A polyformaldehyde modified ethylene-vinyl acetate copolymer composite material and a preparation method thereof

Abstract

The application relates to the field of high polymer composite materials, in particular to a polyformaldehyde modified ethylene-vinyl acetate copolymer composite material and a preparation method thereof. The polyformaldehyde modified ethylene-vinyl acetate copolymer composite material comprises the following raw materials in mass percentage: polyformaldehyde 12-46%, ethylene-vinyl acetate copolymer 54-88%. The polyformaldehyde modified ethylene-vinyl acetate copolymer composite material of the application does not need to add a compatilizer, the material has good toughness and strength balance, and the preparation process is simple and low in cost.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials, and more particularly to a polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material and its preparation method. Background Technology

[0002] Polyoxymethylene (POM) is a highly crystalline engineering plastic with an extremely low coefficient of friction (0.1-0.2), excellent wear resistance (self-lubricating properties), and dimensional stability. POM has a Shore hardness of 85-90D, poor flexibility, low elastic recovery (<30%), and a very narrow processing temperature window. After melting, it rapidly crystallizes upon cooling to 140-148℃, making it extremely difficult to process into films and unsuitable for applications requiring good elasticity.

[0003] Ethylene-vinyl acetate copolymer (EVA) has excellent flexibility, impact resistance, and good extrusion processability. However, its poor mechanical strength, low abrasion resistance, easy surface wear and fuzzing, and low heat distortion temperature limit the application scenarios of EVA.

[0004] Blending ethylene-vinyl acetate copolymer (EVA) with polymethyl methacrylate (POM) offers complementary properties, effectively improving the tensile strength, impact toughness, abrasion resistance, slip properties, and heat stability of EVA materials. However, due to the difference in solubility parameters between POM and EVA, their compatibility is limited. Traditional and existing technologies rely on compatibilizers such as maleic anhydride-grafted EVA (EVA-g-MAH) to improve interfacial bonding. This not only increases raw material costs and complicates the formulation, but the addition of compatibilizers may also adversely affect other properties of the material.

[0005] Developing a POM / EVA blend modified material that does not require the addition of compatibilizers and its preparation method has significant industrial application value. Summary of the Invention

[0006] This invention provides a polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material and its preparation method. The material has a good balance of toughness and strength, and the preparation process is simple and low in cost.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: This invention provides a polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material, comprising the following raw materials in weight percentages: Polyoxymethylene (POM) 12-46%, 54-88% ethylene-vinyl acetate copolymer This invention provides a polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material, which is a composite elastomer system with EVA as the main component and POM as an auxiliary component. This material achieves good compatibility through a simple blending process, eliminating the need for additional compatibilizers and significantly reducing preparation costs. It also effectively solves problems such as poor surface smoothness, insufficient friction and wear resistance, and low tensile strength of EVA, while overcoming the shortcomings of POM, such as poor flexibility and difficulty in film formation. The resulting composite elastomer material is pure in composition and possesses excellent elasticity, low coefficient of friction, high wear resistance, and high tensile strength, achieving a good balance between toughness and strength. Based on this material, this invention also provides methods for preparing its films, sheets, filaments, and tubes. The products can be widely used in protective films, artificial leather, robot skin, textile fabrics, fibers, medical catheters, and dressings, offering significant advantages such as simple processing, low cost, and outstanding comprehensive performance.

[0008] In some specific embodiments, the content of vinyl acetate (VA) in the ethylene-vinyl acetate copolymer is 16wt%~30wt%, preferably 18wt%~28wt%; The melt index (MI, 190℃ / 2.16kg) of the ethylene-vinyl acetate copolymer is 2~13g / 10min, preferably 3~10g / 10min; The tensile strength of the ethylene-vinyl acetate copolymer is ≥12MPa, preferably ≥15MPa. The ethylene-vinyl acetate copolymer in this invention can be purchased, for example, from Yanshan Petrochemical 18J3.

[0009] In some specific embodiments, the polyoxymethylene includes copolyoxymethylene; The melt flow index (MI, 190℃ / 2.16kg) of the polyoxymethylene is 2~15g / 10min, preferably 5~11g / 10min. The polyoxymethylene used in this invention can be purchased, such as K90 from Kailuan Group Zhonghao Chemical, with a measured melt flow index (MI, 190℃ / 2.16kg) of 9.2g / 10min.

[0010] In some specific implementations, functional or aesthetic additives are also included; Based on the total mass of the polyoxymethylene and ethylene-vinyl acetate copolymer, the mass content of the functional or beautifying additive is 0.2% to 25%.

[0011] A second aspect of the present invention also provides a method for preparing a polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material, comprising the following steps: Polyoxymethylene and ethylene-vinyl acetate copolymer are mixed and melt-blended.

[0012] In some specific embodiments, the mixing process may also include the addition of functional or aesthetic additives.

[0013] In some specific embodiments, the melt blending is carried out in a twin-screw extruder.

[0014] A third aspect of the present invention also provides the application of the above-described polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material in protective films, artificial leather, robotic skin, textile fabrics, fibers, medical catheters, or dressings.

[0015] In some specific embodiments, the operating parameters of the twin-screw extruder are as follows: feeding section temperature is 140-160℃, melting section temperature is 170-185℃, mixing section temperature is 185-195℃, extrusion die temperature is 170-185℃, and screw speed is 200-400 rpm.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) No compatibilizer needed: The inventors have found that when the vinyl acetate content in the ethylene-vinyl acetate copolymer is 16-30wt% and the MI (190℃ / 2.16kg) is 2-13g / 10min, EVA and POM copolymers within this range have excellent compatibility and can obtain a stable blend structure without macroscopic phase separation without the addition of compatibilizers such as maleic anhydride grafted EVA.

[0017] (2) Excellent performance balance: By optimizing the VA content and melting parameters of EVA, and when the tensile strength is ≥12MPa, the modified material obtained is in a homogeneous system and significantly improves the mechanical properties, achieving a balance between rigidity and toughness.

[0018] (3) Simple formula and low cost: It only uses two basic resins, POM and EVA, and the raw materials are widely available. The production cost is low and it is suitable for large-scale industrial production.

[0019] (4) Wide processing window: The preparation method of the present invention is simple and easy to control. The processing temperature window includes the entire range from melting to room temperature, which can be directly realized on conventional twin-screw extrusion equipment without the need for special equipment modification.

[0020] (5) This invention solves the problems of poor surface smoothness, insufficient friction and wear resistance, and low tensile strength of EVA. At the same time, it overcomes the defects of poor flexibility and difficult film formation of POM. It provides a new type of composite elastic material with pure composition, lower cost, excellent elasticity, low coefficient of friction, high wear resistance, and high tensile strength. It can be processed into films, sheets, fibers, hoses, etc., and applied in fields such as protective films, artificial leather, robot skin, textile fabrics, fibers, medical catheters and dressings. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments. The embodiments of this application are only examples, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] POM (Polyoxymethylene) is divided into homopolymer POM and copolymer POM. Homopolymer POM (POM-H) is formed by the polymerization of a single formaldehyde monomer. It has a crystallinity of 75-85%, extremely high rigidity, low impact strength, a melting point of 180℃, and a narrow processing window of only 10℃. Copolymer POM (POM-C) is formed by the copolymerization of trioxymethylene and monomers such as dioxolane. It has C-C bonds distributed in its molecular chain, resulting in increased toughness, reduced rigidity, and higher impact strength. Its crystallinity is generally 70-75%, its melting point is 170℃, and its processing window is relatively wider, about 50℃. Therefore, copolymer POM is preferred. Furthermore, copolymer POM with a lower MI value is preferred; an MI of 2-15 g / 10 min at 190℃ / 2.16 kg is suitable for extrusion processing requirements.

[0023] The vinyl acetate content is a key parameter determining the compatibility of EVA and POM, and its selection is based on the following criteria: The solubility parameter of polyethylene (PE) is around 17, while that of the vinyl acetate monomer polymer (PVAC) is around 21. The lower the vinyl acetate content in EVA materials, the closer the properties are to polyethylene, the lower the solubility parameter, and the worse the compatibility with POM. Conversely, the higher the vinyl acetate content, the higher the solubility parameter of EVA and the better its compatibility with POM.

[0024] The solubility parameter of EVA increases with increasing vinyl acetate content. The solubility parameter of POM is approximately 22. Practical experience shows that when the vinyl acetate content of EVA is ≥16%, it is compatible with POM; the higher the VA content, the higher the compatibility. Compatibility with POM determines the lower limit of VA content, which should not be lower than 16%.

[0025] The vinyl acetate content determines the compatibility between EVA and POM, while the MI value determines the processability and mechanical properties of EVA and POM. The control and selection of the MI value has important reference value.

[0026] At the same vinyl acetate content, a lower melt index (MI) indicates higher melt viscosity, larger molecular weight, more complete molecular chain entanglement, and higher tensile and impact strength of the blend. A higher MI corresponds to a lower molecular weight, less molecular chain entanglement, and lower elongation at break and tensile strength. When the melt index (MI, 190℃ / 2.16kg) > 13g / 10min, the strength of EVA decreases significantly, making it suitable for hot melt adhesives and injection-molded thin-walled products with low strength requirements. A high MI and high fluidity prevent effective breakage and polymerization equilibrium with POM in a shear field, failing to guarantee shear refinement and resulting in coarse POM particles, leading to brittleness. When MI < 2, the strength is high, but the melt fluidity is too low, resulting in poor uniformity of mixing and distribution with the POM hot melt, making it difficult to form a homogeneous blend. A MI value corresponding to that of POM is necessary to achieve rheological matching and present a microscopically uniform morphology.

[0027] In addition to determining the vinyl acetate content and MI value of EVA material, it must also have high mechanical strength in order to exhibit good tensile properties, especially the strength after secondary stretching, after being compounded with POM.

[0028] If the tensile strength of EVA is less than 10 MPa, even after modification with POM, the material will still have high rigidity and be prone to brittle fracture.

[0029] Experiments have shown that when the tensile strength of EVA is ≥12MPa, the modification performance of POM is significantly increased.

[0030] EVA tensile strength requires sufficient crystalline regions to act as physical cross-linking points. The primary factor affecting the crystalline region is still the vinyl acetate content. High vinyl acetate content weakens the crystalline region of PE, correspondingly reducing the number of physical cross-linking points and causing a rapid decrease in tensile strength. The upper limit for vinyl acetate content should not exceed 30%, and with VA content below 30%, the tensile strength should not be less than 12 MPa. With EVA as the continuous phase and POM as the dispersed phase, the phase domain control at their interface is also crucial. If the POM content is excessive, forming a continuous POM phase, the elongation at break and notched impact strength will decrease rapidly. If the POM content exceeds 46%, phase inversion will occur, leading to a sharp increase in the composite material's brittleness; therefore, the POM content should not exceed 46%. Conversely, if the POM content is too low, it provides weak reinforcement to the EVA properties, resulting in low practical value.

[0031] Example 1

[0032] EVA-1 (18wt% vinyl acetate (VA), MI (190℃ / 2.16kg) 2.8g / 10min, tensile strength 16MPa) 75%, POM-A (MI (190℃ / 2.16kg) 9g / 10min) 25%.

[0033] Material sources: Yanshan Petrochemical EVA 18J3, Kailuan POM K90.

[0034] The EVA continuous phase provides a large viscoelastic energy dissipation, achieving an optimal strength-toughness balance. Tensile strength is 22 MPa, elongation at break is 520%, and notched impact strength is 9.5 KJ / m. 2 The coefficient of dynamic friction is 0.26, and the wear amount is 7.2mg.

[0035] Compared to the original EVA, the tensile strength is increased by 38%, the elongation at break is decreased by 31%, the coefficient of dynamic friction is decreased by 46%, and the wear is reduced by 70%. Compared to pure POM, the notched impact strength is improved by 58%.

[0036]

[0037] Tests have shown that the resulting product is a perfect combination of strength and toughness, being strong yet not brittle, and soft yet not sticky.

[0038] Example 2

[0039] EVA-2 (28wt%VA, MI (190℃ / 2.16kg) 6g / 10min, tensile strength 24MPa), 54%, POM-A (MI (190℃ / 2.16kg) 9g / 10min) 46%.

[0040] Material source: Lianhong EVA UL00628, Kailuan POM K90.

[0041] The proportion of POM is 46%, which is close to the critical point for the formation of a continuous POM phase and represents the upper limit of POM.

[0042] The product was tested and found to have a tensile strength of 26 MPa, an elongation at break of 380%, a notched impact strength of 7.4 KJ / ㎡, a dynamic friction coefficient of 0.2, and a wear amount of 4.8 mg.

[0043] Compared to the original EVA, the tensile strength is increased by 8%, the elongation at break is decreased by 49%, the coefficient of dynamic friction is decreased by 58%, and the wear is decreased by 80%. Compared to pure POM, the notched impact resistance is increased by 23%.

[0044]

[0045] If the tensile strength is increased by less than 10%, the high POM content will result in the appearance of a continuous POM phase, which will cause the tensile strength to show an unfavorable trend. This proves that 46% POM is the critical safety line to ensure that the impact strength is better than that of pure POM, and it is also the critical safety line to ensure that the tensile strength is better than that of pure EVA. The POM content should not exceed 46%.

[0046] Example 3

[0047] EVA-1 (18wt%VA, MI (190℃ / 2.16kg) 2.8g / 10min, tensile strength 16MPa) 88%, POM-B (MI (190℃ / 2.16kg) 14g / 10min) 12% Material source: Yanshan EVA18J3, DuPont POM 500P Tensile strength 19 MPa, elongation at break 680%, notched impact strength 11 KJ / m 2 The coefficient of dynamic friction is 0.4, and the wear amount is 16.5mg.

[0048] Compared to the original EVA, the tensile strength is increased by 19%, the elongation at break is decreased by 9%, the coefficient of dynamic friction is decreased by 20%, and the wear is decreased by 31%. Compared to pure POM, the notched impact resistance is increased by 83%.

[0049]

[0050] Even lower POM content provides a reinforcing effect, increasing tensile strength by about 20%. Notched impact strength is significantly improved.

[0051] Example 4

[0052] EVA-3 (18wt%VA, MI (190℃ / 2.16kg) 8g / 10min, tensile strength 17MPa) 65%, POM-A (MI (190℃ / 2.16kg) 9g / 10min) 35%.

[0053] Materials sourced from: DuPont ELVAX450 and Kailuan POM K90.

[0054] With similar melt flow index (MI), they are perfectly matched. The resulting phase region is dense, which can effectively improve the strength of the blend and is more conducive to reducing the coefficient of friction.

[0055] Tensile strength 26 MPa, elongation at break 460%, notched impact strength 9 KJ / m 2 The coefficient of dynamic friction is 0.28, and the wear amount is 8.5mg.

[0056] Compared to the original EVA, the tensile strength is increased by 53%, the elongation at break is decreased by 39%, the coefficient of dynamic friction is decreased by 42%, and the wear is decreased by 65%. Compared to pure POM, the notched impact resistance is increased by 50%.

[0057]

[0058] Melt index matching can more effectively compensate for the lack of strength of EVA itself, and can also more effectively improve the toughness of POM.

[0059] Example 5

[0060] EVA-2 (28wt%VA, MI (190℃ / 2.16kg) 6g / 10min, tensile strength 24MPa) 80%, POM-B (MI (190℃ / 2.16kg) 14g / 10min) 20% Material source: Lianhong EVA UL00628, DuPont POM 500P The high VA content is synchronized with the high melt index of POM. With VA content of 28%, the high VA content enhances the polarity and has good compatibility with POM.

[0061] Tensile strength 30 MPa, elongation at break 590%, notched impact strength 10 KJ / m 2 The coefficient of dynamic friction is 0.3, and the wear amount is 9.8mg.

[0062] Compared to the original EVA, the tensile strength is increased by 25%, the elongation at break is decreased by 21%, the coefficient of dynamic friction is decreased by 37.5%, and the wear is decreased by 59%. Compared to pure POM, the notched impact strength is improved by 67%.

[0063]

[0064] Both impact strength and elongation at break are excellent, making for a superb combination.

[0065] Example 6

[0066] EVA-2 (28wt%VA, MI (190℃ / 2.16kg) 6g / 10min, tensile strength 24MPa) 60%, POM-B (MI (190℃ / 2.16kg) 14g / 10min) 40% Material source: Lianhong EVA UL00628, DuPont POM 500P.

[0067] Intermediate general-purpose formulation, with no obvious material weaknesses. Tensile strength 37MPa, elongation at break 420%, notched impact strength 7.5KJ / m. 2 The coefficient of dynamic friction is 0.23, and the wear amount is 6.2 mg.

[0068] Compared to the original EVA, the tensile strength is increased by 54%, the elongation at break is decreased by 44%, the coefficient of dynamic friction is decreased by 52%, and the wear is decreased by 74%. Compared to pure POM, the notched impact strength is improved by 25%.

[0069]

[0070] EVA materials with VA content close to the upper limit and POM materials with MI content close to the upper limit can also form a high-performance composite system. The adjustment of components and the change in performance have a high degree of responsiveness and predictability.

[0071] Comparative Example 1 Pure POM-A (MI (190℃ / 2.16kg) 9g / 10min) Material source: Kailuan POM K90.

[0072] Tensile strength 62MPa, notched impact strength 6KJ / m 2 The elongation at break is 45%, the coefficient of dynamic friction is 0.16, and the wear is 3mg. Using this as a benchmark for comparison, the impact of all embodiments was greater than 7 KJ / m. 2 From 7.4 KJ / m 2 Up to 11 KJ / m 2 The toughness increase ranges from 23% to 83%, effectively enhancing toughness.

[0073] Comparative Example 2 Pure EVA-1 (18wt%VA, MI (190℃ / 2.16kg) 2.8g / 10min, tensile strength 16MPa) Material source: Yanshan Petrochemical 18J3.

[0074] Tensile strength 16MPa, notched impact strength 25 KJ / m 2 The elongation at break is 750%, the coefficient of dynamic friction is 0.48, and the wear is 24mg. The tensile strength of the examples ranges from 19 to 37 MPa, the coefficient of dynamic friction ranges from 0.2 to 0.4, and the wear amount ranges from 4.8 to 16.5 mg. The EVA properties of Examples 1 and 3 were the same as those of Comparative Example 2, with tensile strengths of 22 and 19 MPa, dynamic friction coefficients of 0.26 and 0.4, and wear amounts of 7.2 mg and 16.5 mg, respectively. The tensile strength increased by 19-38%, the friction coefficient decreased by 17-46%, and the wear amount decreased by 31-70%.

[0075] POM is an effective reinforcing agent and wear-resistant modifier for EVA, with significant effects.

[0076] Comparative Example 3 EVA-2 (28wt%VA, MI (190℃ / 2.16kg) 6g / 10min, tensile strength 24MPa) 50%, POM-A (MI (190℃ / 2.16kg) 9g / 10min) 50% (POM exceeds the upper limit of 46%) Material source: Lianhong UL00628, Kailuan POM K90; Tensile strength 15 MPa, elongation at break 110%, notched impact strength 6.2 KJ / m 2 The coefficient of dynamic friction is 0.22, and the wear amount is 22mg. Compared to EVA, the tensile strength decreased by 38%, the elongation at break decreased by as much as 85%, the wear decreased by 8%, the coefficient of friction decreased by 54%, and the impact strength increased by only 3% compared to POM, with almost no toughening effect.

[0077]

[0078] When the POM content exceeds the 46% upper limit (50%), the POM crystalline phase permeates and forms a continuous phase. This continuous POM phase is the root cause of fractures and cracks, turning the blend into a brittle POM and elastomer-filled system. This results in a loss of toughening efficiency and negates the core value of modified EVA. Therefore, limiting the POM content to ≤46% achieves the goal of enhancing strength and reducing wear.

[0079] Comparative Example 4 EVA-4 (12wt%VA, MI (190℃ / 2.16kg) 9g / 10min, tensile strength 10.3MPa) 75%, POM-A (MI (190℃ / 2.16kg) 9g / 10min) 25% (VA<16%) Material source: Beijing Organic EVA 12-9, Kailuan POM K90 The vitamin A content is 12%, below the lower limit of 16%. Excessive interfacial tension and low polarity lead to macroscopic delamination, causing interfacial separation and crack formation, preventing the microstructure from converging. Tense separation occurs, rendering tensile parameters meaningless. The elongation at break is 160%, and the notched impact strength is 6.5 KJ / m. 2 The coefficient of dynamic friction is 0.34, and the wear amount is 21mg.

[0080] Compared with EVA, the elongation at break is reduced by up to 79%, the wear is reduced by 13%, the coefficient of friction is reduced by 29%, the impact strength is only 8% higher than that of POM, and the brittleness is obvious.

[0081] A VA ≥ 16% is a critical threshold for EVA and POM compatibility. Otherwise, macroscopic separation will occur.

[0082]

[0083] Comparative Example 5 EVA-5 (28wt%VA, MI (190℃ / 2.16kg) 400g / 10min, tensile strength 1.7MPa) 70%, POM-A (MI (190℃ / 2.16kg) 9g / 10min) 30% (EVA MI>13) Material source: Beijing organic EVA 28-400, Kailuan POM K90 EVA has an MI value higher than 13. Its high fluidity prevents POM from achieving an effective balance between breakage and polymerization in a shear field. POM has a particle size >10µm and coarse phase domains, which become the initiator of brittleness, resulting in extremely poor toughening effect.

[0084] The tissue separates under tension, making it prone to brittle fracture; tensile strength data is meaningless. The elongation at break is 270%, and the notched impact strength is 6.7 KJ / m. 2 The coefficient of dynamic friction is 0.42, and the wear amount is 30mg.

[0085] Compared with EVA, the elongation at break is reduced by 64%, the wear is reduced by 4%, the coefficient of friction is reduced by 12.5%, the impact strength is only 12% higher than POM, it is more brittle and has a lower elongation.

[0086] An MI ≤ 13 for EVA is a prerequisite for ensuring shear refinement capability.

[0087]

[0088] Comparative Example 6 EVA-4 (28wt%VA, MI (190℃ / 2.16kg) 6g / 10min, tensile strength 10.3MPa) 70%, POM-C (MI (190℃ / 2.16kg) 27g / 10min) 30% (POM's MI>15) Material source: Beijing Organic EVA12-9, Kailuan POM K270 With an excessively high molecular weight index (MI) in POM, low-viscosity POM droplets easily aggregate, making it difficult to stretch into small particles. This results in large, sausage-shaped or spherical particles with a diameter >15µm. These large particles exhibit extremely poor interfacial bonding with the VEA matrix, leading to premature debonding under external force, phase separation, and a reverse viscosity mismatch, resulting in a complete performance collapse. During friction, these large POM particles act as abrasive particles, exacerbating wear. The wear amount in this comparative example was 29mg, while in Example 4, with the same POM content, the wear amount was only 8.5mg. Furthermore, the large POM particles cannot purify cracks; instead, they induce stress concentration due to interfacial voids upon impact, further leading to brittle fracture.

[0089] The tissue separates under tension, is prone to brittle fracture, and the tensile strength data is meaningless. The elongation at break is 210%, the notched impact strength is 6.9 KJ / ㎡, the coefficient of dynamic friction is 0.33, and the wear is 22 mg.

[0090] Compared with EVA, the elongation at break is reduced by 72%, the wear is reduced by 11%, the coefficient of friction is reduced by 31%, the impact strength is increased by 15% compared with POM, and the brittleness is relatively strong.

[0091] The molecular weight (MI) of POM (190℃ / 2.16kg) needs to be limited to ≤15g / 10min to avoid viscosity mismatch leading to uncontrolled phase morphology.

[0092]

[0093] The proportions and performance results of the above embodiments and comparative examples are shown in Table 1.

[0094] Table 1. Formulation ratios and performance results of Examples 1-6 and Comparative Examples 1-6

[0095] Table 2 Comparison of parameter change rates between Examples 1-6 and Comparative Examples 1-6

[0096] Comparative experimental data show that the tensile strength of the examples increased by more than 8%, while the comparative examples showed a negative increase. The decrease in elongation at break of the examples was less than 50%, while that of the comparative examples exceeded 60%. The reduction in wear amount of the examples exceeded 30%, while that of the comparative examples was less than 15%. The improvement in notched impact strength of the examples exceeded 20%, while that of the comparative examples was less than 15%. Both practice and theory have proven that EVA and POM with appropriate parameters can still be well compatible and significantly enhance performance even without compatibilizers, demonstrating high practical value.

[0097] Although preferred embodiments of the invention have been shown and described, it is conceivable that those skilled in the art can devise various modifications to the invention within the spirit and scope of the appended claims, including the addition of functional additives such as compatibilizers, all of which fall within the protection scope of this patent.

Claims

1. A polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material, characterized in that, Raw materials including the following percentages by mass: Polyoxymethylene (POM) 12-46%, Ethylene-vinyl acetate copolymer 54-88%.

2. The polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material according to claim 1, characterized in that, The vinyl acetate content in the ethylene-vinyl acetate copolymer is 16wt%~30wt%. The melt index of the ethylene-vinyl acetate copolymer is 2-13 g / 10 min. The tensile strength of the ethylene-vinyl acetate copolymer is ≥12MPa.

3. The polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material according to claim 1, characterized in that, The polyoxymethylene includes copolyoxymethylene; The copolymerized polyoxymethylene has a melt index of 2-13 g / 10 min at 190℃ and 2.16 kg.

4. The polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material according to claim 1, characterized in that, It also includes functional or aesthetic additives; Based on the total mass of the polyoxymethylene and ethylene-vinyl acetate copolymer, the mass content of the functional or beautifying additives is 0.2% to 25%.

5. A method for preparing the polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material according to any one of claims 1 to 4, characterized in that, Includes the following steps: Polyoxymethylene and ethylene-vinyl acetate copolymer are melt-blended.

6. The method for preparing the polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material according to claim 5, characterized in that, The mixing process also includes the addition of functional or aesthetic additives.

7. The method for preparing the polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material according to claim 5, characterized in that, The melt blending is carried out in a twin-screw extruder.

8. The method for preparing the polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material according to claim 7, characterized in that, The operating parameters of the twin-screw extruder are as follows: The feeding section temperature is 140-160℃, the melting section temperature is 170-185℃, the mixing section temperature is 185-195℃, the extrusion die temperature is 170-185℃, and the screw speed is 200-400rpm.

9. The use of the polyoxymethylene-modified ethylene-vinyl acetate copolymer composite material according to any one of claims 1 to 4 in protective films, artificial leather, robotic skin, textile fabrics, fibers, medical catheters or dressings.

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