High-strength waterproof oil-proof green paper-based packaging material and preparation method thereof

Abstract

The invention discloses a high-strength waterproof and oil-proof green paper-based packaging material and a preparation method thereof. The high-strength water-proof and oil-proof green paper-based packaging material is obtained by coating a wet paper web with carboxylated wood nanocellulose and then carrying out hot pressing and drying, the wet paper web is obtained by mixing bamboo pulp, bagasse pulp and wood nanocellulose prepared by a mechanical method, dispersing the mixture in an aqueous solution, making paper with the wet paper web with the water content of 50-60%, and squeezing at normal temperature to remove water until the water content is 20-30%. The paper-based barrier material is prepared by using plants as raw materials and regulating and controlling the fiber paper-based structure through functional components of the plants, has the characteristics of high oil resistance, high tensile strength, good water resistance, greenness, safety and degradability, and is particularly suitable for the fields of food packaging, medical treatment and public health and the like.

Description

Technical Field

[0001] The invention relates to a paper-based packaging material, in particular to a green paper-based packaging material with high tensile strength, waterproof and oil-proof and a preparation method thereof, belonging to the technical field of packaging. Background Art

[0002] In recent years, with the accelerated pace of life and the change in lifestyle, the fast food economy has developed rapidly, and the demand for disposable packaging materials has increased dramatically. Traditional plastics have become the mainstream material for food packaging due to their low price and convenient production. However, they have problems such as non-biodegradability, low recycling rate and release of microplastics, posing a great threat to the environment and human health. Therefore, green and environmentally friendly plastic substitutes are urgently needed.

[0003] Paper-based materials are three-dimensional structural products made of plant fibers. They are ideal substitutes for plastics because of their low cost and easy degradation. The sources of plant fibers used in papermaking are wood and non-wood, with wood being the main raw material. However, my country is seriously short of wood resources. At the same time, with the development of the economy, the demand for wood is increasing, and the shortage of supply has become the main contradiction in the wood market. Therefore, the development of non-wood raw materials to extract fibers has certain practical significance in alleviating the problem of wood shortage.

[0004] In addition, paper or paperboard made directly from plant fibers has strong hygroscopicity and poor barrier properties, and needs to be treated with water and oil to meet the requirements of food packaging. The current water and oil technologies on the market are mainly plastic coating and adding functional chemical additives. These substances usually contain components that are difficult to degrade and harmful to the human body, and there is a possibility of migration into food, posing a potential threat to human health. Therefore, safe and reliable biomass-based barrier materials have received more and more attention.

[0005] Chinese invention patent CN112210225B discloses a method for preparing a nanocellulose-based oxygen-insulating composite film, wherein larch pulp powder is delignified to obtain wood cellulose, NaBr and tetramethylpiperidinium oxide are dissolved in a Na2CO3-NaHCO3 buffer solution, wood cellulose is added, NaClO solution is added dropwise, pH value is adjusted, and after oxidation reaction, deionized water is used for rinsing and mechanical treatment to obtain carboxylated wood nanocellulose; deionized water and carboxylated wood nanocellulose are added to polyvinyl alcohol, and vacuum drying is performed after mixing to obtain a nanocellulose-based oxygen-insulating composite film. Although the nanocellulose-based oxygen-insulating composite film prepared by this technology has good oxygen-insulating properties, water resistance and mechanical properties, polyvinyl alcohol is an organic compound mainly derived from petroleum raw materials, and there are food safety risks, and its degradation can only be carried out under specific conditions.

[0006] Chinese invention patent application CN107354822A discloses a fresh-keeping wrapping paper and a preparation method thereof, comprising a base paper substrate and a fresh-keeping coating coated on the base paper substrate, wherein the base paper substrate comprises the following raw materials: conifer pulp, broadleaf pulp, titanium dioxide, kaolin, iron yellow, waste paper fiber, nano jute fiber, modified medical stone powder, heavy calcium carbonate, polyethylene glycol, zinc borate, styrene acrylic emulsion, nano-grade β-alumina, lignin, vermiculite, sepiolite powder, paraffin oil, melamine; the fresh-keeping coating comprises the following raw materials: Cistanche deserticola, anthocyanin, trehalose, sesame gum powder, lemon juice, durian extract, fish scale powder, and Shibaoke. Although the fresh-keeping wrapping paper of this technology has good antibacterial and antibacterial properties and fresh-keeping properties, the raw materials of the fresh-keeping wrapping paper prepared by this technology are complex, and when used as food packaging materials, some of its components are in danger of migrating into food, resulting in food safety and flavor risks. Summary of the invention

[0007] The purpose of the present invention is to overcome the problems existing in the prior art. Only plant fibers are used as raw materials. By regulating the fiber components and structure, a green paper-based packaging material and a preparation method thereof are provided, which has good degradation performance, is environmentally friendly, does not pose a safety risk to packaged food, and has high tensile strength, high oil resistance, and good water resistance.

[0008] The purpose of the present invention is achieved by the following steps:

[0009] A high-strength waterproof and oil-proof green paper-based packaging material is obtained by coating carboxylated wood nanocellulose (C-LCNFs) on a wet paper web and then drying it through hot pressing; the wet paper web is obtained by mixing bamboo pulp, bagasse pulp and mechanically prepared wood nanocellulose (M-LCNFs) and dispersing them in an aqueous solution, making wet paper with a water content of 50-60%, and squeezing and removing the water to 20-30% at room temperature.

[0010] To further achieve the purpose of the present invention, preferably, the bamboo pulp and bagasse pulp are unbleached kraft pulp with a beating degree of 30 to 40° SR.

[0011] Preferably, the mechanically prepared wood nanocellulose is prepared by the following method: the beating degree of bamboo pulp is adjusted to 80-90°SR, and then homogenized under a pressure of 130-138 MPa to obtain mechanically prepared wood nanocellulose (M-LCNFs) with a solid content of 0.3-0.7 wt%.

[0012] Preferably, the beating degree of the bamboo pulp is adjusted to 80-90°SR by using a PFI refiner; and the number of homogenization is 8-10 times.

[0013] Preferably, the mixing mass ratio of the bamboo pulp and bagasse pulp is 3:7 to 4:6, and the addition amount of the mechanically prepared wood nanocellulose is 1 to 15% relative to the absolute dry mass of the mixed pulp of the bamboo pulp and bagasse pulp.

[0014] Preferably, the pressing pressure at room temperature is 0.3-0.4 MPa, and the time is 2-5 mins; the hot pressing drying pressure is 2-10 MPa, the temperature is 150-190° C., and the time is 10-30 mins.

[0015] Preferably, the preparation method of the carboxylated wood nanocellulose (C-LCNFs) is TEMPO oxidation combined with high pressure homogenization.

[0016] Preferably, the carboxylated wood nanocellulose has a solid content of 0.7-1.0 wt %, a lignin content of 1.02-2.65%, and a carboxyl content of 0.37-1.10 mmol / g.

[0017] Preferably, the coating amount of the carboxylated wood nanocellulose is 1.5 to 10.0 g / m 2 .

[0018] The method for preparing the high-strength waterproof and oil-proof green paper-based packaging material is characterized by comprising the following steps:

[0019] 1) bamboo pulp, bagasse pulp and mechanically prepared wood nanocellulose (M-LCNFs) are mixed and dispersed in an aqueous solution to form wet paper with a moisture content of 50-60%, and the moisture is removed by pressing at room temperature to 20-30% to obtain a wet paper web;

[0020] 2) Carboxylated wood nanocellulose (C-LCNFs) is coated on a wet paper web, and after hot pressing and drying, a high-strength, waterproof and oil-proof green paper-based packaging material is obtained.

[0021] Compared with the existing technology, the present invention has the following advantages and beneficial effects:

[0022] 1) The present invention makes full use of the coordinated effects of bamboo pulp, bagasse pulp, M-LCNFs, C-LCNFs and hot pressing and drying process to prepare a green paper-based packaging material that has excellent degradation performance and safety performance while also having high tensile strength, high oil resistance and good water resistance. Specifically, the present invention uses bamboo pulp and bagasse pulp as raw materials. Bamboo pulp fibers have a large aspect ratio and good interweaving ability, and bagasse fibers are thick and short. Compounding the two is conducive to increasing the interweaving and entanglement between fibers, increasing the fiber bonding area, and then forming a dense network structure, improving the mechanical strength of paper-based materials. At the same time, M-LCNFs are nanoscale and rich in hydroxyl content. Mixing them with micron-sized pulp fibers can increase the bonding area and bonding strength between fibers through hydrogen bonding, thereby preparing a high-strength paper base. Then, C-LCNFs are coated on the surface of the paper base and combined with hot pressing to further form a dense structure, thereby obtaining a high-strength waterproof and oil-proof paper base material. Finally, the hot pressing process adopted by the present invention after C-LCNFs are coated on the wet paper web shortens the distance between various fibers of the long and short fibers of M-LCNFs, bamboo pulp and bagasse pulp, promotes more hydrogen bonds, thereby forming a dense structure with enhanced mechanical strength and barrier properties.

[0023] 2) The present invention uses non-wood as raw material, which solves the problem of lack of wood resources in my country and the shortage of supply. Among them, bamboo is the most important forest resource after wood. Its appearance structure and chemical composition are similar to wood, and bamboo fiber is slender and has good interweaving performance. At the same time, bamboo fiber has antibacterial properties because it contains natural antibiotics and can absorb ultraviolet rays. At the same time, my country has abundant bamboo resources and low cost, which can make a significant contribution to the sustainable development of the economy.

[0024] 3) The present invention uses only plant fibers as raw materials, and not only has excellent waterproof and oil-proof properties and mechanical strength, but also has excellent natural degradation properties.

[0025] 4) The hot pressing process used in the present invention can melt and reorganize the lignin, promote the densification of the material structure, and enhance the barrier properties of the material.

[0026] 5) The lignin of the present invention is a thermoplastic material with a softening temperature of about 135°C. Under hot pressing conditions, the lignin in the fiber melts and reorganizes and migrates to the surface, further enhancing the waterproof performance of the material.

[0027] 6) The present invention uses only plant fibers as raw materials, and by regulating the fiber components and structure, the provided high-strength waterproof and oil-proof green paper-based packaging material not only has good degradation performance, is environmentally friendly, and does not pose a safety risk to the packaged food, but also has high tensile strength, high oil resistance, good waterproofness, and excellent comprehensive performance, which is far higher than the existing packaging materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Fiber width distribution diagram of bamboo pulp in Example 1

[0029] Figure 2 This is the fiber length distribution diagram of the bamboo pulp in Example 1.

[0030] Figure 3 This is the fiber width distribution diagram of the bagasse pulp in Example 1.

[0031] Figure 4 This is the fiber length distribution diagram of the bagasse pulp in Example 1.

[0032] Figure 5 This is the AFM image of M-LCNFs of Example 1.

[0033] Figure 6 This is the diameter distribution diagram of M-LCNFs in Example 1.

[0034] Figure 7 This is the AFM image of C-LCNFs of Example 1.

[0035] Figure 8 This is the diameter distribution diagram of C-LCNFs in Example 1.

[0036] Fig. 9 This is a comparison chart of the natural degradation performance of the paper-based packaging material of Example 1 and a commercial take-out packaging box. DETAILED DESCRIPTION

[0037] For further understanding of the present invention, the present invention is further explained and described below in conjunction with the examples, but the specific examples do not limit the present invention in any way. Unless otherwise specified, the methods and equipment used in the examples are conventional methods and equipment, and the raw materials used are conventional commercially available raw materials.

[0038] In the technical measures of the present invention, bamboo pulp fibers have a large aspect ratio and good interweaving ability, and bagasse fibers are short and thick. Compounding the two is conducive to increasing the interweaving and entanglement between fibers, increasing the fiber bonding area, and then forming a dense network structure, improving the mechanical strength of paper-based materials. The present invention utilizes the characteristics of these two pulps, gives full play to their matching advantages, and utilizes the characteristics of carboxylated wood nanocellulose (C-LCNFs) and mechanically prepared wood nanocellulose (M-LCNFs), and is proposed in conjunction with a hot pressing and drying process. The wood nanocellulose to which the present invention relates is different from the widely used nanocellulose (CNFs); nanocellulose (CNFs) is a nanomaterial prepared from plant fibers that have been completely delignined, with a diameter of less than 100nm and a length distribution between hundreds of nanometers and several microns, because of its large specific surface area, good film-forming properties and excellent biodegradability. At the same time, CNFs are rich in hydroxyl content, which can give the material excellent mechanical strength through hydrogen bonding. However, the wood nanocellulose (LCNFs) prepared from plant fiber raw materials that retain or partially remove lignin not only has the advantages of CNF, but also retains the characteristics of lignin, and is endowed with waterproof, antibacterial and UV-resistant characteristics. In particular, lignin has thermoplasticity, which allows it to soften and melt at high temperatures and redistribute between fibers, which is beneficial to improving the bonding force between fibers. Compared with CNFs that do not contain lignin, LCNFs retain part or all of the lignin, which not only reduces the chemical treatment cost of wood fibers, but also plays a vital role in improving the barrier and mechanical properties in the field of biomass-based barrier materials of the present invention. On this basis, the M-LCNFs of the present invention have a nanoscale and rich hydroxyl content. When mixed with micron-sized pulp fibers, it can increase the bonding area and bonding strength between fibers through hydrogen bonding, thereby preparing a high-strength paper base; and because the wood nanocellulose prepared by it has poor uniformity in size, but has good fluidity and strong water filtration, it has little effect on the dehydration and molding time of pulp as a paper base additive. The carboxylated wood nanocellulose (C-LCNFs) of the present invention is easy to generate electrostatic repulsion, thus showing good uniform dispersibility. The obtained wood nanocellulose has a small diameter and strong size uniformity, and is easy to combine with the paper base through hydrogen bonding to form a dense and smooth surface structure, thereby hindering the penetration of water and oil, and the presence of lignin is conducive to the improvement of the waterproof performance of the material. The present invention coats C-LCNFs on the surface of the paper base and combines hot pressing to further form a dense structure. The hot pressing process used after the carboxylated wood nanocellulose (C-LCNFs) is coated on the wet paper web shortens the distance between various fibers of the long and short fibers of M-LCNFs, bamboo pulp and bagasse pulp, promotes more hydrogen bonding, thereby forming a dense structure, and the mechanical strength and barrier properties are enhanced.

[0039] The present invention makes full use of the cooperation of the performance characteristics of bamboo pulp and bagasse pulp, combines carboxylated wood nanocellulose (C-LCNFs) and mechanically prepared wood nanocellulose (M-LCNFs) and hot pressing process, and realizes that the green paper-based packaging material has good degradation performance and environmental protection, will not cause safety risks to the packaged food, and has the comprehensive performance of high tensile strength, high oil resistance and good water resistance. Compared with the existing food packaging materials, the degradation advantage is obvious, and it is green and environmentally friendly. More importantly, the present invention realizes the high mechanical strength of the packaging material, and also has high oil resistance and good water resistance. The comprehensive performance is very excellent, far exceeding the disclosed paper-based packaging materials and the packaging materials used in the market.

[0040] Therefore, the high-strength waterproof and oil-proof green paper-based packaging material of the present invention is obtained by coating carboxylated wood nanocellulose (C-LCNFs) on a wet paper web and drying it through hot pressing; the wet paper web is obtained by mixing bamboo pulp, bagasse pulp and mechanically prepared wood nanocellulose (M-LCNFs) and dispersing them in an aqueous solution, forming a wet paper web with a moisture content of 50-60%, and squeezing and removing the moisture to 20-30% at room temperature.

[0041] The method for preparing the high-strength waterproof and oil-proof green paper-based packaging material of the present invention comprises the following steps:

[0042] 1) Mix bamboo pulp, bagasse pulp and M-LCNFs and disperse them in an aqueous solution to make wet paper with a moisture content of 50-60%, and press and remove the moisture to 20-30% at room temperature to obtain a wet paper web;

[0043] 2) C-LCNFs are coated on a wet paper web and then hot-pressed and dried to obtain a high-strength, waterproof, and oil-proof green paper-based packaging material.

[0044] As for the sources of bamboo pulp and bagasse pulp involved in the above technical measures of the present invention, the specific method of mechanically preparing wood nanocellulose, the proportion of bamboo pulp and bagasse pulp, the amount of wood nanocellulose added by mechanical method, the process requirements of pressing at room temperature, and the amount of C-LCNFs coating can be obtained by experimental testing based on the above measures and in combination with the purpose of the present invention. The TEMPO oxidation combined with high pressure homogenization method of the carboxylated wood nanocellulose of the present invention can be prepared according to the prior art document "Wen YB, Yuan ZY, Liu XL, et al. Preparation and Characterization of Lignin-Containing Cellulose Nanofibril from Poplar High-Yield Pulp Via Tempo-Mediated Oxidation and Homogenization [J]. ACS Sustainable Chemistry & Engineering, 2019, 7 (6): 6131-6139." Carboxylated wood nanocellulose was prepared by TEMPO oxidation combined with high pressure homogenization. The process of TEMPO oxidation includes mixing high-yield pulp, TEMPO (0.1mmol / g fiber), NaBr (1mmol / g fiber) and deionized water to prepare a pulp mixture with a solid content of 1wt%. Subsequently, the pH value of the system is adjusted to 10.0-10.5 with 0.5mol / L NaOH solution. After 5mins, NaClO solution is added in an amount of 4-12mmol / g fiber. During the reaction, the pH value of the system is adjusted to 10.5 with 0.5mol / L NaOH solution, and the reaction is terminated when the pH value is equal to 10.0-10.5 and there is no change for 10-20mins. The entire operation process is carried out under mechanical stirring at a speed of 500r / min. The process of high-pressure homogenization is: using a high-pressure homogenizer to treat TEMPO-oxidized fibers. For each sample, 20g of TEMPO-oxidized pulp is diluted to 1wt% and diluted with deionized water. Then, carboxylated wood nanocellulose is obtained by treating 6 times at 80MPa. The wood nanocellulose exhibits good thermal stability. In addition, the increase in lignin content significantly improves the hydrophobicity of the carboxylated wood nanocellulose.

[0045] Example 1

[0046] A method for preparing a green, high-strength, waterproof and oil-proof paper-based material, the preparation steps comprising:

[0047] (1) Raw material preparation:

[0048] Mechanically prepared wood nanocellulose (M-LCNFs) was prepared by using bamboo pulp as raw material, using a PFI refiner to beat the pulp until the beating degree was 80°SR, and then using a homogenizer to homogenize 8 times at a pressure of 138 MPa to prepare M-LCNFs with a solid content of 0.4 wt%.

[0049] The preparation method of carboxylated wood nanocellulose (C-LCNFs) refers to the literature "Wen YB, Yuan ZY, Liu X.L., et al. Preparation and Characterization of Lignin-Containing Cellulose Nanofibril from Poplar High-Yield Pulp Via Tempo-Mediated Oxidation and Homogenization [J]. ACS Sustainable Chemistry & Engineering, 2019, 7 (6): 6131-6139", in which the addition amount of NaClO solution is 2 mmol / g fiber.

[0050] (2) Preparation of green high-strength waterproof and oil-proof paper-based materials:

[0051] Bamboo pulp and bagasse pulp with a beating degree of 30°SR were uniformly mixed in water at a mass ratio of 1:1, and 3% of M-LCNFs relative to the absolute dry mass of bamboo pulp and bagasse pulp were added, and wet paper was made after uniform mixing; then it was pressed at room temperature for 5 minutes at a pressure of 0.4 MPa;

[0052] 6g / m 2 C-LCNFs were coated on the wet paper web with a coating amount of; finally, the wet paper web was placed between stainless steel plates and all placed in a vulcanizer, and hot pressed for 10 minutes at 160°C and 3MPa to obtain a high-strength waterproof and oil-proof paper-based material.

[0053] Figure 1 , Figure 2 The fiber width diagram and fiber length distribution diagram of the bamboo pulp in Example 1 are respectively shown. All the bamboo pulps in this example are the same sulfate bamboo pulp. It can be observed that the average weighted length of the bamboo pulp fiber is 1.63 mm, the average width is 16.3 μm, and the aspect ratio is 100, indicating that the fiber is slender and has good interweaving performance.

[0054] Figure 3 , Figure 4They are respectively the fiber width and fiber length distribution diagrams of bagasse pulp in Example 1. It can be observed that the average weighted length of bagasse pulp fiber is 1.02 mm, the average width is 24.0 μm, and the aspect ratio is 42.5, which is thicker and shorter than bamboo pulp fiber. Therefore, when the two are mixed, it is beneficial to the entanglement between the fibers and promote the mechanical strength of the paper.

[0055] Figure 5 This is an atomic force microscope (AFM) image of M-LCNFs in Example 1. In appearance, M-LCNFs are a uniformly dispersed suspension, and are yellow-brown due to the presence of lignin. Microscopically, the fibers are dispersed and lignin can be observed. Figure 6 This is a diameter distribution diagram obtained by AFM analysis of M-LCNFs. The diameter of M-LCNFs is distributed between 2 and 14 nm, with an average diameter of 8.64 nm and a length of micrometers, showing a high aspect ratio, so it has a large specific surface area and abundant hydroxyl groups. Based on this fiber structure, it is mixed with pulp fibers for papermaking, acting as a bridge between pulp fibers with a width of micrometers, which can further enhance the interweaving and entanglement between fibers, forming a dense fiber network structure, and enhancing the mechanical strength of the finished paper through hydrogen bonding.

[0056] Figure 7 The AFM image of C-LCNFs of Example 1. In appearance, C-LCNFs are viscous, which is conducive to coating technology. Microscopically, they show good uniform dispersion. Figure 8 This is a diameter distribution diagram obtained by counting the AFM images of C-LCNFs. The diameter of C-LCNFs is distributed between 0.4 and 4.0 nm, with an average diameter of 2.03 nm and a length of microns. The aspect ratio is significantly higher than that of M-LCNFs. Moreover, the size distribution range of C-LCNFs is small and the uniformity is good. This is because mechanical action cannot precisely regulate the fiber structure and functional groups like chemical reactions. Uniform size is more conducive to the barrier properties of wood nanocellulose. When C-LCNFs are coated on the surface of paper, the carboxyl and hydroxyl groups of C-LCNFs first form hydrogen bonds with the hydroxyl groups of paper fibers to fill the pores on their surface. Later, as the number of coatings increases, C-LCNFs completely adhere to the surface of the paper to form a smooth and dense film structure, enhancing the barrier properties of the paper.

[0057] Fig. 9The following is a comparison chart of the natural degradation performance of the paper-based packaging material and the commercial takeout packaging box in Example 1. The waterproof and oil-proof paper-based material, hamburger takeout box, foam plastic takeout box and transparent plastic takeout box were used as test objects, cut into squares with a side length of 5 cm, buried in the soil 10 cm above the ground, and photographed and recorded every once in a while to observe their natural degradation. Among them, the hamburger takeout box is mainly composed of a paper base and a waterproof and oil-proof film, the film is mainly an aluminum film or a plastic film; the foam plastic takeout box is mainly composed of polystyrene, and the transparent plastic takeout box is mainly composed of polypropylene.

[0058] Example 2

[0059] A method for preparing a green, high-strength, waterproof and oil-proof paper-based material, the preparation steps comprising:

[0060] (1) Raw material preparation:

[0061] Preparation of M-LCNFs: Bamboo pulp was used as raw material and was pulped using a PFI refiner until the pulping degree was 80°SR. Then, a homogenizer was used to homogenize 10 times at a pressure of 138 MPa to prepare M-LCNFs with a solid content of 0.4 wt%.

[0062] Preparation of C-LCNFs: The preparation method of C-LCNFs refers to the literature “Wen YB, Yuan ZY, Liu XL, et al. Preparation and Characterization of Lignin-Containing Cellulose Nanofibril from Poplar High-Yield Pulp Via Tempo-Mediated Oxidation and Homogenization [J]. ACS Sustainable Chemistry & Engineering, 2019, 7 (6): 6131-6139”, in which the amount of NaClO solution added was 6 mmol / g fiber.

[0063] (2) Preparation of green high-strength waterproof and oil-proof paper-based materials:

[0064] Bamboo pulp and bagasse pulp with a beating degree of 30°SR were uniformly mixed in water at a mass ratio of 4:6, and 9wt% of M-LCNFs relative to the absolute dry pulp mass were added. After mixing evenly, wet paper was made; then it was pressed at room temperature for 5mins at a pressure of 0.4MPa; 2 The C-LCNFs are coated on the wet paper web with a coating amount of; finally, the wet paper web is placed between stainless steel plates and all are placed in a vulcanizer, and hot-pressed for 13 minutes at 150°C and 5MPa to obtain the high-strength waterproof and oil-proof paper-based material.

[0065] Example 3

[0066] A method for preparing a green, high-strength, waterproof and oil-proof paper-based material, the preparation steps comprising:

[0067] (1) Raw material preparation:

[0068] Preparation of M-LCNFs: Bamboo pulp was used as raw material and was pulped using a PFI refiner until the pulping degree was 80°SR. Then, a homogenizer was used to homogenize 10 times at a pressure of 138 MPa to prepare M-LCNFs with a solid content of 0.4 wt%.

[0069] Preparation of C-LCNFs: The preparation method of C-LCNFs refers to the literature “Wen YB, Yuan ZY, Liu XL, et al. Preparation and Characterization of Lignin-Containing Cellulose Nanofibril from Poplar High-Yield Pulp Via Tempo-Mediated Oxidation and Homogenization [J]. ACS Sustainable Chemistry & Engineering, 2019, 7 (6): 6131-6139”, in which the amount of NaClO solution added was 4 mmol / g fiber.

[0070] (2) Preparation of green high-strength waterproof and oil-proof paper-based materials:

[0071] Bamboo pulp and bagasse pulp with a beating degree of 30°SR were uniformly mixed in water at a mass ratio of 3:7, and 3 wt% of M-LCNFs relative to the absolute dry pulp mass were added. After mixing evenly, wet paper was made; then it was pressed at room temperature for 5 mins at a pressure of 0.4 MPa; 2 The C-LCNFs are coated on the wet paper web with a coating amount of; finally, the wet paper web is placed between stainless steel plates and all are placed in a vulcanizer, and hot pressed for 18 minutes at 165°C and 8MPa to obtain the high-strength waterproof and oil-proof paper-based material.

[0072] Example 4

[0073] A method for preparing a green, high-strength, waterproof and oil-proof paper-based material, the preparation steps comprising:

[0074] (1) Raw material preparation:

[0075] Preparation of M-LCNFs: Bamboo pulp was used as raw material and was pulped using a PFI refiner until the pulping degree was 80°SR. Then, a homogenizer was used to homogenize 10 times at a pressure of 138 MPa to prepare M-LCNFs with a solid content of 0.4 wt%.

[0076] Preparation of C-LCNFs: The preparation method of C-LCNFs refers to the literature “Wen YB, Yuan ZY, Liu XL, et al. Preparation and Characterization of Lignin-Containing Cellulose Nanofibril from Poplar High-Yield Pulp Via Tempo-Mediated Oxidation and Homogenization[J]. ACS Sustainable Chemistry & Engineering, 2019, 7(6): 6131-6139”, in which the amount of NaClO solution added was 5 mmol / g fiber.

[0077] (2) Preparation of green high-strength waterproof and oil-proof paper-based materials:

[0078] Bamboo pulp and bagasse pulp with a beating degree of 30°SR were uniformly mixed in water at a mass ratio of 5:5, and 3 wt% of M-LCNFs relative to the absolute dry pulp mass were added. After mixing evenly, wet paper was made; then it was pressed at room temperature for 5 mins at a pressure of 0.4 MPa; 2 C-LCNFs were coated on the wet paper web with a coating amount of; finally, the wet paper web was placed between stainless steel plates and all placed in a vulcanizer, and hot pressed for 12 minutes at 170°C and 6MPa to obtain a high-strength waterproof and oil-proof paper-based material.

[0079] The present invention designs a comparative test of preparing paper-based packaging materials without adding C-LCNFs and / or M-LCNFs, and compares them with hamburger packaging paper.

[0080] Comparative Example 1

[0081] The difference from Example 1 is that the process of coating C-LCNFs on the wet paper web in step (2) is omitted, and the rest is consistent with Example 1 to obtain comparative sample 1. The preparation steps include:

[0082] (1) Raw material preparation:

[0083] Preparation of M-LCNFs: Bamboo pulp was used as raw material and was pulped using a PFI refiner until the pulping degree was 80°SR. Then, a homogenizer was used to homogenize 8 times at a pressure of 138 MPa to prepare M-LCNFs with a solid content of 0.4 wt%.

[0084] (2) Preparation of green high-strength waterproof and oil-proof paper-based materials:

[0085] Bamboo pulp and bagasse pulp with a beating degree of 30°SR were uniformly mixed in water at a mass ratio of 1:1, and 3% M-LCNFs relative to the absolute dry mass of bamboo pulp and bagasse pulp were added, and the mixture was evenly mixed to form a wet paper web; then the wet paper web was pressed at room temperature for 5 minutes at a pressure of 0.4 MPa; finally, the wet paper web was placed between stainless steel plates and all placed in a vulcanizer, and hot pressed for 10 minutes at 160°C and 3 MPa to obtain comparison sample 1.

[0086] Comparative Example 2

[0087] The difference from Example 1 is that the M-LCNFs treatment process in step (2) is omitted, and the rest is consistent with Example 1 to obtain comparative sample 2, and the preparation steps include:

[0088] (1) Raw material preparation:

[0089] The preparation method of C-LCNFs refers to the literature "Wen YB, Yuan ZY, Liu XL, et al. Preparation and Characterization of Lignin-Containing Cellulose Nanofibril from Poplar High-Yield Pulp Via Tempo-Mediated Oxidation and Homogenization [J]. ACSSustainable Chemistry & Engineering, 2019, 7 (6): 6131-6139", in which the amount of NaClO solution added is 2 mmol / g fiber.

[0090] (2) Preparation of green high-strength waterproof and oil-proof paper-based materials:

[0091] Bamboo pulp with a beating degree of 30°SR and bagasse pulp are uniformly mixed in water at a mass ratio of 1:1, and wet paper is formed after being uniformly mixed; then, it is pressed at room temperature for 5 minutes at a pressure of 0.4 MPa;

[0092] 6g / m 2C-LCNFs were coated on the wet paper web with a coating amount of; finally, the wet paper web was placed between stainless steel plates and all placed in a vulcanizer, and hot pressed for 10 minutes at 160°C and 3MPa to obtain comparison sample 2.

[0093] Comparative Example 3

[0094] The difference from Example 1 is that the hot pressing process is omitted, and the other steps are the same as Example 1 to obtain Comparative Sample 3. The preparation steps include:

[0095] 1) Raw material preparation:

[0096] Preparation of M-LCNFs: Bamboo pulp was used as raw material and was pulped using a PFI refiner until the pulping degree was 80°SR. Then, a homogenizer was used to homogenize 8 times at a pressure of 138 MPa to prepare M-LCNFs with a solid content of 0.4 wt%.

[0097] The preparation method of C-LCNFs refers to the literature "Wen YB, Yuan ZY, Liu XL, et al. Preparation and Characterization of Lignin-Containing Cellulose Nanofibril from Poplar High-Yield Pulp Via Tempo-Mediated Oxidation and Homogenization [J]. ACSSustainable Chemistry & Engineering, 2019, 7 (6): 6131-6139", in which the amount of NaClO solution added is 2 mmol / g fiber.

[0098] 2) Preparation of green high-strength waterproof and oil-proof paper-based materials:

[0099] Bamboo pulp and bagasse pulp with a beating degree of 30°SR were uniformly mixed in water at a mass ratio of 1:1, and 3% of M-LCNFs relative to the absolute dry mass of bamboo pulp and bagasse pulp were added, and wet paper was made after uniform mixing; then it was pressed at room temperature for 5 minutes at a pressure of 0.4 MPa;

[0100] 6g / m 2 C-LCNFs were coated on the wet paper web with a coating amount of; finally, the wet paper web was placed between stainless steel plates and all placed in a vulcanizer, and dried for 10 minutes at 100°C and 0 MPa to obtain comparison sample 3.

[0101] Comparative Example 4

[0102] The hamburger takeout box is made of a paper base and plastic, in which the plastic is combined with the paper base in the form of a lamination film to play a waterproof and oil-proof role.

[0103] The paper-based materials prepared in all the examples and comparative examples were tested for mechanical strength and barrier properties.

[0104] Test method:

[0105] Tensile index: GB / T12914-2018 "Determination of tensile strength of paper and paperboard - Constant rate tensile method";

[0106] Burst index: GB / T 454-2020 "Determination of burst resistance of paper";

[0107] Kebo value: GB / T 1540-2002 "Determination of water absorption of paper and paperboard (Kebo method)"

[0108] Contact angle: The water contact angle was measured using a static contact angle meter. 5 μL of water was dropped onto the sample surface and the contact angle of the sample was recorded at 5 seconds. One sample was tested at least three times.

[0109] Oil resistance level: TAPPI T 559cm-02 "Grease resistance test for paper and paperboard": Table 1 shows the formula of different oil resistance test solutions. The higher the value, the better the oil resistance. Take a drop of test solution and drop it on the sample surface about 10mm away from the sample. After 15s, quickly wipe off the test solution with absorbent cotton. If the test area is penetrated, it means that the sample does not meet the oil resistance level. It is necessary to test with the next level of test solution until no penetration occurs.

[0110] Air permeability: GB / T 458-2008 "Determination of air permeability of paper and paperboard".

[0111] Table 1 Composition of test fluids of different oil resistance grades

[0112] Oil resistance level (kit value) Castor oil / g Toluene / mL n-Heptane / mL 1 969.0 0 0 2 872.1 50 50 3 775.2 100 100_ 4 678.3 150 150_ 5 581.4 200 200_ 6 484.5 250 250_ 7 387.6 300 300 8 290.7 350 350_ 9 193.8 400 400_ 10 96.9 450 450 11 0 500 500 12 0 450 550

[0113] The performance test results are shown in Table 2.

[0114] According to Table 2, comparing Example 1 and Comparative Example 1, the oil resistance level of paper after coating with C-LCNFs increased from 0 to 11, indicating that the base paper does not have oil resistance, C-LCNFs can give the paper excellent oil resistance, and the kit value is greater than 5, which meets the oil resistance requirements of food packaging. In addition, after coating, the water contact angle of the material increased from 35.36° to 55.87°, and the kit value decreased by 65.67%, indicating that C-LCNFs can give the paper better waterproof performance, and the gas barrier property is improved, indicating that C-LCNFs has a good waterproof and oil-proof effect. This is mainly attributed to the fact that C-LCNFs is combined with the paper base through hydrogen bonding to form a dense and smooth surface structure, thereby hindering the penetration of water and oil, and the presence of lignin is conducive to the improvement of the waterproof performance of the material.

[0115] Comparing Example 1 with Comparative Example 2, after adding M-LCNFs to paper, the tensile index increased from 70.58 N·m / g to 94.25 N·m / g, and the bursting index increased from 3.96 kPa·m 2 / g increased to 5.66 kPa·m 2 / g, indicating that M-LCNFs significantly improve the mechanical strength of the material. This is mainly attributed to the interweaving of the long and short fibers of M-LCNFs, bamboo pulp and bagasse pulp, which enhances the bonding between fibers through hydrogen bonds, thereby improving its mechanical strength.

[0116] Comparing Example 1 and Comparative Example 3, compared with the sample that has not been subjected to hot pressing treatment, the water contact angle of the material is about twice that of the sample, the Ke Bo value is reduced by 47.11%, the air permeability is reduced by 41.67%, and the tensile index and burst index are increased by 54.28% and 52.98%, respectively, indicating that the hot pressing process can significantly improve the waterproof performance, gas barrier performance and mechanical strength of the paper-based material. This is mainly attributed to the fact that the hot pressing process shortens the distance between the various fibers of the long and short fibers of M-LCNFs, bamboo pulp and bagasse pulp, promotes more hydrogen bonding, thereby forming a dense structure, and enhancing mechanical strength and barrier properties. In addition, as a thermoplastic substance, lignin has a softening temperature of about 135°C. Under hot pressing conditions, the lignin in the fiber melts and reorganizes, migrates to the surface, and further enhances the waterproof performance of the material.

[0117] Table 2 Performance indexes of high strength waterproof and oil-proof paper-based materials

[0118]

[0119] Comparing Example 1 with Comparative Example 4, compared with commercial paper-based packaging paper, the air permeability of the paper-based packaging material is 0.26 times, and the tensile index and burst index are 1.83 times and 1.89 times, respectively, indicating that the material has excellent gas barrier properties and mechanical strength. Fig. 9It was found that the waterproof and oil-proof paper-based material completely disappeared after 10 days, indicating that it was degraded, while the appearance of the hamburger packaging box, white foam plastic and transparent plastic was consistent with the initial state without any signs of degradation, which fully confirmed that the material of the present invention has excellent natural degradability.

[0120] Compared with Chinese invention patent CN112210225B and Chinese invention patent application CN107354822A, the raw material of the present invention is only plant fiber, without adding any chemical raw materials, will not cause harm to the human body, and meet the high requirements for food safety. Moreover, the present invention can be degraded in the natural environment without harsh conditions, and because it is all plants, it has no adverse effects on the soil after degradation. On the other hand, the water contact angle of Chinese invention patent CN112210225B is 70°, while the water contact angle of the present invention can reach 75°, showing a fairly good waterproof performance.

[0121] In summary, the high-strength waterproof and oil-proof paper-based material of the present invention has high mechanical strength, waterproof and oil-proof properties and good natural degradation properties, while meeting high requirements for food safety.

[0122] The implementation methods of the present invention are not limited to the above embodiments, and the above embodiments do not limit the scope of protection of the present invention. Anyone familiar with this technology can make various changes and modifications based on the existing embodiments without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the definition of the claims.

Claims

1. A high-strength waterproof and oil-proof green paper-based packaging material, characterized in that: The wet paper is obtained by coating carboxylated wood nanocellulose on a wet paper web and then drying it by hot pressing. The wet paper web is prepared by mixing bamboo pulp, bagasse pulp and mechanically prepared wood nanocellulose and dispersing them in an aqueous solution to form wet paper with a water content of 50-60%, and then squeezing and removing the water to 20-30% at room temperature.

2. The high-strength waterproof and oil-proof green paper-based packaging material according to claim 1, characterized in that: The bamboo pulp and bagasse pulp are unbleached kraft pulps with a beating degree of 30-40°SR.

3. The high-strength waterproof and oil-proof green paper-based packaging material according to claim 1, characterized in that: The mechanically prepared wood nanocellulose is prepared by the following method: the beating degree of bamboo pulp is adjusted to 80-90°SR, and then homogenized under a pressure of 130-138 MPa to obtain the mechanically prepared wood nanocellulose with a solid content of 0.3-0.7 wt%.

4. The high-strength waterproof and oil-proof green paper-based packaging material according to claim 3, characterized in that: The method of adjusting the beating degree of bamboo pulp to 80-90°SR is to use a PFI pulping machine to adjust the beating degree of bamboo pulp to 80-90°SR; the number of homogenization is 8-10 times.

5. The high-strength waterproof and oil-proof green paper-based packaging material according to claim 1, characterized in that: The mixing mass ratio of the bamboo pulp and the bagasse pulp is 3:7-4:6, and the addition amount of the mechanically prepared wood nanocellulose is 1-15% of the absolute dry mass of the mixed pulp of the bamboo pulp and the bagasse pulp.

6. The high-strength waterproof and oil-proof green paper-based packaging material according to claim 1, characterized in that: The pressing pressure at room temperature is 0.3-0.4 MPa, and the time is 2-5 mins; the hot pressing drying pressure is 2-10 MPa, the temperature is 150-190° C., and the time is 10-30 mins.

7. The high-strength waterproof and oil-proof green paper-based packaging material according to claim 1, characterized in that: The preparation method of the carboxylated wood nanocellulose is a TEMPO oxidation combined with a high-pressure homogenization method.

8. The high-strength waterproof and oil-proof green paper-based packaging material according to claim 7, characterized in that: The carboxylated wood nanocellulose has a solid content of 0.7-1.0 wt%, a lignin content of 1.02-2.65%, and a carboxyl content of 0.37-1.10 mmol / g.

9. The high-strength waterproof and oil-proof green paper-based packaging material according to claim 1, characterized in that: According to the coating area, the coating amount of the carboxylated wood nanocellulose is 1.5-10.0 g / m 2 .

10. The method for preparing the high-strength waterproof and oil-proof green paper-based packaging material according to any one of claims 1 to 9, characterized in that The steps include: 1) mixing bamboo pulp, bagasse pulp and mechanically prepared wood nanocellulose and dispersing them in an aqueous solution to make wet paper with a water content of 50-60%, and pressing and removing the water to 20-30% at room temperature to obtain a wet paper web; 2) Carboxylated wood nanocellulose is coated on a wet paper web, and after hot pressing and drying, a high-strength, waterproof and oil-proof green paper-based packaging material is obtained.

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