CN112725917A

CN112725917A - Preparation method of areca seed cellulose nanofibrils

Info

Publication number: CN112725917A
Application number: CN202011579681.3A
Authority: CN
Inventors: 姚珊; 潘飞兵; 张伟敏
Original assignee: Hunan Kouweiwang Group Co ltd; Hainan Huachuang Betel Nut Research Institute
Current assignee: Hunan Kouweiwang Group Co ltd; Hainan Huachuang Betel Nut Research Institute
Priority date: 2020-12-28
Filing date: 2020-12-28
Publication date: 2021-04-30
Anticipated expiration: 2040-12-28
Also published as: CN112725917B

Abstract

The invention discloses a preparation method of areca seed cellulose nanofibrils, which comprises the following steps: s1, grinding and crushing; s2, degreasing; s3, alkaline leaching; s4, bleaching; s5, acid leaching; s6, high-pressure homogenization, the invention extracts and prepares the areca seed cellulose nanofibrils from the areca seeds for the first time, the concentration of the sulfuric acid used in the invention is lower than 15 percent, the generation of waste acid is reduced, the invention is environment-friendly, and simultaneously, the pressure and the times of homogenization are greatly reduced, and the energy consumption is reduced(ii) a Meanwhile, the betel nut seed cellulose nanofibril monosaccharide component prepared by the method comprises the following components: glucose, mannose, xylose, analyzed by FTIR at 2920cm^‑1、1429cm^‑1、900cm^‑1Has an absorption peak; through X-ray diffraction analysis, main peaks exist at positions with the 2 theta of 16 degrees and the 22 degrees, through DTG thermal stability analysis, the thermal weight loss peak is maximum at the temperature of 327 ℃ of 300-.

Description

Preparation method of areca seed cellulose nanofibrils

Technical Field

The invention belongs to the technical field of nanofibril preparation, and particularly relates to a preparation method of areca seed cellulose nanofibril.

Background

Nanocellulose (NC) is a cellulose material separated from a fibrous raw material by physical, chemical or biological treatment, with at least one dimension in the nanometer size range. Nanocellulose can be classified into 2 types according to its cellulose source, processing conditions, size, function and preparation method: cellulose Nanocrystals (CNC), Cellulose Nanofibrils (CNF). The Cellulose Nanocrystal (CNC) is composed of rodlike cellulose crystals with the width and the length of 5-70nm and 100-200nm respectively, and is mainly applied to the aspects of mechanical reinforcing agents, film packages, heavy metal adsorbents, antibacterial materials and the like in 3D scaffolds. Cellulose Nanofibrils (CNF) are located in the fibre cell wall, consisting of a bundle of long cellulose chain molecules, are entangled nanofibrils with a diameter of 5-60nm and a length of several microns, comprising alternating crystalline and amorphous regions, mainly applied in the fields of alternative plastics, barrier films/coatings, food, etc.

Betel nut (Areca catechu L.) is the first of the four major south medicines, only a very small part of the Areca nut enters the medicinal material market, and most of the Areca nut is used for fresh food and deep processing of betel nuts and is consumed as leisure food. In the process of fresh betel nut and betel nut processing, most of betel nut seeds are waste, and the betel nut seeds are seeds of betel nuts and account for 45 percent of the total weight of the betel nuts. However, during the processing of the betel nuts, the betel nut seeds are discarded. According to 27.42 ten thousand tons of betel nut output in 2018 Hainan province, only 12 ten thousand tons of betel nut seeds generated in Hainan and Hunan each year bring huge pressure on environment maintenance, and simultaneously can cause great waste of resources.

In recent years, researches on betel nut fruits at home and abroad mainly focus on the shells of the betel nut fruits, and researches on betel nut seeds are less. The research of the betel nut seeds mainly focuses on the aspects of active substance extraction, efficacy research and the like: luoshi et al (luoshi et al, arecoline extraction and separation from betel nut and its activity research [ D ]. hainan university, 2011.) use ultrasonic-assisted extraction and thermal reflux extraction to extract arecoline from betel nut; kangliang et al (Kangliang, Quarang, Zengguanlin, etc.. research on the process of subcritical water extraction of arecoline from areca seeds [ J ] food safety quality detection report, 2016(7):3773-3780.) utilizes a single-factor experiment combined with a Box-Benhnken experiment and a response surface analysis method to optimize the process of subcritical water extraction of arecoline from areca seeds; the method comprises the following steps of (1) carrying out heating reflux extraction on different parts (areca flowers, areca shells and areca seeds) of areca seeds by using Korean forest (Korean forest, Zhang Haide, Lizhongsheng, and the like.) and an antioxidant activity test [ J ] reported in agricultural machinery, 2011,41(04): 134-; lilan (Lilan. betelnut oil quality characteristics and application research [ D ]. Zhongnan forestry science and technology university, 2012.) extracts betelnut oil by using a supercritical CO2 technology, purifies the betelnut oil by a molecular distillation method, evaluates the composition, physicochemical properties and safety of the betelnut oil fatty acid, and discusses the application of the betelnut oil to food.

However, no cellulose nanofibrils of areca seeds have been reported in the literature so far.

Disclosure of Invention

In view of the problems in the prior art, the present invention provides a method for preparing areca seed cellulose nanofibrils, wherein the areca seed cellulose nanofibrils prepared by the method comprise: grapeGlucose, mannose, xylose, analyzed by FTIR at 2920cm^-1、1429cm^-1、900cm^-1Has an absorption peak; through X-ray diffraction analysis, main peaks exist at positions with the 2 theta of 16 degrees and the 22 degrees, through DTG thermal stability analysis, the thermal weight loss peak is the largest at the temperature of 300-327 ℃, and meanwhile, the cellulose nanofibrils have high viscosity, elastic modulus and viscous modulus and have great application potential in the field of food.

The invention aims to provide a preparation method of areca seed cellulose nanofibrils.

The preparation method comprises the following steps:

s1, grinding and crushing: putting the dried areca seeds into a grinder to be ground into powder, and storing the powder in a dryer for later use;

s2, degreasing: putting the dried areca seed powder into a subcritical extraction device for a degreasing process, firstly starting a vacuum pump for vacuumizing, closing the vacuum pump when the vacuum degree reaches a set value, opening a solvent valve, allowing n-butane to flow into an extraction tank to completely soak areca seeds, simultaneously opening a hot water pump valve, heating the extraction tank, and completing a primary extraction degreasing process after a period of reaction;

s3, alkaline leaching: putting the degreased areca seeds prepared in the step S2 and a NaOH solution into a beaker, putting the beaker on a magnetic stirrer, heating and stirring, filtering suspension in the beaker after the reaction is finished, and washing the precipitate with a large amount of distilled water;

s4, bleaching treatment: putting the precipitate and the sodium hypochlorite solution in the step S3 into a container, adjusting the pH value of the solution in the container to 5.0 by using glacial acetic acid, putting the container on a magnetic stirrer for heating and stirring, after the reaction is finished, centrifuging the suspension to obtain areca seed cellulose, putting the cellulose into an oven for drying, putting the dried cellulose into a grinder for grinding into powder, and storing the powder in a dryer for later use;

s5, acid leaching: mixing the cellulose powder obtained in step S4 with H with a mass concentration of 1-15%₂SO₄Putting the solution into a reactor for heating reaction, cooling the reactor in an ice bath after the reaction is finished, and then centrifugally washing the precipitate until the precipitate is neutral;

s6, high-pressure homogenization: dissolving the precipitate obtained in the step S5 in water, placing the sample in a beaker, shearing the sample for 5min at a certain rotating speed by using a high-speed shearing machine, and placing the sample in a high-pressure homogenizer, wherein the specific conditions of the high-pressure homogenization are as follows: circulating for 3 times under 20 MPa; and finally, circulating for 5 times under the pressure of 50Mpa to obtain the areca seed cellulose nanofibrils.

Preferably, in the step S2, the vacuum setting value is 0.4Mpa, the heating temperature is 45 ℃, and the extraction degreasing is performed for 4 times.

Preferably, in the step S3, the defatted betel nut seeds obtained in the step S2 and a 6% NaOH solution are put into a beaker according to a material-to-liquid ratio of 1:20(m/v), and reacted for 4 hours at a temperature of 80 ℃.

Preferably, in the step S4, the precipitate in the step S3 and a sodium hypochlorite solution with a mass concentration of 1.7% are placed into a beaker according to a feed-liquid ratio of 1:40(m/v), and are bleached for 1h at a temperature of 80 ℃.

Preferably, the cellulose powder in the step S4 and H with the mass concentration of 1-15% in the step S5₂SO₄Putting the solution into a reactor according to the feed-liquid ratio of 1:20(m/v), and reacting for 1h at the temperature of 80 ℃; the centrifugation conditions were: 10000rpm, 5 ℃, and 20min of centrifugation.

Preferably, in the step S6, the precipitate obtained in the step S5 is dissolved in water to obtain a 0.3% areca seed cellulose solution, then the sample is placed in a beaker and sheared for 5min at a rotation speed of 10000rpm by a high-speed shearing machine, and then the sample is placed in a high-pressure homogenizer, wherein the specific conditions of the high-pressure homogenization are as follows: circulating for 3 times under 20 MPa; finally, the cycle was repeated 5 times in total under a pressure of 50 MPa.

A large number of documents show that the acid concentration and the mass concentration required for preparing the nano-cellulose by acid treatment are generally more than 50 percent, the method can generate a large amount of high-concentration waste acid and impurities, has great environmental pollution and low yield,moreover, the method is easy to cause corrosion of equipment and has higher requirements on reaction equipment. As a result of extensive experimental studies, it has been found that cellulose is hydrolyzed at a high mass concentration of acid (greater than 20%) to produce cellulose nanofibrils in low yield, and therefore, H according to the present invention₂SO₄The quality of the solution is controlled between 1 and 15 percent; in addition, the single high-pressure homogenization treatment for preparing the nano cellulose needs the pressure drop of about 80MPa, and the fiber pulp is circulated and homogenized for about 20 times to obtain the nano cellulose fibrils. However, high pressure homogenization is an energy intensive process, which consumes a lot of energy, and long fibers in plant fibers often cause clogging in the interior of equipment, particularly in movable parts such as valves, and then must be disassembled for cleaning, which not only affects the efficiency of preparation work, but also causes damage to instruments. Therefore, in the invention, the sample is firstly put in a high-speed shearing machine to be sheared for 5min at the rotating speed of 10000rpm, and then the sample is put in a high-pressure homogenizer, wherein the specific conditions of the high-pressure homogenization are as follows: circulating for 3 times under 20Mpa to crush fiber and shorten its particle size, and avoid blocking valve inside high pressure homogenizer; and finally circulating for 5 times under the pressure of 50Mpa to obtain the areca seed nanocellulose filaments.

The invention provides a method for synergistically modifying areca seed cellulose by chemical treatment and high-pressure homogenization treatment. The concentration of the sulfuric acid used in the invention is lower than 15%, the generation of waste acid is reduced, the environment is friendly, the pressure and the frequency of homogenization are greatly reduced, the energy consumption is reduced, and the method is favorable for commercial production.

Another object of the present invention is to provide a cellulose nanofibril of areca seed.

The areca seed cellulose nanofibrils produced by the method of producing areca seed cellulose nanofibrils according to any of claims 1-6.

Preferably, the monosaccharide components of the cellulose nanofibrils include: glucose, mannose, xylose.

Preferably, the cellulose nanofibrils of areca seed are at 2920cm as analyzed by FTIR^-1、1429cm^-1、900cm^-1Has an absorption peak; through X-ray diffraction analysis, the betel nut seed cellulose nanofibrils have main peaks at the positions of 16 degrees and 22 degrees of 2 theta.

Preferably, the betel nut seed cellulose nanofibrils have the largest thermal weight loss peak at 300-327 ℃ through DTG thermal stability analysis.

Compared with the prior art, the invention has the following advantages:

1) the invention extracts and prepares the areca seed cellulose nanofibrils from the areca seeds for the first time;

2) the invention provides a method for synergistically modifying areca seed cellulose by chemical treatment and high-pressure homogenization treatment. The concentration of the sulfuric acid used in the invention is lower than 15%, the generation of waste acid is reduced, the environment is friendly, the pressure and the frequency of homogenization are greatly reduced, the energy consumption is reduced, and the method is beneficial to commercial production;

3) the betel nut seed cellulose nanofibril monosaccharide component prepared by the method comprises the following components: glucose, mannose, xylose, analyzed by FTIR at 2920cm^-1、1429cm^-1、900cm^-1Has an absorption peak; through X-ray diffraction analysis, main peaks exist at positions with the 2 theta of 16 degrees and the 22 degrees, through DTG thermal stability analysis, the thermal weight loss peak is the largest at the temperature of 300-327 ℃, and meanwhile, the cellulose nanofibrils have high viscosity, elastic modulus and viscous modulus and have great application potential in the field of food.

Drawings

FIG. 1 is a diagram showing a sample preparation process in the present invention.

FIG. 2 is a scanning electron micrograph of a sample according to the present invention.

FIG. 3 is a Fourier transform infrared spectrum of a sample according to the present invention.

FIG. 4 is an X-ray diffraction pattern of a sample according to the present invention.

FIG. 5 is a graph of the thermal stability of a sample according to the present invention.

FIG. 6 is a graph of rheological properties of a sample of the present invention (A) shows a graph of viscosity of the sample as a function of shear rate, and (B) shows a graph of modulus as a function of angular frequency).

Detailed Description

In order to make the objects, technical solutions and advantageous technical effects of the present invention more clearly apparent, the technical solutions of the present invention are further described in detail below with reference to examples, and it should be understood that the specific embodiments described in the present specification are only for explaining the present invention and are not intended to limit the present invention.

The subcritical extraction device, the magnetic stirrer, the refrigerated centrifuge, the oven, the grinder, the high-pressure homogenizer, the high-speed shearing machine, the Fourier transform infrared spectroscopy (FTIR), the X-ray diffractometer (XRD), the Laser Particle Size Analyzer (LPSA), the Scanning Electron Microscope (SEM), the vacuum freeze dryer, the thermal analyzer, the rheometer and other instruments and equipment used in the invention can be obtained on the market;

the liquid chromatograph-mass spectrometer (UPLC-MS) and the High Performance Gel Permeation Chromatograph (HPGPC) used in the present invention were purchased from agilent ltd; the types of chromatographic columns are as follows: AGILENT EC-C18(2.7um, 2.1mm 50 mm); BRT105-104-102 can be obtained commercially in series with gel columns (8X 300 mm);

the other obtained chemical reagents are conventional chemical reagents and can be obtained commercially;

in the present invention, all instruments and chemical reagents are commercially available unless otherwise specified.

In the present invention, the experimental data obtained are represented by mean and standard deviation, each group of samples was performed at least 3 replicates and single factor analysis of variance (ANOVA) was performed by SPSS software, where p <0.05 was taken as the significance level.

The method for preparing the cellulose nanofibrils of areca seeds is further described below with reference to specific examples.

Example 1

Preparing betel nut seed cellulose nanofibrils:

s2, degreasing: putting the dried areca seed powder into a subcritical extraction device for a degreasing process, firstly starting a vacuum pump for vacuumizing, closing the vacuum pump when the vacuum degree reaches 0.4Mpa, opening a solvent valve, allowing n-butane to flow into an extraction tank to completely soak areca seeds, simultaneously opening a hot water pump valve, heating the extraction tank to reach 45 ℃, completing an extraction and degreasing process for one time after a period of reaction, and then performing extraction and degreasing for 4 times;

s3, alkaline leaching: putting the degreased areca seeds prepared in the step S2 and a NaOH solution with the mass concentration of 6% into a beaker according to the material-liquid ratio of 1:20(m/v), placing the beaker on a magnetic stirrer, heating and stirring, and reacting for 4 hours at the temperature of 80 ℃; after the reaction is finished, filtering the suspension in the beaker, and then washing the precipitate by using a large amount of distilled water;

s4, bleaching treatment: putting the precipitate obtained in the step S3 and a sodium hypochlorite solution with the mass concentration of 1.7% into a beaker according to the material-liquid ratio of 1:40(m/v), adjusting the pH value of the solution in the container to 5.0 by using glacial acetic acid, placing the container on a magnetic stirrer for heating and stirring, and bleaching for 1h at the temperature of 80 ℃; after the reaction is finished, centrifuging the suspension to obtain areca seed cellulose, placing the cellulose in an oven for drying, then placing the dried cellulose in a grinder for grinding into powder, and storing the powder in a dryer for later use;

s5, acid leaching: mixing the cellulose powder in the step S4 with H having a mass concentration of 1%₂SO₄Putting the solution into a reactor according to the feed-liquid ratio of 1:20(m/v), and reacting for 1h at the temperature of 80 ℃; the reactor was cooled in an ice bath and the pellet was then washed by centrifugation until the pellet was neutral, the centrifugation conditions being: 10000rpm, 5 ℃, centrifuging for 20 min;

s6, high-pressure homogenization: dissolving the precipitate obtained in the step S5 in water to obtain a betel nut seed cellulose solution with the mass concentration of 0.3%, then placing the sample in a high-speed shearing machine to shear for 5min at the rotating speed of 10000rpm, and then placing the sample in a high-pressure homogenizer, wherein the specific conditions of the high-pressure homogenization are as follows: circulating for 3 times under 20 MPa; and finally, circulating for 5 times under the pressure of 50Mpa to obtain the areca seed cellulose nanofibril (1% -SM-IDF).

Example 2

Preparing betel nut seed cellulose nanofibrils:

s5, acid leaching: mixing the cellulose powder in the step S4 with H having a mass concentration of 10%₂SO₄Putting the solution into a reactor according to the feed-liquid ratio of 1:20(m/v), and reacting for 1h at the temperature of 80 ℃; the reactor was cooled in an ice bath and the pellet was then washed by centrifugation until the pellet was neutral, the centrifugation conditions being: 10000rpm, 5 ℃, centrifuging for 20 min;

s6, high-pressure homogenization: dissolving the precipitate obtained in the step S5 in water to obtain a betel nut seed cellulose solution with the mass concentration of 0.3%, then placing the sample in a high-speed shearing machine to shear for 5min at the rotating speed of 10000rpm, and then placing the sample in a high-pressure homogenizer, wherein the specific conditions of the high-pressure homogenization are as follows: circulating for 3 times under 20 MPa; and finally, circulating for 5 times under the pressure of 50Mpa to obtain the areca seed cellulose nanofibril (10% -SM-IDF).

Example 3

Preparing betel nut seed cellulose nanofibrils:

s5, acid leaching: mixing the cellulose powder in the step S4 with H having a mass concentration of 15%₂SO₄Putting the solution into a reactor according to the feed-liquid ratio of 1:20(m/v), and reacting for 1h at the temperature of 80 ℃; the reactor was cooled in an ice bath and the pellet was then washed by centrifugation until the pellet was neutral, the centrifugation conditions being: 10000rpm, 5 ℃, centrifuging for 20 min;

s6, high-pressure homogenization: dissolving the precipitate obtained in the step S5 in water to obtain a betel nut seed cellulose solution with the mass concentration of 0.3%, then placing the sample in a high-speed shearing machine to shear for 5min at the rotating speed of 10000rpm, and then placing the sample in a high-pressure homogenizer, wherein the specific conditions of the high-pressure homogenization are as follows: circulating for 3 times under 20 MPa; and finally, circulating for 5 times under the pressure of 50Mpa to obtain the areca seed cellulose nanofibril (15% -SM-IDF).

Comparative example 1

Prepared according to the steps of S1-S4 of example 1, and the areca seed cellulose (IDF) can be obtained.

Comparative example 2

Prepared according to the steps of S1-S5 of example 1, and the areca seed cellulose (1% -IDF) can be obtained.

Comparative example 3

Prepared according to the steps of S1-S5 of example 2, and the areca seed cellulose (10% -IDF) can be obtained.

Comparative example 4

Prepared according to the steps of S1-S5 of example 3, and the areca seed cellulose (15% -IDF) can be obtained.

Comparative example 5

Prepared according to steps S1-S5 of example 1, and H in step S5₂SO₄The mass concentration of the solution is changed to 20 percent, and the areca seed cellulose (20 percent-IDF) can be obtained.

Comparative example 6

Prepared according to steps S1-S5 of example 1, and H in step S5₂SO₄The mass concentration of the solution is changed to 30 percent, and the areca seed cellulose (30-IDF) can be obtained.

Comparative example 7

The areca powder obtained in step S1 in example 3 was dissolved in water to obtain a 0.3% solution, and then high-pressure homogenization treatment was performed according to step S6 in example 3 to obtain areca seed cellulose (15% -IDF-SM).

Example 5

The betel nut seed cellulose nanofibrils prepared in examples 1 to 3 and the betel nut seed cellulose prepared in comparative example 1 were subjected to monosaccharide composition analysis, molecular weight measurement analysis, particle size analysis, and Zeta potential analysis, respectively,

the monosaccharide composition analysis method comprises the following steps: 10mg of the sample was weighed into a 20mL jar, 10mL of a 2mol/L aqueous trifluoroacetic acid (TFA) solution was added, and the mixture was charged with N₂Sealing the tube (10L/min, 1min), and hydrolyzing in an oven at 100 ℃ for 6 h; after cooling, the lid was opened, 1mL of methanol was added to 1mL of the solution, and the mixture was heated in a 70 ℃ water bath with N₂Blow-drying, repeating the process of adding methanol (purity in chromatographic grade) and adding N₂Blow-drying for 2 times to remove TFA; adding 1mL of 0.3mol/L NaOH solution to fully dissolve residues to obtain polysaccharide hydrolysate, and performing derivatization determination after certain dilution.

Respectively putting 400 mu L of mixed monosaccharide standard solution or polysaccharide hydrolysate into a 5mL test tube with a plug, adding 400 mu L of LPMP methanol solution, and mixing uniformly in a vortex; reacting for 2 hours in a water bath at 70 ℃; taking out, standing and cooling to room temperature; adding 400 mu L of 0.3mol/L HCl for neutralization (pH 6-7); adding water 1200 μ L, adding equal volume of chloroform, vortex mixing, shaking, standing, discarding chloroform phase, and extracting for 2 times. The aqueous phase was filtered through a 0.45 μm microporous membrane (aq) and analyzed by HPLC injection.

Chromatographic conditions are as follows: chromatography column AGILENT EC-C18(2.7 μm, 2.1mm 50 mm); mobile phase A: 50mmol/L ammonium acetate buffer (ammonia adjusted to pH 8.0); mobile phase B: acetonitrile; the flow rate is 0.4 mL/min; the column temperature is 35 ℃; the sample size was 2. mu.L, and the gradient elution conditions are as follows:

TABLE 1 gradient elution Table

Mass spectrum scanning conditions: characteristic ion scan mode (SIR); ESI + spray voltage 2.0 kv; cone voltage 30 v; the ion source temperature is 150 ℃; threshing deviceThe temperature of the solvent is 500 ℃; desolventizing gas (N)₂) 1000L/h; SIR mode detection ion: 481.09, 495.1, 510.1, 511.08, 525.06.

Molecular weight determination analysis method: the molecular weight of the polysaccharide was determined by HPGPC, and the sample and the standard were precisely weighed, the sample was prepared as a 5mg/mL solution, centrifuged at 12000rpm for 10min, the supernatant was filtered through a 0.22 μm microfiltration membrane, and then the sample was transferred to a 1.8mL injection vial.

A chromatographic column: BRT105-104-102 series gel column (8X 300 mm); mobile phase: 0.05M NaCl solution; flow rate: 0.6mL/min, column temperature: 40 ℃; sample introduction amount: 20 mu L of the solution; a detector: and a difference detector RI-502.

Particle size and Zeta potential analysis: the samples were dispersed in deionized water and the particle size distribution and Zeta potential were measured using a laser particle sizer (Mastersizer zs90, Malven, England).

The results are shown in Table 2:

TABLE 2 monosaccharide composition, molecular weight, particle size and Zeta potential

Wherein, the data are marked with a, b and c respectively, which shows that the data have significant difference; the data are labeled with the same letter (e.g., all labeled b), indicating that there is no significant difference between the data.

As can be seen from Table 2, glucose, xylose and mannose are the main components of the cellulose nanofibrils of the areca seeds, and the arabinose, xylose and galactose contents in the samples of examples 1 to 3 are reduced, mainly due to hydrolysis of hemicellulose; the insoluble fiber prepared has higher glucose content along with the increase of the concentration of the sulfuric acid, and the reason is that the removal degree of impurities such as starch, protein and the like is increased, the proportion of cellulose is gradually increased, and the proportion of glucose obtained by hydrolysis is gradually increased; compared with IDF, the total content of 1% SM-IDF, 10% SM-IDF and 15% SM-IDF neutral monosaccharide exceeds 90%. As the acid concentration increases, the molecular weight of the sample decreases, the particle size decreases, and the degree of aggregation of the filamentous fibers decreases, which is consistent with the structure observed by SEM; meanwhile, the Zeta potential value is reduced, and the absolute value of the Zeta potential value is increased, which indicates that the whole sample system is stable.

Example 6

The same quality cellulose powder obtained by bleaching in step S4 in examples 1-3 and comparative examples 5-6 was subjected to acid leaching in step S5 to obtain areca seed cellulose, and the cellulose yield results are shown in Table 3:

TABLE 3 cellulose yield

As is clear from Table 3, examples 1 to 3 used 1%, 10% and 15% by mass of H, respectively₂SO₄The experimental groups were treated in solution, comparative examples 5 to 6 with 20% and 30% by mass of H₂SO₄H used in solution treatment control, examples and comparative examples₂SO₄The cellulose yields of comparative example 5 and comparative example 6, which were 54.74% and 48.12%, respectively, and were lower than the cellulose yields of the experimental group (66.14%, 63.04%, and 59.94%), were different in the concentration of the solution, and the results showed that the hydrolysis of cellulose began with the increase of the acid concentration, and the yield of the obtained cellulose nanofibrils was lower when the acid concentration exceeded 20%; meanwhile, when the acid concentration is too high, environmental pollution may be caused, and thus, the acid concentration used in the present invention ranges from 1 to 15%.

Example 7

The betel nut seed cellulose nanofibrils prepared in examples 1 to 3 and the betel nut seed cellulose prepared in comparative examples 2 to 4 and 7 were used for the particle size analysis, which was the same as in example 5, and the results are shown in table 4:

TABLE 4 particle size analysis

Wherein, the data are marked with a, b, c, d, e and f respectively, which shows that the data have significant difference; the data are labeled with the same letter (e.g., all labeled with f), indicating that there is no significant difference between the data.

As is apparent from Table 4, the products of examples 1 to 3 were obtained by the acid treatment of the present invention in combination with the high-pressure homogenization, the samples of comparative examples 2 to 3 were obtained only by the acid treatment, and the nano-scale cellulose nanofibrils obtained in examples 1 to 3 were changed from 447.08 + -31.76 (nm) to 177.60 + -8.48 (nm) in particle size as the acid concentration increased, because part of the cellulose was decomposed into short chains after the acid treatment, and thus the particle size of the obtained cellulose nanofibrils became smaller; while comparative examples 3-4 only yielded micron-sized cellulose, because absent the high pressure homogenization process, the micron-sized fibers could not be further nanocrystallized;

comparative example 7 only the micron-sized cellulose was obtained by the high-pressure homogenization treatment without the acid treatment process of examples 1 to 3, because the high-pressure homogenization pressure and the number of times were small, and the micron-sized fiber could not be further nanocrystallized;

therefore, the areca seed cellulose nanofibrils can be obtained through the acid treatment and the high-pressure homogenization cooperative treatment, and the nano-scale cellulose nanofibrils cannot be obtained through the acid treatment or the high-pressure homogenization method, and the micron-scale cellulose can be obtained.

Example 8

The betel nut seed cellulose nanofibrils prepared in examples 1 to 3 and the betel nut seed cellulose prepared in comparative examples 1 to 4 were taken to be analyzed by a scanning electron microscope, the sample was fixed on an aluminum short tube by a double-sided tape after vacuum freeze-drying and coated with a gold layer to improve the conductivity, and the coated sample was observed under a scanning electron microscope at an accelerating voltage of 10kV, and the result is shown in fig. 2.

As can be seen from fig. 2, the samples of comparative examples 1 to 4 all exhibited a slightly curled lamellar structure overall, with a few cracks on the surface; the sample filamentous fibers of examples 1-3 were exposed to varying degrees and the degree of aggregation of the filamentous fibers decreased with increasing acid concentration.

Example 9

The betel nut seed cellulose nanofibrils from examples 1-3 and the betel nut seed cellulose from comparative examples 1-4 were analyzed by fourier transform infrared spectroscopy (FTIR), and after vacuum freeze drying the samples were diluted to about 1% by weight KBr by grinding with a mortar and pestle. In the wave number range of 400-4000 cm^-1The resolution was 4cm-1 for 16 scans, and the results are shown in FIG. 3.

As can be seen from FIG. 3, the betel nut seed cellulose nanofibrils obtained in examples 1-3 and the betel nut seed cellulose obtained in comparative examples 1-4 all have similar spectral patterns at 2920cm^-1、1429cm^-1、900cm^-1The absorption peak is shown, which shows that the preparation method combining chemical treatment and high-pressure homogenization has mild conditions, does not change the functional group structure of cellulose, does not greatly damage the prepared areca seed cellulose nanofibril structure, and is beneficial to the application of the areca seed cellulose nanofibril structure.

Example 10

Carrying out XRD analysis on the areca seed cellulose nanofibrils prepared in examples 1-3 and the areca seed cellulose prepared in comparative examples 1-4, and after the sample is subjected to vacuum freeze drying, evaluating the crystallinity of the sample at a scanning rate of 5 degrees/min of 10-60 degrees, wherein the step size is 0.015 degrees; the crystallinity Xc of cellulose was calculated by the Segal method, and the crystallinity was calculated according to the following formula: the results are shown in FIG. 4.

In the formula: xc-the crystallinity of cellulose; i is₀₀₂-diffraction intensity of the 002 crystal plane; i is_am-diffraction intensity of 18.0 ° 2 θ.

As can be seen from fig. 4, the betel nut seed cellulose prepared in comparative examples 1 to 4 exhibited two broad peaks, and the sharp diffraction peaks of the sample at 2 θ ═ 16 ° and 2 θ ═ 22 ° were typical characteristics of cellulose I; the betel nut seed cellulose nanofibrils prepared in examples 1 to 3 have increased diffraction peak intensities at 2 θ 16 ° and 2 θ 22 °, indicating increased crystallinity.

Example 11

The betel nut seed cellulose nanofibrils prepared in examples 1 to 3 and the betel nut seed cellulose prepared in comparative example 1 were subjected to thermogravimetric analysis, respectively, and the samples were subjected to thermogravimetric analysis at a temperature of 25 to 600 ℃ at a flow rate of 100mL/min under a nitrogen atmosphere using a pinhole alumina crucible. The thermogram was obtained on a thermal analyzer with a constant heating rate of 10 ℃/min, and the results are shown in fig. 5.

As can be seen from FIG. 5, the maximum thermal weight loss peak temperatures of the samples of examples 1-3 are higher than those of comparative example 1, and the peak values are larger within the temperature range of 300-; the peak of thermal weight loss in example 3 reached a maximum (327 deg.C), and thus the thermal stability of the sample prepared by the present invention was enhanced.

Example 12

Rheological property analysis was performed on the betel nut seed cellulose nanofibrils prepared in examples 1 to 3 and the betel nut seed cellulose prepared in comparative example 1, respectively, and the rheological property of the sample was measured at 25 ℃ using a strain-controlled rheometer. Equipped with parallel plates 50mm in diameter (plate spacing 1mm) and having an angular frequency in the range of 0.01-10Hz by performing dynamic frequency sweep tests in the Linear Viscoelastic Region (LVR). Drawing a viscosity curve, wherein the shear rate is 0.01-600s^-1The results are shown in FIG. 6.

As can be seen from fig. 6, the samples in examples 1 to 3 show interconnected network structures, and the sample in example 1 has a low viscosity, which may be due to the low acid concentration in example 1 and cannot completely decompose the nanofibers, and may be due to the low zeta potential and weak electrostatic repulsion, which results in a low degree of cross-linking of the network structure; the samples of examples 2 and 3 had a viscosity increase at low shear rates because at low shear rates the shear was not sufficient to disrupt the fiber network structure and increased collisions between fibers causing new interactions resulting in a small viscosity increase; the samples of examples 1-3 have higher viscosity, elastic modulus and viscous modulus and therefore have greater potential for use in the food field.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A preparation method of areca seed cellulose nanofibrils is characterized by comprising the following steps:

s5, acid leaching: mixing the cellulose powder obtained in step S4 with H with a mass concentration of 1-15%₂SO₄The solution is put into a reactor for heating reaction, after the reaction is finished, the reactor is cooled in ice bath, and then the precipitate is centrifugally washedUntil the precipitate is neutral;

2. The method for preparing cellulose nanofibrils of areca seed according to claim 1, wherein the vacuum setting in step S2 is 0.4Mpa, the heating temperature is 45 ℃, and the extraction degreasing is performed for 4 times.

3. The method for preparing cellulose nanofibrils of areca seeds according to claim 1, wherein in step S3, the degreased areca seeds prepared in step S2 and a NaOH solution with a mass concentration of 6% are put into a beaker according to a feed-to-liquid ratio of 1:20(m/v) and reacted for 4 hours at a temperature of 80 ℃.

4. The method for preparing areca seed cellulose nanofibrils according to claim 1, wherein the precipitate of step S3 and a sodium hypochlorite solution with a mass concentration of 1.7% are placed in a beaker according to a feed-to-solution ratio of 1:40(m/v) in step S4, and bleached for 1 hour at a temperature of 80 ℃.

5. The method for preparing areca seed cellulose nanofibrils according to claim 1, wherein the cellulose powder of step S4 and H with a mass concentration of 1-15% are mixed in step S5₂SO₄Putting the solution into a reactor according to the feed-liquid ratio of 1:20(m/v), and reacting for 1h at the temperature of 80 ℃; the centrifugation conditions were: 10000rpm, 5 ℃, and 20min of centrifugation.

6. The method for preparing areca seed cellulose nanofibrils according to claim 1, wherein the step S6 is performed by dissolving the precipitate obtained in the step S5 in water to obtain a solution with a mass concentration of 0.3% areca seed cellulose, placing the sample in a beaker, shearing the sample for 5min at a rotation speed of 10000rpm by a high speed shearing machine, and placing the sample in a high pressure homogenizer, wherein the specific conditions of the high pressure homogenization are as follows: circulating for 3 times under 20 MPa; finally, the cycle was repeated 5 times in total under a pressure of 50 MPa.

7. Areca seed cellulose nanofibrils, characterized in that they are produced by a method according to any of claims 1-6 for the preparation of areca seed cellulose nanofibrils.

8. The areca nut seed cellulose nanofibrils according to claim 7, wherein the monosaccharide composition of the cellulose nanofibrils comprises: glucose, mannose, xylose.

9. The areca seed cellulose nanofibrils according to claim 7, wherein the areca seed cellulose nanofibrils are at 2920cm as analyzed by FTIR^-1、1429cm^-1、900cm^-1Has an absorption peak; through X-ray diffraction analysis, the betel nut seed cellulose nanofibrils have main peaks at the positions of 16 degrees and 22 degrees of 2 theta.

10. The areca seed cellulose nanofibril of claim 7, wherein the areca seed cellulose nanofibril has a maximum peak thermal weight loss at 300-.