An ultralow-melting-point polyester chip and a preparation method thereof

Abstract

The application belongs to the technical field of polymer materials, and particularly relates to a kind of super low melting point polyester chips and a preparation method thereof. The application uses terephthalic acid and adipic acid as main acid source, and is matched with 1,4-butanediol, modified polyether, dimethyl isophthalate, and the melting point of the polyester chips prepared by multiple modification is reduced to the super low interval of 100-120 DEG C, which is suitable for the fields of hot melt adhesive, non-woven fabric, hot melt wire, etc.; the modified polyether is maleic anhydride grafted polyethylene glycol-polypropylene glycol block polyether, which not only reduces the melting point of the polyester chips, but also improves the toughness of the polyester chips; a chain extender composed of adipic dihydrazide and triphenylmethane triisocyanate is added in the later stage of polycondensation, which realizes the slight crosslinking of molecular chain and effectively improves the toughness of the polyester chips.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to an ultra-low melting point polyester chip and its preparation method. Background Technology

[0002] Polyester chips are sheet-like granules processed from polyester raw materials obtained through polymerization. As a core raw material, they are used in many fields such as fibers, containers, packaging materials, films, and engineering plastics. Among them, low-melting-point polyester chips have become key materials in industries such as hot melt adhesives, nonwoven fabrics, and footwear materials due to their unique thermal bonding properties. Among them, polyester chips prepared with purified terephthalic acid (PTA) as the core raw material have become the mainstream product of the polyester industry due to the advantages of readily available raw materials, low cost, good environmental performance, and good controllability of polymerization reaction. Polyethylene terephthalate (PET) chips, which are conventionally prepared with PTA as raw material, are crystalline polymers with melting points typically between 250 and 265°C and glass transition temperatures of 69°C. Although they have good mechanical properties, chemical resistance, and electrical insulation, they have obvious technical shortcomings, especially high melting point, low intrinsic viscosity, insufficient bonding strength, and poor toughness. This results in high processing energy consumption and difficult molding, making it unable to meet the application requirements of low-temperature thermal bonding, precision processing, and high bonding strength. Therefore, developing ultra-low melting point polyester chips with PTA as raw material has become an important direction for expanding the downstream applications of PTA and promoting the differentiated development of the polyester industry.

[0003] Currently, the development of low-melting-point polyester chips and related preparation technologies using PTA as a raw material still has many shortcomings, making it difficult to meet the high-quality and large-scale application needs of downstream industries. On the one hand, the melting points of existing low-melting-point polyester chips using PTA as a raw material are mostly concentrated in the higher range, with very few products achieving ultra-low melting points of 110-130℃ and below. Furthermore, due to the difficulty in controlling the compatibility between modifiers and PTA during the PTA polymerization reaction, the product performance is poor, making it difficult to adapt to high-end scenarios such as precision thermal bonding and low-temperature blending. On the other hand, PTA is a solid-phase raw material, which easily forms a heterogeneous system when mixed with liquid-phase modifiers and monomers such as ethylene glycol, resulting in difficulty in reaction control. Some modifiers used in certain processes (such as specific diols and neopentyl glycol) have a high rate of side reactions during the esterification process with PTA, easily generating harmful byproducts such as cyclic oligomers, affecting product performance and production stability. In addition, some PTA-based ultra-low melting point polyester chips prepared by existing processes have poor toughness and strength, making them difficult to process into fibers. They are also prone to problems such as chip clumping, sticking to the wall, and spinning breakage during processing, which prevents large-scale industrial production. Furthermore, key properties such as thermal stability and bonding strength of the products are difficult to achieve, which limits the further expansion of their application range.

[0004] Chinese patent application CN110684184A discloses a method for preparing diol-modified PETG polyester chips. The method uses terephthalic acid, neopentyl glycol, diethylene glycol, and ethylene glycol in a molar ratio of 1:(0.1–0.5):(0.05–0.1):(0.6–0.8) as raw materials, and carries out a polymerization reaction under the action of a catalyst to obtain diol-modified PETG polyester chips. The formulation uses a combination of neopentyl glycol and diethylene glycol to modify the polyester chips; however, the proportions of both are relatively low. The steric hindrance of neopentyl glycol easily leads to a decrease in the regularity of the polyester molecular chain. Although this improves transparency, long-term use can easily result in a low heat distortion temperature. The addition of diethylene glycol is too low, only improving the toughness shortcomings of simple neopentyl glycol modification, and cannot further optimize melt flowability, processability, and other properties. Furthermore, neopentyl glycol and PTA are prone to side reactions during esterification, affecting product performance. Summary of the Invention

[0005] To address the technical problems of high melting point and poor toughness in the prior art, this invention provides an ultra-low melting point polyester chip and its preparation method.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing ultra-low melting point polyester chips includes the following steps: S1: Add 1,4-butanediol and modified polyether to the reactor and stir to 85-95℃ to dissolve. Add terephthalic acid, dimethyl isophthalate and adipic acid, stir evenly, and then add catalyst, antioxidant and heat stabilizer. Stir evenly to obtain slurry. S2: Esterify the slurry obtained in step S1 to obtain the esterified product; S3: Polycondense the esterified product obtained in step S2 to obtain polyester melt; S4: Filter the melt obtained in step S3, granulate it underwater, vacuum dry it, and sieve it to obtain ultra-low melting point polyester chips. The modified polyether is maleic anhydride-grafted polyethylene glycol-polypropylene glycol block polyether.

[0007] The above scheme uses terephthalic acid as the main acid source to form the basic framework of the polyester, ensuring the basic mechanical properties of the polyester chips. Adipic acid can disrupt the regularity of polyester crystallization, effectively reducing the melting point of the polyester chips. 1,4-Butanediol is a flexible polyol that can synergistically reduce melting point and improve the flexibility of molecular chains. The maleic anhydride grafted functional groups in maleic anhydride-grafted polyethylene glycol-polypropylene glycol block polyether can undergo esterification graft copolymerization with the terminal hydroxyl / carboxyl groups of the polyester molecular chain, achieving molecular-level compatibility between the modified polyether and the polyester matrix. This avoids problems such as phase separation and toughening failure between the polyether and polyester in subsequent processes. At the same time, the maleic anhydride-grafted polyethylene glycol-polypropylene glycol block polyether embeds itself between polyester molecular chains to form entanglements, disrupting the regularity of polyester molecular chain crystallization, reducing the melting point, and significantly improving the elongation at break and impact strength of the polyester chips.

[0008] Furthermore, the modified polyether is prepared by adding block polyether and hydroquinone into a reaction vessel, heating to 80-90°C, adding maleic anhydride and benzoyl peroxide under nitrogen protection, heating to 110-120°C, maintaining the temperature for 3-4 hours, cooling to 70-80°C, adding benzoyl chloride, stirring for 1.5-2 hours, and vacuum drying for 1 hour to obtain the modified polyether.

[0009] In the above scheme, the modification of block polyether by maleic anhydride is achieved through four steps: premixing and heating, grafting reaction, end-group sealing, and vacuum devolatilization. Adding hydroquinone to the reactor before the reaction can effectively prevent maleic anhydride from undergoing self-polymerization during the grafting process, generating random copolymer maleic anhydride impurities and improving product purity. After the reaction, adding benzoyl chloride precisely seals the residual terminal hydroxyl groups of the polyether molecular chain, which not only prevents the polyether terminal hydroxyl groups from undergoing excessive crosslinking during polyester polymerization, but also improves the temperature resistance of the polyether and prevents its thermal degradation during polycondensation.

[0010] Furthermore, the mass fractions of each component in the preparation method of the modified polyether are as follows: 100-120 parts of block polyether, 0.5-1 part of hydroquinone, 8-10 parts of maleic anhydride, 0.5-1 part of benzoyl peroxide, and 2-3 parts of benzoyl chloride.

[0011] Furthermore, the preparation method of the block polyether is as follows: Polyethylene glycol diglycidyl ether is added to a reaction vessel, anhydrous ethanol is added, the temperature is raised to 50-60°C under a nitrogen atmosphere, monoethanolamine is added dropwise while stirring, and the reaction is stirred for 4-6 hours to obtain a hydrophilic prepolymer; Polypropylene glycol diglycidyl ether is added to a reaction vessel, anhydrous ethanol is added, the temperature is raised to 50-60°C under a nitrogen atmosphere, monoethanolamine is added dropwise while stirring, and the reaction is stirred for 4-6 hours to obtain a hydrophobic prepolymer; Equimolar ratios of the hydrophilic and hydrophobic prepolymers are added to a reaction vessel, the temperature is raised to 70-80°C under a nitrogen atmosphere with magnetic stirring, the reaction is carried out for 8-10 hours, vacuum drying is performed at 80-90°C for 4-6 hours, anhydrous acetone is added, the mixture is stirred until completely dissolved, excess anhydrous diethyl ether is added dropwise, the mixture is stirred rapidly, and the mixture is filtered to obtain the block polyether.

[0012] In the above scheme, the epoxy groups at both ends of polyethylene glycol diglycidyl ether and polypropylene glycol diglycidyl ether undergo a nucleophilic ring-opening reaction with the amino group of monoethanolamine. The amino group attacks the carbon atom of the epoxy group, and the epoxy ring breaks, forming a linear prepolymer with reactive groups at both ends. Using the same reaction parameters and independently preparing the hydrophilic and hydrophobic prepolymers can ensure that the molecular weights of the two prepolymers are similar and the end-group reactivity is compatible, laying the foundation for subsequent intercalation. The reactive end groups of the two linear prepolymers undergo a ring-opening reaction at 70-80°C under a nitrogen atmosphere, and the hydrophilic and hydrophobic prepolymers are alternately linked to form a linear block polyether.

[0013] Furthermore, in the preparation method of block polyether, the molar ratio of polyethylene glycol diglycidyl ether to monoethanolamine is 1:1, and the molar ratio of polypropylene glycol diglycidyl ether to monoethanolamine is 1:1.

[0014] Furthermore, the weight parts of each component in step S1 are as follows: 38-45 parts of 1,4-butanediol, 7-10 parts of modified polyether, 30-40 parts of terephthalic acid, 10-15 parts of dimethyl isophthalate, 13-17 parts of adipic acid, 0.4-0.9 parts of catalyst, 0.1-0.4 parts of antioxidant, and 0.02-0.05 parts of heat stabilizer.

[0015] Furthermore, the catalyst described in step S1 is composed of tetrabutyl titanate and antimony glycol in a mass ratio of (2-3):1.

[0016] In the above scheme, a titanium-based + antimony-based composite catalyst is used to balance the efficiency of esterification reaction and the stability of polycondensation reaction, avoiding the reaction runaway or molecular chain degradation caused by a single catalyst, and ensuring the stability of the product's intrinsic viscosity.

[0017] Furthermore, the antioxidant mentioned in step S1 is antioxidant 1010, and the heat stabilizer is triphenyl phosphite.

[0018] Furthermore, the specific process of esterification in step S2 is as follows: the slurry is fed into the first esterification reactor and esterified at 0.10-0.15 MPa and 205-215°C for 2.5-3.0 h, and then discharged and fed into the second esterification reactor and esterified at -0.04--0.02 MPa and 220-230°C for 1.5-2.0 h.

[0019] Furthermore, the specific process of polycondensation in step S3 is as follows: the esterification product is fed into a pre-polycondensation reactor and reacted at 230-240℃ and -0.08--0.06MPa for 40-50 minutes, then fed into a mid-polycondensation reactor and reacted at 240-250℃ and -0.095--0.09MPa for 40-50 minutes, and finally fed into a final polycondensation reactor, where a chain extender is added and the reaction is carried out at 250-255℃ and -0.105--0.10MPa for 60-70 minutes.

[0020] Furthermore, the chain extender is composed of adipamide and triphenylmethane triisocyanate in a mass ratio of (7-9):(3-5), and the amount of chain extender used is 5-8 parts.

[0021] In the above scheme, a chain extender composed of adipamide and triphenylmethane triisocyanate is added in the later stage of polycondensation to enhance intermolecular forces. Adipamide disrupts the regularity of polyester crystallization, resulting in a low melting point. Triphenylmethane triisocyanate reacts with the terminal carboxyl and hydroxyl groups of the polyester molecular chain in the later stage of polycondensation, extending the molecular chain, forming a slight crosslink, and improving the intrinsic viscosity and toughness of the polyester chips.

[0022] The present invention also provides ultra-low melting point polyester chips prepared by the above-described method for preparing ultra-low melting point polyester chips.

[0023] The ultra-low melting point polyester chips obtained by the above method have a melting point reduced to the ultra-low range of 100-120℃ and have good toughness.

[0024] Compared with existing technologies, the ultra-low melting point polyester chip and its preparation method provided by this invention have the following technical advantages: (1) The present invention uses terephthalic acid and adipic acid as the main acid sources, combined with 1,4-butanediol, modified polyether and dimethyl isophthalate, and through multiple modifications, the melting point of the obtained polyester chips is reduced to an ultra-low range of 100-120℃, which is suitable for hot melt adhesives, non-woven fabrics, hot melt wires and other fields. (2) The present invention uses maleic anhydride-grafted polyethylene glycol-polypropylene glycol block polyether as modified polyether, which reduces the melting point of polyester chips and improves the toughness of polyester chips. (3) In the later stage of polycondensation, the present invention adds a chain extender composed of adipamide dihydrazine and triphenylmethane triisocyanate, which realizes mild cross-linking of molecular chains and effectively improves the toughness of polyester chips. Attached Figure Description

[0025] Figure 1 The infrared spectrum of the modified polyether prepared in Example 3. Detailed Implementation

[0026] The following will provide further details with reference to specific embodiments, but the present invention is not limited to these embodiments. Those skilled in the art can make various modifications based on the basic idea of ​​the present invention, but as long as they do not depart from the basic idea of ​​the present invention, they are all within the scope of the present invention. The raw materials described in this specific embodiment are all commercially available.

[0027] Preparation Example 1 The modified polyether is prepared as follows: 1 mol of polyethylene glycol diglycidyl ether is added to a reaction vessel, along with anhydrous ethanol (20% of the mass of polyethylene glycol diglycidyl ether). The mixture is heated to 50°C under a nitrogen atmosphere, and 1 mol of monoethanolamine is added dropwise while stirring. The reaction is stirred for 4 hours. The reaction progress is monitored by epoxy value titration. When the epoxy value drops to 3% of the initial value, the ring-opening reaction is considered to be basically complete, yielding a hydrophilic prepolymer. Alternatively, 1 mol of polypropylene glycol diglycidyl ether is added to a reaction vessel, along with anhydrous ethanol (20% of the mass of polyethylene glycol diglycidyl ether). The mixture is heated to 50°C under a nitrogen atmosphere, and 1 mol of monoethanolamine is added dropwise while stirring. The reaction was stirred for 4 hours, and the reaction progress was monitored by epoxy value titration. When the epoxy value dropped to 3% of the initial value, the ring-opening reaction was considered to be basically completed, and a hydrophobic prepolymer was obtained. Equimolar ratios of hydrophilic and hydrophobic prepolymers were added to the reactor, and the mixture was magnetically stirred under a nitrogen atmosphere and heated to 70°C. The reaction was carried out for 8 hours, and then vacuum dried at 80°C and a vacuum degree of -0.09 MPa for 4 hours to remove unreacted small molecules, solvents, and trace amounts of water generated during the reaction. Anhydrous acetone (solid-liquid ratio of 1:5) was added and stirred until completely dissolved. An excess of anhydrous diethyl ether was added dropwise and stirred rapidly. The product precipitated in the form of flocculent precipitate. The product was filtered, washed twice with anhydrous diethyl ether, and vacuum dried at 60°C for 6 hours to obtain block polyether.

[0028] 100g of block polyether was added to a reaction vessel, heated to 80℃, and 8g of maleic anhydride and 0.5g of benzoyl peroxide were added under nitrogen protection. The temperature was then raised to 110℃ and maintained for 3 hours. The temperature was lowered to 70℃, and 2g of benzoyl chloride was added. The mixture was stirred for 1.5 hours and then vacuum dried at 100℃ and a vacuum degree of -0.09MPa for 1 hour to obtain the modified polyether.

[0029] Preparation Example 2 The modified polyether is prepared as follows: 3 mol of polyethylene glycol diglycidyl ether is added to a reaction vessel, along with anhydrous ethanol (30% of the mass of polyethylene glycol diglycidyl ether). The mixture is heated to 60°C under a nitrogen atmosphere, and 3 mol of monoethanolamine is added dropwise while stirring. The reaction is stirred for 6 hours. The reaction progress is monitored by epoxy value titration. When the epoxy value drops to 5% of the initial value, the ring-opening reaction is considered to be basically complete, yielding a hydrophilic prepolymer. Alternatively, 3 mol of polypropylene glycol diglycidyl ether is added to a reaction vessel, along with anhydrous ethanol (30% of the mass of polyethylene glycol diglycidyl ether). The mixture is heated to 60°C under a nitrogen atmosphere, and 3 mol of monoethanolamine is added dropwise while stirring. The reaction was carried out for 6 hours. The reaction progress was monitored by epoxy value titration. When the epoxy value dropped to 5% of the initial value, the ring-opening reaction was considered to be basically completed, and a hydrophobic prepolymer was obtained. Equimolar ratios of hydrophilic and hydrophobic prepolymers were added to the reactor and heated to 80°C under a nitrogen atmosphere with magnetic stirring. The reaction was carried out for 10 hours and then vacuum dried at 90°C and a vacuum degree of -0.095MPa for 6 hours to remove unreacted small molecules, solvents, and trace amounts of water generated in the reaction. Anhydrous acetone (solid-liquid ratio of 1:5) was added and stirred until completely dissolved. An excess of anhydrous diethyl ether was added dropwise and stirred rapidly. The product precipitated in the form of flocculent material. The product was filtered, washed three times with anhydrous diethyl ether, and vacuum dried at 60°C for 8 hours to obtain block polyether.

[0030] 120g of block polyether was added to a reaction vessel, heated to 90℃, and 10g of maleic anhydride and 1g of benzoyl peroxide were added under nitrogen protection. The temperature was then raised to 120℃ and maintained for 4 hours. The temperature was lowered to 80℃, and 3g of benzoyl chloride was added. The mixture was stirred for 2 hours and then vacuum dried at 100℃ and a vacuum degree of -0.09MPa for 1 hour to obtain the modified polyether.

[0031] Preparation Example 3 The modified polyether is prepared as follows: 2 mol of polyethylene glycol diglycidyl ether is added to a reaction vessel, along with anhydrous ethanol (25% of the mass of polyethylene glycol diglycidyl ether). The mixture is heated to 55°C under a nitrogen atmosphere, and 2 mol of monoethanolamine is added dropwise while stirring. The reaction is stirred for 5 hours. The reaction progress is monitored by epoxy value titration. When the epoxy value drops to 4% of the initial value, the ring-opening reaction is considered to be basically complete, yielding a hydrophilic prepolymer. Alternatively, 2 mol of polypropylene glycol diglycidyl ether is added to a reaction vessel, along with anhydrous ethanol (25% of the mass of polyethylene glycol diglycidyl ether). The mixture is heated to 55°C under a nitrogen atmosphere, and 2 mol of monoethanolamine is added dropwise while stirring. The reaction was stirred for 5 hours, and the reaction progress was monitored by epoxy value titration. When the epoxy value dropped to 4% of the initial value, the ring-opening reaction was considered to be basically completed, and a hydrophobic prepolymer was obtained. Equimolar ratios of hydrophilic and hydrophobic prepolymers were added to the reactor, and the mixture was magnetically stirred under a nitrogen atmosphere and heated to 75°C. The reaction was carried out for 9 hours, and then vacuum dried at 85°C and a vacuum degree of -0.093 MPa for 5 hours to remove unreacted small molecules, solvents, and trace amounts of water generated during the reaction. Anhydrous acetone (solid-liquid ratio of 1:5) was added and stirred until completely dissolved. An excess of anhydrous diethyl ether was added dropwise and stirred rapidly. The product precipitated in the form of flocculent precipitate. The product was filtered, washed three times with anhydrous diethyl ether, and vacuum dried at 60°C for 8 hours to obtain block polyether.

[0032] 110g of block polyether was added to a reactor, heated to 85℃, and 9g of maleic anhydride and 0.7g of benzoyl peroxide were added under nitrogen protection. The temperature was then raised to 115℃ and maintained for 3.5h. The temperature was lowered to 75℃, and 3g of benzoyl chloride was added. The mixture was stirred for 1.8h and then vacuum dried at 100℃ and a vacuum degree of -0.09MPa for 1h to obtain the modified polyether.

[0033] Preparation Example 4 The modified polyether is prepared as follows: 2.5 mol of polyethylene glycol diglycidyl ether is added to a reaction vessel, along with anhydrous ethanol (25% of the mass of polyethylene glycol diglycidyl ether). The mixture is heated to 55°C under a nitrogen atmosphere, and 2.5 mol of monoethanolamine is added dropwise while stirring. The reaction is continued for 5 hours. The reaction progress is monitored by epoxy value titration. When the epoxy value drops to 4.2% of the initial value, the ring-opening reaction is considered basically complete, yielding a hydrophilic prepolymer. Alternatively, 2.5 mol of polypropylene glycol diglycidyl ether is added to a reaction vessel, along with anhydrous ethanol (25% of the mass of polyethylene glycol diglycidyl ether). The mixture is heated to 58°C under a nitrogen atmosphere, and 2.5 mol of monoethanolamine is added dropwise while stirring. The reaction was stirred for 5.2 h. The reaction progress was monitored by epoxy value titration. When the epoxy value dropped to 4.2% of the initial value, the ring-opening reaction was considered to be basically completed, and a hydrophobic prepolymer was obtained. Equimolar ratios of hydrophilic and hydrophobic prepolymers were added to the reactor and magnetically stirred under a nitrogen atmosphere until the temperature was raised to 78°C. The reaction was carried out for 9.2 h and then vacuum dried at 88°C and a vacuum degree of -0.094 MPa for 5.2 h to remove unreacted small molecules, solvents, and trace amounts of water generated during the reaction. Anhydrous acetone (solid-liquid ratio of 1:5) was added and stirred until completely dissolved. An excess of anhydrous diethyl ether was added dropwise and stirred rapidly. The product precipitated in the form of flocculent material. The product was filtered, washed three times with anhydrous diethyl ether, and vacuum dried at 60°C for 7 h to obtain block polyether.

[0034] 115g of block polyether was added to a reactor, heated to 88℃, and 9.3g of maleic anhydride and 0.75g of benzoyl peroxide were added under nitrogen protection. The temperature was then raised to 115℃ and maintained for 3.6h. The temperature was lowered to 78℃, and 2.6g of benzoyl chloride was added. The mixture was stirred for 1.8h and then vacuum dried at 100℃ and a vacuum degree of -0.09MPa for 1h to obtain the modified polyether.

[0035] Example 1 A method for preparing ultra-low melting point polyester chips includes the following steps: S1: 38g of 1,4-butanediol and 7g of modified polyether were added to a reactor, heated to 85°C and stirred to dissolve. Then, 30g of terephthalic acid, 10g of dimethyl isophthalate, and 13g of adipic acid were added and stirred until homogeneous. Next, 0.4g of catalyst, 0.1g of antioxidant 1010, and 0.02g of triphenyl phosphite were added and stirred until homogeneous to obtain a slurry. The catalyst consisted of tetrabutyl titanate and antimony glycolate in a mass ratio of 2:1. The modified polyether was prepared according to Preparation Example 1. S2: Esterify the slurry obtained in step S1. The slurry is fed into the first esterification reactor and esterified at 0.10 MPa and 205℃ for 3.0 h. Then the slurry is discharged and fed into the second esterification reactor and esterified at -0.02 MPa and 220℃ for 2.0 h to obtain the esterified product. S3: The esterified product obtained in step S2 is subjected to polycondensation. The esterified product is fed into a pre-polycondensation reactor and reacted at 230℃ and -0.06MPa for 50 min. Then it is fed into a medium-polycondensation reactor and reacted at 240℃ and -0.09MPa for 50 min. Finally, it is fed into a final polycondensation reactor, 5g of chain extender is added, and it is reacted at 250℃ and -0.105MPa for 70 min to obtain polyester melt. The chain extender is composed of adipamide and triphenylmethane triisocyanate in a mass ratio of 7:3. S4: Filter the melt obtained in step S3 and send it to an underwater pelletizer for underwater pelletizing. Control the pelletizing water temperature at 35℃ and the pelletizing speed at 300 rpm. Place the wet chips into a vacuum dryer and vacuum dry them at 70℃ and -0.08 MPa for 5 hours. Then sieve them to obtain ultra-low melting point polyester chips.

[0036] Example 2 A method for preparing ultra-low melting point polyester chips includes the following steps: S1: 45g of 1,4-butanediol and 10g of modified polyether were added to a reactor, heated to 95℃ and stirred to dissolve. Then, 40g of terephthalic acid, 15g of dimethyl isophthalate, and 17g of adipic acid were added and stirred until homogeneous. Next, 0.9g of catalyst, 0.4g of antioxidant 1010, and 0.05g of triphenyl phosphite were added and stirred until homogeneous to obtain a slurry. The catalyst consisted of tetrabutyl titanate and antimony glycolate in a mass ratio of 3:1. The modified polyether was prepared according to Preparation Example 2. S2: Esterify the slurry obtained in step S1. The slurry is fed into the first esterification reactor and esterified at 0.15 MPa and 215 °C for 2.5 h. Then the slurry is discharged and fed into the second esterification reactor and esterified at -0.04 MPa and 230 °C for 1.5 h to obtain the esterified product. S3: The esterified product obtained in step S2 is subjected to polycondensation. The esterified product is fed into a pre-polycondensation reactor and reacted at 240℃ and -0.08MPa for 40 min. Then it is fed into a medium-polycondensation reactor and reacted at 250℃ and -0.095MPa for 40 min. Finally, it is fed into a final polycondensation reactor, 8g of chain extender is added, and it is reacted at 255℃ and -0.10MPa for 60 min to obtain polyester melt. The chain extender is composed of adipamide and triphenylmethane triisocyanate in a mass ratio of 9:5. S4: Filter the melt obtained in step S3 and send it to an underwater pelletizer for underwater pelletizing. Control the pelletizing water temperature at 45℃ and the pelletizing speed at 400rpm. Place the wet chips into a vacuum dryer and vacuum dry them at 80℃ and -0.08MPa for 6 hours. Then sieve them to obtain ultra-low melting point polyester chips.

[0037] Example 3 A method for preparing ultra-low melting point polyester chips includes the following steps: S1: 40g of 1,4-butanediol and 8g of modified polyether were added to a reactor, heated to 90℃ and stirred to dissolve. Then, 35g of terephthalic acid, 13g of dimethyl isophthalate, and 15g of adipic acid were added and stirred until homogeneous. Next, 0.6g of catalyst, 0.3g of antioxidant 1010, and 0.03g of triphenyl phosphite were added and stirred until homogeneous to obtain a slurry. The catalyst consisted of tetrabutyl titanate and antimony glycolate in a mass ratio of 2.5:1. The modified polyether was prepared according to Preparation Example 3. S2: Esterify the slurry obtained in step S1. The slurry is fed into the first esterification reactor and esterified at 0.14 MPa and 210℃ for 2.7 h. Then the slurry is discharged and fed into the second esterification reactor and esterified at -0.03 MPa and 225℃ for 1.8 h to obtain the esterified product. S3: The esterified product obtained in step S2 is subjected to polycondensation. The esterified product is fed into a pre-polycondensation reactor and reacted at 235℃ and -0.07MPa for 45 min. Then it is fed into a medium-polycondensation reactor and reacted at 245℃ and -0.093MPa for 45 min. Finally, it is fed into a final polycondensation reactor, 8g of chain extender is added, and it is reacted at 252℃ and -0.103MPa for 65 min to obtain polyester melt. The chain extender is composed of adipamide and triphenylmethane triisocyanate in a mass ratio of 8:3. S4: Filter the melt obtained in step S3 and send it to an underwater pelletizer for underwater pelletizing. Control the pelletizing water temperature at 40℃ and the pelletizing speed at 350rpm. Place the wet chips into a vacuum dryer and vacuum dry them at 70-80℃ and -0.08MPa for 5.5h. Then sieve them to obtain ultra-low melting point polyester chips.

[0038] Example 4 A method for preparing ultra-low melting point polyester chips includes the following steps: S1: 42g of 1,4-butanediol and 9g of modified polyether were added to a reactor, heated to 92℃ and stirred to dissolve. Then, 38g of terephthalic acid, 13g of dimethyl isophthalate, and 16g of adipic acid were added and stirred until homogeneous. Next, 0.7g of catalyst, 0.3g of antioxidant 1010, and 0.04g of triphenyl phosphite were added and stirred until homogeneous to obtain a slurry. The catalyst consisted of tetrabutyl titanate and antimony glycolate in a mass ratio of 2:1. The modified polyether was prepared according to Preparation Example 4. S2: Esterify the slurry obtained in step S1. The slurry is fed into the first esterification reactor and esterified at 0.14 MPa and 212 °C for 2.8 h. Then the slurry is discharged and fed into the second esterification reactor and esterified at -0.03 MPa and 228 °C for 1.8 h to obtain the esterified product. S3: The esterified product obtained in step S2 is subjected to polycondensation. The esterified product is fed into a pre-polycondensation reactor and reacted at 237℃ and -0.07MPa for 46 min. Then it is fed into a medium-polycondensation reactor and reacted at 246℃ and -0.092MPa for 45 min. Finally, it is fed into a final polycondensation reactor, 7g of chain extender is added, and it is reacted at 253℃ and -0.102MPa for 65 min to obtain polyester melt. The chain extender is composed of adipamide and triphenylmethane triisocyanate in a mass ratio of 7:5. S4: Filter the melt obtained in step S3 and send it to an underwater pelletizer for underwater pelletizing. Control the pelletizing water temperature at 43℃ and the pelletizing speed at 350rpm. Place the wet chips into a vacuum dryer and vacuum dry them at 75℃ and -0.08MPa for 5.6h. Then sieve them to obtain ultra-low melting point polyester chips.

[0039] Comparative Example 1 The preparation method of the polyester chips in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that in step S1 of this comparative example, an equal amount of terephthalic acid is used instead of modified polyether.

[0040] Comparative Example 2 The preparation method of the polyester chips in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that in step S1 of this comparative example, an equal amount of polyethylene glycol-polypropylene glycol block polyether is used instead of maleic anhydride-grafted polyethylene glycol-polypropylene glycol block polyether.

[0041] Comparative Example 3 The preparation method of polyester chips in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that in step S1 of this comparative example, an equal amount of terephthalic acid is used instead of adipic acid.

[0042] Comparative Example 4 The preparation method of polyester chips in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that in step S1 of this comparative example, an equal amount of terephthalic acid is used instead of dimethyl isophthalate.

[0043] Comparative Example 5 The preparation method of the polyester chips in this comparative example is similar to that in Example 3. The difference between this comparative example and Example 3 is that the chain extender in this comparative example is adipamide.

[0044] Test case Test samples: polyester chips prepared in Examples 1-4 and Comparative Examples 1-5; Intrinsic viscosity test: The intrinsic viscosity of the test samples was tested according to GB / T 14190-2017; Melting point test: The XT-4 binocular micro melting point apparatus was used for the test. The test conditions were: the temperature was increased to near the melting point of the sample at 5℃ / min, and then increased at 1℃ / min. The sample was observed and the temperature at which it was completely melted was recorded. The test was repeated three times and the average value was taken. Toughness test: The elongation at break of the test samples was tested according to GB / T 1040.2-2022; The test results are shown in Table 1.

[0045] Table 1 Performance Test Results

[0046] As shown in Table 1, the intrinsic viscosity of the ultra-low melting point polyester chips provided by the present invention is 0.62-0.71 dl / g, the melting point is 105-115℃, and the elongation at break is 713%-762%, which indicates that the ultra-low melting point polyester chips provided by the present invention have a low melting point and good toughness.

[0047] Compared to Example 3, Comparative Example 1 did not add modified polyether, and the modified polyether in Comparative Example 2 was not grafted with maleic anhydride, but the elongation at break of the resulting polyester chips was significantly reduced, indicating that modified polyether is the key to improving the toughness of polyester chips; Comparative Example 3 did not add adipic acid, and Comparative Example 4 did not add dimethyl isophthalate, but the melting point of the resulting polyester chips increased, indicating that adipic acid and dimethyl isophthalate can disrupt the regularity of polyester crystals, thereby reducing the melting point of polyester chips; the chain extender in Comparative Example 5 was adipamide, but the intrinsic viscosity and elongation at break of the resulting polyester chips decreased, indicating that triphenylmethane triisocyanate can cause mild cross-linking of polyester molecules, improving the intrinsic viscosity and toughness of polyester chips.

[0048] In addition, the modified polyether prepared in Preparation Example 3 was subjected to infrared spectroscopy testing, and the test results are shown in [Figure number missing]. Figure 1 .Depend on Figure 1 It can be seen that at 3401cm -1 The characteristic peak of residual terminal hydroxyl groups appeared at 2926 cm⁻¹. -1 The characteristic peak of -CH2- appeared at 1813 cm⁻¹. -1 The characteristic peak of maleic anhydride C=O appeared at 1710 cm⁻¹. -1 The characteristic peak of C=O in the ester group appeared at 1470 cm⁻¹. -1 725cm -1 A characteristic peak of -CH2- appeared at 1115 cm⁻¹. -1 The presence of the characteristic peak of COC indicates that maleic anhydride was successfully grafted onto the molecule of polyethylene glycol-polypropylene glycol block polyether.

[0049] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A method for preparing ultra-low melting point polyester chips, characterized in that, Includes the following steps: S1: Add 1,4-butanediol and modified polyether to the reactor and stir to 85-95℃ to dissolve. Add terephthalic acid, dimethyl isophthalate and adipic acid, stir evenly, and then add catalyst, antioxidant and heat stabilizer. Stir evenly to obtain slurry. S2: Esterify the slurry obtained in step S1 to obtain the esterified product; S3: Polycondense the esterified product obtained in step S2 to obtain polyester melt; S4: Filter the melt obtained in step S3, granulate it underwater, vacuum dry it, and sieve it to obtain ultra-low melting point polyester chips. The modified polyether is maleic anhydride-grafted polyethylene glycol-polypropylene glycol block polyether.

2. The method for preparing ultra-low melting point polyester chips according to claim 1, characterized in that, The modified polyether is prepared by adding block polyether and hydroquinone into a reaction vessel, heating to 80-90°C, adding maleic anhydride and benzoyl peroxide under nitrogen protection, heating to 110-120°C, maintaining the temperature for 3-4 hours, cooling to 70-80°C, adding benzoyl chloride, stirring for 1.5-2 hours, and vacuum drying for 1 hour to obtain the modified polyether.

3. The method for preparing ultra-low melting point polyester chips according to claim 2, characterized in that, The mass fractions of each component in the preparation method of modified polyether are as follows: 100-120 parts of block polyether, 0.5-1 part of hydroquinone, 8-10 parts of maleic anhydride, 0.5-1 part of benzoyl peroxide, and 2-3 parts of benzoyl chloride.

4. The method for preparing ultra-low melting point polyester chips according to claim 2, characterized in that, The block polyether is prepared as follows: Polyethylene glycol diglycidyl ether is added to a reaction vessel, anhydrous ethanol is added, and the temperature is raised to 50–60°C under a nitrogen atmosphere. Monoethanolamine is added dropwise while stirring, and the reaction is continued for 4–6 hours to obtain a hydrophilic prepolymer. Polypropylene glycol diglycidyl ether is added to a reaction vessel, anhydrous ethanol is added, and the temperature is raised to 50–60°C under a nitrogen atmosphere. Monoethanolamine is added dropwise while stirring, and the reaction is continued for 4–6 hours to obtain a hydrophobic prepolymer. Equimolar ratios of the hydrophilic and hydrophobic prepolymers are added to a reaction vessel, and the temperature is raised to 70–80°C under a nitrogen atmosphere with magnetic stirring. The reaction is continued for 8–10 hours, followed by vacuum drying at 80–90°C for 4–6 hours. Anhydrous acetone is added, and the mixture is stirred until completely dissolved. An excess of anhydrous diethyl ether is added dropwise, and the mixture is stirred rapidly and filtered to obtain the block polyether.

5. The method for preparing ultra-low melting point polyester chips according to claim 4, characterized in that, In the preparation method of block polyether, the molar ratio of polyethylene glycol diglycidyl ether to monoethanolamine is 1:1, and the molar ratio of polypropylene glycol diglycidyl ether to monoethanolamine is 1:

1.

6. The method for preparing ultra-low melting point polyester chips according to claim 1, characterized in that, The weight proportions of each component in step S1 are as follows: 38-45 parts of 1,4-butanediol, 7-10 parts of modified polyether, 30-40 parts of terephthalic acid, 10-15 parts of dimethyl isophthalate, 13-17 parts of adipic acid, 0.4-0.9 parts of catalyst, 0.1-0.4 parts of antioxidant, and 0.02-0.05 parts of heat stabilizer; the catalyst in step S1 is composed of tetrabutyl titanate and antimony glycol in a mass ratio of (2-3):1; the antioxidant is antioxidant 1010, and the heat stabilizer is triphenyl phosphite.

7. The method for preparing ultra-low melting point polyester chips according to claim 1, characterized in that, The specific process of esterification in step S2 is as follows: the slurry is fed into the first esterification reactor and esterified at 0.10-0.15 MPa and 205-215℃ for 2.5-3.0 h. Then the slurry is discharged and fed into the second esterification reactor and esterified at -0.04--0.02 MPa and 220-230℃ for 1.5-2.0 h.

8. The method for preparing ultra-low melting point polyester chips according to claim 1, characterized in that, The specific process of polycondensation in step S3 is as follows: the esterification product is fed into a pre-polycondensation reactor and reacted at 230-240℃ and -0.08--0.06MPa for 40-50 minutes, then fed into a mid-polycondensation reactor and reacted at 240-250℃ and -0.095--0.09MPa for 40-50 minutes, and finally fed into a final polycondensation reactor, where a chain extender is added and the reaction is carried out at 250-255℃ and -0.105--0.10MPa for 60-70 minutes.

9. The method for preparing ultra-low melting point polyester chips according to claim 8, characterized in that, The chain extender is composed of adipamide and triphenylmethane triisocyanate in a mass ratio of (7-9):(3-5), and the amount of chain extender is 5-8 parts.

10. Ultra-low melting point polyester chips prepared by the method of preparing ultra-low melting point polyester chips according to any one of claims 1-9.

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