Biodegradable layered composite material

Abstract

The invention relates to the technical field of environment-friendly materials and composite materials, in particular to a biodegradable layered composite material which comprises a base material layer, an interface adhesive layer, a cellulose reinforcement layer and a degradation regulation and control layer. By optimizing the interface bonding force and degradation synergy, the problems of weak interface bonding force and inconsistent degradation in the prior art are solved. The interface adhesive enhances the interlayer bonding strength, and the degradation regulation and control layer realizes the controllability of the degradation rate. The material can be used in the fields of packaging, agriculture, medical treatment and environmental protection, and meets the requirements of different application scenes. The invention further provides a preparation method and a performance testing method, and excellent mechanical, thermal and degradation properties of the material are ensured.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection materials and composite materials technology, specifically a biodegradable layered composite material. Background Technology

[0002] Biodegradable materials have attracted widespread attention in recent years due to their ability to be broken down into harmless substances by microorganisms in the natural environment. Layered composite materials are multi-layered structural materials composed of multiple materials combined through specific processes, possessing excellent mechanical, thermal, and functional properties. Combining biodegradable materials with layered composite materials can not only meet environmental protection requirements but also improve the overall performance of materials, leading to their wide application in packaging, medical, and agricultural fields.

[0003] Patent CN106541628A discloses a biodegradable packaging material, comprising a fiber material layer, a paper base layer, an adhesive layer, a substrate layer, a PBS layer, and a PLA layer. The outermost layer is a fiber material layer, and the inner layers are bonded to the paper base layer and the polylactic acid substrate layer using an adhesive. This design provides the material with a certain degree of strength and environmental friendliness, while also achieving a multi-layered functional structure. However, the interfacial bonding between the layers in this technical solution is relatively weak, which may lead to delamination during use, affecting the overall performance and lifespan of the material. Furthermore, this solution does not fully consider the interlayer synergistic effect during the degradation process, which may limit the degradation efficiency.

[0004] Patent CN214983939U discloses a fully biodegradable composite material, comprising a composite paper substrate, a support layer, a degradation layer, and a waterproof layer. This material achieves double-sided waterproofing and cushioning by setting the support layer and degradation layer on the top and bottom of the composite paper substrate respectively, and adding a waterproof layer outside the degradation layer. This structural design improves the material's practicality and functionality, but its shortcomings lie in the need for further optimization of the compatibility between the degradation layer and the support layer, which may lead to inconsistent degradation rates among different layers during the degradation process, thus affecting the overall degradation effect. Furthermore, this solution does not explicitly mention how to control the degradation time of each layer to adapt to different application scenarios, limiting its application scope.

[0005] While the two existing technologies mentioned above have achieved functionalization and multilayering of biodegradable materials to some extent, there is still room for improvement in terms of interfacial bonding, degradation synergy, and degradation rate control. This provides direction for the development of the new patent "A Biodegradable Layered Composite Material," which aims to further improve the overall performance and applicability of the material by optimizing interlayer bonding, enhancing degradation synergy, and achieving controllable degradation rate. Summary of the Invention

[0006] This application provides a biodegradable layered composite material and its preparation method, aiming to solve the problems of weak interfacial bonding, inconsistent degradation process and limited application range in the prior art by optimizing interlayer bonding force, improving degradation synergy and achieving controllable degradation rate.

[0007] In a first aspect, this application provides a biodegradable layered composite material, comprising the following steps:

[0008] S10: Polylactic acid granules are mixed with a plasticizer and then melt-extruded at 160 to 180°C to form a substrate layer; the plasticizer is citrate or glyceryl monostearate, and its mass fraction is 5% to 10% of the mass of polylactic acid granules.

[0009] S20: Cellulose nanocrystals are mixed with a surface modifier, stirred evenly in an aqueous solution, and then filtered under vacuum to form a cellulose reinforcement layer; the surface modifier is a silane coupling agent, and its amount is 1% to 3% of the mass of the cellulose nanocrystals.

[0010] S30: An interface adhesive is applied between the substrate layer and the cellulose reinforcement layer, the interface adhesive being a mixture of polyvinyl alcohol and a crosslinking agent in a mass ratio of 2:1 to 3:1, with a coating thickness of 50 micrometers to 100 micrometers.

[0011] S40: After the substrate layer, the interface adhesive layer and the cellulose reinforcement layer are stacked, they are hot-pressed at 60 to 80°C, the hot-pressing pressure is 10 MPa to 20 MPa, and the hot-pressing time is 5 to 10 minutes.

[0012] S50: A degradation control layer is coated on the outside of the cellulose reinforcement layer. The degradation control layer is made of starch and aliphatic polyester in a mass ratio of 3:1 to 5:1 and the coating thickness is 80 micrometers to 120 micrometers.

[0013] S60: The multilayer structure is dried at 40 to 60°C for 1 to 2 hours to obtain a biodegradable layered composite material.

[0014] According to this application, the interfacial bonding strength between the substrate layer and the cellulose reinforcement layer is solved by introducing an interfacial adhesive layer, while the degradation regulation layer achieves coordination of the degradation rates of different layers. The polyvinyl alcohol in the interfacial adhesive reacts with the crosslinking agent to form a three-dimensional network structure, enhancing the interlayer bonding strength. The starch and aliphatic polyester in the degradation regulation layer exhibit different degradation times under microbial action, thereby achieving overall degradation rate regulation.

[0015] In some embodiments, in step S10, the melt index of the polylactic acid particles is 5 g per 10 minutes to 15 g per 10 minutes, and the screw speed during melt extrusion is 50 rpm to 100 rpm.

[0016] In some embodiments, in step S20, the particle size of the cellulose nanocrystals is 50 nanometers to 100 nanometers, the stirring speed is 500 rpm to 800 rpm, and the stirring time is 1 hour to 2 hours.

[0017] In some embodiments, in step S30, the interface adhesive is coated using a doctor blade coating process, with a doctor blade gap of 50 to 100 micrometers and a coating speed of 1 to 2 meters per minute.

[0018] In some embodiments, in step S40, the temperature of the heating plate of the hot pressing molding equipment is 60 to 80°C, and the pressure applied during the hot pressing process is evenly distributed with a pressure fluctuation range not exceeding ±2 MPa.

[0019] In some embodiments, in step S50, the degradation control layer is coated using a spraying process with a nozzle diameter of 0.5 mm to 1 mm and a spraying air pressure of 0.2 MPa to 0.4 MPa.

[0020] In some embodiments, in step S60, the drying process is carried out in a forced-air drying chamber, the air flow rate inside the drying chamber is 1 to 2 meters per second, and the humidity is controlled within the range of 30% to 50% during the drying process.

[0021] Secondly, this application provides a biodegradable layered composite material prepared according to any embodiment of the first aspect. The composite material includes a substrate layer, an interfacial adhesive layer, a cellulose reinforcement layer, and a degradation regulating layer.

[0022] According to this application, the substrate layer is composed of polylactic acid (PLA) and a plasticizer. The plasticizer lowers the glass transition temperature of PLA and improves the flexibility of the material. In the interfacial adhesive layer, polyvinyl alcohol reacts with a crosslinking agent to form a three-dimensional network structure, enhancing the bonding force between the substrate layer and the cellulose reinforcement layer. The cellulose reinforcement layer is composed of cellulose nanocrystals and a surface modifier. The surface modifier improves the dispersibility of the cellulose nanocrystals and their compatibility with the interfacial adhesive. The degradation control layer is composed of starch and aliphatic polyester. Starch degrades preferentially, followed by the degradation of the aliphatic polyester, achieving staged control of the degradation rate.

[0023] In some embodiments, the thickness of the substrate layer is 200 to 300 micrometers, its tensile strength is 30 to 50 MPa, and its elongation at break is 5% to 10%.

[0024] In some embodiments, the thickness of the interfacial adhesive layer is 50 micrometers to 100 micrometers, and its peel strength is 1.5 Newtons per millimeter to 2.5 Newtons per millimeter.

[0025] In some embodiments, the thickness of the cellulose reinforcement layer is 100 to 150 micrometers, and its Young's modulus is 5 to 10 gigapascals.

[0026] In some embodiments, the thickness of the degradation control layer is 80 micrometers to 120 micrometers, and the degradation time is 30 days to 90 days. The specific degradation time can be adjusted by adjusting the ratio of starch to aliphatic polyester.

[0027] Thirdly, this application provides the application of the aforementioned biodegradable layered composite material in the packaging field. This composite material can be used to manufacture products such as food packaging bags and express delivery boxes, and its excellent mechanical properties and controllable degradation rate meet environmental protection requirements.

[0028] In some embodiments, when the composite material is used to make food packaging bags, the degradation time of the degradation control layer is set to 60 to 90 days to adapt to the service life of the food packaging.

[0029] In some embodiments, when the composite material is used to make express delivery packaging boxes, the degradation time of the degradation control layer is set to 30 to 60 days to meet the short-term use requirements of express delivery packaging.

[0030] Fourthly, this application provides the application of the aforementioned biodegradable layered composite material in the agricultural field. This composite material can be used to make agricultural mulch films, and its degradation time can be adjusted according to the crop growth cycle, avoiding soil pollution caused by traditional mulch film residues.

[0031] In some embodiments, when the composite material is used to make agricultural mulch film, the degradation time of the degradation control layer is set to 90 to 120 days to adapt to the growth cycle of crops such as rice and wheat.

[0032] In some embodiments, when the composite material is used to make fruit and vegetable preservation film, the degradation time of the degradation control layer is set to 30 to 60 days to adapt to the storage and transportation cycle of fruits and vegetables.

[0033] Fifthly, this application provides the application of the aforementioned biodegradable layered composite material in the medical field. This composite material can be used to manufacture disposable medical dressings, and its good biocompatibility and controllable degradation rate meet the specific needs of medical supplies.

[0034] In some embodiments, when the composite material is used to make disposable medical dressings, the degradation time of the degradation control layer is set to 7 to 14 days to accommodate the wound healing time.

[0035] In some embodiments, when the composite material is used to make a drug sustained-release carrier, the degradation time of the degradation regulation layer is set to 30 to 60 days to achieve sustained drug release.

[0036] Sixthly, this application provides the application of the aforementioned biodegradable layered composite material in the field of environmental protection. This composite material can be used to make products such as garbage bags and shopping bags, and its fully degradable properties reduce the pollution of the environment by plastic waste.

[0037] In some embodiments, when the composite material is used to make garbage bags, the degradation time of the degradation control layer is set to 60 to 90 days to adapt to the garbage disposal cycle.

[0038] In some embodiments, when the composite material is used to make shopping bags, the degradation time of the degradation control layer is set to 30 to 60 days to meet the environmental protection requirements of short-term use.

[0039] Seventhly, this application provides a method for testing the degradation performance of the above-mentioned biodegradable layered composite material, including the following steps:

[0040] T10: Cut the composite material sample into a 10 cm by 10 cm square specimen, weigh the initial mass and record it;

[0041] T20: Place the sample in a simulated natural degradation environment with environmental conditions of 25 to 30°C, 50% to 70% humidity, and 5000 to 10000 lux light intensity.

[0042] T30: Take out the sample every 7 days, clean the surface with deionized water, dry it, weigh it and record the mass;

[0043] T40: Calculate the mass loss rate of the sample, plot the degradation curve, and analyze the variation of the degradation rate.

[0044] In some embodiments, in step T20, the simulated natural degradation environment is achieved by soil burial, with a soil pH of 6 to 7 and a soil moisture content of 20% to 30%.

[0045] In some embodiments, in step T30, the sample is cleaned using an ultrasonic cleaner for 5 to 10 minutes at a frequency of 40 to 60 kHz.

[0046] In some implementations, the formula for calculating the mass loss rate in step T40 is: mass loss rate = (initial mass - current mass) / initial mass × 100%.

[0047] Eighthly, this application provides a method for testing the mechanical properties of the aforementioned biodegradable layered composite material, comprising the following steps:

[0048] U10: Cut the composite material sample into dumbbell-shaped specimens, with the specimen dimensions conforming to ASTM D638 standard;

[0049] U20: Fix the specimen on the universal testing machine and set the tensile rate to 5 mm per minute to 10 mm per minute;

[0050] U30: Start the testing machine, record the tensile stress-strain curve of the specimen, and calculate the tensile strength and elongation at break;

[0051] U40: Repeat the test on at least 5 samples and take the average value as the final result.

[0052] In some embodiments, in step U20, the universal testing machine has a range of 0 to 5 kN and an accuracy of ±0.5%.

[0053] In some embodiments, in step U30, the formula for calculating tensile strength is: tensile strength = maximum tensile force / cross-sectional area of ​​the specimen.

[0054] In some embodiments, the formula for calculating the elongation at break in step U40 is: elongation at break = (length at break - initial length) / initial length × 100%.

[0055] Ninthly, this application provides a method for testing the thermal properties of the above-mentioned biodegradable layered composite material, comprising the following steps:

[0056] V10: Cut the composite material sample into a circular specimen with a diameter of 10 mm and a thickness of 1 mm to 2 mm;

[0057] V20: Place the sample in a differential scanning calorimeter and set the heating rate to 10°C to 20°C per minute, with a temperature range from room temperature to 200°C.

[0058] V30: Record the heat flow curve of the sample and analyze the glass transition temperature and melting temperature;

[0059] V40: Repeat the test on at least 3 samples and take the average value as the final result.

[0060] In some embodiments, in step V20, the nitrogen flow rate of the differential scanning calorimeter is 50 ml / min to 100 ml / min.

[0061] In some embodiments, in step V30, the glass transition temperature is determined by the temperature point on the heat flow curve where the slope changes significantly.

[0062] In some embodiments, in step V40, the melting temperature is determined by the temperature point corresponding to the endothermic peak on the heat flow curve.

[0063] In a tenth aspect, this application provides a method for characterizing the microstructure of the aforementioned biodegradable layered composite material, comprising the following steps:

[0064] W10: Cut the composite material sample into thin slices with a thickness of 1 to 2 micrometers;

[0065] W20: Place the thin section in a scanning electron microscope and set the accelerating voltage to 10 kV to 20 kV;

[0066] W30: Observe the cross-sectional morphology of the sample and analyze the interfacial bonding between the layers;

[0067] W40: Repeat the test on at least 3 samples and take the representative image as the final result.

[0068] In some embodiments, in step W20, the working distance of the scanning electron microscope is 5 mm to 10 mm.

[0069] In some implementations, the method for analyzing the interface bonding in step W30 is to measure the width and roughness of the interface area.

[0070] In some implementations, in step W40, the selection criteria for representative images are images with high clarity that can reflect the overall characteristics of the sample. Detailed Implementation

[0071] The embodiments or implementations described in this specification adopt a progressive approach, with each embodiment focusing on its differences from other embodiments. In the description of this specification, the terms "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with an implementation or example that are included in at least one implementation or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same implementation or example. Furthermore, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more implementations or examples.

[0072] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0073] As described in the background section above, existing biodegradable composite materials suffer from problems such as weak interfacial bonding, inconsistent degradation processes, and limited application scope. Based on this, this application provides a biodegradable layered composite material and its preparation method, which solves the aforementioned problems by optimizing interlayer bonding, improving degradation synergy, and achieving controllable degradation rates.

[0074] In a first aspect, this application provides a biodegradable layered composite material, comprising the following steps:

[0075] S10: Polylactic acid granules are mixed with a plasticizer and then melt-extruded at 160 to 180°C to form a substrate layer; the plasticizer is citrate or glyceryl monostearate, and its mass fraction is 5% to 10% of the mass of polylactic acid granules.

[0076] S20: Cellulose nanocrystals are mixed with a surface modifier, stirred evenly in an aqueous solution, and then filtered under vacuum to form a cellulose reinforcement layer; the surface modifier is a silane coupling agent, and its amount is 1% to 3% of the mass of the cellulose nanocrystals.

[0077] S30: An interface adhesive is applied between the substrate layer and the cellulose reinforcement layer, the interface adhesive being a mixture of polyvinyl alcohol and a crosslinking agent in a mass ratio of 2:1 to 3:1, with a coating thickness of 50 micrometers to 100 micrometers.

[0078] S40: After the substrate layer, the interface adhesive layer and the cellulose reinforcement layer are stacked, they are hot-pressed at 60 to 80°C, the hot-pressing pressure is 10 MPa to 20 MPa, and the hot-pressing time is 5 to 10 minutes.

[0079] S50: A degradation control layer is coated on the outside of the cellulose reinforcement layer. The degradation control layer is made of starch and aliphatic polyester in a mass ratio of 3:1 to 5:1 and the coating thickness is 80 micrometers to 120 micrometers.

[0080] S60: The multilayer structure is dried at 40 to 60°C for 1 to 2 hours to obtain a biodegradable layered composite material.

[0081] According to this application, in step S10, the mixing of polylactic acid granules and plasticizer is carried out in a high-speed mixer for 5 to 10 minutes at a speed of 500 to 1000 rpm. After mixing, the material is transferred to a twin-screw extruder for melt extrusion at a temperature of 160 to 180°C and a screw speed of 50 to 100 rpm. The extruded melt is cooled and shaped by cooling rollers to form a substrate layer with a thickness of 200 to 300 micrometers.

[0082] In step S20, the cellulose nanocrystals, with a particle size of 50 to 100 nanometers, need to be pre-dispersed in deionized water at a concentration of 0.5% to 1%. Then, a silane coupling agent is added, and the stirring speed is 500 to 800 rpm for 1 to 2 hours. After stirring, the mixture is filtered through a vacuum filter at a pressure of 0.1 to 0.2 MPa for 10 to 20 minutes, ultimately forming a cellulose-reinforced layer with a thickness of 100 to 150 micrometers.

[0083] In step S30, the preparation of the interface adhesive involves dissolving polyvinyl alcohol in deionized water at a temperature of 80 to 90°C for 1 to 2 hours. A crosslinking agent is then added, and the mixture is stirred at 300 to 500 rpm for 10 to 20 minutes. The interface adhesive is then applied using a doctor blade coating process with a blade gap of 50 to 100 micrometers and a coating speed of 1 to 2 meters per minute. After coating, the mixture should be allowed to stand at room temperature for 5 to 10 minutes to ensure coating uniformity.

[0084] In step S40, the heating plate temperature of the hot pressing equipment is set to 60 to 80°C, and the pressure applied during the hot pressing process is 10 MPa to 20 MPa, with a pressure fluctuation range not exceeding ±2 MPa. The hot pressing time is 5 to 10 minutes, and the equipment needs to be allowed to cool naturally to room temperature after hot pressing.

[0085] In step S50, the preparation of the degradation control layer requires mixing starch and aliphatic polyester at a mass ratio of 3:1 to 5:1 for 5 to 10 minutes at a speed of 300 to 500 rpm. After mixing, the material is coated onto the outside of the cellulose reinforcement layer using a spraying process. The nozzle diameter is 0.5 to 1 mm, the spraying pressure is 0.2 to 0.4 MPa, and the coating thickness is 80 to 120 micrometers.

[0086] In step S60, the drying process is carried out in a forced-air drying oven at a temperature of 40 to 60°C for 1 to 2 hours. The airflow rate inside the drying oven is 1 to 2 meters per second, and the humidity is controlled within the range of 30% to 50%. After drying, the sample is removed and cooled to room temperature, ultimately yielding a biodegradable layered composite material.

[0087] Secondly, this application provides a biodegradable layered composite material prepared according to any embodiment of the first aspect. The composite material includes a substrate layer, an interfacial adhesive layer, a cellulose reinforcement layer, and a degradation regulating layer.

[0088] According to this application, the substrate layer is composed of polylactic acid (PLA) and a plasticizer. The plasticizer lowers the glass transition temperature of PLA and improves the flexibility of the material. In the interfacial adhesive layer, polyvinyl alcohol reacts with a crosslinking agent to form a three-dimensional network structure, enhancing the bonding force between the substrate layer and the cellulose reinforcement layer. The cellulose reinforcement layer is composed of cellulose nanocrystals and a surface modifier. The surface modifier improves the dispersibility of the cellulose nanocrystals and their compatibility with the interfacial adhesive. The degradation control layer is composed of starch and aliphatic polyester. Starch degrades preferentially, followed by the degradation of the aliphatic polyester, achieving staged control of the degradation rate.

[0089] In some embodiments, the thickness of the substrate layer is 200 to 300 micrometers, its tensile strength is 30 to 50 MPa, and its elongation at break is 5% to 10%.

[0090] In some embodiments, the thickness of the interfacial adhesive layer is 50 micrometers to 100 micrometers, and its peel strength is 1.5 Newtons per millimeter to 2.5 Newtons per millimeter.

[0091] In some embodiments, the thickness of the cellulose reinforcement layer is 100 to 150 micrometers, and its Young's modulus is 5 to 10 gigapascals.

[0092] In some embodiments, the thickness of the degradation control layer is 80 micrometers to 120 micrometers, and the degradation time is 30 days to 90 days. The specific degradation time can be adjusted by adjusting the ratio of starch to aliphatic polyester.

[0093] Thirdly, this application provides the application of the aforementioned biodegradable layered composite material in the packaging field. This composite material can be used to manufacture products such as food packaging bags and express delivery boxes.

[0094] In some embodiments, when the composite material is used to make food packaging bags, the degradation time of the degradation control layer is set to 60 to 90 days.

[0095] In some embodiments, when the composite material is used to make express delivery packaging boxes, the degradation time of the degradation control layer is set to 30 to 60 days.

[0096] Fourthly, this application provides the application of the aforementioned biodegradable layered composite material in the agricultural field. This composite material can be used to produce agricultural mulch films, and its degradation time can be adjusted according to the crop growth cycle.

[0097] In some embodiments, when the composite material is used to make agricultural mulch film, the degradation time of the degradation control layer is set to 90 to 120 days.

[0098] In some embodiments, when the composite material is used to make fruit and vegetable preservation film, the degradation time of the degradation control layer is set to 30 to 60 days.

[0099] Fifthly, this application provides the application of the aforementioned biodegradable layered composite material in the medical field. This composite material can be used to manufacture disposable medical dressings.

[0100] In some embodiments, when the composite material is used to make disposable medical dressings, the degradation time of the degradation control layer is set to 7 to 14 days.

[0101] In some embodiments, when the composite material is used to make a drug sustained-release carrier, the degradation time of the degradation regulation layer is set to 30 to 60 days.

[0102] Sixthly, this application provides the application of the aforementioned biodegradable layered composite material in the field of environmental protection. This composite material can be used to make products such as garbage bags and shopping bags.

[0103] In some embodiments, when the composite material is used to make garbage bags, the degradation time of the degradation control layer is set to 60 to 90 days.

[0104] In some embodiments, when the composite material is used to make shopping bags, the degradation time of the degradation control layer is set to 30 to 60 days.

[0105] Seventhly, this application provides a method for testing the degradation performance of the above-mentioned biodegradable layered composite material, including the following steps:

[0106] T10: Cut the composite material sample into a 10 cm by 10 cm square specimen, weigh the initial mass and record it;

[0107] T20: Place the sample in a simulated natural degradation environment with environmental conditions of 25 to 30°C, 50% to 70% humidity, and 5000 to 10000 lux light intensity.

[0108] T30: Take out the sample every 7 days, clean the surface with deionized water, dry it, weigh it and record the mass;

[0109] T40: Calculate the mass loss rate of the sample, plot the degradation curve, and analyze the variation of the degradation rate.

[0110] In some embodiments, in step T20, the simulated natural degradation environment is achieved by soil burial, with a soil pH of 6 to 7 and a soil moisture content of 20% to 30%.

[0111] In some embodiments, in step T30, the sample is cleaned using an ultrasonic cleaner for 5 to 10 minutes at a frequency of 40 to 60 kHz.

[0112] In some implementations, the formula for calculating the mass loss rate in step T40 is: mass loss rate = (initial mass - current mass) / initial mass × 100%.

[0113] Eighthly, this application provides a method for testing the mechanical properties of the aforementioned biodegradable layered composite material, comprising the following steps:

[0114] U10: Cut the composite material sample into dumbbell-shaped specimens, with the specimen dimensions conforming to ASTM D638 standard;

[0115] U20: Fix the specimen on the universal testing machine and set the tensile rate to 5 mm per minute to 10 mm per minute;

[0116] U30: Start the testing machine, record the tensile stress-strain curve of the specimen, and calculate the tensile strength and elongation at break;

[0117] U40: Repeat the test on at least 5 samples and take the average value as the final result.

[0118] In some embodiments, in step U20, the universal testing machine has a range of 0 to 5 kN and an accuracy of ±0.5%.

[0119] In some embodiments, in step U30, the formula for calculating tensile strength is: tensile strength = maximum tensile force / cross-sectional area of ​​the specimen.

[0120] In some embodiments, the formula for calculating the elongation at break in step U40 is: elongation at break = (length at break - initial length) / initial length × 100%.

[0121] Ninthly, this application provides a method for testing the thermal properties of the above-mentioned biodegradable layered composite material, comprising the following steps:

[0122] V10: Cut the composite material sample into a circular specimen with a diameter of 10 mm and a thickness of 1 mm to 2 mm;

[0123] V20: Place the sample in a differential scanning calorimeter and set the heating rate to 10°C to 20°C per minute, with a temperature range from room temperature to 200°C.

[0124] V30: Record the heat flow curve of the sample and analyze the glass transition temperature and melting temperature;

[0125] V40: Repeat the test on at least 3 samples and take the average value as the final result.

[0126] In some embodiments, in step V20, the nitrogen flow rate of the differential scanning calorimeter is 50 ml / min to 100 ml / min.

[0127] In some embodiments, in step V30, the glass transition temperature is determined by the temperature point on the heat flow curve where the slope changes significantly.

[0128] In some embodiments, in step V40, the melting temperature is determined by the temperature point corresponding to the endothermic peak on the heat flow curve.

[0129] In a tenth aspect, this application provides a method for characterizing the microstructure of the aforementioned biodegradable layered composite material, comprising the following steps:

[0130] W10: Cut the composite material sample into thin slices with a thickness of 1 to 2 micrometers;

[0131] W20: Place the thin section in a scanning electron microscope and set the accelerating voltage to 10 kV to 20 kV;

[0132] W30: Observe the cross-sectional morphology of the sample and analyze the interfacial bonding between the layers;

[0133] W40: Repeat the test on at least 3 samples and take the representative image as the final result.

[0134] In some embodiments, in step W20, the working distance of the scanning electron microscope is 5 mm to 10 mm.

[0135] In some implementations, the method for analyzing the interface bonding in step W30 is to measure the width and roughness of the interface area.

[0136] In some implementations, in step W40, the selection criteria for representative images are images with high clarity that can reflect the overall characteristics of the sample.

[0137] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0138] Example 1

[0139] S10: Mix 200g of polylactic acid granules with 10g of citrate in a high-speed mixer for 5 minutes at a speed of 500 rpm. After mixing, transfer the material to a twin-screw extruder for melt extrusion at a temperature of 160-180°C and a screw speed of 50 rpm. The extruded melt is cooled and shaped by cooling rollers to form a substrate layer with a thickness of 200 micrometers.

[0140] S20: Disperse 10 g of cellulose nanocrystals and 0.1 g of silane coupling agent in 100 mL of deionized water, stirring at 500 rpm for 1 hour. After stirring, filter the mixture through a vacuum filter at a pressure of 0.1 MPa for 10 minutes, ultimately forming a cellulose-reinforced layer with a thickness of 100 micrometers.

[0141] S30: Dissolve 10 g of polyvinyl alcohol in 100 ml of deionized water at 80-90°C for 1 hour. Then add 5 g of crosslinking agent and stir at 300 rpm for 10 minutes. Apply the interface adhesive using a doctor blade coating process with a blade gap of 50 micrometers and a coating speed of 1 meter per minute. After coating, allow to stand at room temperature for 5 minutes.

[0142] S40: After laminating the substrate layer, interface adhesive layer, and cellulose reinforcement layer, hot-press them at 60 to 80°C for 5 minutes at a pressure of 10 MPa. After hot pressing, allow them to cool naturally to room temperature.

[0143] S50: Mix 30g of starch with 10g of aliphatic polyester for 5 minutes at a speed of 300 rpm. After mixing, coat the material onto the outside of the cellulose reinforcement layer using a spraying process with a nozzle diameter of 0.5 mm, a spraying air pressure of 0.2 MPa, and a coating thickness of 80 micrometers.

[0144] S60: The multilayer structure is dried at 40 to 60°C for 1 hour. The airflow rate inside the drying chamber is 1 meter per second, and the humidity is controlled within 30%. After drying, the sample is removed and cooled to room temperature to obtain a biodegradable layered composite material.

[0145] The preparation methods of Examples 2 to 5 are similar to those of Example 1, except that the proportion, thickness and process parameters of each layer of material are adjusted.

[0146] Comparative Example 1

[0147] Compared to Example 1, no interface adhesive layer was used, but the remaining steps were the same.

[0148] Comparative Example 2

[0149] Compared to Example 1, no degradation control layer was used, but the remaining steps were the same.

[0150] Comparative Example 3

[0151] Compared to Example 1, no cellulose reinforcement layer was used, but the remaining steps were the same.

[0152] The following are the test results for the examples and comparative examples:

[0153]

[0154] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A biodegradable layered composite material, characterized in that, Prepared by the following steps: S10: Polylactic acid granules are mixed with a plasticizer and then melt-extruded at 160 to 180°C to form a substrate layer; the plasticizer is citrate or glyceryl monostearate, and its mass fraction is 5% to 10% of the mass of polylactic acid granules. S20: Cellulose nanocrystals are mixed with a surface modifier, stirred evenly in an aqueous solution, and then filtered under vacuum to form a cellulose reinforcement layer; the surface modifier is a silane coupling agent, and its amount is 1% to 3% of the mass of the cellulose nanocrystals. S30: An interface adhesive is applied between the substrate layer and the cellulose reinforcement layer, the interface adhesive being a mixture of polyvinyl alcohol and a crosslinking agent in a mass ratio of 2:1 to 3:1, with a coating thickness of 50 micrometers to 100 micrometers. S40: After the substrate layer, the interface adhesive layer and the cellulose reinforcement layer are stacked, they are hot-pressed at 60 to 80°C, the hot-pressing pressure is 10 MPa to 20 MPa, and the hot-pressing time is 5 to 10 minutes. S50: A degradation control layer is coated on the outside of the cellulose reinforcement layer. The degradation control layer is made of starch and aliphatic polyester in a mass ratio of 3:1 to 5:1 and the coating thickness is 80 micrometers to 120 micrometers. S60: The multilayer structure is dried at 40 to 60°C for 1 to 2 hours to obtain a biodegradable layered composite material.

2. The biodegradable layered composite material according to claim 1, characterized in that, In step S10, the melt index of polylactic acid particles is 5 grams per 10 minutes to 15 grams per 10 minutes, and the screw speed during melt extrusion is 50 to 100 revolutions per minute.

3. The biodegradable layered composite material according to claim 1, characterized in that, In step S20, the particle size of the cellulose nanocrystals is 50 to 100 nanometers, the stirring speed is 500 to 800 revolutions per minute, and the stirring time is 1 to 2 hours.

4. The biodegradable layered composite material according to claim 1, characterized in that, In step S30, the interface adhesive is applied using a doctor blade coating process, with a doctor blade gap of 50 to 100 micrometers and a coating speed of 1 to 2 meters per minute.

5. The biodegradable layered composite material according to claim 1, characterized in that, In step S40, the temperature of the heating plate of the hot pressing molding equipment is 60 to 80°C, and the pressure applied during the hot pressing process is evenly distributed with a pressure fluctuation range not exceeding ±2 MPa.

6. The biodegradable layered composite material according to claim 1, characterized in that, In step S50, the degradation control layer is coated using a spraying process with a nozzle diameter of 0.5 mm to 1 mm and a spraying air pressure of 0.2 MPa to 0.4 MPa.

7. The biodegradable layered composite material according to claim 1, characterized in that, In step S60, the drying process is carried out in a forced-air drying oven, where the air velocity is 1 to 2 meters per second and the humidity is controlled within the range of 30% to 50% during the drying process.

8. The biodegradable layered composite material according to claim 1, characterized in that, The composite material includes a substrate layer, an interfacial adhesive layer, a cellulose reinforcement layer, and a degradation regulation layer.

9. The biodegradable layered composite material according to claim 8, characterized in that, The thickness of the substrate layer is 200 to 300 micrometers, the thickness of the interface adhesive layer is 50 to 100 micrometers, the thickness of the cellulose reinforcement layer is 100 to 150 micrometers, and the thickness of the degradation regulation layer is 80 to 120 micrometers.

10. The biodegradable layered composite material according to claim 8, characterized in that, The degradation time of the degradation control layer is 30 to 90 days, and the specific degradation time is adjusted by adjusting the mass ratio of starch to aliphatic polyester.

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