Flame-retardant modified pp granules, and preparation method and application thereof

Abstract

The application relates to the field of high polymer materials, and discloses a flame-retardant modified PP particle as well as a preparation method and application thereof. The particle comprises polypropylene resin, modified nano titanium dioxide, modified magnesium hydroxide and an auxiliary agent. The modified nano titanium dioxide is prepared by grafting a functional silane coupling agent on the surface of nano titanium dioxide. The modified melamine derivative is prepared by reacting 1,4-dibromobutane with melamine to obtain a bromine-substituted melamine, and then reacting the bromine-substituted melamine with salicylaldehyde, DOPO and pyridine-3-boronic acid. The modified magnesium hydroxide is prepared by grafting a cashew phenol end thiol plasticizer with double bond hydrogenated magnesium hydroxide. The cashew phenol end thiol plasticizer is prepared by reacting cashew phenol glycidyl ether with diethanolamine to obtain a cashew phenol amine-based polyhydric alcohol, and then sequentially reacting the cashew phenol amine-based polyhydric alcohol with mercaptopropionic acid methyl ester, mercaptopropionic acid and dimethyl itaconate. The material prepared by the application has excellent mechanical properties, heat resistance, antibacterial property and flame retardancy.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer materials, and particularly relates to flame-retardant modified PP granules and a preparation method and application thereof. BACKGROUND

[0002] Polypropylene is a thermoplastic plastic with wide application, and its limiting oxygen index (LOI) is only about 18%, which is easy to burn and has a melt dripping phenomenon during burning, so that the application thereof in many fields is limited, and therefore, the polypropylene needs to be flame-retardant modified, and adding a flame retardant is the most direct and simple method for improving the flame-retardant property of polypropylene.

[0003] According to the type of the flame retardant, the flame retardant can be divided into a halogen-containing flame retardant and a halogen-free flame retardant, wherein the halogen-containing flame retardant has small addition amount and high flame-retardant property, but a large amount of toxic smoke is emitted during burning, causing a "secondary disaster", the traditional halogen-free flame-retardant system has low flame-retardant efficiency, large addition amount and poor compatibility with a base material, and the introduction of the flame retardant causes negative effects on the mechanical property of the material, in addition, the existing polypropylene material has poor antibacterial property, the existing polypropylene antibacterial material is made of polypropylene resin and antibacterial nano-silver components, the nano-silver has poor interface in the polypropylene resin and is easy to agglomerate, which affects the antibacterial effect and the mechanical property of the plastic, causes the antibacterial property of the product to be poor and not durable, and in addition, the existing polypropylene resin has poor heat resistance and impact resistance, which limits the application range of the polypropylene material. SUMMARY

[0004] In order to solve the problems mentioned in the background, the purpose of the present application is to provide flame-retardant modified PP granules and a preparation method and application thereof, by adding modified nano-titanium dioxide and modified magnesium hydroxide, the material prepared has high tensile strength, is not easy to break, has good impact resistance, and has excellent heat resistance, antibacterial property and flame-retardant property.

[0005] The purpose of the present application can be achieved by the following technical solutions.

[0006] The flame-retardant modified PP granules comprise the following components by weight: 100 parts of polypropylene resin, 7-15 parts of modified nano-titanium dioxide, 10-20 parts of modified magnesium hydroxide, 1-3 parts of lubricant and 0.5-1.6 parts of antioxidant.

[0007] The modified nano-titanium dioxide is prepared by grafting a functional silane coupling agent on the surface of nano-titanium dioxide, wherein the functional silane coupling agent is prepared by substitution reaction of 3-chloropropyltrimethoxysilane and modified melamine derivative; the modified melamine derivative is prepared by substitution reaction of 1,4-dibromobutane and melamine, Schiff base reaction of bromo-substituted melamine and salicylaldehyde, and addition of DOPO to the product of the Schiff base reaction, and then quaternary ammonium reaction of the melamine derivative and pyridine-3-boronic acid;

[0008] The modified magnesium hydroxide is prepared by thiol-double bond click reaction of cashew phenol end thiol plasticizer and 3-methacryloyloxypropylmethyldimethoxysilane double bond hydrogenated magnesium hydroxide; the cashew phenol end thiol plasticizer is prepared by reaction of cashew phenol glycidyl ether and diethanolamine to obtain cashew phenol amine polyol, then by thiol-double bond click reaction of methyl thiolpropanoate and the side chain of the cashew phenol amine polyol to obtain cashew phenol plasticizer intermediate, and then by esterification reaction of thiolpropanoic acid and the cashew phenol plasticizer intermediate to obtain the thiolated cashew phenol plasticizer intermediate, and then by thiol-double bond click reaction of the thiolated cashew phenol plasticizer intermediate and dimethyl itaconate.

[0009] Preferably, the preparation method of the modified nano-titanium dioxide comprises the following steps:

[0010] I. melamine, 1,4-dibromobutane and dimethyl sulfoxide are taken in a reactor, potassium carbonate catalyst is added, and stirring is carried out at 85-90℃ for 5-7h; after the reaction is completed, washing and drying are carried out to obtain bromo-substituted melamine;

[0011] II. anhydrous methanol, bromo-substituted melamine and salicylaldehyde are taken in a reactor, and stirring is carried out at 80-85℃ for 3-5h; then DOPO is added to the reactor and constant temperature stirring is carried out for 3-5h; after the reaction is completed, centrifugation, washing and drying are carried out to obtain melamine derivative;

[0012] III. melamine derivative, pyridine-3-boronic acid and dimethyl sulfoxide are taken in a reactor, and stirring is carried out at 65-75℃ for 10-14h; after the reaction is completed, filtration, washing and drying are carried out to obtain modified melamine derivative;

[0013] IV. modified melamine derivative and N,N-dimethylformamide are taken in a reactor, 3-chloropropyltrimethoxysilane and triethylamine are added, and stirring is carried out at 75-85℃ for 5-7h; after the reaction is completed, reduced pressure suction filtration and rotary evaporation are carried out to obtain functional silane coupling agent;

[0014] V. The modified nano-titanium dioxide is prepared by dispersing nano-titanium dioxide in anhydrous ethanol and deionized water, then adding a functional silane coupling agent, stirring and reacting at 60-85°C for 10-12h, and filtering, washing and drying after the reaction is completed.

[0015] Preferably, the molar ratio of melamine to 1,4-dibromobutane in step I is 1:1-1.2.

[0016] Preferably, the molar ratio of bromine-substituted melamine, salicylaldehyde and DOPO in step II is 1:2-2.1:2-2.1.

[0017] Preferably, the molar ratio of melamine derivative to pyridine-3-boronic acid in step III is 1:1-1.3.

[0018] Preferably, the preparation method of the modified magnesium hydroxide comprises the following steps:

[0019] A. The magnesium hydroxide is dispersed in toluene to obtain a dispersion liquid, 3-methacryloyloxypropylmethyldimethoxysilane is added to hydrochloric acid, deionized water, the dispersion liquid and anhydrous ethanol, and the mixture is reacted at 55-70°C for 2-3h, and then the reaction is completed by centrifugation, washing and drying to obtain the double-bonded magnesium hydroxide;

[0020] B. The double-bonded magnesium hydroxide, cashew phenol-based end thiol plasticizer, anhydrous ethanol and photoinitiator 2-hydroxy-2-methylpropiophenone are placed in a reactor, stirred uniformly, and then the reactor is placed under ultraviolet light with a wavelength of 350-365nm for 5-6h to obtain the modified magnesium hydroxide.

[0021] Preferably, the preparation method of the cashew phenol-based end thiol plasticizer in step B comprises the following steps:

[0022] B1. The cashew phenol, epichlorohydrin and benzyltriethylammonium chloride are placed in a reactor, protected by nitrogen, and reacted at 95-100°C for 3-4h, then cooled to 55-60°C, and sodium hydroxide is added in batches within 1h to continue the reaction for 3-4h, and then washed and distilled to obtain cashew phenol glycidyl ether;

[0023] B2. The cashew phenol glycidyl ether and diethanolamine are placed in a reactor, stirred and heated to 65-70°C for 4-5h, and then washed and distilled under reduced pressure to obtain the cashew phenol amine-based polyol.

[0024] B3, taking cardanol amine polyol, mercaptopropionic acid methyl ester and photoinitiator 2-hydroxy-2-methyl propiophenone in a reactor, stirring for 8-12h, then placing the reactor under 300-350nm ultraviolet light for 8-12h, and then removing the unreacted substances by rotary evaporation to prepare a cardanol-based plasticizer intermediate;

[0025] B4, taking the cardanol-based plasticizer intermediate, mercaptopropionic acid and p-toluenesulfonic acid catalyst in a reactor, purging with nitrogen, and placing under 85-90℃ for 3-5h, removing the unreacted substances by rotary evaporation after the reaction is completed to prepare a mercapto cardanol-based plasticizer intermediate;

[0026] B5, taking the mercapto cardanol-based plasticizer intermediate and photoinitiator 2-hydroxy-2-methyl propiophenone in a reactor, then adding dimethyl itaconate and stirring for 8-12h, and then placing the reactor under 300-350nm ultraviolet light for 8-12h to prepare a cardanol-based terminal mercapto plasticizer.

[0027] Preferably, the molar ratio of the cardanol-based plasticizer intermediate and mercaptopropionic acid in step B4 is 1:3; and the molar ratio of the mercapto cardanol-based plasticizer intermediate and dimethyl itaconate in step B5 is 1:2.

[0028] A preparation method of the flame-retardant modified PP granules as described above, comprising the following steps: weighing each component by weight parts, stirring and uniformly mixing polypropylene resin, modified nano titanium dioxide, modified magnesium hydroxide, lubricant and antioxidant, and then extruding and granulating through a double screw extruder to prepare the flame-retardant modified PP granules.

[0029] The lubricant is one or a combination of more than one of stearic acid, polyethylene wax and oxidized polyethylene wax; and the antioxidant is one or a combination of more than one of antioxidant 1010, antioxidant 168, antioxidant 1024 and antioxidant 1076.

[0030] An application of the flame-retardant modified PP granules, which are applied to pipe materials, plate materials, cable protection sleeves and plastic products.

[0031] The beneficial effects of the present application are:

[0032] The present application utilizes 1,4-dibromobutane to substitute one amino group in melamine with one end of bromine atom, and then a bromine-substituted melamine is prepared, and then Schiff base reaction is carried out between the two amino groups not grafted in the bromine-substituted melamine and salicylaldehyde, and then addition reaction is carried out between the formed -N=CH group and -P-H bond in DOPO, and then a melamine derivative is prepared, and then quaternary ammonium reaction is carried out between the introduced bromine atom in the melamine derivative and nitrogen atom on the pyridine ring in pyridine-3-boronic acid, and then a modified melamine derivative is prepared, and then substitution reaction is carried out between 3-chloropropyltrimethoxysilane and the introduced hydroxyl group in the modified melamine derivative, and then a functionalized silane coupling agent is prepared, and finally the functionalized silane coupling agent is grafted on the surface of nano-titanium dioxide through dehydration condensation reaction, and then modified nano-titanium dioxide is prepared.

[0033] The functionalized silane coupling agent prepared by the present application introduces salicylaldehyde, alkyl nitrogen positive ion (quaternary ammonium salt) and boronic acid structural units with antibacterial activity into the structure of the functionalized silane coupling agent, and nano-titanium dioxide as an important inorganic antibacterial agent is beneficial to enhancing the photocatalytic antibacterial ability of nano-titanium dioxide through the grafting of the functionalized silane coupling agent, and the functionalized silane coupling agent structure contains synergistic flame-retardant N-P-B-Si elements, which can play excellent flame-retardant effect, in addition, the grafting reaction can bond the functional components through firm chemical bonds, which can play long-acting antibacterial and flame-retardant effect, avoid the migration and precipitation of the functional components in long-term use or subsequent processing, and the grafting reaction is beneficial to the relatively uniform dispersion of nano-titanium dioxide in the matrix material, which can avoid the agglomeration of nano-titanium dioxide and cause the decrease of mechanical properties.

[0034] The present application utilizes epoxy chloropropane to modify cardanol by epoxidation, and then reacts with diethanolamine to prepare cardanol amido polyol, and then methyl mercaptopropionate reacts with the side chain of cardanol amido polyol to carry out mercapto-double bond click reaction, and then cardanol-based plasticizer intermediate is prepared, and then mercapto-propionic acid reacts with the cardanol-based plasticizer intermediate to carry out esterification reaction, and then the prepared mercapto cardanol-based plasticizer intermediate reacts with dimethyl itaconate to carry out mercapto-double bond click reaction, and then cardanol-based terminal mercapto plasticizer is prepared, and then the present application utilizes 3-methacryloyloxypropylmethyldimethoxysilane to hydrolyze and then carry out dehydration condensation with the surface hydroxyl group of magnesium hydroxide to obtain active double bond structure magnesium hydroxide, and then the mercapto structure in the cardanol-based terminal mercapto plasticizer reacts with the double bond magnesium hydroxide under ultraviolet lamp irradiation to carry out mercapto-double bond click reaction, and then modified magnesium hydroxide is prepared.

[0035] The present application uses cardanol as raw material, uses thiol-double bond click reaction to connect a polar group to improve the plasticizing efficiency, and combines the plasticizer and magnesium hydroxide through a firm chemical bond to avoid the defect that the plasticizer continuously migrates to the external environment during use, so as to realize plasticization and non-migration, in addition, the cardanol-based end thiol plasticizer structure is grafted on the surface of the inorganic flame retardant magnesium hydroxide to realize soft coating of the inorganic nanoparticles, form a rigid-flexible core-shell structure, which is beneficial to improve the impact resistance of the material, and the presence of sulfur element in the cardanol-based end thiol plasticizer can greatly improve the thermal stability of the matrix material, and endow the material with excellent mechanical properties and heat resistance. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be clearly and completely described below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0037] The preparation method of the modified nano titanium dioxide in Example 1 comprises the following steps:

[0038] I, 12.6g melamine, 21.6g 1,4-dibromobutane and 300mL dimethyl sulfoxide are taken in a reactor, 0.2g potassium carbonate catalyst is added, and stirring reaction is carried out at 90℃ for 6h, after the reaction is completed, washing, drying are carried out, and bromine-substituted melamine is prepared;

[0039] II, 300mL anhydrous methanol, 13g bromine-substituted melamine and 12.2g salicylaldehyde are taken in a reactor, stirring reaction is carried out at 80℃ for 4h, then 21.6g DOPO is added to the reactor and constant temperature stirring reaction is carried out for 4h, after the reaction is completed, centrifugation, washing, drying are carried out, and melamine derivative is prepared;

[0040] III, 18g melamine derivative, 3g pyridine-3-boronic acid and 180mL dimethyl sulfoxide are taken in a reactor, stirring reaction is carried out at 70℃ for 12h, after the reaction is completed, filtration, washing, drying are carried out, and modified melamine derivative is prepared;

[0041] IV, 15.3g modified melamine derivative and 160mL N,N-dimethylformamide are taken in a reactor, 4g 3-chloropropyltrimethoxysilane and 1.5g triethylamine are added, stirring reaction is carried out at 80℃ for 6h, after the reaction is completed, reduced pressure suction filtration, rotary evaporation are carried out, and functionalized silane coupling agent is prepared;

[0042] V. 5 g of nano-titanium dioxide was ultrasonically dispersed in 90 mL of anhydrous ethanol and 20 mL of deionized water, then 3.8 g of functionalized silane coupling agent was added, and the mixture was stirred and reacted at 70°C for 10 h. After the reaction was completed, the modified nano-titanium dioxide was prepared by filtration, washing and drying.

[0043] A method for preparing modified magnesium hydroxide according to Example 2 comprises the following steps:

[0044] A. 5 g of magnesium hydroxide was ultrasonically dispersed in 70 mL of toluene to obtain a dispersion liquid. 1 g of 3-methacryloxypropylmethyldimethoxysilane, 0.6 mL of 37% hydrochloric acid, 5 mL of deionized water, the dispersion liquid and 3.5 mL of anhydrous ethanol were added, and the mixture was reacted at 65°C for 3 h. After the reaction was completed, the double-bonded magnesium hydroxide was prepared by centrifugation, washing and drying.

[0045] B. 5 g of double-bonded magnesium hydroxide, 2.5 g of cashew phenol-based terminal mercapto plasticizer, 60 mL of anhydrous ethanol and 0.5 g of photoinitiator 2-hydroxy-2-methylpropiophenone were placed in a reactor, and the mixture was stirred uniformly. The reactor was then placed under ultraviolet light with a wavelength of 365 nm for 5 h to obtain modified magnesium hydroxide.

[0046] The preparation method of the cashew phenol-based terminal mercapto plasticizer in step B comprises the following steps:

[0047] B1. 102 g of cashew phenol, 31.5 g of epichlorohydrin and 1.1 g of benzyltriethylammonium chloride were placed in a reactor, and nitrogen was introduced for protection. The mixture was reacted at 100°C for 4 h, then cooled to 60°C, and 14.4 g of sodium hydroxide was added in batches within 1 h for continuous reaction for 4 h. After the reaction was completed, the cashew phenol glycidyl ether was prepared by washing and distillation.

[0048] B2. 71.2 g of cashew phenol glycidyl ether and 21 g of diethanolamine were placed in a reactor, and the mixture was stirred and heated to 70°C for reaction for 4 h. After the reaction was completed, the cashew phenol amine-based polyol was prepared by washing and organic phase distillation under reduced pressure.

[0049] B3. 23.1 g of cashew phenol amine-based polyol, 18 g of mercaptopropionic acid methyl ester and 0.9 g of photoinitiator 2-hydroxy-2-methylpropiophenone were placed in a reactor, and the mixture was stirred and reacted for 10 h. Then the reactor was placed under ultraviolet light with a wavelength of 320 nm for 10 h, and then the unreacted substances were removed by rotary evaporation to obtain a cashew phenol-based plasticizer intermediate.

[0050] B4. 35 g of cashew phenol-based plasticizer intermediate, 15.9 g of mercaptopropionic acid and 0.9 g of p-toluenesulfonic acid catalyst were placed in a reactor, and nitrogen was introduced for protection. The mixture was reacted at 90°C for 4 h. After the reaction was completed, the unreacted substances were removed by rotary evaporation to obtain a mercapto-cashew phenol-based plasticizer intermediate.

[0051] B5, 48.2 g of the mercapto group modified cardanol-based plasticizer intermediate and 0.9 g of a photoinitiator 2-hydroxy-2-methylpropiophenone were taken in a reactor, then 15.8 g of dimethyl itaconate was added, and stirred for 10 h, then the reactor was placed under a wavelength of 320 nm ultraviolet light for 10 h, to prepare a cardanol-based terminal mercapto plasticizer.

[0052] Example 3 A flame-retardant modified PP granule, comprising the following components by weight: polypropylene resin 100 parts, modified nano-titanium dioxide prepared in Example 1 7.7 parts, modified magnesium hydroxide prepared in Example 2 10.2 parts, lubricant stearic acid 1.2 parts, antioxidant 1010 0.6 parts.

[0053] The preparation method of the above flame-retardant modified PP granule comprises the following steps: weighing each component by weight, stirring and mixing the polypropylene resin, modified nano-titanium dioxide, modified magnesium hydroxide, lubricant and antioxidant uniformly, and then extruding and granulating through a double-screw extruder to prepare the flame-retardant modified PP granule.

[0054] Example 4 A flame-retardant modified PP granule, comprising the following components by weight: polypropylene resin 100 parts, modified nano-titanium dioxide prepared in Example 1 11.3 parts, modified magnesium hydroxide prepared in Example 2 15.5 parts, lubricant stearic acid 2.2 parts, antioxidant 1010 1.1 parts.

[0055] The preparation method of the above flame-retardant modified PP granule is the same as that of Example 3.

[0056] Example 5 A flame-retardant modified PP granule, comprising the following components by weight: polypropylene resin 100 parts, modified nano-titanium dioxide prepared in Example 1 14.4 parts, modified magnesium hydroxide prepared in Example 2 19.3 parts, lubricant stearic acid 2.7 parts, antioxidant 1010 1.4 parts.

[0057] The preparation method of the above flame-retardant modified PP granule is the same as that of Example 3.

[0058] Comparative Example 1 A preparation method of modified nano-titanium dioxide comprises the following steps:

[0059] I, 300 mL of anhydrous methanol, 6.3 g of melamine and 12.2 g of salicylaldehyde were taken in a reactor, and stirred at 80°C for 4 h, then 21.6 g of DOPO was added to the reactor and stirred at constant temperature for 4 h, and after the reaction was completed, centrifugation, washing and drying were performed to prepare a melamine derivative.

[0060] II. Take 11.5 g of melamine derivative and 160 mL of N,N-dimethylformamide in a reactor, add 4 g of 3-chloropropyltrimethoxysilane and 1.5 g of triethylamine, stir at 80°C for 6 h, after the reaction is completed, filter, wash and dry to prepare the functionalized silane coupling agent;

[0061] III. Take 5 g of nano-titanium dioxide and disperse it in 90 mL of anhydrous ethanol and 20 mL of deionized water, then add 3.8 g of the functionalized silane coupling agent, stir at 70°C for 10 h, after the reaction is completed, filter, wash and dry to prepare the modified nano-titanium dioxide.

[0062] Comparative Example 2: A flame-retardant modified PP granule, comprising the following components by weight: polypropylene resin 100 parts, modified nano-titanium dioxide prepared in Comparative Example 1 14.4 parts, modified magnesium hydroxide prepared in Example 2 19.3 parts, lubricant stearic acid 2.7 parts, antioxidant 1010 1.4 parts.

[0063] The preparation method of the above flame-retardant modified PP granule is the same as that of Example 3.

[0064] Comparative Example 3: A flame-retardant modified PP granule, comprising the following components by weight: polypropylene resin 100 parts, nano-titanium dioxide 14.4 parts, modified magnesium hydroxide prepared in Example 2 19.3 parts, lubricant stearic acid 2.7 parts, antioxidant 1010 1.4 parts.

[0065] The preparation method of the above flame-retardant modified PP granule is the same as that of Example 3.

[0066] Comparative Example 4: A flame-retardant modified PP granule, comprising the following components by weight: polypropylene resin 100 parts, modified nano-titanium dioxide prepared in Example 1 14.4 parts, double-bonded magnesium hydroxide prepared in Example 2 19.3 parts, lubricant stearic acid 2.7 parts, antioxidant 1010 1.4 parts.

[0067] The preparation method of the above flame-retardant modified PP granule is the same as that of Example 3.

[0068] Performance testing

[0069] The PP granules prepared in Examples 3-5 and Comparative Examples 2-4 were subjected to performance testing:

[0070] (1) Mechanical property testing: A universal mechanical testing machine was used to test the tensile properties according to GB / T 1040.2-2022, the tensile sample size was 100 mm x 5 mm x 3.5 mm, and the impact strength was tested according to GB / T 1843-2008, the sample size was 80 mm x 10 mm x 4 mm, and the data results are shown in Table 1.

[0071] (2) Heat resistance test: the sample was placed in a TGA-103 thermal gravimetric analyzer, and the initial decomposition temperature of the material was recorded under nitrogen protection at a temperature rising rate of 5℃ / min from room temperature to 800℃, and the heat resistance was evaluated. Generally speaking, the higher the initial decomposition temperature, the stronger the heat resistance, and vice versa. The data results are shown in Table 1.

[0072] (3) Antibacterial performance test: the antibacterial performance test was carried out according to QB / T 2591-2003, and the test bacteria were Staphylococcus aureus and Escherichia coli. The data results are shown in Table 1.

[0073] (4) Flame retardant performance test: the limiting oxygen index test was carried out according to GB / T 2406.2-2009, and the data results are shown in Table 1.

[0074] Table 1: Performance test results of samples

[0075]

[0076] From the data results in Table 1, it can be seen that the materials prepared in Examples 3-5 have high tensile strength, are not easy to break, have good impact resistance, and also have excellent heat resistance, antibacterial performance and flame retardant performance. The modified nano titanium dioxide component added in Comparative Example 2 does not introduce alkyl nitrogen cation and boric acid structural units, and the measured Escherichia coli inhibition rate, Staphylococcus aureus inhibition rate and limiting oxygen index are lower than those of Examples 3-5. In Comparative Example 3, the nano titanium dioxide is not modified, and the measured mechanical properties, Escherichia coli inhibition rate, Staphylococcus aureus inhibition rate and limiting oxygen index are lower than those of Examples 3-5. The reason is that the agglomeration of nano particles leads to a decrease in mechanical properties, and the antibacterial performance is significantly reduced due to the absence of antibacterial active salicylaldehyde, alkyl nitrogen cation (quaternary ammonium salt) and boric acid structural units with bacterial capture ability. In addition, the flame retardant performance is significantly reduced compared with Examples 3-5 due to the absence of synergistic flame retardant N-P-B-Si elements. In Comparative Example 4, the modified magnesium hydroxide is replaced by double-bonded magnesium hydroxide in equal amount, and the measured elongation at break, impact strength and initial thermal decomposition temperature are significantly lower than those of Examples 3-5. The reason is that the coating of cashew phenol-based mercaptan plasticizer realizes plasticization and core-shell structure, which is beneficial to improve the fracture toughness and impact resistance, and the sulfur element introduced in the cashew phenol-based mercaptan plasticizer improves the heat resistance of the material to a certain extent.

[0077] In the description of the specification, the description of the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Also, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0078] The basic principles, main features and advantages of the present application are shown and described above. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. Flame-retardant modified PP granules, characterized in that, It includes the following components by weight: 100 parts polypropylene resin, 7-15 parts modified nano titanium dioxide, 10-20 parts modified magnesium hydroxide, 1-3 parts lubricant, and 0.5-1.6 parts antioxidant; The modified nano-titanium dioxide is prepared by grafting a functionalized silane coupling agent, prepared by a substitution reaction between 3-chloropropyltrimethoxysilane and a modified melamine derivative, onto the surface of nano-titanium dioxide. The modified melamine derivative is prepared by a substitution reaction between 1,4-dibromobutane and melamine to obtain bromo-substituted melamine, then reacting the bromo-substituted melamine with salicylaldehyde in a Schiff base reaction and further adding it to DOPO to prepare a melamine derivative, which is then quaternized with pyridine-3-boronic acid. The modified magnesium hydroxide is prepared by a thiol-double bond click reaction of a cashew phenol-terminated thiol plasticizer with 3-methacryloyloxypropylmethyldimethoxysilane double bonded magnesium hydroxide; the cashew phenol-terminated thiol plasticizer is prepared by reacting cashew phenol glycidyl ether with diethanolamine to prepare cashew phenol amino polyol, then preparing a cashew phenol plasticizer intermediate by reacting methyl mercaptopropionate with the side chain of the cashew phenol amino polyol by a thiol-double bond click reaction, then esterifying the cashew phenol plasticizer intermediate with mercaptopropionic acid, and finally reacting the prepared thiolized cashew phenol plasticizer intermediate with dimethyl itaconic acid by a thiol-double bond click reaction.

2. The flame-retardant modified PP granules according to claim 1, characterized in that, The preparation method of the modified nano-titanium dioxide includes the following steps: I. Melamine, 1,4-dibromobutane and dimethyl sulfoxide were placed in a reactor, potassium carbonate catalyst was added, and the mixture was stirred at 85~90℃ for 5~7h. After the reaction was completed, the mixture was washed and dried to prepare bromine-substituted melamine. II. Anhydrous methanol, bromo-substituted melamine and salicylaldehyde were placed in a reactor and stirred continuously at 80-85°C for 3-5 hours. Then DOPO was added to the reactor and stirred at a constant temperature for 3-5 hours. After the reaction was completed, the melamine derivative was prepared by centrifugation, washing and drying. III. Melamine derivative, pyridine-3-boronic acid and dimethyl sulfoxide are placed in a reactor and stirred at 65~75℃ for 10~14h. After the reaction is completed, the mixture is filtered, washed and dried to prepare the modified melamine derivative. IV. Take the modified melamine derivative and N,N-dimethylformamide in a reactor, add 3-chloropropyltrimethoxysilane and triethylamine, and stir the reaction at 75~85℃ for 5~7h. After the reaction is completed, filter under reduced pressure and evaporate by rotary evaporation to prepare the functionalized silane coupling agent. V. Take nano-titanium dioxide and ultrasonically disperse it in anhydrous ethanol and deionized water, then add functionalized silane coupling agent, and stir the reaction at 60~85℃ for 10~12h. After the reaction is completed, filter, wash and dry to prepare modified nano-titanium dioxide.

3. The flame-retardant modified PP granules according to claim 2, characterized in that, In step I, the molar ratio of melamine to 1,4-dibromobutane is 1:1 to 1.

2.

4. The flame-retardant modified PP granules according to claim 2, characterized in that, In step II, the molar ratio of bromosubstituted melamine, salicylaldehyde, and DOPO is 1:2~2.1:2~2.

1.

5. The flame-retardant modified PP granules according to claim 2, characterized in that, In step III, the molar ratio of melamine derivative and pyridine-3-boronic acid is 1:1 to 1.

3.

6. The flame-retardant modified PP granules according to claim 1, characterized in that, The method for preparing the modified magnesium hydroxide includes the following steps: A. Magnesium hydroxide was ultrasonically dispersed in toluene to obtain a dispersion. 3-Methacryloxypropylmethyldimethoxysilane was added to hydrochloric acid, deionized water, the dispersion and anhydrous ethanol, and reacted at 55-70℃ for 2-3 hours. After the reaction was completed, the magnesium hydroxide was centrifuged, washed and dried to prepare double-bonded magnesium hydroxide. B. Take double-bonded magnesium hydroxide, cashew phenol terminal thiol plasticizer, anhydrous ethanol and photoinitiator 2-hydroxy-2-methylphenylacetone into a reactor, stir evenly, and then place the reactor under ultraviolet light with a wavelength of 350~365nm for 5~6h to prepare modified magnesium hydroxide.

7. The flame-retardant modified PP granules according to claim 6, characterized in that, The preparation method of the cashew phenol-terminated thiol plasticizer in step B includes the following steps: B1. Take cashew phenol, epichlorohydrin and benzyltriethylammonium chloride in a reactor, introduce nitrogen gas for protection, and react at 95~100℃ for 3~4h. Then cool down to 55~60℃, add sodium hydroxide in batches within 1h and continue the reaction for 3~4h. After the reaction is completed, wash and distill to prepare cashew phenol glycidyl ether. B2. Cashew phenol glycidyl ether and diethanolamine were placed in a reactor, stirred and heated to 65-70℃ for 4-5 hours. After the reaction was completed, the cashew phenol amino polyol was prepared by washing and vacuum distillation of the organic phase. B3. Take cashew phenol amino polyol, methyl mercaptopropionate and photoinitiator 2-hydroxy-2-methylphenylacetone in a reactor and stir for 8-12 hours. Then place the reactor under ultraviolet light with a wavelength of 300-350 nm for 8-12 hours. Then remove unreacted substances by rotary evaporation to prepare cashew phenol plasticizer intermediate. B4. Take the cashew phenolic plasticizer intermediate, mercaptopropionic acid and p-toluenesulfonic acid catalyst into a reactor, purge with nitrogen, and react at 85~90℃ for 3~5h. After the reaction is completed, remove the unreacted material by rotary evaporation to prepare the mercapto-modified cashew phenolic plasticizer intermediate. B5. Take the intermediate of the thiolated cashew phenol-based plasticizer and the photoinitiator 2-hydroxy-2-methylphenylacetone into a reactor, then add dimethyl itaconic acid and stir for 8-12 hours. Then place the reactor under ultraviolet light with a wavelength of 300-350 nm for 8-12 hours to prepare the cashew phenol-terminated thiolated plasticizer.

8. The flame-retardant modified PP granules according to claim 7, characterized in that, In step B4, the molar ratio of cashew phenol-based plasticizer intermediate to mercaptopropionic acid is 1:3; in step B5, the molar ratio of mercapto-modified cashew phenol-based plasticizer intermediate to dimethyl itaconic acid is 1:

2.

9. A method for preparing flame-retardant modified PP granules according to any one of claims 1 to 8, characterized in that, Includes the following steps: Weigh each component according to the weight parts, stir and mix the polypropylene resin, modified nano titanium dioxide, modified magnesium hydroxide, lubricant and antioxidant evenly, and then extrude and granulate through a twin-screw extruder to prepare flame-retardant modified PP granules. The lubricant is one or more of stearic acid, polyethylene wax, and oxidized polyethylene wax; the antioxidant is one or more of antioxidant 1010, antioxidant 168, antioxidant 1024, and antioxidant 1076.

10. An application of the flame-retardant modified PP granules according to claim 1, characterized in that, The flame-retardant modified PP granules are used in pipes, sheets, cable sheaths, and plastic products.

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