A plastic master batch based on recycled PET and a preparation method thereof

Abstract

The application discloses a kind of plastic master batch based on recycled PET and preparation method thereof, belong to the technical field of recycled PET.The following weight parts of raw materials are included:70-80 recycled PET bottle pieces, 5-7 nano montmorillonite, 3-6 maleic anhydride graft POE, 3-5 ethylene-vinyl acetate copolymer, 10-20 organic flame retardant, 0.4-1.2 antioxidant and 0.5-1 lubricant.The organic flame retardant constructs P-N-char-forming agent synergistic flame-retardant system, significantly improves the flame retardant performance and certain degree of heat resistance of recycled PET;The nano montmorillonite can enhance the mechanical properties of master batch;The ethylene-vinyl acetate copolymer forms elastic particles dispersed in the matrix, further improves the mechanical properties of master batch;In conclusion, the recycled master batch prepared by the application has mechanical properties, flame retardant performance and certain heat resistance, and has application prospect in the technical field of recycled PET.

Description

Technical Field

[0001] This invention belongs to the field of recycled PET technology, specifically, it relates to a plastic masterbatch based on recycled PET and its preparation method. Background Technology

[0002] With the continuous rise in global plastic consumption, polyethylene terephthalate (PET) is widely used in beverage bottles, food packaging, and textile fibers due to its excellent mechanical properties, transparency, and processing performance. However, its single-use nature leads to the generation of a large amount of solid waste, placing enormous pressure on the environment. Against this backdrop, recycling and reusing waste PET products not only meets the requirements of a circular economy and sustainable development but is also an essential way to alleviate resource scarcity and environmental pollution.

[0003] Recycling PET and reusing it in the production of plastic products through processes such as washing, sorting, and melt granulation has become a common practice in the industry. Currently, one of the main directions for the reuse of rPET is the preparation of plastic masterbatches, which are intended to be used as a matrix material or to partially replace virgin materials in the production of products such as synthetic fibers, sheets, and injection molded parts. While this process achieves waste resource utilization, it also faces the challenge that the performance of recycled PET materials themselves declines due to processing and use throughout their life cycle. In particular, the lack or severe deficiency of flame retardant properties has become a key bottleneck restricting its expansion into high-value-added and high-safety fields.

[0004] PET is a flammable polymer with a low limiting oxygen index. It burns rapidly when exposed to open flames or high temperatures, and the combustion process is accompanied by intense heat release and dripping. The dripping not only accelerates the spread of the flame but can also ignite surrounding combustibles, causing secondary fires and significantly increasing the fire risk. Furthermore, during the recycling, crushing, and melt granulation processes, the molecular chains of recycled PET are prone to partial breakage, resulting in decreased crystallinity and further weakening of its mechanical properties and thermal stability compared to virgin PET. This makes its flame-retardant defects more pronounced, significantly increasing the fire risk.

[0005] Currently, the flame retardancy issue in recycled PET is a major challenge. Existing technologies often involve directly adding flame retardants, such as halogenated and inorganic flame retardants. However, halogenated flame retardants release large amounts of corrosive gases and highly carcinogenic substances like dioxins during combustion, posing significant harm to the environment and human health, contradicting the principles of environmental protection. While inorganic flame retardants are less harmful, they require higher dosages to achieve the desired flame retardant effect. Adding large amounts of inorganic flame retardants severely reduces the mechanical properties and processing flowability of recycled PET, leading to brittle products, increased molding difficulty, and failure to meet practical application requirements. Therefore, it is urgent to solve these problems to meet the higher application demands of the recycled PET technology field. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art and provide a plastic masterbatch based on recycled PET and its preparation method.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A plastic masterbatch based on recycled PET comprises the following raw materials in parts by weight: 70-80 parts recycled PET bottle flakes, 5-7 parts nano-montmorillonite, 3-6 parts maleic anhydride-grafted POE, 3-5 parts ethylene-vinyl acetate copolymer, 10-20 parts organic flame retardant, 0.4-1.2 parts antioxidant, and 0.5-1 part lubricant.

[0009] The nano-montmorillonite in the raw materials of this invention has a layered structure, which is intercalated and dispersed during the melting process. On the one hand, it slows down heat conduction and gas diffusion through physical barrier action, thus helping to improve flame retardant performance. On the other hand, it forms an interfacial bond with the recycled PET molecular chain, thereby improving mechanical properties. Maleic anhydride-grafted POE acts as a compatibilizer, which can improve the interfacial compatibility between the PET matrix and the nano-montmorillonite, ensuring the uniformity of the masterbatch. Finally, the ethylene-vinyl acetate copolymer forms elastic particles dispersed in the masterbatch after melting, which effectively relieves stress concentration and further improves the mechanical properties of the matrix.

[0010] As a further technical solution, the antioxidant is a hindered phenolic antioxidant.

[0011] As a further technical solution, the lubricant is one of calcium stearate and zinc stearate.

[0012] As a further technical solution, the organic flame retardant is prepared through the following steps:

[0013] S1. Add tris(hydroxymethyl)aminomethane and anhydrous tetrahydrofuran to a dry round-bottom flask, purge with nitrogen for 10-20 min, then place the reaction system in an ice-salt bath, turn on magnetic stirring to mix the raw materials, maintain at 0°C, and slowly add triethylamine dropwise to the flask using a constant pressure dropping funnel. After the addition is complete, dissolve dichloromethylphosphine in anhydrous tetrahydrofuran and add it dropwise to the flask. After the addition is complete, remove the ice-salt bath and continue the reaction at room temperature for 3-4 h. After the reaction is complete, perform post-processing to obtain the intermediate product.

[0014] S2. Add 4,4'-diaminodiphenylmethane and anhydrous tetrahydrofuran to a dry round-bottom flask, purge with nitrogen for 10-20 min, then place the reaction system in an ice-salt bath, turn on magnetic stirring to mix the raw materials, maintain at 0°C, and slowly add triethylamine dropwise to the flask using a constant pressure dropping funnel. After the addition is complete, dissolve the intermediate product in anhydrous tetrahydrofuran and add it dropwise to the flask. After the addition is complete, remove the ice-salt bath, continue stirring overnight at room temperature, and react for 12-16 h. After the reaction is complete, perform post-processing to obtain the organic flame retardant.

[0015] As a further technical solution, the ratio of the amounts of tris(hydroxymethyl)aminomethane, anhydrous tetrahydrofuran, triethylamine, and dichloromethylphosphine in step S1 is 12.1g:100mL:10.1g:14.3-15.8g.

[0016] As a further technical solution, in step S2, the ratio of the amounts of 4,4'-diaminodiphenylmethane, anhydrous tetrahydrofuran, triethylamine, and intermediate product is 19.8g:150mL:21.1-22.7g:45.7-48.6g.

[0017] The reaction formulas for the above preparation process are as follows:

[0018]

[0019] In the process of preparing the organic flame retardant of the present invention, in order to accurately obtain the organic flame retardant with the above-mentioned reactive structure, it is necessary to strictly control the amount of raw materials. In step S1, the molar ratio of tris(hydroxymethyl)aminomethane to dichloromethylphosphine is controlled at 1:1, and the latter is in excess. In step S2, the molar ratio of 4,4'-diaminodiphenylmethane to the intermediate product is controlled at 1:2, and the latter is in excess.

[0020] According to the above reaction formula, the organic flame retardant prepared by the present invention contains a variety of flame retardant components, including phosphorus, nitrogen and hydroxyl groups, which constitute the flame retardant system of PN-charring agent. Among them, phosphorus reacts with charring agent to generate char layer; nitrogen generates gas, which causes the char layer to expand, and finally forms an expanded char layer. The expanded char layer can play a triple role of heat insulation, oxygen isolation and smoke suppression, which greatly improves the flame retardant performance of the matrix. In addition, benzene rings are also introduced into the organic flame retardant. As a rigid group, benzene rings improve the mechanical properties of the matrix and enhance the heat resistance of the matrix.

[0021] This invention also provides a method for preparing plastic masterbatch based on recycled PET, comprising the following steps:

[0022] A1. The recycled PET bottle flakes are crushed by a crusher, then washed 3-4 times with deionized water at 50-60℃ to remove surface oil, dust and other impurities, and then placed in a vacuum drying oven to dry to obtain recycled PET granules.

[0023] A2. Add nano-montmorillonite, organic flame retardant, antioxidant and lubricant to a high-speed mixer and mix at 60-70℃ for 3-5 minutes. Then add recycled PET particles, maleic anhydride grafted POE and ethylene-vinyl acetate copolymer and continue mixing at 80-90℃ for 8-10 minutes to obtain the mixture.

[0024] A3. Feed the mixture into the feed hopper of the twin-screw extruder. The mixture stays in the barrel for 3-5 minutes to ensure full melting. It is then extruded through the die head and pelletized to obtain plastic masterbatch based on recycled PET.

[0025] As a further technical solution, the particle size after crushing is 3-5mm.

[0026] As a further technical solution, the drying temperature is 80-100℃ and the time is 4-6 hours.

[0027] As a further technical solution, the high-speed mixer rotates at a speed of 800-1000 rpm.

[0028] The beneficial effects of this invention are:

[0029] 1. This invention introduces a self-synthesized organic flame retardant to construct a PN-char-forming agent synergistic flame retardant system, which significantly improves the flame retardant performance and a certain degree of heat resistance of recycled PET;

[0030] 2. The introduction of nano-montmorillonite can form an interfacial bond with PET molecular chains through intercalation dispersion, thereby enhancing the mechanical properties of the masterbatch;

[0031] 3. The introduction of ethylene-vinyl acetate copolymer to form elastic particles dispersed in the matrix further improves the mechanical properties of the masterbatch;

[0032] 4. Halogen-free organic flame retardants are used, which avoids the problem of releasing toxic gases when traditional halogenated flame retardants burn, and meets the requirements of green environmental protection.

[0033] 5. Using recycled PET bottle flakes as the main raw material, it achieves efficient recycling and high-value-added application of waste PET, which is in line with the concept of circular economy and sustainable development.

[0034] In summary, the recycled masterbatch prepared by this invention combines mechanical properties, flame retardant properties, and certain heat resistance properties, and is environmentally friendly, showing promising application prospects in the field of recycled PET technology. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1

[0037] Preparation of organic flame retardants:

[0038] S1. Add 12.1g of tris(hydroxymethyl)aminomethane and 50mL of anhydrous tetrahydrofuran to a dry round-bottom flask, purge with nitrogen for 10min, then place the reaction system in an ice-salt bath, turn on magnetic stirring to mix the raw materials, maintain at 0℃, and slowly add 10.1g of triethylamine to the flask using a constant pressure dropping funnel. After the addition is complete, dissolve 14.3g of dichloromethylphosphine in 50mL of anhydrous tetrahydrofuran and add it to the flask. After the addition is complete, remove the ice-salt bath and continue the reaction at room temperature for 3h. When the reaction is complete, quench with ice water, transfer the mixture to a separatory funnel, separate the organic phase, wash with saturated brine, dry with anhydrous sodium sulfate, filter, and concentrate under reduced pressure using a rotary evaporator to obtain the intermediate product.

[0039] S2. Add 19.8 g of 4,4'-diaminodiphenylmethane and 50 mL of anhydrous tetrahydrofuran to a dry round-bottom flask. Purge with nitrogen for 10 min. Then place the reaction system in an ice-salt bath and turn on magnetic stirring to mix the raw materials. Keep the temperature at 0°C. Using a constant-pressure dropping funnel, slowly add 21.1 g of triethylamine to the flask. After the addition is complete, dissolve 45.7 g of the intermediate product in 100 mL of anhydrous tetrahydrofuran and add it to the flask. After the addition is complete, remove the ice-salt bath and continue stirring overnight at room temperature. After 12 h, the reaction is complete. Quench the reaction solution with ice water. Transfer the mixture to a separatory funnel, separate the organic phase, wash with saturated brine, dry with anhydrous sodium sulfate, filter, concentrate under reduced pressure using a rotary evaporator, and purify by column chromatography with dichloromethane / methanol = 10 / 1 (v / v) as the eluent to obtain the organic flame retardant.

[0040] A method for preparing plastic masterbatch based on recycled PET includes the following steps:

[0041] A1. 70 portions of recycled PET bottle flakes are crushed (particle size 3mm) by a crusher, then washed 3 times with 50℃ deionized water to remove surface oil, dust and other impurities, and then placed in a vacuum drying oven and dried at 80℃ for 4-6 hours to obtain recycled PET granules.

[0042] A2. Add 5 parts of nano montmorillonite, 10 parts of organic flame retardant, 0.4 parts of antioxidant 1010 and 0.5 parts of calcium stearate to a high-speed mixer (speed of 800 rpm), mix at 60°C for 3 min, then add recycled PET particles, 3 parts of maleic anhydride grafted POE and 3 parts of ethylene-vinyl acetate copolymer, and continue mixing at 80°C for 8 min to obtain the mixture;

[0043] A3. Feed the mixture into the feed hopper of the twin-screw extruder. The mixture stays in the barrel for 3 minutes to ensure full melting. It is then extruded through the die head and pelletized to obtain plastic masterbatch based on recycled PET.

[0044] Example 2

[0045] Preparation of organic flame retardants:

[0046] S1. Add 12.1g of tris(hydroxymethyl)aminomethane and 50mL of anhydrous tetrahydrofuran to a dry round-bottom flask, purge with nitrogen for 20min, then place the reaction system in an ice-salt bath, turn on magnetic stirring to mix the raw materials, maintain at 0℃, and slowly add 10.1g of triethylamine to the flask using a constant pressure dropping funnel. After the addition is complete, dissolve 15.8g of dichloromethylphosphine in 50mL of anhydrous tetrahydrofuran and add it to the flask. After the addition is complete, remove the ice-salt bath and continue the reaction at room temperature for 4h. When the reaction is complete, quench with ice water, transfer the mixture to a separatory funnel, separate the organic phase, wash with saturated brine, dry with anhydrous sodium sulfate, filter, and concentrate under reduced pressure using a rotary evaporator to obtain the intermediate product.

[0047] S2. Add 19.8 g of 4,4'-diaminodiphenylmethane and 50 mL of anhydrous tetrahydrofuran to a dry round-bottom flask. Purge with nitrogen for 20 min. Then place the reaction system in an ice-salt bath and turn on magnetic stirring to mix the raw materials. Maintain the temperature at 0 °C. Using a constant pressure dropping funnel, slowly add 22.7 g of triethylamine to the flask. After the addition is complete, dissolve 48.6 g of the intermediate product in 100 mL of anhydrous tetrahydrofuran and add it to the flask. After the addition is complete, remove the ice-salt bath and continue stirring overnight at room temperature. After 16 h, the reaction is complete. Quench the reaction solution with ice water. Transfer the mixture to a separatory funnel, separate the organic phase, wash with saturated brine, dry with anhydrous sodium sulfate, filter, concentrate under reduced pressure using a rotary evaporator, and purify by column chromatography with dichloromethane / methanol = 10 / 1 (v / v) as the eluent to obtain the organic flame retardant.

[0048] A method for preparing plastic masterbatch based on recycled PET includes the following steps:

[0049] A1. 75 portions of recycled PET bottle flakes were crushed (particle size 5mm) by a crusher, then washed 4 times with deionized water at 60℃ to remove surface oil, dust and other impurities, and then placed in a vacuum drying oven and dried at 100℃ for 6 hours to obtain recycled PET granules.

[0050] A2. Add 6 parts of nano-montmorillonite, 15 parts of organic flame retardant, 0.8 parts of antioxidant 1010 and 0.75 parts of calcium stearate to a high-speed mixer (speed of 1000 rpm), mix at 70°C for 5 min, then add recycled PET particles, 4.5 parts of maleic anhydride grafted POE and 4 parts of ethylene-vinyl acetate copolymer, and continue mixing at 90°C for 10 min to obtain the mixture;

[0051] A3. Feed the mixture into the feed hopper of the twin-screw extruder. The mixture stays in the barrel for 3-5 minutes to ensure full melting. It is then extruded through the die head and pelletized to obtain plastic masterbatch based on recycled PET.

[0052] Example 3

[0053] The only difference between this embodiment and Embodiment 2 is that, in this embodiment, a method for preparing plastic masterbatch based on recycled PET includes the following steps:

[0054] A1. 80 portions of recycled PET bottle flakes were crushed (particle size 5mm) by a crusher, then washed 4 times with deionized water at 60℃ to remove surface oil, dust and other impurities, and then placed in a vacuum drying oven and dried at 100℃ for 6 hours to obtain recycled PET granules.

[0055] A2. Add 7 parts of nano montmorillonite, 20 parts of organic flame retardant, 1.2 parts of antioxidant 1010 and 1 part of zinc stearate to a high-speed mixer (speed of 1000 rpm), mix at 70°C for 5 min, then add recycled PET particles, 6 parts of maleic anhydride grafted POE and 5 parts of ethylene-vinyl acetate copolymer, and continue mixing at 90°C for 10 min to obtain the mixture;

[0056] A3. Feed the mixture into the feed hopper of the twin-screw extruder. The mixture stays in the barrel for 5 minutes to ensure full melting. It is then extruded through the die head and pelletized to obtain plastic masterbatch based on recycled PET.

[0057] Comparative Example 1

[0058] The only difference between this comparative example and Example 3 is that in this comparative example, an equal amount of TCPP flame retardant was used to replace the organic flame retardant to obtain the masterbatch.

[0059] Comparative Example 2

[0060] The only difference between this comparative example and Comparative Example 1 is that in this comparative example, no nano-montmorillonite is added to obtain the masterbatch.

[0061] The following performance tests were conducted on Examples 1, 2, and 3, and on Examples 1 and 2:

[0062] The limiting oxygen index was determined according to GB / T 2406.2-2009 standard;

[0063] Tensile properties were determined according to GB / T 1040.2-2006 standard;

[0064] The heat distortion temperature was determined according to GB / T 1634.2-2019 standard.

[0065] The measurement results are shown in Table 1:

[0066] Table 1

[0067] Test Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Limiting oxygen index / % 30.7 32.5 33.2 27.1 21.5 Tensile strength / MPa 52.9 55.1 55.7 42.2 40.5 Heat distortion temperature / ℃ 75 80 82 68 61

[0068] As shown in Table 1, the mechanical properties, flame retardancy, and heat resistance of the recycled masterbatch prepared in the embodiments of the present invention are all higher than those of the comparative example. Therefore, the present invention has application prospects in the field of recycled PET technology.

[0069] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A plastic masterbatch based on recycled PET, characterized in that, The raw materials include the following parts by weight: 70-80 parts recycled PET bottle flakes, 5-7 parts nano montmorillonite, 3-6 parts maleic anhydride-grafted POE, 3-5 parts ethylene-vinyl acetate copolymer, 10-20 parts organic flame retardant, 0.4-1.2 parts antioxidant and 0.5-1 part lubricant; The organic flame retardant is prepared through the following steps: S1. Add tris(hydroxymethyl)aminomethane and anhydrous tetrahydrofuran to a flask, purge with nitrogen, place in an ice-salt bath, turn on the stirrer to keep the mixture at 0°C, add triethylamine dropwise, and after the addition is complete, dissolve dichloromethylphosphine in anhydrous tetrahydrofuran and add it dropwise to the flask, and after the addition is complete, continue the reaction at room temperature for 3-4 hours until the reaction is complete, and obtain the intermediate product. S2. Add 4,4'-diaminodiphenylmethane and anhydrous tetrahydrofuran to the flask, purge with nitrogen, and place in an ice-salt bath. Turn on the stirrer to keep the raw materials mixed at 0°C. Add triethylamine dropwise. After the addition is complete, dissolve the intermediate product in anhydrous tetrahydrofuran and add it dropwise to the flask. After the addition is complete, react at room temperature for 12-16 hours. The reaction is complete, and an organic flame retardant is obtained. In step S1, the ratio of the amounts of tris(hydroxymethyl)aminomethane, anhydrous tetrahydrofuran, triethylamine, and dichloromethylphosphine is 12.1 g: 100 mL: 10.1 g: 14.3-15.8 g; in step S2, the ratio of the amounts of 4,4'-diaminodiphenylmethane, anhydrous tetrahydrofuran, triethylamine, and the intermediate product is 19.8 g: 150 mL: 21.1-22.7 g: 45.7-48.6 g.

2. The plastic masterbatch based on recycled PET according to claim 1, characterized in that, The antioxidant is a hindered phenolic antioxidant.

3. The plastic masterbatch based on recycled PET according to claim 1, characterized in that, The lubricant is one of calcium stearate and zinc stearate.

4. A method for preparing a plastic masterbatch based on recycled PET, used to prepare the plastic masterbatch based on recycled PET as described in any one of claims 1-3, characterized in that, Includes the following steps: A1. The recycled PET bottle flakes are crushed by a crusher, then washed 3-4 times with deionized water at 50-60℃, and dried to obtain recycled PET granules. A2. Add nano-montmorillonite, organic flame retardant, antioxidant and lubricant to a high-speed mixer and mix at 60-70℃ for 3-5 minutes. Then add recycled PET particles, maleic anhydride grafted POE and ethylene-vinyl acetate copolymer and continue mixing at 80-90℃ for 8-10 minutes to obtain the mixture. A3. Feed the mixture into the feed hopper of the twin-screw extruder. The mixture stays in the barrel for 3-5 minutes, is then extruded, pelletized, and used to obtain plastic masterbatch based on recycled PET.

5. The method for preparing plastic masterbatch based on recycled PET according to claim 4, characterized in that, The drying temperature is 80-100℃, and the time is 4-6 hours.

6. The method for preparing plastic masterbatch based on recycled PET according to claim 4, characterized in that, The high-speed mixer operates at a speed of 800-1000 rpm.

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