Polypropylene grafted modified master batch as well as preparation method and application thereof

Abstract

The invention discloses a polypropylene grafted modified master batch as well as a preparation method and application thereof, and relates to the technical field of functional material modification. According to the preparation method, the polypropylene resin and the maleic anhydride are subjected to solid-phase grafting, the grafting rate of the maleic anhydride is further improved, and then the solid-phase grafting product is subjected to melt extrusion. Compared with a common melt extrusion method for grafting maleic anhydride, the process has the advantages that the polarity, namely the adhesive force, of the final product is improved, and the odor in the production process and the color of the master batch product are improved.

Description

Technical Field

[0001] This invention belongs to the field of functional material modification technology, specifically relating to a polypropylene graft-modified masterbatch, its preparation method, and its application. Background Technology

[0002] Polypropylene (PP), one of the five major general-purpose thermoplastics, is widely used in the automotive, home appliance, and packaging industries due to its advantages such as low density, good mechanical properties, chemical resistance, ease of processing, and high cost-effectiveness. However, polypropylene is a non-polar crystalline polymer with low surface energy and a lack of active functional groups in its molecular chain. This results in extremely poor interfacial adhesion when it is compounded or bonded with polar materials (such as metals, nylon, polyester, and glass fiber); it is also difficult to print, coat, and dye. To overcome this defect, the most mainstream modification method in the industry is to introduce polar monomers (such as maleic anhydride MAH and acrylic acid) into the PP molecular chain through chemical grafting to prepare high-polarity PP.

[0003] Although the research and application of maleic anhydride-grafted polypropylene (PP-g-MAH) are relatively mature, there are still significant technical bottlenecks in the existing industrial preparation technology, mainly in the following aspects:

[0004] Firstly, the most commonly used method in industry is the twin-screw melt grafting method. This method requires a reaction temperature higher than the melting point of PP (typically 180–230°C). However, the tertiary carbon atoms in the PP molecular chain are highly sensitive to free radicals, and under the combined effects of initiator and high-temperature shear, they are prone to uncontrolled β-fracture reactions. This severe degradation effect leads to a sharp decrease in the molecular weight of the matrix resin, a decline in melt strength, and ultimately makes the modified material brittle and sticky, severely limiting its application in high-performance films or structural components. Existing technologies often struggle to maintain the high molecular weight of the PP matrix while achieving a high grafting rate.

[0005] Furthermore, maleic anhydride has a low boiling point and is prone to sublimation. In traditional melt grafting processes, MAH monomers are typically mixed directly with PP granules at the feed inlet. Due to the dense surface of PP granules, monomers have difficulty penetrating the interior, with most monomers adhering only to the surface. Upon entering the high-temperature zone of the extruder, MAH rapidly vaporizes or sublimates due to the high temperature before undergoing a grafting reaction with PP. This not only significantly reduces grafting efficiency, typically making it difficult to exceed 1%, but also results in a large amount of unreacted monomers remaining in the resin or volatilizing into the air, giving the product a strong, pungent odor and deteriorating the production environment.

[0006] To achieve a high grafting rate, existing technologies often require increasing the amount of initiator or raising the reaction temperature. This exacerbates side reactions, resulting in a large amount of residual small-molecule oligomers and oxidation products in the product, causing the prepared grafted masterbatch to turn yellow or even brown. This color deterioration severely affects its application in fields such as films and transparent sheets where appearance is critical.

[0007] Although solid-phase grafting can react at lower temperatures to inhibit PP degradation, its reaction time is long and the post-processing of the product is complicated, making it difficult to achieve continuous large-scale production. On the other hand, solution grafting, although the grafting is uniform, involves the recovery and treatment of a large amount of solvent, which puts great pressure on the environment and is costly.

[0008] In summary, existing technologies lack a preparation process that can effectively balance high grafting rates, low matrix degradation, and low odor / excellent appearance. How to improve the process route to enable monomers to uniformly penetrate and anchor within PP before the reaction, thereby achieving efficient grafting under lower initiation conditions, while simultaneously effectively removing residues through subsequent processes, is a key technical problem urgently needing to be solved in this field. Based on the above technical background, this invention proposes a two-step grafting modification process that combines the advantages of solid-phase pre-swelling and melt extrusion. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing polypropylene graft-modified masterbatch. This invention involves a two-step process: first, solid-phase grafting, followed by twin-screw melt extrusion. The solid-phase grafting step increases the maleic anhydride grafting rate, while the melt extrusion step not only further continues the grafting reaction but also removes unreacted MAH and some byproducts. It does not require large amounts of solvent, has low odor, and emits no toxic substances.

[0010] The technical solution is:

[0011] A method for preparing a polypropylene graft-modified masterbatch includes the following steps:

[0012] (1) Solid-phase grafting step: Polypropylene resin, maleic anhydride, initiator and interface agent for dissolving or dispersing maleic anhydride and initiator are mixed and reacted at a temperature below the melting point of polypropylene resin to obtain solid-phase grafting product.

[0013] (2) Melt extrusion step: The solid graft product obtained in step (1) is melt extruded to obtain the polypropylene graft modified masterbatch.

[0014] The polypropylene resin is selected from one or more combinations of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene.

[0015] The initiator is selected from one or more combinations of benzoyl peroxide, dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, and bis-tert-butyldicumyl peroxide;

[0016] The interface agent is selected from one or more combinations of acetone and xylene.

[0017] The proportions of the raw materials are as follows: based on 100 parts by weight of the polypropylene resin, the amount of maleic anhydride is 0.5-3 parts; the mass ratio of maleic anhydride to the initiator is 1:(0.2-0.8).

[0018] In step (1), a grafting aid is also added; the grafting aid is selected from one or more of oleic acid, styrene, acrylic acid, and acrylate monomers; the amount of the grafting aid is 0.01-0.3 parts based on 100 parts by weight of the polypropylene resin.

[0019] In step (1), a reactive antioxidant was also added;

[0020] The reactive antioxidant is selected from one or more combinations of 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione, 3,9-bis[2-(3-(3-tert-butyl-4-hydroxy-5-methylphenyl)acrylate)-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane, thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], or hindered phenolic derivatives containing acrylate double bonds;

[0021] Based on 100 parts by weight of the polypropylene resin, the amount of the reactive antioxidant is 0.1-2 parts.

[0022] In step (1), a multifunctional group synergistic monomer was also added;

[0023] The multifunctional synergistic monomer is selected from one or more combinations of trimethylolpropane triacrylate, tripropylene glycol diacrylate, pentaerythritol triacrylate, 1,6-hexanediol diacrylate, or other multifunctional unsaturated monomers containing at least two functional groups selected from vinyl, allyl, and epoxy groups.

[0024] Based on 100 parts by weight of the polypropylene resin, the amount of the multifunctional synergistic monomer is 0.1-2 parts.

[0025] The specific operations of step (1) include:

[0026] The maleic anhydride and initiator are dissolved in the interface agent and stirred at 30-50°C for 0.5-1 hour to obtain a reaction mixture.

[0027] The reaction mixture is mixed with the polypropylene resin and reacted at 100-150°C for 5-20 minutes.

[0028] The melt extrusion in step (2) uses a twin-screw extruder, with the process temperature of each zone set to 160-250℃ and the screw speed to 250-350r / min.

[0029] A polypropylene graft-modified masterbatch, which is prepared by any of the methods described herein.

[0030] The application of the aforementioned polypropylene graft-modified masterbatch in the preparation of composite materials, functional films, or as an adhesive layer. The beneficial effects of this invention are:

[0031] (1) This invention effectively improves the production environment and reduces product odor. This invention performs pre-solid-phase grafting treatment in the grafting process and preferably uses acetone as an interface agent instead of the traditional xylene. Acetone has a low boiling point and is easily volatile. Combined with the vacuum devolatilization process in the melt extrusion process, it can effectively remove solvent residues. Compared with direct melt grafting, this process significantly reduces the irritating odor in the production process and the VOC content in the final masterbatch, solving the problems of strong odor and high toxicity in the traditional process, and meeting environmental protection and occupational health requirements. (2) This invention innovatively adopts a two-step grafting process. The first step uses an interface agent to swell the polypropylene resin, bringing the maleic anhydride monomer and initiator into the surface and interior of the resin particles for low-temperature solid-phase pre-grafting, so that the monomer is anchored on the molecular chain before entering the extruder, reducing the sublimation loss of the monomer at high temperature. The second step further initiates the unreacted monomer to complete deep grafting through the strong shear and high-temperature melting of the twin-screw extruder. This synergistic effect greatly improves the final grafting rate of maleic anhydride, thereby giving the material stronger polarity and significantly improving its adhesion to metal or polar substrates in film applications. (3) This invention distributes the grafting load through solid-phase low-temperature reaction, reducing the excessive use of initiators in the high-temperature stage. At the same time, maintaining high-intensity vacuum operation during melt extrusion removes unreacted maleic anhydride monomers and small molecule byproducts in a timely manner, blocking the pathway for these residues to generate chromophores through subsequent oxidative crosslinking, thereby effectively inhibiting the discoloration of the masterbatch and producing a high-quality masterbatch with a white appearance. (4) A reactive antioxidant is introduced in the solid-phase grafting stage. This antioxidant, with its own reactive groups, can preferentially react with PP free radicals and graft itself onto the PP macromolecular chain. On the one hand, it effectively captures the free radicals that trigger PP degradation and blocks the β-fracture chain reaction, thereby protecting the molecular weight and mechanical properties of PP and retaining more active sites for MAH grafting; on the other hand, the thermal stability of the chemically bonded antioxidant is significantly improved, and it can play a continuous and efficient role in the subsequent high-temperature melt extrusion stage, further inhibiting yellowing. Compared with the yellowing and steric hindrance effects caused by traditional non-reactive antioxidants, the present invention achieves enhanced grafting while inhibiting degradation, resulting in a synergistic improvement in grafting rate, mechanical properties and color. (5) The present invention introduces a multifunctional synergistic monomer. In the solid phase stage, it uses multiple unsaturated bonds to react with PP free radicals and MAH to form a slightly cross-linked network on the surface of PP particles, physically anchoring and enriching MAH at the reaction interface, effectively inhibiting its sublimation loss at low temperature. In the high-temperature and high-shear melt extrusion stage, the micro-cross-linked network undergoes controllable rupture, releasing a high concentration of active free radicals and stored MAH in situ. Based on the reaction mode of first storing and then releasing, it creates an extremely high concentration of reactants in the most critical region and moment of the reaction, improving the grafting efficiency of MAH, and thus improving the peel strength of the final product. Detailed Implementation

[0032] The method for preparing polypropylene graft-modified masterbatch provided by this invention mainly includes the following steps:

[0033] Maleic anhydride, the first initiator monomer, and the second grafting agent monomer are stirred at a constant temperature of 30–50 °C for 0.5–1 h to obtain a maleic anhydride-interface agent solution.

[0034] Maleic anhydride-interface agent solution is reacted and grafted with PP resin under certain conditions, and finally melt-extruded in a twin-screw extruder to obtain polypropylene grafted modified masterbatch.

[0035] The first monomer of the initiator includes one or more of benzoyl peroxide (BPO), dicumyl peroxide (DCP), 2,4-dichlorobenzoyl peroxide (DCBP), and bis-tert-butyldicumyl peroxide (BIPB).

[0036] The mass ratio of maleic anhydride to the first monomer is 1:0.2 to 0.8.

[0037] The polypropylene resin includes one or more of isotactic, syndiotactic, or atactic resins.

[0038] The second monomer of the grafting aid includes one or more of oleic acid, styrene, acrylic acid, and acrylate. Its function is to reduce interfacial tension, promote the wetting and dispersion of maleic anhydride on the PP surface, and simultaneously provide additional active sites and co-initiation synergistic effects, thereby improving grafting efficiency and inhibiting side reactions; the dosage can be 0 to 0.3 parts per 100 parts by weight of PP resin.

[0039] This patent also allows the addition of a reactive antioxidant to the maleic anhydride-interface agent solution. The type of antioxidant can be selected from 3114 (1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione), AO-80 (3,9-bis[2-(3-(3-tert-butyl-4-hydroxy-5-methylphenyl)acrylate)-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane), IRGANOX1035 (thiodiethylenebis[3-(3,5-ditert-butyl-4-hydroxy-5-methylphenyl)acrylate) One or more of phenyl propionate or hindered phenolic derivatives containing acrylate double bonds are used in an amount of 0.1–2% of the PP mass. During the solid-phase grafting stage, the reactive antioxidant preferentially couples with the PP tertiary carbon free radicals through active double bonds or phenolic hydroxyl groups to form a PP-antioxidant macromolecular intermediate, which blocks the β-fracture degradation chain reaction and retains more graftable sites. After entering the melt extrusion stage, the intermediate is chemically bonded to the PP chain segment, which significantly improves the thermal stability, continuously captures new free radicals and inhibits yellowing, thereby increasing the MAH grafting rate and achieving a closed-loop synergy of degradation inhibition and grafting enhancement in solid-phase pre-swelling and melt extrusion.

[0040] Multifunctional synergistic monomers can also be added to the maleic anhydride-interface agent solution. The type of monomer can be selected from one or more of trimethylolpropane triacrylate (TMPTA), tripropylene glycol diacrylate (TPGDA), pentaerythritol triacrylate (PETA), 1,6-hexanediol diacrylate (HDDA), or multi-component unsaturated monomers containing vinyl, allyl, and epoxy groups. The amount used is 0.1-2% of the PP mass. During the solid-phase grafting stage, the multifunctional monomers utilize their ≥2 unsaturated bonds to simultaneously undergo partial cross-linking with PP free radicals and MAH, forming a MAH-micro-crosslinked network and anchoring it to the surface of PP particles, inhibiting MAH sublimation loss. During the melt extrusion stage, this micro-crosslinked network undergoes controlled fracture in the shear-thermal field, instantaneously releasing highly active free radicals and unreacted MAH, thereby increasing the grafting rate and peel strength.

[0041] The mass ratio of the polypropylene resin to maleic anhydride is 1:0.005 to 0.03.

[0042] The interface agent includes one or more of acetone and xylene.

[0043] When preparing the maleic anhydride-interface agent solution, the weight ratio of the interface agent to the maleic anhydride is in the range of 2:1 to 1:1.

[0044] Before the PP resin undergoes reaction grafting, an interface agent is used to swell it. The amount of interface agent added during this process is 1-10% of the weight of the PP resin.

[0045] During the extrusion process, the main motor of the screw extruder rotates at 250–350 r / min, the feeding speed is 12–18 kg / h, and the process temperatures of each zone from the screw inlet to the extruder die are as follows: Zone 1: 160–250℃, Zone 2: 160–250℃, Zone 3: 180–250℃, Zone 4: 200–250℃, Zone 5: 200–250℃, Zone 6: 220–250℃, Zone 7: 220–250℃, Zone 8: 180–250℃, Zone 9: 180–250℃, Zone 10: 160–250℃, Zone 11: 160–250℃, and the die temperature is 230–255℃.

[0046] The polypropylene grafted modified masterbatch prepared in this embodiment of the invention was subjected to adhesion performance testing as follows: 2g of polypropylene grafted modified masterbatch was weighed and laminated with aluminum foil into a 1.5cm wide strip using a hot press. Finally, the adhesion performance was tested using a WDW-5A microcomputer-controlled electronic universal testing machine. Peel tests were performed according to standard ASTM D3330.

[0047] Example 1

[0048] This embodiment provides a method for preparing polypropylene graft-modified masterbatch, specifically as follows:

[0049] 1. Maleic anhydride, the first monomer of initiator bis-tert-butyl peroxide diisopropylbenzene, and the interface agent acetone are stirred at 35°C for 0.5 h to obtain a maleic anhydride-acetone solution. The amount of acetone used is twice the weight of maleic anhydride.

[0050] 2. Take 96.62 parts of polypropylene resin, 2.90 parts of maleic anhydride, and the initiator bis(tert-butylperoxide)diisopropylbenzene.

[0051] 0.48 parts, after pre-dissolving in step 1, first pour 96.62 parts of polypropylene resin into a closed stirring device at a constant temperature of 140℃, preheat for 5 minutes, then pour in 3 parts of interface agent acetone for swelling, and after 10 minutes, pour in maleic anhydride-acetone solution for grafting reaction, reaction time 10 minutes.

[0052] 3. The material obtained in step 2 is directly melt-extruded through a twin-screw extruder to obtain polypropylene grafted modified masterbatch.

[0053] 4. Take 2g of polypropylene grafted modified masterbatch for a peeling test.

[0054] Example 2

[0055] The difference between this embodiment and Example 1 is that the initiator is changed to benzoyl peroxide, while the rest of the preparation process is the same as in Example 1, to obtain polypropylene graft-modified masterbatch and film.

[0056] Example 3

[0057] The difference between this embodiment and Example 1 is that the initiator is changed to dicumyl peroxide, while the rest of the preparation process is the same as in Example 1, to obtain polypropylene graft-modified masterbatch and film.

[0058] Example 4

[0059] The difference between this embodiment and Example 1 is that the initiator is changed to 2,4-dichlorobenzoyl peroxide, while the rest of the preparation process is the same as in Example 1, to obtain polypropylene graft-modified masterbatch and film.

[0060] The performance of the materials prepared in the above embodiments was tested, and the comparison results with those of Example 1 are shown in Table 1.

[0061] Table 1

[0062] Average (N) Peel strength (N / mm) Maximum peel strength (N / mm) Example 1 17.74 1.183 1.438 Example 2 16.87 1.125 1.326 Example 3 14.15 0.946 1.079 Example 4 15.68 1.052 1.102 Pure PP 0 0 0

[0063] As shown in Table 1, the masterbatch exhibits excellent adhesion properties when grafted using different initiators, showing a significant improvement compared to pure PP, and is difficult to peel off by hand. Based on the comparison of peel strength, di-tert-butylperoxide diisopropylbenzene is selected as the preferred initiator.

[0064] Example 5

[0065] The difference between this embodiment and Example 1 is that the mass of the initiator, di-tert-butylperoxide diisopropylbenzene, is adjusted to 18g, that is, the mass ratio of polypropylene to initiator is 1:0.015. The rest of the preparation process is the same as in Example 1, and polypropylene graft-modified masterbatch and film are obtained.

[0066] Example 6

[0067] The difference between this embodiment and Example 1 is that the mass of the initiator, di-tert-butylperoxide diisopropylbenzene, is adjusted to 3g, that is, the mass ratio of polypropylene to initiator is 1:0.0025. The rest of the preparation process is the same as in Example 1, and polypropylene graft-modified masterbatch and film are obtained.

[0068] The performance of the materials prepared in the above embodiments was tested, and the results compared with those of Example 1 are shown in Table 2.

[0069] Table 2

[0070] Average (N) Peel strength (N / mm) Maximum peel strength (N / mm) Example 1 17.74 1.183 1.438 Example 5 13.01 0.868 0.902 Example 6 13.79 0.920 0.954

[0071] As shown in Table 2, adjusting the ratio of polypropylene to initiator has a significant impact on material properties. Too much or too little initiator will affect the adhesion of the final film, and excessive initiator will further lead to PP degradation, affecting the color of the final product. The color effects are shown in Table 3 below:

[0072] Table 3

[0073] Masterbatch appearance color Example 1 White Example 5 yellow Example 6 White

[0074] In summary, the preferred mass ratio of polypropylene to initiator is 1:0.005.

[0075] Example 7

[0076] The difference between this embodiment and Example 1 is that the solid-phase grafting reaction time is adjusted to 20 min, while the rest of the preparation process is the same as in Example 1, to obtain polypropylene graft-modified masterbatch and film.

[0077] Example 8

[0078] The difference between this embodiment and Example 1 is that the solid-phase grafting reaction time is adjusted to 5 minutes, while the rest of the preparation process is the same as in Example 1, to obtain polypropylene graft-modified masterbatch and film.

[0079] The performance of the materials prepared in the above embodiments was tested, and the results compared with those of Example 1 are shown in Table 4.

[0080] Table 4

[0081] Average (N) Peel strength (N / mm) Masterbatch appearance color Example 1 17.74 1.183 White Example 7 15.66 1.097 dark brown Example 8 12.65 0.857 White

[0082] As shown in Table 4, the reaction time of the first solid-phase grafting step has a significant impact on the material properties. Excessive reaction time leads to PP degradation and yellowing, thereby reducing the adhesion of the final product. Conversely, insufficient reaction time results in incomplete grafting, directly reducing the adhesion of the final product. Therefore, the preferred reaction time is 10 minutes.

[0083] Example 9

[0084] The difference between this embodiment and Example 1 is that the amount of maleic anhydride is adjusted to 50g, that is, the mass ratio of polypropylene resin to maleic anhydride is 1:0.04. The rest of the preparation process is the same as in Example 1, and polypropylene graft-modified masterbatch and film are obtained.

[0085] Example 10

[0086] The difference between this embodiment and Example 1 is that the amount of maleic anhydride is adjusted to 18g, that is, the mass ratio of polypropylene resin to maleic anhydride is 1:0.015. The rest of the preparation process is the same as in Example 1, and polypropylene graft-modified masterbatch and film are obtained.

[0087] The performance of the materials prepared in the above embodiments was tested, and the results compared with those of Example 1 are shown in Table 5.

[0088] Table 5

[0089] Average (N) Peel strength (N / mm) Masterbatch appearance color Example 1 17.74 1.183 White Example 9 12.21 0.845 tan Example 10 11.36 0.780 White

[0090] As shown in Table 5, adjusting the mass ratio of polypropylene resin to maleic anhydride has a significant impact on material properties. Excessive maleic anhydride leads to incomplete reaction, resulting in a large amount of reactant residue and ultimately PP degradation, thus reducing the adhesion and darkening the color of the final product. Conversely, insufficient maleic anhydride directly reduces the final maleic anhydride grafting rate, thereby decreasing the adhesion of the final product. Therefore, the preferred mass ratio of polypropylene resin to maleic anhydride is 1:0.03.

[0091] Comparative Example 11

[0092] The difference between this comparative example and Example 1 is that the solid-phase grafting reaction temperature was adjusted to 120°C, while the rest of the preparation process was the same as in Example 1, to obtain polypropylene graft-modified masterbatch and film.

[0093] Comparative Example 12

[0094] The difference between this comparative example and Example 1 is that the solid-phase grafting reaction temperature was adjusted to 160°C, while the rest of the preparation process was the same as in Example 1, to obtain polypropylene graft-modified masterbatch and film.

[0095] The performance of the materials prepared in the above embodiments was tested, and the results compared with those of Example 1 are shown in Table 6.

[0096] Table 6

[0097] Average (N) Peel strength (N / mm) Masterbatch appearance color Example 1 17.74 1.183 White Example 11 11.43 0.786 light yellow Example 12 10.83 0.742 yellow

[0098] As shown in Table 7, a low solid-phase grafting reaction temperature leads to incomplete reaction, resulting in residual reactants in the melt extrusion section causing yellowing and reduced adhesion of the final product. Conversely, a high solid-phase grafting reaction temperature directly causes severe degradation of PP during the reaction process, resulting in reduced adhesion and darker color of the final product.

[0099] Example 13

[0100] The difference between this embodiment and Example 11 is that 0.30 parts of reactive antioxidant 3114 (1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione) were added to the preparation of the maleic anhydride-acetone solution. The rest of the preparation process was the same as in Example 1, and polypropylene graft-modified masterbatch and film were obtained.

[0101] Example 14

[0102] The difference between this embodiment and Example 11 is that 0.30 parts of traditional antioxidant 1010 (pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid]) were added to the preparation of the maleic anhydride-acetone solution. The rest of the preparation process is the same as in Example 1, and polypropylene graft-modified masterbatch and film are obtained.

[0103] Example 15

[0104] The difference between this embodiment and Example 11 is that 0.50 parts of the multifunctional synergistic monomer TMPTA (trimethylolpropane triacrylate) were added to the preparation of the maleic anhydride-acetone solution. The rest of the preparation process was the same as in Example 1, and polypropylene graft-modified masterbatch and film were obtained.

[0105] The performance of the materials prepared in the above embodiments was tested, and the comparison results with those of Example 11 are shown in Table 7.

[0106] Table 7

[0107] Average (N) Peel strength (N / mm) Masterbatch appearance color Example 11 11.43 0.786 light yellow Example 13 13.82 1.076 White Example 14 11.64 0.813 yellow Example 15 13.52 0.968 light yellow

[0108] As shown in Table 8, the active double bond of reactive antioxidant 3114 reacts with PP free radicals to generate antioxidant-PP grafts, effectively blocking the β-fracture degradation pathway of PP free radicals, increasing the number of effective grafting sites, and enhancing the mechanical properties of the film. Furthermore, antioxidant 3114 is chemically anchored to the PP chain, increasing the thermogravimetric initiation temperature and playing a stabilizing role throughout the melt extrusion process. Its hindered phenolic structure decomposes into colorless small molecules at high temperatures, rather than yellow quinone products. Although antioxidant 1010 can capture free radicals, its non-reactive nature leads to its large consumption at high temperatures, forming yellow quinone products. At the same time, due to steric hindrance, it hinders the grafting reaction of MAH, which in turn exacerbates the oxidative degradation of PP, resulting in antioxidant-induced yellowing.

[0109] The three acrylate groups of TMPTA form a local micro-crosslinking network, which significantly improves the adsorption capacity of MAH on the surface of PP particles and slows down the diffusion rate of MAH to the gas phase. This micro-crosslinking structure undergoes controlled fracture in the shear field, releasing highly active acrylate free radicals and MAH monomers, forming secondary grafting micro-regions around the antioxidant-PP graft. Through the reaction mode of storage followed by release, the grafting reaction efficiency in the molten section is improved, which promotes the improvement of mechanical properties.

[0110] Comparative Example 1

[0111] The difference between this comparative example and Example 1 is that the interface agent is changed to xylene, while the rest of the preparation process is the same as in Example 1, to obtain polypropylene graft-modified masterbatch and film.

[0112] The performance of the materials prepared in the above embodiments was tested, and the results compared with those of Example 1 are shown in Table 6.

[0113] Table 6

[0114] Average (N) Peel strength (N / mm) odor Example 1 17.74 1.183 Small Comparative Example 1 13.55 0.907 big

[0115] Table 6 shows that the interface agent has a significant impact on the performance of the final product. Xylene has a strong odor during the experiment, which is not conducive to production. Therefore, acetone was chosen as the final interface agent.

[0116] In summary, this invention first performs solid-phase grafting of polypropylene resin and maleic anhydride to increase the grafting rate of maleic anhydride, and then melt-extrudes the solid-phase grafted product. Compared with the conventional melt extrusion method for grafting maleic anhydride, this process not only improves the polarity, i.e., adhesion, of the final product, but also improves the color of the final product.

[0117] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a polypropylene graft-modified masterbatch, characterized in that, Includes the following steps: (1) Solid-phase grafting step: Polypropylene resin, maleic anhydride, initiator and interface agent for dissolving or dispersing maleic anhydride and initiator are mixed and reacted at a temperature below the melting point of polypropylene resin to obtain solid-phase grafting product. (2) Melt extrusion step: The solid graft product obtained in step (1) is melt extruded to obtain the polypropylene graft modified masterbatch.

2. The preparation method according to claim 1, characterized in that, The polypropylene resin is selected from one or more combinations of isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene. The initiator is selected from one or more combinations of benzoyl peroxide, dicumyl peroxide, 2,4-dichlorobenzoyl peroxide, and bis-tert-butyldicumyl peroxide; The interface agent is selected from one or more combinations of acetone and xylene.

3. The preparation method according to claim 1, characterized in that, The proportions of the raw materials are as follows: based on 100 parts by weight of the polypropylene resin, the amount of maleic anhydride is 0.5-3 parts; the mass ratio of maleic anhydride to the initiator is 1:(0.2-0.8).

4. The preparation method according to claim 1, characterized in that, In step (1), a grafting aid is also added; the grafting aid is selected from one or more of oleic acid, styrene, acrylic acid, and acrylate monomers; the amount of the grafting aid is 0.01-0.3 parts based on 100 parts by weight of the polypropylene resin.

5. The preparation method according to claim 1, characterized in that, In step (1), a reactive antioxidant was also added; The reactive antioxidant is selected from 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine. -2,4,6-(1H,3H,5H)-trione, 3,9-bis[2-(3-(3-tert-butyl-4-hydroxy-5-methylphenyl)acrylate)-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane, thiodiethylenebis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], or a combination of one or more hindered phenolic derivatives containing acrylate double bonds; Based on 100 parts by weight of the polypropylene resin, the amount of the reactive antioxidant is 0.1-2 parts.

6. The preparation method according to claim 1, characterized in that, In step (1), a multifunctional group synergistic monomer was also added; The multifunctional synergistic monomer is selected from one or more combinations of trimethylolpropane triacrylate, tripropylene glycol diacrylate, pentaerythritol triacrylate, 1,6-hexanediol diacrylate, or other multifunctional unsaturated monomers containing at least two functional groups selected from vinyl, allyl, and epoxy groups. Based on 100 parts by weight of the polypropylene resin, the amount of the multifunctional synergistic monomer is 0.1-2 parts.

7. The preparation method according to claim 1, characterized in that, The specific operations of step (1) include: The maleic anhydride and initiator are dissolved in the interface agent and stirred at 30-50°C for 0.5-1 hour to obtain a reaction mixture. The reaction mixture is mixed with the polypropylene resin and reacted at 100-150°C for 5-20 minutes.

8. The preparation method according to claim 1, characterized in that, The melt extrusion in step (2) uses a twin-screw extruder, with the process temperature of each zone set to 160-250℃ and the screw speed to 250-350r / min.

9. A polypropylene graft-modified masterbatch, characterized in that, It is prepared by the method of any one of claims 1-8.

10. The use of the polypropylene graft-modified masterbatch of claim 9 in the preparation of composite materials, functional films or as an adhesive layer.