A flame-retardant high-strength PET composite material and its preparation process

Abstract

The invention belongs to the technical field of PET, and discloses a flame-retardant high-strength PET composite material and a preparation process thereof. The composite material comprises 80-97 parts by weight of polyethylene terephthalate, 3-20 parts by weight of rosin-based phosphate polyester flame retardant, and 0.2-0.3 parts by weight of an antioxidant; the PET polyester is blended and modified by the rosin-based phosphate polyester flame retardant; the PET polyester contains an ethylene terephthalate structural unit and has a high structural similarity with the PET polyester, so that the polyester flame retardant can be uniformly dispersed in the PET polyester without affecting the mechanical properties of the material; and the composite material contains a condensed ring structure of rosin tricyclic diterpenes and a phosphate flame retardant group, so that the high temperature resistance and flame retardancy of the PET material are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of PET, and in particular relates to a flame-retardant high-strength PET composite material and a preparation process thereof. Background Art

[0002] PET polyethylene terephthalate has excellent mechanical properties, good electrical insulation, and strong friction resistance. It can be made into plastics, alloys, fibers and other products. It is widely used in the packaging industry, electronic appliances, medical and health fields. However, PET has poor flame retardancy and is easy to burn, so flame retardants are usually required. Inorganic flame retardants, halogen-containing flame retardants, halogen-free flame retardants, etc. Among them, phosphorus-based flame retardants are green and environmentally friendly, with many types, gas phase flame retardant and condensed phase flame retardant effects, and are widely used. However, the addition of flame retardants will have a significant impact on the mechanical properties of the material.

[0003] Countries around the world are vigorously developing bio-based resources, such as rosin acid, castor oil, cardanol, polyphenols and other natural compounds have good practical applications in PET polyester materials. Patent CN106317792B discloses a 190°C grade PET insulating film and its preparation method, using PET resin slices, isocyanate compounds, rosin pentaerythritol esters, pentaerythritol phosphates and the like as raw materials. The obtained PET insulating film has good high temperature resistance and is environmentally friendly. The present invention aims to use a polyester flame retardant containing rosin and phosphate to improve the high temperature resistance and flame retardancy of PET while maintaining good mechanical properties. Summary of the invention

[0004] 1. Technical issues to be resolved

[0005] In view of the deficiencies in the prior art, the present invention provides a flame-retardant high-strength PET composite material, which solves the problems of poor high temperature resistance and flame retardancy of PET materials.

[0006] (II) Technical solution

[0007] A flame-retardant high-strength PET composite material comprises 80-97 parts by weight of polyethylene terephthalate, 3-20 parts by weight of rosin-based phosphate polyester flame retardant, and 0.2-0.3 parts by weight of antioxidant.

[0008] The preparation process of rosin-based phosphate polyester flame retardant is:

[0009] Step a, add 4,4'-bisrosin ester-[1,1'-biphenyl]-3,3'-diformaldehyde, diethyl terephthalate and glacial acetic acid to N,N-dimethylformamide, stir to react, add water to precipitate, filter, wash with water and ethanol in turn, and dry to obtain rosin-based polyester.

[0010] Step b, adding rosin-based polyester and dimethyl phosphite to N,N-dimethylformamide, stirring for reaction, adding water to precipitate, filtering, washing with water and ethanol in sequence, and drying to obtain a rosin-based phosphate polyester flame retardant.

[0011] The structural formula of 4,4'-bis-rosin ester-[1,1'-biphenyl]-3,3'-dicarbaldehyde is formula (1):

[0012]

[0013] The structural formula of diethylamine terephthalate is formula (2):

[0014]

[0015] Preferably, in step a, the weight ratio of 4,4'-bis-rosin ester-[1,1'-biphenyl]-3,3'-dicarbaldehyde to diethylamine terephthalate is 1:(0.28-0.35).

[0016] Preferably, the reaction in step a is carried out at 70-100° C. for 12-24 h.

[0017] Preferably, in step b, the ratio of rosin-based polyester to dimethyl phosphite is 1:(0.18-0.23).

[0018] Preferably, in step b, the reaction is carried out at 55-70° C. for 12-18 h.

[0019] Preferably, the preparation process of 4,4'-bis-rosin acid ester-[1,1'-biphenyl]-3,3'-diformaldehyde is as follows: adding rosin acid into thionyl chloride to carry out chlorination reaction to obtain rosin acid chloride; then adding rosin acid chloride to toluene, adding 4,4'-dihydroxy-[1,1'-biphenyl]-3,3'-diformaldehyde and pyridine, wherein the weight ratio of rosin acid chloride, 4,4'-dihydroxy-[1,1'-biphenyl]-3,3'-diformaldehyde and pyridine is (2.6-2.8):1(0.9-1.2), reacting at 45-60°C for 5-8h, adding saturated sodium chloride solution, shaking and standing to separate, separating and rotary evaporating the toluene organic layer, washing with acetone, and drying to obtain 4,4'-bis-rosin acid ester-[1,1'-biphenyl]-3,3'-diformaldehyde.

[0020] Preferably, the preparation process of diethyl terephthalate is as follows: terephthaloyl chloride, N-(benzyloxycarbonylamino)-1-ethanol, acid binding agent triethylamine and catalyst 4-dimethylaminopyridine in a weight ratio of 1:(1.9-2.2):(1.1-1.2):(0.06-0.08) are added to dichloromethane at 0-5°C, and then reacted at 20-25°C for 18-24h, water is added, and the mixture is allowed to stand for stratification after oscillation. After separation, the dichloromethane organic layer is rotary evaporated, and the product is added to a reactor after drying. Methanol and Pd / C catalyst are added, and hydrogen with a pressure of 0.7-1MPa is introduced. The mixture is reacted at 20-30°C for 24-36h, the catalyst is recovered by filtration, the filtrate is rotary evaporated, and recrystallized from ethyl acetate to obtain diethyl terephthalate.

[0021] Preferably, the preparation process of the flame-retardant high-strength PET composite material is as follows: 80-97 parts by weight of polyethylene terephthalate, 3-20 parts by weight of rosin-based phosphate polyester flame retardant, and 0.2-0.3 parts by weight of antioxidant are added to a twin-screw extruder, the temperature of sections 1-6 is 180-250°C, the screw speed is 80-150r / min, and after extrusion, granulation is performed by a pelletizer to obtain a flame-retardant high-strength PET composite material.

[0022] The technical effect of the present invention is as follows: the present invention utilizes 4,4'-bisrosin ester-[1,1'-biphenyl]-3,3'-diformaldehyde and diethyl terephthalate to carry out Schiff base polymerization reaction, and then the Schiff base imine group of the main chain undergoes addition reaction with diethyl phosphite to obtain a rosin-based phosphate polyester flame retardant.

[0023] The present invention utilizes rosin-based phosphate polyester flame retardant to perform blending modification on PET polyester. The rosin-based phosphate polyester flame retardant contains ethylene terephthalate structural units, which have high structural similarity with ethylene terephthalate glycol structural units in PET polyester. The polyester flame retardant can be evenly dispersed in the PET polyester without affecting the mechanical properties of the material, and still maintains good tensile strength and elongation at break.

[0024] The rosin-based phosphate polyester flame retardant of the present invention contains a condensed ring structure of rosin tricyclic diterpenes, has high thermal stability, and can be pyrolyzed and carbonized at high temperatures, thereby increasing the thermal decomposition temperature and residual carbon content of PET polyester. In addition, the polyester flame retardant contains a phosphate flame retardant group, which pyrolyzes to produce phosphorus-containing oxygen acid, which can promote PET graft dehydration carbonization, and the generated coke layer has the function of isolating heat conduction and preventing oxygen from contacting the substrate, thereby achieving a good flame retardant effect. It exhibits higher high temperature resistance and flame retardant properties. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0026] Example 1

[0027] (1) Add 15 g of rosin acid into 18 mL of thionyl chloride, carry out chlorination reaction at 60° C. for 3 h, remove thionyl chloride by rotary evaporation, and dry to obtain rosin acid chloride. The reaction formula is:

[0028]

[0029] (2) Add 13g of rosin acid chloride to toluene, add 5g of 4,4'-dihydroxy-[1,1'-biphenyl]-3,3'-dicarboxaldehyde and 6g of pyridine, react at 45°C for 8h, add saturated sodium chloride solution, shake and let stand to separate, separate and rotary evaporate the toluene organic layer, wash with acetone, and dry to obtain 4,4'-bisrosin acid ester-[1,1'-biphenyl]-3,3'-dicarboxaldehyde. The reaction formula is:

[0030]

[0031] Example 2

[0032] 14 g of rosin acid chloride (prepared according to the process of Example 1) was added to toluene, and 5 g of 4,4'-dihydroxy-[1,1'-biphenyl]-3,3'-dicarboxaldehyde and 4.5 g of pyridine were added, and the mixture was reacted at 60° C. for 5 h. A saturated sodium chloride solution was added, and the mixture was allowed to stand for stratification after shaking. After separation, the toluene organic layer was rotary evaporated, washed with acetone, and dried to obtain 4,4'-bisrosin acid ester-[1,1'-biphenyl]-3,3'-dicarboxaldehyde.

[0033] Example 3

[0034] At 5°C, add 2g of terephthaloyl chloride, 4.4g of N-(benzyloxycarbonylamino)-1-ethanol, 2.2g of triethylamine and 0.16g of 4-dimethylaminopyridine to 25mL of dichloromethane, and then react at 25°C for 18h, add water, shake and let stand to separate, separate and rotary evaporate the dichloromethane organic layer, dry and add the product to the reactor, add 15mL of methanol and 0.5g of Pd / C catalyst, pass hydrogen at a pressure of 1MPa, react at 20°C for 36h, filter and recover the catalyst, rotary evaporate the filtrate, and recrystallize with ethyl acetate to obtain diethyl terephthalate. The reaction formula is:

[0035]

[0036] Example 4

[0037] At 5°C, add 2g of terephthaloyl chloride, 3.8g of N-(benzyloxycarbonylamino)-1-ethanol, 2.4g of triethylamine and 0.12g of 4-dimethylaminopyridine to 20mL of dichloromethane, and then react at 20°C for 24h. Add water, shake and let stand to separate. After separation, the dichloromethane organic layer is rotary evaporated, and after drying, the product is added to a reactor, 15mL of methanol and 0.5g of Pd / C catalyst are added, and hydrogen with a pressure of 0.7MPa is introduced. The reaction is carried out at 30°C for 24h, and the catalyst is recovered by filtration. The filtrate is rotary evaporated and recrystallized with ethyl acetate to obtain diethyl terephthalate.

[0038] Example 5

[0039] (1) Add 20 g of 4,4'-bis-rosin ester-[1,1'-biphenyl]-3,3'-dicarboxaldehyde (prepared according to the process of Example 1), 5.6 g of diethyl terephthalate (prepared according to the process of Example 3), and 5 mL of glacial acetic acid to 250 mL of N,N-dimethylformamide, stir and react at 90°C for 12 h, add water to precipitate, filter, wash with water and ethanol in turn, and dry to obtain rosin-based polyester. The reaction formula is:

[0040]

[0041] (2) Add 20 g of rosin-based polyester and 4.2 g of dimethyl phosphite to 250 mL of N,N-dimethylformamide, stir and react at 55°C for 18 h, add water to precipitate, filter, wash with water and ethanol in turn, and dry to obtain a rosin-based phosphate polyester flame retardant. The reaction formula is:

[0042]

[0043] (3) 970 g of polyethylene terephthalate, 30 g of rosin-based phosphate polyester flame retardant, and 3 g of antioxidant 1010 were added to a twin-screw extruder, the temperatures of sections 1-6 were 180°C, 225°C, 240°C, 250°C, 250°C, and 250°C, and the screw speed was 100 r / min. After extrusion, the pelletizer was used for granulation to obtain a flame-retardant and high-strength PET composite material.

[0044] Example 6

[0045] (1) To 300 mL of N,N-dimethylformamide, 20 g of 4,4'-bis-rosin ester-[1,1'-biphenyl]-3,3'-dicarboxaldehyde (prepared according to the process of Example 1), 7 g of diethyl terephthalate (prepared according to the process of Example 3), and 6 mL of glacial acetic acid were added, and the mixture was stirred at 70° C. for 24 h. Water was added to precipitate, and the precipitate was filtered, washed with water and ethanol in sequence, and dried to obtain a rosin-based polyester.

[0046] (2) Add 20 g of rosin-based polyester and 3.6 g of dimethyl phosphite to 200 mL of N,N-dimethylformamide, stir and react at 55° C. for 18 h, add water to precipitate, filter, wash with water and ethanol in turn, and dry to obtain a rosin-based phosphate polyester flame retardant.

[0047] (3) 880 g of polyethylene terephthalate, 120 g of rosin-based phosphate polyester flame retardant, and 2.6 g of antioxidant 1010 were added to a twin-screw extruder, the temperatures of sections 1-6 were 180°C, 225°C, 240°C, 250°C, 250°C, and 250°C, the screw speed was 80 r / min, and after extrusion, the pelletizer was used for granulation to obtain a flame-retardant and high-strength PET composite material.

[0048] Example 7

[0049] (1) To 300 mL of N,N-dimethylformamide, 20 g of 4,4'-bis-rosin ester-[1,1'-biphenyl]-3,3'-dicarboxaldehyde (prepared according to the process of Example 1), 6.6 g of diethyl terephthalate (prepared according to the process of Example 3), and 4 mL of glacial acetic acid were added, and the mixture was stirred at 100° C. for 12 h. Water was added to precipitate, and the precipitate was filtered, washed with water and ethanol in sequence, and dried to obtain a rosin-based polyester.

[0050] (2) Add 20 g of rosin-based polyester and 4.6 g of dimethyl phosphite to 300 mL of N,N-dimethylformamide, stir and react at 70° C. for 12 h, add water to precipitate, filter, wash with water and ethanol in turn, and dry to obtain a rosin-based phosphate polyester flame retardant.

[0051] (3) 800 g of polyethylene terephthalate, 200 g of rosin-based phosphate polyester flame retardant, and 2 g of antioxidant 1010 were added to a twin-screw extruder, the temperatures of sections 1-6 were 180°C, 225°C, 240°C, 250°C, 250°C, and 250°C, and the screw speed was 150 r / min. After extrusion, the pelletizer was used for granulation to obtain a flame-retardant and high-strength PET composite material.

[0052] Comparative Example 1

[0053] (3) 970 g of polyethylene terephthalate and 3 g of antioxidant 1010 were added to a twin-screw extruder. The temperatures of sections 1-6 were 180° C., 225° C., 240° C., 250° C., 250° C., and 250° C. The screw speed was 100 r / min. After extrusion, the mixture was pelletized using a pelletizer to obtain a PET composite material.

[0054] Comparative Example 2

[0055] (1) To 250 mL of N,N-dimethylformamide, 20 g of 4,4'-bis-rosin ester-[1,1'-biphenyl]-3,3'-dicarboxaldehyde (prepared according to the process of Example 1), 5.6 g of diethyl terephthalate (prepared according to the process of Example 3), and 5 mL of glacial acetic acid were added, and the mixture was stirred at 90° C. for 12 h. Water was added to precipitate, and the precipitate was filtered, washed with water and ethanol in sequence, and dried to obtain a rosin-based polyester.

[0056] (2) 970 g of polyethylene terephthalate, 30 g of rosin-based polyester, and 3 g of antioxidant 1010 were added to a twin-screw extruder, the temperatures of sections 1-6 were 180°C, 225°C, 240°C, 250°C, 250°C, and 250°C, and the screw speed was 100 r / min. After extrusion, the pelletizer was used for granulation to obtain a flame-retardant and high-strength PET composite material.

[0057] Comparative Example 3

[0058] (1) To 250 mL of N,N-dimethylformamide, 20 g of 4,4'-dihydroxy-[1,1'-biphenyl]-3,3'-dicarboxaldehyde, 5.6 g of diethyl terephthalate (prepared according to the process of Example 3), and 5 mL of glacial acetic acid were added, and the mixture was stirred at 90° C. for 12 h. Water was added to precipitate, and the precipitate was filtered, washed with water and ethanol in turn, and dried to obtain polyester.

[0059] (2) Add 20 g of polyester and 4.2 g of dimethyl phosphite to 250 mL of N,N-dimethylformamide, stir and react at 55° C. for 18 h, add water to precipitate, filter, wash with water and ethanol in turn, and dry to obtain a phosphate polyester flame retardant.

[0060] (3) 970 g of polyethylene terephthalate, 30 g of phosphate polyester flame retardant, and 3 g of antioxidant 1010 were added to a twin-screw extruder, the temperatures of sections 1-6 were 180°C, 225°C, 240°C, 250°C, 250°C, and 250°C, and the screw speed was 100 r / min. After extrusion, the pelletizer was used for granulation to obtain a flame-retardant and high-strength PET composite material.

[0061] Comparative Example 4

[0062] (1) To 250 mL of N,N-dimethylformamide, 20 g of 4,4'-bis-rosin ester-[1,1'-biphenyl]-3,3'-dicarboxaldehyde (prepared according to the process of Example 1), 5.6 g of p-phenylenediamine, and 5 mL of glacial acetic acid were added, and the mixture was stirred at 90° C. for 12 h. Water was added to precipitate, and the precipitate was filtered, washed with water and ethanol in sequence, and dried to obtain a rosin-based polymer.

[0063] (2) Add 20 g of rosin-based polymer and 4.2 g of dimethyl phosphite to 250 mL of N,N-dimethylformamide, stir and react at 55° C. for 18 h, add water to precipitate, filter, wash with water and ethanol in sequence, and dry to obtain a rosin-based phosphate polymer flame retardant;

[0064] (3) 970 g of polyethylene terephthalate, 30 g of rosin-based phosphate polymer flame retardant, and 3 g of antioxidant 1010 were added to a twin-screw extruder, the temperatures of sections 1-6 were 180°C, 225°C, 240°C, 250°C, 250°C, and 250°C, and the screw speed was 100 r / min. After extrusion, the pelletizer was used for granulation to obtain a flame-retardant and high-strength PET composite material.

[0065] 5 mg of the PET composite material was weighed and placed in a thermogravimetric analyzer, and the thermal properties were tested in a nitrogen atmosphere at a heating rate of 10° C. / min and a test temperature range of 30-800° C. The initial thermal decomposition temperature was the temperature at which 5% mass loss occurred.

[0066] 3 mg of PET composite material was weighed and placed in a microcalorimeter with a heating rate of 1°C / s and a test temperature range of 30-900°C to test the combustion performance.

[0067] Table 1 Thermal properties and combustion performance of PET composites

[0068]

[0069]

[0070] The PET composite material was injection molded into a standard specimen by an injection molding machine at an injection temperature of 265°C.

[0071] The tensile properties are tested according to GB / T 1040.1-2018 method.

[0072] Table 2 Tensile properties of PET composites

[0073] Tensile strength(MPa) Elongation at break (%) Example 5 48.7 4.2 Example 6 44.9 4.9 Example 7 40.1 3.7 Comparative Example 1 44.2 4.5 Comparative Example 2 49.5 4.0 Comparative Example 3 43.6 4.3 Comparative Example 4 33.8 2.4

[0074] As shown in the table above, Comparative Example 1 is a common PET composite material. The initial thermal decomposition temperature of the PET composite material is 404.3°C, the residual carbon content at 800°C is 8.1%, and the peak heat release rate is 488.4 W·g -1 , the total heat release is 20.6 kJ·g -1 The tensile strength is 44.2MPa and the elongation at break is 4.5%.

[0075] In Examples 5-7, rosin-based phosphate polyester flame retardant was added, which significantly increased the initial thermal decomposition temperature and residual carbon content of the PET composite material, and greatly reduced the peak heat release rate and total heat release, showing higher high temperature resistance and flame retardant properties. This is because the rosin-based phosphate polyester flame retardant contains ethylene terephthalate structural units. It has a high structural similarity with the ethylene terephthalate structural unit in PET polyester, so that the polyester flame retardant can be evenly dispersed in PET polyester without affecting the mechanical properties of the material, and still maintaining good tensile strength and elongation at break. In addition, the polyester flame retardant contains a condensed ring structure of rosin tricyclic diterpenes, has high thermal stability, and will pyrolyze and carbonize at high temperatures, thereby increasing the thermal decomposition temperature and residual carbon content of PET polyester. In addition, the polyester flame retardant contains phosphate flame retardant groups, which pyrolyze to produce phosphorus oxygen acid, which can promote PET grafting dehydration carbonization. The generated char layer has the function of isolating heat conduction and preventing oxygen from contacting the matrix, thereby achieving a good flame retardant effect.

[0076] The difference between Comparative Example 2 and Example 5 is that a rosin-based polyester without a phosphate group is added to the PET polyester. The rosin-based polyester contains an ethyl terephthalate structural unit and has a high structural similarity with the PET polyester, so that it can be evenly dispersed in the PET polyester without affecting the mechanical properties of the material. In addition, the rosin-based polyester contains a condensed ring structure of rosin tricyclic diterpenes with high thermal stability, and its initial thermal decomposition temperature and residual carbon content are significantly higher than those of Comparative Example 1, and the high temperature resistance is excellent. However, the rosin-based polyester does not contain a phosphate flame retardant group, resulting in poor flame retardancy of the PET material, and a large heat release rate peak and total heat release.

[0077] In Comparative Example 3, 4,4'-dihydroxy-[1,1'-biphenyl]-3,3'-diformaldehyde without a rosin structure is polymerized with diethyl terephthalate. The obtained phosphate polyester flame retardant has a high structural similarity with PET polyester, and can be evenly dispersed in PET polyester without affecting the mechanical properties of the material. However, it does not contain the condensed ring structure of rosin tricyclic diterpenes with high thermal stability, resulting in the initial thermal decomposition temperature and residual carbon content of the PET polyester material being lower than those in Example 5, and the high temperature resistance is poor.

[0078] Comparative Example 4: A rosin-based phosphate polymer flame retardant obtained by polymerization of 4,4'-bis-rosin ester-[1,1'-biphenyl]-3,3'-dicarboxaldehyde and p-phenylenediamine does not contain ethylene terephthalate structural units. The compatibility and dispersibility with PET polyester are very poor, which will have a great impact on the mechanical properties of the material, and the tensile strength and elongation at break are significantly reduced.

Claims

1. A flame retardant high-strength PET composite material, characterized in that: The invention comprises 80-97 parts by weight of polyethylene terephthalate, 3-20 parts by weight of rosin-based phosphate polyester flame retardant, and 0.2-0.3 parts by weight of antioxidant; The preparation process of the rosin-based phosphate polyester flame retardant is: Step a, adding 4,4'-bisrosin ester-[1,1'-biphenyl]-3,3'-dicarboxaldehyde, diethyl terephthalate and glacial acetic acid to N,N-dimethylformamide, stirring to react, precipitating, filtering, washing and drying to obtain rosin-based polyester; Step b, adding rosin-based polyester and dimethyl phosphite to N,N-dimethylformamide, stirring for reaction, separating out the precipitate, filtering, washing, and drying to obtain a rosin-based phosphate polyester flame retardant; The structural formula of the 4,4'-bis-rosin ester-[1,1'-biphenyl]-3,3'-dicarbaldehyde is formula (1): Formula (1); The structural formula of diethylamine terephthalate is formula (2): Formula (2).

2. The flame-retardant high-strength PET composite material according to claim 1, characterized in that: In the step a, the weight ratio of 4,4'-bis-rosin ester-[1,1'-biphenyl]-3,3'-dicarbaldehyde to diethylamine terephthalate is 1:(0.28-0.35).

3. The flame-retardant high-strength PET composite material according to claim 1, characterized in that: The reaction in step a is carried out at 70-100° C. for 12-24 hours.

4. The flame-retardant high-strength PET composite material according to claim 1, characterized in that: The weight ratio of rosin-based polyester to dimethyl phosphite in step b is 1:(0.18-0.23).

5. The flame-retardant high-strength PET composite material according to claim 1, characterized in that: In the step b, the reaction is carried out at 55-70° C. for 12-18 hours.

6. The flame-retardant high-strength PET composite material according to claim 1, characterized in that: The preparation process of 4,4'-bis-rosin acid ester-[1,1'-biphenyl]-3,3'-diformaldehyde is as follows: adding rosin acid to thionyl chloride to carry out chlorination reaction to obtain rosin acid chloride; then adding rosin acid chloride to toluene, adding 4,4'-dihydroxy-[1,1'-biphenyl]-3,3'-diformaldehyde and pyridine, reacting at 45-60° C. for 5-8 hours, separating, washing, and drying to obtain 4,4'-bis-rosin acid ester-[1,1'-biphenyl]-3,3'-diformaldehyde.

7. The flame-retardant high-strength PET composite material according to claim 6, characterized in that: The weight ratio of the rosin acid chloride, 4,4'-dihydroxy-[1,1'-biphenyl]-3,3'-dicarbaldehyde and pyridine is (2.6-2.8):1(0.9-1.2).

8. The flame-retardant high-strength PET composite material according to claim 1, characterized in that: The preparation process of diethyl terephthalate is as follows: adding terephthaloyl chloride, N-(benzyloxycarbonylamino)-1-ethanol, triethylamine and 4-dimethylaminopyridine to dichloromethane at 0-5°C, reacting for 18-24h at 20-25°C, adding the product to a reactor after separation, adding methanol and a Pd / C catalyst, introducing hydrogen with a pressure of 0.7-1MPa, reacting for 24-36h at 20-30°C, filtering, rotary evaporation, and recrystallization to obtain diethyl terephthalate.

9. The flame-retardant high-strength PET composite material according to claim 8, characterized in that: The weight ratio of the terephthaloyl chloride, N-(benzyloxycarbonylamino)-1-ethanol, triethylamine and 4-dimethylaminopyridine is 1:(1.9-2.2):(1.1-1.2):(0.06-0.08).

10. A process for preparing the flame-retardant high-strength PET composite material according to any one of claims 1 to 9, characterized in that: 80-97 parts by weight of polyethylene terephthalate, 3-20 parts by weight of rosin-based phosphate polyester flame retardant, and 0.2-0.3 parts by weight of antioxidant are added into a twin-screw extruder, the temperature of sections 1-6 is 180-250° C., the screw speed is 80-150 r / min, and after extrusion, pelletization is performed by a pelletizer to obtain a flame-retardant high-strength PET composite material.

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