Kudzuvine root residue nano cellulose as well as preparation method and application thereof

Abstract

The invention provides a preparation method of kudzuvine root residue nano cellulose, which comprises the following steps: putting kudzuvine root residue and a NaOH solution in a high-pressure digester for high-pressure alkali boiling, then washing with water, filtering to be neutral, and pulping; carrying out oxidation bleaching on the slurry by using NaClO2 under an acidic condition, then washing with water, filtering to be neutral, and drying to obtain a primary cellulose product of the radix puerariae residue; placing the dried material and dilute sulphuric acid in a high-pressure digester for high-pressure acidolysis, and then centrifugally washing to be neutral; preparing a suspension from the washed material, firstly performing high-speed shearing, and then performing micro-jet homogenization to obtain a radix puerariae residue nanocellulose suspension; concentrating and freeze-drying to obtain the radix puerariae residue nano cellulose. The preparation method of the kudzuvine root residue nanocellulose is short in preparation period, high in yield and small in pollution, and the prepared kudzuvine root residue nanocellulose has good emulsifying performance.

Description

Technical Field

[0001] The invention relates to the technical field of new materials, and in particular to kudzu root residue nanocellulose and a preparation method and application thereof. Background Art

[0002] Emulsion refers to a suspension formed by two immiscible liquid phases, one of which is evenly dispersed in the other phase in the form of fine droplets. Pickering emulsion is an emulsion stabilized by submicron or nanometer solid particles. Compared with traditional emulsions stabilized by traditional surfactants, Pickering emulsions, especially food-grade Pickering emulsions, have the advantages of less emulsifier usage, high safety, environmental friendliness, and strong stability. They have been widely used in cosmetics, medicine, food, chemicals, materials and other fields. With people's pursuit of green, healthy and environmentally friendly, the development of food-grade nanoparticles with natural and healthy sources, green preparation processes and environmentally friendly as Pickering emulsion emulsifiers has become a research hotspot today.

[0003] Cellulose is a polysaccharide and the most abundant natural biological resource. It has the advantages of being biodegradable, non-toxic, non-polluting, easy to modify, biocompatible, and renewable. However, cellulose also has some inherent disadvantages, including insolubility in common solvents, poor wrinkle resistance, poor thermoplasticity, dimensional instability, high hydrophilicity, and lack of antibacterial properties. These factors have hindered the comprehensive development and utilization of cellulose. In order to overcome the shortcomings of cellulose and give cellulose more excellent properties, it is also necessary to carry out controllable physical and chemical modification of natural cellulose, such as modifying it into nanocellulose. Nanocellulose is a rod-shaped cellulose with a diameter of 1nm-100nm and a certain aspect ratio. It has properties such as nanoscale effect, high strength, high specific surface area, and strong surface activity, which has led to a lot of research in the field of materials science, such as food packaging, food additives, papermaking, medicine, tissue engineering, and many other research fields. When nanocellulose is used as an emulsifier to stabilize Pickering emulsions, compared with other food-grade particles, cellulose has a high aspect ratio and therefore requires less. Cellulose particles easily form entangled networks, so the emulsion formed has an additional stabilizing mechanism and is conducive to the development of emulsion gels, so it has good prospects for development and utilization.

[0004] Pueraria root is the dried root of Pueraria lobata, a leguminous plant. It is rich in starch, isoflavones, triterpenes, coumarins, alkaloids, polysaccharides, amino acids and minerals necessary for the human body, and is an important medicinal and edible plant. Pueraria root is often used to extract starch, and Pueraria root residue is the remaining waste after starch is extracted from Pueraria root, which is mainly composed of cellulose, hemicellulose, lignin and other components. Most of the Pueraria root residue in my country is directly incinerated or used as agricultural fertilizer, which not only causes a waste of resources, but also easily causes environmental pollution. Studies have shown that Pueraria root residue is rich in cellulose and is a cellulose resource with great potential. Therefore, extracting cellulose from Pueraria root residue and then modifying it into nanocellulose is of great value in the development of emulsions.

[0005] Chinese patent (CN 107033562A) discloses a kudzu root nanocellulose fiber-polylactic acid plastic film and its preparation method, including a method for preparing kudzu root nanocellulose fibers. In this process, the prepared kudzu root nanocellulose is applied to polymer composite materials, cement, thermal insulation materials, etc., and there is no report on its application in Pickering emulsion.

[0006] At the same time, the preparation method of kudzu root nanocellulose includes ultrasonic cleaning, extraction, acid hydrolysis, oxidative bleaching, high temperature alkali boiling, acid boiling, centrifugal separation, freeze drying and other process steps. In this process, two acid treatments are used to achieve the purpose of purification and modification of cellulose to nanometer level. The steps are complicated and the cycle is long. Among them, the key step of forming nanocellulose in this process is acid boiling, that is, destroying the amorphous region of cellulose by chemical method to reduce the fiber size. The phosphoric acid aqueous solution used for acid boiling has a high concentration, which is easy to cause environmental pollution and takes a long time to process; after acid boiling, it is purified by centrifugal separation, and the product yield is low.

[0007] In view of this, it is necessary to provide a new process to solve the above technical problems. Summary of the invention

[0008] The technical problem to be solved by the present invention is to provide a method for preparing kudzu root residue nanocellulose. Firstly, kudzu cellulose is extracted from kudzu root residue by high-pressure alkali boiling and oxidative bleaching, and then kudzu root residue nanocellulose is modified by high-pressure acid hydrolysis and microfluidization homogenization. The preparation cycle is short, the yield is high, the pollution is small, and the prepared kudzu root residue nanocellulose has good emulsification performance.

[0009] The first aspect of the present invention is to provide a method for preparing kudzu root residue nanocellulose, comprising the following steps:

[0010] Step S1, placing kudzu root residue and NaOH solution in a high-pressure cooking pot for high-pressure alkali cooking, then washing, filtering to neutrality and pulping; wherein the mass fraction of the NaOH solution is 0.5wt%-2wt%, and the high-pressure alkali cooking conditions are: solid-liquid ratio of 1:18-22, pressure of 0.3-0.5MPa, and alkali cooking time of 1-1.5h;

[0011] Step S2, oxidative bleaching the pulp with NaClO2 under acidic conditions, then washing, filtering to neutrality and drying to obtain a primary cellulose product of kudzu root residue; wherein the oxidative bleaching process conditions are: a solid-liquid ratio of kudzu root residue to NaClO2 solution of 1:18-22, a temperature of 85-95°C, and a time of 1.5-3h;

[0012] Step S3, placing the dried material and dilute sulfuric acid in a high-pressure cooking pot for high-pressure acid hydrolysis, and then centrifugally washing until neutral; wherein the mass fraction of sulfuric acid is 1wt%-2wt%, and the high-pressure acid hydrolysis conditions are: solid-liquid ratio of 1:18-22, pressure of 0.1-0.2MPa, and time of 1-1.5h;

[0013] Step S4, the washed material is configured into a suspension, first subjected to high-speed shearing, and then subjected to microfluidization homogenization to obtain a kudzu root residue nanocellulose suspension; wherein the high-speed shearing conditions are: a shearing rate of 12000-13000 r / min, a shearing time of 2-5 min; the microfluidization homogenization conditions are: a pressure of 60 MPa-120 MPa, and a homogenization number of 2-3 times;

[0014] Step S5, concentrating and freeze-drying to obtain kudzu root residue nanocellulose.

[0015] Furthermore, in step S2, during the process of oxidative bleaching of the pulp, the pH value is adjusted to 3-4.

[0016] Furthermore, in step S1 and step S2, the water washing and filtering method is: placing the material on a 200-300 mesh sieve and repeatedly washing it with water.

[0017] Furthermore, in step S2, the drying method is forced air drying, the temperature is 55-65°C, and the time is 24-48h.

[0018] Furthermore, in step S3, the centrifugal washing method is: the feed liquid is centrifuged at 7500-8500 r / min for 5-10 min, the supernatant is discarded and water is added to repeat the operation.

[0019] Furthermore, in step S4, the concentration method is rotary evaporation, the temperature is 50-60°C, the rotation speed is 180-220r / min, and the air pressure is -0.1MPa to -0.3MPa.

[0020] Furthermore, in step S5, during the freeze-drying process, the pre-freezing time is 6-12 hours, the pre-freezing temperature is -20 to -30°C, and the drying time is 36-48 hours.

[0021] The second aspect of the present invention is to provide kudzu root residue nanocellulose, which is prepared by the method of the first aspect.

[0022] The third aspect of the present invention is to provide a use of the kudzu root residue nanocellulose as described in the second aspect in the preparation of Pickering emulsion.

[0023] Furthermore, a method for preparing a Pickering emulsion comprises the following steps:

[0024] The kudzu root residue nanocellulose prepared by the method of any one of claims 1 to 7 is configured into a water suspension with a mass fraction of 0.5 wt%, mixed with soybean oil in a ratio of 9:1, and emulsified by shearing first and then homogenizing to obtain an oil-in-water emulsion.

[0025] Compared with the prior art, the kudzu root residue nanocellulose provided by the present invention and its preparation method and application have the following beneficial effects:

[0026] 1. The method for preparing nanocellulose from kudzu root residue provided by the present invention is to obtain cellulose with high purity after high-pressure alkali boiling and bleaching of kudzu root residue, and then to reduce the particle size of cellulose to micrometer level by high-pressure acid hydrolysis process, and then to obtain nanocellulose material by high-speed shearing and microfluidization homogenization through ion collision, cavitation and shear force to reduce the fiber size. Compared with the prior art, the method for preparing nanocellulose from kudzu root residue of the present invention can simplify the process flow, and the concentration of alkali solution and acid solution required in the process is low, and the pollution is less.

[0027] 2. The kudzu root residue nanocellulose prepared by the present invention is used to prepare Pickering emulsion and has good emulsifying properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0029] Figure 1 FITR images of kudzu root residue nanocellulose prepared in Examples 1-4 of the present invention;

[0030] Figure 2 This is a SEM image of the kudzu root residue nanocellulose prepared in Examples 1-4 of the present invention;

[0031] Figure 3 The particle size distribution diagram of the Pickering emulsion prepared in Examples 1-4 of the present invention;

[0032] Figure 4 This is a laser confocal microscopy image of the Pickering emulsion prepared in Examples 1-4 of the present invention;

[0033] Figure 5 The centrifuged appearance and static appearance of the Pickering emulsion prepared in Examples 1-4 of the present invention are shown. DETAILED DESCRIPTION

[0034] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the specific implementation modes of the present invention are further described below.

[0035] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0036] Example 1

[0037] A method for preparing kudzu root residue nanocellulose comprises the following steps:

[0038] Step S1, weighing 250g of kudzu root residue, adding 5L of 0.5wt% NaOH solution, boiling under high pressure at 0.3MPa for 1h, then placing on a 200-mesh sieve, washing with water until neutral, and then beating;

[0039] Step S2, adding 5L of 1wt% NaClO2 solution to the slurry of step S1, adjusting the pH to 3-4 with 2mol / L HCl, then stirring and heating at 90°C for 2h, washing with water on a 200-mesh sieve until neutral, and finally drying in an oven at 60°C to obtain a primary cellulose product of kudzu root residue;

[0040] Step S3, weighing the material dried in step S2, adding a 2wt% H2SO4 solution at a solid-liquid ratio of 1:20, high-pressure acid hydrolysis at 0.1MPa for 1h, then centrifuging at 8000r / min for 5-10min to discard the supernatant, and repeatedly adding water to wash until neutral;

[0041] Step S4, preparing the material washed in step S3 into a suspension with a concentration of 1 wt%, high-speed shearing at 12500 r / min for 2 min, and then microfluidization homogenization at a pressure of 120 MPa for 2 times to obtain a kudzu root residue nanocellulose suspension;

[0042] Step S5, using a rotary evaporator at 60°C, 200 r / min, -0.1 MPa to evaporate and concentrate the kudzu root residue nanocellulose suspension in step S4, and freeze-drying the obtained concentrated solution to obtain kudzu root residue nanocellulose. The freeze-drying conditions are: pre-freezing time of 12 hours, pre-freezing temperature of -20°C, and drying time of 48 hours.

[0043] The FITR image of the kudzu root residue nanocellulose prepared in Example 1 is as follows: Figure 1 As shown, it presents a typical cellulose peak shape, and the SEM image is shown Figure 2 As shown, it appears as entangled filaments with a large aspect ratio, reaching the nanometer level.

[0044] The kudzu root residue nanocellulose of Example 1 was used as an emulsifier to prepare a Pickering emulsion, and the preparation method was as follows:

[0045] 0.675 g of the obtained kudzu root residue nanofibers were dispersed in 134.325 g of water to obtain a 1 wt% suspension, 15 g of soybean oil was added, and high-speed shearing was performed at 12500 r / min for 2 min, followed by high-pressure homogenization at 30 MPa for 3 times to obtain a Pickering emulsion.

[0046] The droplets of the obtained Pickering emulsion have a smaller particle size, and its specific particle size distribution is as follows: Figure 3 As shown in the laser confocal microscopy images Figure 4 The appearance of the emulsion after centrifugation at 5000r / min for 30min and standing for 30 days is as follows Figure 5 As shown, there is no oil separation phenomenon and only a slight water layer, which shows that the kudzu root residue nanocellulose has good emulsification and the prepared emulsion has good stability.

[0047] Example 2

[0048] A method for preparing kudzu root residue nanocellulose comprises the following steps:

[0049] Step S1, weighing 250g of kudzu root residue, adding 5L of 1wt% NaOH solution, boiling under high pressure at 0.3MPa for 1h, then placing on a 200-mesh sieve, washing with water until neutral, and then beating;

[0050] Step S2, adding 5L of 1wt% NaClO2 solution to the slurry of step S1, adjusting the pH to 3-4 with 2mol / L HCl, then stirring and heating at 90°C for 2h, washing with water on a 200-mesh sieve until neutral, and finally drying in an oven at 60°C to obtain a primary cellulose product of kudzu root residue;

[0051] Step S3, weighing the material dried in step S2, adding a 2wt% H2SO4 solution at a solid-liquid ratio of 1:20, high-pressure acid hydrolysis at 0.1MPa for 1h, then centrifuging at 8000r / min for 5-10min to discard the supernatant, and repeatedly adding water to wash until neutral;

[0052] Step S4, preparing the material washed in step S3 into a suspension with a concentration of 1 wt%, high-speed shearing at 12500 r / min for 2 min, and then microfluidization homogenization at a pressure of 120 MPa for 2 times to obtain a kudzu root residue nanocellulose suspension;

[0053] Step S5, using a rotary evaporator at 60°C, 200 r / min, -0.1 MPa to evaporate and concentrate the kudzu root residue nanocellulose suspension in step S4, and freeze-drying the obtained concentrated solution to obtain kudzu root residue nanocellulose. The freeze-drying conditions are: pre-freezing time of 12 hours, pre-freezing temperature of -20°C, and drying time of 48 hours.

[0054] The FITR image of the kudzu root residue nanocellulose prepared in Example 2 is as follows Figure 1 As shown, it presents a typical cellulose peak shape, and the SEM image is shown Figure 2 As shown, it appears as entangled filaments with a large aspect ratio, reaching the nanometer level.

[0055] The kudzu root residue nanocellulose of Example 2 was used as an emulsifier to prepare a Pickering emulsion, and the preparation method was as follows:

[0056] 0.675 g of the obtained kudzu root residue nanofibers were dispersed in 134.325 g of water to obtain a 1 wt% suspension, 15 g of soybean oil was added, and high-speed shearing was performed at 12500 r / min for 2 min, followed by high-pressure homogenization at 30 MPa for 3 times to obtain a Pickering emulsion.

[0057] The droplets of the obtained Pickering emulsion have a smaller particle size, and its specific particle size distribution is as follows: Figure 3 As shown in the laser confocal microscopy images Figure 4 The appearance of the emulsion after centrifugation at 5000r / min for 30min and standing for 30 days is as follows Figure 5 As shown, there is no oil separation phenomenon, indicating that the kudzu root residue nanocellulose has excellent emulsification properties and the prepared emulsion has excellent stability.

[0058] Example 3

[0059] A method for preparing kudzu root residue nanocellulose comprises the following steps:

[0060] Step S1, weighing 250g of kudzu root residue, adding 5L of 1wt% NaOH solution, boiling under high pressure at 0.3MPa for 1h, then placing on a 200-mesh sieve, washing with water until neutral, and then beating;

[0061] Step S2, adding 5L of 1wt% NaClO2 solution to the slurry of step S1, adjusting the pH to 3-4 with 2mol / L HCl, then stirring and heating at 90°C for 2h, washing with water on a 200-mesh sieve until neutral, and finally drying in an oven at 60°C to obtain a primary cellulose product of kudzu root residue;

[0062] Step S3, weighing the material dried in step S2, adding 1wt% H2SO4 solution at a solid-liquid ratio of 1:20, high-pressure acid hydrolysis at 0.1MPa for 1h, then centrifuging at 8000r / min for 5-10min to discard the supernatant, and repeatedly washing with water until neutral;

[0063] Step S4, preparing the material washed in step S3 into a suspension with a concentration of 1 wt%, high-speed shearing at 12500 r / min for 2 min, and then microfluidization homogenization at a pressure of 120 MPa for 2 times to obtain a kudzu root residue nanocellulose suspension;

[0064] Step S5, using a rotary evaporator at 60°C, 200 r / min, -0.1 MPa to evaporate and concentrate the kudzu root residue nanocellulose suspension in step S4, and freeze-drying the obtained concentrated solution to obtain kudzu root residue nanocellulose. The freeze-drying conditions are: pre-freezing time of 12 hours, pre-freezing temperature of -20°C, and drying time of 48 hours.

[0065] The FITR image of the kudzu root residue nanocellulose prepared in Example 3 is as follows Figure 1 As shown, it presents a typical cellulose peak shape, and the SEM image is shown Figure 2 As shown, it appears as entangled filaments with a large aspect ratio, reaching the nanometer level.

[0066] The kudzu root residue nanocellulose of Example 3 was used as an emulsifier to prepare a Pickering emulsion, and the preparation method was as follows:

[0067] 0.675 g of the obtained kudzu root residue nanofibers were dispersed in 134.325 g of water to obtain a 1 wt% suspension, 15 g of soybean oil was added, and high-speed shearing was performed at 12500 r / min for 2 min, followed by high-pressure homogenization at 30 MPa for 3 times to obtain a Pickering emulsion.

[0068] The droplets of the obtained Pickering emulsion have a smaller particle size, and its specific particle size distribution is as follows: Figure 3 As shown in the laser confocal microscopy images Figure 4 The appearance of the emulsion after centrifugation at 5000r / min for 30min and standing for 30 days is as follows Figure 5 As shown, there is no oil precipitation phenomenon and only slight precipitation, which shows that the kudzu root residue nanocellulose has good emulsification and the prepared emulsion has good stability.

[0069] Example 4

[0070] A method for preparing kudzu root residue nanocellulose comprises the following steps:

[0071] Step S1, weighing 250g of kudzu root residue, adding 5L of 1wt% NaOH solution, boiling under high pressure at 0.3MPa for 1h, then placing on a 200-mesh sieve, washing with water until neutral, and then beating;

[0072] Step S2, adding 5L of 1wt% NaClO2 solution to the slurry of step S1, adjusting the pH to 3-4 with 2mol / L HCl, then stirring and heating at 90°C for 2h, washing with water on a 200-mesh sieve until neutral, and finally drying in an oven at 60°C to obtain a primary cellulose product of kudzu root residue;

[0073] Step S3, weighing the material dried in step S2, adding a 2wt% H2SO4 solution at a solid-liquid ratio of 1:20, high-pressure acid hydrolysis at 0.1MPa for 1h, then centrifuging at 8000r / min for 5-10min to discard the supernatant, and repeatedly adding water to wash until neutral;

[0074] Step S4, preparing the material washed in step S3 into a suspension with a concentration of 1 wt%, high-speed shearing at 12500 r / min for 2 min, and then microfluidization homogenization at a pressure of 60 MPa for 2 times to obtain a kudzu root residue nanocellulose suspension;

[0075] Step S5, using a rotary evaporator at 60°C, 200 r / min, -0.1 MPa to evaporate and concentrate the kudzu root residue nanocellulose suspension in step S4, and freeze-drying the obtained concentrated solution to obtain kudzu root residue nanocellulose. The freeze-drying conditions are: pre-freezing time of 12 hours, pre-freezing temperature of -20°C, and drying time of 48 hours.

[0076] The FITR image of the kudzu root residue nanocellulose prepared in Example 4 is as follows Figure 1 As shown, it presents a typical cellulose peak shape, and the SEM image is shown Figure 2 As shown, it appears as entangled filaments with a large aspect ratio, reaching the nanometer level.

[0077] The kudzu root residue nanocellulose of Example 4 was used as an emulsifier to prepare a Pickering emulsion, and the preparation method was as follows:

[0078] 0.675 g of the obtained kudzu root residue nanofibers were dispersed in 134.325 g of water to obtain a 1 wt% suspension, 15 g of soybean oil was added, and high-speed shearing was performed at 12500 r / min for 2 min, followed by high-pressure homogenization at 30 MPa for 3 times to obtain a Pickering emulsion.

[0079] The droplets of the obtained Pickering emulsion have a smaller particle size, and its specific particle size distribution is as follows: Figure 3 As shown in the laser confocal microscopy images Figure 4 The appearance of the emulsion after centrifugation at 5000r / min for 30min and standing for 30 days is as follows Figure 5 As shown, there is no oil precipitation phenomenon and there is a small amount of water layer, which shows that the kudzu root residue nanocellulose has good emulsification properties and the prepared emulsion has good stability.

[0080] Comparative Example 1

[0081] The kudzu root nanocellulose obtained by the preparation method of kudzu root nanocellulose disclosed in CN 107033562A was used as an emulsifier, and the Pickering emulsion preparation method of Example 1 was used to prepare a Pickering emulsion.

[0082] The Pickering emulsion prepared in Comparative Example 1 showed oil precipitation after centrifugation at 5000 r / min for 30 minutes and after standing for 30 days, and there was a small amount of water layer, indicating that the emulsion prepared with the kudzu root residue nanocellulose prepared by the present invention has better stability. This is because the kudzu root residue nanocellulose prepared by the present invention has uniform particle size and moderate surface charge, which helps to enhance the fiber-to-fiber interaction of the kudzu root residue nanocellulose in the aqueous phase, enhance the gel-like network structure of the emulsion, and thus enhance the stability of the emulsion.

[0083] Comparative Example 2

[0084] Based on the preparation method of kudzu root nanocellulose disclosed in CN 107033562A, the preparation process includes: ultrasonic cleaning of kudzu root residue-extraction-acid hydrolysis-hydrogen peroxide bleaching-high temperature alkali boiling-acid boiling-shearing-microjet homogenization, wherein the process conditions of ultrasonic cleaning, extraction, acid hydrolysis, hydrogen peroxide bleaching, high temperature alkali boiling and acid boiling of kudzu root residue refer to CN 107033562A, and the process conditions of shearing and microjet homogenization refer to Example 1.

[0085] The kudzu root nanocellulose prepared in Comparative Example 2 was used as an emulsifier and the Pickering emulsion preparation method of Example 1 was used to prepare a Pickering emulsion.

[0086] The Pickering emulsion prepared in Comparative Example 2 showed oil precipitation after centrifugation at 5000 r / min for 30 minutes and after standing for 30 days, and there was a small amount of water layer, indicating that the emulsion prepared by the kudzu root residue nanocellulose prepared by the present invention has better stability, indicating that the particle size and uniformity, particle structure and surface charge size of the kudzu root residue nanocellulose obtained by different pretreatment processes and conditions are different, resulting in different emulsion stability.

[0087] Comparative Example 3

[0088] Based on Example 2, the order of high-pressure acid hydrolysis and high-pressure alkali boiling was exchanged to obtain Comparative Example 3.

[0089] The kudzu root nanocellulose prepared in Comparative Example 3 was used as an emulsifier and the Pickering emulsion preparation method of Example 1 was used to prepare a Pickering emulsion.

[0090] The Pickering emulsion prepared in Comparative Example 3 showed oil precipitation after centrifugation at 5000 r / min for 30 min and after standing for 30 days, and there was a small amount of water layer, indicating that the emulsion prepared with the kudzu root residue nanocellulose prepared in the present invention has better stability. This is because the high-pressure alkali boiling before can make the kudzu root residue structure loose, which is more conducive to the subsequent acid hydrolysis and homogenization effect.

[0091] From the above comparative analysis, we can see that:

[0092] 1. The present invention combines chemical and physical methods to reduce the fiber size, and the obtained nanocellulose particles have a more uniform size, so that the prepared Pickering emulsion has a better stabilizing effect.

[0093] 2. The process for preparing nanocellulose from kudzu root residue of the present invention adopts a high-pressure alkali boiling process to dissolve the semi-fibers contained in the kudzu root residue, making the structure of the kudzu root residue loose and the components easy to separate, which is beneficial for subsequent further purification; at the same time, the alkali solution used in high-pressure alkali boiling has a low concentration and a short time, so it has less pollution and higher efficiency.

[0094] 3. The kudzu root residue nanocellulose preparation process of the present invention can obtain cellulose with high purity after high-pressure alkali boiling and bleaching, and then further purified by high-pressure acid hydrolysis; after high-pressure acid hydrolysis, the cellulose particle size changes from millimeter level to micrometer level, and then combined with homogenization treatment, nano-level kudzu root residue cellulose can be obtained. Therefore, the present invention can obtain nano-level cellulose by one-step acid hydrolysis, and the acid concentration used is low, and the pollution is small.

[0095] 4. In the present invention, the kudzu root residue nanocellulose prepared in Example 2 is used as an emulsifier to prepare the Pickering emulsion with the best stability. Therefore, in the preparation process of kudzu root residue nanocellulose, the optimal concentration of NaOH solution used in high-pressure alkali cooking is 1wt%, the optimal concentration of H2SO4 solution used in high-pressure acid hydrolysis is 2wt%, and the optimal pressure of the microfluidization homogenization process is 120MPa.

[0096] 5. Compared with Comparative Example 1, the Pueraria lobata residue nanocellulose prepared by the present invention has better stability in preparing Pickering emulsion; compared with Comparative Example 2, the process of combining high-pressure alkali cooking, high-pressure acid hydrolysis and homogenization of the present invention has a simpler process, a shorter cycle, and the prepared Pickering emulsion is better, indicating that the nanocellulose prepared by the process combining high-pressure alkali cooking and high-pressure acid hydrolysis has a more uniform particle size; compared with Comparative Example 3, the method for preparing Pueraria lobata residue nanocellulose of the present invention, the process of first high-pressure alkali cooking and then high-pressure acid hydrolysis can make the Pueraria lobata residue structure loose, which is more conducive to the subsequent acid hydrolysis and homogenization effects, so the prepared Pueraria lobata residue nanocellulose has better emulsification properties.

[0097] The embodiments of the present invention are described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions and variations made to these embodiments without departing from the principles and spirit of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing kudzu root residue nanocellulose, characterized in that: The steps include: Step S1, placing kudzu root residue and NaOH solution in a high-pressure cooking pot for high-pressure alkali cooking, then washing, filtering to neutrality and pulping; wherein the mass fraction of the NaOH solution is 0.5wt%-2wt%, and the high-pressure alkali cooking conditions are: solid-liquid ratio of 1:18-22, pressure of 0.3-0.5MPa, and alkali cooking time of 1-1.5h; Step S2, oxidative bleaching the pulp with NaClO2 under acidic conditions, then washing, filtering to neutrality and drying to obtain a primary cellulose product of kudzu root residue; wherein the oxidative bleaching process conditions are: a solid-liquid ratio of kudzu root residue to NaClO2 solution of 1:18-22, a temperature of 85-95°C, and a time of 1.5-3h; Step S3, placing the dried material and dilute sulfuric acid in a high-pressure cooking pot for high-pressure acid hydrolysis, and then centrifugally washing to neutrality; wherein the mass fraction of sulfuric acid is 1wt%-2wt%, and the high-pressure acid hydrolysis conditions are: solid-liquid ratio of 1:18-22, pressure of 0.1-0.2MPa, and time of 1-1.5h; Step S4, the washed material is configured into a suspension, first subjected to high-speed shearing, and then subjected to microfluidization homogenization to obtain a kudzu root residue nanocellulose suspension; wherein the high-speed shearing conditions are: a shearing rate of 12000-13000 r / min, a shearing time of 2-5 min; the microfluidization homogenization conditions are: a pressure of 60 MPa-120 MPa, and a homogenization number of 2-3 times; Step S5, concentrating and freeze-drying to obtain kudzu root residue nanocellulose.

2. The method for preparing kudzu root residue nanocellulose according to claim 1, characterized in that: In step S2, during the process of oxidative bleaching of the pulp, the pH value is adjusted to 3-4.

3. The method for preparing kudzu root residue nanocellulose according to claim 1, characterized in that: In step S1 and step S2, the method of water washing and filtering is: placing the material on a 200-300 mesh sieve and repeatedly washing it with water.

4. The method for preparing kudzu root residue nanocellulose according to claim 1, characterized in that: In step S2, the drying method is forced air drying, the temperature is 55-65°C, and the time is 24-48h.

5. The method for preparing kudzu root residue nanocellulose according to claim 1, characterized in that: In step S3, the centrifugal washing method is: the feed liquid is centrifuged at 7500-8500 r / min for 5-10 minutes, the supernatant is discarded, and water is added to repeat the operation.

6. The method for preparing kudzu root residue nanocellulose according to claim 1, characterized in that: In step S4, the concentration method is rotary evaporation, the temperature is 50-60°C, the rotation speed is 180-220r / min, and the air pressure is -0.1MPa to -0.3MPa.

7. The method for preparing kudzu root residue nanocellulose according to claim 1, characterized in that: In step S5, during the freeze-drying process, the pre-freezing time is 6-12 hours, the pre-freezing temperature is -20 to -30°C, and the drying time is 36-48 hours.

8. A kudzu root residue nanocellulose, characterized in that Prepared by the method according to any one of claims 1 to 7.

9. Use of the kudzu root residue nanocellulose as claimed in claim 8 in preparing Pickering emulsion.

10. A method for preparing a Pickering emulsion, characterized in that: The steps include: The kudzu root residue nanocellulose prepared by the method of any one of claims 1 to 7 is configured into a water suspension with a mass fraction of 0.5 wt%, mixed with soybean oil in a ratio of 9:1, and emulsified by shearing first and then homogenizing to obtain an oil-in-water emulsion.

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