Powerful white latex and preparation method thereof

Abstract

The invention relates to the technical field of white latex, in particular to strong white latex and a preparation method thereof. The strong white latex is prepared from the following raw materials in parts by mass: 10 to 20 parts of EVA (Ethylene Vinyl Acetate) emulsion, 5 to 10 parts of polyvinyl alcohol, 25 to 30 parts of modified starch, 3 to 5 parts of pH (Potential of Hydrogen) regulator and 100 to 150 parts of water, the modified starch is obtained by crosslinking starch and nanocellulose and then grafting vinyl acetate and acrylate monomers. According to the strong white latex provided by the invention, through the synergistic effect of multiple components such as the composite modified starch, the EVA emulsion, the polyvinyl alcohol and the pH regulator, the adhesive property, the durability and the environmental adaptability of the latex are remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of white latex, in particular to a strong white latex and a preparation method thereof. Background Art

[0002] White glue is a water-based adhesive widely used in applications such as wood, paper products, and textiles. Its advantages include ease of use, non-toxicity, environmental friendliness, and rapid drying and film-forming. It has gained widespread adoption in industries such as packaging, furniture manufacturing, and architectural decoration. Traditional white glue, primarily based on polyvinyl acetate (PVAc) or polyacrylate emulsions, exhibits considerable bonding and film-forming properties, but suffers from limitations in terms of bond strength, water resistance, and long-term stability.

[0003] In order to improve the performance of latex, natural polymer materials have been gradually introduced as functional additives in recent years. Among them, starch has become one of the hot materials for latex modification because of its abundant sources, renewable nature, low price and good film-forming and bonding properties. However, the original starch has problems such as strong hydrophilicity, easy moisture absorption and poor heat resistance, which limits its wide application in high-performance adhesives. In order to overcome the above defects, researchers have tried to chemically modify starch, such as cross-linking, graft copolymerization, etc., to improve its water resistance, thermal stability and compatibility with the polymer matrix. Although some studies have reported the application of modified starch in water-based adhesives, the modified structure in the existing technology is single and the network construction is insufficient, making it difficult to simultaneously take into account the bonding strength, water resistance and film-forming properties of the latex.

[0004] Therefore, it is still necessary to develop a new modified starch with a reasonable structure, excellent performance and simple preparation process, and apply it to the white latex system to achieve a synergistic improvement in bonding strength, durability and environmental adaptability. Summary of the Invention

[0005] In view of this, the present invention is committed to providing a strong white latex and a preparation method thereof, so as to solve the problems of bonding strength, water resistance and film-forming performance that cannot be taken into account by white latex in the prior art.

[0006] In order to solve the above technical problems, this application is implemented as follows:

[0007] The present invention provides a strong white latex, comprising the following raw materials in parts by mass:

[0008] 10-20 parts of EVA emulsion, 5-10 parts of polyvinyl alcohol, 25-30 parts of modified starch, 3-5 parts of pH regulator and 100-150 parts of water;

[0009] The modified starch is obtained by cross-linking starch and nanocellulose and then grafting vinyl acetate and acrylic ester monomers.

[0010] The strong white latex provided by the present invention significantly improves the latex's adhesive properties, durability, and environmental adaptability through the synergistic effect of multiple components, including composite modified starch, EVA emulsion, polyvinyl alcohol, and a pH adjuster. The modified starch is produced by cross-linking starch with nanocellulose and then grafting vinyl acetate and acrylate monomers. The starch itself can provide bonding properties, nanocellulose enhances its mechanical strength, thermal stability and compatibility with polymer emulsions, and forms a dense network structure through cross-linking with starch to improve bonding strength; grafted monomers (vinyl acetate and acrylates) form a hydrophilic-hydrophobic adjustment network, improve the compatibility of modified starch with polymers, avoid phase separation, and improve the water resistance and film-forming properties of the latex; EVA emulsion provides excellent film-forming properties and flexibility. At the same time, due to the presence of a large number of polar groups and grafted hydrophobic monomers on the surface of the modified starch molecular chain, multiple interaction forces are formed between the hydrophobic EVA emulsion particles, forming a multi-phase cross-linked network structure, which helps to improve the film-forming properties, bonding strength and storage stability of the latex system; combined with the cross-linking structure of the modified starch itself, a three-dimensional cross-linked network structure is finally formed in the strong white latex, which significantly improves the mechanical properties, water resistance and bonding strength of the latex, and achieves excellent application performance. Finally, polyvinyl alcohol, as a film-forming aid, interacts with modified starch and EVA through hydrogen bonds to enhance the adhesion and wettability of the latex; improves the stability and rheological properties of the system, and inhibits sedimentation and agglomeration.

[0011] Preferably, in a strong white latex, the preparation method of the modified starch comprises the following steps:

[0012] S10, dispersing starch in water for swelling, then adding a first initiator, adjusting the pH value to acidic to carry out a first reaction to obtain activated starch; dispersing nanocellulose in water, adding a catalyst and citric acid to carry out a second reaction to obtain modified nanocellulose.

[0013] In this step, starch and nanocellulose are preliminarily functionalized through a free radical reaction triggered by an initiator to introduce active sites. After the introduction of citric acid, nanocellulose provides reactive groups, which improves the cross-linking efficiency with starch and generates a modified structure with multifunctional reaction points, providing a basis for subsequent grafting.

[0014] S20, mixing the activated starch, the modified nanocellulose, the cross-linking agent and the solvent, and reacting them to obtain a first monomer.

[0015] In this step, modified starch and modified nanocellulose participate in forming a network cross-linking structure with cross-linking agents such as HEMA, MBA, and GMA; enhance the bonding strength and water resistance of the system, and provide multi-functional group sites to participate in subsequent polymerization.

[0016] S30, mixing vinyl acetate, acrylic ester monomer, emulsifier and water, adding the first monomer to disperse, and then adding the second initiator to react to obtain modified starch.

[0017] In this step, vinyl acetate and acrylate monomers are emulsified in water and grafted onto activated starch molecular chains; while achieving hydrophobicity and flexibility, the latex's ability to penetrate and bind to the substrate is improved, ultimately forming high-performance functionalized modified starch particles.

[0018] Preferably, in a strong white latex, in step S10, the swelling temperature is 70-80° C., and the swelling time is 30-60 min;

[0019] In step S10, the target pH value is 2.5 to 4;

[0020] In step S10, the temperature of the first reaction is 50-70° C., and the time of the first reaction is 1-2 hours;

[0021] In step S10, the temperature of the second reaction is 65-80° C., and the time of the second reaction is 1-4 hours.

[0022] Preferably, in a strong white latex, in step S10, the mass ratio of the starch to the water is 10-15:100-150;

[0023] In step S10, the mass ratio of the starch to the first initiator is 10-15:0.1-0.45;

[0024] In step S10, the first initiator includes ammonium peroxytoluenesulfonate;

[0025] In step S10, the mass ratio of the nanocellulose to the water is 2-5:20-50;

[0026] In step S10, the mass ratio of the nanocellulose, the citric acid, and the catalyst is 2-5:0.06-0.3:0.02-0.15;

[0027] In step S10, the catalyst includes p-toluenesulfonic acid.

[0028] Preferably, in a strong white latex, in step S20, the reaction temperature is 45-60° C., and the reaction time is 0.5-2 h.

[0029] Preferably, in a strong white latex, in step S20, the mass ratio of the activated starch, the modified nanocellulose and the cross-linking agent is 10-15:3-5:0.05-0.3;

[0030] In step S20, the mass ratio of the activated starch to the solvent is 10-15:100-150;

[0031] The cross-linking agent includes at least one of HEMA, MBA and GMA;

[0032] The solvent includes water.

[0033] Preferably, in a strong white latex, in step S30, the reaction temperature is 70-80° C., and the reaction time is 4-6 hours.

[0034] Preferably, in a strong white latex, in step S30, the mass ratio of the first monomer, the vinyl acetate, the acrylic ester monomer, the emulsifier and the initiator is 15-20:5-10:5-10:1-3:0.3-1;

[0035] In step S30, the mass ratio of the first monomer to the water is 5-20:150-300;

[0036] In step S30, the acrylic acid ester monomer includes at least one of butyl acrylate, methyl acrylate and hydroxyethyl acrylate;

[0037] In step S30, the emulsifier includes OP-10;

[0038] In step S30, the second initiator includes NaHSO3.

[0039] Preferably, in a strong white latex, the pH adjuster comprises sodium bicarbonate.

[0040] The present invention also provides a method for preparing a strong white latex, comprising the following steps:

[0041] The modified starch is dispersed in water, and then EVA emulsion and polyvinyl alcohol are added, and finally a pH regulator is added for dispersion to obtain a strong white latex.

[0042] Through the above technical solution, the beneficial technical effects of the present invention are:

[0043] The present invention provides a strong white latex prepared by using modified starch as a functional base material and compounding EVA emulsion, polyvinyl alcohol (PVA), a pH regulator and other components. By modifying the starch by nanocellulose cross-linking and monomer grafting, the latex has significant advantages in improving the bonding strength, film-forming properties, water resistance and other aspects, and has the following advantages:

[0044] (1) The present invention improves the structural density and rigidity of the adhesive by cross-linking starch and nanocellulose, and further improves the flexibility and interfacial bonding force of the latex by grafting vinyl acetate and acrylate monomers, thereby significantly enhancing the bonding strength. The adhesive is suitable for bonding various materials such as wood, paper, and fabric, and has excellent applicability.

[0045] (2) The hydrophobic monomers (such as vinyl acetate and butyl acrylate) introduced into starch improve the hydrophilic and hydrophobic balance of the latex, enhancing the water immersion resistance and wet stability of the film. At the same time, the EVA emulsion and polyvinyl alcohol synergistically form a film, allowing the latex to form a dense, continuous, and flexible film after drying, effectively improving durability and adhesion.

[0046] (3) The synergistic effect of multiple components, including composite modified starch, EVA emulsion, polyvinyl alcohol, and pH regulator, significantly improved the adhesive properties, durability, and environmental adaptability of the latex. The modified starch is prepared by cross-linking starch with nanocellulose and then grafting vinyl acetate and acrylate monomers. The starch itself provides adhesive properties, while the nanocellulose enhances its mechanical strength and thermal stability. The nanocellulose cross-links with the starch to form a dense network structure, improving the bonding strength. Grafted monomers (vinyl acetate and acrylates) impart hydrophobicity and flexibility, improving the compatibility of modified starch with polymers and enhancing the latex's water resistance and film-forming properties. EVA emulsion provides excellent film-forming properties and flexibility. Simultaneously, the presence of a large number of polar groups and grafted hydrophobic monomers on the surface of the modified starch molecular chains creates multiple interactions with the hydrophobic EVA emulsion particles, forming a multiphase cross-linked network structure that helps improve the latex system's film-forming properties, bonding strength, and storage stability. Combined with the cross-linking structure inherent in the modified starch, this ultimately forms a three-dimensional cross-linked network structure within the strong white latex, significantly enhancing the latex's mechanical properties, water resistance, and bonding strength, achieving excellent application performance. Polyvinyl alcohol, as a film-forming aid, enhances latex adhesion, improves the system's stability and rheological properties, and inhibits sedimentation and agglomeration.

[0047] (4) Each reaction step is carried out at low to medium temperatures, making the initiator readily available and the reaction time controllable, making it suitable for industrial-scale production. The starch and nanocellulose exhibit good synergy, resulting in good product dispersibility and high stability of the final latex system.

[0048] (5) The present invention uses natural starch and nanocellulose as the main raw materials to partially replace traditional petrochemical-based adhesives, which is beneficial to reducing VOC emissions and carbon footprint, and is in line with the current development trend of green environmental protection and sustainable development. DETAILED DESCRIPTION

[0049] The present invention is further described in detail below by way of examples. The raw materials used in the examples can all be obtained through commercial sources.

[0050] Example 1

[0051] (1) Preparation of modified starch, comprising the following steps:

[0052] 10g of native corn starch was added to 100g of deionized water and stirred at 75°C for 40 minutes. 0.3g of ammonium peroxytoluenesulfonate was added as the first initiator, the pH was adjusted to 3.0, and the mixture was reacted at 60°C for 1.5 hours to obtain activated starch.

[0053] 3 g of nanocellulose was dispersed in 30 g of water, and 0.15 g of citric acid and 0.06 g of p-toluenesulfonic acid were added. The mixture was reacted at 65 °C for 2 h to obtain modified nanocellulose.

[0054] 12 g of activated starch, 4 g of modified nanocellulose, and 0.15 g of HEMA crosslinker were added to 150 g of water and reacted at 55 °C for 1 h to obtain the first monomer;

[0055] 15 g of the first monomer, 6 g of vinyl acetate, 6 g of butyl acrylate, and 1.5 g of OP-10 emulsifier were added to 200 g of water and uniformly dispersed. 0.6 g of NaHSO3 initiator was added and polymerization reaction was carried out at 75° C. for 5 hours to obtain modified starch.

[0056] (2) preparation of strong white latex, comprises the following steps:

[0057] Under stirring conditions, 30g of the above-mentioned modified starch was dispersed in 100g of water, 10g of EVA emulsion and 7g of polyvinyl alcohol were added, and the mixture was thoroughly stirred and mixed; finally, 3g of sodium bicarbonate solution was added to adjust the pH to about 7.0, and stirring was continued for 30 minutes to obtain high-performance white latex.

[0058] Example 2

[0059] (1) Preparation of modified starch, comprising the following steps:

[0060] 10g of native corn starch was added to 100g of deionized water and stirred at 75°C for 40 minutes. 0.3g of ammonium peroxytoluenesulfonate was added as the first initiator, the pH was adjusted to 3.0, and the mixture was reacted at 60°C for 1.5 hours to obtain activated starch.

[0061] 3 g of nanocellulose was dispersed in 30 g of water, and 0.15 g of citric acid and 0.06 g of p-toluenesulfonic acid were added. The mixture was reacted at 65 °C for 2 h to obtain modified nanocellulose.

[0062] 12 g of activated starch, 4 g of modified nanocellulose, and 0.15 g of HEMA crosslinker were added to 150 g of water and reacted at 55 °C for 1 h to obtain the first monomer;

[0063] 15 g of the first monomer, 5 g of vinyl acetate, 8 g of hydroxyethyl acrylate, and 1.5 g of OP-10 emulsifier were added to 200 g of water and uniformly dispersed. 0.6 g of NaHSO3 initiator was added and polymerization reaction was carried out at 75° C. for 5 hours to obtain modified starch.

[0064] (2) preparation of strong white latex, comprises the following steps:

[0065] Under stirring conditions, 28g of the above-mentioned modified starch was dispersed in 100g of water, 15g of EVA emulsion and 7g of polyvinyl alcohol were added, and the mixture was thoroughly stirred and mixed; finally, 3g of sodium bicarbonate solution was added to adjust the pH to about 7.0, and stirring was continued for 30 minutes to obtain high-performance white latex.

[0066] Example 3

[0067] The difference from Example 1 is that the amount of vinyl acetate used is 7 g, and butyl acrylate is replaced by methyl acrylate.

[0068] The rest are the same as in Example 1.

[0069] Example 4

[0070] The difference from Example 1 is: 20 g of EVA emulsion, 8 g of polyvinyl alcohol, and 30 g of modified starch.

[0071] The rest are the same as in Example 1.

[0072] Comparative Example 1

[0073] The difference from Example 1 is that the starch is not modified.

[0074] The rest are the same as in Example 1.

[0075] Comparative Example 2

[0076] The difference from Example 1 is that no vinyl acetate was added during the preparation of the modified starch.

[0077] The rest are the same as in Example 1.

[0078] Comparative Example 3

[0079] The difference from Example 1 is that butyl acrylate was not added in the preparation of the modified starch.

[0080] The rest are the same as in Example 1.

[0081] Comparative Example 4

[0082] The difference from Example 1 is that vinyl acetate and butyl acrylate are not added in the preparation of the modified starch.

[0083] The rest are the same as in Example 1.

[0084] Comparative Example 5

[0085] The difference from Example 1 is that no EVA emulsion is added in the strong white latex.

[0086] The rest are the same as in Example 1.

[0087] Performance Testing

[0088] The following performance tests were performed on the strong white latex in the embodiments and comparative examples:

[0089] (1) Bond strength: tested in accordance with the national standard GB / T 39289-2020;

[0090] (2) Water resistance: The strong white latex in the examples and comparative examples was immersed in water for 24 h, and then its shear strength was tested;

[0091] (3) Viscosity: The viscosity at 25°C was measured using a rotational viscometer;

[0092] (4) Solid content: The strong white latex in the examples and comparative examples was dried at 105°C to a constant weight. The test results are shown in Table 1.

[0093] Table 1

[0094]

[0095] As can be seen from Table 1, the bonding strength and water resistance of the strong white latex prepared in Examples 1 to 4 are better than those of the comparative example, indicating that the grafted polymerization modified starch, nanocellulose cross-linking and monomer type optimization used in the present invention can significantly enhance the performance of the white latex; in Example 4, the amount of modified starch, polyvinyl alcohol and EVA is increased to optimize the colloid bonding performance and viscosity; Comparative Example 1 is completely unmodified and has the worst performance; Comparative Examples 2 to 5 lack one or two key monomers respectively, indicating that each grafted monomer has an improving effect on the bonding performance and has a synergistic effect.

[0096] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A strong white latex, characterized in that, Including the following raw materials in parts by weight: 10-20 parts of EVA emulsion, 5-10 parts of polyvinyl alcohol, 25-30 parts of modified starch, 3-5 parts of pH regulator and 100-150 parts of water; The modified starch is obtained by cross-linking starch and nanocellulose and then grafting vinyl acetate and acrylic ester monomers.

2. The strong white latex according to claim 1, characterized in that The preparation method of the modified starch comprises the following steps: S10, dispersing starch in water for swelling, then adding a first initiator, adjusting the pH to acidic to carry out a first reaction to obtain activated starch; dispersing nanocellulose in water, adding a catalyst and citric acid to carry out a second reaction to obtain modified nanocellulose; S20, mixing activated starch, modified nanocellulose, a cross-linking agent, and a solvent, and reacting them to obtain a first monomer; S30, mixing vinyl acetate, acrylic ester monomer, emulsifier and water, adding the first monomer to disperse, and then adding the second initiator to react to obtain modified starch.

3. The strong white latex according to claim 2, characterized in that In step S10, the swelling temperature is 70-80°C, and the swelling time is 30-60 minutes; In step S10, the target pH value is 2.5 to 4; In step S10, the temperature of the first reaction is 50-70° C., and the time of the first reaction is 1-2 hours; In step S10, the temperature of the second reaction is 65-80° C., and the time of the second reaction is 1-4 hours.

4. The strong white latex according to claim 2, characterized in that In step S10, the mass ratio of the starch to the water is 10-15:100-150; In step S10, the mass ratio of the starch to the first initiator is 10-15:0.1-0.45; In step S10, the first initiator includes ammonium peroxytoluenesulfonate; In step S10, the mass ratio of the nanocellulose to the water is 2-5:20-50; In step S10, the mass ratio of the nanocellulose, the citric acid, and the catalyst is 2-5:0.06-0.3:0.02-0.15; In step S10, the catalyst includes p-toluenesulfonic acid.

5. The strong white latex according to claim 2, characterized in that In step S20, the reaction temperature is 45-60° C., and the reaction time is 0.5-2 h.

6. The strong white latex according to claim 2, characterized in that In step S20, the mass ratio of the activated starch, the modified nanocellulose and the cross-linking agent is 10-15:3-5:0.05-0.3; In step S20, the mass ratio of the activated starch to the solvent is 10-15:100-150; The cross-linking agent includes at least one of HEMA, MBA and GMA; The solvent includes water.

7. The strong white latex according to claim 2, characterized in that In step S30, the reaction temperature is 70-80° C., and the reaction time is 4-6 hours.

8. The strong white latex according to claim 2, characterized in that In step S30, the mass ratio of the first monomer, the vinyl acetate, the acrylic ester monomer, the emulsifier and the initiator is 15-20:5-10:5-10:1-3:0.3-1; In step S30, the mass ratio of the first monomer to the water is 5-20:150-300; In step S30, the acrylic acid ester monomer includes at least one of butyl acrylate, methyl acrylate and hydroxyethyl acrylate; In step S30, the emulsifier includes OP-10; In step S30, the second initiator includes NaHSO3.

9. The strong white latex according to claim 1, characterized in that The pH adjuster includes sodium bicarbonate.

10. The method for preparing the strong white latex according to any one of claims 1 to 9, characterized in that: The following steps are involved: The modified starch is dispersed in water, and then EVA emulsion and polyvinyl alcohol are added, and finally a pH regulator is added for dispersion to obtain a strong white latex.

Images