Modified tapioca starch / VAE blend adhesive for paper packaging and its preparation method

Abstract

The application discloses a modified cassava starch / VAE blending adhesive for paper packaging and a preparation method thereof, and relates to the technical field of adhesives. The adhesive is composed of VAE emulsion, modified cassava starch colloid, buffer salt, defoaming agent, preservative and deionized water. The colloid is modified by carboxylation, slight cross-linking of phosphate ester and grafting of vinyl acetate compatibility, so as to form a hydrophilic dispersion, anti-reversion and VAE emulsion particle compatible interface structure. In the preparation, the modified cassava starch colloid is prepared first, and then is mixed with the VAE emulsion at low temperature in steps, defoamed and filtered. The obtained adhesive has moderate viscosity, stable dispersion, good heat resistance and yellowing resistance, and is suitable for bonding of paper boxes, paper bags, paper-plastic composite paper, corrugated paper and paper labels.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, specifically to a modified cassava starch / VAE blend adhesive for paper packaging and its preparation method. Background Technology

[0002] Adhesives for paper packaging are widely used in bonding and molding paper boxes, paper bags, paper-plastic composite paper, corrugated paper, label paper, and food packaging paper products. VAE emulsion, or vinyl acetate-ethylene copolymer emulsion, features good film-forming properties, high initial tack, good flexibility, low odor, and strong workability, making it one of the commonly used water-based adhesive matrices in the paper packaging industry. However, using VAE emulsion alone presents challenges such as high raw material costs, significant environmental influences on drying speed and coating adaptability, and insufficient penetration and interfacial anchoring into porous paper fibers, making it difficult to simultaneously achieve optimal cost, bond strength, workability, and film appearance.

[0003] Starch-based materials are widely available, inexpensive, and renewable. Furthermore, their molecular structure contains numerous hydroxyl groups, enabling them to form hydrogen bonds with paper fibers. Therefore, they are frequently used for compounding and modifying VAE emulsions. However, when ordinary starch is directly blended with VAE emulsions, problems such as excessively high gelatinized viscosity, sticking, clumping, retrogradation, and uneven dispersion can easily occur. Some starch systems are also prone to significant yellowing during high-temperature drying or hot-pressing film formation, affecting the whiteness and stability of paper packaging products. Simultaneously, unmodified starch has insufficient compatibility with VAE latex particles, and its addition can easily lead to decreased film transparency, whitening of the adhesive layer, poor storage stability, and affect the final bonding strength.

[0004] Therefore, developing a modified cassava starch colloid with low viscosity and high solids, stable dispersion, good compatibility with VAE emulsion, controllable whiteness after film formation and no obvious yellowing, and constructing a stable blending system with VAE emulsion, has practical application value for reducing the cost of paper packaging adhesives, improving coating workability, enhancing paper fiber bonding performance, and maintaining the appearance stability of the film. Summary of the Invention

[0005] The purpose of this invention is to address the problems existing in the prior art, such as easy thickening and clumping, insufficient compatibility, whitening of film formation, poor storage stability, and easy yellowing of film at high temperatures when ordinary starch is blended with VAE emulsion. This invention provides a modified cassava starch / VAE blend adhesive for paper packaging and its preparation method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A modified cassava starch / VAE blend adhesive for paper packaging, comprising, by weight, the following raw materials: 68-90 parts VAE emulsion, 10-32 parts modified cassava starch colloid, 0.05-0.45 parts sodium citrate, 0.02-0.30 parts disodium hydrogen phosphate, 0.03-0.25 parts silicone defoamer, 0.02-0.20 parts isothiazolinone preservative, and 0-12 parts deionized water.

[0007] Furthermore, the modified cassava starch colloid has a hydrophilic dispersion structure, an anti-retrogradation stabilizing structure, and a VAE latex particle compatibility interface structure, all formed by the cross-linking structure of hydroxyl groups, carboxyl groups, and phosphate esters on the cassava starch molecular chain and the vinyl acetate-compatible grafted segments.

[0008] Furthermore, the modified cassava starch colloid, by weight, is prepared from the following raw materials: 100 parts cassava starch, 260-420 parts deionized water, 0.04-0.16 parts 2,2,6,6-tetramethylpiperidine oxide, 0.25-0.90 parts sodium bromide, 4.0-12.0 parts sodium hypochlorite solution with an effective chlorine content of 8-12 wt%, 0.10-0.45 parts sodium bisulfite, 0.12-0.55 parts sodium trimetaphosphate, and 0.0 parts sodium tripolyphosphate. 5-0.25 parts, sodium hydroxide 0.60-2.80 parts, hydrochloric acid 0.30-1.80 parts, vinyl acetate 3.0-9.0 parts, butyl acrylate 0.40-2.20 parts, acrylic acid 0.10-0.70 parts, γ-methacryloyloxypropyltrimethoxysilane 0.08-0.45 parts, ammonium persulfate 0.05-0.22 parts, sodium bisulfite 0.03-0.16 parts, fatty alcohol polyoxyethylene ether 0.10-0.55 parts, and polyvinyl alcohol 1788 0.30-1.20 parts.

[0009] Furthermore, the γ-methacryloxypropyltrimethoxysilane is KH550, which mainly enters the compatible grafting segment through free radical copolymerization via its methacrylate double bond. Its trimethoxysilane end group can undergo hydrolysis and condensation to varying degrees under aqueous conditions.

[0010] Furthermore, the preparation method of modified cassava starch colloid is as follows: S1. Cassava starch is passed through a 120-160 mesh sieve and added to deionized water. The solid-liquid ratio of cassava starch to deionized water is controlled at 1g:2.0-3.0mL. The mixture is dispersed at 35-42℃ and 700-1100r / min for 25-45min. The pH is adjusted to 9.2-10.2. 2,2,6,6-Tetramethylpiperidine oxide and sodium bromide are added. Then, sodium hypochlorite solution is added dropwise at a rate of 0.10-0.35mL / min. After the addition is complete, the mixture is reacted at 25-35℃ for 45-90min. During the reaction, the pH is maintained at 9.5-10.5 with sodium hydroxide. Sodium bisulfite is then added to terminate the oxidation reaction, and the pH is adjusted to 6.5-7.2 to obtain selectively carboxylated cassava starch slurry. S2. The selectively carboxylated cassava starch slurry is centrifuged and dehydrated, and washed with deionized water until the conductivity of the washing liquid is lower than 120 μS / cm. It is then vacuum dried at 50-58℃ for 10-16 hours, pulverized and passed through a 160-mesh sieve to obtain carboxylated cassava starch powder. S3. The carboxylated cassava starch powder is redispersed in deionized water, with the solid content controlled at 32-40 wt%. The temperature is raised to 38-48℃, the pH is adjusted to 10.0-10.8, sodium trimetaphosphate and sodium tripolyphosphate are added, and the reaction is carried out at 800-1200 r / min for 1.5-3.5 h. Then the pH is adjusted to 6.2-6.8 to obtain a phosphate ester lightly cross-linked cassava starch slurry. S4. Add vinyl acetate, butyl acrylate, acrylic acid, γ-methacryloyloxypropyltrimethoxysilane, fatty alcohol polyoxyethylene ether and polyvinyl alcohol 1788 to deionized water and pre-emulsify at 1200-1800 r / min for 20-35 min to obtain grafted monomer pre-emulsion. S5. The phosphate ester-compatible lightly crosslinked cassava starch slurry is heated to 58-68℃ and nitrogen gas is passed through for 15-30 min. The grafted monomer pre-emulsion is added dropwise at a rate of 0.08-0.25 mL / min, while an aqueous solution of redox initiator composed of ammonium persulfate and sodium bisulfite is added dropwise at a rate of 0.03-0.12 mL / min. After the addition is completed, the mixture is kept at 60-70℃ and 500-900 r / min for 2-4 h to obtain a vinyl acetate-compatible segment grafted lightly crosslinked carboxylated cassava starch slurry. S6. The lightly cross-linked carboxylated cassava starch slurry grafted with vinyl acetate compatible segments is heated to 78-86℃ and gelatinized for 30-55 minutes. Then, it is processed by a colloid mill 2-4 times. The distance between the stator and rotor of the colloid mill is 40-80 μm, and the processing temperature is 65-78℃. Subsequently, unreacted monomers are removed under -0.06-0.09 MPa and the mixture is concentrated to a solid content of 34-42 wt%. The mixture is cooled to 25-35℃, the pH is adjusted to 6.2-7.0, and the mixture is filtered through a 200-mesh filter to obtain the modified cassava starch colloid.

[0011] Furthermore, the ratio of the dry weight of the VAE emulsion to the dry weight of the modified cassava starch colloid is 100:4.5-18.0.

[0012] Furthermore, the organosilicon defoamer is a polyether-modified polydimethylsiloxane emulsion.

[0013] Furthermore, the isothiazolinone preservative is one or both of 1,2-benzisothiazolin-3-one and 2-methyl-4-isothiazolin-3-one.

[0014] Furthermore, the mass ratio of sodium citrate to disodium hydrogen phosphate is 1:0.3-2.0.

[0015] This invention also provides a method for preparing a modified cassava starch / VAE blend adhesive for paper packaging, characterized by the following steps: At 20-35°C, VAE emulsion is added to a mixing tank and stirred at 200-500 r / min for 5-15 min; sodium citrate and disodium hydrogen phosphate are added, and stirring continues for 5-20 min; modified cassava starch colloid is added to the VAE emulsion at a rate of 0.3-2.0 parts / min, while controlling the system temperature at 20-40°C and the stirring speed at 300-800 r / min during the addition process; after the modified cassava starch colloid is added, stirring continues for 20-60 min; an organosilicon defoamer, isothiazolinone preservative, and deionized water are added to adjust the solid content to 42-52 wt%, and stirring is carried out at 300-700 r / min for 15-40 min; the mixture is then filtered through a 120-200 mesh filter to obtain the modified cassava starch / VAE blend adhesive for paper packaging.

[0016] Furthermore, before adding the modified cassava starch colloid to the VAE emulsion, the modified cassava starch colloid is pre-dispersed for 5-20 minutes at 25-35℃ and 800-1500 r / min; after the modified cassava starch colloid is mixed with the VAE emulsion, it is defoamed for 5-20 minutes at -0.06-0.09 MPa.

[0017] The application of the modified cassava starch / VAE blend adhesive for paper packaging described in this invention in adhesives for paper boxes, paper bags, paper-plastic composite paper, corrugated paper, or paper labels.

[0018] The modified cassava starch / VAE blend adhesive for paper packaging described in this invention can also be used in thermoplastic polyolefin waterproof membranes.

[0019] The formula described in this invention addresses the problems of thickening and clumping, poor compatibility, whitening of the film, insufficient storage stability, and yellowing at high temperatures in ordinary starch / VAE blend adhesives through the synergistic effect of "VAE emulsion film-forming matrix + interface-modified modified cassava starch colloid + buffer stabilizing system + processing aids". Specifically, 68-90 parts of VAE emulsion provide a continuous film-forming phase, flexibility, and initial tack strength; 10-32 parts of modified cassava starch colloid form hydrogen bonds with paper fibers through hydroxyl and carboxyl groups, while its mildly cross-linked phosphate ester structure limits excessive swelling and retrogradation of starch chains; and vinyl acetate-compatible grafted segments improve its compatibility with VAE. The interfacial affinity of E latex particles allows starch to be uniformly embedded in the VAE film-forming network without significant flocculation, whitening, or stratification. Sodium citrate and disodium hydrogen phosphate form a weak buffer and ion-stabilizing system, maintaining the pH of the emulsion and the colloidal dispersion state, reducing the risk of local demulsification and sudden viscosity increases during mixing. Organosilicon defoamers suppress foam defects during high-speed stirring and coating, isothiazolinone preservatives improve the storage stability of the aqueous system, and deionized water adjusts the solid content and application viscosity. Thus, the adhesive reduces the amount of VAE used and the cost while also achieving low viscosity and high solids, leveling coating, paper fiber penetration and anchoring, stable film formation, and whiteness maintenance.

[0020] Compared with the prior art, the beneficial effects of the present invention are: 1. This modified cassava starch / VAE blend adhesive for paper packaging uses VAE emulsion as the main film-forming component and modified cassava starch colloid with a slightly cross-linked, hydrogen-bonded, and VAE-compatible grafted structure as the core modifying component. This allows cassava starch to maintain low viscosity and good flowability even at high solid content, reduces stick climbing, clumping, and retrogradation during gelatinization, and improves the dispersion stability between starch colloid and VAE emulsion.

[0021] 2. This modified cassava starch colloid improves low-temperature stability and resistance to retrogradation by carboxylating cassava starch, controls gelatinization viscosity by forming a slightly cross-linked structure with sodium trimetaphosphate, enhances adhesion to paper fibers by constructing a hydrogen-bonded interpenetrating network with polyvinyl alcohol 1788, and improves interfacial compatibility with VAE latex particles by grafting segments with vinyl acetate and acrylic acid. This reduces the problems of whitening, delamination, and uneven film formation when ordinary starch is added to VAE emulsion.

[0022] 3. When this adhesive is used for paper packaging bonding, it can balance coating leveling, initial tack, drying film formation and paper fiber interfacial bonding strength; at the same time, the use of cassava starch system instead of corn starch system which is prone to yellowing at high temperature is beneficial to control the whiteness and appearance stability of the adhesive film and reduce obvious yellowing under high temperature drying or hot pressing conditions.

[0023] 4. The preparation method adopts a process route of first preparing interface-modified cassava starch colloid and then blending it with VAE emulsion at low temperature. This avoids the local flocculation and sudden increase in viscosity caused by directly adding starch to VAE emulsion, and ensures that each component is uniformly dispersed in the aqueous system. The preparation process does not require organic solvents and is suitable for the continuous production of water-based adhesives for paper packaging. Attached Figure Description

[0024] Figure 1 The image shows the infrared spectrum of the modified cassava starch colloid prepared in Example 1.

[0025] Figure 2 The image shows the shear rate-apparent viscosity flow curve of the modified cassava starch colloid prepared in Example 1.

[0026] Figure 3 The image shows the ascending-descending thixotropic ring curve of the modified cassava starch colloid prepared in Example 1. Detailed Implementation

[0027] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1 Preparation of a modified tapioca starch / VAE blend adhesive for paper packaging: 1. Preparation of modified cassava starch colloid: 1.1 parts by weight of raw material components: The modified cassava starch colloid, by weight, is prepared from the following raw materials: 100.00 parts cassava starch, 405.00 parts deionized water, 0.10 parts 2,2,6,6-tetramethylpiperidine oxide, 0.55 parts sodium bromide, 8.00 parts sodium hypochlorite solution with an effective chlorine content of 10 wt%, 0.25 parts sodium bisulfite, 0.35 parts sodium trimetaphosphate, 0.15 parts sodium tripolyphosphate, 1.70 parts sodium hydroxide, 0.95 parts 37 wt% hydrochloric acid, 6.00 parts vinyl acetate, 1.20 parts butyl acrylate, 0.35 parts acrylic acid, 0.25 parts γ-methacryloyloxypropyltrimethoxysilane, 0.14 parts ammonium persulfate, 0.08 parts sodium bisulfite, 0.30 parts fatty alcohol polyoxyethylene ether AEO-9, and 0.80 parts polyvinyl alcohol 1788.

[0029] Of which, 405.00 parts of deionized water include: 200.00 parts of water for initial dispersion of cassava starch, 150.00 parts of water for weight dispersion of carboxylated cassava starch powder, 40.00 parts of water for pre-emulsification of grafted monomers, and 15.00 parts of water for preparing initiator solution; deionized water for washing is calculated separately and is not included in the above-mentioned parts by weight. Sodium hydroxide is prepared into a 10wt% sodium hydroxide aqueous solution, and the water used for solution preparation is included in the total amount of deionized water mentioned above.

[0030] 1.2 Preparation method: Cassava starch was sieved through a 140-mesh sieve. 100.00 parts of cassava starch were added to 200.00 parts of deionized water and dispersed at 38℃ and 900 rpm for 35 min to obtain a uniform cassava starch suspension. The pH of the system was adjusted to 9.8 with a 10 wt% sodium hydroxide aqueous solution. 0.10 parts of 2,2,6,6-tetramethylpiperidine oxide and 0.55 parts of sodium bromide were added, and stirring was continued for 10 min. Subsequently, 8.00 parts of a sodium hypochlorite solution with an available chlorine content of 10 wt% were added dropwise at 30℃ at a rate of 0.20 mL / min. During the dropwise addition, the pH was maintained at 9.8-10.2 with a 10 wt% sodium hydroxide aqueous solution. After the dropwise addition was complete, the reaction was continued at 30℃ and 900 rpm for 60 min. 0.25 parts of sodium bisulfite were added to terminate the oxidation reaction, and the pH was adjusted to 6.8 with 37 wt% hydrochloric acid to obtain selectively carboxylated cassava starch slurry.

[0031] The selectively carboxylated cassava starch slurry was centrifuged at 4000 r / min for 10 min, the supernatant was discarded, and the precipitate was washed with deionized water 3-4 times until the conductivity of the washing liquid was lower than 120 μS / cm. The washed precipitate was vacuum dried at 55℃ and -0.08 MPa for 12 h, pulverized and passed through a 160-mesh sieve to obtain carboxylated cassava starch powder.

[0032] The obtained carboxylated cassava starch powder was added back into 150.00 parts of deionized water and dispersed at 42℃ and 1000 r / min for 30 min to control the solid content of the system to about 40 wt%. The pH was adjusted to 10.5 with 10 wt% sodium hydroxide aqueous solution, and 0.35 parts of sodium trimetaphosphate and 0.15 parts of sodium tripolyphosphate were added. The reaction was carried out at 42℃ and 1000 r / min for 2.5 h, and the pH was maintained at 10.3-10.6 during the reaction. After the reaction was completed, the pH was adjusted to 6.5 with 37 wt% hydrochloric acid to obtain a phosphate ester lightly cross-linked cassava starch slurry.

[0033] Take another 30.00 parts of deionized water, add 0.80 parts of polyvinyl alcohol 1788, stir and dissolve at 88-92℃ for 45 min, cool to 35℃ and add 0.30 parts of fatty alcohol polyoxyethylene ether AEO-9, then add 6.00 parts of vinyl acetate, 1.20 parts of butyl acrylate, 0.35 parts of acrylic acid and 0.25 parts of γ-methacryloyloxypropyltrimethoxysilane in sequence, pre-emulsify at 1500 r / min for 30 min to obtain the grafted monomer pre-emulsion.

[0034] The above-mentioned lightly cross-linked cassava starch slurry was heated to 64°C and nitrogen gas was introduced for 20 min to reduce the dissolved oxygen content in the system. 0.14 parts of ammonium persulfate were dissolved in 7.50 parts of deionized water to obtain an oxidizing agent solution, and 0.08 parts of sodium bisulfite were dissolved in 7.50 parts of deionized water to obtain a reducing agent solution. Subsequently, the grafted monomer pre-emulsion was added dropwise at a rate of 0.18 mL / min at 64-66°C and 700 r / min, while the oxidizing agent solution and reducing agent solution were added dropwise at a rate of 0.05 mL / min, respectively. After the addition was completed, the reaction was continued at 65°C and 700 r / min for 3 h to obtain a lightly cross-linked carboxylated cassava starch slurry grafted with vinyl acetate compatible segments.

[0035] The obtained slurry was heated to 82℃ and gelatinized at 700 r / min for 40 min. After gelatinization, it was cooled to 72℃ and processed three times by a colloid mill, with the rotor-stator gap of the colloid mill controlled at 60 μm and the processing temperature controlled at 68-72℃. Subsequently, unreacted monomers were removed and the mixture was concentrated under -0.08 MPa until the solid content of the system was 38.0 ± 1.0 wt%. The mixture was cooled to 30℃, and the pH was adjusted to 6.6 with 10 wt% sodium hydroxide aqueous solution or 37 wt% hydrochloric acid. The mixture was then filtered through a 200-mesh filter to obtain modified cassava starch colloid.

[0036] like Figure 1 As shown, the spectrum is at approximately 3400 cm⁻¹ -1 A broad and strong absorption band appears at approximately 2920 cm⁻¹, corresponding to the abundant -OH groups and hydrogen bond association within the starch molecule chain; -1The vicinity is characterized by CH stretching vibration; approximately 1730 cm. -1 Carbonyl absorption is observed nearby, consistent with carbonyl absorption from carboxylation, esterification structures, and polymer segments of vinyl acetate and acrylate; approximately 1600 cm⁻¹ -1 and 1400cm -1 The absorption in the vicinity is related to the carboxylate structure, 1250-1150 cm⁻¹ -1 The region is related to phosphate esters and oxygen-containing structures of ester bonds. 1100-1000 cm -1 Strong absorption is a typical fingerprint peak of the stretching vibrations of COC and CO in starch-glucose units.

[0037] like Figure 2 and Figure 3 As shown, the prepared modified cassava starch colloid exhibits typical non-Newtonian shear thinning rheological properties. With the shear rate gradually increasing from low to high, the apparent viscosity of the system continuously decreases. This indicates that under the high shear force generated by the gap between the stator and rotor of the colloid mill, the entanglement structure between starch molecular chains and some hydrogen bonding interactions can be orderly disrupted, causing a rapid decrease in system viscosity. This improves fluidity and reduces resistance during high-shear processing, which is beneficial for the gelatinized slurry to pass through the colloid mill. Simultaneously, a distinct thixotropic ring is formed during the upward-downward shear scan, indicating that the internal structure of the system undergoes reversible destruction under shear force, and exhibits a certain structural recovery ability after shear reduction. This demonstrates that the starch colloid modified by carboxylation, mild cross-linking of phosphate esters, and compatibility grafting with vinyl acetate does not form an irreversible high-strength gel network, but rather maintains good shear responsiveness and structural stability. Therefore, the rheological results demonstrate that the gelatinized modified cassava starch slurry in this application can be homogenized by a colloid mill at 65-78°C under high shear conditions without significant clogging or overload, thus verifying the feasibility of the colloid mill process.

[0038] 2. Preparation of modified tapioca starch / VAE blend adhesive for paper packaging: 2.1 Raw material components by weight: By weight, the modified cassava starch / VAE blend adhesive for paper packaging is prepared from the following raw materials: 80.00 parts of VAE emulsion, 18.00 parts of the above modified cassava starch colloid, 0.22 parts of sodium citrate, 0.12 parts of disodium hydrogen phosphate, 0.12 parts of silicone defoamer, 0.08 parts of isothiazolinone preservative, and 4.50 parts of deionized water.

[0039] The VAE emulsion, with a solid content of 55 wt%, and the modified cassava starch colloid, with a solid content of 38 wt%, have a dry basis mass ratio of approximately 100:15.5.

[0040] VAE emulsion is WACKER, VINNAPAS ® EP 706, solid content 54-56wt%.

[0041] The silicone defoamer is a polyether-modified polydimethylsiloxane emulsion, manufactured by Evonik and TEGO. ® Foamex 825.

[0042] The isothiazolinone preservative is 1,2-benzisothiazolin-3-one.

[0043] 2.2 Preparation method: 18.00 parts of modified cassava starch colloid were pre-dispersed at 30℃ and 1200 r / min for 10 min and set aside. 80.00 parts of VAE emulsion were added to a stirred tank and stirred at 25℃ and 350 r / min for 10 min. 0.22 parts of sodium citrate and 0.12 parts of disodium hydrogen phosphate were dissolved in 1.50 parts of deionized water to obtain a buffer salt solution. The buffer salt solution was slowly added to the VAE emulsion, and stirring was continued at 400 r / min for 15 min to stabilize the pH of the system at 5.8-6.3. At 30℃, the pre-dispersed modified cassava starch colloid was added to the VAE emulsion system at a rate of 1.0 part / min, while maintaining a stirring speed of 550 r / min during the addition. After the modified cassava starch colloid was completely added, stirring was continued for 40 min to ensure that the modified cassava starch colloid was uniformly embedded in the continuous phase of the VAE latex particles. Subsequently, 0.12 parts of silicone defoamer and 0.08 parts of isothiazolinone preservative were added, followed by the remaining 3.00 parts of deionized water to adjust the solid content of the system. The mixture was stirred for 25 minutes at 450 rpm. After stirring, the mixture was defoamed for 10 minutes at -0.08 MPa and filtered through a 160-mesh filter to obtain a modified cassava starch / VAE blend adhesive for paper packaging.

[0044] Example 2 The preparation of a modified cassava starch / VAE blend adhesive for paper packaging is carried out by referring to the preparation method of Example 1, except that the mass fraction of the modified cassava starch colloid is replaced with 10 parts, and the rest is the same as in Example 1.

[0045] Example 3 The preparation of a modified cassava starch / VAE blend adhesive for paper packaging is carried out according to the preparation method of Example 1, except that the mass fraction of the modified cassava starch colloid is replaced with 32 parts, and the rest is the same as in Example 1.

[0046] Example 4 The preparation of a modified cassava starch / VAE blend adhesive for paper packaging is carried out by referring to the preparation method of Example 1, except that the mass fraction of VAE emulsion is replaced with 68 parts, and the rest is the same as in Example 1.

[0047] Example 5 The preparation of a modified cassava starch / VAE blend adhesive for paper packaging is carried out by referring to the preparation method of Example 1, except that the mass fraction of VAE emulsion is replaced with 90 parts, and the rest is the same as in Example 1.

[0048] Comparative Example 1 The preparation of a modified cassava starch / VAE blend adhesive for paper packaging follows the preparation method in Example 1, except that the modified cassava starch colloid is replaced with ordinary cassava starch gelatinized colloid, while other aspects remain the same as in Example 1. The ordinary cassava starch gelatinized colloid is prepared from 100.00 parts of cassava starch and deionized water, with a solid content controlled at 38.0±1.0wt%. It is gelatinized at 82℃ and 700r / min for 40min, processed three times by a colloid mill with a stator-rotor gap of 60μm and a processing temperature of 72℃. After cooling to 30℃, the pH is adjusted to 6.6, and the mixture is filtered through a 200-mesh filter.

[0049] Comparative Example 2 The preparation of a modified cassava starch / VAE blend adhesive for paper packaging follows the preparation method in Example 1, except that the carboxylated cassava starch powder used to prepare the modified cassava starch colloid is replaced with uncarboxylated cassava starch powder, while other aspects remain the same as in Example 1. The uncarboxylated cassava starch powder is obtained by sieving the cassava starch in Example 1 through a 140-mesh sieve, vacuum drying at 55°C for 12 hours, pulverizing, and then sieving through a 160-mesh sieve. The mass of the uncarboxylated cassava starch powder added is the same as that of the carboxylated cassava starch powder in Example 1.

[0050] Comparative Example 3 The preparation of a modified cassava starch / VAE blend adhesive for paper packaging is carried out according to the preparation method in Example 1, except that 0.35 parts of sodium tripolyphosphate are replaced with an equal mass of sodium tripolyphosphate, and the rest is the same as in Example 1.

[0051] Comparative Example 4 The preparation of a modified cassava starch / VAE blend adhesive for paper packaging is carried out according to the preparation method in Example 1, except that 6.00 parts of vinyl acetate are replaced with an equal mass of methyl methacrylate, and the rest is the same as in Example 1.

[0052] Comparative Example 5 The preparation of a modified cassava starch / VAE blend adhesive for paper packaging is carried out according to the preparation method in Example 1, except that 0.25 parts of γ-methacryloyloxypropyltrimethoxysilane are replaced with an equal mass of γ-glycidyl etheroxypropyltrimethoxysilane, and the rest is the same as in Example 1.

[0053] Comparative Example 6 The preparation of a modified cassava starch / VAE blend adhesive for paper packaging is carried out according to the preparation method in Example 1, except that 0.80 parts of polyvinyl alcohol 1788 are replaced with an equal mass of polyvinyl alcohol 2488, and the rest is the same as in Example 1.

[0054] Comparative Example 7 The preparation of a modified cassava starch / VAE blend adhesive for paper packaging is carried out according to the preparation method in Example 1, except that 0.30 parts of fatty alcohol polyoxyethylene ether AEO-9 are replaced with an equal mass of sodium dodecyl sulfate, and the rest is the same as in Example 1.

[0055] Comparative Example 8 The preparation of a modified cassava starch / VAE blend adhesive for paper packaging is carried out according to the preparation method in Example 1, except that 0.22 parts of sodium citrate are replaced with an equal mass of sodium chloride, and the rest is the same as in Example 1.

[0056] Comparative Example 9 The preparation of a modified cassava starch / VAE blend adhesive for paper packaging is carried out according to the preparation method in Example 1, except that the step of pre-dispersing the modified cassava starch colloid at 30°C and 1200r / min for 10min before adding it to the VAE emulsion is replaced with no pre-dispersion treatment, and the rest is the same as in Example 1.

[0057] Comparative Example 10 The preparation of a modified cassava starch / VAE blend adhesive for paper packaging is carried out according to the preparation method in Example 1, except that the modified cassava starch colloid is added to the VAE emulsion system at a rate of 4.0 parts / min instead of 1.0 parts / min. All other aspects remain the same as in Example 1.

[0058] Performance testing: All blended adhesive samples prepared in the examples and comparative examples were placed in a standard environment of 25±2℃ and 50±5% relative humidity for 24 hours before testing; unless otherwise stated, the test environment temperature was 23±2℃ and the relative humidity was 50±5%.

[0059] 1. Rotational viscosity test: Instrument: Brookfield rotational viscometer, RV type, rotor No. 4.

[0060] Method: Place the sample in a sealed container, stir thoroughly and let stand for 30 min to remove bubbles. After maintaining the temperature in a constant temperature water bath at 25±0.5℃ for 30 min, transfer it to a standard measuring cup and measure the apparent viscosity at a rotation speed of 20 r / min. Record the test value after the reading stabilizes for 30 s. The unit is mPa·s.

[0061] 2. Viscosity stability test: The sample was placed in a clean, dry, sealed glass bottle, with a sample volume of 80±5% of the bottle's volume, and allowed to stand at 25℃ for 0 days and 30 days, respectively. After standing, the sample was observed for obvious stratification, clumping, water separation, or gelation. If no failure was observed, the apparent viscosity was measured according to the rotational viscosity test method described above, and the 30-day viscosity change rate was calculated using the following formula: 30-day viscosity change rate (%) = (η) 30 -η0) / η0×100%; In the formula, η0 is the initial apparent viscosity of the sample, in mPa·s; η 30 The apparent viscosity is measured in mPa·s after being sealed and left to stand at 25°C for 30 days. If the sample exhibits non-redispersible layering, clumping, or gelation, it is recorded as "failure".

[0062] 3. Centrifugal water separation rate test: Take 20.00 g of the adhesive sample after thorough mixing and degassing, place it in a 50 mL stoppered centrifuge tube, and weigh the total mass of the sample before centrifugation, m0. Place the centrifuge tube in a centrifuge and centrifuge at 25℃ and 3000 r / min for 30 min. After centrifugation, observe whether a clear liquid or a water layer appears on the upper layer of the sample. Carefully pipette the upper precipitate and weigh its mass, m1. Calculate the centrifugation water separation rate using the following formula: Centrifugal water separation rate (%) = m1 / m0 × 100%; In the formula, m0 is the mass of the adhesive sample before centrifugation, in grams; m1 is the mass of the precipitate after centrifugation, in grams. The lower the water separation rate after centrifugation, the better the emulsion stability and anti-sedimentation stability of the adhesive system.

[0063] 4. Paper-to-paper 180° peel strength test: Kraft paper with a basis weight of 120±5 g / m² was cut into strips 25 mm wide and 200 mm long. Before the test, the strips were equilibrated for 24 hours at 23±2℃ and 50±5% relative humidity. The adhesive to be tested was evenly coated onto the surface of a kraft paper sample using a wire rod, controlling the wet coating amount to be 25±2 g / m². 2The coating area was 120 mm long and 25 mm wide. Within 30 seconds of coating, it was bonded to another piece of kraft paper of the same specification and pressed for 60 seconds under a pressure of 0.20 ± 0.02 MPa to obtain a paper-paper composite sample. After being placed at 23 ± 2℃ and 50 ± 5% relative humidity for 24 hours, the composite sample underwent a 180° peel test using a universal testing machine. The clamp separation speed was 100 mm / min, and the average peel force during the stable peeling stage was recorded. The results are expressed as N / 25 mm.

[0064] If the paper body tears during the test, the mode of damage should be recorded; however, when comparing the data in Table 1, only the average value is calculated using the samples that can form a continuous peeling interface.

[0065] 5.5-minute initial tack strength test: The sample preparation method is the same as that for the paper-to-paper 180° peel strength test. The difference is that after the adhesive is applied, bonded, and pressed for 60 seconds, the composite sample is placed at 23±2℃ and 50±5% relative humidity for 5 minutes after bonding, and then immediately subjected to the 180° peel test. The test speed is 100 mm / min, and the average peel force during the stable peel stage is recorded. The result is expressed as N / 25 mm. The higher the initial tack strength at 5 minutes, the better the early bonding and fixing ability of the adhesive in the rapid bonding, folding, and forming processes of paper packaging.

[0066] 6. Surface drying time test: After thoroughly stirring and degassing the adhesive to be tested, it was evenly coated onto a clean glass plate surface using a 200μm wire rod to form a continuous wet film with a coating area of ​​not less than 100mm × 100mm. Timing was started immediately after coating, and the film was allowed to air dry naturally at 23±2℃, 50±5% relative humidity, and without forced ventilation. Every 30 seconds, the adhesive film surface was lightly touched with a clean glass rod or a fibrous polyester film. The time when no significant wet adhesive transfer, stringing, or surface damage occurred after contact was recorded as the surface drying time, in minutes.

[0067] 7. Film whiteness test: The adhesive to be tested was evenly coated onto a clean glass plate using a 200μm wire rod and dried for 24 hours at 25℃ and 50% relative humidity to form a film. After removing the film, it was cut and stacked to a total thickness of not less than 1mm. The whiteness W0 of the film before thermal aging was measured using a whiteness meter under D65 standard illumination conditions. The result is expressed as a percentage, with the whiteness of a barium sulfate standard white board as 100%.

[0068] Whiteness retention rate test at 8.80℃ for 2 hours: The above-mentioned dried film was placed in an 80℃ forced-air drying oven for 2 hours of heat aging. After removal, it was cooled and equilibrated for 1 hour at 23±2℃ and 50±5% relative humidity. Subsequently, the whiteness Wt after heat aging was measured according to the film whiteness test method, and the whiteness retention rate was calculated using the following formula: Whiteness retention rate (%) = W t / W0×100%; In the formula, W0 represents the whiteness of the film before heat aging, in %; W t The whiteness of the film after heat aging at 80℃ for 2 hours is expressed as a percentage. A higher whiteness retention rate indicates better resistance to yellowing of the film under high-temperature drying or hot-pressing conditions.

[0069] 9. Water absorption rate test of adhesive film: The adhesive to be tested was coated onto the surface of a polytetrafluoroethylene (PTFE) plate or a demolded glass plate using a 200 μm wire rod. It was dried at 25℃ and 50±5% relative humidity for 24 hours, and then dried in a vacuum drying oven at 50℃ for 4 hours until the mass was essentially constant, yielding a dried adhesive film with a thickness of 0.18-0.25 mm. The adhesive film was cut into 50 mm × 50 mm test pieces, and the dry film mass m2 before immersion in water was measured. The test pieces were then completely immersed in deionized water at 23±2℃ for 24 hours. After removal, the surface moisture was gently absorbed with lint-free paper, and the mass m3 after immersion was measured within 1 minute. The water absorption rate of the adhesive film was calculated using the following formula: Water absorption rate of adhesive film (%) = (m3 - m2) / m2 × 100%; In the formula, m2 is the mass of the dried film before immersion in water, in grams; m3 is the mass of the film after immersion in water for 24 hours, in grams. The lower the water absorption rate of the film, the better its density, water resistance, and interfacial stability with VAE / modified cassava starch.

[0070] Table 1. Performance test data of the examples and comparative examples

[0071] As shown in Table 1, when the solid content is kept within the applicable range for water-based adhesives for paper packaging, Examples 1-5 exhibit a good balance between system viscosity, 30-day viscosity change rate, centrifugal water separation rate, paper-to-paper peel strength, initial tack strength, film whiteness, and heat aging whiteness retention rate. Specifically, Example 1 uses an appropriate amount of VAE emulsion combined with modified cassava starch colloid. The carboxylation structure improves the hydrophilic dispersibility of the starch colloid and its hydrogen bonding effect on paper fibers. The mild cross-linking structure of the phosphate ester limits excessive swelling and retrogradation of starch segments. The vinyl acetate compatibility grafted segments improve the interfacial compatibility between the modified cassava starch colloid and VAE latex particles, enabling the adhesive to maintain suitable application viscosity and storage stability even at higher solid contents, and forming a continuous and uniform film structure. Compared with the examples, Comparative Example 1 used ordinary cassava starch gelatinized colloid, which lacked carboxylation, mild cross-linking, and compatibility grafting structures. Starch molecules were prone to entanglement, regeneration, and local aggregation in the aqueous system, resulting in increased viscosity, increased water separation rate, and decreased whiteness and adhesive strength. After changing the carboxylation, cross-linking agent, or compatibility grafting components in Comparative Examples 2-5, the interfacial anchoring, dispersion stability, and film continuity were all affected. After changing the polyvinyl alcohol, emulsifier, or buffer salt system in Comparative Examples 6-8, the hydrogen bond interpenetration, latex particle stability, and pH / ionic environment control ability of the system decreased. After changing the pre-dispersion or addition rate in Comparative Examples 9-10, the local concentration fluctuation of the modified cassava starch colloid in the VAE emulsion increased, making it easy to form micro-flocculation and uneven film. The above results demonstrate that the present invention, through the synergistic effect of "VAE continuous film-forming phase - interface-modified cassava starch colloid - buffer stabilization system - low-temperature stepwise blending process", can take into account paper fiber interface adhesion, dispersion stability, film whiteness maintenance and thermal aging stability.

[0072] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A modified tapioca starch / VAE blend adhesive for paper packaging, characterized in that, By weight, its raw materials include: 68-90 parts of VAE emulsion, 10-32 parts of modified cassava starch colloid, 0.05-0.45 parts of sodium citrate, 0.02-0.30 parts of disodium hydrogen phosphate, 0.03-0.25 parts of organosilicon defoamer, 0.02-0.20 parts of isothiazolinone preservative, and 0-12 parts of deionized water; The modified cassava starch colloid has a hydrophilic dispersion structure, an anti-retrogradation stabilizing structure, and a VAE latex particle compatibility interface structure, which are formed by the cross-linking structure of hydroxyl groups, carboxyl groups, and phosphate esters on the cassava starch molecular chain and the vinyl acetate compatible grafted chain segments. The modified cassava starch colloid, by weight, is prepared from the following raw materials: 100 parts cassava starch, 260-420 parts deionized water, 0.04-0.16 parts 2,2,6,6-tetramethylpiperidine oxide, 0.25-0.90 parts sodium bromide, 4.0-12.0 parts sodium hypochlorite solution with an effective chlorine content of 8-12 wt%, 0.10-0.45 parts sodium bisulfite, 0.12-0.55 parts sodium trimetaphosphate, and 0.05- 0.25 parts, sodium hydroxide 0.60-2.80 parts, hydrochloric acid 0.30-1.80 parts, vinyl acetate 3.0-9.0 parts, butyl acrylate 0.40-2.20 parts, acrylic acid 0.10-0.70 parts, γ-methacryloyloxypropyltrimethoxysilane 0.08-0.45 parts, ammonium persulfate 0.05-0.22 parts, sodium bisulfite 0.03-0.16 parts, fatty alcohol polyoxyethylene ether 0.10-0.55 parts, and polyvinyl alcohol 1788 0.30-1.20 parts; The method for preparing the modified cassava starch colloid is as follows: S1. Cassava starch is passed through a 120-160 mesh sieve and added to deionized water. The solid-liquid ratio of cassava starch to deionized water is controlled at 1g:2.0-3.0mL. The mixture is dispersed at 35-42℃ and 700-1100r / min for 25-45min. The pH is adjusted to 9.2-10.

2. 2,2,6,6-Tetramethylpiperidine oxide and sodium bromide are added. Then, sodium hypochlorite solution is added dropwise at a rate of 0.10-0.35mL / min. After the addition is complete, the mixture is reacted at 25-35℃ for 45-90min. During the reaction, the pH is maintained at 9.5-10.5 with sodium hydroxide. Sodium bisulfite is then added to terminate the oxidation reaction, and the pH is adjusted to 6.5-7.2 to obtain selectively carboxylated cassava starch slurry. S2. The selectively carboxylated cassava starch slurry is centrifuged and dehydrated, and washed with deionized water until the conductivity of the washing liquid is lower than 120 μS / cm. It is then vacuum dried at 50-58℃ for 10-16 hours, pulverized and passed through a 160-mesh sieve to obtain carboxylated cassava starch powder. S3. The carboxylated cassava starch powder is redispersed in deionized water, with the solid content controlled at 32-40 wt%. The temperature is raised to 38-48℃, the pH is adjusted to 10.0-10.8, sodium trimetaphosphate and sodium tripolyphosphate are added, and the reaction is carried out at 800-1200 r / min for 1.5-3.5 h. Then the pH is adjusted to 6.2-6.8 to obtain a phosphate ester lightly cross-linked cassava starch slurry. S4. Add vinyl acetate, butyl acrylate, acrylic acid, γ-methacryloyloxypropyltrimethoxysilane, fatty alcohol polyoxyethylene ether and polyvinyl alcohol 1788 to deionized water and pre-emulsify at 1200-1800 r / min for 20-35 min to obtain grafted monomer pre-emulsion. S5. The phosphate ester-compatible lightly crosslinked cassava starch slurry is heated to 58-68℃ and nitrogen gas is passed through for 15-30 min. The grafted monomer pre-emulsion is added dropwise at a rate of 0.08-0.25 mL / min, while an aqueous solution of redox initiator composed of ammonium persulfate and sodium bisulfite is added dropwise at a rate of 0.03-0.12 mL / min. After the addition is completed, the mixture is kept at 60-70℃ and 500-900 r / min for 2-4 h to obtain a vinyl acetate-compatible segment grafted lightly crosslinked carboxylated cassava starch slurry. S6. The lightly cross-linked carboxylated cassava starch slurry grafted with vinyl acetate compatible segments is heated to 78-86℃ and gelatinized for 30-55 minutes. Then, it is processed by a colloid mill 2-4 times. The distance between the stator and rotor of the colloid mill is 40-80 μm, and the processing temperature is 65-78℃. Subsequently, unreacted monomers are removed under -0.06-0.09 MPa and the mixture is concentrated to a solid content of 34-42 wt%. The mixture is cooled to 25-35℃, the pH is adjusted to 6.2-7.0, and the mixture is filtered through a 200-mesh filter to obtain the modified cassava starch colloid.

2. The modified cassava starch / VAE blend adhesive for paper packaging according to claim 1, characterized in that, The ratio of the dry weight of the VAE emulsion to the dry weight of the modified cassava starch colloid is 100:4.5-18.

0.

3. The modified cassava starch / VAE blend adhesive for paper packaging according to claim 1, characterized in that, The organosilicon defoamer is a polyether-modified polydimethylsiloxane emulsion.

4. The modified cassava starch / VAE blend adhesive for paper packaging according to claim 1, characterized in that, The isothiazolinone preservative is one or both of 1,2-benzisothiazolin-3-one and 2-methyl-4-isothiazolin-3-one.

5. The modified cassava starch / VAE blend adhesive for paper packaging according to claim 1, characterized in that, The mass ratio of sodium citrate to disodium hydrogen phosphate is 1:0.3-2.

0.

6. A method for preparing the modified cassava starch / VAE blend adhesive for paper packaging according to any one of claims 1-5, characterized in that, Includes the following steps: At 20-35℃, VAE emulsion is added to a mixing tank and stirred at 200-500 rpm for 5-15 min; sodium citrate and disodium hydrogen phosphate are added, and stirring continues for 5-20 min; modified cassava starch colloid is added to the VAE emulsion at a rate of 0.3-2.0 parts / min, while controlling the system temperature at 20-40℃ and the stirring speed at 300-800 rpm during the addition process; after the modified cassava starch colloid is added, stirring continues for 20-60 min; organosilicon defoamer, isothiazolinone preservative, and deionized water are added to adjust the solid content to 42-52 wt%, and stirring is carried out at 300-700 rpm for 15-40 min; after filtration through a 120-200 mesh filter, modified cassava starch / VAE blend adhesive for paper packaging is obtained.

7. The preparation method according to claim 6, characterized in that, Before adding the modified cassava starch colloid to the VAE emulsion, the modified cassava starch colloid is pre-dispersed for 5-20 minutes at 25-35℃ and 800-1500 r / min. After the modified cassava starch colloid is mixed with the VAE emulsion, it is defoamed for 5-20 minutes at -0.06-0.09 MPa.

8. The use of the modified cassava starch / VAE blend adhesive for paper packaging as described in any one of claims 1-5 in adhesives for paper boxes, paper bags, paper-plastic composite paper, corrugated paper or paper labels.

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