Preparation method of Pickering emulsion, prepared Pickering emulsion and application of Pickering emulsion

Abstract

The invention discloses a preparation method of Pickering emulsion, the prepared Pickering emulsion and application of the Pickering emulsion. Comprising the following steps: mixing an aqueous solution containing chitin nano-bundles with an oil phase to obtain Pickering emulsion; the aqueous solution containing the chitin nano-beams is obtained by the following steps: reacting raw materials containing water, p-toluenesulfonic acid and chitin, and separating to obtain the aqueous solution containing the chitin nano-beams. And the lower-layer product obtained in the preparation of the nano chitin is utilized, so that the full-component utilization of the chitin is realized. The prepared Pickering emulsion has no oil-water separation phenomenon within 7 days.

Description

TECHNICAL FIELD

[0001] The application relates to a preparation method of a Pickering emulsion, the prepared Pickering emulsion and application thereof, and belongs to the technical field of nanomaterial preparation. BACKGROUND

[0002] The Pickering emulsion can hinder the aggregation of liquid drops through the physical blocking effect of solid particles at the interface of two phases, so that the emulsion can maintain long-term stability. However, inorganic solid particles can cause certain harm to the environment and human bodies, and especially the practical applicability in food is very limited. Therefore, various bio-based nanoparticles have attracted extensive attention of researchers because of the characteristics of green economy, environmental friendliness, biocompatibility and biodegradability. The nanochitin has rich hydrophilic amino groups, and is beneficial to the affinity with water phase and the self-assembly at the water interface. Compared with traditional surfactants, the nanochitin nanoparticles are environmentally friendly, biodegradable, renewable and non-toxic, and have important research significance in stabilizing emulsions. The nanochitin nanoparticles are analyzed through a three-phase contact angle, and have good wettability, so that the oil-in-water emulsion can be better stabilized. SUMMARY

[0003] The application prepares nanochitin from toluenesulfonic acid, and performs a series of characterization tests on the lower product (nanochitin nanobundle) obtained through centrifugation. It is found that the nanochitin nanobundle has good wettability, and the influences of different mass fractions of the nanochitin nanobundle and different oil-water mass ratios on the morphology, stability and droplet size of the Pickering emulsion are studied, so as to construct a Pickering emulsion stable system. Full-component utilization of the nanochitin is realized.

[0004] The micro-morphology of the nanochitin nanoparticles and the oil phase on the surface of the emulsion droplet can be further observed through a confocal microscope, so that the type of the emulsion is determined. The scanning electron microscope explains the deep mechanism of the nanochitin nanoparticles in stabilizing the Pickering emulsion, and provides a reference for the preparation of the nanochitin nanoparticles in the Pickering emulsion system.

[0005] According to one aspect of the application, a preparation method of a Pickering emulsion is provided, which comprises mixing an aqueous solution containing nanochitin nanobundles with an oil phase to obtain the Pickering emulsion.

[0006] The aqueous solution containing the nanochitin nanobundles is obtained through the following steps:

[0007] The raw materials containing water, p-toluenesulfonic acid and chitin are reacted, and the aqueous solution containing the nanochitin nanobundles is obtained through separation.

[0008] Optionally, in the aqueous solution containing the nanochitin nanobundles, the mass fraction of the nanochitin nanobundles is 0.2-1.6 wt%.

[0009] Optionally, the mass fraction of the chitin nanofibrils in the aqueous solution containing the chitin nanofibrils is 0.2-1.4wt%.

[0010] The mass ratio of the chitin nanofibrils in the aqueous solution containing the chitin nanofibrils to the oil phase is 1:9-9:1.

[0011] The oil phase is selected from at least one of soybean oil, palm oil, castor oil, corn oil, olive oil, tea seed oil, and n-hexadecane.

[0012] The mixing comprises high-speed shearing.

[0013] The shearing speed of the high-speed shearing is 10000-25000rpm.

[0014] The shearing time of the high-speed shearing is 1-5min.

[0015] The temperature of the reaction is 100-150℃.

[0016] The time of the reaction is 1-4h.

[0017] The separation comprises centrifugation and dialysis.

[0018] The speed of the centrifugation is 10000-15000rpm.

[0019] The time of the centrifugation is 1-10min.

[0020] The time of the dialysis is 1-48h.

[0021] Optionally, the separation comprises centrifugation, dialysis, and centrifugation again.

[0022] Optionally, the method comprises the following steps:

[0023] a) hydrolyzing chitin with p-toluenesulfonic acid, obtaining two fractionated products through centrifugation, dialysis, and centrifugation, wherein the lower product is named as chitin nanofibrils;

[0024] b) high-speed shearing the chitin nanofibrils and the oil phase to obtain a Pickering emulsion.

[0025] According to another aspect of the present application, a Pickering emulsion prepared by the above preparation method is provided.

[0026] According to another aspect of the present application, the above Pickering emulsion is applied to a raw material for 3D printing.

[0027] The beneficial effects that can be produced by the present application include:

[0028] (1) The lower product obtained in the preparation of the chitin nanometer particles is used to realize the full component utilization of the chitin.

[0029] (2) The stable Pickering emulsion can be obtained by regulating the chitin nanometer particles of different mass fractions and the oil-water mass ratio through a simple high-speed shearing machine, and no oil-water separation phenomenon occurs within 7 days. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a three-phase contact angle diagram of the chitin nanometer particles in Example 1 of the present application, wherein a is the air phase, and b is the oil phase.

[0031] Figure 2 It is a real photo and an optical microscope diagram of the Pickering emulsion of different oil-water mass ratios in Example 1 of the present application, wherein the scale of the optical microscope diagram is 20 μm.

[0032] Figure 3 It is a particle size diagram of the Pickering emulsion of different oil-water mass ratios in Example 1 of the present application, wherein A-E is at 1 day, and F-J is at 7 days.

[0033] Figure 4 It is a confocal microscope diagram of the Pickering emulsion in Example 1 of the present application, and the scale is 10 μm, wherein A is a diagram of the dyed oil phase, B is a diagram of the dyed chitin nanometer particles, C is a diagram of A and B combined, and D is a bright field diagram.

[0034] Figure 5 It is a scanning electron microscope diagram of the Pickering emulsion in Example 1 of the present application, wherein the scale of A is 1 μm, and the scales of B and C are 100 nm. DETAILED DESCRIPTION

[0035] The present application will be described in detail below in combination with examples, but the present application is not limited to these examples. Unless otherwise specified, the raw materials in the examples of the present application are purchased through commercial channels.

[0036] The analysis methods in the examples of the present application are as follows:

[0037] The Pickering emulsion of the chitin nanometer particles prepared in the examples of the present application is subjected to contact angle analysis, optical microscope testing, particle size testing, confocal microscope testing, and scanning electron microscope testing.

[0038] The contact angle of the chitin nanometer particles in the water phase and the oil phase is analyzed by the three-phase contact angle;

[0039] The contact angle analysis test conditions are: the wettability of chitin nanoparticles at the oil-water interface is characterized by measuring the three-phase contact angle. In a container (4x4 cm) filled with soybean oil, the sample is fixed above the container, and after the soybean oil covers the sample, a water droplet is added to the sample, and a digital camera is used to monitor the change of the contact angle of the sample.

[0040] The morphology and particle size of the Pickering emulsion stabilized by chitin nanoparticles are analyzed by optical microscopy.

[0041] The optical microscopy test conditions are: 0.5 g of the emulsion is taken and diluted 10 times to prepare the sample. A drop of the diluted sample is placed on a glass slide, and a cover glass is carefully placed on it to avoid air bubbles. Place it on the stage, rotate the focusing screw, and observe the morphology of the emulsion droplets under low magnification x20.

[0042] The two-phase interface stability of the Pickering emulsion stabilized by chitin nanoparticles is analyzed by confocal microscopy.

[0043] The confocal microscopy test conditions are: to observe the microstructure of the Pickering emulsion, a confocal microscope with a 20x / NA0.75 objective lens is used. Before preparing the emulsion, staining is performed using a staining agent as follows: mix Nile red solution (1 mg / mL, ethanol solution) with oil phase at a ratio of 1 / 25, and mix FITC solution (1 mg / mL, ethanol solution) with chitin nanoparticles at a ratio of 1 / 25. Finally, the stained oil phase and chitin nanoparticles are mixed under high shear to obtain the emulsion, and 0.5 g of the emulsion is taken and diluted 10 times for testing. A drop of the diluted sample is placed on a glass slide, and a cover glass is placed on it to avoid air bubbles. Place it on the stage, rotate the focusing screw, and observe the morphology of the emulsion droplets under low magnification x20. Use the LU-NV laser device to observe the oil phase and chitin nanoparticles in the emulsion. In addition, the excitation wavelengths of Nile red and FITC used are 488 nm and 543 nm, respectively. Finally, a CMOS camera is used to record the confocal images, and Image J (1.54f, Java 1.8.0_322) is used to process the obtained images.

[0044] The internal mechanism of the Pickering emulsion stabilized by chitin nanoparticles is analyzed by scanning electron microscopy.

[0045] The scanning electron microscopy test conditions are: the morphology of the sample is characterized by scanning electron microscopy. The sample is fixed on the sample stage using conductive glue, and finally the sample is sputtered with platinum using an ion sputtering instrument to improve conductivity.

[0046] Example 1

[0047] (1) The p-toluenesulfonic acid was hydrolyzed at 130℃ for 4h to prepare the chitin nanofiber. After the reaction was completed, the product was separated by centrifugation (15000rpm, 10min), dialysis (24h), and centrifugation (15000rpm, 10min).

[0048] (2) The soybean oil and the chitin nanofiber with a mass fraction of 1% were mixed at a mass ratio of 8:2, 7:3, 6:4, 5:5, and 4:6 by a high-speed shearing machine to form Pickering emulsions.

[0049] The high-speed shearing conditions were as follows: a shearing speed of 20000rpm and a shearing time of 3min.

[0050] Figure 1 The figure is a three-phase contact angle diagram of the chitin nanofiber in Example 1 of the present application, wherein a is an air phase and b is an oil phase. It can be seen from the figure that the θaw value of the chitin nanofiber is about 25° (measured after 120s) and the θow value is about 81° (measured after 120s). This indicates that the chitin nanofiber has good surface wettability, which may be due to the exposure of abundant -OH and -NH2 groups on the surface. In addition, according to the theory, it is assumed that the interface layer is single, and the chitin nanofiber with a θ angle between 15-90° has a good stabilizing effect on the O / W Pickering emulsion:

[0051] Figure 2 The figure is a photograph of the Pickering emulsion with different oil-water mass ratios in Example 1 of the present application and an optical microscope image, wherein the scale of the optical microscope image is 20μm. It can be seen from the figure that the 1wt% chitin nanofiber can only stabilize the Pickering emulsion when the oil-water ratio is 7:3. After standing for 7 days, no layering or demulsification phenomenon occurs. However, the emulsions with other oil-water ratios all show obvious layering phenomenon.

[0052] Figure 3 The figure is a particle size diagram of the Pickering emulsion with different oil-water mass ratios in Example 1 of the present application, wherein A-E are 1 day and F-J are 7 days. It can be seen from the figure that the emulsion particle sizes are 49.4μm, 26.6μm, 39.8μm, 35.6μm and 33.9μm, respectively. Among them, the emulsion particle size is the smallest and uniformly distributed when the oil-water ratio is 7:3. At the same time, the particle size of the ChSR-stabilized emulsion shows a slight growth trend after standing for 7 days.

[0053] Figure 4The confocal microscope image of the Pickering emulsion in Example 1 of the present application is 10 μm in scale, wherein A is a dyed oil phase image, B is a dyed chitin nanobundle image, C is a combined image of A and B, and D is a bright field image; it can be seen from the images that after 24 hours of storage, the emulsion droplets are observed to be regular spherical, the emulsion droplet size is about 24 μm, the emulsion droplets are not coalesced and maintain good separation. The micro-morphology does not show obvious damage, and the emulsion is relatively stable in the storage process and does not show phase separation, indicating that the chitin nanoparticles have good stability. According to the combined image of C, a green outline around the oil droplets is observed, indicating that the chitin nanoparticles are located at the oil-water interface and are successfully wrapped around the oil droplets. This also directly proves that the chitin nanoparticles can stabilize the Pickering O / W emulsion. The prerequisite for the formation of the Pickering O / W emulsion is that the solid particles are dispersed around the oil to form a two-phase interface particle film. When the content of the solid particles is insufficient, the solid particles at the oil-water interface cannot completely cover the surface of the oil droplets, ultimately leading to the coalescence and flocculation of the emulsion. In order to form a stable oil-in-water emulsion, the particle concentration needs to reach the critical value at which the oil droplet surface is completely covered, so that the particles can form a complete physical barrier at the interface to stabilize the emulsion. Figure 4

[0054] Figure 5 The scanning electron microscope image of the Pickering emulsion in Example 1 of the present application is 1 μm in scale for A and 100 nm in scale for B and C. It can be seen from the images that: Figure 5 B and C of the above are enlarged images, from which it can be observed that the chitin nanoparticles are tightly wrapped around the surface of the microspheres, which again confirms that the chitin nanoparticles can be used as a Pickering emulsion stabilizer. According to the observation results of the electron scanning microscope, it can be determined that the mechanism by which the chitin nanoparticles stabilize the Pickering emulsion is that the chitin nanoparticles tightly wrap the surface of the droplets to form a high-efficiency and robust physical interface barrier, thereby achieving the effect of stabilizing the oil droplets.

[0055] Example 2

[0056] The specific operation is the same as that of Example 1, except that the conditions for hydrolysis of p-toluenesulfonic acid to prepare nanochitin are 120°C and 2 h; the lower product (chitin nanobundle particles) is separated and collected by centrifugation (10000 rpm, 5 min), dialysis (12 h) and centrifugation (10000 rpm, 5 min).

[0057] Example 3

[0058] The specific operation is the same as that of Example 1, except that the conditions for high-speed shearing are a shearing speed of 10000 rpm and a shearing time of 5 min.

[0059] Example 4

[0060] ​The specific operation is the same as that in Example 1, except that the oil phase is n-hexadecane, and the high-speed shearing condition is: shearing speed 25000 rpm, shearing time: 5 min.

[0061] The above is only a few embodiments of the present application, and does not limit the present application in any form. Although the preferred embodiments are disclosed above, they are not intended to limit the present application. Any skilled person in the art can make some changes or modifications to the above disclosed technical contents without departing from the scope of the technical solutions of the present application, which are equivalent to equivalent embodiments, and are within the scope of the technical solutions.

Claims

1. A method for preparing a Pickering emulsion, characterized in that, an aqueous solution containing chitin nanofibrils is mixed with an oil phase to obtain a Pickering emulsion; the aqueous solution containing chitin nanofibrils is obtained by the following steps: raw materials containing water, p-toluenesulfonic acid and chitin are reacted, and the aqueous solution containing chitin nanofibrils is obtained by separation. 2.The method according to claim 1, characterized in that, the mass fraction of the chitin nanofibrils in the aqueous solution containing chitin nanofibrils is 0.2-1.6wt%; preferably, the mass fraction of the chitin nanofibrils in the aqueous solution containing chitin nanofibrils is 0.2-1.4wt%. 3.The method according to claim 1, characterized in that, the mass ratio of the chitin nanofibrils in the aqueous solution containing chitin nanofibrils to the oil phase is 1:9-9:

1. 4.The method according to claim 1, characterized in that, the oil phase is selected from at least one of soybean oil, palm oil, castor oil, corn oil, olive oil, tea seed oil and n-hexadecane. 5.The method according to claim 1, characterized in that, the mixing includes high-speed shearing; the shearing speed of the high-speed shearing is 10000-25000rpm; the shearing time of the high-speed shearing is 1-5min. 6.The method according to claim 1, characterized in that, the temperature of the reaction is 100-150℃; the time of the reaction is 1-4h. 7.The method according to claim 1, characterized in that, the separation includes centrifugation and dialysis; the speed of the centrifugation is 10000-15000rpm; the time of the centrifugation is 1-10min; the time of the dialysis is 1-48h. 8.A Pickering emulsion prepared by the method according to any one of claims 1-7. 9.Use of the Pickering emulsion according to claim 8, characterized in that, as a raw material for 3D printing.

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