Core-shell capsules of menthol and preparation method thereof

Abstract

The present disclosure relates to a core-shell capsule comprising menthol as a volatile active and an amphiphilic polymer comprising a polyethylene glycol (PEG) segment and a hydrophobic segment, wherein the menthol and the hydrophobic segment form the core of the capsule, encapsulated within a shell comprising the PEG segment and crosslinked with a polyacid, wherein the amphiphilic polymer is Poloxamer 407, and wherein the core-shell capsule has a thermal stability of more than 400 ℃ and is configured to release the menthol in a controlled manner.

Description

CORE-SHELL CAPSULES OF MENTHOL AND PREPARATION METHOD THEREOF CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore application no.10202403586V filed on 15 November 2024, the contents of it being hereby incorporated by reference in its entirety for all purposes.TECHNICAL FIELD

[0002] The present disclosure generally relates to core-shell capsules and method of preparing the same. In particular, the present disclosure relates to core-shell capsules comprising menthol and method of preparing the same.BACKGROUND

[0003] Perfuming and flavouring of consumer products have been well-known for many years. Menthol is commonly used as a flavouring ingredient to provide a cooling sensate to consumers via inhalation or contact. Menthol could also be used for perfuming or flavouring of consumer products, such as underarm deodorants and antiperspirants, solid sticks and aerosols, laundry detergents powder, fragranced cat litter, etc. However, the stability and volatilization properties of the menthol cause menthol to loss at the dry state, hence the current application of menthol in such consumer products is technically challenging.

[0004] It is therefore desirable to provide an encapsulated menthol and method of preparing the same to address at least one of the problems described hereinabove, or at least to provide an alternative.SUMMARY

[0005] In accordance with a first aspect of the present disclosure, a core-shell capsule is provided. The core-shell capsule comprises menthol as a volatile active and an amphiphilic polymer comprising a polyethylene glycol (PEG) segment and a hydrophobic segment, whereinthe menthol and the hydrophobic segment form the core of the capsule, encapsulated within a shell comprising the PEG segment and crosslinked with a polyacid, wherein the amphiphilic polymer is Poloxamer 407, and wherein the core-shell capsule has a thermal stability of more than 400 °C and is configured to release the menthol in a controlled manner.

[0006] In some embodiments, the core-shell capsule is configured to release the menthol by burst or delayed burst volatilization of the menthol in a solid state.

[0007] In some embodiments, the core-shell capsule is configured to release the menthol by long-lasting, minimized volatilization of the menthol in a waterless liquid state.

[0008] In accordance with a second aspect of the present disclosure, a method of preparing core-shell capsules comprising menthol is provided. The method comprises forming a mixture containing menthol, water, and an amphiphilic polymer comprising a polyethylene glycol (PEG) segment and a hydrophobic segment at room temperature; homogenizing the mixture to obtain an emulsion; adding a polyacid into the emulsion to crosslink the PEG segment of the amphiphilic polymer with the polyacid; and drying the emulsion to obtain the core-shell capsules comprising the menthol and the amphiphilic polymer, wherein the menthol and the hydrophobic segment form the cores of the core-shell capsules, encapsulated within a shell comprising the PEG segment and is crosslinked with the polyacid, wherein the amphiphilic polymer is Poloxamer 407, and wherein the method is performed without heating and without organic solvent.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Various embodiments of the present disclosure are described hereinbelow in the detailed description with reference to the following drawings:FIG. 1 shows a Differential scanning calorimetry (DSC) curve of pure menthol crystals.FIG. 2A shows a DSC curve of an encapsulated menthol prepared with menthol and Poloxamer 407 (F127) at a feed ratio of 1:3.3 without crosslinking, in accordance with an embodiment of the present disclosure.FIG. 2B shows a DSC curve of an encapsulated menthol prepared with menthol and Poloxamer 407 (Fl 27) at a feed ratio of 1:3.3 with crosslinking, in accordance with an embodiment of the present disclosure.FIG.3A shows a DSC curve of an encapsulated menthol prepared with menthol and Polysorbate 20 (Tween 20) at a feed ratio of 1:3.3 without crosslinking.FIG.3B shows a DSC curve of an encapsulated menthol prepared with menthol and Polysorbate 20 at a feed ratio of 1:3.3 with crosslinking.FIG.3C shows a DSC curve of an encapsulated menthol prepared with menthol and Polysorbate 80 (Tween 80) at a feed ratio of 1:3.3 without crosslinking.FIG.3D shows a DSC curve of an encapsulated menthol prepared with menthol and Polysorbate 80 at a feed ratio of 1:3.3 with crosslinking.FIG. 4A shows a TGA curve of pure menthol and an encapsulated menthol prepared with menthol and Polysorbate 20 at a feed ratio of 1 :3.3, with and without crosslinking.FIG. 4B shows a TGA curve of pure menthol and an encapsulated menthol prepared with menthol and Polysorbate 80 at a feed ratio of 1:3.3, with and without crosslinkingFIG. 4C shows a TGA curve of pure menthol and an encapsulated menthol prepared with menthol and Poloxamer 407 at a feed ratio of 1:3.3, with and without crosslinking.FIG. 5 shows the volatilization of solid samples of menthol (denoted as menthol), samples with menthol to Poloxamer 407 at a feed ratio of 1:3.3 without crosslinking (denoted as F127), and the samples with menthol to Poloxamer 407 at a feed ratio of 1:3.3 with crosslinking (denoted as F127+PAA) at ambient conditions (i.e. T= 25 °C; RH = 50%).FIG. 6A shows an SEM image of the particles of the encapsulated menthol with Polysorbate 20 at a feed ratio of 1 :3.3 without crosslinking.FIG. 6B shows an SEM image of the particles of the encapsulated menthol with Polysorbate 20 at a feed ratio of 1 :3.3 with crosslinking.FIG. 6C shows an SEM image of the particles of the encapsulated menthol with Polysorbate 80 at a feed ratio of 1 :3.3 without crosslinking.FIG. 6D shows an SEM image of the particles of the encapsulated menthol with Polysorbate 80 at a feed ratio of 1 :3.3 with crosslinking.FIG. 6E shows an SEM image of the particles of the encapsulated menthol with Pol oxamer 407 at a feed ratio of 1:3.3 without crosslinking in accordance with an embodiment of the present disclosure.FIG. 6F shows an SEM image of the particles of the encapsulated menthol with Poloxamer 407 at a feed ratio of 1 :3 3 with crosslinking in accordance with an embodiment of the present disclosure.DESCRIPTION

[0010] The following description sets forth exemplary methods, parameters, and the like. The embodiments are described in sufficient detail to enable those skilled in the art to practise the invention. Other embodiments may be utilized, and structural and logical changes may be made without departing from the scope of the invention. The various embodiments are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments.

[0011] Features that are described in the context of an embodiment may correspondingly be applicable to the same or similar features in the other embodiments. Features that are described in the context of an embodiment may correspondingly be applicable to the other embodiments, even if not explicitly described in these other embodiments. Furthermore, additions and / or combinations and / or alternatives as described for a feature in the context of an embodiment may correspondingly be applicable to the same or similar feature in the other embodiments.

[0012] In the context of various embodiments, the articles “a”, “an” and “the” as used with regard to a feature or element include a reference to one or more of the features or elements.

[0013] In the context of various embodiments, the term “about” or “approximately” as applied to a numeric value encompasses the exact value and a reasonable variance, e g. within 10% of the specified value.

[0014] As used herein, the term “and / or” includes any and all combinations of one or more of the associated listed items.

[0015] By “comprising” it is meant including, but not limited to, whatever follows the word “comprising”. Thus, use of the term “comprising” indicates that the listed elements are required or mandatory, but that other elements are optional and may or may not be present.

[0016] By “consisting of’ is meant including, and limited to, whatever follows the phrase “consisting of’. Thus, the phrase “consisting of’ indicates that the listed elements are required or mandatory, and that no other elements may be present.

[0017] The term “encapsulated menthol” as used herein refers to a capsule comprising menthol as a volatile active encapsulated within an amphiphilic block copolymer in a manner as described in the present disclosure. For the sake of brevity, the terms “encapsulated menthol”, “core-shell capsule”, and “core-shell particles” will be used interchangeably.

[0018] As used herein, the term “Polysorbate 20” refers to polyoxyethylene (20) sorbitan monolaurate, commercially available as Tween 20. In the present disclosure, the terms “Polysorbate 20” and “Tween 20” are used interchangeably, irrespective of supplier or grade, unless otherwise specified.

[0019] As used herein, the term “Polysorbate 80” refers to polyoxyethylene (20) sorbitan monooleate, commercially available as Tween 80. In the present disclosure, the terms “Polysorbate 80” and “Tween 80” are used interchangeably, irrespective of supplier or grade, unless otherwise specified.

[0020] As used herein, the term “Poloxamer 407” refers to a non-ionic triblock copolymer of polyethylene oxide and polypropylene oxide (PEO-PPO-PEO). Poloxamer 407 is commercially available as Pluronic F-127. In the present disclosure, the terms “Poloxamer 407” and “Pluronic F-127” are used interchangeably, irrespective of supplier or grade, unless otherwise specified.

[0021] The present disclosure relates to a core-shell capsule comprising menthol asavolatile active and an amphiphilic copolymer comprising a polyethylene glycol (PEG) segment and a hydrophobic segment. The shell is crosslinked by reaction with a polyacid crosslinker to provide a core-shell capsule that exhibits a high thermal stability, with controllable release or volatilization properties, including burst and delayed-burst volatilization in the solid state, as well as long-lasting, minimized volatilization in a waterless liquid state.

[0022] According to a first aspect, the core-shell capsule comprises menthol as a volatile active and an amphiphilic polymer comprising a polyethylene glycol (PEG) segment and a hydrophobic segment, wherein the menthol and the hydrophobic segment form the core of the capsule, encapsulated within a shell comprising the PEG segment and crosslinked with a poly acid.

[0023] In some embodiments, the amphiphilic polymer may be selected from Polysorbate 20, Polysorbate 80 and Poloxamer 407. In some preferred embodiments, the amphiphilic polymer is Poloxamer 407.

[0024] In some embodiments, the core-shell capsule may have a thermal stability of more than 400 °C.

[0025] In various embodiments, the core-shell capsule is configured to release the menthol in a controlled manner In some embodiments, the core-shell capsule is configured to release the menthol by burst or delayed burst volatilization of the menthol in a solid state. In other embodiments, the core-shell capsule is configured to release the menthol by long-lasting, minimized volatilization of the menthol in a waterless liquid state.

[0026] In some embodiments, the polyacid may be a poly(carboxylic acid) selected from the group consisting of poly acrylic acid and poly(methacrylic acid).

[0027] In some embodiments, the core-shell capsule has a particle size ranging from 10 nm to 1000 nm, preferably 10 to 500 nm.

[0028] In some embodiments, the menthol may be loaded in the core of the capsule at a loading concentration ranging from 1 % to 30 %.

[0029] In some embodiments, the PEG segment of the amphiphilic polymer may be crosslinked with the polyacid at a crosslinking density of at least 1 %. In some embodiments, at a crosslinking density of at least 5%, at least 10 %, or at least 15 %.

[0030] In various embodiments, the menthol to the amphiphilic polymer may be in a weight ratio ranging from 1 :3.3 to 1 :10. In some embodiments, the weight ratio is about 1 :10, 1 :8. 1 :5 or 1:3.3.

[0031] According to a second aspect of the present disclosure, a method of preparing the core-shell capsule is provided. The method involves a two-step process comprising preparing an emulsion and drying the emulsion to obtain the core-shell capsules containing menthol.

[0032] In various embodiments, the method comprises forming a mixture containing menthol, water, and an amphiphilic polymer comprising a polyethylene glycol (PEG) segment and a hydrophobic segment at room temperature; homogenizing the mixture to obtain an emulsion; adding a polyacid into the emulsion to crosslink the PEG segment of the amphiphilic polymer; and drying the emulsion to obtain the core-shell capsules comprising the menthol and the amphiphilic polymer. The menthol and the hydrophobic segment of the amphiphilic polymer form the cores of the core-shell capsules, and the cores are encapsulated within a shell comprising the PEG segment of the amphiphilic polymer and is crosslinked with the polyacid. The method of the present disclosure is performed without heating and without any organic solvents.

[0033] In some embodiments, the amphiphilic polymer may be selected from Polysorbate 20, Polysorbate 80 and Poloxamer 407. In some preferred embodiments, the amphiphilic polymer is Poloxamer 407. In some embodiments, the mixture may be homogenized at room temperature using a high-shear mixer to obtain a fine and homogeneous emulsion. Any suitable types of high-shear mixer may be employed, including but not limited to, rotor-stator high-shear mixer, inline high-shear mixers and ultra-high shear inline mixers.

[0034] In various embodiments, the step of drying may comprise freeze-drying the emulsion to form core-shell capsules in powder form. In some embodiments, the freeze-drying may be performed for a duration not exceeding 4.8 hours per ml of the emulsion, preferably not exceeding 2.4 hours per ml of the emulsion. Any conventional method of freeze-drying may be employed without departing from the scope of the present disclosure so long as the dried capsules retain their structural integrity.

[0035] In some embodiments, the PEG segment of the amphiphilic polymer may be crosslinked with the poly acid at a crosslinking density of at least 1%. In other embodiments, at a crosslinking density of at least 5 %, at least 10% or at least 15%.

[0036] In some embodiments, the core-shell capsules have a thermal stability of more than 400 °C.

[0037] In some embodiments, the core-shell capsules may be made to controllably release the menthol in a burst or delayed burst volatilization of the menthol in a solid state. In other embodiments, the core-shell capsules may be made to controllably release the menthol by long-lasting, minimized volatilization of the menthol in a waterless liquid state.

[0038] In some embodiments, the polyacid is a poly (carboxylic acid) selected from the group consisting of polyacrylic acid and poly(methacrylic acid).

[0039] In some embodiments, the dried core-shell capsules may have a particle size ranging from 10 nm to 1000 nm, preferably 10 to 500 nm.

[0040] The core-shell capsules of the present disclosure offers several advantages. By encapsulating and crosslinking the menthol, the core-shell capsules exhibit significant improvement in thermal stability, above 400 °C. Furthermore, with encapsulation, the core-shell capsules exhibits a burst volatilization effect. Such burst and delayed burst effects provide the advantage of enabling controlled timing of menthol release, thereby delivering a potent sensory impact either immediately or after a desired delay.

[0041] To facilitate a better understanding of the present disclosure, the following examples of specific embodiments are given. In no way should the following examples be read to limit or define the entire scope of the disclosure. One skilled in the art will recognize that the examples set out below are not an exhaustive list of the embodiments of this disclosure.EXAMPLESExample 1

[0042] Preparation of core-shell capsules with Polysorbate 20 without crosslinking

[0043] L-menthol and Polysorbate 20 were mixed at room temperature in different weight ratios of 1 : 10, 1:8, 1:5 and 1.3.3, respectively. To each mixture, 20 mL of deionized water was added and homogenized using a high shear mixer to obtain a fine and homogeneous emulsion. The homogeneous emulsion was subjected to freeze-drying to afford a translucent liquid.Example 2

[0044] Preparation of core-shell capsules with Polysorbate 20 with crosslinking

[0045] L-menthol and Polysorbate 20 (2g) were mixed at room temperature in a weight ratio of 1 : 10. 20 mL of deionized water was added to the mixture, and the mixture was homogenized using a high shear mixer to obtain a fine and homogeneous emulsion. The homogeneous emulsion was then subjected to a crosslinking process. 0.15 g of polyacrylic acid (mw=5000, 50% solution) was added to the homogeneous emulsion to crosslink the polyethylene (PEG) shell of the capsules, and was further homogenized for about 3 minutes. The final emulsionhas a crosslinking degree of about 10 % calculated using the molar ratio. The final emulsion was subj ected to freeze-drying to afford a translucent liquid.Example 3

[0046] Preparation of core-shell capsules with Polysorbate 80 without crosslinking

[0047] L-menthol and Polysorbate 80 were mixed at room temperature in different weight ratios of 1 : 10, 1 :8, 1 :5 and 1 :3.3, respectively. To each mixture, 20 mL of deionized water was added and homogenized using a high shear mixer to obtain a fine and homogeneous emulsion. The homogeneous emulsion was subjected to freeze-drying to afford a translucent liquid.Example 4

[0048] Preparation of core-shell capsules with Polysorbate 80 with crosslinking

[0049] L-menthol and Polysorbate 80 (2g) were mixed at room temperature in a weight ratio of 1 : 10. 20 mL of deionized water was added to the mixture, and the mixture was homogenized using a high shear mixer to obtain a fine and homogeneous emulsion. The homogeneous emulsion was then subjected to a crosslinking process. 0.15 g of polyacrylic acid (mw=5000, 50% solution) was added to the homogeneous emulsion to crosslink the polyethylene (PEG) shell of the capsules, and was further homogenized for about 3 minutes. The final emulsion has a crosslinking degree of about 10 % calculated using the molar ratio. The final emulsion was subj ected to freeze-drying to afford a translucent liquid.Example 5

[0050] Preparation of core-shell capsules with Pol oxamer 407 without crosslinking

[0051] L-menthol and Poloxamer 407 were mixed at room temperature in different weight ratios of 1 : 10, 1:8, 1:5 and 1.3.3, respectively. To each mixture, 20 mL of deionized water was added and homogenized using a high shear mixer to obtain a fine and homogeneous emulsion. The homogeneous emulsion was subjected to freeze-drying to afford a white powder.Example 6

[0052] Preparation of core-shell capsules with Poloxamer 407 with crosslinking

[0053] L-menthol and Poloxamer 407 (2g) were mixed at room temperature in a weight ratio of 1:10. 20 mL of deionized water was added to the mixture, and the mixture was homogenized using a high shear mixer to obtain a fine and homogeneous emulsion. The homogeneous emulsion was then subjected to a crosslinking process. 0.15 g of polyacrylic acid (mw=5000, 50% solution) was added to the homogeneous emulsion to crosslink the polyethylene (PEG) shell of the capsules, and was further homogenized for about 3 minutes. The final emulsion has a crosslinking degree of about 8 % calculated using the molar ratio. The final emulsion was subjected to freeze-drying to afford a white powder.Example 7

[0054] HPLC Analysis of Menthol Loading

[0055] The content of menthol in the waterless core-shell capsules was quantified via high-performance liquid chromatograph (HPLC). The HPLC measurement of menthol was conducted on an Agilent Lab HPLC with a Inertsil C8-3 column (4.6x250mm, 5micron). The mobile phase was methanol:HzO (90:10), and the flow rate was 1 ml / min. The retention time for menthol is around 14.6 min.

[0056] Table 1 summarizes the HPLC loading of samples prepared at different feed ratios (Examples 1 to 6) of menthol to surfactant by weight. The results in Table 1 are measured after a drying duration of 2.4 hours per ml of emulsion.

[0057] Table 1: Summary of HPLC loading for capsules of menthol prepared at different feed ratio.

[0058] As shown in Table 1, an HPLC loading of more than 10 % of the menthol can be obtained when the feed ratio of the menthol to surfactant is 1:3.3 with or without crosslinker, respectively. It is worth noting that the menthol can be completely lost if the duration of freeze-drying is too long. For sample consisting of menthol and Poloxamer 407 at the feeding ratio of 1:3.3 with crosslinking, a freeze-drying duration of 4.8 hours per ml of emulsion completely removed the ice and the menthol. As a result, the drying duration should not exceed 4.8 hours per ml of emulsion.Example 8

[0059] Size characterisation by Dynamic Light Scattering

[0060] Dynamic Light Scattering (DLS) was used to determine the particle sizes of the coreshell capsules (Examples 1 to 6) in the emulsion, both in the as-prepared state, and the redispersed state after freeze-drying the samples.

[0061] Table 2 summarizes the DLS size of the as-prepared core-shell capsules prepared at different menthol to surfactant feed ratios, and Table 3 summarizes the DLS size of the redispersed core-shell capsules after removal of water with freeze-drying.

[0062] Table 2: The DLS size of the as-prepared core-shell capsules prepared at different feed ratio of menthol to surfactant.

[0063] The results in Table 2 show that the as prepared particle sizes range from 10 nm to 330 nm. In general, the particle sizes of the core-shell capsules prepared with Polysorbate 20 and Polysorbate 80 appear to be smaller in size than the core-shell capsules prepared with Poloxamer 407.

[0064] Table 3: The DLS size of the redispersed core-shell capsules prepared at different feed ratio of menthol to surfactant.

[0065] The results in Table 3 show that the DLS sizes of the core-shell capsules are in the range of 10 nm to 500 nm. For the core-shell capsules prepared from Polysorbate 20 and Polysorbate 80, the particle sizes of the redispersed core-shell capsules are similar to the as-prepared core-shell capsules. The particle sizes of the core-shell capsules prepared using Poloxamer 407 were observed to be larger after re-dispersion. This might be attributed to smaller particles forming clusters or aggregates in the redispersed medium.Example 9

[0066] DSC Analysis

[0067] Differential Scanning Calorimetry (DSC) was used to assess the crystalline state of the core-shell capsules with the feed ratio of menthol: surfactant at 1:3.3 with or without crosslinking. As a benchmark, the DSC curve of menthol is shown in FIG. 1, which shows a DSC endothermic peak at about 43.7 °C.

[0068] FIGs.2A and 2B show the DSC curves of the samples prepared with menthol and Poloxamer 407 (F127) at a feed ratio of 1:3.3, without crosslinking and with crosslinking, respectively. The endothermic peak is observed at about 54.3 °C in both the non-crosslinked (FIG. 2A) and crosslinked (FIG. 2B) samples. This suggests that the crosslinking of the shelloccurred after the formation of the core-shell capsules and does not alter the crystalline structure of the encapsulated menthol.

[0069] FIGs 3A to 3D shows the DSC curve of the core-shell capsules prepared using Polysorbate 20 and Polysorbate 80 at the feed ratio of 1:3.3, with and without crosslinking. For core-shell capsules prepared with Polysorbate 20 (FIG. 3A, non-crosslinked; FIG. 3B with crosslinking), there are only irregular broad peaks observed This indicates that the core-shell capsules formed from Polysorbate 20 could only have a partially crystalline structure and undergo melting at a temperature much lower than room temperature. Similarly, for the coreshell particles prepared from Polysorbate 80 (FIG. 3C, non-crosslinked; FIG. 3D with crosslinking), the peaks are also broad and irregular, indicating the presence of partially crystalline structures after encapsulation of menthol with Polysorbate 80.Example 10

[0070] TGA Analysis

[0071] FIGs. 4A to 4C show the thermogravimetric analysis (TGA) curves of menthol crystals and encapsulated menthol capsules. FIG. 4A illustrates the TGA curve of menthol and encapsulated menthol prepared with Polysorbate 20 at a feed ratio of 1 :3.3, with and without crosslinking. Menthol crystals without encapsulation were completely lost at approximately 100 °C. In contrast, improved thermal stability of menthol was observed following nanoencapsulation. Crosslinked nano-encapsulated menthol prepared with Polysorbate 20 demonstrates greater stability, maintaining weight above 400 °C, as compared to the non-crosslinked counterpart

[0072] FIG. 4B illustrates the TGA curve of menthol crystals and encapsulated menthol prepared with Polysorbate 80 at a feed ratio of 1:3.3, with and without crosslinking. Menthol crystals without encapsulation are completely lost at approximately 100 °C. At temperatures above 400 °C, the crosslinked capsules show better thermal stability compared to the non-crosslinked capsules.

[0073] FIG. 4C illustrates the TGA curve of menthol crystals and encapsulated menthol prepared with Poloxamer 407 at a feed ratio of 1:3.3, with and without crosslinking. Similarly, menthol crystals without encapsulation are completely lost at approximately 100 °C, and the crosslinked capsules exhibit higher thermal stability than the non-crosslinked capsules at temperatures above 400 °C.

[0074] In all cases, encapsulation of menthol with all three types of surfactants enhances the thermal stability of menthol compared to menthol crystals alone. The results as shown in FIG.4A to 4C confirm that crosslinking of the capsule shell provides further improvement in thermal stability at elevated temperatures, e.g., above 400 °C. Such thermally stable core-shell capsules may be applied in flavouring smoking articles or devices, such as cigarettes.Example 11

[0075] Controlled volatilization

[0076] The freeze-dried samples from Examples 1 to 6 were placed in a tube customized to a handheld odour meter. The tube included a tight outlet for the probe tip of the handheld odour meter to minimise the escape of the menthol during volatilization. The freeze-dried sample weight are kept at 0.2 g, and the measurement was conducted for 10 minutes at a 10-second data collecting interval.

[0077] The volatilization intensity of menthol at ambient temperature (i.e., 25 °C) was compared in the non-encapsulated and encapsulated solid state. FIG. 5 shows the normalized curve of volatilization of menthol, and the samples from Examples 5 and 6 for a 10-minute duration. In the absence of encapsulation, the volatilization of menthol increased gradually over time, reaching a peak at the end of the measurement period. In contrast, the encapsulated menthol exhibited a burst effect. Non-crosslinked core-shell capsules (menthol: Poloxamer = 1:3.3) shows a peak at approximately 60 seconds, whereas the crosslinked core-shell capsules (menthol: Poloxamer = 1:3.3, + PAA) exhibited a delayed peak at approximately 200 seconds. The burst effect is attributed to the crystalline structure of the encapsulated particles differingfrom menthol crystals, as confirmed by the DSC measurements (Example 9). The delayed peak observed for the crosslinked core-shell particles is believed to result from the crosslinking, which provides a denser shell for the particles. The burst effect and the delayed burst effect may be employed in applications requiring time-controlled of sensory effects.

[0078] Table 4 summarizes the volatilization intensity of menthol core-shell capsules prepared from Polysorbate 20 and Polysorbate 80, with and without crosslinking, respectively, as monitored by the handheld odour meter for the same period of 10 minutes and at ambient temperature (i.e., 25 °C).

[0079] Table 4: Volatilization intensity of freeze-dried samples prepared with menthol and Polysorbate 20, and with Polysorbate 80, with and without crosslinking, respectively.

[0080] The results in Table 3 show that the volatilization intensity at the waterless state is zero for all samples. This could be due to the nature of partially crystalline structure and the liquid physical stage of the translucent liquid after water removal (freeze-drying). Such properties would be advantageous for producing products with long-lasting scent and extended storage ability. The release of menthol will be triggered by external stimuli, such as but not limited to, pH changes, water dilution, and heat.Example 12

[0081] Morphology

[0082] The morphology of the core-shell capsules was examined using scanning electron microscopy (SEM). The capsules were redispersed in water, coated onto a sample wafer, dried, and subsequently observed. As shown in FIGs. 6A to 6F, distinct morphological features were observed depending on the surfactant and crosslinking conditions.

[0083] FIG. 6A shows that particles of the encapsulated menthol prepared with Polysorbate 20 without crosslinking exhibited irregular shapes, whereas the crosslinked particles (FIG. 6B) appeared to be more spherical. FIG. 6C shows that particles of the encapsulated menthol prepared with Polysorbate 80 without crosslinking tend to cluster during coating, and clustering was observed after crosslinking (FIG. 6D). FIG. 6E shows that the encapsulated menthol prepared with Poloxamer 407 without crosslinking also formed clusters, while the crosslinked particles (FIG. 6F) appeared more spherical than their non-crosslinked counterparts.

[0084] All the SEM images were recorded with a scale bar of 100 nm. Although clustering was observed in certain samples, the particles remained re-dispersible into nanosized particles in water, as confirmed by the DLS analysis (Example 8).

[0085] Although embodiments of the invention have been shown and described, the invention is not limited to the described embodiments. Instead, it would be appreciated by those skilled in the art that various modifications and variations can be made to the embodiments of the invention without departing from the scope of the invention, the scoop of which is set forth in the following claims.

Claims

Claims1. A core-shell capsule comprising menthol as a volatile active and an amphiphilic polymer comprising a polyethylene glycol (PEG) segment and a hydrophobic segment, wherein the menthol and the hydrophobic segment form the core of the capsule, encapsulated within a shell comprising the PEG segment and crosslinked with a polyacid, wherein the amphiphilic polymer is Poloxamer 407, and wherein the core-shell capsule has a thermal stability of more than 400 °C and is configured to release the menthol in a controlled manner.

2. The core-shell capsule of claim 1, wherein the polyacid is a poly(carboxylic acid) selected from the group consisting of polyacrylic acid and poly(methacrylic acid).

3. The core-shell capsule of claim 1, wherein the core-shell capsule has a particle size ranging from 10 nm to 1000 nm.

4. The core-shell capsule of claim 1, wherein the menthol is loaded in the core of the capsule at a loading concentration ranging from 1 % to 30 %.

5. The core-shell capsule of claim 1, wherein the PEG segment of the amphiphilic polymer crosslinked with the polyacid at a crosslinking density of at least 1%.

6. The core-shell capsule of claim 1, wherein the menthol to the amphiphilic polymer is in a weight ratio ranging from 1 :3.3 to 1 : 10.

7. The core-shell capsule of claim 1, the core-shell capsule is configured to release the menthol by burst or delayed burst volatilization of the menthol in a solid state.

8. The core-shell capsule of claim 1, the core-shell capsule is configured to release the menthol by long-lasting, minimized volatilization of the menthol in a waterless liquid state.

9. A method of preparing core-shell capsules comprising menthol, the method comprising:forming a mixture containing menthol, water, and an amphiphilic polymer comprising a polyethylene glycol (PEG) segment and a hydrophobic segment at room temperature;homogenizing the mixture to obtain an emulsion;adding a polyacid into the emulsion to crosslink the PEG segment of the amphiphilic polymer; anddrying the emulsion to obtain the core-shell capsules comprising the menthol and the amphiphilic polymer, wherein the menthol and the hydrophobic segment form the cores of the core-shell capsules, encapsulated within a shell comprising the PEG segment and is crosslinked with the polyacid,wherein the amphiphilic polymer is Poloxamer 407, andwherein the method is performed without heating and without organic solvent.

10. The method of claim 9, wherein the step of drying comprises freeze-drying the emulsion for a duration not exceeding 4.8 hours per ml of the emulsion.

11. The method of claim 9, wherein the PEG segment of the amphiphilic polymer is crosslinked with the polyacid at a crosslinking density of at least 1%.

12. The method of claim 9, wherein the core-shell capsules have a thermal stability of more than 400 °C.

13. The method of claim 9, wherein the core-shell capsules are made to controllab ly release the menthol in a burst or delayed burst volatilization of the menthol in a solid state.

14. The method of claim 9, wherein the core-shell capsules are made to controllab ly release the menthol by long-lasting, minimized volatilization of the menthol in a waterless liquid state.

15. The method of claim 9, wherein the polyacid is a poly(carboxylic acid) selected from the group consisting of poly(acrylic acid) and poly(methacrylic acid).

16. The method of claim 9, wherein the dried core-shell capsules have a particle size ranging from 10 nm to 1000 nm

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