CN115368585B

CN115368585B - Anionized lignocellulose nanofibrils, and preparation method and application thereof

Info

Publication number: CN115368585B
Application number: CN202210961215.4A
Authority: CN
Inventors: 刘秀宇; 胡松; 黄钦; 夏璐
Original assignee: Guangxi University for Nationalities
Current assignee: Guangxi University for Nationalities
Priority date: 2022-08-11
Filing date: 2022-08-11
Publication date: 2023-10-20
Anticipated expiration: 2042-08-11
Also published as: CN115368585A

Abstract

The invention discloses an anionized lignocellulose nanofibril, a preparation method and application thereof, and belongs to the technical field of nanocellulose. The anionic lignocellulose nanofibrils are prepared by pretreating bagasse raw materials by using a eutectic solvent synthesized by choline chloride and lactic acid, then adding succinic anhydride for anion modification and carrying out mechanical microfibrillation. The anionized lignocellulose nanofibrils have the advantages of narrow diameter distribution range, uniform size, greenness, no toxicity, degradability, reproducibility, capability of being used as a reinforcing agent of a polyvinyl alcohol composite film, capability of effectively improving the mechanical property, the hydrophobic property, the ultraviolet resistance, the thermal stability and the like of the composite film. The preparation process of the anionized lignocellulose nanofibrils is green and simple, the reaction condition is mild, the energy consumption is low, and the product is renewable.

Description

Anionized lignocellulose nanofibrils, and preparation method and application thereof

Technical Field

The invention belongs to the technical field of nanocellulose, and particularly relates to an anionized lignocellulose nanofibrillar, and a preparation method and application thereof.

Background

Lignocellulose is the most abundant renewable biopolymer, can be obtained from industrial and agricultural wastes with abundant resources, has the characteristics of low cost, reproducibility and the like, particularly bagasse, is used as a characteristic biomass resource in Guangxi places, is mainly used as biomass fuel or directly abandoned at present, is used for pulping and papermaking, feeds and fertilizers in a small part, has the problems of low utilization rate, low utilization value and the like, and therefore, converts the bagasse into a high-added-value product, and has great significance on the development of local economy. The bagasse has stable and uniform components, the lignocellulose content is up to more than 90%, wherein the cellulose content is 40-50%, the hemicellulose content is 20-25%, and the lignin content is 16-25%.

Nanocellulose is a high added value product obtained by nanocrystallization of cellulose fibers by mechanical, biological, chemical and other methods, wherein the fiber diameter is 3-100 nm, and the length-diameter ratio is more than 10. Lignocellulose nanofibrils (LCNFs) produced from lignocellulose are of interest because of their low production cost, good environmental protection and high yield. LCNF is taken as a green high polymer material, has the inherent characteristics of nano cellulose, contains lignin particles, has good thermal stability, ultraviolet stability and hydrophobicity, and can prevent aggregation of fibers when being positioned between cellulose chains. The strong fiber network structure makes the fiber network structure hopeful to become a reinforcing agent of the composite material. At present, the method for preparing the nanocellulose from the natural lignocellulose has the limitations of using toxic and harmful chemicals, high energy consumption and high water consumption. In addition, the nanocellulose prepared by a mechanical method has the defects of wide diameter distribution range and nonuniform size, and natural fibers with compact structure and firm texture are extremely easy to be entangled together to cause the blockage and abrasion of a high-pressure homogenizer.

Generally, the processing of lignocellulosic biomass requires pretreatment, which can disrupt its dense hierarchical structure and increase fiber accessibility. The eutectic solvents (DESs) have the characteristics of easy preparation, low toxicity and biodegradation, and can be used as green solvents or reactants for the reaction. In addition, the DES can be recycled, thereby being beneficial to reducing the production cost and having good environmental protection. Structurally, it consists of at least one Hydrogen Bond Donor (HBD) and one Hydrogen Bond Acceptor (HBA). Because HBD and HBA form stronger hydrogen bonds, DES has a lower melting point than the individual components. Patent publication No. CN 112853794A discloses a method for preparing nanofiber microfibrils by pretreatment of ternary eutectic solvents, which comprises the steps of pretreating bagasse by using a ternary eutectic solvent consisting of choline chloride, lactic acid or oxalic acid and aluminum trichloride, uniformly mixing the ternary eutectic solvent with the bagasse, and digesting in a microwave digestion tank. Therefore, a preparation method of lignocellulose nanofibrils is needed to be found, which has the advantages of simple preparation process, simple and convenient operation, mild condition, low energy consumption and environmental protection.

Whereas the anionized lignocellulose nanofibrils have the following advantages: (1) The negative charge repulsive force on the surface of the fibril greatly promotes the separation of the cellulose nanofiber from the fiber, and saves the mechanical consumption. (2) The resulting suspension is highly transparent and stable due to limited fibril aggregation and flocculation. (3) The nanocellulose prepared by esterification with cyclic anhydride does not cause a great reduction in molar mass like the traditional Tempo oxidation method, so that the corresponding nanofiber has better thermal stability.

Disclosure of Invention

Aiming at the problems, the invention provides an anionized lignocellulose nanofibril, a preparation method and application thereof, and the material has narrow diameter distribution range and uniform size and can be used as a reinforcing agent of a polyvinyl alcohol composite film. And the preparation process of the material is green and simple, the reaction condition is mild, and the energy consumption is low.

The invention is realized by the following technical scheme:

the anionic lignocellulose nanofibrils are prepared by pretreating bagasse raw materials by using a eutectic solvent synthesized by choline chloride and lactic acid, then adding succinic anhydride for anion modification, and carrying out mechanical microfibrillation.

As the preferable choice of the technical scheme, the diameter distribution of the anionized lignocellulose nanofibrils is 6-56 nm, the carboxyl content is 2.7-2.9 mmol/g, and the relative crystallinity is 71-72%.

A method of preparing an anionized lignocellulosic nanofibrillar as described above, comprising the steps of:

(1) Pre-treating the eutectic solvent: crushing, washing and drying bagasse, then adding the treated bagasse into a eutectic solvent synthesized by choline chloride and lactic acid for pretreatment, and uniformly mixing to obtain a pretreated bagasse solution;

(2) Anion modification: adding succinic anhydride into the bagasse solution pretreated in the step (1) for anion modification, reacting under mechanical stirring, adding ethanol to terminate the reaction after the reaction is finished, centrifugally washing the reacted bagasse to be neutral, and collecting solid to seal and balance water to obtain the bagasse after anion modification;

(3) Mechanical microfibrillation: dispersing the bagasse subjected to anion modification in the step (2) in deionized water to prepare suspension, and carrying out superfine particle grinding treatment to obtain the anionic lignocellulose nanofibrils.

In the step (2) of the invention, the reaction formula of the pretreated bagasse and succinic anhydride is as follows:

r=cellulose, hemicellulose or lignin

As a preferable technical scheme, in the step (1), the mass ratio of the bagasse to the eutectic solvent is 1:20-30; the mol ratio of the choline chloride to the lactic acid is 1:10-20.

As a preferable technical scheme, in the step (2), the mass ratio of bagasse to succinic anhydride is 1:1-2.

Preferably, in the step (2), the reaction is carried out for 4 to 12 hours under mechanical stirring at a temperature of 110 to 130 ℃ and a rotation speed of 200 to 400 rpm.

As a preferable technical scheme, in the step (2), the rotation speed of the centrifugation is 4000-6000 rpm, and the centrifugation time is 10-20 min.

In the step (3), the clearance between the grinding discs for ultra-fine particle grinding is 50-300 n, and the cycle number is 20-30.

Preferably, in the step (3), the concentration of the suspension is 0.5 to 2wt%.

Use of an anionized lignocellulosic nanofibrillar as described above as a reinforcing agent in a polyvinyl alcohol composite film.

The reaction principle of the invention:

in the preparation process of the nano cellulose, the acid eutectic solvent is synthesized by choline chloride and lactic acid, the choline chloride and the lactic acid play a synergistic role, the molecular chain of the cellulose is degraded, and the hydrogen bond of the cellulose is weakened. The linkage between lignin and hemicellulose after treatment with an acidic eutectic solvent is broken by ether bonds in lignin. In the preparation process of the nanocellulose, lactic acid and choline chloride play a synergistic role. In addition, the eutectic solvent has good swelling capacity, can relax a cellulose structure, increases a reaction surface area, and is beneficial to exposing more sites for esterification reaction with succinic anhydride.

As shown in the above reaction formula, the ring-opening reaction of cellulose and succinic anhydride forms two carboxyl groups, one of which can be subjected to esterification reaction with hydroxyl groups on cellulose molecules, and the other of which is a terminal carboxyl group which is attached to cellulose in a functionalized manner and is free in water, so that the pretreatment can not only reduce the particle size of the fiber, hydrolyze part of amorphous areas, but also graft functional groups on the surface of the fiber, which is beneficial to preventing the hydrolysis and dissolution of cellulose in the pretreatment process of eutectic solvent, and the unhydrolyzed cellulose solid residues are subjected to simple mechanical treatment to obtain nanocellulose, so that the energy consumption is obviously reduced. The introduction of charged functional groups into the fiber structure can cause electrostatic repulsion between the fibers, promoting the microfibrillation process of the fibers. The anionic lignocellulose nanofibrils can be efficiently prepared by adopting the eutectic solvent and succinic anhydride treatment and through the hydrolysis, swelling and esterification of bagasse.

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

1. the invention can generate electrostatic repulsive force among fibers by introducing charged groups on the fibers through anion modification, effectively promote the dissociation of the fibers, promote the microfibrillation process of the fibers, and remarkably reduce the energy consumption of mechanical grinding. The modified bagasse can be easily grinded by ultrafine particles to obtain gel, and the prepared anionized lignocellulose nanofibrils have narrow diameter distribution range and uniform size.

2. The invention avoids the high-consumption and high-pollution delignification and hemicellulose removal process, the retained lignin in the lignocellulose nanofibrils can reduce the energy consumption required by mechanical grinding, and the retained lignin has good thermal stability, ultraviolet stability and hydrophobicity due to the fact that the retained lignin is rich in various active groups such as phenolic hydroxyl groups, alcoholic hydroxyl groups, phenyl groups and the like, and meanwhile, the lignin is positioned between cellulose chains to prevent the aggregation of fibers.

3. The pretreatment solvent used in the invention is an acidic eutectic solvent synthesized by choline chloride and lactic acid, and the eutectic solvent has the characteristics of low toxicity and biodegradability, can fully swell lignocellulose, can relax cellulose structure, increases reaction surface area, and is beneficial to exposing more sites for esterification reaction with succinic anhydride. And meanwhile, an acidic environment is provided to protonate the hydroxyl groups of cellulose, hemicellulose and lignin, so that the cellulose/hemicellulose composite material has more activity on the ring-opening reaction of an anionizing agent succinic anhydride, and is effectively grafted with carboxyl groups.

4. The process is green, simple, mild in reaction condition and low in energy consumption, and the prepared anionic lignocellulose nanofibrils are green, nontoxic, degradable and renewable, can be used as a reinforcing agent of a polyvinyl alcohol composite film, and can effectively improve the mechanical property, the hydrophobic property, the ultraviolet resistance, the thermal stability and the like of the composite film.

Drawings

FIG. 1 is a flow chart of the preparation of anionized lignocellulosic nanofibrils and lignin nanoparticles.

FIG. 2 is a physical view of the anionized lignocellulosic nanofibrils produced in example 2.

FIG. 3 is an electron field emission Scanning Electron Microscope (SEM) image of the anionized lignocellulosic nanofibrils produced in example 2.

Fig. 4 is an electric field emission scanning electron microscope image of lignin nanoparticles prepared in example 3.

Fig. 5 is an optical microscope image of bagasse as it is.

FIG. 6 is an optical microscopic view of the anionized lignocellulose produced in example 1.

FIG. 7 is a Fourier transform infrared spectrum of the bagasse as it is, the anionized lignocellulose produced in example 1 and the anionized lignocellulose nanofibrils produced in example 2.

FIG. 8 is a graph of TG and DTG curves for the as-received bagasse, the non-anionized lignocellulose produced in comparative example 1, the anionized lignocellulose produced in example 1, the anionized lignocellulose nanofibrils produced in example 2, and the lignin nanoparticles produced in example 3.

FIG. 9 is a physical view showing 6 kinds of polyvinyl alcohol composite films prepared from various addition amounts of anionized lignocellulose nanofibrils in application example 1.

FIG. 10 is a bar graph of the mechanical properties of a comparative polyvinyl alcohol film and 6 polyvinyl alcohol composite films prepared from different amounts of anionized lignocellulosic nanofibrils in application example 1.

FIG. 11 is a plot of UV-visible light transmittance for a comparative polyvinyl alcohol film versus 6 polyvinyl alcohol composite films prepared from different amounts of anionized lignocellulosic nanofibrils in application example 1.

Fig. 12 is a line graph of water contact angles of 5 different polyvinyl alcohol composite films prepared using different amounts of anionized lignocellulosic nanofibrils in example 1 as a comparison with a pure polyvinyl alcohol film.

Detailed Description

The present invention is further illustrated by the following examples, which are only intended to illustrate the present invention and not to limit the scope of the present invention.

Example 1

Preparation of anionized lignocellulose:

(1) Pre-treating the eutectic solvent: crushing bagasse by using a crusher, collecting 60-80 mesh bagasse by using 60-80 mesh screens, repeatedly using deionized water to soak and wash and ethanol to soak and wash until the washing liquid is clear, then completely drying in an oven at 60 ℃, adding 25g of the treated bagasse into 625g of eutectic solvent to pretreat, and uniformly mixing to obtain pretreated bagasse solution, wherein the eutectic solvent is synthesized by choline chloride and lactic acid according to a molar ratio of 1:15;

(2) Anion modification: adding 25g of succinic anhydride into the bagasse solution pretreated in the step (1) for anion modification, reacting for 6 hours under the mechanical stirring condition of the temperature of 120 ℃ and the rotating speed of 300rpm, adding 1000mL of ethanol and deionized water to terminate the reaction after the reaction is finished, separating the bagasse suspension after the reaction by vacuum filtration, collecting solid residues, adding ethanol to repeatedly wash until filtrate is colorless, adding deionized water, centrifuging for 20 minutes at the rotating speed of 4000rpm, washing until the washing liquid is neutral, and collecting solid sealing balance moisture to obtain the bagasse after anion modification, namely the anionic lignocellulose.

Comparative example 1

Preparation of non-anionized lignocellulose:

comparative example 1 differs from example 1 in that in comparative example 1, no anionic modification was performed, and the other conditions were the same as in example 1, to prepare non-anionized lignocellulose.

Example 2

Preparation of anionized lignocellulose nanofibrils:

the anionized lignocellulose obtained in example 1 was mechanically microfibrillated, in particular by the steps of: the anionic lignocellulose is dispersed in deionized water to prepare a suspension with the concentration of 2wt%, and the suspension is uniformly stirred and subjected to superfine grinding treatment with the grinding disc clearance of 100nm, 200nm and 250nm for 30 times, so that the anionic lignocellulose nanofibrils can be prepared, and the preparation flow chart is shown in figure 1.

FIG. 2 is a physical view of the anionized lignocellulose nanofibrils produced in example 2, and it can be seen from FIG. 2 that the anionized lignocellulose nanofibrils are in a brown yellow gel-like appearance.

FIG. 3 is an electric field emission scanning electron microscope image of the anionized lignocellulose nanofibrils prepared in example 2, and it can be seen from FIG. 3 that the anionized lignocellulose nanofibrils have a well layered wire mesh-like structure with a diameter distribution of 6 to 56nm.

Example 3

Preparation of lignin nanoparticles:

recovering the filtrate obtained in the vacuum filtration separation in the embodiment 1, adding excessive water into the filtrate to precipitate lignin, centrifuging for 20min at 4000rpm, washing until the washing solution is neutral, and collecting the precipitated lignin particles to obtain lignin nano particles, wherein the preparation flow chart is shown in figure 1.

Fig. 4 is an electric field emission scanning electron microscope image of lignin nanoparticles in example 3, and it can be seen from fig. 4 that the lignin nanoparticles are uniformly granular, and the particle size results show that the lignin nanoparticles have a size of around 289 nm.

Example 4

Preparation of anionized lignocellulose nanofibrils:

(1) Pre-treating the eutectic solvent: crushing bagasse by using a crusher, collecting 60-80 mesh bagasse by using 60-80 mesh screens, repeatedly using deionized water to soak and wash and ethanol to soak and wash until the washing liquid is clear, then completely drying in a 50 ℃ oven, adding 30g of the treated bagasse into 600g of eutectic solvent to pretreat, and uniformly mixing to obtain pretreated bagasse solution, wherein the eutectic solvent is synthesized by choline chloride and lactic acid according to a molar ratio of 1:10;

(2) Anion modification: adding 40g of succinic anhydride into the bagasse solution pretreated in the step (1) for anion modification, reacting for 10 hours under the mechanical stirring condition of the temperature of 110 ℃ and the rotating speed of 200rpm, adding 1200mL of ethanol and deionized water after the reaction is finished to terminate the reaction, separating the bagasse suspension after the reaction through vacuum filtration, collecting solid residues, adding the ethanol for repeated washing until filtrate is colorless, adding the deionized water, centrifuging for 10 minutes at the rotating speed of 5000rpm, washing until the washing liquid is neutral, and collecting solid sealing balance moisture to obtain the bagasse after anion modification;

(3) Mechanical microfibrillation: dispersing the bagasse subjected to anion modification in the step (2) in deionized water to prepare suspension with the concentration of 0.5wt%, uniformly stirring, and carrying out superfine particle grinding treatment with the grinding disc clearance of 50nm, 100nm and 200nm for 20 times, so as to obtain the anionic lignocellulose nanofibrils.

Example 5

Preparation of anionized lignocellulose nanofibrils:

(1) Pre-treating the eutectic solvent: crushing bagasse by using a crusher, collecting 60-80 mesh bagasse by using 60-80 mesh screens, repeatedly using deionized water to soak and wash and ethanol to soak and wash until the washing liquid is clear, then completely drying in a 70 ℃ oven, adding 35g of the treated bagasse into 900g of eutectic solvent to pretreat, and uniformly mixing to obtain pretreated bagasse solution, wherein the eutectic solvent is synthesized by choline chloride and lactic acid according to a molar ratio of 1:20;

(2) Anion modification: adding 50g of succinic anhydride into the bagasse solution pretreated in the step (1) for anion modification, reacting for 12 hours under the mechanical stirring condition of 130 ℃ and 400rpm of rotation speed, adding 2000mL of ethanol and deionized water after the reaction is finished to terminate the reaction, separating the bagasse suspension after the reaction through vacuum filtration, collecting solid residues, adding ethanol for repeated washing until filtrate is colorless, adding deionized water, centrifuging for 20 minutes at 6000rpm of rotation speed, washing until the washing liquid is neutral, and collecting solid sealing balance moisture to obtain the bagasse after anion modification;

(3) Mechanical microfibrillation: dispersing the bagasse subjected to anion modification in the step (2) in deionized water to prepare a suspension with the concentration of 1wt%, uniformly stirring, and carrying out superfine particle grinding treatment with the grinding disc clearance of about 30 times in total with the cycle times of 100nm, 200nm and 300nm, thereby obtaining the anionic lignocellulose nanofibrils.

Example 6

Preparation of anionized lignocellulose nanofibrils:

(1) Pre-treating the eutectic solvent: crushing bagasse by using a crusher, collecting 60-80 mesh bagasse by using 60-80 mesh screens, repeatedly using deionized water to soak and wash and ethanol to soak and wash until the washing liquid is clear, then completely drying in an oven at 60 ℃, adding 20g of the treated bagasse into 600g of eutectic solvent to pretreat, and uniformly mixing to obtain pretreated bagasse solution, wherein the eutectic solvent is synthesized by choline chloride and lactic acid according to a molar ratio of 1:10;

(2) Anion modification: adding 40g of succinic anhydride into the bagasse solution pretreated in the step (1) for anion modification, reacting for 4 hours under the mechanical stirring condition of 120 ℃ and 200rpm of rotation speed, adding 800mL of ethanol and deionized water after the reaction is finished to terminate the reaction, separating the bagasse suspension after the reaction through vacuum filtration, collecting solid residues, adding ethanol for repeated washing until filtrate is colorless, adding deionized water, centrifuging for 15 minutes at 5000rpm of rotation speed, washing until the washing liquid is neutral, and collecting solid sealing balance moisture to obtain the bagasse after anion modification;

(3) Mechanical microfibrillation: dispersing the bagasse subjected to anion modification in the step (2) in deionized water to prepare a suspension with the concentration of 2wt%, uniformly stirring, and carrying out superfine particle grinding treatment with the grinding disc clearance of 100nm, 200nm and 250nm for 20 times, so as to obtain the anionic lignocellulose nanofibrils.

Material property detection

The unreacted bagasse (bagasse as it is), the non-anionized lignocellulose of comparative example 1, and the anionized lignocellulose of example 1 were subjected to the detection of the carboxyl content, the relative crystallinity, and the detection results are shown in table 1 below.

TABLE 1 Performance index

From the data in table 1, it is evident that the anionic modification of the anionic lignocellulose of example 1, which is performed by using the eutectic solvent pretreatment in combination with succinic anhydride, has the highest carboxyl content, which is more than 3 times as much as that of bagasse, and is higher than that of the non-anionic lignocellulose of comparative example 1, and it is proved that the anionic modification can effectively increase the carboxyl content, negatively charged groups are introduced during the preparation, the number of charged groups grafted on the fibers is correspondingly increased, and gel-like is generated only by grinding for one hour during the mechanical grinding, which means that the charged groups introduced on the fibers by the modification can generate electrostatic repulsion between the fibers, effectively promote the dissociation of the fibers, and remarkably reduce the energy consumption of the mechanical grinding.

The increase in the relative crystallinity of the wood fiber pretreated with the eutectic solvent in comparative example 1 occurs with respect to the bagasse as it is, because hemicellulose and amorphous regions of cellulose of the bagasse are gradually hydrolyzed, so that the mechanical properties of the wood fiber are enhanced, the density is smaller, and the specific surface area is larger. Whereas the relative crystallinity of the wood fibers anionically modified with the addition of succinic anhydride in example 1 was reduced to a small extent relative to that of comparative example 1, since the electrostatic repulsion generated after grafting of the fibers with charged groups resulted in disruption and partial depolymerization of the crystalline regions of the cellulose, and the more charged groups grafted, the more significant the disruption and depolymerization.

Fig. 5 is an optical microscope image of the bagasse as it is, and fig. 6 is an optical microscope image of the anionized lignocellulose of example 1, and it can be observed from the two images that the bagasse in example 1 is subjected to the pretreatment of the eutectic solvent and combined with the anionic modification of succinic anhydride, the bagasse fiber size is significantly reduced, the tightly and completely hierarchical structure is dissociated while the fiber is swelled, the fiber surface is subjected to the fibrillation phenomenon, and the subsequent nanofibrillation process is promoted.

FIG. 7 is a Fourier transform infrared spectrum of bagasse as it is (A), anionized lignocellulose (B) obtained in example 1 and anionized lignocellulose nanofibrils (C) obtained in example 2, as can be seen from FIG. 7, A, B, C all samples are at 3350, 2900, 1160, 1110, 1034 and 897cm ^-1 There are absorption peaks, which are typical characteristic peaks of cellulose, indicating that the eutectic solvent pretreatment and mechanical grinding have no influence on the molecular structure of cellulose.It was found that the anionized lignocellulose of example 1 was 1250cm compared to the bagasse as it is ^-1 Ether linkage (C-O-C) at lignin aromatic group and 1508cm ^-1 The disappearance of the aromatic ring vibration of the lignin phenylpropyl skeleton indicates that the eutectic solvent pretreatment breaks down the recalcitrant structure of lignin. All samples of A, B, C were found to be 1732cm ^-1 There are peaks representing carbonyl (c=o) vibrational peaks of esters due to the presence of natural ester bonds in bagasse (acetyl groups of hemicellulose, ferulic acid of lignin/hemicellulose and ester bonds of carboxyl groups in p-coumaric acid).

Fig. 8 is a TG curve and a DTG curve of bagasse as it is (a), non-anionic lignocellulose (B) of comparative example 1, anionic lignocellulose (C) of example 1, anionic lignocellulose nanofibrils (D) of example 2 and lignin nanoparticle (E) of example 3. The initial degradation temperature of the sample is found to be between 230 and 330 ℃, the initial degradation temperature of the bagasse as is 305.5 ℃, and the maximum thermal degradation temperature is 354.5 ℃. The non-anionized lignocellulose of comparative example 1 is consistent with the trend of the initial pyrolysis temperature and the trend of the crystallinity of the two materials of anionized lignocellulose of example 1, which is attributed to the removal of hemicellulose and amorphous cellulose, the maximum heat drop temperature is slightly lowered, due to the removal of part of lignin with high thermal stability. The initial pyrolysis temperature and maximum heat drop temperature of the anionized lignocellulosic nanofibrils in example 2 are further reduced because mechanical microfibrillation can reduce the size of the fibers and disrupt the crystalline structure of the fibers, thereby resulting in reduced thermal stability. The maximum heat drop temperature of the lignin nanoparticles of example 3 was highest, and the percentage of residues was much greater than other samples, demonstrating good thermal stability of the lignin nanoparticles.

Application example 1

Preparation of a polyvinyl alcohol composite film:

the anionized lignocellulose nanofibrils prepared in the example 2 are weighed according to different masses, deionized water is added to prepare 200mL suspensions with different concentrations (0.05%, 0.15%, 0.25%, 0.35%, 0.45% and 0.55%) respectively, the suspensions are fully stirred to form uniform suspensions, 5wt% of polyvinyl alcohol is respectively added, the mixed solution is reacted for 2 hours at 90 ℃, after the reaction is finished, the obtained mixed solution is cooled, and then the mixed solution is placed in a vacuum drying oven at 60 ℃ to be dried to form a film by adopting a casting method, so that the polyvinyl alcohol composite film is prepared.

Fig. 9 is a polyvinyl alcohol composite film prepared in application example 1, and it can be seen from fig. 9 that 6 different polyvinyl alcohol composite films prepared in application example 1 are all transparent and uniform composite films.

Fig. 10 is a bar graph of tensile strength of 6 different polyvinyl alcohol composite films prepared by using the anionic lignocellulose nanofibrils of different addition amounts in example 1 in comparison with a pure polyvinyl alcohol film, and it can be seen from fig. 10 that the tensile strength of the composite film is obviously increased by adding only a small amount of anionic lignocellulose nanofibrils, and is proportional to the addition amount thereof, which indicates that the anionic lignocellulose nanofibrils can be used as a reinforcing agent of the composite film, wherein the lignocellulose nanofibrils provide better tensile properties due to the network structure thereof, and can effectively improve the mechanical strength of the composite film.

Fig. 11 is a graph of uv-vis transmittance of 6 different polyvinyl alcohol composite films prepared by using the anionic lignocellulose nanofibrils of different addition amounts in example 1, and it can be seen from fig. 11 that the transmittance of the composite film in the UVA, UVB, UVC uv region is significantly reduced towards zero, but the transmittance in the visible region is not significantly reduced, indicating good optical transmittance and excellent uv resistance, and that the small increase in transmittance in the UVC spectrum indicates uv resistance due to absorption, not due to large particles (reflection). The nano lignin reserved in the anionized lignocellulose nanofibrils contains a large amount of phenol, ketone and intramolecular hydrogen bonds, so that the nano lignin has strong ultraviolet resistance. Therefore, the ultraviolet light shielding material has great potential in the aspect of ultraviolet light protection.

Fig. 12 is a line graph of water contact angles of 5 different polyvinyl alcohol composite films prepared by using the anionic lignocellulose nanofibrils with different addition amounts in example 1, and it can be seen from fig. 12 that the water contact angle of the composite film is obviously increased by adding only a small amount of anionic lignocellulose nanofibrils, and is proportional to the addition amount thereof, which indicates that the lignin nanoparticles in which the lignocellulose nanofibrils remain due to the lignin nanofibrils can effectively improve the hydrophobic strength of the composite film.

Claims

1. The anionized lignocellulose nanofibrils are characterized in that a bagasse raw material is pretreated by using a eutectic solvent synthesized by choline chloride and lactic acid, succinic anhydride is added for anion modification, and the anionized lignocellulose nanofibrils are prepared through mechanical microfibrillation;

the preparation method of the anionized lignocellulose nanofibrils comprises the following steps:

(1) Pre-treating the eutectic solvent: crushing, washing and drying bagasse, then adding the treated bagasse into a eutectic solvent synthesized by choline chloride and lactic acid for pretreatment, and uniformly mixing to obtain a pretreated bagasse solution; the mass ratio of the bagasse to the eutectic solvent is 1:20-30; the mol ratio of the choline chloride to the lactic acid is 1:10-20;

2. The anionized lignocellulosic nanofibrils according to claim 1, wherein the anionized lignocellulosic nanofibrils have a diameter distribution of 6 to 56nm, a carboxyl content of 2.7 to 2.9mmol/g and a relative crystallinity of 71 to 72%.

3. A process for the preparation of an anionized lignocellulosic nanofibril according to claim 1 or 2, characterized in that it comprises the following steps:

4. A process for the preparation of anionized lignocellulosic nanofibrils according to claim 3, characterised in that in step (2) the mass ratio of bagasse to succinic anhydride is between 1:1 and 2.

5. The method for producing an anionized lignocellulose nanofibril according to claim 3, wherein in the step (2), the reaction is carried out under mechanical stirring at a temperature of 110 to 130 ℃ and a rotation speed of 200 to 400rpm of 4 to 12h.

6. The method for producing an anionized lignocellulose nanofibril according to claim 3, wherein in the step (2), the rotational speed of the centrifugation is 4000 to 6000rpm, and the time of the centrifugation is 10 to 20min.

7. The method of producing an anionized lignocellulose nanofibril according to claim 3, wherein in the step (3), the ultra-fine particle grinding is performed with a grinding disc gap of 50 to 300nm and a cycle number of 20 to 30.

8. A process for the preparation of anionized lignocellulosic nanofibrils according to claim 3, characterised in that in step (3) the concentration of the suspension is between 0.5 and 2% by weight.

9. Use of an anionized lignocellulosic nanofibril according to claim 1 or 2 as a reinforcing agent in a polyvinyl alcohol composite film.