An oil-resistant food packaging bag and a method for preparing the same

Abstract

The application provides an oil-resistant food packaging bag and a preparation method thereof. The oil-resistant food packaging bag comprises the following raw materials in parts by mass: 100 parts of low-density polyethylene, 4-8 parts of modified layered filler, 0.05-0.5 parts of lubricant and 0.1-1 parts of antioxidant. The modified layered filler is obtained by grafting polyethylene glycol segments on the surface of the layered filler, and the polyethylene glycol segments are capped by urethane bonds at the end far from the layered filler. By constructing an interface layer with polyethylene glycol segments and urethane capping structure on the surface of the layered filler, the interface structure stability of the material under the condition of oil contact can be improved while ensuring the dispersibility of the filler, thereby effectively prolonging the oil penetration path and improving the oil resistance of the food packaging bag.

Description

Technical Field

[0001] This application relates to the field of food packaging technology, specifically to an oil-resistant food packaging bag and its preparation method. Background Technology

[0002] Food packaging materials often come into direct contact with oily foods during actual use, such as fried foods, meat products, and nuts. In such applications, packaging materials not only need to possess basic mechanical and processing properties, but also good oil resistance to prevent grease from seeping to the outside of the packaging and affecting the product's appearance, hygiene, and user experience.

[0003] Currently, polyethylene materials, especially low-density polyethylene (LDPE), are widely used in food packaging bags due to their good flexibility, processing performance, and cost advantages. However, these materials are non-polar polymers with weak intermolecular forces. Under conditions of oil contact, they are prone to chain relaxation and volume expansion, allowing oil molecules to gradually diffuse and migrate within the polymer, thus limiting the oil resistance of the packaging material. Under prolonged or high-temperature contact with oils, significant oil penetration may even occur.

[0004] To improve the oil resistance of polyethylene materials, existing technologies typically employ the introduction of inorganic fillers to extend the diffusion path of oil molecules by constructing "zigzag paths." For example, layered silicate fillers are composited with the polymer matrix to enhance the material's barrier properties. However, in practical applications, the dispersibility and interfacial compatibility of these fillers within the polymer matrix are often difficult to control effectively. When the fillers are unevenly dispersed or agglomerated, not only is it difficult to form a continuous and effective barrier path, but defective channels may also form in localized areas, reducing the overall oil resistance.

[0005] Furthermore, even when fillers are well dispersed, the interfacial bonding between the filler and the polymer matrix remains a crucial factor affecting material properties. In oily environments, interfacial regions are more prone to structural relaxation or interfacial lubrication, causing the originally constructed barrier pathways to be disrupted by oil, resulting in a gradual decline in oil resistance over time. Therefore, simply relying on the introduction of fillers is insufficient to simultaneously achieve both initial barrier performance and long-term oil resistance stability.

[0006] On the other hand, existing technologies also improve the dispersibility and compatibility of fillers in polymers by organically modifying the filler surface. However, most modification methods mainly focus on improving the dispersion effect during processing, and pay insufficient attention to the stability of the interfacial structure of the material in oil contact environment. As a result, the problem of limited improvement or poor retention of oil resistance still exists in actual use.

[0007] Therefore, how to improve the barrier properties of polyethylene materials under grease contact conditions while ensuring their processing performance, and further enhance the stability of their oil resistance, remains a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] This application provides an oil-resistant food packaging bag and its preparation method, which solves the problem that existing polyethylene food packaging materials are prone to chain segment relaxation and interfacial structure instability under oil contact conditions, resulting in rapid oil penetration, insufficient barrier performance and poor oil resistance retention.

[0009] In a first aspect, this application provides an oil-resistant food packaging bag, comprising the following raw materials in parts by weight: 100 parts low-density polyethylene, 4-8 parts modified layered filler, 0.05-0.5 parts lubricant, 0.1-1 parts antioxidant; The modified layered filler is obtained by grafting polyethylene glycol segments onto the surface of the layered filler, and the ends of the polyethylene glycol segments away from the layered filler are sealed with urethane bonds.

[0010] According to this application, by constructing an interface layer with polyethylene glycol segments and urethane end caps on the surface of layered fillers, the interfacial structure stability of the material under oil contact conditions can be improved while ensuring filler dispersibility, thereby effectively extending the oil penetration path and improving the oil resistance of food packaging bags.

[0011] Specifically, low-density polyethylene (LDPE), as a continuous phase, provides basic film-forming properties and flexibility for packaging bags. However, its intermolecular forces are relatively weak, making it prone to chain relaxation in oily environments, allowing oil molecules to diffuse and migrate within the material. By introducing layered fillers, tortuous barrier paths can be constructed within the polyethylene matrix, thereby extending the diffusion path of oil molecules and improving barrier performance. However, unmodified layered fillers are prone to agglomeration in polyethylene and exhibit poor interfacial compatibility, making it difficult to form a uniform and effective barrier structure.

[0012] This application grafts polyethylene glycol segments onto the surface of layered fillers. On the one hand, the flexible structure of the polyethylene glycol segments improves the dispersion of the layered fillers in the polyethylene matrix, enabling the fillers to be distributed more uniformly and form continuous barrier paths during film formation. On the other hand, the polyethylene glycol segments form a transition interface layer between the filler and the polymer, which helps to alleviate interfacial stress concentration and improve the structural stability of the composite system.

[0013] Furthermore, by introducing urethane end-capping structures at the ends of polyethylene glycol segments away from the layered filler, an end-base layer containing urethane groups can be formed at the interface. These groups contain both carbonyl and amino groups, possessing strong polarity and a certain degree of intermolecular interaction ability. This allows for the formation of a relatively stable intermolecular network in the interfacial region, resulting in a more compact chain arrangement and reduced free volume. Since the diffusion of oil molecules in the polymer depends on free volume and chain segment movement space, this structure helps to reduce the dissolution and diffusion rate of oil molecules in the interfacial region. Compared to uncapped polyethylene glycol (PEG) segments, the terminal hydroxyl structures of PEG segments are more likely to interact with oil molecules in an oily environment, leading to segment swelling or local migration. However, after introducing urethane end-capsulation, the terminal hydroxyl groups are transformed from single polar hydroxyl groups into larger and more stable urethane groups, increasing the steric hindrance at the chain ends and restricting molecular mobility, thereby reducing the tendency of PEG segments to relax excessively under the influence of oil. In addition, the urethane structure has higher structural rigidity than flexible PEG segments. Its introduction into the interfacial region is equivalent to setting "restriction sites" at the ends of flexible segments, which can constrain the movement of segments and prevent overall relaxation or structural rearrangement of the interfacial region during oil contact. This helps maintain the continuity and stability of the tortuous barrier path constructed by the layered filler.

[0014] Therefore, the polyethylene glycol segments and urethane end-capping structures synergistically construct a stable interface layer on the surface of the layered filler, enabling the filler to form an effective barrier path in the polyethylene matrix and maintain the stability of the interface structure in the oily environment, thereby improving the overall oil resistance of food packaging bags.

[0015] Based on the above structural features, the food packaging bag is particularly suitable for food packaging scenarios with high oil content or those that need to be in contact with oil for a long time. For example, it can be used as an inner layer to form a paper-plastic composite packaging with paper base material, which is used to hold fried foods such as fried chicken, French fries, and fried cakes. In actual use, it can effectively inhibit the outward penetration of oil, reduce the wetting and contamination of the outer paper base material, and maintain the integrity of the packaging structure and the cleanliness of the appearance, thereby improving the performance and applicability of the packaging.

[0016] In some embodiments, the method for preparing the modified layered filler includes the following steps: S1: Disperse the layered filler and epoxy silane coupling agent in an aqueous ethanol solution, and hydrolyze the epoxy silane coupling agent to condense with the hydroxyl groups on the surface of the layered filler to obtain epoxy modified layered filler. S2: The epoxy-modified layered filler, polyethylene glycol and triethylamine are dispersed in toluene, and under catalytic conditions, the hydroxyl groups of the polyethylene glycol stage react with the epoxy groups on the epoxy-modified layered filler to obtain the hydroxyl-terminated polyethylene glycol modified layered filler. S3: The hydroxyl-terminated polyethylene glycol modified layered filler and the monoisocyanate compound are dispersed in toluene, and the monoisocyanate compound is used to seal the hydroxyl-terminated polyethylene glycol modified layered filler with urethane bonds under catalytic conditions to obtain the modified layered filler.

[0017] In some of the above embodiments, by sequentially performing silane condensation reaction, epoxy ring-opening grafting reaction, and isocyanate end-capping reaction, an organic segment structure connected by chemical bonds is formed on the surface of the layered filler, and finally a continuous interface structure of "layered filler-silane connecting layer-polyethylene glycol segment-urethane end group" is constructed on the surface of the filler.

[0018] The aforementioned structure allows polyethylene glycol segments to be stably connected to the surface of the layered filler in a single-end manner, with urethane end groups introduced at the ends of the segments furthest from the filler. This creates an interfacial layer with a certain degree of polarity and structural stability between the filler and the polyethylene matrix. This interfacial layer facilitates the uniform dispersion and orientation of the filler during material processing. Under grease contact conditions, it reduces the enrichment and diffusion of oil molecules in the interfacial region and inhibits excessive relaxation of the interfacial segments. This helps maintain the continuity and stability of the barrier pathway constructed by the layered filler, thereby improving the material's oil resistance.

[0019] In some embodiments, S1 includes: dispersing 10 parts of layered filler and 1-3 parts of epoxy silane coupling agent in 150-300 parts of ethanol aqueous solution, and reacting at pH=4.5-5.5 and 60-80℃ for 3-5 hours to obtain epoxy modified layered filler.

[0020] In some of the above embodiments, by controlling the pH value, temperature and reaction time of the reaction system, the epoxy silane coupling agent can be fully hydrolyzed and undergo a condensation reaction with the hydroxyl groups on the surface of the layered filler, thereby forming a relatively stable modified structure on the surface of the layered filler, which is conducive to the smooth progress of subsequent reactions.

[0021] In some embodiments, S2 includes: dispersing 10 parts of the epoxy-modified layered filler, 40-60 parts of polyethylene glycol with a weight-average molecular weight of 600-1200 and 0.3-1 parts of triethylamine in 150-300 parts of toluene, and reacting at 95-105°C for 6-8 hours to obtain hydroxyl-terminated polyethylene glycol-modified layered filler.

[0022] In some of the above embodiments, by using an excess of polyethylene glycol, the polyethylene glycol segments in the reaction system preferentially react with the epoxy groups on the surface of the layered packing, thereby improving the grafting efficiency. At the same time, since the hydroxyl groups at the other end of the polyethylene glycol segments are not easily involved in the reaction due to steric hindrance after they are connected to the surface of the layered packing, the polyethylene glycol segments are mainly connected to the surface of the layered packing in a single-end grafting form, which is beneficial to retain the terminal hydroxyl groups for subsequent end-capping reactions.

[0023] In some embodiments, S3 includes: dispersing 10 parts of the terminal hydroxyl polyethylene glycol modified layered filler, 2-5 parts of monoisocyanate compound and 0.1-0.3 parts of organotin catalyst in toluene, and reacting at 55-70°C for 4-6 hours under a nitrogen atmosphere to obtain the modified layered filler.

[0024] In some of the above embodiments, by reacting under an inert atmosphere and at a suitable temperature, the monoisocyanate compound can fully react with the terminal hydroxyl groups of the hydroxyl-terminated polyethylene glycol segments to form urethane bonds, thereby achieving effective end-capping of the polyethylene glycol segments and obtaining a structurally stable modified layered filler.

[0025] In some embodiments, the monoisocyanate compound includes an aromatic monoisocyanate compound.

[0026] In some of the above embodiments, after the aromatic monoisocyanate compound reacts with the terminal hydroxyl polyethylene glycol segment to form a urethane structure, the aromatic ring structure introduced in its end group has higher molecular rigidity and a more compact spatial configuration. Compared with the flexible segment structure formed by aliphatic monoisocyanate compounds, it is more conducive to forming a relatively dense end base layer structure in the interface region, thereby reducing the diffusion channels of oil molecules in the interface region.

[0027] Meanwhile, the introduction of aromatic structures makes the molecular arrangement of the end-layer layers more regular, which helps to reduce the free volume in the interfacial region. Since the diffusion process of oil molecules in polymers is closely related to the free volume, reducing the free volume can further extend the diffusion path of oil molecules. In contrast, the end-group structures formed by aliphatic monoisocyanate compounds are more flexible and are more prone to chain segment adjustment under oil contact conditions, making it difficult to form a stable and effective barrier structure.

[0028] Therefore, using aromatic monoisocyanate compounds for end-capping is beneficial for forming an interface structure on the surface of layered fillers that is more conducive to hindering the diffusion of oil molecules, thus resulting in better oil resistance.

[0029] In some embodiments, the aromatic monoisocyanate compound comprises phenyl isocyanate and 4-methoxyphenyl isocyanate, wherein the mass ratio of phenyl isocyanate to 4-methoxyphenyl isocyanate is 1:0.4 to 0.8.

[0030] In some of the above embodiments, the inventors found through comparative studies of different monoisocyanate end-capping systems that when only phenyl isocyanate or only 4-methoxyphenyl isocyanate is used to end-cap polyethylene glycol segments, the oil penetration time of the resulting material is improved, but the improvement is limited; while when the two are used in combination in the above proportion, the material shows a more obvious extension effect in the oil penetration time test.

[0031] The inventors believe that the above effects may be related to the synergistic effect of the two types of end-group structures in the interfacial region. The phenyl structure is relatively compact and rigid, which is conducive to forming a denser local structure in the interfacial region, thereby reducing the channels through which oil molecules pass. The 4-methoxyphenyl structure, due to the introduction of a methoxy substituent, has a different molecular polarity and spatial configuration than the phenyl structure, resulting in a different molecular arrangement in the interfacial region compared to a single phenyl structure. When both are present in combination, the interfacial end-group layer is no longer a single structure but exhibits a certain structural difference. This difference helps to form a more complex molecular stacking state in the interfacial region, making it difficult for oil molecules to migrate continuously along a single channel during diffusion, thus further extending their diffusion path. In contrast, the interfacial layer formed by a single end-group structure tends to be more uniform and is more likely to form a relatively continuous diffusion path under the influence of oils.

[0032] Therefore, by compounding phenyl isocyanate and 4-methoxyphenyl isocyanate in a specific ratio for end capping, it is beneficial to construct end base layers with structural differences in the interface region, thereby improving oil resistance.

[0033] In some embodiments, the layered filler comprises sodium montmorillonite. Based on the above embodiments, sodium montmorillonite has a layered structure and a large interlayer spacing, which, after modification, is more conducive to dispersion in a polyethylene matrix, thereby facilitating the formation of a sheet structure.

[0034] In some embodiments, the low-density polyethylene has a melt flow rate of 1.5~2.5 g / 10 min at 190°C and 2.16 kg. Based on the above embodiments, by selecting low-density polyethylene with a melt flow rate within the above range, the material has suitable fluidity during blending and blown film processing, which is beneficial for the uniform dispersion of modified layered fillers in the matrix and ensures the stability of film forming.

[0035] In some embodiments, the lubricant includes at least one of oleamide and calcium stearate. Based on the above embodiments, oleamide and calcium stearate are both commonly used lubricants in the art, which are beneficial for improving the flowability of materials during melt processing and enhancing the surface properties of the film.

[0036] In some embodiments, the antioxidant includes at least one of antioxidant 1010 and antioxidant 168. Based on the above embodiments, the antioxidant can inhibit the thermo-oxidative aging reaction of polyethylene during processing, thereby improving the stability of the material during melt processing and avoiding the impact of molecular chain degradation on film quality.

[0037] It should be noted that, in some embodiments, without affecting the technical solution of this application, conventional additives such as slip agents, opening agents, anti-blocking agents or lubricants may be added to the system as needed.

[0038] Secondly, this application provides a method for preparing oil-resistant food packaging bags, comprising: Provide the raw materials included in the food packaging bag according to any embodiment of the first aspect; The raw materials are melt-blended, granulated, and blown into film to obtain food packaging bags.

[0039] According to this application, by melt-blending a modified layered filler with a specific interface structure with low-density polyethylene and then molding it using a blown film process, the modified layered filler can be uniformly dispersed in the polyethylene matrix and form a sheet-oriented structure, which is beneficial for constructing a continuous barrier path and giving the food packaging bag good oil resistance.

[0040] Compared with the prior art, the beneficial effects of this application are at least as follows: This application constructs an interface layer with polyethylene glycol segments and urethane end caps on the surface of layered fillers. This allows the fillers to be uniformly dispersed in the polyethylene matrix and form a continuous, tortuous barrier path. It also maintains the stability of the interface structure under oil contact conditions, thereby effectively extending the penetration path of oil in the material, reducing the diffusion rate of oil molecules, and significantly improving the oil resistance and retention of food packaging bags.

[0041] In practical applications, the above-mentioned materials can be used as an oil-resistant inner layer to be combined with paper-based materials to prepare paper-plastic composite packaging. When used to hold fried foods and other foods with high oil content, it can effectively inhibit the penetration of oil to the outside, reduce the wetting and contamination of the outer paper layer, maintain the structural integrity and appearance of the packaging, and thus broaden its application scope in the food packaging field. Detailed Implementation

[0042] The various embodiments or implementation schemes in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments.

[0043] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0045] In this specification, unless otherwise specified, "parts" refers to "parts by weight".

[0046] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0047] Sodium-based montmorillonite has an average particle size of approximately 5 μm and an ion exchange capacity of approximately 100 mmol / 100g.

[0048] Low-density polyethylene, model 2426H, Zhongcheng, has a melt flow rate of approximately 2 g / 10 min at 190℃ and 2.16 kg.

[0049] Preparation Example 1 Preparation of modified layered packings: Ten parts of sodium montmorillonite were weighed and added to 200 parts of an 80% (v / v) aqueous ethanol solution. The mixture was mechanically stirred and dispersed at room temperature for 30 min to obtain a uniform suspension. Two parts of γ-glycidoxypropyltrimethoxysilane (KH-560) were added to the suspension, and the pH of the system was adjusted to 5.0 using dilute acetic acid solution. The mixture was stirred and reacted at 70 °C for 4 h. After the reaction was completed, the system was cooled to room temperature, and the solid product was collected by centrifugation. The solid product was washed twice with ethanol to remove unreacted substances and then vacuum dried at 80 °C for 12 h to obtain epoxy-modified layered filler.

[0050] Weigh 10 parts of the above epoxy-modified layered filler and add them to 200 parts of toluene. Stir and disperse at room temperature for 30 min. Add 50 parts of polyethylene glycol (weight average molecular weight of 800) and 0.5 parts of triethylamine to the system. Heat to 100℃ under nitrogen protection and stir for 7 h. After the reaction is completed, cool to room temperature, centrifuge to separate the solid product, wash twice with ethanol to remove unreacted polyethylene glycol, and then vacuum dry at 80℃ for 12 h to obtain hydroxyl-terminated polyethylene glycol modified layered filler.

[0051] Weigh 10 parts of the above-mentioned hydroxyl-terminated polyethylene glycol modified layered filler and add them to 200 parts of anhydrous toluene. Stir and disperse at room temperature for 30 min. Add 3 parts of monoisocyanate compound and 0.2 parts of dibutyltin dilaurate to the system. The monoisocyanate compound is a mixture of phenyl isocyanate and 4-methoxyphenyl isocyanate with a mass ratio of 1:0.6. Under nitrogen protection, heat the system to 60°C and stir for 5 h. After the reaction is completed, cool the system to room temperature, centrifuge to separate the solid product, wash twice with toluene to remove unreacted substances, and then vacuum dry at 80°C for 12 h to obtain modified layered filler A.

[0052] Preparation Example 2 Preparation of modified layered packings: The preparation method is largely the same as in Example 1, except that the monoisocyanate compound is only phenyl isocyanate, and the product is referred to as modified layered filler B.

[0053] Preparation Example 3 Preparation of modified layered packings: The preparation method is largely the same as in Example 1, except that the monoisocyanate compound is only 4-methoxyphenyl isocyanate, and the product is referred to as modified layered filler C.

[0054] Preparation Example 4 Preparation of modified layered packings: The preparation method is largely the same as in Example 1, except that the monoisocyanate compound is only n-butyl isocyanate, and the product is referred to as modified layered filler D.

[0055] Comparative Preparation Example 1 Preparation of modified layered packings: Ten parts of sodium montmorillonite were weighed and added to 200 parts of an 80% (v / v) aqueous ethanol solution. The mixture was mechanically stirred and dispersed at room temperature for 30 min to obtain a uniform suspension. Two parts of γ-glycidoxypropyltrimethoxysilane (KH-560) were added to the suspension, and the pH of the system was adjusted to 5.0 using dilute acetic acid solution. The mixture was stirred and reacted at 70 °C for 4 h. After the reaction was completed, the system was cooled to room temperature, and the solid product was collected by centrifugation. The solid product was washed twice with ethanol to remove unreacted substances and then vacuum dried at 80 °C for 12 h to obtain epoxy-modified layered filler.

[0056] Weigh 10 parts of the above epoxy-modified layered filler and add them to 200 parts of toluene. Stir and disperse at room temperature for 30 min. Add 50 parts of polyethylene glycol (weight average molecular weight of 800) and 0.5 parts of triethylamine to the system. Heat to 100℃ under nitrogen protection and stir for 7 h. After the reaction is completed, cool to room temperature, centrifuge to separate the solid product, wash twice with ethanol to remove unreacted polyethylene glycol, and then vacuum dry at 80℃ for 12 h to obtain hydroxyl-terminated polyethylene glycol modified layered filler E.

[0057] Example 1 Preparation of oil-resistant food packaging bags: Weigh 100 parts of low-density polyethylene as the matrix resin, add 6 parts of modified layered filler A, 0.2 parts of calcium stearate, 0.3 parts of antioxidant 1010 and 0.2 parts of antioxidant 168, and premix in a high-speed mixer at room temperature at 600 rpm for 10 minutes to ensure uniform dispersion of each component and obtain the premix.

[0058] The obtained premixed material was added to a twin-screw extruder for melt blending and extrusion. Before extrusion, the air in the barrel was replaced with nitrogen for 5 minutes. Nitrogen was continuously introduced during the extrusion process. The temperatures of each zone of the extruder were set sequentially as follows: zone 1 150℃, zone 2 165℃, zone 3 175℃, zone 4 185℃, and die head 190℃. The screw speed was 250 rpm. After melt blending, the material was extruded into strips, cooled by water cooling, and then pelletized to obtain modified polyolefin masterbatch.

[0059] The obtained masterbatch was added to a blown film machine for blown film forming. The barrel temperature was set to 160℃, 170℃, 180℃ and 190℃ in sequence, the die head temperature was 190℃, the screw speed was 60 rpm, the blow-up ratio was 2.5 and the traction ratio was 4.0, and an oil-resistant food packaging bag film with a thickness of about 40μm was obtained.

[0060] Example 2 Preparation of oil-resistant food packaging bags: It is largely the same as Example 1, except that modified layered packing B is used instead of modified layered packing A.

[0061] Example 3 Preparation of oil-resistant food packaging bags: It is largely the same as Example 1, except that modified layered packing C is used instead of modified layered packing A.

[0062] Example 4 Preparation of oil-resistant food packaging bags: It is largely the same as Example 1, except that modified layered packing D is used instead of modified layered packing A.

[0063] Comparative Example 1 Preparation of oil-resistant food packaging bags: It is largely the same as Example 1, except that modified layered packing E is used instead of modified layered packing A.

[0064] Test section Oil penetration time test: The films obtained from each example and comparative example were cut into square samples with a side length of 100 mm. Before the test, all samples were placed in an environment of 23°C and 50% relative humidity for 24 h to equilibrate.

[0065] A self-made penetrant testing device was used for testing. This device includes an upper oil storage chamber, a lower support plate, and a sample clamping structure located between the two. The sample is clamped flat in the device, with the upper surface of the membrane in contact with the grease, and a quantitative filter paper (medium-speed quantitative filter paper) attached tightly to the lower surface as an oil absorption indicator layer. During clamping, it was ensured that the sample surface was free of wrinkles and edge leakage, and the effective test area was fixed at 50mm × 50mm.

[0066] Soybean oil was used for the test and preheated in a 60℃ constant temperature water bath for 30 minutes before the test. 5 mL of preheated soybean oil was added to the oil storage chamber to evenly cover the sample surface, and timing was started simultaneously. The entire testing apparatus was placed in a 60℃ constant temperature chamber for testing, and the state of the filter paper below the sample was observed every 5 minutes.

[0067] When a continuous, clear, and visually identifiable oil spot with a diameter of 2 mm or more is first observed on the filter paper, the corresponding time is recorded as the oil penetration time of that sample. Each group of samples was tested in parallel five times, and the average value was taken as the final test result. The results are shown in Table 1.

[0068] Table 1 According to Table 1, the oil penetration time of each embodiment is higher than that of Comparative Example 1, indicating that the modified layered filler provided in this application, formed by grafting polyethylene glycol segments onto the surface of the layered filler and further end-capping, can effectively prolong the penetration time of oil in food packaging bags, thereby improving the oil resistance of the material. The possible reason is that in Comparative Example 1, although polyethylene glycol segments are grafted onto the surface of the layered filler, the ends of the segments still retain free hydroxyl groups, resulting in a relatively simple end structure. Furthermore, the polyethylene glycol segments are more prone to segmental movement under oil contact conditions, thus limiting the barrier effect of the interface region around the filler on oil molecules. Therefore, oil diffuses more easily along the path between the interface region and the filler, resulting in a shorter oil penetration time. In contrast, in Examples 1-4, after end-capping the ends of the polyethylene glycol segments with urethane bonds using monoisocyanate compounds, a more stable end-base structure is formed on the filler surface, further prolonging the diffusion path of oil in the material, ultimately resulting in a significantly improved oil penetration time.

[0069] As shown in Examples 1-4, using different types of monoisocyanate compounds to end-cap modified layered fillers has a certain impact on the oil resistance of food packaging bags. In Example 4, the use of n-butyl isocyanate for end-capping resulted in a slightly longer oil penetration time compared to Comparative Example 1, but the increase was relatively small, indicating that the end-group structure formed by aliphatic monoisocyanates has limited effect on hindering oil diffusion. Examples 2 and 3, using phenyl isocyanate and 4-methoxyphenyl isocyanate for end-capping respectively, showed significantly longer oil penetration times than Example 4, indicating that aromatic monoisocyanate end-capping is more beneficial for improving the oil resistance of the material. This may be because aromatic end groups have higher structural rigidity, which is more conducive to forming a relatively dense interface layer around the filler, thereby improving the barrier effect on oil molecule diffusion. Furthermore, comparing Examples 1, 2 and 3, it can be seen that when phenyl isocyanate and 4-methoxyphenyl isocyanate are used for end capping, the resulting food packaging bag has the highest oil penetration time, indicating that the combination of different aromatic monoisocyanates has a better effect on improving oil resistance and is more conducive to constructing an interface structure suitable for oil-resistant food packaging bags.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. An oil-resistant food packaging bag, characterized in that, Includes the following quantities of raw materials: 100 parts low-density polyethylene, 4-8 parts modified layered filler, 0.05-0.5 parts lubricant, 0.1-1 parts antioxidant; The modified layered filler is obtained by grafting polyethylene glycol segments onto the surface of the layered filler, and the end of the polyethylene glycol segment away from the layered filler is sealed with a urethane bond. The preparation method of the modified layered packing includes the following steps: S1: Disperse the layered filler and epoxy silane coupling agent in an aqueous ethanol solution, and hydrolyze the epoxy silane coupling agent to condense with the hydroxyl groups on the surface of the layered filler to obtain epoxy modified layered filler. S2: The epoxy-modified layered filler, polyethylene glycol and triethylamine are dispersed in toluene, and under catalytic conditions, the hydroxyl groups of the polyethylene glycol stage react with the epoxy groups on the epoxy-modified layered filler to obtain the hydroxyl-terminated polyethylene glycol modified layered filler. S3: The hydroxyl-terminated polyethylene glycol modified layered filler and the monoisocyanate compound are dispersed in toluene. Under catalytic conditions, the monoisocyanate compound is used to cap the hydroxyl-terminated polyethylene glycol modified layered filler with urethane bonds to obtain the modified layered filler. The monoisocyanate compound is phenyl isocyanate and 4-methoxyphenyl isocyanate, and the mass ratio of phenyl isocyanate to 4-methoxyphenyl isocyanate is 1:0.4~0.

8.

2. The food packaging bag according to claim 1, characterized in that, S1 comprises: dispersing 10 parts of layered filler and 1-3 parts of epoxy silane coupling agent in 150-300 parts of ethanol aqueous solution, and reacting at pH=4.5-5.5 and 60-80℃ for 3-5 hours to obtain epoxy modified layered filler.

3. The food packaging bag according to claim 1, characterized in that, S2 comprises: dispersing 10 parts of the epoxy-modified layered filler, 40-60 parts of polyethylene glycol with a weight-average molecular weight of 600-1200 and 0.3-1 parts of triethylamine in 150-300 parts of toluene, and reacting at 95-105°C for 6-8 hours to obtain hydroxyl-terminated polyethylene glycol-modified layered filler.

4. The food packaging bag according to claim 1, characterized in that, S3 comprises: dispersing 10 parts of the terminal hydroxyl polyethylene glycol modified layered filler, 2-5 parts of monoisocyanate compound and 0.1-0.3 parts of organotin catalyst in toluene, and reacting at 55-70°C for 4-6 hours under a nitrogen atmosphere to obtain the modified layered filler.

5. The food packaging bag according to claim 1, characterized in that, The layered filler includes sodium-based montmorillonite.

6. The food packaging bag according to any one of claims 1 to 5, characterized in that, The raw materials meet the following conditions: 1) The melt flow rate of the low-density polyethylene at 190℃ and 2.16kg is 1.5~2.5g / 10min; 2) The lubricant includes at least one of oleamide and calcium stearate; 3) The antioxidants include at least one of antioxidant 1010 and antioxidant 168.

7. A method for preparing oil-resistant food packaging bags, characterized in that, include: Provide the raw materials included in the food packaging bag according to any one of claims 1 to 6; The raw materials are melt-blended, granulated, and blown into film to obtain food packaging bags.

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