Crosslinked biodegradable pof heat shrinkable film and preparation method thereof

Abstract

The application discloses a crosslinking type biodegradable POF heat-shrinkable film and a preparation method thereof, and belongs to the technical field of heat-shrinkable films, and the technical scheme is as follows: the crosslinking type biodegradable POF heat-shrinkable film comprises three layers of films which are sequentially attached, the first layer of film and the third layer of film each comprise the following raw materials in percentage by weight: PP 89.5-94%, degradation master batch 2-6%, opening agent 0.5-3%, and slip agent 1-4%; the second layer of film comprises the following raw materials in percentage by weight: LLDPE-A 30-35%, toughening agent 9-14.5%, degradation master batch 0.5-1%, LLDPE-B 40-45%, and metallocene LLDPE 10-15%; the melt index of the LLDPE-A is 2.5 g / 10 min, the melt index of the LLDPE-B is 2.1 g / 10 min, and the melt index of the metallocene LLDPE is 1.0 g / 10 min; through the synergistic effect between the LLDPE with different melt indexes and the toughening agent, the low-temperature tear resistance of the heat-shrinkable film is effectively improved.

Description

Technical Field

[0001] This invention relates to the field of heat shrink film technology, and in particular to a cross-linked biodegradable POF heat shrink film and its preparation method. Background Technology

[0002] POF heat shrink film holds a significant position in the packaging industry due to its numerous advantages, including being non-toxic and environmentally friendly, highly transparent, having a high shrinkage rate, excellent heat-sealing performance, high gloss, strong toughness, tear resistance, uniform heat shrinkage, and suitability for fully automated high-speed packaging. It is primarily used for packaging both regular and irregularly shaped products, and is widely applied in the packaging of automotive supplies, plastic products, stationery, books, electronics, circuit boards, headphones, handicrafts, wooden products such as picture frames, toys, pesticides, daily necessities, food, cosmetics, canned beverages, dairy products, pharmaceuticals, videotapes, and many other products. With the continuous development of various industries, the demand for POF heat shrink film is increasing daily, indicating a very promising market prospect.

[0003] Traditionally, POF heat shrink film is manufactured using linear low-density polyethylene as the middle layer and copolymer polypropylene as the inner and outer layers, through processes such as extrusion, stretching, and cooling. This method is a common and traditional approach in the industry. By controlling the materials and process parameters of different layers, POF heat shrink film with certain properties can be obtained, meeting the packaging requirements of some products. Through long-term production practice, this method has been continuously optimized and improved, becoming a relatively mature technology.

[0004] However, conventional biodegradable POF heat shrink film has significant drawbacks. When the film is shrunk and exposed to low temperatures, its tear resistance is poor. This makes the heat shrink film prone to tearing in some low-temperature environments, failing to adequately protect the packaged product and reducing the reliability and stability of the packaging. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a cross-linked biodegradable POF heat-shrinkable film and its preparation method. Through the synergistic effect between LLDPE with different melt indices and toughening agents, the low-temperature tear resistance of the heat-shrinkable film is effectively improved.

[0006] The first aspect of this invention is to provide a method for preparing a cross-linked biodegradable POF heat-shrinkable film, employing the following technical solution:

[0007] A method for preparing a cross-linked biodegradable POF heat-shrinkable film, wherein the heat-shrinkable film comprises three layers of film laminated sequentially, wherein the first layer and the third layer of film each contain the following raw materials by weight percentage: PP 89.5-94%, degradation masterbatch 2-6%, opening agent 0.5-3%, and slip agent 1-4%;

[0008] The second layer membrane comprises the following raw materials by weight percentage: LLDPE-A 30-35%, toughening agent 9-14.5%, degradation masterbatch 0.5-1%, LLDPE-B 40-45%, and metallocene LLDPE 10-15%, wherein the toughening agent is composed of POE and EVA in a weight ratio of 1:(0.5-1);

[0009] The melt index of LLDPE-A is 2.5 g / 10 min, the melt index of LLDPE-B is 2.1 g / 10 min, and the melt index of metallocene LLDPE is 1.0 g / 10 min.

[0010] Its preparation includes the following steps:

[0011] S1. Weigh the raw materials according to the formula, mix them evenly, and add them to three film extruders. After plasticizing, they are extruded into the co-extrusion die to obtain the first film bubble. After traction and water cooling, the first film body is obtained.

[0012] S2. The first membrane is stretched, preheated, and then inflated, followed by air cooling, stretching, and irradiation crosslinking to obtain a POF heat-shrinkable film. The irradiation crosslinking includes surface irradiation and intermediate layer irradiation. The surface irradiation electron beam energy is 80 keV and the irradiation dose is 25-30 kGy. The intermediate layer irradiation electron beam energy is 300 keV and the irradiation dose is 80-100 kGy.

[0013] By adopting the above technical solution, PP is selected as the main raw material in the first and third layers of the film. PP itself has good rigidity and toughness, providing a certain basic strength for the heat shrink film. The degradation masterbatch enables the heat shrink film to have biodegradable properties. The opening agent can prevent adhesion between film layers and ensure normal use of the film. The slip agent can improve the surface slip of the film, making it easier to process and use.

[0014] In the second layer, LLDPE-A, LLDPE-B, and metallocene LLDPE have different melt indices. LLDPE-A has a melt index of 2.5 g / 10 min, exhibiting relatively good flowability and better mixing with other raw materials during processing. LLDPE-B has a melt index of 2.1 g / 10 min, maintaining good toughness while ensuring a certain level of flowability. Metallocene LLDPE has a melt index of 1.0 g / 10 min, with a regular molecular chain structure and high crystallinity, which improves the strength and toughness of the heat-shrinkable film. By combining toughening agents with LLDPE and metallocene LLDPE, and dispersing the toughening agents within the LLDPE and metallocene LLDPE matrices, the toughening agents can absorb and disperse energy when the heat-shrinkable film is subjected to external impact, preventing crack propagation. Simultaneously, the different melt indices of LLDPE and metallocene LLDPE result in more complex entanglement and interactions between molecular chains, forming a more stable network structure, further enhancing the toughness and tear resistance of the heat-shrinkable film. By comprehensively selecting and proportioning the raw materials for each layer of the film, the crack resistance of this cross-linked biodegradable POF heat shrink film under low-temperature conditions is significantly improved.

[0015] When the toughening agent is a combination of POE and EVA, it can effectively improve the toughness of the heat shrink film, thereby enhancing its low-temperature crack resistance. This may be because POE with a low melt index has a high long-chain entanglement density, which forms an energy dissipation zone at low temperatures through the high entanglement network. When cracks propagate, more physical cross-linking points need to be broken through. However, when the melt index of POE is too low, the high molecular weight of POE will lead to uneven dispersion in the LLDPE matrix, which will form stress concentration points and reduce the low-temperature crack resistance of the heat shrink film. When the melt index of POE is too high, POE is mainly composed of short chains with a narrow molecular weight distribution, resulting in poorer low-temperature crack resistance.

[0016] When the VA content in EVA is 18wt%, it has good compatibility with the LLDPE matrix and exhibits rubber-like elasticity at low temperatures. When the VA content is greater than 20%, the acetic acid groups tend to migrate to the film surface, leading to a deterioration in slip properties. When EVA is combined with POE, the two can produce a synergistic effect at low temperatures. POE provides the crosslinked network skeleton, while EVA fills the gaps in the network, thus effectively improving the impact strength compared to a single toughening agent.

[0017] In addition, the surface layer is irradiated with an electron beam energy of 80 keV and an irradiation dose of 25-30 kGy, while the intermediate layer is irradiated with an electron beam energy of 300 keV and an irradiation dose of 80-100 kGy. Within this range, the cross-linked biodegradable POF heat-shrinkable film can achieve a good cross-linking effect. An appropriate irradiation dose for the surface layer gives the film suitable hardness and abrasion resistance, ensuring that the surface is not easily damaged during use. An appropriate irradiation dose for the intermediate layer enhances the internal structural stability and toughness of the film, improving its tear resistance, especially after low-temperature shrinkage, ensuring that it is not easily torn in low-temperature environments, thus improving the reliability and stability of packaging. The inventors also found through experiments that if the surface irradiation dose is below 25 kGy, the film surface is insufficiently cross-linked, resulting in poor hardness and abrasion resistance, and is prone to scratches; if it is above 30 kGy, the film surface may be over-cross-linked, becoming brittle and affecting the film's flexibility. If the irradiation dose of the intermediate layer is less than 80 kGy, the internal cross-linking of the membrane is insufficient, and the tear resistance is not significantly improved; if it is more than 100 kGy, the internal structure of the membrane may be excessively damaged, resulting in a decline in the overall performance of the membrane.

[0018] Preferably, the EVA contains 18% vinyl acetate and has a melt index of 2.5 g / 10 min.

[0019] Preferably, the melt flow index of the POE is 1.0 g / 10 min.

[0020] Preferably, the slip agent is maleic anhydride-grafted polyethylene wax.

[0021] By adopting the above technical solution and using maleic anhydride-grafted polyethylene wax as a slip agent, maleic anhydride-grafted polyethylene wax has better stability than oleamide. It can better maintain its performance during the processing of POF heat shrink film and is not easily decomposed or volatilized due to high temperature. It has better compatibility with film layer raw materials and can be more evenly dispersed in the film layer, thereby more effectively reducing the coefficient of friction of the film layer surface. This makes the heat shrink film easier to slide and handle during the packaging process, reduces adhesion, improves packaging efficiency and quality, and also improves the antistatic properties of the film layer, further enhancing the overall performance of the heat shrink film.

[0022] Preferably, the degradation masterbatch comprises 70-79% Ethylene Polyer and 21-30% Metal Salts by weight percentage.

[0023] A second aspect of the present invention is to provide a POF heat shrink film obtained by the preparation method of the cross-linked biodegradable POF heat shrink film as described above.

[0024] In summary, the present invention has the following beneficial effects: by adding toughening agents and metallocene LLDPE to the LLDPE matrix and further limiting the melt index of LLDPE, the entanglement and interaction between the cross-linked matrix molecular chains become more complex, forming a stable network structure, thereby enhancing the toughness and low-temperature tear resistance of the heat shrink film. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the embodiments. All reagents, unless otherwise specified, are commercially available conventional reagent products.

[0026] Example 1

[0027] A method for preparing a cross-linked biodegradable POF heat-shrinkable film, wherein the heat-shrinkable film comprises the following raw materials:

[0028] The POF heat shrink film consists of three layers laminated together in sequence. The first and third layers each contain the following raw materials by weight percentage: PP 94%, degradation masterbatch 2%, opening agent 3%, and slip agent 1%.

[0029] The second membrane comprises the following raw materials by weight percentage: LLDPE-A 30%, toughening agent 10%, degradation masterbatch 1%, LLDPE-B 45%, and metallocene LLDPE 14%;

[0030] The melt index of LLDPE-A is 2.5 g / 10 min, the melt index of LLDPE-B is 2.1 g / 10 min, and the melt index of metallocene LLDPE is 1.0 g / 10 min.

[0031] The degradation masterbatch in each membrane layer includes 70wt% Ethylene Polyer and 30wt% Metal Salts. The CAS registration number of Ethylene Polyer is 9002-88-4, and the CAS registration number of Metal Salts is 3353-05-7.

[0032] The slip agent is maleic anhydride-grafted polyethylene wax;

[0033] The opening agent is silica with a particle size of 3-5 μm;

[0034] The toughening agent is composed of POE and EVA in a weight ratio of 1:0.5. The EVA contains 18% vinyl acetate and has a melt index of 2.5 g / 10 min. The POE has a melt index of 1.0 g / 10 min.

[0035] During preparation, the amount of raw materials added to each layer is controlled according to the total thickness of the heat-shrinkable film being 20 μm and the thickness of the intermediate layer being 12 μm. The specific steps include:

[0036] S1. Weigh out each film layer raw material according to the above formula, mix them evenly, add them to three film extruders, plasticize them, and then extrude them into the co-extrusion die to obtain the first film bubble. After traction and water cooling, the first film body is obtained.

[0037] S2. The first membrane is stretched, preheated and then blown up with a blow-up ratio of 5.5. Then it is successively cooled by air, stretched and irradiated to obtain a POF heat shrink film.

[0038] The irradiation crosslinking includes surface irradiation and intermediate layer irradiation, which are carried out simultaneously. The surface irradiation electron beam energy is 80 keV and the irradiation dose is 25 kGy, while the intermediate layer irradiation electron beam energy is 300 keV and the irradiation dose is 80 kGy.

[0039] Example 2

[0040] A method for preparing a cross-linked biodegradable POF heat-shrinkable film, wherein the heat-shrinkable film comprises the following raw materials:

[0041] The POF heat shrink film consists of three layers laminated together in sequence. The first and third layers each contain the following raw materials by weight percentage: PP 92%, degradation masterbatch 4%, opening agent 1%, and slip agent 3%.

[0042] The second membrane comprises the following raw materials by weight percentage: LLDPE-A 35%, toughening agent 14.5%, degradation masterbatch 0.5%, LLDPE-B 40%, and metallocene LLDPE 10%;

[0043] The melt index of LLDPE-A is 2.5 g / 10 min, the melt index of LLDPE-B is 2.1 g / 10 min, and the melt index of metallocene LLDPE is 1.0 g / 10 min.

[0044] The degradation masterbatch in each membrane layer includes 79wt% Ethylene Polyer and 21wt% Metal Salts. The CAS registration number of Ethylene Polyer is 9002-88-4, and the CAS registration number of Metal Salts is 3353-05-7.

[0045] The slip agent is maleic anhydride-grafted polyethylene wax;

[0046] The opening agent is silica with a particle size of 3-5 μm;

[0047] The toughening agent is composed of POE and EVA in a weight ratio of 1:0.5. The EVA contains 18% vinyl acetate and has a melt index of 2.5 g / 10 min, while the POE has a melt index of 1.0 g / 10 min.

[0048] During preparation, the amount of raw materials added to each layer is controlled according to the total thickness of the heat-shrinkable film being 20 μm and the thickness of the intermediate layer being 12 μm. The specific steps include:

[0049] S1. Weigh out each film layer raw material according to the above formula, mix them evenly, add them to three film extruders, plasticize them, and then extrude them into the co-extrusion die to obtain the first film bubble. After traction and water cooling, the first film body is obtained.

[0050] S2. The first membrane is stretched, preheated and then blown up with a blow-up ratio of 5.5. Then it is successively cooled by air, stretched and irradiated to obtain a POF heat shrink film.

[0051] The irradiation crosslinking includes surface irradiation and intermediate layer irradiation, which are carried out simultaneously. The surface irradiation electron beam energy is 80 keV and the irradiation dose is 30 kGy, while the intermediate layer irradiation electron beam energy is 300 keV and the irradiation dose is 90 kGy.

[0052] Example 3

[0053] A method for preparing a cross-linked biodegradable POF heat-shrinkable film, wherein the heat-shrinkable film comprises the following raw materials:

[0054] The POF heat shrink film consists of three layers laminated together in sequence. The first and third layers each contain the following raw materials by weight percentage: PP 89.5%, biodegradable masterbatch 6%, opening agent 0.5%, and slip agent 4%.

[0055] The second membrane comprises the following raw materials by weight percentage: LLDPE-A 30%, toughening agent 9%, degradation masterbatch 1%, LLDPE-B 45%, and metallocene LLDPE 15%;

[0056] The melt index of LLDPE-A is 2.5 g / 10 min, the melt index of LLDPE-B is 2.1 g / 10 min, and the melt index of metallocene LLDPE is 1.0 g / 10 min.

[0057] The degradation masterbatch in each membrane layer includes 75wt% Ethylene Polyer and 25wt% Metal Salts. The CAS registration number of Ethylene Polyer is 9002-88-4, and the CAS registration number of Metal Salts is 3353-05-7.

[0058] The slip agent is maleic anhydride-grafted polyethylene wax;

[0059] The opening agent is silica with a particle size of 3-5 μm;

[0060] The toughening agent is composed of POE and EVA in a weight ratio of 1:0.5. The EVA contains 18% vinyl acetate and has a melt index of 2.5 g / 10 min. The POE has a melt index of 1.0 g / 10 min.

[0061] During preparation, the amount of raw materials added to each layer is controlled according to the total thickness of the heat-shrinkable film being 20 μm and the thickness of the intermediate layer being 12 μm. The specific steps include:

[0062] S1. Weigh out each film layer raw material according to the above formula, mix them evenly, add them to three film extruders, plasticize them, and then extrude them into the co-extrusion die to obtain the first film bubble. After traction and water cooling, the first film body is obtained.

[0063] S2. The first membrane is stretched, preheated and then blown up with a blow-up ratio of 5.5. Then it is successively cooled by air, stretched and irradiated to obtain a POF heat shrink film.

[0064] The irradiation crosslinking includes surface irradiation and intermediate layer irradiation, which are carried out simultaneously. The surface irradiation electron beam energy is 80 keV and the irradiation dose is 30 kGy, while the intermediate layer irradiation electron beam energy is 300 keV and the irradiation dose is 100 kGy.

[0065] Example 4

[0066] A method for preparing a cross-linked biodegradable POF heat-shrinkable film differs from Example 1 in that the weight ratio of POE to EVA in the toughening agent is 1:1, while all other aspects are the same as in Example 1.

[0067] Example 5

[0068] A method for preparing a cross-linked biodegradable POF heat-shrinkable film differs from Example 1 in that only POE is used as the toughening agent, while all other aspects are the same as in Example 1.

[0069] Example 6

[0070] A method for preparing a cross-linked biodegradable POF heat-shrinkable film differs from Example 1 in that only EVA is used as the toughening agent, while all other aspects are the same as in Example 1.

[0071] Example 7

[0072] A method for preparing a cross-linked biodegradable POF heat-shrinkable film differs from Example 1 in that the surface irradiation dose is 20 KGy and the intermediate layer irradiation dose is 70 KGy, while all other aspects are the same as in Example 1.

[0073] Example 8

[0074] A method for preparing a cross-linked biodegradable POF heat-shrinkable film differs from Example 1 in that the surface irradiation dose is 35 KGy and the intermediate layer irradiation dose is 105 KGy, while all other aspects are the same as in Example 1.

[0075] Comparative Example 1

[0076] A method for preparing a cross-linked biodegradable POF heat-shrinkable film differs from Example 1 in that an equal amount of LLDPE-B is used instead of metallocene LLDPE, while all other aspects are the same as in Example 1.

[0077] Performance testing

[0078] The shrinkage rate, tensile properties at room temperature, and tear strength at low temperature of the heat shrink films obtained in the above embodiments and comparative examples were tested, and the results are shown in Table 1.

[0079] The shrinkage rate was tested at 100℃ according to the relevant provisions in GB / T 13519-1992 "Polyethylene Heat Shrinkable Film", and the tensile strength and elongation at break were tested according to the relevant provisions in GB / T13022-1991 "Tension Properties of Plastic Films".

[0080] Tear strength was tested according to ASTM D1922, "Standard Test Method for Tear Resistance of Plastic Films and Sheets - Pendulum Method". The film was frozen at -30±2℃ for 2 hours, and then the tear performance was tested. The test sample was a rectangular specimen with a size of 76mm×63mm.

[0081] Table 1. Results of Heat Shrink Film Performance Testing

[0082] Sample Heat shrinkage rate (MD / TD)% Tensile strength (MD / TD) MPa Elongation at break (MD / TD)% Tear strength (MD / TD) KN / m Example 1 78 / 80 130 / 135 150 / 155 30 / 32 Example 2 75 / 79 125 / 130 145 / 154 28 / 30 Example 3 76 / 79 126 / 125 144 / 153 29 / 30 Example 4 75 / 80 126 / 128 143 / 154 28 / 32 Example 5 70 / 80 100 / 109 121 / 134 16 / 22 Example 6 71 / 75 105 / 114 116 / 127 12 / 19 Example 7 68 / 75 102 / 112 118 / 130 19 / 24 Example 8 69 / 78 95 / 98 106 / 117 10 / 15 Comparative Example 1 40 / 51 94 / 102 665 / 730 18 / 24

[0083] As can be seen from Table 1:

[0084] The POF heat shrink film obtained in Examples 1-4 of this application has a heat shrinkage rate of 75% or more in the MD direction and a heat shrinkage rate of 75% or more in the TD direction, indicating that the POF heat shrink film obtained in this application has good heat shrinkage performance.

[0085] The tensile strength of the heat shrink film obtained in Examples 1-4 is 120 MPa or higher in both the MD and TD directions. The elongation at break is 140% or higher in the MD direction and 150% or higher in the TD direction. This indicates that the heat shrink film of this application has good strength and flexibility. Furthermore, the tear strength data shows that after being frozen at -30°C for 2 hours, the tear strength of the heat shrink film of this application can still reach up to 30 KN / m in the MD direction and up to 32 KN / m in the TD direction. This indicates that the POF heat shrink film obtained in this application has excellent low-temperature crack resistance and effectively extends its service life at low temperatures.

[0086] Compared with Example 1, when the toughening agent of the intermediate layer is only POE or only EVA, the heat shrinkage rate of the heat shrinkable film obtained in Examples 5 and 6 is lower than that in Example 1. At the same time, the tensile strength and elongation at break are significantly lower than those in Example 1, and the tear strength at low temperature is significantly lower than that in Example 1. It can be seen that when POE and EVA are used in combination, a synergistic effect is produced. The reason is that the high entanglement density of the long chain of POE with low melt index forms an energy dissipation zone at low temperature through the high entanglement network. When the crack propagates, it needs to break through more physical cross-linking points. EVA fills the cross-linking network skeleton provided by POE, so that the impact strength of the two is significantly improved compared with EVA and POE alone, thus significantly improving the impact strength.

[0087] Compared with Example 1, when the surface irradiation crosslinking dose and the intermediate irradiation crosslinking dose are lower or higher than the irradiation crosslinking dose specified in this application, the various properties of the heat shrink film obtained in Examples 7-8 are reduced. In particular, when the irradiation dose of the surface layer and the intermediate layer are higher than the upper limit of this application, the various properties decrease significantly. This further illustrates that the irradiation dose of this application effectively guarantees the various properties of the heat shrink film of this application.

[0088] Compared with Example 1, when metallocene LLDPE was missing from the intermediate layer raw material, the heat shrinkage rate, tensile strength, elongation at break, and tear strength at low temperature of the heat shrink film obtained in Comparative Example 1 were significantly reduced. The different melt indices of LLDPE and metallocene LLDPE made the entanglement and interaction between molecular chains more complex, forming a more stable network structure, which further enhanced the toughness and tear resistance of the heat shrink film.

[0089] The embodiments described herein are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a cross-linked biodegradable POF heat-shrinkable film, wherein the heat-shrinkable film comprises a first film, a second film, and a third film sequentially laminated together, characterized in that: Both the first and third membrane layers contain the following raw materials by weight percentage: PP 89.5-94%, degradation masterbatch 2-6%, opening agent 0.5-3%, and slip agent 1-4%; The second layer membrane comprises the following raw materials by weight percentage: LLDPE-A 30-35%, toughening agent 9-14.5%, degradation masterbatch 0.5-1%, LLDPE-B 40-45%, and metallocene LLDPE 10-15%, wherein the toughening agent is composed of POE and EVA in a weight ratio of 1:(0.5-1); The melt index of LLDPE-A is 2.5 g / 10 min, the melt index of LLDPE-B is 2.1 g / 10 min, and the melt index of metallocene LLDPE is 1.0 g / 10 min. Its preparation includes the following steps: S1. Weigh the raw materials according to the formula, mix them evenly, and add them to three film extruders. After plasticizing, they are extruded into the co-extrusion die to obtain the first film bubble. After traction and water cooling, the first film body is obtained. S2. The first membrane is stretched, preheated, and then inflated, followed by air cooling, stretching, and irradiation crosslinking to obtain a POF heat-shrinkable film. The irradiation crosslinking includes surface irradiation and intermediate layer irradiation. The surface irradiation electron beam energy is 80 keV and the irradiation dose is 25-30 kGy. The intermediate layer irradiation electron beam energy is 300 keV and the irradiation dose is 80-100 kGy.

2. The method for preparing a cross-linked biodegradable POF heat-shrinkable film according to claim 1, characterized in that: The EVA contains 18% vinyl acetate and has a melt index of 2.5 g / 10 min.

3. The method for preparing a cross-linked biodegradable POF heat-shrinkable film according to claim 1, characterized in that: The melt flow index of the POE is 1.0 g / 10 min.

4. The method for preparing a cross-linked biodegradable POF heat-shrinkable film according to claim 1, characterized in that: The slip agent is maleic anhydride-grafted polyethylene wax.

5. The method for preparing a cross-linked biodegradable POF heat-shrinkable film according to claim 1, characterized in that: The degradation masterbatch comprises, by weight percentage, 70-79% Ethylene Polyer and 21-30% Metal Salts.

6. A POF heat shrink film obtained by the preparation method of the cross-linked biodegradable POF heat shrink film according to any one of claims 1-5.