A modified polypropylene and a method for preparing and using the same

Abstract

The application provides a modified polypropylene and a preparation method and application thereof, and the preparation method comprises the following steps: adding an initiator to a first raw material system to perform a first grafting reaction, so as to obtain a first grafting product; and performing a second grafting reaction on the first grafting product and a second raw material system, so as to obtain the modified polypropylene; wherein the first raw material system comprises a first polypropylene, glycidyl methacrylate and styrene; and the second raw material system comprises a second polypropylene and a carboxylic acid compound with a hindered phenol group. Through the two-step grafting reaction, the hindered phenol group is partially grafted on the polypropylene, so that the defect that the antioxidant is prone to precipitation can be effectively overcome, and finally the modified polypropylene with excellent extraction resistance and thermal oxygen stability is obtained.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and specifically relates to a modified polypropylene, its preparation method, and its application. Background Technology

[0002] Polypropylene is oxidized by oxygen in the air when exposed to light and heat, leading to a loss of its mechanical properties. Therefore, antioxidants need to be added to polypropylene to improve its thermal and oxygen stability, delay or inhibit the thermal oxidation process, thereby preventing aging and extending its service life.

[0003] Hindered phenolic antioxidants are compounds with hydroxyl groups on the benzene ring and substituents on one or both sides of the hydroxyl group. They have advantages such as low volatility and strong antioxidant capacity, and are widely used in polypropylene to reduce the thermo-oxidative aging of polypropylene. However, because polypropylene is non-polar and hindered phenolic antioxidants are polar, their compatibility is poor. In practical applications, hindered phenolic antioxidants tend to migrate and precipitate onto the surface of polypropylene products, thus affecting the appearance and thermo-oxidative stability of polypropylene.

[0004] Currently, most methods involve chemically modifying polypropylene and then mixing it with antioxidants to enhance its thermal stability. For example, patent document CN109439240A discloses a method for preparing a heat-resistant PP hot melt adhesive. This method utilizes chemical grafting modification to graft amino acids onto polypropylene, and then mixes the grafted product with antioxidants, followed by complete melting with terpene phenolic resin and hybrid composite materials to prepare a heat-resistant polyolefin hot melt adhesive, thereby enhancing the thermal stability of polypropylene. This method involves many raw materials, complex processing, and while it improves thermal stability, it has little impact on extraction resistance. Patent document CN106633267A discloses the synthesis of a reactive hindered phenolic antioxidant polyolefin additive, which utilizes the synthesized allyl hindered phenolic additive to melt graft blend with polyolefin: a reactive hindered amine radiation-resistant polyolefin additive, a reactive hindered phenolic antioxidant polyolefin additive, an initiator, and polyolefin resin are placed in a screw mixer for melt blending and grafting; in this process, a peroxide initiator is added to attach the hindered phenolic antioxidant polyolefin additive to the macromolecular chain. For PP, this addition may lead to the degradation of the PP matrix, resulting in a decrease in the mechanical properties of the material.

[0005] Therefore, how to overcome the defect of antioxidants easily migrating and precipitating, and provide a polypropylene material with good extraction resistance and good thermo-oxidative stability, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] This invention provides a method for preparing modified polypropylene. This method involves a two-step grafting reaction, which allows hindered phenolic groups to be grafted onto polypropylene. This effectively overcomes the defect of easy precipitation of antioxidants and ultimately yields modified polypropylene with excellent extraction resistance and thermo-oxidative stability.

[0007] This invention provides a modified polypropylene that exhibits excellent performance in terms of extraction resistance and thermo-oxidative stability.

[0008] This invention provides a polypropylene product that, due to the inclusion of the above-mentioned modified polypropylene, has excellent performance and a long service life.

[0009] In one aspect, the present invention provides a method for preparing modified polypropylene, comprising the following steps:

[0010] An initiator is added to the first raw material system to carry out the first grafting reaction, and the first grafted product is obtained.

[0011] The first grafted product is subjected to a second grafting reaction with the second raw material system to obtain modified polypropylene;

[0012] An initiator is added to the first raw material system to carry out the first grafting reaction, and the first grafted product is obtained.

[0013] The first grafted product is subjected to a second grafting reaction with the second raw material system to obtain modified polypropylene;

[0014] The first raw material system includes a first polypropylene, glycidyl methacrylate, and styrene; the second raw material system includes a carboxylic acid compound containing hindered phenolic groups and a second polypropylene.

[0015] In the preparation method described above, the hindered phenolic group is selected from 3,5-di-tert-butyl-4-hydroxyphenyl.

[0016] In the preparation method described above, the carboxylic acid compound containing the hindered phenolic group is selected from 3,5-di-tert-butyl-4-hydroxyphenyl fatty acids.

[0017] In the preparation method described above, the carboxylic acid compound containing the hindered phenolic group is selected from at least one of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid, 3,5-di-tert-butyl-4-hydroxyphenylcarboxylic acid, and 3,5-di-tert-butyl-4-hydroxyphenylacetic acid.

[0018] In the preparation method described above, the reaction temperature is 160℃-280℃.

[0019] The preparation method described above, wherein the first raw material system comprises, by mass parts, 100 parts of polypropylene, 1-20 parts of glycidyl methacrylate, 1-20 parts of styrene, and 0.1-5 parts of initiator;

[0020] The second raw material system comprises, by mass parts, 100 parts of second polypropylene, 1-30 parts of first grafted product, and 0.1-10 parts of carboxylic acid compound containing hindered phenolic groups;

[0021] Preferably, the first raw material system comprises, by weight, 100 parts of polypropylene, 10-20 parts of glycidyl methacrylate, 10-14 parts of styrene, and 0.5-2 parts of initiator;

[0022] The second raw material system comprises, by mass, 100 parts of second polypropylene, 4-25 parts of first grafted product, and 0.5-2 parts of carboxylic acid compound containing hindered phenolic groups.

[0023] In the preparation method described above, the initiator is selected from at least one of dicumyl peroxide and di-tert-butyl peroxide.

[0024] In a second aspect, the present invention provides a modified polypropylene, obtained according to the preparation method described above.

[0025] In the modified polypropylene described above, the molar mass content of hindered phenolic groups is 0.01-5%.

[0026] A third aspect of the present invention provides a polypropylene article comprising the modified polypropylene as described above.

[0027] The implementation of this invention has at least the following beneficial effects:

[0028] The modified polypropylene preparation method provided by this invention involves a first grafting reaction of polypropylene, glycidyl methacrylate, and styrene under the action of an initiator, maximizing the grafting of epoxy groups onto the polypropylene. A second grafting reaction is then conducted, utilizing the reaction between the epoxy groups and carboxyl groups to graft hindered phenolic groups from carboxylic acid compounds onto the polypropylene. This maximizes the thermo-oxidative resistance of the hindered phenolic groups, overcomes the defect of easy precipitation of antioxidants, and ultimately results in modified polypropylene with excellent extraction resistance and thermo-oxidative stability. Detailed Implementation

[0029] The specific embodiments listed below are merely descriptions of the principles and features of the present invention. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention. 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.

[0030] The method for preparing modified polypropylene provided by the present invention includes the following steps: adding an initiator to a first raw material system to carry out a first grafting reaction to obtain a first grafted product; and causing the first grafted product to undergo a second grafting reaction with a second raw material system to obtain modified polypropylene; wherein, the first raw material system includes a first polypropylene, glycidyl methacrylate, and styrene; and the second raw material system includes a carboxylic acid compound containing a hindered phenolic group and a second polypropylene.

[0031] This invention prepares modified polypropylene through a grafting reaction, specifically melt grafting. That is, a first raw material system undergoes a first grafting reaction under molten conditions, and the first grafted product undergoes a second grafting reaction with a second raw material system under molten conditions.

[0032] Grafting reactions (including a first grafting reaction and a second grafting reaction) are initiated by adding an initiator to a first raw material system. Specifically, by adding an initiator to the first raw material system, the presence of the initiator can initiate the first grafting reaction, i.e., initiate polymerization, introducing epoxy groups onto polypropylene.

[0033] The first raw material system of the present invention includes at least polypropylene (PP), glycidyl methacrylate (GMA), and styrene (ST). In the specific implementation of the present invention, the first raw material system is mixed first, and then an initiator is added, which can effectively promote the dispersion of each component in the first raw material system, thereby increasing the grafting rate of epoxy groups.

[0034] In this invention, under the action of an initiator, polypropylene undergoes a hydrogen elimination reaction to form polypropylene free radicals, which are capable of grafting reactions. Glycidyl methacrylate contains epoxy groups; through the first grafting reaction, the epoxy groups on glycidyl methacrylate can be grafted onto the polypropylene.

[0035] In this invention, the first grafting reaction essentially involves grafting a copolymer formed from the reaction of glycidyl methacrylate and styrene onto polypropylene. The glycidyl methacrylate-styrene polymer forms the branched units of the polypropylene main unit. This is because styrene has a higher reactivity than glycidyl methacrylate, and styrene preferentially grafts onto polypropylene, forming styrene radicals. These styrene radicals then react with glycidyl methacrylate, thereby achieving the grafting of epoxy groups onto the polypropylene.

[0036] In this invention, due to the high reactivity of styrene, it can preferentially graft onto polypropylene, and styrene and glycidyl methacrylate readily undergo copolymerization, thereby increasing the grafting rate of epoxy groups onto polypropylene and facilitating subsequent grafting of hindered phenolic groups. Furthermore, the introduction of styrene can prevent the formation of byproducts such as glycidyl methacrylate homopolymers and styrene homopolymers, and inhibit the breaking of the polypropylene backbone.

[0037] The first graft product includes at least a polypropylene backbone-glycidyl methacrylate / styrene copolymer (PP-g-GMA / ST).

[0038] The second raw material system of the present invention comprises a carboxylic acid compound (HP-R-COOH) containing a hindered phenolic group and a second polypropylene. The hindered phenolic group is a group with substituents on one or both sides of the hydroxyl group on the benzene ring, and the hindered phenolic group has excellent resistance to thermo-oxidative aging.

[0039] The second grafting reaction is essentially a reaction between the epoxy groups in the first grafting product and the carboxyl groups in the second raw material system. Specifically, through the reaction of the epoxy groups and carboxyl groups, hindered phenolic groups are grafted onto a portion of the polypropylene. Further, a second polypropylene is added in the second grafting reaction, ultimately yielding modified polypropylene. This modified polypropylene can be used directly as a modifier.

[0040] Modified polypropylene includes at least the polypropylene backbone - glycidyl methacrylate / styrene copolymer - carboxylic acid containing hindered phenolic groups (PP-g-GMA / ST-COO-R-HP).

[0041] The present invention does not limit the apparatus used in preparing modified polypropylene, but may specifically include a mixer, a twin-screw extruder, etc.

[0042] As can be seen from the above steps, the modified polypropylene preparation method provided by this invention grafts hindered phenolic groups onto polypropylene through chemical grafting. Compared to simply physically mixing hindered phenolic antioxidants with polypropylene as additives, introducing hindered phenolic groups into the skeletal branches of polypropylene through grafting can maximize the anti-thermal and oxidative aging effect of hindered phenolic groups. In addition, it can reduce the loss of hindered phenolic antioxidants during subsequent processing of polypropylene products, improve the thermal and oxidative stability of modified polypropylene, and enhance the extraction resistance of modified polypropylene.

[0043] This invention does not limit the specific selection of each raw material. For example, the hindered phenolic group is selected from 3,5-di-tert-butyl-4-hydroxyphenyl. The carboxylic acid compound with the hindered phenolic group is selected from at least one of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid, 3,5-di-tert-butyl-4-hydroxyphenylcarboxylic acid, and 3,5-di-tert-butyl-4-hydroxyphenylacetic acid. The initiator is selected from at least one of organic peroxides, such as dicumyl peroxide and di-tert-butyl peroxide.

[0044] The grafting reaction temperature of this invention is 160℃-280℃. The specific reaction temperature can be determined according to actual needs. The higher the temperature, the faster the activity and reaction rate of the first and second raw material systems, and the higher the probability of grafting, thus increasing the grafting rate of hindered phenolic groups and achieving the purpose of changing and improving the properties of polypropylene.

[0045] The present invention does not limit the amount of each substance added in the first raw material system and the second raw material system. The specific amount added can be determined according to the target grafting amount of hindered phenolic groups on modified polypropylene.

[0046] In one specific embodiment, the first raw material system comprises, by mass parts, 100 parts of first polypropylene, 1-20 parts of glycidyl methacrylate, 1-20 parts of styrene, and 0.1-5 parts of initiator.

[0047] In one specific embodiment, the second raw material system comprises, by mass parts, 100 parts of second polypropylene, 1-30 parts of first grafted product, and 0.1-10 parts of carboxylic acid compound containing hindered phenolic groups.

[0048] Preferably, the first raw material system comprises, by weight, 100 parts of polypropylene, 10-20 parts of glycidyl methacrylate, 10-14 parts of styrene, and 0.5-2 parts of initiator;

[0049] The second raw material system comprises, by mass, 100 parts of second polypropylene, 4-25 parts of first grafted product, and 0.5-2 parts of carboxylic acid compound containing hindered phenolic groups.

[0050] It should be noted that, as the first grafting reaction proceeds, the first grafting products include not only the generated polypropylene main chain-glycidyl methacrylate / styrene copolymer (PP-g-GMA / ST), but also polypropylene main chain-glycidyl methacrylate, polypropylene main chain-styrene, and other first grafting products. At this point, a second raw material system is added to the first grafting products to carry out the second grafting reaction. It can be understood that the essence of the second grafting reaction is that the epoxy groups on the polypropylene main chain-glycidyl methacrylate and the polypropylene main chain-glycidyl methacrylate / styrene copolymer (PP-g-GMA / ST) react with the carboxyl groups on a carboxylic acid compound containing hindered phenolic groups (HP-R-COOH), respectively, to obtain modified polypropylene such as polypropylene main chain-glycidyl methacrylate / styrene copolymer-carboxylic acid compound containing hindered phenolic groups (PP-g-GMA / ST-COO-R-HP) and polypropylene main chain-glycidyl methacrylate-carboxylic acid compound containing hindered phenolic groups (PP-g-GMA-COO-R-HP).

[0051] In a second aspect, the present invention provides a modified polypropylene obtained according to the aforementioned preparation method. Generally, in this modified polypropylene, the mass content of hindered phenolic groups is 0.01-5%.

[0052] Due to the unique nature of the aforementioned preparation method, the modified polypropylene obtained by this method exhibits significant resistance to heat and oxygen and excellent extraction resistance, enabling it to serve for extended periods in harsh high-temperature environments and broadening the application range of polypropylene products.

[0053] A third aspect of the present invention also provides a polypropylene article, the raw material of which is the modified polypropylene of the second aspect described above. Exemplarily, the polypropylene article of the present invention is obtained by extruding or molding a raw material including the modified polypropylene. Furthermore, the modified polypropylene of the present invention can be used directly as a modifier. It can also be mixed with other polymer materials.

[0054] This invention does not limit the application field of the polypropylene product, but can be applied to any field that has a demand for polypropylene products, such as optical materials, medical packaging materials, food packaging, etc.

[0055] Since the raw material of the polypropylene product of the present invention is the aforementioned modified polypropylene, the polypropylene product exhibits excellent heat and oxygen stability and extraction resistance, and is suitable for high-temperature application environments.

[0056] The present invention will be further described below through specific embodiments and comparative examples. Unless otherwise specified, the reagents, materials and instruments used below are all conventional reagents, materials and instruments, all of which are commercially available, and the reagents and materials involved can also be synthesized by conventional synthetic methods.

[0057] In the following examples and comparative examples, the purified polypropylene (grade T30S) homopolymer powder used was provided by Lanzhou Petrochemical Company of China National Petroleum Corporation, with a melt index of 2.2 g / 10 min at 210°C; dicumyl peroxide (99% purity), glycidyl methacrylate (97% purity), and styrene (99% purity) were all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0058] Example 1

[0059] Polypropylene, dicumyl peroxide, glycidyl methacrylate, and styrene were mixed evenly in a mass ratio of 100:0.5:10:10 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 50 rpm, and the mixing time was 10 min. The mixed product was crushed and pelletized to obtain the first grafted product I.

[0060] The second polypropylene, the first graft product I, and 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid were mixed evenly at a mass ratio of 100:10.5:0.5 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 50 rpm, and the mixing time was 10 min. The mixed product was crushed and pelletized to obtain modified polypropylene S1.

[0061] Example 2

[0062] Polypropylene, dicumyl peroxide, glycidyl methacrylate, and styrene were mixed evenly in a mass ratio of 100:0.5:10:10 and then added to an internal mixer for melt blending. The mixing temperature was 230℃, the rotor speed was 50 rpm, and the mixing time was 5 min. The mixed product was crushed and pelletized to obtain the first grafted product II.

[0063] The second polypropylene, the first graft product II, and 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid were mixed evenly at a mass ratio of 100:10.5:0.5, and then fed into a twin-screw extruder for co-extrusion, pelleting, and drying to obtain modified polypropylene S2.

[0064] Example 3

[0065] Polypropylene, dicumyl peroxide, glycidyl methacrylate, and styrene were mixed evenly in a mass ratio of 100:0.5:20:10 and then fed into a twin-screw extruder for reaction extrusion and pelleting. The barrel temperatures of the twin-screw extruder were 170, 180, 200, 200, 190, and 180°C, and the screw speed was 90 rpm. After drying, the first grafted product III was obtained.

[0066] The second polypropylene, the first graft product III, and 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid were mixed evenly at a mass ratio of 100:10:1.0 and then fed into a twin-screw extruder for co-extrusion. After pelleting, the barrel temperatures of the twin-screw extruder were 160, 180, 200, 200, 190, and 180°C, respectively, and the screw speed was 120 rpm. After drying, modified polypropylene S3 was obtained.

[0067] Example 4

[0068] The preparation method is basically the same as that in Example 1, except for the material ratio and preparation conditions in the second raw material system:

[0069] Polypropylene, dicumyl peroxide, glycidyl methacrylate, and styrene were mixed evenly in a mass ratio of 100:0.5:10:10 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 50 rpm, and the mixing time was 10 min. The mixed product was crushed and pelletized to obtain the first grafted product I.

[0070] The second polypropylene, the first graft product I, and 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid were mixed evenly at a mass ratio of 100:5:0.5 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 90 rpm, and the mixing time was 10 min. The mixed product was crushed and pelletized to obtain modified polypropylene S4.

[0071] Example 5

[0072] The preparation method is basically the same as in Example 1, except that the material ratio in the second raw material system is different:

[0073] Polypropylene, dicumyl peroxide, glycidyl methacrylate, and styrene were mixed evenly in a mass ratio of 100:0.5:10:10 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 50 rpm, and the mixing time was 10 min. The mixed product was crushed and pelletized to obtain the first grafted product I.

[0074] The second polypropylene, the first graft product I, and 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid were mixed evenly at a mass ratio of 100:25:0.5 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 50 rpm, and the mixing time was 10 min. The mixed product was crushed and pelletized to obtain modified polypropylene S5.

[0075] Example 6

[0076] The preparation method is basically the same as that in Example 1, except that the types of carboxylic acid compounds containing hindered phenolic groups in the second raw material system are different.

[0077] Polypropylene, dicumyl peroxide, glycidyl methacrylate, and styrene were mixed evenly in a mass ratio of 100:0.5:10:10 and then added to an internal mixer for melt blending. The mixing temperature was 190℃, the rotor speed was 60 rpm, and the mixing time was 15 min. The mixed product was crushed and pelletized to obtain the first grafted product I.

[0078] The second polypropylene, the first graft product I, and 3,5-di-tert-butyl-4-hydroxyphenylcarboxylic acid were mixed evenly at a mass ratio of 100:25:0.5 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 120 rpm, and the mixing time was 6 min. The mixed product was crushed and pelletized to obtain modified polypropylene S6.

[0079] Example 7

[0080] Polypropylene, di-tert-butyl peroxide, glycidyl methacrylate, and styrene were mixed evenly in a mass ratio of 100:0.5:10:10 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 50 rpm, and the mixing time was 10 min. The mixed product was crushed and pelletized to obtain the first grafted product IV.

[0081] The second polypropylene, the first graft product IV, and 3,5-di-tert-butyl-4-hydroxyphenylcarboxylic acid were mixed evenly at a mass ratio of 100:7.5:0.5 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 50 rpm, and the mixing time was 10 min. The mixed product was crushed and pelletized to obtain modified polypropylene S7.

[0082] Example 8

[0083] Polypropylene, di-tert-butyl peroxide, glycidyl methacrylate, and styrene were mixed evenly at a mass ratio of 100:1:15:5 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 80 rpm, and the mixing time was 10 min. The mixed product was crushed and pelletized to obtain the first grafted product V.

[0084] The second polypropylene, the first graft product V, and 3,5-di-tert-butyl-4-hydroxyphenylcarboxylic acid were mixed evenly at a mass ratio of 100:10:1 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 50 rpm, and the mixing time was 10 min. The mixed product was crushed and pelletized to obtain modified polypropylene S8.

[0085] Example 9

[0086] The preparation method is basically the same as that in Example 1, except that the types of carboxylic acid compounds containing hindered phenolic groups in the second raw material system are different.

[0087] Polypropylene, dicumyl peroxide, glycidyl methacrylate, and styrene were mixed evenly in a mass ratio of 100:0.5:10:10 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 50 rpm, and the mixing time was 10 min. The mixed product was crushed and pelletized to obtain the first grafted product I.

[0088] The second polypropylene, the first graft product I, and 3,5-di-tert-butyl-4-hydroxyphenylacetic acid were mixed evenly at a mass ratio of 100:25:0.5 and then added to a Banbury mixer for melt blending. The Banbury temperature was 180℃, the rotor speed was 50 rpm, and the Banbury time was 10 min. The Banbury product was crushed and pelletized to obtain modified polypropylene S9.

[0089] Comparative Example 1

[0090] Polypropylene and 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid were mixed evenly at a mass ratio of 100:0.5 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 50 rpm, and the mixing time was 10 min. The product was then crushed and pelletized to obtain modified polypropylene D1.

[0091] Comparative Example 2

[0092] Polypropylene, dicumyl peroxide, glycidyl methacrylate, and styrene were mixed evenly in a mass ratio of 100:0.5:10:10 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 50 rpm, and the mixing time was 10 min. The mixed product was crushed and pelletized to obtain the first grafted product M (same as the first grafted product I in the previous example).

[0093] The second polypropylene and the first grafted product M were mixed evenly at a mass ratio of 100:10.5 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 50 rpm, and the mixing time was 10 min. The mixed product was crushed and pelletized to obtain modified polypropylene D2.

[0094] Comparative Example 3

[0095] Polypropylene, dicumyl peroxide, glycidyl methacrylate, and styrene were mixed evenly in a mass ratio of 100:0.5:10:10 and then added to an internal mixer for melt blending. The mixing temperature was 180°C, the rotor speed was 50 rpm, and the mixing time was 10 min. The mixed product was crushed and pelletized to obtain the first grafted product N (same as the first grafted product I in the previous example).

[0096] The second polypropylene, the first grafted product DI, and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (i.e., antioxidant 1076, which cannot react with the epoxy groups of the first grafted product I during melt mixing) were mixed evenly at a mass ratio of 100:10.5:0.5 and then added to an internal mixer for melt blending. The mixing temperature was 180℃, the rotor speed was 50 rpm, and the mixing time was 10 min. The product was then crushed and pelletized to obtain modified polypropylene D3.

[0097] Comparative Example 4

[0098] Polypropylene, dicumyl peroxide, glycidyl methacrylate, and styrene were mixed evenly in a mass ratio of 100:0.5:20:10 and then fed into a twin-screw extruder for reactive extrusion and pelletizing. The barrel temperatures of the twin-screw extruder were 170, 180, 200, 200, 190, and 180°C, and the screw speed was 90 rpm. After drying, the first grafted product L (same as the first grafted product III in Example 3) was obtained.

[0099] The second polypropylene and the first grafted product L were mixed evenly at a mass ratio of 100:10 and then fed into a twin-screw extruder for co-extrusion, pelleting, and the barrel temperatures of the twin-screw extruder were 160, 180, 200, 200, 190 and 180°C, respectively, and the screw speed was 120 rpm. The modified polypropylene D4 was obtained after drying.

[0100] Comparative Example 5

[0101] Polypropylene, dicumyl peroxide, glycidyl methacrylate, styrene, and 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid were mixed evenly in a mass ratio of 100:0.2:2:2:0.4 and then fed into a twin-screw extruder for reactive extrusion and pelletizing. The barrel temperatures of the twin-screw extruder were 170, 180, 200, 200, 190, and 180°C, respectively, and the screw speed was 90 rpm. The mixture was then dried to obtain modified polypropylene D5.

[0102] Comparative Example 6

[0103] Polypropylene, dicumyl peroxide, glycidyl methacrylate, styrene, and octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (i.e., antioxidant 1076) were mixed evenly in a mass ratio of 100:0.2:1:1:0.25 and then fed into a twin-screw extruder for reactive extrusion and pelletizing. The barrel temperatures of the twin-screw extruder were 170, 180, 200, 200, 190, and 180°C, respectively, and the screw speed was 90 rpm. The mixture was then dried to obtain modified polypropylene D6.

[0104] Test case

[0105] The modified polypropylene prepared in the above examples and comparative examples was molded into test samples with sides of 100mm × 100mm × 0.5mm using a plate vulcanizer at 190℃ and 10MPa. The oxidation induction temperature of the test samples was tested using differential scanning calorimetry (DSC). After the test samples were extracted with dichloromethane at 60℃ for 3.5h, they were dried and their oxidation induction temperature* was measured. The results are shown in Table 1.

[0106] Specifically, the test samples from Examples 1 and 5, as well as the control sample D1, were extracted in dichloromethane at 60°C for 1 h, 3.5 h, 10 h, and 20 h, respectively, and then dried before the oxidation induction temperature* was measured. The results are shown in Table 2.

[0107] Each sample was placed in an oven at 120℃ for accelerated aging. After 72 hours of aging, the carbonyl index of each sample was determined by infrared spectroscopy at the same aging time. The results are shown in Table 1.

[0108] Table 1

[0109]

[0110]

[0111] Table 2

[0112]

[0113] As shown in Tables 1 and 2, the modified polypropylene preparation method provided by this invention can produce modified polypropylene materials with good extraction resistance and good thermo-oxidative stability. Specifically, the oxidation induction temperature of the modified polypropylene in the examples does not change much before and after aging, the carbonyl index of the modified polypropylene in the examples is lower than that of the comparative example after aging, and the oxidation induction temperature of the modified polypropylene in the examples is higher than that of the comparative example after aging.

[0114] The preferred embodiments and experimental verifications of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing modified polypropylene, characterized in that, Includes the following steps: An initiator is added to the first raw material system to carry out the first grafting reaction, and the first grafted product is obtained. The first grafted product is subjected to a second grafting reaction with the second raw material system to obtain modified polypropylene; The first raw material system includes a first polypropylene, glycidyl methacrylate, and styrene; the second raw material system includes a carboxylic acid compound containing hindered phenolic groups and a second polypropylene; the first raw material system includes, by mass, 100 parts of the first polypropylene, 1-20 parts of glycidyl methacrylate, 1-20 parts of styrene, and 0.1-5 parts of initiator. The second raw material system comprises, by mass parts, 100 parts of second polypropylene, 1-30 parts of first grafted product, and 0.1-10 parts of carboxylic acid compound containing hindered phenolic groups; The carboxylic acid compounds containing hindered phenolic groups are selected from 3,5-di-tert-butyl-4-hydroxyphenyl fatty acids.

2. The preparation method according to claim 1, characterized in that, The carboxylic acid compound containing the hindered phenolic group is selected from at least one of 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid, 3,5-di-tert-butyl-4-hydroxyphenylcarboxylic acid, and 3,5-di-tert-butyl-4-hydroxyphenylacetic acid.

3. The preparation method according to any one of claims 1-2, characterized in that, The first grafting reaction temperature is 170℃-280℃; the second grafting reaction temperature is 160℃-280℃.

4. The preparation method according to any one of claims 1-2, characterized in that, The first raw material system comprises, by weight, 100 parts of polypropylene, 10-20 parts of glycidyl methacrylate, 10-14 parts of styrene, and 0.5-2 parts of initiator; The second raw material system comprises, by mass, 100 parts of second polypropylene, 4-25 parts of first grafted product, and 0.5-2 parts of carboxylic acid compound containing hindered phenolic groups.

5. The preparation method according to any one of claims 1-2, characterized in that, The initiator is selected from at least one of dicumyl peroxide and di-tert-butyl peroxide.

6. A modified polypropylene, characterized in that, It is obtained according to the preparation method according to any one of claims 1-5.

7. The modified polypropylene according to claim 6, characterized in that, In the modified polypropylene, the mass content of hindered phenolic groups is 0.01-5%.

8. A polypropylene product, characterized in that, Includes the modified polypropylene as described in claim 6 or 7.

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