Method for coextruding a starch comprising an acid and a glyoxal-containing crosslinker

Abstract

The invention relates to a method for producing a starch product, having the steps of: (a) providing a starch and (b) coextruding the starch, which comprises (i) an acid and / or a salt of an acid and (ii) a glyoxal-containing crosslinker, in order to obtain a starch product. The invention is characterized in that the acid or the salt of the acid has a pKs value of 2.7 or less, and the quantity of the glyoxal-containing crosslinker ranges from 0.1 to 5.0 wt.%, based on the weight of the starch. The invention additionally relates to a starch product which can be obtained using the method according to the invention, wherein the starch product has a glyoxal-containing crosslinker quantity ranging from 0.1 to 5.0 wt.%, based on the total weight of the starch product, to a coating color which has the starch product in a quantity of 0.5 to 14.0 wt.%, based on the total weight of the coating color, and to an adhesive formulation which has a starch product in a quantity of 5.0 to 65.0 wt.%, based on the total weight of the adhesive formulation.

Description

[0001] Process for coextrusion of a starch with an acid and a glyoxal-containing crosslinker

[0002] The present invention relates to a process for producing a starch product, comprising the steps:

[0003] (a) providing a strength, and

[0004] (b) coextruding the starch with (i) an acid and / or a salt of an acid, and (ii) a glyoxal-containing crosslinker to obtain a starch product.

[0005] By adding acids to starches, the latter can be hydrolyzed and thus degraded. Acids can also be used as plasticizers for starches. To stabilize the viscosity of starches during and after their degradation, it is known in the art to add a crosslinker.

[0006] For example, WO 2016 / 097149 A1 describes a process for destructuring starches, wherein an organic acid can be added as a depolymerizing agent in an amount of 0.1 to 10 wt%, based on the amount of starch. Glyoxal can be added as a crosslinking agent in an amount of 0.1 to 5 wt%, also based on the amount of starch. The resulting destructured starch can be added to elastomer mixtures to reduce hysteresis.

[0007] EP 2 370 503 A1 discloses the production of a biolatex conjugate composition, wherein starch, a plasticizer (e.g., citric acid), and an additive are added to an extruder. Shearing creates a biopolymer-additive complex, to which a crosslinker (e.g., glyoxal) is added in a zone of the extruder downstream of the feed zone. The crosslinker can prevent the biolatex conjugate composition from dissolving when dispersed in water.

[0008] CN 103 467 609 A describes the production of a nano-carboxymethyl starch, whereby a mixture of starch, a plasticizer, monochloroacetic acid, and an alkalizing agent is fed into an extruder. A crosslinker (e.g., glyoxal) is then added to the extruder for coextrusion with this mixture.

[0009] EP 0 087 847 A1 discloses the production of cold-soluble starch powders for the food industry, in which starch is extruded with a blowing agent. An organic or inorganic acid can be added as a blowing agent in an amount of 0.01 to 10 wt.%, based on the starch content. To modify the starch, a crosslinking agent, such as glyoxal, can also be added during extrusion to improve the water resistance of the starch powder.

[0010] CN 103 924 480 A concerns a process in the papermaking industry. It uses a "functional reinforcing agent" containing 40-60 wt% starch, 5-30 wt% of a charge modifier, 1-20 wt% grafting agent, 1-15 wt% crosslinker, 1-8 wt% sodium hydroxide, and 1-3 wt% acid. However, CN 103 924 480 A provides no indication of using glyoxal as the crosslinker, nor of using a crosslinker amount in the range of 0.1-5.0 wt% (based on the weight of the starch).

[0011] WO 00 / 69916 A1 relates to a process for producing biopolymer nanoparticles, in particular starch nanoparticles, wherein a composition comprising starch and a crosslinker (such as glyoxal) is coextruded. US 2004 / 149165 A1 discloses a starch composition from which thermoplastic fibers are subsequently produced, wherein the composition contains 50-75 wt% of a modified starch, 0.1-10 wt% of an aldehyde crosslinker, and 25-50 wt% water; an acid catalyst may also be included to adjust a pH of 1.5-5.0. However, in this document, no coextrusion of the starch with a glyoxal-containing crosslinker and the acid takes place; instead, the compositions are prepared in a beaker by stirring at elevated temperature.

[0012] CN 104 031 583 A relates to a process for producing a biopolymer binder for coating paper, wherein first, an aqueous solution containing an initiator is prepared. The starch is then mixed with the solution, and the temperature is raised to 60-80°C, whereupon the previously obtained hydrogen peroxide is mixed with the starch and sulfuric acid. Then, at 70-90°C, an aqueous initiator solution, as well as a cationic monomer and a silane, are added to the resulting product. Finally, a crosslinker is added, followed by cooling to 25°C and adding a neutralizing agent to obtain the polymer. This process also does not disclose coextrusion of the starch with the crosslinker and an acid.

[0013] The starch products obtainable using the processes known in the prior art exhibit high viscosity, poor viscosity stability, and / or poor solubility, which is disadvantageous in terms of application. Therefore, there is a need for starch products with improved application properties. An object of the present invention is to alleviate or eliminate at least some of these disadvantages of the prior art and to provide an improved starch product. Such an improved starch product should preferably exhibit the highest possible solubility and / or a low viscosity and / or good viscosity stability and / or few or no nanoparticles (in the range <1000 nm).

[0014] Accordingly, the present invention relates to a process as mentioned above, in which the acid or the salt of the acid has a pKa value of 2.7 or below, and wherein the amount of the glyoxal-containing crosslinker is in the range of 0.1 to 5.0 wt%, based on the weight of the starch, wherein the glyoxal-containing crosslinker is preferably added in a compression zone of an extruder, whereby a starch product is produced which does not have nanoparticles in the range of less than 1000 nm.

[0015] Surprisingly, starch products produced according to the invention exhibit both low viscosity and good viscosity stability and solubility. Furthermore, the starch products according to the invention contain no detectable nanoparticles, i.e., they are essentially free of starch particles with a size of less than 1000 nm. This makes them highly suitable for use in adhesive formulations and coatings. According to the invention, particle size is preferably determined using dynamic light scattering (DLS), in particular as shown in the examples.

[0016] However, if the amount of the glyoxal-containing crosslinker is below 0.1 wt%, based on the weight of the starch, the starch product exhibits a low degree of degradation and / or insufficient viscosity stability. If the amount of the glyoxal-containing crosslinker is above 5.0 wt%, based on the weight of the starch, this leads to a deterioration in the processing properties of the starch product. If the pKa value of the acid is above 2.7, the resulting starch products exhibit low solubility, high viscosity, and / or poor viscosity stability.

[0017] The starch provided can be any starch, including a waxy starch. The use of modified starches, for example, cationized and / or hydrophobized starches, is also possible. Preferably, the starch is selected from the group comprising corn starch, waxy maize starch, and wheat starch, or a mixture thereof. The starch products obtained according to the invention are particularly suitable for use in adhesive formulations and coatings.

[0018] The amount of the glyoxal-containing crosslinker is preferably in the range of 0.1 to 2.0 wt%, preferably 0.5 to 2.0 wt%, particularly preferably 1.0 to 1.5 wt%, based on the weight of the starch. In this range, the good viscosity and solubility properties of the starch product obtained by the process are particularly evident.

[0019] The glyoxal-containing crosslinker can be selected from the group comprising glyoxal and glyoxal-containing resins, or a mixture thereof. Preferably, the glyoxal-containing crosslinker is glyoxal. The starch product then exhibits particularly good viscosity stability. The glyoxal-containing resin can comprise Berset 2125, Berset 2169, or a mixture thereof (both available from Bercen Chemicals, USA).

[0020] The glyoxal can be in the form of an aqueous solution containing 20 to 40 wt% glyoxal, preferably 30 to 40 wt% glyoxal, based on the total weight of the aqueous solution. This can increase the stability of the glyoxal. The higher the glyoxal concentration in the aqueous solution, the lower the amount of aqueous solution that needs to be added to obtain a starch product with the desired amount of glyoxal. Consequently, the lower the amount of water that needs to be subsequently removed to obtain a dry starch product, and the more energy-efficient the starch product can be dried. A 35 to 40 wt% aqueous solution of glyoxal is particularly preferred. This allows a good balance to be achieved between glyoxal stability and process efficiency.

[0021] The acid and / or the acid salt preferably has a pKa of 2.5 or below, more preferably 2.35 or below, particularly preferably 2.2 or below. Furthermore, the acid and / or the acid salt preferably has a pKa of -3 or above, more preferably 0 or above, even more preferably 1.2 or above, particularly preferably 1.9 or above. The pKa of the acid and / or the salt is preferably in the range of -3 to 2.7, more preferably 0 to 2.7, even more preferably 1.2 to 2.5, even more preferably 1.2 to 2.35, most preferably 1.9 to 2.2. This allows the viscosity and solubility properties of the starch product to be further improved.

[0022] The acid is preferably selected from the group comprising sulfuric acid (pKa of -3), nitric acid (pKa of -1.32), phosphoric acid (pKa of 2.16), and a dicarboxylic acid, or a mixture thereof. The dicarboxylic acid preferably comprises oxalic acid (pKa of 1.27) and / or maleic acid (pKa of 1.93). The salt of the acid preferably comprises a hydrogen sulfate, in particular sodium hydrogen sulfate (pKa of 1.96). It has been found that a starch product produced using these acids or salts has particularly good application properties, in particular good viscosity stability and a short curing time, when used in an adhesive formulation.However, it was found that the use of malonic acid (pKa value of 2.83), tartaric acid (pKa value of 2.93) and citric acid (pKa value of 3.13), which have a pKa value above 2.7, leads to starch products with inadequate properties, in particular with low solubility and a comparatively high viscosity or low viscosity stability.

[0023] The amount of acid or salt is preferably in the range of 1.0 to 6.0 wt%, more preferably 1.5 to 5.5 wt%, based on the weight of the starch. The degree of starch degradation is then in an optimal range, i.e., the starch is sufficiently degraded, while at the same time, its stability can be maintained (also due to the presence of the glyoxal-containing crosslinker during coextrusion). If an acid and a salt are coextruded with the starch in step (b), these amounts refer to the sum of the amounts of acid and salt.

[0024] The acid or salt of the acid can be solid. If a solid acid or salt is used, a premix can be prepared with the starch, and this premix can then be extruded. Alternatively, the solid acid or salt can be added to the starch in an extruder, particularly in a feed zone of the extruder.

[0025] Alternatively, the acid or the acid salt can be in an aqueous solution. The aqueous solution preferably contains 20 to 40 wt% of the acid or salt, more preferably 25 to 35 wt%, based on the total weight of the aqueous solution. The aqueous solution of the acid or salt can then be fed into the extruder, in particular into a compression zone of the extruder. Alternatively, a starch slurry comprising water and 20 to 50 wt% starch, preferably 30 to 40 wt% starch, can be prepared (the amount of starch is based on the total weight of the starch slurry). Acid or salt can then be added to this starch slurry until a specific pH is reached. The pH of the starch slurry is preferably adjusted to 3 or below by adding the acid or salt, more preferably to 2 or below, and even more preferably to 1.5 or below.The starch acidified in this way can then be dewatered, for example in a centrifuge. The starch can then be dried. After drying, the starch preferably comprises a water content of 20% by weight or less, more preferably 15% by weight or less, based on the weight of the starch, and can be used in the process according to the invention. During dewatering, some of the previously added acid or some of the previously added salt can also be removed, so that the amount of acid or salt with which the starch is coextruded can be somewhat lower compared to an amount of acid or salt if it is added directly to the extruder. The amount of acid or salt can range from 0.1 to 6.0% by weight, preferably from 1.0 to 6.0% by weight, more preferably from 1.5 to 5.5% by weight, based on the weight of the starch.

[0026] Preferably, a viscosity stabilizer is added to the starch during coextrusion in step (b). This can further improve the extrudability of the starch and the viscosity properties of the starch product. The viscosity stabilizer preferably comprises a fatty alcohol. A fatty alcohol is understood to be an aliphatic, monohydric alcohol, preferably a primary alcohol. The fatty alcohol preferably contains 10 to 20 carbon atoms per molecule, more preferably 14 to 18, and especially 16. Such fatty alcohols can be readily mixed and coextruded with the starch, the glyoxal-containing crosslinker, and the acid or salt.

[0027] The viscosity stabilizer is preferably added in an amount of 0.1 to 1.5 wt%, more preferably 0.3 to 1.3 wt%, and even more preferably 0.5 to 1 wt%, based on the weight of the starch. This can further improve the homogeneity of the starch product.

[0028] If a viscosity stabilizer is added to the starch, the amount of the glyoxal-containing crosslinker is preferably in the range of 0.2 to 0.7 wt%, more preferably 0.4 to 0.6 wt%, based on the weight of the starch. This allows for optimized stabilization of the starch's viscosity during coextrusion. However, the amount of the glyoxal-containing crosslinker can also be above this preferred range, and process parameters during extrusion, such as the speed and / or temperature in the extruder, can be adjusted.

[0029] During coextrusion in step (b), at least some of the functional groups, in particular hydroxyl groups, of the starch are hydrolyzed in the presence of the acid or salt, whereby the starch is at least partially degraded (i.e., destructured). At least some of the functional groups of the starch react with the glyoxal-containing crosslinker, thereby increasing the crosslinking density and / or the degree of branching of the starch. Accordingly, a comparatively high specific mechanical energy can be introduced during the extrusion of the starch product according to the invention in order to produce a homogeneous starch product.

[0030] A screw extruder, as preferably used in the process according to the invention, comprises an extruder screw and is generally divided into three zones that perform different tasks (see also Fig. 1). The so-called feed zone is located at the rear of the screw barrel. The material to be extruded, which may be in the form of solids such as granules or powder, is fed into this zone via a hopper ("feeding"). The rotation of the screw advances the material. This zone is followed by the compression zone, in which the material is further compacted by the reduced flight depth of the screw, thus building up the pressure required for discharge into the tool. In the subsequent reaction zone, the starch gelatinizes and any chemical reactions take place. Finally, the discharge zone or metering zone ensures a homogeneous material flow to the tool.

[0031] Extruders are available with one, two, or more screw shafts. In single-screw and (co-rotating) twin-screw extruders, conveying and pressure buildup are achieved by the friction of the mass rotating with the screw against the stationary barrel wall (barrel) ("friction conveying"). The mass thus retained in the rotation is pushed by the helical screw flights to the outlet nozzle. In counter-rotating twin-screw extruders, the principle of forced conveying predominates.

[0032] Twin-screw extruders are preferably used in the process according to the invention. For example, in a co-rotating twin-screw extruder, the screws rotate in the same direction, while in a counter-rotating twin-screw extruder, they rotate in the opposite direction. The screws can be arranged parallel or conically. Since the clearance between the screws is particularly tight and the tendency to wear is correspondingly higher, they must meet the highest quality criteria in terms of strength and hardness.

[0033] The coextrusion according to the invention can be carried out in a twin-screw extruder. This allows a homogeneous starch product to be obtained. The (optionally acidified) starch can be added in a feed zone of the extruder. If no acid or salt has yet been added, the addition can take place in the extruder, as described above.

[0034] In step (b), the temperature in the discharge zone of the extruder is preferably in the range of 100 to 180 °C, more preferably 120 to 150 °C, and even more preferably 135 to 145 °C. From the feed zone to the discharge zone, the temperature is preferably increased gradually. In the feed zone itself, the temperature can be in the range of 20 to 30 °C. This also allows for good plasticization and mixing.

[0035] During coextrusion, 90 wt% or more of the glyoxal-containing crosslinker can react with the starch, preferably 95 wt% or more, more preferably 99 wt% or more, based on the weight of the starch. The high yield of the reaction of the starch with the glyoxal-containing crosslinker according to the invention can be determined by exhaust air analysis of the vapors emerging from the extruder. If the melt temperature in the extruder during coextrusion exceeds the boiling point of the glyoxal-containing crosslinker, this results in the evaporation of any unreacted glyoxal-containing crosslinker. For example, a 40 wt% aqueous solution of glyoxal has a boiling point of 104°C. A melt temperature of 104°C can be reached or exceeded in the process simply due to the preset temperature (which can increase further due to shear).Surprisingly, the glyoxal-containing crosslinker according to the invention is nevertheless undetectable in the exhaust air, indicating an essentially complete reaction with the starch. Thus, the process according to the invention can be carried out efficiently and in an environmentally friendly manner.

[0036] The process may comprise a further step (c): drying the starch product. This can make the starch product harder and / or more brittle, which can facilitate further processing, particularly milling. A dryer, preferably a fluidized-bed dryer, can be used to dry the starch product. This allows the starch product to be thoroughly dried without thermal damage.

[0037] After drying in step (c), the starch product can be ground. This makes the starch product storable and ready for sale. In this form, it can also be used for the production of adhesive formulations or coatings. Preferably, the starch product is ground into a powder with a d5o particle size of 200 to 400 μm, more preferably 250 to 350 μm. The starch product can then be easily mixed into a formulation, which is advantageous for the production of adhesive formulations or coatings. The d5o particle sizes stated in this paragraph and below are determined according to the ISO 8130-13:2019 standard.

[0038] The invention further relates to a starch product obtainable by the process according to the invention and comprising an amount of the glyoxal-containing crosslinker in the range of 0.1 to 5.0 wt.%, preferably from 0.2 to 2.0 wt.%, more preferably from 0.5 to 2.0 wt.%, even more preferably from 1.0 to 1.5 wt.%, based on the total weight of the starch product. Such a starch product exhibits both a low viscosity and good viscosity stability and good solubility.

[0039] The starch product preferably contains an amount of acid or salt in the range of 0.3 to 6.0 wt%, more preferably 1.0 to 5.5 wt%, based on the total weight of the starch product. If the starch product contains an acid and a salt, these amounts refer to the sum of the amounts of acid and salt.

[0040] The starch product preferably has a solubility of 70% or higher, more preferably 80% or higher, even more preferably 85% or higher, and most preferably 90% or higher. This can facilitate the production of coatings or adhesive formulations in which the starch product is used. The solubility data in this paragraph and below are determined according to Method 2 of this description.

[0041] The starch product preferably has a viscosity of 5000 mPas or below, more preferably 2500 mPas or below, even more preferably 2000 mPas or below, even more preferably 600 mPas or below, particularly preferably in the range from 100 to 600 mPas. A lower viscosity can simplify the production of coating slips or adhesive formulations. A low viscosity can also bring advantages from an application point of view, since the application of such coating slips or adhesive formulations can then be carried out easily. The viscosity of the starch product for use in coating slips, in particular paper coating slips, is preferably 2000 mPas or below (for 25 wt% of the starch product in water). Furthermore, the viscosity of the starch product for use in adhesives is preferably 5000 mPas or below (for 50 wt% starch product in water).The viscosity data in this paragraph and below are determined according to Method 1 of this description.

[0042] The starch product preferably has a viscosity stability of 2.1 or below, more preferably 1.4 or below, even more preferably 1.15 or below, and most preferably 0.96 or below. This means that the viscosity changes little or not significantly between 24 and 168 hours after the starch product is manufactured. The starch product then has good storage stability. The viscosity stability data in this paragraph and below are determined according to Method 1 of this description.

[0043] The starch product preferably has a d5o particle size of 200 to 400 pm, more preferably 250 to 350 pm. This can result in easy mixing of the starch product, which is advantageous for the production of adhesive formulations or coatings.

[0044] The invention further relates to a coating composition comprising the starch product according to the invention in an amount of 0.5 to 14.0 wt.%, preferably 1.0 to 8.0 wt.%, based on the total weight of the coating composition. Such a coating composition is easy to produce due to the good viscosity and solubility properties of the starch product and has good application properties.

[0045] The invention further relates to an adhesive formulation comprising the starch product according to the invention in an amount of 5.0 to 65.0 wt.%, preferably 10.0 to 50.0 wt.%, based on the total weight of the adhesive formulation. Such an adhesive formulation is easy to produce due to the good viscosity and solubility properties of the starch product and has good application properties.

[0046] The curing time of the adhesive formulation is preferably 70 °C or below, preferably 60 °C or below, determined according to Method 3. This ensures sufficient adhesive strength and stability quickly.

[0047] The adhesive formulation preferably has a water content of 40% by weight or less, more preferably 35% by weight or less, based on the total weight of the adhesive formulation. Accordingly, the water ingress into the material to be bonded (e.g., paper) and thus the drying time can be reduced.

[0048] Furthermore, the use of the starch product according to the invention in a coating color or an adhesive formulation is disclosed.

[0049] All percentages in this description are in weight percent (wt%) unless expressly stated otherwise.

[0050] The invention particularly relates to the following embodiments:

[0051] 1. A process for producing a starch product, comprising the steps of:

[0052] (a) providing a strength, and

[0053] (b) coextruding the starch with (i) an acid and / or a salt of an acid, and (ii) a glyoxal-containing crosslinker to obtain a starch product, wherein the acid or the salt of the acid has a pKa of 2.7 or below, and wherein the amount of the glyoxal-containing crosslinker is in the range of 0.1 to 5.0 wt%, based on the weight of the starch.

[0054] 2. The method according to embodiment 1, wherein the starch is selected from the group comprising corn starch, waxy maize starch and wheat starch, or a mixture thereof.

[0055] 3. The process according to embodiment 1 or 2, wherein the amount of the glyoxal-containing crosslinker is in the range of 0.2 to 2.0 wt%, preferably 0.5 to 2.0 wt%, more preferably 1.0 to 1.5 wt%, based on the weight of the starch.

[0056] 4. The process according to any one of embodiments 1 to 3, wherein the glyoxal-containing crosslinker is selected from the group comprising glyoxal and glyoxal-containing resins, or a mixture thereof, preferably glyoxal.

[0057] 5. The process according to embodiment 4, wherein the glyoxal is in aqueous solution, wherein the aqueous solution contains 20 to 40 wt% glyoxal, preferably 30 to 40 wt%, more preferably 35 to 40 wt%, based on the total weight of the aqueous solution.

[0058] 6. The process according to any one of embodiments 1 to 5, wherein the acid and / or the salt has a pKa of 2.5 or below, preferably 2.35 or below, more preferably 2.2 or below; ; and / or wherein the acid and / or the salt has a pKa of -3 or above, more preferably 0 or above, even more preferably 1.2 or above, particularly preferably 1.9 or above; wherein the pKa of the acid and / or the salt is preferably in the range from -3 to 2.7, more preferably from 0 to 2.7, even more preferably from 1.2 to 2.5, even more preferably from 1.2 to 2.35, most preferably from 1.9 to 2.2. 7. The process according to any one of embodiments 1 to 6, wherein the acid is selected from the group comprising sulfuric acid, nitric acid, phosphoric acid and a dicarboxylic acid, or a mixture thereof.

[0059] 8. The process of embodiment 7, wherein the dicarboxylic acid comprises oxalic acid and / or maleic acid.

[0060] 9. The method according to any one of embodiments 1 to 8, wherein the salt comprises a hydrogen sulfate.

[0061] 10. The method of embodiment 9, wherein the salt comprises sodium hydrogen sulfate.

[0062] 11. The process according to any one of embodiments 1 to 10, wherein the amount of acid and / or salt is in the range from 0.1 to 6.0 wt%, preferably from 1.0 to 6.0 wt%, more preferably from 1.5 to 5.5 wt%, based on the weight of the starch.

[0063] 12. The process according to any one of embodiments 1 to 11, wherein the acid or salt is solid, preferably prior to step (b) the starch is mixed with the acid or salt to obtain a premix.

[0064] 13. The process according to any one of embodiments 1 to 11, wherein the acid or salt is solid, and wherein the acid or salt is added to the starch in a feed zone of an extruder.

[0065] 14. The process according to any one of embodiments 1 to 11, wherein the acid or salt is in an aqueous solution, wherein an amount of the acid or salt in the aqueous solution is preferably in the range of 20 to 40 wt%, more preferably 25 to 35 wt%, based on the total weight of the aqueous solution.

[0066] 15. The process according to embodiment 14, wherein the acid or salt is added to the starch in a compression zone of the extruder, wherein the extruder is preferably a screw extruder or a (co-rotating) twin-screw extruder.

[0067] 16. The process according to embodiment 14, wherein the acid or salt is added prior to step (a) to a starch slurry containing 20 to 50 wt% starch (based on the total weight of the starch slurry), preferably until a pH of the starch slurry of 3 or below, more preferably 2 or below, particularly preferably 1.5 or below, is reached.

[0068] 17. The process according to any one of embodiments 1 to 16, wherein the starch in step (b) is additionally coextruded with a viscosity stabilizer.

[0069] 18. The method of embodiment 17, wherein the viscosity stabilizer comprises a fatty alcohol.

[0070] 19. The process according to embodiment 18, wherein the fatty alcohol contains 10 to 20 carbon atoms per molecule, preferably 14 to 18, in particular 16.

[0071] 20. The process according to any one of embodiments 17 to 19, wherein the viscosity stabilizer is added in an amount of 0.1 to 1.5 wt%, more preferably 0.3 to 1.3 wt%, even more preferably 0.5 to 1 wt%, based on the weight of the starch.

[0072] 21. The process according to any one of embodiments 1 to 20, wherein the coextrusion in step (b) is carried out in a twin-screw extruder.

[0073] 22. The process according to any one of embodiments 1 to 21, wherein the starch is added in a feed zone of an extruder, wherein the extruder is preferably a screw extruder or a (co-rotating) twin-screw extruder. 23. The process according to any one of embodiments 1 to 22, wherein the glyoxal-containing crosslinker, in particular a glyoxal solution, is added in a compression zone of an extruder, wherein the extruder is preferably a screw extruder or a (co-rotating) twin-screw extruder.

[0074] 24. The process according to any one of embodiments 1 to 23, wherein in step (b) the temperature in the discharge zone of an extruder is in the range from 100 to 180°C, preferably from 120 to 150°C, more preferably from 135 to 145°C.

[0075] 25. The process according to any one of embodiments 1 to 24, further comprising step (c): drying the starch product.

[0076] 26. The process according to embodiment 25, wherein the drying of the starch product in step (c) is carried out in a fluid bed dryer.

[0077] 27. The process according to embodiment 25 or 26, wherein the starch product is milled after step (c), preferably to a powder having a d5o particle size of 200 to 400 pm, more preferably 250 to 350 pm.

[0078] 28. A starch product obtainable by a process according to any one of embodiments 1 to 27, wherein the starch product has an amount of the glyoxal-containing crosslinker in the range from 0.1 to 5.0 wt%, preferably from 0.2 to 2.0 wt%, more preferably from 0.5 to 2.0 wt%, even more preferably from 1.0 to 1.5 wt%, based on the total weight of the starch product.

[0079] 29. A starch product according to embodiment 28, wherein the starch product has an amount of the acid and / or the salt of the acid in the range of 0.3 to 6.0 wt%, preferably 1.0 to 5.5 wt%, based on the total weight of the starch product.

[0080] 30. A starch product according to embodiment 28 or 29, wherein the starch product has a solubility of 70% or above, more preferably 80% or above, even more preferably 85% or above, most preferably 90% or above.

[0081] 31. Starch product according to any one of embodiments 28 to 30, wherein the starch product has a viscosity of 5000 mPas or below, preferably of 2500 mPas or below, more preferably of 2000 mPas or below, even more preferably of 600 mPas or below, particularly preferably in the range of 100 to 600 mPas.

[0082] 32. Starch product according to any one of embodiments 28 to 31, wherein the starch product has a viscosity stability of 2.1 or below, more preferably 1.4 or below, even more preferably 1.15 or below, most preferably 0.96 or below.

[0083] 33. Starch product according to any one of embodiments 28 to 32, wherein the starch product has a d5o particle size of 200 to 400 pm, more preferably of 250 to 350 pm.

[0084] 34. A coating colour comprising a starch product according to any one of embodiments 28 to 33 in an amount of 0.5 to 14.0 wt%, preferably 1.0 to 8.0 wt%, based on the total weight of the coating colour.

[0085] 35. An adhesive formulation comprising a starch product according to any one of embodiments 28 to 33 in an amount of 5.0 to 65.0 wt.%, preferably 10.0 to 50.0 wt.%, based on the total weight of the adhesive formulation. 36. An adhesive formulation according to embodiment 35, wherein a curing time of the adhesive formulation is 70 sec or less, preferably 60 sec or less, determined according to method 3.

[0086] 37. Adhesive formulation according to embodiment 35 or 36, wherein the adhesive formulation has a water content of 40 wt% or less, preferably 35 wt% or less, based on the total weight of the adhesive formulation.

[0087] 38. Use of a starch product according to any one of embodiments 28 to 33 in a coating or adhesive formulation.

[0088] The invention is illustrated in more detail in the following examples and the drawing figure, but of course is not limited thereto.

[0089] Fig. 1 and Fig. 2 show schematic representations of the structures of slightly different screw configurations: at the very top is the "Screw configuration 2" from WO 00 / 69916 A1, in the middle the screw configuration used in the Theyson TSK 30 / 28D (used in the present examples) and below Coperion ZSK26MC18, with an extended reaction zone. The compression zone is the area after the feed zone and before the zones with the first shear elements. Here, no reactions or gelatinization of the starch occur. In the subsequent reaction zone, the starch is gelatinized with the help of kneading, mixing and shearing elements and reactions such as degradation and crosslinking take place. The metering of glyoxal according to WO 00 / 69916 A1 also takes place in the reaction zone (zone 5) (Fig. 2, B). The metering of glyoxal according to the invention preferably takes place in the compression zones, before gelatinization of the starch (Fig.2, A), since this leads to a starch product which - in contrast to the process according to WO 00 / 69916 A1 - does not contain any nanoparticles in the range of less than 1000 nm.

[0090] Fig. 3 shows the DLS measurement of SBR latex 10%: dilution 10 pl to 1 mL (A); the DLS measurement of starch latex: dilution 10 pl to 1 mL (B); the DLS measurement of product 1: dilution 10 pl to 1 mL (C); the DLS measurement of product 2: dilution 10 pl to 1 mL (D); the DLS measurement of extruded native WMS with maleic acid: dilution 10 pl to 1 mL (E); the DLS measurement of extruded native WMS: dilution 10 pl to 1 mL (F).

[0091] Examples

[0092] Example 1 - Production and analysis of starch products

[0093] The 20 experiments listed in Table 1 were conducted. Wheat starch (WS), corn starch (MS), and waxy maize starch (WMS) were used for the experiments. Sodium hydrogen sulfate (NaHSO4), oxalic acid, sulfuric acid (H2SO4), phosphoric acid (H3PO4), maleic acid, citric acid, and tartaric acid were used as acids or acid salts. The wt% values ​​given in Table 1 refer to the weight of the starch.

[0094] In experiments 1-9, 14, and 16-20, the acid or salt was added to the starch in solid form, and a premix was prepared in a drum mixer (Zimmermann Rhönradbau und Rohrbiegefertigungs GmbH, Germany) to obtain an acidified starch. In experiments 10, 11, and 15, starch slurries containing water and 35 wt% starch were first prepared in a large plastic stirred tank. The pH of these starch slurries was then adjusted to the value specified in Table 1 by adding the acid. The starch slurries were then dewatered in a centrifuge and dried using a flash dryer (Anhydro Spin Flash Dryer, SPX Flow Technology Germany GmbH, Germany). After drying, the acidified starches still contained approximately 12 wt% water.

[0095] In experiments 12 and 13, the acid (aqueous solution of phosphoric acid) was dosed directly into the compression zone of the extruder.

[0096] Experiments 19 and 20 correspond to Example 1 on pages 19-20 of WO 2016 / 097149 A1, whereby 14.4 wt% glycerol was added in Experiment 19 (based on the total weight of the starch product) to identically reproduce Example 1 of this document, while no glycerol was included in Experiment 20 to allow better comparability with the other experiments.

[0097] A twin-screw extruder (TSK-30 / 28D, Theysohn Extrusionstechnik GmbH, Germany) was used for extrusion. The starch (acidified if necessary) was added to the extruder in the feed zone. Water and a 40 wt% aqueous solution of glyoxal were added in the compression zone. Aqueous solutions of acids (in experiments 12 and 13) were also added in the compression zone. Sufficient water was added to achieve a dry matter content of 83 wt% (based on the total weight of the mixture to be extruded). Adding water can reduce shear during extrusion and thus the degradation of the starch products. The following parameters were used for extrusion: capacity: 10 kg / h; speed: 300 rpm; die geometry: 2 x 3.5 mm; Temperature in the individual zones (from the intake zone to the discharge zone): 20 / 30 / 40 / 50 / 80 / 100 / 120 / 140 °C.

[0098] The extruded starch products were dried in a fluid bed dryer (Jöst GmbH + Co. KG, Germany) and ground to a powder with a d5o particle size of approximately 300 pm using a fine impact mill (Ultraplex UPZ 100, Hosokawa Alpine, Germany) equipped with a sieve insert with 1 mm mesh size.

[0099] Subsequently, the viscosity, viscosity stability, and solubility of the starch products were determined using Methods 1 and 2 specified in this description. The results are shown in Table 1. In experiments 1-8 and 10-15, starch products according to the invention with low viscosity, good viscosity stability, and good solubility were obtained. The concentration of the starch products when determining viscosity is also shown in Table 1.

[0100] It is clearly evident from Table 1 that the required properties are not achieved with acids with a pKa value of 2.83 or higher (Experiments 16-20). In particular, the solubility of these starch products is comparatively low, at 60% or less. Experiments 16-19 also exhibit a comparatively high viscosity, while the viscosity stability of Experiment 20 is comparatively low.

[0101] Furthermore, it is evident that the starch product without added glyoxal (test no. 9) exhibits a very high viscosity immediately after production, making it unsuitable for use in adhesive formulations or coatings. The viscosity was already 10,000 mPas after 24 hours and increased so sharply over the course of the week that the viscosity could not be determined after 168 hours, and consequently, neither could the viscosity stability.

[0102] Table 1: Starting components for the production of starch products, as well as viscosity (time t=0), viscosity stability (168 h / 24 h) and solubility of starch products

[0103] 1 WS = waxy starch, MS = corn starch, WMS = waxy maize starch

[0104] 2 enough acid was added until the pH value reached the specified value

[0105] 3 corresponds to 5 wt% of a 30 wt% aqueous solution of phosphoric acid

[0106] 4 the stated glyoxal amounts of 0.4 to 2.0 wt% correspond to 1.0 to 5.0 wt% of a 40 wt% aqueous solution of glyoxal

[0107] 5 nb ... not determinable Example 2 - Production and analysis of coating colours

[0108] Some of the starch products prepared in Example 1 were used to produce coatings. Reference coatings were prepared using commercially available starch products. Amitrocoat 8903 (Agrana, Austria) and iCoat (Cargill, USA) were used.

[0109] Calcium carbonate (Omya Hydrocarb 90, Omya, Switzerland) and the majority of the required deionized water were initially charged, and the respective starch product was stirred in with a turbine stirrer at 1000 rpm for 10 min. After adding latex (Styronal D 809, BASF, Germany), stirring was continued for a further 3 min at 1000 rpm. During stirring, 0.5 M NaOH was added dropwise until a pH of 8.5 was reached. Then, the remaining deionized water was added. 350 g of coating color was produced per batch. The compositions and properties of the coating colors are shown in Table 3.

[0110] After measuring the viscosity (according to Method 1), a small amount of a thickener, Sterocoll FS (BASF, Germany), an aqueous dispersion of an acrylic copolymer, was added with a pipette while stirring at a viscosity below 1000 mPas. The mixture was then stirred for 10 minutes, after which the viscosity was measured again, and if necessary, more Sterocoll was added until a viscosity of 1000 mPas or higher was reached. The viscosity of all coating colors tested ranged from 1024 to 2164 mPas.

[0111] A defined amount of the coating color was filtered through a sieve with a pore size of 45 pm. The residue was dried at 100 °C and then weighed. The values ​​were in the ppm range, as shown in Table 2.

[0112] The determination of high shear viscosity at a shear rate of 50 000 s 1and a temperature of 25 °C was carried out using the Physica MCR 301 rheometer (Anton Paar, Austria) with a special cylinder-cup measuring system (C-CC 48.55 / ST / CUST1 from Anton Paar, Austria) with a gap distance of 100 pm by measuring the viscosity as a function of the shear rate, which ranged from 100 s 1 up to 50,000 s' 1 was varied. The results are shown in Table 2.

[0113] Table 2: Compositions and properties of coating colors

[0114] 1 pph ... parts per hundred

[0115] Example 3 - Preparation and analysis of adhesive formulations

[0116] Adhesive formulations comprising starch, calcium carbonate as a filler (Omyacarb 1, Omya, Austria), and a biocide (Acticide MBS, Thor, Germany) were prepared. All components were mixed with deionized water, the pH was adjusted to approximately 10 using 30 wt% NaOH, and the mixture was stirred for 30 min with a toothed disc stirrer at 3000 rpm. The composition was selected so that the viscosity of the adhesives was in a comparable range between 1000 and 3000 mPas (Brookfield viscosity, 100 rpm, 25 °C). Amitrocoll C57 and Dextrin 20.921 (both from Agrana, Austria) served as references. The compositions of the adhesive formulations can be found in Table 3.

[0117] The curing time of the adhesive formulations was determined using Method 3, testing two layer thicknesses (60 and 120 μm). As can be seen from Table 3, a much smaller amount of water needs to be added to the adhesive formulations according to the invention than to Amitrocoll C57 in order to adjust the viscosity to a value within the range specified above. The water content in the adhesive formulations containing the inventive starch products from Experiments 3 and 13 is 31% by weight, whereas in the adhesive formulation containing Amitrocoll C57 it is 46.7% by weight (in each case based on the total weight of the adhesive formulation). This makes it possible to reduce the water input into the material to be bonded (e.g. paper) and accordingly the drying time. As can also be seen from Table 3, the adhesive formulations according to the invention have a significantly shorter curing time than Dextrin 20,921.

[0118] Table 3: Compositions and properties of adhesive formulations

[0119] Example 4 - Comparative Example: Extrusion according to the invention (addition of the glyoxal-containing crosslinker, in particular glyoxal in a compression zone) compared to extrusion according to WO 00 / 69916 A1 (addition of glyoxal after the compression zone)

[0120] Fig. 1 and Fig. 2 show schematic representations of the structures of slightly different screw configurations: at the very top is the "Screw configuration 2" from WO 00 / 69916 A1, in the middle the screw configuration used in the Theyson TSK 30 / 28D (used in the above examples) and below Coperion ZSK26MC18, with an extended reaction zone. In the compression zone (the area after the feed zone and before the zones with the first shear elements), no reactions or gelatinization of the starch occur. In the subsequent reaction zone, the starch is gelatinized with the help of kneading, mixing and shearing elements, and reactions such as degradation and crosslinking take place. The metering of glyoxal according to WO 00 / 69916 A1 also takes place in the reaction zone ("Zone 5") (Fig. 1, B). The metering of glyoxal according to the invention preferably takes place in the compression zones, before gelatinization of the starch (Fig.2, A), since this leads to a starch product which - in contrast to the process according to WO 00 / 69916 A1 - does not contain any nanoparticles in the range of less than 1000 nm.

[0121] WO 00 / 69916 Agrana Research

[0122] Bersdorff

[0123] Extruder ZE40 Coperion ZSK26MC18 Theyson TSK 30 / 28D

[0124] Product Product 1 Product 2

[0125] Zones [number] 9 12 7

[0126] L / D 38 48 28

[0127] Glyoxal dosage at D 22 (Zone 5) 32 (Zone 8) 8 (Zone 2)

[0128] Compression zone bf !i D 2- 3 2 - 5 2 - 3

[0129] Application WO 00 / 69916 A1 describes the production of nanoparticles via a reactive extrusion process, using glyoxal as a crosslinker. Example 10 of application WO 00 / 69916 A1 also describes the use of maleic acid, whereby a 10% glyoxal solution in water was introduced into the fifth zone ("22D") of the extruder described therein with a "screw configuration 2" (see also Fig. 1). In contrast to the production of nanoparticles described in WO 00 / 69916 A1, the formation of nanoparticles is avoided in the production process according to the invention by adding the glyoxal-containing crosslinker in a compression zone.

[0130] To illustrate these differences, Example 10 of WO 00 / 69916 A1 was reproduced below. A twin-screw extruder of the type ZSK26 (26 mm screw diameter, 48D) was used, which is essentially the same as the (longer) Bestorff ZE40 extruder used in WO 00 / 69916 A1. The system consists of 12 zones (separate barrels) and is powered by a 36.9 kW motor that allows a maximum speed of 1200 rpm. Raw materials are fed into the extruder via dosing units integrated into the control system (2 gravimetric for solids, 1 gravimetric for liquids, 2 volumetric for liquids).

[0131] Glyoxal was metered into the 8th zone (32D) due to the available metering options. The screw configuration was adapted to the longer extruder.

[0132] Analyses of the product samples: The solutions were prepared as described (latex preparation 1) and the viscosities were determined. Contrary to the description in WO 00 / 69916 A1, no viscosity could be measured at a concentration of 35%.

[0133] Product rework,

[0134] Inventive

[0135] WO 00 / 69916 Al Product

[0136] Product 1 Product 2

[0137] 10% 35% 35%

[0138] 100 55 Not measurable 490

[0139] 50 40 700

[0140] RV

[0141] Brookfield 20 24 1380

[0142] 2h [mPas] Temp 24 23 pH 2.7 1.4

[0143] Solubility [%] 99 99

[0144] Determination of particle sizes after dispersion

[0145] For nanoparticle measurements, 10% starch solutions were prepared and centrifuged for 10 min at 3000 rpm, then filtered with a 1 pm filter to remove coarse particles. This was also performed with a styrene-butadiene latex (SBR latex) as a reference.

[0146] The DLS measurements were performed on the following device: The Zetasizer Nano ZSP from Malvern Pananalytical is a high-performance particle characterization system that can be used to measure the following:

[0147] Particle size and molecular size

[0148] • Measuring range: 10 nm - 10.0 pm (diameter)

[0149] • Measuring principle: Dynamic light scattering

[0150] • Minimum sample volume: 12 pL

[0151] • Sensitivity: 0.1 mg / ml (lysozyme)

[0152] The dilution of 10 pL to 1 mL was chosen to obtain the best possible scattering signal.

[0153] In the SBR latex (synthetic reference product), small particles in the range just above 100 nm were measured (Fig. 3 A). In the starch latex, particles in the range of 600 nm were also easily measurable (Fig. 3 B). In product 1 (test according to WO 00 / 69916 A1), nanoparticles were detected (Fig. 3 C). In extruded native waxy maize starch (with and without maleic acid and without glyoxal crosslinker), nanoparticles in the range of 330 nm and 150 nm were also visible (Fig. 3 E, F). In product 2, produced according to the invention, no nanoparticles were measurable in the range < 1000 nm (Fig. 3 D; wheat starch was used in the present case, but other starches can also be used, in particular waxy maize starch, corn starch, or mixtures of different starches).

[0154] Methods

[0155] Method 1 - Determination of viscosity and viscosity stability

[0156] 1 to 2 g of NaOH (5 M, approximately 20 wt% in water) were placed in a beaker and made up to 187.5 g with deionized water. The starch product (prepared, for example, according to Example 1) was weighed in such an amount that the total weight was 250 g (250 g - 187.5 g = 62.5 g starch product; corresponding to 25 wt% starch product in water). The mixture was stirred for 30 minutes using a toothed disc stirrer at 1500 rpm, and the starch product was sprinkled in while stirring. The pH was adjusted to approximately 7.5 to 8.0 with NaOH (3 wt% in water). The more NaOH required, the more NaOH should be added at the beginning to prevent excessive dilution. The paste produced in this way was then subjected to a viscosity test. Alternatively, the beaker can be filled to 125 g with deionized water and then 125 g of starch can be added (corresponding to 50 wt% starch product in water).

[0157] The viscosity (Brookfield viscosity) was determined using a rotational viscometer (Brookfield DV-II+Pro, Brookfield, Germany) at 25 °C and a rotational speed of 100 rpm with spindle 5 (Brookfield, Germany; spindle 1 of the rotational viscometer is suitable for low-viscosity substances and spindle 7 for high-viscosity substances). The first measurement was taken immediately after the paste preparation (at time t = 0), with further measurements after 24 h and 168 h to assess viscosity stability. The quotient of the viscosities after 168 h and 24 h was used as a measure of viscosity stability.

[0158] Method 2 - Determination of solubility

[0159] 10 g of a starch product (prepared, for example, according to Example 1) in dry matter was stirred into deionized water in a beaker using a turbine stirrer (1500 rpm, 15 min) to obtain a 10 wt% solution. This solution was centrifuged for 10 min at 3000 rpm, and the starch concentration in the supernatant was determined using a refractometer (PAL-1, Atago, Japan). The solubility in % is the ratio of the measured starch concentration to the initial starch concentration of 10 wt%.

[0160] Method 3 - Determination of the adhesive properties of adhesive formulations

[0161] A hand squeegee was applied with the desired layer thickness (60 or 120 pm) to the outside of a corrugated paper (basis weight of 110 g / m 2), filled with an adhesive formulation containing a starch product (prepared, for example, according to Example 3) and pulled over the corrugated paper. A strip of display board (basis weight of 170 g / m 2) was placed with the inside facing onto the glued corrugated paper. The folded pieces of paper were then scraped off with the flat of the hand and then scraped off again on the back in the same way. The bonded laminate was then slowly pulled apart piece by piece by hand (with slight jerks) until a complete fiber tear was detected. A complete fiber tear is understood to be a fiber tear that extends across the entire bonded width, i.e. in a direction that is essentially perpendicular to the direction of pull. The time at which the fiber tear occurs is the time at which the adhesive formulation has achieved sufficient adhesive strength. The time it takes for the fibers to be pulled apart until the adhesive strength is completely broken is used as a measure of the curing time until this level of bond strength is reached. It is given in seconds and is calculated from the average of three individual measurements.If after 150 seconds no complete fiber tear, and thus no sufficient bonding, could be detected, the measurement was aborted.

[0162] Method 4 - Determination of particle size using dynamic light scattering (DLS)

[0163] For the nanoparticle measurement, 10% starch solutions were prepared and centrifuged for 10 min at 3000 rpm, then filtered with a 1 μm filter to remove coarse particles. As a reference, this was also performed with a styrene-butadiene latex (SBR latex). 1 mL of distilled water was placed in a cuvette, and 10 μL of starch dispersion was added by pipetting and shaken briefly.

[0164] The DLS measurements were performed on the following device: The Zetasizer Nano ZSP from Malvern Pananalytical is a high-performance particle characterization system that can be used to measure the following: particle size and molecular size

[0165] • Measuring range: 10 nm - 10.0 pm (diameter)

[0166] • Measuring principle: Dynamic light scattering

[0167] • Minimum sample volume: 12 pL

[0168] • Sensitivity: 0.1 mg / ml (lysozyme)

[0169] The evaluation was carried out in the Zetasizer program with the size distribution according to intensity.

Claims

Claims 1. A process for producing a starch product, comprising the steps of: (a) providing a strength, and (b) coextruding the starch with (i) an acid and / or a salt of an acid, and (ii) a glyoxal-containing crosslinker to obtain a starch product, wherein the acid or the salt of the acid has a pKa of 2.7 or below, and the amount of the glyoxal-containing crosslinker is in the range of 0.1 to 5.0 wt%, based on the weight of the starch, wherein the glyoxal-containing crosslinker is added in a compression zone of an extruder.

2. Process according to claim 1, characterized in that the amount of the glyoxal-containing crosslinking agent is in the range of 0.5 to 2.0% by weight, based on the weight of the starch.

3. Process according to claim 1 or 2, characterized in that the glyoxal-containing crosslinker is glyoxal.

4. Process according to one of claims 1 to 3, characterized in that the acid and / or the salt has a pKa value of 2.35 or below.

5. Process according to one of claims 1 to 4, characterized in that the amount of acid and / or salt is in the range of 1.0 to 6.0% by weight, based on the weight of the starch.

6. Process according to one of claims 1 to 5, characterized in that the acid is selected from the group comprising sulfuric acid, nitric acid, phosphoric acid and a dicarboxylic acid, or a mixture thereof.

7. The process according to claim 6, characterized in that the dicarboxylic acid comprises oxalic acid and / or maleic acid.

8. Process according to one of claims 1 to 7, characterized in that the starch in step (b) is additionally coextruded with a viscosity stabilizer.

9. The method according to claim 6, characterized in that the viscosity stabilizer comprises a fatty alcohol, wherein the fatty alcohol contains 10 to 20 carbon atoms per molecule.

10. Process according to claim 8 or 9, characterized in that the viscosity stabilizer is added in an amount of 0.1 to 1.5% by weight, based on the weight of the starch.

11. A starch product obtainable by a process according to any one of claims 1 to 10, wherein the starch product has an amount of the glyoxal-containing crosslinker in the range of 0.1 to 5.0% by weight, based on the total weight of the starch product.

12. A starch product according to claim 11, wherein the starch product has a viscosity stability of 0.96 or below at 25°C, determined according to the description.

13. A starch product according to claim 11 or 12, wherein the starch product has a viscosity of 600 mPas or less at 25°C, determined according to the description.

14. A coating composition comprising a starch product according to any one of claims 11 to 13 in an amount of 0.5 to 14.0% by weight, based on the total weight of the coating composition.

15. An adhesive formulation comprising a starch product according to any one of claims 11 to 13 in an amount of 5.0 to 65.0 wt%, based on the total weight of the adhesive formulation.

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