A flexible degradable barrier heat seal film and a method of making the same

Abstract

This invention relates to the field of packaging materials technology, and particularly to a flexible, biodegradable barrier heat-sealing film and its preparation method. The film, from the inside out, consists of a PGA barrier layer, a polylactic acid (PLA) substrate layer, a PPC-reinforced heat-sealing layer, and a PLA heat-sealing layer. The PGA barrier layer mainly comprises the following raw materials: poly(lactic acid-glycolic acid) copolymer (PLGA), poly(caprolactone-glycolic acid) copolymer (PGCL), chain extender, antioxidant, opening agent, and slip agent. The PLA substrate layer mainly comprises the following raw material: polylactic acid-polyester block copolymer. The flexible, biodegradable barrier heat-sealing film provided by this invention has good flexibility and excellent barrier properties, with a heat-sealing strength greater than 15 N / 15 mm. While maintaining good mechanical properties, optical properties, and heat shrinkage, it reduces the adhesive coating and lamination process, making it particularly suitable for inflatable aviation food packaging applications.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, and in particular to a flexible biodegradable barrier heat-sealing film and its preparation method. Background Technology

[0002] Polylactic acid (PLA), poly(lactic acid-glycolic acid) copolymer (PLGA), and propylene oxide copolymer (PPC) contain ester bonds (-COO-) in their main molecular chain. These bonds can be broken under humid and hot environments, microorganisms, or enzymes, enabling the gradual degradation of the materials. Under the guidance of ecological civilization construction, the research and industrialization of biodegradable polymer materials have ushered in a tremendous development opportunity, and non-degradable plastic products are being gradually replaced by biodegradable materials.

[0003] In real-world applications, biodegradable materials face limitations in industrialization due to their inherent shortcomings, restricting their use. For example, PLA suffers from poor barrier properties and flexibility; poly(lactic acid-glycolic acid) copolymer (PLGA) combines good mechanical properties, gas barrier properties, biodegradability, and biocompatibility, making it a relatively ideal barrier packaging film material, but it suffers from poor toughness and excessively rapid degradation; poly(carbon dioxide-propylene oxide) copolymer (PPC) has good water-blocking properties and excellent heat-sealing performance, but its amorphous nature and low glass transition temperature make it difficult to use alone.

[0004] In inflatable protective food packaging, not only are barrier properties, flexibility, and mechanical strength required to provide a longer shelf life, a soft touch, and protection against punctures and other external forces, but also a heat seal strength of ≥12N / 15mm is required to prevent air leakage under different pressure environments and during transportation.

[0005] Existing biaxially oriented films often suffer from insufficient heat-sealing performance. For example, a directly heat-sealable biaxially oriented polylactic acid (PLA) film disclosed in patent application number 202010415595.2 has a maximum heat-sealing strength of 9.5 N / 15 mm. Commercially available BIONLY® ESL or NATIVIA® NTSS PLA films have a heat-sealing strength ≤7 N / 15 mm.

[0006] Therefore, it is still necessary to develop a flexible, biodegradable barrier heat-sealing film to meet the requirements of inflatable food packaging for barrier properties, flexibility, and high heat-sealing strength. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a flexible biodegradable barrier heat-sealing film. The film has a four-layer structure, comprising, from the inside out, a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer, and a PLA heat-sealing layer. The PGA barrier layer comprises, by mass fraction, the following raw materials: 54-78.7% poly(lactic acid-glycolic acid) copolymer, 20-40% poly(caprolactone-glycolic acid) copolymer, 1-3% chain extender, 0.1-1% antioxidant, 0.1-1% opening agent, and 0.1-1% slip agent.

[0008] Furthermore, the PLA substrate layer is composed of polylactic acid-polyester block copolymer; in the polylactic acid-polyester block copolymer, the mass ratio of polyester to polylactic acid is 10-30:70-90; and the molar ratio of L-lactide to D-lactide in the polylactic acid-polyester block copolymer is 94-99:1-6.

[0009] Furthermore, the PLA heat-sealing layer, by mass fraction, comprises the following raw materials: 98-99.8% heat-sealing PLA resin, 0.1-1% opening agent, and 0.1-1% slip agent; The PPC-reinforced heat-sealing layer component, by mass fraction, consists of the following raw materials: 100% carbon dioxide epoxy propylene copolymer (PPC) resin.

[0010] Furthermore, the chain extender is one or more of ethylene-methyl acrylate-glycidyl methacrylate, styrene and glycidyl acrylate copolymer, hexamethylene diisocyanate, 4,4'-methylene diphenyl isocyanate, and polycarbodiimide.

[0011] Furthermore, the antioxidant is one or more of antioxidant 1010, antioxidant 1098, antioxidant 2246, antioxidant 168, antioxidant 330, antioxidant DNP, antioxidant SEED, and antioxidant phosphite.

[0012] Furthermore, the opening agent is composed of one or more of silicon dioxide, calcium carbonate, organosilicon, and acrylic. The slip agent is composed of one or more of PE wax, oleamide, silicone wax, paraffin wax, and erucamide.

[0013] Furthermore, the polylactic acid-polyester block copolymer is selected from one or more combinations of polybutylene terephthalate-polylactic acid copolymer, polycaprolactone-polylactic acid copolymer, and polybutylene succinate-polylactic acid copolymer.

[0014] Preferably, the melt index of the polylactic acid-polyester block copolymer is controlled at 2-4 g / 10 min at 190℃ / 2.16 kg.

[0015] Furthermore, the flexible biodegradable barrier heat-sealing film has a thickness of 30-50 μm, the PGA barrier layer has a thickness of 1-5 μm, the PPC reinforced heat-sealing layer has a thickness of 8-10 μm, and the PLA heat-sealing layer has a thickness of 1-2 μm.

[0016] Furthermore, the PGA barrier layer is formed from PGA barrier layer resin, which is prepared using a twin-screw extruder. The screw element assembly of the twin-screw extruder is composed of the following elements arranged in the following order: Conveyor blocks: 45 / 45A, 75 / 75SK, 75 / 75SK, 75 / 75SK, 90 / 90, 60 / 60; Commonly used kneading thread elements: K22.5 / 5 / 75, K30 / 5 / 45, K45 / 5 / 45; Reverse thread block: 30 / 30L; Conveyor blocks: 75 / 75, 75 / 75, 90 / 90, 90 / 90, 90 / 90; Irregular meshing threaded elements: LFKB90 / 7 / 75, LFKB90 / 7 / 75, LFKB90 / 7 / 75; Standard kneading thread element: K45 / 5 / 45L; Reverse thread block: 30 / 30L; Conveyor blocks: 60 / 60, 60 / 60, 60 / 60, 60 / 60; Standard kneading thread elements: K45 / 5 / 45, K45 / 5 / 45; Toothed disk: C1; Disk: CY; Conveyor blocks: 90 / 90, 75 / 75, 75 / 75, 75 / 75, 60 / 60, 60 / 60.

[0017] It should be noted that K is a conventional kneading thread element, LFKB is an irregular meshing thread element, L is a reverse thread block, C1 is a toothed disc, and CY is a disc.

[0018] Preferably, the length-to-diameter ratio of the twin-screw extruder is 40:1-60:1. The present invention also provides a method for preparing the flexible biodegradable barrier heat-sealing film as described above, comprising the following steps: S1. Preparation of PGA barrier layer resin includes mixing poly(lactic acid-glycolic acid) copolymer, poly(caprolactone-glycolic acid) copolymer, chain extender and antioxidant in proportion, melting and plasticizing through a twin-screw extruder, adding opening agent and slip agent during plasticizing, and obtaining the PGA barrier layer resin by extrusion, cooling, pelletizing and drying. S2. Using a multi-layer co-extrusion biaxial stretching process, the PGA barrier layer resin, polylactic acid-polyester block copolymer, carbon dioxide-propylene oxide copolymer resin and heat-sealing PLA resin are respectively fed into the corresponding extruders to co-extrude and form a multi-layer melt consisting of a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer and a PLA heat-sealing layer from the inside out. S3. After casting the multilayer melt sheet, perform synchronous bidirectional stretching to obtain the flexible biodegradable barrier heat-sealing film.

[0019] Preferably, the preparation process of the PGA barrier layer specifically includes the following steps: S100, according to the mass parts, poly(lactic acid-glycolic acid) copolymer (PLGA), poly(caprolactone-glycolic acid) copolymer (PGCL), chain extender, antioxidant, stir for 1-3 min to obtain mixture P; S200, add mixture P through the main feed screw, and add the opening agent and slip agent through the side feed scale; The S300 extruder temperature is set at 160-210℃. The material is melted and plasticized through the twin-screw extruder. The extruder speed is 200-400 rpm, and the capacity is 250-350 kg / h. S400: The melt passes through the die and is cooled and drawn in a water bath at a temperature of 20-40℃. S500, after being dehydrated and pelletized by a pelletizer, is drawn into a drying tank and dried at 60-90°C for 3-5 hours to obtain the PGA barrier resin.

[0020] Preferably, the preparation process of the flexible biodegradable barrier heat-sealing film specifically includes the following steps: Step 1: Mix PLA heat-sealing material and anti-sticking agent in proportion, melt-blend, extrude and granulate through a twin-screw extruder, and dry the resulting high-concentration concentrated masterbatch for later use; Step 2: The PGA barrier layer resin obtained from S500 is fed into extruder A to make layer A; polylactic acid-polyester block copolymer is fed into extruder B to make layer B; PPC is fed into extruder C to make layer C; PLA heat-sealing material and concentrated masterbatch obtained in step 1 are fed into extruder D in proportion to make layer D. The temperature of each extruder and T-die is controlled between 180 and 210°C. Step 3: Using the LISIM simultaneous stretching method, the layers from Step 2 are extruded, rapidly cooled, and then biaxially stretched at a temperature of 70-90℃ and a setting temperature of 80-120℃, with a stretching ratio of 2.0. 2.0-5.5 5.5; Step 4: Roll up, slit, and package the biaxially oriented polylactic acid film obtained in step 3.

[0021] Compared with existing technologies, the flexible biodegradable barrier heat-sealing film provided by this invention comprises, from the inside out, a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer, and a PLA heat-sealing layer. The PGA barrier layer provides excellent oxygen and water vapor barrier properties; the PLA substrate layer serves as a mechanical support layer, ensuring the film's strength and dimensional stability; the PPC reinforced heat-sealing layer provides excellent heat-sealing strength and flexibility; and the PLA heat-sealing layer acts as a protective layer, preventing the PPC layer from becoming sticky and affecting subsequent processing and use. The four layers work synergistically, giving the film high barrier properties, high heat-sealing strength, good flexibility, and processing adaptability. Furthermore, this application introduces poly(caprolactone-glycolic acid) copolymer (PGCL) into the PGA barrier layer, effectively reducing the polarity and melting point of the PGA barrier layer resin, ensuring that it does not undergo thermal degradation during processing, while simultaneously improving the adhesion to the PLA substrate layer and preventing delamination of the composite film.

[0022] In the preferred embodiment, the resin is prepared under specially designed threaded elements and specific screw combinations, which can provide lower shear and longer residence time, as well as excellent dispersibility. This ensures that the PGA barrier layer resin is fully dispersed, reacts completely, and does not cause thermal degradation. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] It should be noted that, where no specific technology or conditions are specified in the embodiments, the technology or conditions described in the literature in this field or the product instructions shall be followed. If the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be obtained commercially.

[0025] Example 1 A flexible biodegradable barrier heat-sealing film includes a four-layer structure, consisting of a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer, and a PLA heat-sealing layer from the inside out. The PGA barrier layer is composed of the following raw materials by mass fraction: 66.5% poly(lactic acid-glycolic acid) copolymer (PLGA), 30% poly(caprolactone-glycolic acid) copolymer (PGCL), 2% ADR chain extender (styrene and glycidyl acrylate copolymer), 0.5% antioxidant 1010, 0.5% silica, and 0.5% erucamide.

[0026] The PLA substrate layer is composed of the following raw materials by mass fraction: 100% polylactic acid-polyester block copolymer; the mass ratio of polyester to polylactic acid in the polylactic acid-polyester block copolymer is 20:80; the molar ratio of L-lactide to D-lactide in the polylactic acid-polyester block copolymer is 96:4.

[0027] The PPC-reinforced heat-sealing layer component is composed of the following raw materials by mass fraction: 100% carbon dioxide epoxy propylene copolymer (PPC) resin.

[0028] The PLA heat-sealing layer is composed of the following raw materials by mass fraction: 99% heat-sealing PLA resin, 0.5% silica and 0.5% erucamide.

[0029] Example 2 A flexible biodegradable barrier heat-sealing film includes a four-layer structure, consisting of a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer, and a PLA heat-sealing layer from the inside out. The PGA barrier layer is composed of the following raw materials by mass fraction: 54% poly(lactic acid-glycolic acid) copolymer (PLGA), 40% poly(caprolactone-glycolic acid) copolymer (PGCL), 3% ADR chain extender, 1% antioxidant 1010, 1% silica and 1% erucamide.

[0030] The PLA substrate layer is composed of the following raw materials by mass fraction: 100% polylactic acid-polyester block copolymer; the mass ratio of polyester to polylactic acid in the polylactic acid-polyester block copolymer is 30:70; the molar ratio of L-lactide to D-lactide in the polylactic acid-polyester block copolymer is 99:1.

[0031] The PPC-reinforced heat-sealing layer component is composed of the following raw materials by mass fraction: 100% carbon dioxide epoxy propylene copolymer (PPC) resin.

[0032] The PLA heat-sealing layer is composed of the following raw materials by mass fraction: 98% heat-sealing PLA resin, 1% silica and 1% erucamide.

[0033] Example 3 A flexible biodegradable barrier heat-sealing film includes a four-layer structure, consisting of a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer, and a PLA heat-sealing layer from the inside out. The PGA barrier layer is composed of the following raw materials by mass fraction: 78.7% poly(lactic acid-glycolic acid) copolymer (PLGA), 20% poly(caprolactone-glycolic acid) copolymer (PGCL), 1% ADR chain extender, 0.1% antioxidant 1010, 0.1% silica, and 0.1% erucamide.

[0034] The PLA substrate layer is composed of the following raw materials by mass fraction: 100% polylactic acid-polyester block copolymer; the mass ratio of polyester to polylactic acid in the polylactic acid-polyester block copolymer is 10:90; the molar ratio of L-lactide to D-lactide in the polylactic acid-polyester block copolymer is 94:6.

[0035] The PPC-reinforced heat-sealing layer component is composed of the following raw materials by mass fraction: 100% carbon dioxide epoxy propylene copolymer (PPC) resin.

[0036] The PLA heat-sealing layer is composed of the following raw materials by mass fraction: 99.8% heat-sealing PLA resin, 0.1% silica, and 0.1% erucamide.

[0037] Example 4 A flexible biodegradable barrier heat-sealing film includes a four-layer structure, consisting of a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer, and a PLA heat-sealing layer from the inside out. The PGA barrier layer is composed of the following raw materials by mass fraction: 66.5% poly(lactic acid-glycolic acid) copolymer (PLGA), 30% poly(caprolactone-glycolic acid) copolymer (PGCL), 2% chain extender EMA-GMA (ethylene-methyl acrylate-glycidyl methacrylate), 0.5% antioxidant 1098, 0.5% acrylic and 0.5% oleamide.

[0038] The PLA substrate layer is composed of the following raw materials by mass fraction: 100% polylactic acid-polyester block copolymer; the mass ratio of polyester to polylactic acid in the polylactic acid-polyester block copolymer is 20:80; the molar ratio of L-lactide to D-lactide in the polylactic acid-polyester block copolymer is 96:4.

[0039] The PPC-reinforced heat-sealing layer component is composed of the following raw materials by mass fraction: 100% carbon dioxide epoxy propylene copolymer (PPC) resin.

[0040] The PLA heat-sealing layer is composed of the following raw materials by mass fraction: 99% heat-sealing PLA resin, 0.5% acrylic and 0.5% oleamide.

[0041] This invention also provides a method for preparing the PGA barrier layer of Examples 1-4 above: S100, according to the mass parts, poly(lactic acid-glycolic acid) copolymer (PLGA), poly(caprolactone-glycolic acid) copolymer (PGCL), chain extender, antioxidant, stir for 1-3 min to obtain mixture P; S200, add mixture P through the main feed screw, and add the opening agent and slip agent through the side feed scale; The S300 extruder temperature is set at 160-210℃. The material is melted and plasticized through the twin-screw extruder. The extruder speed is 300 rpm, and the capacity is 280 kg / h. S400: The melt passes through the die and is cooled and drawn in a water bath at 30°C. S500, after being dehydrated and pelletized by a pelletizer, is drawn into a drying tank and dried at 80°C for 4 hours to obtain the PGA barrier resin; The PGA barrier layer is formed from PGA barrier layer resin, which is prepared using a twin-screw extruder. The screw element assembly of the twin-screw extruder is composed of the following elements arranged in the following order: Conveyor blocks: 45 / 45A, 75 / 75SK, 75 / 75SK, 75 / 75SK, 90 / 90, 60 / 60; Commonly used kneading thread elements: K22.5 / 5 / 75, K30 / 5 / 45, K45 / 5 / 45; Reverse thread block: 30 / 30L; Conveyor blocks: 75 / 75, 75 / 75, 90 / 90, 90 / 90, 90 / 90; Irregular meshing threaded elements: LFKB90 / 7 / 75, LFKB90 / 7 / 75, LFKB90 / 7 / 75; Standard kneading thread element: K45 / 5 / 45L; Reverse thread block: 30 / 30L; Conveyor blocks: 60 / 60, 60 / 60, 60 / 60, 60 / 60; Standard kneading thread elements: K45 / 5 / 45, K45 / 5 / 45; Toothed disk: C1; Disk: CY; Conveyor blocks: 90 / 90, 75 / 75, 75 / 75, 75 / 75, 60 / 60, 60 / 60.

[0042] The twin-screw extruder has a length-to-diameter ratio of 48:1.

[0043] This invention also provides preparation methods for Examples 1-4 above: Step 1: Mix PLA heat-sealing material and anti-sticking agent in proportion, melt-blend, extrude and granulate through a twin-screw extruder, and dry the resulting high-concentration concentrated masterbatch for later use; Step 2: The PGA barrier layer resin obtained in S5 is fed into extruder A to make layer A; the polylactic acid-polyester block copolymer is fed into extruder B to make layer B; the PPC is fed into extruder C to make layer C; the PLA heat-sealing material and the concentrated masterbatch obtained in step 1 are fed into extruder D in proportion to make layer D. The temperature of each extruder and the T-die is controlled between 180 and 210°C. Step 3: Using the LISIM simultaneous stretching method, the layers from Step 2 are extruded, rapidly cooled, and then biaxially stretched at a temperature of 85℃ and a setting temperature of 115℃, with a stretching ratio of 3.0. 3.0; Step 4: Roll up, slit, and package the biaxially oriented polylactic acid film obtained in step 3.

[0044] Comparative Example 1 (Ordinary PLA film) A biaxially oriented polylactic acid film comprising a three-layer structure, consisting of a PLA surface layer, a PLA core layer, and a PLA heat-sealing surface layer from the inside out; The PLA surface layer is composed of the following raw materials by mass fraction: PLA 99%, silicon dioxide 0.5%, and erucamide 0.5%.

[0045] The polylactic acid substrate layer is composed of the following raw materials by mass fraction: PLA 100%.

[0046] The polylactic acid surface layer component is composed of the following raw materials by mass fraction: 99% PLA heat-sealing material, 0.5% silica, and 0.5% erucamide.

[0047] The preparation method is the same as in the examples.

[0048] Comparative Example 2 (without PGA barrier layer resin) A flexible biodegradable barrier heat-sealing film includes a three-layer structure, consisting of a PLA substrate layer, a PPC reinforced heat-sealing layer, and a PLA heat-sealing layer from the inside out. The PLA substrate layer is composed of the following raw materials by mass fraction: 100% polylactic acid-polyester block copolymer; the mass ratio of polyester to polylactic acid in the polylactic acid-polyester block copolymer is 20:80; the molar ratio of L-lactide to D-lactide in the polylactic acid-polyester block copolymer is 96:4.

[0049] The PPC-reinforced heat-sealing layer component is composed of the following raw materials by mass fraction: 100% carbon dioxide epoxy propylene copolymer (PPC) resin.

[0050] The PLA heat-sealing layer is composed of the following raw materials by mass fraction: 99% heat-sealing PLA resin, 0.5% silica and 0.5% erucamide.

[0051] The preparation method is the same as in the examples.

[0052] Comparative Example 3 (without PPC reinforced heat seal layer) A flexible biodegradable barrier heat-sealing film includes a three-layer structure, consisting of a PGA barrier layer, a PLA substrate layer, and a PLA heat-sealing layer from the inside out. The PGA barrier layer is composed of the following raw materials by mass fraction: 66.5% poly(lactic acid-glycolic acid) copolymer (PLGA), 30% poly(caprolactone-glycolic acid) copolymer (PGCL), 2% ADR chain extender, 0.5% antioxidant 1010, 0.5% silica, and 0.5% erucamide.

[0053] The PLA substrate layer is composed of the following raw materials by mass fraction: 100% polylactic acid-polyester block copolymer; the mass ratio of polyester to polylactic acid in the polylactic acid-polyester block copolymer is 20:80; the molar ratio of L-lactide to D-lactide in the polylactic acid-polyester block copolymer is 96:4.

[0054] The PLA heat-sealing layer is composed of the following raw materials by mass fraction: 99% heat-sealing PLA resin, 0.5% silica and 0.5% erucamide.

[0055] The preparation method is the same as in the examples.

[0056] Comparative Example 4 (PGA barrier layer is pure PGA resin) A flexible biodegradable barrier heat-sealing film includes a four-layer structure, consisting of a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer, and a PLA heat-sealing layer from the inside out. The PGA barrier layer is composed of the following raw materials by mass fraction: 99% poly(lactic acid-glycolic acid) copolymer (PLGA), 0.5% silica, and 0.5% erucamide.

[0057] The PLA substrate layer is composed of the following raw materials by mass fraction: 100% polylactic acid-polyester block copolymer; the mass ratio of polyester to polylactic acid in the polylactic acid-polyester block copolymer is 20:80; the molar ratio of L-lactide to D-lactide in the polylactic acid-polyester block copolymer is 96:4.

[0058] The PPC-reinforced heat-sealing layer component is composed of the following raw materials by mass fraction: 100% carbon dioxide epoxy propylene copolymer (PPC) resin.

[0059] The PLA heat-sealing layer is composed of the following raw materials by mass fraction: 99% heat-sealing PLA resin, 0.5% silica and 0.5% erucamide.

[0060] The preparation method is the same as in the examples.

[0061] Comparative Example 5 (without PGCL) A flexible biodegradable barrier heat-sealing film includes a four-layer structure, consisting of a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer, and a PLA heat-sealing layer from the inside out. The PGA barrier layer is composed of the following raw materials by mass fraction: 96.5% poly(lactic acid-glycolic acid) copolymer (PLGA), 2% ADR chain extender, 0.5% antioxidant 1010, 0.5% silica, and 0.5% erucamide.

[0062] The PLA substrate layer is composed of the following raw materials by mass fraction: 100% polylactic acid-polyester block copolymer; the mass ratio of polyester to polylactic acid in the polylactic acid-polyester block copolymer is 20:80; the molar ratio of L-lactide to D-lactide in the polylactic acid-polyester block copolymer is 96:4.

[0063] The PPC-reinforced heat-sealing layer component is composed of the following raw materials by mass fraction: 100% carbon dioxide epoxy propylene copolymer (PPC) resin.

[0064] The PLA heat-sealing layer is composed of the following raw materials by mass fraction: 99% heat-sealing PLA resin, 0.5% silica and 0.5% erucamide.

[0065] Comparative Example 6 (without chain extender) A flexible biodegradable barrier heat-sealing film includes a four-layer structure, consisting of a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer, and a PLA heat-sealing layer from the inside out. The PGA barrier layer is composed of the following raw materials by mass fraction: 68.5% poly(lactic acid-glycolic acid) copolymer (PLGA), 30% poly(caprolactone-glycolic acid) copolymer (PGCL), 0.5% antioxidant 1010, 0.5% silica, and 0.5% erucamide.

[0066] The PLA substrate layer is composed of the following raw materials by mass fraction: 100% polylactic acid-polyester block copolymer; the mass ratio of polyester to polylactic acid in the polylactic acid-polyester block copolymer is 20:80; the molar ratio of L-lactide to D-lactide in the polylactic acid-polyester block copolymer is 96:4.

[0067] The PPC-reinforced heat-sealing layer component is composed of the following raw materials by mass fraction: 100% carbon dioxide epoxy propylene copolymer (PPC) resin.

[0068] The PLA heat-sealing layer is composed of the following raw materials by mass fraction: 99% heat-sealing PLA resin, 0.5% silica and 0.5% erucamide.

[0069] The preparation method is the same as in the examples.

[0070] Comparative Example 7 (without added antioxidants) A flexible biodegradable barrier heat-sealing film includes a four-layer structure, consisting of a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer, and a PLA heat-sealing layer from the inside out. The PGA barrier layer is composed of the following raw materials by mass fraction: 67% poly(lactic acid-glycolic acid) copolymer (PLGA), 30% poly(caprolactone-glycolic acid) copolymer (PGCL), 2% ADR chain extender, 0.5% silica, and 0.5% erucamide.

[0071] The PLA substrate layer is composed of the following raw materials by mass fraction: 100% polylactic acid-polyester block copolymer; the mass ratio of polyester to polylactic acid in the polylactic acid-polyester block copolymer is 20:80; the molar ratio of L-lactide to D-lactide in the polylactic acid-polyester block copolymer is 96:4.

[0072] The PPC-reinforced heat-sealing layer component is composed of the following raw materials by mass fraction: 100% carbon dioxide epoxy propylene copolymer (PPC) resin.

[0073] The PLA heat-sealing layer is composed of the following raw materials by mass fraction: 99% heat-sealing PLA resin, 0.5% silica and 0.5% erucamide.

[0074] Comparative Example 8 A flexible biodegradable barrier heat-sealing film includes a four-layer structure, consisting of a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer, and a PLA heat-sealing layer from the inside out. The PGA barrier layer is composed of the following raw materials by mass fraction: 36.5% poly(lactic acid-glycolic acid) copolymer (PLGA), 60% poly(caprolactone-glycolic acid) copolymer (PGCL), 2% ADR chain extender, 0.5% antioxidant 1010, 0.5% silica, and 0.5% erucamide.

[0075] The PLA substrate layer is composed of the following raw materials by mass fraction: 100% polylactic acid-polyester block copolymer; the mass ratio of polyester to polylactic acid in the polylactic acid-polyester block copolymer is 40:60; the molar ratio of L-lactide to D-lactide in the polylactic acid-polyester block copolymer is 96:4.

[0076] The PPC-reinforced heat-sealing layer component is composed of the following raw materials by mass fraction: 100% carbon dioxide epoxy propylene copolymer (PPC) resin.

[0077] The PLA heat-sealing layer is composed of the following raw materials by mass fraction: 99% heat-sealing PLA resin, 0.5% silica and 0.5% erucamide.

[0078] Comparative Example 9 A flexible biodegradable barrier heat-sealing film includes a four-layer structure, consisting of a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer, and a PLA heat-sealing layer from the inside out. The PGA barrier layer is composed of the following raw materials by mass fraction: 86.5% poly(lactic acid-glycolic acid) copolymer (PLGA), 10% poly(caprolactone-glycolic acid) copolymer (PGCL), 2% ADR chain extender, 0.5% antioxidant 1010, 0.5% silica, and 0.5% erucamide.

[0079] The PLA substrate layer is composed of the following raw materials by mass fraction: 100% polylactic acid-polyester block copolymer; the mass ratio of polyester to polylactic acid in the polylactic acid-polyester block copolymer is 5:95; the molar ratio of L-lactide to D-lactide in the polylactic acid-polyester block copolymer is 96:4.

[0080] The PPC-reinforced heat-sealing layer component is composed of the following raw materials by mass fraction: 100% carbon dioxide epoxy propylene copolymer (PPC) resin.

[0081] The PLA heat-sealing layer is composed of the following raw materials by mass fraction: 99% heat-sealing PLA resin, 0.5% silica and 0.5% erucamide.

[0082] Comparative Example 10 (using a conventional screw extrusion for PGA barrier layer) The difference from Example 1 is that the PGA barrier layer resin is extruded using a conventional screw extruder, with the following screw combination conditions: Conveyor blocks: 45 / 45A, 75 / 75SK, 75 / 75SK, 75 / 75SK, 90 / 90, 60 / 60; Commonly used kneading thread elements: K22.5 / 5 / 75, K30 / 5 / 45, K45 / 5 / 45; Reverse thread block: 30 / 30L; Conveyor blocks: 75 / 75, 75 / 75, 90 / 90, 90 / 90, 90 / 90; Irregular meshing threaded elements: LFKB90 / 7 / 75, LFKB90 / 7 / 75, LFKB90 / 7 / 75; Standard kneading thread element: K45 / 5 / 45L; Reverse thread block: 30 / 30L; Conveyor blocks: 60 / 60, 60 / 60, 60 / 60, 60 / 60; Standard kneading thread elements: K45 / 5 / 45, K45 / 5 / 45; Toothed disk: C1; Disk: CY; Conveyor blocks: 90 / 90, 75 / 75, 75 / 75, 75 / 75, 60 / 60, 60 / 60; Wherein, K is a conventional kneading thread element, LFKB is an irregular meshing thread element, L is a reverse thread block, C1 is a toothed disc, and CY is a circular disc.

[0083] The twin-screw extruder has a length-to-diameter ratio of 48:1.

[0084] Performance testing Various performance tests were performed on each embodiment and comparative example, and the test standards are as follows: Thickness: Tested in accordance with GB / T20220-2006 "Average thickness of plastic film and sheet samples, average thickness of rolls and surface area per unit mass"; The test method for film heat seal strength is to test the film heat seal strength according to QB / T 2358-98, with a heat seal pressure of 135 kPa, a heat seal temperature of 85℃, and a heat seal time of 2 s; Haze and transmittance: Tested according to GB / T2410-2008 "Standard for Determination of Transmittance and Haze of Transparent Plastics"; Tensile strength and elongation at break: tested according to GB / T 1040-3 "Determination of tensile properties of plastics - Part 3: Test conditions for thin plastics and sheets"; Heat shrinkage rate: GB / T12027-2004 Test method for dimensional change rate of plastic films and sheets under heat, test temperature is 100℃, test time is 10min.

[0085] Water vapor transmission rate: The water vapor transmission rate of the thin film was tested according to GB / T 1037-1988; Oxygen permeability: The oxygen permeability of the membrane was tested according to GB / T 1038-2000; the test conditions were 23℃ and 50%RH.

[0086] Film-forming properties of stretched films: No film formation is indicated by X; continuous film breakage during stretching is indicated by... ○ indicates poor film thickness that does not meet requirements; ◎ indicates good film thickness that meets requirements.

[0087] The thin film test evaluation results of the examples and comparative examples are shown in Tables 1-3: Table 1

[0088] Table 2

[0089] Table 3

[0090] As shown in Tables 1-2, the heat seal strength of Examples 1-4 all reached above 16.5 N / 15 mm, with the highest being 17.8 N / 15 mm, significantly higher than Comparative Example 1 (7.5 N / 15 mm) and Comparative Example 3 (7.3 N / 15 mm). This indicates that the synergistic design of the PPC-reinforced heat seal layer and the PLA heat seal layer is the key to achieving high heat seal strength. Meanwhile, the oxygen permeability of Examples 1-4 was all below 4.3 cc / m²·day, and the water vapor permeability was all below 6.1 g / m²·24h, far superior to Comparative Example 1 (oxygen permeability 216 cc / m²·day, water vapor permeability 253 g / m²·24h) and Comparative Example 2 (oxygen permeability 93 cc / m²·day, water vapor permeability 84 g / m²·24h), proving that the PGA barrier layer played a decisive role in improving barrier performance.

[0091] As shown in Tables 1-3, Comparative Example 4 (pure PGA) and Comparative Example 5 (without PGCL) failed to form a film, Comparative Example 6 (without chain extender) had poor film-forming properties, and Comparative Example 7 (without antioxidant) experienced continuous film breakage. In contrast, Examples 1-4 all formed stable films with uniform thickness. This indicates that the specific ratio of PLGA to PGCL, along with the addition of chain extender and antioxidant, collectively ensured the melt strength and thermal stability of the PGA barrier layer resin, enabling it to adapt to the biaxial stretching process. Comparative Example 8 (high PGCL content) formed a film, but its haze significantly increased to 6.9%, and its barrier performance decreased. Comparative Example 9 (low PGCL content) failed to form a film, verifying the criticality of the formulation range of this invention.

[0092] Comparative Example 10 showed continuous film rupture when using a conventional screw assembly, while Examples 1-4, using the screw assembly specified in this invention, all achieved stable production. This demonstrates that the screw assembly effectively avoids thermal degradation of PGA-type materials while ensuring dispersibility by providing lower shear force and longer residence time.

[0093] Examples 1-4 exhibit tensile modulus below 2800 MPa, demonstrating good flexibility; heat shrinkage below 2.5%, resulting in good dimensional stability; haze below 1.5%, and light transmittance above 94%, showcasing excellent optical performance. This balanced performance in barrier properties, heat-sealing strength, flexibility, and optical properties makes them particularly suitable for applications with stringent comprehensive performance requirements, such as inflatable aerospace food packaging.

[0094] In summary, the flexible biodegradable barrier heat-sealing film of the present invention has excellent barrier properties, optical properties, flexibility (low tensile modulus) and dimensional stability (low thermal shrinkage), and ultra-high heat-sealing strength. It is particularly suitable for inflatable food packaging, which can extend the shelf life of food and meet the requirements of packaging that is not deformed and does not leak air.

[0095] Although this document frequently uses terms such as PGA barrier layer, PLA substrate layer, PPC reinforced heat-sealing layer, and PLA heat-sealing layer, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of the invention; interpreting them as any additional limitation would contradict the spirit of the invention.

[0096] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention 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; and these 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 the present invention.

Claims

1. A flexible, biodegradable barrier heat-sealing film, characterized in that: The film has a four-layer structure, which includes, from the inside out, a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer, and a PLA heat-sealing layer. The PGA barrier layer comprises, by mass fraction, the following raw materials: 54-78.7% poly(lactic acid-glycolic acid) copolymer, 20-40% poly(caprolactone-glycolic acid) copolymer, 1-3% chain extender, 0.1-1% antioxidant, 0.1-1% opening agent, and 0.1-1% slip agent.

2. The flexible biodegradable barrier heat-sealing film according to claim 1, characterized in that: The PLA substrate layer is composed of polylactic acid-polyester block copolymer; in the polylactic acid-polyester block copolymer, the mass ratio of polyester to polylactic acid is 10-30:70-90; the molar ratio of L-lactide to D-lactide in the polylactic acid-polyester block copolymer is 94-99:1-6.

3. The flexible biodegradable barrier heat-sealing film according to claim 1, characterized in that: The PLA heat-sealing layer comprises the following raw materials by mass fraction: The composition includes 98-99.8% heat-sealing PLA resin, 0.1-1% opening agent, and 0.1-1% slip agent. The PPC-reinforced heat-sealing layer component, by mass fraction, consists of the following raw materials: 100% carbon dioxide epoxy propylene copolymer (PPC) resin.

4. The flexible biodegradable barrier heat-sealing film according to claim 1, characterized in that: The chain extender is one or more of the following: ethylene-methyl acrylate-glycidyl methacrylate, styrene and glycidyl acrylate copolymer, hexamethylene diisocyanate, 4,4'-methylene diphenyl isocyanate, and polycarbodiimide.

5. The flexible biodegradable barrier heat-sealing film according to claim 1, characterized in that: The antioxidant is one or more of antioxidant 1010, antioxidant 1098, antioxidant 2246, antioxidant 168, antioxidant 330, antioxidant DNP, antioxidant SEED, and antioxidant phosphite.

6. The flexible biodegradable barrier heat-sealing film according to claim 1, characterized in that: The opening agent is composed of one or more of silicon dioxide, calcium carbonate, organosilicon, and acrylic. The slip agent is composed of one or more of PE wax, oleamide, silicone wax, paraffin wax, and erucamide.

7. The flexible biodegradable barrier heat-sealing film according to claim 1, characterized in that: The polylactic acid-polyester block copolymer is selected from one or more combinations of polybutylene terephthalate-polylactic acid copolymer, polycaprolactone-polylactic acid copolymer, and polybutylene succinate-polylactic acid copolymer.

8. The flexible biodegradable barrier heat-sealing film according to claim 1, characterized in that: The flexible biodegradable barrier heat-sealing film is 30-50 μm thick, the PGA barrier layer is 1-5 μm thick, the PPC reinforced heat-sealing layer is 8-10 μm thick, and the PLA heat-sealing layer is 1-2 μm thick.

9. The flexible biodegradable barrier heat-sealing film according to claim 1, characterized in that: The PGA barrier layer is formed from PGA barrier layer resin, which is prepared using a twin-screw extruder. The screw element assembly of the twin-screw extruder is composed of the following elements arranged in the following order: Conveyor blocks: 45 / 45A, 75 / 75SK, 75 / 75SK, 75 / 75SK, 90 / 90, 60 / 60; Commonly used kneading thread elements: K22.5 / 5 / 75, K30 / 5 / 45, K45 / 5 / 45; Reverse thread block: 30 / 30L; Conveyor blocks: 75 / 75, 75 / 75, 90 / 90, 90 / 90, 90 / 90; Irregular meshing threaded elements: LFKB90 / 7 / 75, LFKB90 / 7 / 75, LFKB90 / 7 / 75; Standard kneading thread element: K45 / 5 / 45L; Reverse thread block: 30 / 30L; Conveyor blocks: 60 / 60, 60 / 60, 60 / 60, 60 / 60; Standard kneading thread elements: K45 / 5 / 45, K45 / 5 / 45; Toothed disk: C1; Disk: CY; Conveyor blocks: 90 / 90, 75 / 75, 75 / 75, 75 / 75, 60 / 60, 60 / 60.

10. A method for preparing a flexible biodegradable barrier heat-sealing film as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. Preparation of PGA barrier layer resin includes mixing poly(lactic acid-glycolic acid) copolymer, poly(caprolactone-glycolic acid) copolymer, chain extender and antioxidant in proportion, melting and plasticizing through a twin-screw extruder, adding opening agent and slip agent during plasticizing, and obtaining the PGA barrier layer resin by extrusion, cooling, pelletizing and drying. S2. Using a multi-layer co-extrusion biaxial stretching process, the PGA barrier layer resin, polylactic acid-polyester block copolymer, carbon dioxide-propylene oxide copolymer resin and heat-sealing PLA resin are respectively fed into the corresponding extruders to co-extrude and form a multi-layer melt consisting of a PGA barrier layer, a PLA substrate layer, a PPC reinforced heat-sealing layer and a PLA heat-sealing layer from the inside out. S3. After casting the multilayer melt sheet, perform synchronous bidirectional stretching to obtain the flexible biodegradable barrier heat-sealing film.

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