CN110915801A

CN110915801A - Modified carboxymethyl chitosan pesticide microsphere and preparation method thereof

Info

Publication number: CN110915801A
Application number: CN201911272048.7A
Authority: CN
Inventors: 周红军; 周新华; 赵明; 陈龙; 郝丽
Original assignee: Zhongkai University of Agriculture and Engineering
Current assignee: Zhongkai University of Agriculture and Engineering
Priority date: 2019-12-11
Filing date: 2019-12-11
Publication date: 2020-03-27

Abstract

The invention discloses a preparation method of modified carboxymethyl chitosan pesticide microspheres, which takes allyl glycidyl ether as an intermediate, and grafts an organic silicon surfactant onto a molecular chain of carboxymethyl chitosan to prepare an amphiphilic modified carboxymethyl chitosan carrier; then the prepared modified carboxymethyl chitosan carrier is used for encapsulating pesticides, and the modified carboxymethyl chitosan pesticide microspheres are self-assembled. The modified carboxymethyl chitosan pesticide microsphere prepared by the invention can be well adhered to the leaves and well spread on the leaves, and can also effectively slow down the decomposition of the pesticide under ultraviolet rays, improve the photostability of the pesticide, continuously release the pesticide and not influence the efficacy exertion of the pesticide. Therefore, the modified carboxymethyl chitosan pesticide microsphere can effectively reduce the loss rate of pesticide, improve the effective utilization rate of the pesticide and reduce the pollution of the pesticide to the environment.

Description

Modified carboxymethyl chitosan pesticide microsphere and preparation method thereof

Technical Field

The invention relates to the technical field of pesticides, in particular to a modified carboxymethyl chitosan pesticide microsphere and a preparation method thereof.

Background

Pesticides are the primary means used in agriculture to control disasters and pests. However, the traditional pesticide has poor adhesion, and the effective components are easy to lose, so that the pesticide effect is poor. Moreover, when the traditional pesticide is used, a large amount of organic solvent such as toluene, xylene and the like needs to be matched, so that a large amount of pesticide and organic solvent flow into soil and water areas, and the ecological environment is greatly damaged.

The controlled pesticide releasing technology is one pesticide processing method to release pesticide in required dosage and specific time for effective control of pests. Compared with the traditional preparation formulation, the slow-release pesticide can prolong the activity of the pesticide, reduce leaching, evaporation and degradation and reduce the risk of percutaneous poisoning, and is an effective method for solving the contradiction between the low utilization rate of the pesticide and environmental pollution.

The water-based pesticide preparation is a pesticide processing formulation taking water as a medium or diluent. The preparation has the characteristics of low toxicity, easy dilution, easy use, difficult explosion and environment friendliness and the like.

Therefore, in order to improve the efficiency of pesticides and reduce the ecological impact of pesticide use, it is necessary to develop a controlled-release environment-friendly water-based pesticide preparation.

Disclosure of Invention

In order to overcome the defects in the prior art, the invention aims to provide a modified carboxymethyl chitosan pesticide microsphere and a preparation method thereof.

In order to realize the purpose, the invention adopts the technical scheme that:

a modified carboxymethyl chitosan pesticide microsphere is prepared by taking Allyl Glycidyl Ether (AGE) as an intermediate, and grafting an organic silicon surfactant to a molecular chain of carboxymethyl chitosan (CMCS) to prepare an amphiphilic modified carboxymethyl chitosan carrier; and packaging the pesticide by using the prepared modified carboxymethyl chitosan carrier, and self-assembling into the modified carboxymethyl chitosan pesticide microsphere.

The invention also provides a preparation method of the modified carboxymethyl chitosan pesticide microsphere, which comprises the following steps:

(1) dissolving carboxymethyl chitosan in deionized water, adding allyl glycidyl ether, and stirring at room temperature for 1-2 h to obtain a solution A;

(2) dissolving an organic silicon surfactant with deionized water, adding potassium peroxodisulfate, and stirring at 60-80 ℃ for 1-2 h in an inert gas atmosphere to obtain a solution B;

(3) slowly dropwise adding the solution B into the solution A at the temperature of 60-80 ℃, stirring for 3-6 h after dropwise adding is finished, and freeze-drying to obtain a modified carboxymethyl chitosan carrier;

(4) preparing a liquid medicine with the concentration of 10-50 mg/mL by using an organic solvent and a pesticide;

(5) adding the modified carboxymethyl chitosan carrier into deionized water, stirring and dissolving at 60-80 ℃, and cooling to room temperature to obtain a carrier solution;

(6) and adding the liquid medicine into the carrier solution, and stirring at 150-200 rpm for 2h to prepare the modified carboxymethyl chitosan pesticide microspheres.

Preferably, the silicone surfactant is a trisiloxane surfactant (TSS). The wettability of the pesticide on plant leaves is very important for improving the pesticide efficiency, while TSS has excellent surface activity, good wettability, spreadability and pore permeability, strong adhesion and rain wash resistance. According to the invention, TSS is grafted to CMCS to form a drug-loaded carrier, so that the affinity of the leaves of the microspheres can be improved, pesticide liquid can be better spread on the leaves, the use amount and the loss rate of pesticide can be effectively reduced, and environmental pollution can be reduced.

Preferably, the mass ratio of carboxymethyl chitosan (CMCS), Allyl Glycidyl Ether (AGE) and trisiloxane surfactant (TSS) is, CMCS: AGE: TSS is 2 (0.1-0.4): (0.5 to 1.5). The modified carboxymethyl chitosan pesticide microsphere can be successfully prepared by the above preparation ratio.

Most preferably, the mass ratio of carboxymethyl chitosan (CMCS), Allyl Glycidyl Ether (AGE), and trisiloxane surfactant (TSS) is, CMCS: AGE: TSS ═ 2:0.4: 1.5. The modified carboxymethyl chitosan pesticide microsphere prepared according to the proportion has the advantages of high grafting ratio of TSS (cellulose-styrene-sulfonate) and high encapsulation ratio of pesticide, excellent ultraviolet resistance and slow release performance, good dispersivity and adhesiveness on blades and uniform particle size distribution.

Preferably, the modified carboxymethyl chitosan carrier should be further purified before use, specifically: and (3) placing the freeze-dried modified carboxymethyl chitosan carrier in a Soxhlet extractor, extracting for 48h by using absolute ethyl alcohol, and then placing in an oven at 70 ℃ for 12h to obtain the purified modified carboxymethyl chitosan carrier.

Preferably, the organic solvent comprises at least one of isopropanol, ethanol, toluene, acetone.

Preferably, the pesticide comprises at least one of abamectin, ivermectin, chlorpyrifos, 2, 4-dichlorophenoxyacetic acid, emamectin benzoate, chlorantraniliprole and lambda-cyhalothrin.

The invention has the beneficial effects that: the modified carboxymethyl chitosan pesticide microsphere prepared by the invention is a water-based pesticide, can be well adhered to the leaves and well spread on the leaves, and can also effectively slow down the decomposition of the pesticide under ultraviolet rays, improve the photostability of the pesticide, continuously release the pesticide and not influence the efficacy exertion of the pesticide. Therefore, the modified carboxymethyl chitosan pesticide microsphere can effectively reduce the loss rate of pesticide, improve the effective utilization rate of the pesticide and reduce the pollution of the pesticide to the environment.

Drawings

FIG. 1 is a FTIR spectrum of TSS, CMCS, CMCS-AGE-TSS, AVM and CMCS-AGE-TSS @ AVM;

FIG. 2 shows CMCS (a), TSS (b) and CMC-AGE-TSS (c)¹H NMR spectrum chart;

FIG. 3 is an XRD pattern of CMCS, CMCS-AGE-TSS, CMCS-AGE-TSS @ AVM and AVM;

FIG. 4 is a TGA (a) and DTG (b) plot of CMCS, TSS and CMCS-AGE-TSS;

FIG. 5 is a DSC curve of CMCS and CMCS-AGE-TSS prepared in examples 1 to 5;

FIG. 6 is an SEM image of CMCS-AGE-TSS (a), CMCS-AGE-TSS @ AVM (b, d) and the particle size distribution of CMCS-AGE-TSS @ AVM in the SEM (c);

FIG. 7 is a graph of contact angle (a) and liquid holding capacity (b) for CMCS, AVM and CMCS-AGE-TSS @ AVM prepared in examples 1-3;

FIG. 8 shows the residual amount of AVM after UV irradiation of the AVM solution, AVM emulsifiable concentrate, and CMCS-AGE-TSS @ AVM of examples 1-3;

FIG. 9 is a sustained release profile of CMCS-AGE-TSS @ AVM of examples 1-3;

FIG. 10 is a sustained release profile of CMCS-AGE-TSS @ AVM of examples 2,4 and 5;

FIG. 11 is a sustained release profile of CMCS-AGE-TSS @ AVM of example 2 at various pH values.

Detailed Description

To better illustrate the objects, aspects and advantages of the present invention, the present invention is further illustrated by the following examples. It is apparent that the following examples are only a part of the embodiments of the present invention, and not all of them. It should be understood that the embodiments of the present invention are only for illustrating the technical effects of the present invention, and are not intended to limit the scope of the present invention.

The sources of the materials used in the examples are as follows:

carboxymethyl chitosan (CMCS), Allyl Glycidyl Ether (AGE) and isopropanol were purchased from michelin biochemical technologies, inc (shanghai, china). Potassium peroxodisulfate and ethanol were purchased from Tianjin Maotai Chemicals, Inc. (Tianjin, China). The above chemicals are all analytically pure and can be used without further purification. Avermectin (AVM) was purchased from West Biochemical Co., Ltd, Hebei, and AVM emulsifiable concentrate was purchased from Beijing Green agriculture technology group Co., Ltd, Beijing, China. Trisiloxane surfactants (TSS) were obtained by methods in the literature (Xie, h., Yue, h., Zhang, w., Hu, w., Zhou, x., Prinsen, p., & Luque, R. (2018). achitosan modified Pt/SiO2 catalyst for the synthesis of 3-poly (ethylene glycol) propylether-acetylated trisiloxane applied as an aggregate synthesis.

Examples 1-5 preparation of modified carboxymethyl chitosan pesticide microspheres

2.0g of CMCS was dissolved in a flask containing 100mL of deionized water, AGE (in the amount shown in Table 1) was added, and the mixture was magnetically stirred at room temperature for 1 hour to obtain solution A. TSS (in amounts as shown in Table 1) was dissolved in 30mL of deionized water, then 0.5g of potassium peroxodisulfate was added and magnetically stirred at 80 ℃ for 1h under nitrogen atmosphere to give solution B. Slowly dripping the solution B into the solution A at the speed of 1 drop in two seconds at the temperature of 80 ℃, carrying out magnetic stirring for 6 hours, and carrying out freeze drying to obtain the spongy modified carboxymethyl chitosan carrier (hereinafter referred to as CMCS-AGE-TSS). Placing the CMCS-AGE-TSS in a Soxhlet extractor, extracting with absolute ethanol for 48h, and then placing in an oven at 70 ℃ for 12h to obtain the purified CMCS-AGE-TSS. The pesticide is prepared into 50mg/mL liquid medicine by isopropanol. To a brown Erlenmeyer flask, 0.2g CMCS-AGE-TSS and 90mL deionized water were added and heated to 80 ℃ with magnetic stirring to dissolve the CMCS-AGE-TSS. And cooling to room temperature, adding 1mL of liquid medicine, fixing the volume to 100mL by using deionized water, and magnetically stirring at 150-200 rpm for 2 hours to obtain the modified carboxymethyl chitosan pesticide microsphere solution.

In the embodiments 1-5 of the invention, Avermectin (AVM) is used as a model pesticide, and the modified carboxymethyl chitosan pesticide microsphere (hereinafter referred to as CMCS-AGE-TSS @ AVM) is prepared according to the method.

TABLE 1

Numbering	AGE amount/g	TSS dosage/g
			Example 1	0.4	0.5
Example 2	0.4	1.0
			Example 3	0.4	1.5
Example 4	0.1	1.0
			Example 5	0.2	1.0

The CMCS-AGE-TSS @ AVM prepared in the above examples 1 to 5 was subjected to structure and performance tests, and the results were as follows:

first, structural characterization

(1) FTIR analysis: fourier infrared spectra of TSS, CMCS, CMCS-AGE-TSS, AVM and CMCS-AGE-TSS @ AVM are compressed by KBr to 450-4000 cm^–1Measurements were made within the range. (Fourier Infrared Spectroscopy model Spectrum100, Perkin Elmer Inc., USA).

As a result: FT-IR spectra of TSS, CMCS, CMCS-AGE-TSS, AVM and CMCS-AGE-TSS @ AVM are shown in FIG. 1. At 2871cm^-1The peak at (A) is-CH on the TSS polyether segment₂Tensile vibration peak of (1), in 1256cm^-1The peak at (A) is a bending vibration absorption peak of the Si-C bond of TSS, observed at 3414cm on CMCS^-1Is caused by stretching vibration of O-H, N-H, 2904cm^-1Caused by aliphatic asymmetric C-H stretching vibrations in methylene groups, 1420cm was observed on CMCS-AGE-TSS^-1And 1327cm^-1The peak of (A) is Si-CH on TSS₃Tensile shock absorption peak of (1), in turn, in the TSS of 1256cm^-1The bending vibration absorption peak of the Si-C bond of (A) also appears on the CMCS-AGE-TSS.

The above results indicate that TSS has been successfully grafted onto CMCS. 1735cm were observed on CMCS-AGE-TSS^-1This is due to tensile vibration of C ═ O on the AVM, indicating that the AVM has been successfully encapsulated in CMC-AGE-TSS nanoparticles.

(2)¹H NMR nuclear magnetic hydrogen spectroscopy: of CMCS, TSS and CMCS-AGE-TSS¹H NMR spectrum was obtained using D₂O or CDCl₃Solvent, on a nuclear magnetic resonance spectrometer (Ascend400, Bruker, switzerland) operating at 400 MHz.

As a result: of CMCS, TSS and CMCS-AGE-TSS¹The H NMR spectrum is shown in FIG. 2. In FIG. 2, a is CMCS¹H NMR spectrum, b is CDCl₃Of TSS in (1)¹H NMR spectrum, c is D₂Of CMCS-AGE-TSS in O¹H NMR spectrum. Their proton signals are as follows (ppm), respectively: for CMCS, 2.60(H2), 3.23-3.64(H3, H4, H5, H6), 4.38(H1), 3.88 (H7: -O-CH₂-COOD)，1.94(a：COCH₃) Is acetyl chitosan; 3.62 (CH) of TSS₂CH₂O)，3.38(SiCH₂CH₂CH₂)，1.58(SiCH₂CH₂)，0.42(SiCH₂CH₂)，0.09(SiCH₃). In CMCS-AGE-TSS¹In the H NMR spectrum, the signals were also present as 3.62ppm and 0.09ppm, respectively, polyether protons and methyl protons of TSS. The results show that TSS has been successfully grafted into CMCS.

(3) X-ray diffraction (XRD) analysis XRD patterns of CMCS, CMCS-AGE-TSS, CMCS-AGE-TSS @ AVM and AVM were obtained by D8X-ray diffractometer (Rigaku) the X-ray source was Cu K α radiation (40kV, 30 mA). The samples were irradiated at 10 min^-1Is scanned at the scanning rate of (a).

As a result: the XRD patterns of CMCS, CMCS-AGE-TSS, CMCS-AGE-TSS @ AVM and AVM are shown in FIG. 3. The XRD patterns of CMCS, CMCS-AGE-TSS @ AVM and AVM have sharp peaks at 2 θ ═ 20 ° due to their crystalline nature, which corresponds to form II. The peak of CMCS-AGE-TSS broadened at 20 ° 2 θ, indicating a decrease in crystallization, but smaller crystalline phase fractions appeared at 30.8 °, 32.0 ° and 44.8 ° 2 θ. After AVM encapsulation, the peak value of CMCS-AGE-TSS @ AVM is lower than that of CMCS-AGE-TSS, which can improve the biodegradability of the polymer. AVM shows a sharp peak at 12.5 ° at 2 θ, indicating that AVM is a highly crystalline structure. However, no significant AVM crystallization peak was observed in the X-ray diffraction pattern of CMCS-AGE-TSS @ AVM, and thus the AVM was present in the nanoparticle in amorphous form, indicating that CMC-AGE-TSS @ AVM nanoparticles can render the AVM more dispersible and enhance drug efficacy.

(4) TGA thermogravimetric analysis: the thermal stability of the samples was measured using a thermogravimetric analyzer (TGA2, mettler toledo, switzerland) at a rate of 10 ℃/min at a rate of 40 ℃ to 800 ℃ under a nitrogen atmosphere of 50 mL/min.

As a result: FIG. 4 is a TGA (a) and DTG (b) plot of CMCS, TSS and CMCS-AGE-TSS. From the TGA curve, CMCS has three stages of mass loss. The first stage lost 14.4% before 170 ℃, the crystalline water and water physically adsorbed on the surface of the CMCS lost, and the second stage lost 41.4% at 225-530 ℃, which corresponds to the cleavage of side chains and molecular chains in the CMCS. The structure of the CMCS, volatilization of small molecules and formation of carbonized products, the third stage lost 19.4% at 600 to 800 f, which corresponds to further decomposition of the carbonized products and removal of residual volatile components. As can be seen from the DTG curve, the temperature of the peak of maximum weight loss of CMCS-AGE-TSS is higher than that of CMCS, indicating that the decomposition temperature of CMC-AGE-TSS is higher than that of CMCS. The maximum weight loss peak of the CMCS-AGE-TSS is obviously smaller than that of the CMCS, which shows that the maximum weight loss rate of the CMCS-AGE-TSSLower than the maximum weight loss rate of the CMCS because the crosslinking reaction improves the thermal stability of the CMCS. After heating to 800 ℃, the mass residue rate of the CMCS-AGE-TSS is higher than that of the CMCS, which is the residual SiO after decomposition of the CMCS-AGE-TSS₂It was further demonstrated that TSS had been successfully grafted into CMCS.

(5) DSC analysis: CMCS and CMCS-AGE-TSS prepared in examples 1 to 5 were used as samples. Samples from 40 ℃ to 800 ℃ were thermally analyzed using a Q200 differential scanning calorimeter (TAInstructions, USA) under a nitrogen atmosphere at 20mL/min at a rate of 10 ℃/min.

As a result: FIG. 5 is a DSC curve of CMCS and CMCS-AGE-TSS prepared in examples 1 to 5. Glass transition temperature (T) of CMCS_g) The temperature was 113 ℃. When 0.4g of AGE was added to synthesize CMCS-AGE-TSS, T was observed to decrease with the amount of TSS_gA gradual increase to 134 ℃ indicates a gradual increase in molecular weight, since the reaction increases the molecular weight interactions and the migration of molecular segments is difficult, resulting in T_gAnd (4) increasing. At the same time, T_gIncreasing with increasing AGE indicates an increase in molecular weight.

(6) SEM analysis: the sample was dropped on a copper plate, dried with a high-power lamp, then subjected to a gold-spraying treatment on the surface of the solid sample, and finally placed on a scanning electron microscope (SU-8010, hitachi, japan), and the microstructure of the sample was observed under a nitrogen atmosphere. The sample morphology was obtained at an accelerating voltage of 5 kV.

As a result: FIG. 6(a) is an SEM image of CMCS-AGE-TSS, and FIG. 6(b, d) is an SEM image of CMCS-AGE-TSS @ AVM. As shown in FIG. 6(a), the CMCS-AGE-TSS resembles a fibrous particle because the surface energy of the CMC-AGE-TSS is greatly reduced after the TSS is grafted to the CMCS, and thus the CMCS-AGE-TSS can easily slide in water and aggregate to form a fibrous particle. After loading, the AVM and CMCS-AGE-TSS self-assemble into spheres by hydrophobic interactions and the AVM is coated in a spherical shell composed of CMCS-AGE-TSS to form a core. The nanoparticles after drug loading are easy to agglomerate in water, the dispersibility is poor, and the particle surface is covered by a film.

FIG. 6(c) is the particle size distribution of CMCS-AGE-TSS @ AVM in SEM. As shown in fig. 6(c), the average particle size of the nanoparticles analyzed by Image-prodlus software was about 210nm, which is less than 243.89nm as measured by DLS. The difference in size between SEM and DLS analysis is due to the different principles involved in these two techniques. DLS measurements relate to the hydrodynamic state of the nanoparticles, which are dry in SEM measurements.

(7) Analysis of zeta potential and average particle size: the sample was placed in a sample cell at 1.0mL, diluted with water to low concentration, and then the average particle size and Zeta potential of the sample were measured by the Dynamic Light Scattering (DLS) principle (90 plusapals, bruke hei, usa).

Table 2 shows the conversion, average particle size, PDI, Zeta potential and encapsulation efficiency of the CMC-AGE-TSS @ AVM prepared in examples 1 to 5.

TABLE 2

The grafting yield of CMCS-AGE-TSS was calculated by the following formula.

Grafting rate(％)＝(m_CMCS-AGE-TSS-m_CMCS)/m_CMCS×100％

Wherein m is_CMCS-AGE-TSSFor the quality of the synthesized CMCS-AGE-TSS, m_CMCSThe mass of CMCS added for the start of the reaction.

As shown in Table 2, the average particle size of CMCS-AGE-TSS @ AVM increased gradually from 187.82 + -3.96 of example 1 to 243.89 + -1.78 graft of example 3 when 0.4g AGE was added. At the same time, the encapsulation efficiency (encapsulation efficiency) increased from 50.67% in example 1 to 59.72% in example 3. Because more TSS is grafted as the grafting rate increases, higher hydrophobicity can be achieved and more AVM can be coated to increase particle size. Since the AVM is negatively charged, the zeta potential will drop accordingly. When the same amount of 1.0g of TSS was added, the amount of AGE increased from 0.1g to 0.2g, and the average particle size of the nanoparticles also increased. This is because as the amount of AGE increases, the degree of crosslinking of the CMCS-AGE-TSS increases and the polymeric shell structure of the microspheres thickens and thus the particles increase. When the amount of AGE is increased to 0.4g, the conversion rate decreases because AGE is mainly used to cause a crosslinking reaction. The average particle size is reduced because the CMCS-AGE-TSS is too crosslinked, resulting in some CMCS-AGE-TSS being insoluble in water and the water-insoluble portion being insoluble and encapsulating the AVM, and some water-soluble CMCS-AGE-TSS having a lower degree of crosslinking and a smaller average particle size. The Particle Distribution Index (PDI) of the nanoparticles synthesized by changing various variables is less than 0.2, which indicates that the microsphere prepared by the invention has narrow particle size distribution, and the particle size distribution can provide a basis for further synthesizing specific particle size. When the distribution index is 0.01, it is considered to be close to monodispersity; when the distribution index is greater than 0.7, it is considered to be widely distributed.

(8) Encapsulation efficiency analysis

5mL of CMCS-AGE-TSS @ AVM solution was placed in a centrifuge tube and centrifuged at 12000r/min for 10 minutes. After centrifugation, 1mL of the supernatant was transferred to a 25mL brown volumetric flask and made to volume with absolute ethanol. The absorbance A of free AVM was measured with a UV spectrophotometer (Lambda 365, Perkinelmer Instrument Co. Ltd, USA) at a wavelength of 245 nm. The concentration of free AVM in the supernatant can be determined by standard curve a ═ 0.03321C-0.006 (R)²0.9998). Then, the encapsulation performance of the product against AVM was calculated using the following equation (2):

m_{total AVM}when it is the total weight of AVM used in the preparation of the microspheres, m_{free AVM}Is the weight of free AVM in the supernatant after centrifugation.

As shown in Table 2, the effect of CMCS-AGE-TSS synthesized from different feedstocks on the encapsulation efficiency of AVM, which increases with increasing TSS when 0.4g AGE is added, indicates that 0.4g AGE can react with more TSS. More TSS was grafted to encapsulate more AVM and improve the encapsulation efficiency of the sample.

When 1g of TSS was added, the AGE dose increased from 0.1g to 0.2g, but encapsulation efficiency decreased. This phenomenon may be due to the increased dose of AGE and the degree of crosslinking of the CMCS-AGE-TSS. A portion of the CMCS-AGE-TSS was insoluble in water, and this result was obtained by the particle size analysis of example 5, resulting in a decrease in encapsulation efficiency. When the AGE dose is increased to 0.4g, the encapsulation efficiency is increased because the portion of the CMCS-AGE-TSS that is soluble in water is more TSS, and the hydrophobicity of the CMCS increases to encapsulate more AVM.

Third, blade contact angle and liquid holding capacity test

TSS is a surfactant that significantly lowers the surface tension of a liquid. Grafting of TSS onto CMCS can improve the leaf affinity of the latter and allow better spreading of the pesticide solution on the leaves. Aqueous CMCS solutions and aqueous AVM solutions are prepared at concentrations such as CMCS-AGE-TSS @ AVM. Contact angles of CMCS aqueous solution, AVM aqueous solution and CMCS-AGE-TSS @ AVM prepared in examples 1 to 3 on cucumber leaves were measured using a contact angle measuring instrument (Theta, Biolin Scientific co. ltd, Sverige), fresh cucumber leaves were collected and cleaned leaves were spread out and dried on clean glass slides without damaging the surface of the cucumber leaves. Different samples were dropped onto the leaves with a micro-syringe. After 30 seconds, the water drop on the leaf was photographed with a contact angle meter camera. Three measurements were made for each sample at different positions of the blade to reduce errors caused by different surfaces of the blade.

Cutting the dried leaves into 2X 2cm pieces²The same size leaves were soaked in the sample solution for 15s and then lifted vertically using tweezers. The leaf was weighed after the liquid stopped low and the Liquid Holding Capacity (LHC) was calculated using equation (3).

Wherein M is₀And M₁Respectively represent the weight of the leaves before and after soaking, and S represents the area of the leaves.

As a result: FIG. 7 shows contact angles (a) and liquid holding capacities (b) of CMCS, AVM and CMCS-AGE-TSS @ AVM prepared in examples 1-3. FIG. 7(a) shows the contact angle on cucumber leaf for CMCS, AVM and different CMCS-AGE-TSS @ AVM samples. The contact angle of CMCS-AGE-TSS @ AVM decreases compared to CMCS and AVM, and gradually decreases as TSS increases. The contact angle decreased from 73.62 ° for CMCS to 49.32 ° for example 3. The contact angle is reduced because TSS is an organosilicon synergist, which is a surfactant that lowers the surface energy of the pesticide solution and allows the pesticide solution to spread better over the blade.

As shown in FIG. 7(b), the Liquid Holdup (LHC) of the leaves was adjusted from 5.05mg/cm of the AVM solution²Increased to 10.3mg/cm for example 3²The increase is 103.79%. Due to the dual effects of the high viscosity of the CMCS and TSS and the reduced surface energy of the liquid, the liquid medicine quickly spreads and adheres to the leaves. The result shows that the novel water-based pesticide can effectively prevent the pesticide from running off and improve the pesticide utilization rate.

Fourth, ultraviolet resistance test

The CMCS-AGE-TSS @ AVM solution with the concentration of 500mg/L prepared in the embodiment 1-3 is diluted to 200mg/L by deionized water, and 1mL of AVM isopropanol solution and AVM emulsified oil are diluted to 200mg/L by deionized water. 50mL of the diluted sample was then placed in a photochemical reactor and the sample was placed at a distance of 15cm from the light source. The spot was irradiated with a 300W mercury lamp (Emax 365 nm). At specific irradiation intervals, 1mL of sample was transferred to a brown volumetric flask, then made up to 25mL with absolute ethanol and the absorbance was measured with a uv spectrophotometer at a wavelength of 245 nm. Then, the Residual Rate (RR) of AVM is calculated using the following equation (4).

Wherein A is_iIs the absorbance of AVM after UV irradiation, and A₀Is the absorbance of AVM after no UV irradiation.

As a result: abamectin is easily decomposed by ultraviolet rays, and thus there is a need to improve the photostability of AVM during use. The residual ratio of avermectins of each sample after the ultraviolet irradiation is shown in fig. 8. The half-lives of the AVM emulsified oil and AVM under strong UV irradiation were 5 minutes and 45 minutes, respectively, whereas the half-life of example 3, the most resistant AVM, was 83 min. After 85 minutes of irradiation, the AVM encapsulated in the CMCS-AGE-TSS is released from the nanoparticle interior, so the UV degradation rate is slower and the AVM solution continues to decompose rapidly because it does not have any UV barrier. After 125min of irradiation, the residual rate of AVM was 25%, which was significantly lower than 47% of example 3. Therefore, CMCS-AGE-TSS has significant UV-screening properties. The AVM emulsifiable concentrate completely decomposed in 85 minutes, probably because AVM is more readily photodegradable after complete dissolution in organic solvents. As the shell material of the AVM microsphere, the CMCS has excellent ultraviolet absorption performance and can effectively block ultraviolet rays to serve as a barrier. It is therefore a good agent for promoting the release of a persistent pesticide, in particular during the release of the photosensitive component.

Fifth, testing sustained release performance

5mL of CMCS-AGE-TSS @ AVM of examples 1-3 were placed in a dialysis bag and placed in a brown erlenmeyer flask. 50mL of 40% aqueous ethanol solution was added to the Erlenmeyer flask, and the Erlenmeyer flask was placed in a shaking box at 26 ℃. Periodically, 1mL of the solution was transferred to a brown volumetric flask and then made up to 10mL with 40% aqueous ethanol. An equal volume of 40% aqueous ethanol was added to the flask, the absorbance of the diluted solution was measured at 245nm using a uv spectrophotometer, and the concentration of the sample in the flask C-0.00456 was calculated by standard curve a ═ 0.0317 (R2 ═ 0.998). The cumulative release rate R of the AVM is then calculated using the following equation (5)_i。

Wherein, c_iIs the mass concentration (mg/L) of AVM at different times, m_AVMIs the total mass of AVM added to the dialysis bag.

As a result: FIG. 9 is a sustained release profile of CMCS-AGE-TSS @ AVM of examples 1-3. As can be seen from the figure, different amounts of TSS had little effect on the release of AVM from CMC-AGE-TSS @ AVM. CMCS-AGE-TSS @ AVM is released rapidly in the initial phase of 50h due to the release of AVM that is not encapsulated in the nanoparticles. After 200 hours of continuous release, the release rate of AVM tends to stabilize. At this time, the cumulative release rates of example 1, example 2 and example 3 were 82.02 ± 2.98%, 76.63 ± 2.97% and 78.17 ± 3.16%, respectively. The low encapsulation efficiency and the presence of large amounts of free AVM in example 1 resulted in an accumulated release of 82.02 ± 2.98% for example 1. The remaining AVM will eventually be released for a longer time due to the biodegradable nature of the CMCS.

FIG. 10 is a sustained release profile of CMCS-AGE-TSS @ AVM of examples 2,4 and 5. As can be seen from the figure, example 2 has the best sustained release effect. The grafting yield of example 2 was higher than that of example 4. Example 2 is more hydrophobic and more cross-linked, and therefore the polymeric shell of the microsphere is stronger. Meanwhile, the larger Zeta potential absolute value of example 2 indicates that the drug-loaded microspheres of example 2 are more stable, and thus the cumulative release of example 2 is minimal. Since example 5 has the lowest encapsulation efficiency and more free AVM is released continuously, the cumulative release of example 5 is the highest at 200h, which can be analyzed from the larger particle size.

FIG. 11 is a sustained release profile of CMCS-AGE-TSS @ AVM of example 2 at various pH values. As can be seen from the figure, the CMCS-AGE-TSS @ AVM release rate of example 2 is the slowest at pH 7. And when the pH value is 3, the slow release rate is fastest. It can be seen that AVM is rapidly released under acidic condition, and the cumulative release rate reaches 96.9%. This is because, when the pH is 3, the possibility of collision of Si-O-Si bonds with water molecules is greatly increased, so that both are easily combined to promote the hydrolysis reaction, and thus the TSS cannot be stabilized under acidic conditions. When the TSS is decomposed, the hydrophobicity of CMCS-AGE-TSS is deteriorated, the AVM inside the microspheres is released rapidly, and the AVM is released completely at 50 h. The sustained release effect at pH 9 is worse than at pH 7, probably due to accelerated hydrolysis of Si-O-Si bonds in an alkaline environment. Under the neutral condition, the TSS is relatively stable, the slow release effect of the CMCS-AGE-TSS @ AVM is slowest, and the release rate of the AVM gradually tends to be stable after 110 hours. Therefore, the release of AVM can be effectively controlled by adjusting the pH value. This phenomenon applies to plants that require large amounts of pesticide at the initial growth stage, and then require only little pesticide for a longer period of time to protect the plant from damage.

Sixth, toxicity test

The CMCS-AGE-TSS @ AVM and AVM emulsifiable concentrates prepared in examples 2,4 and 5 were diluted with deionized water to 200, 100, 50, 25, 12.5 and 6.25mg/L, respectively. The same area of vegetable leaves was prepared, immersed in a range of concentrations of CMCS-AGE-TSS @ AVM for 10 minutes, then allowed to dry naturally, and vegetable leaves without AVM were used as a blank. And (3) placing the dried leaves in a culture dish with filter paper at the bottom, then placing the 10s larva of the diamondback moth in the culture dish, and finally placing the culture dish in an incubator. Diamondback moth deaths were analyzed after 48 hours. The experiment was repeated 3 times for each concentration of sample and blank. Median lethal concentration (LC50) and toxicity regression equations were calculated based on probability analysis.

As a result: as shown in table 3.

TABLE 3 toxicity test results

Sample (I)	Regression equation of toxicology	LC₅₀(mg L^-1)	SE	95% confidence Limit	R²
						AVM	Y＝4.3278+0.9827X	4.83	3.83	1.02～22.85	0.8668
CMCS-AGE-TSS@AVM	Y＝3.8400+1.0593X	12.45	5.81	4.99～31.08	0.9269

As can be seen from table 3, the toxicological regression equations for AVM and CMCS-AGE-TSS @ AVM are Y-4.3278 +0.9827X and Y-3.8400 +1.0593X, respectively. Furthermore, the 95% confidence limit for AVM is 1.02 to 22.85, which means that a complete out of this range is likely to be 5%, indicating a significant difference in toxicity. Although LC of CMCS-AGE-TSS @ AVM₅₀(12.45mg/L) is higher than AVM (4.83mg/L), but the confidence limit of CMCS-AGE-TSS @ AVM is 4.99-31.08, which demonstrates that the toxicity difference between AVM and CMCS-AGE-TSS @ AVM is not significant. It is shown that the CMCS-AGE-TSS @ AVM package of the present invention can improve various properties of AVM without significantly affecting its toxicological drug effects.

Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A preparation method of modified carboxymethyl chitosan pesticide microspheres is characterized in that allyl glycidyl ether is used as an intermediate, and an organic silicon surfactant is grafted to a molecular chain of carboxymethyl chitosan to prepare an amphiphilic modified carboxymethyl chitosan carrier; and encapsulating the pesticide by using the prepared modified carboxymethyl chitosan carrier to prepare the modified carboxymethyl chitosan pesticide microsphere.

2. The preparation method of the modified carboxymethyl chitosan pesticide microsphere as claimed in claim 1, which is characterized by comprising the following steps:

3. The method for preparing modified carboxymethyl chitosan pesticide microspheres as claimed in claim 2, wherein the silicone surfactant is a trisiloxane surfactant.

4. The preparation method of the modified carboxymethyl chitosan pesticide microsphere as claimed in claim 2, wherein the mass ratio of the carboxymethyl chitosan, the allyl glycidyl ether and the trisiloxane surfactant is 2 (0.1-0.4) to (0.5-1.5).

5. The preparation method of the modified carboxymethyl chitosan pesticide microsphere as claimed in claim 2, wherein the mass ratio of the carboxymethyl chitosan, the allyl glycidyl ether and the trisiloxane surfactant is 2:0.4: 1.5.

6. The method for preparing modified carboxymethyl chitosan pesticide microspheres as claimed in claim 2, wherein the organic solvent comprises at least one of isopropanol, ethanol, toluene and acetone.

7. The method for preparing modified carboxymethyl chitosan pesticide microspheres as claimed in claim 2, wherein the pesticide comprises at least one of abamectin, ivermectin, chlorpyrifos, 2, 4-dichlorophenoxyacetic acid, emamectin benzoate, chlorantraniliprole and lambda-cyhalothrin.

8. The preparation method of the modified carboxymethyl chitosan pesticide microsphere as claimed in claim 2, wherein the modified carboxymethyl chitosan carrier is purified before use, and the purification method comprises the following steps: and (3) placing the freeze-dried modified carboxymethyl chitosan carrier in a Soxhlet extractor, extracting for 48h by using absolute ethyl alcohol, and then placing in an oven at 70 ℃ for 12h to obtain the purified modified carboxymethyl chitosan carrier.

9. A modified carboxymethyl chitosan pesticide microsphere is characterized by being prepared by the preparation method of the modified carboxymethyl chitosan pesticide microsphere as claimed in any one of claims 1 to 8.