Synthesis and application of carbon nanotube dispersing agent prepared through lignin modification

Abstract

The invention discloses synthesis and application of a carbon nano tube dispersing agent prepared through lignin modification, the dispersing agent is prepared from natural and renewable lignin through epoxy modification, the initiator lignin contains a plurality of aromatic ring hydrophobic skeleton structures and can form strong pi-pi interaction with CNTs, and the carbon nano tube dispersing agent can be used for dispersing carbon nano tubes. After being subjected to epoxy grafting modification, the epoxy resin has a plurality of polyether chain segments at the same time, is a high-molecular polymer with a plurality of anchoring points and a plurality of solvated chain segments, and is strong in dispersion effect on carbon nanotubes, good in viscosity reduction effect, good in stability and low in foam. The raw material lignin is a byproduct of wood hydrolysis industry and papermaking industry, resources are fully recycled, and the product is green and environment-friendly.

Description

Technical Field

[0001] The invention relates to the technical field of carbon nanotube dispersion, and in particular to the synthesis and application of a carbon nanotube dispersant prepared by modifying lignin. Background Art

[0002] Since its discovery in 1991, carbon nanotubes (CNTs) have attracted extensive attention from scientists for their excellent electrical conductivity, thermal conductivity, field emission effect, toughness, rigidity and high melting point. It is a tubular carbon molecule. Each carbon atom on the tube adopts sp2 hybrid orbitalization, and is bonded to each other by carbon-carbon σ and π bonds to form a honeycomb structure composed of hexagons as the skeleton of the nanotube. According to the number of layers of the tube, it is divided into single-walled carbon nanotubes and multi-walled carbon nanotubes, which can be used as filling materials for polymers, filling materials for fuel cell ion exchange membranes, field effect transistors, field emission displays, electrode module modification and gas detector modification. However, carbon nanotubes have a very large aspect ratio and specific surface area, and there is a strong van der Waals force between CNTs, which makes it easy for carbon nanotubes to entangle and agglomerate, making it difficult to effectively disperse in the matrix, which seriously restricts the performance of the product. Therefore, in order to give full play to the excellent performance of CNTs, how to evenly and stably disperse CNTs is a key issue that needs to be solved urgently.

[0003] Chinese patent application CN 108017049 A uses carbazole-based conjugated polymers as carbon nanotube dispersants, which can efficiently and quickly disperse carbon nanotubes in an organic phase. The combination of the carbazole-based conjugated polymers and carbon nanotubes is mainly through non-covalent interaction and will not cause damage to the surface of the carbon nanotubes. However, the production process of this type of structural material is complicated and difficult to obtain.

[0004] Chinese patent application CN 106587013 A designs a switchable dispersant that can disperse CNTs in an aqueous solution. However, the dispersant needs to be introduced with nitrogen, air or heated for decomposition during use, and can only be dispersed in an aqueous solution, so its application conditions are relatively limited. Summary of the invention

[0005] Based on the above shortcomings of the prior art, the technical problem solved by the present invention is to provide a lignin modified carbon nanotube dispersant, which has a strong dispersion effect on carbon nanotubes, good viscosity reduction effect, good stability and low foam. The raw material lignin is a by-product of the wood hydrolysis industry and the papermaking industry, and the resources are fully reused, and the product is green and environmentally friendly.

[0006] In order to solve the above technical problems, the present invention provides a carbon nanotube dispersant prepared by modifying lignin, characterized in that: the dispersant is prepared from natural renewable lignin by epoxy grafting modification, and is a high molecular polymer containing multiple aromatic ring anchoring points and multiple polyether segments.

[0007] As a preferred embodiment of the above technical solution, the lignin modified carbon nanotube dispersant provided by the present invention further includes part or all of the following technical features:

[0008] As an improvement of the above technical solution, the structural formula of the dispersant is as follows:

[0009]

[0010] In the structural formula, due to the large molecular weight and complex molecular structure of lignin, lignin is usually used to replace the remaining structure of lignin; wherein m=8-25, n=3-14.

[0011] The present invention also provides a synthetic method for preparing a carbon nanotube dispersant by modifying lignin, comprising the following steps: firstly, placing the initiator purified lignin, a graft polymerization catalyst, and an aromatic hydrocarbon solvent into a reaction kettle, and adding ethylene oxide and propylene oxide in proportion in sequence to carry out a graft polymerization reaction at a temperature of 85 to 145° C. and a pressure of 0.1 to 0.5 MPa; adding a neutralizing agent for neutralization, and removing the solvent and the low-boiling point fraction by reduced pressure distillation to obtain the carbon nanotube dispersant.

[0012] As a preferred embodiment of the above technical solution, the synthetic method for preparing a carbon nanotube dispersant by modifying lignin provided by the present invention further includes some or all of the following technical features:

[0013] As an improvement of the above technical solution, the graft polymerization catalyst is one or more of potassium hydroxide, sodium hydroxide, sodium methoxide, potassium methoxide and methylamine, and its feed amount is 0.1-1% of the total feed amount by mass.

[0014] As an improvement of the above technical solution, the aromatic hydrocarbon solvent is one or more of benzene, toluene and xylene, and the feed amount thereof is 10 to 30% by mass of the total feed amount.

[0015] As an improvement of the above technical solution, the feed mass ratio of the initiator purified lignin, ethylene oxide and propylene oxide is 1:2-7:1-5.

[0016] As an improvement of the above technical solution, the neutralizing agent is one or more of acetic acid, oxalic acid, and phosphoric acid.

[0017] As a preferred embodiment of the above technical scheme, the synthesis method is to put the initiator purified lignin, graft polymerization catalyst and aromatic hydrocarbon solvent into a reactor, and add ethylene oxide and propylene oxide in proportion to carry out graft polymerization reaction under the conditions of temperature of 85-145°C and pressure of 0.1-0.5MPa. The steps include: slowly adding ethylene oxide under the conditions of temperature of 100-125°C and reaction pressure of 0.1-0.3Mpa until the pressure of the reactor no longer decreases; slowly adding propylene oxide under the conditions of temperature of 120-145°C and reaction pressure of 0.2-0.4Mpa until the pressure of the reactor no longer decreases; continuing to mature for 0.5-1h; adding a neutralizer for neutralization, and removing the solvent and low-boiling point fractions by reduced pressure distillation to obtain the carbon nanotube dispersant.

[0018] As an improvement of the above technical solution, the structure of the carbon nanotube dispersant conforms to the above structural formula.

[0019] An application of a carbon nanotube dispersant prepared by modifying lignin as described above, characterized in that the carbon nanotube dispersant is applied to the fields of positive and negative electrode conductive pastes for batteries, conductive composite materials, and optoelectronic semiconductor materials.

[0020] The carbon nanotube dispersant provided by the invention is applied to the fields of positive and negative electrode conductive pastes of batteries, conductive composite materials, photoelectric semiconductor materials, etc.

[0021] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0022] 1. The dispersant of the present invention uses lignin, a natural renewable resource, to turn the main pollutants in the papermaking industry into treasure, reduce environmental pollution in the papermaking industry, fully reuse lignin as a resource, and broaden the resource utilization of lignin in high-performance composite materials. In addition, lignin is biodegradable, and the modified dispersant has a low COD value and is green and environmentally friendly.

[0023] 2. The raw material purified lignin of the present invention is a natural polyaromatic macromolecular compound composed of hydrophobic non-polar groups of a phenylpropane skeleton, with multiple adsorption sites. The benzene ring aromatic unit is similar to the six-membered ring structure on the carbon nanotube, and can produce an electron attraction similar to π-π superposition, and can form a good affinity with the carbon nanotube, and be adsorbed on the surface of the carbon nanotube to form multiple anchoring groups. Moreover, this non-covalent effect will not destroy the microstructure of the carbon nanotube, thereby affecting its application performance, especially the electrical performance.

[0024] 3. The dispersant of the present invention is prepared by epoxy modification, and ethylene oxide and propylene oxide block polyether are grafted as solvating segments. Ethylene oxide is a polarized segment, which increases the wetting and dispersing ability of the dispersant and can accelerate the wetting of the surface of carbon nanotubes; propylene oxide is a non-polarized segment, which enhances the ability to suppress foaming and defoaming. In addition, according to the different solvent media of the dispersion system, by controlling the grafting ratio and amount of ethylene oxide and propylene oxide, the polarity of the dispersant can be adjusted so that the solvating segments can be well dissolved in the solvent medium to be dispersed, and are evenly dispersed and arranged outside the surface of the carbon nanotubes, achieving the best steric stabilization effect, effectively avoiding the re-entanglement of the dispersed carbon nanotube particles to cause flocculation and agglomeration, thereby forming a stable dispersion and ensuring the long-term storage of the CNTs slurry.

[0025] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the following is a detailed description in combination with the preferred embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solution of the embodiment of the present invention, the drawings of the embodiment are briefly introduced below.

[0027] Figure 1 This is a comparison diagram of the states of CNTs slurry dispersed by the carbon nanotube dispersant prepared by modifying lignin synthesized in Examples 1-3 and CNTs slurry dispersed by the commercial carbon nanotube dispersant (market samples 1 and 2). DETAILED DESCRIPTION

[0028] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0030] Example 1

[0031] Using purified lignin as the initiator, 0.3% potassium methoxide as the catalyst, and 10% of the total mass of toluene as the solvent, ethylene oxide (EO) is slowly added at a temperature of 100°C and a reaction pressure of 0.3MPa until the pressure in the reactor no longer decreases; propylene oxide (PO) is slowly added at a temperature of 120°C and a reaction pressure of 0.3MPa until the pressure in the reactor no longer decreases, and the aging is continued for 0.5h. The feed mass ratio of purified lignin, ethylene oxide and propylene oxide is m(lignin):m(EO):m(PO) is 1:2:1. Finally, acetic acid is added for neutralization, and the solvent and low-boiling fraction are removed by reduced pressure distillation to obtain a lignin-modified carbon nanotube dispersant with a structure that meets the design requirements.

[0032] Example 2

[0033] Using purified lignin as the initiator, 0.5% potassium hydroxide as the catalyst, and 20% of the total mass of xylene as the solvent, ethylene oxide (EO) is slowly added at a temperature of 125°C and a reaction pressure of 0.1MPa until the pressure in the reactor no longer decreases; propylene oxide (PO) is slowly added at a temperature of 140°C and a reaction pressure of 0.2MPa until the pressure in the reactor no longer decreases, and the aging is continued for 1h. The feed mass ratio of purified lignin, ethylene oxide and propylene oxide is m(lignin):m(EO):m(PO) is 1:7:5. Finally, oxalic acid is added for neutralization, and the solvent and low-boiling fraction are removed by reduced pressure distillation to obtain a lignin-modified carbon nanotube dispersant with a structure that meets the design requirements.

[0034] Example 3

[0035] Using purified lignin as the initiator, 0.8% methylamine as the catalyst, and 30% of the total mass of benzene as the solvent, ethylene oxide (EO) is slowly added at a temperature of 110°C and a reaction pressure of 0.25MPa until the pressure in the reactor no longer decreases; propylene oxide (PO) is slowly added at a temperature of 130°C and a reaction pressure of 0.3MPa until the pressure in the reactor no longer decreases, and the aging is continued for 0.5h. The feed mass ratio of purified lignin, ethylene oxide and propylene oxide is m(lignin):m(EO):m(PO) is 1:5:3. Finally, phosphoric acid is added for neutralization, and the solvent and low-boiling fraction are removed by reduced pressure distillation to obtain a lignin-modified carbon nanotube dispersant with a structure that meets the design requirements.

[0036] The carbon nanotube dispersant prepared by modifying the lignin synthesized in the above Examples 1-3 and the carbon nanotube dispersant on the market were used to disperse carbon nanotubes to obtain CNTs slurry (the materials were added to a nano grinder according to the dispersion formula introduced below, and ground at 25°C for 5 hours to prepare CNTs slurry). The dispersant samples synthesized in Examples 1-3 and the comparative samples of the commercial dispersant were tested for their dispersibility and stability on CNTs under the same conditions. The carbon nanotube dispersion formula is shown in Table 1, and the test results are shown in Table 2.

[0037] Table 1 CNTs dispersion formula

[0038] Components Content (w%) CNTs (Model TNIM8) 14 Solvent (pure water as an example) 83 Dispersants 3 total 100

[0039] Table 2 Test results of CNTs dispersion by different dispersant samples

[0040]

[0041]

[0042] It can be seen from Table 2 that the dispersant samples synthesized by Examples 1-3 have significantly better dispersion, viscosity reduction and stabilization effects on carbon nanotubes than the market dispersant comparison samples (market samples 1 and 2), and can prevent carbon nanotube particles from flocculating and settling for a certain period of time, thereby ensuring good storage stability of the slurry.

[0043] from Figure 1 It can be seen that the CNTs slurry dispersed by the carbon nanotube dispersant synthesized by Examples 1-3 has a better dispersion state than the CNTs slurry dispersed by the commercial samples 1 and 2.

[0044] The invention discloses a carbon nanotube dispersant prepared by lignin modification. The dispersant is prepared by epoxy modification of natural renewable lignin, wherein the initiator lignin contains multiple aromatic ring hydrophobic skeleton structures, can form a strong π-π interaction with CNTs, and has multiple polyether segments after epoxy grafting modification. It is a high molecular polymer with multiple anchor points and multiple solvation segments, has a strong dispersing effect on carbon nanotubes, has a good viscosity reduction effect, is stable, and has low foam. The raw material lignin is a byproduct of the wood hydrolysis industry and the papermaking industry, and the resources are fully reused, and the product is green and environmentally friendly. In addition, the polarity of the dispersant can be adjusted by controlling the grafting amount of ethylene oxide / propylene oxide in the modification preparation process, so that it has good solubility in different dispersing solvent media, and has the advantages of controllable structure and wide applicability. It can be widely used in the fields of battery positive and negative electrode conductive paste, conductive composite materials, photoelectric semiconductor materials, etc. related to carbon nanotube dispersion. It also opens up new ideas for the application of lignin in high-performance composite materials.

[0045] The raw materials listed in the present invention, as well as the upper and lower limits and interval values ​​of the raw materials of the present invention, and the upper and lower limits and interval values ​​of the process parameters (such as temperature, time, etc.) can all realize the present invention, and the embodiments are not listed one by one here.

[0046] The above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A method for preparing a carbon nanotube dispersant by modifying lignin, characterized in that: The dispersant is prepared from natural renewable lignin through epoxy grafting modification and is a high molecular polymer containing multiple aromatic ring anchoring points and multiple polyether chain segments.

2. The carbon nanotube dispersant prepared by modifying lignin according to claim 1, characterized in that: The structural formula of the dispersant is as follows: In the structural formula, Lignin is the residual structure of lignin; wherein m=8-25, n=3-14.

3. A method for preparing a carbon nanotube dispersant by modifying lignin, characterized in that: The method comprises the following steps: firstly, placing the initiator purified lignin, the graft polymerization catalyst and the aromatic hydrocarbon solvent into a reaction kettle, and adding ethylene oxide and propylene oxide in proportion to carry out a graft polymerization reaction under the conditions of a temperature of 85 to 145° C. and a pressure of 0.1 to 0.5 MPa; adding a neutralizing agent to carry out neutralization, and removing the solvent and the low-boiling-point fraction by reduced pressure distillation to obtain the carbon nanotube dispersant.

4. The method for preparing a carbon nanotube dispersant by modifying lignin as claimed in claim 3, characterized in that: The graft polymerization catalyst is one or more of potassium hydroxide, sodium hydroxide, sodium methoxide, potassium methoxide and methylamine, and the feed amount thereof is 0.1-1% of the total feed amount by mass.

5. The method for preparing a carbon nanotube dispersant by modifying lignin as claimed in claim 1, characterized in that: The aromatic hydrocarbon solvent is one or more of benzene, toluene and xylene, and the feeding amount thereof is 10-30% of the total feeding amount by mass.

6. The method for preparing a carbon nanotube dispersant by modifying lignin as claimed in claim 3, characterized in that: The feed mass ratio of the initiator purified lignin, ethylene oxide and propylene oxide is 1:2-7:1-5.

7. The method for preparing a carbon nanotube dispersant by modifying lignin as claimed in claim 3, characterized in that: The neutralizing agent is one or more of acetic acid, oxalic acid and phosphoric acid.

8. The method for preparing a carbon nanotube dispersant by modifying lignin as claimed in claim 3, characterized in that: The synthesis method comprises the following steps: putting the initiator purified lignin, the graft polymerization catalyst and the aromatic hydrocarbon solvent into a reactor, and adding ethylene oxide and propylene oxide in proportion to carry out a graft polymerization reaction under the conditions of a temperature of 85 to 145° C. and a pressure of 0.1 to 0.5 MPa. The steps include: slowly adding ethylene oxide under the conditions of a temperature of 100 to 125° C. and a reaction pressure of 0.1 to 0.3 MPa until the pressure of the reactor no longer decreases; slowly adding propylene oxide under the conditions of a temperature of 120 to 145° C. and a reaction pressure of 0.2 to 0.4 MPa until the pressure of the reactor no longer decreases; continuing to mature for 0.5 to 1 hour; adding a neutralizing agent for neutralization, and removing the solvent and the low-boiling-point fraction by distillation under reduced pressure to obtain the carbon nanotube dispersant.

9. The method for preparing a carbon nanotube dispersant by modifying lignin according to claims 3-8, characterized in that: The structure of the carbon nanotube dispersant conforms to the structural formula as claimed in claim 2.

10. An application of lignin modification as claimed in any one of claims 1 to 9 to prepare a carbon nanotube dispersant, characterized in that: The carbon nanotube dispersant is used in the fields of battery positive and negative electrode conductive pastes, conductive composite materials, and photoelectric semiconductor materials.

Images