A starch-based pure propylene core-shell emulsion and its application in wood-based panels

Abstract

This invention discloses a starch-based pure propylene core-shell emulsion and its application in engineered wood products, belonging to the field of polymer materials technology. This invention uses acid-hydrolyzed acetate-esterified double-modified starch with specific parameters as the macromolecular backbone, combined with acrylate-based soft and hard monomers and a core-layer crosslinking agent, to prepare a hard-core, soft-shell structure pure propylene core-shell emulsion using a semi-continuous in-situ seeded emulsion polymerization method. Through acid hydrolysis to reduce viscosity combined with acetic acid esterification hydrophobic modification, the compatibility between starch and acrylate monomers is improved, the chloride ion content of starch is controlled, and the polymerization demulsification and flocculation problems are improved. This invention relies on the slight crosslinking of the core layer to construct a stable network structure, effectively locking starch molecules and avoiding phase separation and component migration. The resulting emulsion has high solids content, excellent storage and centrifugal stability, outstanding water resistance, mechanical properties, and heat stability of the film. It has a high bio-based content and is environmentally friendly, and can be widely used in the manufacture of engineered wood products such as plywood, blockboard, engineered wood, and particleboard.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a starch-based pure propylene core-shell emulsion and its application in engineered wood products. Background Technology

[0002] Acrylic emulsions (pure acrylic emulsions) are widely used in adhesives, coatings, textiles, and other fields due to their excellent weather resistance, flexibility, and environmental friendliness. However, traditional pure acrylic emulsions are highly dependent on petroleum-based raw materials, and the small-molecule emulsifiers used in production are prone to migration after film formation, leading to decreased water resistance and performance degradation of the film.

[0003] Starch, as a renewable natural polymer, is used to modify or partially replace acrylate emulsions to reduce costs and improve environmental friendliness. Current technologies often employ graft copolymerization of single modified starches such as oxidized starch, cationic starch, and anionic starch with acrylate monomers, but these methods have significant drawbacks:

[0004] (1) Single modified starch has excessive hydrophilicity, wide molecular weight distribution, high viscosity, poor compatibility with acrylate, and is prone to phase separation and polymerization gelation;

[0005] (2) The starch grafting rate is low, which makes it difficult to lock in the film effectively. The film is easy to migrate after film formation and has poor water resistance.

[0006] (3) The core-shell structure design is unreasonable, with soft core and hard shell being used, resulting in weak starch retention, poor stability, and easy cracking of the film.

[0007] (4) Residual electrolytes in starch interfere with free radical polymerization, making it prone to demulsification and flocculation.

[0008] Existing technology discloses a method for preparing oxidized starch-modified acrylic emulsion. After oxidizing starch, the solid content of pure acrylic emulsion is increased and the production cost is reduced. However, after introducing carboxyl groups, its hydrophilicity and dispersibility in water are enhanced. In emulsion polymerization, this anionic starch tends to remain in the aqueous phase and is difficult to effectively adsorb on the surface of monomer droplets or latex particles to play an emulsifying and stabilizing role. It is more prone to phase separation, which ultimately leads to defects such as poor water resistance, low strength and poor stability in the product.

[0009] The journal *China Pulp & Paper* published a study on the synthesis and application of highly substituted cationic starch-based styrene-acrylic emulsions in its 9th issue of 2024. The resulting emulsions exhibited high latex synthesis yield, small average particle size, strong positive charge, and excellent storage stability. However, this cationic starch primarily incorporates strongly hydrophilic and charged groups such as quaternary ammonium salts and tertiary ammonium salts, without fundamentally improving its hydrophobicity, limiting its application to paper sizing agents. Furthermore, these modified starches (oxidized starch, anionic starch, and cationic starch) are themselves polyelectrolytes; the introduction of a large amount of charge severely interferes with the stability of free radical polymerization, making gelation more likely.

[0010] Therefore, developing a bio-based modified pure acrylic emulsion that can fully utilize the properties of starch, efficiently combine with pure acrylic monomers, produce emulsions with good film-forming properties, excellent water resistance, strong adhesion, and stable performance is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0011] To address the shortcomings of existing technologies, this invention provides a starch-based pure propylene core-shell emulsion and its application in engineered wood products. By modifying starch through a dual process of acid hydrolysis for viscosity reduction and esterification for hydrophobicity, combined with a specific hard-core / soft-shell core-shell structure design and a mild cross-linking system of the core layer, efficient grafting and compounding of starch and acrylate monomers is achieved. This solves the problems of emulsion polymerization phase separation, demulsification, and flocculation, ultimately yielding a high-solids-content, high-stability, excellent water resistance, strong adhesion, and environmentally friendly bio-based pure propylene core-shell emulsion.

[0012] To achieve the above objectives, the present invention adopts the following technical solution:

[0013] This invention provides a starch-based pure propylene core-shell emulsion, prepared from raw materials comprising the following parts by weight:

[0014] 10-25 parts of acid-hydrolyzed acetic acid esterified starch.

[0015] 45-55 parts of olefinic soft monomers,

[0016] 40-50 parts of olefinic hard monomers,

[0017] 1-4 parts of carboxyl-containing alkene monomers,

[0018] 0.1-0.4 parts of core layer crosslinking agent,

[0019] Emulsifier 1-2.0 parts,

[0020] Initiator 0.40-0.65 parts,

[0021] 0.5-0.6 parts buffer,

[0022] 150-290 parts of deionized water;

[0023] The intrinsic viscosity of the acid-hydrolyzed acetic acid esterified starch is 40-80 mL / g, the degree of substitution is 0.05-0.2, and the chloride ion concentration is ≤100 ppm.

[0024] The core layer of the core-shell structure is a copolymer of acid-hydrolyzed acetic acid-esterified starch, olefin hard monomers, and a core layer crosslinking agent; the shell layer is a copolymer of olefin soft monomers and carboxyl-containing olefin monomers.

[0025] The olefinic hard monomer is one or more of styrene, methylstyrene, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, and tert-butylstyrene.

[0026] The olefinic soft monomer is one or more of butadiene, methyl acrylate, ethyl acrylate, n-propyl acrylate, hydroxypropyl acrylate, n-butyl acrylate, tert-butyl acrylate, n-hexyl acrylate, isooctyl acrylate, isoprene, and isopentyl acrylate.

[0027] The core layer crosslinking agent is selected from one or more combinations of ethylene glycol dimethacrylate (EGDMA), diethylene glycol dimethacrylate (DEGDMA), triethylene glycol dimethacrylate (TEGDMA), trimethylolpropane trimethacrylate (TMPTMA), and pentaerythritol tetramethacrylate (PETMA);

[0028] The carboxyl-containing olefin monomers are selected from one or more combinations of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid.

[0029] The emulsifier is selected from nonylphenol polyoxyethylene ether ammonium sulfate;

[0030] The initiator is selected from ammonium persulfate.

[0031] The buffer is selected from sodium bicarbonate.

[0032] This invention provides a method for preparing a starch-based pure propylene core-shell emulsion, comprising the following steps:

[0033] S1. Preparation of acid-hydrolyzed acetate esterified starch:

[0034] The original starch was prepared into a starch milk with a mass concentration of 35%-40%. An inorganic acid of 1.0%-3.0% of the dry weight of the starch was added at 45-60℃ to carry out an acid hydrolysis reaction for 4-6 hours. After the reaction was completed, the mixture was neutralized, washed, and dried to obtain acid hydrolyzed starch.

[0035] The acid-hydrolyzed starch was prepared into a starch milk with a mass concentration of 40%-50%. At 25-30°C, 5%-25% vinyl acetate (by dry weight of the acid-hydrolyzed starch) was added, and the esterification reaction was carried out under alkaline conditions for 1-2 hours, with the pH of the reaction system controlled at 8.5-10.5. After the reaction was completed, the mixture was neutralized, washed, and dried to obtain acid-hydrolyzed acetate esterified starch.

[0036] S2. In-situ seed emulsion polymerization:

[0037] (1) Preparation of pre-emulsion: Dissolve the emulsifier and buffer in some deionized water and divide into two parts. One part is emulsified with all olefin hard monomers and core layer crosslinking agent at high speed for 15 minutes to obtain core pre-emulsion; the other part is mixed and emulsified with all olefin soft monomers and carboxyl-containing olefin monomers to obtain shell pre-emulsion; the initiator is prepared into an initiator solution with the remaining deionized water for later use.

[0038] (1) Gelatinization: Add acid-hydrolyzed acetic acid starch and deionized water to the reaction vessel, stir and heat to 80-90℃, keep warm for 30-40 min, until the starch is completely gelatinized (transparent); add buffer and stir to dissolve, cool to 75-80℃, and set aside;

[0039] (2) Seed preparation: Add 1 / 5 of the initiator solution to the reaction vessel, stir for 5 min, and then slowly add 10% of the nuclear preemulsion; keep the temperature at 75℃-82℃ for 25 min;

[0040] (3) Core layer polymerization: The remaining core pre-emulsion is added dropwise at a uniform rate, while 1 / 3 of the initiator solution is added dropwise simultaneously; the dropping time is controlled at 50~80 min, and the reaction temperature is stabilized at 75℃-82℃; after the dropping is completed, the temperature is maintained for 30-40 min.

[0041] (4) Shell polymerization: Maintain the reaction temperature and add the shell pre-emulsion at a uniform rate while simultaneously adding the remaining initiator solution; control the addition time to 60-120 min to ensure that the shell layer uniformly coats the core layer; after the addition is completed, keep warm for 60-80 min.

[0042] (5) Post-treatment: Cool the emulsion to below 40°C, adjust the pH to 7.5~8.0 with 28% ammonia water, stir for 10-15 minutes; filter with a 100-mesh filter to obtain the finished emulsion.

[0043] Thirdly, the present invention provides the application of the above-mentioned starch-based pure propylene shell emulsion in artificial boards, which can be used in the manufacture of artificial boards such as plywood, blockboard, engineered wood and particleboard.

[0044] The beneficial effects of this invention are as follows:

[0045] (1) Through a combination of acid hydrolysis and esterification, the molecular weight of starch was controlled (reducing viscosity and improving processability) and the hydrophilic-hydrophobic balance (introducing hydrophobic acetyl groups). Acid hydrolysis provides starch with more accessible reaction sites, while esterification significantly improves its compatibility with acrylate monomers, enabling it to effectively act as a macromolecular emulsifier and grafting active site. Chloride ion control of ≤100 ppm ensures the stable progress of subsequent free radical polymerization, solving the problem of emulsion demulsification caused by residual electrolytes in traditional wet starch processing.

[0046] (2) Utilizing the amphiphilic nature of acid-hydrolyzed esterified starch, micelles are formed in the aqueous phase. Through in-situ seed emulsion polymerization, the acetyl groups on the surface of the esterified starch guide the preferential polymerization of soft monomers on the starch micelles to form a hard core. Then, a core-layer reaction occurs, ultimately forming composite latex particles with a hard core and a soft shell. This structure endows the emulsion with excellent stability, water resistance, film-forming properties, and strong adhesion, and achieves molecular-level composite of starch and synthetic polymers, avoiding phase separation.

[0047] (3) The emulsion has high solid content and good storage stability. The film has low water absorption, excellent tensile strength and elongation at break, and bio-based content ≥10%. It is green and environmentally friendly and can replace petroleum-based products.

[0048] (4) This emulsion can be used directly to prepare artificial boards such as plywood, blockboard, engineered wood and particleboard, and is a formaldehyde-free adhesive. Detailed Implementation

[0049] To make the above-mentioned objectives, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to examples. The following content is merely illustrative and explanatory of the concept of the present invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the inventive concept, all of which should fall within the protection scope of the present invention. The preparation method of the present invention will be described below through specific embodiments.

[0050] Experimental Materials and Methods

[0051] Preparation of acid-hydrolyzed acetic acid esterified starch: Refer to step S1 in the invention description.

[0052] Emulsion performance testing:

[0053] Solid content: determined according to GB / T 2793-1995.

[0054] Viscosity: Measured at 25°C using a Brookfield viscometer (rotor LV3, 60 rpm).

[0055] Particle size: determined using a Malvern laser particle size analyzer.

[0056] Stability: Centrifuge the emulsion at 3000 rpm for 15 minutes and observe whether it separates into layers or precipitates; store at room temperature for 6 months and observe its condition.

[0057] Adhesive film performance testing:

[0058] The emulsion was cast onto a polytetrafluoroethylene plate, dried at room temperature for 7 days, and then dried in a 50°C oven to constant weight to obtain a film.

[0059] Water absorption rate: Immerse a known mass of film in deionized water for 24 hours, remove it, blot the surface moisture with filter paper, weigh it, and calculate the water absorption rate.

[0060] Tensile strength and elongation at break: tested on a universal testing machine according to GB / T 1040.3-2006 standard.

[0061] Board application performance testing:

[0062] Specimen preparation: The emulsion to be tested was evenly coated onto a poplar veneer (300mm×300mm×1.5mm), with glue applied to both sides at a rate of 120 g / m². After aging for 5 minutes, two veneers were joined together with their grain perpendicular to each other and hot-pressed at 105℃ and 1.0 MPa for 5 minutes to form a three-layer plywood. After curing for 24 hours, the plywood was cut into standard specimens.

[0063] Dry shear strength: Tested according to the dry state test method for Class I boards (weathering resistant) in GB / T 17657-2013, 4.15 "bonding strength".

[0064] Wet shear strength: The test method for Class II boards (water resistance) in GB / T 17657-2013, 4.15 "bonding strength", is to immerse the specimen in hot water at (63±3)℃ for 3 hours, cool it at room temperature for 10 minutes, and then conduct the test.

[0065] Formaldehyde emission: determined according to GB / T 17657-2013, section 4.60, “1m³ climate chamber method”.

[0066] Example 1

[0067] S1. Preparation of Acid-hydrolyzed Acetate-Acid-Oxidated Starch

[0068] Take 100g of corn starch (dry basis) and prepare a starch milk with a mass concentration of 35%. Heat the mixture to 45℃ and add concentrated hydrochloric acid accounting for 1.0% of the dry starch. The mixture is kept at a constant temperature for 6 hours for acid hydrolysis. After the reaction is completed, neutralize the mixture to pH 6.5, filter it, wash it repeatedly with deionized water, and dry it to obtain acid hydrolyzed starch.

[0069] Acid-hydrolyzed starch was prepared into a 40% (w / w) starch slurry, cooled to 25°C, and vinyl acetate (5% of the dry weight of the acid-hydrolyzed starch) was added. The pH of the system was adjusted to 8.5 with 3% NaOH solution, and the esterification reaction was carried out at a constant temperature for 2 hours. After the reaction, the solution was neutralized to pH 6.5 with dilute hydrochloric acid, washed, and dried to obtain acid-hydrolyzed acetate esterified starch. Its intrinsic viscosity was measured to be 40 mL / g, degree of substitution 0.05, and chloride ion content 38 ppm.

[0070] S2. Preparation of pure propenyl core-shell emulsion

[0071] Raw material formula (parts by weight):

[0072] Acid-hydrolyzed acetic acid esterified starch: 10 parts

[0073] Alkene soft monomer (n-butyl acrylate): 45 parts

[0074] Alkene hard monomer (methyl methacrylate): 40 parts

[0075] Carboxylated olefin monomers (methacrylic acid): 1 part

[0076] Core layer crosslinking agent (trimethylolpropane trimethacrylate): 0.1 parts

[0077] Emulsifier (nonylphenol polyoxyethylene ether ammonium sulfate): 1 part

[0078] Initiator (ammonium persulfate): 0.40 parts

[0079] Buffer (sodium bicarbonate): 0.5 parts

[0080] Deionized water: 150 parts

[0081] Preparation steps:

[0082] (1) Pre-emulsification: Dissolve the emulsifier and buffer in 60 parts of deionized water and divide them into two equal parts; emulsify one part with methyl methacrylate, 15 parts of n-butyl acrylate and core layer crosslinking agent at high speed for 15 min to obtain core pre-emulsion; emulsify the other part with the remaining n-butyl acrylate and methacrylic acid for 15 min to obtain shell pre-emulsion; dissolve ammonium persulfate in an appropriate amount of deionized water to prepare initiator solution.

[0083] (2) Gelatinization: Add acid-hydrolyzed acetic acid starch to the reactor, add all deionized water, stir and heat to 85°C, keep warm for 30 minutes until the starch is completely gelatinized and transparent, add buffer, and cool down to 78°C.

[0084] (3) Seed preparation: Add 1 / 5 of the initiator solution, stir for 5 min, slowly add 10% of the nuclear pre-emulsion, keep warm at 78℃ for 25 min, until the emulsion shows obvious blue light.

[0085] (4) Core layer polymerization: The remaining core pre-emulsion and 1 / 3 of the initiator solution are added dropwise at a uniform rate, and the dropping time is controlled at 50 min while the temperature is maintained at 75℃. After the dropping is completed, the temperature is kept warm for 30 min.

[0086] (5) Shell polymerization: All shell pre-emulsion and the remaining initiator solution are added dropwise at a uniform rate, and the dropping time is controlled at 60 min while the temperature is maintained at 75℃. After the dropping is completed, the temperature is kept warm for 60 min.

[0087] (6) Post-treatment: Cool down to below 40℃, adjust pH to 7.5 with 28% ammonia water, stir for 10 min, filter with a 100-mesh filter to obtain the finished emulsion, and label the emulsion as EA-1.

[0088] S3. Plywood preparation and application performance testing

[0089] Using emulsion EA-1 as an adhesive, three-layer poplar plywood was prepared according to the above-mentioned "Test Method for Application Performance of Boards" and specimens were cut to test its dry / wet shear strength and formaldehyde release.

[0090] Example 2

[0091] S1. Preparation of Acid-hydrolyzed Acetate-Acid-Oxidated Starch

[0092] Take 100g of corn starch (dry basis) and prepare a starch milk with a mass concentration of 38%. Heat the mixture to 52℃ and add concentrated hydrochloric acid accounting for 2.0% of the dry starch. The mixture is kept at a constant temperature for 5 hours for acid hydrolysis. After the reaction is completed, the mixture is neutralized, washed, and dried to obtain acid-hydrolyzed starch.

[0093] Acid-hydrolyzed starch was prepared into a starch milk with a mass concentration of 45%, cooled to 28°C, and vinyl acetate, accounting for 15% of the dry basis of acid-hydrolyzed starch, was added. The pH of the system was adjusted to 9.5, and the esterification reaction was carried out for 1.5 hours. After neutralization, washing, and drying, the intrinsic viscosity of the modified starch was measured to be 60 mL / g, the degree of substitution was 0.12, and the chloride ion content was 45 ppm.

[0094] S2. Preparation of pure propenyl core-shell emulsion

[0095] Raw material formula (parts by weight):

[0096] Acid-hydrolyzed acetic acid esterified starch: 18 parts

[0097] Alkene soft monomer (isooctyl acrylate): 50 parts

[0098] Alkene hard monomers (methyl methacrylate, styrene, mass ratio 1:1): 45 parts

[0099] Carboxylated olefin monomers (acrylic acid): 2.5 parts

[0100] Core layer crosslinking agent (ethylene glycol dimethacrylate): 0.25 parts

[0101] Emulsifier (nonylphenol polyoxyethylene ether ammonium sulfate): 1.5 parts

[0102] Initiator (ammonium persulfate): 0.52 parts

[0103] Buffer (sodium bicarbonate): 0.55 parts

[0104] Deionized water: 210 parts

[0105] Preparation steps:

[0106] (1) Pre-emulsification: Dissolve the emulsifier and buffer in 75 parts of deionized water and divide them into two equal parts; one part is emulsified with mixed hard monomers, 15 parts of isooctyl acrylate and core layer crosslinking agent at high speed for 15 min to obtain core pre-emulsion; the other part is emulsified with the remaining isooctyl acrylate and acrylic acid to obtain shell pre-emulsion; the initiator is dissolved in an appropriate amount of deionized water for later use.

[0107] (2) Gelatinization: Mix starch with the remaining deionized water, heat to 88°C, keep warm for 35 minutes until completely gelatinized, add buffer and cool to 78°C.

[0108] (3) Seed preparation: Add 1 / 5 of the initiator, add 10% of the nuclear pre-emulsion, and keep warm at 80℃ for 25 minutes until blue light appears.

[0109] (4) Core layer polymerization: The remaining core pre-emulsion and 1 / 3 of the initiator were added dropwise simultaneously. The addition was completed in 65 minutes, and the mixture was kept at 80°C for 35 minutes.

[0110] (5) Shell polymerization: The shell pre-emulsion and the remaining initiator were added dropwise simultaneously, and the addition was completed in 90 min. The mixture was then kept at 80℃ for 70 min.

[0111] (6) Post-treatment: Cool down and adjust pH to 7.5, stir for 12 min, filter to obtain the finished emulsion, and label it as EA-2.

[0112] S3. Plywood preparation and application performance testing

[0113] Using emulsion EA-2 as an adhesive, plywood was prepared according to the above method and its performance was tested.

[0114] Example 3

[0115] S1. Preparation of Acid-hydrolyzed Acetate-Acid-Oxidated Starch

[0116] Take 100g of corn starch (dry basis) and prepare a starch milk with a mass concentration of 40%. Heat the mixture to 60℃ and add concentrated hydrochloric acid accounting for 3.0% of the dry starch. The mixture is kept at a constant temperature for 4 hours for acid hydrolysis. After neutralization, washing and drying, acid hydrolyzed starch is obtained.

[0117] Acid-hydrolyzed starch was prepared into a starch milk with a mass concentration of 50%, cooled to 30°C, and vinyl acetate, accounting for 25% of the dry basis of acid-hydrolyzed starch, was added. The pH of the system was adjusted to 10.5, and the esterification reaction was carried out for 1 hour. After neutralization, washing, and drying, the intrinsic viscosity of the modified starch was measured to be 80 mL / g, the degree of substitution was 0.2, and the chloride ion content was 62 ppm.

[0118] S2. Preparation of pure propenyl core-shell emulsion

[0119] Raw material formula (parts by weight):

[0120] Acid-hydrolyzed acetate esterified starch: 25 parts

[0121] Alkene soft monomer (ethyl acrylate): 55 parts

[0122] Alkene hard monomer (tert-butyl methacrylate): 50 parts

[0123] Carboxylated olefin monomers (itaconic acid): 4 parts

[0124] Core layer crosslinking agent (pentaerythritol tetramethacrylate): 0.4 parts

[0125] Emulsifier (nonylphenol polyoxyethylene ether ammonium sulfate): 2.0 parts

[0126] Initiator (ammonium persulfate): 0.65 parts

[0127] Buffer (sodium bicarbonate): 0.6 parts

[0128] Deionized water: 290 parts

[0129] Preparation steps:

[0130] (1) Pre-emulsification: Dissolve the emulsifier and buffer in 90 parts of deionized water and divide them into two equal parts; emulsify one part with tert-butyl methacrylate, 20 parts of ethyl acrylate and core layer crosslinking agent at high speed for 15 min to obtain the core pre-emulsion; emulsify the other part with the remaining ethyl acrylate and itaconic acid to obtain the shell pre-emulsion; dissolve the initiator in an appropriate amount of deionized water for later use.

[0131] (2) Gelatinization: Mix starch with the remaining deionized water, heat to 90°C, keep warm for 40 minutes until completely gelatinized, add buffer and cool to 80°C.

[0132] (3) Seed preparation: Add 1 / 5 of the initiator, add 10% of the nuclear pre-emulsion, and keep warm at 82℃ for 25 minutes until blue light appears.

[0133] (4) Core layer polymerization: The remaining core pre-emulsion and 1 / 3 of the initiator were added dropwise simultaneously. The addition was completed in 80 min, and the mixture was kept at 82℃ for 40 min.

[0134] (5) Shell polymerization: The shell pre-emulsion and the remaining initiator were added dropwise simultaneously, and the addition was completed in 120 min. The mixture was then kept at 82℃ for 80 min.

[0135] 6. Post-processing: Cool down and adjust pH to 8.0, stir for 15 minutes, filter to obtain the finished emulsion, labeled as EA-3.

[0136] S3. Plywood preparation and application performance testing

[0137] Plywood was prepared and its properties were tested using emulsion EA-3 as an adhesive, following the method described above.

[0138] Comparative Example 1

[0139] Unmodified corn starch was used instead of the acid-hydrolyzed acetate starch in Example 1, with the same dosage and preparation steps as in Example 1. Gelation occurred during the preparation process, resulting in a unstable emulsion that could not be used for subsequent board application testing.

[0140] Comparative Example 2

[0141] Referring to the "soft core, hard shell" structural concept mentioned in the background technology, the polymerization process was adjusted: starch, all butyl acrylate (soft monomer), and crosslinking agent (trimethylolpropane triacrylate) were used as the core layer pre-emulsion; methyl methacrylate (hard monomer) and acrylic acid were used as the shell layer pre-emulsion. This prepared a "soft core, hard shell" structured emulsion. Other raw material ratios were the same as in Example 1. The resulting emulsion was labeled CE-2, and its performance in sheet applications was tested.

[0142] 4. Performance Testing and Results

[0143] The performance of the emulsions and films obtained in Examples 1-3 and Comparative Examples 1-2 was tested, and the results are shown in the table below:

[0144]

[0145] Conclusion: Examples 1-3 successfully prepared stable emulsions with small particle size and good storage stability. The resulting films exhibited high transparency, excellent water resistance (low water absorption), and superior mechanical properties, demonstrating the advantages of the "hard core, soft shell" structure and effective starch modification. The acrylate core-shell emulsion adhesive based on acid-hydrolyzed acetate esterified starch provided by this invention not only possesses excellent emulsion stability and film-forming properties but also exhibits high dry / wet bonding strength in wood bonding applications. With no formaldehyde added, it achieves a perfect balance between mechanical and environmental performance, offering significant advantages in engineered wood products, particularly in applications requiring high weather resistance and environmental friendliness.

Claims

1. A starch-based pure propane core-shell emulsion, characterized in that, Prepared from the following parts by weight of raw materials: The mixture consists of 10-25 parts acid-hydrolyzed acetic acid esterified starch, 45-55 parts soft olefin monomers, 40-50 parts hard olefin monomers, 1-4 parts carboxyl-containing olefin monomers, 0.1-0.4 parts core-layer crosslinking agent, 1-2.0 parts emulsifier, 0.40-0.65 parts initiator, 0.5-0.6 parts buffer, and 150-290 parts deionized water. The intrinsic viscosity of the acid-hydrolyzed acetic acid esterified starch is 40-80 mL / g, and the chloride ion content is ≤100 ppm; The pure propylene core-shell emulsion has a hard core and soft shell structure. The core layer is a copolymer of acid-hydrolyzed acetic acid esterified starch, olefin hard monomers and core layer crosslinking agent, and the shell layer is a copolymer of olefin soft monomers and carboxyl-containing olefin monomers.

2. The starch-based pure propane core-shell emulsion according to claim 1, characterized in that, The olefinic hard monomers are selected from one or more of styrene, methylstyrene, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, and tert-butylstyrene. The olefinic soft monomer is selected from one or more of butadiene, methyl acrylate, ethyl acrylate, n-propyl acrylate, hydroxypropyl acrylate, n-butyl acrylate, tert-butyl acrylate, n-hexyl acrylate, isooctyl acrylate, isoprene, and isopentyl acrylate.

3. The starch-based pure propane core-shell emulsion according to claim 1, characterized in that, The core layer crosslinking agent is selected from one or more of ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, and pentaerythritol tetramethacrylate; The carboxyl-containing olefin monomers are selected from one or more of acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid.

4. The starch-based pure propane core-shell emulsion according to claim 1, characterized in that, The emulsifier is nonylphenol polyoxyethylene ether ammonium sulfate, the initiator is ammonium persulfate, and the buffer is sodium bicarbonate.

5. A method for preparing the starch-based pure propane core-shell emulsion according to any one of claims 1-4, characterized in that, Includes the following steps: S1 Preparation of acid-hydrolyzed acetic acid esterified starch The original starch was prepared into a starch milk with a mass concentration of 35%-40%. An inorganic acid of 1.0%-3.0% of the dry weight of the starch was added at 45-60℃, and the acid hydrolysis reaction was carried out for 4-6 hours. After neutralization, washing and drying, the acid hydrolyzed starch was obtained. Acid-hydrolyzed starch was prepared into a starch milk with a mass concentration of 40%-50%. Vinyl acetate with a dry basis of 5%-25% of the acid-hydrolyzed starch was added at 25-30℃. The pH was controlled at 8.5-10.5 under alkaline conditions, and the esterification reaction was carried out for 1-2 hours. After neutralization, washing, and drying, acid-hydrolyzed acetate esterified starch was obtained. S2 in-situ seed emulsion polymerization (1) Pre-emulsification: The emulsifier and buffer are dissolved in a portion of deionized water and divided into two parts. One part is sheared and emulsified with all olefin hard monomers and core layer crosslinking agent to obtain core pre-emulsion; the other part is emulsified with all olefin soft monomers and carboxyl-containing olefin monomers to obtain shell pre-emulsion; the initiator is dissolved in deionized water to prepare initiator solution. (2) Gelatinization: Mix the acid-hydrolyzed acetic acid esterified starch with the remaining deionized water, keep it at 80-90℃ for 30-40 minutes to complete gelatinization, add buffer, and cool down to 75-80℃; (3) Seed preparation: Add 1 / 5 of the initiator solution, stir, and then add 10% of the nuclear pre-emulsion. Keep warm at 75-82℃ for 25 min. (4) Core layer polymerization: Simultaneously add the remaining core preemulsion and 1 / 4 of the initiator solution, with a dropping time of 50-80 min, and keep warm at 75-82℃ for 30-40 min; (5) Shell polymerization: Simultaneously add shell preemulsion and remaining initiator solution, with a dropping time of 60-120 min, and keep warm at 75-82℃ for 60-80 min; (6) Post-processing: Cool down to below 40℃, adjust the pH to 7.0-8.0 with ammonia water, and filter to obtain pure core-shell emulsion.

6. The application of the starch-based pure propylene core-shell emulsion according to any one of claims 1-4 in engineered wood products, characterized in that, It is used in the manufacture of engineered wood products such as plywood, blockboard, engineered wood, and particleboard.

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