阅读说明：本技术 一种制备硅烷偶联剂-二氧化硅-植物纤维复合物的方法 (Method for preparing silane coupling agent-silicon dioxide-plant fiber composite ) 是由 赵丽 刘辰一 李�杰 曹潇允 郭新萍 朱瑞 于 2021-08-06 设计创作，主要内容包括：本发明公开一种制备硅烷偶联剂-二氧化硅-植物纤维复合物的方法：S1、植物纤维预处理；S2、制备硅烷偶联剂水解液；S3、制备硅烷偶联剂-植物纤维复合物；S4、制备二氧化硅纳米粒子分散液；S5、制备硅烷偶联剂-二氧化硅纳米粒子-植物纤维复合物。本发明利用硅烷偶联剂水解形成的硅醇基团(Si-OH)、二氧化硅的Si-OH、植物纤维表面的羟基(-OH)三者之间的共价作用,使二氧化硅纳米粒子接枝在植物纤维表面；利用硅烷偶联剂形成的疏水膜阻碍有害离子入侵,提高纤维体积稳定性,利用二氧化硅的火山灰活性降低纤维周围碱性和氢氧化钙含量,改善纤维与水泥基体界面微结构,协同提高植物纤维在水泥基体中的耐蚀性和粘结性能。(The invention discloses a method for preparing a silane coupling agent-silicon dioxide-plant fiber compound, which comprises the following steps: s1, pretreating the plant fibers; s2, preparing silane coupling agent hydrolysate; s3, preparing a silane coupling agent-plant fiber compound; s4, preparing a silicon dioxide nanoparticle dispersion liquid; s5, preparing the silane coupling agent-silica nanoparticle-plant fiber composite. The invention makes use of the covalent interaction among silanol groups (Si-OH) formed by the hydrolysis of a silane coupling agent, Si-OH of silicon dioxide and hydroxyl groups (-OH) on the surface of plant fibers to graft silicon dioxide nano particles on the surface of the plant fibers; the hydrophobic membrane formed by the silane coupling agent is used for preventing harmful ions from invading, the volume stability of the fiber is improved, the pozzolanic activity of the silicon dioxide is used for reducing the alkalinity and calcium hydroxide content around the fiber, the interface microstructure of the fiber and a cement matrix is improved, and the corrosion resistance and the bonding property of the plant fiber in the cement matrix are synergistically improved.)

1. A method for preparing a silane coupling agent-silica-plant fiber composite, comprising the steps of:

s1, preprocessing the plant fiber;

s2, preparing silane coupling agent hydrolysate;

s3, preparing a silane coupling agent-plant fiber composite: immersing the pretreated plant fibers into the silane coupling agent hydrolysate for full immersion, taking out and airing;

s4, preparing a silicon dioxide nanoparticle dispersion liquid;

s5, preparing a silane coupling agent-silica nanoparticle-plant fiber compound: and spraying the silicon dioxide nano particle dispersion liquid on the silane coupling agent-plant fiber compound, and drying to obtain the silicon dioxide nano particle composite material.

2. The method for preparing a silane coupling agent-silica-plant fiber composite according to claim 1, wherein the step S1 of pre-treating the plant fiber comprises the following steps:

s1-1, cutting the plant fibers according to the requirements of the toughened cement-based composite material;

s1-2, cleaning the surface of the plant fiber after cutting;

s1-3, soaking the plant fibers in an alkaline solution after cleaning; after soaking, cleaning to be neutral, and then drying.

3. The method for preparing a silane coupling agent-silica-plant fiber composite according to claim 2, wherein the alkaline solution is selected from NaOH or KOH solution having pH of 13-14 at step S1-3; the soaking time is 0.5-1 hour; the drying temperature is 60-80 ℃.

4. The method for preparing the silane coupling agent-silica-plant fiber composite as claimed in claim 1, wherein the step S2 of preparing the silane coupling agent hydrolysate comprises the steps of:

s2-1, dissolving the silane coupling agent in a mixed system of absolute ethyl alcohol and deionized water, and uniformly stirring to obtain a mixed solution;

and S2-2, adding glacial acetic acid into the mixed solution to adjust the pH value to acidity, and stirring to obtain the silane coupling agent hydrolysate.

5. The method of claim 4, wherein the silane coupling agent is selected from any one of KH550, KH560, KH570 and KH792 in the step S2-1; the volume ratio of the absolute ethyl alcohol to the deionized water is (4-10): 1; the concentration of the silane coupling agent in the mixed solution is 0.1-1.0 mol/L.

6. The method for preparing the silane coupling agent-silica-plant fiber composite as claimed in claim 4, wherein the silane coupling agent hydrolysate is obtained by adding 10-30 wt% of glacial acetic acid into the mixed solution to adjust the pH value to 4-5 and electromagnetically stirring for 0.5-2 hours in step S2-2.

7. The method for preparing a silane coupling agent-silica-plant fiber composite according to claim 1, wherein the step S3 of preparing the silane coupling agent-plant fiber composite is: immersing the pretreated plant fibers into the silane coupling agent hydrolysate, performing ultrasonic treatment for 0.5-1 hour to fully immerse the plant fibers, and then taking out and drying the plant fibers; the bath ratio of the plant fiber immersed in the silane coupling agent hydrolysate is (30-50): 1.

8. the method for preparing a silane coupling agent-silica-plant fiber composite according to claim 1, wherein the step S4 of preparing a silica nanoparticle dispersion liquid: and ultrasonically dispersing the silicon dioxide nano particles in deionized water to obtain silicon dioxide nano particle dispersion liquid.

9. The method for preparing a silane coupling agent-silica-plant fiber composite according to claim 8, wherein the concentration of the silica nanoparticles is 2-20 mg/mL; the particle size of the silicon dioxide nano particles is 5-100 nm.

10. The method for preparing the silane coupling agent-silica-plant fiber composite according to claim 1, wherein the step S5 is to prepare the silane coupling agent-silica nanoparticle-plant fiber composite: spreading the dried silane coupling agent-plant fiber composite on gauze in the step S3, filling the silicon dioxide nano dispersion liquid into a spray can, uniformly spraying the silane coupling agent-plant fiber composite on the gauze in a spraying mode, and uniformly spraying the silane coupling agent-plant fiber composite on the back of the gauze; repeating the spraying process for 2-5 times to ensure that the mass ratio of the plant fiber to the nano silicon dioxide nano particles is as follows: 1 g: (30-100) mg; the drying temperature is 115 ℃ and 125 ℃, and the drying time is 12-15 hours.

Technical Field

The invention relates to the technical field of building materials, in particular to a method for preparing a silane coupling agent-silicon dioxide-plant fiber compound.

Background

Cement-based materials are currently the most widely used building materials in the world, but are brittle materials and prone to cracking. Research shows that the fiber has good inhibiting effect on cracking of the cement-based material. The steel fiber and the artificial synthetic fiber can improve the toughness of the concrete to a certain extent, but also improve the cost of the concrete. In order to effectively reduce the cost of fiber concrete, researchers began to replace traditional synthetic fibers with plant fibers which are widely distributed in the nature, low in price and convenient to obtain materials. The plant fiber is applied to the cement-based composite material, can improve the toughness, can promote sustainable development, has ecological effect, and accords with the important strategy of developing circular economy.

The strong adhesion of the interface between the fiber and the cement matrix is a necessary condition for obtaining high toughness of the fiber modified cement-based composite material. However, the interface adhesion between the plant fiber and the cement matrix is poor, and it is necessary to modify the surface of the plant fiber to improve the interface adhesion between the plant fiber and the cement matrix. The corrosion resistance problem of the plant fiber in the cement-based composite material also limits the application of the plant fiber in the field of building materials. The calcium hydroxide generated by cement hydration is dissolved in water, so that the pore solution of the cement paste is alkaline. The alkaline environment can dissolve hemicellulose and lignin in the plant fiber, and the structure of the fiber is damaged, so that the strength and the toughness of the fiber are reduced. In addition, calcium ions enter the internal pores of the plant fibers for crystallization, so that the fibers are mineralized, gradually lose flexibility and are hardened, and brittle fracture is easy to occur. Therefore, the method improves the corrosion resistance of the plant fiber in the cement matrix and the interface bonding performance between the plant fiber and the cement matrix, and is a precondition for toughening the cement-based composite material by replacing the artificial synthetic fiber with the plant fiber.

Disclosure of Invention

Aiming at the problem that the corrosion resistance and the interface bonding property of plant fiber in a cement matrix are poor, the invention provides a method for preparing a silane coupling agent-silicon dioxide-plant fiber compound, which utilizes the covalent action among a silanol group (Si-OH) formed after the silane coupling agent is hydrolyzed, the Si-OH of silicon dioxide and hydroxyl (-OH) on the surface of plant fiber to ensure that silicon dioxide nano particles are firmly grafted on the surface of the plant fiber; a hydrophobic film formed by a silane coupling agent is used for preventing harmful ions from invading, the volume stability of the plant fiber is improved, the pozzolanic activity of the silicon dioxide nano particles is used for reducing the alkalinity and calcium hydroxide content around the fiber, the interface microstructure of the fiber and a cement matrix is improved, and the corrosion resistance and the fiber-matrix interface bonding performance of the plant fiber in the cement matrix are synergistically improved; the method is simple and easy to operate, is expected to be applied to the green building industry on a large scale, and reduces the carbon emission of the building.

The invention is realized by the following technical scheme:

a method for preparing a silane coupling agent-silica-plant fiber composite, comprising the steps of:

s1, preprocessing the plant fiber;

s2, preparing silane coupling agent hydrolysate;

s3, preparing a silane coupling agent-plant fiber composite: immersing the pretreated plant fibers into the silane coupling agent hydrolysate for full immersion, taking out and airing; ventilating and airing to keep the activity of the silane coupling agent;

s4, preparing a silicon dioxide nanoparticle dispersion liquid;

s5, preparing a silane coupling agent-silica nanoparticle-plant fiber compound: and spraying the silicon dioxide nano particle dispersion liquid on the silane coupling agent-plant fiber compound, and drying to obtain the silicon dioxide nano particle composite material.

The method of the invention utilizes the covalent interaction among silanol groups (Si-OH) formed after the silane coupling agent is hydrolyzed, Si-OH of silicon dioxide and hydroxyl (-OH) on the surface of the plant fiber to ensure that silicon dioxide nano particles are firmly grafted on the surface of the plant fiber; the hydrophobic membrane formed by the silane coupling agent is used for preventing harmful ions from invading, the volume stability of the plant fiber is improved, the pozzolanic activity of the silicon dioxide nano particles is used for reducing the alkalinity and calcium hydroxide content around the fiber, the interface microstructure of the fiber and a cement matrix is improved, and the corrosion resistance and the fiber-matrix interface bonding performance of the plant fiber in the cement matrix are synergistically improved.

Specifically, the plant fiber can be selected from plant fibers such as sisal fiber, coconut shell fiber and the like.

Further, step S1, pre-treating the plant fiber, including the following steps:

s1-1, cutting the plant fibers according to the requirements of the toughened cement-based composite material;

s1-2, cleaning the surface of the plant fiber after cutting; cleaning impurities on the surface of the plant fiber with clean water;

s1-3, soaking the plant fibers in an alkaline solution after cleaning; after soaking, cleaning to be neutral, and then drying.

Further, step S1-3, the alkaline solution is selected from NaOH or KOH solution with pH of 13-14; the soaking time is 0.5-1 hour; the drying temperature is 60-80 ℃.

Further, the step S2 of preparing the silane coupling agent hydrolysate includes the following steps:

s2-1, dissolving the silane coupling agent in a mixed system of absolute ethyl alcohol and deionized water, and uniformly stirring to obtain a mixed solution;

and S2-2, adding glacial acetic acid into the mixed solution to adjust the pH value to acidity, and stirring to obtain the silane coupling agent hydrolysate.

Further, in step S2-1, the silane coupling agent is selected from any one of KH550, KH560, KH570 and KH 792; the volume ratio of the absolute ethyl alcohol to the deionized water is (4-10): 1; the concentration of the silane coupling agent in the mixed solution is 0.1-1.0 mol/L.

Further, step S2-2, adding 10-30 wt% of glacial acetic acid into the mixed solution to adjust the pH value to 4-5, and electromagnetically stirring for 0.5-2 hours to obtain the silane coupling agent hydrolysate.

Further, step S3, preparing a silane coupling agent-plant fiber composite: immersing the pretreated plant fibers into the silane coupling agent hydrolysate, performing ultrasonic treatment for 0.5-1 hour to fully immerse the plant fibers, and then taking out and drying the plant fibers; the bath ratio of the plant fiber immersed in the silane coupling agent hydrolysate is (30-50): 1. specifically, the plant fiber can be placed in a ventilation position and naturally dried in the presence of illumination; the airing standard is as follows: when the surface is covered with absorbent paper, the absorbent paper is not significantly wetted.

Further, step S4, preparing a silica nanoparticle dispersion liquid: ultrasonically dispersing the silicon dioxide nano particles in deionized water to obtain silicon dioxide nano particle dispersion liquid.

Further, the concentration of the silicon dioxide nano particles is 2-20 mg/mL; the particle size of the silicon dioxide nano particles is 5-100 nm.

Further, step S5, preparing a silane coupling agent-silica nanoparticle-plant fiber composite: spreading the dried silane coupling agent-plant fiber composite on gauze in the step S3, filling the silicon dioxide nano dispersion liquid into a spray can, uniformly spraying the silane coupling agent-plant fiber composite on the gauze in a spraying mode, and uniformly spraying the silane coupling agent-plant fiber composite on the back of the gauze; repeating the spraying process for 2-5 times to ensure that the mass ratio of the plant fiber to the nano silicon dioxide nano particles is 1 g: (30-100) mg; the drying temperature is 115 ℃ and 125 ℃, and the drying time is 12-15 hours.

Specifically, in step S5, preparing the silane coupling agent-silica nanoparticle-plant fiber composite: spreading the silane coupling agent-plant fiber composite subjected to ventilation and air drying in the step S3 on gauze, uniformly spraying a spraying pot filled with the silicon dioxide nano dispersion liquid on the gauze once by adopting a spraying mode, and uniformly spraying the silicon dioxide nano dispersion liquid on the back of the gauze once; in order to increase the amount of the silicon dioxide nano particles coated on the surface of the plant fiber, after the plant fiber is dried for 30-60 minutes at room temperature, shaking gauze to change the angle of the fiber, then carrying out next spraying, repeating the spraying process for 2-5 times to ensure that the mass ratio of the plant fiber to the nano silicon dioxide nano particles is 1 g: (30-100) mg, wherein the mass of the plant fiber is the mass after pretreatment and drying; and (3) placing the plant fiber in a blast drying box for drying at the temperature of 115-125 ℃ for 12-15 hours to ensure that stable covalent bonds are formed among the plant fiber, the silane coupling agent and the silicon dioxide nano particles.

The invention has the beneficial effects that:

(1) the invention adopts a two-step method to modify the plant fiber, firstly the silane coupling agent is coated on the surface of the plant fiber, and then the silicon dioxide nano particles are coated on the surface of the plant fiber. If the hydrolyzed solution of the silane coupling agent is firstly compounded with the silica nanoparticles, and then the plant fiber is immersed into the composite dispersion, a competition relationship is formed between silanol groups (Si-OH) formed by hydrolysis of the silane coupling agent and Si-OH of the silica nanoparticles when the Si-OH reacts with hydroxyl groups (-OH) on the surface of the plant fiber, so that the film formation of the silane coupling agent on the surface of the plant fiber is influenced, and the hydrophobic effect is greatly reduced.

(2) According to the invention, the silane coupling agent-plant fiber compound is dried by adopting a natural airing method, so that the condensation reaction of Si-OH groups of the silane coupling agent in a high-temperature environment can be effectively avoided, the activity of the silane coupling agent can be retained, and the redundant moisture can be removed.

(3) The method adopts a spraying method, the silicon dioxide nanoparticle dispersion liquid is sprayed to the surface of the silane coupling agent-plant fiber composite, and the silane coupling agent-plant fiber composite is not immersed in the silicon dioxide nanoparticle dispersion liquid, so that the silane coupling agent coated on the surface of the plant fiber can be prevented from being secondarily hydrolyzed and falling off.

(4) According to the invention, the silane coupling agent-silica nanoparticle-plant fiber composite is dried at a higher temperature (115-.

(5) The silicon dioxide nano particles coated on the surface of the plant fiber have higher activity, can perform volcanic ash reaction with hydration product calcium hydroxide, can reduce the alkalinity and calcium hydroxide content around the fiber, reduce the erosion to the plant fiber, and can improve the cohesiveness of the interface of the plant fiber and a water matrix by the generated hydrated calcium silicate, thereby being applicable to toughening cement-based composite materials.

(6) The silane coupling agent forms a hydrophobic film on the surface of the plant fiber, so that the hydrophilicity of the plant fiber can be reduced, on one hand, the suction of a pore solution of cement slurry can be reduced, the corrosion resistance of the plant fiber is improved, on the other hand, the volume stability of the plant fiber is improved, the microstructure of a transition region of the plant fiber and a cement matrix interface is optimized, and the bonding performance of the fiber-matrix interface is improved.

(7) In the silane coupling agent-silicon dioxide nano particle-plant fiber compound prepared by the invention, the synergistic effect of the alkane coupling agent coated on the surface of the plant fiber and the silicon dioxide nano particle can improve the corrosion resistance of the plant fiber in a cement matrix, and simultaneously improve the bonding characteristic of the interface of the plant fiber and the cement matrix, so that the plant fiber has a great application prospect in the aspect of toughening and crack-resistant cement-based materials.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.

FIG. 1 is a Scanning Electron Microscope (SEM) of pretreated sisal fibers in example 1 of the present invention;

FIG. 2 is an SEM image of the silane coupling agent-silica nanoparticle-sisal fiber composite in example 1 of the present invention;

FIG. 3 is an SEM image of the silane coupling agent-silica nanoparticle-sisal fiber composite after high-speed shearing treatment;

FIG. 4 is an SEM image of the silane coupling agent-silica nanoparticle-sisal fiber composite after ultrasonic oscillation treatment.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

A method of preparing a silane coupling agent-silica-plant fiber composite comprising the steps of: wherein the plant fiber is sisal fiber;

s1, preprocessing sisal fibers; the pretreatment process comprises the following specific steps:

s1-1, cutting the sisal fibers into long fibers according to the requirements of the toughened cement-based composite material

Short fibers with a length of 100 mm;

s1-2, after cutting, cleaning the sand and the scraps on the surface of the sisal fibers with clean water, and drying in a blast drier at 60 ℃;

s1-3, after cleaning, soaking the sisal fibers in 0.15mol/L NaOH solution for 30 minutes; repeatedly washing the soaked materials with clear water to be neutral, and drying the materials in a forced air drier at 60 ℃; namely finishing the pretreatment of the sisal fibers;

s2, preparing silane coupling agent hydrolysate; wherein the preparation of the silane coupling agent hydrolysate comprises the following steps:

s2-1, dissolving a silane coupling agent KH550 in a mixed system of absolute ethyl alcohol and deionized water, and uniformly stirring to obtain a mixed solution; wherein: the volume ratio of the absolute ethyl alcohol to the deionized water is 4: 1, the concentration of KH550 in the mixed solution is 0.2 mol/L;

s2-2, adding 30 wt% of glacial acetic acid into the mixed solution to adjust the pH to 4.66, and electromagnetically stirring for 1 hour to obtain silane coupling agent (KH550) hydrolysate;

s3, preparing a silane coupling agent-sisal fiber compound: soaking 6.0g of the pretreated sisal fibers in 200mL of silane coupling agent (KH550) hydrolysate, performing ultrasonic treatment for 0.5 hour to fully soak the sisal fibers, then placing the taken-out sisal fibers on gauze to drain excessive moisture, and naturally airing the sisal fibers in a ventilated place for 24 hours to obtain a silane coupling agent-sisal fiber compound;

s4, preparing a silicon dioxide nanoparticle dispersion liquid: adding 0.3g of silicon dioxide nano particles into 20mL of deionized water, electromagnetically stirring for 0.5 hour, then ultrasonically oscillating for 30 minutes at the power of 600W to obtain silicon dioxide nano particle dispersion, and then loading the silicon dioxide nano particle dispersion into a 100mL spraying pot with scales for next spraying; the diameter of the silicon dioxide nano-particles is 50 nm;

s5, preparing a silane coupling agent-silicon dioxide nano particle-sisal fiber compound: spreading the silane coupling agent-sisal fiber compound obtained after air drying in the step S3 on gauze, uniformly spraying a spray can filled with the silicon dioxide nano dispersion liquid on the gauze in a spray mode aiming at the silane coupling agent-sisal fiber compound, and uniformly spraying the compound from the back of the gauze; in order to increase the amount of silicon dioxide nano particles coated on the surface of the sisal fibers, after the sisal fibers are aired for 30 minutes at room temperature, the gauze is shaken to change the angle of the fibers, and then the next spraying is carried out; the total spraying amount of the front side and the back side is 5mL each time, repeating the step for 4 times, and completely spraying 20mL of silicon dioxide nanoparticle dispersion liquid to the surface of the sisal fibers, wherein the mass ratio of the sisal fibers to the silicon dioxide nanoparticles is 1g/50 mg; and after the spraying is finished, drying for 15 hours in a blast drying oven at 120 ℃ to obtain the silane coupling agent-silicon dioxide nano particle-sisal fiber compound.

And (3) testing:

taking the sisal fibers pretreated in the above example 1, and testing the sisal fibers by using a Scanning Electron Microscope (SEM), wherein the result is shown in FIG. 1; the silane coupling agent-silica nanoparticle-sisal fiber composite prepared in the above example 1 was tested by SEM, as shown in fig. 2.

Taking the silane coupling agent-silicon dioxide nano particle-sisal fiber composite prepared in the embodiment 1 to perform a high-speed shear test; the high-speed shearing test is to simulate the stress condition of the fiber in a stirring pot; the specific method comprises the following steps: adding two thirds of water in a beaker, adding the prepared silane coupling agent-silicon dioxide nano particle-sisal fiber compound, adding magnetons, shearing at high speed for 10 minutes, taking out and drying, and observing SiO on the surface of the fiber under an electron scanning microscope₂The particles were exfoliated, and the results are shown in FIG. 3, where SiO is shown in FIG. 3₂The particles are stably coated on the surface of the plant fiber.

Taking the silane coupling agent-silicon dioxide nano particle-sisal fiber compound prepared in the embodiment 1 to perform an ultrasonic oscillation test, wherein the ultrasonic oscillation treatment is a commonly used dispersing means for nano materials, and nano aggregates are dispersed under the oscillation action of ultrasonic waves; the experiment adopts an ultrasonic method to verify whether the modified fiber surface silica nanoparticles are stable under the action of ultrasonic oscillation; the specific method comprises the following steps: two thirds of the volume of water was added to the beaker, the modified fiber was added, the mixture was shaken at 600W for 10 minutes in an ultrasonic shaker, the dried mixture was taken out, and the falling-off of silica particles on the surface of the fiber was observed under a scanning electron microscope, and as a result, as shown in FIG. 4, it was similarly seen from FIG. 4 that the silica particles were stably coated on the surface of the plant fiber.

The method of the invention focuses on 'stable coating', and the shearing and ultrasonic oscillation test is a destructive test on the compounded fiber, because in concrete production practice, stirring and friction can play a role in abrasion damage on the coating layer on the surface of the fiber.

Example 2

A method of preparing a silane coupling agent-silica-plant fiber composite comprising the steps of: wherein the plant fiber is coconut shell fiber;

s1, preprocessing the coconut fibers; the pretreatment process comprises the following specific steps:

s1-1, cutting the coconut fibers into short fibers with the length of 50mm according to the requirements of the toughened cement-based composite material;

s1-2, after cutting, cleaning the silt and the scraps on the surface of the coconut shell fiber with clear water, and drying in a blast drier at 60 ℃;

s1-3, after cleaning, soaking the sisal fibers in 0.2mol/L NaOH solution for 30 minutes; repeatedly washing the soaked coconut shell fibers to be neutral by using clear water, and drying the coconut shell fibers in a forced air dryer at 60 ℃ to finish the pretreatment of the coconut shell fibers;

s2, preparing silane coupling agent hydrolysate; wherein the preparation of the silane coupling agent hydrolysate comprises the following steps:

s2-1, dissolving a silane coupling agent KH792 in a mixed system of absolute ethyl alcohol and deionized water, and uniformly stirring to obtain a mixed solution; wherein: the volume ratio of the absolute ethyl alcohol to the deionized water is 9: 1, the concentration of KH792 in the mixed solution is 0.1 mol/L;

s2-2, adding 10 wt% of glacial acetic acid into the mixed solution to adjust the pH to 4.98, and electromagnetically stirring for 0.5 hour to obtain a silane coupling agent (KH792) hydrolysate;

s3, preparing a silane coupling agent-coconut shell fiber compound: soaking 4.0g of the pretreated coconut shell fiber in 150mL of silane coupling agent (KH792) hydrolysate, performing ultrasonic treatment for 0.5 hour to fully soak the coconut shell fiber, placing the fished coconut shell fiber on gauze to drain excessive water, and naturally airing the coconut shell fiber in a ventilated place for 24 hours to obtain a silane coupling agent-coconut shell fiber compound;

s4, preparing a silicon dioxide nanoparticle dispersion liquid: adding 0.3g of silicon dioxide nano particles into 30mL of deionized water, electromagnetically stirring for 0.5 hour, then ultrasonically oscillating for 30 minutes at the power of 600W to obtain silicon dioxide nano particle dispersion, and then loading the silicon dioxide nano particle dispersion into a 100mL spraying pot with scales for next spraying; the diameter of the silicon dioxide nano particles is 10 nm;

s5, preparing a silane coupling agent-silicon dioxide nano particle-coconut shell fiber compound: spreading the silane coupling agent-coconut fiber compound obtained after air drying in the step S3 on gauze, uniformly spraying a spray can filled with the silicon dioxide nano dispersion liquid on the gauze in a spraying mode aiming at the silane coupling agent-coconut fiber compound on the gauze, and uniformly spraying the compound from the back of the gauze; in order to increase the amount of silicon dioxide nano particles coated on the surface of the coconut shell fiber, after the coconut shell fiber is aired for 60 minutes at room temperature, the gauze is shaken to change the angle of the fiber, and then the next spraying is carried out; the total spraying amount of the front side and the back side is 10mL each time, repeating the steps for 3 times, and completely spraying 30mL of silicon dioxide nanoparticle dispersion liquid to the surface of the coconut shell fiber, wherein the mass ratio of the coconut shell fiber to the silicon dioxide nanoparticles is 1g/75 mg; and after the spraying is finished, drying the mixture in a blast drying oven at 120 ℃ for 12 hours to obtain the silane coupling agent-silicon dioxide nano particle-coconut shell fiber compound.

The method of the invention utilizes the covalent interaction among silanol groups (Si-OH) formed after the silane coupling agent is hydrolyzed, Si-OH of silicon dioxide and hydroxyl (-OH) on the surface of the plant fiber to ensure that silicon dioxide nano particles are firmly grafted on the surface of the plant fiber; the hydrophobic membrane formed by the silane coupling agent is used for preventing harmful ions from invading, the volume stability of the plant fiber is improved, the pozzolanic activity of the silicon dioxide nano particles is used for reducing the alkalinity and calcium hydroxide content around the fiber, the interface microstructure of the fiber and a cement matrix is improved, and the corrosion resistance and the fiber-matrix interface bonding performance of the plant fiber in the cement matrix are synergistically improved. The synergistic effect of the alkane coupling agent coated on the surface of the plant fiber and the silicon dioxide nano particles in the compound prepared by the invention can improve the corrosion resistance of the plant fiber in a cement matrix, and simultaneously improve the bonding characteristic of the plant fiber and the cement matrix interface, so that the plant fiber has a great application prospect in the aspect of toughening and crack-resistant cement-based materials.

The above-mentioned preferred embodiments of the present invention are provided for illustration only and not for the purpose of limiting the invention. Obvious variations or modifications of the present invention are within the scope of the present invention.