Degradable heat-shrinkable film and method for preparing the same

Abstract

The application relates to the technical field of high polymer materials, in particular to a degradable heat-shrinkable film and a preparation method thereof. The heat-shrinkable film is mainly composed of polyhydroxyalkanoate, polylactic acid and polybutylene adipate terephthalate, and simultaneously contains functional auxiliaries such as an epoxy functional group chain extender and a bio-based plasticizer. The preparation method comprises the steps of raw material blending, melt extrusion, casting sheet and bidirectional stretching. A functional coating composed of polylactic acid and a bio-based wax can be coated on the surface of the film. The heat-shrinkable film provided by the application has excellent heat-shrinkable performance, mechanical strength and transparency, can be completely biodegraded in a composting environment, solves the environmental pollution problem caused by the non-degradability of traditional polyolefin heat-shrinkable films, and overcomes the defects that bio-based materials are difficult to balance in performance and processability.

Description

Technical Field

[0001] This application relates to the field of polymer materials technology, and in particular to a packaging film material and its preparation method, specifically a biodegradable heat shrink film and its preparation method. Background Technology

[0002] Heat shrink film is a plastic film that undergoes directional stretching during production and shrinks upon heating during use to tightly adhere to the packaged goods. It is widely used in the bulk packaging of food, beverages, and daily chemical products. Currently, the dominant heat shrink film on the market is polyolefin heat shrink film (such as POF film). This type of heat shrink film uses petroleum-based resins such as polyethylene (PE) and polypropylene (PP) as its main raw materials and has excellent heat shrinkage rate, transparency, strength, and cost advantages.

[0003] However, traditional polyolefin heat-shrinkable films are difficult to degrade in the natural environment, and the plastic waste generated from their extensive use puts continuous pressure on the environment. With increasingly stringent global environmental regulations and growing consumer awareness of environmental protection, developing fully biodegradable alternatives with equivalent performance has become an urgent need for the industry.

[0004] Therefore, developing a heat-shrinkable film that is comparable to traditional POF film in terms of heat shrinkage and mechanical properties, can achieve complete biodegradation under industrial composting conditions, and has good processing and storage stability is key to promoting the green transformation of the packaging industry. Summary of the Invention

[0005] The purpose of this application is to provide a biodegradable heat-shrinkable film and its preparation method, thereby solving the problem in the prior art that it is difficult to balance heat shrinkability and biodegradability.

[0006] In a first aspect, this application provides a biodegradable heat-shrinkable film, employing the following technical solution: A biodegradable heat-shrinkable film is prepared from the following raw materials in parts by weight: 50-80 parts of polyhydroxyalkanoate; 10-30 parts of polylactic acid; 10-30 parts of polybutylene adipate / terephthalate; 0.1-3 parts of epoxy functional chain extender; 2-10 parts of plasticizer; 0.1-1 part of nucleating agent; 0.1-2 parts of anti-hydrolysis agent; and 0.1-1 part of lubricant.

[0007] By adopting the above technical solutions, polyhydroxyalkanoates, polylactic acid, and poly(butylene adipate / terephthalate) form the basic resin skeleton for biodegradability; epoxy functional chain extenders enhance the connection between molecular chains through reaction, providing the film with the necessary melt strength and thermal shrinkage "memory" effect; plasticizers improve processability and flexibility; nucleating agents optimize crystallization, improving transparency and shrinkage uniformity; and anti-hydrolysis agents and lubricants respectively ensure processing stability and film surface properties.

[0008] Optionally, the epoxy functional group chain extender is selected from at least one of styrene-acrylate epoxy functionalized copolymer and ethylene-acrylate-glycidyl methacrylate terpolymer.

[0009] Optionally, the bio-based plasticizer is selected from at least one of acetylated tributyl citrate, triethyl citrate, and epoxidized soybean oil.

[0010] Optionally, the nucleating agent is selected from at least one of zinc phenyl phosphate and cyanuric acid.

[0011] Optionally, the lubricant is selected from at least one of stearamide and polyethylene wax.

[0012] Optionally, the anti-hydrolysis agent is polycarbodiimide, and its dosage is 0.2-1 parts by weight.

[0013] By employing the above technical solutions, specific chain extenders can effectively react with polyester end groups to construct a moderately cross-linked network structure, which is key to obtaining high and stable heat shrinkage rates. Bio-based plasticizers provide excellent plasticizing effects while ensuring the complete biodegradability of the entire formulation system. Highly efficient nucleating agents refine spherulite size, thereby improving film transparency, surface gloss, and heat shrinkage uniformity. Suitable lubricants reduce processing resistance and improve film release and surface slip properties. Polycarbodiimide effectively captures carboxyl groups generated by hydrolysis, inhibiting molecular chain degradation and significantly improving the material's stability during processing and storage.

[0014] Optionally, based on 65 parts by weight of the polyhydroxyalkanoate, the raw material may also include 5 parts of microfibrillated cellulose.

[0015] By adopting the above technical solution, the introduction of microfibrillated cellulose can serve as a reinforcing phase, improving the tensile strength, modulus, and tear resistance of the film. At the same time, its natural properties help promote microbial attachment and accelerate the final degradation process.

[0016] Optionally, the biodegradable heat shrink film includes a functional coating comprising 50-80 parts polylactic acid, 20-45 parts bio-based wax, and 5-15 parts adhesion promoter.

[0017] By adopting the above technical solution, the coating provides excellent moisture barrier properties at room temperature, solves the problem of easy hydrolysis of PHA-based materials, and extends the product shelf life; while the coating structure changes under the high temperature of composting, it does not hinder overall biodegradation.

[0018] Secondly, the preparation of the biodegradable heat-shrinkable film as described in the first aspect includes the following steps: The raw materials are mixed, melt-blended and granulated to obtain membrane resin particles; The membrane is melt-extruded with resin particles and cast to form a thick sheet; The thick sheet is subjected to biaxial stretching and heat setting to obtain the biodegradable heat shrink film.

[0019] By adopting the above technical solutions, melt blending ensures uniform dispersion and reaction of each component; biaxial stretching process orients the polymer molecular chains, thereby giving the film the property of shrinking under heat; heat setting treatment is used to precisely control the final heat shrinkage rate and dimensional stability.

[0020] Optionally, after the heat setting treatment, the process further includes a step of coating the surface of the resulting biodegradable heat shrinkable film with a functional coating.

[0021] In summary, this application includes at least one of the following beneficial technical effects: 1. A biodegradable heat shrink film is provided, which has almost no difference in performance from traditional non-degradable polyolefin shrink film, achieving a balance between environmental friendliness and performance. 2. Through the synergistic effect of a specific ternary blend system and functional additives, the shortcomings of single bio-based polyester materials in terms of toughness, processability and storage stability are effectively overcome; 3. By introducing a functional coating, the moisture-proof performance of the film is improved without affecting degradation, solving the problem of easy hydrolysis of biodegradable films during storage and transportation, and expanding the application range. Detailed Implementation

[0022] The present application will be further described in detail below with reference to preparation examples and embodiments.

[0023] The following are some of the raw materials used in the embodiments and comparative examples of this application. Unless otherwise specified, they are all industrial-grade or commercially available in common specifications: Among them, poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) was selected from EM10080 of Shandong Yikeman; polylactic acid (PLA) was selected from LX175 of Total; polybutylene adipate / terephthalate (PBAT) was selected from TH801T of Tunhe of Lanshan, Xinjiang; epoxy chain extender ADR-4468 was selected from BASF; ethylene-acrylate-glycidyl methacrylate terpolymer was selected from Arkema, catalog number LOTADER® AX8900; polylactic acid grafted maleic anhydride (PLA-g-MAH) was selected from NatureWorks, catalog number 4032D; tributyl acetylacetonate (ATBC), CAS number 77-90-7, ester content 99.36%, acid value ≤0.04 mg KOH / g; zinc phenyl phosphate (PPZn), CAS number 77-90-7, CAS number 77-90-7, ester content 99.36%, acid value ≤0.04 mg KOH / g; zinc phenyl phosphate (PPZn), CAS number 77-90-7, CAS number 77-90-7, acetylacetonate terephthal ... 34335-10-9, analytical grade, content ≥99%; polycarbodiimide selected from NWIITC, catalog number C40, active ingredient content 40%; stearamide CAS number 124-26-5, content ≥98%; polyethylene wax PE520 selected from Clariant; microfibrillated cellulose: solid content 2%, diameter 100-1000 nm, length >20 μm, crystal form is cellulose type I; sugarcane wax, CAS number 91722-22-4, saponification value 70-95 mg KOH / g; ethyl acetate: purity ≥99.5%, CAS 141-78-6.

[0024] Preparation of coating liquid The components include: 5 parts polylactic acid, 3.5 parts sugarcane wax, 1 part maleic anhydride-grafted PLA, and 90.5 parts ethyl acetate.

[0025] Preparation method: Polylactic acid and maleic anhydride-grafted PLA were vacuum dried at 60°C for 4 hours. Under stirring, the dried polylactic acid and maleic anhydride-grafted PLA were dissolved in a portion of ethyl acetate to form a clear solution, yielding mixture A. Add sugarcane wax to the remaining solvent and heat to 70°C to completely melt and disperse it, resulting in mixture B. Mixture B is slowly added to mixture A under high-speed shearing, and the temperature is maintained at 50°C to form a uniform emulsion. After cooling to room temperature, it is filtered to obtain the coating liquid for later use.

[0026] Example 1

[0027] The components include: Main substrate: 70 parts of P34HB; Blended resins: PLA 15 parts, PBAT 15 parts; Functional additives: 0.5 parts of epoxy chain extender ADR-4468, 5 parts of bio-based plasticizer ATBC, 0.3 parts of nucleating agent PPZn, 0.5 parts of anti-hydrolysis agent polycarbodiimide, and 0.3 parts of lubricant stearamide.

[0028] Pre-treatment mixing: P34HB, PLA, and PBAT granules were vacuum dried at 80°C for 6 hours. Then, all raw materials were put into a high-speed mixer and mixed at room temperature for 10 minutes to obtain a premix. Melt blending and granulation: The premixed material was melt-blended and extruded into granules using a twin-screw extruder. The temperatures of each section of the extruder were set as follows: Zone 1 150℃, Zone 2 165℃, Zone 3 170℃, Zone 4 175℃, and Die Head 170℃. The melt was then water-cooled and pelletized to obtain heat-shrinkable film granules.

[0029] Thin film forming: Casting: Heat shrinkable film granules are dried at 75°C for 4 hours and fed into a single-screw extruder. At a melting temperature of 155-170°C, they are extruded through a T-die and rapidly cooled on a cooling roller at 25°C to obtain an amorphous sheet with a thickness of approximately 800 μm.

[0030] Biaxial stretching: The thick sheet is stretched longitudinally and laterally.

[0031] Longitudinal stretching (MDO): After preheating at 75°C, stretching is performed at 78°C with a stretching ratio of 3.0 times.

[0032] Transverse stretching (TDO): After preheating at 80°C, stretching is performed at 85°C with a stretching ratio of 3.5 times.

[0033] Heat setting and winding: The stretched film is heat-set at 90°C for 5 seconds, then cooled to below 40°C. After corona treatment, it is wound up to obtain a biodegradable heat-shrinkable film with a thickness of approximately 20 μm.

[0034] Example 2

[0035] The difference between this embodiment and Embodiment 1 is that the main substrate is adjusted to: 65 parts of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB), 20 parts of polylactic acid (PLA), and 15 parts of polybutylene adipate / terephthalate (PBAT); the reactive chain extender is replaced with: 3 parts of commercially available ethylene-acrylate-glycidyl methacrylate (E-GMA) terpolymer; and the lubricant is replaced with: 0.3 parts of polyethylene wax.

[0036] Example 3

[0037] The difference between this embodiment and Embodiment 1 is that the main substrate is adjusted to: 65 parts of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB), 20 parts of polylactic acid (PLA), and 15 parts of polybutylene adipate / terephthalate (PBAT); and the lubricant is replaced with: 0.3 parts of polyethylene wax.

[0038] Example 4

[0039] The difference between this embodiment and Example 1 is that the main substrate is adjusted to: 68 parts of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB), 16 parts of polylactic acid (PLA), and 16 parts of polybutylene adipate / terephthalate (PBAT); the epoxy chain extender (ADR-4468) is adjusted to 0.8 parts; and the bio-based plasticizer (ATBC) is adjusted to 8 parts.

[0040] Example 5

[0041] The difference between this embodiment and Embodiment 1 is that microfibrillated cellulose (MFC) was added as a reinforcing filler, with an addition amount of 5 parts.

[0042] Example 6

[0043] The difference between this embodiment and Embodiment 2 is that a functional coating is further added to the surface of the substrate film obtained by the method described in Embodiment 2, and the coating liquid is prepared by the preparation example.

[0044] The specific steps are as follows: The substrate film was coated on one side using a microgravure coating method at a coating speed of 20 m / min. It was then dried and cured through a three-stage drying channel. The first temperature is 50℃, mainly to gently evaporate most of the solvent and prevent the coating from blistering. The second stage: At 65℃, the wax and PLA are fully intertwined in the molten state to form a dense composite film and complete the adhesion to the substrate; Third stage: Cool and cure at 40℃, and control the final dry coating thickness to 2.0μm±0.5μm.

[0045] Example 7

[0046] The difference between this embodiment and Embodiment 1 is that the formulation of the substrate film has been adjusted, specifically: poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) has been adjusted to 65 parts, polylactic acid (PLA) has been adjusted to 20 parts, and epoxy chain extender (ADR-4468) has been adjusted to 0.8 parts.

[0047] The outer layer of the resulting membrane has a coating liquid, and the coating method is the same as in Example 6.

[0048] Example 8

[0049] The difference between this embodiment and Embodiment 1 is that the formulation of the substrate film has been adjusted. Specifically, the amounts of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) and polylactic acid (PLA) were adjusted to 68 parts, 16 parts, and epoxy chain extender (ADR-4468) to 0.8 parts. Additionally, 5 parts of microfibrillated cellulose (MFC) were added as a reinforcing filler.

[0050] The outer layer of the resulting membrane has a coating liquid, and the coating method is the same as in Example 6.

[0051] Comparative Example 1 The difference between this comparative example and Example 1 is that the epoxy chain extender (ADR-4468) is completely omitted, while the remaining components, contents, and preparation process are the same as in Example 1.

[0052] Comparative Example 2 The difference between this comparative example and Example 1 is that the bio-based plasticizer acetylthiol tributyl citrate (ATBC) is replaced with an equal amount (5 parts) of dioctyl phthalate (DOP), while the other components, contents, and preparation process are the same as in Example 1.

[0053] Comparative Example 3 The difference between this comparative example and Example 1 is that the proportion of the main substrate is adjusted to: 40 parts of P34HB, 45 parts of PLA, and 15 parts of PBAT (i.e., significantly increasing the PLA content and decreasing the PHA content). The other additives and their contents, as well as the preparation process, are the same as in Example 1.

[0054] Comparative Example 4 This comparative example does not use the formulation of this invention, but uses commercially available ordinary polyolefin heat shrink film (POF) as a comparison sample, which is a three-layer co-extruded heat shrink film with polypropylene (PP) and polyethylene (PE) as the main raw materials.

[0055] Performance testing: The thin films obtained in the above embodiments and comparative examples were subjected to system performance tests. Unless otherwise specified, all tests were conducted in a standard environment at room temperature and 50% relative humidity, and the samples were conditioned for more than 24 hours before testing.

[0056] 1. Light transmittance: The test standard is based on ASTM D1003. The test method is to measure the ratio of the transmitted light flux to the incident light flux after passing through the sample.

[0057] 2. Haze: The testing standard is based on ASTM D1003. The test method is to measure the ratio of the scattered light flux after passing through the sample to the total transmitted light flux.

[0058] 3. Tensile strength: As specified in ASTM D882.

[0059] 4. Heat shrinkage rate: as specified in ASTM D1204.

[0060] 5. Oxygen permeability: Tested according to GB / T 1038—2000 using an oxygen permeability meter. The sample size is 10 cm. 2 The sample is circular and a special sealant is used to adhere it to the effective test area. After each test, the instrument directly reads the oxygen permeability value.

[0061] 6. Water vapor transmission rate: Determined according to GB / T 26253—2010, using a moisture permeability meter, with a sample size of 2 cm. 2 The circular sample is adhered to the effective test area using a special sealant. After the test, the instrument directly reads the water vapor transmission rate value.

[0062] 7. Soil Burial Degradation Weight Loss: The biodegradability of the film in soil at room temperature was evaluated according to ISO 11465. The sample was a 5cm × 5cm square, buried in a flowerpot to a depth of approximately 5cm. To maintain soil moisture, 10 mL of deionized water was sprayed evenly daily. Before the experiment, the sample was dried at 65℃ to constant weight and recorded as w0. Every 10 days, the sample was removed, wiped clean, dried for 2 hours, and its mass w was recorded. n The weight loss rate was calculated according to the following formula. The experiment lasted for 70 days, and the weight loss rate was used to measure the degradation performance of the membrane.

[0063] Weight loss rate due to soil degradation (%) = .

[0064] Table 1

[0065] Table 2

[0066] Based on a comprehensive comparative analysis of the performance of each embodiment and comparative example, the following are the relevant results: Example 1, as the basic scheme, successfully constructed a ternary blend system with polyhydroxyalkanoates as the core, exhibiting balanced overall performance, particularly achieving a basic balance between heat shrinkage and biodegradability. Comparative Example 1, however, shows that the lack of epoxy chain extenders leads to a significant deterioration in the film's formability and heat shrinkage properties, thus demonstrating the crucial role of this component in constructing a stable polymer network.

[0067] Example 2 uses an ethylene-acrylate-glycidyl methacrylate terpolymer with a long-chain structure to replace the conventional small-molecule chain extender. Tests show that this substitution improves the toughness of the film while maintaining its basic properties, demonstrating that the impact resistance of materials can be directionally enhanced through the molecular structure design of the chain extender.

[0068] Examples 3 and 4, by adjusting the lubrication system and plasticizing ratio, respectively, verified the optimization effect of formula fine-tuning on processing stability and film flexibility, demonstrating that the recorded formula system has good process adaptability.

[0069] Example 5 demonstrates a synergistic effect achieved by introducing microfibrillated cellulose. Microfibrillated cellulose not only enhances the mechanical strength of the film as a reinforcing phase, but its natural properties also promote the microbial erosion process of the film matrix, achieving a dual effect of reinforcement and accelerated degradation.

[0070] Examples 6, 7, and 8 highlight the design value of functional coatings. These coatings provide excellent moisture protection at room temperature, significantly improving the storage stability of polyhydroxyalkanoate-based films; while in composting environments, the coatings undergo "thermally induced peeling" without hindering the overall degradation process. Example 8, in particular, incorporates microfibrillated cellulose reinforcement, successfully preparing a film with high mechanical strength, high barrier properties, and high degradability, demonstrating the good compatibility and functional synergy of multiple technologies within this system.

[0071] Comparative Example 2 demonstrates that the use of non-bio-based plasticizers has a severe negative impact on the final biodegradability of the film, highlighting the necessity of adopting a fully bio-based / degradable formulation system. Comparative Example 4 (conventional polyolefin heat shrink film) confirms its inherent defects in terms of non-environmental degradation.

[0072] In summary, this invention provides a complete technical solution for a series of biodegradable heat-shrinkable films through specific formulation design and multi-level structural construction. Each embodiment not only confirms the feasibility of the basic formulation but also endows the film with additional properties such as film reinforcement and high barrier properties through functional modification. Furthermore, all designs ensure the core objective of ultimate complete biodegradation. In particular, the synergistic effect of reinforcement and degradation promotion produced by microfibrillated cellulose, and the dual-mode behavior of protection and degradation triggering achieved by the coating, provide valuable technical insights for the field. This invention successfully solves the environmental problem of non-degradability while maintaining performance comparable to traditional polyolefin heat-shrinkable films, demonstrating significant technological advancement and practical application value.

[0073] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A biodegradable heat-shrinkable film, characterized in that, It is prepared from the following raw materials in parts by weight: 50-80 parts of polyhydroxyalkanoate; Polylactic acid 10-30 parts; 10-30 parts of poly(butylene adipate / terephthalate); 0.1-3 parts of epoxy functional group chain extender; 2-10 parts of bio-based plasticizer; Nucleating agent 0.1-1 part; Anti-hydrolysis agent 0.1-2 parts; Lubricant 0.1-1 part.

2. The biodegradable heat-shrinkable film according to claim 1, characterized in that, The epoxy functional group chain extender is selected from at least one of styrene-acrylate epoxy functionalized copolymer and ethylene-acrylate-glycidyl methacrylate terpolymer.

3. The biodegradable heat-shrinkable film according to claim 1, characterized in that, The bio-based plasticizer is selected from at least one of acetylated tributyl citrate, triethyl citrate, and epoxidized soybean oil.

4. The biodegradable heat-shrinkable film according to claim 1, characterized in that, The nucleating agent is selected from at least one of zinc phenyl phosphate and cyanuric acid.

5. The biodegradable heat-shrinkable film according to claim 1, characterized in that, The lubricant is selected from at least one of stearamide and polyethylene wax.

6. The biodegradable heat-shrinkable film according to claim 1, characterized in that, The anti-hydrolysis agent is polycarbodiimide, and its dosage is 0.2-1 parts by weight.

7. The biodegradable heat-shrinkable film according to claim 1, characterized in that, Based on a weight of 65 parts of the polyhydroxy fatty acid ester, the raw material also includes 5 parts of microfibrillated cellulose.

8. The biodegradable heat-shrinkable film according to any one of claims 1-7, characterized in that, The biodegradable heat shrink film includes a functional coating comprising 50-80 parts polylactic acid, 20-45 parts bio-based wax, and 5-15 parts adhesion promoter.

9. A method for preparing a biodegradable heat-shrinkable film as described in any one of claims 1-8, characterized in that, Includes the following steps: The raw materials are mixed, melt-blended and granulated to obtain membrane resin particles; The membrane is melt-extruded with resin particles and cast to form a thick sheet; The thick sheet is subjected to biaxial stretching and heat setting to obtain the biodegradable heat shrink film.

10. The method for preparing the biodegradable heat-shrinkable film according to claim 9, characterized in that, Following the heat setting treatment, the process further includes a step of coating the surface of the resulting biodegradable heat shrinkable film with a functional coating.

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