A method for preparing cellulose-based conductive film by combining deep eutectic solvent with ultrasound

Abstract

The present invention discloses a method for preparing a cellulose-based conductive film by combining a low eutectic solvent with ultrasound, and belongs to the technical field of preparing biomass cellulose nanofibers containing lignin. A low eutectic solvent is used to pretreat lignocellulose resources under mild conditions to separate and obtain a cellulose-rich solid; the cellulose solid is diluted into a suspension, and high-intensity ultrasound treatment is used to promote the separation and fibrillation of cellulose; multi-walled carbon nanotubes are added to the lignin-containing cellulose nanofiber suspension, homogenized, and then vacuum filtered and hot-pressed to obtain a cellulose-based film with good strength, toughness and conductivity. The low eutectic solvent used in the present invention is environmentally friendly, low-cost and recyclable; the conditions for preparing the composite conductive film are mild, simple to operate, low-pollution, low-cost and short-cycle.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of biomass lignin-containing cellulose nanofibers, and specifically relates to a method for preparing cellulose nanofibers by combining low eutectic solvent pretreatment with high-intensity ultrasound, and a method for preparing a composite conductive film by combining vacuum filtration with hot pressing. Background Art

[0002] Cellulose nanofibers are high-strength polymer fibrils that offer advantages over other nanofibers due to their low cost, colloidal properties, biodegradability, mechanical stability, bacterial activity, and barrier properties. Compared to pure cellulose, lignin-containing cellulose nanofibers offer higher yields, lower production costs, and less pollution, thanks to the fact that they do not require a bleaching process. Lignin-containing cellulose nanofibers also incorporate the properties of lignin, such as thermal stability, UV stability, and hydrophobicity, and stabilize the lignin-cellulose network through strong hydrogen bonds. Furthermore, the softening and amorphous nature of lignin creates a binding effect in the formation of lignin-containing cellulose nanopaper, filling the gaps between fibers and making the nanopaper smoother. This makes lignin-containing cellulose nanofibers a promising thin film material. In the field of conductive materials, nanocellulose is typically used as a carrier, while conductive materials (such as silver nanoparticles, carbon nanotubes, and graphene) serve as network fillers, forming composite materials with nanocellulose as the base material and interconnected conductive materials.

[0003] Separating sugar resources from biomass has always been a bottleneck in agricultural waste treatment. The environmental pollution caused by the acid and alkaline reagents used in traditional methods is becoming increasingly serious. However, DES, as a green solvent, has attracted the attention of researchers in biological and chemical applications due to its low cost, easy preparation, biodegradability, and recyclability. One of these applications involves cleaving the ether bonds between phenylpropane units in lignin to extract lignin from biomass and purify cellulose. Numerous researchers have used deep eutectic solvents to pretreat biomass resources to obtain high-purity cellulose, which is then used to prepare lignin-containing cellulose nanofibers. However, there are currently few reports on the use of lignin-containing cellulose nanofibers in the field of conductive materials. Therefore, the use of deep eutectic solvents combined with ultrasound to prepare lignin-containing cellulose nanofibers and their application in conductive materials has broad potential. Summary of the Invention

[0004] In order to reduce the environmental pollution and energy consumption caused by traditional preparative methods and promote the application of renewable resources in the field of electronics, the present invention provides a method for preparing lignin-containing cellulose nanofibers based on the gentle separation of cellulose with a low eutectic solvent combined with high-intensity ultrasound, and uniformly dispersing multi-walled carbon nanotubes with the lignin-containing cellulose nanofibers to prepare a conductive composite film.

[0005] The technical solution adopted by the present invention is a method for preparing a cellulose-based conductive film by combining a deep eutectic solvent with ultrasound, which is carried out according to the following steps:

[0006] (1) Synthesis of deep eutectic solvent: Choline chloride, p-toluenesulfonic acid, and ethylene glycol were weighed and mixed in molar ratio, heated at 90°C with continuous stirring for 1 h until a transparent, homogeneous liquid was formed, and then cooled to room temperature in a drying dish;

[0007] (2) Pretreatment of lignocellulose: Pretreatment was performed in a stoppered glass pressure tube, with walnut shells and the low eutectic solvent from step (1) added. The reaction vessel was heated in a water bath with magnetic stirring for a certain period of time. 20 mL of ethanol was added to the mixture to reduce the viscosity, and the mixture was centrifuged at 8000 rpm for 5 min to separate the cellulose solids. The mixture was washed with ethanol and water (7:3 v / v) until the supernatant was colorless, and then freeze-dried to obtain the solids.

[0008] (3) Preparation of cellulose nanofibers by ultrasonic treatment: The cellulose solids from step (2) were prepared into a 0.5% w / v suspension in distilled water and ultrasonically treated using an ultrasonic cell disruptor equipped with a metal probe. Prior to ultrasonic treatment, the cells were homogenized using a homogenizer at 10,000 rpm for 3 minutes.

[0009] (4) Preparation of a composite conductive film: A certain amount of multi-walled carbon nanotubes was added to the suspension homogenized in step (3), and distilled water was added to adjust the total solids concentration to 0.5% w / v. The composite suspension was then homogenized at 10,000 rpm for 3 minutes. A certain amount of the composite suspension was vacuum filtered to form a smooth filter pulp. The filter membrane and the filter pulp were then hot-pressed and dried at 50°C for 6 hours at a pressure of -0.05 MPa. The filter membrane was then separated to obtain a conductive film.

[0010] The molar ratio of choline chloride, p-toluenesulfonic acid and ethylene glycol in step (1) is 1:0.5:1.

[0011] The mass ratio of the walnut shell to the deep eutectic solvent in step (2) is 1:10, the wood fiber pretreatment time is 2.5 hours, and the temperature is 90°C.

[0012] The ultrasonic treatment time in step (3) is 30 min, the frequency is 20 kHz, the power is 600 W, and the on / off time is 5 s each.

[0013] The mass of the multi-walled carbon nanotubes in step (4) is 5-20% of the mass of the cellulose solids.

[0014] The composite conductive film prepared by the above method has wide application value in the field of degradable electronic materials.

[0015] Beneficial effects of the present invention:

[0016] (1) The deep eutectic solvent used in the present invention is simple to synthesize, low in cost, effective, low in pollution, and recyclable, and can effectively decompose lignocellulosic biomass under mild conditions.

[0017] (2) The present invention has mild conditions for preparing lignin-containing cellulose nanofibers, simple operation, low cost and low pollution, and meets the production standards of green chemistry; the lignin-containing cellulose nanofibers are uniformly and stably dispersed in water.

[0018] (3) The cellulose-based composite conductive film prepared by the present invention has good tensile strength, toughness and conductivity, and has application prospects in degradable flexible electronic materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is the ζ-potential of the composite suspensions prepared in Example 1, Example 2, Example 3, Example 4 and Comparative Example 1; the abscissa is the ζ-potential value and the ordinate is the composite film sample; wherein NF-0C, NF-5C, NF-10C, NF-15C and NF-20C correspond to the composite suspensions in Comparative Example 1, Example 1, Example 2, Example 3 and Example 4, respectively.

[0020] Figure 2 1 is the tensile curve of the conductive film prepared in Example 1, Example 2, Example 3, Example 4 and Comparative Example 1; the horizontal axis is the elongation rate and the vertical axis is the tensile stress; among them, NF-0C, NF-5C, NF-10C, NF-15C and NF-20C correspond to the composite films in Comparative Example 1, Example 1, Example 2, Example 3 and Example 4, respectively.

[0021] Figure 3 It is the Young's modulus of the conductive films prepared in Example 1, Example 2, Example 3, Example 4 and Comparative Example 1; the abscissa is the composite film sample, and the ordinate is the Young's modulus value; among them, NF-0C, NF-5C, NF-10C, NF-15C and NF-20C correspond to the composite films in Comparative Example 1, Example 1, Example 2, Example 3 and Example 4, respectively.

[0022] Figure 4 is the conductivity of the conductive films prepared in Example 1, Example 2, Example 3, Example 4 and Comparative Example 1; the abscissa is the composite film sample, and the ordinate is the conductivity value; wherein NF-0C, NF-5C, NF-10C, NF-15C and NF-20C correspond to the composite films in Comparative Example 1, Example 1, Example 2, Example 3 and Example 4, respectively. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below with reference to specific embodiments, which are intended to explain the present invention rather than to limit it.

[0024] Example 1:

[0025] (1) Synthesis of deep eutectic solvent: 139.62 g of choline chloride, 95.10 g of p-toluenesulfonic acid, and 62.06 g of ethylene glycol were weighed, mixed, and heated at 90° C. for 1 h under continuous stirring until a transparent, homogeneous liquid was formed.

[0026] (2) Walnut Shell Pretreatment: 2 g of dried walnut shell and 20 g of a deep eutectic solvent were added to a stoppered glass pressure tube. The reaction vessel was heated in a 90°C water bath with magnetic stirring for 2.5 h. 20 mL of ethanol was added to the mixture to reduce viscosity. The cellulose solids were separated by centrifugation at 10,000 rpm. The solids were washed with ethanol and water (7:3 v / v) until the supernatant was colorless and then dried at 60°C for 24 h.

[0027] (3) Ultrasonic Treatment: Cellulose solids were prepared into a 0.5% w / v suspension in distilled water and ultrasonically treated for 30 min using an ultrasonic cell disruptor at a frequency of 20 kHz, a power of 600 W, and an on / off time of 5 s. Homogenize the mixture for 3 min using a homogenizer at 10,000 rpm before ultrasonic treatment.

[0028] (4) Preparation of composite suspension: Multi-walled carbon nanotubes were added to the sonicated suspension at a concentration of 5% of the cellulose solids. Distilled water was then added to adjust the total solids concentration to 0.5% w / v. The sample was named NF-5C. The suspension was then homogenized at 10,000 rpm for 3 min. The ζ-potential of the composite suspension was -16.26 mV. Figure 1 shown.

[0029] (5) Preparation of conductive film: 10 mL of the homogenized composite suspension was taken and vacuum filtered to form a smooth filter pulp. The vacuum filtration membrane used was a polyvinylidene fluoride with a pore size of 80 μm and a diameter of 5 cm. The filter membrane and the filter pulp were then hot-pressed and dried at 50°C for 6 h at a pressure of -0.05 MPa. After separating the filter membrane, a composite conductive film was obtained. The film was named NF-5C. The tensile curve of the film is shown in FIG. Figure 2 As shown, the tensile strength is 49.44MPa and the elongation is 1.41%. The Young's modulus is 37.32MPa, as shown Figure 3 As shown. The conductivity of the film is 0.12S / m, as shown Figure 4 shown.

[0030] Example 2:

[0031] (1) Synthesis of deep eutectic solvent: 139.62 g of choline chloride, 95.10 g of p-toluenesulfonic acid, and 62.06 g of ethylene glycol were weighed, mixed, and heated at 90° C. for 1 h under continuous stirring until a transparent, homogeneous liquid was formed.

[0032] (2) Walnut Shell Pretreatment: 2 g of dried walnut shell and 20 g of a deep eutectic solvent were added to a stoppered glass pressure tube. The reaction vessel was heated in a 90°C water bath with magnetic stirring for 2.5 h. 20 mL of ethanol was added to the mixture to reduce viscosity. The cellulose solids were separated by centrifugation at 10,000 rpm. The solids were washed with ethanol and water (7:3 v / v) until the supernatant was colorless and then dried at 60°C for 24 h.

[0033] (3) Ultrasonic Treatment: Cellulose solids were prepared into a 0.5% w / v suspension in distilled water and ultrasonically treated for 30 min using an ultrasonic cell disruptor at a frequency of 20 kHz, a power of 600 W, and an on / off time of 5 s. Homogenize the mixture for 3 min using a homogenizer at 10,000 rpm before ultrasonic treatment.

[0034] (4) Preparation of composite suspension: Multi-walled carbon nanotubes were added to the sonicated suspension at a concentration of 10% of the cellulose solids, and distilled water was added to adjust the total solids concentration to 0.5% w / v. The sample was named NF-10C. The suspension was then homogenized at 10,000 rpm using an IKA T18 homogenizer for 3 min. The ζ-potential of the composite suspension was -15.48 mV. Figure 1 shown.

[0035] (5) Preparation of conductive film: 10 mL of the homogenized composite suspension was taken and vacuum filtered to form a smooth filter pulp. The vacuum filtration membrane used was a polyvinylidene fluoride with a pore size of 80 μm and a diameter of 5 cm. The filter membrane and the filter pulp were then hot-pressed and dried at 50°C for 6 h at a pressure of -0.05 MPa. After separating the filter membrane, a composite conductive film was obtained. The film was named NF-10C. The tensile curve of the film is shown in FIG. Figure 2 As shown, the tensile strength is 58.36MPa and the elongation is 1.88%. The Young's modulus is 35.34MPa, as shown Figure 3 As shown. The conductivity of the film is 2.67S / m, as shown Figure 4 shown.

[0036] Example 3:

[0037] (1) Synthesis of deep eutectic solvent: 139.62 g of choline chloride, 95.10 g of p-toluenesulfonic acid, and 62.06 g of ethylene glycol were weighed, mixed, and heated at 90° C. for 1 h under continuous stirring until a transparent, homogeneous liquid was formed.

[0038] (2) Walnut Shell Pretreatment: 2 g of dried walnut shell and 20 g of a deep eutectic solvent were added to a stoppered glass pressure tube. The reaction vessel was heated in a 90°C water bath with magnetic stirring for 2.5 h. 20 mL of ethanol was added to the mixture to reduce viscosity. The cellulose solids were separated by centrifugation at 10,000 rpm. The solids were washed with ethanol and water (7:3 v / v) until the supernatant was colorless and then dried at 60°C for 24 h.

[0039] (3) Ultrasonic Treatment: Cellulose solids were prepared into a 0.5% w / v suspension in distilled water and ultrasonically treated for 30 min using an ultrasonic cell disruptor at a frequency of 20 kHz, a power of 600 W, and an on / off time of 5 s. Homogenize the mixture for 3 min using a homogenizer at 10,000 rpm before ultrasonic treatment.

[0040] (4) Preparation of composite suspension: Multi-walled carbon nanotubes were added to the sonicated suspension at a concentration of 15% of the cellulose solids. Distilled water was then added to adjust the total solids concentration to 0.5% w / v. The sample was designated NF-15C. The suspension was then homogenized at 10,000 rpm for 3 min using an IKA T18 homogenizer. The ζ-potential of the composite suspension was -14.38 mV. Figure 1 shown.

[0041] (5) Preparation of conductive film: 10 mL of the homogenized composite suspension was taken and vacuum filtered to form a smooth filter pulp. The vacuum filtration membrane used was a polyvinylidene fluoride with a pore size of 80 μm and a diameter of 5 cm. The filter membrane and the filter pulp were then hot-pressed and dried at 50°C for 6 h at a pressure of -0.05 MPa. After separating the filter membrane, a composite conductive film was obtained. The film was named NF-15C. The tensile curve of the film is shown in FIG. Figure 2 As shown, the tensile strength is 66.33MPa and the elongation is 2.35%. The Young's modulus is 33.63MPa, as shown Figure 3 The conductivity of the film is 9.18S / m, as shown in Figure 4 shown.

[0042] Example 4:

[0043] (1) Synthesis of deep eutectic solvent: 139.62 g of choline chloride, 95.10 g of p-toluenesulfonic acid, and 62.06 g of ethylene glycol were weighed, mixed, and heated at 90° C. for 1 h under continuous stirring until a transparent, homogeneous liquid was formed.

[0044] (2) Walnut Shell Pretreatment: 2 g of dried walnut shell and 20 g of a deep eutectic solvent were added to a stoppered glass pressure tube. The reaction vessel was heated in a 90°C water bath with magnetic stirring for 2.5 h. 20 mL of ethanol was added to the mixture to reduce viscosity. The cellulose solids were separated by centrifugation at 10,000 rpm. The solids were washed with ethanol and water (7:3 v / v) until the supernatant was colorless and then dried at 60°C for 24 h.

[0045] (3) Ultrasonic Treatment: Cellulose solids were prepared into a 0.5% w / v suspension in distilled water and ultrasonically treated for 30 min using an ultrasonic cell disruptor at a frequency of 20 kHz, a power of 600 W, and an on / off time of 5 s. Homogenize the mixture for 3 min using a homogenizer at 10,000 rpm before ultrasonic treatment.

[0046] (4) Preparation of composite suspension: Multi-walled carbon nanotubes were added to the sonicated suspension at a concentration of 20% of the cellulose solids. Distilled water was then added to adjust the total solids concentration to 0.5% w / v. The sample was designated NF-20C. The suspension was then homogenized at 10,000 rpm using an IKA T18 homogenizer for 3 min. The ζ-potential of the composite suspension was -12.75 mV. Figure 1 shown.

[0047] (5) Preparation of conductive film: 10 mL of the homogenized composite suspension was taken and vacuum filtered to form a smooth filter pulp. The vacuum filtration membrane used was a polyvinylidene fluoride with a pore size of 80 μm and a diameter of 5 cm. The filter membrane and the filter pulp were then hot-pressed and dried at 50°C for 6 h at a pressure of -0.05 MPa. After separating the filter membrane, a composite conductive film was obtained. The film was named NF-20C. The tensile curve of the film is shown in FIG. Figure 2 As shown, the tensile strength is 63.58MPa and the elongation is 2.10%. The Young's modulus is 33.06MPa, as shown Figure 3 The conductivity of the film is 15.60S / m, as shown in Figure 4 shown.

[0048] Comparative Example 1:

[0049] (1) Synthesis of deep eutectic solvent: 139.62 g of choline chloride, 95.10 g of p-toluenesulfonic acid, and 62.06 g of ethylene glycol were weighed, mixed, and heated at 90° C. for 1 h under continuous stirring until a transparent, homogeneous liquid was formed.

[0050] (2) Walnut Shell Pretreatment: 2 g of dried walnut shell and 20 g of a deep eutectic solvent were added to a stoppered glass pressure tube. The reaction vessel was heated in a 90°C water bath with magnetic stirring for 2.5 h. 20 mL of ethanol was added to the mixture to reduce viscosity. The cellulose solids were separated by centrifugation at 10,000 rpm. The solids were washed with ethanol and water (7:3 v / v) until the supernatant was colorless and then dried at 60°C for 24 h.

[0051] (3) Ultrasonic Treatment: Cellulose solids were prepared into a 0.5% w / v suspension in distilled water and ultrasonically treated for 30 min using an ultrasonic cell disruptor at a frequency of 20 kHz, a power of 600 W, and an on / off time of 5 s. Homogenize the mixture for 3 min using a homogenizer at 10,000 rpm before ultrasonic treatment.

[0052] (4) Preparation of suspension: The suspension after ultrasonic treatment was homogenized by IKA T18 homogenizer at 10000 rpm for 3 min. The sample was named NF-0C, and the ζ-potential of the suspension was -17.65 mV. Figure 1 shown.

[0053] (5) Preparation of film: 10 mL of the homogenized suspension was taken and vacuum filtered to form a smooth filter pulp. The vacuum filtration membrane used was a polyvinylidene fluoride with a pore size of 80 μm and a diameter of 5 cm. The filter membrane and the filter pulp were then hot-pressed and dried at 50°C for 6 h at a pressure of -0.05 MPa. The film was obtained after separating the filter membrane. The film was named NF-0C. The tensile curve of the film is shown in FIG. Figure 2 As shown, the tensile strength is 47.21MPa and the elongation is 1.40%. The Young's modulus is 35.89MPa, as shown Figure 3 As shown. The film is in a non-conductive state with a conductivity of 0S / m. Figure 4 shown.

Claims

1. A method for preparing a cellulose-based conductive film by combining a deep eutectic solvent with ultrasound, characterized in that Follow the steps below: (1) Synthesis of a deep eutectic solvent: Weigh a certain amount of choline chloride, p-toluenesulfonic acid, and ethylene glycol, mix them evenly, and heat them at 90 °C in a sealed container for 1 h until a transparent and uniform liquid is formed; (2) Pretreatment of lignocellulosic biomass: The biomass and the low eutectic solvent were added to a stoppered glass pressure tube at a certain mass ratio, reacted at a certain temperature for a certain time, and then centrifuged at 8000 rpm for 5 min to separate the solids. The solids were washed with ethanol-water solution at a volume ratio of 7:3, and then freeze-dried. (3) Ultrasonic preparation of lignin-containing cellulose nanofibers: The dried solids in step (2) were diluted with distilled water to form a 0.5% w / v suspension, homogenized at 10,000 rpm for 3 min, and the suspension was ultrasonically treated using a cell disruptor equipped with a circular metal probe to obtain lignin-containing cellulose nanofibers; (4) Preparation of composite suspension: Add a certain amount of multi-walled carbon nanotubes to the suspension after ultrasonic treatment in step (3), and then add distilled water to a total solid concentration of 0.5% w / v; homogenize the composite suspension using a homogenizer at 10,000 rpm for 3 minutes; (5) Preparation of composite conductive film: The composite suspension in step (4) was vacuum filtered, and the filter membrane and filter pulp after filtration were hot-pressed and dried at 50 °C and -0.05 MPa for 6 h. After separating the filter membrane, a cellulose-based composite conductive film was obtained; The molar ratio of choline chloride, p-toluenesulfonic acid and ethylene glycol in the deep eutectic solvent of step (1) is 1:0.5:1; The mass ratio of the biomass to the deep eutectic solvent in step (2) is 1:10; The deep eutectic solvent pretreatment temperature in step (2) is 90°C and the time is 2.5 h; The ultrasonic treatment conditions described in step (3) are a frequency of 20 kHz, an output power of 600 W, and an on / off pulse of 5 / 5 s.

2. The method for preparing a cellulose-based conductive film by combining a deep eutectic solvent with ultrasound according to claim 1, characterized in that The mass of the multi-walled carbon nanotubes in step (4) is 5-20% of the mass of the cellulose solids.

3. The method for preparing a cellulose-based conductive film by combining a deep eutectic solvent with ultrasound according to claim 1, characterized in that The composite conductive film described in step (5) has wide application value in the field of degradable electronic materials.

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