Preparation of Inclusion Complexes with Argan Oils and Their Application of Hair Treatment

Abstract

Inclusion complexes of argan oil with β-CD were prepared by two different methods—evaporation and coprecipitation—to improve the stability and usability of hydrophobic oils in aqueous hair-treatment formulations. The complexes were characterized using SEM, XRD, DSC, TGA, and DTG to confirm structural changes accompanying encapsulation. The encapsulation efficiencies (EE%) were 68.4% for the evaporation method and 51.2% for the coprecipitation method. A hair treatment formulation containing the β-CD complexes was then prepared and evaluated. The formulation exhibited antibacterial activity against Staphylococcus aureus and provided uniform coating behavior on hair fibers. Texture profile analysis showed hardness (456.424 g), fracturability (428.26 g), adhesiveness (−4021.403 g·s), springiness (0.974), and cohesiveness (0.868), indicating that the complexes contributed positively to mechanical performance. OM and SEM confirmed smoother surface morphology after treatment, and tensile measurements demonstrated improved structural durability of bleached hair. These results suggest that β-CD-based inclusion complexes of argan oil can serve as effective and stable functional ingredients for cosmetic applications.

1. Introduction

Argan oil is a naturally derived oil extracted from the fruit of the argan tree native to Morocco. Argan oil is valued in hair care formulations, but practical performance is often limited not by high volatility but by oxidative degradation and odor changes during storage and on-hair use. Thin surface films on hair can gradually lose light components and undergo oxidation, which reduces sensory quality and functional lifetime. Strategies that protect the oil from oxygen and light, and that moderate delivery on the fiber, are therefore desirable. It is rich in vitamin E and essential fatty acids, offering various benefits for skin and hair health. In particular, it has been reported to add shine and softness to hair, repair damaged strands, and promote scalp health. However, argan oil has certain disadvantages, such as high viscosity and slow skin absorption. In addition, it easily oxidizes during long-term storage in air, so improved stability is needed. It cannot be applied easily in aqueous media because of its hydrophobic properties. Therefore, its usability in aqueous media is limited; improved usability is needed [1,2,3].

Encapsulation of essential oils into cyclodextrins is performed for several important reasons, primarily to improve stability, usability, and effectiveness [4,5,6]. β-cyclodextrin (β-CD) hosts hydrophobic guests in its toroidal cavity and can improve oxidative stability and handling by converting liquids into water-dispersible powders with more controlled delivery. However, head-to-head comparisons of the evaporation and coprecipitation routes under matched stoichiometry and controlled processing are scarce. Because many studies report these routes separately, it is difficult to separate true process effects from formulation differences. Essential oils are volatile and prone to degradation (oxidation, photodegradation, evaporation) [7,8]. Cyclodextrins (especially β-cyclodextrin) can encapsulate essential-oil molecules within their hydrophobic cavity, protecting them from light, oxygen, heat, and moisture [9,10,11]. Encapsulation allows slow and sustained release of the essential oil, which is useful in pharmaceuticals (e.g., extended drug delivery), cosmetics (e.g., prolonged fragrance), and food preservation [12,13,14]. Most essential oils are hydrophobic (water-insoluble). Cyclodextrins improve water dispersibility by forming inclusion complexes, allowing easier formulation into aqueous solutions and broader application in water-based systems (e.g., drinks, lotions) [15,16,17,18]. Essential oils tend to be strong-smelling and volatile. Encapsulation helps mask intense odors and minimize rapid evaporation, especially in cosmetic and pharmaceutical formulations [12,19]. In pharmaceutical or nutraceutical applications, encapsulation with cyclodextrin may increase absorption of the oil’s active components and enhance therapeutic efficacy. Encapsulated essential oils are typically less flammable, easier to dose and handle, and more chemically stable under various environmental conditions [20].

This study addresses two specific scientific questions related to the formation and functional performance of β-CD inclusion complexes. First, we investigate how the preparation route-evaporation vs. coprecipitation-affects the formation of the inclusion complex, including variations in encapsulation efficiency, crystallographic patterns, particle morphology, and thermal transitions. These structural descriptors provide insight into how the guest oil interacts with the β-CD cavity and how processing conditions influence the organization of the resulting solid. Second, we examine whether these route-dependent structural differences lead to measurable differences in hair treatment performance, such as antibacterial behavior, coating uniformity, and textural/mechanical properties. Establishing this link is essential for identifying a preparation method that provides both stable encapsulation and practical benefits in cosmetic formulations. By preparing both complexes under matched stoichiometric conditions and characterizing them using SEM, XRD, DSC, TGA, DTG, texture analysis, and microscopy, this work provides a controlled, side-by-side comparison that connects processing conditions to both physicochemical properties and real-world performance on hair.

2. Experimental

2.1. Reagents

β-cyclodextrin (β-CD) and ethanol were purchased from Samchun Chemical Co., Ltd., Pyeongtaek, Korea. Argan oil was obtained from A&C Corporation, Incheon, Korea. Glycerin and 1,2-hexanediol were supplied by JKY Company, Gimpo, Korea. 1,3-Butylene glycol was purchased from Shinan Co., Ltd., Seoul, Korea. Hydroxyacetophenone was obtained from IAN Chemical Co., Ltd., Busan, Korea. Stearyl alcohol and BTMS-25 were supplied by LOHAS Nature Co., Ltd., Daegu, Korea. The dimethicone (XIAMETER PMX 200®) was purchased from Dow Chemical Company, Midland, MI, USA. Cyclopentasiloxane (SF0005z®) was supplied by CNK International Co., Ltd., Seoul, Korea. All aqueous solutions were prepared using ultrapure water from a Milli-Q Plus purification system.

2.2. Analytical Instruments

Scanning electron microscopy (SEM, JSM-7610F Plus, JEOL, Ltd., Akishima, Japan), optical microscopy (OM), and X-ray diffractometer (XRD, D2 PHASER, Bruker, Billerica, MA, USA) were used for morphological and crystallographic analyses. Differential scanning calorimetry (DSC, N 650, SCINCO, Seoul, Korea) and thermogravimetric analysis (TGA/DTG, TG 209 F3 Tarsus, Netzsch, Selb, Germany) were employed for thermal characterization. UV–Vis spectrophotometry (Evolution One Plus, Thermo Scientific, Waltham, MA, USA) was used for quantification at 208 nm.

2.2.1. SEM and OM Conditions

Samples were sputter-coated with a thin platinum layer. Typical SEM magnifications were 2000–3000× for β-CD powders and 500× for hair samples. OM images were taken at 400×; sample preparation followed the Methods.

2.2.2. XRD Conditions

Diffraction patterns were recorded over 2θ = 5–50° at a scan speed of 0.02°·s⁻¹, with step size and counting time set to the instrument’s default.

2.2.3. DSC Conditions

Approximately 3.0 mg of each sample was sealed in an aluminum pan and heated from 30 °C to 350 °C at 10 °C min⁻¹ under a nitrogen purge.

2.2.4. TGA/DTG Conditions

Approximately 5 mg of each sample was heated from 25 °C to 500 °C at 10 °C min⁻¹ in a nitrogen atmosphere; both TGA and derivative (DTG) curves were recorded.

2.3. Preparation of Inclusion Complexes of Argan Oils into β-CD

Table 1. Preparation of inclusion complex using argan oil and β-cyclodextrin (β-CD).

Method	Evaporation Method (No. 1)	Coprecipitation Method (No. 2)
β-cyclodextrin	0.363 g	5.000 g
Argan oil	0.024 g	0.882 g
Ethanol	–	21.07 g
Water	20.00 g	33.33 g

shows the preparation of argan oil inclusion complexes by the evaporation and coprecipitation methods, respectively.

In the evaporation method, β-CD (0.363 g) was dissolved in 20 mL of distilled water by stirring at 300 rpm and 50 °C for 1 h. Argan oil as guest molecules was added to the β-CD solution at a molar ratio of 85:15 (β-CD: argan oil), calculated using an effective molecular weight of approximately 425 g·mol⁻¹ for argan oil, and the mixture was stirred under the same conditions for an additional 1 h. In the coprecipitation method, β-CD (5.00 g) was dissolved in 33.3 mL of distilled water at 50 °C for 1 h with stirring at 300 rpm. Separately, argan oil was dissolved in 26.7 mL of ethanol at 25 °C for 1 h with stirring at 300 rpm. The molar ratio of host to guest was 85:15. The argan oil solution was then added dropwise to the β-CD solution, and the combined mixture was stirred under the same conditions for at least 1 h. After stirring, the suspension was allowed to stand at room temperature for 2 h to induce coprecipitation. The precipitated inclusion complex was dried at room temperature for at least 12 h to obtain inclusion complexes (No. 2).

2.4. Formulation of Hair Treatment Using the Prepared Inclusion Complexes

Table 2. Formulation of hair treatment including No. 2 powder with stirring 100 rpm at 50 °C for 1 h.

Classification	Ingredients	Content (wt. %)
Solvent	Distilled water	78.0
Alcoholic compound	1,3-Butylene glycol	1.00
	Glycerin	2.00
	Hydroxyacetophenone	0.50
	1,2-Hexanediol	1.00
	Stearyl alcohol	4.00
	BTMS25 (Behentrimonium Methosulfate + Cetearyl Alcohol)	5.50
Organo-silicon compound	Dimethicone	4.00
	Cyclopentasiloxane	3.00
Inclusion complex	Argan oil powder	1.00

presents the formulation of the hair treatment using the inclusion complexes of argan oil (No. 2). The formulation was carried out at 50 °C with stirring at 100 rpm, according to an internal standard operating procedure. The hair samples (5 cm in length) were rinsed with distilled water and dried at room temperature for 2 h before treatment. The hair treatment formulation (1 mL per strand) was applied uniformly along the fiber direction using gentle finger spreading. The treated samples were left to equilibrate for 10 min, followed by air drying for 12 h at room temperature prior to texture analysis, microscopy, and tensile measurements.

2.5. Entrapment Efficiency by UV–Vis

UV–Vis spectra were measured at 208 nm in acetonitrile, and absorbance was kept below 1.0. Measurements were performed in triplicate (n = 3). Sample solutions were prepared by dissolving 0.01 g of powder in 10 mL (No. 1) or 30 mL (No. 2) of solvent (see Table 1). Because β-CD powder can remain buoyant after dissolution and stirring, which causes light scattering and artificially increases absorbance, the suspensions were centrifuged to pellet the undissolved solid. The clear supernatant, containing argan oil released/extracted into acetonitrile, was transferred to cuvettes for UV–Vis measurements; the pellet was discarded. This clarification step minimized turbidity and ensured that only dissolved oil was quantified.

Quantification followed the Beer–Lambert law using a fixed molar absorptivity (ε, L·mol⁻¹·cm⁻¹) at 208 nm determined for the same oil lot and solvent. With a 1 cm path length (l = 1 cm), the molar concentration was calculated as c = (A/(ε·l)) × D, where A is the measured absorbance and D is the dilution factor (D = 1 if undiluted). The extracted oil mass was obtained by m_found = c × M_eff × V_total, where M_eff is the effective molar mass used for this oil lot and V_total is the total extraction volume used in the assay. V_total was 10 mL (No. 1) or 30 mL (No. 2), unless further dilution was applied. M_eff for this lot is listed in Table 1. A fixed ε = 7948 L·mol⁻¹·cm⁻¹ at 208 nm was used together with M_eff to convert A to mass. No multi-point external calibration was used in this approach.

Definitions: ε, molar absorptivity at 208 nm (L·mol⁻¹·cm⁻¹); l, optical path length (cm); D, dilution factor; c, molar concentration (mol·L⁻¹); m_found, mass of extracted argan oil (g); M_eff, effective molar mass for this oil lot (g·mol⁻¹); V_total, total extraction volume (L).

2.6. Antibacterial Assay

Plates were prepared on potato dextrose agar (PDA). The screening was performed once as a preliminary check; a 100 µL inoculum was used to prepare the lawn. Because only a single run was available, results are presented qualitatively without statistics. The test organism was Staphylococcus aureus. Discs or wells were loaded with 40 µL of the sample (formulated hair treatment with inclusion complexes) and incubated at room temperature for 24 h. Zones of inhibition (ZOI) were measured. Controls included the base formulation without inclusion complexes and a blank.

2.7. Texture Analysis

Texture profile analysis was conducted using a cylindrical P50 probe at 25 °C. Hardness, adhesiveness, springiness, and cohesiveness were recorded following the instrument’s default method for semi-solid cosmetics. Trigger force and speed parameters followed the manufacturer’s default. All measurements were performed five times (n = 5).

2.8. Tensile Strength Measurement

Tensile properties of bleached hair fibers were measured using a universal testing machine (AG-X, Shimadzu, Kyoto, Japan). Individual strands were mounted with a gauge length of 20 mm and pulled at a crosshead speed of 5 mm·min⁻¹ until fracture. The fracture time, stroke, and load were recorded from the stress–displacement curves. All measurements were repeated five times (n = 5).

3. Results & Discussion

3.1. Characterization of Inclusion Complexes Prepared by Evaporation and Coprecipitation Methods

Figure 1 shows the surface morphology of β-CD, No. 1, and No. 2 observed by scanning electron microscopy (SEM).

In the case of the β-CD image, small particles are aggregated to form larger particles. In the case of No. 1, relatively uniform square-shaped particles are observed because the solvent evaporates slowly, giving the solute sufficient time and space to crystallize in a stable manner, resulting in uniform crystals. In contrast, No. 2 exhibits rectangular-shaped particles, likely because rapid precipitation leads to random nucleation and rapid growth of elongated, non-uniform crystals.

Figure 2 exhibits the X-ray diffraction (XRD) results of β-CD, No. 1, and No. 2.

The XRD patterns of the pure host material (β-CD) and the inclusion complexes are compared as follows: (1) The appearance of new diffraction peaks, which are absent in both the host compounds, indicates the formation of a new crystalline structure corresponding to the inclusion complex. (2) The specific diffraction peaks of the β-CD compound become weaker or disappear. It suggests that their original crystalline structures have changed due to inclusion. (3) Inclusion may cause distortions in the crystal lattice, leading to a shift in Bragg diffraction angles (2θ). As shown in Figure 2, β-CD exhibits diffraction peaks around 2θ values of 9°, 10°, 12°, and 18°. In contrast, for the inclusion complexes No. 1 and No. 2, the peak at 18° disappears, and new diffraction patterns are observed at 2θ values of 6°, 20°, and 23°. These results indicate the successful preparation of an inclusion complex of Argan oil.

Figure 3 shows the differential scanning calorimetry (DSC) results of β-CD, No. 1, and No. 2, respectively.

In the case of an inclusion complex, the guest molecule is encapsulated within the internal cavity of cyclodextrin, which restricts its thermal mobility. As a result, the characteristic thermal peak of the guest tends to diminish or disappear. On the other hand, A new thermal peak may appear, which indicates the formation of a new phase. β-CD exhibits an endothermic peak at about 100 °C, which is considered to result from the evaporation of water contained in β-CD itself. The endothermic peak observed around 320 °C is considered to be due to the thermal decomposition of β-CD. In the case of inclusion complex No. 1, a new endothermic peak appeared at 130 °C, and another endothermic peak was observed around 330 °C, showing a thermal pattern different from that of β-CD. In the case of inclusion complex No. 2, a new endothermic peak appeared at 80 °C. This result indicated that an inclusion complex was successfully formed.

Figure 4 represents thermogravimetric analysis (TGA) results of β-CD, No. 1, and No. 2, respectively.

β-CD showed a first weight loss at about 90 °C due to the evaporation of surface moisture, and a second weight loss starting from 307 °C, attributed to the thermal decomposition of β-CD. In the inclusion complex of No. 1, the first weight loss at about 90 °C was due to the vaporization of surface moisture, and the second weight loss from 300 °C was due to the decomposition of the inclusion complex. In the inclusion complex of No. 2, the first weight loss was not observed, while the second weight loss was observed at 300 °C due to the decomposition of the inclusion complex. The weight loss patterns of β-CD and the inclusion complexes appeared slightly different. From these results, we concluded that the inclusion complexes were successfully prepared by two methods: evaporation and coprecipitation.

Figure 5 indicates derivative thermogravimetric (DTG) curves of β-CD, No. 1 and No. 2.

When comparing the first and second DTG peaks of the host material β-CD with those of the inclusion complexes No. 1 and No. 2, noticeable changes in the original peaks were observed, confirming that the inclusion complexes were successfully formed.

Table 3. Encapsulation efficiency (EE) of the No. 1, No. 2.

	EE%
No. 1	68.4
No. 2	51.2

exhibits the encapsulation efficiency (EE) of inclusion complexes such as No. 1, No. 2, respectively.

The EE(%) was determined by the molar absorption coefficient (ε) of guest molecules in acetonitrile by UV-Vis spectroscopy.

$$\mathrm{E}\mathrm{E}\left(\%\right)={\displaystyle \frac{m_{\mathrm{f}\mathrm{o}\mathrm{u}\mathrm{n}\mathrm{d}}}{w_{\mathrm{f}\mathrm{e}\mathrm{e}\mathrm{d}}\times m_{\mathrm{p}\mathrm{o}\mathrm{w}\mathrm{d}\mathrm{e}\mathrm{r}}}}\times 100$$

where m_found = (A/(ε·l)) × M_eff × V_total (l = 1 cm), m_powder is the weighed powder mass, and w_feed is the theoretical mass fraction of oil (100% basis). As a result, the EE (%) was 68.4% for No. 1 and 51.2% for No. 2 inclusion complexes. Although the encapsulation efficiency of No. 1 was higher, it could not be produced on a large scale; therefore, the inclusion complex of No. 2 was used in the formulation of the hair treatment (see Table 2).

3.2. Characterization of the Hair Treatment with Inclusion Complexes and Its Application to Hair Samples

Antibacterial activity is relevant in hair treatments because external contaminants such as sweat, dust, and microbes can adhere to hair fibers and cause odor or scalp irritation. Bacteria from external sources such as pollution, sweat, and dust can adhere to the hair, but antibacterial ingredients help suppress bacterial contamination on the hair surface, contributing to the maintenance of healthy hair. For this reason, we tested the antibacterial activity of the formulated hair treatment.

Figure 6 demonstrates the antimicrobial activity of the formulated hair treatment containing inclusion complexes against Staphylococcus aureus.

When the hair treatment was not applied, no clear zone was observed, whereas strong, clear zones appeared when the hair treatment formulated with the inclusion complex was used (see B in Figure 6).

Table 4. Texture profile analysis results of the prepared hair treatment.

Characteristic	Hardness (g)	Fracturability (g)	Adhesiveness (g·s)	Springiness	Cohesiveness
AVERAGE	456.424	428.26	−4021.403	0.974	0.868
SD	21.743	0	121.898	0.001	0.105
CV (%)	4.764	0	−3.031	0.103	12.097

displays the Texture profile analysis results of the prepared hair treatment.

The average values (measured five times) of the formulated hair treatment with inclusion complexes were Hardness (456.424 g), Fracturability (428.26 g), Adhesiveness (−4021.403 g·s), Springiness (0.974), and Cohesiveness (0.868). These results indicate that the formulated hair treatment with the inclusion complex showed improved coating performance.

Figure 7 shows optical microscopy (OM) images of hair samples before and after coating treatment.

We used two hair samples, such as the damaged hair samples and the normal hair samples. After coating treatment, the surface morphology changed to smooth and uniform.

Figure 8 shows scanning electron microscopy (SEM) images of hair samples before and after coating treatment.

Before coating treatment, the hair surface exhibited fractured cuticle layers and a coarse surface (left side), whereas after coating treatment, the hair surface improved to a smooth form (right side). These results suggest that the formulated hair treatment could be applied to commercial products.

Table 5. Fracture time, fracture stroke, and representative tensile images of bleached and treated bleached hair samples.

Characteristic	Bleached Hair	Treated Bleached Hair
Fracture Time (s)	8.40	98.14
Fracture Stroke (mm)	1.39	16.34
Fracture Load (N)	−0.09	−0.08

shows the average tensile strength test results (measured five times) of bleached hair samples tested by a Universal Testing Machine (UTM).

The fracture time of the bleached hair sample before coating treatment was 8.40 s, whereas after coating treatment it increased to 98.14 s. The fracture stroke before coating was 1.39 mm and increased to 16.34 mm after treatment. The fracture load before coating was −0.09 N and increased slightly to −0.08 N after treatment. As a result, the formulated hair treatment shows potential for application in commercial products.

4. Conclusions

The inclusion complexes with argan oil were prepared by evaporation and coprecipitation methods, respectively, because argan oil is not soluble in aqueous media, whereas the inclusion complexes dissolve in the hair treatment aqueous medium. The successful preparation of the inclusion complexes was confirmed via SEM, XRD, DSC, TGA, and DTG analyses, as well as encapsulation efficiency (%) evaluation by UV–Vis spectroscopy. The hair treatment solution was formulated using the inclusion complexes and evaluated. From these results, we concluded as follows:

(1)

The formulated hair treatment has antibacterial effects for Staphylococcus aureus.

(2)

The formulated hair treatment showed hardness (456.424 g), fracturability (428.26 g), adhesiveness (−4021.403 g·s), springiness (0.974), and cohesiveness (0.868).

(3)

The formulated hair treatment possesses the good properties of hair surface coating, which is detected by OM and SEM analysis.

(4)

After coating the bleached hair sample, fracture time and stroke increased; tensile load values were affected by baseline offsets.

From these results, the formulated hair treatment could be applied to commercial products.