A fully biodegradable high-barrier packaging material and its preparation method and application

Abstract

The present invention discloses a fully biodegradable high-barrier packaging material, its preparation method, and its application. The packaging material uses plant fiber pulp and polylactic acid as its main raw materials. A sizing agent and barrier particles are added to the pulp to modify nanocellulose. A papermaking machine is used to produce multilayered paper. A polyvinyl alcohol aqueous solution is sprayed between the material layers, and the paper is subjected to high-temperature hot pressing to obtain the fully biodegradable high-barrier packaging material. The multilayer structure of the present invention can greatly improve product yield. The resulting packaging material has excellent water vapor barrier properties, processing properties, and mechanical properties, and can be used in the field of environmentally friendly packaging materials.

Description

Technical Field

[0001] The present invention relates to the field of fully biodegradable materials, and in particular to a fully biodegradable high-barrier packaging material and a preparation method and application thereof. Background Art

[0002] With the ban on the use of traditional non-degradable plastics and increasing attention to environmental issues, the use of fully biodegradable materials in packaging has become a trend to achieve safe and efficient food preservation and green development. However, both traditional natural fully biodegradable materials and the newly synthesized and modified fully biodegradable materials developed in recent years have poor water vapor barrier properties, largely due to the presence of hydrophilic groups and excellent hydrophilicity, which endow the materials with good biodegradability. This is particularly true under high temperature and high humidity conditions.

[0003] Polylactic acid (PLA) is a biodegradable aliphatic polyester with excellent processing properties and biocompatibility. As a type of thermoplastic material, it can be made into products of various shapes through extrusion, injection molding, blow molding, weaving, etc., and these products can be naturally degraded into simple molecules such as H2O and CO2 under composting conditions. Natural plant fibers have the advantages of wide availability, low price, and biodegradability, and are the most widely used packaging materials. In the existing solutions, a layer of PLA film is applied to the surface of paper made from plant fiber pulp to improve the barrier properties of the paper. Although the barrier properties are improved to a certain extent compared with pure plant fiber pulp paper, the improvement effect is extremely limited due to the poor barrier properties of the polylactic acid film itself to water vapor.

[0004] Chinese patent applications (publication numbers CN 111155356 A and CN 109594411 A) utilize a papermaking process to produce paper from plant fibers and polylactic acid fibers as a cooling material for cigarettes. While polylactic acid has a superior water vapor barrier capability to plant fiber pulp, the packaging material produced by coating the paper surface with a film is inherently brittle and has poor folding resistance, limiting the thickness of the polylactic acid film. Summary of the Invention

[0005] The primary purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for preparing a fully biodegradable high-barrier packaging material.

[0006] Another object of the present invention is to provide a completely biodegradable high-barrier packaging material prepared by the method.

[0007] Another object of the present invention is to provide an application of the fully biodegradable high barrier packaging material.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] A method for preparing a fully biodegradable high-barrier packaging material comprises the following steps:

[0010] (1) Preparation of modified nanocellulose (nanobarrier material)

[0011] Stearic acid (C 17 H 35 dissolving CaCl2 and NaHCO3 in water, adding NaOH to adjust the alkalinity of the solution, and stirring and mixing at 70°C to 90°C to obtain a mixed solution of NaHCO3 / stearic acid; then adding nanocellulose to the CaCl2 solution, stirring thoroughly, and squeezing dry, and then adding the nanocellulose to the mixed solution of NaHCO3 / stearic acid, stirring thoroughly, filtering out the nanocellulose, and washing until the filtrate is clear and the pH is neutral to obtain modified nanocellulose;

[0012] (2) Preparation of high barrier packaging materials

[0013] ① Preparation of a double-layer high-barrier packaging material: using plant fiber pulp with a beating degree of 20°SR to 70°SR as a surface layer pulp; using a mixed pulp obtained by adding plant fiber pulp with a beating degree of 20°SR to 70°SR and polylactic acid, a sizing agent, and the modified nanocellulose prepared in step (1) as a bottom layer pulp; using a papermaking machine to make paper in one go, spraying a polyvinyl alcohol (PVA) aqueous solution between the surface layer and the bottom layer, and then hot-pressing the dried paper through a calender to obtain a double-layer high-barrier packaging material, that is, the fully biodegradable high-barrier packaging material;

[0014] or

[0015] ② Preparation of a three-layer high-barrier packaging material: using plant fiber pulp with a beating degree of 20°SR to 70°SR as the surface layer pulp and the bottom layer pulp; using a mixed pulp obtained by mixing plant fiber pulp with a beating degree of 20°SR to 70°SR with polylactic acid, adding a sizing agent and the modified nanocellulose prepared in step (1) as the core layer (middle layer) pulp; using a papermaking machine to make paper in one go, spraying a polyvinyl alcohol (PVA) aqueous solution between the surface layer and the core layer and between the core layer and the bottom layer, and then hot-pressing the dried paper through a calender to obtain a three-layer high-barrier packaging material, that is, the described fully biodegradable high-barrier packaging material.

[0016] The stearic acid (C 17 H 35 The mass ratio of COOH) and NaHCO3 is (2:8) to (9:1); preferably (3:7) to (7:3).

[0017] The water described in step (1) is preferably deionized water.

[0018] The mass ratio of NaOH to NaHCO3 in step (1) is 0.1 to 2:1, preferably 0.5 to 1.2:1.

[0019] The temperature for stirring and mixing uniformly in step (1) is preferably 75°C to 80°C.

[0020] The nanocellulose described in step (1) is nanocellulose (MFC) prepared by a conventional high-pressure homogenization method; preferably, it is prepared by the following method:

[0021] Freeze-dried bleached softwood pulp, 2,2,6,6-tetramethylpiperidin-1-oxyl free radical (TEMPO) and NaBr are added to water, and sodium hypochlorite solution is added dropwise to stir the reaction. During the reaction, the pH value of the reaction mixture is adjusted to about 10.0. After the reaction is completed, ethanol is added to terminate the reaction. The pulp is then washed to neutrality, diluted with water, and ground using an ultrafine refiner. After the grinding is completed, the slurry is collected and freeze-dried to obtain nanocellulose.

[0022] The mass ratio of the bleached softwood pulp, 2,2,6,6-tetramethylpiperidin-1-oxyl free radical (TEMPO) and NaBr is 50:4:25.

[0023] The dosage of the sodium hypochlorite is calculated based on adding 3 mmol of sodium hypochlorite per gram of bleached softwood pulp (cellulose).

[0024] The pH value is adjusted using a NaOH solution; preferably, it is adjusted using a 0.5 mol / L NaOH solution.

[0025] The stirring reaction time is preferably 1 hour.

[0026] The washing to neutrality is washing with deionized water for multiple times to neutrality.

[0027] The dilution with water is to dilute the cellulose to a mass concentration of 2%.

[0028] The rotation speed of the grinding process is 2500 rpm.

[0029] The grinding time is 1 hour.

[0030] The concentration of the CaCl2 solution described in step (1) is 0.1-0.5 mol / L; preferably 0.2-0.4 mol / L; more preferably 0.2 mol / L.

[0031] The amount of nanocellulose used in step (1) is calculated based on 10 to 50 ml of CaCl2 solution per gram of nanocellulose; preferably, it is calculated based on 32 ml of CaCl2 solution per gram of nanocellulose.

[0032] In step (1), nanocellulose is added to the CaCl2 solution and stirred for about 1 hour.

[0033] The washing in step (1) is performed using deionized water.

[0034] The beating degree of the plant fiber pulp described in steps ① and ② is preferably 35°SR to 45°SR.

[0035] The plant fiber pulp described in steps ① and ② includes at least one of bamboo pulp, coniferous wood pulp, broadleaf wood pulp and other types of plant fiber pulp; preferably at least one of bleached coniferous wood pulp, unbleached coniferous wood pulp, natural coniferous wood pulp, bleached broadleaf wood pulp, unbleached broadleaf wood pulp, bleached bamboo pulp and unbleached bamboo pulp.

[0036] The plant fiber pulp in the surface layer pulp described in step ① is a mixed pulp composed of at least one of bamboo pulp and coniferous wood pulp, and broadleaf wood pulp; further preferably, it is a mixed pulp composed of bamboo pulp and broadleaf wood pulp in a mass ratio of (6:4) to (9:1), or a mixed pulp composed of coniferous wood pulp and broadleaf wood pulp in a mass ratio of (6:4) to (9:1); further preferably, it is a mixed pulp composed of bamboo pulp and broadleaf wood pulp in a mass ratio of (6:4) to (8:2), or a mixed pulp composed of coniferous wood pulp and broadleaf wood pulp in a mass ratio of (6:4) to (8:2).

[0037] The mass ratio of plant fiber pulp to polylactic acid in the bottom slurry described in step ① is (4:6) to (9:1); preferably (5:5) to (7:3).

[0038] The polylactic acid described in steps ① and ② is at least one of polylactic acid fibers and polylactic acid particles; preferably, it is at least one of polylactic acid fibers having an average length of 0.5 mm to 8 mm and polylactic acid particles having a particle size of 100 mesh to 1800 mesh; more preferably, it is at least one of polylactic acid fibers having an average length of 5 mm to 6 mm and polylactic acid particles having a particle size of 800 mesh.

[0039] The sizing agent in steps ① and ② is at least one of alkyl ketene dimer emulsion AKD and alkenyl succinic anhydride ASA; preferably alkyl ketene dimer emulsion AKD.

[0040] The amount of the sizing agent added in steps ① and ② is 0.2-2.0% of the total mass of the plant fiber pulp and the polylactic acid; preferably 0.2% of the total mass of the plant fiber pulp and the polylactic acid.

[0041] The amount of modified nanocellulose added in steps ① and ② is 0.1 to 3% of the total mass of the plant fiber pulp and the polylactic acid; preferably 0.1 to 0.3% of the total mass of the plant fiber pulp and the polylactic acid.

[0042] The polyvinyl alcohol described in steps ① and ② is 1799 polyvinyl alcohol (model 1799, degree of polymerization 1700, alcoholysis degree 99%).

[0043] The concentration of the polyvinyl alcohol aqueous solution in steps ① and ② is 0.1-2% by mass, preferably 0.8-1.2% by mass.

[0044] The spraying amount of the polyvinyl alcohol aqueous solution in step ② is 0.1 g / m 2 ~10g / m 2 Spraying; preferably according to its quantitative after drying of 1g / m 2 ~5g / m 2 More preferably, the amount after drying is 2g / m 2 Spray.

[0045] The calender described in steps ① and ② is a soft roller calender, a common calender or various roller calenders commonly used in the papermaking industry. The material is passed through the calender nip to achieve the calendering effect. When the composite material has a double-layer structure or a three-layer structure, the surface layer contacts the heated roller of the calender, and the bottom layer contacts the non-heated roller.

[0046] The papermaking machine described in steps ① and ② is a Fourdrinier papermaking machine, a cylinder papermaking machine or a clamped papermaking machine.

[0047] The conditions for hot pressing of the calender described in steps ① and ② are: calendering temperature 80-300°C, calendering line pressure 20-400 kN / m, and machine speed 100 m / min-1000 m / min; preferably: calendering temperature 180-220°C, calendering line pressure 200-250 kN / m, and paper machine speed 600 m / min.

[0048] The surface layer of the double-layer high barrier packaging material described in step ① has a basis weight of 15 to 60 g / m 2 (Preferably 30g / m 2 ), the bottom layer is 50~150g / m 2 (Preferably 120g / m 2 ).

[0049] The plant fiber pulp in the surface layer pulp and the bottom layer pulp described in step ② are both mixed pulps composed of at least one of bamboo pulp and coniferous wood pulp, and broadleaf wood pulp; further preferably, it is a mixed pulp composed of bamboo pulp and broadleaf wood pulp in a mass ratio of (6:4) to (9:1), or a mixed pulp composed of coniferous wood pulp and broadleaf wood pulp in a mass ratio of (6:4) to (9:1); further preferably, it is a mixed pulp composed of bamboo pulp and broadleaf wood pulp in a mass ratio of (6:4) to (8:2), or a mixed pulp composed of coniferous wood pulp and broadleaf wood pulp in a mass ratio of (6:4) to (8:2).

[0050] The mass ratio of plant fiber pulp to polylactic acid in the core layer slurry described in step ② is (4:6) to (9:1); preferably (5:5) to (7:3).

[0051] The surface layer of the three-layer high barrier packaging material described in step ② has a weight of 15 to 50 g / m 2 (Preferably 25g / m 2 ), the core layer is 50~140g / m 2 (Preferably 110 g / m 2 ), the bottom layer is 15~50g / m 2 (Preferably 25g / m 2 ).

[0052] A completely biodegradable high-barrier packaging material is prepared by any of the methods described above.

[0053] Application of the fully biodegradable high-barrier packaging material in food packaging materials.

[0054] The food packaging material includes disposable food packaging materials, preferably disposable food packaging bags, including disposable tea packaging bags and disposable biscuit packaging bags.

[0055] The present invention has the following advantages and effects compared to the prior art:

[0056] 1. The present invention provides a method for producing a fully biodegradable material with excellent barrier properties. A high-barrier, fully biodegradable packaging material is produced using plant fiber pulp and polylactic acid as main raw materials and a traditional papermaking method. The specific steps are: using plant fiber pulp and polylactic acid as main raw materials, adding sizing agents and barrier particles (modified nanocellulose) and other substances in the pulp by adding them into the pulp, and using a papermaking machine to paper multi-layer structure paper, spraying polyvinyl alcohol aqueous solution between material layers, and undergoing high-temperature hot pressing inside or outside the machine to obtain a high-barrier, fully biodegradable packaging material with excellent water vapor barrier properties. The multi-layer structure can greatly improve the product yield.

[0057] 2. The plant fiber / PLA composite material produced by the papermaking method of the present invention can significantly increase the mass proportion of polylactic acid in the material and enhance the barrier properties of the material. Since the high temperature and hot pressing increase the density and tightness of the material, and work synergistically with the pulp, it obtains better barrier properties and processing capabilities than pure polylactic acid. At the same time, the barrier effects of nano-barrier materials and polyvinyl alcohol are superimposed to achieve high barrier properties of the fully biodegradable composite material.

[0058] 3. The main materials used in the present invention are plant fibers and polylactic acid, and the main auxiliary materials are modified nanocellulose and polyvinyl alcohol, all of which are completely biodegradable and environmentally friendly. The traditional papermaking method is used to overcome the defects of the coating processing method, and plant fiber / PLA composite materials with a polylactic acid mass ratio of more than 10% can be prepared.

[0059] 4. The present invention uses plant fibers and polylactic acid as raw materials. By adding various substances, the gaps between fibers can be effectively filled, thereby improving the barrier properties of the material. At the same time, polyvinyl alcohol is sprayed to form a dense film on the surface of the material, further enhancing the barrier properties of the material. The barrier properties of the material to water vapor can reach a water vapor permeability of 0.3885g·m -2 day -1 .

[0060] 5. The present invention adopts a multi-layer structure to produce plant fiber / PLA composite materials, which can greatly improve the yield rate during high-temperature calendering and reduce production costs. The papermaking method is used to produce fully biodegradable packaging materials with good processing properties, mechanical properties, and gas barrier properties, which is of great significance in the field of environmentally friendly packaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is a graph showing the raw data of the water vapor transmission test of the high barrier packaging material prepared in Example 3.

[0062] Figure 2 This is a physical picture of the high barrier packaging material prepared in Example 5. DETAILED DESCRIPTION

[0063] The present invention will be described in further detail below in conjunction with the examples, but embodiments of the present invention are not limited thereto. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the art. The test methods in the following examples where specific experimental conditions are not specified are generally based on conventional experimental conditions. Unless otherwise specified, the reagents and raw materials used in the present invention can be obtained commercially.

[0064] The bleached coniferous pulp for preparing nanocellulose involved in the embodiments and comparative examples of the present invention was purchased from Hubei Chemical Fiber Co., Ltd.; 2,2,6,6-tetramethylpiperidin-1-oxyl free radical (TEMPO, purity>98%) was purchased from Sigma-Aldrich; ethanol (purity>95%) was purchased from Guangzhou Chemical Reagent Co., Ltd.; sodium hydroxide (NaOH, purity≥97%), ammonia water (purity≥25%), sodium periodate (NaIO4, purity≥99%) and sodium bromide (NaBr, purity≥98%) were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0065] The bleached bamboo pulp involved in the embodiments and comparative examples of the present invention was purchased from Sichuan Yongfeng Paper Co., Ltd.; the bleached softwood pulp was Stone brand, purchased from SMURFIT-STONE Contanier Co., Ltd.; the hardwood pulp was purchased from Shandong Sun Paper Co., Ltd.; and the unbleached softwood pulp was purchased from Shandong Sun Paper Co., Ltd.

[0066] The polylactic acid involved in the embodiments and comparative examples of the present invention includes polylactic acid fibers and polylactic acid particles, wherein the average length of the polylactic acid fibers (polylactic acid chopped fibers) is 0.5 mm to 8 mm, and they are purchased from Zhejiang Haining Saiyupu Chemical Technology Co., Ltd.; the particle size of the polylactic acid particles is 100 mesh to 1800 mesh, and they are purchased from Zhejiang Haining Saiyupu Chemical Technology Co., Ltd.

[0067] The sizing agent involved in the examples and comparative examples of the present invention is alkyl ketene dimer emulsion (AKD), purchased from Yueyang Antai Tairui Fine Chemical Co., Ltd., with an implementation standard of Q / JBRG001-2009, a solid content of ≥15%, and a pH value of 2-4.

[0068] The brand of polyvinyl alcohol involved in the examples and comparative examples of the present invention is Wokai, purchased from Sinopharm Chemical Reagent Co., Ltd., with a model number of 1799, a degree of polymerization of 1700, and a degree of alcoholysis of 99%.

[0069] Example 1

[0070] A method for producing a fully biodegradable high-barrier packaging material comprises the following steps:

[0071] (1) Freeze-dried bleached softwood pulp (0.5000 g, absolutely dry) and 500 ml of deionized water were added to a 1000 mL flask. TEMPO (0.0040 g) and NaBr (0.0250 g) were then added to the flask in sequence, and sodium hypochlorite solution was slowly added dropwise, with the amount of sodium hypochlorite added being controlled to be 3 mmol per gram of cellulose (bleached softwood pulp). During the reaction, the pH of the reaction mixture was adjusted to approximately 10.0 using a 0.5 mol / L NaOH solution. The reaction was continued at 500 rpm for 1 h, and 10 mL of ethanol was added after the reaction time was reached to terminate the reaction. The suspension was filtered and washed several times with deionized water until neutral, then diluted with deionized water to a mass fraction of 2%, and then ground using an ultrafine refiner (MKCA6-2J, Masuko Sangyo Co., Ltd. Japan) at 2500 rpm for 1 h. After grinding, the slurry was collected and freeze-dried to obtain nanocellulose powder for later use.

[0072] (2) Stearic acid (C 17 H 35 COOH) and NaHCO3 according to the mass ratio C 17 H 35 Dissolve and disperse COOH:NaHCO3 in deionized water in a ratio of 3:7, and add a certain amount of NaOH to adjust the alkalinity of the solution to NaOH:NaHCO3=0.5:1 (mass ratio). Keep the temperature in a water bath at 75°C and stir to mix evenly to obtain a NaHCO3 / stearic acid mixed solution for later use.

[0073] (3) The nanocellulose obtained in step (1) was added to a 0.2 M CaCl2 solution at a solid-liquid ratio of 1:32 (g / ml), stirred for 1 hour, and then squeezed dry. The mixture was then added to the mixed solution of NaHCO3 / stearic acid obtained in step (2), and the mixture was stirred thoroughly before termination. The nanocellulose was filtered out and repeatedly washed with deionized water until the filtrate was clear and the pH was neutral to obtain modified nanocellulose (as a nano barrier material) for later use.

[0074] (4) 1799 polyvinyl alcohol is prepared into a polyvinyl alcohol aqueous solution with a concentration of 0.8% by mass and set aside.

[0075] (5) Beat the bleached bamboo pulp to a beating degree of 40°SR, and beat the hardwood pulp to a beating degree of 35°SR, and set aside.

[0076] (6) Mix the bleached bamboo pulp with a beating degree of 40°SR in step (5) with the broadleaf pulp with a beating degree of 35°SR, with the mixing ratio of bleached bamboo pulp: broadleaf pulp = 8:2 (the absolute dry mass ratio of the two pulps) to obtain a surface layer pulp for standby use.

[0077] (7) The bleached bamboo pulp with a beating degree of 40°SR in step (5) and polylactic acid fibers (the average length of the polylactic acid fibers is 5 mm) are mixed in a ratio of 7:3 (absolute dry mass ratio of the bleached bamboo pulp with a beating degree of 40°SR to the polylactic acid fibers), and 0.2 wt% of AKD (absolute dry mass ratio of the sizing agent to the pulp (i.e., the bamboo pulp with a beating degree of 40°SR + polylactic acid fibers)) is added to the mixed pulp, and then the mixed pulp is deflaked (the deflaking machine speed is 3000 rpm / min) for 20 minutes. Then, the modified nanocellulose prepared in step (3) is added in an amount of 0.3 wt% (absolute dry mass ratio of the modified nanocellulose to the pulp (i.e., the bleached bamboo pulp with a beating degree of 40°SR + polylactic acid fibers)) to obtain a bottom slurry for standby use.

[0078] (8) Paper is made using a fourdrinier papermaking machine with a double-layer stacked net arrangement, wherein the surface layer is made of the surface layer slurry in step (6), and the surface layer is 30 g / m 2 The bottom layer adopts the bottom layer slurry in step (7), and the bottom layer is quantitatively 120g / m 2 ; and spray the 0.8wt% polyvinyl alcohol aqueous solution prepared in step (4) between the surface layer and the bottom layer, the spraying quantity is 2g / m 2 The dried paper was calendered on a soft roller calender at 200°C, a calendering line pressure of 200 kN / m, and a paper machine speed of 600 m / min.

[0079] Example 2

[0080] A method for producing a fully biodegradable high-barrier packaging material comprises the following steps:

[0081] (1) Freeze-dried bleached softwood pulp (0.5000 g, absolutely dry) and 500 ml of deionized water were added to a 1000 mL flask. TEMPO (0.0040 g) and NaBr (0.0250 g) were then added to the flask in sequence, and sodium hypochlorite solution was slowly added dropwise, with the amount of sodium hypochlorite added being controlled to be 3 mmol per gram of cellulose. During the reaction, the pH value of the reaction mixture was adjusted to approximately 10.0 using a 0.5 mol / L NaOH solution. The reaction was continued at 500 rpm for 1 h, and 10 mL of ethanol was added after the reaction time was reached to terminate the reaction. The suspension was filtered and washed with deionized water several times until neutral, then diluted with deionized water to a mass fraction of 2%, and then ground with an ultrafine refiner (MKCA6-2J, Masuko Sangyo Co., Ltd. Japan) at 2500 rpm for 1 h. After grinding, the slurry was collected and freeze-dried to obtain nanocellulose powder for later use.

[0082] (2) Stearic acid (C 17 H 35 COOH) and NaHCO3 according to the mass ratio C 17 H 35 Dissolve and disperse COOH:NaHCO3 in deionized water in a ratio of 3:7, and add a certain amount of NaOH to adjust the alkalinity of the solution to NaOH:NaHCO3=0.5:1 (mass ratio). Keep the temperature in a water bath at 75°C and stir to mix evenly to obtain a NaHCO3 / stearic acid mixed solution for later use.

[0083] (3) The nanocellulose obtained in step (1) was added to a 0.2 M CaCl2 solution at a solid-liquid ratio of 1:32 (g / ml), stirred for 1 hour, and then squeezed dry. The mixture was then added to the mixed solution of NaHCO3 / stearic acid obtained in step (2), and the mixture was stirred thoroughly before termination. The nanocellulose was filtered out and repeatedly washed with deionized water until the filtrate was clear and the pH was neutral to obtain modified nanocellulose for later use.

[0084] (4) Prepare 1799 polyvinyl alcohol into a polyvinyl alcohol aqueous solution with a concentration of 1.0% by mass and set aside.

[0085] (5) Beat the bleached softwood pulp to a beating degree of 45°SR, and beat the hardwood pulp to a beating degree of 35°SR, and set aside.

[0086] (6) Mix the bleached coniferous pulp with a beating degree of 45°SR in step (5) with the broadleaf pulp with a beating degree of 35°SR, with the mixing ratio of coniferous pulp: broadleaf pulp = 7:3 (the absolute dry mass ratio of the two pulps) to obtain a surface layer pulp for later use.

[0087] (7) The bleached coniferous pulp with a beating degree of 45°SR in step (5) and the polylactic acid particles with a particle size of 800 mesh are mixed in a ratio of 6:4 (the absolute dry mass ratio of the bleached coniferous pulp with a beating degree of 45°SR to the polylactic acid particles), and 0.2 wt% of AKD (the absolute dry mass ratio of the sizing agent to the pulp (i.e., the bleached coniferous pulp with a beating degree of 45°SR + polylactic acid particles)) is added to the mixed pulp, and then the mixed pulp is deflaked (the deflaking machine speed is 3000 rpm / min) for 20 minutes; then the modified nanocellulose prepared in step (3) is added in an amount of 0.3 wt% (the absolute dry mass ratio of the modified nanocellulose to the pulp (i.e., the bleached coniferous pulp with a beating degree of 45°SR + polylactic acid particles)) to obtain a bottom slurry for standby use.

[0088] (8) Paper is made using a fourdrinier papermaking machine with a double-layer stacked net arrangement, wherein the surface layer is made of the surface layer slurry in step (6), and the surface layer is 30 g / m 2The bottom layer adopts the bottom layer slurry in step (7), and the bottom layer is quantitatively 120g / m 2 ; and spray the 1.0wt% polyvinyl alcohol aqueous solution prepared in step (4) between the surface layer and the bottom layer, the spraying quantity is 2g / m 2 The dried paper was calendered on a soft roller calender at 190°C, a calendering line pressure of 220 kN / m, and a paper machine speed of 600 m / min.

[0089] Example 3

[0090] A method for producing a fully biodegradable high-barrier packaging material comprises the following steps:

[0091] (1) Freeze-dried bleached softwood pulp (0.5000 g, absolutely dry) and 500 ml of deionized water were added to a 1000 mL flask. TEMPO (0.0040 g) and NaBr (0.0250 g) were then added to the flask in sequence, and sodium hypochlorite solution was slowly added dropwise, with the amount of sodium hypochlorite added being controlled to be 3 mmol per gram of cellulose. During the reaction, the pH value of the reaction mixture was adjusted to approximately 10.0 using a 0.5 mol / L NaOH solution. The reaction was continued at 500 rpm for 1 h, and 10 mL of ethanol was added after the reaction time was reached to terminate the reaction. The suspension was filtered and washed with deionized water several times until neutral, then diluted with deionized water to a mass fraction of 2%, and then ground with an ultrafine refiner (MKCA6-2J, Masuko Sangyo Co., Ltd. Japan) at 2500 rpm for 1 h. After grinding, the slurry was collected and freeze-dried to obtain nanocellulose powder for later use.

[0092] (2) Stearic acid (C 17 H 35 COOH) and NaHCO3 according to the mass ratio C 17 H 35 Dissolve and disperse COOH:NaHCO3=5:5 in deionized water, and add a certain amount of NaOH to adjust the alkalinity of the solution, wherein NaOH:NaHCO3=1:1 (mass ratio). Keep the temperature in a water bath at 80°C and stir to mix evenly to obtain a NaHCO3 / stearic acid mixed solution for later use.

[0093] (3) The nanocellulose obtained in step (1) was added to a 0.2 M CaCl2 solution at a solid-liquid ratio of 1:32 (g / ml), stirred for 1 hour, and then squeezed dry. The mixture was then added to the mixed solution of NaHCO3 / stearic acid obtained in step (2), and the mixture was stirred thoroughly before termination. The nanocellulose was filtered out and repeatedly washed with deionized water until the filtrate was clear and the pH was neutral to obtain modified nanocellulose for later use.

[0094] (4) Prepare 1799 polyvinyl alcohol into a polyvinyl alcohol aqueous solution with a concentration of 1.2% by mass and set aside.

[0095] (5) Beat the natural softwood pulp to a beating degree of 42°SR, and beat the hardwood pulp to a beating degree of 35°SR, and set aside.

[0096] (6) Mix the natural softwood pulp with a beating degree of 42°SR in step (5) with the broadleaf pulp with a beating degree of 35°SR in a mixing ratio of softwood pulp: broadleaf pulp = 7:3 (the absolute dry mass ratio of the two pulps) to obtain a surface layer pulp for later use.

[0097] (7) The natural coniferous pulp with a beating degree of 42°SR in step (5) and polylactic acid fiber (the average length of the polylactic acid fiber is 6 mm) are mixed in a ratio of 5:5 (the absolute dry mass ratio of the natural coniferous pulp with a beating degree of 42°SR to the polylactic acid fiber), and 0.2 wt% of AKD (the absolute dry mass ratio of the sizing agent to the pulp (i.e., the natural coniferous pulp with a beating degree of 42°SR + polylactic acid fiber)) is added to the mixed pulp, and then the mixed pulp is deflaked (the deflaking machine speed is 3000 rpm / min) for 20 minutes; then the modified nanocellulose prepared in step (3) is added in an amount of 0.1 wt% (the absolute dry mass ratio of the modified nanocellulose to the pulp (i.e., the natural coniferous pulp with a beating degree of 42°SR + polylactic acid fiber)) to obtain a bottom slurry for standby use.

[0098] (8) Paper is made using a fourdrinier papermaking machine with a double-layer stacked net arrangement, wherein the surface layer is made of the surface layer slurry in step (6), and the surface layer is 30 g / m 2 The bottom layer adopts the bottom layer slurry in step (7), and the bottom layer is quantitatively 120g / m 2 ; and spray the 1.2wt% polyvinyl alcohol aqueous solution prepared in step (4) between the surface layer and the bottom layer, the spraying quantity is 2g / m 2 The dried paper was calendered on a soft roller calender at 180°C, a calendering line pressure of 250 kN / m, and a paper machine speed of 600 m / min.

[0099] Example 4

[0100] A method for producing a fully biodegradable high-barrier packaging material comprises the following steps:

[0101] (1) Freeze-dried bleached softwood pulp (0.5000 g, absolutely dry) and 500 ml of deionized water were added to a 1000 mL flask. TEMPO (0.0040 g) and NaBr (0.0250 g) were then added to the flask in sequence, and sodium hypochlorite solution was slowly added dropwise, with the amount of sodium hypochlorite added being controlled to be 3 mmol per gram of cellulose. During the reaction, the pH value of the reaction mixture was adjusted to approximately 10.0 using a 0.5 mol / L NaOH solution. The reaction was continued at 500 rpm for 1 h, and 10 mL of ethanol was added after the reaction time was reached to terminate the reaction. The suspension was filtered and washed with deionized water several times until neutral, then diluted with deionized water to a mass fraction of 2%, and then ground with an ultrafine refiner (MKCA6-2J, Masuko Sangyo Co., Ltd. Japan) at 2500 rpm for 1 h. After grinding, the slurry was collected and freeze-dried to obtain nanocellulose powder for later use.

[0102] (2) Stearic acid (C 17 H 35 COOH) and NaHCO3 according to the mass ratio C 17 H 35 Dissolve and disperse COOH:NaHCO3=5:5 in deionized water, and add a certain amount of NaOH to adjust the alkalinity of the solution, wherein NaOH:NaHCO3=1:1 (mass ratio). Keep the temperature in a water bath at 80°C and stir to mix evenly to obtain a NaHCO3 / stearic acid mixed solution for later use.

[0103] (3) The nanocellulose obtained in step (1) was added to a 0.2 M CaCl2 solution at a solid-liquid ratio of 1:32 (g / ml), stirred for 1 hour, and then squeezed dry. The mixture was then added to the mixed solution of NaHCO3 / stearic acid obtained in step (2), and the mixture was stirred thoroughly before termination. The nanocellulose was filtered out and repeatedly washed with deionized water until the filtrate was clear and the pH was neutral to obtain modified nanocellulose for later use.

[0104] (4) Prepare 1799 polyvinyl alcohol into a polyvinyl alcohol aqueous solution with a concentration of 0.9% by mass and set aside.

[0105] (5) Beat the bleached bamboo pulp to a beating degree of 38°SR, and beat the hardwood pulp to a beating degree of 35°SR, and set aside.

[0106] (6) Mix the bleached bamboo pulp with a beating degree of 38°SR in step (5) with the broadleaf pulp with a beating degree of 35°SR, with the mixing ratio of bamboo pulp: broadleaf pulp = 8:2 (the absolute dry mass ratio of the two pulps) to obtain a surface layer pulp for standby use.

[0107] (7) The bleached bamboo pulp with a beating degree of 38°SR in step (5) and polylactic acid fiber (the average length of the polylactic acid fiber is 5 mm) are mixed in a ratio of 7:3 (the absolute dry mass ratio of the bleached bamboo pulp with a beating degree of 38°SR to the polylactic acid fiber), and 0.2wt% of AKD (the absolute dry mass ratio of the sizing agent to the pulp (i.e., the bleached bamboo pulp with a beating degree of 38°SR + polylactic acid fiber)) is added to the mixed pulp, and then the mixed pulp is deflaked (the deflaking machine speed is 3000rpm / min) for 20min; then the modified nanocellulose prepared in step (3) is added in an amount of 0.3wt% (the absolute dry mass ratio of the modified nanocellulose to the pulp (i.e., the bleached bamboo pulp with a beating degree of 38°SR + polylactic acid fiber)) to obtain a bottom slurry for standby use.

[0108] (8) Paper is made using a fourdrinier papermaking machine with a double-layer stacked net arrangement, wherein the surface layer is made of the surface layer slurry in step (6), and the surface layer is 30 g / m 2 The bottom layer adopts the bottom layer slurry in step (7), and the bottom layer is quantitatively 120g / m 2 ; and spray the 0.9wt% polyvinyl alcohol aqueous solution prepared in step (4) between the surface layer and the bottom layer, the spraying quantity is 2g / m 2 The dried paper was calendered on a soft roller calender at 220°C, a calendering line pressure of 210 kN / m, and a paper machine speed of 600 m / min.

[0109] Example 5

[0110] A method for producing a fully biodegradable high-barrier packaging material comprises the following steps:

[0111] (1) Freeze-dried bleached softwood pulp (0.5000 g, absolutely dry) and 500 ml of deionized water were added to a 1000 mL flask. TEMPO (0.0040 g) and NaBr (0.0250 g) were then added to the flask in sequence, and sodium hypochlorite solution was slowly added dropwise, with the amount of sodium hypochlorite added being controlled to be 3 mmol per gram of cellulose. During the reaction, the pH value of the reaction mixture was adjusted to approximately 10.0 using a 0.5 mol / L NaOH solution. The reaction was continued at 500 rpm for 1 h, and 10 mL of ethanol was added after the reaction time was reached to terminate the reaction. The suspension was filtered and washed with deionized water several times until neutral, then diluted with deionized water to a mass fraction of 2%, and then ground with an ultrafine refiner (MKCA6-2J, Masuko Sangyo Co., Ltd. Japan) at 2500 rpm for 1 h. After grinding, the slurry was collected and freeze-dried to obtain nanocellulose powder for later use.

[0112] (2) Stearic acid (C17 H 35 COOH) and NaHCO3 according to the mass ratio C 17 H 35 Dissolve and disperse COOH:NaHCO3 in deionized water in a ratio of 7:3, and add a certain amount of NaOH to adjust the alkalinity of the solution to NaOH:NaHCO3=1.2:1 (mass ratio). Keep the temperature in a water bath at 80°C and stir to mix evenly to obtain a NaHCO3 / stearic acid mixed solution for later use.

[0113] (3) The nanocellulose obtained in step (1) was added to a 0.2 M CaCl2 solution at a solid-liquid ratio of 1:32 (g / ml), stirred for 1 hour, and then squeezed dry. The mixture was then added to the mixed solution of NaHCO3 / stearic acid obtained in step (2), and the mixture was stirred thoroughly before termination. The nanocellulose was filtered out and repeatedly washed with deionized water until the filtrate was clear and the pH was neutral to obtain modified nanocellulose for later use.

[0114] (4) Prepare 1799 polyvinyl alcohol into a polyvinyl alcohol aqueous solution with a concentration of 1.1% by mass and set aside.

[0115] (5) Beat the bleached softwood pulp to a beating degree of 45°SR, and beat the hardwood pulp to a beating degree of 35°SR, and set aside.

[0116] (6) Mix the bleached coniferous pulp with a beating degree of 45°SR in step (5) with the broadleaf pulp with a beating degree of 35°SR, with the mixing ratio of bleached coniferous pulp: broadleaf pulp = 7:3 (the absolute dry mass ratio of the two pulps) to obtain a surface layer pulp for later use.

[0117] (7) The bleached coniferous pulp with a beating degree of 45°SR in step (5) and the polylactic acid particles with a particle size of 800 mesh are mixed in a ratio of 6:4 (the absolute dry mass ratio of the bleached coniferous pulp with a beating degree of 45°SR to the polylactic acid particles), and 0.2 wt% of AKD (the absolute dry mass ratio of the sizing agent to the pulp (bleached coniferous pulp with a beating degree of 45°SR + polylactic acid particles)) is added to the mixed pulp, and then the mixed pulp is deflaked (the deflaking machine speed is 3000 rpm / min) for 20 minutes; then the modified nanocellulose prepared in step (3) is added in an amount of 0.2 wt% (the absolute dry mass ratio of the modified nanocellulose to the pulp (bleached coniferous pulp with a beating degree of 45°SR + polylactic acid particles)) to obtain an intermediate layer pulp for standby use.

[0118] (8) The bleached coniferous pulp with a beating degree of 45°SR in step (5) is mixed with the broadleaf pulp with a beating degree of 35°SR, and the mixing ratio is bleached coniferous pulp: broadleaf pulp = 7:3 (the absolute dry mass ratio of the two pulps), to obtain a bottom pulp for standby use.

[0119] (9) Paper is made using a fourdrinier papermaking machine with a three-layer stacked net arrangement, wherein the surface layer is made of the surface layer slurry in step (6), and the surface layer is 25 g / m 2 The intermediate layer adopts the intermediate layer slurry in step (7), and the intermediate layer is quantitatively 110g / m 2 The bottom layer adopts the bottom layer slurry in step (8), and the bottom layer is quantitatively 25g / m 2 ; and spray the 1.1wt% polyvinyl alcohol aqueous solution prepared in step (4) between the surface layer and the middle layer, and between the middle layer and the bottom layer, with a spraying quantity of 2g / m 2 After that, the paper is dried. The dried paper is calendered by a soft roller calender at 210℃, calendering line pressure 220kN / m, and the paper machine speed is 600m / min. The actual picture of the high barrier packaging material is as follows: Figure 2 shown.

[0120] Example 6

[0121] A method for producing a fully biodegradable high-barrier packaging material comprises the following steps:

[0122] (1) Freeze-dried bleached softwood pulp (0.5000 g, absolutely dry) and 500 ml of deionized water were added to a 1000 mL flask. TEMPO (0.0040 g) and NaBr (0.0250 g) were then added to the flask in sequence, and sodium hypochlorite solution was slowly added dropwise, with the amount of sodium hypochlorite added being controlled to be 3 mmol per gram of cellulose. During the reaction, the pH value of the reaction mixture was adjusted to approximately 10.0 using a 0.5 mol / L NaOH solution. The reaction was continued at 500 rpm for 1 h, and 10 mL of ethanol was added after the reaction time was reached to terminate the reaction. The suspension was filtered and washed with deionized water several times until neutral, then diluted with deionized water to a mass fraction of 2%, and then ground with an ultrafine refiner (MKCA6-2J, Masuko Sangyo Co., Ltd. Japan) at 2500 rpm for 1 h. After grinding, the slurry was collected and freeze-dried to obtain nanocellulose powder for later use.

[0123] (2) Stearic acid (C 17 H 35 COOH) and NaHCO3 according to the mass ratio C 17 H 35 Dissolve and disperse COOH:NaHCO3 in deionized water in a ratio of 7:3, and add a certain amount of NaOH to adjust the alkalinity of the solution to NaOH:NaHCO3=1.2:1 (mass ratio). Keep the temperature in a water bath at 80°C and stir to mix evenly to obtain a NaHCO3 / stearic acid mixed solution for later use.

[0124] (3) The nanocellulose obtained in step (1) was added to a 0.2 M CaCl2 solution at a solid-liquid ratio of 1:32 (g / ml), stirred for 1 hour, and then squeezed dry. The mixture was then added to the mixed solution of NaHCO3 / stearic acid obtained in step (2), and the mixture was stirred thoroughly before termination. The nanocellulose was filtered out and repeatedly washed with deionized water until the filtrate was clear and the pH was neutral to obtain modified nanocellulose for later use.

[0125] (4) Prepare 1799 polyvinyl alcohol into a polyvinyl alcohol aqueous solution with a concentration of 1.1% by mass and set aside.

[0126] (5) Beat the natural softwood pulp to a beating degree of 43°SR, and beat the hardwood pulp to a beating degree of 35°SR, and set aside.

[0127] (6) Mix the natural coniferous pulp with a beating degree of 43°SR in step (5) with the broadleaf pulp with a beating degree of 35°SR, with the mixing ratio of natural coniferous pulp: broadleaf pulp = 6:4 (the absolute dry mass ratio of the two pulps) to obtain a surface layer pulp for standby use.

[0128] (7) The natural coniferous pulp with a beating degree of 43°SR in step (5) and polylactic acid fiber (the average length of the polylactic acid fiber is 6 mm) are mixed in a ratio of 5:5 (the absolute dry mass ratio of the natural coniferous pulp with a beating degree of 43°SR to the polylactic acid fiber), and 0.2 wt% of AKD (the absolute dry mass ratio of the sizing agent to the pulp (i.e., the natural coniferous pulp with a beating degree of 43°SR + polylactic acid fiber)) is added to the mixed pulp, and then the mixed pulp is deflaked (the deflaking machine speed is 3000 rpm / min) for 20 minutes; then the modified nanocellulose prepared in step (3) is added in an amount of 0.1 wt% (the absolute dry mass ratio of the modified nanocellulose to the pulp (i.e., the natural coniferous pulp with a beating degree of 43°SR + polylactic acid fiber)) to obtain an intermediate layer pulp for standby use.

[0129] (8) Mix the natural coniferous pulp with a beating degree of 43°SR in step (5) with the broadleaf pulp with a beating degree of 35°SR in a mixing ratio of natural coniferous pulp: broadleaf pulp = 6:4 (the absolute dry mass ratio of the two pulps) to obtain a bottom slurry for later use.

[0130] (9) Paper is made using a fourdrinier papermaking machine with a three-layer stacked net arrangement, wherein the surface layer is made of the surface layer slurry in step (6), and the surface layer basis weight is 25 g / m 2 The intermediate layer adopts the intermediate layer slurry in step (7), and the intermediate layer is quantitatively 110g / m 2 The bottom layer adopts the bottom layer slurry in step (8), and the bottom layer is quantitatively 25g / m 2; and spray the 1.1wt% polyvinyl alcohol aqueous solution prepared in step (4) between the surface layer and the middle layer, and between the middle layer and the bottom layer, with a spraying quantity of 2g / m 2 The dried paper is then calendered using a soft roller calender at 200°C, a calendering line pressure of 230 kN / m, and a paper machine speed of 600 m / min.

[0131] Example 7

[0132] A method for producing a fully biodegradable high-barrier packaging material comprises the following steps:

[0133] (1) Freeze-dried bleached softwood pulp (0.5000 g, absolutely dry) and 500 ml of deionized water were added to a 1000 mL flask. TEMPO (0.0040 g) and NaBr (0.0250 g) were then added to the flask in sequence, and sodium hypochlorite solution was slowly added dropwise, with the amount of sodium hypochlorite added being controlled to be 3 mmol per gram of cellulose. During the reaction, the pH value of the reaction mixture was adjusted to approximately 10.0 using a 0.5 mol / L NaOH solution. The reaction was continued at 500 rpm for 1 h, and 10 mL of ethanol was added after the reaction time was reached to terminate the reaction. The suspension was filtered and washed with deionized water several times until neutral, then diluted with deionized water to a mass fraction of 2%, and then ground with an ultrafine refiner (MKCA6-2J, Masuko Sangyo Co., Ltd. Japan) at 2500 rpm for 1 h. After grinding, the slurry was collected and freeze-dried to obtain nanocellulose powder for later use.

[0134] (2) Stearic acid (C 17 H 35 COOH) and NaHCO3 according to the mass ratio C 17 H 35 Dissolve and disperse COOH:NaHCO3 in deionized water in a ratio of 7:3, and add a certain amount of NaOH to adjust the alkalinity of the solution to NaOH:NaHCO3=1.2:1 (mass ratio). Keep the temperature in a water bath at 80°C and stir to mix evenly to obtain a NaHCO3 / stearic acid mixed solution for later use.

[0135] (3) The nanocellulose obtained in step (1) was added to a 0.4 M CaCl2 solution at a solid-liquid ratio of 1:32 (g / ml), stirred for 1 hour, and then squeezed dry. The mixture was then added to the mixed solution of NaHCO3 / stearic acid obtained in step (2), and the mixture was stirred thoroughly before termination. The nanocellulose was filtered out and repeatedly washed with deionized water until the filtrate was clear and the pH was neutral to obtain modified nanocellulose for later use.

[0136] (4) Prepare 1799 polyvinyl alcohol into a polyvinyl alcohol aqueous solution with a concentration of 1.1% by mass and set aside.

[0137] (5) Beat the natural softwood pulp to a beating degree of 43°SR, and beat the hardwood pulp to a beating degree of 35°SR, and set aside.

[0138] (6) Mix the natural coniferous pulp with a beating degree of 43°SR in step (5) with the broadleaf pulp with a beating degree of 35°SR, with the mixing ratio of natural coniferous pulp: broadleaf pulp = 6:4 (the absolute dry mass ratio of the two pulps) to obtain a surface layer pulp for standby use.

[0139] (7) The natural coniferous pulp with a beating degree of 43°SR in step (5) and polylactic acid fiber (the average length of the polylactic acid fiber is 6 mm) are mixed in a ratio of 5:5 (the absolute dry mass ratio of the natural coniferous pulp with a beating degree of 43°SR to the polylactic acid fiber), and 0.2 wt% of AKD (the absolute dry mass ratio of the sizing agent to the pulp (i.e., the natural coniferous pulp with a beating degree of 43°SR + polylactic acid fiber)) is added to the mixed pulp, and then the mixed pulp is deflaked (the deflaking machine speed is 3000 rpm / min) for 20 minutes; then the modified nanocellulose prepared in step (3) is added in an amount of 0.1 wt% (the absolute dry mass ratio of the modified nanocellulose to the pulp (i.e., the natural coniferous pulp with a beating degree of 43°SR + polylactic acid fiber)) to obtain an intermediate layer pulp for standby use.

[0140] (8) Mix the natural coniferous pulp with a beating degree of 43°SR in step (5) with the broadleaf pulp with a beating degree of 35°SR in a mixing ratio of natural coniferous pulp: broadleaf pulp = 6:4 (the absolute dry mass ratio of the two pulps) to obtain a bottom slurry for later use.

[0141] (9) Paper is made using a fourdrinier papermaking machine with a three-layer stacked net arrangement, wherein the surface layer is made of the surface layer slurry in step (6), and the surface layer basis weight is 25 g / m 2 The intermediate layer adopts the intermediate layer slurry in step (7), and the intermediate layer is quantitatively 110g / m 2 The bottom layer adopts the bottom layer slurry in step (8), and the bottom layer is quantitatively 25g / m 2 ; and spray the 1.1wt% polyvinyl alcohol aqueous solution prepared in step (4) between the surface layer and the middle layer, and between the middle layer and the bottom layer, with a spraying quantity of 2g / m 2 The dried paper is then calendered using a soft roller calender at 200°C, a calendering line pressure of 230 kN / m, and a paper machine speed of 600 m / min.

[0142] Comparative Example 1

[0143] A biodegradable packaging material having a single-layer structure, wherein the production method comprises the following steps:

[0144] (1) Beat the natural softwood pulp to a beating degree of 43°SR and the hardwood pulp to a beating degree of 35°SR, and set aside.

[0145] (2) The natural coniferous pulp with a beating degree of 43°SR in step (1) and polylactic acid fiber (the average length of the polylactic acid fiber is 6 mm) are mixed in a ratio of 5:5 (the absolute dry mass ratio of the natural coniferous pulp with a beating degree of 43°SR to the polylactic acid fiber), and 0.2 wt% of AKD (the absolute dry mass ratio of the sizing agent to the pulp (i.e., the natural coniferous pulp with a beating degree of 43°SR + polylactic acid fiber)) is added to the mixed pulp, and then the mixed pulp is deflaked (the deflaking machine speed is 3000 rpm / min) for 20 minutes; a certain amount of the natural coniferous pulp and broadleaf pulp beaten in step (1) are added to the deflaked pulp, so that the pulp ratio in the pulp is coniferous pulp: broadleaf pulp: polylactic acid fiber = 85:20:55 (the absolute dry mass ratio of the three pulps is consistent with the pulp dosage ratio in Example 6), to obtain papermaking pulp for standby use.

[0146] (3) Paper is made using a Fourdrinier papermaking machine, the pulp is the papermaking pulp in step (2), and the basis weight is 160 g / m 2 The dried paper was calendered at 200°C, calender line pressure of 230 kN / m and a paper machine speed of 600 m / min using a soft roller calender.

[0147] Comparative Example 2

[0148] A biodegradable packaging material having a three-layer structure, wherein the production method comprises the following steps:

[0149] (1) Freeze-dried bleached softwood pulp (0.5000 g, absolutely dry) and 500 ml of deionized water were added to a 1000 mL flask. TEMPO (0.0040 g) and NaBr (0.0250 g) were then added to the flask in sequence, and sodium hypochlorite solution was slowly added dropwise, with the amount of sodium hypochlorite added being controlled to be 3 mmol per gram of cellulose. During the reaction, the pH value of the reaction mixture was adjusted to approximately 10.0 using a 0.5 mol / L NaOH solution. The reaction was continued at 500 rpm for 1 h, and 10 mL of ethanol was added after the reaction time was reached to terminate the reaction. The suspension was filtered and washed with deionized water several times until neutral, then diluted with deionized water to a mass fraction of 2%, and then ground with an ultrafine refiner (MKCA6-2J, Masuko Sangyo Co., Ltd. Japan) at 2500 rpm for 1 h. After grinding, the slurry was collected and freeze-dried to obtain nanocellulose powder for later use.

[0150] (2) The nanocellulose obtained in step (1) was added to a 0.2 M CaCl2 solution at a solid-to-liquid ratio of 1:32 (g / ml), stirred for 1 hour, and then squeezed dry. The nanocellulose was repeatedly washed with deionized water until the filtrate was clear and the pH was neutral to obtain modified nanocellulose, which was set aside.

[0151] (3) Prepare a polyvinyl alcohol aqueous solution with a concentration of 1.1% by mass with 1799 polyvinyl alcohol for later use.

[0152] (4) Beat the natural softwood pulp to a beating degree of 43°SR, and beat the hardwood pulp to a beating degree of 35°SR, and set aside.

[0153] (5) Mix the natural coniferous pulp with a beating degree of 43°SR in step (4) with the broadleaf pulp with a beating degree of 35°SR, with the mixing ratio of natural coniferous pulp: broadleaf pulp = 6:4 (the absolute dry mass ratio of the two pulps) to obtain a surface layer pulp for standby use.

[0154] (6) The natural coniferous pulp with a beating degree of 43°SR in step (4) and polylactic acid fiber (the average length of the polylactic acid fiber is 6 mm) are mixed in a ratio of 5:5 (the absolute dry mass ratio of the natural coniferous pulp with a beating degree of 43°SR to the polylactic acid fiber), and 0.2 wt% of AKD (the absolute dry mass ratio of the sizing agent to the pulp (i.e., the natural coniferous pulp with a beating degree of 43°SR + polylactic acid fiber)) is added to the mixed pulp, and then the mixed pulp is deflaked (the deflaking machine speed is 3000 rpm / min) for 20 minutes; then the modified nanocellulose prepared in step (2) is added in an amount of 0.1 wt% (the absolute dry mass ratio of the modified nanocellulose to the pulp (i.e., the natural coniferous pulp with a beating degree of 43°SR + polylactic acid fiber)) to obtain an intermediate layer pulp for standby use.

[0155] (7) Mix the natural coniferous pulp with a beating degree of 43°SR in step (4) with the broadleaf pulp with a beating degree of 35°SR in a mixing ratio of natural coniferous pulp: broadleaf pulp = 6:4 (the absolute dry mass ratio of the two pulps) to obtain a bottom slurry for later use.

[0156] (8) Paper is made using a fourdrinier papermaking machine with a three-layer stacked net arrangement, wherein the surface layer is made of the surface layer slurry in step (5), and the surface layer basis weight is 25 g / m 2 The intermediate layer adopts the intermediate layer slurry in step (6), and the intermediate layer is quantitatively 110g / m 2 The bottom layer adopts the bottom layer slurry in step (7), and the bottom layer is quantitatively 25g / m 2 ; and spray the 1.1wt% polyvinyl alcohol aqueous solution prepared in step (3) between the surface layer and the middle layer, and between the middle layer and the bottom layer, with a spraying quantity of 2g / m 2 The dried paper is then calendered using a soft roller calender at 200°C, a calendering line pressure of 230 kN / m, and a paper machine speed of 600 m / min.

[0157] Comparative Example 3

[0158] A biodegradable packaging material having a three-layer structure, wherein the production method comprises the following steps:

[0159] (1) Freeze-dried bleached softwood pulp (0.5000 g, absolutely dry) and 500 ml of deionized water were added to a 1000 mL flask. TEMPO (0.0040 g) and NaBr (0.0250 g) were then added to the flask in sequence, and sodium hypochlorite solution was slowly added dropwise, with the amount of sodium hypochlorite added being controlled to be 3 mmol per gram of cellulose. During the reaction, the pH value of the reaction mixture was adjusted to approximately 10.0 using a 0.5 mol / L NaOH solution. The reaction was continued at 500 rpm for 1 h, and 10 mL of ethanol was added after the reaction time was reached to terminate the reaction. The suspension was filtered and washed with deionized water several times until neutral, then diluted with deionized water to a mass fraction of 2%, and then ground with an ultrafine refiner (MKCA6-2J, Masuko Sangyo Co., Ltd. Japan) at 2500 rpm for 1 h. After grinding, the slurry was collected and freeze-dried to obtain nanocellulose powder for later use.

[0160] (2) Stearic acid (C 17 H 35 COOH) and NaHCO3 according to the mass ratio C 17 H 35 Dissolve and disperse COOH:NaHCO3 in deionized water in a ratio of 7:3, and add a certain amount of NaOH to adjust the alkalinity of the solution to NaOH:NaHCO3=1.2:1 (mass ratio). Keep the temperature in a water bath at 80°C and stir to mix evenly to obtain a NaHCO3 / stearic acid mixed solution for later use.

[0161] (3) The nanocellulose obtained in step (1) is added to the mixed solution of NaHCO3 / stearic acid obtained in step (2) at a solid-liquid ratio of 1:32 (g / ml), and the mixture is stirred thoroughly before termination. The nanocellulose is filtered out and repeatedly washed with deionized water until the filtrate is clear and the pH is neutral to obtain modified nanocellulose for later use.

[0162] (4) Prepare 1799 polyvinyl alcohol into a polyvinyl alcohol aqueous solution with a concentration of 1.1% by mass and set aside.

[0163] (5) Beat the natural softwood pulp to a beating degree of 43°SR, and beat the hardwood pulp to a beating degree of 35°SR, and set aside.

[0164] (6) Mix the natural coniferous pulp with a beating degree of 43°SR in step (5) with the broadleaf pulp with a beating degree of 35°SR, with the mixing ratio of natural coniferous pulp: broadleaf pulp = 6:4 (the absolute dry mass ratio of the two pulps) to obtain a surface layer pulp for standby use.

[0165] (7) The natural coniferous pulp with a beating degree of 43°SR in step (5) and polylactic acid fiber (the average length of the polylactic acid fiber is 6 mm) are mixed in a ratio of 5:5 (the absolute dry mass ratio of the natural coniferous pulp with a beating degree of 43°SR to the polylactic acid fiber), and 0.2 wt% of AKD (the absolute dry mass ratio of the sizing agent to the pulp (i.e., the natural coniferous pulp with a beating degree of 43°SR + polylactic acid fiber)) is added to the mixed pulp, and then the mixed pulp is deflaked (the deflaking machine speed is 3000 rpm / min) for 20 minutes; then the modified nanocellulose prepared in step (3) is added in an amount of 0.1 wt% (the absolute dry mass ratio of the modified nanocellulose to the pulp (i.e., the natural coniferous pulp with a beating degree of 43°SR + polylactic acid fiber)) to obtain an intermediate layer pulp for standby use.

[0166] (8) Mix the natural coniferous pulp with a beating degree of 43°SR in step (5) with the broadleaf pulp with a beating degree of 35°SR in a mixing ratio of natural coniferous pulp: broadleaf pulp = 6:4 (the absolute dry mass ratio of the two pulps) to obtain a bottom slurry for later use.

[0167] (9) Paper is made using a fourdrinier papermaking machine with a three-layer stacked net arrangement, wherein the surface layer is made of the surface layer slurry in step (6), and the surface layer is 25 g / m 2 The intermediate layer adopts the intermediate layer slurry in step (7), and the intermediate layer is quantitatively 110g / m 2 The bottom layer adopts the bottom layer slurry in step (8), and the bottom layer is quantitatively 25g / m 2 ; and spray the 1.1wt% polyvinyl alcohol aqueous solution prepared in step (4) between the surface layer and the middle layer, and between the middle layer and the bottom layer, with a spraying quantity of 2g / m 2 The dried paper is then calendered using a soft roller calender at 200°C, a calendering line pressure of 230 kN / m, and a paper machine speed of 600 m / min.

[0168] Effect embodiment

[0169] The barrier properties of the high-barrier packaging materials prepared in Examples 1 to 7 and the packaging materials prepared in Comparative Examples 1 to 3 were tested. The barrier properties were tested as follows: This experiment was based on the ASTM-E96 standard. A W413 2.0 water vapor transmission rate meter (infrared method) was used to measure the water vapor transmission rate of paper-based materials to characterize the water vapor barrier properties of paper-based composite materials. The test temperature and humidity conditions were (23±0.5)°C and (50±1)% RH. Water vapor transmission rate refers to the total mass of water vapor that passes through the sample per unit time and per unit area, and the unit is g·m -2 day -1 The experiment was repeated three times.

[0170] The barrier performance test results of the materials prepared in the examples and comparative examples are shown in Table 1, wherein the original test data of the high barrier packaging material prepared in Example 3 (commissioned by Guangzhou Biaoji Packaging Equipment Co., Ltd.) are shown in Table 1. Figure 1 As shown in Table 1, it can be seen that the high-barrier packaging materials prepared in Examples 1 to 7 can effectively block oxygen and water vapor, and have good barrier properties to water vapor. It is realized that a fully biodegradable composite material with high barrier to water vapor is prepared using degradable materials, and the water vapor transmission rate can be as low as 0.3885 g·m -2 day -1 This is due to the fact that the papermaking method used to produce plant fiber / PLA composites significantly increases the mass proportion of polylactic acid in the material, improving the material's barrier properties. High-temperature hot pressing increases the material's density and tightness, which synergizes with paper pulp to achieve better barrier properties and processing capabilities than pure polylactic acid. Simultaneously, the barrier effects of nano-barrier materials and polyvinyl alcohol are superimposed. Composite materials prepared from multiple biodegradable materials through a specific process impart new high-barrier properties. Plant fiber / PLA composites produced using a multi-layer structure can significantly improve the yield rate during high-temperature calendering, reducing production costs.

[0171] Table 1 Barrier performance test results

[0172]

[0173]

[0174] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for preparing a fully biodegradable high barrier packaging material, characterized in that: The steps include: (1) Preparation of modified nanocellulose Dissolve stearic acid and NaHCO3 in water, add NaOH to adjust the alkalinity of the solution, and stir and mix uniformly at 70°C to 90°C to obtain a NaHCO3 / stearic acid mixed solution; then add nanocellulose to the CaCl2 solution, stir thoroughly, and squeeze dry, then add the solution to the NaHCO3 / stearic acid mixed solution, stir thoroughly, filter out the nanocellulose, and wash until the filtrate is clear and the pH is neutral to obtain modified nanocellulose; (2) Preparation of high barrier packaging materials ① Preparation of a double-layer high-barrier packaging material: using plant fiber pulp with a beating degree of 20°SR to 70°SR as a surface layer pulp; using a mixed pulp obtained by adding plant fiber pulp with a beating degree of 20°SR to 70°SR and polylactic acid, a sizing agent, and the modified nanocellulose prepared in step (1) as a bottom layer pulp; using a papermaking machine to make paper in one go, spraying a polyvinyl alcohol aqueous solution between the surface layer and the bottom layer, and then hot-pressing the dried paper through a calender to obtain a double-layer high-barrier packaging material, that is, the completely biodegradable high-barrier packaging material; or ② Preparation of a three-layer high-barrier packaging material: using plant fiber pulp with a beating degree of 20°SR to 70°SR as the surface layer pulp and the bottom layer pulp; using a mixed pulp obtained by adding plant fiber pulp with a beating degree of 20°SR to 70°SR and polylactic acid, a sizing agent and the modified nanocellulose prepared in step (1) as the core layer pulp; using a papermaking machine to make paper in one go, spraying a polyvinyl alcohol aqueous solution between the surface layer and the core layer and between the core layer and the bottom layer, and then hot-pressing the dried paper through a calender to obtain a three-layer high-barrier packaging material, that is, the described fully biodegradable high-barrier packaging material.

2. The method for preparing a fully biodegradable high barrier packaging material according to claim 1, characterized in that: The mass ratio of stearic acid to NaHCO3 in step (1) is 2:8 to 9:1; The mass ratio of NaOH to NaHCO3 in step (1) is 0.1 to 2:1; The concentration of the CaCl2 solution described in step (1) is 0.1 to 0.5 mol / L; The concentration of the polyvinyl alcohol aqueous solution in steps ① and ② is 0.1 to 2% by mass; The spraying amount of the polyvinyl alcohol aqueous solution in step ② is 0.1 g / m 2 ~10g / m 2 Spray.

3. The method for preparing a fully biodegradable high barrier packaging material according to claim 2, characterized in that: The mass ratio of stearic acid and NaHCO3 described in step (1) is 3:8 to 7:3; The mass ratio of NaOH to NaHCO3 in step (1) is 0.5 to 2:1; The concentration of the CaCl2 solution described in step (1) is 0.2-0.4 mol / L; The concentration of the polyvinyl alcohol aqueous solution in steps ① and ② is 0.8 to 1.2% by mass; The spraying amount of the polyvinyl alcohol aqueous solution in step ② is 1g / m 2 ~5g / m 2 Spray.

4. The method for preparing a fully biodegradable high barrier packaging material according to claim 1, characterized in that: The polylactic acid described in steps ① and ② is at least one of polylactic acid fibers and polylactic acid particles; The sizing agent in steps ① and ② is at least one of alkyl ketene dimer emulsion AKD and alkenyl succinic anhydride ASA; The polyvinyl alcohol described in steps ① and ② is 1799 polyvinyl alcohol.

5. The method for preparing a fully biodegradable high barrier packaging material according to claim 4, characterized in that: The polylactic acid in steps ① and ② is at least one of polylactic acid fibers having an average length of 0.5 mm to 8 mm and polylactic acid particles having a particle size of 100 mesh to 1800 mesh; The sizing agent described in steps ① and ② is alkyl ketene dimer emulsion AKD.

6. The method for preparing a fully biodegradable high barrier packaging material according to claim 1, characterized in that: The plant fiber pulp in the surface layer pulp in step ① is a mixed pulp composed of at least one of bamboo pulp and coniferous wood pulp, and hardwood pulp; The beating degree of the plant fiber pulp in steps ① and ② is 35°SR to 45°SR; The mass ratio of plant fiber pulp to polylactic acid in the bottom slurry described in step ① is 4:6 to 9:1; The amount of the sizing agent added in steps ① and ② is 0.2 to 2.0% of the total mass of the plant fiber pulp and the polylactic acid; The amount of modified nanocellulose added in steps ① and ② is 0.1 to 3% of the total mass of the plant fiber pulp and the polylactic acid; The plant fiber pulp in the surface layer pulp and the bottom layer pulp in step ② is a mixed pulp composed of at least one of bamboo pulp and coniferous wood pulp, and hardwood pulp; The mass ratio of plant fiber pulp to polylactic acid in the core layer slurry described in step ② is 4:6 to 9:

1.

7. The method for preparing a fully biodegradable high barrier packaging material according to claim 6, characterized in that: The plant fiber pulp in the surface layer slurry in step ① is a mixed slurry composed of bamboo pulp and hardwood pulp in a mass ratio of 6:4 to 9:1, or a mixed slurry composed of softwood pulp and hardwood pulp in a mass ratio of 6:4 to 9:1; The mass ratio of plant fiber pulp to polylactic acid in the bottom slurry described in step ① is 5:5 to 7:3; The amount of the sizing agent added in steps ① and ② is 0.2% of the total mass of the plant fiber pulp and the polylactic acid; The amount of modified nanocellulose added in steps ① and ② is 0.1 to 0.3% of the total mass of the plant fiber pulp and the polylactic acid; The plant fiber pulp in the surface layer pulp and the bottom layer pulp described in step ② is a mixed pulp composed of bamboo pulp and hardwood pulp in a mass ratio of 6:4 to 9:1, or a mixed pulp composed of softwood pulp and hardwood pulp in a mass ratio of 6:4 to 9:1; The mass ratio of plant fiber pulp to polylactic acid in the core layer slurry described in step ② is 5:5 to 7:

3.

8. The method for preparing a fully biodegradable high barrier packaging material according to claim 1, characterized in that: The conditions for hot pressing in the calender described in steps ① and ② are: calendering temperature 80-300° C., calendering line pressure 20-400 kN / m, and locomotive speed 100 m / min-1000 m / min; The surface layer of the double-layer high barrier packaging material described in step ① has a basis weight of 15 to 60 g / m 2 The bottom layer is 50-150g / m 2 ; The surface layer of the three-layer high barrier packaging material described in step ② has a weight of 15 to 50 g / m 2 The core layer is 50 to 140 g / m 2 The base layer is 15 to 50 g / m 2 .

9. A fully biodegradable high barrier packaging material, characterized by: It is prepared by the method according to any one of claims 1 to 8.

10. Use of the fully biodegradable high barrier packaging material according to claim 9 in food packaging materials.

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