Pegylated cellulose nanocrystal as well as preparation method and application thereof

Abstract

The invention relates to a pegylated cellulose nanocrystal and a preparation method and application thereof, in particular to the technical field of nanomaterials, the preparation method comprises the following steps: modifying polyethylene glycol into chlorinated polyethylene glycol; carrying out alkaline treatment on the cellulose nanocrystal to enhance the activity of the cellulose nanocrystal; then mixing and reacting the polyethylene glycol cellulose nanocrystal and the polyethylene glycol cellulose nanocrystal to obtain a polyethylene glycol cellulose nanocrystal; according to the invention, polyethylene glycol is grafted on the surface of the cellulose nanocrystal through chemical reaction, so that the action mechanism of the cellulose nanocrystal is changed and enhanced, on one hand, the grafting of polyethylene glycol not only exerts the steric hindrance effect, but also enhances the characteristics (crystallinity, thermal stability and dispersity) of the cellulose nanocrystal; on the other hand, due to the existence of polyethylene glycol, the short-circuit diffusion effect and the nucleation effect can be enhanced, so that the cement hydration degree is improved; and polyethylene glycol has an internal curing effect, so that the self-constriction of the cement-based material can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of nanomaterials, and particularly to a polyethylene glycolylated cellulose nanocrystal, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, low water-cement ratio cement-based materials (such as high-performance / ultra-high-performance concrete) have been widely used in fields such as bridges and super high-rise buildings due to their excellent mechanical properties. However, when the water-cement ratio is lower than 0.42, the cement cannot be completely hydrated. The low water-cement ratio leads to an increase in the density of the material, making it difficult for external water to penetrate into the interior, and the uneven distribution of the mixing water exacerbates the problem of uneven hydration. How to overcome these defects of low water-cement ratio cement-based materials has become an urgent problem to be solved. Summary of the Invention

[0003] The purpose of the present invention is to provide a polyethylene glycolylated cellulose nanocrystal, a preparation method thereof, and an application thereof to improve the above problems. To achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0004] In a first aspect, the present application provides a preparation method of a polyethylene glycolylated cellulose nanocrystal, including:

[0005] Mix polyethylene glycol and Lucas reagent for reaction to obtain a first intermediate;

[0006] Mix a cellulose nanocrystal suspension and a sodium hydroxide solution for reaction to obtain a second intermediate;

[0007] Mix the first intermediate and the second intermediate for reaction to obtain a polyethylene glycolylated cellulose nanocrystal.

[0008] Optionally, the mixing of polyethylene glycol and Lucas reagent for reaction includes:

[0009] Mix polyethylene glycol and Lucas reagent according to a mass ratio of 1:(0.8 - 1.2), and react at 65 - 75 °C for 1.5 - 3 h.

[0010] Optionally, the mass concentration of the cellulose nanocrystal suspension is 1.5 - 3 wt%.

[0011] Optionally, the concentration of the sodium hydroxide solution is 0.5 - 2 mol / L, and the volume ratio of the cellulose nanocrystal suspension to the sodium hydroxide solution is (1 - 3):1.

[0012] Optionally, the mixing of the cellulose nanocrystal suspension and the sodium hydroxide solution for reaction includes:

[0013] Mix the cellulose nanocrystal suspension with the sodium hydroxide solution, stir and react at 55 - 65 °C for 2 - 4 h, centrifuge and wash the product, adjust the pH to neutral, and finally freeze-dry.

[0014] Optionally, the mass ratio of the first intermediate to the second intermediate is (4.5 - 5.5):1.

[0015] Optionally, the mixing of the first intermediate and the second intermediate for reaction includes:

[0016] Mix the first intermediate and the second intermediate and formulate them into a solution, react at 65 - 75 °C for 8 - 14 h to obtain a polyethylene glycolated cellulose nanocrystal solution.

[0017] Optionally, the method further includes:

[0018] Adjust the pH of the polyethylene glycolated cellulose nanocrystal solution to neutral, then centrifuge and wash with water, then perform dialysis separation on the solution with water to remove ionic impurities, and finally freeze-dry to obtain polyethylene glycolated cellulose nanocrystals.

[0019] In a second aspect, the present application also provides a polyethylene glycolated cellulose nanocrystal, which is prepared by the above-mentioned preparation method of polyethylene glycolated cellulose nanocrystals.

[0020] In a third aspect, the present application also provides a cement-based composite material, and the cement-based composite material includes the polyethylene glycolated cellulose nanocrystal as described above.

[0021] The beneficial effects of the present invention are as follows:

[0022] In the present application, polyethylene glycol is grafted onto the surface of cellulose nanocrystals through a chemical reaction without destroying the hydroxyl groups, which changes and enhances its action mechanism. On the one hand, the grafting of polyethylene glycol not only plays a steric hindrance role and enhances the properties of cellulose nanocrystals (crystallinity, thermal stability, and dispersibility); on the other hand, polyethylene glycol introduces a large number of hydroxyl groups, creating more water-transporting channels, which is beneficial for the transmission of water to the unhydrated regions inside the cement particles and promotes cement hydration; moreover, polyethylene glycol has an internal curing effect, can retain water, compensate for the decrease in relative humidity inside the cement-based material, and reduce the autogenous shrinkage of the cement-based material.

[0023] Other features and advantages of the present invention will be described in the subsequent specification, and some will be obvious from the specification or understood by implementing the embodiments of the present invention. Description of the Drawings

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the attached drawings required for the embodiments. It should be understood that the following attached drawings only show some embodiments of the present invention, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other relevant attached drawings can also be obtained based on these attached drawings.

[0025] Figure 1 For the test block compressive strength of Example 6 and Comparative Example 1 of this application;

[0026] Figure 2 For the test block compressive strength of Example 7 and Comparative Example 2 of this application;

[0027] Figure 3 For the test block compressive strength of Example 8 and Comparative Example 3 of this application.

[0028] Figure 4 For the heat release rate curve of the cement slurry of Example 6 and Comparative Example 1 of this application;

[0029] Figure 5 For the total heat release curve of the cement slurry of Example 6 and Comparative Example 1 of this application;

[0030] Figure 6 For the heat release rate curve of the cement slurry of Example 7 and Comparative Example 2 of this application;

[0031] Figure 7 For the total heat release curve of the cement slurry of Example 7 and Comparative Example 2 of this application;

[0032] Figure 8 For the heat release rate curve of the cement slurry of Example 8 and Comparative Example 3 of this application;

[0033] Figure 9 For the total heat release curve of the cement slurry of Example 8 and Comparative Example 3 of this application;

[0034] Figure 10 For the molecular structural formula diagram of CNC and the nuclear magnetic resonance carbon spectrum diagrams of CNC and PCNC prepared in Example 1, where Figure (a) is the molecular structural formula diagram, Figure (b) is the nuclear magnetic resonance carbon spectrum diagram of CNC, and Figure (c) is the nuclear magnetic resonance carbon spectrum diagram of PCNC.

[0035] Figure 11 For the content curves of calcium, sulfur, aluminum, and silicon in the pore solution at different hydration stages of the embodiments of this application. Detailed implementation manners

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention.

[0037] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0038] It should be noted that in the following embodiments, CNC is cellulose nanocrystal, PEG-Cl is chlorinated polyethylene glycol, DCNC is cellulose nanocrystal after NaOH treatment, and PCNC is polyethylene glycolated cellulose nanocrystal.

[0039] This application provides a method for preparing polyethylene glycolated cellulose nanocrystals, including:

[0040] S1. Mix polyethylene glycol and Lucas reagent in a mass ratio of 1:0.8 - 1.2, and heat at 65 - 75 °C for 1.5 - 3 h to obtain a first intermediate, namely chlorinated polyethylene glycol PEG-Cl; the preferred reaction conditions are heating at 70 °C for 2 h; due to the electron pair of the oxygen atom combining with Zn 2+ to form a complex with polyethylene glycol, and further undergoing a nucleophilic substitution reaction with halogen, the reaction mechanism is as shown in formula (1):

[0041]

[0042] Lucas reagent (English: Lucas'reagent) is a solution prepared by dissolving anhydrous zinc chloride in high-concentration hydrochloric acid. The preparation conditions are relatively harsh, and this solution is usually used to distinguish low-molecular-weight alcohols.

[0043] S2. Mix a cellulose nanocrystal suspension (the concentration of cellulose nanocrystals is about 1.5 - 3 wt%) and a NaOH (the concentration of NaOH is 0.5 - 2 mol / L) solution in a volume ratio of (1 - 3):1, and stir at 55 - 65 °C for 2 - 4 hours. After the reaction, first centrifuge and wash, adjust to pH = 7, and then perform freeze-drying to finally obtain a second intermediate powder, denoted as DCNC, and the reaction mechanism is as shown in formula (2):

[0044]

[0045] Through alkaline treatment, the molecular structure of cellulose nanocrystals changes. In the molecular structure, the sulfonic acid group (-SO3H) of cellulose nanocrystals is replaced by Na, expanding the molecular size (swelling), enhancing the reactivity of CNC, and providing a basic condition for subsequent smooth grafting.

[0046] S3. Mix the first intermediate and the second intermediate in a mass ratio of (4.5 - 5.5):1, and prepare a solution with an appropriate amount of water. React at 65 - 75 °C for 8 - 14 h to achieve the grafting of PEG on the surface of CNC. The grafted CNC is denoted as PCNC; adjust the PCNC solution to pH = 7 with sodium hydroxide, then centrifuge and retain the solution. Place the solution in a dialysis membrane with a molecular weight cut-off of 14000 Da (g / mol), immerse the dialysis membrane in a container filled with 4 L of water for 4 days, and change the water in the container every day to remove Zn 2+ , Na + and other plasma. Finally, freeze-dry the PCNC to obtain solid powder of polyethylene glycolated cellulose nanocrystals. The reaction mechanism is as shown in Equation (3):

[0047]

[0048] DCNC conducts a nucleophilic attack on PEG-Cl, promotes cellulose grafting, and releases halogen in the reaction medium to form PCNC.

[0049] In this application, polyethylene glycol is grafted onto the surface of cellulose nanocrystals through a chemical reaction without destroying the internal structure of polyethylene glycol, changing and enhancing its mechanism of action. On the one hand, a large number of hydroxyl groups are introduced by polyethylene glycol, creating more water-transporting channels, which is beneficial for the transfer of water to the unhydrated regions inside cement particles and promotes cement hydration; on the other hand, the grafting of polyethylene glycol not only plays a steric hindrance role and enhances the properties of cellulose nanocrystals (crystallinity, thermal stability, and dispersibility); moreover, polyethylene glycol has an internal curing effect, can retain water, compensate for the decrease in relative humidity inside the cement-based material, and reduce the autogenous shrinkage of the cement-based material.

[0050] Compared with the prior art, the polyethylene glycolated cellulose nanocrystals of this application also have great advantages in terms of cost. Specifically:

[0051] Chinese Patent CN 107473659 A and "Graft Modified Cellulose Nanocrystals Reinforced Polylactic Acid" (Plastics Industry, Vol. 45, No. 12) respectively provide different methods for grafting polyethylene glycol onto cellulose nanocrystals. The amino polyethylene glycol used (191.12 yuan per gram) and polyethylene glycol diglycidyl ether (559.92 yuan per 100 ml) are extremely expensive, while the polyethylene glycol 1500 used in the present invention is only 56.72 yuan per 500 grams, significantly reducing the preparation cost.

[0052] In addition, compared with using zinc chloride catalyst (97.9 yuan per 5 grams) and concentrated hydrochloric acid as raw materials, the present invention uses Lucas reagent (a mixture of concentrated hydrochloric acid and zinc chloride prepared in a certain ratio), and the price of Lucas reagent is 75 yuan per 100 ml, which is more economical and environmentally friendly.

[0053] Through the above comparison, it can be clearly seen that the raw materials of the present application are inexpensive and the preparation cost is significantly reduced.

[0054] Moreover, in the preparation methods of the above two prior arts, in the reaction process of polyethylene glycol amination in Chinese Patent CN 107473659 A, a large amount of hydroxyl groups on polyethylene glycol will be replaced by amino groups; in "Graft Modified Cellulose Nanocrystals Reinforced Polylactic Acid" (Plastics Industry, Vol. 45, No. 12), the internal monomer structure of polyethylene glycol will be damaged during the grafting process; the reaction mechanism of the present application will neither cause a large reduction in the hydroxyl group content on the surface of polyethylene glycol nor damage the internal structure of polyethylene glycol. The reduction of hydroxyl groups will lead to the weakening of the short-circuit diffusion effect in cement, that is, the cement hydration effect becomes worse. Therefore, the present application can achieve a better hydration effect in cement-based materials compared with the first two technologies.

[0055] Based on the same inventive concept, the present application also provides a polyethylene glycolated cellulose nanocrystal, which is prepared by the above-mentioned preparation method of polyethylene glycolated cellulose nanocrystal.

[0056] Based on the same inventive concept, the present application also provides a cement-based composite material, and the cement-based composite material includes the polyethylene glycolated cellulose nanocrystal as described above.

[0057] The following provides specific examples to illustrate the implementation manners of the present invention. In the following examples, polyethylene glycol uses PEG-1500.

[0058] Example 1

[0059] A preparation method of a polyethylene glycolated cellulose nanocrystal, comprising:

[0060] S1. Mix polyethylene glycol and Lucas reagent according to a mass ratio of 1:1, and heat at 70 °C for 2 h to obtain a first intermediate, namely chlorinated polyethylene glycol;

[0061] S2. Mix 100 mL of the cellulose nanocrystal suspension (with a cellulose nanocrystal concentration of approximately 2 wt%) with 50 mL of the NaOH solution (NaOH concentration is 2 mol / L), and stir at 60 °C for 3 hours. After the reaction is completed, first centrifuge and wash, then adjust to pH = 7 with dilute hydrochloric acid, and then perform freeze-drying to finally obtain the second intermediate powder, denoted as DCNC;

[0062] S3. Mix the first intermediate and the second intermediate in a mass ratio of 5:1 (weigh 2 g of the second intermediate powder), and add 100 g of water to prepare a solution, and react at 70 °C for 10 h to achieve the grafting of PEG on the surface of CNC. The grafted CNC is denoted as PCNC; then centrifuge and wash with water, and adjust the PCNC solution to pH = 7 with sodium hydroxide. Place the solution in a dialysis membrane with a molecular weight cut-off of 14000 Da (g / mol), immerse the dialysis membrane in a container containing 4 L of water for 4 days, and change the water in the container every day to remove Zn 2+ 、Na + ions. Finally, perform freeze-drying on PCNC to obtain the polyethylene glycolated cellulose nanocrystal solid powder.

[0063] Example 2

[0064] A method for preparing polyethylene glycolated cellulose nanocrystals, comprising:

[0065] S1. Mix polyethylene glycol and Lucas reagent in a mass ratio of 1:0.8, and heat at 75 °C for 3 h to obtain the first intermediate, namely chlorinated polyethylene glycol;

[0066] S2. Mix 120 mL of the cellulose nanocrystal suspension (with a cellulose nanocrystal concentration of approximately 2 wt%) with 50 mL of the NaOH solution (NaOH concentration is 1 mol / L), and stir at 65 °C for 3 hours. After the reaction is completed, first centrifuge and wash, then adjust to pH = 7 with dilute hydrochloric acid, and then perform freeze-drying to finally obtain the second intermediate powder, denoted as DCNC;

[0067] S3. Mix the first intermediate and the second intermediate in a mass ratio of 4.5:1 (weigh 2 g of the second intermediate powder), and add 100 g of water to prepare a solution, and react at 65 °C for 8 h to achieve the grafting of polyethylene glycol on the surface of cellulose nanocrystals. The grafted cellulose nanocrystals are denoted as PCNC; then centrifuge and wash with water, and adjust the PCNC solution to pH = 7 with sodium hydroxide. Place the solution in a dialysis membrane with a molecular weight cut-off of 14000 Da (g / mol), immerse the dialysis membrane in a container containing 4 L of water for 4 days, and change the water in the container every day to remove Zn 2+ 、Na +Plasma. Finally, the PCNC was freeze-dried to obtain solid powder of polyethylene glycolated cellulose nanocrystals.

[0068] Example 3

[0069] A preparation method of polyethylene glycolated cellulose nanocrystals, comprising:

[0070] S1. Mix polyethylene glycol and Lucas reagent according to a mass ratio of 1:1.2, and heat at 65 °C for 2.5 h to obtain a first intermediate, i.e., chlorinated polyethylene glycol;

[0071] S2. Mix 80 mL of cellulose nanocrystal suspension (the concentration of cellulose nanocrystals is about 3 wt%) with 50 mL of NaOH (NaOH concentration is 0.5 mol / L) solution, and stir at 55 °C for 4 hours. After the reaction, centrifuge and wash first, then adjust to pH = 7 with dilute hydrochloric acid, and then perform freeze-drying to finally obtain a second intermediate powder, denoted as DCNC;

[0072] S3. Mix the first intermediate and the second intermediate according to a mass ratio of 5.5:1 (2 g of the second intermediate powder is weighed), and add 100 g of water to prepare a solution, and react at 75 °C for 14 h to achieve the grafting of polyethylene glycol on the surface of cellulose nanocrystals. The grafted cellulose nanocrystals are denoted as PCNC; then centrifuge and wash with water, and adjust the PCNC solution to pH = 7 with sodium hydroxide. Put the solution into a dialysis membrane with a molecular weight cut-off of 14000 Da (g / mol), immerse the dialysis membrane in a container containing 4 L of water for 4 days, and change the water in the container every day to remove Zn 2+ 、Na + Plasma. Finally, the PCNC was freeze-dried to obtain solid powder of polyethylene glycolated cellulose nanocrystals.

[0073] Example 4

[0074] A preparation method of polyethylene glycolated cellulose nanocrystals, comprising:

[0075] S1. Mix polyethylene glycol and Lucas reagent according to a mass ratio of 1:1.1, and heat at 72 °C for 1.5 h to obtain a first intermediate, i.e., chlorinated polyethylene glycol;

[0076] S2. Mix 150 mL of cellulose nanocrystal suspension (the concentration of cellulose nanocrystals is about 1.5 wt%) with 50 mL of NaOH (NaOH concentration is 1.5 mol / L) solution, and stir at 58 °C for 2 hours. After the reaction, centrifuge and wash first, then adjust to pH = 7 with dilute hydrochloric acid, and then perform freeze-drying to finally obtain a second intermediate powder, denoted as DCNC;

[0077] S3. Mix the first intermediate and the second intermediate in a mass ratio of 4.8:1 (weigh 2 g of the second intermediate powder), add 100 g of water to prepare a solution, and react at 72 °C for 12 h to achieve the grafting of polyethylene glycol on the surface of cellulose nanocrystals. The grafted cellulose nanocrystals are denoted as PCNC; then centrifuge and wash with water, and adjust the pH of the PCNC solution to 7 with sodium hydroxide. Place the solution in a dialysis membrane with a molecular weight cut-off of 14,000 Da (g / mol), immerse the dialysis membrane in a container containing 4 L of water for 4 days, and change the water in the container every day to remove Zn 2+ and Na + ions. Finally, freeze-dry the PCNC to obtain the solid powder of polyethylene glycolylated cellulose nanocrystals.

[0078] Example 5

[0079] A method for preparing polyethylene glycolylated cellulose nanocrystals, comprising:

[0080] S1. Mix polyethylene glycol and Lucas reagent in a mass ratio of 1:0.9, and heat at 68 °C for 2 h to obtain the first intermediate, i.e., chloro-polyethylene glycol;

[0081] S2. Mix 110 mL of cellulose nanocrystal suspension (the concentration of cellulose nanocrystals is about 3 wt%) with 50 mL of NaOH (the concentration of NaOH is 1 mol / L) solution, and stir at 62 °C for 2.5 h. After the reaction, first centrifuge and wash, then adjust to pH = 7 with dilute hydrochloric acid, and then perform freeze-drying to finally obtain the second intermediate powder, denoted as DCNC;

[0082] S3. Mix the first intermediate and the second intermediate in a mass ratio of 5.2:1 (weigh 2 g of the second intermediate powder), add 100 g of water to prepare a solution, and react at 68 °C for 10 h to achieve the grafting of polyethylene glycol on the surface of cellulose nanocrystals. The grafted cellulose nanocrystals are denoted as PCNC; then centrifuge and wash with water, and adjust the pH of the PCNC solution to 7 with sodium hydroxide. Place the solution in a dialysis membrane with a molecular weight cut-off of 14,000 Da (g / mol), immerse the dialysis membrane in a container containing 4 L of water for 4 days, and change the water in the container every day to remove Zn 2+ and Na + ions. Finally, freeze-dry the PCNC to obtain the solid powder of polyethylene glycolylated cellulose nanocrystals.

[0083] Example 6

[0084] Prepare cement paste specimens with a water-cement ratio of 0.25 using portland cement and the polyethylene glycolated cellulose nanocrystals of Example 1. A total of four specimens are prepared according to the addition amounts of polyethylene glycolated cellulose nanocrystals of 0.05 wt%, 0.1 wt%, 0.2 wt%, and 0.3 wt%.

[0085] Example 7

[0086] Prepare cement paste specimens with a water-cement ratio of 0.3 using portland cement and the polyethylene glycolated cellulose nanocrystals of Example 1. A total of four specimens are prepared according to the addition amounts of polyethylene glycolated cellulose nanocrystals of 0.05 wt%, 0.1 wt%, 0.2 wt%, and 0.3 wt%.

[0087] Example 8

[0088] Prepare cement paste specimens with a water-cement ratio of 0.35 using portland cement and the polyethylene glycolated cellulose nanocrystals of Example 1. A total of four specimens are prepared according to the addition amounts of polyethylene glycolated cellulose nanocrystals of 0.05 wt%, 0.1 wt%, 0.2 wt%, and 0.3 wt%.

[0089] Comparative Example 1

[0090] Prepare cement paste specimens with a water-cement ratio of 0.25 using portland cement and unmodified cellulose nanocrystals. A total of four specimens are prepared according to the addition amounts of cellulose nanocrystals of 0.05 wt%, 0.1 wt%, 0.2 wt%, and 0.3 wt%.

[0091] Comparative Example 2

[0092] Prepare cement paste specimens with a water-cement ratio of 0.3 using portland cement and unmodified cellulose nanocrystals. A total of four specimens are prepared according to the addition amounts of cellulose nanocrystals of 0.05 wt%, 0.1 wt%, 0.2 wt%, and 0.3 wt%.

[0093] Comparative Example 3

[0094] Prepare cement paste specimens with a water-cement ratio of 0.35 using portland cement and unmodified cellulose nanocrystals. A total of four specimens are prepared according to the addition amounts of cellulose nanocrystals of 0.05 wt%, 0.1 wt%, 0.2 wt%, and 0.3 wt%.

[0095] Test the compressive strength of the cement specimens at 7 days and 28 days according to GB / T 50107—2010. CNC represents unmodified cellulose nanocrystals, PCNC represents polyethylene glycolated cellulose nanocrystals, and the numbers represent the added percentages. For example, CNC-0.1 means the addition amount of CNC is 0.1 wt% of the total amount of cement; and a blank control group is set, that is, cement paste without adding cellulose, denoted as R.

[0096] When the water-cement ratio is 0.25, the compressive strength is as Figure 1 shown, and the change rate of compressive strength is shown in Table 1;

[0097] Table 1

[0098]

[0099] When the water-cement ratio is 0.3, the compressive strength is as Figure 2 shown, and the change rate of compressive strength is shown in Table 2;

[0100] Table 2

[0101]

[0102] When the water-cement ratio is 0.35, the compressive strength is as Figure 3 shown, and the change rate of compressive strength is shown in Table 3;

[0103] Table 3

[0104]

[0105] From Figures 1 to 3 and Tables 1 to 3, it can be seen that compared with CNC, PCNC has a more obvious improvement in compressive strength. Among them, when the water-cement ratio is 0.25, PCNC can increase the compressive strength of cement paste by more than 30%, while CNC can only increase the compressive strength of cement paste by less than 20%; when the water-cement ratio is 0.3 and 0.35, PCNC can increase the compressive strength of cement paste by nearly 40%, while CNC only increases the compressive strength of cement paste by about 20%. Moreover, it is worth noting that when the water-cement ratio is 0.25, the addition of 0.3% CNC instead causes the 7-day and 28-day compressive strengths of cement paste to decrease by about 3.61% and 1.59% respectively, which may be due to insufficient dispersion effect, resulting in agglomeration of CNC in cement paste and defects in specimens. Generally speaking, the addition of PCNC has a much greater improvement in the 7-day and 28-day compressive strengths of cement paste than CNC.

[0106] Moreover, it can be seen that under the three water-cement ratio conditions of the present invention, the optimal addition amount of PCNC is 0.1 wt%, while in the prior art (CN 107473659 A), the optimal addition amount of CNC-g-PEG is 0.2 wt%. Therefore, in terms of the optimal dosage, this application reduces it by half and reduces the material usage cost.

[0107] The roles of traditional CNC in cement hydration include short-circuit diffusion and nucleation effect. The modification of CNC in the present invention successfully grafts PEG onto the surface of CNC through chemical reaction, changing and enhancing its mechanism of action.

[0108] The heat release rate and total heat release of the cement slurries in Examples 6 to 8 and Comparative Examples 1 to 3 were tested to evaluate the degree of hydration, and the results are as Figures 4 - 6 shown;

[0109] Figure 4 and Figure 5 are the curves of the heat release rate and total heat release of the cement slurry when the water-cement ratio is 0.25;

[0110] Figure 6 and Figure 7 are the curves of the heat release rate and total heat release of the cement slurry when the water-cement ratio is 0.3;

[0111] Figure 8 and Figure 9 are the curves of the heat release rate and total heat release of the cement slurry when the water-cement ratio is 0.35;

[0112] Figure 10 The molecular structural formula of CNC and the carbon nuclear magnetic resonance spectra of CNC and PCNC are given.

[0113] Among them, the connection between Figure (b) and the molecular structural formula is as follows: the chemical shifts of 63 ppm and 64 ppm are attributed to carbon (a) Figure 6 No.; the chemical shifts of 71.6 ppm and 74 ppm are attributed to carbon (a) Figure 2 , 3, 5 No.; the chemical shifts of 83 ppm and 88 ppm are attributed to carbon (a) Figure 4 No.; the chemical shift of 104 ppm is attributed to carbon (a) Figure 1 No. In the carbon nuclear magnetic resonance spectrum of PCNC in Figure (c), it can be clearly observed that new chemical shift changes of 72.1 ppm and 73.4 ppm appear between 71.6 - 74 ppm, which are attributed to the aldehyde groups (CH2O) formed by the grafting of carbon 2 and carbon 3 with PEG, while the change at 63 ppm is attributed to the newly added terminal methylene (CH2) group combined with OH after the grafting of carbon 6 with PEG. Therefore, the grafting of PRG is confirmed by the increase in the intensities of 72.1 ppm, 73.4 ppm, and 63 ppm in PCNC.

[0114] The following analyzes the different mechanisms of action of CNC and PCNC during the cement hydration process:

[0115] It is divided into 4 stages: (a) induction period; (B) acceleration period; (c) deceleration period; (d) stable period.

[0116] During the induction period, the cement immediately enters the pre-induction stage after being mixed with CNC and PCNC. In this stage, CNC is adsorbed on the surface of cement particles due to electrostatic interaction, forming a network-like covering, while for PCNC, the electrostatic interaction is weakened due to the grafting of PEG on its surface, so most of the PCNC is dispersed in the pore solution of the cement. After the cement particles come into contact with water, the hydration reaction occurs at the surface lattice defects, releasing Ca 2+ and OH - into the pore solution, resulting in the formation of a calcium-deficient and silicon-rich layer on the surface of the cement particles. The Ca 2+ in the solution is adsorbed on the surface to form a double electric layer, which hinders the continuous dissolution of the cement particles and leads to the formation of the induction period. When the concentration of calcium hydroxide (Ca(OH)2) meets the requirements for Ca(OH)2 crystallization, the double electric layer effect weakens and disappears, and the cement particles can continue to dissolve, which represents the end of the induction period and the start of the acceleration period. Due to the stronger dispersion ability of PCNC on cement particles due to the steric hindrance effect than the electrostatic repulsion of CNC, the cement particles in the PCNC group are more fully in contact with free water, so the cement particles in the PCNC group dissolve more fully. It can be observed in the hydration rate curve that the hydration rates of the 4 dosages in the PCNC group are always higher than those of the control group, and the duration of the induction period in the PCNC group has changed to a certain extent. Among them, as the dosage decreases, the duration of the induction period also shortens. The induction period of PCNC-0.05% ends nearly 1 h earlier. For the CNC group, except for the dosage of CNC-0.3%, the other 3 dosages have a delaying and inhibitory effect on the induction period compared with the control group due to the adsorption on the surface of the cement particles. The reason why no inhibition occurs for CNC-0.3% may be that due to the excessive concentration of CNC, agglomeration phenomenon occurs, so compared with the other 3 dosages, its adsorption effect on the cement particles weakens.

[0117] During the acceleration period, subsequently, during the accelerated hydration process, Ca(OH)2 continuously crystallizes, and C-S-H gel also continuously precipitates and accumulates. CNC and PCNC in the pore solution serve as additional nucleation sites, and the Ca 2+ adsorbed on their surfaces can react with the silicate ions (H3SiO4 - ) generated by the hydration of silicate in the solution, promoting the enrichment and growth of C-S-H gel wrapped around CNC and PCNC. At the same time, the two can also promote hydration through short-circuit diffusion. However, these two mechanisms show different effects for CNC and PCNC. Due to the grafting of PEG, PCNC not only has a higher surface area, thus providing more sites for Ca 2+ to react with H3SiO4 -The reaction provides more nucleation sites. Moreover, the channels where the short-circuit diffusion effect plays a role are composed of hydrophilic hydroxyl groups arranged. Due to the chemical grafting of PEG in PCNC, PEG contains a large number of hydroxyl groups, and these hydroxyl groups play a role due to hydrophilicity, so the role of this "water channel" becomes more prominent. Therefore, due to the combined action of the two effects, obvious differences can be observed between the CNC group and the PCNC group and the control group in the hydration rate curve. First, the first main exothermic peak corresponds to the silicate exothermic peak, and the order of the peak values of the exothermic rates is

[0118] PCNC-0.1% > PCNC-0.05% > PCNC-0.2% > PCNC-0.3% > CNC-0.1% > CNC-0.05% > CNC-0.2% > control group > CNC-0.3%. The peak values of the 4 dosages in the PCNC group are much larger than those in the CNC group and the control group. The peak values of the 3 dosages in the CNC group are slightly larger than those in the control group. The reason why the peak value of the CNC-0.3% dosage is less than that in the control group may be due to the agglomeration phenomenon of CNC. Among them, in the CNC and PCNC groups, the peak value of the PCNC-0.1% dosage is the largest, corresponding to a reaction rate of 2.95 mW / g, the peak value of the CNC-0.1% dosage is the largest, with a reaction rate of 2.78 mW / g, and the reaction rate corresponding to the peak value of the control group is 2.73 mW / g. The second exothermic peak corresponds to the sulfate depletion peak, and the apex of the peak represents the depletion of sulfate, marking the end of the reaction between tricalcium aluminate and gypsum. It can be seen from the hydration rate curve that both CNC and PCNC have obvious promoting effects on the reaction between tricalcium aluminate and gypsum, and the order of the peak values of the exothermic rates is PCNC-0.1% > PCNC-0.05% > PCNC-0.2% > PCNC-0.3% > CNC-0.1% > CNC-0.05% > CNC-0.2% > CNC-0.3% > control group. The peak values of the hydration rates of all dosages in the PCNC group are significantly higher than those in the CNC group and the control group. Among them, in the CNC and PCNC groups, the peak value of the PCNC-0.1% dosage is the largest, corresponding to a reaction rate of 3.01 mW / g, the peak value of the CNC-0.1% dosage is the largest, with a reaction rate of 2.72 mW / g, and the reaction rate corresponding to the peak value of the control group is 2.47 mW / g. Due to the combined action of the two mechanisms, in the cumulative heat of hydration release diagram, the final cumulative heat release of the PCNC-0.1% dosage has a 23.61% increase compared to the lowest control group, while the relatively better CNC-0.1% in the CNC group only has a 5.35% increase compared to the control group.

[0119] During the deceleration period, due to the hydration promotion effect of CNC and PCNC on aluminate, the sulfate depletion peak is advanced. Therefore, at 22 h of the deceleration period, only a small and indistinct shoulder peak appears in the hydration rate curve of the control group, which is the sulfate depletion peak of the control group. Since the hydration of aluminate in the control group is not affected, the hydration products normally transform from tricalcium sulfoaluminate hydrate (Aft) to monosulfate calcium sulfoaluminate (AFm), so the sulfate depletion peak appears later.

[0120] During the steady period, the hydration rates of the three groups are basically similar, and the hydration rates are very low at this time. At the same time, the hydration reactants decrease, and the hydration products intertwine to form a dense network structure, continuously filling the pores between cement particles, and the reaction basically tends to be stable.

[0121] The ion concentrations in the pore solution during the hydration stage of the cement slurries of Example 8 and Comparative Example 3 were measured, and the results are as Figure 11 shown, Figure 11 which are the concentrations of calcium, sulfur, aluminum and silicon in the pore solution at different hydration stages. The concentration changes of the four elements respectively represent the changes of various phases during the hydration process.

[0122] Ca: During the induction period, due to the rapid dissolution of the silicate phase and aluminate phase in the initial stage, the calcium content in the pore solution reaches about 27 mmol / L only after 10 minutes of hydration and continues until the concentration of Ca(OH)2 meets the requirements for Ca(OH)2 crystallization. Then, at 30 minutes, the content decreases due to the nucleation and precipitation of calcium hydroxide. Subsequently, due to the destruction of Ca(OH)2 saturation precipitation, the cement particles can continue to dissolve, and the calcium content in the solution continues to increase. During the acceleration period, it decreases sharply due to the large precipitation of C-S-H and unreacted silicates (C3S and C2S). Throughout this process, due to the combined action of the two mechanisms of nucleation effect and short-circuit diffusion, the calcium content in the PCNC group is always higher than that in the CNC group and the control group, that is, the calcium content: PCNC-0.1% > PCNC-0.3% > CNC-0.1% > CNC-0.3% > control group.

[0123] S: During the induction period, due to the continuous dissolution of gypsum, the sulfur content in the pore solution remains almost at a high level within the first few hours of cement hydration. During the acceleration period, when reaching the sulfate depletion peak, the gypsum is exhausted and the sulfur concentration rapidly drops to a very low level within a short time. The presence of CNC and PCNC leads to a slight increase in sulfur content during the induction period and advances the time point of the sharp decline. The promotion degree of the dosage of the PCNC group on the dissolution of gypsum is higher than that of the CNC group, and the degree of decline is also more obvious. In addition, CNC and PCNC can provide additional sites for the formation of ettringite during cement hydration. Among them, gypsum participates in this process. And due to the grafting of PEG, PCNC has more nucleation sites than CNC. Therefore, the degree of decline in the sulfur content of PCNC-0.1% and PCNC-0.3% is more significant than that of the two dosages of the CNC group. At the same time, it shows that PCNC has a more obvious promotion effect on the consumption of gypsum than CNC.

[0124] Since CNC and PCNC can promote the hydration of C3A through adsorption and short-circuit diffusion, and the formation of ettringite by the hydration of C3A requires the participation of gypsum, it indirectly accelerates and promotes the consumption of gypsum. This corresponds to the rule that the sulfate depletion peaks of the PCNC and CNC groups are higher than those of the control group in the hydration rate curve. At the same time, it can be found that from the induction period to the end of gypsum consumption, the sulfur content of the two dosages of the PCNC group is always higher than that of the two dosages of the CNC group, and the sulfur content of the two dosages of the CNC group is always higher than that of the control group. This corresponds to the rule of the size of the sulfate depletion peak corresponding to the peak value of the hydration rate in the hydration rate curve. These differences in changes indicate that the promotion effect of PCNC on the hydration of C3A is better than that of CNC. The possible reasons are as follows: First, the adsorption of CNC and PCNC on the surface of C3A. Although PEG is successfully grafted on the surface of CNC, there are still some negative charges on the surface of PCNC. Both can be adsorbed on the surface of C3A. Since the surface of cellulose nanocrystals contains a large number of hydrophilic hydroxyl groups, more free water can be brought for the hydration of C3A. And due to the grafting of PEG on the surface of PCNC, the sulfate depletion peak of the PCNC group is higher. Second, the short-circuit diffusion effect, and the mechanism is the same as that of the hydration of the silicate phase.

[0125] Al: During the induction period, aluminum comes from the rapid dissolution of C3A in the ordinary Portland cement paste. The dissolution of C3A is slowed down due to being absorbed onto C3A. This process explains the reason for the decrease in aluminum content over time, as Figure 11As shown in the figure, in the acceleration period, after the gypsum is exhausted, the redissolution of C3A is accelerated; the aluminum content increases with time and is then controlled by the dosage of CNC and PCNC. At 10 minutes, in the presence of CNC and PCNC, the aluminum content in the pore solution was observed to be slightly higher due to the combined effect of CNC and PCNC on the adsorption and short-circuit diffusion of C3A. Among them, the aluminum content of the two dosages of the PCNC group was higher than that of the CNC combination control group, indicating that the initial adsorption effect of PCNC was weaker than that of CNC. Then, due to the hydration of the aluminate phase, the aluminum content decreased, and the aluminum content of the four dosages of the PCNC and CNC groups gradually decreased before the end of the acceleration period. Among them, the aluminum content of the two dosages of the PCNC group decreased slightly more than that of the two dosages of the CNC group, but the changes were not obvious. With the end of the acceleration period, the aluminate phase redissolved and the aluminum content in the pore solution gradually increased. Among them, the increase of PCNC-0.1% was the largest, indicating that PCNC had a certain promoting effect on the dissolution of the aluminate phase compared with the adsorption of CNC.

[0126] Si: During the whole process, the silicon content is always at a very low level. During the induction period, the silicon comes from the rapid dissolution of the silicate phase in the ordinary silicate cement paste, and the content gradually increases. During the acceleration period, with the large-scale generation of CSH gel, the content gradually decreases. During the deceleration period, the silicate phase continues to dissolve, and the silicon content gradually increases. The silicon content of the PCNC and CNC groups can show their promotion effect on the formation of CSH gel. CNC can also serve as an additional nucleation site to complex Ca 2+ and H3SiO4 - , promoting the formation of CSH gel coating on the surface of CNC. PCNC can provide more nucleation sites compared with CNC due to the grafting of PEG. From the silicon content graph, it can be seen that the sharp decline of silicon content in PCNC-0.1% and PCNC-0.3% during the acceleration period is higher than that in the CNC group, and the lowest silicon content of PCNC-0.1% and PCNC-0.3% is earlier than that of the CNC group, corresponding to the advance of the silicate exothermic peak in the hydration rate curve.

[0127] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing polyethylene glycolized cellulose nanocrystals, characterized in that ,include: Mixing polyethylene glycol and Lucas reagent to react to obtain a first intermediate; The cellulose nanocrystal suspension and the sodium hydroxide solution are mixed and reacted to obtain a second intermediate; The first intermediate and the second intermediate are mixed and reacted to obtain polyethylene glycol-modified cellulose nanocrystals.

2. The method for preparing PEGylated cellulose nanocrystals according to claim 1, characterized in that The step of mixing polyethylene glycol and Lucas reagent for reaction comprises: Mix polyethylene glycol and Lucas reagent in a mass ratio of 1:(0.8-1.2) and react at 65-75°C for 1.5-3h.

3. The method for preparing PEGylated cellulose nanocrystals according to claim 1, characterized in that , the mass concentration of the cellulose nanocrystal suspension is 1.5-3wt%.

4. The method for preparing PEGylated cellulose nanocrystals according to claim 3, characterized in that , the concentration of the sodium hydroxide solution is 0.5-2 mol / L, and the volume ratio of the cellulose nanocrystal suspension to the sodium hydroxide solution is (1-3):

1.

5. The method for preparing PEGylated cellulose nanocrystals according to claim 1, characterized in that The step of mixing the cellulose nanocrystal suspension and the sodium hydroxide solution for reaction comprises: The cellulose nanocrystal suspension is mixed with a sodium hydroxide solution, stirred and reacted at 55-65° C. for 2-4 hours, the product is centrifuged and washed, the pH is adjusted to neutral, and finally freeze-dried.

6. The method for preparing PEGylated cellulose nanocrystals according to claim 1, characterized in that , the mass ratio of the first intermediate to the second intermediate is (4.5-5.5):

1.

7. The method for preparing PEGylated cellulose nanocrystals according to claim 1, characterized in that , the mixing of the first intermediate and the second intermediate for reaction comprises: The first intermediate and the second intermediate are mixed and prepared into a solution, and reacted at 65-75° C. for 8-14 hours to obtain a polyethylene glycolized cellulose nanocrystal solution.

8. The method for preparing PEGylated cellulose nanocrystals according to claim 7, characterized in that , the method further comprises: The pH of the PEGylated cellulose nanocrystal solution is adjusted to neutral, then centrifuged to remove solids, and the remaining solution is dialyzed with water to remove ionic impurities, and finally freeze-dried to obtain PEGylated cellulose nanocrystals.

9. A polyethylene glycol cellulose nanocrystal, characterized in that , is obtained by the method for preparing polyethylene glycolized cellulose nanocrystals according to any one of claims 1-8.

10. A cement-based composite material, characterized in that , the cement-based composite material includes the polyethylene glycolized cellulose nanocrystals as described in claim 9.

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