A modified pet composition, its preparation and use

Abstract

This invention relates to the field of polymer materials technology, and discloses a modified PET composition, its preparation method, and its application. The modified PET composition, by weight, comprises the following components: 70-85 parts isosorbide-modified PET resin, 2-5 parts rutile titanium dioxide, 3-5 parts needle-shaped calcium carbonate, 2-3 parts spherical calcium carbonate, 1-3 parts hydroxyl- or carboxyl-terminated hyperbranched dispersant, 0.2-0.6 parts antioxidant, 0.3-0.5 parts sodium stearate, and 0.1-0.3 parts nucleating agent. The modified PET composition of this invention achieves high heat resistance and heatability while also exhibiting high impact resistance, low warpage, and excellent processing flowability. It is suitable for thin-walled injection molding of food containers, possessing good dimensional stability and food contact safety.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a modified PET composition, its preparation method, and its application. Background Technology

[0002] Polyethylene terephthalate (PET) is widely used in disposable food containers and other packaging containers due to its excellent transparency, mechanical properties, and food contact safety. However, traditional PET has a glass transition temperature of only 75-80℃ and a low heat distortion temperature, making it unable to withstand the high temperatures of microwave heating (≥100℃) or hot filling (≥85℃), which severely limits its application in the field of heatable food containers. The industry commonly uses methods such as adding nucleating agents or increasing crystallinity to improve the heat resistance of PET resin. However, existing technologies, while improving heat resistance, struggle to simultaneously address its warping resistance, impact resistance, and processing performance as packaging boxes. On the one hand, while increasing crystallinity can raise the heat distortion temperature, it leads to a significant increase in melt viscosity, making mold filling difficult when injection molding thin-walled food containers, and easily causing processing defects such as short shots or flow marks. Simultaneously, high crystallinity increases the brittleness of the product, reduces its impact resistance, and makes it prone to cracking during transportation or use. On the other hand, the uniformity of nucleating agent dispersion directly affects crystallization efficiency. Once agglomerates, it not only fails to effectively improve heat resistance but also causes local shrinkage differences, exacerbating product warping and deformation, and affecting the stacking stability and sealing effect of food containers. Furthermore, PET is prone to thermo-oxidative degradation during high-temperature processing. To inhibit this degradation, existing technologies generally employ the addition of stabilizing agents. However, different agents are prone to mutual interference or functional cancellation, making it difficult to simultaneously improve thermal stability while maintaining the material's processing flowability and the final product's mechanical properties. Overall, existing PET modification technologies often sacrifice other properties when pursuing improvements in a single performance characteristic. For example, improving thermal stability may lead to decreased flowability, while improving processability may weaken heat resistance or impact resistance. Therefore, existing systems struggle to simultaneously meet multiple performance requirements such as microwave heating resistance, high impact resistance, low warping, and ease of processing, making them particularly unsuitable for the industrial production of food containers.

[0003] Therefore, developing a PET composition that can synergistically balance the aforementioned contradictory properties and its preparation method has significant application value and market prospects. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a modified PET composition, its preparation method, and its applications.

[0005] This invention provides a modified PET composition, comprising, by weight, the following components: 70-85 parts of isosorbide-modified PET resin, such as 70, 72, 75, 78, 80, 82, or 85 parts; 2-5 parts of rutile titanium dioxide, such as 2, 2.5, 3, 3.5, 4, 4.5, or 5 parts; 3-5 parts of needle-shaped calcium carbonate, such as 3, 3.5, 4, 4.5, or 5 parts; 2-3 parts of spherical calcium carbonate, such as 2, 2.2, 2.4, 2.6, 2.8, or 3 parts; and 1-3 parts of a hyperbranched dispersant with terminal hydroxyl or carboxyl groups. Examples of dosages include 1, 1.2, 1.5, 1.8, 2, 2.3, 2.5, 2.8, and 3 parts; antioxidants include 0.2-0.6 parts, such as 0.2, 0.3, 0.4, 0.5, and 0.6 parts; sodium stearate includes 0.3-0.5 parts, such as 0.3, 0.35, 0.4, 0.45, and 0.5 parts; and nucleating agents include 0.1-0.3 parts, such as 0.1, 0.15, 0.2, 0.25, and 0.3 parts.

[0006] This invention's formulation system, through isosorbide copolymerization modification, morphological synergy of multi-morphological inorganic fillers, interface regulation of anchored hyperbranched dispersants, multiple free radical capture by composite antioxidants, and the two-component nucleation effect of sodium stearate and nucleating agents, constructs an overall reinforcing network with complementary functions and synergistic effects among its components. This comprehensively overcomes the technical bottleneck of PET compositions struggling to balance multiple properties such as heat resistance, warpage resistance, impact resistance, and processing flowability. Specifically, after isosorbide, as a rigid bicyclic ether diol monomer, copolymerizes into the PET backbone, it significantly increases the glass transition temperature by restricting the rotational movement of molecular chain segments, enabling the product to maintain dimensional stability under microwave heating or hot filling conditions. Simultaneously, its rigid molecular structure also imparts a higher intrinsic modulus to the matrix resin. Meanwhile, this invention also achieves complementary anisotropic and isotropic reinforcement at the filling reinforcement level through the compound system of needle-shaped calcium carbonate and spherical calcium carbonate: needle-shaped calcium carbonate provides a significant orientation reinforcement effect in the injection flow direction with its high aspect ratio, greatly improving the flexural modulus, while spherical calcium carbonate balances the shrinkage rate in the vertical flow direction through its isotropic geometry. When the two are combined in a specific ratio, they can effectively suppress product warping deformation, and the rigid nature of the two also gives the composition higher flexural stiffness. This invention also creatively introduces hydroxyl- or carboxyl-terminated hyperbranched dispersants into the system. Leveraging their multi-branched molecular structure and end-group anchoring capabilities, these dispersants solve problems such as filler agglomeration, poor interfacial bonding, and impact embrittlement caused by stress concentration resulting from the introduction of inorganic powders. The hydroxyl- or carboxyl-terminated hyperbranched dispersants, through tight adsorption onto the surfaces of calcium carbonate and titanium dioxide, prevent secondary agglomeration of inorganic powders through steric hindrance and significantly reduce melt viscosity during melt processing, improving the mold filling flowability of thin-walled injection molding. Simultaneously, the uniformly dispersed filler eliminates local stress concentration points, thus maintaining good impact resistance even under high-filling conditions. The combination of sodium stearate and a nucleating agent constitutes a two-component nucleation system: sodium stearate synergistically works with the nucleating agent to provide more heterogeneous nucleation sites, refine grain size, and increase crystallization rate, enabling the composition to achieve a high heat distortion temperature while avoiding increased brittleness due to over-crystallization. This invention achieves a unified combination of multiple properties in PET compositions, including high heat resistance, high impact resistance, low warpage, and easy processing, through the synergistic effect of the components, such as restricted molecular chain movement, complementary filler morphology, interfacial anchoring and dispersion, multiple capture of free radicals, and synergistic nucleation sites.

[0007] Furthermore, the needle-shaped calcium carbonate has a length of 2-7 μm and a diameter of 0.3-1.0 μm, with an aspect ratio of (5-8):1 as determined by scanning electron microscopy. The spherical calcium carbonate has a particle size D50 of 1-3 μm, as determined by laser diffraction. When the aspect ratio of the needle-shaped calcium carbonate is too small, its anisotropic characteristics are essentially lost, preventing it from forming an effective orientation enhancement effect in the injection molding flow direction. The morphological complementarity between the needle-shaped calcium carbonate and the spherical calcium carbonate is greatly weakened, making it difficult to effectively offset the shortcomings of the spherical calcium carbonate in isotropic shrinkage. This results in a decrease in the overall shrinkage control capability of the product and also affects the improvement effect on the flexural modulus. Furthermore, due to the reduced specific surface area, the dispersion uniformity of needle-shaped calcium carbonate in the matrix decreases, thus becoming stress concentration points and deteriorating impact resistance. While an excessively large aspect ratio of needle-shaped calcium carbonate can enhance orientation reinforcement in the flow direction to some extent, it is more prone to fracture under the high shear environment of a twin-screw extruder. The resulting short fragments lose their original orientation reinforcement function, further reducing the reinforcement effect. Simultaneously, an excessively large aspect ratio significantly increases melt viscosity, reduces processing fluidity, and, due to the stronger orientation effect in the injection flow direction, causes anisotropic warping, while also reducing notched impact strength. For spherical calcium carbonate, when the particle size is too large, the reduced specific surface area weakens the interfacial bonding with the PET matrix, making it prone to interfacial debonding under external force, thus reducing flexural strength and impact toughness. At the same time, large particles are difficult to disperse uniformly, easily disrupting the continuity of the matrix. During impact, cracks easily propagate along the particle edges, leading to a decrease in notched impact strength and difficulty in improving warping problems. When the particle size is too small, the high surface energy of the particles makes them prone to agglomeration, forming defect sources and deteriorating mechanical properties. Excessively fine particles can also easily form a three-dimensional network in the melt, increasing melt viscosity and reducing processing fluidity.

[0008] Furthermore, the mass ratio of needle-shaped calcium carbonate to spherical calcium carbonate is (1-3):1. When the mass ratio is too large, i.e., the proportion of needle-shaped calcium carbonate is too high, the anisotropic filler in the system dominates, and the needle-shaped particles produce a strong orientation effect in the injection flow direction, resulting in a significant increase in the difference in shrinkage rate between the flow direction and the perpendicular direction, and anisotropic warping of the product. Excessive needle-shaped calcium carbonate can also easily increase the melt viscosity significantly, which to some extent degrades the processing fluidity. When the mass ratio is too small, i.e., the proportion of spherical calcium carbonate is too high, the balance between isotropy and enhanced orientation in the system is weakened, and the flexural modulus of the composition decreases to some extent, making the lunch box prone to bending deformation during stacking or handling. At the same time, due to the lack of sufficient needle-shaped filler in the system to regulate the shrinkage in the flow direction, the overall shrinkage rate control capability of the system decreases, and the warping problem becomes more prominent.

[0009] Furthermore, the isosorbide-modified PET resin contains 10-15 mol% isosorbide, as determined by 1H NMR spectroscopy. 1 H NMR) test. When the molar content of isosorbide is too low, its copolymerization modification effect is insufficient to raise the glass transition temperature of PET to the target level. The product is prone to softening and deformation under microwave heating or hot filling conditions, making it difficult to meet the requirements for heat-resistant food containers. At the same time, too low isosorbide content has limited effect on improving the intrinsic modulus of the matrix, weakens the synergistic reinforcement effect with the subsequent calcium carbonate filler system, and has no significant effect on improving the flexural modulus. In addition, too low isosorbide content can easily cause the resin to form large-sized grains during injection molding cooling, reducing impact resistance and aggravating anisotropic shrinkage, making it prone to warping problems; when the molar content of isosorbide is too low, its copolymerization modification effect is insufficient to raise the glass transition temperature of PET to the target level. When the molar content of sorbitol is too high, although the glass transition temperature can be further increased, the regularity of the copolyester molecular chain will be destroyed, the crystallization ability of the resin will be almost lost, the melt strength will be low, and sticking or deformation will easily occur during injection molding demolding, affecting production efficiency. Furthermore, the nucleating effect of subsequent nucleating agents and sodium stearate will be difficult to exert effectively, the heat resistance and rigidity will decrease to a certain extent, and the cost will also increase. At the same time, the interfacial compatibility between the copolyester and inorganic fillers such as calcium carbonate and titanium dioxide will decrease to a certain extent, making it difficult to disperse the fillers, and they will easily agglomerate to form stress concentration points, resulting in deterioration of impact resistance.

[0010] Furthermore, the intrinsic viscosity of the isosorbide-modified PET resin is 0.65-1.20 dL / g, the test standard is GB / T 14190-2017, and the solvent used for testing is a phenol-tetrachloroethane mixture (mass ratio 1:1).

[0011] Furthermore, the isosorbide-modified PET resin can be obtained in-house, and two preparation methods are provided below as examples: Method 1: Terephthalic acid, ethylene glycol, and isosorbide are fed at an alkyd-acid molar ratio of (1.2-1.8):1, with isosorbide accounting for 5%-20% of the total glycols. The mixture is catalytically reacted at 230-250℃ for 2-4 hours to generate ethylene glycol terephthalate oligomers. Subsequently, pre-polymerization is carried out at 250-265℃ and 1-5 kPa for 40-100 minutes, followed by final polymerization at 270-280℃ under vacuum for 1.5-3 hours to obtain isosorbide-modified PET resin. The second method involves feeding diethyl terephthalate (BHET) and isosorbide at a molar ratio of isosorbide to BHET of 5%-80%, and catalytically reacting them for 20-60 minutes at a temperature of 190-220℃ and a pressure of 70-100 kPa to generate ethylene glycol isosorbide terephthalate. Subsequently, pre-polymerization is carried out at a temperature of 250-265℃ and a pressure of 1-50 kPa for 40-100 minutes, and then the temperature is raised to 270-280℃ for final polymerization under vacuum to obtain isosorbide-modified PET resin.

[0012] Furthermore, the antioxidant comprises a primary antioxidant and a secondary antioxidant, wherein the primary antioxidant is a hindered phenolic antioxidant and the secondary antioxidant is a phosphite antioxidant.

[0013] Furthermore, the number-average molecular weight of the terminal hydroxyl or terminal carboxyl hyperbranched dispersant is 3000-8000 g / mol, and is tested using gel permeation chromatography-multi-angle laser light scattering. When the number-average molecular weight of the hyperbranched dispersant is too small, due to the short molecular chain, it cannot form a stable coating layer on the surface of calcium carbonate and titanium dioxide, and the dispersant is prone to desorption, causing secondary agglomeration of the filler and forming stress concentration points, thereby reducing the impact resistance. During high-temperature processing, the low molecular weight dispersant is prone to escape from the melt, reducing the effective concentration, which also has a certain impact on heat resistance and flexural modulus. When the number-average molecular weight of the hyperbranched dispersant is too large, it will increase the overall viscosity of the composition, reduce the processing performance, and because the terminal functional group density of the high molecular weight dispersant is low, the anchoring groups provided per unit mass are reduced, making it difficult for the filler to be fully coated, and the dispersion effect is reduced. At the same time, the compatibility of hyperbranched polymers with excessively large molecular weights with PET becomes poor, and a weak boundary layer is easily formed at the interface, which is easily destroyed under external force, reducing the flexural modulus and impact resistance.

[0014] Furthermore, the nucleating agent is an amide-based nucleating agent. The specific amide-based nucleating agent used in this invention can first form an ideal synergistic nucleating system with sodium stearate. Both act independently yet complement each other, significantly increasing the crystallization rate and refining the grain size, thereby raising the heat distortion temperature of the composition while avoiding increased brittleness due to over-crystallization, achieving a balance between heat resistance and impact resistance. Moreover, its amide groups can form hydrogen bonds with the terminal hydroxyl or carboxyl groups of the hyperbranched dispersant, further improving the uniformity of the nucleating agent's dispersion in the system.

[0015] The present invention also provides a method for preparing the modified PET composition, comprising the following steps: S1: Dry the isosorbide-modified PET resin at 120-140℃ for 4-6 hours to prevent hydrolysis and degradation caused by moisture during high-temperature processing; S2: Weigh out spherical calcium carbonate, rutile titanium dioxide and hyperbranched dispersant with terminal hydroxyl or terminal carboxyl groups according to the weight parts, and premix them in a high-speed mixer at a speed of 800-1200 r / min for 3-5 minutes to make the hyperbranched dispersant uniformly adsorbed on the surface of the inorganic powder to obtain pre-dispersed powder. S3: Preheat the twin-screw extruder to the set temperature, and feed the dried isosorbide-modified PET resin into the extruder through the main feed port. After the resin melts, add the pre-dispersed powder, sodium stearate, antioxidant and nucleating agent obtained in step S2 through the side feed port. At the same time, add needle-shaped calcium carbonate separately through the second side feed port located further downstream (avoiding the high shear kneading zone of the melt section to maximize the protection of its aspect ratio). Melt blend extrusion. S4: The melt extruded in step S3 is cooled in a water bath and air-dried, and then fed into a pelletizer to granulate, thereby obtaining the PET composition granules.

[0016] Furthermore, the length-to-diameter ratio of the twin-screw extruder is (36-44):1, the temperature of each section of the extruder is set as follows: Zone 1 220-240℃, Zones 2-5 240-260℃, Zones 6-8 245-255℃, and the screw speed of the twin-screw extruder is 300-450 r / min.

[0017] The present invention also provides the use of the modified PET composition in the preparation of food containers.

[0018] In summary, compared with the prior art, the present invention achieves the following technical effects: (1) The modified PET composition provided by the present invention, through the introduction of end-hydroxyl or end-carboxyl hyperbranched dispersants, utilizes their multi-branched molecular structure and end-group anchoring ability to tightly adsorb onto the surface of calcium carbonate and titanium dioxide, prevents the agglomeration of inorganic powders through steric hindrance effect, and at the same time significantly reduces the melt viscosity and improves the processing performance during the melt processing.

[0019] (2) The modified PET composition provided by the present invention combines the morphological properties of needle-shaped calcium carbonate and spherical calcium carbonate, and with the uniform dispersion effect of hyperbranched dispersant, eliminates the stress concentration points formed by filler agglomeration. Needle-shaped calcium carbonate provides orientation enhancement, and spherical calcium carbonate balances anisotropy. The two work together to avoid the impact embrittlement caused by filler agglomeration or poor interfacial bonding in traditional high-filler systems. At the same time, the grain size is refined by isosorbide copolymerization and the synergistic nucleation of sodium stearate and nucleating agent, avoiding the increase in brittleness caused by excessive crystallization, improving impact resistance, and the resulting lunch box is not easy to crack during drop or transportation.

[0020] (3) The modified PET composition provided by the present invention has excellent bending stiffness, and the product is not easily bent or deformed during stacking or handling, and has good dimensional stability.

[0021] (4) The modified PET composition provided by the present invention improves the heat distortion temperature and performance stability of the PET composition system through isosorbide copolymerization modification and a two-component nucleation system of amide nucleating agent and sodium stearate, combined with a composite antioxidant system. The product can withstand microwave heating and hot filling, meeting the requirements for use of heat-resistant lunch boxes.

[0022] (5) All components used in the modified PET composition provided by the present invention are food contact permitted substances. The total migration and heavy metal migration meet the requirements of GB 4806 series standards. The acetaldehyde content is low and there is no odor. It is suitable for food container applications that come into direct contact with food. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, 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 should fall within the scope of protection of the present invention.

[0024] Example The present invention will be further illustrated below with reference to specific embodiments and comparative embodiments. The following specific embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the following embodiments, and are not in particular limited to the types of raw materials used in the following specific embodiments.

[0025] I. The sources of raw materials for the examples and comparative examples are as follows: Isosorbide-modified PET resin #1: The isosorbide molar content is 5 mol%, prepared in-house. The preparation method is as follows: terephthalic acid, ethylene glycol, and isosorbide are fed at an alkyd-acid molar ratio of 1.2:1, wherein the isosorbide molar ratio of the total glycols is 5%. The mixture is reacted at 230℃ for 4 hours to generate ethylene glycol terephthalate oligomers. Then, pre-polymerization is carried out at 250℃ and 5 kPa for 100 minutes, followed by heating to 270℃ and final polymerization under vacuum for 3 hours to obtain the modified PET resin with an isosorbide molar content of 5 mol% and an intrinsic viscosity of 0.68 dL / g. Isosorbide-modified PET resin #2: Isosorbide molar content is 10 mol%, prepared in-house. The preparation method is as follows: terephthalic acid, ethylene glycol and isosorbide are fed at an alkyd-acid molar ratio of 1.3:1, wherein isosorbide accounts for 10% of the total glycols. The reaction is carried out at 235℃ for 3.5 hours to generate ethylene glycol terephthalate oligomer. Then, pre-polymerization is carried out at 255℃ and 4 kPa for 80 minutes, and then the temperature is raised to 275℃ and final polycondensation is carried out under vacuum for 2.5 hours to obtain modified PET resin with isosorbide molar content of 10 mol% and intrinsic viscosity of 0.66 dL / g. Isosorbide-modified PET resin #3: Isosorbide molar content is 15 mol%, prepared in-house. The preparation method is as follows: Terephthalic acid, ethylene glycol and isosorbide are fed at an alkyd molar ratio of 1.5:1, wherein isosorbide accounts for 15% of the total glycols. The reaction is carried out at 245℃ for 2.5 hours to generate ethylene glycol terephthalate oligomer. Then, pre-polymerization is carried out at 260℃ and 2 kPa for 60 minutes, and then the temperature is raised to 280℃ and final polycondensation is carried out under vacuum for 2 hours to obtain modified PET resin with isosorbide molar content of 15 mol% and intrinsic viscosity of 0.65 dL / g. Isosorbide-modified PET resin #4: Isosorbide molar content is 18 mol%, prepared in-house. The preparation method is as follows: Terephthalic acid, ethylene glycol and isosorbide are fed at an alkyd molar ratio of 1.8:1, wherein isosorbide accounts for 18% of the total glycols. The reaction is carried out at 250℃ for 2 hours to generate ethylene glycol terephthalate oligomers. Then, pre-polymerization is carried out at 265℃ and 1 kPa for 40 minutes, and then the temperature is raised to 280℃ and final polycondensation is carried out under vacuum for 1.5 hours to obtain modified PET resin with isosorbide molar content of 18 mol% and intrinsic viscosity of 0.62 dL / g. PET resin: intrinsic viscosity 0.74 dL / g, grade CLEARTUF TURBO II, M&G Chemicals; Rutile titanium dioxide: Commercially available; the same substance was used in parallel tests. Needle-shaped calcium carbonate #1: aspect ratio 5:1, grade MP-Ro, Guangxi Huana; Needle-shaped calcium carbonate #2: aspect ratio 8:1, grade W-8, Walter; Needle-shaped calcium carbonate #3: aspect ratio 10:1, grade DS-A10, Dongsheng New Materials; Spherical calcium carbonate: particle size D50 is 2 μm, commercially available; Hydroxyl-terminated or carboxyl-terminated hyperbranched dispersant #1: Hydroxyl-terminated hyperbranched polyester, brand name SeHBP H104, number average molecular weight is 5200 g / mol, Xibao Biotechnology; Hydroxyl-terminated or carboxyl-terminated hyperbranched dispersant #2: Carboxyl-terminated hyperbranched polyester, brand name HyPer C402, number average molecular weight is 3400 g / mol, Wuhan hyperbranched resin; Dispersant #3: Oxidized polyethylene wax, brand name Licowax PED 521, Clariant; Main antioxidant: hindered phenolic antioxidant, antioxidant 1010, the same substance was used in parallel experiments; Co-antioxidant; phosphite antioxidant, antioxidant 168, the same substance was used in parallel experiments; Sodium stearate: CAS: 822-16-2, the same substance was used in parallel experiments; Nucleating agent: a polyamide compound, brand name TMC-328, and the same substance was used in parallel experiments.

[0026] The preparation method of the modified PET composition in the embodiments and comparative examples of the present invention includes the following steps: S1: Dry the isosorbide-modified PET resin at 120-140℃ for 4-6 hours to prevent hydrolysis and degradation caused by moisture during high-temperature processing; S2: Weigh out spherical calcium carbonate, rutile titanium dioxide and hyperbranched dispersant with terminal hydroxyl or terminal carboxyl groups according to the weight parts, and premix them in a high-speed mixer at a speed of 800-1200 r / min for 3-5 minutes to make the hyperbranched dispersant uniformly adsorbed on the surface of the inorganic powder to obtain pre-dispersed powder. S3: Preheat the twin-screw extruder to the set temperature, and feed the dried isosorbide-modified PET resin into the extruder through the main feed port. After the resin melts, add the pre-dispersed powder, sodium stearate, antioxidant and nucleating agent obtained in step S2 through the side feed port. At the same time, add needle-shaped calcium carbonate separately through the second side feed port located further downstream (avoiding the high shear kneading zone of the melt section to maximize the protection of its aspect ratio). Melt blend extrusion. S4: The melt extruded in step S3 is cooled in a water bath and air-dried, and then fed into a pelletizer to granulate, thereby obtaining the PET composition granules. The twin-screw extruder has a length-to-diameter ratio of (36-44):1, and the temperature settings for each section of the extruder are: Zone 1 220-240℃, Zones 2-5 240-260℃, Zones 6-8 245-255℃, and the screw speed of the twin-screw extruder is 300-450 r / min.

[0027] II. Performance Testing Methods (1) Heat distortion temperature test: The test shall be conducted in accordance with the standard GB / T 1634.2-2019.

[0028] (2) Impact strength test: The test shall be conducted in accordance with the standard GB / T 1843-2008.

[0029] (3) Bending modulus test: The test shall be conducted in accordance with the standard GB / T 9341-2008.

[0030] (4) Melt mass flow rate (MFR) test: The test shall be conducted in accordance with the standard GB / T 3682.1-2018. The test conditions are 265℃ and 2.16 kg. The test result is ≥15 g / 10min to be qualified.

[0031] Table 1. Technical solutions and effects of the embodiments (unit: parts by weight)

[0032] Table 2 Comparative technical solutions and effects (unit: parts by weight)

[0033] Example 1 The method simultaneously introduces isosorbide-modified PET resin, compounded calcium carbonate (needle-shaped + spherical), hydroxyl-terminated / carboxyl-terminated hyperbranched dispersant, composite antioxidant, sodium stearate, and nucleating agent. The resulting modified PET compositions maintain excellent processing fluidity while synergistically achieving high heat resistance, high impact resistance, high rigidity, and low warpage. The heat distortion temperature can reach 102℃ and above, allowing for stable resistance to high-temperature hot filling, and the cantilever beam impact strength can reach 5.1 kJ / m². 2 With a flexural modulus of 2650 MPa or higher, it is not easy to crack or break during transportation and use. The flexural modulus can reach 2650 MPa or higher, and the lunch boxes are not easy to bend or deform when stacked and handled. The melt flow rate can reach 15.5 g / 10min or higher, truly achieving the unity of heat resistance, high impact resistance, low warpage and easy processing, and is fully suitable for the industrial production and actual use of food contact grade lunch boxes.

[0034] Comparative Example 1 All five examples were compared with Example 1. Comparative Example 1 did not include a hyperbranched dispersant, resulting in severe filler agglomeration, stress concentration, a significant decrease in impact strength, high melt viscosity, and unacceptable fluidity. Comparative Example 2 used ordinary PET resin, which had insufficient rigidity of molecular chain segments, significantly lower glass transition temperature and heat distortion temperature, making it prone to softening and deformation at high temperatures. At the same time, its crystallization behavior and interfacial compatibility deteriorated, leading to a significant decrease in rigidity and impact resistance, failing to meet the core requirements for heatable lunch boxes. Comparative Example 3 used only needle-shaped calcium carbonate, and Comparative Example 4 used only spherical calcium carbonate, resulting in a significant reduction in the flexural modulus of the system. The lunch boxes lacked rigidity and were prone to deformation under pressure, while their impact resistance and dimensional stability were significantly deteriorated. Comparative Example 5 did not use a hydroxyl-terminated / carboxyl-terminated hyperbranched dispersant, but instead used ordinary oxidized polyethylene wax. The inorganic filler had weak interfacial bonding with the resin matrix and uneven dispersion, easily forming agglomerates and creating stress concentration points, significantly reducing impact toughness. At the same time, the melt viscosity increased, fluidity deteriorated, and heat resistance and rigidity also deteriorated simultaneously. None of the above comparative examples can simultaneously achieve high heat resistance, high impact resistance, low warpage, and good processing flowability, making it difficult to meet the comprehensive requirements of industrialized production and safe use of food containers.

[0035] Based on the test data for heat distortion temperature, impact strength, flexural modulus, and melt mass flow rate in Tables 1 and 2, the modified PET compositions prepared by Examples 1-8 have significant advantages over the comparative examples and can effectively meet the high standards of customers and the market.

[0036] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A modified PET composition, characterized in that, By weight, it includes the following components: Isosorbide-modified PET resin 70-85 copies; Rutile titanium dioxide 2-5 portions; Needle-shaped calcium carbonate 3-5 portions; Spherical calcium carbonate 2-3 portions; Hyperbranched dispersants with terminal hydroxyl or carboxyl groups 1-3 servings; antioxidants 0.2-0.6 parts; Sodium stearate 0.3-0.5 portions; nucleating agent 0.1-0.3 portions.

2. The modified PET composition according to claim 1, characterized in that, The aspect ratio of the needle-shaped calcium carbonate is (5-8):1, and the particle size D50 of the spherical calcium carbonate is 1-3 μm.

3. The modified PET composition according to claim 1, characterized in that, The mass ratio of needle-shaped calcium carbonate to spherical calcium carbonate is (1-3):

1.

4. The modified PET composition according to claim 1, characterized in that, The isosorbide-modified PET resin contains 10-15 mol of isosorbide.

5. The modified PET composition according to claim 1, characterized in that, The antioxidant comprises a primary antioxidant and a secondary antioxidant, wherein the primary antioxidant is a hindered phenolic antioxidant and the secondary antioxidant is a phosphite antioxidant.

6. The modified PET composition according to claim 1, characterized in that, The number average molecular weight of the terminal hydroxyl or terminal carboxyl hyperbranched dispersant is 3000-8000 g / mol.

7. The modified PET composition according to claim 1, characterized in that, The nucleating agent is an amide-based nucleating agent.

8. A method for preparing the modified PET composition according to any one of claims 1-7, characterized in that, Includes the following steps: S1: Dry the isosorbide-modified PET resin at 120-140℃ for 4-6 hours; S2: Weigh each component according to the weight parts, and premix the spherical calcium carbonate, rutile titanium dioxide and the hyperbranched dispersant with terminal hydroxyl or terminal carboxyl groups in a high-speed mixer for 3-5 minutes to obtain the pre-dispersed powder; S3: The dried isosorbide-modified PET resin, pre-dispersed powder, sodium stearate, antioxidant, nucleating agent, and needle-shaped calcium carbonate are fed into a twin-screw extruder and melt-blended and extruded. S4: Extrusion granulation, i.e., obtaining the PET composition granules.

9. The method for preparing the modified PET composition according to claim 8, characterized in that, The twin-screw extruder has a length-to-diameter ratio of (36-44):1, and the temperature settings for each section of the extruder are: Zone 1 220-240℃, Zones 2-5 240-260℃, Zones 6-8 245-255℃. The screw speed of the twin-screw extruder is 300-450 r / min.

10. The use of the modified PET composition according to any one of claims 1-7 in the preparation of food containers.

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