A nano corn stalk cellulose dispersion liquid, a preparation method and products of a film thereof

Abstract

The application discloses a preparation method of a nano corn straw cellulose dispersion liquid and a film, and has the advantages that the preparation method is beneficial to the solvation of Cl+(DMAC / Li) ions on cellulose molecules, and further forms a six-membered intermediate complex, so that cellulose molecular chains are separated and dissolved; the method is a "green" pretreatment method, and effectively avoids pollution to the environment; the method is simple and rapid, raw materials are easy to obtain, the cost is low, and the method is suitable for large-scale production. The application further discloses a nano corn straw cellulose film, and the film has good dispersing property, degradation, separation characteristics and tensile property, and has important application prospects in the fields of environmental pollution treatment and the like; and is expected to be applied to organic pollution environments such as water bodies, soil and atmosphere, and has wide application prospects in agricultural fully-degradable materials, and provides more choices for high-value utilization of similar agricultural wastes and the like.

Description

Technical Field

[0001] This invention relates to a method for preparing nanofibers and the products thereof, and more particularly to a nano-corn stalk cellulose film dispersion and the method for preparing the film and the products thereof, belonging to the field of new agricultural materials and applications. Background Technology

[0002] Straw cellulose is one of the most abundant and inexpensive renewable resources on Earth. my country is a major agricultural country with abundant straw resources, producing 700 million tons of crop straw annually. However, the utilization rate of straw is low, with over 30% being discarded or burned, resulting not only in resource waste but also serious pollution. In recent years, with the depletion of non-renewable fossil fuel resources such as coal and oil, and the increasing severity of environmental problems, the efficient utilization of straw resources has attracted growing attention. Cellulose is widely used in textiles, light industry, chemicals, defense, petroleum, pharmaceuticals, environmental protection, and energy sectors. Due to the presence of intramolecular and intermolecular hydrogen bonds in natural cellulose molecules and its complex structure with coexisting crystalline and amorphous regions, it is difficult to dissolve in common solvents. The DMAC / LiCl dispersion system is considered a good solvent for cellulose, offering advantages such as stable solubility and easy solvent recovery. However, due to the crystalline structure of cellulose, a large number of highly reactive hydroxyl groups are trapped within the crystalline regions, making them difficult for solvents to access. Therefore, certain pretreatment is necessary before dissolution. Corn stalk cellulose has become a novel nanodegradable material with broad application prospects due to its fully degradable properties.

[0003] With the increasing severity of environmental pollution, it is of great significance to develop environmentally friendly pretreatment methods that avoid the use of corrosive chemical reagents such as acids and alkalis. Ball milling pretreatment, as a physical treatment method, is environmentally friendly, can destroy the crystalline structure of cellulose, and is a "green" pretreatment method. It does not require any corrosive chemical reagents, can be performed at room temperature and pressure, and does not produce any toxic or harmful substances after treatment. However, it is an energy-intensive method, and many studies have focused on combining ball milling pretreatment with other pretreatment methods to improve efficiency and reduce energy consumption. However, research on low-cost and simple preparation methods for nano-corn stalk cellulose dispersions and films is rarely reported. The existing methods for dissolving corn stalk cellulose (Chinese patents CN108636989A and CN201710947155.X) generally suffer from serious environmental pollution, high costs, difficulty in molding, and poor degradation ability.

[0004] While existing technologies include methods for ball milling corn stalk powder (patent number: CN103320483B), the resulting nano-corn stalk cellulose powder has a particle size in the micrometer range. Excessively large particle sizes are detrimental to the formation of dispersions and films. Furthermore, this method involves adding enzymes to the corn stalk powder, causing it to be enzymatically hydrolyzed into small-molecule sugars, which further hinders the formation of nano-corn stalk cellulose and film materials. Therefore, there is a need for an effective method that is more conducive to the formation of nano-corn stalk cellulose dispersions and films. Summary of the Invention

[0005] Purpose of the invention: The technical problem to be solved by the present invention is to provide a green and environmentally friendly method for preparing nano-corn stalk cellulose dispersion and its film, which is simple and rapid, uses readily available raw materials, is low in cost, and is suitable for large-scale production. The nano-corn stalk cellulose film material prepared by this method has good dispersibility, degradation and separation characteristics.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a nano-corn stalk cellulose dispersion, comprising the following steps:

[0008] 1) The corn stalk powder was ball-milled to obtain nano-corn stalk cellulose powder. The ball milling rate was 100-300 rpm / min and the ball milling time was 2-8 h. The particle size of the nano-corn stalk cellulose powder was less than 1000 nm.

[0009] 2) Add nano-corn stalk cellulose powder to N,N-dimethylacetamide / lithium chloride solution, condense and reflux to obtain nano-corn stalk cellulose dispersion, the dispersed particle size of the nano-corn stalk cellulose dispersion is less than 400 nm.

[0010] In step 2), the condensation reflux temperature is 80-150℃ and the time is 2-10h.

[0011] In step 2), the concentration of the N,N-dimethylacetamide / lithium chloride solution is 0.01-0.1 g / ml.

[0012] In step 2), the ratio of nano-corn stalk cellulose powder to N,N-dimethylacetamide / lithium chloride solution is 1:10-100, and the resulting nano-corn stalk cellulose dispersion has a good dispersion effect.

[0013] The present invention also provides a method for preparing a nano-corn stalk cellulose film, the preparation method including steps 1) and 2) of the preparation method of nano-corn stalk cellulose dispersion, and further including step 3) drying the nano-corn stalk cellulose dispersion at a constant temperature to obtain a nano-corn stalk cellulose film.

[0014] In step 3), the drying and molding temperature is 20-60℃.

[0015] Preferably, when the ball milling rate is 300 rpm / min and the ball milling time is 6 h, the nano-corn stalk cellulose film prepared can be transferred for tensile testing. The tensile strength was measured to be 2.15 MPa and the elongation was 10.76%, indicating good tensile properties.

[0016] The present invention also provides a nano-corn stalk cellulose film prepared by the method.

[0017] The nano-corn stalk cellulose film has a tensile strength of 2.15 MPa and an elongation of 10.76%.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0019] 1. The preparation method of this invention is beneficial to Cl + (DMAC / Li) ions solubilize cellulose molecules, forming a six-membered intermediate complex, which causes the cellulose molecular chains to separate and dissolve. This is a "green" pretreatment method that effectively avoids environmental pollution.

[0020] 2. The preparation method of the nano-corn stalk cellulose film material of the present invention is simple and rapid, the raw materials are readily available, the cost is low, and it is suitable for large-scale production;

[0021] 3. The nano-corn stalk cellulose film material prepared by this invention has good dispersibility, degradation and separation characteristics, and has important application prospects in the field of environmental pollution treatment;

[0022] 4. The nano-corn stalk cellulose dispersion and film prepared by this invention are expected to be used in organic polluted environments such as water, soil, and atmosphere. They have broad application prospects in agricultural fully degradable materials and provide more options for the high-value utilization of similar agricultural wastes. Attached Figure Description

[0023] Figure 1 (a) Particle size distribution of nano-corn straw cellulose dispersed in water at ball milling speed of 100 rpm and ball milling time of 2 h, 4 h, 6 h and 8 h; Figure 1 (b) Particle size distribution of nano-corn straw cellulose in DMAC / LiCl dispersion at ball milling speed of 100 rpm and ball milling time of 2 h, 4 h, 6 h and 8 h; Figure 1 (c) Particle size distribution of nano-corn straw cellulose dispersed in water at ball milling speed of 200 rpm and ball milling time of 2 h, 4 h, 6 h and 8 h; Figure 1(d) Particle size distribution of nano-corn straw cellulose in DMAC / LiCl dispersion at ball milling speed of 200 rpm and ball milling time of 2 h, 4 h, 6 h and 8 h; Figure 1 (e) Particle size distribution of nano-corn straw cellulose dispersed in water at ball milling speed of 300 rpm and ball milling time of 2 h, 4 h, 6 h and 8 h; Figure 1 (f) shows the particle size distribution of nano-corn straw cellulose in DMAC / LiCl dispersion at a ball milling speed of 300 rpm and ball milling times of 2 h, 4 h, 6 h and 8 h;

[0024] Figure 2 XRD patterns of nano-corn stalk cellulose powder under different ball milling conditions;

[0025] Figure 3 The FTIR spectrum of nano-corn stalk cellulose powder in DMAC / LiCl dispersion under optimal ball milling conditions;

[0026] Figure 4 Photographs of nano-corn stalk cellulose powder dispersed in DMAC and DMAC / LiCl solutions;

[0027] Figure 5 Nano-corn stalk cellulose films prepared under different ball milling times and speeds;

[0028] Figure 6 Figure showing the transfer of nano-corn stalk cellulose films prepared under different ball milling times and speeds;

[0029] Figure 7 (a) is a SEM image of corn stalk powder without ball milling treatment; Figure 7 (b) is a magnified SEM image of corn stalk powder without ball milling treatment; Figure 7 (c) is a SEM image of nano-corn straw cellulose powder under optimal ball milling conditions; Figure 7 (d) is a magnified SEM image of nano-corn straw cellulose powder under the optimal ball milling treatment conditions; Figure 7 (e) is a SEM image of the surface of the nano-corn stalk cellulose film under the optimal ball milling treatment conditions; Figure 7 (f) is a magnified SEM image of the surface of the nano-corn stalk cellulose film under the optimal ball milling treatment conditions;

[0030] Figure 8 The stress-strain curves of nano-corn stalk cellulose films under optimal ball milling conditions are shown. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0032] Planetary ball mill: Changsha Miqi Instrument Equipment Co., Ltd., YXQM-0.4L; Zeta potentiometer: Malvern Instruments, UK, Zetaasizer Nano ZSE; CNC ultrasonic cleaner: Kunshan Ultrasonic Co., Ltd., KQ-300DE; Condenser reflux device: Gongyi Yuhua Instrument Co., Ltd., DF-101S; Scanning electron microscope: Zeiss, Germany, EVO-LS10; Universal testing machine: Shanghai Hengyi Precision Instrument Co., Ltd., CFBLSM-500N.

[0033] Corn stalk powder: Jiangsu Academy of Agricultural Sciences; Lithium chloride: Shanghai Aladdin Biochemical Technology Co., Ltd., A2126036; N,N-dimethylacetamide: Shanghai Maclean Biochemical Technology Co., Ltd., C14007158.

[0034] Example 1: Determination of Optimal Ball Milling Conditions

[0035] A planetary ball mill is equipped with two corundum jars (150 mL each). Two grinding jars are symmetrically mounted on the same turntable. When the mill rotates, the grinding jars undergo planetary motion, that is, they revolve around an axis while simultaneously rotating on their own axis. During milling, the corn stalk powder undergoes a series of structural changes under the mechanical forces of friction, impact, and shear forces generated by the collision of small balls within the jars. A certain amount of corn stalk powder was passed through a 30-mesh sieve and then placed in an 8 mm diameter planetary ball mill. It was milled at milling rates of 100, 200, and 300 rpm / min for 2, 4, 6, and 8 hours respectively to prepare nano-corn stalk cellulose powder. 4 g of lithium chloride was dispersed in 80 mL of N,N-dimethylacetamide solution by ultrasonic stirring (40 kHz for 15 min), and mixed thoroughly to form a 0.05 g / mL N,N-dimethylacetamide / lithium chloride solution (DMAC / LiCl dispersion). Two g of each of the 12 groups of nano-corn stalk cellulose powder were dispersed in 80 ml of 0.05 g / ml DMAC / LiCl dispersion. The mixture was refluxed at 80℃ for 10 hours, and after cooling, nano-corn stalk cellulose dispersions were prepared. The particle size and particle size distribution of the nano-corn stalk cellulose dispersions were observed, as shown in Table 1. Figure 1 As shown.

[0036] Table 1. Particle size and particle size distribution of nano-corn straw cellulose at different ball milling rates and times.

[0037]

[0038] From Table 1 and Figure 1It can be seen that when the rotation speed is 300 rpm / min and the ball milling time is 6 h and 8 h, the particle size distribution in the DMAC / LiCl dispersion is less than 5 nm. However, when the rotation speed is 300 rpm / min and the ball milling time is 8 h, the particle size of the nano-corn stalk cellulose powder is relatively large. Therefore, the optimal sample processing conditions are a rotation speed of 300 rpm / min, a ball milling time of 6 h, and a DMAC / LiCl dispersion.

[0039] Example 2: Determination of crystallinity index, microstructure, and observation of dispersion effect of nano-corn stalk cellulose powder

[0040] Crystallinity index determination: Using unmilled corn stalk powder as a control, XRD analysis was performed on nano-corn stalk cellulose powder under optimal ball milling conditions. Figure 2 As shown in Table 2, the crystallinity of nano-corn stalk cellulose powder is higher than that of corn stalk powder (47.65%), and the crystallinity of nano-corn stalk cellulose powder under the optimal ball milling treatment conditions is 84.47%.

[0041] Table 2 Crystallinity of nano-corn straw cellulose powder under different ball milling rates and times

[0042]

[0043] Microscopic morphology observation: Using unmilled corn stalk powder as a control, the FTIR spectra of nano-corn stalk cellulose powder in DMAC / LiCl dispersion under optimal ball milling conditions were measured. The results are as follows: Figure 3 As shown, the characteristic peaks of both did not change significantly, indicating that the nano-corn stalk cellulose powder still maintains the basic chemical structure of cellulose. This also indicates that the special characteristics of nano-corn stalk cellulose are due to its nano-size effect.

[0044] Dispersion effect observation: Nano-corn stalk cellulose powder of equal mass under optimal ball milling conditions was dispersed in DMAC solution and DMAC / LiCl dispersion, respectively. Figure 4 As shown in the image, the left photo shows the dispersion of nano-corn stalk cellulose powder in a DMAC solution. A large amount of nano-corn stalk cellulose powder is deposited at the bottom of the bottle and is not uniformly dispersed in the solution. The right photo shows the dispersion of nano-corn stalk cellulose powder in a DMAC / LiCl dispersion. The nano-corn stalk cellulose powder is uniformly dispersed in the DMAC / LiCl dispersion. It is evident that the dispersion effect of nano-corn stalk cellulose powder in the DMAC / LiCl dispersion is better.

[0045] Example 3: Preparation of nano-corn stalk cellulose dispersion and film

[0046] Two g of each of the 12 groups of ball-milled nano-corn stalk cellulose powders prepared in Example 1 were added to 20 ml of the DMAC / LiCl dispersion in Example 1, and refluxed at 120°C for 6 hours. After cooling, nano-corn stalk cellulose dispersions were prepared. Then, 10-20 ml of the nano-corn stalk cellulose dispersions were poured into a petri dish and dried at a constant temperature of 60°C to obtain nano-corn stalk cellulose films. The results are as follows. Figure 5 As shown, when the ball milling rate is 100-300 rpm / min and the ball milling time is 2-8 h, nano-corn stalk cellulose powder can form a thin film in DMAC / LiCl dispersion.

[0047] After the film formed by the nano-corn stalk cellulose dispersion dried, it was transferred from the petri dish with tweezers for a tensile test. Figure 6 It can be seen that when the ball milling speed is 100 rpm and the ball milling time is 2h, 4h, 6h and 8h respectively, the nano-corn stalk cellulose film all showed obvious micro-cracks, which prevented complete transfer. When the ball milling speed is 200 rpm and the ball milling time is 2h, 4h, 6h and 8h respectively, although no micro-cracks appeared, large-area rupture occurred during the transfer process, which prevented the complete transfer of large-area films. When the ball milling speed is 300 rpm and the ball milling time is 2h, 4h and 8h respectively, the nano-corn stalk cellulose film either showed inconspicuous micro-cracks or large cracks during the transfer process, which prevented complete transfer or resulted in large-area relatively intact films. Only the nano-corn stalk cellulose film with a ball milling speed of 300 rpm and a ball milling time of 6h could be transferred, that is, the film formed by the nano-corn stalk cellulose dispersion prepared under the optimal conditions can be transferred.

[0048] The thin film formed from the nano-corn stalk cellulose dispersion prepared under the optimal conditions was subjected to scanning electron microscopy (SEM). Figure 7 As shown in (a) and (b), the non-crystalline regions of unmilled corn stalk powder are not destroyed, while the crystalline regions of cellulose are relatively intact and relatively long, making them prone to flocculent formation. Figure 7 As shown in (c) and (d), after ball milling, the non-crystalline region of the corn stalk powder is destroyed, but the crystalline region of the cellulose remains relatively intact and shorter, making it less prone to flocculation. Figure 7 As shown in (e, f), the surface of nano-sized corn stalk cellulose exposes a large number of hydroxyl groups, which can form a stable colloidal solution in N,N-dimethylacetamide and lithium chloride solutions. The colloidal solution of nano-corn stalk cellulose remains relatively stable. This further confirms the differences in their size and morphology; nano-corn stalk powder is mainly composed of larger particles, while the nano-corn stalk cellulose film exhibits a more uniform distribution (see...). Figure 7 e, f).

[0049] The tensile properties of the film formed from the nano-corn stalk cellulose dispersion prepared under the transferred optimal conditions were measured using a universal testing machine. The results are as follows: Figure 8 As shown, the tensile strength of this nano-corn stalk cellulose film is 2.15 MPa, and its elongation is 10.76%, indicating excellent tensile properties. This is because the nano-corn stalk cellulose film has the largest aspect ratio and a high degree of interlacing, resulting in the lowest film density and the highest porosity. Furthermore, the formation of numerous hydrogen bonds during the assembly of the nanocellulose filaments further enhances its mechanical properties.

[0050] Example 4: Preparation of nano-corn stalk cellulose dispersion and its film under optimal ball milling conditions

[0051] 0.8 g and 8 g of lithium chloride were dispersed in 80 ml of N,N-dimethylacetamide solution by ultrasonic stirring (40 kHz for 15 min), respectively, to form DMAC / LiCl dispersions of 0.01 g / ml and 0.1 g / ml. 0.8 g of nano-corn stalk cellulose powder treated under optimal ball milling conditions was dispersed in 80 ml of the 0.01 g / ml and 0.1 g / ml DMAC / LiCl dispersions, respectively. The dispersions were refluxed at 150 °C for 2 hours. After cooling, nano-corn stalk cellulose dispersions of different concentrations were prepared and observed. The dispersion effect of nano-corn stalk cellulose powder in DMAC / LiCl dispersions of different concentrations was good. Then, 10 ml of the nano-corn stalk cellulose dispersion was poured into a petri dish and dried at a constant temperature of 20 °C to obtain nano-corn stalk cellulose films.

Claims

1. A method for preparing a nanocornstalk cellulose film, characterized by, The method comprises the following steps: 1) ball milling corn stalk powder to obtain nano corn stalk cellulose powder, the ball milling rate is 300 rpm / min, the ball milling time is 6 h, and the particle size of the nano corn stalk cellulose powder is less than 1000 nm; 2) adding the nano corn stalk cellulose powder into an N, N-dimethylacetamide / lithium chloride solution, condensing and refluxing to obtain a nano corn stalk cellulose dispersion, and the dispersion particle size of the nano corn stalk cellulose dispersion is less than 400 nm; 3) drying and forming the nano corn stalk cellulose dispersion at a constant temperature to obtain a nano corn stalk cellulose film.

2. The production method according to claim 1, characterized by, The condensing and refluxing temperature in step 2) is 80-150 ℃, and the time is 2-10 h.

3. The production method according to claim 1, characterized by, The concentration of the N, N-dimethylacetamide / lithium chloride solution in step 2) is 0.01-0.1 g / ml.

4. The method of claim 1, wherein, The ratio of the nano corn stalk cellulose powder to the N, N-dimethylacetamide / lithium chloride solution in step 2) is 1:10-100.

5. The preparation method according to claim 1, characterized in that, The drying and forming temperature in step 3) is 20-60 ℃.

6. The nano corn stalk cellulose film prepared by the preparation method in any one of claims 1-5.

7. The nano-corn stalk cellulose film according to claim 6, characterized by, The tensile strength of the nano corn stalk cellulose film is 2.15 MPa, and the elongation rate is 10.76 %.

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