METHOD FOR THE PRODUCTION OF DERIVATIVE STARCH

Description

[0001] The present invention relates to a process for producing derivatized starch of high purity applicable in the manufacture of paper or cardboard, in which a starch raw material is subjected to at least the following steps: purification, slurry formation, derivatization, gelatinization, pH adjustment and application.

[0002] Starches, both cationic and anionic, are used in the paper and board industry as bulk starch, surface starch, spray starch, and coating starch. Depending on the application, different properties of the paper or board are modified by the starch used. Bulk starch, for example, aids in dewatering, increases the strength of the paper or board, and also helps to protect sizing agents or eliminate contaminants. Surface starches, on the other hand, influence the strength and stiffness of the paper or board and improve the printability of the manufactured paper or board products. It is also known that native starches without charge can be used as surface starches.

[0003] It is essential for the starch used in the paper or cardboard industry that it is essentially free of impurities such as cellulose fibers, shell fragments, fats or proteins, as these substances can massively reduce the positive effects desired by the use of starch on the paper or cardboard and, in particular, can lead to non-reproducible results in the quality of the manufactured paper or cardboard.To avoid these adverse effects, the starch derived from corn, potatoes, or wheat, which is primarily used in the paper and cardboard industry, undergoes purification before the glucose units on the starch molecule are substituted. This process removes potentially interfering impurities and / or accompanying substances as much as possible. However, due to the pH level present during purification, only a relatively small portion of the fats and proteins contained in the starch can be removed. After the removal of impurities and / or accompanying substances, the starch is subjected to either derivatization (cationization) or anionization. The majority of starches used are cationic starches, in which glucose units are replaced, for example, by quaternary amines or similar compounds.The starches are substituted, resulting in cationic, derivatized starches with a predetermined degree of substitution. In industrial starch production for paper and cardboard manufacturing, a variety of starch products are typically offered, differing in their manufacturer-selected degree of substitution, which usually ranges from approximately 0.04 to 0.1. To use the derivatized starch in paper and cardboard production, it must be made water-soluble in a further step. This is achieved by boiling the starch, after which the resulting starch suspension or solution is further diluted to the concentration required for its final application. This boiling step can be carried out either at the starch manufacturer or at the end user.

[0004] EP 0 031 744 A2 describes a process for the production of cationic starch ether, in which purification is carried out after pH adjustment.

[0005] WO 2006 / 007045 A1 describes a process for the derivatization of starch, in particular for the production of cross-linked starch, which, however, does not provide for a purification step after derivatization.

[0006] From EP 0 233 336 B1 a process for the dry cationization of starch is known in which starch is reacted with alkylidene epoxides in the presence of a powdered mixture of a calcium hydroxide or oxide and silica.

[0007] US Patent 5,368,690 describes a papermaking process in which cross-linked, cationized starch is gelatinized under pressure. In this process, the starch is wet-cationized by slurrying it in water with the addition of sodium hydroxide, (3-chloro-2-hydroxypropyl)trimethylammonium chloride, and epichlorohydrin. After neutralization and washing with water, it is dried. The dried starch is then boiled by slurrying it in water until the desired viscosity is reached.

[0008] A disadvantage of this approach is twofold: firstly, not every degree of starch substitution is commercially available, since, as noted, only certain frequently requested substitute starches are produced; and secondly, either large quantities of derivatized, gelatinized starch solution must be transported to the end customer, or an energy-intensive drying step must be carried out to avoid transporting unnecessary amounts of liquid. In such cases, the derivatized starch granules are typically filtered, washed, and dried, and then transported to the end customer as a derivatized, but not gelatinized, powder.In any case, such starch products still contain non-negligible amounts of contaminants, such as proteins, which cannot be removed during the purification step or can only be partially removed, and are therefore present as interfering contaminants in the derivatized starch used in paper or cardboard production.

[0009] Recently, there has been talk of carrying out starch processing directly on-site in paper or cardboard production, which could result in energy savings and also provide the desired degree of substitution of the derivatized starch for the respective manufacturer. However, the problem of product contamination with proteins and reaction byproducts has not yet been solved, regardless of which of the two common derivatization methods, dry or wet derivatization, is used for the native starch.

[0010] The present invention therefore aims to provide a process by which it is possible to separate interfering impurities and / or accompanying substances from a derivatized starch and furthermore to minimize the energy expenditure and raw material or chemical input in such a process.

[0011] To solve this problem, the process according to the invention is essentially characterized in that a slurry of derivatized starch obtained after the process steps of slurrying and derivatization, carried out in any sequence, is subjected to purification by washing and concentration in an apparatus selected from a decanter, hydroclone, or separators at an alkaline pH, and that the purified and gelatinized, derivatized starch obtained after gelatinization is subjected to at least one reaction with dilute acid. By selecting the process such that the purification of the starch only takes place after the process steps of slurrying and derivatizing the native starch, carried out in any sequence, the process is optimized by ensuring that the starch is free of contaminants.By performing the purification step on the starch raw material, a significantly higher purity of the derivatized starch product is surprisingly achieved compared to when the purification step is carried out directly on the starch raw material or after acid treatment. In particular, this purification step almost completely removes proteins contained in the starch raw material, as well as fibers, shell fragments, and the like. Furthermore, in addition to the impurities originating from the starch raw material or the native starch, this process also removes chemicals used in derivatization, especially their excesses. As a result, the overall impurity content of the derivatized starch used in subsequent gelatinization is significantly reduced compared to conventional methods.In addition, contaminating materials such as reaction by-products, reagents, low molecular weight starch degradation products, as well as salts such as sodium salts and, of course, water can be separated from the starch suspension in the purification step.

[0012] According to the invention, the purification step is carried out such that the slurry of derivatized starch is washed and concentrated in a device selected from a decanter, hydrocyclone, or separators at an alkaline pH. By performing the purification step in an alkaline environment through washing and subsequent concentration in a device selected from a decanter, hydrocyclone, or separators, water-soluble salts such as sodium salts, water-soluble reaction byproducts such as glycols, as well as low-molecular-weight water-soluble starch degradation products, residual reagents, and all other water-soluble substances can be removed from the starch in a first step by adding a washing substance, in particular water. This significantly reduces the burden of potentially interfering substances on the subsequent gelatinization process.In a further step, such as decanting or further cleaning of the pre-cleaned material in a hydrocyclone, residual impurities originating from the starch raw material, such as shell fragments, fibers, and the like, can be separated. This process, in which derivatization is performed first and then purification, significantly reduces the degree of impurity in the derivatized starch compared to conventional methods. This purification effect can be further enhanced by selecting specialized cleaning equipment such as a decanter, hydrocyclone, or separators.By further purifying the derivatized starch slurry in at least two steps—namely, a first alkaline washing step and a second step of washing and concentrating the slurry—it is possible to remove even more impurities from the derivatized starch slurry, in particular substances such as fibers and proteins, which are especially readily washed out by alkaline solutions. Moreover, this method maintains the pH of the starch suspension within an optimal alkaline range, thus not only preventing premature gelatinization in a washing step but, more importantly, achieving more efficient gelatinization in the subsequent gelatinization step. This is because, as is known to those skilled in the art, alkaline starch boils significantly better than neutral or even slightly acidic starch.In any case, such a process makes it possible to achieve better swelling of the starch, resulting in a significantly higher quality product overall, and in particular a product of particularly high purity.

[0013] In connection with the present invention, the term "starch raw material" is understood to mean any plant starch or native plant starch that can be used in the process according to the present invention without any prior purification. Such a product contains, in addition to the starch required for the reaction, considerable amounts of fibers, plant husk fragments, proteins, and the like. In the present process, not only potato starch and / or corn starch can be used as starch raw material, but also, for example, tapioca starch, waxy maize starch, wheat starch, barley starch, rice starch, fruit starch, and the like.

[0014] High-purity starch is defined as starch whose non-starch-bound nitrogen content is reduced by at least 60%, preferably at least 75%, and particularly preferably at least 90%, compared to that of the starting material. Nitrogen content is understood here as the total amount of nitrogen in the derivatized starch, i.e., nitrogen originating from the starch itself, including protein nitrogen, as well as nitrogen introduced during derivatization with derivatization reagents and / or activators or the like, or possibly originating from derivatization reaction products.

[0015] In the context of this application, derivatized starch is understood to be a starch in which glucose units on the starch have been substituted by either cationic, anionic, or both cationic and anionic residues. Derivatized starches obtained through such derivatization are subsequently referred to as cationic, anionic, biionic, or amphoteric starches, depending on the derivatization method chosen and the ionic charge of the residues introduced during the derivatization.

[0016] To avoid leaving the pH too strongly in the alkaline range, according to a further development of the invention, the second washing step in the cleaning step is carried out with the addition of at least one acid, selected from mineral acids such as hydrochloric acid, sulfuric acid, or phosphoric acid, or organic acids such as fumaric acid or citric acid, while simultaneously adjusting the pH to values ​​between 7 and 9. This method makes it possible to adjust the pH value optimal for subsequent gelatinization during the washing of the derivatized starch, in order to achieve the most complete and, in particular, rapid gelatinization possible. In the cleaning step described above, all acids known to a person skilled in the art in the field of starch derivatization can be used, either alone or in combination. The only essential point is that the cleaning takes place after derivatization and before cooking or...the gelatinization process is preferably carried out at an alkaline pH value.

[0017] By concentrating the derivatized starch slurry to a solids content of 2 to 42 wt.%, particularly 5 to 35 wt.%, during the purification step, as is the case with a further development of the process, it is possible to obtain a concentrated starch slurry for subsequent gelatinization or cooking, with which gelatinization can be carried out directly without the addition of any further moisture. Since the process according to the invention omits any drying step, a significant energy saving is achieved while simultaneously obtaining a highly purified product that can be used directly in papermaking, for example as bulk starch or surface starch, such as a sizing agent.By omitting any drying step, it is also possible to prevent impurities such as proteins, which become insoluble in water during drying due to denaturation and adhere to the starch granules, from remaining in the subsequent cooking process and, consequently, in the starch prepared for use. For the actual application of the product, the starch solution must then be diluted to the desired concentration and adjusted to the desired pH value. Furthermore, the omission of a drying step ensures that no surface keratinization of the starch granules of the derivatized starch can occur, which could lead to a loss of efficiency in the production of paper or cardboard.

[0018] To adjust the desired pH value after gelatinization, a further development of the inventive process essentially involves subjecting the purified, gelatinized, and derivatized starch obtained after gelatinization to a two-stage acidification. This method makes it possible to adjust the pH value of the gelatinized starch in a first acidification step to, for example, values ​​of 6.0 to approximately 8.5, a pH value at which gelatinized starch can be stored for extended periods without deterioration. Storing the gelatinized starch may be necessary for various reasons, such as the pre-production of larger quantities of gelatinized starch or required repairs or maintenance work on the paper machine during continuous production of gelatinized starch.In a second acidification step, the pre-acidified or essentially neutral derivatized and gelatinized starch can then be adjusted to the optimal pH value for its specific application on the paper machine. For example, lower pH values ​​are more advantageous for sizing applications, such as those using alkenyl succinic anhydride, than for use as bulk starch. When the gelatinized starch is used as bulk starch in the pulp, the process can be carried out in such a way that the starch is adjusted to a lower pH value. This eliminates the need to lower the pH of the pulp fiber mixture used in this process step by adding aluminum sulfate or sulfuric acid, since the pH can be adjusted solely by the bulk starch.This type of process not only achieves a significant saving in chemicals such as aluminum sulfate, but also eliminates the need for a pH adjustment step in the cellulose fiber mixture. It is known to those skilled in the art that thick starch can have a consistency range of 3 to 35 wt.%, particularly 4 to 30 wt.%. This process thus offers two significant advantages for large-scale industrial applications: the gelatinized, purified starch can be stored for extended periods without deterioration, and the two-stage pH adjustment allows for substantial chemical savings.

[0019] Due to the predominant importance of cationized starch in the paper and cardboard industry, according to a further development of the invention, the process is carried out such that the derivatization is a cationization with a base selected from the group of alkali hydroxides, such as NaOH, KOH, LiOH, alkali carbonates, such as Na₂CO₃ or alkaline earth oxides, such as CaO or alkaline earth hydroxides, such as Ca(OH)₂, in particular NaOH, a cationization reagent, in particular 3-chloro-2-hydroxypropyl-trimethylammonium chloride or an epoxide cationization reagent such as 2,3-epoxypropyl-trimethylammonium chloride, and optionally further substitution reagents and facultative auxiliaries selected from activators, such as silicates, calcium oxide or calcium hydroxide.Cationic derivatization can be carried out either as dry cationization or as wet cationization. In the former case, the dry starch is first derivatized under alkaline conditions and subsequently suspended in acidified water. In the latter case, wet derivatization, the raw material, the starch, is first suspended in water containing swelling protection salts, such as sodium sulfate, sodium chloride, calcium chloride, and alkali or alkaline earth hydroxides. It is then cationized with a cationizing reagent, such as 3-chloro-2-hydroxy-propyl-trimethylammonium chloride or 2,3-epoxy-propyl-trimethyl-ammonium chloride, at pH values ​​of 11 to 12.The process parameters regarding pH values, temperatures, concentrations and reaction times are known from the prior art in both cases; however, it has surprisingly been shown that both dry-cationized and wet-cationized starch can be purified to a significantly higher purity than starch derivatized by a conventional process if the purification step of the starch is carried out after cationization in the alkaline range and not before.

[0020] According to a further development of the invention, the process is carried out such that sodium hydroxide, in particular sodium hydroxide recycled from pulp production, is used in the cationization stage. By using sodium hydroxide, especially recycled sodium hydroxide from pulp production, as the cationizing agent in this case, the chemical requirement is reduced, and it is ensured that the sodium hydroxide, which is always present in paper and pulp production, can be used effectively. Surprisingly, it has been shown that, with regard to the contamination of the cationized starch produced, the subsequent purification is able to remove all impurities that may have been introduced with the recycled base.

[0021] A particularly advantageous aspect of the present process is that the cationization is carried out to a degree of cationization between 0.02 and 0.5, and especially between 0.04 and 0.35, as required in subsequent paper or board production. This makes it possible to precisely meet the requirements of the respective paper and pulp production process, and unlike commercially available starches, it is not necessary to compromise between available and required degrees of starch substitution. Instead, the substitution can be carried out exactly to the point that is required and particularly advantageous in the respective paper and board production process.While this advantage could theoretically be achieved using state-of-the-art methods, it is not practically feasible, particularly when starch has to be supplied or purchased from a third party, as only certain products can be manufactured identically and industrial production cannot be customized. For this reason, on-site application of the process in a wood pulp, paper, or board mill is preferred, as this allows for the precise provision of the required cationization, anionization, or derivatization levels.

[0022] Finally, it was found that, surprisingly, a wide variety of starch raw materials can be used with the process according to the invention without any deterioration in the process yield. For this reason, the process according to the invention has been further developed such that a native starch selected from tuber starch, such as potato starch or tapioca starch, cereal starch such as corn starch, waxy corn starch, wheat starch, barley starch, rice starch, or fruit starch, such as starch from pulses, or mixtures of two or more of these, is used as the starch raw material.In addition to starches commonly used in paper and cardboard production, such as potato starch, corn starch or possibly wheat starch, all other starch-containing plants can be used as raw materials supplying the starch, since, due to the possibility of efficient purification after derivatization, even higher levels of impurities, which may originate from cereal starches, for example, can be separated at any time.

[0023] The invention is explained in more detail below with reference to a drawing and exemplary embodiments, and in particular a comparison of the process according to the prior art and the process according to the invention is shown, from which it can be seen that the derivatized starch obtainable with the process according to the invention has a significantly higher purity than that obtainable with the processes according to the prior art.

[0024] The drawing shows a flowchart illustrating the possible process sequences for producing derivatized starch according to the invention.

[0025] In this flowchart, 1 denotes a starch storage silo containing any unpurified starch, selected from tuber starch such as potato or tapioca starch, cereal starch such as corn, wheat, or barley starch, or fruit starch such as pulse starch, or mixtures thereof. From this starch storage silo 1, the starch is conveyed either to a wet derivatization process, generally designated 2, or to a dry derivatization process, generally designated 3. In wet derivatization 2, starch from the starch storage silo 1 is conveyed by a screw conveyor into a slurry tank 4, where it is mixed with water to form a starch suspension with a starch concentration of 30 to 40 wt% by stirring. A protective salt, for example, Na₂SO₄, is added to this starch suspension and further stirred.Either in the slurry tank 4 itself or in a separate derivatization tank 5, the wet derivatization is subsequently carried out by adding a cationizing reagent, such as 2,3-epoxypropyltrimethylammonium chloride, optionally activators, or further substitution reagents, such as salts for phosphorization. This mixture is stirred for approximately 20 minutes, and then the pH is gradually increased to 11.8 by adding 4% NaOH and stirring continues. To complete the cationization, the temperature is increased to approximately 40 °C, and the reaction mixture is maintained at a pH of 11.8 throughout the entire reaction time by adding sodium hydroxide solution as needed. After completion of the reaction, the pH of the reaction mixture is adjusted by adding dilute mineral acid, such as...Hydrochloric acid was lowered to a pH of 9 in cleaning step 6 and held for a short time.

[0026] To separate excess cationizing agent, reaction byproducts, added and formed salts, dissolved proteins, and raw material impurities, the cationized starch suspension is purified by adding further water using a decanter, hydrocyclone, or separators. This purification step can be repeated a second or several times, if necessary, to remove any remaining impurities.

[0027] The cationized starch produced in this way can, if necessary, be stored at a temperature between 4 and 25 °C and a pH of 7.1 to 9, which can be adjusted by adding dilute acid if required. The starch then has a density between 12° Beaume and 21° Beaume, or 15% to 39% by weight starch in the slurry. Of course, the starch can also be processed directly without storage.

[0028] An alternative method is dry derivatization, which is carried out according to cycle 3. For this purpose, unpurified starch is fed from starch storage silo 1 into mixing reactor 7 via a screw conveyor, where it is mixed with solid calcium hydroxide and an activator, such as silicates. To carry out the derivatization, a small amount of water and sodium hydroxide solution is sprayed onto the dry starch mixture and mixed. Subsequently, the cationizing agent, such as 2,3-epoxypropyltrimethylammonium chloride, is sprayed on and mixed. The temperature is then gradually increased to a reaction temperature of 30 to 80 °C and allowed to stand at this temperature for 24 to 120 hours to complete the reaction and achieve the desired degree of starch substitution.The cationized starch is then suspended in a slurry with dilute mineral acid at step 8 until the pH is lowered to approximately 7 to 10. This cationized starch is then subjected to purification step 6 to remove excess cationizing agent, reaction byproducts, added and formed salts, raw material impurities, dissolved proteins, and the like. This is achieved by adding water and purifying the starch using a decanter, hydrocyclone, or separators. After purification, the starch can be stored, if necessary, or immediately sent for gelatinization. Such cationized starch is stored at temperatures between 4 °C and 25 °C, a pH of 7.1 to 9 (adjusted by adding dilute mineral acid), and a density between 12° and 21° Beaumé, or a starch content of 15% to 39% by weight in the slurry.

[0029] Immediately after purification or from a storage tank, the cationized starch is subsequently subjected to gelatinization at step 9 by cooking it in a steam injection cooker at approximately 125 °C for 1 to 20 minutes with a starch suspension concentration in the cooker between 4 wt.% and 38 wt.%.

[0030] The gelatinized starch can then be stored in a storage tank at approximately 70 °C and a pH of 7 to 8.5, achieved by adding diluted mineral acid, and subsequently further diluted or its pH adjusted for specific applications in the paper and pulp industry. In the storage tank, the gelatinized starch has a temperature of approximately 70 °C, a concentration of 3 to 35% by weight, and a pH between 7 and 8.5.

[0031] In the storage tank 10, the starch can subsequently be further processed in an alkenyl succinic anhydride (ASA) process 11, in which the gelatinized starch (1 to 4 wt%) is adjusted to a pH of 2 to 6.5 by adding dilute acid, in particular mineral acid. Another possible application is the use of the gelatinized starch as the bulk starch in the pulp, as indicated in 12. Here, the content of gelatinized starch in the suspension will be 1 to 4 wt%, and the pH will again be between 2 and 6.5, adjusted by adding dilute mineral acid. This pH can be adjusted, if necessary, depending on the desired pH of the paper pulp pulp.The third possible application is the use of gelatinized starch as bulk starch in thin form, as indicated in 13, whereby the concentration of the starch suspension is essentially the same as that of the ASA or thick form application, but the pH value is chosen to be somewhat higher, namely 5 to 7, which pH value is also adjusted by the use of dilute mineral acid.

[0032] Compared to the conventional method for producing derivatized, gelatinized starch, the inventive method differs in the purification step provided after derivatization. This purification step was previously unknown in the case of dry-cationized starch, since dry-cationized starch according to the prior art is used without any further purification. It differs from wet-cationized starch in that, instead of simply rinsing with water, a specially selected purification device, such as a hydrocyclone, decanter, or separator, is used. Surprisingly, this device succeeds not only in removing water-soluble impurities but also, due to the alkaline nature of the purification step, in removing all alkali-soluble proteins, starch impurities, reaction byproducts such as glycols, residual reagents, and other contaminants.such as residual epoxides and low-molecular-weight starch degradation products. This process therefore makes it possible to obtain a derivatized starch of high purity from an unpurified starch raw material, which subsequently results in better starch swelling during gelatinization, thus yielding an overall higher-quality product with greater purity.

[0033] The above-described process for producing high-purity derivatized starch is subsequently compared with conventional cationization methods, both wet and dry, using various pre-purified starting starches. For these comparative experiments, wet and dry cationization were carried out as described in the literature. In the dry cationization process, the reaction mixture was pre-dried in a hot air dryer at 50 °C after the cationization procedure, and fumaric acid was added until a 5% suspension of the resulting powder in water at a pH of 5.5 was obtained.In the wet cationization process according to the state of the art, cationization was carried out as described in the literature, and the resulting reaction mixture was acidified to a pH of 5.5 with dilute hydrochloric acid after the reaction was complete, filtered, washed twice with water, and the filter cake was dried to a dry powder in a hot air dryer at 50 °C.

[0034] The dry cationization process or wet cationization process according to the invention was carried out as shown in the flow diagram. In the wet cationization process, purification was performed at the end of the reaction by adding dilute mineral acid until a pH of 9 was reached and concentrating the suspension in a hydrocyclone. The concentrated starch suspension thus obtained was adjusted to pH 7 by adding dilute mineral acid and dried in a hot air dryer at 50 °C to obtain a sample for subsequent analysis. In the case of dry cationization, water with pH 8 was added after the reaction was complete until a suspension with a content of 30 wt.-% starch was obtained, the suspension was adjusted to pH 8 by adding further dilute mineral acid, the slurry was purified in a hydrocyclone and the concentrate thus obtained was adjusted to pH 7 with dilute mineral acid, filtered and the resulting filter cake was dried in a hot air dryer at 50 °C to a dry powder in order to obtain a sample for subsequent analysis.

[0035] The experiments were carried out with potato starch and corn starch, and when verifying the efficiency of the inventive process, the total nitrogen after purification according to Kjeldahl was determined, where % N according to the normalized Kjeldahl method gives the sum of nitrogen present in the sample, which corresponds to the % nitrogen that was actually substituted + the % nitrogen from the reaction by-products + the % nitrogen from the proteins obtained.

[0036] A second verification criterion concerned the insoluble components in the dry substance. For this, 100 g of sample were reacted after acid hydrolysis in 600 ml of 0.1 normal hydrochloric acid at 100 °C for 30 minutes, and the insoluble residue was determined gravimetrically after filtration and two washes with distilled water. The results are shown in Table 1 below. Table 1 Test number Strength type State of the art invention % N of dry matter according to Kjeldahl Insoluble matter of the dry substance 1 Potato starch 1 Dry process 0,40 630 mg / kg 2 Potato starch 1 Dry process 0,26 100 mg / kg 3 Cornstarch 1 Dry process 0,37 570 mg / kg 4 Cornstarch 1 Dry process 0,29 120 mg / kg 5 Cornstarch 2 Wet process 036 2400 mg / kg 6 Cornstarch 2 Wet process 0,29 450 mg / kg 7 Cornstarch 2 Wet process 0,22 630 mg / kg 8 Cornstarch 2 Wet process 0,16 290 mg / kg 9 Cornstarch 3 Dry process 0,42 330 mg / kg 10 Cornstarch 3 Dry process 0,29 130 mg / kg 11 Potato starch 2 Wet process 0,41 910 mg / kg 12 Potato starch 2 Wet process 0,31 100 mg / kg

[0037] Table 1 shows that in all experiments carried out according to the method of the present invention, the total nitrogen according to Kjeldahl after purification according to the invention is lower than that after purification according to the prior art, and the content of insoluble substances in the dry substance could be significantly reduced compared to the prior art method, in some cases even by about 90%.

[0038] The purified, derivatized starches produced in this way were subsequently used in thickened solids, thin solids and sizing agents in the following concentrations and under the following conditions, and possible improvements and savings in chemicals were investigated.

[0039] Examples: Application in thick materials: High-purity derivatized starch, particularly corn starch, potato starch, or mixtures thereof, which can be used cationically, anionically, or amphotericly, is added to the bulk pulp in a consistency range of 3 to 35 wt% (corresponding to 30 to 350 g dry pulp / l water), especially 4 to 30 wt%, in an amount of 0.05 to 2.5% based on the dry pulp or paper. This is used to increase paper strength, particularly dry strength, and also for impurity fixation. The application, which takes place at pH values ​​of 5 to 9, optionally with the addition of other processing aids, and at temperatures of 30 to 80 °C, is generally carried out using pre-milled pulp to which high-purity derivatized starch is added. Unmilled pulp can also be used if necessary.Furthermore, the fibrous material may have previously undergone high-consistency, medium-consistency, and / or low-consistency milling (fiber content: high-consistency milling: 20–35%, medium-consistency milling: 10–20%, low-consistency milling: 3–10%). By using high-purity derivatized starch in the thickened solids, the amount of aluminum sulfate required was reduced by approximately 30%. This was achieved because, firstly, starch acidified specifically for the intended application could be used (due to the on-site production of the high-purity derivatized starch), and secondly, only significantly reduced amounts of defoamer were required in the thickened solids. This reduction stemmed from the substantial decrease in the non-starch-bound nitrogen content of the derivatized starch, which in turn reduced foaming even without the addition of defoamer. Application in thin materials

[0040] High-purity derivatized starch, particularly corn starch, potato starch, or mixtures thereof, which can be used cationically, anionically, or amphotericly, is added in bulk to the thin solids in the consistency range of 0.15–3%, especially 0.18–2%, at a quantity of 0.05–0.5% based on the dry pulp or paper to increase fine particle retention and impurity fixation. Application takes place at pH values ​​of 5 to 8, temperatures of 30–80 °C, and optionally with the addition of other processing aids.

[0041] By using a high-purity derivatized starch in the thin slurry, the reactivity is improved, and in particular, the sieving water can be adjusted to the optimal, desired pH value. This allows for control of the fine fiber load and reduces the need for retention agents. Furthermore, only reduced amounts of defoamer were required in the thin slurry. This is because the non-starch-bound nitrogen content in the derivatized starch was significantly reduced, thus minimizing foaming even without the addition of defoamer. Application in the ASA sizing process

[0042] Derivatized starches of high purity, in particular corn starch, potato starch, or mixtures thereof, which can be used cationically, anionically, or amphotericly, are preferably used in an acidified state with a pH of 2 to < 7 in the production of emulsions with sizing agents such as ASA (alkenyl succinic anhydride). Here, the starches are used as a protective colloid in an amount of 0.05–0.3% based on the dry pulp or paper to produce a stable sizing agent emulsion. The temperatures used are max. 60 °C, and the pH values ​​are preferably max. 8.7, particularly preferably in the range between pH 2 and pH 7, since otherwise degradation products from the sizing agent are to be expected, which is inefficient overall, and furthermore the formation of deposits and deposition of these degradation products on various parts of the paper machine is unfavorable for the operation of the paper machine, since in this case cleaning of the machine using cleaning chemicals is necessary.

[0043] By using a high-purity derivatized starch, the pH value can be adjusted to the lowest possible, and therefore ideal, level. This prevents the starch from hydrolyzing and thus results in better sizing properties. Tests have shown that using this high-purity derivatized starch achieved Cobb values ​​according to ISO 535:2014 that were comparable to those of conventional sizing methods, which, however, required at least 10% more ASA to achieve the same Cobb values.

[0044] In each of these applications, it was shown that when using the derivatized starch produced according to the invention, a significant saving in chemicals such as aluminium sulfate could be achieved, and moreover, pH adjustment of the cellulose fiber mixture treated with the starch could be omitted with this process.

Claims

1. Method for producing high-purity derivatised starch which can be used in the manufacture of paper and cardboard in which method a starch raw material is subjected to at least the following steps: purification, slurrying, derivatisation, gelatinisation, pH adjustment, characterized in that a slurry of the derivatised starch obtained after the slurrying and derivatisation method steps carried out in any sequence is subjected to purification by washing and concentrating in a device selected from a decanter, hydrocyclone or separators at an alkaline pH and that the purified and gelatinised derivatised starch obtained after gelatinisation is mixed at least once with dilute acid.

2. Method according to claim 1, characterized in that the slurry of derivatised starch is purified in at least two steps, a first alkaline washing step and a second step of washing and concentrating the slurry.

3. Method according to claim 1 or 2, characterized in that the second step of washing is carried out by adding at least one acid selected from mineral acids and / or organic acids and setting the pH to pH 7 to 9.

4. Method according to any one of claims 1 to 3, characterized in that in the purification the slurry of derivatised starch is concentrated to a solid content of 2 to 42 wt.%, in particular 5 to 35 wt.%.

5. Method according to any one of claims 1 to 4, characterized in that the purified and gelatinised derivatised starch obtained after the gelatinisation is subjected to a two-stage acidification.

6. Method according to any one of claims 1 to 5, characterized in that as derivatisation, a cationisation is carried out with a base selected from the group of alkali hydroxides such as, for example, NaOH, KOH, LiOH, alkali carbonates such as, for example, Na2CO3 or alkaline earth oxides such as, for example, CaO or alkaline earth hydroxides such as Ca(OH)2, in particular NaOH, a cationisation reagent, in particular 3-chloro-2-hydroxy-propyl-trimethylammonium chloride or an epoxidic cationisation reagent such as 2,3 epoxy-propyl-trimethyl-ammonium chloride and optionally further substitution reagents and optional adjuvants selected from activators such as silicates, calcium oxide or calcium hydroxide.

7. Method according to claim 6, characterized in that sodium hydroxide solution, in particular sodium hydroxide solution recycled from a pulp production, is used in the cationisation.

8. Method according to any one of claims 1 to 7, characterized in that the cationisation is performed to a degree of cationisation between 0.02 and 0.5, in particular a degree of cationisation between 0.04 and 0.35 required in the subsequent paper or cardboard production.

9. Method according to any one of claims 1 to 8, characterized in that a native starch selected from bulbous starch such as potato starch or tapioca starch, cereal starch such as maize starch, waxy maize starch, wheat starch, barley starch, rice starch or fruit starch such as starch from legumes or mixtures of two or more thereof is used as starch raw material.

10. Method according to any one of claims 1 to 9, characterized in that the starch is used immediately after its derivatisation in wood pulp, pulp, paper or cardboard manufacture.