CN109316461B - Lignin wall material microcapsule based on Pickering emulsion interface crosslinking, preparation method and application in drug carrier - Google Patents
Lignin wall material microcapsule based on Pickering emulsion interface crosslinking, preparation method and application in drug carrier Download PDFInfo
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Abstract
The invention belongs to the technical field of microcapsule preparation, and discloses a lignin wall material microcapsule based on Pickering emulsion interfacial crosslinking, a preparation method thereof and application thereof in a drug carrier. The preparation method comprises the steps of preparing lignin particle dispersion by alkali dissolution and acidification of lignin in water, and adding a water phase cross-linking agent to serve as a water phase; dissolving an oil phase cross-linking agent in an organic solvent to serve as an oil phase; mixing the water phase and the oil phase, and emulsifying to prepare O/W type Pickering emulsion; adding a catalyst, and heating to perform a crosslinking reaction to obtain the lignin wall material microcapsule. The invention also provides the lignin wall material microcapsule, which has high capsule wall strength and can be used for encapsulating hydrophobic substances, a large number of hindered phenol structures in lignin molecules serving as wall materials are favorable for improving the stability of photosensitive or oxygen-sensitive encapsulated objects, and the encapsulation rate of the lignin wall material microcapsule on abamectin reaches 90%; after being irradiated by ultraviolet light for 72 hours, the retention rate reaches 85 percent, and the retention rate of the original medicine is only 10.68 percent.
Description
Technical Field
The invention belongs to the technical field of microcapsule preparation, and particularly relates to a lignin wall material microcapsule based on Pickering emulsion interfacial crosslinking, a preparation method thereof and application thereof in a drug carrier.
Background
The lignin is the second most renewable resource next to cellulose in plants, is a reticular high polymer formed by connecting three phenyl propane units through ester bonds, ether bonds and carbon-carbon bonds, and has the structural characteristics of high carbon content and high benzene ring content. Industrial lignin is a major component of paper pulping waste liquor, including alkali lignin from alkaline pulping (insoluble in neutral and acidic water) and lignosulfonate from acid pulping; wherein the alkali lignin accounts for more than 95 percent, about 2 million tons are generated in China every year, and the price is low. With the exhaustion of petrochemical resources, the global research on how to fully utilize lignin, a large amount of biomass resources, has been greatly increased, and particularly, the lignin is applied to the field of materials with huge demand. However, the existing research shows that the composite material prepared by blending and copolymerizing lignin and high polymer materials such as rubber, plastic and the like has the defects of surplus rigidity and insufficient toughness, and the industrialization can not be realized up to now. The lignin is applied to the preparation of the microcapsule with low mechanical property requirement, so that the performance disadvantage of the microcapsule can be avoided, the application in the material field can be realized, the wall material cost is reduced, the wall material biodegradability is improved, and the molecule of the microcapsule contains a large amount of benzene rings, conjugated structures and phenolic hydroxyl groups capable of effectively removing free radicals, so that the microcapsule has good thermal stability, ultraviolet absorption and oxidation resistance, the photostability of an encapsulated substance can be obviously improved, and the microcapsule has unique advantages when being applied in the microcapsule field.
Although the lignin has such excellent properties for preparing the microcapsule, the current preparation method of the microcapsule using the lignin as the wall material has more disadvantages and shortcomings. There are studies conducted by layer-by-layer self-assembly [ Fine Chemicals 2008,25(7): 625-; ACS Sustainable chem.Eng.2016,4(4): 1946-1953; ACS Sustainable chem.Eng.2017(5): 3321-; or preparing hollow nano capsules [ Rsc Advances 2014(4):11661-11663] by a phase separation method and utilizing self-assembly of lignin for loading the medicines. However, the two methods have poor film forming property, low operation concentration, complicated steps and great industrialization difficulty. The recent research tends to prepare microcapsules by the crosslinking reaction of lignin, and the basic method is to prepare O/W or W/O emulsion by using lignosulfonate aqueous solution or lignin alkaline aqueous solution as water phase, and dissolve crosslinking agents (such as toluene diisocyanate [ RscAdvances 2014(4):11661-11663], epichlorohydrin [ Soft mate, 2015(11):2046-2054], 3-mercaptopropionate [ ACS Sustainable chem. Eng.2016,4(10):5204-5211], etc.) in oil phase, so that the lignin and the crosslinking agents are crosslinked at the emulsion droplet interface to generate nano/microcapsules. The surface of the capsules is compact and smooth, but lignin can participate in the reaction only by diffusing from the water phase to the interface, the crosslinking degree is low, and the generated capsules are thin and easy to break. In view of this, a new method for preparing lignin wall material microcapsules with dense capsule walls and high structural strength is needed.
Disclosure of Invention
In order to overcome the defects and shortcomings of the prior art, the invention aims to provide a preparation method of a lignin wall material microcapsule based on Pickering emulsion interfacial crosslinking.
According to the method, a large amount of lignin particles adsorbed on an emulsion interface are crosslinked by using a crosslinking agent to form a continuous microcapsule wall, and the lignin wall material microcapsule with higher wall strength is prepared under a mild condition, so that the defects of the prior art are successfully overcome. Firstly, preparing lignin particle dispersion by alkali dissolution and acidification of lignin, and adding a water phase cross-linking agent as a water phase; an oil phase cross-linking agent and an organic solvent form an oil phase; mixing and emulsifying the water phase and the oil phase to prepare O/W type Pickering emulsion, so that the lignin particles are adsorbed on an oil-water interface at high density; then adding a catalyst, and initiating the lignin particles and the cross-linking agent to generate cross-linking polymerization reaction at an oil-water interface at a certain temperature to form the lignin microcapsule.
The invention also aims to provide the lignin wall material microcapsule prepared by the method.
The invention further aims to provide the application of the lignin wall material microcapsule in a drug carrier.
The purpose of the invention is realized by the following scheme:
a preparation method of a lignin wall material microcapsule based on Pickering emulsion interface crosslinking comprises the steps of preparing lignin particle dispersion by alkali dissolution and acidification of lignin in water, and adding a water phase crosslinking agent to serve as a water phase; dissolving an oil phase cross-linking agent in an organic solvent to serve as an oil phase; mixing the water phase and the oil phase, and emulsifying to prepare O/W type Pickering emulsion; adding a catalyst, and heating to perform a crosslinking reaction to obtain the lignin wall material microcapsule.
The preferable dosage of each component is as follows by mass: 100 parts of water; 0.1-10 parts of lignin; 0.01-10 parts of a water-phase crosslinking agent; 0.05-10 parts of an oil phase crosslinking agent; 10-100 parts of an organic solvent; 0.001-0.1 part of catalyst.
The aqueous phase crosslinking agent can comprise at least one of formaldehyde (with the mass concentration of 37 percent preferably), glutaraldehyde, dimethylol ethylene urea, citric acid and ethylene glycol diglycidyl ether.
The oil phase crosslinking agent can comprise at least one of epichlorohydrin, 1, 4-dibromobutane and 1, 6-dibromohexane.
The catalyst may include at least one of potassium iodide, sodium chloride, zinc nitrate, and sodium hypophosphite.
The organic solvent may comprise one of cyclohexanone, isophorone, toluene and n-pentanol.
The lignin may comprise at least one of alkali lignin and enzymatic lignin.
In order to further and better achieve the purpose of the invention, the alkali lignin can be selected from one of wood pulp black liquor, bamboo pulp black liquor, wheat straw pulp black liquor, reed pulp black liquor, bagasse pulp black liquor, asparagus pulp black liquor, cotton stalk pulp black liquor and cotton pulp black liquor, and is subjected to acid precipitation and drying to obtain acid precipitation lignin powder. The enzymatic hydrolysis of lignin may comprise separating and extracting lignin from the residue of alcohol production by fermentation of cellulose in plant material.
The emulsification is preferably carried out for 1-10 min at 8000-13000 rpm.
The heating crosslinking reaction is preferably carried out at a stirring speed of 150-400 rpm and at a temperature of 40-80 ℃ for 1-8 h.
In the preparation method, the lignin is subjected to alkali dissolution and acidification in water to prepare the lignin particle dispersion, namely, the lignin is dissolved in alkali liquor, and then acid is added to separate out the lignin to form the lignin particle dispersion.
The alkali can comprise at least one of sodium hydroxide, potassium hydroxide and ammonia water.
The acid may comprise at least one of hydrochloric acid, sulfuric acid, nitric acid.
More specifically, adding lignin into water, adding alkali to adjust the pH to 9-12 to obtain a lignin solution, and adding acid to adjust the pH of the system to 2-6 to separate out the lignin to form a lignin particle dispersion liquid. The lignin solution may be filtered to remove undissolved impurities and then subjected to acid precipitation.
The preparation method specifically comprises the following steps:
(1) preparation of lignin particle dispersion: adding lignin into water, adding alkali to adjust the pH value to 9-12 to obtain a lignin solution, filtering to obtain a filtrate, and adding acid to adjust the pH value to 2-6 to obtain a lignin particle dispersion liquid;
(2) preparation of Pickering emulsion: adding a water phase cross-linking agent into the lignin particle dispersion liquid to serve as a water phase, dissolving an oil phase cross-linking agent into an organic solvent to serve as an oil phase, mixing the oil phase and the water phase, and emulsifying to obtain an oil-in-water (O/W) type Pickering emulsion with stable lignin particles;
(3) and (3) synthesizing a lignin microcapsule: adding a catalyst into the emulsion, and heating to initiate an emulsion interface crosslinking reaction to obtain the lignin wall material microcapsule suspension based on Pickering emulsion interface crosslinking.
The lignin wall material microcapsule suspension based on Pickering emulsion interface crosslinking prepared by the preparation method is dried to obtain the lignin wall material microcapsule.
The preparation method has simple process and mild reaction conditions, and the prepared microcapsule has high capsule wall strength and can be used for encapsulating hydrophobic substances.
The invention also provides application of the lignin wall material microcapsule in a drug carrier. In the preparation process of the lignin wall material microcapsule, a hydrophobic substance to be encapsulated is dissolved in an oil phase, and then mixing, emulsifying and crosslinking are carried out to obtain the lignin wall material microcapsule encapsulating the hydrophobic substance. A large number of hindered phenol structures in lignin molecules serving as wall materials are beneficial to improving the stability of photosensitive or oxygen-sensitive encapsulated objects.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. the method adopts an alkali dissolution and acid precipitation method to prepare lignin particles, takes the lignin particles as solid dispersion particles to prepare O/W Pickering emulsion, and ensures that the lignin is adsorbed on an oil-water interface, thereby better performing a crosslinking reaction with a crosslinking agent in an oil phase and a water phase directly, having high lignin content participating in the formation of a wall material, and having thicker prepared capsule wall and high strength.
2. The method for preparing the lignin microcapsule can regulate and control the particle size of the prepared Pickering emulsion drop by changing the concentration and the speed of the dropping acid in the preparation stage of the lignin particle dispersion liquid and changing the concentration and the oil-water ratio of the lignin particle and the emulsification conditions of the emulsification strength, the emulsification time and the like of a homogenizer in the emulsification stage, thereby regulating and controlling the size of the prepared microcapsule.
3. The lignin has the characteristics of alkali dissolution and acid precipitation, namely lignin particles are dissolved under an alkaline condition and precipitated under an acidic condition, so that the microcapsule prepared by the invention can change the stability of the microcapsule wall material by changing the pH value, thereby controlling the release rate of the encapsulated substance, namely the microcapsule prepared by the invention has pH responsiveness.
4. According to the invention, lignin derived from industrial byproducts is used as a main raw material for synthesizing the microcapsule wall material, so that the production cost of the microcapsule is effectively reduced, and the resource utilization of waste biomass is realized; meanwhile, the lignin can be degraded, so that the microcapsule can be slowly degraded in the nature, is environment-friendly, and solves the environmental problem that the microcapsule prepared by common organic polymer materials is difficult to degrade.
5. Because the lignin wall material microcapsule is prepared based on O/W type Pickering emulsion interface crosslinking, hydrophobic substances can be dissolved in an organic solvent to form an oil phase in the emulsion preparation process, and then subsequent operation is carried out, so that the encapsulation of the hydrophobic substances (such as functional grease, medicines, essences, pesticides, dyes and the like) by the lignin microcapsule can be realized. A large number of hindered phenol structures in lignin molecules serving as wall materials are beneficial to improving the stability of photosensitive or oxygen-sensitive encapsulated objects.
Drawings
Fig. 1 is a particle size distribution diagram of the lignin microcapsule prepared in example 1.
Fig. 2 is a fluorescence microscope image of the lignin microcapsule prepared in example 1.
Fig. 3 to 5 are SEM images of the lignin microcapsules prepared in example 1.
Fig. 6 is a wall material infrared spectrum of the lignin microcapsule prepared in example 1.
Detailed Description
The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.
The materials referred to in the following examples are commercially available. The using amount of each component is calculated by mass portion.
Example 1
(1) Preparation of lignin particle dispersion: adding 5 parts by mass of acid-out lignin powder from the asparagus pulp black liquor into 100 parts by mass of water, adding sodium hydroxide to adjust the pH of the solution to 11 so as to completely dissolve the lignin, filtering, dropwise adding nitric acid into the filtrate until the pH of the solution is 4, and continuously stirring to obtain the lignin particle dispersion.
(2) Preparation of lignin Pickering emulsion: firstly, uniformly mixing lignin particle dispersion liquid prepared in the step (1) with 1.5 parts by mass of glutaraldehyde to obtain a water phase; uniformly mixing 4 parts by mass of 1, 6-dibromohexane and 25 parts by mass of cyclohexanone to prepare an oil phase; then mixing the oil phase and the water phase, and carrying out emulsification treatment for 5min at 11000rpm by using an emulsifier to obtain a lignin O/W Pickering emulsion.
(3) And (3) synthesizing a lignin microcapsule: to the above emulsion, 0.05 part by mass of potassium iodide was added, and the mixture was reacted at 55 ℃ for 5 hours at a stirring speed of 250rpm to obtain an aqueous suspension of lignin microcapsules.
The particle size distribution of the lignin microcapsules in the aqueous suspension of the lignin microcapsules prepared in this example was measured by a Malvern laser particle sizer, and the average particle size was 1.0. mu.m, as shown in FIG. 1.
Example 2
(1) Preparation of lignin particle dispersion: adding 0.1 part by mass of acid-out lignin powder from wood pulp black liquor into 100 parts by mass of water, adding potassium hydroxide to adjust the pH of the solution to 9 so as to completely dissolve lignin, filtering, dropwise adding hydrochloric acid into the filtrate until the pH of the solution is 2, and continuously stirring to obtain the lignin particle dispersion liquid.
(2) Preparation of lignin Pickering emulsion: firstly, uniformly mixing lignin particle dispersion liquid prepared in the step (1) and 0.01 part by mass of glutaraldehyde to obtain a water phase; 0.05 part by mass of 1, 4-dibromobutane and 10 parts by mass of toluene are uniformly mixed to prepare an oil phase; then mixing the oil phase and the water phase, and carrying out emulsification treatment for 10min at 8000rpm by using an emulsifier to obtain the lignin O/W Pickering emulsion.
(3) And (3) synthesizing a lignin microcapsule: to the above emulsion, 0.001 part by mass of potassium iodide was added, and the mixture was reacted at 40 ℃ for 8 hours at a stirring speed of 150rpm to obtain an aqueous suspension of lignin microcapsules.
The average particle diameter of the lignin microcapsules in the aqueous suspension of lignin microcapsules prepared in this example was determined to be 2.1 μm by means of a malvern laser particle sizer.
Example 3
(1) Preparation of lignin particle dispersion: adding 1 part by mass of acid-out lignin powder from the bamboo pulp black liquor into 100 parts by mass of water, adding sodium hydroxide to adjust the pH of the solution to 10 so as to completely dissolve the lignin, filtering, dropwise adding sulfuric acid into the filtrate until the pH of the solution is 3, and continuously stirring to obtain the lignin particle dispersion liquid.
(2) Preparation of lignin Pickering emulsion: firstly, uniformly mixing the lignin particle dispersion prepared in the step (1), 0.1 part by mass of formaldehyde (with the mass concentration of 37%) and 0.1 part by mass of citric acid to obtain a water phase; 0.9 parts by mass of epichlorohydrin and 30 parts by mass of isophorone are uniformly mixed to prepare an oil phase; then mixing the oil phase and the water phase, and carrying out emulsification treatment for 8min at 10000rpm by using an emulsifier to obtain a lignin O/W Pickering emulsion.
(3) And (3) synthesizing a lignin microcapsule: 0.01 part by mass of sodium hypophosphite is added into the emulsion, and after reaction for 1 hour at the stirring speed of 200rpm and the temperature of 80 ℃, the aqueous suspension of the lignin microcapsule is obtained.
The average particle diameter of the lignin microcapsules in the aqueous suspension of lignin microcapsules prepared in this example was determined to be 2.9 μm by means of a malvern laser particle sizer.
Example 4
(1) Preparation of lignin particle dispersion: adding 3 parts by mass of enzymatic hydrolysis lignin into 100 parts by mass of water, adding ammonia water to adjust the pH of the solution to 10 so as to completely dissolve the lignin, filtering, dropwise adding hydrochloric acid into the filtrate until the pH of the solution is 4, and continuously stirring to obtain the lignin particle dispersion.
(2) Preparation of lignin Pickering emulsion: firstly, uniformly mixing the lignin particle dispersion liquid prepared in the step (1) and 1.2 parts by mass of dimethylolethyleneurea to obtain a water phase; 2.1 parts by mass of 1, 6-dibromohexane and 35 parts by mass of n-amyl alcohol are uniformly mixed to prepare an oil phase; then mixing the oil phase and the water phase, and carrying out emulsification treatment for 5min at 11000rpm by using an emulsifier to obtain a lignin O/W Pickering emulsion.
(3) And (3) synthesizing a lignin microcapsule: to the above emulsion, 0.03 parts by mass of zinc nitrate and 0.03 parts by mass of potassium iodide were added, and the mixture was reacted at 65 ℃ for 5 hours with a stirring speed of 300rpm to obtain an aqueous suspension of lignin microcapsules.
The average particle diameter of the lignin microcapsules in the aqueous suspension of lignin microcapsules prepared in this example was measured to be 4.3 μm by a malvern laser particle sizer.
Example 5
(1) Preparation of lignin particle dispersion: adding 8 parts by mass of acid-out lignin powder from the wheat straw pulp black liquor into 100 parts by mass of water, adding sodium hydroxide to adjust the pH of the solution to 12 so as to completely dissolve the lignin, filtering, dropwise adding sulfuric acid into the filtrate until the pH of the solution is 5, and continuously stirring to obtain the lignin particle dispersion liquid.
(2) Preparation of lignin Pickering emulsion: firstly, uniformly mixing lignin particle dispersion liquid prepared in the step (1) with 3.2 parts by mass of ethylene glycol diglycidyl ether to obtain a water phase; uniformly mixing 6.4 parts by mass of epoxy chloropropane and 40 parts by mass of cyclohexanone to prepare an oil phase; then, the oil phase and the water phase were mixed, and emulsified for 10min at 13000rpm using an emulsifier to obtain a lignin O/W Pickering emulsion.
(3) And (3) synthesizing a lignin microcapsule: to the above emulsion, 0.04 part by mass of sodium chloride was added, and the mixture was reacted at 75 ℃ for 8 hours at a stirring speed of 400rpm to obtain an aqueous suspension of lignin microcapsules.
The average particle diameter of the lignin microcapsules in the aqueous suspension of lignin microcapsules prepared in this example was determined to be 6.2 μm by means of a malvern laser particle sizer.
Example 6
(1) Preparation of lignin particle dispersion: adding 10 parts by mass of acid-out lignin powder from reed pulp black liquor into 100 parts by mass of water, adding sodium hydroxide to adjust the pH of the solution to 12 so as to completely dissolve lignin, filtering, dropwise adding sulfuric acid into the filtrate until the pH of the solution is 6, and continuously stirring to obtain the lignin particle dispersion liquid.
(2) Preparation of lignin Pickering emulsion: uniformly mixing the lignin particle dispersion prepared in the step (1) with 5 parts by mass of glutaraldehyde and 5 parts by mass of ethylene glycol diglycidyl ether to obtain a water phase; uniformly mixing 10 parts by mass of epoxy chloropropane and 100 parts by mass of isophorone to prepare an oil phase; then, the oil phase and the water phase were mixed, and emulsified for 10min at 13000rpm using an emulsifier to obtain a lignin O/W Pickering emulsion.
(3) And (3) synthesizing a lignin microcapsule: 0.1 part by mass of sodium chloride was added to the above emulsion, and the mixture was reacted at 65 ℃ for 6 hours at a stirring speed of 400rpm to obtain an aqueous suspension of lignin microcapsules.
The average particle diameter of the lignin microcapsules in the aqueous suspension of lignin microcapsules prepared in this example was determined to be 5.1 μm by means of a malvern laser particle sizer.
Example 7
(1) Preparation of lignin particle dispersion: adding 4 parts by mass of acid-out lignin powder from bagasse pulp black liquor into 100 parts by mass of water, adding sodium hydroxide to adjust the pH of the solution to 10.5 so as to completely dissolve lignin, filtering, dropwise adding sulfuric acid into the filtrate until the pH of the solution is 4, and continuously stirring to obtain the lignin particle dispersion.
(2) Preparation of lignin Pickering emulsion: firstly, uniformly mixing lignin particle dispersion liquid prepared in the step (1) with 2 parts by mass of glutaraldehyde to obtain a water phase; uniformly mixing 2.4 parts by mass of 1, 4-dibromobutane and 60 parts by mass of cyclohexanone to prepare an oil phase; then mixing the oil phase and the water phase, and carrying out emulsification treatment for 5min at 11000rpm by using an emulsifier to obtain a lignin O/W Pickering emulsion.
(3) And (3) synthesizing a lignin microcapsule: 0.04 part by mass of potassium iodide was added to the above emulsion, and the mixture was reacted at 55 ℃ for 5 hours with stirring at 300rpm to obtain an aqueous suspension of lignin microcapsules.
The average particle diameter of the lignin microcapsules in the aqueous suspension of lignin microcapsules prepared in this example was 2.0 μm as determined by a malvern laser particle sizer.
Example 8
(1) Preparation of lignin particle dispersion: adding 6 parts by mass of acid-out lignin powder from the cotton stalk pulp black liquor into 100 parts by mass of water, adding potassium hydroxide to adjust the pH of the solution to 11 so as to completely dissolve the lignin, filtering, dropwise adding hydrochloric acid into the filtrate until the pH of the solution is 5, and continuously stirring to obtain the lignin particle dispersion liquid.
(2) Preparation of lignin Pickering emulsion: firstly, uniformly mixing the lignin particle dispersion liquid prepared in the step (1) with 13 parts by mass of formaldehyde (with the mass concentration of 37%) to obtain a water phase; uniformly mixing 6 parts by mass of 1, 6-dibromohexane and 50 parts by mass of isophorone to prepare an oil phase; then, the oil phase and the water phase were mixed, and emulsified for 5min at 13000rpm using an emulsifier to obtain a lignin O/W Pickering emulsion.
(3) And (3) synthesizing a lignin microcapsule: 0.06 potassium iodide was added to the above emulsion, and the mixture was reacted at 65 ℃ for 6 hours with a stirring speed of 400rpm to obtain an aqueous suspension of lignin microcapsules.
The average particle diameter of the lignin microcapsules in the aqueous suspension of lignin microcapsules prepared in this example was determined to be 3.4 μm by means of a malvern laser particle sizer.
Example 9
The application of the microcapsule in drug loading is realized by simultaneously dissolving hydrophobic drugs such as pesticides, medicines and the like and an oil phase cross-linking agent in an oil phase in the preparation process of the microcapsule and then carrying out subsequent emulsification and interfacial cross-linking operations. Wherein the weight ratio of the medicine to the organic solvent is (1-20): 100.
(1) adding 9 parts by mass of acid-out lignin powder from cotton pulp black liquor into 100 parts by mass of water, adding sodium hydroxide to adjust the pH of the solution to 12 so as to completely dissolve lignin, filtering, dropwise adding sulfuric acid into the filtrate until the pH of the solution is 6, and continuously stirring to obtain the lignin particle dispersion liquid.
(2) Preparation of lignin Pickering emulsion: firstly, uniformly mixing the lignin particle dispersion liquid prepared in the step (1) with 4.5 parts by mass of dimethylolethyleneurea to obtain a water phase; uniformly mixing 7.5 parts by mass of photolysis pesticide avermectin, 5.4 parts by mass of 1, 6-dibromohexane and 75 parts by mass of cyclohexanone to prepare an oil phase; then, the oil phase and the water phase were mixed, and emulsified for 8min at 13000rpm using an emulsifier to obtain a lignin O/W Pickering emulsion.
(3) Synthesizing the avermectin-encapsulated lignin microcapsule: to the above emulsion were added 0.05 part by mass of zinc nitrate and 0.09 part by mass of KI, and the mixture was reacted at 55 ℃ for 7 hours with a stirring speed of 400rpm to obtain an aqueous suspension of lignin microcapsules.
The average particle diameter of the lignin microcapsules in the aqueous suspension of lignin microcapsules prepared in this example was determined to be 5.7 μm by means of a malvern laser particle sizer. Through determination, the encapsulation rate of the abamectin reaches 90 percent; after the abamectin is irradiated by ultraviolet for 72 hours, the retention rate of the effective content of the abamectin reaches 85%, and the retention rate of the abamectin original drug is only 10.68% after the abamectin original drug is irradiated by the ultraviolet for 72 hours.
Description of the effects of the examples:
the effects will be described by taking example 1 as an example.
Figure 1 is a particle size distribution of lignin microcapsules in aqueous suspension of example 1 measured using a malvern laser particle sizer and is seen to have a bimodal distribution with a low peak around 200nm and a high peak around 1 um. FIG. 2 is a fluorescent microscope photograph of the lignin microcapsule prepared in example 1 of the present invention, which shows that the microcapsule is in a regular spherical shape and the wall is formed by cross-linking granular lignin. Fig. 3 to 5 are scanning electron micrographs of the lignin microcapsules prepared in this example, and it can be seen that the microcapsules are in a regular spherical shape, have a smooth surface, an average particle size of about 1 μm, and are consistent with the results of the laser particle sizer. As can be seen from the ruptured microcapsules (see FIG. 5), the microcapsules are hollow, indicating that the interior thereof is loaded with an oil phase prior to rupture; and the capsule wall has certain thickness and rigidity, and has better mechanical strength.
To further verify that the lignin did cross-link, the raw Alkali Lignin (AL) and microcapsule (ALMC) wall were characterized by ir spectroscopy, as shown in fig. 6.
For the raw material alkali lignin, the absorption peak caused by stretching vibration on phenolic hydroxyl and alcoholic hydroxyl is 3405-3450cm-1At least one of (1) and (b); 2933cm-1C-H stretching vibration peaks in methyl and methylene are nearby; 1033-1030cm-1The nearby absorption peak was assigned to the C-O stretching vibration absorption peak. Compared with alkali lignin as raw material, the ALMC has a cell wall of 2933cm-1And 1033cm-1The absorption peaks at these two positions are clearly enhanced. This is caused by an increase in ether bonds and methylene bonds in the molecular structure after the reaction of the alkali lignin with the crosslinking agent. The ir spectrum thus confirms that lignin forms the capsule wall by a cross-linking reaction.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (3)
1. A preparation method of a lignin wall material microcapsule based on Pickering emulsion interfacial crosslinking is characterized by comprising the following steps: preparing lignin particle dispersion liquid by alkali dissolution and acidification of lignin in water, and adding a water phase cross-linking agent to serve as a water phase; dissolving an oil phase cross-linking agent in an organic solvent to serve as an oil phase; mixing the water phase and the oil phase, and emulsifying to prepare O/W type Pickering emulsion; adding a catalyst, and heating to perform a crosslinking reaction to obtain a lignin wall material microcapsule;
the dosage of each component is as follows by mass: 100 parts of water; 0.1-10 parts of lignin; 0.01-10 parts of a water-phase crosslinking agent; 0.05-10 parts of an oil phase crosslinking agent; 10-100 parts of an organic solvent; 0.001-0.1 part of catalyst;
adding lignin into water, adding alkali to adjust the pH to 9-12 to obtain a lignin solution, and adding an acid to adjust the pH of a system to 2-6 to separate out the lignin to form a lignin particle dispersion liquid;
the heating crosslinking reaction is carried out at a stirring speed of 150-400 rpm and at a temperature of 40-80 ℃ for 1-8 h;
the organic solvent is one of cyclohexanone, isophorone, toluene and n-amyl alcohol;
the catalyst is at least one of potassium iodide, sodium chloride, zinc nitrate and sodium hypophosphite;
the water phase cross-linking agent is at least one of formaldehyde, glutaraldehyde, dimethylol ethylene urea, citric acid and ethylene glycol diglycidyl ether; the oil phase crosslinking agent is at least one of epichlorohydrin, 1, 4-dibromobutane and 1, 6-dibromohexane;
the emulsification is carried out for 1-10 min at 8000-13000 rpm.
2. The preparation method of the Pickering emulsion interface crosslinking-based lignin wall material microcapsule according to claim 1, wherein the preparation method comprises the following steps: the lignin is at least one of alkali lignin and enzymatic hydrolysis lignin; the alkali lignin is acid-out lignin powder which is obtained by acid-out and drying one of wood pulp black liquor, bamboo pulp black liquor, wheat straw pulp black liquor, reed pulp black liquor, bagasse pulp black liquor, asparagus pulp black liquor, cotton stalk pulp black liquor and cotton pulp black liquor; the enzymatic hydrolysis lignin is lignin separated and extracted from residues of alcohol prepared by fermenting cellulose in plant raw materials.
3. The preparation method of the Pickering emulsion interface crosslinking-based lignin wall material microcapsule according to claim 1, which is characterized by comprising the following steps:
(1) preparation of lignin particle dispersion: adding lignin into water, adding alkali to adjust the pH value to 9-12 to obtain a lignin solution, filtering to obtain a filtrate, and adding acid to adjust the pH value to 2-6 to obtain a lignin particle dispersion liquid;
(2) preparation of Pickering emulsion: adding a water phase cross-linking agent into the lignin particle dispersion liquid as a water phase, dissolving an oil phase cross-linking agent into an organic solvent as an oil phase, mixing the oil phase and the water phase, and emulsifying to obtain an oil-in-water Pickering emulsion with stable lignin particles;
(3) and (3) synthesizing a lignin microcapsule: adding a catalyst into the emulsion, and heating to initiate an emulsion interface crosslinking reaction to obtain the lignin wall material microcapsule suspension based on Pickering emulsion interface crosslinking.
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