Flame-retardant PET (Polyethylene Terephthalate) material with electromagnetic shielding effect and preparation method thereof

Abstract

The invention relates to the technical field of electromagnetic shielding materials, in particular to a flame-retardant PET (Polyethylene Terephthalate) material with an electromagnetic shielding effect and a preparation method of the flame-retardant PET material. DOPO and alkenyl silane are modified on a linear conductive nano material to synthesize a DOPO modified linear conductive nano material; a DOPO linear conductive nano material and a layered nano material are used as raw materials, then the DOPO linear conductive nano material, an antioxidant, a lubricant, a layered conductive material and a bio-based charring agent are uniformly added into PET through a double-screw extruder to prepare the PET master batch, the DOPO linear conductive nano material and the layered nano material cooperate to form a continuous conductive network, and the PET is endowed with an excellent electromagnetic shielding effect; meanwhile, the DOPO is firstly degraded when heated, on one hand, the DOPO has a free radical quenching effect, and on the other hand, the DOPO can catalyze the bio-based charring agent to generate a cross-linking carbonization reaction and exert an efficient heat insulation and oxygen isolation effect, so that the PET master batch prepared by the method has an excellent electromagnetic shielding effect and flame retardant property and has a wide application prospect.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of electromagnetic shielding materials, in particular to a flame-retardant PET material with electromagnetic shielding effect and a preparation method thereof. BACKGROUND

[0002] With the advent of the information age, information technology is developing rapidly, and communication equipment such as mobile phones, computers and 5G signal towers has become an indispensable part of people's life. As the carrier of information transmission, electromagnetic waves have filled every corner around people. Electromagnetic waves bring great convenience to people's life, but also bring serious electromagnetic pollution. Electromagnetic radiation can endanger people's health, and electromagnetic interference can affect the normal work of electronic equipment, which may affect people's life experience or even harm national security. Therefore, it is very important to eliminate electromagnetic pollution. At present, one of the most effective methods is to shield electromagnetic waves outside through electromagnetic shielding materials. Among the electromagnetic shielding materials, polymer-based electromagnetic shielding materials have broad application prospects due to their light weight, low cost, easy processing and corrosion resistance.

[0003] However, in recent years, major fire accidents have occurred frequently, among which electrical fire accidents account for more than one-third. On the one hand, short circuits and overloads in electrical equipment occur from time to time and are difficult to avoid, on the other hand, high molecular materials are widely used in the electrical field and are extremely flammable. Therefore, it is of great significance to improve the flame retardant properties of polymer-based electromagnetic shielding materials. However, the conductive additives used to impart electromagnetic shielding effect to polymers often also have good thermal conductivity, which can promote the degradation of the surrounding polymers during combustion, further improve the flammability of polymers, and bring great difficulties to the flame-retardant modification of polymer-based electromagnetic shielding materials. At the same time, the addition of flame retardants often affects the uniform distribution of conductive fillers and destroys the continuity of the conductive path, thereby deteriorating the electromagnetic shielding performance. Therefore, there is often a contradiction between electromagnetic shielding effect and flame retardant performance, and how to balance the two is a great challenge.

[0004] In view of this, the present application aims to provide a flame-retardant PET material with electromagnetic shielding effect and a preparation method thereof, so as to better solve the above technical problems. SUMMARY

[0005] To solve the above problems, the application provides a flame-retardant PET material with electromagnetic shielding effect and a preparation method thereof, which synthesizes DOPO modified linear conductive nanomaterials by coupling DOPO to linear conductive nanomaterials through alkenyl coupling agent, and adds the DOPO modified linear conductive nanomaterials, antioxidants, lubricants, layered conductive materials and bio-based char-forming agents into PET through a twin-screw extruder by controlling the processing technology to prepare a flame-retardant PET master batch with electromagnetic shielding effect, which has a wide application prospect.

[0006] The technical scheme adopted by the present application is:

[0007] A preparation method of a flame-retardant PET material with electromagnetic shielding effect comprises the following preparation steps:

[0008] S1. Synthesis of silane-modified DOPO

[0009] In a reaction kettle, solvent A and DOPO are added, and DOPO is fully dispersed by mechanical stirring for 5-60 min. The reaction temperature of the reaction kettle is adjusted to 70-110 DEG C. The initiator and alkenyl silane are dissolved in solvent A, and then dropped into the reaction kettle within 0.5-2 h. After dropping, the reaction is continued for 12-36 h. After the reaction is completed, a mixed solution A is obtained.

[0010] S2. Synthesis of DOPO-modified linear conductive nanomaterial

[0011] In the mixed solution A, linear conductive nanomaterial is added, and is fully dispersed by mechanical stirring and ultrasonic action. The pH regulator is dissolved in solvent B, and is dropped into the mixed solution A. The pH is adjusted to 2-14. The reaction temperature of the reaction kettle is controlled to 70-100 DEG C. The reaction is carried out for 6-24 h. After the reaction is completed, the mixed solution is centrifuged. The precipitate is washed with solvent A and solvent B. After drying, a DOPO-modified linear conductive nanomaterial is obtained.

[0012] S3. Preparation of a flame-retardant material

[0013] PET granules, 0.1-0.8 phr antioxidant, 0.5-1.2 phr lubricant, 5.0-15.0 phr layered conductive material, 5.0-15.0 phr bio-based char-forming agent, and 10.0-20.0 phr DOPO-modified linear conductive nanomaterial are uniformly mixed in a high-speed mixer, and then are melt-blended in a twin-screw extruder to obtain a flame-retardant PET material with electromagnetic shielding effect.

[0014] Further improvement of the above technical scheme is that in step S1, the mass ratio of the alkenyl silane to DOPO is 0.5-1.1:1, and the mass ratio of the initiator to DOPO is 0.005-0.035:1.

[0015] Further improvement of the above technical scheme is that,

[0016] In step S1, the initiator is any one of cyclohexanone peroxide, dibenzoyl peroxide, diisopropyl peroxydicarbonate, tert-butyl hydroperoxide, azobisisobutyronitrile, and azobisisoheptyl nitrile.

[0017] The alkenyl silane in step S1 is any one of vinyl trimethoxysilane, vinyl triethoxysilane, methyl vinyl dimethoxysilane, methyl vinyl diethoxysilane, allyl trimethoxysilane and allyl triethoxysilane.

[0018] Further improvement of the above technical solution is that in step S2, the mass ratio of the linear conductive nanomaterial and DOPO is 0.5-1:1.

[0019] Further improvement of the above technical solution is that in step S2, the linear conductive nanomaterial is any one of single-walled carbon nanotubes, multi-walled carbon nanotubes, silver nanowires, polypyrrole nanowires and poly(3,4-ethylenedioxythiophene) nanowires.

[0020] Further improvement of the above technical solution is that in step S2, the pH regulator is any one of sodium hydroxide, potassium hydroxide, hydrochloric acid, phosphoric acid and sulfuric acid.

[0021] Further improvement of the above technical solution is that the solvent A and the solvent B are any one of ethanol, isopropanol, toluene, dioxane, dimethylformamide and deionized water.

[0022] Further improvement of the above technical solution is that in step S3, the parameters of the twin-screw extruder are set as follows: 1 zone 180-210℃, 2-4 zone temperature gradually increases and is at 185-230℃, 4-9 zone temperature remains the same, 9-11 zone temperature gradually decreases and is at 190-225℃, die temperature 195-225℃, screw speed 250-400r / min, and feeding speed 12-45kg / h.

[0023] Further improvement of the above technical solution is that in step S3,

[0024] The antioxidant is any one of 168, 264, 616, 626, 923, 1010 and 1076;

[0025] The lubricant is any one of PET wax, stearic acid alcohol, oleic acid amide, erucic acid amide, stearic acid amide, glycerol monostearate and pentaerythritol stearate;

[0026] The layered conductive material is any one of graphene nanosheet, graphene nanobelt, MXene and graphite;

[0027] The bio-based char-forming agent is any one of cellulose, carboxymethyl cellulose, chitosan, carboxymethyl chitosan and sodium alginate.

[0028] Based on the same inventive concept, the application also provides a flame-retardant PET material with electromagnetic shielding effect prepared by the preparation method.

[0029] The beneficial effects of the present application are as follows:

[0030] 1、The preparation method provided by the present application, by coupling DOPO to linear conductive nanomaterials through alkenyl coupling agent, synthesizes DOPO modified linear conductive nanomaterials, and adds them into PET through a twin-screw extruder by controlling the processing technology, together with antioxidants, lubricants, layered conductive materials and bio-based char-forming agents, to prepare a flame-retardant PET master batch with electromagnetic shielding effect. After modification by DOPO and alkenyl silane, the linear conductive nanomaterials can be uniformly dispersed in PET, and form a continuous conductive network with the layered nanomaterials, giving the PET excellent electromagnetic shielding effect. At the same time, the linear conductive nanomaterials have high thermal conductivity, so that the DOPO around the material is degraded first when the material is subjected to burning. The degradation products of DOPO can inhibit the radical chain thermal degradation of PET molecules on the one hand, and can catalyze the crosslinking carbonization reaction of bio-based char-forming agents on the other hand, forming a carbonized layer on the surface of the PET matrix to play a high-efficiency heat and oxygen isolation role. Therefore, the PET composite material provided by the present application has excellent electromagnetic shielding effect and flame-retardant performance, and can effectively overcome the problem that electromagnetic shielding effect and flame-retardant performance of polymers are difficult to be considered at the same time. It has important significance for the electronic information field. At the same time, the preparation process of the present application is simple, easy to control, has low requirements for production equipment, and has high yield. The prepared flame-retardant PET master batch with electromagnetic shielding effect can be widely used in the field of electronic information.

[0031] 2、The shielding and flame-retardant material provided by the present application has good electromagnetic shielding effect and good flame-retardant performance, which can effectively solve the problem that current polymer-based electromagnetic shielding materials are difficult to simultaneously consider electromagnetic shielding effect and flame-retardant performance. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 SEM images of (A) polypyrrole and (B) DOPO modified linear conductive nanomaterials in Example 1. DETAILED DESCRIPTION

[0033] In order to facilitate the understanding of the present application, the present application will be described more fully below by examples. The preferred embodiments of the present application are given below. However, the present application can be realized in many different forms and is not limited to the embodiments described herein. Any modification or equivalent replacement of the technical solutions of the present application without creative achievement will obtain other embodiments within the protection scope of the present application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0035] The numerical values disclosed in the present application are approximate values, not definite values. All values within the error range can be included without being limited to the specific numerical values disclosed in the present application, if the error or experimental conditions permit.

[0036] Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0037] Example 1

[0038] The preparation method of the flame-retardant PET material with electromagnetic shielding effect provided in the present embodiment includes the following preparation steps:

[0039] Synthesis of DOPO modified linear conductive nanomaterials:

[0040] 1) Synthesis of silane modified DOPO: Toluene and DOPO were added to a reaction kettle, and DOPO was fully dispersed by mechanical stirring for 10 min. The reaction temperature of the reaction kettle was adjusted to 80℃, and azobisisobutyronitrile (mass ratio of 0.005:1 to DOPO) and allyltrimethoxysilane (mass ratio of 0.75:1 to DOPO) were dissolved in toluene and added dropwise into the reaction kettle within 1 h. After the dropwise addition was completed, the reaction was continued for 24 h. After the reaction was completed, a mixed solution A was obtained;

[0041] 2) Synthesis of DOPO modified linear conductive nanomaterials: Multi-walled carbon nanotubes (mass ratio of 0.5:1 to DOPO) were added to the mixed solution A and fully dispersed by mechanical stirring and ultrasonic treatment for 60 min. Hydrochloric acid was dissolved in deionized water and added dropwise into the mixed solution A to adjust the pH to 3. The reaction temperature of the reaction kettle was controlled at 80℃, and the reaction was carried out for 18 h. After the reaction was completed, the mixed solution was centrifuged, the precipitate was washed with toluene and deionized water, and dried to obtain DOPO modified linear conductive nanomaterials;

[0042] 3) Preparation of flame-retardant PET material with electromagnetic shielding effect: PET granules, 0.3 phr 1010 antioxidant, 0.8 phr pentaerythritol stearate, 10.0 phr graphene nanosheet, 10.0 phr carboxymethyl cellulose and 15.0 phr DOPO modified linear conductive nanomaterial are uniformly mixed in a high-speed mixer, and then melt blended in a twin-screw extruder. The parameter settings of the twin-screw extruder are as follows: the temperatures of zones 1-11 are 190℃, 195℃, 200℃, 205℃, 205℃, 205℃, 205℃, 205℃, 205℃, 200℃, 195℃, respectively, the die temperature is 200℃, the screw rotation speed is 350 r / min, and the feeding speed is 25 kg / h.

[0043] Example 2

[0044] The difference between this example and Example 1 is that:

[0045] The reaction temperature in step 1) is reduced to 70℃, and allyl trimethoxysilane is replaced by vinyl trimethoxysilane;

[0046] In step 2), polypyrrole nanowires are replaced by single-walled carbon nanotubes;

[0047] In step 2, 1010 antioxidant is replaced by 616 antioxidant, pentaerythritol stearate is replaced by stearic acid amide, and 10 phr carboxymethyl cellulose is replaced by 5 phr sodium alginate.

[0048] The rest is the same as Example 1.

[0049] Example 3

[0050] The difference between this example and Example 1 is that:

[0051] In step 1), azobisisobutyronitrile is replaced by diisopropyl peroxydicarbonate, the dropping time is extended to 2h, and the reaction time is extended to 36h;

[0052] In step 2), the mass ratio of polypyrrole nanowires to DOPO is 0.75:1, hydrochloric acid is replaced by sodium hydroxide, and the pH value is adjusted to 14; in step 2, pentaerythritol stearate is replaced by stearic acid alcohol, and the addition amount of graphene nanosheet is increased from 10 phr to 15 phr,

[0053] In step 3), the temperatures of zones 1-11 are changed to 210℃, 215℃, 220℃, 225℃, 225℃, 225℃, 225℃, 225℃, 225℃, 220℃, 215℃, the die temperature is changed to 220℃, the screw rotation speed is reduced from 350 r / min to 250 r / min, and the feeding speed is reduced from 25 kg / h to 15 kg / h.

[0054] The rest is the same as example 1.

[0055] Example 4

[0056] The difference between this example and example 1 is that:

[0057] The toluene in step 1) is replaced with ethanol, and the allyl trimethoxysilane is replaced with methyl vinyl diethoxysilane;

[0058] The polypyrrole nanowires in step 2) are replaced with silver nanowires, and the mechanical stirring and ultrasonic treatment time is shortened to 30 min;

[0059] The 1010 antioxidant in step 2) is replaced with 1076 antioxidant, the graphene nanosheet is replaced with graphene nanoribbon, and the addition amount of DOPO modified linear conductive nanomaterial is increased from 15 phr to 20 phr.

[0060] The rest is the same as example 1.

[0061] Example 5

[0062] The difference between this example and example 1 is that:

[0063] The azobisisobutyronitrile in step 1) is replaced with tert-butyl hydroperoxide, the allyl trimethoxysilane is replaced with allyl triethoxysilane, and the mass ratio of allyl triethoxysilane to DOPO is 1.1:1;

[0064] The reaction temperature in step 2) is reduced to 70°C, and the reaction time is extended to 24 h; the addition amount of 1010 antioxidant in step 2 is increased from 0.3 phr to 0.6 phr, pentaerythritol stearate is replaced with glycerol monostearate, and carboxymethyl cellulose is replaced with carboxymethyl chitosan.

[0065] The rest is the same as example 1.

[0066] Example 6

[0067] The difference between this example and example 1 is that:

[0068] The azobisisobutyronitrile in step 1) is replaced with peroxide cyclohexanone, and the mass ratio of peroxide cyclohexanone to DOPO is 0.01:1;

[0069] The polypyrrole nanowires in step 2) are replaced with poly(3,4-ethylenedioxythiophene) nanowires, and the mass ratio of poly(3,4-ethylenedioxythiophene) nanowires to DOPO is 1:1;

[0070] The 1010 antioxidant in step 2) is replaced with 923 antioxidant, pentaerythritol stearate is replaced with erucic acid amide, and the addition amount of graphene nanosheet is reduced from 10 phr to 7 phr;

[0071] The temperature of zone 1-11 in step 3) is changed to 180℃, 185℃, 190℃, 195℃, 195℃, 195℃, 195℃, 195℃, 195℃, 190℃, 185℃, and the temperature of the head is changed to 190℃.

[0072] The rest is the same as example 1.

[0073] Example 7

[0074] The difference between this example and example 1 is that:

[0075] The toluene in step 1) is replaced by dioxane, the mechanical stirring time is extended to 30 min, and the allyl trimethoxysilane is replaced by allyl triethoxysilane;

[0076] The mechanical stirring and ultrasonic action time in step 2) is extended to 120 min, the hydrochloric acid is replaced by potassium hydroxide, and the pH value is adjusted to 12;

[0077] The graphene nanosheet in step 2) is replaced by graphite, the addition amount of carboxymethyl cellulose is increased from 10 phr to 15 phr, and the addition amount of DOPO modified linear conductive nanomaterial is reduced from 15 phr to 12 phr.

[0078] The rest is the same as example 1.

[0079] Example 8

[0080] The difference between this example and example 1 is that:

[0081] The toluene in step 1) is replaced by dimethyl formamide, the reaction temperature is increased to 110℃, the azobisisobutyronitrile is replaced by azobisisoheptane, and the mass ratio of azobisisoheptane to DOPO is 0.035:1;

[0082] The polypyrrole nanowire in step 2) is replaced by multi-walled carbon nanotube, and the reaction temperature is increased to 100℃;

[0083] The 1010 antioxidant in step 2) is replaced by 168 antioxidant, 0.8 phr pentaerythritol stearate is replaced by 1.2 phr oleic acid amide, the screw speed is increased from 350 r / min to 400 r / min, and the feeding speed is increased from 25 kg / h to 40 kg / h.

[0084] The rest is the same as example 1.

[0085] Example 9

[0086] The difference between this example and example 1 is that:

[0087] In step 1), azobisisobutyronitrile is replaced by dibenzoyl peroxide, the dropping time is shortened to 0.5 h, and the reaction time is shortened to 12 h;

[0088] In step 2), hydrochloric acid is replaced by sulfuric acid, and the reaction time is shortened to 8 h;

[0089] In step 2), 1010 antioxidant is replaced by 626 antioxidant, the addition amount of antioxidant is reduced from 0.3 phr to 0.1 phr, and carboxymethyl cellulose is replaced by chitosan;

[0090] In step 3), the temperature of 1-11 zones is changed to 200℃, 205℃, 210℃, 215℃, 215℃, 215℃, 215℃, 215℃, 215℃, 210℃, 205℃, and the die temperature is changed to 210℃.

[0091] The rest is the same as example 1.

[0092] Example 10

[0093] The difference between this example and example 1 is that:

[0094] In step 1), toluene is replaced by isopropyl alcohol, the mechanical stirring time is extended to 60 min, allyl trimethoxysilane is replaced by allyl triethoxysilane, and the mass ratio of allyl triethoxysilane to DOPO is 1:1;

[0095] In step 2), hydrochloric acid is replaced by phosphoric acid, and the pH value is adjusted to 4;

[0096] In step 2), 1010 antioxidant is replaced by 264 antioxidant, the addition amount of pentaerythritol stearate is reduced from 0.8 phr to 0.5 phr, graphene nanosheet is replaced by MXene, and carboxymethyl cellulose is replaced by cellulose.

[0097] The rest is the same as example 1.

[0098] Comparative example 1

[0099] In order to prove that the present application can endow PET substrate with excellent electromagnetic shielding effect and flame retardant performance, pure PET is used.

[0100] Comparative example 2

[0101] In order to prove that the modification of DOPO to linear conductive nanomaterials can overcome the difficulty of flame retardant of polymer-based electromagnetic shielding materials, unmodified linear conductive nanomaterials are used to replace DOPO modified linear conductive nanomaterials added to PET as a comparison.

[0102] PET granules, 0.3 phr 1010 antioxidant, 0.8 phr pentaerythritol stearate, 5.0 phr graphene nanosheet, 10.0 phr carboxymethyl cellulose and 10.0 phr linear conductive nanomaterial were mixed uniformly in a high-speed mixer, and then were added into a twin-screw extruder for melt blending to prepare a PET material. The parameter settings of the twin-screw extruder were as follows: the temperatures of zones 1-11 were 190°C, 195°C, 200°C, 205°C, 205°C, 205°C, 205°C, 205°C, 205°C, 200°C, 195°C, respectively, the die temperature was 200°C, the screw rotation speed was 350 r / min, and the feeding speed was 25 kg / h.

[0103] Test methods

[0104] 1. Scanning electron microscope (SEM): performed on a hot field emission scanning electron microscope (Carl Zeiss, Germany, model: Merlin). The sample was adhered to the sample stage by conductive glue and was treated with surface gold spraying. The sample surface morphology was observed by scanning imaging with an electron beam at an acceleration voltage of 5 kV.

[0105] 2. Electromagnetic shielding performance test: the flake sample was clamped in the waveguide clamp of an N5227B network analyzer, and the electromagnetic shielding effectiveness of the X band (8.2-12.4 GHz), Ku band (11.8-18 GHz) and K band (18-27.6 GHz) was tested, respectively. According to the measured S11, S21 parameters and the following formula, the reflectivity R, transmittance T, absorption rate A, total electromagnetic shielding effectiveness SET, reflection shielding effectiveness SER and absorption shielding effectiveness SEA of the PET composite material were calculated:

[0106] R = |S 11 | 2

[0107] T = |S 21 | 2

[0108] A = 1 - R - T

[0109] SE R = -10 log (1 - R)

[0110] SE A = -10 log [T / (1 - R)]

[0111] SE T = SE R + SE A + SE M

[0112] 3. Limiting Oxygen Index (LOI) Test: Performed according to ASTM D2863 standard, with a sample size of 120mm × 6.5mm × 3mm.

[0113] 4. Vertical Burning (UL-94) Test: Conducted according to ASTM 635-2003 standard, with sample dimensions of 127mm × 12.7mm × 3.2mm.

[0114] See Table 1 below for the electromagnetic shielding performance of the samples in Examples 1-10 and Comparative Examples 1-2.

[0115]

[0116] See Table 2 below for the flame retardant properties of the samples in Examples 1-10 and Comparative Examples 1-2.

[0117]

[0118]

[0119] See Figure 1 As shown, SEM images of (A) polypyrrole and (B) DOPO-modified linear conductive nanomaterials in Example 1 are presented. The SEM images show that polypyrrole exhibits a smooth, uniform linear structure; while the DOPO-modified linear conductive nanomaterials obtained after modification with alkenylsilane (such as...) Figure 1 (B) The surface becomes rough and the diameter of the nanowires increases significantly, indicating that DOPO-modified linear conductive nanomaterials have been successfully synthesized.

[0120] As can be seen from the data in Tables 1 and 2, DOPO-modified linear conductive nanomaterials synthesized through different processes using dilute silanes, linear conductive nanomaterials, initiators, and pH adjusters can all be used to prepare composite materials with excellent electromagnetic shielding and flame retardant properties when added to PET with layered conductive materials, bio-based charring agents, antioxidants, and lubricants in different proportions and under different process conditions.

[0121] As can be seen from Table 1, the PET composite provided by the present application has good electromagnetic shielding performance. The electromagnetic shielding performance of the PET material provided in Example 1 is 42 dB, 35 dB and 45 dB in the X band (8.2-12.4 GHz), Ku band (11.8-18 GHz) and K band (18-27.6 GHz), respectively. In comparison, the electromagnetic shielding performance of the pure PET material of Comparative Example 1 in the X band, Ku band and K band is close to 0. This is because the layered conductive material and the DOPO modified linear conductive nanomaterial form a continuous conductive network in the PET, which endows the PET with good conductivity, and meanwhile the layered conductive material is arranged in the transverse direction, which can reflect the incoming electromagnetic waves in the opposite direction, thereby reducing the proportion of electromagnetic waves passing through the material. It is worth noting that the electromagnetic shielding performance of Example 1 is even better than that of the pure electromagnetic shielding material (Comparative Example 2). This is because after modification by DOPO, the dispersibility of the linear conductive nanomaterial in the PET is effectively improved, which significantly improves the continuity of the conductive network of the material.

[0122] As can be seen from Table 2, the PET composite provided by the present application has excellent flame retardant performance. The pure PET material (Comparative Example 1) is extremely flammable, and the limiting oxygen index (LOI) is only 22.5%, and it is completely burned out in the vertical burning test without grade. For the pure electromagnetic shielding material (Comparative Example 2), the flame retardant performance is even worse than that of the pure PET, and the oxygen index decreases to 20.4%. This is because the conductive material has good thermal conductivity, which can accelerate the thermal degradation of the polymer during combustion. In comparison, the scheme provided by the present application endows the PET material with excellent flame retardant performance. The LOI of the PET material provided in Example 4 is as high as 33.6%, and it reaches UL-94 V-0 grade in the vertical burning test. This is because after modification of the linear conductive nanomaterial by DOPO and alkenyl silane, the periphery of the material is first degraded during burning. The degradation products of DOPO have a free radical quenching effect on one hand, which can inhibit the free radical chain thermal degradation of the PET molecules, and on the other hand can catalyze the crosslinking carbonization reaction of the bio-based charring agent to form a carbonized layer on the surface of the PET matrix to play a high-efficiency heat insulation and oxygen insulation role.

[0123] In summary, the PET composite provided by the present application has excellent electromagnetic shielding effect and flame retardant performance, which can effectively overcome the problem that the electromagnetic shielding performance and flame retardant performance of polymer-based electromagnetic shielding materials are difficult to be considered together, and has important significance for the electronic information field.

[0124] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the patent scope of the present application. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A method for preparing a flame-retardant PET material having electromagnetic shielding effect, characterized in that, The preparation steps include: S1. Synthesis of silane-modified DOPO In a reaction kettle, solvent A and DOPO are added, and DOPO is fully dispersed by mechanical stirring for 5-60 min. The reaction temperature of the reaction kettle is adjusted to 70-110°C. The initiator and alkenyl silane are dissolved in solvent A, and then dropped into the reaction kettle within 0.5-2 h. After dropping, the reaction is continued for 12-36 h. After the reaction is completed, a mixed solution A is obtained. S2. Synthesis of DOPO-modified linear conductive nanomaterial In the mixed solution A, linear conductive nanomaterial is added, and is fully dispersed by mechanical stirring and ultrasonic action. A pH adjuster is dissolved in solvent B, and is dropped into the mixed solution A. The pH is adjusted to 2-14. The reaction temperature of the reaction kettle is controlled to 70-100°C. The reaction is carried out for 6-24 h. After the reaction is completed, the mixed solution is centrifuged. The precipitate is washed with solvent A and solvent B. After drying, a DOPO-modified linear conductive nanomaterial is obtained. S3. Preparation of flame-retardant material PET granules, 0.1-0.8 phr antioxidant, 0.5-1.2 phr lubricant, 5.0-15.0 phr layered conductive material, 5.0-15.0 phr bio-based charring agent, and 10.0-20.0 phr DOPO-modified linear conductive nanomaterial are uniformly mixed in a high-speed mixer, and then are melt-blended in a twin-screw extruder to obtain a flame-retardant PET material with electromagnetic shielding effect.

2. The method of claim 1, wherein the flame-retardant PET material having electromagnetic shielding effect is prepared by adding 0.1 to 0.5 parts by weight of the electromagnetic shielding agent to 100 parts by weight of the PET material. In step S1, the mass ratio of the alkenyl silane to DOPO is 0.5-1.1:1, and the mass ratio of the initiator to DOPO is 0.005-0.035:

1.

3. The preparation method of the flame-retardant PET material with electromagnetic shielding effect according to claim 1, characterized in that, In step S1, the initiator is any one of cyclohexanone peroxide, dibenzoyl peroxide, diisopropyl peroxydicarbonate, tert-butyl hydroperoxide, azobis isobutyronitrile, and azobis isohexyl nitrile. In step S1, the alkenyl silane is any one of vinyl trimethoxysilane, vinyl triethoxysilane, methyl vinyl dimethoxysilane, methyl vinyl diethoxysilane, allyl trimethoxysilane, and allyl triethoxysilane.

4. The method of claim 1, wherein the flame retardant PET material having electromagnetic shielding effect is prepared by adding 0.1 to 0.5 parts by weight of the electromagnetic shielding agent to 100 parts by weight of the PET material. In step S2, the mass ratio of the linear conductive nanomaterial to DOPO is 0.5-1:

1.

5. The method of claim 1, wherein the flame retardant PET material having electromagnetic shielding effect is prepared by adding 0.1 to 0.5 parts by weight of the electromagnetic shielding agent to 100 parts by weight of the PET material. In step S2, the linear conductive nanomaterial is any one of single-walled carbon nanotube, multi-walled carbon nanotube, silver nanowire, polypyrrole nanowire, and poly(3,4-ethylenedioxythiophene) nanowire.

6. The method for preparing the flame-retardant PET material with electromagnetic shielding effect according to claim 1, characterized in that, In step S2, the pH adjuster is any one of sodium hydroxide, potassium hydroxide, hydrochloric acid, phosphoric acid, and sulfuric acid.

7. The method for preparing the flame-retardant PET material with electromagnetic shielding effect according to claim 1, characterized in that, The solvent A and the solvent B are any one of ethanol, isopropyl alcohol, toluene, dioxane, dimethylformamide, and deionized water.

8. The method for preparing the flame-retardant PET material with electromagnetic shielding effect according to claim 1, characterized in that, In step S3, the parameters of the twin-screw extruder are set as follows: 180-210 DEG C in zone 1, the temperature gradually increases and is at 185-230 DEG C in zones 2-4, the temperature remains consistent in zones 4-9, the temperature gradually decreases and is at 190-225 DEG C in zones 9-11, the die temperature is 195-225 DEG C, the screw rotation speed is 250-400 r / min, and the feeding speed is 12-45 kg / h.

9. The method for preparing the flame-retardant PET material with electromagnetic shielding effect according to claim 1, characterized in that, In step S3, The antioxidant is any one of 168, 264, 616, 626, 923, 1010 and 1076; The lubricant is any one of PET wax, stearic acid alcohol, oleic acid amide, erucic acid amide, stearic acid amide, glycerol monostearate and pentaerythritol stearate; The layered conductive material is any one of graphene nanosheet, graphene nanoribbon, MXene and graphite; The bio-based char-forming agent is any one of cellulose, carboxymethyl cellulose, chitosan, carboxymethyl chitosan and sodium alginate.

10. A flame-retardant PET material with electromagnetic shielding effect prepared by the preparation method in any one of claims 1-9.

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