Method for promoting starch dissolution by eutectic ionic liquid

Abstract

The present invention discloses a method for promoting the dissolution of starch by a deep eutectic ionic liquid. The deep eutectic ionic liquid is selected from any one of deep eutectic ionic liquids such as KSCN / urea, KSCN / acetamide, KSCN / betaine, KSCN / ethylene glycol, betaine / zinc acetate / acetamide, betaine / ethylene glycol, choline / acetamide, etc., enabling the starch to undergo a phase change under mild conditions, reducing energy consumption, not requiring high-temperature and high-pressure equipment, with less production investment, low cost, short dissolution time, and having the advantages of environmental friendliness and simple operation, solving the problems of high energy consumption, environmental pollution, and difficult degradation in the prior art for starch dissolution.

Description

Technical Field:

[0001] The present invention relates to a method for promoting starch dissolution by eutectic ionic liquids. Background Art:

[0002] As described in Patent CN112358627A, thermally induced phase change and dissolution are the basis and prerequisite for starch applications. Starch solution properties such as dispersibility, gelation, and retrogradation are crucial for starch processing and applications. For example, in starch chemical modification, in order to obtain a high degree of substitution, a homogeneous reaction needs to be carried out in a relatively homogeneous solution system. The properties of the starch solution system are not only related to the structure of starch, but also the selection of the solvent is crucial. Currently, in the starch processing process, the commonly used solvent systems mainly include water, alkali solutions, and organic media such as dimethylacetamide and dimethyl sulfoxide. However, these solvent systems all have their application limitations. For example, starch is insoluble in water at room temperature, and even after thermally induced gelatinization, the dispersibility of starch molecules is not ideal, resulting in heterogeneous systems for its chemical modification, low substitution degrees of the prepared starch derivatives, limited reaction sites, and uneven products. Organic solvents require a relatively high temperature to cause phase change of starch, and usually have environmental problems such as toxicity, instability, difficulty in recovery, and volatility. Therefore, developing new green solvents is one of the most important topics.

[0003] CN114736401A discloses an application method for dissolving starch with ionic liquids. The ionic liquid is put into a reactor, the reactor is placed in an oil bath, 10 - 15% starch is added, the stirring and temperature control mechanisms are turned on. When the starch is dissolved to a transparent state, monomers are added, and the reaction is carried out at this temperature for 3 - 5 hours. Ethanol is added, and stirring is continued for 20 - 40 minutes. The cation of the ionic liquid is an imidazole type, and the anion is one of Cl, phosphate ester, and F. The ionic liquid and ethanol can be reused, greatly reducing the production cost. The starch derivatives produced by this method have flexibility and diversity, and can produce esterified starch, etherified starch, and grafted starch, and their properties are much higher than those of starch derivatives prepared by traditional methods. However, organic solvents and imidazole-based ionic liquids have certain biological toxicity and low biodegradability, which do not meet the requirements of green chemistry and biological utilization, nor the green processing, safety, and clean production of starch-based products.

[0004] Currently, there are no reports on the application of KSCN / urea, KSCN / acetamide, KSCN / ethylene glycol, KSCN / betaine, betaine / zinc acetate / ethylene glycol or acetamide, choline / zinc acetate, betaine / ethylene glycol eutectic ionic liquids in starch modification or as starch solvents. Summary of the Invention:

[0005] The object of the present invention is to provide a method for promoting the dissolution of starch by using a deep eutectic ionic liquid, enabling the starch to undergo a phase change under mild conditions, reducing energy consumption, eliminating the need for high-temperature and high-pressure equipment, with low production investment and cost, short dissolution time, and having the advantages of environmental friendliness and simple operation, solving the problems of high energy consumption, large environmental pollution, and difficult degradation in the prior art for starch dissolution.

[0006] The present invention is realized through the following technical solutions:

[0007] A method for promoting the dissolution of starch by using a deep eutectic ionic liquid, the method comprising the following steps:

[0008] 1) Prepare a deep eutectic ionic liquid, which is selected from any one of KSCN / urea, KSCN / acetamide, KSCN / betaine, betaine / zinc acetate / acetamide, betaine / ethylene glycol, choline / acetamide, and KSCN / ethylene glycol deep eutectic ionic liquids;

[0009] (2) Add starch according to 3 - 10 wt% of the dry basis mass of starch to the deep eutectic ionic liquid solvent system, stir evenly, and stir within the temperature range of 60 - 110 °C until the starch is completely dissolved to obtain a starch - deep eutectic ionic liquid homogeneous sol system; wherein, when the deep eutectic ionic liquid is betaine / zinc acetate / acetamide, a small amount of water needs to be added when dissolving starch.

[0010] Preferably, the molar ratio of KSCN to urea in KSCN / urea is 1:2, the molar ratio of KSCN / acetamide in KSCN / acetamide is 1:3, the molar ratio of KSCN to betaine in KSCN / betaine is 2:1, the molar ratio of betaine, zinc acetate, and acetamide in betaine / zinc acetate / acetamide is 2:1:4, the molar ratio of betaine to ethylene glycol in betaine / ethylene glycol is 1:2 - 1:3, the molar ratio of KSCN to ethylene glycol in KSCN / ethylene glycol is 1:2 - 1:6, and the ratio of choline to acetamide in choline / acetamide is 1:2 - 1:6.

[0011] The preparation method of the deep eutectic ionic liquid is: magnetically stir the raw materials at a temperature of 80 - 100 °C for a certain period of time according to the corresponding ratio until the solution becomes clear.

[0012] Preferably, in step (2), the stirring time is 10 - 60 min and the stirring speed is 0.2 - 0.4 kr / min.

[0013] The starch is natural starch, any one of corn starch, potato starch, cassava starch, and wheat starch.

[0014] Preferably, in step (2), when the deep eutectic ionic liquid is KSCN / acetamide or KSCN / urea deep eutectic ionic liquid, adding water during the dissolution of starch helps to accelerate the dissolution.

[0015] When the deep eutectic ionic liquid is KSCN / acetamide or KSCN / urea deep eutectic ionic liquid, stir within the temperature range of 60 - 100 °C until the starch is completely dissolved to obtain a starch - deep eutectic ionic liquid homogeneous sol system; when the deep eutectic ionic liquid is KSCN / betaine, betaine / zinc acetate / acetamide, betaine / ethylene glycol, choline / acetamide, KSCN / ethylene glycol, it is more preferably stirred within the temperature range of 80 - 100 °C (within the range of 90 - 110 °C) until the starch is completely dissolved and clarified to obtain a starch - deep eutectic ionic liquid homogeneous sol system.

[0016] The inventors found that the greater the polarity of the hydrogen bond donor of the deep eutectic ionic liquid and the higher the polarization degree of the hydrogen bond acceptor ion of the deep eutectic ionic liquid, the more favorable it is for starch dissolution. The mechanism may be that the high ionic polarizability of the hydrogen bond donor leads to an increase in the polarity of the hydrogen bond donor, enhancing its solubility.

[0017] The present invention also protects the application of the starch - deep eutectic ionic liquid homogeneous sol system in the food field, starch chemical modification, and the preparation of degradable packaging films.

[0018] The beneficial effects of the present invention are as follows:

[0019] 1) The conditions for the starch dissolution process are mild, without the need for high - temperature and high - pressure equipment, with low production investment and cost, and a short dissolution time. It has the advantages of being green, environmentally friendly, and easy to operate, solving the problems of high energy consumption and non - green environmental protection in the existing starch dissolution technology.

[0020] 2) By adjusting the mass fraction of water in the deep eutectic ionic liquid, the interaction between the anions and cations of the deep eutectic ionic liquid, water molecules and the starch molecular chain can be regulated, endowing the starch solution with a homogeneous sol system. The obtained starch - deep eutectic ionic liquid homogeneous sol system has stable performance and is particularly suitable for applications in the food field, starch chemical modification, and the field of preparation of degradable packaging films. Description of the Drawings:

[0021] Figure 1 is the XRD pattern of starch treated by the deep eutectic ionic liquid;

[0022] Figure 2 is the SEM image of starch treated by the deep eutectic ionic liquid;

[0023] Among them, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, and A11 respectively represent the numbers of deep eutectic ionic liquids formed by KSCN / acetamide, KSCN / urea, betaine / KSCN, betaine / urea, zinc acetate / betaine / acetamide, zinc acetate / choline, choline / acetamide, betaine / ethylene glycol, choline / urea, zinc acetate / betaine, and ZnCl2 / urea. Specific implementation method:

[0024] The following is a further description of the present invention, rather than a limitation of the present invention.

[0025] Example 1:

[0026] KSCN and acetamide were magnetically stirred at 80 °C until the solution was clear according to the molar ratio of KSCN to acetamide of 1:3 to obtain a deep eutectic ionic liquid of KSCN / acetamide (denoted as A1). Take 50 ml of the deep eutectic ionic liquid of KSCN / acetamide, add 3 g of corn starch, mix evenly, place it in a stirrer at 90 °C, heat and dissolve the starch for 10 min until the starch is completely dissolved. Take the transparent solution and precipitate the starch with absolute ethanol or 80% absolute ethanol, wash it repeatedly, filter it three times, and dry it at a constant temperature of 45 °C to obtain starch; see Figure 1 and Figure 2 , and use SEM and XRD to characterize the structure of the starch treated with the deep eutectic ionic liquid. It can be concluded from the XRD and SEM structure characterizations of the starch that the deep eutectic ionic liquid has damaged the crystalline structure of the starch, and the starch has reacted in the deep eutectic ionic liquid. This reaction can be seen as the destruction of the hydrogen bonds between the starch molecules, that is, the starch has dissolved.

[0027] In addition, it was found in the experiment that when the deep eutectic ionic liquid of KSCN / acetamide was heated to dissolve starch at 90 °C, adding 2 ml of water could accelerate the dissolution of starch, and it could be observed that the starch was completely dissolved in 5 min. In addition, from room temperature to about 60 °C for two or three days, the transparent state after the starch was completely dissolved was still maintained without any change.

[0028] Example 2

[0029] KSCN and urea were mixed at a molar ratio of 1:2. KSCN and urea were magnetically stirred at 80 °C until the solution became clear to obtain the KSCN / urea deep eutectic ionic liquid (denoted as A2). Take 50 ml of the KSCN / urea deep eutectic ionic liquid, add 3 g of corn starch according to the dry basis mass of starch being 6 wt% of the deep eutectic ionic liquid solvent system. After mixing evenly, place it in a stirrer at 60 or 90 °C and heat to dissolve. It was found that when dissolving starch at 60 °C, the required time was longer, and it took 12 h to observe complete dissolution of starch. At 90 °C, it only took 10 min to completely dissolve. It remained transparent after standing for two or three days. Take the transparent solution and precipitate the starch with absolute ethanol or 80% absolute ethanol, wash repeatedly, filter three times, and dry at a constant temperature of 45 °C to obtain starch; use SEM and XRD to characterize the structure of the starch treated with the deep eutectic ionic liquid. See Figure 1 and Figure 2 , it can be concluded from the XRD and SEM structure characterizations of starch that the deep eutectic ionic liquid has damaged the crystalline structure of starch, and starch has interacted in the deep eutectic ionic liquid. This interaction can be seen as the destruction of hydrogen bonds between starch molecules, that is, starch has dissolved. In addition, when dissolving starch by heating at 90 °C, adding 2 ml of water can accelerate the dissolution of starch, and a transparent solution can be observed in only 5 min.

[0030] Example 3

[0031] KSCN and ethylene glycol were magnetically stirred at 80 °C until the solution became clear according to the molar ratio of KSCN to ethylene glycol of 1:4 to obtain the KSCN / ethylene glycol deep eutectic ionic liquid (denoted as A14). Take 50 ml of the KSCN / ethylene glycol deep eutectic ionic liquid, add 3 g of corn starch, mix evenly, place it in a stirrer at 90 °C, and heat to dissolve for 10 min until the starch is completely dissolved. The results are shown in Table 1.

[0032] Example 4

[0033] KSCN and betaine were magnetically stirred at 90 °C until the solution became clear according to the molar ratio of KSCN to betaine of 2:1 to obtain the KSCN / betaine deep eutectic ionic liquid (denoted as A3). Take 50 ml of the prepared KSCN / betaine deep eutectic ionic liquid, add 3 g of corn starch, mix evenly, place it in a stirrer at 90 °C, and heat to dissolve for 30 min until the starch is completely dissolved. Subsequently, precipitate the starch with absolute ethanol or 80% absolute ethanol, wash repeatedly, filter three times, and dry at a constant temperature of 45 °C to obtain starch; use SEM and XRD to characterize the structure of the starch treated with the deep eutectic ionic liquid. See Figure 1 and Figure 2, it can be concluded from the XRD and SEM structural characterizations of starch that the deep eutectic ionic liquid has damaged the crystalline structure of starch, and starch has interacted in the deep eutectic ionic liquid. This interaction can be seen as the disruption of hydrogen bonds in starch, that is, starch has dissolved.

[0034] Example 5

[0035] According to the molar ratio of betaine, zinc acetate and acetamide of 2:1:4, betaine, zinc acetate and acetamide were magnetically stirred at 80 °C until the solution became clear to obtain the betaine / zinc acetate / acetamide deep eutectic ionic liquid (denoted as A5). Take 50 ml, add 3 g of corn starch, add 2 ml of water, mix well, place it in a stirrer at 90 °C, heat and dissolve the starch for 30 min until the starch is completely dissolved. Subsequently, precipitate the starch with absolute ethanol or 80% absolute ethanol, wash repeatedly, filter three times, and dry at a constant temperature of 45 °C to obtain starch; use SEM and XRD to characterize the structure of the starch treated with the deep eutectic ionic liquid. See Figure 1 and Figure 2 , it can be concluded from the XRD and SEM structural characterizations of starch that the deep eutectic ionic liquid has damaged the crystalline structure of starch, and starch has interacted in the deep eutectic ionic liquid. This interaction can be seen as the disruption of hydrogen bonds in starch, that is, starch has dissolved.

[0036] Example 6:

[0037] Mix choline and acetamide in a molar ratio of 1:4, and magnetically stir at 90 °C until the solution becomes clear to obtain the choline / acetamide deep eutectic ionic liquid (denoted as A7). Take 50 ml, add corn starch according to 6 wt% of the mass of the deep eutectic ionic liquid based on the dry mass of the starch, mix well, and dissolve the starch at 90 °C for 30 min. The results are shown in Table 1.

[0038] Example 7

[0039] Mix betaine and ethylene glycol in a molar ratio of 1:2 and magnetically stir at 90 °C until the solution becomes clear to obtain the betaine / ethylene glycol deep eutectic ionic liquid (denoted as A8). Take 50 ml of the prepared betaine / ethylene glycol deep eutectic ionic liquid (denoted as A8), add 3 g of corn starch, mix well, place it in a stirrer at 110 °C, heat and dissolve the starch for 30 min until the starch is completely dissolved. Subsequently, precipitate the starch with absolute ethanol or 80% absolute ethanol, wash repeatedly, filter three times, and dry at a constant temperature of 45 °C to obtain starch; use SEM and XRD to characterize the structure of the starch treated with the deep eutectic ionic liquid. It can be concluded from the XRD and SEM structural characterizations of starch that the deep eutectic ionic liquid has damaged the crystalline structure of starch, and starch has interacted in the deep eutectic ionic liquid. This interaction can be seen as the disruption of hydrogen bonds in starch, that is, starch has dissolved.

[0040] Example 8

[0041] Referring to Reference Example 1, the difference is that corn starch is added at 10 wt% of the mass of the deep eutectic ionic liquid solvent system based on the dry starch. The structure of the starch treated with the deep eutectic ionic liquid is characterized by SEM and XRD. It can be concluded from the XRD and SEM structure characterizations of the starch that the deep eutectic ionic liquid has damaged the crystalline structure of the starch, and the starch has interacted in the deep eutectic ionic liquid. This interaction can be seen as the disruption of hydrogen bonds in the starch, that is, the starch has dissolved.

[0042] Example 9

[0043] Referring to Reference Example 2, the difference is that corn starch is added at 10 wt% of the mass of the deep eutectic ionic liquid solvent system based on the dry starch. After mixing evenly, it is placed in a stirrer at 90 °C and heated to dissolve for 10 min. Subsequently, the starch is precipitated with absolute ethanol or 80% absolute ethanol, washed repeatedly, filtered three times, and dried at a constant temperature of 45 °C to obtain the starch; the structure of the starch treated with the deep eutectic ionic liquid is characterized by SEM and XRD. It can be concluded from the XRD and SEM structure characterizations of the starch that the deep eutectic ionic liquid has damaged the crystalline structure of the starch, and the starch has interacted in the deep eutectic ionic liquid. This interaction can be seen as the disruption of hydrogen bonds in the starch, that is, the starch has dissolved.

[0044] Example 10

[0045] Referring to Reference Example 3, the difference is that corn starch is added at 10 wt% of the mass of the deep eutectic ionic liquid solvent system based on the dry starch. After mixing evenly, it is placed in a stirrer at 90 °C and heated to dissolve for 10 min. Subsequently, the starch is precipitated with absolute ethanol or 80% absolute ethanol, washed repeatedly, filtered three times, and dried at a constant temperature of 45 °C to obtain the starch; the structure of the starch treated with the deep eutectic ionic liquid is characterized by SEM and XRD. It can be concluded from the XRD and SEM structure characterizations of the starch that the deep eutectic ionic liquid has damaged the crystalline structure of the starch, and the starch has interacted in the deep eutectic ionic liquid. This interaction can be seen as the disruption of hydrogen bonds in the starch, that is, the starch has dissolved.

[0046] Example 11

[0047] Referring to Example 6, the difference is that corn starch is added at 10 wt% of the dry basis mass of the starch to the eutectic ionic liquid solvent system. After mixing evenly, it is placed in a stirrer at 90 °C and heated to dissolve for 10 min. Subsequently, the starch is precipitated with absolute ethanol or 80% absolute ethanol, washed repeatedly, filtered three times, and dried at a constant temperature of 45 °C to obtain starch; the structure of the starch treated with the eutectic ionic liquid is characterized by SEM and XRD. It can be concluded from the XRD and SEM structural characterization of the starch that the eutectic ionic liquid has damaged the crystalline structure of the starch, and the starch has reacted in the eutectic ionic liquid. This reaction can be seen as the destruction of the hydrogen bonds between the starch molecules, that is, the starch has dissolved.

[0048] Comparative Example 1

[0049] Choline and urea were magnetically stirred at a molar ratio of 1:2 at 80 °C until the solution became clear to obtain choline / urea eutectic ionic liquid (denoted as A9). 50 ml was taken and 3 g of corn starch was added. After mixing evenly, the starch was dissolved at 90 °C for 30 min, but no dissolution was observed. However, the starch could be dissolved at 110 °C, and the result required 45 minutes. See Table 1.

[0050] Comparative Example 2

[0051] Choline and ethylene glycol were mixed at a molar ratio of 1:2 and heated to 90 °C until the solution became clear to obtain choline / ethylene glycol solution (denoted as A15). 50 ml was taken and starch accounting for 6% of the solution volume was added. An attempt was made to dissolve the starch at 90 °C. The results are shown in Table 1.

[0052] Comparative Example 3:

[0053] Ethylene glycol, betaine, and zinc acetate were mixed at a molar ratio of 4:2:1 and heated to 90 °C until the solution became clear to obtain betaine / zinc acetate / ethylene glycol solution (denoted as A16). 50 ml was taken and starch accounting for 6% of the solution volume was added. An attempt was made to dissolve the starch at 90 °C. The results are shown in Table 1.

[0054] Comparative Example 4

[0055] Betaine (25.9 g) and urea (30 g) were mixed at a molar ratio of 1:2, 2 ml of water was added, and the mixture was magnetically stirred at 90 °C until the solution became clear to obtain betaine / urea eutectic ionic liquid (denoted as A4). 3 g of corn starch was added. After mixing evenly, the starch was dissolved at 90 °C for 30 min, but no dissolution was observed. At 110 °C, it took 60 minutes to completely dissolve the starch. See Table 1.

[0056] Comparative Example 5

[0057] Mix zinc chloride and acetamide at a molar ratio of 1:4, heat to 90 °C and dissolve until the solution is clear to obtain a zinc chloride / acetamide solution (denoted as A17). Take 50 ml and add starch accounting for 6% of the solution volume, and attempt to dissolve the starch at 90 °C. The results are shown in Table 1.

[0058] Comparative Example 6

[0059] Mix zinc chloride and urea at a molar ratio of 1:4, heat to 90 °C and dissolve until the solution is clear to obtain a zinc chloride / urea solution (denoted as A11). Take 50 ml and add starch accounting for 6% of the solution volume, and attempt to dissolve the starch at 90 °C. The results are shown in Table 1.

[0060] Comparative Example 7

[0061] Mix zinc chloride and ethylene glycol at a molar ratio of 1:4, heat to 90 °C and dissolve until the solution is clear to obtain a zinc chloride / ethylene glycol solution (denoted as A18). Take 50 ml and add starch accounting for 6% of the solution volume, and attempt to dissolve the starch at 90 °C. The results are shown in Table 1.

[0062] Comparative Example 8

[0063] Magnetically stir zinc acetate and choline at a molar ratio of 2:1 at 90 °C until the solution is clear to obtain a choline / zinc acetate eutectic ionic liquid (denoted as A6). Take 50 ml of the prepared choline / zinc acetate eutectic ionic liquid, add 3 g of corn starch, mix well, and place it in an incubator at 90 °C and 110 °C for 120 min. No starch dissolution was observed. However, when 15 ml of water was added to 50 ml of the choline / zinc acetate eutectic ionic liquid and stirred at 90 °C for 60 min, and then left to stand in an incubator at 60 °C for 12 h, starch swelling was observed.

[0064] Comparative Example 9

[0065] Stir choline and sodium salicylate at a molar ratio of 1:1 and heat to 90 °C until a solution is formed to obtain a choline / sodium salicylate eutectic ionic liquid (denoted as A13). Take 50 ml of the ionic liquid, add 3 g of corn starch and stir. React at 90 °C and 110 °C for 120 min, and no starch dissolution was seen. See Table 1.

[0066] Comparative Example 10

[0067] Mix 20 g of betaine with 15.64 g of zinc acetate (the molar ratio of betaine to zinc acetate is 2:1). It is necessary to add 3 - 4 ml of aqueous solution (adding a certain amount of ethanol can accelerate this condition). Stir and heat at 90 °C until a transparent liquid is formed to obtain a zinc acetate / betaine eutectic ionic liquid (denoted as A10). This solvent has a high viscosity and is prone to solidification at room temperature. Take 50 ml of the prepared zinc acetate / betaine eutectic ionic liquid solution, add 3 g of corn starch, and attempt to dissolve the starch at 90 °C and 110 °C for 120 min. The results are shown in Table 1 and no dissolution is observed.

[0068] Comparative Example 11:

[0069] Take 50 ml of the ionic liquid BMIMCL (denoted as A12), add starch accounting for 6% of the solution volume, and attempt to dissolve the starch at 110 °C. The results are shown in Table 1.

[0070] Table 1

[0071]

[0072]

[0073] Among them, A1, A2, A3, A4, A5, A6, A7, A8, A9, A10, A11, A12, A13, A14, A15, A16, A17, A18 represent KSCN / acetamide, KSCN / urea, betaine / KSCN, betaine / urea, zinc acetate / betaine / acetamide, zinc acetate / choline, choline / acetamide, betaine / ethylene glycol, choline / urea, betaine / zinc acetate, ZnCl2 / urea, ionic liquid BMIMCL, choline / sodium salicylate, KSCN / ethylene glycol, choline / ethylene glycol, betaine / zinc acetate / ethylene glycol, ZnCl2 / acetamide, ZnCl2 / ethylene glycol, respectively.

[0074] As shown in Table 1, it can be seen that the dissolution of starch is greatly affected by hydrogen bond acceptors and less affected by hydrogen bond donors. However, to a certain extent, it is also affected by the polarity of hydrogen bond donor substances. Taking choline-based deep eutectic ionic liquids as an example, at the same temperature and time, higher polarity of the substance is more conducive to dissolution (choline / acetamide (90 °C, 30 min), choline / urea, choline / ethylene glycol (110 °C, 60 min)); from the perspective of hydrogen bond donors, we can roughly infer from the ionic polarization theory that the degree of ionic polarization is KCSN > choline > betaine > zinc acetate, betaine > ZnCl2, which is consistent with the fact that starch dissolves in deep eutectic ionic liquids formed by different salts in less time and at lower temperatures; it can be inferred that the dissolution of starch is greatly affected by ionic polarization. The polarization of ions causes the internal hydrogen bond structure to be damaged, thus enabling the dissolution of starch, which is consistent with the phenomena observed after starch treatment. From the comparison of choline and betaine ionic liquids in Table 1, with the cation unchanged, the change in the anion leads to differences in starch dissolution, indicating that there is indeed a polarization effect between ionic liquids and other substances (the ionic polarizability is mainly affected by the anion).

[0075] Note: If the zinc acetate / choline (A6) and zinc acetate / betaine solutions (A10) are in an anhydrous state, no starch dissolution can be observed regardless of how the heating time and temperature are adjusted. The deep eutectic ionic liquid formed by ZnCl2 / urea decomposes when heated to 110 °C, and the solvent properties are unstable. However, from the characterization, at this temperature, the starch structure is damaged. Solvents such as KSCN / acetamide and KSCN / urea can dissolve starch within a certain period of time even without adding water. By comparing Example 5 and Comparative Example 10, it can be seen that the addition of acetamide to the deep eutectic ionic liquid betaine / zinc acetate / acetamide in the present invention improves the starch dissolution performance compared to betaine / zinc acetate; it should also be noted that deep eutectic ionic liquids formed with betaine as the hydrogen bond donor generally require the addition of water, and the addition of zinc acetate can replace the role of water, but the dissolution effect on starch will be weakened and the starch dissolution time will be prolonged. This actually reflects from the side that the dissolution of starch in deep eutectic ionic liquids is affected by polarization.

[0076] In summary, we can obtain the method for dissolving starch: the greater the polarity of the hydrogen bond donor of the deep eutectic ionic liquid and the higher the degree of ionic polarization of the hydrogen bond acceptor ion of the deep eutectic ionic liquid, the more favorable for starch dissolution. The mechanism may be that the high ionic polarizability of the hydrogen bond donor leads to an increase in the polarity of the hydrogen bond donor, enhancing its solubility. Currently, there is no report on the application of KSCN / urea, KSCN / acetamide, KSCN / ethylene glycol, KSCN / betaine, betaine / zinc acetate / ethylene glycol or acetamide, choline / zinc acetate, betaine / ethylene glycol deep eutectic ionic liquids in starch modification or as starch solvents. From the data in Table 1, it can be seen that KSCN / urea (A2), KSCN / acetamide (A1), and KSCN / ethylene glycol (A14) have the best effects, followed by choline / acetamide (A7), betaine / zinc acetate / acetamide (A5), and KSCN / betaine (A3). The betaine / urea deep eutectic ionic liquid (denoted as A4) with water added and betaine / ethylene glycol (A8) are less effective. Therefore, in the present invention, KSCN / urea (A2), KSCN / acetamide (A1), KSCN / ethylene glycol (A14), KSCN / betaine (A3), choline / acetamide (A7), betaine / zinc acetate / acetamide (A5), and betaine / ethylene glycol (A8) deep eutectic ionic liquids are finally selected.

Claims

1. A method for promoting the dissolution of starch by a deep eutectic ionic liquid, characterized in that, The method comprises the following steps: (1) Prepare a deep eutectic ionic liquid, which is selected from any one of KSCN / urea, KSCN / acetamide, KSCN / ethylene glycol, KSCN / betaine, betaine / zinc acetate / acetamide, and choline / acetamide deep eutectic ionic liquids; the molar ratio of KSCN to urea in KSCN / urea is 1:2, the molar ratio of KSCN to acetamide in KSCN / acetamide is 1:3, the molar ratio of KSCN to betaine in KSCN / betaine is 2:1, the molar ratio of betaine, zinc acetate, and acetamide in betaine / zinc acetate / acetamide is 2:1:4, the molar ratio of KSCN to ethylene glycol in KSCN / ethylene glycol is 1:2 to 1:6, and the molar ratio of choline to acetamide in choline / acetamide is 1:2 to 1:4; (2) Add starch according to 3-10 wt% of the dry basis mass of starch to the deep eutectic ionic liquid solvent system, stir evenly, and stir within the temperature range of 60-110 °C until the starch is completely dissolved to obtain a starch-deep eutectic ionic liquid homogeneous sol system; the starch is any one of corn starch, potato starch, cassava starch, and wheat starch; wherein, when the deep eutectic ionic liquid is betaine / zinc acetate / acetamide, a certain amount of water needs to be added when dissolving the starch.

2. The method according to claim 1, wherein The preparation method of the deep eutectic ionic liquid is: magnetically stir the raw materials at a temperature of 80-100 °C for a certain time according to the corresponding ratio until the solution is clear.

3. The method according to claim 1, wherein In step (2), the stirring time is 10-60 min.

4. The method according to claim 1, wherein In step (2), the stirring speed is 0.2-0.4 kr / min.

5. The method according to claim 1, characterized in that, In step (2), when the deep eutectic ionic liquid is KSCN / acetamide or KSCN / urea deep eutectic ionic liquid, water is also added when dissolving the starch.

6. The method according to claim 1, characterized in that, In step (2), when the deep eutectic ionic liquid is KSCN / acetamide or KSCN / urea deep eutectic ionic liquid, stir within the temperature range of 60-100 °C until the starch is completely dissolved to obtain a starch-deep eutectic ionic liquid homogeneous sol system; when the deep eutectic ionic liquid is KSCN / betaine, betaine / zinc acetate / acetamide, choline / acetamide, or KSCN / ethylene glycol, stir within the temperature range of 90-110 °C until the starch is completely dissolved and clarified to obtain a starch-deep eutectic ionic liquid homogeneous sol system.

7. The method according to claim 1, wherein When the deep eutectic ionic liquid is KSCN / betaine, betaine / zinc acetate / acetamide, choline / acetamide, or KSCN / ethylene glycol, stir at 80-100 °C until the starch is completely dissolved and clarified.

8. Application of the starch-deep eutectic ionic liquid homogeneous sol system obtained by the method according to claim 1 in the food field, starch chemical modification, and preparation of degradable packaging films.

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