PCL / LIG composite film and preparation method thereof
By compounding PCL with lignin particles, surface hydrophobic modification and the synergistic effect of nanocellulose crystals and zein nanoparticles, the problems of poor gas barrier performance and high cost of PCL were solved, and a high-performance, low-cost food packaging film was achieved.
Patent Information
- Application Number
- CN202510961010.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-12
- Publication Date
- 2025-09-16
AI Technical Summary
PCL materials have poor gas barrier properties and high costs, which limit their application in food packaging.
PCL is composited with lignin particles, with the addition ratio of lignin particles being 5-15%. After surface hydrophobic modification, nanocellulose crystals and zein nanoparticles are combined to form core-shell hybrid particles, which are evenly dispersed in the PCL matrix to optimize film performance.
The gas barrier and mechanical properties of the film are improved, production costs are reduced, and biodegradability is maintained, making it suitable for commercial applications in the food packaging field.
Abstract
Description
Technical Field
[0001] The present application relates to the field of food packaging materials, and more specifically, to a PCL / LIG composite film and a preparation method thereof. Background Art
[0002] Polycaprolactone (PCL), a bioresorbable polymer approved by the U.S. Food and Drug Administration (FDA), has found widespread application in the biomedical field, for example as a tissue engineering scaffold and a sustained-release drug delivery vehicle, thanks to its excellent biocompatibility, biodegradability, and processability. Furthermore, its biodegradability aligns with environmental trends, leading to its application in low-temperature food packaging and storage, offering a viable path to reducing pollution from traditional plastics.
[0003] However, PCL has significant performance limitations. First, its gas barrier properties are poor, making it difficult to effectively block gases like oxygen and carbon dioxide, failing to meet the core gas-tightness requirements of food packaging. Second, PCL's relatively high production cost restricts its commercial application in large-scale food packaging. These limitations severely limit PCL's application in food packaging applications other than low-temperature food packaging, such as fresh food preservation and shelf-life extension. With the growing global demand for sustainable packaging materials, the development of packaging materials that combine biodegradability with excellent gas barrier properties and manageable costs has become a research hotspot. Existing PCL modification methods (such as blending and cross-linking) often struggle to simultaneously address both barrier properties and cost. Therefore, exploring new composite systems to overcome PCL application bottlenecks is crucial for expanding the application of biodegradable polymers in food packaging. Summary of the Invention
[0004] In order to solve the problem of poor gas barrier properties of existing PCL materials, the present application provides a PCL / LIG composite film and a preparation method thereof.
[0005] The PCL / LIG composite film provided in this application adopts the following technical solution: A PCL / LIG composite film, comprising the following components by mass percentage: Polycaprolactone: 85-95%; Lignin particles: 5-15%; The lignin particles are alkaline lignin or one of its derivatives, and the particle size of the lignin particles is 100 nm-5 μm.
[0006] By adopting this technical solution, a 5-15% addition of lignin (LIG) leverages its naturally rigid structure to enhance the film's gas barrier properties (especially against oxygen and carbon dioxide) while avoiding the increased brittleness of the film caused by an excessively high addition, thereby preserving the inherent flexibility of the PCL matrix. Alkaline lignin and its derivatives exhibit good compatibility with PCL, and a particle size range of 100nm-5μm reduces particle agglomeration, ensuring uniformity in the composite system and stabilizing the film's mechanical properties. As an industrial byproduct, the low cost of lignin reduces the overall production cost of the composite film, addressing the high cost of pure PCL and paving the way for its commercial application in food packaging. Furthermore, the composite film achieved with this ratio remains biodegradable, meeting environmental requirements.
[0007] Optionally, the lignin particles are subjected to surface hydrophobic modification treatment, and the modifier used in the surface hydrophobic modification treatment is one of a silane coupling agent and a fatty acid ester.
[0008] By adopting the above technical solution, the surface hydrophobic modification of lignin particles significantly improves their interfacial compatibility with the hydrophobic PCL matrix. Unmodified lignin, due to the presence of hydrophilic groups such as hydroxyl groups, easily agglomerates in PCL, resulting in defects in the composite film. However, after hydrophobic modification, the surface polarity of lignin is reduced, and the interfacial bonding force with PCL is enhanced, which can reduce interfacial voids, thereby improving the mechanical properties and gas barrier properties of the film. In addition, the modified lignin particles have better dispersibility and can be evenly distributed in the PCL matrix, avoiding fluctuations in film performance caused by local excessive concentration. At the same time, it enhances the thermal stability of the composite system and reduces degradation caused by interfacial incompatibility during processing.
[0009] Optionally, the PCL has a molecular weight of 10,000-50,000 g / mol and a crystallinity of 40-60%.
[0010] By adopting the above technical solution, the molecular weight of PCL is limited to 10,000-50,000 g / mol and the crystallinity is limited to 40-60%, achieving a balance between processing and performance. Within this molecular weight range, PCL exhibits suitable fluidity in the molten state, facilitating uniform mixing with lignin particles and reducing processing difficulty. If the molecular weight is too high, the melt viscosity is high, which can easily lead to uneven mixing; too low a molecular weight can reduce the mechanical strength of the film. Setting a crystallinity of 40-60% ensures that PCL provides sufficient rigidity and impact resistance while avoiding the increased film brittleness caused by excessive crystallinity (excessive crystallinity tends to tightly arrange the molecular chains, reducing flexibility). At the same time, a moderate crystalline structure enhances the film's barrier ability to gas molecules (the crystalline regions hinder gas diffusion), further optimizing the core performance required for food packaging.
[0011] Optionally, nanocellulose crystals are further included, wherein the added amount of the nanocellulose crystals is 15-25% of the mass of the lignin particles, and the aspect ratio of the nanocellulose crystals is ≥50.
[0012] By adopting the above-mentioned technical solution and adding nanocellulose crystals, the comprehensive performance of the composite film can be synergistically improved through the "nano-enhancement" effect. Nanocellulose crystals have extremely high strength and aspect ratio, and can form a three-dimensional network structure at a low addition amount, significantly improving the tensile strength and Young's modulus of the film, compensating for the loss of mechanical properties that may be caused by the addition of lignin. At the same time, its nanoscale effect and high aspect ratio can extend the penetration path of gas molecules, and synergize with lignin to enhance the gas barrier performance (especially for oxygen and water vapor). In addition, the biocompatibility and degradability of nanocellulose crystals are consistent with PCL and lignin, and will not affect the environmental characteristics of the composite film. The low addition amount can avoid increasing excessive costs, taking into account both performance and economy.
[0013] Optionally, the nanocellulose crystals and lignin particles are compounded by in-situ hybridization pretreatment, and the specific method of the in-situ hybridization pretreatment is: Lignin particles and nanocellulose crystals are dispersed in an aqueous phase, 0.5-2wt% polydopamine is added, and self-polymerization reaction is carried out at pH = 8.5 for 2-4 hours to obtain core-shell hybrid particles with a particle size distribution dispersion of ≤15%.
[0014] By employing this technical solution, nanocellulose crystals and lignin particles undergo in-situ hybridization pretreatment, addressing the dispersibility issues of both fillers within the PCL matrix. Polydopamine self-polymerizes at pH 8.5, forming a sticky coating on the lignin surface. It then bonds to the nanocellulose through hydrogen and covalent bonds, forming core-shell hybrid particles with a uniform particle size distribution (discreteness ≤ 15%). This structure creates a synergistic effect between the lignin (core) and the nanocellulose (shell): the core-shell structure reduces the agglomeration of individual fillers and improves the uniformity of dispersion within the PCL. The enhanced interfacial bonding promotes the effective transfer of stress between the two fillers and the matrix, significantly enhancing the film's mechanical properties. Furthermore, the dense arrangement of the core-shell structure further extends the diffusion path for gas molecules, resulting in improved barrier properties and greater stability.
[0015] Optionally, zein nanoparticles are further included, wherein the addition amount of the zein nanoparticles is 5-15% of the mass of the polycaprolactone, and the particle size of the zein nanoparticles is 50-200 nm.
[0016] By adopting the above-mentioned technical solution and adding zein nanoparticles, the composite film can be endowed with multiple additional functionalities. Zein exhibits excellent film-forming and gas barrier properties, especially for oxygen. Its nanoscale structure allows for uniform dispersion within the composite system, forming a complementary barrier structure with PCL and lignin, further reducing gas permeability. Furthermore, zein itself possesses certain antibacterial and antioxidant properties, which can inhibit the growth of microorganisms in food packaging and extend the shelf life of food. Its biocompatibility and degradability are consistent with the system, posing no environmental burden. Low addition levels avoid excessive cost increases while leveraging its compatibility with other components, such as its hydrophobic interaction with PCL, to ensure stable film performance.
[0017] In a second aspect, the present application provides a method for preparing a PCL / LIG composite film, which adopts the following technical solution: A method for preparing a PCL / LIG composite film comprises the following steps: Heat and melt polycaprolactone, then add lignin particles into the polycaprolactone and mix them evenly; The molten composite is pressed into a film.
[0018] Optionally, include the following steps: The polycaprolactone is heated and melted, and then the lignin particles, nanocellulose crystals and zein nanoparticles are added to the polycaprolactone and mixed evenly; The molten composite is pressed into a film.
[0019] By adopting the above technical solution, lignin particles, nanocellulose crystals, and zein nanoparticles are added simultaneously during the preparation process, achieving a synergistic effect of the multiple components through a one-step melt mixing process. This method ensures the uniform dispersion of the three fillers in the PCL matrix, avoiding the local concentration imbalances that may result from step-by-step addition. The multiple components are fully contacted in the molten state, utilizing intermolecular forces to form a stable composite system. This fully utilizes the reinforcing effect of nanocellulose, the barrier effect of lignin, and the antimicrobial effect of zein. The resulting film exhibits significantly improved mechanical properties, barrier properties, and functional characteristics (such as antimicrobial properties) compared to single-filler systems. Furthermore, the integrated mixing process simplifies the production process, improves production efficiency, and is suitable for industrial scale-up.
[0020] Optionally, include the following steps: The polycaprolactone is heated and melted, and core-shell hybrid particles obtained by in-situ hybridization pretreatment of lignin particles and nanocellulose crystals and zein nanoparticles are added to the polycaprolactone and mixed evenly; The molten composite is pressed into a film.
[0021] By adopting the above technical solution and mixing core-shell hybrid particles that have undergone in-situ hybridization pretreatment, the performance of the composite film can be further optimized. The core-shell hybrid particles have achieved a close combination of nanocellulose and lignin during the pretreatment stage, avoiding secondary agglomeration of the two fillers during melt mixing and ensuring a more uniform dispersion in the PCL matrix. At the same time, the stability of the core-shell structure can reduce interfacial separation during processing, making stress transfer more efficient and improving mechanical properties. In addition, the synergistic effect of the hybrid particles and zein nanoparticles can further enhance the gas barrier and antibacterial properties, making the overall performance of the film better, with less performance fluctuations during mass production and higher product consistency.
[0022] In summary, this application has the following beneficial effects: 1. This application enhances the gas barrier and mechanical properties through the synergistic effect of components such as lignin and nanocellulose, solving the problems of poor barrier and single performance of pure PCL.
[0023] 2. This application takes into account both environmental protection and economic efficiency, uses industrial by-product lignin to reduce costs, and all components are biodegradable. At the same time, the preparation process is simplified and suitable for industrial production.
[0024] 3. The method of the present application realizes antibacterial and antioxidant functions by adding zein and the like, and improves the stability of the film and the food preservation ability by combining structural optimization such as core-shell hybridization. DETAILED DESCRIPTION
[0025] The present application is further described in detail below with reference to the examples. It is particularly noted that if no specific conditions are specified in the following examples, the reactions are carried out according to conventional conditions or the conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following examples can be obtained from common commercial sources.
[0026] Preparation Example 1 A method for pretreating nanocellulose crystals and lignin particles by in-situ hybridization: Material preparation: alkaline lignin particles: particle size 2.5 μm, derived from papermaking black liquor byproduct; nanocellulose crystals (NCC): aspect ratio, in the range of 60-70, length approximately 1.5 μm, diameter approximately 20 nm, homemade by sulfuric acid hydrolysis; polydopamine: analytical grade; Tris-HCl buffer: 0.1 mol / L; deionized water. 10 g of alkaline lignin particles were weighed, added to 90 g of deionized water, and ultrasonically crushed at a power of 300 W for 15 min to prepare a 10% lignin dispersion. Separately, 2 g of nanocellulose crystals were weighed, added to deionized water, magnetically stirred at a speed of 500 rpm, and ultrasonicated at an auxiliary power of 200 W for 10 min to prepare a 0.5% NCC dispersion. The above lignin dispersion and NCC dispersion were mixed at a mass ratio of 9:1 (total solid content 10.5 g), placed in a 500 mL three-necked flask, and magnetically stirred at 800 rpm for 30 min to form a uniform suspension. 1.25 wt% polydopamine was added to the mixed solution, stirred and dissolved, and the pH of the system was adjusted to 8.5 with 1 mol / LTris-HCl buffer. The mixture was magnetically stirred in a constant temperature water bath at 30°C for 3 h, during which the pH was kept stable. After the reaction, the product was centrifuged, the supernatant was discarded, and the precipitate was washed with deionized water until the pH of the filtrate was neutral. It was then dried in a vacuum drying oven at 60°C for 12 h and ground through a 100-mesh sieve to obtain lignin-nanocellulose core-shell hybrid particles.
[0027] Preparation Example 2 A method for pretreating nanocellulose crystals and lignin particles by in-situ hybridization: the difference from Preparation Example 1 is that the amount of nanocellulose crystals used is 1.5 g.
[0028] Preparation Example 3 A method for pretreating nanocellulose crystals and lignin particles by in-situ hybridization: the difference from Preparation Example 1 is that the amount of nanocellulose crystals used is 2.5 g.
[0029] Preparation Example 4 A method for pretreating nanocellulose crystals and lignin particles by in-situ hybridization: the difference from Preparation Example 1 is that the alkaline lignin is replaced by lignin sodium sulfonate.
[0030] Example 1 A method for preparing a PCL / LIG composite film: Material preparation: Polycaprolactone (PCL): molecular weight 30,000 g / mol, crystallinity 50%, granular; Lignin particles: alkaline lignin is selected from papermaking black liquor by-product, with a particle size range of 100 nm-5 μm, and is screened through a 100-mesh sieve to ensure uniform particle size. 9000 g of PCL pellets were added to a two-roll mill. The temperature of the two rolls was set to 60°C and the speed of the two rolls was set to 1.8 rpm. The equipment was turned on to allow the PCL to melt and plasticize for 30 minutes until the PCL was completely melted and a uniform polymer melt was formed. Take 1000g of lignin particles and evenly sprinkle them on the polymer melt area between the twin rollers of the mill. Keep the twin roller temperature at 60°C and the speed at 1.8rpm. Continue milling for 60min to ensure that the lignin particles and the PCL melt are fully mixed to form a uniform composite material. After the blending is completed, the obtained composite material is collected and cut into discs of about 5 g each using a blade. The discs are placed in a room temperature environment to cool until they are completely solidified, thereby obtaining precursor material discs. Take a piece of precursor material disc and put it into the mold of the hydraulic flat plate vulcanizer. First set the pressure to 1MPa and pre-pressurize the disc to initially form it. Then raise the temperature to 90℃ and maintain the pressure at this pressure for 60 minutes to further melt and plasticize the material. Adjust the pressure of the flat vulcanizer to 10 MPa, maintain the temperature at 90°C, and maintain the pressure for 30 minutes to allow the material to fully level under high pressure and eliminate internal bubbles. The heating was turned off and the pressure was maintained until the equipment cooled to room temperature. The film was then taken out and placed at room temperature for another 24 h to obtain a uniform composite film with a thickness of about 0.1 mm.
[0031] Example 2 A method for preparing a PCL / LIG composite film: The method differs from Example 1 in that 8500 g of polycaprolactone and 1500 g of lignin particles are added.
[0032] Example 3 A method for preparing a PCL / LIG composite film: The method differs from Example 1 in that 9500 g of polycaprolactone and 500 g of lignin particles are added.
[0033] Example 4 A method for preparing a PCL / LIG composite film: The method differs from Example 1 in that alkaline lignin is replaced with sodium sulfonate lignin.
[0034] Example 5 A method for preparing a PCL / LIG composite film: The difference from Example 1 is that the lignin particles are subjected to surface hydrophobic modification, as follows: 1000 g of lignin particles were added to deionized water and ultrasonically dispersed at a power of 300 W for 30 minutes to remove impurities on the particle surface. After centrifugation, the particles were placed in a vacuum drying oven at 60°C and dried for 24 hours. The dried lignin particles were taken, 5000 mL of ethanol-water mixed solvent was added, and magnetic stirring was performed to form a suspension. The pH was adjusted to 4.5-5.0 with glacial acetic acid. A silane coupling agent KH-570 was added according to 4% of the lignin mass, and the temperature was raised to 60°C and stirred continuously for 3 hours to allow the silane coupling agent to hydrolyze and undergo a condensation reaction with the hydroxyl groups on the lignin surface. After the reaction, the particles were centrifuged, the precipitate was washed with anhydrous ethanol, vacuum dried at 60°C for 12 hours, and passed through a 100-mesh sieve to obtain hydrophobically modified lignin particles.
[0035] Example 6 A method for preparing a PCL / LIG composite film: The method differs from Example 5 in that the silane coupling agent is replaced with methyl stearate.
[0036] Example 7 A method for preparing a PCL / LIG composite film: The method differs from Example 1 in that the molecular weight of polycaprolactone is 10,000 g / mol and the crystallinity is 60%.
[0037] Example 8 A method for preparing a PCL / LIG composite film: The method differs from Example 1 in that the molecular weight of the polycaprolactone is 50,000 g / mol and the crystallinity is 40%.
[0038] Example 9 A method for preparing a PCL / LIG composite film: The difference from Example 1 is that nanocellulose crystals are added simultaneously with the addition of lignin particles to the molten polycaprolactone. The amount of nanocellulose crystals added is 20% of the mass of the lignin particles, and the aspect ratio of the nanocellulose crystals is 60-70.
[0039] Example 10 A method for preparing a PCL / LIG composite film: The difference from Example 9 is that the amount of nanocellulose crystals added is 15% of the mass of the lignin particles.
[0040] Example 11 A method for preparing a PCL / LIG composite film: The difference from Example 9 is that the amount of nanocellulose crystals added is 25% of the mass of the lignin particles.
[0041] Example 12 A method for preparing a PCL / LIG composite film: The difference from Example 9 is that the aspect ratio of the nanocellulose crystals is 30-40.
[0042] Example 13 A method for preparing a PCL / LIG composite film: The difference from Example 9 is that core-shell hybrid particles obtained by in-situ hybridization pretreatment of lignin particles and nanocellulose crystals are added to the molten polycaprolactone, and the core-shell hybrid particles are prepared by the method of Preparation Example 1.
[0043] Example 14 A method for preparing a PCL / LIG composite film: The difference from Example 13 is that the core-shell hybrid particles are prepared by the method of Preparation Example 2.
[0044] Example 15 A method for preparing a PCL / LIG composite film: The difference from Example 13 is that the core-shell hybrid particles are prepared by the method of Preparation Example 3.
[0045] Example 16 A method for preparing a PCL / LIG composite film: The difference from Example 13 is that the core-shell hybrid particles are prepared by the method of Preparation Example 4.
[0046] Example 17 A method for preparing a PCL / LIG composite film: The difference from Example 13 is that core-shell hybrid particles obtained by in-situ hybridization pretreatment of lignin particles and nanocellulose crystals are added to molten polycaprolactone, and zein nanoparticles are also added. The amount of zein nanoparticles added is 10% of the mass of polycaprolactone, and the particle size of the zein nanoparticles is 50-200 nm.
[0047] Example 18 A method for preparing a PCL / LIG composite film: The difference from Example 17 is that the added amount of zein nanoparticles is 5% of the mass of polycaprolactone.
[0048] Example 19 A method for preparing a PCL / LIG composite film: The difference from Example 17 is that the added amount of zein nanoparticles is 15% of the mass of polycaprolactone.
[0049] Comparative Example 1 A method for preparing a PCL / LIG composite film: The method differs from Example 1 in that 8000 g of polycaprolactone and 2000 g of lignin particles are added.
[0050] Comparative Example 2 A method for preparing a PCL / LIG composite film: The method differs from Example 1 in that 9900 g of polycaprolactone and 100 g of lignin particles are added.
[0051] Comparative Example 3 A method for preparing a PCL / LIG composite film: The method is different from Example 1 in that the particle size of the lignin particles is 5-50 μm.
[0052] Performance testing experiment
[0053] Oxygen Transmission Rate (O2TR): In accordance with GB / T19789-2005, using the coulometer method, test conditions are 23°C, relative humidity 50%, test area 50 cm², unit: cm³ / (m²・d・0.1MPa), and the average value of three parallel tests is taken.
[0054] Carbon dioxide transmission rate (CO2TR): In accordance with GB / T21529-2008, using the coulometer method, the test conditions are the same as those for oxygen transmission rate, unit: cm³ / (m²・d・0.1MPa), and the average value of three parallel tests is taken.
[0055] Tensile strength and elongation at break: in accordance with GB / T1040.3-2006, using a universal material testing machine, type A specimen, a tensile speed of 50 mm / min, units are MPa and %, respectively. The average value is obtained by performing 5 parallel tests.
[0056] Table 1 Test data Combining Example 1 with Comparative Examples 1-2 and Table 1, we can see that when the lignin addition level is 10% (Example 1), the composite film exhibits an oxygen permeability of 90 cm³ / (m²・d・0.1MPa), a carbon dioxide permeability of 280 cm³ / (m²・d・0.1MPa), a tensile strength of 38 MPa, and an elongation at break of 380%, demonstrating balanced overall performance. However, when the lignin addition level reaches 20% in Comparative Example 1, while the oxygen and carbon dioxide permeabilities decrease somewhat (100 and 310), the tensile strength drops to 28 MPa and the elongation at break is only 230%, significantly increasing brittleness and deteriorating mechanical properties. When the lignin addition level is only 1% in Comparative Example 2, the oxygen and carbon dioxide permeabilities rise to 150 and 480, respectively, significantly decreasing barrier properties and failing to meet food packaging requirements. This demonstrates that controlling the lignin addition level within the 5-15% range can ensure both mechanical properties and a barrier-enhancing effect. Excessive or insufficient lignin additions can lead to unbalanced performance.
[0057] Combining Example 1 and Comparative Example 3 with Table 1, we can see that in Example 1, when the lignin particle size is 100nm-5μm, the oxygen permeability is 90cm³ / (m²・d・0.1MPa), the carbon dioxide permeability is 280cm³ / (m²・d・0.1MPa), the tensile strength is 38MPa, and the elongation at break is 380%. In contrast, in Comparative Example 3, when the lignin particle size is 5-50μm, the oxygen permeability rises to 110, the carbon dioxide permeability rises to 330, the tensile strength drops to 33MPa, and the elongation at break drops to 320%. This indicates that excessively large lignin particle size (over 5μm) leads to uneven dispersion and easy agglomeration in the polycaprolactone matrix, forming interfacial defects, thereby reducing gas barrier and mechanical properties. This demonstrates the importance of a particle size range of 100nm-5μm for ensuring film performance.
[0058] Combining Examples 1-3 with Table 1, we can see that as the lignin addition level increases from 5% (Example 3) to 15% (Example 2), the oxygen transmission rate decreases from 120 to 75 cm³ / (m²・d・0.1MPa) and the carbon dioxide transmission rate decreases from 380 to 230 cm³ / (m²・d・0.1MPa), gradually improving barrier properties. However, the tensile strength decreases from 40 MPa to 35 MPa, and the elongation at break decreases from 410% to 330%, slightly degrading mechanical properties. At a 10% addition level (Example 1), the oxygen transmission rate is 90, the carbon dioxide transmission rate is 280, the tensile strength is 38 MPa, and the elongation at break is 380%, achieving optimal overall performance. This indicates that a performance balance exists within the 5-15% lignin addition level, with a level of around 10% offering a balance between barrier properties and mechanical properties, making it an optimal choice.
[0059] Combining Examples 1 and 4 with Table 1, we can see that Example 1, using alkaline lignin, achieved an oxygen permeability of 90 cm³ / (m²・d・0.1MPa), a carbon dioxide permeability of 280 cm³ / (m²・d・0.1MPa), a tensile strength of 38MPa, and an elongation at break of 380%. Example 4, using sodium lignin sulfonate (a lignin derivative), achieved an oxygen permeability of 92, a carbon dioxide permeability of 275, a tensile strength of 37MPa, and an elongation at break of 370%. The performance differences between the two are minimal. This demonstrates that both alkaline lignin and its derivatives can be used as effective components in this system, exhibiting similar compatibility and reinforcement effects, broadening the range of lignin raw material options.
[0060] Combining Examples 1, 5, and 6 with Table 1, we can see that in Example 1, which was not hydrophobically modified, the oxygen permeability was 90 cm³ / (m²・d・0.1MPa), the carbon dioxide permeability was 280 cm³ / (m²・d・0.1MPa), and the tensile strength was 38MPa. In Example 5, which was modified with a silane coupling agent, and Example 6, which was modified with a fatty acid ester, the oxygen permeability dropped to 65 and 68, respectively, and the carbon dioxide permeability dropped to 200 and 210, respectively, while the tensile strength increased to 43 and 42 MPa, and the elongation at break remained above 390%. This indicates that hydrophobic modification reduces the surface polarity of lignin, significantly improves its interfacial compatibility with polycaprolactone, reduces interfacial voids and particle agglomeration, and thus synergistically enhances the gas barrier and mechanical properties. The two modifiers have similar effects.
[0061] Combining Examples 1, 7, and 8 with Table 1, we can see that when the polycaprolactone has a molecular weight of 30,000 g / mol and a crystallinity of 50% (Example 1), the oxygen transmission rate is 90 cm³ / (m²・d・0.1MPa), the tensile strength is 38 MPa, and the elongation at break is 380%, demonstrating balanced overall performance. In Example 7, with a molecular weight of 10,000 g / mol and a crystallinity of 60%, the oxygen transmission rate is 95, the tensile strength slightly decreases (36 MPa), but the elongation at break increases to 420%, indicating improved processing fluidity. In Example 8, with a molecular weight of 50,000 g / mol and a crystallinity of 40%, the oxygen transmission rate is 88, the tensile strength increases to 41 MPa, but the elongation at break decreases to 360%, indicating a more stable structure. This demonstrates that polycaprolactone within the range of 10,000-50,000 g / mol and a crystallinity of 40-60% can achieve a balance between processing fluidity, mechanical properties, and barrier properties, meeting the needs of various scenarios.
[0062] Combining Examples 1, 9-12, and Table 1, we can see that in Example 1, which lacks nanocellulose, the oxygen transmission rate is 90 cm³ / (m²・d・0.1MPa) and the tensile strength is 38MPa. In Examples 9-11, which incorporate nanocellulose with an aspect ratio ≥50, the oxygen transmission rate drops to 52-60 and the tensile strength increases to 46-50MPa, significantly enhancing both barrier and mechanical properties. In contrast, in Example 12, with an aspect ratio of 30-40, the oxygen transmission rate is 70 and the tensile strength is 42MPa, demonstrating weaker performance. This suggests that nanocellulose (aspect ratio ≥50) can extend gas diffusion paths by forming a three-dimensional network structure and exert a nano-enhancement effect, synergistically improving performance with lignin. However, nanocellulose with a low aspect ratio exhibits limited network-building capacity, resulting in limited enhancement.
[0063] Combining Examples 1, 9, and 13-16 with Table 1, we can see that in Example 9, which did not undergo in-situ hybridization (only physically mixing nanocellulose and lignin), the oxygen transmission rate was 55 cm³ / (m²・d・0.1MPa) and the tensile strength was 48MPa. In contrast, in Examples 13-16, which underwent in-situ hybridization, the oxygen transmission rate dropped to 43-46, while the tensile strength increased to 51-54MPa. This is because in-situ hybridization, through the mediation of polydopamine, formed core-shell hybrid particles, reducing secondary agglomeration of the two fillers. This resulted in a more uniform dispersion in the polycaprolactone and stronger interfacial bonding, thereby enhancing the synergistic barrier and reinforcement effects and surpassing the performance of simple physical mixing.
[0064] Combining Examples 13, 17-19, and Table 1, we can see that in Example 13, without zein, the oxygen transmission rate was 45 cm³ / (m²・d・0.1 MPa). In Examples 17-19, with 5-15% zein nanoparticles added, the oxygen transmission rate dropped to 32-40, with the barrier effect becoming more pronounced with increasing zein nanoparticle dosage. Meanwhile, the tensile strength remained at 49-51 MPa. This demonstrates that zein nanoparticles, through their dense structure, further hinder oxygen penetration, synergistically enhancing the barrier properties with the core-shell hybrid particles, imparting additional freshness-preserving properties to the film and resulting in superior overall performance.
[0065] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.
Claims
1. A PCL / LIG composite film, characterized in that: Its components by mass percentage include: Polycaprolactone: 85-95%; Lignin particles: 5-15%; The lignin particles are alkaline lignin or one of its derivatives, and the particle size of the lignin particles is 100 nm-5 μm.
2. The PCL / LIG composite film according to claim 1, wherein: The lignin particles are subjected to surface hydrophobic modification treatment, and the modifier used in the surface hydrophobic modification treatment is one of a silane coupling agent and a fatty acid ester.
3. The PCL / LIG composite film according to claim 1, wherein: The polycaprolactone has a molecular weight of 10,000-50,000 g / mol and a crystallinity of 40-60%.
4. The PCL / LIG composite film according to claim 1, wherein: It also includes nanocellulose crystals, wherein the added amount of the nanocellulose crystals is 15-25% of the mass of the lignin particles, and the aspect ratio of the nanocellulose crystals is ≥50.
5. The PCL / LIG composite film according to claim 4, characterized in that: The nanocellulose crystals and lignin particles are compounded by in-situ hybridization pretreatment, and the specific method of the in-situ hybridization pretreatment is: Lignin particles and nanocellulose crystals are dispersed in an aqueous phase, 0.5-2wt% polydopamine is added, and self-polymerization reaction is carried out at pH = 8.5 for 2-4 hours to obtain core-shell hybrid particles with a particle size distribution dispersion of ≤15%.
6. The PCL / LIG composite film according to claim 1, wherein: The invention also comprises zein nanoparticles, wherein the addition amount of the zein nanoparticles is 5-15% of the mass of the polycaprolactone, and the particle size of the zein nanoparticles is 50-200 nm.
7. A method for preparing a PCL / LIG composite film according to any one of claims 1 to 6, characterized in that: The following steps are involved: Heat and melt polycaprolactone, then add lignin particles into the polycaprolactone and mix them evenly; The molten composite is pressed into a film.
8. The method for preparing a PCL / LIG composite film according to claim 7, wherein: The following steps are involved: The polycaprolactone is heated and melted, and then the lignin particles, nanocellulose crystals and zein nanoparticles are added to the polycaprolactone and mixed evenly; The molten composite is pressed into a film.
9. The method for preparing a PCL / LIG composite film according to claim 7, wherein: The following steps are involved: The polycaprolactone is heated and melted, and core-shell hybrid particles obtained by in-situ hybridization pretreatment of lignin particles and nanocellulose crystals and zein nanoparticles are added to the polycaprolactone and mixed evenly; The molten composite is pressed into a film.