Preparation method and application of high-toughness bamboo holocellulose nanofiber

Abstract

The application discloses a preparation method of high-strength and high-toughness bamboo holocellulose nanofiber and application thereof, and belongs to the technical field of cellulose treatment. The method adopts a choline chloride-xylose low eutectic solvent to treat bamboo holocellulose, solid-liquid separation is carried out after the treatment, the solid is dispersed, and bamboo holocellulose nanofiber is obtained through ultrasonic crushing. A bamboo nanoholocellulose film with high tensile strength and high toughness is prepared by taking the material as a substrate. The application not only effectively protects the hemicellulose content in the nanoholocellulose, but also realizes the strengthening of the mechanical performance of the nanoholocellulose film. The obtained bamboo nanoholocellulose has the advantages of uniform dispersion and the like. Meanwhile, the method itself has the advantages of simple process, mild reaction condition, environmental friendliness, easy operation and the like, realizes the utilization of the bamboo hemicellulose decomposition product, and has high application potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of cellulose processing, and in particular relates to a preparation method of high-strength and toughness bamboo holocellulose nanofiber and application thereof. Background Art

[0002] In recent years, with the rapid development of global industry, environmental pollution and the depletion of non-renewable resources have become increasingly severe. High-performance new green materials have attracted widespread attention from researchers both domestically and internationally. Lignocellulose, primarily composed of cellulose, hemicellulose, and lignin, offers advantages such as low cost, widespread availability, high biocompatibility, and environmental friendliness, making it a promising renewable resource for replacing non-renewable resources. Cellulose is the most abundant natural polymer on Earth and is widely used as a raw material for functional applications. Nanocellulose, derived from lignocellulose through chemical and mechanical pretreatment, is a type of elongated nanoscale (1-100 nm) fibers or crystals. It can be widely used in the preparation of new green materials and exhibits excellent mechanical, optical, and electrical properties. Retaining hemicellulose during the nanocellulose preparation process yields nanoholocellulose nanofibers (HCNFs). Nanoholocellulose retains some of the natural components of the plant, forming a unique "core-shell" structure. Compared to nanocellulose, nanoholocellulose containing hemicellulose often exhibits superior mechanical properties, optical transmittance, and thermal stability, offering significant performance advantages.

[0003] The main reported methods for preparing nanoholocellulose include the following: CN 202410172854.1 describes a ball-milling-assisted enzymatic method for preparing bamboo holocellulose of varying morphologies. This method involves ball-milling bamboo pulp, then adding deionized water, a buffer solution, an enzyme, and tetracycline for enzymatic hydrolysis. After enzymatic hydrolysis, the pulp is boiled, inactivated, washed, and dried to obtain bamboo fibers. The fibers are then ultrasonically dispersed to produce a suspension of bamboo holocellulose. By varying the ball-milling time and enzyme dosage, nanocellulose with aspect ratios ranging from 1.2 to 4.5 nm is produced, with concentrations consistently exceeding 160 mg / L. Yang et al. [Yang X, Berthold F, Berglund L A. Preserving cellulose structure: delignified wood fibers for paper structures of high strength and transparency [J]. Biomacromolecules, 2018, 19(7): 3020-3029.] used peracetic acid delignified spruce wood as raw material and mechanically nanosized it using a kitchen blender to produce small-diameter HCNFs. Because the wood was not subjected to additional chemical treatment, the hemicellulose on the individual fibers in the wood plant cell wall was largely retained. The resulting HCNFs had a diameter of less than 5 nm and a length of approximately 2.5 μm. Ding et al. [Ding Q, Rao J, Lv Z, et al. Efficient preparation of holocellulose nanofibers and their reinforcement potential[J]. Cellulose, 2022, 29(15): 8229-8242.] used a simple mechanical grinding method to prepare HCNFs from different types of lignocellulosic biomass such as wheat straw, bamboo, hardwood, and softwood. The resulting HCNFs retained a high hemicellulose content and a complete "core-shell" structure. Galland et al. [Galland S, Berthold F, Prakobna K, et al. Holocellulose nanofibers of high molar massand small diameter for high-strength nanopaper[J]. Biomacromolecules, 2015,16(8): 2427-2435.] microfluidized pretreatment of delignified poplar and spruce wood and successfully prepared HCNFs with a hemicellulose content of 24%.Hemicellulose plays a role in transferring stress between fibers, greatly improving the stretchability of HCNFs nanofilms.

[0004] It can be seen that the existing preparation methods of nano-holocellulose often have problems such as single preparation method, high processing energy consumption, long processing time and insufficient research on subsequent application methods, and cannot fully meet the needs of use in actual production. Summary of the Invention

[0005] The first object of the present invention is to provide a method for preparing high-strength and toughness bamboo holocellulose nanofibers, which has a simple process, mild reaction conditions, is environmentally friendly, and is easy to operate.

[0006] The second object of the present invention is to disclose a high-strength and toughness bamboo holocellulose nanofiber, which is evenly dispersed and can effectively protect the hemicellulose content in the nano-holocellulose.

[0007] The third object of the present invention is to disclose the use of high-strength and tough bamboo holocellulose nanofibers in the preparation of bamboo nano holocellulose films, and the obtained bamboo nano holocellulose films have good mechanical properties.

[0008] In order to solve the above problems, the technical solutions adopted by the present invention are as follows:

[0009] A method for preparing high-strength and toughness bamboo holocellulose nanofibers comprises first preparing a deep eutectic solvent using D-xylose and choline chloride, treating the bamboo holocellulose with the deep eutectic solvent, then performing solid-liquid separation, dispersing the solid, and obtaining the bamboo holocellulose nanofibers through ultrasonic treatment.

[0010] The hemicellulose content in the bamboo holocellulose nanofibers is not less than 19%; the cellulose content in the bamboo holocellulose nanofibers is not less than 68%.

[0011] Furthermore, the molar ratio of D-xylose to choline chloride is 1:2.

[0012] Furthermore, the solid-liquid mass ratio of the bamboo holocellulose to the low eutectic solvent is 1g:20g.

[0013] Furthermore, during the treatment of the bamboo holocellulose with the low eutectic solvent, the mixture was stirred and mixed evenly using a glass rod, and the mixture was heated in an oil bath at 100-130° C. for 120 min.

[0014] Furthermore, the oil bath heating temperature is 110°C.

[0015] Furthermore, the solid is dispersed by cooling the bamboo holocellulose residue after solid-liquid separation to room temperature, washing it with deionized water and freeze-drying it, and then re-dispersing the bamboo holocellulose residue in deionized water.

[0016] Furthermore, the ultrasonic treatment method is: the power of the cell disruptor used is 650W, the treatment time is 20 minutes, and the ultrasonic treatment is performed for 5 seconds with a pause of 5 seconds.

[0017] Furthermore, the preparation method of any of the above-mentioned high-strength and toughness bamboo holocellulose nanofibers comprises the following steps:

[0018] (1) D-xylose and choline chloride were uniformly mixed in a molar ratio of 1:2 and magnetically stirred at 85°C for 30 min until a uniform transparent liquid appeared;

[0019] (2) 3 g of bamboo holocellulose powder and 60 g of DES were mixed, and the mixture was heated in an oil bath at 100-130 °C for 120 min, cooled to room temperature, and thoroughly washed with deionized water. After washing, the powder residue was freeze-dried;

[0020] (3) The cell disruptor used had a power of 650W and a processing time of 20 min. The bamboo holocellulose nanofibers were broken by ultrasonicating for 5 s and pausing for 5 s, and then rapidly centrifuged to separate the HCNFs from the solid residue.

[0021] Furthermore, the high-strength and toughness bamboo holocellulose nanofibers are prepared by any of the above methods.

[0022] Furthermore, the high-strength and tough bamboo holocellulose nanofibers are used in the preparation of bamboo nano-holocellulose films, and the method is as follows: the prepared bamboo holocellulose nanofibers are configured into a nano-holocellulose suspension with a mass fraction of 1%, and the film is prepared by a vacuum filtration method.

[0023] This invention leverages the interaction between hemicellulose and cellulose in bamboo cell walls and their mechanical support structure, applying their enhanced mechanical strength to nanofiber production. Bamboo holocellulose is treated with a choline chloride-xylose deep eutectic solvent, followed by solid-liquid separation. The solids are then dispersed and, after simple ultrasonication, are obtained to produce bamboo holocellulose nanofibers. High-strength bamboo nano-holocellulose films are then prepared. This method achieves the conversion and utilization of bamboo nano-holocellulose, addressing the issues of high processing energy consumption and low hemicellulose content in nanofibers. It also promotes the full component utilization of bamboo bioconversion.

[0024] Compared with the prior art, the advantages of the present invention are as follows:

[0025] 1) The present invention can not only effectively prepare nano-holocellulose with high hemicellulose content, but also the obtained bamboo nano-holocellulose film has the advantages of high light transmittance, high tensile stress and high toughness.

[0026] 2) The present invention not only effectively protects the hemicellulose content in the nano-holocellulose, but also enhances the mechanical properties of the nano-holocellulose film. The obtained bamboo nano-holocellulose has the advantages of uniform dispersion.

[0027] 3) The present invention not only has many advantages such as simple process, mild reaction conditions, environmental friendliness, and easy operation, but also utilizes the decomposition product (xylose) of bamboo hemicellulose, which is beneficial to the full component utilization of bamboo lignocellulose raw materials in bioconversion. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The figure shows the atomic force microscope (AFM) image, Tyndall effect diagram, and height distribution diagram of nanoholocellulose after pretreatment with a deep eutectic solvent.

[0029] Figure 2 is the particle size distribution and zeta potential diagram of nanoholocellulose after pretreatment with deep eutectic solvent;

[0030] Figure 3 Schematic diagram of visible light transmittance of the nano-holocellulose film prepared in this application, tensile stress curve, toughness and Young's modulus comparison chart and cell activity comparison chart of the nano-cellulose film prepared by the traditional Tempo oxidation method;

[0031] Figure 4 This is a schematic diagram of the preparation of different molar ratios of choline chloride / D-xylose. From left to right, the molar ratios of choline chloride:xylose are 1:1, 1:2, 1:3, 2:1, and 3:1, respectively. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with specific embodiments.

[0033] The raw material bamboo holocellulose used in the following examples is a commercially available product. Its main components are: cellulose (approximately 56%), hemicellulose (approximately 25%), a small amount of lignin (approximately 6%), and other components (the remainder). This raw material bamboo holocellulose can also be produced by bleaching bamboo with sodium chlorite / acetic acid, etc.

[0034] The characterization methods of the HCNF products prepared in the following examples are as follows:

[0035] AFM observation: The nanoholocellulose suspension was diluted 0.5% and dropped onto a smooth mica sheet. After natural air drying, the nanofiber morphology was observed using an atomic force microscope to obtain the average length (nm), average width (nm) and aspect ratio.

[0036] Determination of crystallinity: The instrument used is an X-ray diffractometer, and crystallinity (%) = crystalline region peak area / (crystalline region peak area + amorphous region peak area)*100%.

[0037] Determination of glucan and xylan content: The U.S. Energy Laboratory's dedicated wood fiber component determination method was used to determine the content of components in the hydrolyzate after sulfuric acid hydrolysis using ion chromatography;

[0038] Glucose content (%) = glucose content in hydrolyzate (g) / mass of original enzymatic hydrolysis material (g) * 100%;

[0039] Xylan content (%) = xylose content in hydrolyzate (g) / mass of original enzymatic hydrolysis material (g) * 100%.

[0040] Example 1

[0041] A method for preparing high-strength and toughness bamboo holocellulose nanofibers, comprising the following steps:

[0042] (1) Preparation of deep eutectic solvent (DES): D-xylose (D-xyl) and choline chloride (ChCl) were uniformly mixed in a molar ratio of 1:2 and magnetically stirred at 85°C for 30 min until a uniform transparent liquid appeared;

[0043] (2) Pretreatment: Add 3 g of bamboo holocellulose powder and 60 g of DES to a glass conical flask, stir and mix thoroughly with a glass rod, and heat the mixture in an oil bath at 100°C for 120 min. After pretreatment, cool the mixture to room temperature and rinse thoroughly with deionized water. After rinsing, freeze-dry the powder residue.

[0044] (3) Preparation of HCNF: The powder residue after freeze-drying in step (2) was dispersed in water at a mass ratio of 1:20, and then ultrasonically disrupted to prepare bamboo holocellulose nanofibers; the power of the cell disruptor used for ultrasonication was 650W, the processing time was 20min, and the ultrasonication was paused for 5s after every 5s. After ultrasonic treatment, the sample was rapidly centrifuged to separate the supernatant and the solid residue. The supernatant finally obtained was the bamboo holocellulose nanofiber (HCNF) suspension, named CX-100.

[0045] Example 2

[0046] A method for preparing high-strength and toughness bamboo holocellulose nanofibers, comprising the following steps:

[0047] (1) Preparation of deep eutectic solvent (DES): D-xylose (D-xyl) and choline chloride (ChCl) were uniformly mixed in a molar ratio of 1:2 and magnetically stirred at 85°C for 30 min until a uniform transparent liquid appeared;

[0048] (2) Pretreatment: Add 3 g of bamboo holocellulose powder and 60 g of DES to a glass conical flask, stir and mix thoroughly with a glass rod, and heat the mixture in an oil bath at 110°C for 120 min. After pretreatment, cool the mixture to room temperature and rinse thoroughly with deionized water. After washing, freeze-dry the powder residue.

[0049] (3) Preparation of HCNF: The powder residue after freeze-drying in step (2) was dispersed in water at a mass ratio of 1:20, and then ultrasonically disrupted to prepare bamboo holocellulose nanofibers; the power of the cell disruptor used for ultrasonication was 650W, the processing time was 20min, and the ultrasonication was paused for 5s after every 5s. After ultrasonic treatment, the sample was rapidly centrifuged to separate the supernatant and the solid residue. The supernatant finally obtained was the bamboo holocellulose nanofiber (HCNF) suspension, named CX-110.

[0050] Example 3

[0051] A method for preparing high-strength and toughness bamboo holocellulose nanofibers, comprising the following steps:

[0052] (1) Preparation of deep eutectic solvent (DES): D-xylose (D-xyl) and choline chloride (ChCl) were uniformly mixed in a molar ratio of 1:2 and magnetically stirred at 85°C for 30 min until a uniform transparent liquid appeared;

[0053] (2) Pretreatment: Add 3 g of bamboo holocellulose powder and 60 g of DES to a glass conical flask, stir and mix thoroughly with a glass rod, and heat the mixture in an oil bath at 120°C for 120 min. After pretreatment, cool the mixture to room temperature and rinse thoroughly with deionized water. After washing, freeze-dry the powder residue.

[0054] (3) Preparation of HCNF: The powder residue after freeze-drying in step (2) was dispersed in water at a mass ratio of 1:20, and then ultrasonically disrupted to prepare bamboo holocellulose nanofibers; the power of the cell disruptor used for ultrasonication was 650W, the processing time was 20min, and the ultrasonication was paused for 5s after every 5s. After ultrasonic treatment, the sample was rapidly centrifuged to separate the supernatant and the solid residue. The supernatant finally obtained was the bamboo holocellulose nanofiber (HCNF) suspension, named CX-120.

[0055] Example 4

[0056] A method for preparing high-strength and toughness bamboo holocellulose nanofibers, comprising the following steps:

[0057] (1) Preparation of deep eutectic solvent (DES): D-xylose (D-xyl) and choline chloride (ChCl) were uniformly mixed in a molar ratio of 1:2 and magnetically stirred at 85°C for 30 min until a uniform transparent liquid appeared;

[0058] (2) Pretreatment: Add 3 g of bamboo holocellulose powder and 60 g of DES to a glass conical flask, stir and mix thoroughly with a glass rod, and heat the mixture in an oil bath at 130°C for 120 min. After pretreatment, cool the mixture to room temperature and rinse thoroughly with deionized water. After washing, freeze-dry the powder residue.

[0059] (3) Preparation of HCNF: The powder residue after freeze-drying in step (2) was dispersed in water at a mass ratio of 1:20, and then ultrasonically disrupted to prepare bamboo holocellulose nanofibers; the power of the cell disruptor used for ultrasonication was 650W, the processing time was 20min, and the ultrasonication was paused for 5s after every 5s. After ultrasonic treatment, the sample was rapidly centrifuged to separate the supernatant and the solid residue. The supernatant finally obtained was the bamboo holocellulose nanofiber (HCNF) suspension, named CX-130.

[0060] Example 5

[0061] 1. Chemical composition analysis of CX-100, CX-110, CX-120, and CX-130 prepared in Examples 1-4 was performed, and the results are shown in Table 1 below. After treatment with a deep eutectic solvent (DES), the cellulose content in the lignocellulosic feedstock significantly increased from an initial approximately 55% to 68%-69%, while the hemicellulose retention rate reached approximately 20%. The data from the examples demonstrate that the DES system exhibits significant selective retention of hemicellulose components, effectively avoiding the problem of excessive hemicellulose degradation in traditional pretreatment processes. Because hemicellulose acts as an interface reinforcement between cellulose microfibrils, its moderate retention improves the mechanical strength of the subsequently prepared nanoholocellulose.

[0062] Table 1 Comparison of component analysis data of nano-holocellulose prepared in Examples 1 to 4

[0063]

[0064] 2. AFM observation and crystallinity determination were performed on CX-100, CX-110, CX-120 and CX-130 prepared in Examples 1 to 4. Figure 1 、 Figure 2 shown.

[0065] Figure 1 are the atomic force microscopy (AFM) images, the Tyndall effect schematic diagram, and the height distribution diagram of the nanocellulose pretreated by deep eutectic solvent; Figure 2 are the particle size distribution and zeta potential diagram of the nanocellulose pretreated by deep eutectic solvent. From Table 1, Figure 1 and Figure 2 It can be seen that the nanocellulose has a typical nanofiber morphology, is uniformly dispersed, and contains a large amount of hemicellulose. Among them, the sample pretreated at 110°C (CX-110) has the smallest average height (about 2 nm) and the largest average particle size distribution (about 313 nm), which indicates that the fiber diameter of CX-110 is the smallest, and the fiber length is the largest.

[0066] 3. Preparation of high-strength and high-toughness bamboo nanocellulose film: The HCNF suspension prepared in Examples 1-4 was configured into a nanocellulose suspension with a mass fraction of 1%, and a traditional mass fraction of 1% Tempo-oxidized cellulose nanofiber was used as a control. A film was prepared by vacuum filtration, and the tensile strength was tested by a universal testing machine. The results are shown in Figure 3 .

[0067] Figure 3 are the visible light transmittance schematic diagram of the nanocellulose film prepared in the present application, the tensile stress curve, the toughness and Young's modulus comparison diagram, and the cell activity comparison diagram of the traditional Tempo-oxidized nanocellulose film. It can be seen that the prepared nanocellulose film has more significant flexibility and tensile strength compared with the Tempo-oxidized nanocellulose film, and has high application potential. Among them, the maximum tensile stress of the prepared nanocellulose film reaches 112.34 MPa, and the maximum toughness is 44.13 MJ / m 3 .

[0068] The results of the examples of the present application show that the elongated fibers can play a role in transmitting the stress inside the film, and the higher the mechanical strength of the prepared nanofiber film. The pretreatment at a too high temperature may lead to the degradation of the fibers, thereby leading to the decrease of the mechanical strength of the film.

[0069] Example 6

[0070] For the preparation of DES step in Example 1, in order to verify the feasibility of different ratios of choline chloride / D-xylose based DES, different molar ratios of choline chloride / D-xylose were used for preparation, and the selected molar ratios were choline chloride: xylose = 1:1, 1:2, 1:3, 2:1, 3:1. Among them, 2:1 is the final selected ratio of the present application. The choline chloride / xylose mixture under all ratios was magnetically stirred at 85°C water bath heating for 30 min. The results are shown in Figure 4As shown in the figure, only the mixture with a choline chloride / xylose molar ratio of 2:1 selected in this application exhibited a clear and transparent liquid state, successfully preparing DES. The mixtures with other molar ratios all exhibited a white turbid solid-liquid mixture or an unmelted solid, failing to form DES.

[0071] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing high-strength and tough bamboo holocellulose nanofibers, characterized in that: First, a low eutectic solvent is prepared using D-xylose and choline chloride, and bamboo holocellulose is treated with the low eutectic solvent. Subsequently, solid-liquid separation is performed, the solid is dispersed, and bamboo holocellulose nanofibers are obtained by ultrasonic treatment. The molar ratio of D-xylose to choline chloride is 1:2; the solid-liquid mass ratio of bamboo holocellulose to the low eutectic solvent is 1g:20g; during the treatment of the bamboo holocellulose with the low eutectic solvent, the mixture is stirred and mixed uniformly using a glass rod, and the mixture is heated in an oil bath at 100-130°C for 120 minutes. The ultrasonic treatment method is as follows: the power of the cell disruptor used is 650W, the treatment time is 20 minutes, and the ultrasonic treatment is paused for 5 seconds every 5 seconds.

2. The method for preparing high-strength and toughness bamboo holocellulose nanofiber according to claim 1, characterized in that: The oil bath was heated at a temperature of 110°C.

3. The method for preparing high-strength and toughness bamboo holocellulose nanofiber according to claim 1, characterized in that: The method for dispersing the solid is as follows: cooling the bamboo holocellulose residue after solid-liquid separation to room temperature, washing with deionized water and freeze-drying, and then re-dispersing the bamboo holocellulose residue in deionized water.

4. The method for preparing high-strength and toughness bamboo holocellulose nanofiber according to any one of claims 1 to 3, characterized in that: Here are the steps: (1) D-xylose and choline chloride were uniformly mixed in a molar ratio of 1:2 and magnetically stirred at 85°C for 30 min until a uniform transparent liquid appeared; (2) 3 g of bamboo holocellulose powder and 60 g of DES were mixed, and the mixture was heated in an oil bath at 100-130 °C for 120 min, cooled to room temperature, and thoroughly washed with deionized water. After washing, the powder residue was freeze-dried; (3) The cell disruptor used had a power of 650W and a processing time of 20 min. The bamboo holocellulose nanofibers were broken by ultrasonicating for 5 s and pausing for 5 s, and then rapidly centrifuged to separate the HCNFs from the solid residue.

5. The high-strength and toughness bamboo holocellulose nanofiber prepared according to the method of any one of claims 1 to 4.

6. The use of the high-strength and tough bamboo holocellulose nanofibers according to claim 5 in preparing bamboo nano-holocellulose films, characterized in that: The prepared bamboo holocellulose nanofibers were configured into a nano-holocellulose suspension with a mass fraction of 1%, and a film was prepared by vacuum filtration.

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