A formaldehyde-free zero VOC starch-based adhesive and a preparation method thereof

Abstract

The application discloses a kind of formaldehyde-free zero VOC starch-based adhesive and preparation method thereof, with natural quality corn starch as main raw material, corn starch is widely used, green and environmental protection, low price, meet the requirements of sustainable development;The application will be dispersed into water Corn starch Stir evenly, with concentrated sulfuric acid as catalyst Hydrolysis reaction, while with potassium permanganate as oxidant Oxidation reaction, obtain Hydrolyzed oxidized starch;Hydrolyzed oxidized starch again Urea is added to Condensation reaction, obtain Hydrolyzed oxidized starch-urea condensate;Preparation Condensate, in turn Konjac Glucoside, milk protein, borax and boric acid are added to Composite modification, then carry out conditioning, green formaldehyde-free zero VOC starch-based adhesive is prepared.The adhesive prepared by the application is formaldehyde-free, zero VOC emission, has good adhesion and water resistance, solves the problem of formaldehyde and synthetic organic pollution of current adhesive;Preparation method is simple and easy to operate, high stability, good repeatability, has industrial value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer materials, and relates to a preparation method of an adhesive, in particular to a formaldehyde-free zero-VOC starch-based adhesive and a preparation method thereof. BACKGROUND

[0002] The adhesive is widely used in the fields of building and decoration, and currently commonly used adhesives are urea-formaldehyde adhesives, phenol-formaldehyde adhesives and melamine-formaldehyde adhesives. The raw materials of the currently used adhesives mainly come from petroleum resources, which are non-renewable, and can release a large amount of formaldehyde and volatile organic compounds in the use process, with a release period of 15 years. The released formaldehyde and volatile organic compounds can seriously endanger people's health and cause environmental pollution. With the development of economy and the improvement of living standards, people pay more and more attention to the environmental protection and safety of the adhesive, and it is an inevitable requirement for the development of the industry to produce a non-toxic, harmless, green, formaldehyde-free and zero-VOC adhesive.

[0003] In recent years, the adhesive using biomass resources as raw materials has attracted widespread attention, such as tannin, lignin, protein and starch adhesives. Corn starch is an ideal natural adhesive raw material source because of its wide source, rich resources and easy modification. However, the adhesive prepared by pure starch has poor bonding performance, and the presence of a large number of hydroxyl groups in the starch leads to poor water resistance. Therefore, the starch adhesive needs to be modified to improve the performance of the starch-based adhesive. SUMMARY

[0004] In order to solve the pollution problems of formaldehyde and volatile organic compounds in the traditional adhesive and the problems of poor bonding performance and water resistance of the adhesive prepared by pure starch, the application provides a formaldehyde-free zero-VOC starch-based adhesive and a preparation method thereof.

[0005] In order to solve the above problems, the technical scheme adopted by the application is as follows:

[0006] A formaldehyde-free zero-VOC starch-based adhesive comprises the following raw materials by weight:

[0007] 20-40 parts by weight of corn starch;

[0008] 40-70 parts by weight of deionized water;

[0009] 0.3-2.5 parts by weight of sulfuric acid;

[0010] 0.5-3.0 parts by weight of potassium permanganate;

[0011] 5-30 parts by weight of urea;

[0012] 2-15 parts by weight of a modifier.

[0013] The modifier comprises the following components by weight fraction:

[0014] 1-5 parts by weight of konjac glucomannan;

[0015] 1-5 parts by weight of milk protein;

[0016] 0.5-3 parts by weight of borax;

[0017] 0.5-3 parts by weight of boric acid.

[0018] A formaldehyde-free zero VOC starch-based adhesive and a preparation method thereof, comprising the following steps:

[0019] Step 1): The deionized water and corn starch are weighed according to the formula and added to the reaction container, and the electric stirring is carried out at a rotation speed of 200-250 r / min under condensation reflux;

[0020] Step 2): After mixing uniformly, the sulfuric acid is taken according to the formula and added to the reaction container for hydrolysis reaction;

[0021] Step 3): The potassium permanganate is weighed according to the formula and added to the reaction container in 2-4 times, and the temperature is increased to 40-60 DEG C, and the constant-temperature constant-speed stirring reaction is carried out for 50-80 min;

[0022] Step 4): The pH is adjusted to 4.0-6.0 by using 98% concentrated sulfuric acid or saturated sodium hydroxide solution, gradually heated to 60-80 DEG C, and the constant-temperature constant-speed stirring reaction is carried out for 10-30 min; continue to heat to 90-100 DEG C, and the constant-temperature constant-speed stirring reaction is carried out for 20-50 min; urea is added twice for condensation reaction;

[0023] Step 5): The modifiers konjac glucomannan, milk protein, borax and boric acid are added in turn, wherein the ratio of konjac glucomannan, milk protein, borax and boric acid is 2:2:1:1; the pH is adjusted to 4-8 by using 98% concentrated sulfuric acid or saturated sodium hydroxide solution, and the temperature is maintained at 90-100 DEG C for constant-speed stirring reaction for 40-80 min;

[0024] Step 6): The material obtained in step 5) is conditioned, cooled to 20-40 DEG C, and discharged to obtain a formaldehyde-free zero VOC starch-based adhesive with a microcapsule structure on the surface, a viscosity of 100-3000 mPa·s and a solid content of 40-70%.

[0025] Compared with the prior art, the beneficial effects of the present application are:

[0026] After the hydrolysis and oxidation of starch by the hydrolysis method and the oxidation method, urea is condensed with the hydrolysis and oxidation starch, and the condensate is modified by konjac glucomannan, milk protein, borax and boric acid, so that the starch-based adhesive prepared has high solid content, high viscosity, high adhesion and high water resistance; the formaldehyde-free zero VOC starch-based adhesive and the preparation method thereof are simple and easy to operate, have short preparation time, high stability, good repeatability and practical industrial value; more importantly, the starch-based adhesive has no formaldehyde and zero VOC emission, has good adhesion and water resistance, solves the formaldehyde and synthetic organic matter pollution problems of the current adhesive, and meets the green development prospect of the adhesive. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a surface topography map of example 14 of the present application at 2000 times;

[0028] Figure 2 is a wood block gluing and bonding structure mode diagram. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and effect of the present application more clear and explicit, the present application will be further described below in combination with specific examples, and it should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the technical scheme provided by the present application.

[0030] The formaldehyde-free zero VOC starch-based adhesive and the preparation method thereof are as follows: starch and water are added to a reaction container and stirred and dispersed; sulfuric acid is added and fully stirred and dispersed for hydrolysis reaction; potassium permanganate is added to the mixture, and oxidation reaction is carried out under the condition of stirring and heating; after full reaction, urea is added for condensation reaction to obtain hydrolysis and oxidation starch-urea condensate adhesive; konjac glucomannan, milk protein, borax and boric acid are added to the hydrolysis and oxidation starch-urea condensate adhesive, and fully stirred for composite modification; the quality is adjusted, and the temperature is cooled to room temperature to obtain the formaldehyde-free zero VOC starch-based adhesive.

[0031] The % used, if not specifically stated, represents the mass percentage content, i.e. wt%.

[0032] Example 1

[0033] A formaldehyde-free zero VOC starch-based adhesive and a preparation method thereof are as follows:

[0034] 30 g of corn starch and 45 g of water were added to a reaction vessel, dispersed by stirring at 200-250 r / min, then 1 mL of 98% concentrated sulfuric acid was added, and the mixture was dispersed by constant stirring, and a hydrolysis reaction was carried out; 1.5 g of potassium permanganate was added to the mixture, and an oxidation reaction was carried out under the condition of stirring at 200-250 r / min; after sufficient reaction, the temperature was continued to be raised, 5 g of urea was added, a condensation reaction was carried out, and the quality was adjusted to obtain an aldehyde-free zero-VOC starch-based adhesive, which was cooled to room temperature. The performance indicators of the obtained aldehyde-free zero-VOC starch-based adhesive were tested and are shown in Table 1.

[0035] Example 2

[0036] An aldehyde-free zero-VOC starch-based adhesive and a preparation method thereof are as follows:

[0037] 30 g of corn starch and 45 g of water were added to a reaction vessel, dispersed by stirring at 200-250 r / min, then 1 mL of 98% concentrated sulfuric acid was added, and the mixture was dispersed by constant stirring, and a hydrolysis reaction was carried out; 1.5 g of potassium permanganate was added to the mixture, and an oxidation reaction was carried out under the condition of stirring at 200-250 r / min; after sufficient reaction, the temperature was continued to be raised, 5 g of urea was added, a condensation reaction was carried out, and the quality was adjusted to obtain an aldehyde-free zero-VOC starch-based adhesive, which was cooled to room temperature. The performance indicators of the obtained aldehyde-free zero-VOC starch-based adhesive were tested and are shown in Table 1.

[0038] Example 3

[0039] An aldehyde-free zero-VOC starch-based adhesive and a preparation method thereof are as follows:

[0040] 30 g of corn starch and 45 g of water were added to a reaction vessel, dispersed by stirring at 200-250 r / min, then 1 mL of 98% concentrated sulfuric acid was added, and the mixture was dispersed by constant stirring, and a hydrolysis reaction was carried out; 1.5 g of potassium permanganate was added to the mixture, and an oxidation reaction was carried out under the condition of stirring at 200-250 r / min; after sufficient reaction, the temperature was continued to be raised, 5 g of urea was added, a condensation reaction was carried out, and the quality was adjusted to obtain an aldehyde-free zero-VOC starch-based adhesive, which was cooled to room temperature. The performance indicators of the obtained aldehyde-free zero-VOC starch-based adhesive were tested and are shown in Table 1.

[0041] Example 4

[0042] An aldehyde-free zero-VOC starch-based adhesive and a preparation method thereof are as follows:

[0043] 30 g of corn starch and 45 g of water were added to a reaction container, stirred and dissolved at 200-250 r / min, then 1 mL of 98% concentrated sulfuric acid was added, and the mixture was fully dispersed and stirred at constant speed for hydrolysis reaction; 1.5 g of potassium permanganate was added to the mixture, and the mixture was heated and stirred at 200-250 r / min for oxidation reaction; after sufficient reaction, the temperature was further increased, 20 g of urea was added, and the mixture was subjected to condensation reaction and conditioning to obtain an aldehyde-free zero-VOC starch-based adhesive, which was cooled to room temperature. The performance indicators of the obtained aldehyde-free zero-VOC starch-based adhesive were tested and are shown in Table 1.

[0044] Example 5

[0045] An aldehyde-free zero-VOC starch-based adhesive and a preparation method thereof are as follows:

[0046] 30 g of corn starch and 45 g of water were added to a reaction container, stirred and dispersed at 200-250 r / min, then 1 mL of 98% concentrated sulfuric acid was added, and the mixture was fully dispersed and stirred at constant speed for hydrolysis reaction; 1.5 g of potassium permanganate was added to the mixture, and the mixture was heated and stirred at 200-250 r / min for oxidation reaction; after sufficient reaction, the temperature was further increased, 25 g of urea was added, and the mixture was subjected to condensation reaction and conditioning to obtain an aldehyde-free zero-VOC starch-based adhesive, which was cooled to room temperature. The performance indicators of the obtained aldehyde-free zero-VOC starch-based adhesive were tested and are shown in Table 1.

[0047] Example 6

[0048] An aldehyde-free zero-VOC starch-based adhesive and a preparation method thereof are as follows:

[0049] 30 g of corn starch and 50 g of water were added to a reaction container, stirred and dispersed at 200-250 r / min, then 1 mL of 98% concentrated sulfuric acid was added, and the mixture was fully dispersed and stirred at constant speed for hydrolysis reaction; 1.5 g of potassium permanganate was added to the mixture, and the mixture was heated and stirred at 200-250 r / min for oxidation reaction; after sufficient reaction, the temperature was further increased, 15 g of urea was added, and the mixture was subjected to condensation reaction and conditioning to obtain a hydrolyzed and oxidized starch-urea condensation adhesive; 0.5 g of modified konjac glucomannan, milk protein, borax, and boric acid (in a ratio of 2:2:1:1) were added to the hydrolyzed and oxidized starch-urea condensation adhesive, and the mixture was fully modified and reacted, conditioned, and cooled to room temperature to obtain an aldehyde-free zero-VOC starch-based adhesive. The performance indicators of the obtained aldehyde-free zero-VOC starch-based adhesive were tested and are shown in Table 1.

[0050] Example 7

[0051] An aldehyde-free zero-VOC starch-based adhesive and a preparation method thereof are as follows:

[0052] 30 g of corn starch and 50 g of water are added to a reaction container, dispersed by stirring at 200-250 r / min, then 1 mL of 98% concentrated sulfuric acid is added, and the mixture is dispersed by constant stirring, and a hydrolysis reaction is carried out; 1.5 g of potassium permanganate is added to the mixture, and an oxidation reaction is carried out under the condition of stirring at 200-250 r / min; after sufficient reaction, the temperature is further increased, 15 g of urea is added, and a hydrolysis-oxidation starch-urea condensation adhesive is obtained; 1.5 g of modified agent konjac glucomannan, milk protein, borax, boric acid (ratio of 2:2:1:1) is added to the hydrolysis-oxidation starch-urea condensation adhesive, and a modification reaction is carried out, the quality is adjusted, and the temperature is cooled to room temperature. A formaldehyde-free zero-VOC starch-based adhesive is prepared. The performance indicators of the formaldehyde-free zero-VOC starch-based adhesive obtained are shown in Table 1.

[0053] Example 8

[0054] A formaldehyde-free zero-VOC starch-based adhesive and a preparation method thereof are as follows:

[0055] 30 g of corn starch and 50 g of water are added to a reaction container, dispersed by stirring at 200-250 r / min, then 1 mL of 98% concentrated sulfuric acid is added, and the mixture is dispersed by constant stirring, and a hydrolysis reaction is carried out; 1.5 g of potassium permanganate is added to the mixture, and an oxidation reaction is carried out under the condition of stirring at 200-250 r / min; after sufficient reaction, the temperature is further increased, 15 g of urea is added, and a hydrolysis-oxidation starch-urea condensation adhesive is obtained; 1.5 g of modified agent konjac glucomannan, milk protein, borax, boric acid (ratio of 2:2:1:1) is added to the hydrolysis-oxidation starch-urea condensation adhesive, and a modification reaction is carried out, the quality is adjusted, and the temperature is cooled to room temperature. A formaldehyde-free zero-VOC starch-based adhesive is prepared. The performance indicators of the formaldehyde-free zero-VOC starch-based adhesive obtained are shown in Table 1.

[0056] Example 9

[0057] A formaldehyde-free zero-VOC starch-based adhesive and a preparation method thereof are as follows:

[0058] 30 g of corn starch and 50 g of water are added to a reaction container, dispersed by stirring at 200-250 r / min, then 1 mL of 98% concentrated sulfuric acid is added, and the mixture is dispersed by constant stirring, and a hydrolysis reaction is carried out; 1.5 g of potassium permanganate is added to the mixture, and an oxidation reaction is carried out under the condition of stirring at 200-250 r / min; after sufficient reaction, the temperature is continued to rise, 15 g of urea is added, and a hydrolysis-oxidation starch-urea condensation adhesive is obtained; 3.5 g of modified agent konjac glucomannan, milk protein, borax, boric acid (ratio of 2:2:1:1) is added to the hydrolysis-oxidation starch-urea condensation adhesive, and a composite modification reaction is carried out, the quality is adjusted, and the temperature is cooled to room temperature. A formaldehyde-free zero-VOC starch-based adhesive can be prepared. The performance indicators of the formaldehyde-free zero-VOC starch-based adhesive are shown in Table 1.

[0059] Example 10

[0060] A formaldehyde-free zero-VOC starch-based adhesive and a preparation method thereof are as follows:

[0061] 30 g of corn starch and 50 g of water are added to a reaction container, dispersed by stirring at 200-250 r / min, then 1 mL of 98% concentrated sulfuric acid is added, and the mixture is dispersed by constant stirring, and a hydrolysis reaction is carried out; 1.5 g of potassium permanganate is added to the mixture, and an oxidation reaction is carried out under the condition of stirring at 200-250 r / min; after sufficient reaction, the temperature is continued to rise, 15 g of urea is added, and a hydrolysis-oxidation starch-urea condensation adhesive is obtained; 4.5 g of modified agent konjac glucomannan, milk protein, borax, boric acid (ratio of 2:2:1:1) is added to the hydrolysis-oxidation starch-urea condensation adhesive, and a composite modification reaction is carried out, the quality is adjusted, and the temperature is cooled to room temperature. A formaldehyde-free zero-VOC starch-based adhesive can be prepared. The performance indicators of the formaldehyde-free zero-VOC starch-based adhesive are shown in Table 1.

[0062] Example 11

[0063] A formaldehyde-free zero-VOC starch-based adhesive and a preparation method thereof are as follows:

[0064] 30 g of corn starch and 50 g of water are added to a reaction container, dispersed by stirring at 200-250 r / min, then 1 mL of 98% concentrated sulfuric acid is added, and the mixture is dispersed by constant stirring, and a hydrolysis reaction is carried out; 1.5 g of potassium permanganate is added to the mixture, and an oxidation reaction is carried out under the condition of stirring at 200-250 r / min; after sufficient reaction, the temperature is continued to rise, 15 g of urea is added, and a hydrolysis-oxidation starch-urea condensation adhesive is obtained; 5.5 g of modified agent konjac glucomannan, milk protein, borax, boric acid (ratio of 2:2:1:1) is added to the hydrolysis-oxidation starch-urea condensation adhesive, and a modification reaction is carried out, the quality is adjusted, and the temperature is cooled to room temperature. A formaldehyde-free zero-VOC starch-based adhesive is prepared. The performance indicators of the formaldehyde-free zero-VOC starch-based adhesive obtained are shown in Table 1.

[0065] Example 12

[0066] A formaldehyde-free zero-VOC starch-based adhesive and a preparation method thereof are as follows:

[0067] 30 g of corn starch and 50 g of water are added to a reaction container, dispersed by stirring at 200-250 r / min, then 1 mL of 98% concentrated sulfuric acid is added, and the mixture is dispersed by constant stirring, and a hydrolysis reaction is carried out; 1.5 g of potassium permanganate is added to the mixture, and an oxidation reaction is carried out under the condition of stirring at 200-250 r / min; after sufficient reaction, the temperature is continued to rise, 15 g of urea is added, and a hydrolysis-oxidation starch-urea condensation adhesive is obtained; 6.5 g of modified agent konjac glucomannan, milk protein, borax, boric acid (ratio of 2:2:1:1) is added to the hydrolysis-oxidation starch-urea condensation adhesive, and a modification reaction is carried out, the quality is adjusted, and the temperature is cooled to room temperature. A formaldehyde-free zero-VOC starch-based adhesive is prepared. The performance indicators of the formaldehyde-free zero-VOC starch-based adhesive obtained are shown in Table 1.

[0068] Example 13

[0069] A formaldehyde-free zero-VOC starch-based adhesive and a preparation method thereof are as follows:

[0070] 30 g of corn starch and 50 g of water are added to a reaction container, dispersed by stirring at 200-250 r / min, then 1 mL of 98% concentrated sulfuric acid is added, and the mixture is dispersed by constant stirring, and a hydrolysis reaction is carried out; 1.5 g of potassium permanganate is added to the mixture, and an oxidation reaction is carried out under the condition of stirring at 200-250 r / min; after sufficient reaction, continue to heat, add 15 g of urea, and obtain a hydrolysis-oxidation starch-urea condensation adhesive; 7.5 g of modified agent konjac glucomannan, milk protein, borax, boric acid (ratio of 2:2:1:1) is added to the hydrolysis-oxidation starch-urea condensation adhesive, and a modification reaction is carried out, the quality is adjusted, and the temperature is cooled to room temperature, to obtain a formaldehyde-free zero VOC starch-based adhesive. The performance indicators of the formaldehyde-free zero VOC starch-based adhesive obtained are shown in Table 1.

[0071] Example 14

[0072] A formaldehyde-free zero VOC starch-based adhesive and a preparation method thereof are as follows:

[0073] 30 g of corn starch and 50 g of water are added to a reaction container, dispersed by stirring at 200-250 r / min, then 1 mL of 98% concentrated sulfuric acid is added, and the mixture is dispersed by constant stirring, and a hydrolysis reaction is carried out; 1.5 g of potassium permanganate is added to the mixture, and an oxidation reaction is carried out under the condition of stirring at 200-250 r / min; after sufficient reaction, continue to heat, add 15 g of urea, and obtain a hydrolysis-oxidation starch-urea condensation adhesive; 8.5 g of modified agent konjac glucomannan, milk protein, borax, boric acid (ratio of 2:2:1:1) is added to the hydrolysis-oxidation starch-urea condensation adhesive, and a modification reaction is carried out, the quality is adjusted, and the temperature is cooled to room temperature, to obtain a formaldehyde-free zero VOC starch-based adhesive. The performance indicators of the formaldehyde-free zero VOC starch-based adhesive obtained are shown in Table 1.

[0074] Example 15

[0075] A formaldehyde-free zero VOC starch-based adhesive and a preparation method thereof are as follows:

[0076] 30 g corn starch and 50 g of water into the reaction vessel, 200-250 r / min stirring dispersion, then add 1 mL 98% concentrated sulfuric acid, fully constant speed stirring dispersion, hydrolysis reaction; 1.5 g of potassium permanganate is added to the mixture under the condition of stirring and heating to carry out oxidation reaction; after sufficient reaction, continue to heat, add 15 g of urea, get hydrolysis oxidation starch-urea condensation adhesive; 9.5 g of modified agent konjac glucomannan, milk protein, borax, boric acid (ratio of 2:2:1:1) is added to the hydrolysis oxidation starch-urea condensation adhesive, fully composite modification reaction, conditioning, cooling down to room temperature, can be made into no formaldehyde zero VOC starch-based adhesive. The performance index of the obtained no formaldehyde zero VOC starch-based adhesive is shown in Table 1.

[0077] Example 16

[0078] A no formaldehyde zero VOC starch-based adhesive and a preparation method thereof, specifically as follows:

[0079] 30 g corn starch and 50 g of water into the reaction vessel, 200-250 r / min stirring dispersion, then add 1 mL 98% concentrated sulfuric acid, fully constant speed stirring dispersion, hydrolysis reaction; 1.5 g of potassium permanganate is added to the mixture under the condition of stirring and heating to carry out oxidation reaction; after sufficient reaction, continue to heat, add 15 g of urea, get hydrolysis oxidation starch-urea condensation adhesive; 10.5 g of modified agent konjac glucomannan, milk protein, borax, boric acid (ratio of 2:2:1:1) is added to the hydrolysis oxidation starch-urea condensation adhesive, fully composite modification reaction, conditioning, cooling down to room temperature, can be made into no formaldehyde zero VOC starch-based adhesive. The performance index of the obtained no formaldehyde zero VOC starch-based adhesive is shown in Table 1.

[0080] To test the performance of the adhesive in the examples, the experiment selects the size of the pine board as 46.5 mm×25.0 mm×5.0 mm and 30.5 mm×25.0 mm×5.0 mm. Two pieces of board with a size of 46.5 mm×25.0 mm×5.0 mm are arranged according to the cross pattern, and the inner surface of the board is evenly coated with a brush, and the coating area is 13 mm×25 mm. Then the two pieces of coated wood are bonded together and placed on a flat vulcanizing machine for pressing. Then, in the uncoated area at both ends of the bonded wood, a wood piece with a size of 30.5 mm×25 mm×5 mm is coated and bonded, and pressing is carried out under the same conditions. The wood piece coating and bonding structure is shown in Figure 2Examples 1-5 were pressed at room temperature for 20 min; Examples 6-14 were hot-pressed at a hot-pressing temperature of 130°C, a hot-pressing pressure of 0.5 MPa, and a hot-pressing time of 10 min, to obtain the plywood. The formed plywood was placed in a constant-temperature air-drying oven at 60°C for 27 h, and then subjected to mechanical property testing. Each group had no less than 10 samples, which were immersed in cold water at 20°C for 3 h, and then subjected to mechanical property testing under wet conditions to obtain the wet shear strength.

[0081] The shear strength of the samples in the above examples was tested, and the statistical results are shown in Table 1.

[0082] .

Claims

1. A formaldehyde-free, zero-VOC starch-based adhesive, characterized in that: Includes the following components: 30 g of corn starch; 50 g of deionized water; 1 mL of 98% concentrated sulfuric acid; 1.5 g of potassium permanganate; 15 g of urea; Modifier 4.5–15 g, wherein the adhesive preparation process is as follows: Step 1). Weigh out deionized water and corn starch according to the formula, add them to the reaction vessel, reflux, and stir with an electric motor at a speed of 200-250 r / min; Step 2). After mixing thoroughly, take the amount of sulfuric acid according to the formula and add it to the reaction vessel to carry out the hydrolysis reaction; Step 3). Weigh out potassium permanganate according to the formula, add it to the reaction vessel in 2 to 4 portions, and heat it to 40 to 60°C. Stir the mixture at a constant temperature and speed for 50 to 80 minutes. Step 4). Adjust the pH to 4.0–6.0 with 98% concentrated sulfuric acid or saturated sodium hydroxide solution, gradually heat to 60–80°C, and stir at a constant temperature and speed for 10–30 min. Continue heating to 90–100°C and stir at a constant temperature and speed for 20–50 min. Add urea in two batches for the condensation reaction. Step 5). Add the modifier konjac glucomannan, milk protein, borax, and boric acid in sequence, wherein the ratio of konjac glucomannan, milk protein, borax, and boric acid is 2:2:1:

1. Adjust the pH to 4-8 with 98% concentrated sulfuric acid or saturated sodium hydroxide solution, and maintain the temperature at 90-100℃ with constant stirring for 40-80 minutes. Step 6). The material obtained in Step 5) is conditioned and cooled to 20-40℃, and discharged to obtain a formaldehyde-free, zero-VOC starch-based adhesive with a microcapsule structure on the surface, a viscosity of 100-3000 mPa·s, and a solid content of 40-70%.

2. A method for preparing a formaldehyde-free, zero-VOC starch-based adhesive as described in claim 1, characterized in that: Specifically, the following steps are included: Step 1). Weigh out deionized water and corn starch according to the formula, add them to the reaction vessel, reflux, and stir with an electric motor at a speed of 200-250 r / min; Step 2). After mixing thoroughly, take the amount of sulfuric acid according to the formula and add it to the reaction vessel to carry out the hydrolysis reaction; Step 3). Weigh out potassium permanganate according to the formula, add it to the reaction vessel in 2 to 4 portions, and heat it to 40 to 60°C. Stir the mixture at a constant temperature and speed for 50 to 80 minutes. Step 4). Adjust the pH to 4.0–6.0 with 98% concentrated sulfuric acid or saturated sodium hydroxide solution, gradually heat to 60–80°C, and stir at a constant temperature and speed for 10–30 min. Continue heating to 90–100°C and stir at a constant temperature and speed for 20–50 min. Add urea in two batches for the condensation reaction. Step 5). Add the modifier konjac glucomannan, milk protein, borax, and boric acid in sequence, wherein the ratio of konjac glucomannan, milk protein, borax, and boric acid is 2:2:1:

1. Adjust the pH to 4-8 with 98% concentrated sulfuric acid or saturated sodium hydroxide solution, and maintain the temperature at 90-100℃ with constant stirring for 40-80 minutes. Step 6). The material obtained in Step 5) is conditioned and cooled to 20-40℃, and discharged to obtain a formaldehyde-free, zero-VOC starch-based adhesive with a microcapsule structure on the surface, a viscosity of 100-3000 mPa·s, and a solid content of 40-70%.

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