阅读说明：本技术 一种纳米纤维素的改性方法及在尼龙6原位开环聚合中的应用 (Modification method of nano-cellulose and application of nano-cellulose in-situ ring-opening polymerization of nylon 6 ) 是由 阚泽 史豪 孙阿彬 张晓潭 于 2021-09-03 设计创作，主要内容包括：本发明公开了一种纳米纤维素的改性方法及在尼龙6原位开环聚合中的应用,涉及高分子新材料技术领域,利用2,4-甲苯二异氰酸酯邻位和对位的异氰酸根反应活性的不同来设计反应条件,使得纳米纤维素先与对位异氰酸根反应,由于异氰酸根非常活泼,容易与空气中的水分和二氧化碳反应,故采用己内酰胺对剩余的邻位异氰酸根进行封端,制备得到改性纳米纤维素,改性后的纳米纤维素不仅能够起到减少其本身的活性基团对原位开环聚合过程的阻聚作用,还可以使纳米纤维素与尼龙基体之间产生一定的界面相互作用。本发明解决了纳米纤维素与尼龙6加工难的问题,同时为实现纳米纤维素在聚合物中理想的分散及界面粘接提供了一种可行的方案。(The invention discloses a method for modifying nanocellulose and application thereof in nylon 6 in-situ ring-opening polymerization, and relates to the technical field of new polymer materials, wherein reaction conditions are designed by utilizing different reactivity of isocyanate groups at ortho-position and para-position of 2, 4-toluene diisocyanate, so that the nanocellulose is firstly reacted with the isocyanate groups at para-position, and the isocyanate groups are very active and are easy to react with moisture and carbon dioxide in the air, so that the remaining ortho-position isocyanate groups are blocked by adopting caprolactam to prepare the modified nanocellulose, and the modified nanocellulose not only can play a role in reducing the polymerization inhibition effect of active groups of the nanocellulose on the in-situ ring-opening polymerization process, but also can generate a certain interface interaction between the nanocellulose and a nylon matrix. The invention solves the problem of difficult processing of the nano-cellulose and the nylon 6, and provides a feasible scheme for realizing ideal dispersion and interface bonding of the nano-cellulose in a polymer.)

1. A method for modifying nano-cellulose is characterized in that 2, 4-toluene diisocyanate is adopted to modify the nano-cellulose, and then ortho-position isocyanic acid radical is blocked to prepare the modified nano-cellulose.

2. The modification method according to claim 1, characterized by comprising in particular the steps of:

1) isocyanate functionalization of nanocellulose:

firstly, vacuumizing and dehydrating the nano cellulose at 100-150 ℃, and then cooling to room temperature;

② taking toluene as solvent, adding nano-cellulose, catalyst and 2, 4-toluene diisocyanate therein for ultrasonic dispersion, and dispersing in N₂Lower protection at temperature T₁Carrying out reaction;

thirdly, centrifuging, pouring out supernatant, collecting precipitate, cleaning with toluene, and finally drying in vacuum to obtain the nano-cellulose grafted 2, 4-toluene diisocyanate;

2) functionalized nanocellulose grafted caprolactam:

weighing nano-cellulose grafted 2, 4-toluene diisocyanate, adding toluene under a vacuum condition, stirring, dispersing and ultrasonically treating to obtain a toluene solution of the nano-cellulose grafted toluene diisocyanate;

weighing caprolactam, vacuumizing at 100-130 ℃, cooling, adding toluene, and stirring until the caprolactam is completely dissolved to obtain a toluene solution of caprolactam;

thirdly, adding toluene solution of caprolactam into toluene solution of nano-cellulose grafted 2, 4-toluene diisocyanate and adding into N₂Heating at 80-100 ℃ in the atmosphere, centrifuging to remove liquid supernatant, and drying in vacuum to obtain the nano-cellulose grafted caprolactam.

3. The modification method according to claim 2, wherein the nanocellulose is one of microcrystalline cellulose, cellulose nanofibres or cellulose nanocrystals.

4. The modification method according to claim 2, wherein the catalyst is one or more of dibutyltin dilaurate, stannous octoate, ethyl magnesium bromide or triethylamine.

5. Modification method according to claim 2, characterized in that said temperature T₁Is 35 to 50 ℃.

6. The modification method according to claim 2, wherein the ratio of toluene to nano-cellulose in the step 1) is (10-50) mL: 1g of the total weight of the composition.

7. The modification method according to claim 2, wherein the ratio of the nano-cellulose to the 2, 4-toluene diisocyanate in step 1) is 1 g: (3-10) mL.

8. The modification method according to claim 2, wherein the volume ratio of the catalyst to the 2, 4-toluene diisocyanate in the step 1) is (1-1.5): 1.

9. use of the modified nanocellulose obtained by the modification method of any one of claims 1 to 8 in situ ring-opening polymerization of nylon 6.

Technical Field

The invention relates to the technical field of new polymer materials, in particular to a modification method of nanocellulose and application of nanocellulose in-situ ring-opening polymerization of nylon 6.

Background

Nylon 6(PA6) is widely used as engineering plastic in industrial and daily life products, and has the advantages of high strength, high toughness, wear resistance, self-lubrication, chemical resistance, strong chemical solvent resistance and the like. However, PA6 has poor impact resistance at low temperatures and in a dry state, insufficient rigidity and heat resistance under strong external forces and heating conditions, poor dimensional stability of products, and the like, which have limited some of its applications. In order to overcome the above disadvantages, it is common practice to modify it by blending fillers, blocks and grafts. The filling with nanoparticles is an important way to realize the high performance and functionalization of polymers at present.

For example, the invention patents CN112978736A, CN112982003A, CN110835377A and CN110423494A can achieve the purpose of changing surface properties by surface modification of nanoparticles to eliminate or reduce their surface active groups. However, when the particle size of the nanoparticles is less than 100nm, the surface energy of the nanoparticles is greatly increased, and the particles have a strong tendency to self-aggregate, so that the conventional blending technology is difficult to obtain nano-scale dispersion. In addition, the non-uniformity of mixing makes it difficult for existing interfacial modification techniques to completely eliminate the interfacial tension between the nanoparticles and the polymer matrix, making it difficult to achieve ideal interfacial bonding. Therefore, how to uniformly disperse the nanoparticles in the polymer matrix to achieve a nano-scale dispersion level to improve the performance of the polymer is a technical difficulty in the field of materials at present and is also a hot problem in the research of composite materials in recent years.

The in-situ polymerization method is to fully mix the nano particles and the polymer monomer, disperse the nano particles in the monomer in an original ecological form under the action of ultrasonic waves or strong stirring, and polymerize the monomer under proper conditions to prepare the in-situ nano composite material. The method has the advantages that the product is only polymerized and formed once without being processed by heat, thereby avoiding the degradation caused by the polymerization and keeping the stability of various performances of the polymer; meanwhile, compared with a high-viscosity system in melt processing, the low viscosity of in-situ polymerization is beneficial to the dispersion of the nano particles. Based on the above advantages, the in-situ polymerization method for preparing polymer-based nanocomposite materials is more and more emphasized by people. Such as the patent: CN112940493A, CN112920415A, CN 111961337A. However, the nanocomposites obtained by the in-situ polymerization method described above do not show good mechanical properties (such as impact resistance, toughness and strength) and are not suitable for processing and molding.

Cellulose is the most abundant natural polymer on earth, and is a precious natural renewable resource. Natural cellulose is a semi-crystalline fibrous material, and products with different forms such as microcrystalline cellulose, cellulose nanofibers and cellulose nanocrystals can be obtained by processing. The nano-cellulose has excellent performances of high strength, high crystallinity, high elastic modulus, huge specific surface area, larger reactivity, larger adsorbability and the like. However, the heat resistance of the cellulose material is not high, so that the application of the cellulose material in the field of engineering plastics is very limited.

In addition, PA6 is susceptible to inhibition by protic impurities due to severe conditions for in situ ring-opening polymerization, but nanocellulose has a molecular structure with a large number of active hydroxyl groups and terminal reducing aldehyde groups, and both of these groups are susceptible to some chemical reactions during in situ ring-opening polymerization, which affects smooth progress of polymerization, and thus further modification of nanocellulose is required.

Disclosure of Invention

The invention aims to solve the problems of poor interface caused by polymerization inhibition of nano-cellulose in the nylon 6 in-situ ring-opening polymerization process and agglomeration in a polymer matrix, and provides a modification method of nano-cellulose and application of the nano-cellulose in the nylon 6 in-situ ring-opening polymerization.

In order to achieve the purpose, the invention provides the following scheme:

a method for modifying nanocellulose comprises the steps of modifying nanocellulose by 2, 4-toluene diisocyanate, and then blocking ortho-position isocyanic acid radical to prepare modified nanocellulose.

Further, the modification method is carried out in two steps, and specifically comprises the following steps:

1) isocyanate functionalization of nanocellulose:

placing the nano-cellulose in a reactor, vacuumizing at 100-150 ℃ to remove water for 40-50 h, and then cooling to room temperature;

② taking toluene as solvent, adding nano-cellulose, catalyst and 2, 4-Toluene Diisocyanate (TDI) into a reactor for ultrasonic dispersion for 25-35 min, and dispersing in N₂Lower protection at temperature T₁Carrying out reaction;

thirdly, removing the residual reactant after the reaction by centrifugation, pouring out the supernatant, collecting the precipitate, cleaning the precipitate with toluene, and finally drying the precipitate in vacuum at 20-40 ℃ for 10-15 hours to obtain the nano-cellulose grafted TDI, wherein the reaction equation is as follows:

2) functionalized nanocellulose grafted caprolactam:

weighing nano-cellulose grafted TDI in a reactor, vacuumizing for 20-40 min, adding toluene, stirring for dispersing, and performing ultrasonic treatment for 20-40 min to obtain a toluene solution of the grafted TDI;

weighing caprolactam in another reactor, vacuumizing for 20-40 min at 100-130 ℃, cooling, adding toluene, and stirring until the toluene is completely dissolved to obtain a toluene solution of caprolactam;

thirdly, slowly adding the toluene solution of caprolactam into the toluene solution of nano-cellulose grafted TDI, and adding into N₂Heating at 80-100 ℃ in the atmosphere, centrifuging to remove liquid supernatant, and drying in vacuum to obtain the nano-cellulose grafted caprolactam, wherein the grafting rate is 5% -75%, and the reaction equation is as follows:

further, the nanocellulose is one of microcrystalline cellulose (MCC), Cellulose Nanofibre (CNF) or Cellulose Nanocrystalline (CNC).

Further, the catalyst is one or more of dibutyltin dilaurate, stannous octoate, ethyl magnesium bromide or triethylamine.

Further, the temperature T₁Is 35 to 50 ℃.

Further, in the step 1), the ratio of toluene to nano-cellulose material liquid is (10-50) mL: 1g of the total weight of the composition.

Further, in the step 1), the ratio of the nano-cellulose to the 2, 4-toluene diisocyanate in the liquid to the nano-cellulose is 1 g: (3-10) mL.

Further, the volume ratio of the catalyst to the 2, 4-toluene diisocyanate in the step 1) is (1-1.5): 1.

the invention also provides application of the modified cellulose obtained by the modification method in nylon 6 in-situ ring-opening polymerization.

The invention designs reaction conditions by utilizing the different reactivity of the isocyanic acid radical at ortho position and para position of the 2, 4-toluene diisocyanate, so that the nano cellulose reacts with the isocyanic acid radical at para position. The isocyanate is very active and is easy to react with moisture and carbon dioxide in the air, so that the remaining ortho isocyanate is blocked by caprolactam to prepare the modified nano-cellulose. The modified nano-cellulose not only can reduce the polymerization inhibition of active groups of the nano-cellulose to the in-situ ring-opening polymerization process, but also can generate certain interfacial interaction between the nano-cellulose and a nylon matrix. The invention solves the problem of difficult processing of the nano-cellulose and the nylon 6, and provides a feasible scheme for realizing ideal dispersion and interface bonding of the nano-cellulose in a polymer.

The in-situ ring-opening polymerization method of nylon 6(PA6) has lower polymerization temperature (140-180 ℃) and can effectively prevent the degradation of nano-cellulose. Meanwhile, the in-situ ring-opening polymerization PA6 has the advantages of short reaction time, high crystallinity, large molecular weight and the like, and the strength, rigidity, dimensional stability, water absorption, drug resistance and other properties of the product are superior to those of the common nylon 6.

The invention discloses the following technical effects:

1. after 2, 4-toluene diisocyanate is adopted to modify the nanocellulose, a certain covering effect can be achieved on polar groups on the surface of the cellulose nanocrystal, the influence of the polar groups on the in-situ ring-opening polymerization process is reduced, and the in-situ ring-opening polymerization is more complete.

2. According to the invention, after the caprolactam is adopted to block the isocyanated nanocellulose, the amide group carried by the caprolactam can enable the interface action between the cellulose nanocrystal and the resin matrix to be stronger, so that the performance of the composite material is more excellent.

3. The self-agglomeration phenomenon of the modified nano-cellulose is obviously improved, the particles reach nano-grade dispersion in the polymer, and the superiority of the nano-material modified polymer is better reflected.

In summary, the research and development and production aspects of adding nano-cellulose products into engineering plastics are not many, the invention not only adds a preparation method of nano-filler for nylon 6 composite materials, but also enables the nano-cellulose to be widely applied in the field of high polymer materials, improves the utilization level of the nano-cellulose, and can stimulate the development of the nano-cellulose industry.

Detailed Description

Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The description and examples are intended to be illustrative only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.

Example 1

Weighing 5.00g of cellulose nanocrystal, placing in a flask, vacuumizing at 120 ℃ to remove water for 48h, cooling to room temperature, and adding N₂Adding 50mL of toluene under the atmosphere, performing ultrasonic dispersion for 30min, then sequentially adding 15.0mL of triethylamine and 13.5mL of 2, 4-toluene diisocyanate, stirring and heating at 45 ℃, reacting for 24h, centrifuging after the reaction to obtain a precipitate, washing with toluene, repeating for three times to remove unreacted triethylamine and 2, 4-toluene diisocyanate, centrifuging to remove a supernatant, drying the precipitate in a vacuum drying oven at 30 ℃ for 12h to obtain isocyanated cellulose nanocrystalline powder;

then, the dried isocyanated cellulose nanocrystalline powder was placed in a flask and evacuated for 30min under N₂Adding 50mL of toluene in the atmosphere, and carrying out ultrasonic treatment for 30min to obtain a toluene solution of the isocyanated cellulose nanocrystal;

weighing 21.4g of caprolactam, vacuumizing at 110 ℃ to remove water for 30min, cooling and adding N₂Adding 50mL of toluene, and stirring until the toluene is completely dissolved to obtain a toluene solution of caprolactam;

slowly adding a toluene solution of caprolactam into a toluene solution of isocyanated cellulose nanocrystalline, raising the temperature to 90 ℃, installing a condenser pipe, stirring and heating at 90 ℃ for 4 hours, centrifuging after reaction to obtain a precipitate, washing with toluene to remove unreacted caprolactam, centrifuging to remove a supernatant, drying and precipitating in a vacuum drying oven at 30 ℃ for 12 hours to obtain the nano-cellulose grafted caprolactam (mCNC, modified nano-cellulose), wherein the grafting rate is 35%.

The modified nanocellulose in the embodiment is used as a raw material, and the cellulose nanocrystal reinforced nylon 6 composite material is prepared by nylon 6 in-situ ring-opening polymerization, and the method comprises the following steps: adding 200.00g of caprolactam monomer into a flask, heating to 110 ℃ for melting, vacuumizing for draining for 30min, heating to 120 ℃, adding 20.61g of prepared cellulose nanocrystalline grafted caprolactam, vacuumizing for draining for 15min, finally adding 63mL of initiator ethyl magnesium bromide, uniformly mixing, vacuumizing for 10min, pouring into a mold which is placed in an oven at 170 ℃ and preheated for 2h, preserving heat for 30min, and naturally cooling the mold to obtain the mCNC/PA6 composite material. The performance test indexes are shown in table 1.

TABLE 1 mCNC/PA6 composite material Performance test Table

Wherein, the conversion rate refers to the polymerization degree of caprolactam monomer, and the calculation formula isWherein DOC' is the degree of polymerization of caprolactam monomer, m_polIs the mass of the polymer, m_totM is the total mass_CNCIs the mass of the cellulose nanocrystals.

Example 2

Weighing 5.00g of microcrystalline cellulose, placing in a flask, vacuumizing at 120 ℃ for dewatering for 48h, cooling to room temperature, and then adding N₂Adding 150mL of toluene under the atmosphere, performing ultrasonic treatment for 30min, then sequentially adding 30mL of triethylamine and 27mL of 2, 4-toluene diisocyanate, stirring and heating at 45 ℃, reacting for 24h, centrifuging after the reaction to obtain a precipitate, washing with toluene, and repeating for three times to remove unreacted triethylamine and 2, 4-toluene diisocyanateCentrifuging isocyanate, pouring out supernatant liquid, and drying and precipitating in a vacuum drying oven at 30 ℃ for 12 hours to obtain isocyanated microcrystalline cellulose powder;

then, the dried isocyanated microcrystalline cellulose powder was placed in a flask and evacuated for 30min under N₂Adding 100mL of toluene in the atmosphere, and carrying out ultrasonic treatment for 30min to obtain a toluene solution of isocyanated microcrystalline cellulose;

weighing 21.4g of caprolactam, vacuumizing at 110 ℃ for dewatering for 30min, cooling, and adding N₂Then adding 120mL of toluene, and stirring until the toluene is completely dissolved to obtain a toluene solution of caprolactam;

slowly adding a toluene solution of caprolactam into a toluene solution of isocyanated microcrystalline cellulose, raising the temperature to 90 ℃, installing a condensing tube, stirring and heating at 90 ℃ for 4 hours, centrifuging after reaction to obtain a precipitate, washing with toluene to remove unreacted caprolactam, centrifuging to remove supernatant, drying the precipitate in a vacuum drying oven at 30 ℃ for 12 hours to obtain microcrystalline cellulose grafted caprolactam (mMCC, modified nano-cellulose), wherein the grafting rate is 45%.

The modified nanocellulose prepared in this example was used as a raw material, and nylon 6 in-situ ring-opening polymerization was used to prepare a cellulose nanocrystal reinforced nylon 6 composite material, the preparation method was the same as example 1, and the performance test indexes thereof are shown in table 2.

TABLE 2 Performance test Table for mMCC/PA6 composite material

Example 3

Weighing 10.00g of cellulose nano-fiber, placing in a flask, vacuumizing at 120 ℃ to remove water for 48h, cooling to room temperature, and then adding N₂Adding 500mL of toluene under the atmosphere, performing ultrasonic treatment for 30min, sequentially adding 60mL of triethylamine and 54mL of 2, 4-toluene diisocyanate, stirring and heating at 45 ℃, reacting for 24h, centrifuging after the reaction to obtain a precipitate, washing with toluene, repeating for three times to remove unreacted triethylamine and 2, 4-toluene diisocyanate, centrifuging and pouring out the supernatantAfter the solution is obtained, drying and precipitating the solution in a vacuum drying oven at the temperature of 30 ℃ for 12 hours to obtain isocyanated cellulose nanofiber powder;

then, the dried isocyanated cellulose nanofiber powder was placed in a flask and evacuated for 30min under N₂Adding 250mL of toluene in the atmosphere, and performing ultrasonic treatment for 30min to obtain a toluene solution of the isocyanated cellulose nanofibers;

weighing 42.80g of caprolactam, vacuumizing at 110 ℃ for dewatering for 30min, cooling, and adding N₂Adding 250mL of toluene, and stirring until the toluene is completely dissolved to obtain a toluene solution of caprolactam;

slowly adding a toluene solution of caprolactam into a toluene solution of isocyanated cellulose nano-fiber, raising the temperature to 90 ℃, installing a condensing tube, stirring and heating at 90 ℃ for 4 hours, centrifuging after reaction to obtain a precipitate, washing with toluene to remove unreacted caprolactam, centrifuging to remove a supernatant, drying and precipitating in a vacuum drying oven at 30 ℃ for 12 hours to obtain cellulose nano-fiber grafted caprolactam (mCNF, modified nano-cellulose)), wherein the grafting rate is 38%.

The modified nanocellulose of this example was used as a raw material, and nylon 6 in-situ ring-opening polymerization was used to prepare a cellulose nanocrystal reinforced nylon 6 composite material, the preparation method was the same as example 1, and the performance test indexes thereof are shown in table 3.

TABLE 3 mCNF3/PA6 composite material performance test table

Example 4

Weighing 10.00g of microcrystalline cellulose, placing in a flask, vacuumizing at 120 ℃ for dewatering for 48h, cooling to room temperature, and then adding N₂Adding 300mL of methylbenzene under the atmosphere, performing ultrasonic treatment for 30min, sequentially adding 30mL of dibutyltin dilaurate and 27.0mL of 2, 4-toluene diisocyanate, stirring and heating at 50 ℃, reacting for 24h, centrifuging after the reaction to obtain a precipitate, washing with methylbenzene, repeating for three times to remove unreacted dibutyltin dilaurate and 2, 4-toluene diisocyanate, centrifuging, pouringAfter supernatant liquid is removed, drying and precipitating for 12 hours in a vacuum drying oven at the temperature of 30 ℃ to obtain isocyanated microcrystalline cellulose powder;

then, the dried isocyanated microcrystalline cellulose powder was placed in a flask and evacuated for 30min under N₂Adding 150mL of toluene in the atmosphere, and carrying out ultrasonic treatment for 30min to obtain a toluene solution of isocyanated microcrystalline cellulose;

weighing 42.80g of caprolactam, vacuumizing at 110 ℃ for dewatering for 30min, cooling, and adding N₂Adding 150mL of toluene, and stirring until the toluene is completely dissolved to obtain a toluene solution of caprolactam;

slowly adding a toluene solution of caprolactam into a toluene solution of isocyanated microcrystalline cellulose, raising the temperature to 90 ℃, installing a condensing tube, stirring and heating at 90 ℃ for 4 hours, centrifuging after reaction to obtain a precipitate, washing with toluene to remove unreacted caprolactam, centrifuging to pour out a supernatant, drying and precipitating in a vacuum drying oven at 30 ℃ for 12 hours to obtain microcrystalline cellulose grafted caprolactam (mMCC-2, modified nano-cellulose), wherein the grafting ratio is 58%.

The modified nanocellulose of this example was used as a raw material, and nylon 6 in-situ ring-opening polymerization was used to prepare a microcrystalline cellulose-reinforced nylon 6 composite material, the preparation method was the same as example 1, and the performance test indexes were as shown in table 4.

TABLE 4 Performance test Table for mMCC-2/PA6 composite material

Example 5

Weighing 5.00g of cellulose nanocrystal, placing in a flask, vacuumizing at 120 ℃ to remove water for 48h, cooling to room temperature, and adding N₂Adding 60mL of toluene under the atmosphere, performing ultrasonic treatment for 30min, then sequentially adding 16mL of stannous octoate and 15mL of 2, 4-toluene diisocyanate, stirring and heating at 35 ℃, reacting for 24h, centrifuging after the reaction to obtain a precipitate, washing with toluene, repeating for three times to remove unreacted stannous octoate and 2, 4-toluene diisocyanate, centrifuging to remove a supernatant, and drying in vacuum at 30 DEGDrying and precipitating in a box for 12 hours to obtain isocyanated cellulose nanocrystalline;

then, the dried isocyanated cellulose nanocrystalline powder was placed in a flask and evacuated for 40min under N₂Adding 60mL of toluene in the atmosphere, and performing ultrasonic treatment for 20min to obtain a toluene solution of the isocyanated cellulose nanocrystal;

weighing 21.4g of caprolactam, vacuumizing at 120 ℃ for dewatering for 25min, cooling, and adding N₂Then adding 120mL of toluene, and stirring until the toluene is completely dissolved to obtain a toluene solution of caprolactam;

slowly adding a toluene solution of caprolactam into a toluene solution of isocyanated cellulose nanocrystalline, raising the temperature to 90 ℃, installing a condenser pipe, stirring and heating at 90 ℃ for 4 hours, centrifuging after reaction to obtain a precipitate, washing with toluene to remove unreacted caprolactam, centrifuging to remove supernatant, drying and precipitating in a vacuum drying oven at 30 ℃ for 12 hours to obtain the nano-cellulose grafted caprolactam (mCNC-2, modified nano-cellulose), wherein the grafting rate is 62%.

The modified nanocellulose prepared in this example was used as a raw material, and nylon 6 in-situ ring-opening polymerization was used to prepare a cellulose nanocrystal reinforced nylon 6 composite material, the preparation method was the same as example 1, and the performance test indexes thereof are shown in table 5.

TABLE 5 mCNC-2/PA6 composite Material Performance test Table

Example 6

Weighing 5.00g of cellulose nano-fiber, placing the cellulose nano-fiber in a flask, vacuumizing at 120 ℃ to remove water for 48h, cooling to room temperature, and then adding N₂Adding 50mL of toluene under the atmosphere, performing ultrasonic treatment for 30min, sequentially adding 16.0mL of ethyl magnesium bromide and 15mL of 2, 4-toluene diisocyanate, stirring and heating at 40 ℃, reacting for 24h, centrifuging after the reaction to obtain a precipitate, washing with toluene, repeating for three times to remove unreacted ethyl magnesium bromide and 2, 4-toluene diisocyanate, centrifuging to remove a supernatant, drying and precipitating in a vacuum drying oven at 30 DEG CStanding for 12h to obtain isocyanated cellulose nanofibers;

then, the dried isocyanated cellulose nanofiber powder was placed in a flask and evacuated for 40min under N₂Adding 30mL of toluene in the atmosphere, and performing ultrasonic treatment for 20min to obtain a toluene solution of the isocyanated cellulose nanofibers;

weighing 21.4g of caprolactam, vacuumizing at 120 ℃ for dewatering for 25min, cooling, and adding N₂Then adding 120mL of toluene, and stirring until the toluene is completely dissolved to obtain a toluene solution of caprolactam;

slowly adding a toluene solution of caprolactam into a toluene solution of isocyanated cellulose nano-fiber, raising the temperature to 90 ℃, installing a condenser pipe, stirring and heating at 90 ℃ for 4 hours, centrifuging after reaction to obtain a precipitate, washing with toluene to remove unreacted caprolactam, centrifuging to remove supernatant, drying and precipitating in a vacuum drying oven at 30 ℃ for 12 hours to obtain nano-cellulose grafted caprolactam (mCNF-2, modified nano-cellulose), wherein the grafting rate is 72%.

The modified nanocellulose prepared in this example was used as a raw material, and nylon 6 in-situ ring-opening polymerization was used to prepare a cellulose nanocrystal reinforced nylon 6 composite material, the preparation method was the same as example 1, and the performance test indexes thereof are shown in table 6.

TABLE 6 mCNF-2/PA6 composite material performance test table

Comparative example 1

Weighing 5.00g of cellulose nanocrystal, placing in a flask, vacuumizing at 120 ℃ to remove water for 48h, cooling to room temperature, and adding N₂Adding 50mL of toluene under the atmosphere, performing ultrasonic treatment for 30min, sequentially adding 15mL of ethyl magnesium bromide and 13.5mL of 2, 4-toluene diisocyanate, stirring and heating at 40 ℃, reacting for 24h, centrifuging after the reaction to obtain a precipitate, washing with toluene, repeating for three times to remove unreacted ethyl magnesium bromide and 2, 4-toluene diisocyanate, centrifuging to remove a supernatant, drying the precipitate in a vacuum drying oven at 30 ℃, and drying the precipitate 12h, obtaining isocyanated cellulose nanocrystals (mCNC 1', modified nanocellulose).

The modified nanocellulose prepared by the comparative example is used as a raw material, the cellulose nanocrystal reinforced nylon 6 composite material is prepared by nylon 6 in-situ ring-opening polymerization, the preparation method is the same as that of example 1, and the performance test indexes are shown in table 7.

TABLE 7 testing table for performance of mCNC'/PA 6 composite material

Comparative example 2

Unmodified nanocellulose (CNC) was used directly for in situ polymerization of PA6, prepared as in example 1, and the performance test indices are shown in table 8.

TABLE 8 test chart for the properties of CNC/PA6 composite materials

The embodiment and the comparative example show that the invention solves the problem of difficult processing of the nano-cellulose and the nylon 6, and provides a feasible scheme for realizing ideal dispersion and interfacial adhesion of the nano-cellulose in the polymer. The in-situ ring-opening polymerization method of nylon 6(PA6) has lower polymerization temperature (140-180 ℃) and can effectively prevent the degradation of the nanocellulose.

The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.