A method for preparing a maleic anhydride grafted modified ethylene-vinyl acetate copolymer

Abstract

The application discloses a preparation method of maleic anhydride grafted modified ethylene-vinyl acetate copolymer and relates to the technical field of polymer polymerization and material preparation. The preparation method comprises the following steps: adding EVA and uniformly premixed maleic anhydride and an initiator under the condition of 55-60 DEG C, and uniformly mixing; extruding in a screw machine under the condition of 160-180 DEG C, granulating and drying under hot water to obtain the maleic anhydride grafted modified ethylene-vinyl acetate copolymer. The raw material mixing temperature is always in the low temperature range of 55-60 DEG C by using the melt grafting method, so that the low melting point raw material is not decomposed and can be fully mixed at the melting point; the low temperature condition is easier to obtain and operate, the use of toxic and harmful solvent to dissolve the raw material is effectively avoided, and the production process is more environmentally friendly. The reaction is rapid and the operation is convenient under the reaction condition of 160-180 DEG C, so that the industrial production is facilitated; after granulation under hot water, drying can make the residual free monomer maleic anhydride dissolved in hot water and removed.

Description

Technical Field

[0001] This invention relates to the field of polymer polymerization and material preparation technology, and particularly to a method for preparing maleic anhydride-grafted modified ethylene-vinyl acetate copolymer. Background Technology

[0002] EVA is a random copolymer obtained by copolymerizing non-polar ethylene monomers (E) with highly polar vinyl acetate (VA). It is the fourth largest ethylene copolymer after low-density polyethylene (LDPE), high-density polyethylene (HDPE), and linear low-density polyethylene (LLDPE). Based on its vinyl acetate content, EVA can be broadly classified into three categories: when the vinyl acetate content is 80-95% by mass, it is usually in latex form and is mainly used as an adhesive, coating, and paint; when the vinyl acetate content is 40-80% by mass, it is generally called EVA elastomer and is mainly used as a rubber elastomer and polyvinyl chloride modifier; when the vinyl acetate content is 5-40% by mass, it is called EVA resin and is mainly used to modify materials such as polyethylene.

[0003] EVA contains both polar and nonpolar segments. According to the principle of similarity compatibility, EVA exhibits some compatibility with both polar and nonpolar materials. However, due to the limited number of acetate groups in EVA resin and the steric hindrance effect of acetate, it cannot effectively fulfill its function. To broaden the application range of EVA and effectively improve its compatibility with polar polymers and / or inorganic fillers, current research primarily focuses on grafting polar groups, such as maleic anhydride (MAH), methyl acrylate (MMA), and acrylic acid (AA), onto the EVA backbone.

[0004] Currently, there are four main methods for grafting modification of ethylene-vinyl acetate copolymers: solution grafting, radiation grafting, emulsion grafting, and melt grafting.

[0005] Solution grafting involves dissolving the polymer to be modified in a suitable organic solvent, then adding the initiator and the monomer to be grafted into the polymer solution for reaction. This method offers high grafting rates and few side reactions, but the grafting reaction cycle is long, the solvents used are generally highly toxic, and the post-processing of the product is complex. Therefore, solution grafting is not suitable for industrial production.

[0006] Radiation grafting involves removing side groups or hydrogen atoms from polymer macromolecules under high-energy radiation to form active free radicals. Grafting monomers then complete the grafting reaction at these active free radical sites. This method requires no additional additives, is simple to operate, and produces pure products. However, its applicability is limited, it is costly, and it is not suitable for industrial production.

[0007] Emulsion grafting is a method of modifying polymers in emulsion state by using a water-soluble initiator to initiate a grafting reaction between the seed emulsion and monomers such as methyl methacrylate and styrene; it is suitable for the modification of EVA emulsion series products.

[0008] Melt grafting involves pre-weighing and mixing auxiliaries (such as initiators) with grafting monomers, followed by a high-temperature molten state to initiate the grafting reaction. Melt grafting has a high reaction temperature and a short reaction cycle, making it the most widely used grafting modification method in industrial production. For example, the melt grafting method used in Chinese patent CN101245125B involves adding all reactants separately through different extruder feed ports and directly melting and extruding them at high temperatures. However, this method suffers from uneven mixing or partial decomposition of low-melting-point substances. Another example is the literature "Research on the Blend System of Nylon 66 / Ethylene-Vinyl Acetate Copolymer Grafted with Maleic Anhydride" (Chen Minjie, Zhang Jun, Wan Wujun, 2003), which describes using organic solvents such as acetone, employing a method of pre-dissolving and uniformly mixing before melt extrusion. However, this method is not suitable for large-scale industrial production.

[0009] Therefore, there is an urgent need for a method for grafting maleic anhydride onto ethylene-vinyl acetate copolymers that is suitable for large-scale industrial production, has a simple process and operation, and does not require high-temperature grafting reaction conditions. Summary of the Invention

[0010] To address the existing problems of the melt grafting method and to increase the compatibility of EVA with polar and non-polar polymers, this invention provides a method for preparing maleic anhydride-grafted modified ethylene-vinyl acetate copolymer. This method is simple to operate; no solvent is needed to aid dissolution when mixing all materials, nor is high-temperature melting required. Stirring at 55-60℃ is sufficient. Low-temperature melting and mixing not only ensures uniform mixing but also avoids the risk of partial decomposition of low-melting-point substances. The mixed material is extruded using a screw extruder, granulated under hot water, and then dried to obtain the product. Since hot water can dissolve and remove free maleic anhydride monomers that did not participate in the grafting reaction, the product is purified. The specific technical solution of this invention is as follows.

[0011] A method for preparing maleic anhydride-grafted modified ethylene-vinyl acetate copolymer includes the following steps:

[0012] At 55-60℃, add EVA, along with pre-mixed maleic anhydride and initiator, and mix thoroughly.

[0013] The product is extruded at 160-180℃ in a screw press, granulated and dried in hot water to obtain a maleic anhydride-grafted modified ethylene-vinyl acetate copolymer.

[0014] In the preparation method of this invention, EVA is added beforehand, and the material mixer is started and continuously stirred. The material temperature is controlled at 55-60°C by adjusting the rotation speed. During stirring, pre-mixed maleic anhydride and an initiator (e.g., dicumyl peroxide) are added. Taking dicumyl peroxide (DCP) as the initiator as an example, since the melting point of MAH is 51-56°C and that of DCP is 39-41°C, controlling the material temperature at 55-60°C, without using any solvent and ensuring that the maleic anhydride monomer does not decompose, the molten MAH and DCP are thoroughly mixed with EVA by adjusting the rotation speed. Microscopic observation reveals that the surface of the EVA particles is uniformly covered. Subsequently, extrusion at 160-180°C in a screw extruder is easier to operate and facilitates large-scale industrial production. Compared with the solution grafting method, this invention uses a melt grafting method, which effectively avoids the use of toxic and harmful solvents to dissolve the raw materials.

[0015] Furthermore, the mass fraction of vinyl acetate in the EVA is 12-28%.

[0016] Furthermore, the mass fraction of vinyl acetate in the EVA is 28%.

[0017] Furthermore, the extrusion temperature in the screw extruder is 165-175℃.

[0018] Furthermore, the extrusion temperature in the screw extruder is 165-170℃.

[0019] Furthermore, the temperature of the hot water is 80-95℃.

[0020] Furthermore, the temperature of the hot water is 90°C.

[0021] Furthermore, the mass ratio of EVA, maleic anhydride and initiator is 100:(1-6):(0.2-0.6).

[0022] Furthermore, the mass ratio of EVA, maleic anhydride, and initiator is 100:4:0.5.

[0023] Furthermore, the initiator is a peroxide. For example, benzoyl peroxide, dicumyl peroxide, or tert-butyl peroxynil can be selected.

[0024] Furthermore, the initiator is dicumyl peroxide.

[0025] The present invention also provides a maleic anhydride graft-modified ethylene-vinyl acetate copolymer prepared by the above preparation method.

[0026] Compared with the prior art, the advantages of the present invention are:

[0027] 1. The melt grafting method used in this invention keeps the mixing temperature of the raw materials within a low temperature range of 55-60℃, which ensures that the low melting point raw materials do not decompose and can melt and be fully mixed at their melting point. Low temperature conditions are easier to obtain and operate, and can effectively avoid the use of toxic and harmful solvents to dissolve raw materials, making the production process more environmentally friendly.

[0028] 2. This invention uses a screw extruder to extrude the product under reaction conditions of 160-180℃, resulting in a rapid reaction, convenient operation, and suitability for industrial production. The method of granulation followed by drying in hot water can dissolve and remove residual free monomer maleic anhydride in hot water. Attached Figure Description

[0029] Figure 1 This is a microscopic image of EVA before mixing.

[0030] Figure 2 This is a microscopic image of EVA, maleic anhydride, and DCP after they have been heated and mixed in a material mixer.

[0031] Figure 3 Microscopic photograph of PP:EVA after being blended at a mass ratio of 1:1.

[0032] Figure 4 The image shows a microscopic photograph of the blended system of PP, EVA, and sample 1 in Example 1, after being blended in a mass ratio of 49.5:49.5:1.

[0033] Figure 5 The image shows a microscopic photograph of the blended system of PP, EVA, and sample 2 in Example 2, after being blended in a mass ratio of 49.5:49.5:1.

[0034] Figure 6 The image shown is a microscopic photograph of the blended system of PP, EVA, and sample 3 in Example 3, after being blended in a mass ratio of 49.5:49.5:1.

[0035] Figure 7 The image shows a microscopic photograph of the blended system of PP, EVA, and sample 5 in Comparative Example 1, after being blended in a mass ratio of 49.5:49.5:1. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0037] In some embodiments of the present invention, the method for preparing maleic anhydride graft-modified ethylene-vinyl acetate copolymer includes the following steps:

[0038] S1. At 55-60℃, add EVA, along with pre-mixed maleic anhydride and initiator, and mix thoroughly.

[0039] S2. Extrusion at 160-180℃ in a screw press, followed by granulation and drying under hot water, yields maleic anhydride-grafted modified ethylene-vinyl acetate copolymer.

[0040] Optionally, the EVA contains 12-28% vinyl acetate by mass. Specifically, the EVA contains 28% vinyl acetate by mass.

[0041] Optionally, the extrusion temperature in the screw extruder is 165-175°C. Further, the extrusion temperature in the screw extruder is 165-170°C.

[0042] Optionally, the temperature of the hot water is 80-95°C. Further, the temperature of the hot water is 90°C.

[0043] Optionally, the mass ratio of EVA, maleic anhydride, and initiator is 100:(1-6):(0.2-0.6). Specifically, the mass ratio of EVA, maleic anhydride, and initiator is 100:4:0.5.

[0044] Optionally, the initiator is a peroxide. For example, benzoyl peroxide, dicumyl peroxide, or tert-butyl peroxyheptaate can be selected. Further, the initiator is dicumyl peroxide.

[0045] Example 1

[0046] In the preparation method of maleic anhydride graft-modified ethylene-vinyl acetate copolymer provided in this embodiment, the ethylene-vinyl acetate copolymer (EVA) used has a vinyl acetate mass fraction of 28%. A microscopic photograph of the EVA before mixing is shown below. Figure 1 As shown; dicumyl peroxide (DCP) was selected as the initiator, and the mass ratio of EVA, MAH, and DCP was 100:4:0.5. The specific steps are as follows:

[0047] S1. Weigh out EVA, MAH and DCP, and mix MAH and DCP evenly beforehand;

[0048] First, add EVA to the material mixer, start the mixer and stir continuously, controlling the material temperature to 56℃ by adjusting the speed. During stirring, add pre-mixed MAH and DCP powders, adjusting the speed to ensure thorough mixing. Maintain the material temperature at 56℃ throughout the process.

[0049] Take a picture of the mixed material under an electron microscope, such as... Figure 2 .

[0050] S2. Set the screw extruder temperature to 170℃. After the temperature stabilizes, add the mixed material from S1 into the screw extruder and extrude it. Then granulate it in hot water at 80℃ and dry it to obtain sample 1. After testing, the grafting rate of sample 1 is 1.76%.

[0051] Microscopic images of polypropylene (PP) and ethylene-vinyl acetate copolymer (EVA) blended at a mass ratio of 1:1 (blank control) are shown below. Figure 3 As shown. A microscopic photograph of the mixture of polypropylene (PP), ethylene-vinyl acetate copolymer (EVA), and sample 1 at a mass ratio of 49.5:49.5:1 is shown. Figure 4 As shown in the figure, compared to the blend without sample 1, the blend with sample 1 has smaller voids and a significant compatibility effect.

[0052] Example 2

[0053] The preparation method of maleic anhydride graft-modified ethylene-vinyl acetate copolymer provided in this embodiment is basically the same as that in Example 1, except that: the screw extruder temperature is set to 175°C; benzoyl peroxide is used as the initiator; and granulation is carried out in hot water at 80°C. The final sample 2 has a grafting rate of 1.73%.

[0054] A microscopic photograph of the blended system after polypropylene (PP), ethylene-vinyl acetate copolymer (EVA), and sample 2 were blended at a mass ratio of 49.5:49.5:1 is shown below. Figure 5 As shown in the figure, compared to the blend without sample 2, the blend with sample 2 has smaller voids and a significant compatibility effect.

[0055] Example 3

[0056] The preparation method of maleic anhydride graft-modified ethylene-vinyl acetate copolymer provided in this embodiment is basically the same as that in Example 1, except that: tert-butyl peroxynil is used as the initiator; the screw extruder temperature is set to 165°C; and granulation is carried out in hot water at 95°C. The final sample 3 has a grafting rate of 1.70%.

[0057] A microscopic photograph of the blended system after blending polypropylene (PP), ethylene-vinyl acetate copolymer (EVA), and sample 3 at a mass ratio of 49.5:49.5:1 is shown below. Figure 6 As shown in the figure, compared to the blend without sample 3, the blend with sample 3 has smaller voids and a significant compatibility effect.

[0058] Example 4

[0059] The preparation method of maleic anhydride graft-modified ethylene-vinyl acetate copolymer provided in this embodiment is basically the same as that in Example 1, except that the mass fraction of vinyl acetate in the ethylene-vinyl acetate copolymer (EVA) is 12%, and other conditions are the same as in Example 1. Sample 4 with a grafting rate of 1.75% was finally obtained.

[0060] Comparative Example 1

[0061] The preparation method of the maleic anhydride graft-modified ethylene-vinyl acetate copolymer provided in this comparative example is basically the same as that in Example 1, except that the hot water temperature for granulation is 60°C, and sample 5 with a grafting rate of 1.94% is obtained.

[0062] A microscopic photograph of the blended system after polypropylene (PP), ethylene-vinyl acetate copolymer (EVA), and sample 5 were blended at a mass ratio of 49.5:49.5:1 is shown below. Figure 7 As shown. By comparison Figure 4 (Example 1) and Figure 7 It can be seen that the compatibilizer after granulation at 80℃ hot water has a better compatibility effect. The reason may be that too much free maleic anhydride will affect the compatibility effect.

[0063] Comparative Example 2

[0064] The preparation method of the maleic anhydride graft-modified ethylene-vinyl acetate copolymer provided in this comparative example is basically the same as that in Example 1, except that the material temperature is maintained at 50 and 65°C when mixing EVA, MAH and DCP, respectively, to obtain sample 6 with a grafting rate of 1.5% and sample 7 with a grafting rate of 1.62%.

[0065] Polypropylene (PP), ethylene-vinyl acetate copolymer (EVA), and sample 6 / sample 7 were blended at a mass ratio of 49.5:49.5:1. The images of the blended system observed under a microscope show that, compared with Example 1, the maleic anhydride melting effect was poor and the material was not mixed evenly below 50°C, resulting in a decrease in the grafting rate of the sample; above 60°C, the grafting rate of the sample decreased due to the partial decomposition of maleic anhydride.

[0066] Comparative Example 3

[0067] The preparation method of the maleic anhydride graft-modified ethylene-vinyl acetate copolymer provided in this comparative example is basically the same as that in Example 1, except that the screw extruder temperature is set to 150 and 190°C respectively, and sample 8 with a grafting rate of 1.61% and sample 9 with a grafting rate of 1.68% are obtained respectively.

[0068] After polypropylene (PP), ethylene-vinyl acetate copolymer (EVA) and sample 8 / sample 9 were blended at a mass ratio of 49.5:49.5:1, the photos of the blended system were observed under a microscope. Compared with Example 1, it can be seen that the grafting rate decreased regardless of whether the extrusion temperature was increased or decreased, and the color of samples 8 and 9 became darker.

[0069] Comparative Example 4

[0070] The preparation method of the maleic anhydride graft-modified ethylene-vinyl acetate copolymer provided in this comparative example is basically the same as that in Example 1, except that the mass fraction of vinyl acetate in EVA is 8% and 35%, respectively, and sample 10 with a grafting rate of 1.2% and sample 11 with a grafting rate of 2.8% are obtained respectively.

[0071] Polypropylene (PP), ethylene-vinyl acetate copolymer (EVA), and sample 10 / sample 11 were blended at a mass ratio of 49.5:49.5:1. The images of the blended system were observed under a microscope. Compared with Example 1, it can be seen that when the vinyl acetate content in EVA is too low, the grafting rate is lower than the experimental design requirement of more than 1.7%; when the vinyl acetate content in EVA is too high, it is easy to lead to overperformance, and EVA with high vinyl acetate content has a higher cost.

[0072] The above detailed embodiments describe the implementation of the present invention; however, the present invention is not limited to the specific details described in the above embodiments. Within the scope of the claims and technical concept of the present invention, various simple modifications and changes can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing maleic anhydride-grafted modified ethylene-vinyl acetate copolymer, characterized in that, Includes the following steps: EVA, along with pre-mixed maleic anhydride and initiator, are added at 55-60℃ and mixed thoroughly. The mass fraction of vinyl acetate in the EVA is 12-28%, and the mass ratio of EVA, maleic anhydride, and initiator is 100:(1-6):(0.2-0.6). The mixture is extruded at 160-180℃ in a screw press, granulated and dried in hot water to obtain a maleic anhydride-grafted modified ethylene-vinyl acetate copolymer; the temperature of the hot water is 80-95℃.

2. The method for preparing maleic anhydride-grafted modified ethylene-vinyl acetate copolymer according to claim 1, characterized in that, The mass fraction of vinyl acetate in the EVA is 28%.

3. The method for preparing maleic anhydride-grafted modified ethylene-vinyl acetate copolymer according to claim 1, characterized in that, The extrusion temperature in the screw extruder is 165-175℃.

4. The method for preparing a maleic anhydride-grafted modified ethylene-vinyl acetate copolymer according to claim 3, characterized in that, The extrusion temperature in the screw extruder is 165-170℃.

5. The method for preparing a maleic anhydride-grafted modified ethylene-vinyl acetate copolymer according to claim 1, characterized in that, The temperature of the hot water is 90℃.

6. The method for preparing a maleic anhydride-grafted modified ethylene-vinyl acetate copolymer according to claim 1, characterized in that, The mass ratio of EVA, maleic anhydride and initiator is 100:4:0.

5.

7. The method for preparing a maleic anhydride-grafted modified ethylene-vinyl acetate copolymer according to claim 1, characterized in that, The initiator is one of benzoyl peroxide, dicumyl peroxide, and tert-butyl peroxyheptanate.

8. The method for preparing a maleic anhydride-grafted modified ethylene-vinyl acetate copolymer according to claim 7, characterized in that, The initiator is dicumyl peroxide.

9. A maleic anhydride-grafted modified ethylene-vinyl acetate copolymer prepared by the preparation method according to any one of claims 1-8.

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