Double-layer plant essential oil microcapsule and preparation method thereof

Abstract

This invention provides a bilayer plant essential oil microcapsule and its preparation method, belonging to the field of textile technology. The invention involves emulsifying a carboxyl-containing plant essential oil derivative with unmodified plant essential oil, then adding chitosan / ε-polylysine via an amidation reaction to form a first wall material. Subsequently, sodium alginate oxide is added and reacts with the first wall material via a Schiff base reaction to form a second interlocking wall material. Finally, the bilayer plant essential oil microcapsules are obtained through centrifugal washing. This invention achieves slow release of essential oils through a dual mechanism of covalent anchoring and dynamic interlocking, endowing the microcapsules with a long-lasting sustained-release function. Furthermore, the wall and core materials exert antibacterial effects, making it suitable for use in textiles such as clothing, home textiles, and automotive interiors.

Description

Technical Field

[0001] This invention relates to the field of textile technology, specifically to a double-layer plant essential oil microcapsule and its preparation method. Background Technology

[0002] With increasing demands for comfort, functionality, and safety, plant essential oils, due to their multiple natural activities such as aromatherapy, antibacterial properties, anti-inflammatory effects, and insect repellency, have shown broad application potential in both civilian and industrial fields, including textile fragrances, personal care, indoor environmental regulation, active packaging, and agricultural protection. However, plant essential oils are highly volatile, easily oxidized, and have poor physicochemical stability. Furthermore, high concentrations can cause irritation or allergies. Directly adding them to products often leads to rapid fragrance decay, difficulty in controlling dosage, skin / contact safety issues, and poor compatibility with substrates, limiting their large-scale and reliable application and promotion.

[0003] Microencapsulation technology utilizes natural or synthetic polymers as wall materials to encapsulate essential oils within micron- or nano-sized capsules. The physical barrier effect of the wall material isolates the essential oils from the external environment, thereby reducing the rate of volatilization and oxidation and enabling controlled release of active ingredients. Sodium alginate and chitosan are the most commonly used wall materials for preparing essential oil microcapsules. Sodium alginate is a natural anionic polysaccharide with good biocompatibility and gelling properties; chitosan is the only alkaline polysaccharide found in nature, possessing excellent film-forming properties and natural antibacterial activity.

[0004] However, existing essential oil microcapsules rely solely on physical forces to bond the wall and core materials, lacking stable chemical bonds between essential oil molecules and the wall material. Essential oil molecules can still slowly diffuse outwards through micropores or structural defects in the wall material, resulting in low encapsulation efficiency and unsatisfactory sustained-release effects. Bilayer microcapsules prepared using sodium alginate / chitosan electrostatic self-assembly rely solely on non-covalent forces such as electrostatic attraction or hydrogen bonds between the two wall layers. Under external forces such as drying, friction, washing, or heat treatment, delamination and cracking easily occur, leading to microcapsule structural damage and loss of protective function. Microcapsules prepared by existing methods generally have low encapsulation efficiency and rapid essential oil release rates at room temperature, failing to meet the needs of textile and home textile applications requiring long-lasting sustained release. Therefore, there is an urgent need to develop a novel microcapsule structure that can stably anchor essential oil molecules to the wall material at the molecular level while significantly enhancing the interlayer bonding force of the wall material, fundamentally solving the long-standing technical challenges of volatile, unstable, and uncontrollable release of plant essential oils. Summary of the Invention

[0005] Technical Problem to be Solved: This invention addresses the problems of low encapsulation efficiency, poor sustained-release properties, and easy delamination and breakage of existing essential oil microcapsules by providing a double-layer plant essential oil microcapsule and its preparation method. Through the covalent anchoring of amide bonds between the essential oil and the wall material, and the dynamic interlocking of Schiff base bonds between the two wall materials, efficient encapsulation and long-term sustained release of the essential oil are achieved, while improving the structural stability of the microcapsule.

[0006] Technical solution: A double-layer plant essential oil microcapsule, comprising, from the inside out, a core material, a first wall material, and a second wall material. The core material contains a carboxyl plant essential oil derivative modified by an anhydride semi-esterification and unmodified plant essential oil. The first wall material is composed of chitosan / ε-polylysine, whose amino groups are covalently anchored to the carboxyl groups in the core material via amide bonds. The second wall material is composed of sodium alginate oxide, whose aldehyde groups are dynamically interlocked with the amino groups in the first wall material via Schiff base bonds.

[0007] The preparation method of the above-mentioned double-layer plant essential oil microcapsules includes the following steps: S1. Hydroxyl-containing components in plant essential oils are modified by acid anhydride semi-esterification to obtain carboxyl-containing plant essential oil derivatives; S2. Sodium alginate is oxidized to obtain sodium alginate containing aldehyde groups; S3. Mix carboxyl-containing plant essential oil derivatives with unmodified plant essential oils to obtain composite plant essential oils. Dissolve emulsifiers in water to form an aqueous phase. Add the composite plant essential oils to the aqueous phase and homogenize at high speed to form an oil-in-water plant essential oil core material emulsion. S4. Add chitosan and ε-polylysine to the plant essential oil core material emulsion of S3, add an amidation promoter and stir to carry out an amidation reaction, forming a first wall material on the surface of the plant essential oil core material, and obtain a microcapsule suspension coated with the first wall material; S5. Add the microcapsule suspension coated with the first wall material to the sodium alginate oxidase solution, stir to carry out the Schiff base reaction, and form a second wall material on the outside of the first wall material to obtain a double-layer plant essential oil microcapsule suspension. S6. Centrifuge, wash, and dry the double-layer plant essential oil microcapsule suspension to obtain double-layer plant essential oil microcapsules.

[0008] Preferably, in step S1, the plant essential oil includes one or more of lavender essential oil, tea tree essential oil, peppermint essential oil, lemon essential oil, orange blossom essential oil, rose essential oil, eucalyptus essential oil, rosemary essential oil, cypress essential oil, sandalwood essential oil, and chamomile essential oil. In the anhydride semi-esterification modification, the amount of anhydride used is 1% to 80% of the mass of the plant essential oil, the reaction temperature is 20 to 90°C, and the reaction time is 0.5 to 24 h. The anhydride is one or more of succinic anhydride, maleic anhydride, itaconic anhydride, glutaric anhydride, and phthalic anhydride.

[0009] Preferably, the oxidation treatment in step S2 involves reacting sodium alginate with periodate under light-protected conditions, with the degree of oxidation of sodium alginate being 5% to 60%.

[0010] Preferably, in step S3, the mass ratio of carboxyl-containing plant essential oil derivatives to unmodified plant essential oils in the compound essential oil is 1-9:9-1, the emulsifier is any one of Tween 20, Tween 40, Tween 60, Tween 80, and Span 80, the high-speed homogenization speed is 2000-15000 rpm, the time is 1-20 min, and the concentration of the plant essential oil core material emulsion is 5-20 g / L.

[0011] Preferably, in step S4, the mass ratio of chitosan to ε-polylysine is 1:10 to 10:1, the amidation accelerator is one or more of EDC, NHS, EDC / NHS, DCC, and CDI, the pH of the amidation reaction is 4.0 to 7.0, the reaction temperature is 20 to 60 °C, and the reaction time is 0.5 to 8 h.

[0012] Preferably, in step S5, the concentration of the sodium alginate oxidizing solution is 0.1–100 g / L, the pH of the Schiff base reaction is 3.5–7, the reaction temperature is 30–60°C, the stirring speed is 100–700 rpm, and the stirring time is 4–8 h.

[0013] The application of a double-layer plant essential oil microcapsule in clothing, home textiles, automotive interiors, curtains, carpets, outdoor products, industrial fabrics, or bags, wherein the application involves applying the double-layer plant essential oil microcapsule to the fabric, and the finishing method includes one or more of padding, soaking, spraying, coating, rolling, hot pressing, and hot air drying.

[0014] Beneficial effects: The double-layer plant essential oil microcapsule of the present invention has the following advantages: This invention modifies the hydroxyl-containing components in plant essential oils through anhydride semi-esterification, introducing carboxyl groups into the essential oil molecules. These carboxyl groups form stable amide covalent bonds with chitosan / ε-polylysine, anchoring some essential oil molecules to the first wall material, preventing free migration. Release is only possible through the breaking of these chemical bonds, thus slowing down the release rate of the essential oil. Unanchored free essential oil molecules must penetrate the dense shell composed of two wall materials to diffuse outwards. Because the two wall materials form a dynamic covalent interlocking structure through Schiff base bonds, the shell is chemically welded together, ensuring the integrity and density of the shell structure. Essential oil molecules can only slowly permeate through the micropores of the wall material itself.

[0015] The two layers of the microcapsule in this invention are chemically cross-linked and interlocked through Schiff base bonds, resulting in a dense and stable shell structure that is not easily broken during centrifugal washing, drying, and subsequent fabric finishing processes. Chitosan, ε-polylysine, and sodium alginate are all natural polymer materials with good affinity to the fiber substrate, allowing the microcapsules to adhere evenly to the fiber surface. Textiles treated with this invention have a long-lasting fragrance function without affecting the comfort of wearing the fabric, and reduce the exposure of free essential oils, thereby reducing skin irritation.

[0016] The chitosan and ε-polylysine in the first wall material of the microcapsule of this invention are both natural cationic antibacterial polymers that can act on bacterial cells to form the first antibacterial barrier. The plant essential oil in the core material itself has broad-spectrum antibacterial activity. After being continuously and slowly released by the shell, it works synergistically with the antibacterial effect of the first wall material to enhance the overall antibacterial performance of the microcapsule. Moreover, both the wall material and the core material are derived from natural materials and are safe and non-toxic. Attached Figure Description

[0017] Figure 1 SEM images of double-layered microcapsules; Figure 2 Infrared image of double-layered microcapsules; Figure 3 Ultraviolet absorption spectra of lavender essential oil at different concentrations; Figure 4 A standard curve diagram for lavender essential oil; Figure 5 Optical microscope image of lavender essential oil emulsion; Figure 6 The antibacterial properties of microcapsules; Figure 7 Fabric treated with microcapsules. Detailed Implementation

[0018] The present invention will be further described below with reference to embodiments. These embodiments are illustrative of the present invention, but the present invention is not limited to these embodiments: Example 1

[0019] A method for preparing double-layered plant essential oil microcapsules includes the following steps: S1. Take 0.4 g of lavender essential oil and 0.15 g of glutaric anhydride, and then put them into a dry reagent bottle. Then add 10 ml of dichloromethane as a solvent. Then stir continuously at 300 rpm for 6 h at 50 ℃. Finally, remove the solvent by rotary evaporation at 40 ℃ and 80 rpm to obtain a lavender essential oil derivative containing carboxyl groups. S2. Dissolve 0.25 g sodium alginate in 50 mL of water, add 0.2 g sodium periodate, and stir continuously at 50 °C for 400 rpm for 4 h under light-protected conditions to obtain oxidized sodium alginate with an oxidation degree of 30%. S3. Mix 0.2 mL of carboxyl-containing lavender essential oil derivative with 0.2 mL of unmodified lavender essential oil to obtain a compound plant essential oil. Dissolve 0.15 mL of Tween 80 in water to form an aqueous phase. Add the compound plant essential oil to the aqueous phase and homogenize at 10,000 rpm for 2 min to form an oil-in-water plant essential oil core material emulsion with a concentration of 7 g / L. S4. Add 0.025 g chitosan and 0.1 g ε-polylysine to the plant essential oil core material emulsion of S3, add EDC, adjust the pH to 5.0, stir and react at 50℃ for 4 h to form the first wall material on the surface of the plant essential oil core material, and obtain the microcapsule suspension coated with the first wall material. S5. The microcapsule suspension coated with the first wall material was added to a 10 g / L sodium alginate solution, the pH was adjusted to 6.0, and the mixture was stirred at 40°C for 5 h at a stirring speed of 400 rpm to form a second wall material on the outside of the first wall material, thus obtaining a double-layer plant essential oil microcapsule suspension. S6. Centrifuge the double-layer plant essential oil microcapsule suspension at 8000 rpm for 10 min, wash, and dry to obtain double-layer plant essential oil microcapsules.

[0020] Example 2

[0021] A method for preparing double-layered plant essential oil microcapsules includes the following steps: S1. Take 0.4 g of peppermint essential oil and 0.15 g of glutaric anhydride, then put them into a dry reagent bottle, add 10 ml of dichloromethane as solvent, and then stir continuously at 300 rpm for 6 h at 50 ℃. Finally, remove the solvent by rotary evaporation at 40 ℃ and 80 rpm to obtain a peppermint essential oil derivative containing carboxyl groups. S2. Dissolve 0.25 g sodium alginate in 50 mL of water, add 0.2 g sodium periodate, and stir continuously at 400 rpm for 4 h under light-protected conditions at 50 °C to obtain oxidized sodium alginate with an oxidation degree of 60%. S3. Mix 0.2 mL of carboxyl-containing peppermint essential oil derivative with 0.2 mL of unmodified peppermint essential oil to obtain a compound plant essential oil. Dissolve 0.15 mL of Tween 20 in water to form an aqueous phase. Add the compound plant essential oil to the aqueous phase and homogenize at 15000 rpm for 1 min to form an oil-in-water plant essential oil core material emulsion with a concentration of 7 g / L. S4. Add 0.025 g chitosan and 0.1 g ε-polylysine to the plant essential oil core material emulsion of S3, add NHS, adjust the pH to 4.0, stir and react at 50℃ for 4 h to form the first wall material on the surface of the plant essential oil core material, and obtain the microcapsule suspension coated by the first wall material. S5. The microcapsule suspension coated with the first wall material was added to a 10 g / L sodium alginate solution, the pH was adjusted to 4.5, and the mixture was stirred at 40°C for 8 h at a stirring speed of 400 rpm to form a second wall material on the outside of the first wall material, thus obtaining a double-layer plant essential oil microcapsule suspension. S6. Centrifuge the double-layer plant essential oil microcapsule suspension at 2000 rpm for 60 min, wash, and dry to obtain double-layer plant essential oil microcapsules.

[0022] Example 3

[0023] A method for preparing double-layered plant essential oil microcapsules includes the following steps: S1. Take 0.4 g of rose essential oil and 0.15 g of glutaric anhydride, then put them into a dry reagent bottle, add 10 ml of dichloromethane as a solvent, and then stir continuously at 300 rpm for 6 h at 50 ℃. Finally, remove the solvent by rotary evaporation at 40 ℃ and 80 rpm to obtain a carboxyl-containing rose essential oil derivative. S2. Dissolve 0.25 g sodium alginate in 50 mL of water, add 0.2 g sodium periodate, and stir continuously at 400 rpm for 4 h under light-protected conditions at 60 ℃ to obtain oxidized sodium alginate with an oxidation degree of 60%. S3. Mix 0.2 mL of carboxyl-containing rose essential oil derivative with 0.2 mL of unmodified rose essential oil to obtain a compound plant essential oil. Dissolve 0.15 mL of Tween 80 in water to form an aqueous phase. Add the compound plant essential oil to the aqueous phase and homogenize at 10,000 rpm for 2 min to form an oil-in-water plant essential oil core material emulsion with a concentration of 7 g / L. S4. Add 0.5 g chitosan and 0.2 g ε-polylysine to the plant essential oil core material emulsion of S3, add CDI, adjust the pH to 5.0, stir and react at 50℃ for 4 h to form the first wall material on the surface of the plant essential oil core material, and obtain the microcapsule suspension coated with the first wall material. S5. The microcapsule suspension coated with the first wall material was added to a 10 g / L sodium alginate solution, the pH was adjusted to 6.0, and the mixture was stirred at 40°C for 5 h at a stirring speed of 400 rpm to form a second wall material on the outside of the first wall material, thus obtaining a double-layer plant essential oil microcapsule suspension. S6. Centrifuge the double-layer plant essential oil microcapsule suspension at 12000 rpm for 1 min, wash, and dry to obtain double-layer plant essential oil microcapsules.

[0024] Example 4

[0025] A method for preparing double-layered plant essential oil microcapsules includes the following steps: S1. Take 0.4 g lemon essential oil and 0.1 g succinic anhydride, then put them into a dry reagent bottle, add 20 ml dichloromethane as solvent, and then stir continuously at 300 rpm for 24 h at 50 ℃. Finally, remove the solvent by rotary evaporation at 60 ℃ and 80 rpm to obtain a lemon essential oil derivative containing carboxyl groups. S2. Dissolve 0.5 g sodium alginate in 50 mL of water, add 0.2 g sodium periodate, and stir continuously at 400 rpm for 6 h under light-protected conditions at 50 °C to obtain oxidized sodium alginate with an oxidation degree of 40%. S3. Mix 0.05 mL of carboxyl-containing lemon essential oil derivative with 0.15 mL of unmodified lemon essential oil to obtain a compound plant essential oil. Dissolve 0.2 mL of Tween 80 in water to form an aqueous phase. Add the compound plant essential oil to the aqueous phase and homogenize at 10,000 rpm for 2 min to form an oil-in-water plant essential oil core material emulsion with a concentration of 7 g / L. S4. Add 0.025 g chitosan and 0.1 g ε-polylysine to the plant essential oil core material emulsion of S3, add NHS, adjust the pH to 4.0, stir and react at 60℃ for 6h to form the first wall material on the surface of the plant essential oil core material, and obtain the microcapsule suspension coated by the first wall material. S5. The microcapsule suspension coated with the first wall material was added to a 10 g / L sodium alginate solution, the pH was adjusted to 6.0, and the mixture was stirred at 40°C for 6 h at a stirring speed of 400 rpm to form a second wall material on the outside of the first wall material, thus obtaining a double-layer plant essential oil microcapsule suspension. S6. Centrifuge the double-layer plant essential oil microcapsule suspension at 8000 rpm for 10 min, wash, and dry to obtain double-layer plant essential oil microcapsules.

[0026] Example 5

[0027] A method for preparing double-layered plant essential oil microcapsules includes the following steps: S1. Take 0.4 g of rosemary essential oil and 0.15 g of maleic anhydride, then put them into a dry reagent bottle, add 10 ml of dichloromethane as solvent, and then stir continuously at 300 rpm for 6 h at 50 ℃. Finally, remove the solvent by rotary evaporation at 40 ℃ and 80 rpm to obtain a carboxyl-containing rosemary essential oil derivative. S2. Dissolve 0.25 g sodium alginate in 50 mL of water, add 0.2 g sodium periodate, and stir continuously at 50 °C for 400 rpm for 6 h under light-protected conditions to obtain oxidized sodium alginate with an oxidation degree of 30%. S3. Mix 0.2 mL of carboxyl-containing rosemary essential oil derivative with 0.2 mL of unmodified rosemary essential oil to obtain a compound plant essential oil. Dissolve 0.15 mL of Tween 80 in water to form an aqueous phase. Add the compound plant essential oil to the aqueous phase and homogenize at 10,000 rpm for 2 min to form an oil-in-water plant essential oil core emulsion with a concentration of 7 g / L. S4. Add 0.025 g chitosan and 0.1 g ε-polylysine to the plant essential oil core material emulsion of S3, add EDC, adjust the pH to 5.0, stir and react at 50℃ for 4 h to form the first wall material on the surface of the plant essential oil core material, and obtain the microcapsule suspension coated with the first wall material. S5. The microcapsule suspension coated with the first wall material was added to a 10 g / L sodium alginate solution, the pH was adjusted to 6.0, and the mixture was stirred at 40°C for 5 h at a stirring speed of 400 rpm to form a second wall material on the outside of the first wall material, thus obtaining a double-layer plant essential oil microcapsule suspension. S6. Centrifuge the double-layer plant essential oil microcapsule suspension at 8000 rpm for 10 min, wash, and dry to obtain double-layer plant essential oil microcapsules.

[0028] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that Tween 80 is not used in S3 of Comparative Example 1, and the aqueous phase is replaced with an equal amount of water, while the rest is the same as Example 1.

[0029] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that Comparative Example 2 does not have the chitosan / ε-polylysine layer coating of S4, but only the sodium oxidized alginate monolayer coating of S5, and the rest is the same as Example 1.

[0030] Comparative Example 3 The difference between Comparative Example 3 and Example 1 is that the plant essential oil in Comparative Example 3 is not modified by acid anhydride semi-esterification, the sodium alginate is not modified by oxidation, and physical double-layer encapsulation is performed.

[0031] Comparative Example 4 The difference between Comparative Example 4 and Example 1 is that Comparative Example 4 does not have the sodium alginate layer coating of S5, but only the chitosan / ε-polylysine monolayer coating of S4, and the rest is the same as Example 1.

[0032] Comparative Example 5 The difference between Comparative Example 5 and Example 1 is that Comparative Example 5 does not perform emulsification or encapsulation steps, but directly mixes carboxyl-containing plant essential oil derivatives, unmodified plant essential oils, chitosan, ε-polylysine, and sodium oxidized alginate in the same proportion as in Example 1 and then dries them.

[0033] Comparative Example 6 The difference between Comparative Example 6 and Example 1 is that the sodium alginate in Comparative Example 6 is not oxidized, while the rest is the same as in Example 1.

[0034] Comparative Example 7 The difference between Comparative Example 7 and Example 1 is that the plant essential oil in Comparative Example 7 is not modified by acid anhydride semi-esterification, but otherwise it is the same as Example 1.

[0035] Comparative Example 8 The difference between Comparative Example 8 and Example 1 is that ε-polylysine is omitted in step S4 of Comparative Example 8, and only chitosan is added, while the rest is the same as in Example 1.

[0036] Comparative Example 9 The difference between Comparative Example 9 and Example 1 is that the order of steps S4 and S5 in Comparative Example 9 is reversed. Sodium oxidized alginate is added first, followed by chitosan / ε-polylysine. The rest is the same as in Example 1.

[0037] Application example: The plant essential oil microcapsules obtained in the examples and comparative examples were dispersed in water to obtain a plant essential oil microcapsule finishing solution with a concentration of 10 g / L. The solution was then used to impregnate cotton fabric and dried in an oven at 80 ℃ for 5 min to obtain plant essential oil microcapsule finished textiles.

[0038] Test Example 1: Encapsulation Rate Test The encapsulation efficiency of microcapsules was quantitatively determined using a UV-Vis spectrophotometer. The steps are as follows: (1) Plotting the standard curve: Add 100 μL of plant essential oil to a 50 mL volumetric flask, dilute to the mark with anhydrous ethanol, and shake well. Add 50 μL, 100 μL, 150 μL, 200 μL, and 250 μL of the above solution to 10 mL centrifuge tubes, respectively, and dilute to 5 mL with anhydrous ethanol to obtain standard solutions with concentrations of 0.02 μL / mL, 0.04 μL / mL, 0.06 μL / mL, 0.08 μL / mL, and 0.1 μL / mL, respectively. Place the standard solutions of different concentrations into cuvettes for UV full-spectrum scanning in the wavelength range of 200~300 nm to find their maximum absorption wavelength, and measure the absorbance of the standard solutions of different concentrations at the maximum absorption wavelength. Plot the standard curve of absorbance versus concentration, and calculate the linear correlation coefficient, such as... Figure 4 , Figure 3 As shown.

[0039] (2) Extraction of plant essential oils from microcapsules Accurately weigh 1g of microcapsule sample and add it to 50 mL of anhydrous ethanol. Heat in a 40 °C water bath for 30 min, then treat the solution with ultrasound for 1 h, centrifuge, and take 100 μL, 200 μL, and 300 μL of the supernatant into 10 mL graduated test tubes, respectively. Make up to 5 mL with anhydrous ethanol to obtain the sample of unknown concentration.

[0040] (3) Calculate the encapsulation rate of essential oil microcapsules: Measure the absorbance of the sample with unknown concentration at the maximum absorption wavelength, substitute it into the standard curve above, and calculate the essential oil concentration. Then, calculate the encapsulation rate using the formula. .

[0041] In the formula: W1 is the mass of the essential oil in the microcapsule; W2 is the total amount of essential oil added during the preparation process.

[0042] Table 1. Encapsulation efficiency of bilayer plant essential oil microcapsules prepared in the examples and comparative examples.

[0043] The overall encapsulation rates of the comparative examples were lower than those of the examples. This was due to the absence or defects in their chemical bonding networks, leading to significant leakage of the core material during preparation and washing. Comparative Examples 3, 5, and 7 lacked amide bonds because the essential oils were not modified with anhydride; the essential oils were only physically retained. Comparative Example 5, with its purely physical mixing, had an encapsulation rate of only 29.39%. Comparative Example 3, without chemical modification and double-layer encapsulation, had an encapsulation rate of only 36.76%. Comparative Example 7, lacking only amide bonds, achieved an encapsulation rate of 69.43%, but this was slightly higher due to the integrity of the outer Schiff base, still lower than all examples (≥68.67%). Comparative Example 6, due to the lack of Schiff base cross-linking caused by the unoxidized sodium alginate, had a loose outer shell and an encapsulation rate of only 57.49%. In Comparative Example 1, the lack of Tween 80 emulsification led to interface assembly failure and uneven wall material coverage, resulting in an embedding rate of only 49.69%. In Comparative Example 8, the omission of ε-polylysine resulted in excessively low crosslinking density, leading to an embedding rate of only 66.73%. In Comparative Example 9, the reversed S4 / S5 order caused the Schiff base to incorrectly crosslink into flocculent precipitate in the aqueous phase instead of forming a shell on the oil droplet surface, causing the embedding rate to plummet to 9.76%. In contrast, all examples chemically anchored the core material to the first wall material through inner amide bonds and covalently welded the wall material into a dense shell through outer Schiff bases. The synergistic effect of the dual chemical bonds ensured a high embedding rate (73.19%~85.23%).

[0044] Test Example 2: Slow-Release Evaluation (1) Room temperature sustained release: A certain amount of essential oil microcapsules were evenly spread on a petri dish and placed open at 25 ℃ (room temperature). Samples (approximately 1 g) were taken at regular intervals (5 days, 10 days, 20 days, 30 days, and 60 days). The essential oil content in the microcapsules was measured using the method described above, and the essential oil release was calculated using the following formula: .

[0045] (2) High-temperature slow release: A certain mass of microcapsules was weighed and placed in a glass container, then placed in an oven at 80 ℃. Samples were taken at regular intervals (0, 5, 10, 20, 30 min) to calculate the essential oil content in the microcapsules. Curves showing the change in essential oil content in the microcapsules over time and the release rate were plotted to characterize the protective effect of the microcapsules on the essential oils under high temperature conditions.

[0046] Table 2. Encapsulation efficiency, room temperature and high temperature sustained-release performance of the examples and comparative examples

[0047] The controlled-release effect of the comparative examples was significantly worse than that of the examples, mainly due to the absence or defects in their chemical bonding networks: Comparative examples 3, 5, and 7 lacked amide bonds because the essential oils were not modified with anhydride, and the essential oils were only physically encapsulated, resulting in complete release within 60 days at room temperature, and nearly 100% release within 30 minutes at high temperature. Comparative examples 3 and 6 lacked Schiff base cross-linking because the sodium alginate was not oxidized, and the shells swelled and became porous upon contact with water, leading to a rapid increase in release rate. Although comparative example 9 contained wall material raw materials, the reversed S4 / S5 order caused the Schiff base to incorrectly cross-link in the aqueous phase, forming flocculent precipitates, and it did not form a complete shell layer on the surface of the oil droplets, releasing 85% within 5 days at room temperature and completely disintegrating within 30 minutes at high temperature. Comparative example 8 had an excessively low cross-linking density due to the omission of ε-polylysine, and comparative example 1 had uneven wall material coating due to the lack of emulsifier, both resulting in rapid leakage of essential oils. In contrast, the embodiment forms a double covalent defense in the wall material through inner amide bonds and outer Schiff bases. At high temperatures, the covalent bonds are much stronger than physical interactions, thus the sustained-release performance is superior to the comparative example.

[0048] Test Example 3: Performance Testing of Finished Textiles in Examples and Comparative Cases 1. Antibacterial properties: Refer to GB / T 20944.3-2008 Evaluation of antibacterial properties of textiles - Part 3: Vibration method: Both the sample and the control sample (100% cotton fabric) were cut into approximately 5 mm × 5 mm fragments. 0.1 g of each fragment was weighed, sterilized, and placed in a 24-well plate. A specific concentration of test bacterial suspension was then inoculated into each well. The plates were incubated at 37 ℃ with shaking at 150 r / min for 18–24 h. Samples were taken before and after shaking, diluted, and plated for incubation. The viable bacterial count was then determined, and the inhibition rate was calculated based on the difference between the control and sample values. This method was used to evaluate the antibacterial performance of the samples. .

[0049] 2. Air permeability: Refer to GB / T 5453-2025 "Textiles - Determination of Air Permeability of Fabrics". 3. Mechanical properties: Refer to GB / T 3923.1-2013 Textiles - Tensile properties of fabrics - Part 1: Determination of breaking strength and elongation at break - Bar method.

[0050] Table 3 Antibacterial properties

[0051] Table 4 Breathability

[0052] Table 5 Tensile Properties

[0053] The antibacterial function of the microcapsule-finished textiles of this invention originates from the synergistic antibacterial effect of chitosan and ε-polylysine in the wall material and the slow release of essential oils from the core material. The protonated amino groups of chitosan electrostatically adsorb onto bacterial cell membranes, disrupting membrane integrity, while ε-polylysine, with its higher positive charge density, penetrates the cell membrane and interferes with intracellular metabolism. These two mechanisms complement each other, producing a significant synergistic effect. Example 1 achieved an antibacterial rate of 99.99%, while Comparative Example 8, omitting ε-polylysine, saw a decrease to 97.20% and 96.80%, confirming the crucial role of this synergistic effect. The double-layer wall material structure forms a dense protective layer through amide bonds and Schiff base crosslinking, allowing for the slow release of essential oils to provide long-lasting antibacterial protection. Comparative Example 4 only had a single-layer coating; the microcapsules were easily damaged, leading to premature leakage of the core material, and the antibacterial rate decreased to 98.50% and 98.20%. Comparative Example 9 showed that due to the reversed operation sequence, the wall material cross-linked and agglomerated prematurely without a core material, which could not effectively encapsulate the essential oil, resulting in an antibacterial rate of only 85.00% and 82.00%.

[0054] The small change in tensile strength is due to the extremely low amount of finishing agent used, which cannot form a reinforcing skeleton. In this invention, the concentration of the microcapsule finishing solution is only 10 g / L, resulting in a very low quality of wall material actually adhering to the fabric. These polymeric substances exist on the fiber surface in the form of microcapsule wall material and cannot penetrate into the fiber interior to covalently cross-link with cellulose molecules. Unlike resin finishing, where the resin solid content is typically 50–100 g / L and can penetrate into the fiber interior to form a three-dimensional cross-linked network, the microcapsule wall material cannot build a reinforcing skeleton inside the fiber and does not substantially contribute to the tensile strength of the fiber itself. Furthermore, the finishing process involves drying at 80 °C for only 5 minutes, far below the conditions for significant heat damage to cotton fibers. Therefore, the strength retention rate of the fabric before and after finishing is between 95% and 99%, with a change of only 2% to 5%.

[0055] The minimal change in air permeability is due to the fact that the microcapsules adhere as discrete particles rather than forming a continuous film to block pores. The microcapsule size is in the micrometer range, while the pores between fibers and the gaps between yarns in cotton fabric are much larger than the microcapsule size. These discrete particles, after attaching to the surface of a single fiber, do not bind adjacent fibers together, nor do they form a continuous sealing film on the fabric surface. Air molecules can still pass smoothly through the pore channels between fibers. Even if some samples exhibit localized agglomeration due to improper emulsification, the air permeability only decreases by about 4%, far less than the 30%–50% decrease in air permeability observed in coating finishing. This result fully demonstrates that the microcapsule finishing process of this invention imparts highly efficient antibacterial function to fabrics while preserving the original wearing comfort and mechanical properties of the fabric.

[0056] Figure 1The image shows a scanning electron microscope (SEM) image of a double-layered plant essential oil microcapsule. The prepared microcapsules exhibit a spherical morphology with a relatively dense and smooth surface, and no obvious adhesion or breakage between the particles. The inner layer of this invention is composed of a first wall material made of chitosan / ε-polylysine, and the outer layer is composed of a second wall material made of sodium alginate oxide. This dense shell composed of inner and outer layers can provide an effective physical sealing barrier for the core material encapsulated in the innermost layer, ensuring the integrity and stability of the overall structure of the microcapsule.

[0057] Figure 2 The image shows the infrared spectrum of the double-layered plant essential oil microcapsules. Characteristic absorption peaks of amide bonds and Schiff base bonds appear in the spectrum. The characteristic peak of the amide bonds confirms that the amino group of chitosan / ε-polylysine underwent a covalent condensation reaction with the carboxyl group in the carboxylated essential oil derivative, achieving chemical anchoring between the core material and the first wall material. The characteristic peak of the Schiff base bonds confirms that a dynamic covalent cross-linking was formed between the aldehyde group of oxidized sodium alginate and the amino group in the first wall material.

[0058] The C=N stretching vibration peak of the zigzag base bond can be identified at approximately 1640 cm⁻¹, proving that a dynamic covalent cross-linking is formed between the aldehyde group of sodium alginate oxide and the amino group of the first wall material, thus constructing a chemically welded network for the outer wall material.

[0059] Figure 5 This is an optical microscope image of the lavender essential oil core emulsion. After high-speed homogenization, the essential oil droplets formed are in a relatively uniform spherical dispersion state in the aqueous phase. The droplet size is moderate and the distribution is relatively uniform. This indicates that under the action of Tween series emulsifiers, the composite plant essential oil can form a stable oil-in-water emulsion system, providing an ideal spherical template for the subsequent interfacial amidation reaction of the wall material at the oil-water interface.

[0060] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A double-layered microcapsule of a plant essential oil, characterized by, The microcapsule comprises, from the inside out, a core material, a first wall material, and a second wall material. The core material contains a carboxyl plant essential oil derivative modified by acid anhydride semi-esterification and an unmodified plant essential oil. The first wall material is composed of chitosan / ε-polylysine, whose amino groups are covalently anchored to the carboxyl groups in the core material via amide bonds. The second wall material is composed of sodium alginate oxide, whose aldehyde groups are dynamically interlocked with the amino groups in the first wall material via Schiff base bonds.

2. The method for preparing a double-layer plant essential oil microcapsule according to claim 1, characterized in that, The preparation method includes the following steps: S1. Hydroxyl-containing components in plant essential oils are modified by acid anhydride semi-esterification to obtain carboxyl-containing plant essential oil derivatives; S2. Sodium alginate is oxidized to obtain sodium alginate containing aldehyde groups; S3. Mix carboxyl-containing plant essential oil derivatives with unmodified plant essential oils to obtain composite plant essential oils. Dissolve emulsifiers in water to form an aqueous phase. Add the composite plant essential oils to the aqueous phase and homogenize at high speed to form an oil-in-water plant essential oil core material emulsion. S4. Add chitosan and ε-polylysine to the plant essential oil core material emulsion of S3, add an amidation promoter and stir to carry out an amidation reaction, forming a first wall material on the surface of the plant essential oil core material, and obtain a microcapsule suspension coated with the first wall material; S5. Add the microcapsule suspension coated with the first wall material to the sodium alginate oxidase solution, stir to carry out the Schiff base reaction, and form a second wall material on the outside of the first wall material to obtain a double-layer plant essential oil microcapsule suspension. S6. Centrifuge, wash, and dry the double-layer plant essential oil microcapsule suspension to obtain double-layer plant essential oil microcapsules.

3. The method for preparing a double-layer plant essential oil microcapsule according to claim 2, characterized in that: In step S1, the plant essential oils include one or more of the following: lavender essential oil, tea tree essential oil, peppermint essential oil, lemon essential oil, neroli essential oil, rose essential oil, eucalyptus essential oil, rosemary essential oil, cypress essential oil, sandalwood essential oil, and chamomile essential oil. In the anhydride semi-esterification modification, the amount of anhydride used is 1% to 80% of the mass of the plant essential oil, the reaction temperature is 20 to 90 ℃, and the reaction time is 0.5 to 24 h. The anhydride is one or more of the following: succinic anhydride, maleic anhydride, itaconic anhydride, glutaric anhydride, and phthalic anhydride.

4. The method for preparing a double-layer plant essential oil microcapsule according to claim 2, characterized in that: In step S2, the oxidation treatment involves reacting sodium alginate with periodate under light-protected conditions, with the degree of oxidation of sodium alginate being 5% to 60%.

5. The method for preparing a double-layer plant essential oil microcapsule according to claim 2, characterized in that: In step S3, the mass ratio of carboxyl-containing plant essential oil derivatives to unmodified plant essential oils in the compound essential oil is 1-9:9-1. The emulsifier is any one of Tween 20, Tween 40, Tween 60, Tween 80, and Span 80. The high-speed homogenization speed is 2000-15000 rpm, and the time is 1-20 min. The concentration of the plant essential oil core material emulsion is 5-20 g / L.

6. The method for preparing a double-layer plant essential oil microcapsule according to claim 2, characterized in that: In step S4, the mass ratio of chitosan to ε-polylysine is 1:10 to 10:

1. The amidation accelerator is one or more of EDC, NHS, EDC / NHS, DCC, and CDI. The pH of the amidation reaction is 4.0 to 7.0, the reaction temperature is 20 to 60 °C, and the reaction time is 0.5 to 8 h.

7. The method for preparing a double-layer plant essential oil microcapsule according to claim 2, characterized in that: In step S5, the concentration of the sodium alginate oxidizing solution is 0.1–100 g / L, the pH of the Schiff base reaction is 3.5–7, the reaction temperature is 30–60℃, the stirring speed is 100–700 rpm, and the stirring time is 4–8 h.

8. The application of the double-layer plant essential oil microcapsule according to claim 1 in clothing, home textiles, automotive interiors, curtains, carpets, outdoor products, industrial fabrics or bags.

9. The application according to claim 8, characterized in that, The application involves applying double-layer plant essential oil microcapsules to a fabric, and the finishing method includes one or more of padding, soaking, spraying, coating, rolling, hot pressing, and hot air drying.

Images