A high-whiteness cross-linked polyvinylpyrrolidone and its preparation method and application

Abstract

The present invention provides a high-whiteness cross-linked polyvinylpyrrolidone and its preparation method and application, the preparation method comprises the following steps: cross-linked polyvinylpyrrolidone, water, Lewis acid and oxidant are mixed, reacted, and the high-whiteness cross-linked polyvinylpyrrolidone is obtained. Through the aqueous solution system, the oxidation of the oxidant is strengthened with Lewis acid, and the impurities such as N-vinylpyrrolidone, acetaldehyde and aldehyde condensation products adsorbed in the cross-linked polyvinylpyrrolidone are thoroughly oxidized and decomposed, fundamentally solving the problem of causing the cross-linked polyvinylpyrrolidone product to turn yellow; at the same time, cross-linked polyvinylpyrrolidone is further subjected to strong oxidation bleaching, so that the whiteness of the cross-linked polyvinylpyrrolidone product is significantly improved, and the whiteness value can reach 90%, and the preparation method will not additionally introduce impurities to affect the quality of the product, and the product can meet the requirements of the pharmacopoeia, and the process is simple, the process energy consumption is low, the cost is low, the pollution is low, and it is green and environmentally friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer polymerization, and in particular relates to a high-whiteness cross-linked polyvinylpyrrolidone and a preparation method and application thereof. Background Art

[0002] Cross-linked polyvinyl pyrrolidone (PVPP, cross-linked polyvinyl pyrrolidone) is a super absorbent resin with strong water absorption and water retention capabilities. Its water absorption capacity can reach several times or even dozens of times its own weight, and hydrogen bonds can be formed between the matrix and the adsorbed water. Even under a certain pressure, the adsorbed water will not be lost and can be recycled and reused. PVPP has excellent physiological safety, water absorption, water insolubility, complexation and other excellent properties, and has broad application prospects in the fields of medicine and food.

[0003] Cross-linked polyvinylpyrrolidone (PVPP) products are porous, granular, non-ionic products with strong interfacial activity through a unique popcorn polymerization process. Popcorn polymerization is a special polymerization method, and its reaction mechanism is still unclear. The polymer obtained by popcorn polymerization is highly cross-linked, but its cross-linking is mainly formed by the entanglement between long molecular chains. At present, cross-linked polyvinylpyrrolidone is generally produced by popcorn polymerization using alkali metal hydroxide, purified water, and N-vinylpyrrolidone (NVP). However, the PVPP prepared by this method may adsorb a small amount of impurities such as residual NVP, acetaldehyde, and aldehyde condensation products in the PVPP. The semi-finished PVPP prepared by this process is alkaline. When impurities such as residual NVP, acetaldehyde, and aldehyde condensation products are heated together with alkali, condensation reaction and dehydration reaction will occur to generate crotonaldehyde. Crotonaldehyde contacts air and undergoes oxidation reaction to generate crotonic acid, which makes the PVPP product yellow. In addition, the generated crotonaldehyde can also undergo condensation reaction with acetaldehyde to generate semi-solid resin, which causes the PVPP to turn yellow. The whiteness of cross-linked polyvinylpyrrolidone (PVPP) has decreased, affecting product sales.

[0004] CN106800616A discloses a method for preparing high bulk density cross-linked polyvinylpyrrolidone. The method is optimized on the basis of the preparation method of common cross-linked polyvinylpyrrolidone to obtain high bulk density cross-linked polyvinylpyrrolidone, and the bulk density can reach 0.35g / mL-0.4g / mL. The optimization method comprises: polymerization reaction and drying. The technical effect is that under the condition of traditional preparation of cross-linked polyvinylpyrrolidone, a high bulk density cross-linked polyvinylpyrrolidone can be produced by a simple optimized preparation method, and the bulk density can reach 0.35g / mL-0.4g / mL, which not only improves the bulk density, but also greatly improves the fluidity. However, it is easy to turn yellow and has poor whiteness, which affects its use.

[0005] CN106883333A discloses a method for preparing large-particle cross-linked polyvinylpyrrolidone. Under the condition that the mass ratio of monomer NVP: water is 9:1, 3.0% alkali metal hydroxide is added, nitrogen protection is introduced, and the mixture is heated to 55°C to initiate popcorn polymerization, and the stirring speed is 60 rpm; when the temperature rises to 70°C, 0.5%-5.0% of a molding agent is added, and the stirring speed is reduced to 20 rpm; after the particles are formed, they are washed and dried to finally obtain cross-linked polyvinylpyrrolidone with a particle size between 140 and 200 μm; the molding agent is generally at least one of tert-butyl hydroperoxide, benzoyl peroxide, di-tert-butyl peroxide, azobisisobutyronitrile, and tert-butyl perbenzoate. By adding the molding agent during the polymerization process, the surface tension of the particles during forming is changed, so that the particles are suspended in the water phase in the form of larger particles, so that the product particle size between 140 and 200 μm accounts for more than 80%, and the NVP residue in the synthesis process increases the possibility of yellowing of the product.

[0006] Since the cross-linked polyvinylpyrrolidone in the prior art has problems such as yellowing and poor whiteness, it is an urgent problem to be solved in the art to develop a cross-linked polyvinylpyrrolidone with high whiteness and simple preparation process to meet the application requirements of cross-linked polyvinylpyrrolidone. Summary of the invention

[0007] In view of the deficiencies in the prior art, the object of the present invention is to provide a high-whiteness cross-linked polyvinylpyrrolidone and a preparation method and application thereof. The preparation method uses an aqueous solution system and a Lewis acid to enhance the oxidizing action of an oxidant, thereby thoroughly oxidizing and decomposing impurities such as NVP, acetaldehyde and aldehyde condensates adsorbed in PVPP, and further performs strong oxidative bleaching on PVPP, thereby significantly improving the whiteness of PVPP.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a method for preparing high-whiteness cross-linked polyvinylpyrrolidone, the method comprising the following steps: mixing cross-linked polyvinylpyrrolidone, water, a Lewis acid and an oxidant, and reacting to obtain the high-whiteness cross-linked polyvinylpyrrolidone.

[0010] Preferably, the Lewis acid comprises any one of aluminum chloride, ferric chloride, zinc chloride, boron trifluoride, sulfur trioxide, ferric bromide or magnesium bromide, or a combination of at least two thereof.

[0011] Preferably, the oxidant comprises any one of peroxide, tert-butyl peroxide or persulfate, or a combination of at least two thereof.

[0012] Preferably, the oxidant comprises any one of peracetic acid, tert-butyl hydroperoxide, di-tert-butyl hydroperoxide, sodium persulfate, ammonium persulfate or potassium persulfate, or a combination of at least two thereof.

[0013] The cross-linked polyvinylpyrrolidone includes any one of a PVPP XL finished product, a PVPP XL-10 finished product or a cross-linked polyvinylpyrrolidone polymer intermediate.

[0014] Preferably, the mass ratio of the cross-linked polyvinylpyrrolidone to water is 100:(500-900), for example, it can be 100:500, 100:600, 100:700, 100:800, 100:900, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0015] Preferably, the mass ratio of the cross-linked polyvinylpyrrolidone to the Lewis acid is 100:(0.001-0.01), for example, it can be 100:0.001, 100:0.002, 100:0.003, 100:0.004, 100:0.005, 100:0.006, 100:0.007, 100:0.008, 100:0.009, 100:0.01, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0016] Preferably, the mass ratio of the cross-linked polyvinylpyrrolidone to the oxidant is 100:(0.1-1), for example, it can be 100:0.1, 100:0.2, 100:0.3, 100:0.4, 100:0.5, 100:0.6, 100:0.7, 100:0.8, 100:0.9, 100:1, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0017] Preferably, the reaction temperature is 70-90°C, for example, 70°C, 75°C, 80°C, 85°C, 90°C, and specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific points included in the range.

[0018] Preferably, the reaction time is 30-60 min, for example, 30 min, 40 min, 50 min, 60 min, and specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific points included in the range.

[0019] Preferably, after the reaction is completed, the process further comprises washing, alkalization, centrifugal dehydration and drying to obtain the high-whiteness cross-linked polyvinylpyrrolidone.

[0020] Preferably, the water washing comprises adding hot water for stirring.

[0021] Preferably, the temperature of the hot water is 60-80°C, for example, it can be 60°C, 65°C, 70°C, 75°C, 80°C, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0022] Preferably, the mass ratio of the cross-linked polyvinylpyrrolidone to hot water is 1:(5-9), for example, it can be 1:5, 1:6, 1:7, 1:8, 1:9, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0023] In the present invention, water washing is performed at least once, and the water washing includes heating water, dehydrating, adding hot water, stirring evenly, and then alkalizing according to the soluble matter in the water sampled and tested, which is less than 1%. After alkalization, it can be directly transferred to a centrifuge for centrifugal dehydration, and then a drying step is performed.

[0024] Preferably, the stirring rate is 500-1000r / min, for example, it can be 500r / min, 600r / min, 700r / min, 800r / min, 900r / min, 1000r / min, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0025] Preferably, the stirring time is 30-60 min, for example, 30 min, 40 min, 50 min, 60 min, and specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific points included in the range.

[0026] Preferably, the alkalization comprises using an alkaline solution to adjust the pH value to 7.0-9.0, for example, it can be 7.0, 7.5, 8.0, 8.5, 9.0, and specific values ​​between the above points. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific points included in the range.

[0027] Preferably, the alkaline solution comprises concentrated aqueous ammonia and / or sodium hydroxide solution.

[0028] Preferably, the drying method comprises air flow drying.

[0029] Preferably, the inlet air temperature of the air flow drying is 150-180°C, for example, it can be 150°C, 160°C, 170°C, 180°C, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0030] Preferably, the air outlet temperature of the air flow drying is 70-90°C, for example, it can be 70°C, 75°C, 80°C, 85°C, 90°C, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0031] Preferably, the preparation method specifically comprises the following steps:

[0032] The cross-linked polyvinylpyrrolidone, water, Lewis acid and oxidant are mixed, reacted at 70-90° C. for 30-60 minutes, washed with water, alkalized to adjust the pH to 7.0-9.0, centrifuged and dehydrated, and air-dried to obtain the high-whiteness cross-linked polyvinylpyrrolidone;

[0033] The Lewis acid includes any one of aluminum chloride, ferric chloride, zinc chloride, boron trifluoride, sulfur trioxide, ferric bromide or magnesium bromide, or a combination of at least two of them; the oxidant includes any one of peracetic acid, tert-butyl hydroperoxide, di-tert-butyl hydroperoxide, sodium persulfate, ammonium persulfate or potassium persulfate, or a combination of at least two of them.

[0034] The "high whiteness" in the high-whiteness cross-linked polyvinylpyrrolidone described in the present invention refers to a whiteness of more than 80%, for example, it can be 80%, 82%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99%, and specific point values ​​between the above point values. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the said range.

[0035] In a second aspect, the present invention provides a high-whiteness cross-linked polyvinylpyrrolidone, which is prepared by the preparation method described in the first aspect.

[0036] In a third aspect, the present invention provides a use of the high-whiteness cross-linked polyvinylpyrrolidone as described in the first aspect in the preparation of medicines and foods.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] The high-whiteness cross-linked polyvinylpyrrolidone provided by the invention uses a Lewis acid to strengthen the oxidizing effect of an oxidant through an aqueous solution system, and thoroughly oxidizes and decomposes impurities such as NVP, acetaldehyde and aldehyde condensates adsorbed in PVPP, thereby fundamentally solving the problem of yellowing of PVPP products; at the same time, PVPP is further subjected to strong oxidative bleaching, so that the whiteness of the PVPP product is significantly improved, and the whiteness value can reach 90%. The preparation method does not additionally introduce impurities to affect the quality of the product, and the product can meet the requirements of the pharmacopoeia, and the process is simple, low in process energy consumption, low in cost, low in pollution, and green and environmentally friendly. DETAILED DESCRIPTION

[0039] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0040] The experimental materials used in the embodiments and comparative examples of the present invention are as follows:

[0041] Cross-linked polyvinylpyrrolidone, brand name PVPP XL, manufacturer Yuang Technology Co., Ltd.; brand name PVPP XL, manufacturer Yanhong Sifang; brand name Kollidon CL, manufacturer BASF.

[0042] Example 1

[0043] This embodiment provides a method for preparing high-whiteness cross-linked polyvinylpyrrolidone, the method comprising the following steps:

[0044] (1) Add 100 kg PVPP and 500 kg purified water into the reactor, heat to 70 °C, start stirring, and set the speed to 500 rpm;

[0045] (2) Add 0.001 kg of aluminum chloride and 0.1 kg of peracetic acid to the reactor, continue stirring for 30 min, and then stop stirring;

[0046] (3) Transfer the reaction mass to a clean filter equipped with a 1000-mesh filter cloth, start stirring, and vacuum dehydrate;

[0047] (4) Add 500 kg of hot water at 60° C. to the cleaning filter, control the speed to 500 rpm, stir and react for 30 min, and then take a sample to test the soluble matter in the water, which is 0.9%;

[0048] (5) After adding concentrated ammonia water to adjust the pH of the material to 7.0, the material in the cleaning filter is transferred to a centrifuge for centrifugal dehydration;

[0049] (6) Control the air inlet temperature at 150-180°C and the air outlet temperature at 70-90°C, and obtain a high-whiteness cross-linked polyvinylpyrrolidone product by air drying.

[0050] Example 2

[0051] This embodiment provides a method for preparing high-whiteness cross-linked polyvinylpyrrolidone, the method comprising the following steps:

[0052] (1) Add 100 kg PVPP and 600 kg purified water into the reactor, heat to 75 °C, start stirring, and set the speed to 600 rpm;

[0053] (2) Add 0.001 kg of aluminum chloride, 0.001 kg of ferric chloride, 0.001 kg of zinc chloride and 0.3 kg of tert-butyl hydroperoxide to the reactor, continue stirring for 40 minutes, and then stop stirring;

[0054] (3) Transfer the reaction mass to a clean filter equipped with a 1000-mesh filter cloth, start stirring, and vacuum dehydrate;

[0055] (4) Add 600 kg of hot water at 65° C. to the cleaning filter, control the speed to 600 rpm, stir and react for 40 min, and then take a sample to detect the soluble matter in the water, which is 0.8%;

[0056] (5) After adding concentrated ammonia water to adjust the pH of the material to 7.5, the material in the cleaning filter is transferred to a centrifuge for centrifugal dehydration;

[0057] (6) Control the air inlet temperature at 150-180°C and the air outlet temperature at 70-90°C, and obtain a high-whiteness cross-linked polyvinylpyrrolidone product by air drying.

[0058] Example 3

[0059] This embodiment provides a method for preparing high-whiteness cross-linked polyvinylpyrrolidone, the method comprising the following steps:

[0060] (1) Add 100 kg PVPP and 700 kg purified water into the reactor, heat to 80 °C, start stirring, and set the speed to 700 rpm;

[0061] (2) Add 0.001 kg of ferric chloride, 0.002 kg of zinc chloride, 0.002 kg of ferric bromide, 0.25 kg of tert-butyl hydroperoxide, and 0.3 kg of di-tert-butyl hydroperoxide to the reactor, continue stirring for 45 minutes, and then stop stirring;

[0062] (3) Transfer the reaction mass to a clean filter equipped with a 1000-mesh filter cloth, start stirring, and vacuum dehydrate;

[0063] (4) Add 700 kg of hot water at 70° C. to the cleaning filter, control the speed to 700 rpm, stir and react for 45 minutes, and then evacuate and dehydrate;

[0064] (5) Repeat step (4) once more and take a sample to detect 0.6% of soluble matter in water;

[0065] (6) After adding concentrated ammonia water to adjust the pH of the material to 8.0, the material in the cleaning filter is transferred to a centrifuge for centrifugal dehydration;

[0066] (7) Control the air inlet temperature at 150-180°C and the air outlet temperature at 70-90°C, and obtain a high-whiteness cross-linked polyvinylpyrrolidone product by air drying.

[0067] Example 4

[0068] This embodiment provides a method for preparing high-whiteness cross-linked polyvinylpyrrolidone, the method comprising the following steps:

[0069] (1) Add 100 kg PVPP and 800 kg purified water into the reactor, heat to 80 °C, start stirring, and set the speed to 800 rpm;

[0070] (2) Add 0.004 kg of sulfur trioxide, 0.004 kg of boron trifluoride, 0.2 kg of sodium persulfate, 0.3 kg of ammonium persulfate, and 0.3 kg of potassium persulfate to the reactor, continue stirring for 45 minutes, and then stop stirring;

[0071] (3) Transfer the reaction mass to a clean filter equipped with a 1000-mesh filter cloth, start stirring, and vacuum dehydrate;

[0072] (4) Add 700 kg of hot water at 70° C. to the cleaning filter, control the speed to 800 rpm, stir and react for 45 minutes, and then evacuate and dehydrate;

[0073] (5) Repeat step (4) once more and take a sample to detect 0.8% of soluble matter in water;

[0074] (6) After adding sodium hydroxide solution to adjust the pH of the material to 8.5, the material in the cleaning filter is transferred to a centrifuge for centrifugal dehydration;

[0075] (7) Control the air inlet temperature at 150-180°C and the air outlet temperature at 70-90°C, and obtain a high-whiteness cross-linked polyvinylpyrrolidone product by air drying.

[0076] Example 5

[0077] This embodiment provides a method for preparing high-whiteness cross-linked polyvinylpyrrolidone, the method comprising the following steps:

[0078] (1) Add 100 kg PVPP and 900 kg purified water into the reactor, heat to 85 °C, start stirring, and set the speed to 900 rpm;

[0079] (2) Add 0.008 kg of sulfur trioxide, 0.002 kg of magnesium bromide, 0.5 kg of peracetic acid and 0.5 kg of sodium persulfate to the reactor, continue stirring for 50 min, and then stop stirring;

[0080] (3) Transfer the reaction mass to a clean filter equipped with a 1000-mesh filter cloth, start stirring, and vacuum dehydrate;

[0081] (4) Add 900 kg of hot water at 75° C. to the cleaning filter, control the speed to 900 rpm, stir and react for 50 min, and then evacuate and dehydrate;

[0082] (5) Repeat step (4) twice and take samples to test the soluble matter in water at 0.6%;

[0083] (6) After adding sodium hydroxide solution to adjust the pH of the material to 9.0, the material in the cleaning filter is transferred to a centrifuge for centrifugal dehydration;

[0084] (7) Control the air inlet temperature at 150-180°C and the air outlet temperature at 70-90°C, and obtain a high-whiteness cross-linked polyvinylpyrrolidone product by air drying.

[0085] Example 6

[0086] This embodiment provides a method for preparing high-whiteness cross-linked polyvinylpyrrolidone, the method comprising the following steps:

[0087] (1) Add 100 kg PVPP and 900 kg purified water into a reactor, heat to 90 °C, start stirring, and set the speed to 1000 rpm;

[0088] (2) Add 0.004 kg of sulfur trioxide, 0.05 kg of peracetic acid, and 0.05 kg of di-tert-butyl hydroperoxide to the reactor, continue stirring for 60 min, and then stop stirring;

[0089] (3) Transfer the reaction mass to a clean filter equipped with a 1000-mesh filter cloth, start stirring, and vacuum dehydrate;

[0090] (4) Add 900 kg of hot water at 80° C. to the cleaning filter, control the speed to 1000 rpm, stir and react for 60 min, and then evacuate and dehydrate;

[0091] (5) Repeat step (4) twice and take samples to test 0.4% of soluble matter in water;

[0092] (6) After adding sodium hydroxide solution to adjust the pH of the material to 8.0, the material in the cleaning filter is transferred to a centrifuge for centrifugal dehydration;

[0093] (7) Control the air inlet temperature at 150-180°C and the air outlet temperature at 70-90°C, and obtain a high-whiteness cross-linked polyvinylpyrrolidone product by air drying.

[0094] Comparative Example 1

[0095] A cross-linked polyvinylpyrrolidone, which differs from Example 6 only in that no Lewis acid is added; the types, amounts and preparation methods of other components are the same as those in Example 6.

[0096] Comparative Example 2

[0097] A cross-linked polyvinylpyrrolidone, which differs from Example 6 only in that no oxidant is added; the types, amounts and preparation methods of other components are the same as those in Example 6.

[0098] Comparative Example 3

[0099] A cross-linked polyvinylpyrrolidone, which differs from Example 6 only in that Lewis acid and oxidant are not added; the types, amounts and preparation methods of other components are the same as those in Example 6.

[0100] Comparative Example 4

[0101] A crospovidone, initial PVPP XL powder without any treatment.

[0102] Comparative Example 5

[0103] This comparative example provides a commercially available product A, cross-linked polyvinylpyrrolidone PVPP XL purchased from Zhongyan Hongsifang.

[0104] Comparative Example 6

[0105] This comparative example provides a commercially available product B, cross-linked polyvinylpyrrolidone PVPP XL purchased from BASF.

[0106] The performance test of the high whiteness cross-linked polyvinylpyrrolidone provided in Examples 1-6 and Comparative Examples 1-6 was carried out, and the specific method was as follows:

[0107] (1) Whiteness

[0108] Test method: Use WSD-3C fully automatic whiteness meter to test the whiteness of the product according to the method specified in the national standard GB / T 15595-2008.

[0109] The various properties of the high whiteness cross-linked polyvinylpyrrolidone obtained in Examples 1-6 and the cross-linked polyvinylpyrrolidone obtained in Comparative Examples 1-6 were tested according to the above-mentioned performance testing method. The test results are shown in Table 1.

[0110] (2) The tests for pH, soluble matter in water and residue on ignition shall be carried out in accordance with the relevant provisions of "Cross-linked Polyvinylpyrrolidone" in the "Chinese Pharmacopoeia" (2020 edition).

[0111] Table 1

[0112]

[0113]

[0114] From the data in Table 1, it can be seen that the high-whiteness cross-linked polyvinylpyrrolidone prepared according to the technology of the present invention has a whiteness between 83% and 90%, which is significantly higher than the cross-linked polyvinylpyrrolidone products of Comparative Examples 1 to 6; the pH value, soluble matter in water and ignition residue meet the requirements of the pharmacopoeia, indicating that the preparation method will not introduce additional impurities to affect the quality of the product.

[0115] The applicant declares that the present invention uses the above-mentioned embodiments to illustrate a high-whiteness cross-linked polyvinylpyrrolidone and its preparation method and application, but the present invention is not limited to the above-mentioned embodiments, that is, it does not mean that the present invention must rely on the above-mentioned embodiments to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing high-whiteness cross-linked polyvinylpyrrolidone with a whiteness of more than 80%, characterized in that: The preparation method comprises the following steps: Mixing cross-linked polyvinylpyrrolidone, water, Lewis acid and an oxidant to react and obtain the high-whiteness cross-linked polyvinylpyrrolidone; The Lewis acid includes any one of aluminum chloride, ferric chloride, zinc chloride, boron trifluoride, sulfur trioxide, ferric bromide or magnesium bromide, or a combination of at least two thereof.

2. The preparation method according to claim 1, characterized in that: The oxidant includes any one of peroxide, tert-butyl peroxide or persulfate, or a combination of at least two thereof.

3. The preparation method according to claim 2, characterized in that: The oxidant includes any one of peracetic acid, tert-butyl hydroperoxide, di-tert-butyl hydroperoxide, sodium persulfate, ammonium persulfate or potassium persulfate, or a combination of at least two thereof.

4. The preparation method according to claim 1, characterized in that: The mass ratio of the cross-linked polyvinylpyrrolidone to water is 1:(5-9).

5. The preparation method according to claim 1, characterized in that: The mass ratio of the cross-linked polyvinylpyrrolidone to the Lewis acid is 100:(0.001-0.01).

6. The preparation method according to claim 1, characterized in that: The mass ratio of the cross-linked polyvinylpyrrolidone to the oxidant is 100:(0.1-1).

7. The preparation method according to claim 1, characterized in that: The reaction temperature is 70-90°C.

8. The preparation method according to claim 1, characterized in that: The reaction time is 30-60 min.

9. The preparation method according to claim 1, characterized in that: After the reaction is completed, the steps include washing, alkalization, centrifugal dehydration and drying to obtain the high-whiteness cross-linked polyvinylpyrrolidone.

10. The preparation method according to claim 9, characterized in that: The water washing includes adding hot water and stirring.

11. The preparation method according to claim 10, characterized in that: The temperature of the hot water is 60-80°C.

12. The preparation method according to claim 10, characterized in that: The stirring rate is 500-1000 r / min.

13. The preparation method according to claim 10, characterized in that: The stirring time is 30-60 min.

14. The preparation method according to claim 9, characterized in that: The alkalization comprises adjusting the pH value to 7.0-9.0 using an alkali solution.

15. The preparation method according to claim 14, characterized in that: The alkaline solution includes concentrated ammonia water and / or sodium hydroxide solution.

16. The preparation method according to claim 9, characterized in that: The drying method includes air flow drying.

17. The preparation method according to claim 16, characterized in that: The air inlet temperature of the airflow drying is 150-180°C.

18. The preparation method according to claim 16, characterized in that: The air outlet temperature of the airflow drying is 70-100°C.

19. The preparation method according to claim 1, characterized in that: The preparation method specifically comprises the following steps: The cross-linked polyvinylpyrrolidone, water, Lewis acid and oxidant are mixed, reacted at 70-90° C. for 30-60 minutes, washed with water, alkalized to adjust the pH to 7.0-9.0, centrifuged for dehydration, and air-dried at an inlet air temperature of 150-180° C. and an outlet air temperature of 70-100° C. to obtain the high-whiteness cross-linked polyvinylpyrrolidone; The Lewis acid includes any one of aluminum chloride, ferric chloride, zinc chloride, boron trifluoride, sulfur trioxide, ferric bromide or magnesium bromide, or a combination of at least two of them; the oxidant includes any one of peracetic acid, tert-butyl hydroperoxide, di-tert-butyl hydroperoxide, sodium persulfate, ammonium persulfate or potassium persulfate, or a combination of at least two of them.

20. A high whiteness cross-linked polyvinylpyrrolidone, characterized in that: The high-whiteness cross-linked polyvinylpyrrolidone is prepared by the preparation method according to any one of claims 1 to 19.

21. Use of the high-whiteness cross-linked polyvinylpyrrolidone as claimed in claim 20 in the preparation of medicines and foods.

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