Production Method of a High-Strength Textile Material in Which Raw Material Stress Is Eliminated and This Material

The present invention relates to a high-strength polyacrylate textile material in the field of textiles and a method for its production.

In particular, the invention relates to a high-strength polyacrylate textile material and the production method for the said material, which includes the process of eliminating the stress in the raw material (polyacrylonitrile-based textile material) before the crosslinking, hydrolysis, acid and salt processes without allowing the material to physically shrink, so that the amount of shrinkage in crosslinking, hydrolysis, acid and salt processes decreases spontaneously.

Polyacrylate textile materials can be produced by chemical modification of polyacrylonitrile (acrylic) based textile materials.

In the production of polyacrylate textile materials, polyacrylonitrile fibers are usually first converted into polyacrylate fibers. Then, polyacrylate textile materials (various yarns and fabrics) are produced by applying known textile production methods to the obtained polyacrylate fibers. The said polyacrylonitrile (acrylic) fiber refers to textile fibers containing at least 35% acrylonitrile in its structure.

However, all polyacrylonitrile-based textile materials (e.g. fibers, yarns, fabrics, etc.) or their semi-finished products or wastes are suitable for polyacrylating. However, since the material shows a radical shrinkage during the polyacrylating process when the polyacrylonitrile yarn or fabric is converted into polyacrylate, form of the material is severely deformed and the resulting product is not particularly pleasing in terms of appearance and feel (tactile properties). For this reason, in industrial conditions, it is preferred to convert polyacrylonitrile fibers into polyacrylate fibers and then to produce yarns and fabrics from the resulting polyacrylate fibers. The reason for this is that the yarns and fabrics produced from already shrunk polyacrylate fibers do not exhibit additional shrinkage.

Obtaining polyacrylate textile materials in the known technique is usually done by applying the following four process steps: subjecting the polyacrylonitrile-based textile material to cosslinking process; hydrolysis of the said crosslinked polyacrylonitrile-based textile material to obtain the polyacrylate textile material; acid treatment of the obtained polyacrylate textile material; treatment of the said acid-treated polyacrylate textile material with metal salts.

Polyacrylating takes place mainly in the second step (hydrolysis step) and crosslinking in the first step is necessary for the material to retain its fiber form without dissolving in the second step. The third and fourth steps are preferably used to differentiate product properties.

Polyacrylate fibers and textile materials derived from them have superior performance properties, which are listed below.

Although polyacrylate fibers have many superior performance properties, they are inadequate in terms of mechanical properties (especially tensile strength). These fibers cannot be widely used in the textile industry because they cannot withstand the mechanical forces in textile processes such as yarn and fabric production.

The strength of polyacrylonitrile fibers used as raw material (precursor fiber) in the polyacrylating process is generally in the range of 25-45 cN/tex, depending on the production conditions of the fiber, and this strength level is sufficient for yarn and fabric production. However, when these polyacrylonitrile fibers are converted into polyacrylate fibers by the method in the known art, their strength decreases to the range of 10-16 cN/tex.

In the patent document numbered WO2013114159A1, a method is described for producing high-strength polyacrylate fibers from polyacrylonitrile fibers. In the said document, it is stated that the strength of polyacrylate fibers is increased from 15 cn/tex to 23 cn/tex by adding nano additives. It is known that nano additives are used to strengthen various synthetic fibers. However, their commercial use is limited due to the difficulties of their use in fiber production and the additional cost they create. On the other hand, the root cause of the low strength of polyacrylate fibers is the disorientation of the polymer chains due to the radical shrinkage of polyacrylonitrile fibers during polyacrylating processes and the inability of the polymer chains to form bonds between each other with sufficient efficiency in terms of quantity and quality. Therefore, nano-additives do not eliminate the root cause of the problem. However, it is considered that nano-additives may provide some benefit to the product, which loses its strength at a radical level due to their nature.

Another method that can be applied to strengthen the polyacrylate fibers is to physically limit the shrinkage (shortening) of the material during the mentioned chemical processes. In this method, the shrinkage of the material is limited by applying a force to the material during the chemical processes, so that the orientation of the polymer chains is largely maintained and an increase in strength can be achieved.

However, this method also has disadvantages. First of all, the process becomes more complex due to the nature of the method. Namely, in order to prevent shrinkage, the material must be held (clamped or tied) at two ends (beginning and end). However, holding only the two ends is not enough to prevent shrinkage; every point of the material must be kept under tension. Otherwise, the material will shrink. One way to keep every point of the material under tension is to position the beginning and end on the same line segment. Considering that the material to be processed at one time is at least hundreds of meters long, it is obvious that a machine in which the beginning and end of such a long material are positioned on the same line segment is not industrially viable. On the other hand, it is conceivable that the requirement to keep every point of the material under tension could be achieved simply by winding the tow (rope or cable made up of thousands of fibers) into a roll or coil, layer upon layer, and fixing the beginning and end in some way. However, in such a form, many problems arise, such as insufficient penetration of chemicals into the inner layers. One of the most important of these problems is the following: It is not possible to prevent shrinkage completely, and ruptures occur when the material is not allowed to shrink at all during the process. Therefore, some shrinkage must be allowed during the process. A system is needed for this, that will allow shrinkage at exactly the desired moment, at the desired level and at every point of the material. A system that meets these requirements is very difficult to implement when the tow is wound in layers, layer by layer, in the form of rolls or coils.

For the reasons mentioned above, instead of the method in which the tow is wound layer by layer in the form of a roll or coil, a system can be used in which the beginning and end of the tow are pinched or tied and supported by wrapping them in turns around two opposite metal cylinders (rollers) with a certain distance between them. However, in such a system, when the distance between the support points (rollers) is more than 2-3 meters, it becomes difficult to control the tow during the process. For this reason, even if the tow is held only at the beginning and end, support points are needed at intervals of 2-3 meters to keep the tow under control. In the known technique, the standard low strength polyacrylate fiber is produced by placing the polyacrylonitrile fiber tow in the form of a pressed cake (the form obtained by wetting and pressing the appropriate amount of tow, usually 300 kg to 1000 kg, into the basket of a standard dyeing vessel) into a standard fiber dyeing vessel and treating the cakes with appropriate chemicals in this dyeing vessel for sufficient time and temperature. It is obvious that adding a holding or support point every 2-3 meters to an industrially highly efficient and simple system where thousands of meters of tow can be processed at once in cake form will complicate the process. In addition, the dead volume caused by the holding or support points reduces the amount of tow that can be filled into the vessel, thus reducing the production amount and making the process inefficient. The said dead volume is not only the volume occupied by the parts providing holding or support, but also the empty volume between the holding or support points, as the material is under tension. That is to say, if we consider that the material is clamped or tied at the beginning and end and supported by wrapping around two opposite metal cylinders with a distance of 2-3 meters between them, there will be an empty volume between the metal cylinders that neither the tow nor the metal cylinders fill, since the tow is under tension. The size of this empty volume is directly proportional to the distance between the rollers, the roller diameter and the roller length. Even if the cylinder diameter is kept as small as possible, it must be kept to a certain size due to the risk of cutting the material under tension. Therefore, the mentioned empty volume cannot be eliminated. Since this empty volume will also be filled with the treatment solution, this creates additional costs.

On the other hand, it is not possible to completely prevent shrinkage and ruptures occur when the material is not allowed to shrink at all. For this reason, some shrinkage must be allowed during the process, which makes the process much more complicated if a mechanism is included in the system to allow shrinkage at exactly the desired moment and at the desired level.

In the method where shrinkage is limited, due to the mentioned requirements (keeping the material under a certain tension continuously, allowing shrinkage at the desired level at the desired time, needing a support point every 2-3 meters, the pressure of the material on the support surface at the support points creating resistance to the shrinkage of the material in these areas and the absorption of chemicals into the structure, loss in throughput due to dead volume and the need for more solution), it may be preferable to perform the process in a continuous (continuously flowing, moving) system rather than a batch (fixed, intermittent, non-continuous) system such as a fiber dyeing vessel. In this system, tow or tows fed to the system side by side can be held by rollers or a pair of rollers rotating at a certain speed every 2-3 meters. In this way, some of the mentioned problems can be avoided. Compared to a closed batch system completely filled with solution, the support points (rollers) and therefore the tow can be moved (flow) much more easily and different parts constantly contact the support points. Also, since the peripheral speed of the rollers can be easily controlled, the required amount of shrinkage can be allowed when needed.

However, such a system would pose a number of additional problems. First of all, due to the very long processing times, the tow has to move very slowly along the production line (machine) or the production line has to be very long in order to treat the material with the appropriate chemicals for a sufficient time. A low feed rate of the tow is not desirable in terms of production efficiency and cost. If the line is too long, it results in a very high machine investment cost. Finally, practices that shorten processing times, such as the use of higher temperature and more concentrated processing solutions, increase the tendency of the material to rupture, although the exact cause is not known. Presumably, when chemical transformation processes are carried out more slowly and over a longer period of time, the material has the opportunity to stabilize itself against rupture at the molecular level. As a result, such approaches to reduce the processing time cannot be applied in practice.

In addition, when chemicals, which are very harmful to human health and the environment, are used in a line with a length of at least 100 meters and a huge volume instead of a simple system such as a fiber dyeing vessel, which is completely closed and has a volume of a few cubic meters, it becomes very difficult to manage chemical emissions.

Another disadvantage of this method where shrinkage is limited is that, apart from the cross-links formed in the first step, the other bonds that hold the polymer chains together and provide fiber strength are broken in the second step due to the nature of the second step. As a matter of fact, if the second step is applied directly without applying the first step, the material completely dissolves and loses its fiber form, as there are no bonds left to hold the structure together. Therefore, the first step of crosslinking is a prerequisite to prevent dissolution in the second step (hydrolysis step), where polyacrylating occurs, to maintain the fiber form of the material and to provide some strength to the material. In the case where the shrinkage of the material is limited, it is necessary to perform much more crosslinking in the first step in order to avoid rupture in the second step. The reason for this is that the restraining of the shrinkage of the material increases the tension on the material. Even if some shrinkage is allowed, the increased tension causes the tow, which already has a limited strength, to break. When more shrinkage is allowed, the desired strength level cannot be achieved. As a result, in the method where shrinkage is limited, there is no choice but to perform much more crosslinking in the first step to prevent rupture in the second step. Performing excessive crosslinking adversely affects the mechanical and performance properties of the product. First of all, the more the amount of crosslinking increases, the more rigid and brittle the product becomes. Textile fibers are desired to be flexible and easily formable, not rigid and brittle. On the other hand, what provides the superior performance properties of polyacrylate fiber is that the —CN groups in the polyacrylonitrile polymer chains are transformed into other functional groups as a result of the applied processes. Since the cross-links formed in the first step are made between these —CN groups, the more the crosslinking level increases, the less —CN groups that can be converted into functional groups that will provide performance properties.

Therefore, due to the drawbacks mentioned above and the inadequacy of the existing solutions, it has become necessary to make an improvement in the relevant technical field.

The method of producing high strength polyacrylate textile material developed by the present invention comprises the steps of: subjecting the polyacrylonitrile-based textile material used as raw material to a crosslinking process; hydrolyzing the said crosslinked polyacrylonitrile-based textile material to obtain the polyacrylate textile material; subjecting the obtained polyacrylate textile material to acid treatment; treating the said acid-treated polyacrylate textile material with metal salts. In the developed production method;

In an exemplary embodiment of the present invention, prior to the aforementioned process steps, the polyacrylonitrile-based textile material (e.g. acrylic fibers in tow form) is subjected to saturated steam treatment (annealing process) in a pressurized vessel (autoclave) in a form in which shrinkage is not possible (e.g. the form in which the head and end are fixed and the tow is wound layer by layer on a roller in the form of a bobbin, which will not be deformed by the shrinkage force). Since the polyacrylonitrile-based textile material is very strong at this stage, the tension caused by not allowing shrinkage does not cause rupture. Also, the fact that the process is carried out in the form of a coil in which the tow is wound layer by layer on a roller does not pose any problem due to the very good ability of the saturated steam in a pressurized vessel to penetrate into the material. The fact that the autoclave to be used for the process is a type B autoclave makes it even easier for the steam to penetrate into the material. In type B autoclaves, the air in the autoclave and the material is purged by vacuuming before the steam is introduced into the autoclave for better penetration of the steam into the material. Then, steam is introduced into the autoclave to allow the steam to penetrate into the material better. By means of the process mentioned above, the stress in the molecular structure that causes shrinkage is eliminated, the molecular structure is fixed and most importantly, the polymer chain orientation is maintained, as shrinkage is not allowed during the process. In the known technique, commercial polyacrylonitrile fibers produced for standard textile uses (carpet, knitwear, etc.) are also subjected to saturated steam treatment in a pressure vessel, also called annealing, after production. However, in this standard application of the annealing process, shrinkage of the material is not prevented, in fact it is especially desired. The reason for this is that, as a result of shrinkage, some properties such as increasing the dye uptake rate, which is important for the textile industry, are also provided to the material. For this reason, in the standard application of the annealing process, the polyacrylonitrile tow is subjected to autoclave by filling it freely into perforated boxes without any obstruction. As a result of this process, the material shrinks by approximately 30%, the polymer chain orientation is disrupted, the strength of the material decreases, but the elongation feature and dye uptake speed increase and shrinkage in subsequent hot-wet textile processes (since the stress in the material is eliminated) is prevented.

In the method of the invention, prior to the polyacrylating process, the polyacrylonitrile-based textile material is treated with saturated steam in a pressurized container (autoclave) in a form where shrinkage is not possible. With this process, the stress that causes shrinkage of the material in polyacrylating processes is eliminated by maintaining the polymer chain orientation. In this way, the amount of shrinkage of the material in the said polyacrylating processes decreases spontaneously (without physically limiting the shrinkage) and the strength of the obtained polyacrylate textile material is increased significantly.

The invention is inspired by the existingsituation and aims to solve the above-mentioned problems.

The objective of the invention is to develop a polyacrylate textile material production method that reduces the shrinkage tendency and shrinkage of the material by eliminating the stress in the material.

An objective of the invention is to develop a high-strength polyacrylate textile material and an efficient, economical, environmentally friendly and sustainable production method thereof.

An objective of the invention is to develop a method of producing polyacrylate textile materials in which the shrinkage of the material in polyacrylating processes is not physically limited by a force

In order to achieve the objectives mentioned above, the subject matter of the invention is a method of producing a high-strength polyacrylate textile material comprising the steps of preparing polyacrylonitrile textile material as raw material; subjecting said polyacrylonitrile-based textile material to a crosslinking process; hydrolyzing said crosslinked polyacrylonitrile-based textile material to obtain polyacrylate textile material; treating the obtained polyacrylate textile material with acid; treating said acid-treated polyacrylate textile material with metal salts, wherein the said method comprises the process step of,

Production method for high-strength polyacrylate textile material, which is the subject of the invention, comprises the reduction of the shrinkage tendency by eliminating the stress in the raw material before the processing step i) or the processing step ii) or both processing steps

Production method for high-strength polyacrylate textile material, which is the subject of the invention, comprises the process step (iii) wherein the polyacrylate textile material obtained after the processing step ii) is subjected to acid treatment.

Production method for high-strength polyacrylate textile material, which is the subject of the invention, comprises process step (iv) for the treatment of the said acid-treated polyacrylate textile material with metal salts.

Production method for high-strength polyacrylate textile material, which is the subject of the invention wherein the said polyacrylonitrile-based textile material is acrylic fiber or its semi-finished products or its wastes, acrylic yarn or its semi-finished products or its wastes or acrylic fabric or its semi-finished products or its wastes.

The invention is a high-strength polyacrylate fiber obtained by the production method of a high-strength polyacrylate textile material.

The invention is a high-strength polyacrylate yarn obtained by the production method of a high-strength polyacrylate textile material.

The invention is a high-strength polyacrylate fabric obtained by the production method of a high-strength polyacrylate textile material.

The structural and characteristic features and all advantages of the invention will be more clearly understood through the detailed description and therefore evaluation should be made by taking the detailed description into consideration.

In this detailed description, preferred embodiments of the method of manufacturing the polyacrylate textile material, which is the subject of the invention, are described only for a better understanding of the subject matter.

Artificial textile fibers are basically produced by two different fiber extrusion methods: fiber extrusion from melt and fiber extrusion from solution. In order to make fiber extrusion, the polymer used as raw material is converted into a fluid structure with a viscosity suitable for fiber extrusion. The polymer used for this purpose is either melted or dissolved in a suitable solvent. The viscous polymer, which becomes suitable for fiber extrusion, is passed through perforated spinnerets and thus produced as endless filaments. Fiber is obtained by re-solidifying the filaments coming out of the spinnerets. In the melt fiber extrusion method, solidification is achieved by cooling. In the method of fiber extrusion from solution, solidification is achieved by volatilizing the solvent with an inert gas (dry fiber extrusion) or by washing with a nonsolvent (e.g. water) and replacing the solvent with the nonsolvent (wet fiber extrusion).

Polyacrylonitrile (acrylic) fiber, which is an example of a polyacrylonitrile-based textile material, is obtained by wet or dry fiber extrusion methods. In the production method of these polyacrylonitrile fibers; polyacrylonitrile polymer, which is generally used as a copolymer, is made into a solution with a suitable solvent (specifically preferably DMF, DMAc or DMSO) and this polymer solution is passed through perforated spinnerets and produced as endless filaments. The solvent in the fiber is replaced with water by washing with water and then the water in the fiber is removed using a drying system. In addition to the method mentioned above, the solvent in the fiber can be volatilized with inert gas, allowing the fiber to pass into the solid phase. During the process, the fibers are stretched (drawing process). By means of this drawing process, the polymer chains become oriented (parallel) at a certain level. In this way, the polymer chains can approach each other and form bonds between them called secondary attraction forces. These bonds are one of the most important factors determining fiber strength. As the orientation increases, more and stronger bonds are formed, which increase fiber strength.

Polyacrylate fibers, which are examples of polyacrylate textile materials, can be obtained by chemical modification of polyacrylonitrile fibers. Basically, polyacrylonitrile fibers can be converted into polyacrylate fibers by subjecting them to four different reactions (process steps). However, due to the radical shrinkage of polyacrylonitrile fibers during the mentioned processes, the orientation of the polymer chains is disrupted and accordingly, the polymer chains cannot form bonds between each other with sufficient efficiency in terms of quantity and quality, leading to loss of strength. The obtained polyacrylate fibers are not suitable for use in textile processes and textile products due to their low strength. Accordingly, with the present invention, a high-strength polyacrylate textile material and a method of producing this polyacrylate textile material are developed.

The method of producing a high-strength polyacrylate textile material developed by the present invention comprises the steps of; crosslinking of the polyacrylonitrile-based textile material used as raw material; hydrolyzing said crosslinked polyacrylonitrile-based textile material to obtain polyacrylate textile material; treating the obtained polyacrylate textile material with acid; treating said acid-treated polyacrylate textile material with metal salts. In the developed production method;

In one embodiment of the method of the invention, the shrinkage tendency of the polyacrylonitrile-based textile material fed as raw material to the said processes is reduced before the crosslinking step, and thus the shrinkage of the material is automatically reduced during the aforementioned processes.

In one embodiment of the method of the invention, the shrinkage tendency of the polyacrylonitrile-based textile material fed as raw material to the said processes is reduced before the hydrolysis step, and thus the shrinkage of the material is automatically reduced during the aforementioned processes.

In one embodiment of the method of the invention, the shrinkage tendency of the polyacrylonitrile-based textile material fed as raw material to the said processes is reduced before both the crosslinking and the hydrolysis steps, and thus the shrinkage of the material is automatically reduced during the aforementioned processes.

In one embodiment of the method of the invention, shrinkage tendency is reduced by eliminating the stress in the raw material, preferably by treating the material with a substance to aid heat transfer, preferably at a temperature above 80° C. without allowing the material to physically shrink. The said substance is solid (hot metal roll surfaces), liquid (hot water or other hot liquids suitable for the purpose) or gas (water vapor, hot air or other gases suitable for the purpose).

In one embodiment of the method of the invention, the process of eliminating the stress in the raw material is carried out under atmospheric conditions, under pressure, under vacuum or under conditions consisting of a combination thereof.

In an exemplary embodiment of the present invention, prior to the process steps mentioned above, the polyacrylonitrile-based textile material (e.g. acrylic fibers in tow form) is subjected to saturated steam treatment (annealing process) in a pressurized vessel (autoclave) in a form in which shrinkage is not possible (e.g. the form in which the beginning and end are fixed and the tow is wound layer by layer on a roller in the form of a bobbin, which will not be deformed by the shrinkage force). Since the polyacrylonitrile-based textile material is very strong at this stage, the tension caused by not allowing shrinkage does not cause rupture. Also, the fact that the process is carried out in the form of a coil in which the tow is wound layer by layer on a roller does not pose any problem due to the very good ability of the saturated steam in a pressurized vessel to penetrate into the material. The fact that the autoclave to be used for the process is a type B autoclave makes it even easier for the steam to penetrate into the material. In type B autoclaves, the air in the autoclave and the material is purged by vacuuming before the steam is introduced into the autoclave for better penetration of the steam into the material. Then, steam is introduced into the autoclave to allow the steam to penetrate into the material better. By means of the process mentioned above, the stress in the molecular structure that causes shrinkage is eliminated, the molecular structure is fixed and most importantly, the polymer chain orientation is maintained, as shrinkage is not allowed during the process. In the known technique, commercial polyacrylonitrile fibers produced for standard textile uses (carpet, knitwear, etc.) are also subjected to saturated steam treatment in a pressure vessel, also called annealing, after production. However, in this standard application of the annealing process, shrinkage of the material is not prevented, in fact it is especially desired. The reason for this is that, as a result of shrinkage, some properties such as increasing the dye uptake rate, which is important for the textile industry, are also provided to the material. For this reason, in the standard application of the annealing process, the polyacrylonitrile tow is subjected to autoclave by filling it freely into perforated boxes without any obstruction. As a result of this process, the material shrinks by approximately 30%, the polymer chain orientation is disrupted, the strength of the material decreases, but the elongation feature and dye uptake speed increase and shrinkage in subsequent hot-wet textile processes (since the stress in the material is eliminated) is prevented.

In the method of the invention, before the polyacrylating process, the polyacrylonitrile-based textile material is treated with saturated steam in a pressurized container (autoclave) in a form where shrinkage is not possible. With this process, the stress that causes shrinkage of the material in polyacrylating processes is eliminated by maintaining the polymer chain orientation. In this way, the amount of shrinkage of the material in the mentioned polyacrylating processes decreases spontaneously (without physically limiting the shrinkage) and the strength of the polyacrylate textile material obtained is increased significantly.

Different polyacrylate fiber samples obtained by the polyacrylate textile material production method developed by the present invention and the properties of these samples are given below.