing mainly phosphoric acid will take a long time.

 US Pat. No. 5,368,385 teaches that dissolving in water polymers that are very readily soluble in water is very difficult due to the formation of an impermeable film on the wet surface of the resulting polymer lumps. Without resorting to any theory, the applicant suggests that during the dissolution of cellulose particles in phosphoric acid, the outer layer of cellulose dissolves relatively quickly, forming an impermeable layer, similar to that described in US patent US 5368385. This impermeable layer makes it difficult and slows down the further dissolution of cellulose, which is under this layer. Several methods have been found that provide an answer to the question of how to solve this problem.

 One of the solutions can be seen is to quickly and thoroughly mix the cellulose and the phosphoric acid-containing solvent, the mixing being preferably such that the pulped cellulose in the solvent is obtained until an impermeable layer is too thick on the pulp pieces that could too slow down further dissolution. The speed at which an impermeable layer is formed, i.e. the rate at which cellulose dissolves in a solvent containing phosphoric acid can be reduced by lowering the temperature at which the cellulose is in contact with the solvent. When there is ground pulp in a solvent, said dispersed cellulose being preferably in the form of microparticles, for example in the form of cellulose fibrils, dissolving these small particles in a short time will give a solution containing cellulose and inorganic phosphorus acids. It can be seen that an alternative solution to the problem is to process the cellulose during its mixing with a solvent containing phosphoric acid, in which an impenetrable outer layer formed on the surface of the cellulose is regularly removed from it with a high removal frequency.

 The mixing of cellulose with a solvent containing phosphoric acid will be faster, the smaller the pieces of cellulose in the solvent will be. To this end, cellulose can already be converted into a dispersed form in advance, for example, by spraying, before mixing with the solvent. Alternatively, the cellulose and the solvent can be mixed in such a device that will not only provide mutual mixing with the solvent, but also reduce the size of the pieces of cellulose present in the mixture.

When preparing a solution containing cellulose using cellulose and a solvent containing phosphoric acid, three stages can be distinguished, in addition to the stage of adding cellulose to the solvent, namely:
1) reduction of particle sizes of cellulose,
2) mixing cellulose with a solvent containing phosphoric acid,
3) dissolution of cellulose in a solvent.

 At a given dissolution rate of cellulose in a solvent containing phosphoric acid, steps 2 and 3 cannot be considered independently. When the cellulose and the solvent are mixed together, the cellulose will also dissolve in the solvent. As indicated above, the dissolution of cellulose can be slowed down by lowering the temperature.

 Stage 1 can be separated from stages 2 and 3. An example of this is the preparation of a solution of powdered cellulose and a solvent containing phosphoric acid. As mentioned above, all three stages can also be combined, i.e. combine particle size reduction (pulverization), mixing and dissolving cellulose in one device equipped so that the pulp can be pulverized and mixed in the presence of a solvent.

 In cases where cellulose solutions need to be prepared on an economically acceptable scale, it is especially advantageous to combine the above three stages in one device, especially if this makes it possible to obtain a cellulose solution in such a device in a continuous way, i.e. by such a process in which the starting materials are supplied to the device in the form of more or less constant streams, and the cellulose solution is also discharged from the device in the form of a more or less constant stream.

 It has been found that solutions can be prepared if the cellulose and the solvent containing phosphoric acid are mixed in a device in which the shear forces created by the mixers and mixers allow intensive mixing of one or more added components. In a suitable embodiment, the mixing and stirring device used to carry out the method of the invention is a high shear mixer. Examples of high shear mixers known to those skilled in the art are Linden-Z, IKA-duplex, Conterna, or twin screw extruder kneading machines.

 In one of the most suitable embodiments of the invention, a device is used that also allows the grinding of particles. Preferably, such a high shear apparatus is a twin screw extruder.

 By properly selecting the devices for mixing, mixing and grinding and placing them on the shafts of a twin-screw extruder, many different forms of cellulose, such as sheets, strips, pieces, cuttings and powder, can be ground where necessary and thoroughly mixed with a phosphoric solvent acid before the dissolution of cellulose in the solvent slows down too much due to the formation of an impermeable layer.

 After combining the solvent containing phosphoric acid and the cellulose in the stirring or mixing device, the cellulose is mixed with the solvent and cellulose dissolves. The degree of mixing should be such as to prevent the cellulose dissolution from slowing down too much due to the formation of an impermeable layer on the cellulose surface. Cellulose dissolution can be slowed down by lowering the temperature.

In one preferred embodiment of the invention, the cellulose and solvent are combined in a device at a temperature in a section of the device where the cellulose and solvent are combined and mixed, less than 30 ^° C., preferably from 0 ^° C. to 20 ^° C. In another preferred embodiment, the solvent is before coupling with cellulose is cooled so that its temperature is below 25 ^o C. In this case, the solvent can be either in solid or in liquid state. You can cool the solvent before adding cellulose to it so that it is in the form of small pieces of solid.

 According to another preferred embodiment of the invention, part of the solvent is mixed with cellulose, after which the rest of the solvent is added to the resulting mixture / solution in one or more stages.

 In a preferred embodiment of the method, a device is used which is designed so that, during mixing and stirring, the starting products and the resulting solution move from the hole in the device where the solvent and cellulose enter, to another hole where the solution leaves the device. Examples of such devices are the twin screw extruder and kneading machines Conterna, Linden-Z and Bush.

 In a preferred embodiment of the method, a twin-screw extruder is used as a device for mixing and mixing with the conveying system. In such a device, there may be several different zones through which the products in the device pass. In the first zone, the initial mixing of the pulp supplied to the device with the solvent and particle size reduction will occur. In the next zone, the dissolution of cellulose will also play a major role. In the zone following it, there will be a mainly formed solution, which will undergo further homogenization and mixing with still undissolved cellulose.

 In such a device, the temperature selected for different zones can influence the dissolution of cellulose and the properties of the forming solution.

By choosing a temperature for the first zone below 30 ^° C., preferably in the range from 0 ^° C. to 20 ^° C., the dissolution of the pulp can be slowed down. With increasing temperature, for example in the next zone, the dissolution of cellulose is accelerated. In this regard, it should be noted that heat can be generated both during the dissolution of cellulose, and when the solvent and cellulose are mixed.

 By selecting the temperature and residence time in the mixing zone and mixing the device, which mainly contains cellulose in solution, it is possible to control the SP of the cellulose solution. Generally speaking, it is believed that the higher the temperature and the longer the residence time at this temperature, the greater the decrease in the SP of cellulose. In addition, the SP value of the starting material can affect the decrease in SP for a given temperature and length of stay in the device.

 Since heat transfer between the products in the device and the device itself, as a rule, will not be ideal, there may be differences in temperature between the products in the device and the device itself. Further, the device may have a zone in which the resulting solution is deaerated, for example, by passing the solution through a zone with reduced pressure. In addition, in this zone or in another separate zone, water or other components can be removed from the resulting solution or added to it.

 To remove any remaining small insoluble particles from the solution, it can be filtered either in the device or after unloading from it.

The resulting solution is highly viscous. It can be used immediately after receipt, but can also be stored for some time at low temperature, for example at a temperature of from -20 ^o C to 10 ^o C. Generally speaking, the longer it is desirable to store the solution, the lower the temperature should be.

 It should be noted that the resulting solution may harden, for example as a result of crystallization, if it is stored for some time at a low temperature. Heating the resulting solid mass will again give a highly viscous solution.

 The method described above makes it possible to prepare cellulose solutions in a short period of time and with a controlled decrease in cellulose SP. For example, it was found that in 15 minutes or even in less time, a cellulose solution can be prepared from powdered cellulose and a solvent containing phosphoric acid. This time period can be further increased by choosing a higher temperature for the preparation of the solution.

 The solution according to this invention can be prepared using all available types of cellulose, such as Arbocell BER 600/30, Arbocell L 600/30, Buckeye V5, Buckeye V60, Buckeye V65, Viscokraft, hemp, flax, ramie and eucalyptus cellulose. All of these types of cellulose are known to those skilled in the art. Cellulose can be added in a variety of forms, for example, in the form of sheets, strips, scraps, shavings, or in powder form. The form in which cellulose can be added is limited by the type of mixing and mixing apparatus. If the cellulose used is in a form that cannot be loaded into the device, it should be crushed outside the device by any known method, for example, with a hammer mill or grinder.

 The cellulose to be used must be α-cellulose with a consistency of preferably greater than 90%, more preferably greater than 95%. To form good-quality fibers from solutions, it is recommended to use so-called dissolving cellulose with a high content of α-cellulose, for example, one that is commonly used in the manufacture of fibers for industry or textile products. Examples of suitable types of pulp are Arcobell BER 600/30, Buckeye V60, Buckeye V65 and Viscokraft. SP cellulose, determined by the methodology described below, is preferably in the range of 250 to 1500, more preferably in the range of 350 to 1350. The cellulose SP in solution is preferably in the range of 215 to 1300, more preferably in the range of 325 up to 1200.

 Cellulose, supplied by industry, usually contains some water and can be used in this form without any obstacles. Of course, you can also use dried pulp, but this is not necessary.

If a mixture of various inorganic phosphoric acids is used to obtain a solvent containing the desired amount of acid converted to anhydride, the acids after mixing are preferably heated to a temperature in the range of 30 to 80 ^° C. and the solvent is kept heated for 1 / 2-12 hours . In some cases, depending on which acids are used, other periods of time and / or temperature may be desirable. For example, a very homogeneous solution without surface heterogeneities can be obtained using a solvent prepared by melting phosphoric acid at a temperature in the range of about 40 to 60 ^o C, adding the desired amount of polyphosphoric acid, mixing the two acids and cooling the mixture to about 20 ^o C.

 According to a suitable method, the solvent is left to stand for some time, for example from 30 minutes to several hours before adding it to the pulp.

 Other components (substances that improve the processability of the cellulose solution, solvents other than phosphoric acid, or additives, for example, to counteract cellulose degradation to the fullest extent, or dyes) can be added to the solvent before mixing with the solvent. Alternatively, other components may be added to the cellulose before mixing it. Other components can also be added when the solvent is mixed with cellulose. In addition, of course, other components can be added after the solvent and cellulose have already been mixed.

 It was found that the time, temperature at which the solution was stored, and the acid concentration had a significant effect on the phosphorus content associated with cellulose in the solution.

It is believed that phosphorus is bound to cellulose if, after thorough washing and optionally after neutralization, the coagulated solution still contains phosphorus. It was found that the solution obtained according to the present invention containing 18 wt.% Cellulose, which was obtained by dissolving cellulose in a solvent containing 80 wt.% Orthophosphoric acid and 20 wt.% Polyphosphoric acid, will contain approximately 0.25 wt. % of bound phosphorus after storage for 1 hour at 30 ^° C. However, if such a solution is stored at 50 ^° C, it will contain approximately 0.8% by weight of bound phosphorus after 1 hour of storage.

 It was found that the solution obtained according to the present invention, in any case, will contain at least 0.02% of phosphorus bound to cellulose.

 It was found that by adding a small amount of water to the solvent immediately before adding cellulose simultaneously with adding cellulose or immediately after adding cellulose, a solution with a low phosphorus content bound to the cellulose can be obtained.

 The resulting solution can be used for various purposes. For example, the solution can be used for the manufacture of fibers for both technical applications and for textile products, hollow fibers, membranes, non-woven materials, films, and other well-known applications of solutions containing cellulose. In addition, this solution can be used to obtain cellulose derivatives.

Anisotropic Spinning
The resulting solution can be spun (molded) or extruded through a die having the desired number of holes, or molded to form a film. Spinning solutions with a cellulose concentration of 15 to 25% by weight are preferably extruded at a temperature of from 0 to 75 ^° C., and the residence time of the solution at higher temperatures will be as short as possible. Preferably, such solutions are extruded at a temperature of from 20 to 70 ^° C., more preferably from 40 to 65 ^° C. For other concentrations, it is true that when the concentration is higher, the spinning temperature will also preferably be higher than the temperature ranges indicated here to compensate for the increased viscosity solution, and vice versa. However, it should be noted that a higher spinning temperature can lead to a higher phosphorus content associated with cellulose.

 The required number of holes in the die depends on the subsequent use of the resulting fibers. Thus, one die can be used not only for the extrusion of monofilaments, but also for the extrusion of multifilament yarns, widely used for practical purposes, which contain from 30 to 10,000, preferably from 100 to 2,000 elementary fibers. The production of such multifilament yarns is preferably carried out on a cluster spinning installation where there are a number of spinning holes, as described in European patent EP 168876, or using a die, as described in the publication of international application WO 95/20696.

 After extrusion, the extrudates pass through an air gap, the length of which is selected depending on the conditions of the method (for example, the spinning temperature and cellulose concentration) and the desired degree of extrusion of the extrudates. Typically, the air gap has a length in the range of 4 to 200 mm, preferably in the range of 10 to 100 mm. Following this, the obtained extrudates are passed through a coagulation bath in a known manner. Suitable coagulants include low boiling organic liquids in which cellulose, water, or mixtures of cellulose with water do not swell. Examples of such coagulants are alcohols, ketones, esters and water or mixtures thereof. Preference is given to using isopropanol, n-propanol, acetone or butanone as coagulants, since they exhibit a very good coagulating effect and in most cases have good properties from the point of view of safety and ease of handling. For this reason, mixtures of water with these coagulants are also very suitable.

The coagulation bath preferably has a temperature ranging from -40 ^° C (provided that the selected coagulant allows such a temperature to be used) to 30 ^° C, and very good results have been obtained at temperatures of the coagulation bath below 20 ^° C.

After coagulation, flushing may be carried out in combination with or without neutralization. Washing can be carried out by placing a coagulated filament bobbin in a vessel containing a washing substance, or, alternatively, continuously passing the fiber through a bath containing a suitable liquid, and then wrapping it on a roller. According to a method suitable for practical use, washing is carried out using so-called jet washing devices, such as described in GB Patent GB 762,959. Low-boiling organic liquids that do not cause cellulose swelling, for example alcohols, ketones and esters, water and mixtures thereof can be used as washing agents. Preference is given to using isopropanol, n-propanol, butanone, water or mixtures thereof as such substances. Water or a mixture of water and a coagulant are very suitable for use. The washing can be carried out at any temperature below the boiling point of the washing substance in any range, preferably below 100 ^o C.

 It was found that when the solution obtained according to the present invention is stored for a longer period of time or at an elevated temperature, it cannot be spun with an air gap if the solution is coagulated in a water bath or if the fibers are washed with water after coagulation, since the fibers will swell to a large extent upon contact with water.

 It was also found that if the amount of water absorbed by the fiber during coagulation in the water bath or when washing the fiber in the water bath is higher than 50% relative to the dry weight of the fiber, then the individual fibers in the bundle will no longer be different. Water absorption above 1300% will result in gel formation. In order for the fibers to have good mechanical properties, it is preferable that the moisture absorption of the fiber is less than 570%.

 It has been found that a reduced phosphorus content associated with cellulose leads to reduced moisture absorption.

 It was also found that if the solution prepared according to the present invention contains less than 3 wt.% Bound phosphorus, and the solution is coagulated in a bath that contains less than 10 wt.% Water, for example, in an acetone coagulation bath, and the fiber is washed in a water bath , then the individual fibers in the bundle can obviously still be distinguished. In addition, it was found that if the solution contains less than 1.3 wt.% Of bound phosphorus and the solution coagulates in water, then the individual fibers in the bundle are still clearly visible during washing in water.

 When fibers with good mechanical properties are obtained, the solution preferably contains less than 0.8 wt.%, More preferably less than 0.5 wt.% Of bound phosphorus.

Neutralization can be carried out either immediately after the washing step, or between the coagulation and washing steps. Alternatively, the neutralization step may be carried out after the washing step, and after it the next washing step will be carried out. Another possible option is that the thread is dried after coagulation and washing and then carry out the stage of neutralization. In a cost-effective process, neutralization is carried out after washing the filament. It was found that the fibers obtained by the above method and washed and neutralized so that their acidity is less than 7, there is a decrease in tensile strength during a 5-minute heat treatment at 175 ^o C, and this decrease in strength is more noticeable when the degree acidity is lower. If the degree of acidity of the fibers is at least equal to 7, then there is almost no or almost no decrease in tensile strength during the aforementioned heat treatment.

It was found that aqueous solutions of Na ₂ CO ₃ , NaHCO ₃ or NaOH are very suitable for use as neutrilizing agents in the preparation of extrudates having an acidity greater than or equal to 7, more preferably greater than or equal to 8. The lowest sensitivity of the extrudates to heat treatment was found for a degree of acidity greater than or equal to 9. Extrudates could be neutralized using a batch process, such as immersion in a neutralizing solution, or a continuous process, such as passing through NNU containing such a solution, or applying such a solution to the extrudates by spraying or using a roller that touches them, for example, using jet washing devices, washing plates or an applicator for applying an adhesive layer.

 The solution obtained according to the present invention is particularly advantageous because its preparation and spinning (molding) can be carried out as a continuous process on one line. In addition, this solution has the advantage that when fibers are prepared from it, especially when no other components are used except phosphoric acid, water and cellulose, cellulose and phosphoric acid almost do not react with each other and, therefore, there is little or no need in the regeneration of cellulose.

 The cellulosic fibers obtained in this way, which has great advantages, are especially suitable for use in rubber products subjected to mechanical stress, such as tires for vehicles, conveyor belts, rubber hoses, etc. These fibers are particularly suitable for use as a reinforcing material in tires for vehicles, for example in tires for cars and trucks.

 It was found that fibers obtained by spinning from a solution according to the present invention have good resistance to dynamic compressive loading. It was found that this resistance increases with decreasing phosphorus content associated with cellulose in solution. This resistance can be measured, for example, using the so-called GBF test (Goodrich fatigue test).

 Generally speaking, the fibers provided are a good alternative to industrial yarns such as nylon, rayon, polyester and aramids.

 Then the fibers can be turned into pulp (pulp). Such pulp, which can be mixed with other materials, such as carbon mass, glass melt, aramid mass or polyacrylonitrile mass, is not suitable for use as a reinforcing material, for example for asphalt, cement and / or friction materials.

Properties of fibers obtained by spinning from anisotropic solutions
The resulting cellulose fibers have very good mechanical properties, such as strength, modulus, and good elongation. Since it was found that the solvent hardly reacts with cellulose, properties depending on the structure of the cellulose, such as chain modulus, are retained, while the anisotropy of the solution makes it possible to achieve properties that are desirable for many mechanical applications.

Using the solution obtained according to the present invention, it is possible to obtain fibers having significantly better properties than the known cellulose fibers used for technical applications, for example Cordenka 660 ^R and Cordenka 700 ^R , which are obtained using the so-called viscose method.

 Using the solution obtained according to the present invention, it is possible to produce cellulose yarns that have a tensile strength of more than 700 mn / tex, more preferably higher than 850 mn / tex, a maximum modulus of less than 2% elongation of at least 14 n / tex, and elongation at break at least 4%, more preferably above 6%.

 Depending on the nature of the spinning solution and the coagulant, the fibers contain from 0.02 to 1.3% by weight of phosphorus bound to cellulose if the fibers are coagulated in water, or from 0.02 to 3.0% by weight of phosphorus bound to cellulose if the fibers are coagulated in a coagulant that does not contain water, and washed with water. Preferably, the fibers contain from 0.02 to 0.5% by weight of phosphorus bound to cellulose.

 In the publication of international application WO 85/05115, multifiber filaments formed from cellulose obtained by spinning from anisotropic solutions containing phosphoric acid are reported. The filaments have a morphology, which, apparently, is built of concentric layers that are located around the axis of the fibers and which, in addition, change pseudo-periodically along the axis of the fibers. In the publication of international application WO 94/17136, an assumption is made that the morphology is associated with the anisotropic solution from which the fibers are obtained.

 Although the filaments obtained according to the present invention are obtained from an anisotropic solution that contains phosphoric acid, the filaments do not exhibit the morphology described in WO 85/05115.

Measurement methods
Determination of isotropy / anisotropy in solution
Visual determination of isotropy or anisotropy was carried out using a polarization microscope (Leitz Ortoplan-Pol (100x)). To this end, about 100 mg of the test solution was placed between two glass slides and placed on the surface of a heated microscope stage (Mettlor FP 82), heating was turned on, and the sample was heated at a rate of about 5 ^° C / min. In the transition from the dyed (with birefringence) to the dark field, the thermometer readings were taken, noting the value of the temperature in an actually dark field. This temperature is called the transition temperature T _ni . The visual assessment during the phase transition was compared with intensity measurement using a photocell mounted on a microscope. For this intensity measurement, a sample with a thickness of 10-30 μm was placed on a glass slide so that no color was visible when using a transverse polarizer. Heating was performed as described above. A photocell connected to the recorder was used to record the intensity as a function of time. Above a certain temperature (different for different solutions), a linear decrease in intensity was observed. Extrapolation of this line to an intensity of zero yielded a value of T _ni . In all cases, the found value was in good agreement with the value found by the above method.

 Solutions are considered anisotropic if birefringence is observed at rest. Generally speaking, this is true for measurements taken at room temperature. However, the solutions obtained according to the present invention, which can be processed, for example by molding into fibers, at a temperature below room temperature and exhibit anisotropy at the indicated low temperature, are also considered anisotropic.

Determination of acidity
The degree of acidity of the extrudates is determined by placing 1 g of coagulated, washed and optionally neutralized, trimmed and / or dried extrudate in 100 ml of demineralized and deionized water (milli-Q water, pH = 6). The pH of the water containing the extrudate is then determined using a calibrated pH meter. The degree of acidity of the extrudate is equal to the pH found for water containing the extrudate. Determination of phosphorus content.

The phosphorus content associated with cellulose in a solution or in cellulose products obtained from this solution can be determined as follows. The following are placed in a decomposition flask: (a) 300 mg of a cellulose solution that has been coagulated, dried in vacuum for 16 hours at 50 ^° C. after thorough washing with water and then stored in a hermetically sealed sample container, and (b) 5 ml of concentrated sulfuric acid and 0.5 ml of a solution of yttrium salt containing 1000 mg / l of yttrium. Cellulose was carbonized by heating. After carbonization, hydrogen peroxide was added to the mixture in 2 ml portions until a clear solution was obtained. After cooling, water was added to the solution to a volume of 50 ml. Using a calibration curve for phosphorus, constructed from reference samples containing 100, 40, 20 and 0 mg / l of phosphorus, respectively, the phosphorus content in the analyzed solution was determined using the method of atomic absorption spectrography (Inductive Coupled Plasma-Emission Spectrometry (ICP-ES )), and calculating the phosphorus content in the solution according to the following equation:
phosphorus content (%) = (P _conc (mg / l) • 50) / (C _w (mg) • 10),
where P _conc = phosphorus concentration in the analyzed solution and C _w = weighed amount of coagulated and washed cellulose.

 Yttrium was added as an internal standard to amend for solutions having different viscosities. The phosphorus content was measured at a length of 213.6 nm, the internal standard was measured at a wavelength of 224.6 nm.

Determination of moisture content
The amount of water absorbed by the fiber during coagulation in a water bath or when washing the fiber with water can be determined by washing the fiber with water, then removing excess moisture by filtering through a Buchner funnel. The moisture content (in wt.% Of the weight of the dry fiber) can be determined by measuring the weight loss resulting from heating for 20 minutes at 160 ^o C.

Mechanical properties
The mechanical properties of single fibers and filaments were determined according to ASTM D 2256-90 using the following methods and instruments.

The properties of elementary (single) fibers were measured on fibers fixed between the surfaces of an Arnitel ^R fixture 10x10 mm. The elementary fibers were conditioned for 16 hours at 20 ^° C. and 65% relative humidity. The fiber length between the clamps was 100 mm and the fibers were stretched at a constant elongation rate of 10 mm / min.

The properties of the yarn were determined on the yarn fastened in the clamps of the Instron 4C machine. The filaments were conditioned for 16 hours at 20 ^° C. and 65% relative humidity. The length of the thread between the clamps was 500 mm and the threads were stretched at a constant elongation speed of 50 mm / min. The threads were twisted and the number of torsions per meter was 400 / V weight number of the fiber (d _tex ).

The weight number of yarn fiber, expressed in d _tex , was calculated based on the functional resonant frequency (ASTM D 1577-66, Part 25, 1968); the weight number of the thread bundle was determined by weighing. Tensile strength, elongation, and modulus at low loads were determined from the load-elongation curve and the measured linear density.

 The modulus of elasticity at low loads (In. Mod.) Was determined as the maximum modulus with an elongation of less than 2%.

 The invention will be further explained by way of examples.

Example A
In a Linden-Z mixer with an extruder-type discharge, 13,300 g of phosphoric acid (98.8% H ₃ PO ₄ ) was melted and stirred at 30-46 ^° C. until a clear, viscous liquid was obtained. To this liquid was added 3350 g of polyphosphoric acid. After 90 minutes of homogenization at 48 ^° C., the mixture was cooled to 18 ^° C. and 3600 g of pulp was added. The mixture was stirred for 45 minutes (the last 25 of them in vacuum) until a homogeneous solution was obtained. This solution was molded at 60 ^° C. through a die with 375 capillary holes, each 65 μm in diameter, passing it through a 40 mm air gap into a coagulation bath filled with acetone at a temperature of -12 ^o C. The degree of drawing in the air gap was about 7. Then the thread was washed with water at a temperature of 23 ^o C. In this way one sample was obtained (A-1), which was only dried and wound on a bobbin. Other samples were not dried, but again washed and neutralized with such solutions, which are given in table. 1. To prepare these solutions, CaCO ₃ , NaOH, and Na ₂ CO ₃ • 10H ₂ O were used. After neutralization, the thread was washed again with water.

For samples of threads thus obtained, the tensile strength was determined before and after a 5-minute heat treatment in air at a temperature of 175 ^o C. The effectiveness of maintaining the strength of the threads can be determined using the following equation:
BT _eff = (BT _a / BT _b ) • 100
where BT _eff denotes the strength retention efficiency, BT _a is the tensile strength after heat treatment, and BT _b represents the tensile strength before heat treatment. In addition, the degree of acidity of the yarn samples was measured before heat treatment according to the procedure described in this description. The results are shown in table. 1.

Example B
In a Linden-Z mixer with an extruder-type discharge, 13480 g of phosphoric acid (99.5% H ₃ PO ₄ ) was melted and stirred at 30-40 ^° C. until a clear, viscous liquid was obtained. 3240 g of polyphosphoric acid was added to this liquid. After 90 minutes of homogenization at 40 ^° C., the mixture was cooled to 12 ^° C. and 3,600 g of pulp was added. The mixture was stirred for 90 minutes (the last 70 of them in vacuum) until a homogeneous solution was obtained. This solution was formed at 59 ^° C through a die with 375 capillary holes, each 65 μm in diameter, through a 40 mm air gap into a coagulation bath filled with acetone at a temperature of + 10 ^o C. The degree of drawing in the air gap was about 7. Then the thread washed with water at a temperature of 23 ^o C and neutralized with solutions, which are given in table. 1. To prepare these solutions, NaHCO ₃ , NaOH, and Na ₂ CO ₃ • 10H ₂ O were used. After neutralization, the thread was washed again with water.

 The strength retention efficiency and acidity of the yarn samples were measured as described in Example A.

 The results are shown in table. 1.

Example C
In the same manner as described in Example B, a 16 wt.% Cellulose solution was prepared in a Linden-Z mixer. This solution was molded at 59 ^° C. through a die with 375 capillary holes, each 65 μm in diameter, through an air gap. The thread was washed with softened water and without additional drying was wound on a bobbin and stored in a plastic bag for 16 days. Then the yarn was neutralized with the solutions listed in the table. 1. To prepare these solutions, Na ₂ CO ₃ • 10H ₂ O, KOH, K ₂ CO ₃ , LiOH, and Ba (OH) _{2 were used} . After neutralization, the thread was washed again with water.

 The strength retention efficiency and acidity of the yarn samples were measured as described in Example A.

 The results are shown in table. 1.

Claims (5)

 1. A method of producing cellulose fibers from an optically anisotropic solution containing 94-100 wt.% Of the following components: cellulose, phosphoric acid and / or its anhydrides, water and 0-6 wt.% Of other components, by extruding the solution and coagulating the resulting fibers, characterized in that the fibers are further neutralized to obtain fibers having an acidity of at least 7, a strength retention efficiency of equal to or more than 80%, and a phosphorus content associated with cellulose of 0.02 to 3.00 wt.%.  2. The method according to p. 1, characterized in that the degree of acidity of the fibers after additional neutralization is at least 8.  3. The method according to p. 2, characterized in that the degree of acidity of the fibers after additional neutralization is at least 9.  4. A rubber product capable of withstanding mechanical stress containing cellulose reinforcing threads, characterized in that the reinforcing threads contain fibers with an acidity of equal to or more than 7, strength retention efficiency of equal to or more than 80%, and phosphorus content associated with cellulose , 0.02 - 3.00 wt.%, And the reinforcing yarns obtained by the method according to any one of claims 1 to 3.  5. A tire for vehicles containing reinforcing threads of cellulose, characterized in that the reinforcing threads contain fibers with a degree of acidity equal to or more than 7, the efficiency of maintaining strength equal to or more than 80%, and the phosphorus content associated with cellulose, 0, 02 - 3.00 wt.%, And the reinforcing yarns obtained by the method according to any one of claims 1 to 3.

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