Rosin-based pH-responsive emulsion system as well as preparation method and application thereof

Abstract

The invention discloses a rosinyl pH response type emulsion system as well as a preparation method and application thereof. The rosinyl pH response type emulsion system is formed by dispersing a pH response type rosinyl surfactant and nano cellulose in a water phase and an oil phase, when the pH value is less than or equal to 5.2, the rosin-based pH response type emulsion system is a Pickering gel emulsion with large liquid drops and high viscosity; when the pH value is greater than or equal to 9.1, the rosin-based pH response type emulsion system is an oil-in-dispersion emulsion with small liquid drops and low viscosity; the pH response type rosin-based surfactant is prepared by carrying out an imidization reaction on maleopimaric acid and amine. By adjusting the pH value, the emulsion system can be converted between a Pickering gel emulsion and an oil-in-dispersion emulsion, and the particle size, the viscosity and the stability of drops can be flexibly and accurately regulated and controlled by adjusting the pH value, so that the application requirements under different conditions are met.

Description

Technical Field

[0001] The invention belongs to the field of rosin chemical utilization and colloid and interface chemistry, and specifically relates to a rosin-based pH-responsive emulsion system, a preparation method and application thereof. Background Art

[0002] Emulsion is a typical liquid / liquid dispersion system, which is widely used in food, cosmetics, pesticide formulations, etc. Surfactants, polymers or solid particles play an important role in the stability of emulsions. Compared with surfactants or polymers, solid particles can be irreversibly adsorbed on the oil / water interface, making the emulsion extremely stable. However, some emulsions only need to remain stable temporarily, and they need to be demulsified after the emulsion application is completed. For example, in emulsion polymerization, the emulsion must remain stable during the polymerization stage, and after the polymerization reaction is completed, it needs to be demulsified quickly so that the product can be collected smoothly; in the process of emulsified crude oil transportation, the crude oil emulsion needs to remain stable, but after reaching the destination, it needs to be demulsified to release the crude oil, which gives rise to a new type of emulsion: stimulus-responsive emulsion. Stimuli-responsive emulsion is a type of emulsion that can be reversibly switched between "stable" and "unstable" on demand by environmental stimuli. It can achieve emulsification and demulsification through simple and effective adjustment methods such as pH, light, magnetic field, CO2 / N2, etc. However, current stimulus-responsive surfactants lose their hydrophilicity after demulsification and are easily dissolved in the oil phase, making them difficult to recover and reuse, thus affecting the quality of the oil phase.

[0003] Nanocellulose is a kind of natural nanoparticles with the characteristics of modifiability, renewability, biodegradability, non-toxicity and excellent mechanical properties. It is a kind of food-grade emulsifier. However, the process of introducing responsive groups on the surface of nanocellulose by chemical modification is complicated and the conditions are harsh, which limits the application of stimulus-responsive nanocellulose Pickering emulsions. In situ hydrophobic modification of nanocellulose by adsorbing surfactants of opposite charge is a simple and effective method for preparing stimulus-responsive Pickering emulsions. Changing the structure of the surfactant can indirectly regulate the hydrophilicity and hydrophobicity of nanocellulose, and then regulate the performance of the Pickering emulsion. Rosin is a natural renewable resin secreted by pine trees and is a special biomass resource in my country. The main component of rosin is rosin resin acid, which has a unique tricyclic diterpene rigid structure and super hydrophobicity. It is an important raw material for preparing green surfactants. Rosin-based surfactants not only have strong emulsification, but also can increase the viscosity of the emulsion. Using nanocellulose and rosin-based surfactants as emulsifiers to prepare emulsions can give full play to their respective advantages.

[0004] The present invention uses nanocellulose and a pH-responsive rosin-based surfactant as emulsifiers to prepare a rosin-based pH-responsive emulsion system. By changing the pH value of the system, it can be converted between a Pickering gel emulsion and an oil-in-dispersion emulsion. When the pH is less than or equal to 5.2, the emulsion system is a Pickering gel emulsion with high viscosity; when the pH is greater than or equal to 9.1, the emulsion is an oil-in-dispersion emulsion with a smaller particle size and lower viscosity. On the one hand, the particle size, viscosity and stability of the droplets in the rosin-based pH-responsive emulsion system can be flexibly and accurately controlled by pH adjustment to meet the application requirements in different situations; on the other hand, the pH-responsive surfactant and nanocellulose can be recycled and reused multiple times in the rosin-based pH-responsive emulsion system. Based on the unique pH responsiveness, excellent recyclability and low production cost, the rosin-based pH-responsive emulsion system has good economic benefits and potential for sustainable application. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a rosin-based pH-responsive emulsion system, a preparation method thereof and applications thereof.

[0006] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0007] A rosin-based pH-responsive emulsion system is formed by dispersing a pH-responsive rosin-based surfactant and nanocellulose in a water phase and an oil phase; wherein the pH-responsive rosin-based surfactant is prepared by an imidization reaction of maleopimaric acid and an amine.

[0008] In the rosin-based pH-responsive emulsion system of the present application, the particle size, viscosity and stability of the droplets can be flexibly and accurately controlled by pH adjustment to meet different application requirements.

[0009] The rosin-based pH-responsive emulsion system of the present application can be cyclically switched between a Pickering gel emulsion and an oil-in-dispersion emulsion.

[0010] Adjust the pH, the rosin-based pH-responsive emulsion system switches between the Pickering gel emulsion and the oil-in-dispersion emulsion, and can be repeatedly cycled. The specific process is as follows: adjust the pH of the Pickering gel emulsion to pH ≥ 9.1, completely demulsify, directly homogenize or homogenize after renewing the oil phase to form an oil-in-dispersion emulsion; adjust the pH of the oil-in-dispersion emulsion to pH ≤ 5.2, completely demulsify, directly homogenize or homogenize after renewing the oil phase to form a Pickering gel emulsion; the above process can be repeatedly cycled. The above homogenization is dispersed for 3 to 5 minutes under the condition of 8000 to 10000 r / min.

[0011] The above properties can be utilized to recover the oil phase after demulsification, reuse the emulsifier multiple times, etc.

[0012] The pH-responsive rosin-based surfactant and nanocellulose used as emulsifiers in the present application can be separated and recovered multiple times.

[0013] The rosin-based pH-responsive emulsion system of the present application can be used in drug delivery or emulsified crude oil delivery. For example, in the initial stage of crude oil delivery, the crude oil emulsion needs to remain stable. After reaching the destination, an acidic or alkaline solution is added to break the emulsion to release the crude oil without polluting the crude oil; or it can be used for emulsion polymerization. In the polymerization stage, a pickering gel emulsion is prepared. The emulsion can remain stable. After the polymerization reaction is completed, an acidic or alkaline solution is added to quickly break the emulsion so that the product can be collected smoothly; or it can be used to improve oil recovery. The emulsifier can be used as an oil displacement agent to reduce the interfacial tension between oil and water and reduce the wettability of oil and rock, thereby improving the recovery rate; or it can be used for two-phase catalytic reactions, the synthesis of nanomaterials and polymer particles. For example, the emulsion system can provide an appropriate pH environment for different stages of the reaction, control the stability of the emulsion and the appropriate emulsion viscosity to adapt to the catalytic activity of the reaction, promote the recovery of the obtained products and catalysts, and reduce the reaction cost.

[0014] In order to ensure the stability and sensitivity of the rosin-based pH-responsive emulsion system, the structure of the pH-responsive rosin-based surfactant is as follows:

[0015] n=2 or 3;

[0016] The preparation method of the pH-responsive rosin-based surfactant is as follows: maleopimaric acid and amine are added to an organic solvent for imidization reaction to obtain a pH-responsive rosin-based surfactant; after the reaction is completed, the precipitate is filtered out, washed, and dried to obtain a pure product.

[0017] In order to improve the product yield and reduce the side reaction, the molar ratio of maleopimaric acid and amine is 1:(1.05-1.20); the amine is one of N,N-dimethylethylenediamine or N,N-dimethylpropylenediamine; the organic solvent is ethanol (EtOH); the reaction temperature is 60-90°C, and the reaction time is 5-12h.

[0018] The regulation mechanism of pH-responsive rosin-based surfactants is as follows:

[0019]

[0020] , wherein R is Na or K, and n=2 or 3.

[0021] When pH≤5.2, the pH-responsive rosin-based surfactant is a cationic surfactant; when pH≥9.1, the carboxylic acid of the pH-responsive rosin-based surfactant is completely converted into a carboxylate, and the cationic amine salt is converted into a hydrophobic tertiary amine, thereby converting into an anionic surfactant; by adjusting the pH≤5.2 or pH≥9.1, the pH-responsive rosin-based surfactant can be reversibly converted between a cationic surfactant and an anionic surfactant, and both surfactants have good water solubility.

[0022] In order to take into account both the stability of the emulsion and the sensitivity of the response, the mass fraction of nanocellulose relative to the water phase is 0.1% to 0.5%. The concentration of the pH-responsive rosin-based surfactant relative to the water phase is 0.001 to 5 mmol·L -1 .

[0023] The oil phase is at least one of n-hexane, n-octane, n-decane or soybean oil.

[0024] The preparation method of the above-mentioned rosin-based pH-responsive emulsion system comprises the following steps:

[0025] S1, adding nanocellulose to deionized water 1 and ultrasonically dispersing for 0.5 to 1 h to prepare solution A;

[0026] S2, deionized water 2 and pH-responsive rosin-based surfactant were mixed evenly and added to solution A, and then ultrasonically dispersed for 0.5 to 1 h to obtain solution B;

[0027] S3, 0.5 mol·L -1 NaOH / KOH solution or HCl solution, adjust the pH of solution B to ≤5.2 to obtain solution C1, and adjust the pH of solution B to ≥9.1 to obtain solution C2;

[0028] S4. Add the oil phase to solution C1 and homogenize to obtain a Pickering gel emulsion. Add the oil phase to solution C2 and homogenize to obtain an oil-in-dispersion emulsion. The homogenization speed is 8000-15000 rpm and the time is 3-8 min.

[0029] The technologies not mentioned in the present invention are all referred to the prior art.

[0030] The present invention uses a pH-responsive rosin-based surfactant and nanocellulose as emulsifiers to prepare an ultra-stable stimulus-responsive emulsion system. The emulsion system can be converted between a Pickering gel emulsion and an oil-in-dispersion emulsion. When the pH is ≤5.2, the emulsion system is a Pickering gel emulsion with high viscosity; when the pH is ≥9.1, the emulsion system is an oil-in-dispersion emulsion with a small droplet size and low viscosity. The particle size, viscosity and stability of the droplets in the rosin-based pH-responsive emulsion system can be flexibly and accurately controlled by pH adjustment to meet application requirements in different situations. In addition, by adjusting the pH, the emulsifier and the oil phase in the emulsion system can be repeatedly recycled and reused, and the quality of the oil phase remains unchanged before and after recycling, which has good economic benefits and potential for sustainable application. It plays an important role in drug delivery, oil emulsification transportation, emulsion polymerization, oil extraction, two-phase catalytic reaction, nanomaterials and synthesis of polymer particles. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The MPAA obtained in Example 1 1 H NMR spectra;

[0032] Figure 2 MPAA (1 g·L -1 ) / pH variation with HCl volume in NaOH aqueous solution;

[0033] Figure 3 The MPAAH and MPAANa obtained in Example 2 1 H NMR spectra;

[0034] Figure 4 The graph is a graph showing the change in surface tension of the aqueous solution of MPAA obtained in Example 3 at pH = 10.0 and pH = 4.0 as a function of concentration;

[0035] Figure 5The appearance photos of the n-decane / water (O / W type) emulsion stabilized by nanocellulose (mass fraction of 0.5%, relative to the water phase) and different concentrations of surfactant MPAAH in Example 4; a to c are the appearance photos after standing for one day, seven days and one month respectively. (The concentrations of the solutions from left to right are 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5 mmol × L -1 );

[0036] Figure 6 Optical microscopy images of n-decane / water (O / W type) emulsions stabilized by nanocellulose (mass fraction of 0.5%, relative to the water phase) and surfactant MPAAH at different concentrations in Example 4 at one day, seven days and one month;

[0037] Figure 7 The particle size diagrams of n-decane / water (O / W type) emulsions stabilized by nanocellulose (mass fraction of 0.5%, relative to the water phase) and surfactant MPAAH at different concentrations in Example 4 after seven days (a) and one month (b);

[0038] Figure 8 The appearance photos of the n-decane / water (O / W type) emulsion stabilized by nanocellulose (mass fraction of 0.5%, relative to the water phase) and different concentrations of surfactant MPAANa in Example 4; a to c are the appearance photos after standing for one day, seven days and one month respectively. (The concentrations of the solutions from left to right are 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5 mmol×L -1 );

[0039] Fig. 9 Optical microscopy images of n-decane / water (O / W type) emulsions stabilized by nanocellulose (mass fraction of 0.5%, relative to the water phase) and surfactant MPAANa at different concentrations in Example 4 at one day, seven days and one month;

[0040] Fig.10 The appearance of the n-decane / water (O / W type) emulsion stabilized by surfactant MPAA at pH = 4.0 or pH = 10.0 in Comparative Example 1 and the 5mmol·L -1 One month optical micrograph of MPAAH-stabilized emulsion;

[0041] Fig.11 The different concentrations of nanocellulose and 1 mmol × L in Example 5 -1 Appearance photos of n-decane / water (O / W type) emulsions stabilized by surfactant MPAAH; (from left to right, the mass fraction of nanocellulose is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, relative to the water phase);

[0042] Fig.12 For different nanocellulose and 1mmol×L in Example 5 -1 Optical micrograph of n-decane / water (O / W type) emulsion co-stabilized by surfactant MPAAH;

[0043] Fig.13 The different concentrations of nanocellulose and 1 mmol × L in Example 5 -1 Appearance photos of n-decane / water (O / W type) emulsions stabilized by surfactant MPAANa; (from left to right, the mass fraction of nanocellulose is 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, relative to the water phase);

[0044] Fig.14 The different concentrations of nanocellulose and 1 mmol × L in Example 5 -1 Optical micrograph of n-decane / water (O / W type) emulsion co-stabilized by surfactant MPAANa;

[0045] Fig.15 0.5% nanocellulose and 1 mmol × L in Example 6 -1 Stimulus-response appearance of n-decane without replacement of the oil phase during the cycle of surfactant MPAA;

[0046] Fig.16 0.5% nanocellulose and 1 mmol × L in Example 6 -1 Optical microscopy image of n-decane in the oil phase without replacement during the circulation of surfactant MPAA;

[0047] Fig.17 0.5% nanocellulose and 1 mmol × L in Example 6 -1 Rheological diagram of n-decane without replacing the oil phase during the circulation of surfactant MPAA;

[0048] Fig.18 The 0.5% nanocellulose and 0.1 mmol × L -1 Stimulus-response appearance of replacing oil phase n-decane during the cycle of surfactant MPAA;

[0049] Fig.19 The 0.5% nanocellulose and 0.1 mmol × L -1 Optical microscopy image of the replacement of n-decane in the oil phase during the circulation of surfactant MPAA;

[0050] Fig. 20 The 0.5% nanocellulose and 0.1 mmol × L -1Rheological diagram of replacing oil phase n-decane during the circulation of surfactant MPAA;

[0051] Fig.21 The interfacial tension between the fresh n-decane obtained in Application Example 1 and the ultrapure water and between the separated oil phase and the ultrapure water;

[0052] Fig. 22 The fresh n-decane obtained in Application Example 1 and the separated oil phase 1 H NMR spectra. DETAILED DESCRIPTION

[0053] In order to better understand the present invention, the content of the present invention is further explained below in conjunction with the embodiments, but the content of the present invention is not limited to the following embodiments.

[0054] Example 1

[0055] The preparation of pH-responsive rosin-based surfactant comprises the following steps:

[0056] 1) Synthesis of pH-responsive rosin-based surfactant MPAA: 10 g (0.025 mol) of maleopimaric acid, 2.81 g (0.0275 mol) of N,N-dimethylpropylenediamine and 80 g of EtOH were added to a 250 mL three-necked flask. A magnetic bar was added to connect the reflux condenser, and the mixture was stirred at 80°C for 5 h. The reaction solution was cooled to room temperature, the precipitate was filtered out and washed twice with EtOH, and dried to obtain a white solid with a yield of 82.3%. 1 HNMR Figure 1 As shown, the structure is

[0057]

[0058] 2) Synthesis of pH-responsive rosin-based surfactant MPAB: 10 g (0.025 mol) of maleopimaric acid, 2.42 g (0.0275 mol) of N,N-dimethylethylenediamine and 80 g of EtOH were added to a 250 mL three-necked flask. A magnetic stirrer was added and a reflux condenser was connected. The mixture was stirred at 80°C for 5 h. The reaction solution was cooled to room temperature. The precipitate was filtered out and washed twice with EtOH and dried to obtain a white solid with a yield of 83.5%. The structure is

[0059]

[0060] Example 2

[0061] pH responsiveness of pH-responsive rosin-based surfactant (prepared in Example 1):

[0062] The two ends of the MPAA molecule structure contain a tertiary amine group and a carboxylic acid group, both of which are pH-responsive groups. Dissolve 0.05 g of MPAA in 50 ml of NaOH solution (0.1 mol·L -1 ), the change of MPAA structure with pH was detected by acid-base titration. Figure 2 As shown, initially during the titration, the presence of NaOH causes the carboxyl group of MPAA to be converted into sodium carboxylate. With the addition of HCl, the pH initially drops slowly, due to the neutralization of NaOH in the solution with HCl. When NaOH is completely neutralized by HCl, the pH drops rapidly. When the pH is 9.1, the pH drop slows down, indicating that after the addition of HCl, the tertiary amine group is protonated into amine hydrochloride and the sodium carboxylate is protonated into carboxyl group. At a pH of 5.2, the pH drops rapidly again, indicating that MPAA has been completely converted into acid. Therefore, when pH ≤ 5.2, MPAA is converted into its cationic form (MPAAH); by adjusting the pH ≥ 9.1, its anionic form (MPAANa) can be obtained. In addition, the 1 H NMR Figure 3 At MPAAH 1 In the H NMR spectrum, a chemical shift due to H protons on the amine hydrochloride group was found at 10.78 ppm, and a chemical shift due to H protons on the carboxyl group was found at 12.12 ppm. 1 Compared with HNMR, MPAANa has no chemical shift at 10.78 ppm and 12.12 ppm, indicating that the amine hydrochloride is deprotonated to become a tertiary amine group, and the carboxyl group is converted to a sodium carboxylate. Therefore, the pH-responsive rosin-based surfactant can be reversibly switched between a cationic surfactant and an anionic surfactant by changing the pH.

[0063] Example 3

[0064] Determination of critical micelle concentration of pH-responsive rosin-based surfactant (prepared in Example 1)

[0065] The critical micelle concentration is an important parameter to characterize the aggregation ability of surfactants. In this study, the critical micelle concentration (cmc) of surfactants was determined by the Wilhelmy plate method using a Sigma 701 surface tension meter. The measurement temperature was 25°C, and the Wilhelmy plate was 19.44 mm wide, 0.1 mm thick, and 65 mm high. Each point was measured three times, and the measurement error of each point was set to 0.05 mN×m -1 . Draw a curve of the surface tension of the surfactant as it changes with its concentration, such as Figure 4 When the pH is 10.0, the cmc of MPAANa is 2.9 mmol·L -1 , its surface tension (γ cmc) is 44.6mN·m -1 When the pH dropped to 4.0, the cmc of MPAAH increased to 7.0 mmol·L -1 , γ cmc 39.5 mN·m -1 Compared with anionic surfactants under alkaline conditions, cationic surfactants under acidic conditions can effectively reduce the surface tension of water, thereby enhancing the stability of the emulsion.

[0066] Example 4

[0067] Preparation of rosin-based pH-responsive emulsion

[0068] S1, adding nanocellulose to deionized water and ultrasonically dispersing it at a power of 170 W for 0.5 h to prepare a nanocellulose solution with a mass concentration of 1%;

[0069] S2. Mix deionized water and MPAA of different masses evenly to obtain MPAA dispersions of different concentrations (0, 0.02, 0.04, 0.1, 0.2, 0.4, 1, 2, 4, 10 mmol × L -1 );

[0070] S3, adding 4.5 ml of 1% nanocellulose solution into 4.5 ml of MPAA dispersions of different concentrations, and dispersing them ultrasonically at a power of 170 W for 0.5 h to obtain a series of different mixed solutions B;

[0071] S4, respectively, the mixed solution B was 0.5 mol·L -1 NaOH solution or 0.5 mol·L -1 HCl solution to adjust the pH to obtain solutions of pH = 10.0 and pH = 4.0;

[0072] S5. Add 9 ml of n-decane to 9 ml of the solution at pH = 10.0 and pH = 4.0 respectively, and disperse using a high-speed disperser (homogenizing at a rotation speed of 10,000 rpm for 5 minutes) to prepare a series of emulsions.

[0073] Figure 5 Appearance of the emulsion (water-in-oil Pickering gel emulsion) with pH = 4.0 after inversion for 24 h (a), 7 days (b) and 30 days (c). The mass concentration of nanocellulose relative to the aqueous phase is 0.5%. The concentrations of MPAA solutions from left to right are 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5 mmol × L -1 .Depend on Figure 5It can be seen that the obtained Pickering gel emulsion can support its own gravity and has the properties of a gel. -1 When the Pickering gel emulsion is used, it can still remain stable for 30 days without demulsification. Figure 6 As shown, when the concentration is lower than 5mmol·L -1 When the concentration of MPAA increases, the average particle size of the Pickering gel emulsion gradually decreases and the stability increases. -1 When the droplet size of the Pickering gel emulsion increases again, this is because most of the surfactants self-assemble in water, and only a small amount of surfactants are adsorbed at the oil-water interface to stabilize the emulsion. Figure 7 As shown, the average particle size of the Pickering gel emulsion hardly changed within 30 days, and the results showed that the gel emulsion was stable for at least 1 month.

[0074] Figure 8 Appearance of the emulsion (oil-in-dispersion emulsion) with pH = 10.0 after 24h, 7 days and 30 days of inversion. The mass concentration of nanocellulose relative to the aqueous phase is 0.5%. The concentrations of MPAA solutions from left to right are 0, 0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 5 mmol × L -1 .like Figure 8 As shown in the figure, the oil-in-dispersion emulsion can remain stable for 30 days without demulsification. -1 When the emulsification index reaches 100%. Fig. 9 As shown in Figure 2, the average droplet size of the emulsion decreases with the increase of MPAA concentration. In addition, when the MPAA concentration is 0.2 mmol·L -1 The droplet size of the oil-in-dispersion emulsion remained unchanged at 7 and 30 days, and the other concentrations also had this property. The results showed that the oil-in-dispersion emulsion was stable for at least 1 month.

[0075] Comparative Example 1

[0076] Referring to the method of Example 4, emulsions with a nanocellulose content of 0, different concentrations of MPAA, pH = 4.0, and an oil phase of n-decane were prepared. Fig.10 As shown in the figure, at pH = 4.0, all emulsions cannot stand upside down without cellulose. -1 The emulsion broke in 7 days, even at 10mmol·L -1At this concentration, the emulsification index cannot reach 80%. -1 Taking the particle size of as an example, the particle size of the emulsion is ten times smaller than the particle size of cellulose added in Example 4 at the same concentration.

[0077] Referring to the method of Example 4, emulsions with a nanocellulose content of 0, different concentrations of MPAA, pH = 10.0, and an oil phase of n-decane were prepared. Fig.10 As shown in the figure, when the pH is adjusted to 10.0, even if the concentration of MPAA is 10 mmol·L -1 , the emulsification index still cannot reach 30%, and the emulsion cannot be stable for 1 month. -1 Taking the emulsion as an example, the droplet size of the emulsion stabilized by MPAA alone is similar to the droplet size of the oil-in-dispersion emulsion in Example 4 at the same concentration.

[0078] Example 5

[0079] Referring to the method of Example 4, different nanocellulose contents were prepared, and MPAA was 1 mmol·L -1 , pH = 4.0, the oil phase is an emulsion of n-decane. Fig.11 As shown, even when the nanocellulose content is as low as 0.1%, the emulsion can remain stable for 30 days without demulsification, but the emulsification index is relatively low; the emulsification index of the emulsion increases monotonically with the increase of nanocellulose content. When the nanocellulose content is greater than 0.3%, the Pickering emulsion is able to support its own gravity to form a Pickering gel emulsion. After 30 days, slight separation was observed in the Pickering emulsion gel with a nanocellulose content of less than 0.3%, while no separation was observed in the Pickering emulsion gel with a content of 0.4% and 0.5%. As Fig.12 As shown in Figure 2, with the increase of nanocellulose content, the droplet size of Pickering emulsion gradually decreases. The study shows that the higher the nanocellulose content, the better the emulsification and the better the stability of the emulsion.

[0080] Referring to the method of Example 4, different nanocellulose contents were prepared, and MPAA was 1 mmol·L -1 , pH = 10.0, the oil phase is an emulsion of n-decane. Fig.13 As shown. The emulsification index of the emulsion increases monotonically with the increase of nanocellulose content. After 7 days, liquid separation was observed in the emulsion with a nanocellulose content of less than 0.4%, while no separation was observed in the emulsion with a content of 0.5%. Moreover, the emulsion with a nanocellulose content of less than 0.3% could not be stable for more than 14 days. Under the same conditions, the stability of the oil-in-dispersion emulsion is lower than that of the Pickering emulsion. Fig.14 The droplet size of the oil-in-dispersion emulsions changed little with increasing nanocellulose content.

[0081] Example 6

[0082] Stimuli-responsive properties of rosin-based pH-responsive emulsion systems

[0083] Referring to the method of Example 4, the nanocellulose content was 0.5% and the MPAA content was 1 mmol·L -1 , pH = 4.0, the oil phase is a Pickering gel emulsion of n-decane. Fig.15 As shown, a concentration of 0.5 mmol·L -1 The pH of the NaOH aqueous solution was adjusted to 10.0, and the cationic surfactant was deprotonated to an anionic surfactant. The Pickering gel emulsion was completely demulsified, and no droplets were observed under the microscope. After the oil-water mixture was homogenized, an oil-in-dispersion emulsion with a smaller droplet size (10-15μm, Fig.15 ). Further add 0.5mmol·L -1 The pH value was adjusted to 4.0 again by adding HCl aqueous solution. MPAA was protonated to cationic form and desorbed from the oil / water interface. The oil-in-dispersion emulsion was demulsified and further formed into a Pickering gel emulsion with a larger droplet diameter (20-25 μm) after homogenization. Fig.16 ). The above reaction process is completely reversible by adding NaOH or HCl, and after 4 cycles, there is no significant change in the macroscopic appearance and microscopic image of the droplets. The emulsion in each cycle has a particle size distribution similar to that of the original emulsion. In addition, compared with the original emulsion, the viscous modulus G″ and elastic modulus G′ of the emulsion after 4 cycles also have no significant change ( Fig.17 ), indicating that pH control has little effect on the viscoelasticity of Pickering gel emulsion and oil-in-dispersion emulsion. The above results show that the emulsion system has excellent and unique pH response properties.

[0084] Example 7

[0085] Recovery and reuse of emulsifier in rosin-based pH-responsive emulsion system

[0086] Referring to the method of Example 4, the nanocellulose content was 0.5% and the MPAA content was 1 mmol·L -1 , pH 4.0, Pickering gel emulsion with n-decane as the oil phase. Fig.18 As shown, a concentration of 0.5 mol·L-1 The NaOH aqueous solution was added to completely demulsify the emulsion. About 9 mL of the oil phase was removed, and then an equal volume of new oil was added and homogenized (homogenized at a speed of 10000 rpm for 5 min) to form an oil-in-dispersion emulsion. -1 The pH value of the oil-in-dispersion emulsion was adjusted to 4.0 with HCl aqueous solution, and the emulsion could be demulsified quickly. The separated oil was replaced with new oil, and a new Pickering gel emulsion was obtained after homogenization (homogenization at a speed of 10000 rpm for 5 min). Even though the oil phase was replaced 6 times, the microscopic morphology of the Pickering gel emulsion and the oil-in-dispersion emulsion ( Fig.19 ), emulsion particle size and G″ and G′( Fig. 20 ) is basically the same as the original emulsion. The results show that the newly prepared Pickering gel emulsion and oil-in-dispersion emulsion have similar stability and viscoelasticity to the original emulsion. Therefore, MPAA and nanocellulose can be separated and recovered multiple times by changing the pH.

[0087] Application Example 1

[0088] Recovery and reuse of oil phase

[0089] Referring to the method of Example 4, the nanocellulose content was 0.5% and the MPAA content was 1 mmol·L -1 , pH = 4.0, the oil phase is a Pickering gel emulsion of n-decane. Add 0.5 mol·L -1 After standing, take out about 9 mL of the oil phase, then add an equal volume of new oil and homogenize (homogenize at a speed of 10000 rpm for 5 min) to form an oil-in-dispersion emulsion. -1 The pH value of the oil-in-dispersion emulsion is adjusted to 4.0 by using HCl aqueous solution, and the emulsion can be demulsified quickly. After standing, the oil phase is taken out and the separated oil is replaced with new oil. After homogenization (homogenization at a speed of 10000 rpm for 5 minutes), a new Pickering gel emulsion can be obtained. Fig.21 It can be seen that after 6 cycles, the interfacial tension of the separated oil to pure water is similar to the interfacial tension of fresh n-decane to pure water, which shows that the content of surfactant in the separated oil phase can be ignored. Fig. 22 As shown, the oil phase taken out 1 H NMR spectroscopy showed that there was no surfactant in the oil phase.

Claims

1. A rosin-based pH-responsive emulsion system, characterized in that: It is formed by dispersing pH-responsive rosin-based surfactant and nanocellulose in water and oil phases; When pH≤5.2, the rosin-based pH-responsive emulsion system is a Pickering gel emulsion with large droplets and high viscosity; when pH≥9.1, the rosin-based pH-responsive emulsion system is an oil-in-dispersion emulsion with small droplets and low viscosity; The pH-responsive rosin-based surfactant was prepared by imidization reaction of maleopimaric acid and amine.

2. The rosin-based pH-responsive emulsion system according to claim 1, characterized in that: By adjusting the pH, the rosin-based pH-responsive emulsion system can be switched between the Pickering gel emulsion and the oil-in-dispersion emulsion, and the cycle can be repeated.

3. The rosin-based pH-responsive emulsion system according to claim 1 or 2, characterized in that: The pH of the Pickering gel emulsion is adjusted to pH ≥ 9.1, the emulsion is completely broken, and the oil phase is directly homogenized or homogenized after the oil phase is renewed to form an oil-in-dispersion emulsion; the pH of the oil-in-dispersion emulsion is adjusted to pH ≤ 5.2, the emulsion is completely broken, and the oil phase is directly homogenized or homogenized after the oil phase is renewed to form a Pickering gel emulsion; the above process can be repeated.

4. The rosin-based pH-responsive emulsion system according to claim 1 or 2, characterized in that: The structure of the pH-responsive rosin-based surfactant is shown below: n=2 or 3.

5. The rosin-based pH-responsive emulsion system according to claim 4, characterized in that: The regulation mechanism of pH-responsive rosin-based surfactants is as follows: Wherein R is Na or K, and n=2 or 3.

6. The rosin-based pH-responsive emulsion system according to claim 1 or 2, characterized in that: The mass fraction of nanocellulose relative to the water phase is 0.1% to 0.5%.

7. The rosin-based pH-responsive emulsion system according to claim 1 or 2, characterized in that: The concentration of pH-responsive rosin-based surfactant relative to the aqueous phase is 0.001-5 mmol·L -1 .

8. The rosin-based pH-responsive emulsion system according to claim 1 or 2, characterized in that: The oil phase is at least one of n-hexane, n-octane, n-decane or soybean oil.

9. A method for preparing a rosin-based pH-responsive emulsion system according to any one of claims 1 to 8, characterized in that: The following steps are involved: S1, adding nanocellulose to deionized water 1 and ultrasonically dispersing for 0.5 to 1 h to prepare solution A; S2, deionized water 2 and pH-responsive rosin-based surfactant were mixed evenly and added to solution A, and then ultrasonically dispersed for 0.5 to 1 h to obtain solution B; S3, 0.5 mol·L -1 NaOH / KOH solution or HCl solution, adjust the pH of solution B to ≤5.2 to obtain solution C1, and adjust the pH of solution B to ≥9.1 to obtain solution C2; S4. Add the oil phase to solution C1 and homogenize to obtain a Pickering gel emulsion. Add the oil phase to solution C2 and homogenize to obtain an oil-in-dispersion emulsion. The homogenization speed is 8000-15000 rpm and the time is 3-8 min.

10. An application of the rosin-based pH-responsive emulsion system according to any one of claims 1 to 8, characterized in that: It is used in drug delivery or emulsified crude oil delivery; or in emulsion polymerization; or in improving oil recovery; or in the synthesis of biphasic catalytic reactions, nanomaterials and polymer particles.

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