Maleic anhydride grafted polyethylene composition with high grafting rate and low gel content as well as preparation method and application of maleic anhydride grafted polyethylene composition

Abstract

The invention belongs to the technical field of high polymer materials, and particularly relates to a maleic anhydride grafted polyethylene composition with high grafting rate and low gel content as well as a preparation method and application thereof. The maleic anhydride grafted polyethylene composition is prepared from raw materials such as linear low-density polyethylene, EVA (Ethylene Vinyl Acetate), r-PP (Resin-Propene Polymer), a compound initiator and MAH (Maleic Anhydride). In the maleic anhydride grafted polyethylene composition, the r-PP and the compound initiator are used as an initiation system to synergistically improve the reaction degree so as to improve the grafting rate; in addition, the synergistic initiator system reduces the dosage of a compound initiator, so that the influence of a cage shielding effect caused by excessive initiators on the gel content of the product is avoided while the cost is reduced; the grafting rate is further improved by adding a small amount of EVA. Therefore, when a product with a high grafting rate (greater than 0.9%) is obtained, the gel content is low (less than 4%), a blow-molded casting product has few crystal points, and the product also has good mechanical properties and can be better applied to the field of high-end functional adhesives.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials. More specifically, it relates to a maleic anhydride grafted polyethylene composition with a high grafting rate and a low gel content, and a preparation method and application thereof. Background Art

[0002] Polyolefins are the most consumed and produced general plastics in the world today. However, due to their low polarity, their adhesiveness, antistatic property, hydrophilicity, etc. are relatively poor, which limits their applications in many fields. By introducing polar groups through grafting, the deficiencies in the properties of polyolefins can be effectively improved. Among them, maleic anhydride grafted products are the most widely used and have the highest demand. Currently, the total market demand for maleic anhydride grafted products > 200,000 tons, including types such as maleic anhydride grafted PE, PP, POE, ethylene-propylene-diene rubber, etc., and are involved in aspects such as compatibilizers, toughening agents, hot melt adhesives, etc. The grafted products for high-end application functional adhesives require a high grafting rate, a low gel content, and a low residual monomer rate, which have relatively high requirements for the quality and process equipment of the grafted products. Due to the influence of side reactions during the grafting process, it is difficult to prepare grafted products with a high grafting rate, high quality, and good production stability, and it is necessary to suppress the degree of side reactions occurring during the reaction grafting process.

[0003] Scholars such as Li Ming (Li Ming, Zhang Changming, Huang Fenghua, etc. Preparation of maleic anhydride modified polyethylene with high grafting rate and low gel content [J]. China Plastics, 2001, (08): 46 - 48. DOI: 10.19491 / j.issn.1001 - 9278.2001.08.010.) studied the influence of diphenyl phosphite on the grafting rate and gel content of maleic anhydride grafted polyethylene, and found that it has a good effect of inhibiting crosslinking, thereby reducing the gel content. However, the effect of this method is limited by the dosage and feeding time of diphenyl phosphite. When the dosage of diphenyl phosphite is too large, although the gel content can be significantly reduced, it will also cause a significant decrease in the grafting rate, which may affect the performance of the product. In addition, precise control of the feeding time is also required, increasing the complexity of production operations.

[0004] Therefore, there is an urgent need to develop a new process for preparing maleic anhydride modified polyethylene that does not require precise control of the feeding time and can maintain a high grafting rate while significantly reducing the gel content. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the existing technical problems and provide a maleic anhydride grafted polyethylene composition with a high grafting rate and a low gel content.

[0006] The object of the present invention is to provide the maleic anhydride grafted polyethylene composition with a high grafting rate and a low gel content.

[0007] Another object of the present invention is to provide an application of the maleic anhydride grafted polyethylene composition with high grafting rate and low gel content.

[0008] The above object of the present invention is achieved by the following technical solutions:

[0009] The present invention protects a maleic anhydride grafted polyethylene composition, which comprises the following components in parts by weight: 80-95 parts of linear low density polyethylene (LLDPE); 5-20 parts of ethylene-vinyl acetate copolymer (EVA); 1-3 parts of irradiated pre-treated polypropylene (r-PP); 1-2 parts of maleic anhydride (MAH); 0.05-0.2 parts of a compound initiator.

[0010] Among them, the compound initiator includes a first initiator and a second initiator; the first initiator is a non-cyclic alkyl peroxide initiator, and the second initiator is a cyclic alkyl peroxide initiator.

[0011] The present invention selects r-PP and a compound initiator as an initiation system. Among them, r-PP can form free radicals inside PP, and the generated free radicals remain inside the particles. When the grafting reaction is carried out under high temperature conditions, it can serve as a stable active initiation point, selectively react with MAH, quickly and efficiently form reactive free radical sites, and cooperate with the compound initiator to improve the reaction degree and thus increase the grafting rate. In addition, the synergistic initiator system reduces the dosage of the compound initiator, while reducing costs, avoiding the influence of the cage effect caused by excessive initiators on the gel content of the product. The present invention also introduces a small amount of EVA to increase the grafting rate. The vinyl acetate groups on the side chains of EVA can form weak hydrogen bonds with MAH, which is beneficial to the dispersion of MAH in the resin matrix and improves the grafting priority.

[0012] Furthermore, the maleic anhydride grafted polyethylene composition further comprises 0.05-0.1 parts of an antioxidant; 0-0.03 parts of a polymerization inhibitor and 0-0.5 parts of an odor removal masterbatch.

[0013] Specifically, the mass percentage of LLDPE in the maleic anhydride grafted polyethylene composition is not less than 76%.

[0014] Specifically, LLDPE can be 83 parts, 85 parts, 88 parts, 90 parts, 93 parts, etc., or an interval range formed by any of the above values.

[0015] Preferably, the non-cyclic alkyl peroxide initiator is selected from one or more of dicumyl peroxide, bis(tert-butylperoxyisopropyl)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, tert-butylperoxyisopropylbenzene, and di-tert-butyl peroxide.

[0016] Preferably, the cyclic alkyl peroxide initiator is selected from one or more of 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxynonane and 3,6,9-trimethyl-3,6,9-tris(ethyl-propyl) derivative.

[0017] Furthermore, the structure of the 3,6,9-trimethyl-3,6,9-tris(ethyl-propyl) derivative is shown as follows: It is commercially available.

[0018] Furthermore, the half-life of the cyclic alkyl peroxide initiator is >1 min at a temperature of 180 °C. Generally speaking, the longer the half-life of the initiator at a certain temperature, the slower the decomposition, the milder the reaction, and generally fewer side reactions.

[0019] Preferably, the mass ratio of the acyclic alkyl peroxide initiator to the cyclic alkyl peroxide initiator is 1:(0.3 - 4), more preferably 1:(0.5 - 1.5).

[0020] Furthermore, when using the composite initiator, a polar organic solvent can be added and fully dissolved before use.

[0021] Furthermore, the polar organic solvent is selected from one or more of N,N-dimethylformamide and N,N-dimethylacetamide.

[0022] Furthermore, the mass ratio of the composite initiator to the polar organic solvent is (3 - 5):1.

[0023] Preferably, the density of the r-PP before irradiation is 0.89 - 0.90 g / cm 3 , and the melt index is 2 - 4 g / 10 min. The test standard for the melt index is ASTM D1238, and the test conditions are a temperature of 190 °C and a load of 2.16 kg.

[0024] Furthermore, the melt index of the r-PP is 15 - 40 g / 10 min. The test standard for the melt index is ASTM D1238, and the test conditions are a temperature of 190 °C and a load of 2.16 kg.

[0025] Furthermore, the preparation method of the r-PP includes the following steps: irradiating polypropylene with an electron beam at an irradiation dose of 1 - 2 Mrad for 30 - 45 s to obtain it.

[0026] Even further, the polypropylene is placed at room temperature and sealed for 16 - 24 h before irradiation and then irradiated.

[0027] Preferably, the melt index of the linear low density polyethylene is 0.8 - 25 g / 10 min. The test standard for the melt index is ASTM D1238, and the test conditions are a temperature of 230 °C and a load of 2.16 kg.

[0028] Preferably, the melt index of the linear low density polyethylene is 15 - 22 g / 10 min.

[0029] Preferably, the density of the linear low density polyethylene is 0.910 - 0.930 g / cm 3 。

[0030] Preferably, the ethylene vinyl acetate (VA) content of the ethylene - vinyl acetate copolymer is 15% - 30%, preferably 25 - 30%.

[0031] Furthermore, the inhibitor is selected from one or more of triphenyl phosphite, 1,1 - diphenyl - 2 - picrylhydrazyl, dimethyl carbonate, cuprous chloride.

[0032] Furthermore, the antioxidant is selected from one or more of antioxidant 1010, antioxidant 300, antioxidant 168.

[0033] The maleic anhydride grafted polyethylene composition of the present invention can be processed and formed by any common process in the art. For example, after mixing the components, extrusion granulation is carried out to obtain the maleic anhydride grafted polyethylene composition. To fully mix the components, a process preferably including the following steps is adopted:

[0034] S1. Fully mix the linear low density polyethylene with the ethylene - vinyl acetate copolymer, irradiated pre - treated polypropylene, deodorizing masterbatch, and antioxidant to obtain a mixed material;

[0035] S2. Heat maleic anhydride to a molten state, dilute the compounded initiator and inhibitor with white oil, then mix them evenly with the mixed material obtained in step S1, carry out melt extrusion, pelletize, and dry to obtain the maleic anhydride grafted polyethylene composition.

[0036] Furthermore, the mass ratio of the compounded initiator to white oil is 1:(3 - 8).

[0037] Furthermore, the temperature of the melt extrusion is 170 - 200 °C.

[0038] Furthermore, in step S1, the full mixing is to first premix the raw materials and then further mix them evenly through a high - speed mixer.

[0039] Furthermore, in step S2, the heating temperature is 80 - 90 °C, and the heating time is 1 - 2 h.

[0040] Further, the specific operation of heating to the molten state is as follows: maleic anhydride is heated to 80-90 °C and kept at a constant temperature for 1-2 h by a high-temperature liquid pump.

[0041] Further, in step S2, the extrusion is carried out using a twin-screw extruder.

[0042] The present invention also protects the application of the maleic anhydride grafted polyethylene composition in the preparation of adhesives.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] The present invention uses raw materials such as linear low-density polyethylene, EVA, r-PP, a compound initiator, and MAH to prepare a maleic anhydride grafted polyethylene composition. In the above maleic anhydride grafted polyethylene composition, r-PP and the compound initiator act as an initiation system to synergistically increase the reaction degree and thus increase the grafting rate; in addition, the synergistic initiator system reduces the dosage of the compound initiator, avoiding the influence of the cage effect caused by excessive initiator on the gel content of the product while reducing costs; the addition of a small amount of EVA further increases the grafting rate. Therefore, the present invention obtains a product with a high grafting rate (>0.9%) and a low gel content (<4%), the blown film and cast film products have fewer crystal points, and also have good mechanical properties, and can be better applied to the field of high-end functional adhesives. Specific Embodiments

[0045] The following specific examples are used to further illustrate the present invention, but the examples do not limit the present invention in any form. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field.

[0046] The raw materials of the examples and comparative examples are as follows:

[0047] Linear low-density polyethylene-1 (LLDPE-1): LLDPE M2320, melt index is 20 g / 10 min, test standard ASTM D1238, test conditions 190 °C, 2.16 Kg; density is 0.925 g / cm 3 ; Manufacturer: Maoming Petrochemical.

[0048] Linear low-density polyethylene-2 (LLDPE-2): LLDPE 7042, melt index is 2.0 g / 10 min, test standard ASTM D1238, test conditions 190 °C, 2.16 Kg; density is 0.920 g / cm 3 ; Manufacturer: Sichuan Petrochemical.

[0049] Linear Low Density Polyethylene - 3 (LLDPE - 3): LLDPE 2010PA, melt index is 1.0 g / 10 min, test standard ASTM D1238, test conditions 190 °C, 2.16 Kg; density is 0.920 g / cm 3 ; Manufacturer: ExxonMobil.

[0050] Ethylene - Vinyl Acetate Copolymer - 1 (EVA - 1): EVA 00328, VA content is 28%, manufacturer: ExxonMobil.

[0051] Ethylene - Vinyl Acetate Copolymer - 2 (EVA - 2): EVA 18J3 (grade), VA content is 18%, manufacturer: Yanshan Petrochemical.

[0052] Irradiated Pretreated Polypropylene (r - PP): Self - made, melt index is 20 - 35 g / 10 min, test standard ASTM D1238, test conditions 190 °C, 2.16 Kg; Polypropylene before treatment: melt index is 2 - 4 g / 10 min, test standard ASTM D1238, test conditions 190 °C, 2.16 Kg; density is 0.90 g / cm3; manufacturer: Maoming Petrochemical.

[0053] The irradiation conditions for polypropylene are as follows: The polypropylene resin particles are encapsulated in a transparent self - sealing bag, filled with a little air, placed at room temperature for 24 h, and then irradiated with high - energy electron beam. The irradiation dose is 1 Mrad and the irradiation time is 30 s.

[0054] Maleic Anhydride (MAH): Maleic anhydride, commercially available.

[0055] Compound Initiator - 1: Mass ratio (First Initiator - 1: Second Initiator) = 1:1.

[0056] Compound Initiator - 2: Mass ratio (First Initiator - 1: Second Initiator) = 3:1.

[0057] Compound Initiator - 3: Mass ratio (First Initiator - 2: Second Initiator) = 1:3.

[0058] First Initiator - 1: Dicumyl peroxide, commercially available.

[0059] First Initiator - 2: (2,4 - Di - tert - butylperoxyisopropylbenzene), commercially available.

[0060] Second Initiator: 3,6,9 - Triethyl - 3,6,9 - trimethyl - 1,4,7 - triperoxynonane, Trigonox 301, manufacturer: Nouryon company.

[0061] When using a single initiator, it is mixed and used in a mass ratio of 4:1.

[0062] Inhibitor: triphenyl phosphite, commercially available.

[0063] Antioxidant: 168, commercially available.

[0064] Deodorizing masterbatch: SW-100, manufacturer: Foshan Yite.

[0065] Unless otherwise specified, the components used in the parallel embodiments and comparative examples are all the same commercially available products.

[0066] Example 1 Maleic anhydride grafted polyethylene composition and preparation method thereof

[0067] The weight parts of the raw materials used in Example 1 are shown in Table 1.

[0068] A method for preparing a maleic anhydride grafted polyethylene composition with a high grafting rate and low gel content, the specific steps comprising:

[0069] LLDPE is premixed with EVA, r-PP, deodorizing masterbatch and antioxidant, and the materials are added after being fully mixed in a high-speed mixer. MAH is heated to 90°C by a high-temperature liquid pump and kept at a constant temperature for 2 hours and then injected from the third screw barrel. The compound initiator and inhibitor are diluted with white oil and injected from the fourth screw barrel through a horizontal flow pump. Subsequently, the mixture is extruded at a temperature of 170-200°C by a twin-screw extruder and pelletized by underwater cutting. After drying at 80°C for 6 hours, a maleic anhydride grafted polyethylene composition can be obtained.

[0070] Examples 2 to 8 Maleic anhydride grafted polyethylene composition and preparation method thereof

[0071] The weight parts of the raw materials used in the following examples are shown in Table 1.

[0072] The specific preparation steps of the following examples are the same as those of Example 1.

[0073] Comparative Examples 1 to 7 Maleic anhydride grafted polyethylene compositions

[0074] The weight parts of the raw materials used in the following comparative examples are shown in Table 2.

[0075] The specific preparation steps of other comparative examples are the same as those of Example 1.

[0076] Table 1 Weight parts of raw materials used in each embodiment

[0077]

[0078]

[0079] Table 2 Weight parts of raw materials used in each comparative example

[0080] Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 LLDPE-1 90 90 90 90 90 90 90 EVA-1 / 12 12 12 12 12 12 r-PP 2 2.1 / 8 2 2 2 MAH 1.5 1.5 1.5 1.5 1.5 1.5 1.5 Compound Initiator-1 0.1 / 2.1 0.1 0.4 / / First Initiator-1 / / / / / 0.1 / Second Initiator / / / / / / 0.1 Antioxidant 0.08 0.08 0.08 0.08 0.08 0.08 0.08 Polymerization Inhibitor 0.02 0.02 0.02 0.02 0.02 0.02 0.02 Deodorant Masterbatch 0.4 0.4 0.4 0.4 0.4 0.4 0.4

[0081] Experimental Example Performance Measurement

[0082] The maleic anhydride grafted polyethylene compositions prepared in the above examples and comparative examples were tested using the following test methods.

[0083] (1) Absolute Grafting Rate Test

[0084] Acid-base titration method: Weigh 0.5 g of maleic anhydride grafted polyethylene and dissolve it in 50 mL of hot xylene. After complete dissolution, add V1 mL of C1 mol / L KOH-ethanol solution to the system, reflux for 10 min, and allow the anhydride groups in maleic anhydride to react fully with the base. Then, add a small amount of deionized water to the system while it is still hot to promote the hydrolysis of the anhydride into carboxylic acid. At the same time, add 3 drops of phenolphthalein indicator solution and titrate to the end point with C2 mol / L hydrochloric acid-isopropanol mixed solution. If the concentration of hydrochloric acid / isopropanol is C2 (mol / L), the volume of the solution consumed for titrating M (g) of the sample is V2 (mL), then the grafting rate G is calculated by the following formula:

[0085]

[0086] V1 - Volume of the excess KOH-ethanol solution, mL;

[0087] V2 - Volume of the hydrochloric acid-isopropanol solution in the back titration, mL;

[0088] C1 - Concentration of the KOH-ethanol standard solution, mol / L;

[0089] C2 - Concentration of the hydrochloric acid-isopropanol solution, mol / L;

[0090] m - Mass of the purified graft, g.

[0091] (2) Gel Content Determination

[0092] Weigh the weight of the specimen m1, soak the specimen in xylene at 120 °C, carry out condensation reflux and maintain for 48 h. Take out the insoluble matter after soaking, dry it in vacuum and weigh the weight of the insoluble matter m2. The gel content = m2 / m1 * 100%.

[0093] (3) Melt Index Test

[0094] The test standard is ASTM D1238, and the test is carried out under the conditions of 190 °C and 2.16 Kg.

[0095] (4) Conventional Mechanical Properties

[0096] Press tablets on a flat vulcanizer at 180 °C for 10 min, with a pressure of 15 Mpa and a sample thickness of 3 mm. Test the tensile strength and elongation at break, referring to the standard GB / T 1040.2-2022.

[0097] Tables 3 and 4 show the performance test results of each example and comparative example respectively.

[0098] Performance test results of each example in Table 3

[0099]

[0100]

[0101] Performance test results of each comparative example in Table 4

[0102] Index / Group Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 Grafting Ratio % 0.78 0.70 0.76 0.82 0.82 0.84 0.80 Gel Content % 2.78 1.78 8.84 10.22 11.75 6.12 2.82 Melt Index g / 10min 1.74 2.25 0.28 0.24 0.11 1.45 1.88 Tensile Strength Mpa 15.5 15.7 16.1 16.2 16.8 15.8 16.0 Elongation at Break % 412 436 225 256 227 324 389

[0103] As shown in Tables 3 and 4, it can be seen from the above data that:

[0104] It can be seen from the results of Examples 1 to 3 that for LLDPE resin substrates with different melt indices, the higher the melt index of the substrate, the stronger the fluidity, the easier it is to graft, and after grafting, the gel content is low and the melt index is relatively high, which is beneficial to subsequent application processing.

[0105] It can be seen from the results of Examples 1 and 4 that Examples 1 and 4 use EVA with different VA contents, and the higher the VA content, the higher the grafting rate.

[0106] It can be seen from the results of Examples 1, 5, and 6 that Examples 1, 5, and 6 use compound initiators in different proportions. When there is more of the first initiator, the reaction rate is too fast, the actual gel content increases, side reactions increase, and the grafting rate decreases slightly. When the proportion of the second initiator is relatively large, the reaction rate is relatively slow, and the grafting rate drops to 0.92.

[0107] Compared with Example 1, in Comparative Example 1, no EVA was added, and the grafting rate decreased.

[0108] Compared with Example 1, in Comparative Example 2, only r-PP was added and no initiator was added, and the grafting rate decreased.

[0109] Compared with Example 1, in Comparative Example 3, when no r-PP was added and the grafting reaction was only initiated by the initiator, the grafting rate was slow and the grafting rate decreased.

[0110] Compared with Example 1, in Comparative Example 4, too much r-PP was added. During the actual grafting process, the free radical content was too high, and the cage effect was likely to occur, resulting in local free radical aggregation, an increase in cross-linking side reactions, a significant increase in the actual gel content, and a significant decline in mechanical properties, which was not conducive to subsequent applications.

[0111] Compared with Example 1, in Comparative Example 5, the initiator content was too high, and similarly, the free radical content was too high, and the cage effect was likely to occur, resulting in a high gel content.

[0112] Comparative Example 6 and Comparative Example 7, compared with Example 1, use a single initiator, and the reaction rate is faster or slower, unable to maintain the balance between high grafting efficiency and the need to suppress side reactions. The grafting rate decreases significantly compared with Example 1, and the gel content increases.

[0113] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A maleic anhydride grafted polyethylene composition, characterized in that: The composition comprises the following components by weight: 80-95 parts of linear low-density polyethylene; 5-20 parts of ethylene-vinyl acetate copolymer; 1-3 parts of radiation pretreated polypropylene; 1-2 parts of maleic anhydride; and 0.05-0.2 parts of compound initiator. Wherein, the composite initiator comprises a first initiator and a second initiator; the first initiator is a non-cyclic alkyl peroxide initiator, and the second initiator is a cyclic alkyl peroxide initiator.

2. The maleic anhydride grafted polyethylene composition according to claim 1, characterized in that: The maleic anhydride grafted polyethylene composition further comprises 0.05-0.1 parts of antioxidant, 0-0.03 parts of polymerization inhibitor and 0-0.5 parts of deodorizing masterbatch.

3. The maleic anhydride grafted polyethylene composition according to claim 1, characterized in that: The non-cyclic alkyl peroxide initiator is selected from one or more of diisopropylbenzene peroxide, bis(tert-butylperoxide isopropyl)benzene, 2,5-dimethyl-2,5-di-tert-butylperoxide, tert-butylperoxide isopropylbenzene, and di-tert-butyl peroxide.

4. The maleic anhydride grafted polyethylene composition according to claim 1, characterized in that: The cyclic alkyl peroxide initiator is selected from one or more of 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxynonane and 3,6,9-trimethyl-3,6,9-tri(ethyl-propyl) derivatives.

5. The maleic anhydride grafted polyethylene composition according to any one of claims 1 to 4, characterized in that: The mass ratio of the non-cyclic alkyl peroxide initiator to the cyclic alkyl peroxide initiator is 1:(0.3-4).

6. The maleic anhydride grafted polyethylene composition according to claim 1, characterized in that: The melting index of the radiation pretreated polypropylene is 15 to 40 g / 10 min.

7. The maleic anhydride grafted polyethylene composition according to claim 1, characterized in that: The irradiation conditions of the polypropylene are as follows: the polypropylene is subjected to electron beam irradiation for 30 to 45 seconds under the condition of an irradiation dose of 1 to 2 Mrad.

8. The maleic anhydride grafted polyethylene composition according to claim 1, characterized in that: The ethylene-vinyl acetate copolymer has an ethylene acetate content of 15% to 30%.

9. The method for preparing the maleic anhydride grafted polyethylene composition according to any one of claims 1 to 8, comprising the following steps: mixing the components, extruding and granulating to obtain the maleic anhydride grafted polyethylene composition.

10. Use of the maleic anhydride grafted polyethylene composition according to any one of claims 1 to 8 in the preparation of an adhesive.

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