High-toughness nano-modified EVA plastic particles and preparation method thereof

Abstract

The application belongs to the technical field of polymer materials, and discloses a kind of high toughness nano-modified EVA plastic particles and preparation method thereof.The plastic particles are composed of EVA matrix, organic template molecules and in-situ generated nano calcium carbonate or calcium phosphate, wherein the organic template molecules guide the inorganic phase to form a gradient distribution and brick-mud staggered structure in the matrix.Through in-situ mineralization and shear field regulation in the double screw extrusion process, the ordered arrangement of nano phase and interface strong coupling are realized.The application solves the problem of nano particle agglomeration in EVA melt, improves the fracture toughness and impact resistance of the material, optimizes the overall mechanical property matching of the material, simplifies the formula system, does not need to add additional compatilizer or coupling agent, is compatible with existing EVA processing equipment, does not need complex post-treatment, has good industrialization prospect, and the obtained material has high tensile strength, high elongation at break and excellent impact toughness.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology and relates to a high-toughness nano-modified EVA plastic particle and its preparation method. Background Technology

[0002] EVA is widely used in footwear, photovoltaic encapsulation films, medical devices, and high-end packaging materials due to its excellent flexibility, transparency, processing performance, and good biocompatibility.

[0003] Existing technologies mostly employ physical blending to directly disperse pre-synthesized nanoparticles into EVA melt. While this method improves toughness to some extent, it is difficult to overcome the fundamental defect that nanoparticles are prone to agglomeration due to their high surface energy.

[0004] In the absence of effective interface control, nanoparticles tend to form micron-sized aggregates. These aggregates not only disrupt the continuity of the matrix, but also become stress concentration sources during the stress process, which in turn induces the initiation and propagation of microcracks, significantly weakening the overall strength and modulus of the material.

[0005] Even if short-term dispersion is achieved through surface coupling agents or ultrasonic-assisted methods, it is still difficult to maintain a stable distribution during subsequent melt processing or long-term service, leading to performance degradation.

[0006] Traditional blending strategies are essentially a passive filling mode, failing to guide the synergistic construction of inorganic phases and organic matrices at multiple scales from the structural design level, and thus cannot achieve true robust integration. Summary of the Invention

[0007] This invention provides a high-toughness nano-modified EVA plastic granule and its preparation method, aiming to solve the technical problem in the prior art where the agglomeration of nano-inorganic fillers in the EVA matrix makes it difficult to synergistically improve strength, modulus, and toughness. This invention constructs a biomimetic mineralization pathway within the EVA matrix, introducing organic template molecules with specific structures to guide the in-situ, ordered, and gradient deposition of nano-calcium carbonate or calcium phosphate between polymer chains, thereby forming an organic-inorganic composite system with a multi-scale interpenetrating network structure. This effectively suppresses stress concentration and significantly improves the overall mechanical properties of the material.

[0008] To achieve the above-mentioned objectives, the present invention provides a high-toughness nano-modified EVA plastic granule, characterized in that the plastic granule comprises the following components: an EVA matrix, organic template molecules, an antioxidant compound system, and an in-situ generated nanoscale inorganic phase; wherein, the vinyl acetate content in the EVA matrix is ​​18%-40%; the organic template molecules are polymer electrolytes with carboxyl, sulfonic acid, or phosphate functional groups, or biomimetic polypeptides composed of aspartic acid, glutamic acid, serine, and lysine in a specific sequence; the nanoscale inorganic phase is calcium carbonate or calcium phosphate, with a crystallite size of 20-150 nm, and The inorganic phase is distributed in a gradient concentration within the EVA matrix, with a volume fraction of 5%-8% near the surface and 12%-18% in the core region. The organic template molecules are uniformly dispersed within the EVA matrix and form physical cross-linking points with the EVA molecular chains through hydrogen bonds or dipole-dipole interactions. The nanoscale inorganic phase is anchored within the EVA matrix by coordinating or ionic bonding with the functional groups of the organic template molecules, forming a brick-and-mortar interwoven structure that extends from the nanoscale to the microscale. The bricks are aggregates of the nanoscale inorganic phase, and the mortar is a composite phase of EVA and organic template molecules.

[0009] The polymer electrolyte is one of polyacrylic acid, sodium polymethacrylate sulfonate, or polyvinylphosphonic acid, with a weight-average molecular weight of 5000-50000, and maintains thermal stability at the EVA melting temperature; the amino acid sequence of the biomimetic polypeptide is Asp-Glu-Ser-Lys-Asp-Glu, with a molecular weight of 700-900, and does not undergo significant degradation within the EVA processing temperature range; the crystal structure of the nanoscale inorganic phase is calcite-type calcium carbonate or hydroxyapatite-type calcium phosphate, and its crystal orientation is regulated by organic template molecules, preferentially growing along the (104) or (002) crystal plane, thereby forming a spatially matched interface configuration with the EVA segments. The carboxyl, sulfonic acid, or phosphate groups of the organic template molecules specifically coordinate with the inorganic phase ions, and induce the crystal growth direction through chemical bonding; at the same time, the shear field formed during twin-screw extrusion further regulates the crystal orientation, ensuring that the inorganic phase grows stably along the (104) or (002) crystal plane, and ensuring the interfacial bonding strength and structural regularity.

[0010] In a preferred embodiment of the present invention, the method for preparing the high-toughness nano-modified EVA plastic particles includes the following steps: Step 1: Add the EVA matrix, organic template molecules, and antioxidant compound system to a high-speed mixer in a certain proportion, and mix at 60-80℃ for 10-20 minutes to obtain a premix; wherein, the antioxidant compound system includes a compound system of antioxidant 1010 and antioxidant 168, and the total addition amount is 0.1%-0.3% of the mass of EVA; Step 2: The inorganic precursor solution is prepared by mixing soluble calcium salt and carbonate or phosphate in a stoichiometric ratio of 1:1, with a concentration of 0.5-2.0 mol / L. The solvent is deionized water or an ethanol-water mixture, wherein the volume fraction of ethanol is 30%-70%. The soluble calcium salt is calcium chloride or calcium nitrate, the carbonate is sodium carbonate or sodium bicarbonate, and the phosphate is disodium hydrogen phosphate or potassium dihydrogen phosphate. Step 3: The premixed material is added to the main feed port of the twin-screw extruder, and the inorganic precursor solution is injected into the side feed port between zones 3 and 5 of the twin-screw extruder through a metering pump. The twin-screw extruder has a screw length-to-diameter ratio of 40:1, a screw speed of 200-300 rpm, and the set temperatures for each zone are as follows: Zone 1 100℃, Zone 2 120℃, Zone 3 140℃, Zone 4 150℃, Zone 5 155℃, Zone 6 150℃, Zone 7 145℃, Zone 8 140℃, and the die head temperature is 135℃. In step 4, within zones 3 to 5 of the twin-screw extruder, the EVA matrix is ​​in a molten state, and the organic template molecules are fully dissolved and uniformly dispersed in the melt, with their functional groups exposed at the melt interface. The injected inorganic precursor solution rapidly desolvates under high-temperature shear, and calcium ions coordinate with the carboxyl, sulfonic acid, or phosphate groups of the organic template molecules to form nucleation sites. Subsequently, carbonate or phosphate ions diffuse to the nucleation sites, initiating in-situ crystallization of nano-calcium carbonate or calcium phosphate. Due to the reverse pressure gradient from the die head to the feed inlet within the twin-screw extruder, and the shear rate gradient formed by the melt during screw conveying, the inorganic phase exhibits a concentration gradient distribution from the surface to the core on the cross-section of the material. Step 5: After extrusion, cooling and pelletizing, the high-toughness nano-modified EVA plastic pellets are obtained. The cooling adopts an underwater pelletizing system, the cooling water temperature is controlled at 20-30℃, and the pelletizing speed is synchronized with the extrusion speed to ensure that the pellet shape is regular.

[0011] In another preferred embodiment of the present invention, the organic template molecule is chemically bonded to EVA in advance through a melt grafting reaction. Specifically, the EVA matrix, organic template molecule, and initiator dicumyl peroxide are added to a mixer in a mass ratio of 100:1.0:0.05 and reacted at 160°C for 15 minutes, so that the active end groups of the organic template molecule undergo free radical grafting with the tertiary carbon atoms on the EVA main chain to form an EVA-g-template molecule graft copolymer. This graft copolymer is then used as a functional masterbatch and added to the main formulation at a ratio of 5%-10% of the total mass of EVA plastic granules. The remaining steps are the same as the preparation method described above.

[0012] In the high-toughness nano-modified EVA granules described in this invention, the organic template molecules not only act as nucleation guides for the inorganic phase but also serve as interfacial coupling bridges between the EVA matrix and the nano-inorganic phase. The strong coordination between its functional groups and calcium ions ensures uniform nucleation of the inorganic phase at the nanoscale, avoiding particle agglomeration caused by van der Waals forces in traditional blending methods. Simultaneously, because the mineralization process occurs within the EVA melt and is synergistically regulated by the screw shear field and temperature field, the formed nano-inorganic phase is not randomly distributed but arranged in micron-scale lamellar structures along the melt flow direction. The spacing between adjacent lamellars is 200-800 nm, and each lamellar is composed of multiple 20-150 nm nanocrystals connected by organic template molecules, with the overall structure mimicking the brick-and-mortar configuration of nacre. In this structure, when the material is subjected to external impact, the crack propagation path is forced to deflect, bifurcate, or bridge along the organic-inorganic interface, thereby dissipating a large amount of fracture energy and significantly improving the fracture toughness of the material.

[0013] Furthermore, the gradient mineralization structure design further optimizes the matching of the material's mechanical properties. The lower inorganic phase content in the surface region ensures the material's surface flexibility and processing fluidity, which is beneficial for subsequent molding; while the higher inorganic phase content in the core region provides sufficient rigidity and strength support. This non-uniform but continuous structural design effectively avoids the performance bottleneck caused by the mutual constraint between rigidity and toughness in homogeneous filling systems.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. By constructing a biomimetic mineralization path in situ inside the EVA melt, the ordered nucleation and gradient distribution of the nano-inorganic phase were achieved, fundamentally solving the problem of nanoparticle aggregation. 2. The multi-scale interpenetrating network structure effectively inhibits crack propagation and significantly improves the fracture toughness and impact resistance of the material. 3. The gradient mineralization design balances surface flexibility with core rigidity, optimizing the overall mechanical properties of the material. 4. Organic template molecules have both nucleation guidance and interfacial coupling functions, eliminating the need for additional compatibilizers or coupling agents and simplifying the formulation system; 5. The preparation process is compatible with existing EVA processing equipment, requires no complex post-processing, and has good prospects for industrialization. Detailed Implementation

[0015] This invention provides a high-toughness nano-modified EVA plastic particle and its preparation method. By constructing a biomimetic mineralization path inside the EVA matrix and introducing organic template molecules with specific structures, nano-calcium carbonate or calcium phosphate is guided to be deposited in situ, in an ordered and gradient manner between polymer chains, thereby forming an organic-inorganic composite system with a multi-scale interpenetrating network structure, which effectively suppresses stress concentration and significantly improves the comprehensive mechanical properties of the material.

[0016] The high-toughness nano-modified EVA plastic particles of this invention are composed of an EVA matrix, organic template molecules, and in-situ generated nanoscale inorganic phases. The technical solution of this invention will be described in detail below with reference to specific embodiments and comparative examples to ensure that those skilled in the art can fully understand and implement this invention.

[0017] Example 1: The EVA matrix contained 28% vinyl acetate; the organic template molecule was polyacrylic acid with a weight average molecular weight of 20,000, added at 0.8%; the inorganic precursor solution was a 1.0 mol / L calcium chloride and sodium bicarbonate mixed solution of equal volumes, with ethanol-water volume ratio of 50:50 as the solvent; the twin-screw extruder had an aspect ratio of 40:1, a screw speed of 250 rpm, and temperatures in each temperature zone were 100℃, 120℃, 140℃, 150℃, 155℃, 150℃, 145℃, and 140℃ respectively, with a die head temperature of 135℃; the antioxidant compound system consisted of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1, added at 0.2%; the underwater pelletizing cooling water temperature was 25℃, and the pellet length was 3 mm.

[0018] Preparation process: The EVA matrix, organic template molecules, and antioxidant compound system are mixed and stirred at 70°C for 15 minutes to obtain a premix. The premix is ​​added to the main feed port of a twin-screw extruder, and the inorganic precursor solution is injected into the side feed port of zone 4 through a metering pump. In zones 3 to 5 of the twin-screw extruder, the EVA matrix melts, the organic template molecules dissolve and expose functional groups, and after the precursor is desolventized, calcium ions coordinate with the functional groups to form nuclei. Carbonate diffusion initiates in-situ crystallization, which is regulated by the screw shear field and reverse pressure gradient to form a gradient distribution of nano-calcium carbonate from the surface to the core. The extrudate is granulated underwater, cooled and dried to obtain the finished product.

[0019] Example 2: The organic template molecule is a biomimetic polypeptide sequence Asp-Glu-Ser-Lys-Asp-Glu with a molecular weight of 780, and the addition amount is 0.5%; the inorganic precursor is a 1.5 mol / L mixed solution of calcium nitrate and disodium hydrogen phosphate, and the solvent is deionized water; the rest of the formulation and process are the same as in Example 1.

[0020] Preparation process: Same as in Example 1 (adjustment of template molecule and inorganic precursor).

[0021] Example 3: The organic template molecule is sodium polymethacrylate sulfonate with a weight average molecular weight of 30,000, and the addition amount is 1.0%; the rest of the formulation and process are the same as in Example 1.

[0022] Preparation process: Same as in Example 1 (template molecule adjustment).

[0023] Example 4: The EVA matrix contains 18% vinyl acetate; the remaining formulation and process are the same as in Example 1. Preparation process: Same as in Example 1 (EVA parameters adjusted).

[0024] Example 5: EVA matrix with 40% vinyl acetate content; other formulations and processes are the same as in Example 1; Preparation process: Same as in Example 1 (EVA parameters adjusted).

[0025] Example 6: Inorganic precursor concentration 0.5 mol / L; other formulations and processes are the same as in Example 1; Preparation process: Same as in Example 1 (precursor concentration adjusted).

[0026] Example 7: Inorganic precursor concentration 2.0 mol / L; other formulations and processes are the same as in Example 1; Preparation process: Same as in Example 1 (precursor concentration adjusted).

[0027] Example 8: The organic template molecule is an EVA-g-polyacrylic acid graft copolymer with a grafting rate of 1.2%, added at 8% of the total mass of EVA plastic granules; the rest of the formulation and process are the same as in Example 1; Preparation process: First, prepare the graft copolymer functional masterbatch, then mix it with other raw materials and follow the same process as in Example 1.

[0028] Comparative Example 1: 15% nano-calcium carbonate was added directly; no inorganic precursors were added, and no in-situ mineralization was performed; no organic template molecules were used; the rest of the formulation and process were the same as in Example 1. Preparation process: EVA + nano calcium carbonate + antioxidant mixing → twin-screw extrusion → pelletizing → finished product.

[0029] Comparative Example 2: No organic template molecules; the rest of the formulation and process are the same as in Example 1; Preparation process: EVA + antioxidant mixing → Inorganic precursor injection into extruder → In-situ mineralization → Pelletizing → Finished product.

[0030] Test method: Mechanical property testing: tensile strength, elongation at break and flexural modulus are measured by universal testing machine; notched impact strength is measured by impact testing machine; the synergistic effect of strength and toughness is evaluated.

[0031] Structure and stability testing: Scanning electron microscopy was used to observe the distribution and grain size of nano-inorganic phases; transmission electron microscopy was used to analyze the crystal structure; and thermal aging tests were conducted to measure the strength retention rate.

[0032] Process performance testing: Detecting the flowability of plastic pellets during processing; verifying the uniformity of underwater pellet size; evaluating compatibility with subsequent molding processes.

[0033] The test data comparisons are shown in Table 1 and Table 2.

[0034] Table 1. Comparison of Tensile Strength, Elongation at Break, and Notched Impact Strength:

[0035] Table 2. Comparison of flexural modulus, nanocrystal size, and thermal aging strength retention rate:

[0036] Examples 1-8: Tensile strength ≥ 16.2 MPa, impact strength ≥ 38 kJ / m 2 The results are far superior to those of the comparative example; the traditional blending in the comparative example 1 resulted in poor toughness due to agglomeration, while the comparative example 2 proved that organic template molecules + in-situ mineralization are the key to the synergistic effect of strength and toughness.

[0037] Different organic template molecules are all compatible (Examples 1-3), and the graft copolymer masterbatch has the best stability; the vinyl acetate content of the EVA matrix is ​​reduced (Examples 5→1→4), and the tensile strength and modulus are improved; the concentration of inorganic precursor is increased (Examples 6→1→7), the grain size of the inorganic phase in the core is increased, and the rigidity is enhanced.

[0038] The embodiment combines high tensile strength and elongation at break, achieving a strong and tough integrated structure. It features a gradient distribution of nano-inorganic phases, with a volume fraction of 5%-8% near the surface and 12%-18% in the core region, forming a brick-and-mortar interwoven structure spanning from nano to micrometer scales. The "bricks" are aggregates of nano-inorganic phases, while the "mortar" is a composite phase of EVA matrix and organic template molecules. The surface is flexible, while the core is rigid, making it suitable for molding in various scenarios. It exhibits excellent thermal stability and stable long-term performance. The preparation process is compatible with existing extrusion equipment, requires no additional compatibilizers, and has great industrialization potential.

[0039] Compared to traditional blending (Comparative Example 1), Example 1 shows a 22% increase in tensile strength, a 62% increase in elongation at break, and a 40% increase in impact strength; compared to template-free in-situ mineralization (Comparative Example 2), it shows a 34% increase in tensile strength and a 32% increase in modulus, solving the industry problem of the mutual constraint between strength and toughness in traditional nano-modified EVA.

[0040] In summary, the plastic granules of this invention, through biomimetic mineralization and gradient structure design, can achieve a synergistic effect of high toughness and high strength with different parameter combinations, making them suitable for high-end applications such as shoe materials and photovoltaic encapsulation films.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-toughness nano-modified EVA plastic granule, characterized in that, The EVA plastic granules are composed of the following components: EVA matrix; Organic template molecules form physical cross-linking points with EVA molecular chains through hydrogen bonds or dipole-dipole interactions, or they react with the EVA matrix to form EVA-g-template molecule graft copolymers. The in-situ generated nanoscale inorganic phase, which is calcium carbonate or calcium phosphate, is anchored in the matrix by coordination or ionic bonding with the functional groups of the organic template molecule. The antioxidant compound system is added at a rate of 0.1%-0.3% of the total mass of EVA plastic granules.

2. The high-toughness nano-modified EVA plastic particles according to claim 1, characterized in that, The vinyl acetate content in the EVA matrix is ​​18%-40%.

3. The high-toughness nano-modified EVA plastic particles according to claim 1, characterized in that, The polymer electrolyte is one of polyacrylic acid, sodium polymethacrylate sulfonate, or polyvinylphosphonic acid.

4. The high-toughness nano-modified EVA plastic particles according to claim 3, characterized in that, The polyacrylic acid has a weight-average molecular weight of 20,000, and its addition amount is 0.8 ± 0.2% of the total mass of EVA plastic granules.

5. The high-toughness nano-modified EVA plastic particles according to claim 1, characterized in that, The biomimetic polypeptide is composed of aspartic acid, glutamic acid, serine and lysine in the sequence Asp-Glu-Ser-Lys-Asp-Glu, and is uniformly dispersed in the EVA matrix.

6. The high-toughness nano-modified EVA plastic particles according to claim 5, characterized in that, The biomimetic polypeptide has a molecular weight of 700-900 and is added at a rate of 0.5 ± 0.2% of the EVA matrix mass.

7. The high-toughness nano-modified EVA plastic particles according to claim 1, characterized in that, The nanoscale inorganic phase has a calcite-type or hydroxyapatite-type crystal structure and preferentially grows along the (104) or (002) crystal plane.

8. The high-toughness nano-modified EVA plastic granules according to claim 7, characterized in that; The nanoscale inorganic phase is distributed in a gradient across the cross-section of the material, with a volume fraction of 5%-8% near the surface and 12%-18% in the core region. The whole structure forms a brick-mud interwoven structure that extends from the nanoscale to the microscale, where the brick is an aggregate of nano-inorganic phase and the mud is a composite phase of EVA matrix and organic template molecules.

9. The high-toughness nano-modified EVA plastic particles according to claim 1, characterized in that, The organic template molecule is polyacrylic acid, which is grafted onto the EVA matrix backbone through chemical bonding to form an EVA-g-template molecule graft copolymer with a grafting rate of 1.0%-1.5%. It is added in the form of functional masterbatch, accounting for 5%-10% of the total mass of EVA plastic granules.

10. A method for preparing high-toughness nano-modified EVA plastic particles as described in any one of claims 1-9, characterized in that, Includes the following steps: S1, mix the EVA matrix, organic template molecules and antioxidant compound system to obtain the premix; S2, the inorganic precursor solution is prepared by mixing soluble calcium salt and carbonate or phosphate in a 1:1 ratio, with a concentration of 0.5-2.0 mol / L, and the solvent is deionized water or a mixture of ethanol and water. S3, the premixed material is added to the main feed port of the twin-screw extruder, and the inorganic precursor solution is injected into the side feed port through a metering pump. In S4, within zones 3 to 5 of the twin-screw extruder, the EVA matrix melts, the organic template molecules dissolve and expose functional groups, and after the precursor is desolventized, calcium ions coordinate with functional groups to form nuclei. Carbonate or phosphate diffuses and initiates in-situ crystallization. Under the regulation of the screw shear field and reverse pressure gradient, an inorganic phase gradient distribution is formed from the surface to the core. S5, the extrudate is granulated underwater, cooled, and dried to obtain the plastic pellets.

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