High-barrier polyglycolic acid multilayer composite films, their preparation methods and applications

Abstract

This invention discloses a high-barrier polyglycolic acid (PGA) multilayer composite film and its preparation method. It mainly addresses the problems of low melt strength of PGA, poor toughness of single-layer pure PGA films, and susceptibility to hydrolysis in existing technologies, making it difficult to meet the application requirements of barrier materials. By employing a high-barrier PGA multilayer composite film comprising a barrier layer, a protective layer, and an adhesive layer; wherein the protective layer is at least the outermost layer, the adhesive layer is at least located between the barrier layer and the protective layer, and the barrier layer contains at least polyglycolic acid with a multi-peak molecular weight distribution, this invention effectively solves the problem and can be used in the industrial production of high-barrier PGA films.

Description

Technical Field

[0001] This invention belongs to the field of polymer processing and modification technology, and relates to a high-barrier polyglycolic acid multilayer composite film, its preparation method and application. Background Technology

[0002] Polyglycolic acid (PGA), also known as polyglycolic acid or polyhydroxyacetic acid, is a fully biodegradable material that can completely degrade under natural conditions within 1-3 months. Due to its large density and molecular volume, PGA has excellent gas barrier properties. PGA's oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) are both lower than those of common barrier materials such as ethylene-vinyl alcohol copolymer (EVOH), polyvinylidene chloride (PVDC), polyethylene terephthalate (PET), and polyamide (PA). Its barrier effect against oxygen and water vapor is 100 times that of PET, and its barrier properties are less affected by ambient temperature.

[0003] However, on the one hand, PGA is unstable and prone to degradation during polymerization, resulting in low molecular weight and low melt flow rate. The synthesized PGA with a single-peak molecular weight distribution has extremely low melt strength, making it unsuitable for direct blown film or cast film formation, thus hindering the effective utilization of its barrier properties. Furthermore, even after certain modifications (such as the significantly improved melt strength of the multi-peak molecular weight distribution polyglycolic acid used in this invention, which solves the problem of PGA's inability to be blown film processed), the toughness of PGA can be improved to some extent, but the improvement is still limited and cannot meet the requirements of applications requiring high toughness. On the other hand, although PGA has excellent water vapor barrier properties, it is easily hydrolyzed, resulting in a short lifespan when used directly as a single-layer film. Therefore, from a practical application perspective, PGA is used as the barrier layer, with a polyolefin layer that has good water resistance and high toughness as the outer protective layer. However, since polyolefin is a non-polar polymer while PGA is a strongly polar polymer, their compatibility is very poor, resulting in poor adhesion when directly composited, leading to film delamination and failing to meet the requirements of practical applications.

[0004] CN 101945749A (Kurenai Co., Ltd., 2011.01.12) discloses a sequentially biaxially stretched polyglycolic acid (PGA) film, a method for manufacturing the PGA film, and a multilayer film. The method involves sequentially biaxially stretching an amorphous PGA sheet to obtain a high-barrier single-layer biaxially stretched PGA film, and then using this film as a substrate to prepare a multilayer film. Because the PGA used in this patent has insufficient melt strength, a casting method is still employed, followed by lamination with other materials to prepare a biodegradable multilayer composite high-barrier film. Although the multilayer composite biodegradable film prepared by this method possesses excellent barrier properties, the equipment investment for biaxial stretching is very large, the multi-step lamination process is complex, and the production cost is high. Furthermore, because there is no adhesive layer in between, the interlayer bonding is weak, and oxygen and water vapor easily remain between the PGA biaxially stretched film and other material layers during the multi-step lamination process. This can easily lead to performance degradation for PGA, which degrades rapidly.

[0005] CN 104349900A (Criowac, ​​February 11, 2015) discloses a disposable container polymer film suitable for constructing bioprocess containers. The film includes a first barrier layer and a second barrier layer, wherein the first barrier layer comprises polyglycolic acid, polyamide, EVOH, and / or a blend of EVOH. The film preparation method disclosed in this patent differs from that of this invention; it is prepared by casting co-extrusion. The polyglycolic acid thickness is 8–13 μm, but due to the large number of layers (9 in total), the total thickness is approximately 280 μm.

[0006] CN 108377821B (Zhejiang University, 2020.03.24) discloses a biodegradable barrier film. The film is prepared by multilayer co-extrusion, multilayer co-blowing, or multilayer casting and biaxial stretching of a first melt and a second melt. The second melt forms a barrier film as an intermediate layer. PGA is used as one of the blend components, but not as the main component of the barrier layer. The barrier resin that mainly performs the barrier function is PBAT containing barrier filler. Due to the poor oxygen and water barrier properties of PBAT, the resulting multilayer co-extruded biaxial film does not meet the requirements for high barrier performance.

[0007] CN 110921099A (Jiangsu Jinzhihong New Material Co., Ltd., 2020.03.27) discloses a high-barrier biodegradable stand-up pouch and its preparation method. The stand-up pouch consists of a high-barrier biodegradable self-sealing strip and a five-layer composite high-barrier biodegradable bag body. The five-layer composite high-barrier biodegradable bag body is composed of single-sided white kraft paper, an adhesive layer, a first barrier layer, a second barrier layer, and a heat-sealing layer, integrally formed using a four-layer co-extrusion and lamination process. However, the first barrier layer comprises 90 parts of polyglycolic acid (PGA), 5 parts of tributyl acetylglucosamine citrate, 5 parts of polyvinyl acetate, and 0.5 parts of antioxidant. It is not pure PGA but a PGA blend, resulting in low barrier performance. Furthermore, the kraft paper decomposes upon contact with water, lacking water-blocking protection. The resulting composite material has poor barrier and water resistance properties, failing to meet the requirements for versatility (e.g., rain resistance) and high barrier performance. Furthermore, since the PGA used is unmodified PGA, the melt strength is too low, so only co-extrusion casting can be used.

[0008] CN 113442401A (Guangdong University of Technology, 2021.09.28) discloses a high-strength, high-barrier PGA / PBAT food packaging film and its preparation method, including blending PBAT, PGA, and a compatibilizer to prepare a PBAT / PGA composite material, and then casting it into a film. Although this patent uses a three-layer co-extrusion casting machine, only the middle layer is actually used, resulting in a single-layer film. Therefore, PGA does not form a continuous phase, and its barrier properties are still relatively poor; the lowest oxygen permeability coefficient in the embodiment is 186.8 cm⁻¹. 3 / (m 2 ·day·atm).

[0009] In summary, although polyglycolic acid (PGA) has the best gas barrier properties among all biodegradable plastics and is the preferred material for applications with high barrier requirements, PGA itself has problems such as low melt strength, poor toughness, easy hydrolysis, and poor compatibility with other biodegradable plastics. This makes it very difficult and impractical and uncommon for PGA to be used in multilayer co-extrusion blown film processes with other biodegradable plastics. Summary of the Invention

[0010] In view of the problems in the prior art, such as the low melt strength of PGA, the poor toughness of single-layer pure PGA film, the easy hydrolysis which makes it difficult to meet the application requirements of barrier materials, and the poor compatibility of PGA with other biodegradable plastics which leads to poor interlayer adhesion when it is multilayered, the present invention provides a high-barrier polyglycolic acid multilayer composite film, its preparation method and application.

[0011] One objective of this invention is to provide a high-barrier polyglycolic acid multilayer composite film comprising a barrier layer, a protective layer, and an adhesive layer; wherein the protective layer is at least the outermost layer, the adhesive layer is at least located between the barrier layer and the protective layer, and the barrier layer contains at least polyglycolic acid with a multi-peak molecular weight distribution.

[0012] According to the present invention, the barrier layer has at least one layer, with a single layer thickness of 1 to 50 micrometers, such as one, two, or three layers. Preferably, the barrier layer is polyglycolic acid with a multi-peak molecular weight distribution. And / or, the protective layer has at least two layers, such as two to seven layers. The material of each protective layer can be the same or different, and the single layer thickness is 3 to 80 micrometers. The outermost layer of the multilayer composite film must be the protective layer. And / or, the adhesive layer has at least two layers, with a single layer thickness of 0.5 to 20 micrometers. And / or, the total thickness of the multilayer composite film is 8 to 250 micrometers.

[0013] According to the present invention, the protective layer is a polyolefin with good water-blocking properties and good toughness. Preferably, the polyolefin includes any one or more mixtures of low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, polypropylene, ethylene-propylene-diene-nonconjugated diene copolymer, metallocene polyethylene, metallocene polypropylene, poly(1-butene) and its derivatives, and cyclic olefin polymers (COP).

[0014] According to the present invention, the adhesive layer is a polyolefin graft copolymer or an ethylene-polar monomer copolymer. Preferably, the polyolefin graft copolymer includes any one or more mixtures of polyethylene grafted with maleic anhydride, polyethylene grafted with acrylic acid, polyethylene grafted with methyl methacrylate, polypropylene grafted with maleic anhydride, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer.

[0015] According to the present invention, the barrier layer is a high-barrier polyglycolic acid with a multi-peak molecular weight distribution.

[0016] According to the above technical solution, the multi-peak molecular weight distribution polyglycolic acid contains two polyglycolic acid components with different chemical structures, including a polyglycolic acid graft copolymer and a polyglycolic acid homopolymer; wherein, the polyglycolic acid graft copolymer has an ethylene-vinyl alcohol copolymer segment and / or a polyvinyl alcohol segment as its main chain and a glycolic acid monomer derivative, glycolic acid oligomer or glycolic acid polymer as its side chain.

[0017] In a preferred embodiment of the present invention, the structure of the polyglycolic acid graft copolymer is shown in structural formula (Ⅰ):

[0018]

[0019] In structural formula (I), x and m are both positive integers, and y1, y2 and z are all natural numbers; preferably, the sum of x, y1, y2 and z is not less than 50, preferably 50-6000, more preferably 200-2500; and / or, m is not less than 50, preferably 50-1000; and / or, z accounts for 0%-50% of x+y1+y2+z, and when z is 0, the main chain of the polyglycolic acid graft copolymer is a polyvinyl alcohol segment; and / or, y1 accounts for 0%-32% of x+y1+y2, and when y1 is 0, the main chain of the polyglycolic acid graft copolymer is an ethylene-vinyl alcohol copolymer segment.

[0020] According to the present invention, when the main chain of the polyglycolic acid graft copolymer is an ethylene-vinyl alcohol copolymer segment, the proportion of z to the sum of x+y1+y2+z is 1%-50%, preferably 20%-45%, and the proportion of y1 to the sum of x+y1+y2 is 0.1%-6%; and / or, when the main chain of the polyglycolic acid graft copolymer is a polyvinyl alcohol segment, z is 0, and the proportion of y1 to the sum of x+y1+y2 is 1%-32%.

[0021] According to the present invention, the sum of x+y1+y2+z is the degree of polymerization of the ethylene-vinyl alcohol copolymer, which can be calculated from the number average molecular weight of the raw material ethylene-vinyl alcohol copolymer and is related to the ethylene content in the ethylene-vinyl alcohol copolymer; while the ratio of x to y2 can be calculated from the integral area of ​​the corresponding peak in the 1H NMR spectrum.

[0022] According to the present invention, the degree of alcoholysis of the ethylene-vinyl alcohol copolymer is a known parameter from the raw material factory, and can also be detected by various detection methods in the art such as nuclear magnetic resonance and near-infrared spectroscopy.

[0023] According to the present invention, the range of values ​​for m is relatively wide. In a preferred embodiment of the present invention, m is an integer greater than 10, and more preferably m is an integer greater than 50.

[0024] According to the present invention, if the structure of the initial ethylene-vinyl alcohol copolymer macromolecular initiator is known, then m = (number-average molecular weight of the high molecular weight PGA fraction - number-average molecular weight of the macromolecular initiator (ethylene-vinyl alcohol copolymer)) / (x * molecular weight of the repeating unit of PGA). If the high molecular weight PGA of the graft copolymer structure described in this invention is obtained directly, it can be fully hydrolyzed first, the initiator collected, its structure analyzed, and then tested according to the above method. According to the embodiments described later in this invention, the calculated m values ​​in the obtained polymers are all greater than 50.

[0025] According to a preferred embodiment of the present invention, the structure of the polyglycolic acid homopolymer is shown in structural formula (II):

[0026]

[0027] In structural formula (II), n1, n2, ..., n i All are natural numbers; M1, M2, ..., M i Each is an imino, subamino, or ether bond; i is an integer not less than 1, preferably greater than 1; R is an alkane or aromatic group with a molecular weight of 14-1000 g / mol; preferably, i ranges from 1 to 20, and the preferred range of i is 2-6, for example, 2, 3, 4, 5, 6; and / or, n1, n2, ..., n i The sum is between 50 and 5000, for example, 50, 100, 500, 1500, 2000, 3000, 4000, 5000, and any two values ​​or any interval of any two values. When i = 1, R can be H or a hydrocarbon group, including but not limited to.

[0028] According to the present invention, in formula (II), n1, n2, ..., n i Each has a wide range of choices, and their respective values ​​are difficult to calculate. In a preferred embodiment of the present invention, n1, n2, ..., n in equation (II) i The sum of the values ​​is not less than 100. According to the present invention, n1, n2, ..., n i The sum of the values ​​can be calculated by dividing the number-average molecular weight of the lower molecular weight peak in the GPC results by the molecular weight of the PGA repeating unit. According to the embodiments described later in this invention, the calculated values ​​of n1, n2, ..., n in the obtained polymer are... i The sum of all values ​​is greater than 100.

[0029] According to the present invention, the selection range of the content of each polymer segment in the multi-peak molecular weight distribution polyglycolic acid of the present invention is relatively wide. In a preferred embodiment of the present invention, the content of each polymer segment is selected relative to 100 parts by mass of polyglycolic acid segments. The polyglycolic acid with a multimodal molecular weight distribution contains 0.001-10 parts by mass of ethylene-vinyl alcohol copolymer segments. Containing 0.001-10 parts by weight

[0030] In a more preferred embodiment of the invention, relative to 100 parts by mass of polyglycolic acid segments The polyglycolic acid with a multimodal molecular weight distribution contains 0.01-1 parts by mass of ethylene-vinyl alcohol copolymer segments. Contains 0.01-1 parts by weight The mass content of each of the above segments can be detected using methods known in the art, or it can be calculated by the amount of material fed during the preparation process.

[0031] According to the present invention, the weight-average molecular weight of the polyglycolic acid with multimodal molecular weight distribution has a wide selection range. In a preferred embodiment of the present invention, the weight-average molecular weight of the polyglycolic acid with multimodal molecular weight distribution is 200,000-1,500,000 g / mol, preferably 250,000-500,000 g / mol, for example, it can be 250,000 g / mol, 300,000 g / mol, 350,000 g / mol, 400,000 g / mol, 450,000 g / mol, 500,000 g / mol, as well as any two values ​​and any range.

[0032] According to the present invention, the molecular weight distribution index of the multimodal molecular weight distribution polyglycolic acid has a wide selection range. The molecular weight distribution index of the multimodal molecular weight distribution polyglycolic acid is 1.5-20, preferably 2-3.5.

[0033] According to the present invention, the number of molecular weight distribution peaks of the multi-peaked molecular weight distribution polyglycolic acid is selected within a wide range. The number of molecular weight distribution peaks of the multi-peaked molecular weight distribution polyglycolic acid is at least two, for example, including but not limited to two or three.

[0034] According to the present invention, the number of molecular weight distribution peaks can be detected by gel permeation chromatography (GPC).

[0035] According to the present invention, the weight-average molecular weight of the polyglycolic acid graft copolymer has a wide selection range. In a preferred embodiment of the present invention, the weight-average molecular weight of the polyglycolic acid graft copolymer is 500,000-10,000,000 g / mol, preferably 1,000,000-6,000,000 g / mol, for example, it can be 1,000,000 g / mol, 1,500,000 g / mol, 2,000,000 g / mol, 3,000,000 g / mol, 4,000,000 g / mol, 5,000,000 g / mol, 6,000,000 g / mol, as well as any two values ​​and any range.

[0036] According to the present invention, the polydispersity index of the polyglycolic acid graft copolymer has a wide selection range. In a preferred embodiment of the present invention, the polydispersity index of the polyglycolic acid graft copolymer is 1.01-3.0, preferably 1.05-1.5.

[0037] According to the present invention, the weight-average molecular weight of the polyglycolic acid homopolymer has a wide range. In a preferred embodiment of the present invention, the weight-average molecular weight of the polyglycolic acid homopolymer is 50,000-350,000 g / mol, preferably 100,000-200,000 g / mol, for example, it can be 100,000 g / mol, 120,000 g / mol, 140,000 g / mol, 160,000 g / mol, 180,000 g / mol, 200,000 g / mol, as well as any two values ​​and any range.

[0038] According to the present invention, the polydispersity index of the polyglycolic acid homopolymer has a wide selection range. In a preferred embodiment of the present invention, the polydispersity index of the polyglycolic acid homopolymer is 1-3, preferably 1.4-2.9.

[0039] According to the present invention, the selection range of the content of the polyglycolic acid graft copolymer and the polyglycolic acid homopolymer in the multimodal molecular weight distribution polyglycolic acid is relatively wide. In a preferred embodiment of the present invention, relative to the total mass of the multimodal molecular weight distribution polyglycolic acid, the content of the polyglycolic acid graft copolymer is 0.1%-80% by mass, preferably 1%-30% by mass; the content of the polyglycolic acid homopolymer is 20%-99.9% by mass, preferably 70%-99% by mass.

[0040] The weight-average molecular weight, molecular weight distribution index, number of molecular weight distribution peaks, weight-average molecular weight of the polyglycolic acid graft copolymer, molecular weight polydispersity index of the polyglycolic acid graft copolymer, molecular weight polydispersity index of the polyglycolic acid homopolymer, mass fraction of the polyglycolic acid graft copolymer, and mass fraction of the polyglycolic acid homopolymer, as described above, can be detected by gel permeation chromatography (GPC). Specific detection methods can employ conventional detection parameters known in the art. For example, but not limited to, the following method can be used: the test instrument is an Angilent PL-GPC50 gel permeation chromatograph (USA), and the processing software is GPC offline. During the test, the mobile phase is hexafluoroisopropanol containing 5 mmol / L sodium trifluoroacetate, the flow rate is 1 mL / min, the column temperature is 40℃, the injection volume is 100 μL, the standard is PMMA, and the sample concentration is 1 mg / mL. The specific values ​​of the above parameters are obtained according to analytical methods known in the art.

[0041] In a preferred embodiment of the present invention, the melt flow rate (MFR) of the multi-peak molecular weight distribution polyglycolic acid at 230°C / 2.16 kg is not higher than 20 g / 10 min, preferably 0.01-20 g / 10 min, more preferably 0.5-10 g / 10 min, for example, it can be 0.5 g / 10 min, 1 g / 10 min, 2 g / 10 min, 3 g / 10 min, 4 g / 10 min, 5 g / 10 min, 6 g / 10 min, 7 g / 10 min, 8 g / 10 min, 9 g / 10 min, 10 g / 10 min, as well as any two values ​​and any range.

[0042] The melt flow rate can be determined using methods known in the art, such as, but not limited to, the following: The test was conducted on a CEAST MF20 melt flow rate tester from Instron Corporation, USA. The test temperature was 230°C, the load weight was 2.16 kg, and the preheating time was 4 min.

[0043] In a preferred embodiment of the present invention, the melt strength of the multi-peak molecular weight distribution polyglycolic acid at 235°C is not less than 6 cN, and preferably not less than 8 cN.

[0044] Melt strength can be determined using methods known in the art, such as, but not limited to, the following: the test was conducted on a Rosand RH7 high-pressure capillary rheometer from Malvern Panaco in China. The nozzle size was Haul Off (diameter: 2.0 mm, length: 20 mm), the barrel pusher speed was 15 mm / min, the test temperature was 235 °C, the initial drawing speed was 3 mm / min, the final drawing speed was 50 mm / min, and the ramp-up time was 3 min.

[0045] According to the present invention, the oxygen transmissivity (OTR) of the multilayer composite membrane under the conditions of 23±0.5℃ and 65%±5% relative humidity is not greater than 100 cm⁻¹. 3 / (m 2 (day atm), preferably no larger than 30cm 3 / (m 2 ·day·atm).

[0046] According to the present invention, the multilayer composite membrane has a water vapor transmission rate (WVTR) of no more than 30 g / (m³) under the following conditions: 38±0.5℃, relative humidity 90%±5%, and 1 standard atmosphere. 2 (day·atm), preferably no more than 15g / (m 2 (day / atm). According to the present invention, the heat-sealing strength of the multilayer composite film is not less than 3N / 15mm, preferably not less than 5N / 15mm.

[0047] According to the present invention, the interlayer peel strength of the multilayer composite film is not less than 0.5N / 15mm, preferably not less than 1.5N / 15mm.

[0048] A second objective of this invention is to provide a method for preparing the high-barrier polyglycolic acid multilayer composite film described above, comprising:

[0049] The multi-peak molecular weight distribution polyglycolic acid, polyolefin, and polyolefin graft copolymer are separately added to a screw extruder and melted, compressed, and extruded. They are then individually formed into films through a casting or blown film die. Finally, the multiple films are hot-pressed to form the high-barrier polyglycolic acid multilayer composite film. Alternatively,

[0050] More preferably, the multi-peak molecular weight distribution polyglycolic acid, polyolefin, and polyolefin graft copolymer are respectively added to at least three different screw extruders, and after melting and compression, they are extruded through a co-extrusion distributor and a film-forming die, cooled, and wound up to obtain the high-barrier polyglycolic acid multilayer composite film. Preferably, the product is stretched by a unidirectional stretching unit before winding.

[0051] According to the present invention, the screw extruder is a single-screw extruder or a twin-screw extruder; the film-forming die is a blown film die or a cast film die.

[0052] In a preferred embodiment of the present invention, the film-forming mold is a blown film mold, and the blow-out ratio during blown film is (1-6):1, preferably (2-5):1.

[0053] The single-screw extrusion blown film machines applicable to the present invention include blown film machines of different designs, such as the Dr. Collin E30P single-screw extrusion blown film machine from Germany.

[0054] In one specific embodiment of blown film, the film can be formed by a blown film process, wherein a gas (e.g., air) is used to inflate the extruded polymer through a bubble formed by an annular die. The blow-up ratio and film thickness are controlled by adjusting the pressure of the gas in the bubble; the higher the pressure, the larger the bubble, the thinner the film, and the higher the degree of lateral orientation of the film. Then the bubble (e.g.) Figure 1 After being flattened by the double rollers above, the film is cut into two flat films and then wound up. The faster the winding speed, the higher the longitudinal stretching orientation, and the thinner the film. Figure 1 and Figure 2 A method for producing blown films is described. Figure 3 A method for producing cast films is described.

[0055] According to the invention, the preparation process includes a unidirectional stretching unit before winding. Regardless of whether the film is blown or cast, it can optionally be oriented in one or more directions before winding to further improve the film's orientation and reduce its thickness. For example, the film can be heated by guide rollers to a temperature below the melting point of one or more polymers in the film (above the glass transition temperature), but high enough to allow the composition to be continuously and controllably stretched. The heated "softened" film is stretched stepwise by guide rollers rotating at different speeds, such that it is stretched to the desired draw ratio in the machine direction (MD). This "unidirectionally" oriented film can then be drawn and wound.

[0056] Figure 2 A method for forming uniaxially oriented films is demonstrated. For example... Figure 2 As shown, the blown film 01b is guided to a unidirectional stretching unit 70 (MDO, commercially available, for example, from Marshall and Williams, Co. of Providence, RI). The MDO has multiple stretching rollers (e.g., from 5 to 8) that gradually stretch and thin the film in the MD direction, which is the direction of film travel in the process shown in the figure. Although Figure 2 and Figure 3 The MDO 100 shown has seven rollers, but it should be understood that the number of rollers can be more or fewer, depending on the required stretching ratio and the degree of stretching between each roller. The film can be stretched in a single or multiple stretching units connected in series. It should be noted that some guide rollers in the MDO equipment may operate at arbitrary speeds. If desired, some guide rollers in the MDO can be used as preheating rollers. If present, these initial few rollers heat the film 01b above the lowest glass transition temperature in the polymer (e.g., to 50°C). The gradually increasing speed of adjacent rollers in the MDO serves to stretch the film 01b. The rotational speed of the stretching rollers determines the amount of film stretching and the final film thickness. The resulting film 01c can then be wound and collected on the take-up roller 60. Although not shown here, various additional potential processing and / or finishing steps known in the art, such as slitting, treatment, perforation, printing patterns, or lamination, can be used to process films with additional layers without departing from the spirit and scope of the invention.

[0057] In a preferred embodiment of the present invention, the rotational speed of the screw extruder is preferably 10 to 200 rpm; and / or the extrusion temperature is preferably 180°C to 260°C; preferably, the ratio (blowing ratio) of the diameter of the blown film bubble to the diameter of the blown film die is 1:1 to 6:1, and more preferably 2:1 to 5:1.

[0058] In a preferred embodiment of the present invention, the preparation method further includes a step of preparing polyglycolic acid with a multi-peak molecular weight distribution, wherein the method for preparing polyglycolic acid with a multi-peak molecular weight distribution comprises: polymerizing polyglycolic acid segments to obtain polyglycolic acid segments. The monomer, ethylene-vinyl alcohol copolymer (and / or polyvinyl alcohol), and optionally a small molecule co-initiator are melt-polymerized in the presence of a catalyst and optionally an antioxidant to obtain the multi-peak molecular weight distribution polyglycolic acid. That is, in a preferred embodiment of the invention, the method for preparing the membrane includes polymerizing segments capable of yielding polyglycolic acid. The monomer, ethylene-vinyl alcohol copolymer (and / or polyvinyl alcohol) and optional small molecule co-initiator are melt-polymerized in the presence of a catalyst and optional antioxidant to obtain the multi-peak molecular weight distribution polyglycolic acid particles. The multi-peak molecular weight distribution polyglycolic acid particles are then added to at least one screw extruder, melted, compressed, extruded through a film forming die, cooled, stretched, and wound to obtain the multi-peak molecular weight distribution polyglycolic acid composition film.

[0059] According to the present invention, the monomer can be selected from a wide range. In a preferred embodiment of the present invention, the monomer includes at least one selected from methyl glycolate, glycolic acid, and glycolide; more preferably glycolide.

[0060] According to the present invention, the ethylene-vinyl alcohol copolymer can be selected within a wide range. In a preferred embodiment of the present invention, the ethylene segment content in the ethylene-vinyl alcohol copolymer is 25-50 mol%, for example, 25 mol%, 35 mol%, 45 mol%, 50 mol%, and any two values ​​and any range thereof; and / or, the degree of polymerization of the ethylene-vinyl alcohol copolymer is 50-6000, preferably 300-2000, for example, 300, 500, 1000, 1500, 2000, and any two values ​​and any range thereof.

[0061] According to the present invention, the polyvinyl alcohol can be selected within a wide range. According to a preferred embodiment of the present invention, the degree of alcoholysis of the polyvinyl alcohol is 68%-100%, for example 68%, 75%, 85%, 95%, 99%, 100%, and any two values ​​or any range of any two values.

[0062] According to the present invention, the melt flow rate of the ethylene-vinyl alcohol copolymer can be selected within a wide range. In a preferred embodiment of the present invention, the melt flow rate of the ethylene-vinyl alcohol copolymer at 190°C / 2.16 kg is 0.1-50 g / 10 min.

[0063] According to the present invention, the small molecule co-initiator can be selected from a wide range. In a preferred embodiment of the present invention, the small molecule co-initiator is a small molecule containing hydroxyl or amino groups with a boiling point greater than 160°C, preferably with a molecular weight not greater than 1000 g / mol; more preferably 60-300 g / mol. Examples include, but are not limited to: ethylene glycol, butanediol, glycerol, serine, leucine, pentaerythritol, sorbitol, xylitol, amino acids, phenol, hydroquinone, resorcinol, benzyl alcohol, aniline, benzylamine, p-phenylenediamine, m-phenylenediamine, hexamethylenediamine, dodecanediamine, etc.

[0064] According to the present invention, the catalyst can be selected from a wide range. In a preferred embodiment of the present invention, the catalyst is a salt compound corresponding to at least one of group IIA-VA metal elements and transition metal elements, or an organic guanidine catalyst. Preferably, the catalyst is a salt compound corresponding to at least one of Sn, Bi, Mg, Al, Ca, Fe, Mn, Ti, and Zn, and more preferably a Sn salt.

[0065] According to the present invention, the antioxidant can be selected from a wide range. In a preferred embodiment of the present invention, the antioxidant is selected from hindered phenolic antioxidants and / or phosphite antioxidants, that is, it can be hindered phenolic and phosphite antioxidants and any combination thereof, including but not limited to 2,6-di-tert-butyl-p-cresol, 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 2,2'-methylenebis(6-tert-butyl-4-methylphenol), hexanediol bis[β-(3,5-dibutyl-4-hydroxyphenyl)propionate], pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (such as BASF's antioxidant Irganox). 1010), N,N'-bis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl]hydrazine (e.g., antioxidant 1024), N,N'-bis-(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl)hexamethylenediamine (e.g., antioxidant 1098), β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester (e.g., BASF's antioxidant Irganox) 1076), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, triphenyl phosphite, tri(4-nonylphenyl) phosphite, diphenyl isooctyl phosphite, diphenyl isodecanyl phosphite, phenyl di(2-ethylhexyl) phosphite, phenyl diisodecyl phosphite, tri(2-ethylhexyl) phosphite, triisodecyl phosphite, tri(dodecyl) phosphite, pentaerythritol diisodecyl diphosphite, tri[2,4-di-tert-butylphenyl] phosphite (such as antioxidant 168), bis(2,4-dicumylphenyl) pentaerythritol diphosphite (such as antioxidant 686), and pentaerythritol diphosphite of bis(2,4-di-tert-butylphenyl)propionate (such as antioxidant 626).

[0066] According to the present invention, the amount of the antioxidant can be selected within a wide range. In a preferred embodiment of the present invention, the amount of the antioxidant, by weight, is 0-2 parts, preferably 0.01-1 parts (phr), relative to 100 parts of monomer.

[0067] According to the present invention, the amount of the ethylene-vinyl alcohol copolymer (and / or polyvinyl alcohol) can be selected within a wide range. In a preferred embodiment of the present invention, the amount of the ethylene-vinyl alcohol copolymer (and / or polyvinyl alcohol) is 0.001-10 parts by weight relative to 100 parts of monomer, preferably 0.01-1 parts.

[0068] According to the present invention, the amount of the small molecule co-initiator can be selected within a wide range. In a preferred embodiment of the present invention, the amount of the small molecule co-initiator, by weight, is 0.001-10 parts relative to 100 parts of monomer, preferably 0.01-1 parts.

[0069] According to the present invention, the amount of catalyst can be selected within a wide range. In a preferred embodiment of the present invention, the amount of catalyst, by weight, is 0.005-1 part, preferably 0.01-0.2 parts, relative to 100 parts of monomer.

[0070] According to the present invention, the conditions for the melt polymerization reaction can be selected within a wide range. In a preferred embodiment of the present invention, the conditions for the melt polymerization reaction include a temperature of 160-250°C, preferably 200-240°C.

[0071] According to the present invention, the time conditions for the melt polymerization reaction can be selected within a wide range. In a preferred embodiment of the present invention, the reaction time is 0.5-60 min, preferably 1-10 min.

[0072] In a more preferred embodiment of the present invention, the temperature of the melt polymerization reaction is 160-250°C, preferably 200-240°C; and the reaction time is 0.5-60 min, preferably 1-10 min.

[0073] The melt polymerization reaction is carried out in a melt mixing device; preferably, the melt mixing device is a combination of one or more of the following: a batch reactor, a tubular reactor, a mixer, a Farrel continuous mixer, a Banbury mixer, a single-screw extruder, a multi-screw extruder, and a reciprocating single-screw extruder, preferably a mixer or a twin-screw extruder.

[0074] In one preferred embodiment of the present invention, the melt polymerization reaction is carried out in a continuous twin-screw extruder, and preferably the processing conditions of the continuous twin-screw extruder include:

[0075] The processing temperature is 180-250℃, preferably 210-240℃; and / or, the screw speed is 5-300rpm, preferably 40-150rpm; and / or, the length-to-diameter ratio is 30-80, preferably 40-70.

[0076] The melt polymerization reaction is carried out in at least two continuous twin-screw extruders connected in series, and preferably the processing conditions of each twin-screw extruder connected in series include:

[0077] The processing temperature is 180-250℃, preferably 210-240℃; and / or, the screw speed is 5-300rpm, preferably 40-150rpm; and / or, the length-to-diameter ratio is 30-80, preferably 40-70.

[0078] In one preferred embodiment of the present invention, the preparation process is carried out in an internal mixer; preferably, the mixing temperature is 180-250℃, more preferably 200-230℃, the rotation speed is 5-150 rpm, more preferably 20-80 rpm, and the reaction time is 1-20 min, more preferably 3-10 min.

[0079] The internal mixers applicable to this invention include internal mixers of various designs, such as the PolyLab HAAKE manufactured by Thermo Fisher Scientific in the United States. TM Rheomex OS 567-1000 internal mixer module, etc. Continuous twin-screw extrusion equipment applicable to this invention includes twin-screw extruders of different designs, such as the HAAKE Eurolab16 benchtop parallel co-rotating twin-screw extruder manufactured by Thermo Fisher in the United States, and co-rotating parallel twin-screw extruders such as the ZSK Mcc18 or ZSK 40 manufactured by Coperion in Germany.

[0080] The third objective of this invention is to provide an application of the high-barrier polyglycolic acid multilayer composite film described above or the high-barrier polyglycolic acid multilayer composite film prepared by the preparation method described above.

[0081] The above technical solutions are not specifically limited in their application. Those skilled in the art can apply them according to existing technologies and processes, such as but not limited to applications in biodegradable packaging bags, pharmaceutical packaging films, food preservation films, agricultural films, barrier containers, and other fields.

[0082] Compared with the prior art, the present invention has the following advantages:

[0083] The high-barrier polyglycolic acid multilayer composite film of this invention maintains excellent biodegradability while possessing superior gas barrier properties, as well as good comprehensive mechanical and processing properties. Its heat-sealing strength is not less than 3 N / 15 mm, its interlayer peel strength is not less than 0.5 N / 15 mm, and its oxygen permeability and water vapor permeability are both not greater than 100 cm³. 3 / (m 2 ·day·atm) and 30g / (m 2 (day atm). In addition, the thin film preparation method in this invention is relatively simple, has relatively low equipment requirements, high production efficiency, can prepare composite thin films with low thickness, and has low overall production cost.

[0084] The inventors of this invention believe, through research and verification, that the reasons for the above advantages are as follows:

[0085] (1) This invention utilizes polyglycolic acid raw materials with high melt strength and multi-peak molecular weight distribution, enabling direct blown film production without any post-modification steps. Compared to other film preparation methods, blown film production involves simpler equipment, lower investment, faster returns, and easier production of wide-width films. Furthermore, the edge material at both ends of the film obtained from casting has significantly different properties from the middle material and needs to be trimmed before use. Therefore, compared to casting, the blown film production process produces no edge material and less waste.

[0086] (2) Since the polyglycolic acid with multi-peak molecular weight distribution in the multilayer film obtained by the present invention is a homogeneous continuous phase, its barrier performance is far superior to that of films of other barrier materials or films of polyglycolic acid blends with non-continuous polyglycolic acid.

[0087] (3) The present invention uses polyolefin with good water resistance and good toughness as a protective layer. Compared with single-layer PGA film, it not only has better toughness, but also slows down the hydrolysis of PGA due to the protective effect of the protective layer, thereby extending the life of the film.

[0088] (4) The present invention uses polyolefin grafted with polar monomers as the adhesive layer, which improves the interlayer adhesion between the barrier layer and the protective layer. Attached Figure Description

[0089] Figure 1 GPC curves for some embodiments and comparative examples are shown below. Figure 1 As can be seen, conventional commercially available PGA has a single-peak molecular weight distribution with a peak molecular weight Mp of less than 500,000 g / mol (i.e., Log(M) is less than 5.7), while Examples 2 and 3 have a multi-peak distribution, with peaks with a molecular weight Mp of less than 500,000 g / mol (i.e., polymer B) and peaks with a molecular weight Mp of greater than 500,000 g / mol (i.e., polymer A).

[0090] Figure 2 The melt strength test results are for Manufacturing Example 1 and Comparative Example 1. (From...) Figure 3 It is evident that the melt strength of Manufacturing Example 1 at 230°C is significantly higher than that of Comparative Example 1 (commercially available PGA), reaching approximately 20 cN, while the melt strength of Comparative Example 2 is less than 1 cN.

[0091] Figure 3This is a schematic diagram of a multilayer co-extrusion blown film preparation apparatus with a unidirectional stretching device. In the diagram, 10a, 10b, and 10c are hoppers; 20a, 20b, and 20c are extruders; 30a, 30b, and 30c are melt pumps; 40a is a feed pipe; 40b is a co-extrusion distributor; 50a is a blown film die; 50b is an air ring; 60 is a herringbone clamp; 70a is a clamping roller; 80 is the unidirectional stretching device; 90 is a take-up roller; 01a is a film bubble; 01b is the precursor film; and 01c is the stretched film. Hoppers 10a, 10b, and 10c respectively contain the outer protective layer material, the adhesive material, and the barrier layer material (polyglycolic acid).

[0092] Figure 4 This is a schematic diagram of a multilayer co-extrusion cast film preparation apparatus with a unidirectional stretching device. In the diagram, 10a, 10b, and 10c are hoppers; 20a, 20b, and 20c are extruders; 30a, 30b, and 30c are melt pumps; 40a is a feed pipe; 40b is a co-extrusion distributor; 50c is a casting die; 70b is a cooling roller; 80 is a unidirectional stretching device; 90 is a take-up roller; 01b is the precursor film; and 01c is the stretched film.

[0093] Figure 5 This is a schematic diagram of the polyglycolic acid multilayer composite film structure according to an embodiment of the present invention. Figure 6 This is an optical microscope photograph of Example 3. As shown in Figure 6, the left and right sides of the image show metal supports, and the center shows a cross-section of the multilayer film. The magnification of the photograph is 400x. As can be seen from the figure, the film is a 5-layer composite film: the lighter layer in the center is a polyglycolic acid barrier layer, approximately 15 μm thick; the outermost lighter layer with white reflective material is a polyethylene protective layer, approximately 20 μm thick; and the darker layer between the barrier layer and the protective layer is an adhesive layer, approximately 15 μm thick. Detailed Implementation

[0094] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0095] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0096] Raw material source:

[0097] All raw materials used in this invention are commercially available.

[0098] The glycolide was purchased from Shenzhen Boli Biomaterials Co., Ltd., with a purity of ≥99.5%.

[0099] Anhydrous stannous chloride, stannous octoate, and 1,4-butanediol were all purchased from Sinopharm Chemical Reagent Co., Ltd. The purity of anhydrous stannous chloride and stannous octoate was AR grade, and the purity of 1,4-butanediol was CP grade.

[0100] Antioxidant 1010 was purchased from BASF (China) Co., Ltd., and antioxidant 626 (THP-24) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., with a purity of ≥95%.

[0101] The ethylene-vinyl alcohol copolymer (EVOH) was purchased from Kuraray Corporation, Japan, under the brand name EVAL. TM H171B, with an ethylene content of 38 mol%; a melt flow rate of 1.7 g / 10 min at 190℃ / 2.16 kg; and polyvinyl alcohol (PVA) purchased from Chongqing Chuanwei Chemical Co., Ltd. of China Petrochemical Corporation, grade 0588, with a degree of polymerization of 500 and a degree of alcoholysis of 88%.

[0102] Polyglycolic acid (PGA) was purchased from KEBIN-PRAK AB in the Netherlands. It is a GMP-grade homopolymer of glycolide with an average intrinsic viscosity of 1.2 dl / g.

[0103] The performance of this invention was determined according to the following method:

[0104] Melt flow rate determination: The test was conducted using a CEAST MF20 melt flow rate tester from Instron Corporation, USA. The test temperature was 230℃, the load weight was 2.16kg, and the preheating time was 4min.

[0105] Gel permeation chromatography (GPC): The test was performed on an Anglienti PL-GPC50 gel permeation chromatograph (USA), and the processing software was GPC offline. During the test, the mobile phase was hexafluoroisopropanol containing 5 mmol / L sodium trifluoroacetate, the flow rate was 1 mL / min, the column temperature was 40℃, the injection volume was 100 μL, the standard was PMMA, and the sample concentration was 1 mg / mL.

[0106] Melt strength test: The test was conducted on a Rosand RH7 high-pressure capillary rheometer from Malvern Panaco Co., Ltd. in China. The nozzle size was Haul Off (diameter: 2.0 mm, length: 20 mm), the barrel pusher speed was 15 mm / min, the test temperature was 235℃, the initial drawing speed was 3 mm / min, the final drawing speed was 50 mm / min, and the acceleration time was 3 min.

[0107] Multilayer film thickness testing: Images were taken using a Japanese HIROX KH-1300M 3D video microscope. After fixing the film with a self-made film clamp, it was cut with a blade, and the cross-section was observed. The thickness was measured using the software's built-in measurement tool at a magnification of 400x.

[0108] Interlayer peel strength test: Referring to Method A in GB 8808-1988, the multilayer film was cut into strips 15mm wide and 200mm long. After peeling off 50mm of one section, a tensile test was performed on a 3344 material testing machine from Instron Corporation in the United States. The unpeeled part was T-shaped with the tensile direction, and the tensile rate was 300mm / min.

[0109] Heat seal strength: Refer to QB / T2358-1998, the sample width is 15mm, the clamp spacing is 50mm, and the test speed is 300mm / min.

[0110] Oxygen barrier performance testing: The test was conducted using a MOCON OX-TRAN Model 2 / 22 oxygen transmission rate tester. Following international standard ISO 15105-2, the film sample was cut using a circular sampler, and the thickness was measured. High-vacuum sealant was applied along the sealing ring on one side of the sample, and the sample was fixed in the test chamber. The test temperature was 23℃, and the relative humidity (RH) was 65%. The oxygen transmission volume per unit area per unit time was recorded to calculate the oxygen transmission coefficient (OP). The oxygen transmission coefficient was then divided by the sample thickness to calculate the oxygen transmission rate (OTR).

[0111] Water vapor barrier performance testing: A MOCON PERMATRAN-W Model 3 / 61 water vapor transmission rate tester was used. Following international standard ISO 15106-2, the infrared detector method was employed to test the water vapor barrier performance of the film samples. Circular film samples were collected using a sampler, and their thickness was measured. The test temperature was 38℃, humidity was 90%, and pressure was 1 standard atmosphere (atm). The test duration was 24 hours. The mass of water vapor transmitted per unit volume and unit area was recorded to calculate the water vapor transmission coefficient (WVP). The water vapor transmission coefficient was then divided by the sample thickness to calculate the water vapor transmission rate (WVTR).

[0112]

Manufacturing Example 1

[0113] The following components were mixed uniformly at a mass ratio of 100:0.1:0.015:0.035:0.3:0.6: glycol, antioxidant 1010, and antioxidant 626, and then extruded and granulated using a Labtech parallel co-rotating twin-screw extruder (screw diameter: 20 mm, L / D ratio: 40). The extruder consisted of 11 sections from the feed inlet to the die, numbered 1-11. Section 1 only served as the feeding section and did not require heating. The temperatures of sections 2-11 were 160℃, 200℃, 220℃, 220℃, 220℃, 220℃, 230℃, 235℃, and 240℃, respectively. The raw material particles were collected and characterized for molecular weight using GPC. The weight-average molecular weight of the polyglycolic acid with a multimodal molecular weight distribution was 268,200 g / mol, and the molecular weight distribution index was 2.1. Among them, the weight-average molecular weight of the graft copolymer was 2,011,500 g / mol, the molecular weight distribution index was 1.1, and the mass percentage was 7.4%. The weight-average molecular weight of the homopolymer was 199,200 g / mol, the molecular weight distribution index was 1.6, and the mass percentage was 92.6%. The melt flow rate of the polyglycolic acid particles with a multimodal molecular weight distribution was tested to characterize its melt flow rate at the processing temperature, which was 5.4 g / 10 min. The melt strength at 235 °C was 10 cN, and the melt fracture elongation was 320 mm / s.

[0114]

Manufacturing Example 2

[0115] The synthesis method is similar to that of Manufacturing Example 1, except that the ethylene-vinyl alcohol copolymer (EVOH) is replaced with polyvinyl alcohol (PVA), and the ratio of glycolide, stannous octoate, polyvinyl alcohol (PVA), 1,4-butanediol, antioxidant 1010 and antioxidant 626 is set to 100:0.1:0.02:0.04:0.5:0.3. Multimodal polyglycolic acid (PEG) particles were collected and characterized by molecular weight using GPC. The weight-average molecular weight of the PEG was 204,500 g / mol, and the molecular weight distribution index (MDI) was 1.8. The PEG-PEG graft copolymer had a weight-average molecular weight of 1,430,800 g / mol, a MDI of 1.1, and accounted for 3.8% of the total mass. The PEG homopolymer had a weight-average molecular weight of 173,800 g / mol, a MDI of 1.6, and accounted for 96.2% of the total mass. Melt flow rate tests were performed on the PEG particles to characterize their melt flow rate at the processing temperature, which was 9.9 g / 10 min. The melt strength at 235 °C was 20 cN.

[0116] [Comparison with Manufacturing Example 1]

[0117] The synthesis method was similar to that of Manufacturing Example 1, except that no macromolecular initiator was added, and the ratio of glycolide, stannous octoate, 1,4-butanediol, antioxidant 1010, and antioxidant 626 was changed to 100:0.1:0.5:0.3:0.6. Polyglycolic acid particles were collected and characterized for molecular weight using GPC. The polyglycolic acid exhibited only one peak, with a number-average molecular weight of 124,900 g / mol, a weight-average molecular weight of 197,800 g / mol, and a molecular weight distribution index of 1.58. Melt flow rate tests were performed on the polyglycolic acid particles to characterize its melt flow rate at the processing temperature, which was 26.2 g / 10 min. The melt strength at 235 °C was 3 cN.

[0118] Comparative Example 1

[0119] Commercially available pure polyglycolic acid (PGA) was purchased from KEBIN-Prak GmbH in the Netherlands as GMP-grade homopolymer of glycolide, with an average intrinsic viscosity of 1.2 dl / g.

[0120] The raw material ratios for the above embodiments and comparative examples are shown in Table 1.

[0121] Table 1

[0122]

[0123] Note: The proportions in the table above are based on 100 parts by weight (phr) of glycolide monomer.

[0124]

Example 1

[0125] like Figure 3 As shown, a multilayer film was prepared using a Labtech LCR-33HD multilayer co-extrusion blown film mill. The protective layer used low-density polyethylene (Dow LDPE 310E), and the adhesive layer used maleic anhydride-grafted linear low-density polyethylene (Dow BYNEL). TM The polyglycolic acid (PEG) with a multi-peak molecular weight distribution used in Example 1 (41E687B) and the barrier layer were added to the hoppers of three single-screw extruders (10a, 10b, and 10c), respectively. After melting and extrusion, the PEG was pressurized by a melt pump, distributed by a co-extrusion distributor, and then extruded from a blown film die. Finally, after stretching, cooling, drawing, and winding, the high-barrier PEG multilayer composite film was obtained. The screw speeds of the three single-screw extruders (20a, 20b, and 20c) were 58 rpm, 42 rpm, and 25 rpm, respectively. The extruder, melt pump, and die temperatures were set to 180°C, 230°C, 230°C, and 230°C, respectively. The melt pump speeds of the three melt pumps (30a, 30b, and 30c) were 30 rpm, 15 rpm, and 10 rpm, respectively, and the melt pump outlet pressures were 120 bar, 110 bar, and 47 bar, respectively. The total film thickness was approximately 80 μm.

[0126]

Example 2

[0127] The preparation method was similar to that of Example 1, but the barrier layer material was changed to polyglycolic acid with a multi-peak molecular weight distribution, as used in Example 2. The screw speeds of the three single-screw extruders (20a, 20b, and 20c) were set to 50 rpm, 42 rpm, and 35 rpm, respectively, and the speeds of the three melt pumps (30a, 30b, and 30c) were set to 30 rpm, 15 rpm, and 25 rpm, respectively. The melt pump outlet pressures were 120 bar, 110 bar, and 58 bar, respectively. The total film thickness was approximately 88 μm.

[0128]

Example 3

[0129] The preparation method was similar to that in Example 2, but the screw speeds of the three single-screw extruders (20a, 20b, and 20c) were set to 40 rpm, 40 rpm, and 30 rpm, respectively, and the speeds of the three melt pumps (30a, 30b, and 30c) were set to 15 rpm, 15 rpm, and 5 rpm, respectively. The melt pump outlet pressures were 102 bar, 97 bar, and 58 bar, respectively. The total film thickness was approximately 50 μm.

[0130]

Example 4

[0131] The preparation method was similar to that in Example 2, but the screw speeds of the three single-screw extruders (20a, 20b, and 20c) were set to 40 rpm, 40 rpm, and 20 rpm, respectively, and the speeds of the three melt pumps (30a, 30b, and 30c) were set to 15 rpm, 15 rpm, and 3 rpm, respectively. The melt pump outlet pressures were 102 bar, 99 bar, and 51 bar, respectively. The total film thickness was approximately 50 μm.

[0132]

Example 5

[0133] The preparation method was similar to that in Example 2, but the screw speeds of the three single-screw extruders (20a, 20b, and 20c) were set to 40 rpm, 20 rpm, and 20 rpm, respectively, and the speeds of the three melt pumps (30a, 30b, and 30c) were set to 15 rpm, 15 rpm, and 1 rpm, respectively. The melt pump outlet pressures were 95 bar, 62 bar, and 39 bar, respectively. The total film thickness was approximately 80 μm.

[0134] Comparative Example 2

[0135] The preparation method is similar to that of Example 1, but the barrier layer material is changed to polyglycolic acid in Comparative Example 1. However, due to the poor melt performance (melt strength and melt toughness) of Comparative Example 1, the film bubble is easy to break and thus cannot be blown continuously.

[0136] Comparative Example 3

[0137] The preparation method is similar to that of Example 1, but without the barrier layer. That is, low-density polyethylene (Dow LDPE 310E) is used instead of the polyglycolic acid obtained in Example 1 and placed in a 10c hopper, while other process conditions remain unchanged.

[0138] Comparative Example 4

[0139] The preparation method is similar to that of Example 1, but without the adhesive layer; that is, low-density polyethylene (Dow LDPE 310E) is used instead of maleic anhydride-grafted linear low-density polyethylene (Dow BYNEL). TM 41E687B) is placed into hopper 10b, with other process conditions remaining unchanged.

[0140] Comparative Example 5

[0141] The polyglycolic acid particles obtained in Manufacturing Example 1 were processed using a Dr. Collin E30P single-screw extruder (screw diameter 30 mm, L / D ratio 30:1) and a Dr. Collin BL 180 / 600 blown film extruder. After melting, extrusion, stretching, cooling, drawing, and winding, the single-layer polyglycolic acid film was obtained. The extruder screw speed was 50 rpm, and the extruder and die temperatures were set to 180°C, 230°C, 230°C, and 230°C, respectively. The film thickness was 24 μm.

[0142]

Example 1

[0143] Interlayer peel force tests were conducted on some of the embodiments and Comparative Example 4. The width of the strip was 15 mm. The test results are listed in Table 2.

[0144] Table 2

[0145] Interlayer peel force (N / 15mm) Example 1 3.61 Example 2 1.55 Example 3 1.99 Example 4 2.06 Comparative Example 4 ～0.1

[0146] Comparing the interlayer peel strength of each embodiment in Table 2 with that of Comparative Example 4 (multilayer film without adhesive layer), it can be seen that the interlayer adhesion is significantly improved after the addition of adhesive layer, and the interlayer peel strength is increased by at least one order of magnitude, reaching a maximum of 3.61 N / 15 mm, making it difficult for the layers to peel off.

[0147]

Example 2

[0148] The heat seal strength of the examples and Comparative Example 5 was tested, with a strip width of 15 mm. The test results are listed in Table 3.

[0149] Table 3

[0150] Heat seal strength (N / 15mm) Example 1 ≥6.63 Example 2 ≥5.63 Example 3 ≥5.26 Example 4 ≥5.81 Example 5 ≥6.66 Comparative Example 5 Unable to heat seal

[0151] Note: Since the heat seal strength is greater than the interlayer peel force, the actual separation between the layers during the test makes it impossible to obtain an accurate heat seal strength. Therefore, the maximum load is used as the lower limit of the heat seal strength.

[0152] As shown in Table 3, the use of polyolefin as the outer layer in this invention not only protects the polyglycolic acid barrier layer, but also significantly improves the heat-sealing performance of the multilayer film, from being completely unsealable to having a heat-sealing strength of at least 5N / 15mm.

[0153]

Example 3

[0154] The barrier performance of the examples and comparative examples was tested. The oxygen barrier performance was tested at a temperature of 23°C and a relative humidity (RH) of 65%. The water vapor barrier performance was tested at a temperature of 38°C and a relative humidity of 90%. The pressure was 1 standard atmosphere (atm), and the test time was 24 hours. The test results are shown in Table 4.

[0155] Table 4

[0156]

[0157] As shown in Table 4, the oxygen and water barrier properties of each embodiment are excellent. The water vapor transmission rate is comparable to that of the polyethylene multilayer film (Comparative Example 3), while the oxygen transmission rate is significantly lower than that of the polyethylene multilayer film (Comparative Example 3), reaching as low as 1.52 cm. 3 / (m 2 The oxygen barrier properties (days atm) are close to those of pure polyglycolic acid. In other words, the multilayer composite membrane of this invention effectively enhances the oxygen barrier properties of the multilayer membrane by utilizing the high barrier properties of polyglycolic acid with a multi-peak molecular weight distribution, while simultaneously leveraging the hydrophobic and water-blocking properties of the polyolefin itself to protect the polyglycolic acid from contact with water, thereby slowing down its degradation rate and extending its shelf life and service life.

[0158] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

[0159] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0160] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0161] The endpoints and any values ​​of the ranges disclosed in this application are not limited to the precise ranges or values; such ranges or values ​​should be understood to include values ​​close to them. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In principle, various technical solutions can be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0162] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

[0163] Furthermore, any implementation described herein can be freely combined with one or more other implementations described herein, and the resulting technical solutions or technical ideas shall be regarded as part of the original disclosure or original record of the present invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider the combination to be obviously unreasonable.

Claims

1. A high-barrier polyglycolic acid multilayer composite film, comprising a barrier layer, a protective layer, and an adhesive layer; wherein, The protective layer is at least the outermost layer, the adhesive layer is at least located between the barrier layer and the protective layer, and the barrier layer contains at least polyglycolic acid with a multi-peak molecular weight distribution; The multi-peak molecular weight distribution polyglycolic acid contains polyglycolic acid graft copolymers and polyglycolic acid homopolymers; wherein, the main chain of the polyglycolic acid graft copolymer is an ethylene-vinyl alcohol copolymer segment and / or a polyvinyl alcohol segment, and the side chain is a glycolic acid monomer derivative, a glycolic acid oligomer, or a glycolic acid polymer. The adhesive layer is a polyolefin graft copolymer or an ethylene-polar monomer copolymer.

2. The high-barrier polyglycolic acid multilayer composite film according to claim 1, characterized in that: The barrier layer has at least one layer, with a single layer thickness of 1-50 micrometers; and / or, The protective layer has at least two layers, with each layer having a thickness of 3-80 micrometers; and / or, The adhesive layer has at least two layers, with each layer having a thickness of 0.5 to 20 micrometers; and / or, The total thickness of the multilayer composite film is 8~250 micrometers.

3. The high-barrier polyglycolic acid multilayer composite film according to claim 1, characterized in that: The protective layer is a polyolefin; and / or, The polyolefin graft copolymer or ethylene-polar monomer copolymer includes any one or more mixtures of polyethylene grafted with maleic anhydride, polyethylene grafted with acrylic acid, polyethylene grafted with methyl methacrylate, polypropylene grafted with maleic anhydride, ethylene-acrylic acid copolymer, and ethylene-methacrylic acid copolymer.

4. The high-barrier polyglycolic acid multilayer composite film according to claim 3, characterized in that: The polyolefins include any one or more mixtures of low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, polypropylene, ethylene-propylene-nonconjugated diene copolymer, metallocene polyethylene, metallocene polypropylene, poly-1-butene and its derivatives, and cyclic olefin polymers.

5. The high-barrier polyglycolic acid multilayer composite film according to claim 1, characterized in that: The multimodal molecular weight distribution of the polyglycolic acid has a weight-average molecular weight of 200,000-1,500,000 g / mol; and / or, The multi-peaked molecular weight distribution polyglycolic acid has a molecular weight distribution index of 1.5-20; and / or, the multi-peaked molecular weight distribution polyglycolic acid composition has at least two molecular weight distribution peaks.

6. The high-barrier polyglycolic acid multilayer composite film according to claim 5, characterized in that: The multimodal molecular weight distribution of the polyglycolic acid has a weight-average molecular weight of 250,000-500,000 g / mol; and / or, The molecular weight distribution index of the polyglycolic acid with the multi-peak molecular weight distribution is 2-3.

5.

7. The high-barrier polyglycolic acid multilayer composite film according to claim 1, characterized in that: The multi-peak molecular weight distribution polyglycolic acid has a melt flow rate of no more than 20 g / 10 min at 230 °C / 2.16 kg; and / or, The multi-peak molecular weight distribution polyglycolic acid has a melt strength of not less than 6 cN at 235°C.

8. The high-barrier polyglycolic acid multilayer composite film according to claim 7, characterized in that: The multi-peak molecular weight distribution polyglycolic acid exhibits a melt flow rate of 0.5-10 g / 10 min at 230°C / 2.16 kg; and / or, The multi-peak molecular weight distribution polyglycolic acid has a melt strength of not less than 8 cN at 235°C.

9. The high-barrier polyglycolic acid multilayer composite film according to any one of claims 1 to 8, characterized in that: The oxygen permeability of the multilayer composite membrane is no greater than 100 cm³ under the conditions of 23±0.5℃ and 65%±5% relative humidity. 3 / (m 2 (day / atm); and / or, The water vapor transmission rate of the multilayer composite membrane is no greater than 30 g / (m²) under the conditions of 38±0.5℃, relative humidity 90%±5%, and 1 standard atmosphere. 2 ·day·atm).

10. The high-barrier polyglycolic acid multilayer composite film according to claim 9, characterized in that: The oxygen permeability of the multilayer composite membrane is no greater than 30 cm³ under the conditions of 23±0.5℃ and 65%±5% relative humidity. 3 / (m 2 (day / atm); and / or, The water vapor transmission rate of the multilayer composite membrane is no greater than 15 g / (m²) under the conditions of 38±0.5℃, relative humidity 90%±5%, and 1 standard atmosphere. 2 ·day·atm).

11. The high-barrier polyglycolic acid multilayer composite film according to any one of claims 1 to 8, characterized in that: The heat-sealing strength of the multilayer composite film is not less than 3 N / 15 mm; and / or, the interlayer peel strength of the multilayer composite film is not less than 0.5 N / 15 mm.

12. The high-barrier polyglycolic acid multilayer composite film according to claim 11, characterized in that: The heat-sealing strength of the multilayer composite film is not less than 5 N / 15 mm; and / or, the interlayer peel strength of the multilayer composite film is not less than 1.5 N / 15 mm.

13. A method for preparing a high-barrier polyglycolic acid multilayer composite film according to any one of claims 1-12, comprising: The barrier layer (polyglycolic acid with a multi-peak molecular weight distribution), the protective layer (polyolefin), and the adhesive layer (polyolefin graft copolymer) are separately added to a screw extruder and melted, compressed, and extruded. Each layer is then individually formed into a film through a casting or blown film die. These films are then combined using hot pressing to create the high-barrier polyglycolic acid multilayer composite film. Alternatively... The barrier layer is made of polyglycolic acid with a multi-peak molecular weight distribution, the protective layer is made of polyolefin, and the adhesive layer is made of polyolefin graft copolymer. Each of these layers is added to at least three different screw extruders. After melting and compression, each layer is extruded through a co-extrusion distributor and a film forming die, cooled, stretched, and wound up to obtain the high-barrier polyglycolic acid multilayer composite film.

14. The method for preparing a high-barrier polyglycolic acid multilayer composite film according to claim 13, characterized in that: The screw extruder is a single-screw extruder or a twin-screw extruder; and / or, the film-forming die is a blown film die or a cast film die; and / or, The preparation method involves a unidirectional stretching unit before winding.

15. The application of a high-barrier polyglycolic acid multilayer composite film according to any one of claims 1-12 or a high-barrier polyglycolic acid multilayer composite film prepared by any one of claims 13-14 in the fields of biodegradable packaging bags, pharmaceutical packaging films, food preservation films, agricultural films, and barrier containers.

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