Nanometer oxygen barrier functional master batch for packaging bottle outer surface and preparation method thereof

Abstract

This invention discloses a nano-oxygen barrier functional masterbatch for the outer surface of packaging bottles and its preparation method, belonging to the field of polymer packaging material technology. The method involves first homogenizing and ultrasonically dispersing nisin, glycerol, montmorillonite K10, and silver nanoparticles in an aqueous phase, then adding nanocellulose to obtain a hybrid oxygen barrier suspension. Next, polylactic acid, polypropylene carbonate, and triglycidyl isocyanate are melted and laterally injected into the suspension. The mixture is then subjected to twin-screw extrusion, vacuum devolatilization, and granulation to obtain the masterbatch. This masterbatch can form an oriented "brick-and-mortar" barrier structure in the matrix, enhancing interfacial bonding and the stability of the nano-silver, significantly improving the oxygen barrier, moisture barrier, peel strength, and long-lasting antibacterial properties of the packaging outer surface.

Description

Technical Field

[0001] This invention belongs to the field of polymer packaging materials technology, specifically, it relates to a nano-oxygen barrier functional masterbatch for the outer surface of packaging bottles and its preparation method. Background Technology

[0002] With the rapid development of the packaging industry, the environmental problems caused by the difficulty in degradation of traditional general-purpose plastics such as polypropylene (PP) and polyethylene terephthalate (PET) have become increasingly prominent. In recent years, bio-based biodegradable polymers, represented by polylactic acid (PLA) and polypropylene carbonate (PPC), have gradually become a research hotspot for replacing traditional plastics. However, the molecular chain arrangement characteristics and large free volume of these polymers result in poor natural barrier properties against oxygen and water vapor, with typically high oxygen and water vapor permeability, making it difficult to meet the packaging requirements of high-value-added food, pharmaceuticals, or sensitive chemicals with stringent shelf-life requirements.

[0003] To improve the barrier properties of polymer matrices, existing technologies often employ the method of doping resins with two-dimensional sheet-like inorganic nanoparticles (such as montmorillonite and graphene), aiming to construct a "zigzag diffusion path" within the matrix to block the permeation of gas molecules. However, in actual industrial processing, nanoscale inorganic powders, due to their extremely high specific surface energy, are prone to severe electrostatic agglomeration and interfacial debonding in traditional dry blending or direct melt extrusion flow fields, forming macroscopic stress concentration points. This non-uniform dispersion not only fails to effectively extend the permeation path of gas molecules but also induces interfacial micropores around the agglomerates, leading to a dual deterioration in the mechanical peel strength and barrier properties of the material system.

[0004] Furthermore, to address the functional requirement of modern packaging to inhibit the growth of microbial films, the conventional approach is to incorporate inorganic antibacterial building blocks such as silver nanoparticles through blending. However, zero-dimensional metal nanoparticles are highly susceptible to Oswald ripening under the strong shear and thermodynamic forces of high-temperature melt extrusion, leading to irreversible macroscopic aggregation and a significant loss of specific surface area. Simultaneously, inorganic particles lacking steric anchoring are prone to unexpected migration within the polymer network, resulting in an explosive release of silver ions and making it difficult to maintain long-lasting antibacterial activity.

[0005] In resin matrix structure design, blending polylactic acid (PLA), which has a certain degree of crystalline rigidity, with amorphous polypropylene carbonate (PPC), which has polar carbonate bonds, is a conventional method for adjusting free volume. However, the two have inherent thermodynamic interfacial compatibility defects, and simple physical blending easily leads to large-scale phase separation. Without in-situ chemical bonding, the interface between the two phases easily becomes a channel for microscopic gas leakage; furthermore, the high polarity of PPC readily induces hydrogen bonding adsorption and swelling dissolution effects on water vapor, severely weakening the water barrier function of the film.

[0006] In summary, overcoming the thermodynamic agglomeration tendency of multidimensional nanofillers (zero-dimensional metals, one-dimensional rigid phases, and two-dimensional layered silicates) in polymer melts and achieving their highly parallel orientation and defect-free arrangement in the extrusion flow field; eliminating phase separation voids in binary resin blend systems; and achieving effective spatial anchoring of nano-antibacterial units under harsh high-temperature thermal processing conditions, thereby preparing packaging outer layer functional masterbatches with extreme oxygen barrier, moisture barrier, and long-lasting antibacterial properties at low cost, are key technical bottlenecks that urgently need to be solved in the field of polymer barrier packaging materials. Summary of the Invention

[0007] To address the technical bottlenecks in existing technologies, such as the large inherent free volume of biodegradable packaging materials (e.g., polylactic acid / polypropylene carbonate blends leading to poor oxygen and moisture barrier properties), the tendency of multi-dimensional nanofillers to electrostatically aggregate and induce stress defects during traditional dry blending and melting, and the susceptibility of inorganic antibacterial units (e.g., silver nanoparticles) to Oswald curing (agglomeration and inactivation) during high-temperature, high-shear processing, this invention provides a nano-oxygen barrier functional masterbatch for the outer surface of packaging bottles and its preparation method. This invention achieves highly oriented, defect-free dispersion of multi-scale nanofillers in a polymer matrix through the synergy of liquid-phase pre-dispersion assisted lateral extrusion and bio-crosslinking network anchoring technology, thus constructing a hierarchical barrier.

[0008] The present invention adopts the following technical solution: a method for preparing nano-oxygen barrier functional masterbatch for the outer surface of packaging bottles, comprising the following steps: Step S1: adding nisin and glycerol to water and stirring to form a hydrated solution; mixing montmorillonite K10 dispersion with the hydrated solution and homogenizing it, then adding silver nanoparticles for ultrasonic dispersion to obtain a first composite dispersion slurry; Step S2: providing nanocellulose and mixing it into the first composite dispersion slurry to form an oxygen barrier functional suspension of multi-dimensional scale hybrid filler; Step S3: mixing polylactic acid and polypropylene carbonate as a degradable carrier resin and melting it, injecting the oxygen barrier functional suspension into the carrier resin melt for composite processing; controlling the exhaust parameters to remove moisture and then extruding and granulating to obtain nano-oxygen barrier functional masterbatch.

[0009] Preferably, in step S1, the homogenization treatment speed is set to 2000-4000 rpm and the time is 20-40 min; the ultrasonic dispersion frequency is set to 40-50 kHz, the operation mode is double cycle and the interval between single cycles is 10-20 s; the mass percentage of nisin and montmorillonite K10 satisfies the following: 1-7 parts by mass of montmorillonite K10 and 1.5-3 parts by mass of nisin are dispersed in every 100 parts by mass of water.

[0010] Preferably, in step S2, the nanocellulose is nanocellulose with a surface rich in carboxyl groups; the anionic carboxyl groups on the surface of the nanocellulose undergo a proton transfer effect with the cationic amino groups of nisin in the system of step S1 to form an electrostatic complex network.

[0011] Preferably, in step S3, the mass ratio of polylactic acid to polypropylene carbonate in the carrier resin is in the range of (50:50) to (80:20); and 1%-3% of the total mass of triglycidyl isocyanurate is added during the melting stage of the carrier resin.

[0012] Preferably, the extrusion compounding process in step S3 uses a co-rotating twin-screw extruder. The oxygen barrier functional suspension is injected laterally under high pressure in the self-compression section and the water and glycerol are removed in the vacuum exhaust section. Under the shearing and stretching action of the screw, the montmorillonite K10 sheets and cellulose nanocrystals are forced to form a two-dimensional layered orientation array parallel to the flow field direction in the carrier resin.

[0013] Preferably, in the preparation process, the isoelectric point of the silver nanoparticles forms an electric double layer adsorption boundary with the negatively charged surface region of the nanocellulose and montmorillonite K10; the amount of silver nanoparticles added is limited to five parts per million to five parts per hundred thousand of the mass of the montmorillonite K10.

[0014] Preferably, when preparing the masterbatch and coating it for use, a dense inorganic silica layer with a thickness of 5-50 nanometers is grown on the outer surface of the formed coating using plasma-assisted chemical vapor deposition technology.

[0015] Preferably, before the nano-oxygen barrier functional masterbatch is co-extruded and attached to the outer surface of the polypropylene of the packaging bottle, the surface of the polypropylene is subjected to oxygen plasma bombardment modification, with the exposure time parameter set to 40-80s and the plasma power set to 5-10W.

[0016] Preferably, by mass percentage, the nanocellulose accounts for 3%-5% of the total amount of the carrier resin, and the montmorillonite K10 accounts for 1%-5% of the total amount of the carrier resin; the amorphous regions of polylactic acid macromolecules are encapsulated by layered montmorillonite K10 to achieve heterogeneous nucleation and confined crystallization.

[0017] A nano-oxygen barrier functional masterbatch for the outer surface of packaging bottles, wherein the nano-oxygen barrier functional masterbatch for the outer surface of packaging bottles is obtained by the preparation method described above.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: (1) It is beneficial to improve the oxygen and moisture barrier properties of the material. The present invention adopts a combination of aqueous pre-dispersion and liquid-phase assisted lateral extrusion, so that montmorillonite K10 and nanocellulose can be better dispersed and oriented in the resin matrix, which is beneficial to form a more continuous barrier structure inside the material, prolonging the permeation path of oxygen and water vapor, thereby reducing the oxygen permeability and water vapor permeability of the outer surface of the packaging. (2) It is beneficial to improve the interfacial compatibility and interlayer bonding strength of the system. The present invention introduces triglycidyl isocyanate as a reactive compatibilizer in the polylactic acid / polypropylene carbonate system, which can improve the interfacial compatibility between the two resins and reduce the interfacial defects and micropores caused by phase separation; at the same time, when applied to the outer surface of the packaging bottle, it is beneficial to improve the bonding stability between the functional layer and the substrate, thereby improving the peel strength and reliability of use. (3) It is beneficial to improve the dispersion stability and antibacterial durability of the antibacterial components. This invention utilizes the synergistic effect between nisin, nanocellulose, montmorillonite K10, and silver nanoparticles to enhance the dispersion and anchoring effect of silver nanoparticles in the system, reduce their tendency to agglomerate during processing, thereby helping to maintain antibacterial activity and improve the long-term antibacterial performance of packaging materials. (4) It is beneficial to balance functional performance and environmental protection properties of materials. This invention selects polylactic acid, polypropylene carbonate, and nanocellulose to construct a functional system. While improving the barrier properties, interfacial bonding properties, and antibacterial properties of packaging materials, it also takes into account the bio-based or biodegradable characteristics of the material system, which has good application prospects. Attached Figure Description

[0019] Figure 1 This is the infrared spectrum of the nano-oxygen barrier functional masterbatch prepared in Example 1. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to specific embodiments. However, these embodiments are only for illustrating the present invention and do not constitute any limitation on the scope of protection of the present invention. For those skilled in the art, simple deductions or substitutions made without departing from the concept of the present invention should be considered as falling within the scope of protection defined by the claims of the present invention. In the present invention, unless otherwise specified, intermediate values ​​are used for undefined parameter ranges by default.

[0021] Unless otherwise stated, all raw materials used in this invention are commercially available, and industrial grade or analytical grade specifications can be selected according to actual production needs. Polylactic acid is a commercially available polylactic acid resin (CAS No.: 26100-51-6, weight-average molecular weight approximately 150,000, from Nature). The following materials were provided by Works Corporation: polypropylene carbonate (CAS No. 25511-85-7, weight-average molecular weight approximately 100,000, provided by Changchun Institute of Applied Chemistry, Chinese Academy of Sciences); triglycidyl isocyanurate (TGIC, CAS No. 2451-62-9, purity not less than 99%); montmorillonite K10 was acid-activated montmorillonite (CAS No. 1318-93-0, interlayer spacing approximately 1.5 nm); silver nanoparticles were spherical silver powder with an average particle size of approximately 20 nm (CAS No. 7440-22-4); nanocellulose was carboxylated modified nanocellulose TL-001, sourced from Nanjing Tianlu Nanotechnology Co., Ltd., with a diameter of 4-10 nm and a length of 1-3 μm; nisin (CAS No. 1414-45-5, potency not less than 1000 IU / mg); and glycerol (CAS No. 56-81-5) was of analytical grade. Deionized water (CAS No.: 7732-18-5) was prepared online using laboratory ultrapure water equipment.

[0022] I. Examples and Comparative Examples (I) Example 1 (Preferred Implementation) This embodiment provides the preferred basic formulation and process conditions of the present invention, covering all key technical features. The masterbatch obtained in this embodiment is subsequently used for coating the outer surface of the bottle. After synergistic effect with the silica dense layer, typical high barrier and antibacterial properties can be obtained.

[0023] 1. Step (1): Preparation of the first composite dispersion slurry In a glass reactor equipped with a water bath thermostat, the water bath temperature was controlled at 40℃. Deionized water, glycerol, and nisin were added sequentially, and the pH was adjusted to 5 (using sodium hydroxide). Magnetic stirring was started, and the stirring speed was set to 600 rpm for 30 minutes to ensure complete dissolution of the nisin and the formation of a homogeneous hydrated system. Subsequently, under continuous stirring, a pre-prepared aqueous dispersion of montmorillonite K10 was slowly added dropwise, maintaining a stable temperature of 40℃ within the reactor during the addition. After the addition was complete, the system was transferred to a high-shear homogenizer and homogenized at 3000 rpm for 30 minutes to promote further exfoliation and fine dispersion of the montmorillonite sheets. Then, a pre-prepared aqueous dispersion of silver nanoparticles was added, and ultrasonic dispersion was performed using an ultrasonic cell disruptor at a frequency of 45 kHz, employing an intermittent mode of 15 seconds of operation followed by 15 seconds of rest, for a total ultrasonic time of 20 minutes, resulting in a homogeneous and stable first composite dispersion slurry.

[0024] Table 1. Mass dosage of each component in step (1) of Example 1 2. Step (2): Preparation of nanocellulose composite suspension Nanocellulose (carboxylated modified nanocellulose TL-001) was directly added to the first composite dispersion slurry and dispersed by mechanical stirring at room temperature. The stirring speed was set to 800 r / min, and the stirring time was 60 min. As stirring proceeded, the carboxyl groups on the surface of the nanocellulose interacted electrostatically with the protonated amino groups on the nisin molecules, gradually forming a spatially interconnected complex network. At the same time, this facilitated the stable anchoring of silver nanoparticles on the montmorillonite surface, thus obtaining an oxygen-barrier suspension with a multi-scale hybrid structure.

[0025] 3. Step (3): Masterbatch melt blending and granulation Weigh out polylactic acid (CAS No.: 26100-51-6, density: 1.33 g / cm³). 3 Polypropylene carbonate (CAS No.: 25511-85-7, density: 1.23 g / cm³) 3 The resin mixture was mixed with triglycidyl isocyanurate according to the mass ratio in Table 2. The resin mixture was continuously fed into the main feed port of a co-rotating twin-screw extruder. The extruder used was a Coperion ZSK 26 model with a length-to-diameter ratio of 40:1. The temperatures of each heating zone were set sequentially from front to back to 150℃, 160℃, 170℃ and 180℃ to form a temperature gradient. After the resin was basically melted in the machine, the oxygen barrier suspension obtained in step (2) was injected into the side injection port of the extruder compression section through a horizontal flow pump at a stable flow rate. This ensured that the resin near the injection point was in the high melt viscosity zone, so that the liquid phase carrier could be rapidly vaporized under the high temperature shear field and promote further dispersion and orientation of the nanofiller.

[0026] A two-stage vacuum exhaust section is installed at the tail end of the extruder, with the vacuum level controlled at approximately -0.09 MPa, to fully remove residual moisture and some volatile glycerol from the system. After being cooled in a water bath, the extruded material is dried by an air knife and pelletized to obtain the nano-oxygen barrier functional masterbatch (2-3 mm in diameter and 3-5 mm in length) of Example 1 of this invention. Its infrared spectrum is shown below. Figure 1 As shown.

[0027] Table 2. Mass amounts of each component in steps (2) and (3) of Example 1 4. Step (4): Co-extrusion coating and plasma / CVD modification Commercial polypropylene (PP) bottles were selected as the substrate. The bottles were placed in a vacuum plasma treatment device, oxygen was introduced, the gas flow rate was adjusted to 50 sccm, the plasma radio frequency power was set to 7.2W, and the treatment time was 60s. This allowed the PP surface to obtain a certain density of oxygen-containing polar groups, thereby improving the interfacial adhesion between the PP and subsequent coatings.

[0028] After plasma treatment, a co-extrusion process was used to co-extrude the functional masterbatch obtained in Example 1 with the PP substrate, so that the molten layer of the functional masterbatch was uniformly coated on the outer surface of the bottle, and the coating thickness was controlled at about 20 μm. The parameters of co-extrusion molding were as follows: temperature of each zone of the extruder (from the feeding section to the die): Zone 1 (feeding section): 160℃, Zone 2: 170℃, Zone 3: 175℃, Zone 4 (metering section): 180℃, die temperature: 185℃, PP bottle preheating temperature: 80℃, die outlet pressure: 10MPa. After cooling and shaping, a dense inorganic layer of silica with a thickness of about 30 nm was deposited on the outer surface of the coating using plasma-enhanced chemical vapor deposition equipment with a silane-based organosilicon compound (hexamethyldisiloxane, CAS No.: 107-46-0) as a precursor under low temperature conditions, as the outermost barrier layer. The equipment used for the deposition operation is as follows: a radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) system (13.56MHz), equipped with a vacuum chamber, an HMDSO liquid vaporizer, a mass flow controller (MFC), and automatic thickness monitoring. Substrate temperature (bottle / coating surface): 60℃; chamber background vacuum: <5×10⁻⁶. -4 Torr. Operating pressure: 0.59 Torr; Deposition mode: continuous RF plasma; Precursor: HMDSO (hexamethyldisiloxane), introduced after liquid vaporization (temperature 50℃, Ar carrier gas). HMDSO flow rate: 1.56 ccm; Reaction gas: high-purity oxygen (99.999%); Oxygen flow rate: 20 sccm; Oxygen / HMDSO flow rate ratio ≈ 13; RF power: 140 W; Power density ≈ 0.6 W / cm³. 2 Deposition time: 20s; corresponding deposition rate ≈ 1.5nm / s. The deposition process is as follows: After coating and cooling, the functional bottle is placed into the chamber, vacuumed to the background, oxygen is introduced for pretreatment for 45s, HMDSO + oxygen is introduced simultaneously, RF power is started to the set value, deposition is carried out for 20s, the precursor is turned off, oxygen is continued to be introduced for 15s for post-treatment (stabilizing the film), vacuum is drawn, nitrogen is introduced to break the vacuum and remove the bottle.

[0029] (II) Example 2 This embodiment adjusts the carrier resin composition and reactive compatibilizer dosage based on Example 1 to investigate the effects of changes in the PLA to PPC mass ratio and TGIC content on barrier properties and interfacial bonding properties. Except for the parameters explicitly listed in Table 3, all other process conditions and operating steps are the same as in Example 1.

[0030] In Example 2, the mass of polylactic acid was adjusted to 8000.0 g, the mass of polypropylene carbonate was adjusted to 2000.0 g, and the PLA:PPC mass ratio was 80:20; the mass of triglycidyl isocyanate was adjusted to 100.0 g, accounting for 1.0% of the total resin mass. The components such as montmorillonite K10, nanocellulose, and nisin, as well as the temperature, stirring time, and extrusion conditions in each step, remained consistent with those in Example 1. This resulted in a nano-oxygen barrier functional masterbatch with a higher PLA content and a slightly lower TGIC content.

[0031] (III) Example 3 Example 3 primarily examines the overall performance of the formulation and filler dosage at a different or higher level compared to Example 1. Unless otherwise specified, the other conditions are the same as in Example 1.

[0032] Specifically, the mass of both polylactic acid (PLA) and polypropylene carbonate (PPC) was adjusted to 5000.0 g, i.e., the PLA:PPC mass ratio was 50:50; triglycidyl isocyanate was adjusted to 300.0 g, accounting for 3.0% of the total resin mass; montmorillonite K10 was adjusted to 500.0 g, accounting for approximately 5.0% of the total resin mass, and 5.0 parts per 10000.0 g of water; and nisin was adjusted to 300.0 g. The process flow, temperature, and equipment parameters for other steps were the same as in Example 1, thereby obtaining a masterbatch sample with a high montmorillonite content and a PLA:PPC mass ratio close to 1:1.

[0033] (iv) Comparative Example 1 (Key Two-Dimensional Inorganic Sheets Missing) Comparative Example 1 was used to verify the key role of the two-dimensional lamellar structure of montmorillonite in forming the "tortuous diffusion path". This comparative example completely removed montmorillonite K10, while the amounts of other components and the operating conditions of each step were kept consistent with Example 1.

[0034] In step (1), montmorillonite K10 was not added, i.e., the mass of montmorillonite was set to 0.0g, and the resulting dispersion system contained only nisin, glycerol, silver nanoparticles, and nanocellulose. Subsequently, the melt blending, granulation, and coating processes of Example 1 were repeated to obtain functional masterbatch and corresponding coating samples without two-dimensional sheet filler.

[0035] (v) Comparative Example 2 (lacking reactive compatibilizer) Comparative Example 2 was used to investigate the effect of changes in the interfacial compatibility between PLA and PPC, and between the coating and the PP substrate, on barrier properties and peel strength without the addition of TGIC. In this comparative example, triglycidyl isocyanate was not added in step (3), only the physical blending of PLA and PPC was retained, and the other raw materials and conditions were the same as in Example 1.

[0036] Specifically, the mass of polylactic acid was 6500.0 g, the mass of polypropylene carbonate was 3500.0 g, and the mass ratio of the two was 65:35; the mass of TGIC was 0.0 g. Granulation and coating were completed according to the process operation of Example 1 to obtain comparative masterbatch and coating samples without reactive compatibilizer.

[0037] (vi) Comparative Example 3 (Direct Dry Blending Extrusion) Comparative Example 3 aims to compare the differences in the dispersion state and related properties of nanofillers between the conventional dry-mix extrusion process and the liquid-phase pre-dispersion-side injection process of the present invention. The total mass of the formulation is the same as in Example 1, but instead of using aqueous pre-dispersion and high-pressure side injection, a one-time dry blending is performed.

[0038] Specifically, 300.0 g of dried montmorillonite K10, 400.0 g of nanocellulose, and 0.0060 g of silver nanoparticles were added to a high-speed mixer along with PLA, PPC, and TGIC. The mixture was stirred at approximately 800 rpm for 13 minutes to ensure macroscopic homogenization of the powders. The mixture was then fed into the main feed port of a twin-screw extruder in a single operation. The extruder model, temperature settings, and vacuum degassing conditions were the same as in Example 1, but the liquid-phase lateral injection step was omitted. The resulting masterbatch and coating samples were prepared using a conventional dry-blending method.

[0039] (vii) Comparative Example 4 (Bio-crosslinking agent missing and replaced with conventional surfactant) Comparative Example 4 was used to investigate the role of nisin in constructing a biological cross-linking network and stabilizing the dispersion of silver nanoparticles. In this comparative example, nisin was not added in step (1), but an equal mass of sodium dodecyl sulfate (SDS) was used as a conventional anionic surfactant. The amounts of other components, process steps and conditions were the same as in Example 1.

[0040] Under these conditions, the resulting dispersion system primarily relies on the physical adsorption and stabilization of inorganic fillers and silver nanoparticles by SDS, rather than forming a biocrosslinking domain with nisin-cellulose nanoparticles as the backbone. The final masterbatch and coating samples were used for subsequent comparative tests of antibacterial and barrier properties.

[0041] (viii) Summary of differences between the formulations of the examples and the comparative examples For ease of comparison, the key formulation parameters of each embodiment and comparative example are summarized in Table 3. Other raw material types and amounts not listed in Table 3 are the same as in Example 1.

[0042] Table 3 Summary of key variable parameters for Examples 1-3 and Comparative Examples 1-4 II. Test Methods and Performance Evaluation To systematically evaluate the overall performance of the various embodiments and comparative examples of the present invention, the obtained functional masterbatch was prepared into a film with a thickness of (50±2) μm by a casting process to simulate the actual state of the coating on the outer surface of the bottle. After depositing a dense layer of silicon dioxide of about 30 nm on the outside of the film, the test was performed.

[0043] 1. Oxygen Transmission Rate (OTR) Oxygen transmission rate testing was conducted according to ASTM D3985 standard using a MOCON OX-TRAN2 / 22 oxygen transmission rate tester at 23°C and 50% relative humidity. The sample was a conditioned flat film, and the test area was set according to the instrument requirements. After the equipment stabilized, the oxygen transmission rate per unit area, per unit time, and per unit pressure difference was recorded, with units expressed as cc / (m²). 2 ·day·atm).

[0044] 2. Water vapor transmission rate (WVTR) Water vapor transmission rate testing was conducted according to ASTM F1249 standard using a MOCON PERMATRAN-W3 / 33 water vapor transmission rate tester at 38℃ and 90% relative humidity. The samples were also coated films with a thickness of approximately (50±2) μm, clamped and sealed according to instrument requirements. The water vapor transmission rate during the steady-state phase was recorded, with units of g / (m²). 2 ·day).

[0045] 3. Antibacterial performance test Antimicrobial performance testing was conducted according to JIS Z 2801 standard, using *Escherichia coli* (ATCC 8739) as the representative strain. Samples were cut to specified dimensions, pretreated with ultraviolet light, and then fully contacted with the bacterial solution. The samples were then incubated at 37°C for 24 hours in a constant temperature and humidity incubator. After incubation, the logarithmic difference in bacterial count before and after contact was obtained using the plate count method, and the antimicrobial rate (%) was calculated.

[0046] 4. Peel strength test The interlayer peel strength between the coating and the PP substrate was tested according to ASTM D3330 standard, using an Instron 5965 universal testing machine for 180° peel tests. Coated samples were cut into strips of specified width, and the coating was peeled off at a constant tensile speed on the testing machine. The average peel force during the steady-state phase of the peeling process was recorded and converted to peel strength per unit width, expressed in N / cm.

[0047] The test results of each embodiment and comparative example are listed in Table 4.

[0048] Table 4. Overall performance test results of the examples and comparative examples As can be seen from Table 4, the oxygen permeability and water vapor permeability of Examples 1-3 of the present invention are significantly lower than those of the comparative examples, indicating that they have higher gas and water vapor barrier performance. At the same time, the antibacterial rate of the sample of the examples is generally close to or reaches 99.9%, and the peel strength is maintained above 8.0 N / cm, reflecting that the coating and the substrate have a high interfacial bonding force.

[0049] III. Results Analysis and Mechanism Discussion 1. Synergistic barrier and interfacial enhancement effects of two-dimensional sheet-like fillers and reactive compatibilizers Comparing Example 1 and Comparative Example 1, it can be seen that, without changing other parameters, removing montmorillonite K10 reduced the oxygen permeability from 3.2 cc / (m²). 2 The daily atm level significantly increased to 38.5 cc / (m 2 (day·atm), water vapor transmission rate increased from 1.8 g / (m 2 The level rose to 15.6 g / (m²) on day 1. 2 The barrier properties deteriorated significantly over the first day, while the antibacterial rate and peel strength changed relatively little, indicating that the two-dimensional montmorillonite sheets mainly played the role of extending the diffusion path and reducing the gas permeation rate.

[0050] Based on existing research on inorganic lamellar fillers in polylactic acid / polypropylene carbonate blends, it can be concluded that when montmorillonite is dispersed in the resin melt in the form of peeling or partial peeling, it will form a "brick" structure with a high aspect ratio along the flow direction. This forces gas molecules to bypass a large number of lamellar interfaces when passing through the coating, forming a "tortuous diffusion path", thereby significantly improving the overall barrier performance.

[0051] Comparing Example 1 and Comparative Example 2, it can be found that in the presence of montmorillonite but without the addition of TGIC, the oxygen permeability increased from 3.2 cc / (m²) 2 The daily atm level rose to 18.4 cc / (m 2(day·atm), water vapor transmission rate from 1.8 g / (m 2 The level rose to 12.1 g / (m²) on day 2. 2 The peel strength decreased significantly from 8.5 N / cm to 4.2 N / cm (day). This indicates that in the PLA / PPC blend system, simple physical blending is insufficient to obtain a uniform and stable co-continuous phase structure, and the increased interfacial defects lead to an increase in gas leakage channels.

[0052] Triglycidyl isocyanurate has multiple epoxy functional groups, which can undergo ring-opening reactions with the hydroxyl or carboxyl groups at the ends of polylactic acid and polypropylene carbonate molecular chains to achieve chain extension and cross-linking. This not only improves the compatibility between PLA / PPC, but also establishes relatively stable chemical bonds and van der Waals interactions between the coating and the PP substrate treated with oxygen plasma, thereby achieving a balance between barrier properties and peel strength.

[0053] 2. Rheological arrangement advantages of liquid phase pre-dispersion and lateral injection processes Examples 1-3 all employed an aqueous pre-dispersion, ultrasonic depolymerization, and high-pressure lateral liquid phase injection process, while Comparative Example 3 used a traditional dry-state blending extrusion method. Comparative results showed that, with essentially the same formulation, Comparative Example 3 achieved an oxygen permeability of 25.6 cc / (m²). 2 (day·atm), water vapor transmission rate is 18.3 g / (m²) 2 The antibacterial rate of Comparative Example 3 was significantly higher than that of Example 1 (day); meanwhile, the antibacterial rate of Comparative Example 3 decreased to 85.2%, and the peel strength was 5.1 N / cm, which was also lower than the corresponding value of Example 1.

[0054] This indicates that in the absence of aqueous phase ultrasonic pre-dispersion and liquid phase lateral injection, montmorillonite and silver nanoparticles are more prone to electrostatic aggregation and localized accumulation, leading to localized stress concentration, micropores, and ineffective aggregates within the coating. This is detrimental to constructing a continuous, dense, and highly oriented "brick-and-mortar" structure. Meanwhile, the instantaneous volume expansion generated during the liquid phase flash evaporation process facilitates the rearrangement and orientation of the filler in the shear flow field, which is one of the important process factors for achieving high barrier performance.

[0055] 3. The effect of bio-crosslinking networks on the stability and antibacterial durability of silver nanoparticles Comparing Example 1 and Comparative Example 4, it can be seen that, without changing the amount of silver nanoparticles added and replacing nisin with sodium dodecyl sulfate, the oxygen and water vapor permeability increased (to 12.3 cc / (m²)). 2 ·day·atm) and 6.5g / (m 2However, the most significant change was in the antibacterial properties. The antibacterial rate of Comparative Example 4 was only 68.4%, far lower than the 99.9% of Example 1. This indicates that in this system, nisin not only functions as an antibacterial component but also plays a crucial role in the dispersion stability and antibacterial durability of silver nanoparticles.

[0056] Based on publicly available research in the field of silver nanoparticle-cellulose nanocrystal composites, it can be inferred that nisin, as a polypeptide molecule with multiple polar groups, can form a stable electrostatic complex network with carboxyl-containing nanocellulose. Furthermore, it can fix silver nanoparticles on the surface of montmorillonite and cellulose through steric hindrance and multi-point adsorption, inhibiting their ripening and irreversible aggregation during melt processing, maintaining a high specific surface area and a stable silver ion release rate, thereby achieving a highly efficient and long-lasting antibacterial effect. Sodium dodecyl sulfate, on the other hand, is a conventional small-molecule anionic surfactant that mainly provides electrostatic repulsion through single-point adsorption. It is difficult to stably constrain the position of silver nanoparticles under high temperature and high shear conditions for a long period, leading to aggregation and loss of effective active surface area during processing, ultimately resulting in a significant decrease in antibacterial rate.

[0057] 4. The impact of formula parameter adjustment on overall performance Examples 2 and 3 extended the parameters of Example 1 by considering the PLA:PPC mass ratio and the amounts of TGIC and montmorillonite. It can be seen that when the PLA ratio increased to 80% and the TGIC mass decreased to 100.0 g (Example 2), the oxygen and water vapor permeability slightly increased (OTR was 4.8 cc / (m²)). 2 WVTR is 2.5 g / (m·day·atm). 2 The peel strength decreased slightly (day), but remained at a high level, and the antibacterial rate was close to 99.7%. When the PLA to PPC ratio was adjusted to 50:50, the montmorillonite mass was increased to 500.0 g, and the TGIC mass was increased to 300.0 g (Example 3), the oxygen permeability was further reduced to 2.5 cc / (m²) while ensuring processing flowability. 2 (day·atm), water vapor transmission rate decreased to 1.6 g / (m 2 (day), peel strength increased to 8.8 N / cm, and antibacterial rate maintained at 99.9%.

[0058] The above results indicate that, within the defined range, appropriately increasing the mass amounts of montmorillonite and nisin, and balancing the PLA / PPC ratio and TGIC dosage, is beneficial for comprehensively optimizing barrier properties, antibacterial properties, and the interfacial bonding strength between the coating and the substrate. Conversely, the complete absence of any key component (such as montmorillonite, TGIC, or nisin), or the use of a significantly simplified dry blending process, will lead to a significant degradation of at least one or more key properties. This further confirms the clear causal relationship and technical advantages between the key components and their defined ranges, the key process steps, and the technical problems solved in this invention.

Claims

1. A method for preparing nano-oxygen barrier functional masterbatch for the outer surface of packaging bottles, characterized in that, Includes the following steps: Step S1: Add nisin and glycerol to water and stir to form a hydrated solution; mix montmorillonite K10 dispersion with the hydrated solution and homogenize it, then add silver nanoparticles and ultrasonically disperse to obtain a first composite dispersion slurry; Step S2: Provide nanocellulose and mix it into the first composite dispersion slurry to form an oxygen barrier functional suspension of multidimensional scale hybrid filler; Step S3: Mix polylactic acid and polypropylene carbonate as a carrier resin and melt to obtain a carrier resin melt, inject the oxygen barrier functional suspension into the resin melt for composite processing; then control the exhaust parameters to remove moisture and extrude granulate to obtain nano oxygen barrier functional masterbatch; In step S3, the mass ratio of polylactic acid to polypropylene carbonate in the carrier resin is in the range of (50:50) to (80:20); and 1%-3% of the total mass of triglycidyl isocyanurate is added during the carrier resin melting stage.

2. The method for preparing nano-oxygen barrier functional masterbatch for the outer surface of packaging bottles according to claim 1, characterized in that: In step S1, the homogenization process speed is set to 2000-4000 rpm and the time is 20-40 min; the ultrasonic dispersion frequency is set to 40-50 kHz, the operation mode is double cycle and the interval between each cycle is 10-20 s.

3. The method for preparing nano-oxygen barrier functional masterbatch for the outer surface of packaging bottles according to claim 1, characterized in that: The mass percentage of nisin to montmorillonite K10 is such that, in every 100 parts by mass of water, 1-7 parts by mass of montmorillonite K10 and 1.5-3 parts by mass of nisin are dispersed.

4. The method for preparing nano-oxygen barrier functional masterbatch for the outer surface of packaging bottles according to claim 1, characterized in that: In step S2, the nanocellulose is nanocellulose with a surface rich in carboxyl groups.

5. The method for preparing nano-oxygen barrier functional masterbatch for the outer surface of packaging bottles according to claim 1, characterized in that: The extrusion granulation process in step S3 uses a co-rotating twin-screw extruder. The oxygen barrier functional suspension is injected laterally under high pressure from the self-compression section and the water and glycerol are removed in the vacuum exhaust section.

6. The method for preparing nano-oxygen barrier functional masterbatch for the outer surface of packaging bottles according to claim 1, characterized in that: Before the nano-oxygen barrier masterbatch is co-extruded and attached to the outer layer of polypropylene on the packaging bottle, the outer layer of polypropylene is modified by oxygen plasma bombardment. The exposure time parameter is set to 40-80s and the plasma power is set to 5-10W.

7. The method for preparing nano-oxygen barrier functional masterbatch for the outer surface of packaging bottles according to claim 1, characterized in that: By mass percentage, the nanocellulose accounts for 3%-5% of the total amount of the carrier resin, and the montmorillonite K10 accounts for 1%-5% of the total amount of the carrier resin.

8. A nano-oxygen barrier functional masterbatch for the outer surface of packaging bottles, characterized in that, The nano oxygen barrier functional masterbatch for the outer surface of packaging bottles is obtained by the preparation method according to any one of claims 1-7.

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