LU502794B1

LU502794B1 - Method for preparing starch-based bio-latex by hydrolysis using immobilized enzyme

Info

Publication number: LU502794B1
Application number: LU502794A
Authority: LU
Inventors: Liqin Liu
Original assignee: Tianjin Univ Of Science And Technology
Priority date: 2022-08-03
Filing date: 2022-09-14
Publication date: 2023-03-21
Also published as: CN115286719B; CN115286719A

Abstract

The present invention discloses a method for preparing a starch-based bio-latex by hydrolysis using an immobilized enzyme. The present invention adopts immobilized α-amylase to hydrolyze starch, which can improve the hydrolysis efficiency of starch, fully degrade the starch molecules with high molecular weight, and reduce the production of monosaccharides. Through the cross-linking reaction in the later stage and the dispersion of cellulose nanocrystals, starch-based bio-latex with a three-dimensional stable network structure is obtained. The starch-based bio-latex obtained by the present invention has excellent rheological properties and boning performance, so it can be used as a coating binder to replace petroleum-based latex in a high proportion and show perfect bonding performance. The present starch-based bio-latex can also be used as a surface sizing agent to significantly improve the enhancement efficiency of surface sizing starch on the mechanical properties of corrugated paper board.

Description

METHOD FOR PREPARING STARCH-BASED BIO-LATEX BY HYDROLYSIS USING 502794

IMMOBILIZED ENZYME

TECHNICAL FIELD

The present invention relates to the technical field of adhesive preparation, particularly, to a method for preparing a starch-based bio-latex by hydrolysis using an immobilized enzyme.

BACKGROUND

Starch is mainly stored in plants as carbohydrates, acts as renewable and degradable polymer biomass resources abundant in nature, and is widely used in various industries, such as the chemical industry, biology, food, papermaking, and other fields. Starch-based bio- latex prepared with starch as the primary raw material is a kind of green water-soluble natural adhesive, which has been considered an ideal substitute for petroleum-based latex (such as styrene-butadiene latex and styrene-acrylic latex) in recent years. Starch-based bio-latex will have great application value and economic benefits in papermaking, packaging, construction, and other fields.

Currently, the only industrialized starch-based bio-latex reported in the world comes from EcoSphere® Biolatex products prepared by EcoSynthetix company by a dry method, and the deficiency of the dry preparation process is that the unreacted components in the reaction process are difficult to separate from the reaction system. In addition, the emulsion formulated by the product at room temperature has the maximum concentration of only 25 wt%, where starch accounts for a limited proportion of the active components of the emulsion.

However, the preparation of starch-based bio-latex using a wet process which involves a simple process, yields a high solid content and a high bonding strength, and achieves a high coatability and printability cannot be easily achieved. The currently reported starch-based bio-latex that are prepared by the wet method use different processes and exist in different forms. Mostly, oxidizers, acids, or biological enzymes are first used to degrade the natural starch. Then, the hydrolyzed starch molecules are cross-linked with each other by a chemical cross-linking method to finally obtain a liquid starch-based bio-latex. In recent years,

cellulose nanocrystals have been generally recognized as playing an enhancement role 4n,502794 adhesives and coatings due to having good macroscopic surface effects and quantum size effects. Furthermore, some studies have shown that adding a certain amount of cellulose nanocrystals in the wet preparation process of starch-based bio-latex can promote the oxidation reaction and subsequent cross-linking reaction of starch polysaccharide molecules to obtain starch-based bio-latex with high stability and cross-linking degree. The reported preparation methods are generally concerned with improving the oxidation degree and cross- linking degree of starch to improve the performance of starch adhesives. However, the basic structural unit of starch-based adhesives lies with the size and distribution behavior of the starch molecular chain. Therefore, how efficiently obtaining the ideal structural unit of starch-based bio-latex is the key to the preparation of high-performance starch-based bio- latex, and it has become a significant technical problem.

SUMMARY

The purpose of the present invention is to provide a method for preparing a starch-based bio-latex by hydrolysis using an immobilized enzyme. In the present invention, owing to the high specific surface area, adsorbability, stability, and enhancement performance of cellulose nanocrystals, cellulose nanocrystals can be used to obtain a starch-based bio-latex with high bonding strength, high coatability, and high printing adaptability using a simple preparation process with low energy consumption.

The technical solution provided by the present invention includes a method for preparing a starch-based bio-latex by hydrolysis using an immobilized enzyme, which includes the following steps:

Step 1: Using a citric acid-disodium hydrogen phosphate buffer solution as a solvent, preparing cellulose nanocrystals (CNCs) into a cellulose nanocrystal dilute solution with a concentration of 0.05 wt%-0.5 wt%.

Step 2: diluting a-amylase in the citric acid-disodium hydrogen phosphate buffer solution to prepare a a-amylase diluent with a concentration of 0.05 u/ml-0.3 u/ml, mixing the a-amylase diluent and the cellulose nanocrystal dilute solution, and incubating a resulting mixed solution at 1°C-8°C for 1 hour-3 hours to complete an immobilized reaction of q;502794 amylase to obtain a CNC immobilized a-amylase, wherein the amount of a-amylase in the mixed solution is 0.5 u/g-5 u/g of the absolute dry starch mass, and the amount of cellulose in the mixed solution is 0.05 wt%-2 wt% of the absolute dry starch mass.

Step 3: Adding the CNC immobilized a-amylase obtained in step 2 to a starch slurry with a concentration of 1%-50%, stirring at 20°C-40°C for 10 min, heating to 80°C-95°C, adding a 0.1 wt%-10 wt% plasticizer, keeping the temperature for 10 min-30 min, naturally cooling to 40°C-65°C, and adding a 0.1 wt%-10 wt% cross-linking agent to react for 10 min- 40 min to obtain a starch-based bio-latex product.

In the method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme described above, the solid content of starch-based bio-latex is 1%-50%.

In the method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme described above, the cellulose nanocrystals are one or any combination of anionic cellulose nanocrystals, cationic cellulose nanocrystals, and neutral cellulose nanocrystals.

In the method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme described above, the cellulose nanocrystals each have the length of 200 nm-300 nm, the diameter of 20 nm-40 nm, and the solid content of 0.01%-5%.

In the method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme described above, the pH value of the citric acid-disodium hydrogen phosphate buffer solution is 5.5-7.

In step 2 of the method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme described above, the mixed solution is incubated in a constant temperature gas bath shaker at 4°C and at a rate of 100 rpm-300 rpm for 1 hour-3 hours.

In step 3 of the method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme described above, the starch of the starch slurry is one or any combination of corn starch, cassava starch, potato starch, and sweet potato starch.

In the method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme described above, the plasticizer is one or any combination of glycerol,

urea, ethylene glycol, polyethylene glycol, propylene glycol, sorbitol, and ethanolamine. | 502794

In the method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme described above, the cross-linking agent is one or any combination of formaldehyde, acetaldehyde, glyoxal, glutaraldehyde, polyglyoxal, triglyceride, sodium trimetaphosphate, sodium hexametaphosphate, and ammonium zirconium carbonate.

Compared with the prior art, the present invention has the following beneficial effects: (1) In the present invention, the cellulose nanocrystals are used. The cellulose nanocrystals play an enhancement role and act as an excellent carrier of amylase, a dispersant, and stabilizer, so that the prepared starch-based bio-latex has excellent bonding performance and coating printability. In addition, the cellulose nanocrystals can also effectively increase the steric hindrance between the molecular chains of the enzymolytic starch, inhibit the retrogradation phenomenon of the starch molecular chains during the cooling or storage process, and further improve the performance stability of the starch-based bio-latex. The present invention adopts immobilized a-amylase to hydrolyze starch, which can improve the hydrolysis efficiency of starch, fully degrade the polysaccharide polymer with high molecular weight, and reduce the production of monosaccharides. Through the cross-linking reaction in the later stage and the dispersion of cellulose nanocrystals, starch-based bio-latex with a three-dimensional stable network structure and excellent stability, bonding performance, and rheological properties are obtained. The starch-based bio-latex obtained by the present invention has excellent rheological properties and bonding performance, so it can be used as a coating binder to replace petroleum-based latex in a high proportion and show perfect bonding performance. The present starch-based bio-latex can also be used as a surface sizing agent to significantly improve the enhancement efficiency of the surface sizing starch on the mechanical properties of corrugated paper board. The present invention also has the characteristics of a simple process, easy industrialization, low cost, and no pollution. (2) The present invention adopts cellulose nanocrystals as the carrier for immobilizing a-amylase, which optimizes the catalytic hydrolysis performance of a-amylase. The stability of low-concentration starch slurry is improved, and the hydrolysis efficiency of high- concentration starch is increased, so that the amylase has excellent diffusion performance in a high-viscosity and high-concentration starch pasting solution. The uniformity and,502794 efficiency of hydrolysis of a high-concentration starch slurry is improved, which ensures the starch adhesive has an excellent structural unit. The starch-based bio-latex with a stable three-dimensional network structure is formed after a cross-linking reaction, exhibiting high stability and bonding performance. (3) The present invention disperses the diluents of a-amylase and cellulose nanocrystals in the citric acid-disodium hydrogen phosphate buffer solution and incubates directly at low temperature to promote the complete combination of amylase and cellulose nanocrystals, providing a simple and efficient immobilization method. Using a buffer solution and a low- temperature gas bath shaker can fully guarantee the stable enzyme activity of a-amylase in the immobilization reaction process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanning electron microscope image of the starch-based bio-latex prepared by the present invention.

FIG. 2 is an enlarged view of the 3D network structure marked with the dotted frame of

FIG. 1.

FIG. 3 is a schematic diagram of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention is further described in combination with embodiments and drawings below, which, however, does not serve as a basis for limiting the present invention.

Embodiment 1: A method for preparing a starch-based bio-latex by hydrolysis using an immobilized enzyme specifically includes the following steps:

Step 1: A citric acid-disodium hydrogen phosphate buffer solution is used as a solvent, and cellulose nanocrystals are prepared into a cellulose nanocrystal dilute solution with a concentration of 0.05 wt%-0.5 wt%.

In the present embodiment, the cellulose nanocrystals are cationic cellulose nanocrystals, which are obtained by modifying with quaternary ammonium salts the cellulose nanocrystals (CNCs) that are prepared by hydrolysis using concentrated sulfuric acid. The specific preparation method includes adding a certain amount of a NaOH solution having 3502794 mass fraction of 30% to a CNC solution having a mass fraction of 9% to obtain a mixed solution with the final mass fraction of NaOH being 7%. After stirring for 30 min at room temperature, 2,3-epoxypropyl trimethyl ammonium chloride (EPTMAC) is added to the mixed solution according to the mass ratio of cationic modifier to absolute dry CNC at 2:1, and anhydrous ethanol is added to the mixed solution according to the mass ratio of anhydrous ethanol to water of the mixed solution at 1:1. After reacting for 5 hours at 65°C, the reaction is terminated by diluting the reacting system with aqueous solution at an amount of five times the reacting system. The reacting system is placed in a dialysis bag for dialysis for 15 days and then evaporated at room temperature and under reduced pressure. When the mass fraction is 0.6%, the reacting system is transferred to a reagent bottle, and its surface charge is +0.27+0.03 mmol/g.

Step 2: The cationic CNC (CCNC) solution is diluted to 0.1 wt% using a citric acid- disodium hydrogen phosphate buffer solution (pH=7) as a solvent and a-amylase is added to the citric acid-disodium hydrogen phosphate buffer solution to prepare a 0.1 u/ml enzyme diluent. After mixing the two, the resulting solution is incubated in a constant temperature gas bath shaker at 4°C and at a rate of 100 rpm-300 rpm for 1 hour-3 hours to complete the immobilization of a-amylase and obtain cationic cellulose nanocrystal immobilized a- amylase (CCNC immobilized a-amylase).

Step 3: 45 g of absolute dry cassava starch (in other embodiments, starch is one or any combination of corn starch, cassava starch, potato starch, and sweet potato starch) is weighed and added with 45 g of solvent to form a starch slurry with a mass fraction of 50 wt%. The solvent is composed of 22.5 g of citric acid-disodium hydrogen phosphate buffer solution (pH=6.9-7) and 22.5 g of deionized water. The starch slurry is stirred evenly at room temperature. The starch slurry is placed in a water bath at 38°C and stirred for 10 min to make the slurry temperature uniform. CCNC immobilized a-amylase is added and stirred for min to ensure that the CCNC immobilized a-amylase is uniformly dispersed in the starch slurry. The starch slurry is heated up at a rate of 1 °C/min until the temperature is 95°C, followed by adding glycerol at an amount of 0.2 wt% relative to the absolute dry starch and keeping the temperature for 30 min. In other embodiments, the plasticizer may also be on@,5p2794 or any combination of glycerol, urea, ethylene glycol, polyethylene glycol, propylene glycol, sorbitol, and ethanolamine in addition to the glycerol. The starch slurry is cooled down to 60°C, followed by adding sodium trimetaphosphate at an amount of 3 wt% relative to the absolute dry starch to react for 30 min and screening to obtain the starch-based bio-latex with a solid content of 50 wt%. In other embodiments, the cross-linking agent is one or any combination of formaldehyde, acetaldehyde, glyoxal, glutaraldehyde, polyglyoxal, triglyceride, sodium trimetaphosphate, sodium hexametaphosphate, and ammonium zirconium carbonate in addition to the sodium trimetaphosphate.

The bio-latex prepared in the present embodiment includes the following components: a cassava starch slurry with a solid content of 50%; cationic cellulose nanocrystals at an amount of 0.1 wt% relative to the absolute dry starch, where the length and the diameter of each cellulose nanocrystal are 200 nm-300 nm and 20 nm-40 nm, respectively; liquid a- amylase at an amount of 2.5 u/g relative to the absolute dry starch; glycerol at an amount of 0.2 wt% relative to the absolute dry starch, and sodium trimetaphosphate at an amount of 3 wt % relative to the absolute dry starch mass. The present invention uses cellulose nanocrystals as the carrier for immobilizing a-amylase, which optimizes the catalytic hydrolysis performance of a-amylase to starch. The stability of low-concentration starch slurry is improved and the hydrolysis efficiency of high-concentration starch is increased, so that the amylase has excellent diffusion performance in a high-viscosity and high- concentration starch pasting solution. The uniformity and efficiency of hydrolysis of a high- concentration starch slurry is improved, which ensures the starch adhesive has an excellent structural unit. The starch-based bio-latex with a stable three-dimensional network structure is formed after a cross-linking reaction, exhibiting high stability and bonding performance.

FIG. 1 shows a scanning electron microscope image of the freeze-dried bio-latex, which shows that the starch-based bio-latex of the present invention has a 3D network structure (3D porous network). FIG. 2 is an enlarged view of the 3D network structure marked with the dotted frame of FIG. 1. FIG. 3 shows a schematic diagram of the present invention.

The bio-latex prepared in the present embodiment is used in a coating application. The starch-based bio-latex with a solid content of 50 wt% is used to replace 50% carboxylj502794 styrene-butadiene latex and applied to a pigment-coated paper. The total amount of the binder in the coating is 12 pph, and the pigment is ground calcium carbonate. The binder and the pigment are prepared into the coating with a solid content of 65%, which is applied to the coated paper with a coating amount of 32+2 g/m? The sample is placed in a constant temperature and humidity laboratory at 23+1°C and 50+2% RH for 24 hours, and the coating and printing performance of the coated paper is tested. The experimental results are shown in Table 1.

Embodiment 2: A method for preparing a starch-based bio-latex by hydrolysis using an immobilized enzyme specifically includes the following steps:

Step 1: A 9 wt% CNC (surface charge 1s-3.24+0.31 mmol/g) solution is diluted with a citric acid-disodium hydrogen phosphate buffer solution (pH=7) as a solvent to 0.1 wt%.

Step 2: The a-amylase is diluted in the citric acid-disodium hydrogen phosphate buffer solution to prepare a 0.1 u/ml enzyme diluent. After mixing the two, the resulting solution is incubated in a constant temperature gas bath shaker at 4°C and at a rate of 100 rpm-300 rpm for 1 hour-3 hours to complete the immobilization of a-amylase and obtain CNC immobilized a-amylase. The amount of a-amylase in the mixed solution is 0.5 u/g-5 u/g of the absolute dry starch mass, and the amount of cellulose in the mixed solution is 0.05 wt%-2 wt% of the absolute dry starch mass.

Step 3: 45 g of absolute dry cassava starch is weighed and added with 45 g of solvent to form a starch slurry with a mass fraction of 50 wt%. The solvent is composed of 22.5 g of citric acid-disodium hydrogen phosphate buffer solution (pH=6.9-7) and 22.5 g of deionized water. The starch slurry is stirred evenly at room temperature. The starch slurry is placed in a water bath at 38°C and stirred for 10 min to make the slurry temperature uniform. CNC immobilized a-amylase is added and stirred for 10 min to ensure that the CNC immobilized a-amylase is uniformly dispersed in the starch slurry. The starch slurry is heated up at a rate of 1 °C/min until the temperature is 95°C, followed by adding glycerol at an amount of 0.2 wt% relative to the absolute dry starch and keeping the temperature for 30 min. The starch slurry is cooled down to 60°C, followed by adding sodium trimetaphosphate at an amount of

3 wt% relative to the absolute dry starch to react for 30 min and screening to obtain thg;502794 starch-based bio-latex with a solid content of 50 wt%.

The bio-latex prepared in the present embodiment includes the following components: a cassava starch slurry with a solid content of 50%; cellulose nanocrystals at an amount of 0.1 wt% relative to the absolute dry starch, where the length and the diameter of each cellulose nanocrystal are 200 nm-300 nm and 20 nm-40 nm, respectively; liquid a-amylase at an amount of 2.5 u/g relative to the absolute dry starch; glycerol at an amount of 0.2 wt% relative to the absolute dry starch, and sodium trimetaphosphate at an amount of 3 wt% relative to the absolute dry starch mass.

The bio-latex prepared in the present embodiment is used in a coating application. The starch-based bio-latex with a solid content of 50 wt% is used to replace 40% carboxyl styrene-butadiene latex and applied to a pigment-coated paper. The total amount of the binder in the coating is 12 pph, and the pigment is ground calcium carbonate. The binder and the pigment are prepared into the coating with a solid content of 65%, which is applied to the coated paper with a coating amount of 32+2 g/m? The sample is placed in a constant temperature and humidity laboratory at 23+1°C and 50+2% RH for 24 hours, and the coating and printing performance of the coated paper is tested. The experimental results are shown in Table 1.

Embodiment 3: A method for preparing a starch-based bio-latex by hydrolysis using an immobilized enzyme specifically includes the following steps:

In the present embodiment, the cellulose nanocrystals are cationic cellulose nanocrystals. Cationic modification of the cellulose nanocrystals is performed the same way as in Embodiment 1. The obtained cationic cellulose nanocrystals have a surface charge of +0.27+0.2 mmol/g.

Step 2: The enzyme immobilization using the cationic cellulose nanocrystals (CCNCs) is performed the same way as in Embodiment 1. The cationic cellulose nanocrystal immobilized a-amylase (CCNC immobilized a-amylase) is obtained. LU502794

Step 3: 25 g of absolute dry corn starch is weighed and added with 75 g of deionized water to form a starch slurry with a mass fraction of 25 wt%. The starch slurry is stirred evenly at room temperature. The starch slurry is placed in a water bath at 38°C and stirred for 10 min to make the slurry temperature uniform. CCNC immobilized a-amylase is added and stirred for 10 min to ensure that the CCNC immobilized a-amylase is uniformly dispersed in the starch slurry. The starch slurry is heated up at a rate of 1 °C/min until the temperature is 80°C, followed by adding glycerol at an amount of 0.1 wt% relative to the absolute dry starch, keeping the temperature for 30 min, and screening to obtain the starch- based bio-latex with a solid content of 50 wt%.

The bio-latex prepared in the present embodiment includes the following components: a corn starch slurry with a solid content of 25%; cellulose nanocrystals at an amount of 0.1 wt% relative to the absolute dry starch, where the length and the diameter of each cellulose nanocrystal are 200 nm-300 nm and 20 nm-40 nm, respectively; liquid a-amylase at an amount of 4 u/g relative to the absolute dry starch.

The bio-latex prepared in the present embodiment is used in a surface sizing application. wt% starch-based bio-latex is diluted to 10 wt% and applied to the surface sizing of corrugated base paper at a sizing amount of 3.0+0.2 g/m°. The sample is placed in a constant temperature and humidity laboratory at 23+1°C and 50+2% RH for 24 hours, and the mechanical properties of the corrugated board are tested. The experimental results are shown in Table 2.

Embodiment 4: A method for preparing a starch-based bio-latex by hydrolysis using an immobilized enzyme specifically includes the following steps:

Step 2: The method for immobilizing a-amylase by cellulose nanocrystals is the same as that described in Embodiment 2(2). CNC immobilized a-amylase is obtained.

Step 3: 25 g of absolute dry corn starch is weighed and added with 75 g of deionized water to form a starch slurry with a mass fraction of 25 wt%. The starch slurry is stirred,592794 evenly at room temperature. The starch slurry is placed in a water bath at 38°C and stirred for 10 min to make the slurry temperature uniform. CNC immobilized a-amylase is added, stirred for 10 min to ensure that the CNC immobilized a-amylase is uniformly dispersed in the starch slurry, and heated up at a rate of 1 °C/min until the temperature is 80°C. glycerol is added at an amount of 0.1 wt% relative to the absolute dry starch followed by keeping the temperature for 30 min, and screening to obtain the starch-based bio-latex with a solid content of 25 wt%.

The bio-latex prepared in the present embodiment includes the following components: a corn starch slurry with a solid content of 25%; cellulose nanocrystals at an amount of 0.1 wt% relative to the absolute dry starch, where the length and the diameter of each cellulose nanocrystal are 200 nm-300 nm and 20 nm-40 nm, respectively; and liquid a-amylase at an amount of 4 u/g relative to the absolute dry starch.

The bio-latex prepared in the present embodiment is used in a surface sizing application.

The 25 wt% starch-based bio-latex is diluted to 10 wt% and applied to the surface sizing of corrugated base paper at a sizing amount of 3.0+0.2 g/m°. The sample is placed in a constant temperature and humidity laboratory at 23+1°C and 50+2% RH for 24 hours, and the mechanical properties of the corrugated paper board are tested. The experimental results are shown in Table 2.

Contrast Example 1: The only differences of Contrast Example 1 from Embodiment 1 include: the enzyme used for hydrolyzing starch is a non-immobilized a-amylase, the cellulose nanocrystals are anionic cellulose nanocrystals, and the anionic cellulose nanocrystals are added after the enzymatically hydrolyzed starch is subjected to cross-linking reaction and cooling to room temperature.

Contrast Example 2: The only differences of Contrast Example 2 from Embodiment 3 include: the enzyme used for hydrolyzing starch is a non-immobilized a-amylase, the cellulose nanocrystals are anionic cellulose nanocrystals, and the anionic cellulose nanocrystals are directly added to the starch slurry after the enzymatic hydrolysis of starch.

Test Example

1. Coating starch-based bio-latex and testing its application performance in coated paper,502794

Test method: (1) The coating surface porosity is determined by applying the coating to a polyester film surface, drying the coated surface at room temperature, and allowing the silicone oil to penetrate the coated surface. The coated sample is cut into an area of 0.01 m? and the weight of the sample is recorded. The dimethyl silicone oil is uniformly applied on the sample surface and allowed to stand for 10 min so that the silicone oil is fully immersed in the pores of the coating. The excess dimethyl silicone oil is fully removed from the coating surface using a tissue paper that hardly sheds, and the weight of the sample is recorded. The difference between the two weights is the mass of silicone oil absorbed by the coating. Since the volume of the silicone oil is equal to the volume of the pores in the coating, the volume of silicone oil absorbed by the coating can be obtained according to the density of silicone oil. The volume of the pigments and bio-latexs in the coating is calculated according to the density of the solid pigments and the mass of the coating by using formula 1: [MB = Vimb

Vp ; (1) - 7IMB | Co Vim

In the formula: denotes the porosity of the coating with a unit of %, imb denotes the volume of silicone oil being absorbed with a unit of m?, Vb denotes the total volume of the coating with a unit of m*. (2) The diameter of the printing dot in the coated paper is determined by selecting IGT

AIC-2 standard printing dots, printing with pink medium viscous ink, drying the printed sample at room temperature, and placing the dried sample under a stereoscopic microscope to observe the dot morphology and measure the dot diameter. The dot diameter of each sample is the average value of all dot diameters in the field of vision. The test results are shown in Table 1 below:

Table 1 LU502794

Contrast

Embodiment 1 | Embodiment 2

Example 1

Viscosity /mpa-s(25°C) 119.8+0.8 162.4+0.1 256.3+0.6

Glass transition temperature /°C

Coating surface porosity 25.3+0.2 45.0+0.1 60.3+0.3 1%

Surface strength of coated 1.39+0.07 1.27+0.16 1.16+0.21 paper /m/s

Printing dot diameter /um 9.77+0.12 9.92+0.09 10.39+1.01 (35% dot density )

Table 1 shows that the stability, coating performance, coating surface strength, and printing performance of the starch-based bio-latex prepared by hydrolyzing starch with the cellulose nanocrystal immobilized enzyme in the present invention are obviously better than those of the adhesive in the contrast example. 2. Testing mechanical properties of corrugated paper board that is subject to surface sizing with starch-based bio-latex.

Test method: (1) The viscosity stability is determined by diluting the 25 wt% starch- based bio-latex to 10 wt%, cooling to room temperature, dividing the viscosity value measured immediately by the viscosity value measured after being allowed to stand at room temperature for 24 hours, and then multiplying by 100%. The calculation formula is shown in formula 2: = A x100%

OÖ

; (2)

In the formula, 0 denotes the viscosity stability with a unit of %; No denotes tH#502794 viscosity value measured immediately when the 10 wt% starch-based bio-latex is cooled to room temperature with a unit of mpa-s; h denotes the viscosity value measured after the wt% starch-based bio-latex is cooled to room temperature and then allowed to stand for 24 hours with a unit of mpa -s. (2) The determination of mechanical properties: The determination of folding endurance refers to GB/T2679.5-2002 "Paper and board--Determination of folding endurance". The determination of burst strength refers to GB/T6545-1998 "Corrugated board--Determination of bursting strength". The test of ring crush strength refers to GB/T2679.8-1995 "Paper and board--Determination of compressive strength--Ring crush method". The test of tensile strength refers to GB/T12914-1991 "Paper and board--Determination of tensile properties--

Constant rate of elongation method".

The test results are shown in Table 2 below:

Table 2

Contrast

Embodiment 3 | Embodiment 4

Example 2

Viscosity/mpa-s 14.37+0.01 22.65+0.04 36.89+0.02 (25°C, 10 wt%)

Folding endurance per 19.2+6.6 16.6+3.2 12.4+5.1 time

Ring crush index/N-m/g 13.47+0.79 12.67+0.64 10.30+0.32

Transverse tensile 22.67Æ0.67 20.60+0.82 17.09+1.07 index/N-m/g

Table 2 shows that the starch-based bio-latex prepared by hydrolyzing starch with the cellulose nanocrystal immobilized enzyme in the present invention, as a surface sizing agent,

is superior to the common sizing agent in terms of viscosity and viscosity stability and al§Q;502794 has excellent mechanical strength when applied in corrugated paper board.

To sum up, the present invention adopts immobilized a-amylase to hydrolyze starch, which can improve the hydrolysis efficiency of starch, fully degrade the polysaccharide polymer with high molecular weight, and reduce the production of monosaccharides.

Through the cross-linking reaction in the later stage and the dispersion of cellulose nanocrystals, starch-based bio-latex with a three-dimensional stable network structure and excellent stability, bonding performance, and rheological properties are obtained.

Claims

1. A method for preparing a starch-based bio-latex by hydrolysis using an immobilized enzyme, comprising the following steps: step 1: using a citric acid-disodium hydrogen phosphate buffer solution as a solvent, preparing cellulose nanocrystals (CNCs) into a cellulose nanocrystal dilute solution with a concentration of 0.05 wt%-0.5 wt%; step 2: diluting a-amylase in the citric acid-disodium hydrogen phosphate buffer solution to prepare a a-amylase diluent with a concentration of 0.05 u/ml-0.3 u/ml, mixing the a-amylase diluent and the cellulose nanocrystal dilute solution, and incubating a resulting mixed solution at 1°C-8°C for 1 hour-3 hours to complete an immobilized reaction of a- amylase to obtain a CNC immobilized a-amylase, wherein an amount of a-amylase in the mixed solution is 0.5 u/g-5 u/g of an absolute dry starch mass, and an amount of cellulose in the mixed solution is 0.05 wt%-2 wt% of the absolute dry starch mass; step 3: adding the CNC immobilized a-amylase obtained in step 2 to a starch slurry with a concentration of 1%-50%, stirring at 20°C-40°C for 10 min, heating to 80°C-95°C, adding a 0.1 wt%-10 wt% plasticizer, keeping the temperature for 10 min-30 min, naturally cooling to 40°C-65°C, and adding a 0.1 wt%-10 wt% cross-linking agent to react for 10 min-40 min to obtain a starch-based bio-latex product.

2. The method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme according to claim 1, wherein a solid content of the starch-based bio- latex 1s 1%-50%.

3. The method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme according to claim 1, wherein the cellulose nanocrystals are one or any combination of anionic cellulose nanocrystals, cationic cellulose nanocrystals, and neutral cellulose nanocrystals.

4. The method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme according to claim 1, wherein the cellulose nanocrystals each have a length of 200 nm-300 nm, a diameter of 20 nm-40 nm, and a solid content of 0.01%-5%.

5. The method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme according to claim 1, wherein a pH value of the citric acid-disodium 502794 hydrogen phosphate buffer solution is 5.5-7.

6. The method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme according to claim 1, wherein in step 2, the mixed solution is incubated in a constant temperature gas bath shaker at 4°C and at a rate of 100 rpm-300 rpm for 1 hour- 3 hours.

7. The method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme according to claim 1, wherein in step 3, starch of the starch slurry is one or any combination of corn starch, cassava starch, potato starch, and sweet potato starch.

8. The method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme according to claim 1, wherein the plasticizer is one or any combination of glycerol, urea, ethylene glycol, polyethylene glycol, propylene glycol, sorbitol, and ethanolamine.

9. The method for preparing the starch-based bio-latex by hydrolysis using the immobilized enzyme according to claim 1, wherein the cross-linking agent is one or any combination of formaldehyde, acetaldehyde, glyoxal, glutaraldehyde, polyglyoxal, triglyceride, sodium trimetaphosphate, sodium hexametaphosphate, and ammonium zirconium carbonate.