Cold-resistant PET material and preparation method thereof

Abstract

The invention discloses a cold-resistant PET (polyethylene terephthalate) material and a preparation method thereof, and belongs to the technical field of high polymer materials, and the cold-resistant PET material is composed of a PET matrix, a dynamic reversible sulfur-doped epoxy resin network, an ion cluster supramolecular network and a surface oriented organic silicon nano layer. The preparation method comprises the following steps: firstly, carrying out melt blending extrusion on PET, episulfide resin containing dynamic disulfide bonds, ionic liquid containing carboxylic acid functional groups, an organosiloxy polymer with a specific structure and a catalyst to form master batches; and then, carrying out hydrolysis-polycondensation treatment on the master batch at specific temperature and humidity to form a compact organic silicon nano layer on the surface of the material. By constructing a triple synergistic system of the dynamic reversible covalent network, the ion cluster supramolecular network and the surface nano protective layer, the technical problems that a traditional cold-resistant PET material is insufficient in low-temperature toughness, easy to be subjected to cold whitening, incapable of resisting grease stress cracking and free of damage repairing capacity are solved.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a cold-resistant PET material and its preparation method. Background Technology

[0002] Polyethylene terephthalate (PET) is widely used in food packaging, fibers, and electronics due to its excellent mechanical properties, transparency, chemical stability, and recyclability. However, conventional PET materials have inherent defects in low-temperature environments (such as below 0°C). Their molecular chain mobility decreases significantly, causing the material to transform from tough to brittle, and its impact resistance deteriorates sharply. When PET products (especially transparent packaging containers) are used under refrigerated or frozen conditions, they are not only prone to brittle fracture due to drops or impacts, but also experience "stress-whitening" due to the generation of microcracks and stress within the material. This results in the material becoming opaque or developing a white, hazy appearance, severely affecting the product's appearance and the consumer experience.

[0003] To improve the cold resistance of PET, existing technologies typically employ copolymerization modification (such as introducing third monomers like isophthalic acid and 1,4-cyclohexanediol) or blending modification (such as adding elastomers or core-shell impact modifiers). While copolymerization modification can reduce the crystallinity of PET and improve toughness to some extent, it often comes at the cost of sacrificing the material's rigidity and heat resistance, and is also costly. Blending modification is a more commonly used method, but it has several problems: 1) Impact modifiers have poor compatibility with the PET matrix, easily leading to decreased material transparency; 2) The dispersed phase size of the modifier is difficult to control, and it may still become a stress concentration point at low temperatures, causing streaks and whitening; 3) Most impact modifiers cannot effectively inhibit stress cracking of the material in oily environments, which is particularly prominent when packaging oily foods.

[0004] Furthermore, scratches and microcracks that occur in existing cold-resistant modified PET materials during use are irreversible. This not only affects aesthetics but also becomes a source of damage under subsequent stress, shortening the material's lifespan. Therefore, developing a new type of PET material that retains the original advantages of PET while achieving high toughness, high transparency (anti-cold whitening), and grease resistance at low temperatures, and additionally endowing it with self-healing capabilities, has significant theoretical importance and enormous market value. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a cold-resistant and high-toughness PET material and its preparation method. This material retains the original advantages of PET while achieving high toughness, high transparency (anti-cold whitening), and oil resistance at low temperatures, and additionally endows it with damage self-healing ability.

[0006] The objective of this invention can be achieved through the following technical solutions: A first aspect of the present invention provides a cold-resistant PET material, the cold-resistant PET material comprising: (a) PET matrix; (b) A first network formed in the PET matrix, wherein the first network is a dynamic reversible thiohexene epoxy resin network; (c) A second network formed in the PET matrix, the second network being an ion cluster supramolecular network; and (d) A nanolayer covering the surface of the PET substrate, wherein the nanolayer is a surface-oriented organosilicon nanolayer.

[0007] The core innovation of this invention lies in the fact that, through the "one-pot" process of melt reactive extrusion, two synergistic interpenetrating networks are constructed in situ in the PET matrix, and a functional nano-coating is formed on the material surface by combining post-processing, thus forming a triple-effect system that combines "body-surface" and systematically solves the problem of low-temperature application of PET materials.

[0008] First-stage system: Dynamically reversible thiohexene epoxy resin network (first network): This invention introduces a special cyclic sulfur resin monomer containing dynamic disulfide bonds, preferably bis(2,3-epoxypropylthio) disulfide (DETS). During melt blending, under the action of catalysts such as tertiary amines or quaternary phosphine salts, the highly reactive cyclic sulfur groups (thiacyclopropane) undergo ring-opening reactions with the carboxyl and hydroxyl groups at the ends of the PET molecular chains, grafting the monomer onto the PET chains. Simultaneously, ring-opening polymerization also occurs between the cyclic sulfur groups, forming polysulfide segments. Since each monomer molecule contains two cyclic sulfur groups and one dynamic disulfide bond, a chemically cross-linked but reversible intercalated polymer network is ultimately formed in the PET matrix.

[0009] The network has yielded two key effects: 1) Low-temperature toughening: The formed polysulfide network has a low glass transition temperature and good flexibility, acting as a "molecular spring" in the PET matrix. When the material is impacted, this flexible network can effectively absorb and dissipate impact energy, inhibit the generation and propagation of microcracks, and thus maintain extremely high impact toughness at temperatures of -40℃ or even lower.

[0010] 2) Low-Temperature Self-Healing: Disulfide bonds in the network are dynamically reversible covalent bonds. When excited by external energy (such as heat, light, or mechanical force), disulfide bonds can break and recombine. When cracks or fractures occur in the material at low temperatures, although the movement of molecular chain segments is restricted, the disulfide bonds at the fracture surface can undergo an exchange reaction at room temperature or with slight heating (e.g., 40–60°C), reconnecting the broken polymer network, thereby healing the cracks and restoring the material's mechanical and barrier properties. This is an unexpected technical effect, a function not possessed by conventional impact modifiers.

[0011] Second system: Ion cluster supramolecular network (second network): This invention introduces an ionic liquid containing carboxylic acid functional groups, preferably 1-(2-carboxyethyl)-3-methylimidazolium chloride (CMIM-Cl). In the molten state, this ionic liquid exhibits good compatibility with PET. The imidazolium cations and chloride ions in its molecule can generate strong ion-dipole interactions with the polar ester groups on the PET backbone. Upon cooling, these ionic groups tend to aggregate, forming "ionic clusters" that serve as physical crosslinking points, constructing a supramolecular network distributed throughout the PET matrix.

[0012] The network has yielded the following key effects: 1) Synergistic toughening and resistance to cold whitening: This physical cross-linking network restricts the local rearrangement and crystallization of PET molecular chains at low temperatures, effectively inhibiting stress-induced crystallization and the formation of microvoids, which are the main causes of the "cold whitening" phenomenon. When the material is subjected to stress, the ion-dipole interaction is reversible, allowing for dissociation and recombination, thereby dissipating energy. This synergistic effect with the first chemical network further improves the material's toughness and fundamentally ensures the material's high transparency under low-temperature tensile or bending conditions.

[0013] 2) Improved processing fluidity: Surprisingly, during high-temperature melt processing, the ionic liquid acts as a plasticizer and internal lubricant, reducing the melt viscosity of the system and improving processing fluidity. This is an effect that is usually difficult to achieve while pursuing toughening.

[0014] The third system: surface-oriented organosilicon nanolayers This invention introduces a specially designed organosilyl oxypolymer with hydrolyzable silane groups (such as triethoxysilane) at both ends and a flexible polyether segment (PEG) in the middle. During melt blending, this polymer is uniformly dispersed in the system. Due to its low compatibility with PET, the polymer spontaneously migrates to the material surface during subsequent hydrothermal treatment. The high humidity environment on the surface induces hydrolysis of the silane groups, generating highly reactive silanol groups (-Si-OH). These silanol groups, and primarily those undergoing Si-OH polymerization, form a Si-O-Si network, which may also form limited Si-OC anchoring with a small amount of -OH on the PET surface, creating a highly cross-linked, dense nanolayer with Si-O-Si as the main chain, firmly anchored to the PET material surface.

[0015] Specifically, the above-mentioned organosilyl alkoxy polymer is prepared by the following steps: A1. Under an inert gas atmosphere, dissolve polyethylene glycol in tetrahydrofuran, stir until homogeneous, then place in an ice bath to maintain 5°C, add sodium hydride in batches, and continue stirring at 5°C for 30 min to obtain a suspension. A2. Bring the suspension to room temperature, add potassium iodide, then purge with nitrogen gas, and add a solution of 3-chloropropyltriethoxysilane dissolved in tetrahydrofuran to the system dropwise over 30 minutes. After completion, stir at room temperature for 12 hours to obtain the etherified product. A3. Isopropanol and glacial acetic acid were added dropwise to the etherification reactants under an inert gas atmosphere, stirred for 10-15 min, allowed to stand, and then filtered and rotary evaporated to obtain the crude product. A4. Dissolve the crude product in tetrahydrofuran, then add 10 times the volume of diethyl ether at 5°C, stir thoroughly, let stand and settle, then discard the supernatant. Repeat the redissolution-reprecipitation process 2-3 times. After drying the precipitate, obtain the solid product, which is the target product, organosilane oxypolymer.

[0016] A second aspect of the present invention provides a method for preparing a cold-resistant PET material, comprising the following steps: S1. PET resin, cyclic sulfur resin monomer containing dynamic disulfide bonds, ionic liquid containing carboxylic acid functional groups, organosiloxane polymer and catalyst are mixed evenly, and melt-blended and extruded through a twin-screw extruder at 250-270°C, cooled and pelletized to obtain modified PET masterbatch. S2. Place the masterbatch obtained in S1 or the product injection molded from it in an environment with a temperature of 60-80℃ and a relative humidity of 85%-95% for 2-4 hours to obtain cold-resistant PET material.

[0017] The above-mentioned method for preparing cold-resistant PET materials is simple, compatible with existing PET processing equipment, and easy to industrialize.

[0018] Furthermore, the weight fractions of each component in S1 are as follows: PET resin: 100 parts; Cyclosulfide resin monomers containing dynamic disulfide bonds: 3-8 parts; Ionic liquids containing carboxylic acid functional groups: 1–5 parts; Organosilane-based polymers: 0.5–2 parts; Triphenylphosphine: 0.1 to 0.5 parts.

[0019] Furthermore, the catalyst described in S1 is triphenylphosphine.

[0020] A third aspect of the present invention provides the application of the above-mentioned cold-resistant PET material in the manufacture of cold chain packaging containers, outdoor electronic device housings, or structural components used in low-temperature environments.

[0021] The beneficial effects of this invention are: This invention provides a cold-resistant PET material and its preparation method, aiming to solve a series of technical problems inherent in existing PET materials at low temperatures, such as insufficient toughness, susceptibility to "cold whitening," inability to resist grease stress cracking, and lack of damage repair capabilities. This invention achieves the following technical effects by constructing a triple synergistic system of a "dynamically reversible thiohexa-epoxy resin network," an "ion cluster supramolecular network," and a "surface-oriented organosilicon nanolayer" on the material surface: 1. It fundamentally solves the problem of low-temperature brittleness, achieving unprecedented low-temperature high toughness: Existing technology indicates that conventional PET undergoes a brittle-ductile transition at low temperatures, resulting in a sharp deterioration in impact resistance. The advantage of this invention lies in the synergistic toughening effect of two internal networks. First, Comparative Example 2, which only added bis(2,3-epoxypropylthio)disulfide (DETS), achieved an impact strength increase to 8.5 kJ / m. 2 This clearly confirms that the dynamically reversible thiohexene epoxy resin network formed in situ by DETS, with its flexible polysulfide segments, can effectively absorb and dissipate impact energy, which is key to improving low-temperature toughness. Secondly, Comparative Example 3, with the addition of only 1-(2-carboxyethyl)-3-methylimidazolium chloride (CMIM-Cl), also achieved an impact strength increase to 5.2 kJ / m. 2 This indicates that the supramolecular network of ionic clusters formed by ionic liquids, acting as physical cross-linking points, also contributes to toughening. Simultaneously, a powerful synergistic toughening effect exists between the chemically cross-linked flexible network and the physically cross-linked ionic cluster network. When the material is subjected to impact, the two networks work together to absorb and disperse energy through a more efficient mechanism, thereby endowing the material with excellent toughness even under harsh conditions of -40℃, completely overcoming the low-temperature brittleness bottleneck of traditional PET.

[0022] 2. While achieving high toughness, it effectively suppresses "cold whitening" and maintains high transparency: In existing technologies, toughening modification often comes at the cost of transparency. This invention introduces CMIM-Cl. The presence of CMIM-Cl greatly improves the dispersion and compatibility of the DETS network in the matrix, suppresses microphase separation, and thus solves the industry problem of reduced transparency caused by toughening agents while achieving synergistic toughening, and fundamentally eliminates the "cold whitening" problem at low temperatures.

[0023] 3. It endows the material with a unique low-temperature self-healing function, extending its service life: Damage to traditional PET materials is irreversible. This invention, by introducing DETS containing dynamic disulfide bonds, endows the material with self-healing capabilities. The supramolecular network of ionic clusters, which itself does not possess healing capabilities, can more effectively bind broken interfaces together through their physical cross-linking, creating a superior physical environment for disulfide bond exchange reactions at the interface, thereby significantly improving healing efficiency.

[0024] 4. A highly efficient surface protective layer was constructed, achieving excellent grease resistance and anti-fogging function: PET materials are prone to stress cracking when in contact with oily substances, which is a major drawback in their use in food packaging and other fields. This invention fundamentally solves this problem by introducing an organosilaneoxygenated polymer (SPO) and subjecting it to hydrothermal treatment to form a nano-protective layer on the material surface. Examples 2, 3, and 4 further extend the oil resistance time to over 72 hours, demonstrating the synergistic "body-surface" protective effect of combining a robust surface protective layer with a strong internal matrix. Furthermore, this surface layer also endows the material with excellent anti-fogging properties (as shown in Comparative Example 4 and Examples 2, 3, and 4), which has extremely high practical value for applications such as refrigerated display packaging.

[0025] In summary, the cold-resistant PET material prepared by this invention has a triple synergistic system: the dynamic reversible thiohexene epoxy resin network provides the basis for low-temperature toughness and self-healing; the ion cluster supramolecular network synergistically toughens the material on this basis and solves the core contradiction between transparency and cold whitening resistance, while also promoting self-healing efficiency; the surface-oriented organosilicon nanolayer endows the material with grease resistance and anti-fogging function. Detailed Implementation

[0026] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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. Furthermore, unless otherwise specified, the raw materials, reagents, or devices used in the following embodiments can be obtained from conventional commercial channels or by existing known methods.

[0027] (1) PET resin: food-grade slices with an intrinsic viscosity of 0.80 dL / g, commercially available.

[0028] (2) Bis(2,3-epoxypropylthio) disulfide (DETS): purity >98%, commercially available.

[0029] (3) 1-(2-Carboxyethyl)-3-methylimidazolium chloride (CMIM-Cl): Purity >99%, commercially available.

[0030] Catalyst: Triphenylphosphine (TPP), analytical grade, commercially available.

[0031] Polyethylene glycol PEG 2000: (HO-(CH2-CH2-O) n -H, average molecular weight Mn≈2000, n≈45), Sigma-Aldrich, purity ≥99%.

[0032] 3-Chloropropyltriethoxysilane (CTES): Sigma-Aldrich, purity ≥95%.

[0033] Sodium hydride (NaH), tetrahydrofuran (THF), N,N-dimethylformamide (DMF, ultra-dry), potassium iodide (KI), isopropanol (anhydrous, ≥99.5%), acetic acid (glacial acetic acid, analytical grade), diethyl ether (anhydrous, ≥99%) or hexane (anhydrous, ≥99.5%): Sigma-Aldrich.

[0034] Example 1 Preparation of organosilaneoxy polymers (SPO): The idealized structure of the target product is: (EtO)3Si-(CH2)3-O-CH2-(CH2-CH2-O) n -CH2-O-(CH2)3-Si(OEt)3; essentially, it is a PEG encapsulated at both ends with α,ω-terminals of polyethylene glycol (PEG) diol as the main body and 3-triethoxysilylpropyl end groups connected by ether bonds. n can vary with the molecular weight of the selected PEG.

[0035] Detailed preparation steps: Pre-drying: Polyethylene glycol (PEG 2000) was dried overnight in a vacuum oven at 50°C; tetrahydrofuran (THF) and N,N-dimethylformamide (DMF) were placed in a 4 Å molecular sieve for 24 h; glassware was dried and then cooled under an inert gas for later use.

[0036] Preparation of disodium polyethylene glycol: Under inert gas (argon / nitrogen) protection, dissolve 10.0 g of polyethylene glycol in 120 mL of anhydrous tetrahydrofuran and stir until homogeneous (heating to 30°C can help dissolve, followed by cooling to 5°C). Then place in an ice bath to maintain 5°C. Add 0.420 g of sodium hydride (NaH) in batches, controlling the addition rate to avoid violent hydrogen release. Keep stirring and observe until no more bubbles are continuously generated. Continue stirring at 5°C for 30 min to ensure complete and uniform dispersion of the disodium salt. At this point, the system is usually a suspension.

[0037] Etherification and end-capping: The above system was heated from 5°C to room temperature, and 0.166 g of potassium iodide (KI) was added. The system was then purged with nitrogen for protection. 3.61 g of 3-chloropropyltriethoxysilane (CTES) dissolved in 30 mL of tetrahydrofuran (THF) was added dropwise over 30 min. During the dropwise addition, the reaction system should not show significant temperature increases or increased turbidity. After the addition was complete, the mixture was stirred at room temperature for 12 h. If necessary, a small sample could be taken and 1H NMR (DMSO-d6) was used to roughly monitor the end-group changes (note that the operation should be rapid and moisture should be avoided). If the reaction did not meet expectations (NMR showed residual -OH ends or uncapped PEG signals), a small amount of CTES (0.2–0.5 equivalents to -OH each time) could be added, and the reaction continued for 6 h. In this example, sufficient CTES was already added and no further addition was necessary. After completion, the etherified reactant was obtained.

[0038] Quenching and preliminary desalting: Under an inert gas atmosphere, 1.0 mL of isopropanol was added dropwise to the etherification reactants to gently quench any remaining NaH / alkoxy active sites. Then, 0.2 mL of glacial acetic acid was added to neutralize the system. The system was then stirred under an inert gas atmosphere for 10–15 min. After standing, the inorganic salts and insoluble matter were removed by filtration through a PTFE membrane (0.45 μm). The filtrate was evaporated at room temperature to remove THF, yielding a viscous crude product.

[0039] Purification (without washing to avoid hydrolysis): Dissolve the crude product in 50 mL of tetrahydrofuran, then slowly pour in 10 times its volume of diethyl ether at 5°C for precipitation (PEG and its derivatives are generally poorly soluble in ether and easily form precipitates; small molecule byproducts and unreacted CTES are retained in the supernatant). After thorough stirring and settling, discard the supernatant and repeat the redissolution-reprecipitation process 2-3 times to remove residual small molecules. Finally, dry the precipitate overnight in a vacuum oven (50°C) to obtain the solid product, namely the target product organosilaneoxy polymer (SPO), with a yield of 85.4%. The organosilaneoxy polymer (SPO) needs to be stored in a dry, inert gas environment (argon or nitrogen), sealed in a dry amber bottle. A calcined molecular sieve can be placed inside the bottle to avoid moisture and acidic environments. Low-temperature storage can delay the hydrolysis of the triethoxysilane terminus.

[0040] Example 2 Preparation of cold-resistant PET materials: 100 parts by weight of PET resin (pre-dried at 140°C for 4 hours), 3 parts by weight of bis(2,3-epoxypropylthio)disulfide (DETS), 1 part by weight of 1-(2-carboxyethyl)-3-methylimidazolium chloride (CMIM-Cl), 0.5 parts by weight of the organosilaneoxy polymer (SPO) prepared in Example 1 above, and 0.1 parts by weight of triphenylphosphine (TPP) were mixed uniformly in a high-speed mixer. The mixture was added to a twin-screw extruder with zone temperatures set to 270°C, 265°C, 265°C, 260°C, and 250°C, and a screw speed of 300 rpm. The extruded strip was cooled in a water bath and then pelletized to obtain modified PET masterbatch M1. After drying masterbatch M1 at 140°C for 4 hours, it was injection molded into various standard test strips using an injection molding machine. The injection-molded sample was placed in a constant temperature and humidity chamber at 60℃ and 85% relative humidity for 2 hours to allow the organosilane alkoxy polymer to undergo a hydrolysis-condensation reaction on the material surface, forming a surface-oriented organosilicon nanolayer, thus obtaining the cold-resistant PET material. The above-mentioned method for preparing the cold-resistant PET material is simple, compatible with existing PET processing equipment, and easy to implement for industrial production.

[0041] Example 3 Preparation of cold-resistant PET materials: 100 parts by weight of PET resin (pre-dried at 140°C for 4 hours), 5 parts by weight of bis(2,3-epoxypropylthio)disulfide (DETS), 3 parts by weight of 1-(2-carboxyethyl)-3-methylimidazolium chloride (CMIM-Cl), 1 part by weight of the organosiloxane-oxygenated polymer (SPO) prepared in Example 1 above, and 0.3 parts by weight of triphenylphosphine (TPP) were mixed uniformly in a high-speed mixer. The mixture was added to a twin-screw extruder with zone temperatures set to 270°C, 265°C, 265°C, 260°C, and 250°C, and a screw speed of 300 rpm. The extruded strip was cooled in a water bath and then pelletized to obtain modified PET masterbatch M1. After drying masterbatch M1 at 140°C for 4 hours, it was injection molded into various standard test strips using an injection molding machine. The injection-molded sample was placed in a constant temperature and humidity chamber at 70°C and 90% relative humidity for 3 hours to allow the organosilane alkoxy polymer to undergo a hydrolysis-condensation reaction on the material surface, forming a surface-oriented organosilicon nanolayer, thus obtaining the cold-resistant PET material. The above-mentioned method for preparing the cold-resistant PET material is simple, compatible with existing PET processing equipment, and easy to implement for industrial production.

[0042] Example 4 Preparation of cold-resistant PET materials: 100 parts by weight of PET resin (pre-dried at 140°C for 4 hours), 8 parts by weight of bis(2,3-epoxypropylthio)disulfide (DETS), 5 parts by weight of 1-(2-carboxyethyl)-3-methylimidazolium chloride (CMIM-Cl), 2 parts by weight of the organosiloxane-oxygenated polymer (SPO) prepared in Example 1 above, and 0.5 parts by weight of triphenylphosphine (TPP) were mixed uniformly in a high-speed mixer. The mixture was added to a twin-screw extruder with zone temperatures set to 270°C, 265°C, 265°C, 260°C, and 250°C, and a screw speed of 300 rpm. The extruded strip was cooled in a water bath and then pelletized to obtain modified PET masterbatch M1. After drying masterbatch M1 at 140°C for 4 hours, it was injection molded into various standard test strips using an injection molding machine. The injection-molded samples were placed in a constant temperature and humidity chamber at 80°C and 95% relative humidity for 4 hours to allow the organosilane alkoxy polymer to undergo a hydrolysis-condensation reaction on the material surface, forming a surface-oriented organosilicon nanolayer, thus obtaining the cold-resistant PET material. The above-mentioned method for preparing the cold-resistant PET material is simple, compatible with existing PET processing equipment, and easy to implement for industrial production.

[0043] Comparative Example 1 Comparative Example 1 served as the control group for Example 3. The technical solution of Comparative Example 1 was basically the same as that of Example 3, but DETS, CMIM-Cl and SPO were not added. Only 0.3 parts by weight of TPP were added to obtain PET material.

[0044] Comparative Example 2 Comparative Example 2 served as the control group for Example 3. The technical solution of Comparative Example 2 was basically the same as that of Example 3, but without the addition of CMIM-Cl and SPO, resulting in the final PET material.

[0045] Comparative Example 3 Comparative Example 3 serves as the control group for Example 3. The technical solution of Comparative Example 3 is basically the same as that of Example 3, but without the addition of DETS and SPO, resulting in the final PET material.

[0046] Comparative Example 4 Comparative Example 4 served as the control group for Example 3. The technical solution of Comparative Example 4 was basically the same as that of Example 3, but DETS and CMIM-Cl were not added, and PET material was finally obtained.

[0047] Test Example 1 The PET materials prepared in Examples 2 to 4 and Comparative Examples 1 to 4 were subjected to performance tests. The performance test process is as follows, and the test results are shown in Table 1: (1) Notched impact strength: Tested using a simply supported beam impact testing machine. The sample was placed in a low temperature chamber at -40℃ for 4 hours and then tested immediately. The sample size was 80mm×10mm×4mm, with a type A notch.

[0048] (2) Haze and transmittance: tested using a haze meter according to GB / T 2410-2008 standard. The sample was a 1mm thick sheet.

[0049] (3) Cold whitening resistance: A 1 mm thick sample was stretched at a speed of 50 mm / min in an environment of -40℃. The tensile strain at which obvious whitening phenomenon began to appear was observed and recorded. The greater the strain, the better the cold whitening resistance.

[0050] (4) Low-temperature self-healing efficiency (impact strength recovery rate): The two cross-sections of the fractured specimen after the impact test were brought into close contact and heat-treated in an oven at 60℃ for 6 hours. After cooling to room temperature, the notched impact strength was tested again at -40℃ according to method 1. Healing efficiency = (healed impact strength / original impact strength) × 100%.

[0051] (5) Oil stress cracking test: According to ASTM D543, the specimen was bent and fixed on a semi-circular fixture with an adjustable radius, and a strain of 1.5% was applied. Soybean oil was applied to the center of the tensile surface of the specimen, and the specimen was placed in an environment of 23°C. The time from cracking to complete fracture was recorded.

[0052] (6) Contact angle test: Using a contact angle measuring instrument, deionized water and peanut oil were used as test liquids to measure the static contact angle of the surface of a 1mm thick sheet.

[0053] (7) Anti-fog performance test: Cover the mouth of a beaker containing 80℃ hot water with a 1mm thick sample, place the whole device in an environment of 5℃, and observe the fogging on the inner surface of the sample after 1 minute.

[0054] Table 1 Test Results Analysis of the data in Table 1: 1. -40℃ Notched Impact Strength Analysis: The impact strength of Comparative Example 1 (pure PET) was only 2.0 kJ / m. 2 This confirms that unmodified PET materials exhibit typical brittleness at low temperatures.

[0055] The impact strength of Comparative Example 2 (containing only DETS) was increased to 8.5 kJ / m. 2 The value is significantly higher than that of Comparative Example 1. This directly proves that the "dynamically reversible thiohexene epoxy resin network" formed by DETS can effectively absorb and dissipate impact energy as a flexible network, which is one of the key factors in improving the low-temperature toughness of materials.

[0056] The impact strength of Comparative Example 3 (containing only CMIM-Cl) was 5.2 kJ / m. 2 Compared to Comparative Example 1, this represents a certain improvement. This indicates that the "ion cluster supramolecular network" formed by CMIM-Cl, acting as physical cross-linking points, can also absorb energy to some extent, contributing to low-temperature toughness.

[0057] The impact strength of Comparative Example 4 (containing only SPO) is 3.1 kJ / m. 2 The improvement compared to pure PET (Comparative Example 1) is not significant, indicating that the surface nanolayer formed by SPO contributes very little to the overall low-temperature impact performance of the material.

[0058] The impact strengths of Examples 2, 3, and 4 reached 12.5, 15.8, and 18.2 kJ / m, respectively. 2 The impact strength was significantly higher than that of any comparative example with only one modifier added. This result clearly demonstrates a significant synergistic toughening effect between the chemical network formed by DETS and the physical network formed by CMIM-Cl. The two networks work together to greatly improve the impact resistance of the material at low temperatures. Furthermore, as the amounts of DETS and CMIM-Cl increased from Example 2 to Example 4, the impact strength also steadily increased.

[0059] 2. Transmittance and Haze Analysis: Comparative Example 1 (pure PET) has the highest light transmittance (92.0%) and very low haze (1.5%), which are due to its inherent optical properties.

[0060] Comparative Example 2 (containing only DETS) showed a decrease in transmittance to 86.5% and a significant increase in haze to 5.8%. This indicates that the polymer network formed by DETS is not perfectly compatible with the PET matrix, and may have formed a micron-scale phase separation structure, leading to light scattering and thus reducing transparency.

[0061] Comparative Example 3 (containing only CMIM-Cl) showed transmittance (91.0%) and haze (2.0%) very close to those of pure PET. This indicates that the ionic liquid CMIM-Cl has excellent compatibility with the PET matrix.

[0062] Examples 2, 3, and 4 exhibited excellent light transmittance (88.8%–90.2%) and haze (2.2%–2.8%). Particularly noteworthy is that, despite containing DETS, which reduces transparency (as shown in Comparative Example 2), the final haze of these examples was significantly lower than that of Comparative Example 2, while the light transmittance remained at a high level. This demonstrates that the presence of CMIM-Cl improves the dispersibility and compatibility of DETS in the PET matrix, suppresses the degree of phase separation, and thus maintains high transparency of the material while achieving high toughness.

[0063] 3. Analysis of resistance to cold whitening: The tensile strain of Comparative Example 1 (pure PET) against cold whitening was only 10%, indicating that it is very easy to whiten due to stress-induced crystallization or the formation of microvoids when stretched at low temperature.

[0064] The strain of Comparative Example 2 (containing only DETS) increased to 80%, indicating that the DETS network can partially suppress crack initiation, but the effect is limited.

[0065] Comparative Example 3 (containing only CMIM-Cl) showed a strain increase of 120%, significantly outperforming Comparative Example 2. This directly confirms that the "ion cluster supramolecular network" can effectively restrict the local rearrangement and crystallization of PET molecular chains, which is the main reason for resisting cold whitening.

[0066] Comparative Example 4 (containing only SPO) had a strain of 15%, which was almost the same as that of pure PET, indicating that the surface layer had no effect on this performance.

[0067] Examples 2, 3, and 4 all exhibited extremely high resistance to cold whitening tensile strain (over 150%), far exceeding that of the comparative examples. This further demonstrates the synergistic effect of the DETS network and the CMIM-Cl network: the CMIM-Cl network fundamentally inhibits the occurrence of whitening, while the DETS network further enhances the toughness of the matrix. The combination of the two allows the material to remain transparent even when subjected to huge deformation.

[0068] 4. Low-temperature self-healing efficiency analysis: The self-healing efficiency of Comparative Examples 1, 3, and 4 was 0. This is because pure PET, materials containing CMIM-Cl (physical network), or materials containing SPO (surface layer) do not have the ability to recombine chemical bonds after breakage.

[0069] Comparative Example 2 (containing only DETS) exhibited a self-healing efficiency of 60%. This clearly demonstrates that the self-healing function originates entirely from the dynamic reversible disulfide bonds in the DETS network. Under heating conditions, the disulfide bonds at the fracture surface undergo an exchange reaction, reconnecting the network and thus restoring some mechanical properties.

[0070] The self-healing efficiencies of Examples 2, 3, and 4 reached 75%, 82%, and 78%, respectively, all higher than those of Comparative Example 2, which only added DETS. This reveals an important synergistic effect: although the ion cluster network formed by CMIM-Cl does not heal itself, it can bind the broken interfaces together more tightly, creating more favorable conditions for the exchange reaction of disulfide bonds in the DETS network, thereby improving the healing efficiency.

[0071] 5. Analysis of stress cracking time under grease resistance: The grease resistance times of Comparative Examples 1, 2, and 3 were all very short (2-5 hours), indicating that pure PET and materials modified solely by DETS or CMIM-Cl cannot resist grease erosion and stress cracking.

[0072] Comparative Example 4 (containing only SPO) showed a significantly extended grease resistance time to 48 hours. This directly demonstrates that the organosilicon nanolayer formed by SPO on the surface is the core component resisting grease stress cracking. This dense nanolayer with low surface energy effectively prevents grease wetting and penetration.

[0073] The grease resistance times of Examples 2, 3, and 4 were 72, 84, and 96 hours, respectively, far exceeding those of the comparative examples. This indicates that, based on the SPO surface protective layer, the internal DETS and CMIM-Cl network structure further enhances the substrate's resistance to stress cracking, demonstrating a synergistic protective effect of the "body-surface" combination.

[0074] 6. Contact angle and anti-fog performance analysis: Contact angle: Comparative Examples 1, 2, and 3 showed low water contact angles (75–78°) and extremely low oil contact angles (20–22°), exhibiting hydrophilic and oleophilic properties, and therefore were not resistant to oil stains. Comparative Example 4 and Examples 2, 3, and 4, due to the formation of an organosilicon nanolayer on their surfaces, showed significantly increased water contact angles (>100°) and oil contact angles (>68°), exhibiting hydrophobic and oleophobic properties, which perfectly corresponded to the grease resistance test results.

[0075] Anti-fogging performance: Only Comparative Example 4 and Examples 2, 3, and 4, which contained SPO, exhibited excellent anti-fogging performance. This confirms that the anti-fogging function is entirely attributed to the surface nanolayer formed after the hydrolysis and condensation of SPO. This nanolayer, containing unreacted silanol groups, possesses a certain degree of hydrophilicity, enabling it to spread condensed water droplets into a water film, thereby achieving anti-fogging.

[0076] This analysis is based entirely on the technical solution and test data you provided. It is logically rigorous, and the conclusions are clear, fully demonstrating the significant advantages and inventiveness of this invention compared to existing technologies and single modification methods.

[0077] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0078] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A cold-resistant PET material, characterized in that, The cold-resistant PET material comprises the following components: (a) PET matrix; (b) A first network formed in the PET matrix, wherein the first network is a dynamic reversible thiohexene epoxy resin network; (c) A second network formed in the PET matrix, the second network being an ion cluster supramolecular network; and (d) A nanolayer covering the surface of the PET substrate, wherein the nanolayer is a surface-oriented organosilicon nanolayer.

2. The cold-resistant PET material according to claim 1, characterized in that, The dynamic reversible thiohexene epoxy resin network is formed by the self-polymerization of cyclic thiohexene resin monomers containing dynamic disulfide bonds with the terminal carboxyl and terminal hydroxyl groups in the PET matrix under the action of a catalyst.

3. The cold-resistant PET material according to claim 2, characterized in that, The cyclic sulfur resin monomer containing dynamic disulfide bonds is a bis(2,3-epoxypropylthio) disulfide.

4. The cold-resistant PET material according to claim 1, characterized in that, The ion cluster supramolecular network is a physical cross-linked network formed by an ionic liquid containing carboxylic acid functional groups and ester groups in a PET matrix through ion-dipole interactions.

5. The cold-resistant PET material according to claim 4, characterized in that, The ionic liquid containing the carboxylic acid functional group is 1-(2-carboxyethyl)-3-methylimidazolium chloride.

6. The cold-resistant PET material according to claim 1, characterized in that, The surface-oriented organosilicon nanolayer is formed by the hydrolysis and condensation reaction of an organosilicon alkoxy polymer on the surface of the PET matrix.

7. The cold-resistant PET material according to claim 6, characterized in that, The organosilyl alkoxy polymer is prepared by the following steps: A1. Under inert gas, dissolve polyethylene glycol in tetrahydrofuran, stir until homogeneous, then place in an ice bath to maintain 5°C, add sodium hydride in batches, and continue stirring at 5°C for 30 min to obtain a suspension. A2. Bring the suspension to room temperature, add potassium iodide, then purge with nitrogen gas, and add a solution of 3-chloropropyltriethoxysilane in tetrahydrofuran dropwise over 30 min. After the addition is complete, stir at room temperature for 12 h to obtain the etherified product. A3. Isopropanol and glacial acetic acid were added dropwise to the etherification reactants under an inert gas atmosphere, stirred for 10-15 min, allowed to stand, and then filtered and rotary evaporated to obtain the crude product. A4. Dissolve the crude product in tetrahydrofuran, then add 10 times the volume of diethyl ether at 5°C, stir thoroughly, let stand and settle, then discard the supernatant. Repeat the redissolution-reprecipitation process 2-3 times. After drying the precipitate, obtain the solid product, which is the target product, organosilane oxypolymer.

8. A method for preparing a cold-resistant PET material according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1. PET resin, cyclic sulfur resin monomer containing dynamic disulfide bonds, ionic liquid containing carboxylic acid functional groups, organosiloxane polymer and catalyst are mixed evenly, and melt-blended and extruded through a twin-screw extruder at 250-270°C, cooled and pelletized to obtain modified PET masterbatch. S2. Place the masterbatch obtained in S1 or the product injection molded from it in an environment with a temperature of 60-80℃ and a relative humidity of 85%-95% for 2-4 hours to obtain cold-resistant PET material.

9. The method for preparing a cold-resistant PET material according to claim 8, characterized in that, The weight fractions of each component in S1 are: PET resin: 100 parts; Cyclosulfide resin monomers containing dynamic disulfide bonds: 3-8 parts; Ionic liquids containing carboxylic acid functional groups: 1–5 parts; Organosilane-based polymers: 0.5–2 parts; Catalyst: 0.1 to 0.5 parts.

10. The method for preparing a cold-resistant PET material according to claim 9, characterized in that, The catalyst is triphenylphosphine.

Images