Temperature-responsive essential oil microcapsules and a method for preparing the same

Abstract

This invention discloses a temperature-responsive essential oil microcapsule and its preparation method, belonging to the field of microcapsule preparation technology. Using essential oil as the core material and gum arabic (GA), gelatin (GEL), and poly(N-isopropylacrylamide) (PNIPAM) as composite wall materials, a core-shell structure is formed through composite coagulation. This results in an essential oil microcapsule system that combines the structural stability of natural polymers with the temperature-sensitive response characteristics of intelligent polymers, achieving the functional effects of inhibiting volatilization at room temperature and promoting release at high temperatures. This solves the problems of insufficient responsiveness to environmental temperature changes, limited release behavior regulation, and difficulty in achieving the functional switching between "low-temperature aroma locking and high-temperature enhanced release" in existing essential oil microcapsule systems.

Description

Technical Field

[0001] This invention relates to a temperature-responsive essential oil microcapsule and its preparation method, belonging to the field of microcapsule preparation technology. Background Technology

[0002] Lavender essential oil is a type of natural plant volatile oil rich in monoterpenols, esters, and a small amount of terpenes. It possesses bioactivities such as soothing nerves, aiding sleep, antibacterial properties, and air freshening effects, and has broad application prospects in daily chemical products, functional textiles, and environmental control materials. However, lavender essential oil is a highly volatile and heat-sensitive substance, and is prone to volatilization loss and oxidative degradation during storage and use. This leads to a decrease in the content of active ingredients, rapid aroma decay, and a short duration of function, severely limiting its long-term application.

[0003] To improve the stability of essential oils and achieve controlled release, microencapsulation technology has been widely adopted. Currently, most essential oil microcapsule wall materials are natural polymers, such as gelatin, gum arabic, chitosan, or starch derivatives, with the gum arabic / gelatin composite coagulation system being the most mature. This system achieves phase separation of oppositely charged polymers by adjusting the pH, allowing them to deposit on the surface of oil droplets to form a shell. It offers advantages such as high encapsulation efficiency, mild processing, and suitability for heat-sensitive substances. However, the shell of these microcapsules primarily serves as a physical barrier and slow diffusion control; release behavior largely depends on concentration gradients or shell breakage, lacking the ability to actively respond to environmental stimuli (such as temperature changes), making it difficult to meet the application requirements of intelligently regulated release.

[0004] Temperature-responsive polymers have gained attention in recent years for their role in drug release control and smart materials. Among them, poly(N-isopropylacrylamide) (PNIPAM) is a typical thermosensitive polymer with a low critical solution temperature (LCST) of approximately 32°C in aqueous solution. Below the LCST, its molecular chains are in a hydrophilic extended state; above the LCST, the molecular chains undergo hydrophobic collapse, leading to significant changes in the material's microstructure and swelling properties. Currently, PNIPAM is primarily used in hydrogel particles, surface-grafted coatings, or drug carrier systems to regulate the release behavior of water-soluble substances; however, there is a lack of applications for incorporating PNIPAM as a temperature-sensitive regulating component into gum arabic / gelatin composite coagulation systems.

[0005] However, in microencapsulation systems containing hydrophobic and volatile core materials such as essential oils, existing technologies mainly focus on two types of temperature-dependent release mechanisms: one utilizes lipid or paraffin-based phase change materials as carriers to achieve release through melting; the other achieves passive release through shell thermal softening or rupture. These methods often suffer from insufficient structural stability, significant performance degradation after thermal cycling, or high requirements for processing conditions. Meanwhile, when PNIPAM is used directly as an independent wall material for embedding oily core materials, it often faces technical challenges such as poor emulsification stability and insufficient shell mechanical strength.

[0006] In addition, although the natural polymer shells formed by traditional composite coagulation methods have good film-forming properties and biocompatibility, their structure is relatively fixed and it is difficult to produce reversible regulatory behavior when the external temperature changes.

[0007] Therefore, how to introduce functional polymers with temperature-responsive capabilities while retaining the advantages of high encapsulation efficiency and mild process of composite condensation method, and to construct a stable and controllable composite shell structure, has become a technical problem that urgently needs to be solved in the field of temperature-responsive microcapsule preparation technology. Summary of the Invention

[0008] To address the aforementioned issues, this invention provides a temperature-responsive essential oil microcapsule and its preparation method. Specifically, this invention uses essential oil as the core material and gum arabic (GA), gelatin (GEL), and poly(N-isopropylacrylamide) (PNIPAM) as composite wall materials. Through composite coagulation, a core-shell structure is formed, resulting in an essential oil microcapsule system that combines the structural stability of natural polymers with the temperature-sensitive response characteristics of intelligent polymers. This achieves the functional effects of inhibiting volatilization at room temperature and promoting release at high temperatures. It solves the problems of insufficient responsiveness to changes in ambient temperature, limited control over release behavior, and difficulty in achieving the functional switching between "low-temperature aroma locking and high-temperature enhanced release" in existing essential oil microcapsule systems.

[0009] The first objective of this invention is to provide a method for preparing temperature-responsive essential oil microcapsules, comprising the following steps:

[0010] (1) Molecular conformation regulation:

[0011] The poly(N-isopropylacrylamide) solution and gelatin solution were mixed evenly and subjected to physical-induced conformation pre-regulation treatment to obtain a mixed system.

[0012] (2) Emulsification:

[0013] Essential oils are added to the mixture, and high-speed shear emulsification is performed to form an O / W type emulsion;

[0014] (3) Composite cohesion:

[0015] Add gum arabic solution to O / W type emulsion, mix well, and adjust pH to 3.8-4.5 so that gelatin and gum arabic begin to coagulate and deposit on the surface of essential oil droplets, thus obtaining a coagulated system.

[0016] (4) Shell gradient structure:

[0017] After the composite condensation deposition begins, PNIPAM solution is slowly added dropwise to the composite condensation system while stirring is continued, so that PNIPAM forms a gradient distribution structure along the shell thickness direction during the shell formation process;

[0018] (5) Curing:

[0019] After the addition is complete, the temperature is lowered, and a cross-linking agent is added for cross-linking treatment to obtain a temperature-responsive essential oil microcapsule suspension.

[0020] In one embodiment of the present invention, the essential oil in the temperature-responsive essential oil microcapsule is the core material, and the composite wall material is composed of gum arabic, gelatin and poly(N-isopropylacrylamide) (including PNIPAM in steps (1) and (4)); the mass ratio of the core material to the composite wall material is 1:1-5; the mass ratio of gum arabic to gelatin in the composite wall material is 1-3:1-3, and poly(N-isopropylacrylamide) accounts for 15%-25% of the total mass of the composite wall material.

[0021] In one embodiment of the present invention, the number average molecular weight of poly(N-isopropylacrylamide) (PNIPAM) is 5,000-200,000 Da, and its low critical solution temperature (LCST) is 28-40°C, which enables the microcapsules to maintain a stable shell structure under normal temperature storage conditions, while generating a structural response under conditions close to human body temperature or ambient temperature rise.

[0022] In one embodiment of the present invention, the poly(N-isopropylacrylamide) solution in step (1) is an aqueous solution of poly(N-isopropylacrylamide) with a mass concentration of 1%-6%.

[0023] In one embodiment of the present invention, the gelatin solution in step (1) is an aqueous gelatin solution with a mass concentration of 4%-8%.

[0024] In one embodiment of the present invention, the uniform mixing in step (1) is achieved by stirring and mixing at 30-50°C and 300-600 rpm for 10-30 min.

[0025] In one embodiment of the present invention, the physical induced conformation pre-regulation treatment in step (1) is performed by ultrasonic treatment or high-speed shearing treatment; wherein, ultrasonic treatment is performed at a temperature of 25-45℃, an ultrasonic frequency of 20-40 kHz, and a power density of 200-600 W / L for 5-20 min; high-speed shearing treatment is performed at a temperature of 25-45℃ and a rotation speed of 6000-12000 rpm for 3-10 min.

[0026] In one embodiment of the present invention, the physical induction conformation pre-regulation treatment in step (1) is used to induce the PNIPAM molecular chain to form a loose transient entanglement structure in the protein molecular environment, thereby improving its subsequent restricted embedding degree in the shell network.

[0027] In one embodiment of the present invention, the essential oil in step (2) is lavender essential oil.

[0028] In one embodiment of the present invention, the high-speed shear emulsification in step (2) is emulsification at 40-50°C and 7000-10000 rpm for 3-8 min.

[0029] In one embodiment of the present invention, the gum arabic solution in step (3) needs to be stirred during the process of adding it to the O / W type emulsion, and the stirring speed is 200-600 rpm.

[0030] In one embodiment of the present invention, the pH adjustment in step (3) is achieved by using an aqueous solution of acetic acid with a mass fraction of 5%-10%.

[0031] In one embodiment of the present invention, the timing for the start of composite coagulation deposition in step (4) is when the addition of gum arabic solution is completed and the pH adjustment is completed.

[0032] In one embodiment of the present invention, in step (4), the PNIPAM solution is an aqueous solution of poly(N-isopropylacrylamide) (PNIPAM) with a mass concentration of 1%-6%; the dropping rate is 0.5-2 mL / min; and the dropping process is continuously stirred; the stirring speed is 200-600 rpm.

[0033] In one embodiment of the present invention, in step (4), the stirring is continued at 200-600 rpm for 20-40 min.

[0034] In one embodiment of the present invention, the mass ratio of the PNIPAM solution in step (4) to the PNIPAM solution in step (1) is 1:0.1-3.

[0035] In one embodiment of the present invention, the cooling in step (5) is to cool down to 10-15°C and keep stirring at 200-600 rpm for 30-90 min; the cooling rate is 0.5-2°C / min.

[0036] In one embodiment of the present invention, the crosslinking agent in step (5) is a glutaraldehyde solution or a natural crosslinking agent solution, wherein the glutaraldehyde solution is an aqueous solution of glutaraldehyde with a mass concentration of 0.05%-1%; the natural crosslinking agent solution is an aqueous solution of a natural crosslinking agent, and the natural crosslinking agent includes one or more of glutamine transaminase, tannic acid, and phytic acid with a mass concentration of 0.1%-0.5%.

[0037] In one embodiment of the present invention, the mass ratio of crosslinking agent to composite wall material in step (5) is 0.2-1:100.

[0038] In one embodiment of the present invention, the crosslinking in step (5) is performed at 10-15°C for 20-60 min.

[0039] In one embodiment of the present invention, the temperature-responsive essential oil microcapsule suspension in step (5) can be dried to obtain powdered temperature-responsive essential oil microcapsules; wherein, the drying includes spray drying or freeze drying, spray drying is spray drying at an inlet air temperature of 140-180℃ and an outlet air temperature of 70-90℃; freeze drying is freeze drying at -80 to -50℃ for 24-48h.

[0040] In one embodiment of the present invention, the gelatin solution in step (1) and the gum arabic solution in step (3) can be interchanged.

[0041] The second objective of this invention is to prepare temperature-responsive essential oil microcapsules using the method described herein.

[0042] In one embodiment of the present invention, the shell thickness of the temperature-responsive essential oil microcapsules is 0.5-10 μm, and the average particle size is 5-100 μm.

[0043] The third objective of this invention is the application of the temperature-responsive essential oil microcapsules described herein in the preparation of daily chemical products, functional textiles, and environmental control materials.

[0044] The fourth objective of this invention is to provide a method for improving the temperature response performance of essential oil microcapsules, comprising the following steps:

[0045] (1) Molecular conformation regulation:

[0046] The poly(N-isopropylacrylamide) solution and gelatin solution were mixed evenly and subjected to physical-induced conformation pre-regulation treatment to obtain a mixed system.

[0047] (2) Emulsification:

[0048] Essential oils are added to the mixture, and high-speed shear emulsification is performed to form an O / W type emulsion;

[0049] (3) Composite cohesion:

[0050] Add gum arabic solution to O / W type emulsion, mix well, and adjust pH to 3.8-4.5 so that gelatin and gum arabic begin to coagulate and deposit on the surface of essential oil droplets, thus obtaining a coagulated system.

[0051] (4) Shell gradient structure:

[0052] After the composite condensation deposition begins, PNIPAM solution is slowly added dropwise to the composite condensation system while stirring is continued, so that PNIPAM forms a gradient distribution structure along the shell thickness direction during the shell formation process;

[0053] (5) Curing:

[0054] After the addition is complete, the temperature is lowered, and a cross-linking agent is added for cross-linking treatment to obtain a temperature-responsive essential oil microcapsule suspension.

[0055] The technical effects of this invention are as follows:

[0056] (1) In this invention, gum arabic and gelatin undergo compound coagulation under pH adjustment conditions and are deposited on the surface of essential oil droplets to form a basic shell skeleton. PNIPAM molecular chains are embedded in this composite network structure during the shell formation process, forming a semi-interpenetrating network composite shell structure composed of a natural polymer electrostatic composite network and temperature-sensitive polymer chain segments.

[0057] (2) Regarding the introduction of PNIPAM, although PNIPAM itself has a low critical solution temperature (LCST) characteristic, when it is directly added to the traditional gum arabic / gelatin composite microcapsule system, due to the physical binding effect of the natural polymer network on its molecular chains and the buffering effect of the high water content environment inside the shell, its chain segment conformational transformation is significantly restricted, and the effect of temperature change on the microcapsule shell structure and essential oil release behavior is not obvious.

[0058] Therefore, ultrasonic treatment or high-speed shearing of PNIPAM / gelatin mixtures at 25-45℃ does not simply improve dispersibility, but rather promotes the formation of loose transient entanglements and localized associations of PNIPAM molecular chains within the protein molecular environment. These structures are further fixed by the natural polymer network below the LCST, remaining in a state of "restricted stretching," while they are more prone to synergistic collapse as the temperature rises closer to the LCST, resulting in abrupt changes in the microscopic free volume of the shell.

[0059] (3) The present invention adopts a phased introduction of PNIPAM, that is, a portion of PNIPAM is first introduced together with gelatin in the emulsification process, and the remaining portion is slowly added dropwise after the composite coagulation deposition begins, so that PNIPAM forms a gradient distribution structure in the thickness direction of the shell. This gradient distribution structure makes the inner and outer layers of the shell respond differently to temperature changes. When the temperature rises, a stress difference and micropore rearrangement are generated in the shell, thereby significantly amplifying the shell's ability to regulate diffusion channels.

[0060] (4) The shell thickness of the temperature-responsive essential oil microcapsules of the present invention is 0.5-10 μm, and the average particle size is 5-100 μm. The structure is relatively dense when the temperature is below the LCST of PNIPAM, and the essential oil diffusion rate is low; when the temperature rises above the LCST, the PNIPAM chain segments undergo hydrophobic collapse, resulting in an increase in the free volume inside the shell and a decrease in diffusion resistance, thereby improving the essential oil release rate and realizing temperature-triggered release.

[0061] (5) This invention introduces PNIPAM into the shell of traditional GA / GEL composite condensed microcapsules and solves the problem of insignificant temperature sensitivity when directly introduced, forming a reversible temperature-sensitive control structure. This enables the shell microstructure to be dynamically adjusted with temperature changes, thereby endowing essential oil microcapsules with the functional characteristics of "low-temperature fragrance locking and high-temperature fragrance release". At the same time, this structure does not rely on shell rupture or phase change melting, and has better structural stability and repeatable response capability. The preparation process is completed under aqueous conditions, which is suitable for industrial scale-up and practical application. Attached Figure Description

[0062] Figure 1 The effect of the formulation ratios of Examples 1, 2, 3, 7 and Comparative Examples 2, 8 on the phase transition temperature of microcapsules.

[0063] Figure 2 The effect of the formulation ratios of Examples 1, 2, 3, 7 and Comparative Examples 2, 8 on the temperature-sensitive response amplitude of the microcapsules.

[0064] Figure 3 The results show the test results of the response amplitude of the microcapsules of Examples 1, 5, 6 and Comparative Example 1 at different cycles. Detailed Implementation

[0065] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0066] Test method:

[0067] 1. Average particle size test:

[0068] Approximately 10 mg of essential oil microcapsule sample was added to 10 mL of deionized water and stirred at 300 rpm for 5 min using a magnetic stirrer to ensure thorough dispersion of the microcapsules into a uniform suspension. To avoid the influence of multiple scattering effects on the measurement results, the sample was further diluted to an appropriate concentration according to instrument requirements, resulting in a slightly milky white system with no obvious sedimentation. Subsequently, the microcapsule particle size was measured using a laser particle size analyzer. The measurement temperature was set to 25℃, and the refractive index parameters were set as follows: wall material refractive index 1.52, dispersion medium refractive index 1.33.

[0069] 2. Embedding rate test:

[0070] Accurately weigh 100 mg of the microcapsule sample and first determine the content of unencapsulated essential oils on its surface. Add 10 mL of anhydrous ethanol to the sample and gently shake for 30 s to fully dissolve the free essential oils adsorbed on the microcapsule surface without damaging the microcapsule wall structure. Then centrifuge the suspension at 5000 rpm for 10 min, collect the supernatant, and determine the essential oil content using ultraviolet-visible spectrophotometry, which is recorded as the surface essential oil content.

[0071] Another 100 mg of microcapsule sample of the same mass was taken, added to 10 mL of anhydrous ethanol, and sonicated for 30 min. Simultaneously, it was extracted by shaking in a 40 ℃ water bath to fully destroy the microcapsule wall structure and completely release the encapsulated essential oils. The extract was then centrifuged and the supernatant was collected. The total essential oil content was determined using the same method and recorded as the total essential oil content of the microcapsules.

[0072] The encapsulation efficiency of microcapsules is calculated using the following formula:

[0073]

[0074] 3. Essential oil release rate test:

[0075] Accurately weigh 50 mg of microcapsule sample and place it in a stoppered conical flask. Add 50 mL of 30% (v / v) ethanol aqueous solution as the release medium. Place the conical flask in a constant-temperature shaking water bath at a shaking speed of 100 rpm to ensure uniform dispersion of the system and avoid microcapsule sedimentation affecting release stability. Release the system at the target temperature for 120 min, and then measure the absorbance of the solution. Take another 50 mg sample and extend the release time to 300 min to obtain the total essential oil release concentration. Calculate the corresponding release amount based on a pre-established standard curve.

[0076] The formula for calculating the essential oil release rate is as follows:

[0077]

[0078] 4. Repeatability test:

[0079] Accurately weigh 50 mg of microcapsule sample and place it in a stoppered conical flask. Add 50 mL of 30% ethanol aqueous solution as the release medium. Place the conical flask in a constant temperature shaking water bath and set the shaking speed to 100 rpm to ensure uniform dispersion of the system and avoid microcapsule sedimentation affecting release stability.

[0080] First, the system was placed at 25 °C for 60 min for release. After the release, 1 mL of the release medium was taken, filtered through a 0.45 μm microporous membrane, and the essential oil concentration was measured. An equal volume of fresh release medium was then added back to the system to maintain a constant total volume. Subsequently, the same system was quickly transferred to a 40 °C constant-temperature shaking water bath for another 60 min of release, and the release amount was measured using the same method as above. After completing the high-temperature phase, the system was cooled to 25 °C and the release was continued for another 60 min. The heating and cooling process was repeated for a total of 5 complete temperature cycles.

[0081] The essential oil content in the release solution was determined using UV-Vis spectrophotometry, and the corresponding release amount was calculated based on a pre-established standard curve. The release rate was defined as the percentage of the released amount relative to the total essential oil encapsulation in the microcapsules, used to evaluate the release behavior of the microcapsules under different temperature conditions. The temperature response reversibility and repeatability stability of the microcapsules were evaluated by comparing the release rate ratio (response amplitude) at 40℃ and 25℃ in each cycle.

[0082] 5. Testing of Low Critical Solution Temperature (LCST):

[0083] Microcapsule samples were dissolved in deionized water to prepare a 1% (w / w) solution. To ensure solution homogeneity, the sample was filtered through a 0.45 μm filter after dissolution to remove undissolved substances. The sample solution was added to a cuvette with a 1 cm path length, and the transmittance (T0) was recorded at the initial temperature using a transmittance meter. The microcapsule solution was then placed in a temperature-controlled water bath and slowly heated at a rate of 1 °C / min, typically within a range 10 °C below and above the expected LCST temperature. The transmittance change was recorded for every 1 °C or 0.5 °C increase. Heating continued until the phase transition temperature (LCST) of the solution was reached. The LCST was determined using a transmittance vs. temperature curve; the LCST is the temperature point where transmittance drops sharply, indicating a structural change in the microcapsules leading to a rapid decrease in solubility.

[0084] Raw materials used in the examples:

[0085] PNIPAM: Poly(N-isopropylacrylamide), number average molecular weight approximately 50,000 Da;

[0086] Lavender essential oil: Purity > 90%;

[0087] All other raw materials are sourced from commercially available sources.

[0088] Unless otherwise specified, the solvent used in the solutions mentioned in the examples and comparative examples is water; unless otherwise specified, the reaction temperature refers to room temperature (15-30°C); and unless otherwise specified, the stirring speed is 400 rpm.

[0089] Example 1

[0090] A method for preparing temperature-responsive essential oil microcapsules includes the following steps:

[0091] (1) Molecular conformation regulation:

[0092] Weigh 6 g of gelatin and add it to 94 g of water. Stir and dissolve the gelatin in a water bath at 45°C to obtain a gelatin solution with a mass fraction of 6%.

[0093] Weigh 3 g of poly(N-isopropylacrylamide) and add it to 97 g of water. Stir at room temperature until completely dissolved to obtain a 3% PNIPAM solution.

[0094] Part of the poly(N-isopropylacrylamide) solution and gelatin solution were thoroughly stirred and mixed at 45°C and 400 rpm for 15 min; then, physical-induced conformation pre-regulation treatment was performed by ultrasonic treatment at 30°C, 30 kHz, and 200 W / L for 10 min to obtain the mixed system.

[0095] (2) Emulsification:

[0096] 10g of lavender essential oil was added to the mixture, and emulsification was carried out at 45℃ and 8000 rpm for 5 min using a high-speed shear emulsifier to form an O / W type emulsion; the average droplet size was approximately 8-15 μm.

[0097] (3) Composite cohesion:

[0098] Weigh 6 g of gum arabic and dissolve it in 94 g of water to obtain a gum arabic solution with a mass fraction of 6%.

[0099] While stirring (400 rpm), the gum arabic solution was added to the O / W type emulsion, and the pH was adjusted to 4.2 with a 10% acetic acid aqueous solution, so that the gelatin and gum arabic began to coagulate and deposit on the surface of the essential oil droplets (forming the primary shell of microcapsules), thus obtaining a coagulated system.

[0100] (4) Shell gradient structure:

[0101] After the composite condensation deposition begins, the remaining 3% PNIPAM solution is slowly added dropwise (1 mL / min) to the composite condensation system, and stirring is continued at 400 rpm for 30 min, so that PNIPAM forms a gradient distribution structure along the shell thickness direction during the shell formation process.

[0102] (5) Curing:

[0103] After the addition was completed, the temperature was slowly lowered (at a rate of 1°C / min) to 12°C, and the mixture was stirred at 400 rpm for 60 min to promote the solidification of the shell layer. Then, a glutaraldehyde aqueous solution with a crosslinking agent mass fraction of 0.5% was added, and the mixture was crosslinked at 12°C for 30 min to obtain a temperature-responsive essential oil microcapsule suspension.

[0104] (6) Drying:

[0105] Temperature-responsive essential oil microcapsule suspension was spray-dried at an inlet air temperature of 160℃ and an outlet air temperature of 80℃ to obtain temperature-responsive essential oil microcapsules.

[0106] In step (4), the mass ratio of the PNIPAM solution to the PNIPAM solution in step (1) is 1:1;

[0107] In step (5), the mass ratio of glutaraldehyde aqueous solution to composite wall material (gelatin, gum arabic, PNIPAM) is 0.5:100;

[0108] In the temperature-responsive essential oil microcapsules, lavender essential oil is used as the core material, and gum arabic, gelatin and poly(N-isopropylacrylamide) (including PNIPAM in steps (1) and (4)) constitute the composite wall material; the mass ratio of the core material to the composite wall material is 10:15; the mass ratio of gum arabic to gelatin in the composite wall material is 1:1, and poly(N-isopropylacrylamide) accounts for 20% of the total mass of the composite wall material.

[0109] The obtained microcapsules were subjected to performance testing, and the test results are as follows:

[0110] The temperature-responsive essential oil microcapsules have an average particle size of 25-40 μm and an encapsulation rate of 78.2%.

[0111] Results of storage tests under sealed conditions: The essential oil release rate was 10.1% after 2 hours of release at 25℃; 23.2% after 2 hours of release at 40℃; and approximately 2.3 times that at 25℃, the amount of essential oil released was significantly higher, demonstrating a clear temperature-responsive release characteristic.

[0112] Example 2

[0113] The mass ratio of PNIPAM solution in step (4) to PNIPAM solution in step (1) of Example 1 was adjusted to 3:7; all other steps remained the same as in Example 1, and microcapsules were obtained.

[0114] Example 3

[0115] The mass ratio of PNIPAM solution in step (4) to PNIPAM solution in step (1) of Example 1 was adjusted to 6:4; all other steps remained the same as in Example 1, and microcapsules were obtained.

[0116] Example 4

[0117] In Example 1, the gelatin solution in step (1) and the gum arabic solution in step (3) can be interchanged. That is, gum arabic solution is used in step (1) and gelatin solution is used in step (3), while the rest remains the same as in Example 1, to obtain microcapsules.

[0118] Example 5

[0119] The mass of lavender essential oil in step (2) of Example 1 was adjusted to 12g, while other steps remained the same as in Example 1, to obtain microcapsules.

[0120] Example 6

[0121] The ultrasonic treatment in step (1) of Example 1 was adjusted to high-speed shearing treatment, specifically high-speed shearing treatment at 35°C and 8000rpm for 5 minutes, while the rest remained the same as in Example 1, to obtain microcapsules.

[0122] Example 7

[0123] The mass ratio of PNIPAM solution in step (4) to PNIPAM solution in step (1) of Example 1 was adjusted to 8:2; all other steps remained the same as in Example 1, and microcapsules were obtained.

[0124] Comparative Example 1

[0125] Step (4) of Example 1 is omitted (PNIPAM solution and stirring treatment are omitted). All of the PNIPAM solution is added in step (1). Everything else is the same as in Example 1 to obtain microcapsules.

[0126] The obtained microcapsules were subjected to performance testing, and the test results are as follows:

[0127] The average particle size of the microcapsules was 22-38 μm, and the encapsulation efficiency was 70.0%.

[0128] Results of storage tests under sealed conditions: After 2 hours of release at 25°C, the essential oil release rate was 13.0%; after 2 hours of release at 40°C, the essential oil release rate was 15.6%; after 2 hours of release at 40°C, the amount of essential oil released was approximately 1.2 times that at 25°C, and no significant temperature-responsive regulation behavior was observed.

[0129] Comparative Example 2

[0130] The addition of PNIPAM solution in steps (1) and (4) of Example 1 was omitted, and the rest remained the same as in Example 1 to obtain microcapsules.

[0131] Comparative Example 3

[0132] In Example 1, PNIPAM (polymer) was changed to INPAM monomer in steps (1) and (4), while other steps remained the same as in Example 1, to obtain microcapsules.

[0133] Comparative Example 4

[0134] In Example 1, PNIPAM (polymer) was changed to poly(N,N-diethylacrylamide) in steps (1) and (4), while other steps remained the same as in Example 1, to obtain microcapsules.

[0135] Comparative Example 5

[0136] In Example 1, PNIPAM (polymer) was changed to poly(methyl vinyl ether) in steps (1) and (4), while other steps remained the same as in Example 1, to obtain microcapsules.

[0137] Comparative Example 6

[0138] Omit the PNIPAM solution in step (1) of Example 1, and add all of the PNIPAM solution in step (4); keep everything else the same as in Example 1 to obtain microcapsules.

[0139] Comparative Example 7

[0140] The ultrasonic treatment in step (1) of Example 1 is omitted; everything else remains the same as in Example 1 to obtain microcapsules.

[0141] Comparative Example 8

[0142] Omit the PNIPAM solution in step (4) of Example 1, and add all of the PNIPAM solution in step (1); keep everything else the same as in Example 1 to obtain microcapsules.

[0143] The obtained microcapsules were subjected to performance testing, and the test results are as follows:

[0144] Table 1

[0145]

[0146] Note: "-" indicates that no temperature sensitivity was observed.

[0147] Table 2

[0148]

[0149] Figure 3 The results show the test amplitude of the response of the microcapsules of Examples 1, 5, 6, and Comparative Example 1 at different cycles. From... Figure 3 It can be seen that microcapsules with different structures all exhibit good temperature-responsive reversible release performance. Among them, microcapsules treated with ultrasound and with PNIPAM uniformly distributed in the wall material structure have the best response stability. Increasing the essential oil content can improve the overall release level without affecting the temperature response characteristics. Using high-speed shearing instead of ultrasound treatment results in a more porous microcapsule structure, higher basic release, and a slightly lower response amplitude. Thermosensitive substances are concentrated near the core, resulting in a significantly weaker response than in Examples 1, 5, and 6, and therefore poorer repeatability.

[0150] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing temperature-responsive microcapsules of essential oils, characterized by, Includes the following steps: (1) Molecular conformation regulation: The poly(N-isopropylacrylamide) solution and gelatin solution were mixed evenly and subjected to physical-induced conformation pre-regulation treatment to obtain a mixed system. Among them, the physical-induced conformation pre-regulation treatment is performed by ultrasonic treatment or high-speed shearing treatment; Ultrasonic treatment is performed at a temperature of 25-45℃, an ultrasonic frequency of 20-40 kHz, and a power density of 200-600 W / L for 5-20 minutes. High-speed shearing is performed at a temperature of 25-45℃ and a rotation speed of 6000-12000 rpm for 3-10 minutes. (2) Emulsification: Essential oils are added to the mixture, and high-speed shear emulsification is performed to form an O / W type emulsion; (3) Composite cohesion: Add gum arabic solution to O / W type emulsion, mix well, and adjust pH to 3.8-4.5 so that gelatin and gum arabic begin to coagulate and deposit on the surface of essential oil droplets, thus obtaining a coagulated system. (4) Shell gradient structure: After the composite condensation deposition begins, PNIPAM solution is slowly added dropwise to the composite condensation system while stirring is continued, so that PNIPAM forms a gradient distribution structure along the shell thickness direction during the shell formation process; (5) Curing: After the addition is complete, the temperature is lowered, and a cross-linking agent is added for cross-linking treatment to obtain a temperature-responsive essential oil microcapsule suspension.

2. The method of claim 1, wherein, In temperature-responsive essential oil microcapsules, essential oil is the core material, and gum arabic, gelatin, and poly(N-isopropylacrylamide) (PNIPAM) constitute the composite wall material. The mass ratio of the core material to the composite wall material is 1:1-5. The mass ratio of gum arabic to gelatin in the composite wall material is 1-3:1-3, and poly(N-isopropylacrylamide) accounts for 15%-25% of the total mass of the composite wall material.

3. The method of claim 1, wherein, The essential oil used in step (2) is lavender essential oil.

4. The method according to claim 1, characterized in that, In step (4), the PNIPAM solution is an aqueous solution of poly(N-isopropylacrylamide) (PNIPAM) with a mass concentration of 1%-6%.

5. The method according to claim 1, characterized in that, In step (4), the PNIPAM solution is added at a rate of 0.5-2 mL / min.

6. The method according to claim 1, characterized in that, The mass ratio of the PNIPAM solution in step (4) to the PNIPAM solution in step (1) is 1:0.1-3.

7. The method according to claim 1, characterized in that, In step (5), the mass ratio of crosslinking agent to composite wall material is 0.2-1:

100.

8. Temperature-responsive essential oil microcapsules prepared by the method according to any one of claims 1-7.

9. The application of the temperature-responsive essential oil microcapsules according to claim 8 in the preparation of daily necessities or functional textiles.

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