CN113622051B - A preparation method of bamboo heddled cellulose nanofibers with high aspect ratio and high hemicellulose content - Google Patents

Abstract

The invention discloses a preparation method of bamboo heddled cellulose nanofibers with high aspect ratio and high hemicellulose content. Acetic acid is used to assist a deep eutectic solvent, and the bamboo heddled cellulose is treated under microwave radiation conditions. After the end, the solid-liquid separation is carried out, and the solid is dispersed, and after homogenization, the bamboo cellulose nanofibers are prepared by a micro-fluidizer; wherein, the aspect ratio of the bamboo cellulose nanofibers is not less than 300, and the hemicellulose content is not low at 14%. This method can not only effectively improve the aspect ratio of nano-hemicellulose (HCNF), but also the obtained HCNF hemicellulose content and the degree of acetylation of cellulose are high, and the obtained bamboo nano-hemicellulose has adjustable scale and uniform dispersion. Etc. At the same time, the method itself also has many advantages such as simple process, mild reaction conditions, environmental friendliness, easy operation, etc., and has high application potential.

Description

Preparation of bamboo heddled cellulose nanofibers with high aspect ratio and high hemicellulose content method

technical field

The invention relates to the technical field of cellulose treatment, in particular to a preparation method of bamboo heddle cellulose nanofibers with high aspect ratio and high hemicellulose content.

Background technique

In recent years, due to the increasingly severe environmental pollution and resource shortage, the exploration and research on nanostructured materials are gradually attracting people's attention, and renewable and sustainable materials from biomass have become a research hotspot. Environmentally friendly lignocellulosic resources not only have good renewability, but also have high potential for chemical or physical modification. Cellulose is the most abundant natural polymer on earth and is widely used as a raw material for functional applications. As the major component of lignocellulosic biomass, cellulose consists of D-glucopyranose linked by β(1-4) glycosidic linkages. Due to its unique two-phase and aggregated structure, nanocellulose with unique properties can usually be formed through multiple methods. Nanocellulose includes cellulose nanocrystals (CNC) and cellulose nanofibers (CNF). Among them, CNF contains crystalline and amorphous regions of cellulose supramolecular chains, usually with a diameter of 3-100 nm and a length of >500 nm. CNF has strong mechanical properties and can be prepared by mechanical, chemical and biological methods. The final strength is 2-6GPa, and the crystal modulus can reach 138GPa.

The main reported methods for preparing nanocellulose are as follows:

CN110128555A discloses a method of obtaining cellulose nanocrystals by using pretreated biomass as raw material, using organic solvents, ionic liquids and cellulose solvents, but the processing time is longer and more organic solvents are used, and the final fiber The highest yield of prime nanocrystals was 71%.

Sonakshi Maitia et al [Maiti S, Jayaramudu J, Das K, et al. Preparation and characterization of nano-cellulose with new shape from different precursor [J]. Carbohydrate Polymers, 2013, 98 (1): 562-567.] used Chinese Cotton, African cotton, and waste napkins are used as raw materials to prepare nanocellulose with particle sizes of 30-60nm, 10-90nm, and 2-10nm respectively by acid (47% sulfuric acid) hydrolysis and stirring. The method uses more strong acids and is more violent.

A，et al.A study of theproduction of cellulose nanocrystals through subcritical water hydrolysis[J].Industrial Crops and Products，2016，93：88-95.]利用亚临界水的高电离效率、高活性和高扩散作用水解纤维素，将纯水加热并加压到亚临界状态处理MCC，制备出了直径约55nm、长度约242nm的CNC，其结晶度为79％、得率为21.9％。The Novo team from the University of Sao Paulo in Brazil [Novo LP, Bras J,

A, et al. A study of the production of cellulose nanocrystals through subcritical water hydrolysis [J]. Industrial Crops and Products, 2016, 93: 88-95.] Utilizing the high ionization efficiency, high activity and high diffusion of subcritical water for hydrolysis For cellulose, pure water was heated and pressurized to a subcritical state to process MCC, and a CNC with a diameter of about 55nm and a length of about 242nm was prepared, with a crystallinity of 79% and a yield of 21.9%.

Rostami et al. [Rostami J, Mathew AP, Edlund U. Zwitterionic Acetylated Cellulose Nanofibrils [J]. Molecules, 2019, 24(17): 3147.] employed acetylation, oxidation, Schiff base reaction, hydroboration reduction, and quaternary ammonium salts Zwitterionic acetylated CNF was prepared by a series of reactions. Among them, the acetylation is carried out in glacial acetic acid, and the reaction time is short, only 90 minutes, to produce monoacetylated CNF with hydroxyl groups, which can be used for further post-modification. It can be seen that acetylation provides a good basis for the multifunctional modification of CNF.

It can be seen that the existing nanocellulose preparation methods have problems such as low chemical composition diversity of the obtained nanofiber materials, high energy consumption, long processing time, and low content of nanofiber hemicellulose, which cannot fully meet the needs of use.

Contents of the invention

In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a kind of preparation method of bamboo heddled cellulose nanofibers with high aspect ratio and high hemicellulose content, which can not only effectively improve the long diameter of HCNF ratio, and the obtained HCNF hemicellulose content and acetylation degree of cellulose are higher, and the obtained bamboo nano-hemicellulose has the advantages of adjustable scale and uniform dispersion.

A preparation method of bamboo heddled cellulose nanofibers with high aspect ratio and high hemicellulose content: acetic acid is used to assist the deep eutectic solvent, and under the condition of microwave radiation, the bamboo heddled cellulose is treated, and after the treatment, the solid-liquid Separating, dispersing and homogenizing the solids to obtain bamboo heddled cellulose nanofibers through a micro-fluidizer; wherein, the aspect ratio of the bamboo heddled cellulose nanofibers is not less than 300, and the hemicellulose content is not higher than 20%.

The hydrogen bond donor of the deep eutectic solvent is zinc acetate, the hydrogen bond acceptor is choline chloride, and the molar ratio of the hydrogen bond donor to the hydrogen bond acceptor is 1:2.

The solid-to-liquid mass volume ratio of the bamboo cellulose to the deep eutectic solvent is 1g:50mL.

The molar ratio of the acetic acid to the deep eutectic solvent is 1:1-3.

The microwave radiation power is 600W, the treatment temperature is 120-140° C., and the treatment time is 10 minutes.

The dispersing of the solid is as follows: cooling the bamboo heddled cellulose residue after solid-liquid separation to room temperature, thoroughly washing with deionized water and freeze-drying, and then redispersing the bamboo heddled cellulose residue in deionized water.

In the preparation method of bamboo heddled cellulose nanofibers with high aspect ratio and high hemicellulose content, the homogenizer power used for homogenization is 650W, and the homogenization treatment time is 15 minutes. After the samples were homogenized, they were centrifuged quickly and the supernatant was passed through a microfluidizer.

The preparation method of the bamboo heddled cellulose nanofibers with high aspect ratio and high hemicellulose content, fast centrifugation after the sample is homogenized, and the supernatant is passed through a micro-fluidizer; the operating pressure of the micro-fluidizer used is 600bar, the operation is carried out more than 3 times.

The preparation method of the bamboo heddled cellulose nanofiber of described high aspect ratio high hemicellulose content, concrete steps are as follows:

(1) preparing a deep eutectic solvent; wherein, the hydrogen bond donor is zinc acetate, the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor and the hydrogen bond acceptor are in a molar ratio of 1:2;

(2) Get bamboo cellulose powder and deep eutectic solvent to microwave reactor, the solid-liquid ratio of bamboo cellulose powder and DES is 1g: 50mL, and add acetic acid, the mol ratio of acetic acid and deep eutectic solvent is 1 : 1～3; after mixing evenly, carry out the treatment at 120～140°C for 10 minutes under the microwave irradiation power of 600W;

(3) Cool to room temperature after treatment, separate the solid from the liquid, thoroughly wash the solid with deionized water, and freeze-dry the powder residue after washing; and disperse in deionized water;

(4) Carry out mechanical homogenization and prepare bamboo helical cellulose nanofiber by micro-jet machine; Wherein, the homogenizer power that homogenization adopts is 650W, and homogenization processing time is 15min; The micro-jet machine operating pressure used It is 600bar, and the operation is carried out more than 3 times.

Inspired by the relationship between cellulose and hemicellulose matrix in higher plants, this application applies the improvement of plant mechanical strength by the interaction of polysaccharides to the field of nanofiber preparation. Rapid production of hemicellulose-enriched bamboo hemicellulose nanofibers (HCNFs) by dilute acetic acid-assisted zinc acetate (ZnAc)/choline chloride (ChCl) deep eutectic solvent (DES) treatment under microwave irradiation . To a certain extent, the chemical composition diversity of nanofiber materials is controllable, and the problems of high energy consumption, long processing time and low content of nanofiber hemicellulose are solved.

Beneficial effect: compared with the prior art, the present invention has the advantages of:

1) This method can not only effectively increase the aspect ratio of HCNF, but also obtain HCNF with high hemicellulose content and acetylation degree of cellulose, and the obtained bamboo nano-hemicellulose has the advantages of adjustable scale and uniform dispersion.

2) This method not only has many advantages such as simple process, mild reaction conditions, environmental friendliness, and easy operation, but also has the characteristics of short time and high efficiency, and is practical for preparing bamboo heddle cellulose nanofibers from pretreated bamboo raw materials.

Description of drawings

Fig. 1 is the transmission electron microscope (TEM) figure of the nano-helical cellulose after deep eutectic solvent pretreatment;

Fig. 2 is the particle size distribution figure of the nano-helical cellulose after deep eutectic solvent pretreatment;

Fig. 3 is a comparison chart of the mechanical strength of the nano-sized cellulose film prepared by the present application and the mechanical strength of the nano-cellulose film prepared by the traditional Tempo oxidation method.

Detailed ways

In order to make the present invention easier to understand, the following will be described in detail in conjunction with specific embodiments of the present invention, but this is only for illustration rather than limitation of the present invention.

The raw material bamboo cellulose used in the following examples can be directly commercially available or self-made. A typical method is: bleaching bamboo with sodium chlorite/acetic acid to prepare bamboo cellulose. The main components of bamboo cellulose are: cellulose (53.4%), hemicellulose (22.8%) and a small amount of lignin (9.6%).

Example 1

The preparation method of the bamboo heddled cellulose nanofiber with high aspect ratio and high hemicellulose content, the steps are as follows:

(1) Preparation of deep eutectic solvent (DES): zinc acetate (ZA) was used as hydrogen bond donor, choline chloride (ChCl) was used as hydrogen bond acceptor, and the molar ratio of donor and acceptor was 1:2. , the mixture was heated at 80 °C with magnetic stirring for 4 h until a homogeneous clear liquid appeared.

(2) Pretreatment: Add 0.5 g bamboo cellulose powder and 25 mL zinc acetate/choline chloride (ZAC) to the Teflon container of the microwave reactor. The solid-liquid ratio of bamboo cellulose powder and DES is 1:50 (g/mL), and acetic acid is added, and the molar ratio of acetic acid and DES is 1:1 (ZAC1-1) or 1:2 (ZAC2-1) , or 1:3 (ZAC3-1). Use a glass rod to stir to mix well. The mixture was treated at 120° C. for 10 minutes under a microwave irradiation power of 600 W. After pretreatment, the mixture was cooled to room temperature, washed thoroughly with deionized water, and the powder residue was freeze-dried after washing.

(3) Preparation of HCNF: The pretreated bamboo heddled cellulose was redispersed in deionized water at a concentration of 5% (w/v), and the sample was homogenized for 15 minutes with a homogenizer. Then, it was centrifuged rapidly, and the supernatant was passed through a microfluidizer, and the operating pressure was 600 bar, and the operation was carried out 5 times to obtain HCNF.

Example 2

The preparation method of the bamboo heddled cellulose nanofiber with high aspect ratio and high hemicellulose content, the steps are as follows:

(1) Preparation of deep eutectic solvent (DES): zinc acetate (ZA) was used as hydrogen bond donor, choline chloride (ChCl) was used as hydrogen bond acceptor, and the molar ratio of donor and acceptor was 1:2. , the mixture was heated at 80 °C with magnetic stirring for 4 h until a homogeneous clear liquid appeared.

(2) Pretreatment: Add 0.5 g bamboo cellulose powder and 25 mL zinc acetate/choline chloride (ZAC) to the Teflon container of the microwave reactor. The solid-liquid ratio of bamboo cellulose powder and DES is 1:50 (g/mL), and acetic acid is added, and the molar ratio of acetic acid and DES is 1:1 (ZAC1-2), or 1:2 (ZAC2-2) , or 1:3 (ZAC3-2). Use a glass rod to stir to mix well. The mixture was treated at 140° C. for 10 minutes under a microwave irradiation power of 600 W. After pretreatment, the mixture was cooled to room temperature, washed thoroughly with deionized water, and the powder residue was freeze-dried after washing.

(3) Preparation of HCNF: The pretreated bamboo heddled cellulose was redispersed in deionized water at a concentration of 5% (w/v), and the sample was homogenized for 15 minutes with a homogenizer. Then it was centrifuged quickly, and the supernatant was passed through a microfluidizer, and the operating pressure was 600 bar, and the operation was carried out 5 times to obtain HCNF.

Example 3

Six HCNF products named ZAC1-1, ZAC2-1, (ZAC3-1, ZAC1-2, ZAC2-2, ZAC3-2) prepared in Examples 1 and 2 were characterized, and the results are shown in Table 1. The specific method is as follows:

1) The formula for calculating the recovery rate is: recovery rate=HCNF mass (g)/bamboo cellulose powder mass (g)*100%.

2) AFM observation: Dilute the suspension of nanofiber cellulose by 0.5%, and drop it on a smooth mica sheet. After natural air-drying, use an atomic force microscope to observe the morphology of nanofibers, and obtain the average length (nm), average width (nm) and length Diameter ratio.

3) Determination of crystallinity: the instrument used is X-ray diffractometer, crystallinity (%)=peak area of crystalline region/(peak area of crystalline region+peak area of amorphous region)*100%.

4) Determination of dextran and xylan content: adopt the special lignocellulosic component determination method of American Energy Laboratory, after sulfuric acid hydrolysis, utilize ion chromatography to determine the component content in the hydrolyzate; Wherein,

Glucose content (%)=glucose content (g) in hydrolyzate/mass of original enzymolysis material (g)*100%;

Xylan content (%)=xylose content in the hydrolyzate (g)/original enzymolysis material mass (g)*100%;

5) Determination of acetylation: X-ray photoelectron spectrometer is used to measure the lyophilized sample by peak fitting, acetylation degree=288.5eV peak area/(284.7eV peak area+286eV peak area).

Table 1 The recovery rate and component analysis data of nano-helical cellulose

Fig. 1 is the transmission electron microscope (TEM) figure of the nano-helical cellulose after deep eutectic solvent pretreatment;

Fig. 2 is the particle size distribution diagram of the nano-helical cellulose after the deep eutectic solvent pretreatment; From the results of Fig. 1, Fig. 2 and Table 1, it can be seen that the nano-heald cellulose has a typical fiber morphology, is uniformly dispersed, and has a long diameter. Relatively high and the scale can be adjusted; the scale distribution of nano-hemicellulose prepared in each embodiment is reasonable, and the obtained HCNF hemicellulose content and acetylation degree of cellulose are high.

Example 4

Film preparation: the HCNF prepared in Examples 1 and 2 were configured into a nano-helical cellulose suspension with a mass fraction of 1%, and the traditional Tempo oxidized cellulose nanofiber with a mass fraction of 1% was used as a control to prepare by vacuum filtration The film was taken out, and the tensile strength test was carried out by a universal tensile machine.

The results are shown in Figure 3. It can be seen that the prepared nano-helical cellulose film has more significant flexibility and tensile strength than the Tempo oxidized nano-cellulose film, and has higher application potential.

It should be noted that the embodiments of the present invention are not limited by the above examples, and any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent Substitution methods are all included within the protection scope of the present invention.

Claims (1)

1. a preparation method of bamboo heddled cellulose nanofibers with high aspect ratio and high hemicellulose content, characterized in that: use acetic acid to assist the deep eutectic solvent, and under microwave radiation conditions, bamboo heddled cellulose is processed After the treatment, the solid-liquid separation is carried out, the solid is dispersed, and after homogenization, the bamboo heddled cellulose nanofiber is prepared by a microfluidic machine; wherein, the aspect ratio of the bamboo heddled cellulose nanofiber is not less than 300, and the hemicellulose content Not less than 14%; the specific steps are as follows: (1) preparing a deep eutectic solvent; wherein, the hydrogen bond donor is zinc acetate, the hydrogen bond acceptor is choline chloride, and the hydrogen bond donor and the hydrogen bond acceptor are in a molar ratio of 1:2; (2) Get bamboo cellulose powder and deep eutectic solvent to microwave reactor, the solid-liquid ratio of bamboo cellulose powder and DES is 1g: 50mL, and add acetic acid, the mol ratio of acetic acid and deep eutectic solvent is 1 : 1～3; after mixing evenly, carry out the treatment at 120～140°C for 10 minutes under the microwave irradiation power of 600W; (3) Cool to room temperature after treatment, separate the solid from the liquid, thoroughly wash the solid with deionized water, and freeze-dry the powder residue after washing; and disperse in deionized water; (4) Carry out mechanical homogenization and prepare bamboo helical cellulose nanofiber by micro-jet machine; Wherein, the homogenizer power that homogenization adopts is 650W, and homogenization processing time is 15min; The micro-jet machine operating pressure used It is 600bar, and the operation is carried out more than 3 times.

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