Preparation of sustained-release fragrance based on the cavity structure of β-cyclodextrin and its application in cotton fabric

Abstract

The present study reported the formation of fragrance/β-cyclodextrin (β-CD) inclusion complexes aimed to promote thermal stability and controlled release. Then, the fragrance/β-CD inclusion complexes were applied in cotton fabrics through impregnation to obtain aromatic cotton fabrics. The surface morphology and structures of the fragrance/β-CD inclusion complexes were examined via scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy; these analysis results confirmed the formation of inclusion complexes. The stability tests were performed by thermogravimetric analysis and the results confirmed these inclusion complexes had good thermal stability. The surface morphology of the cotton fabrics impregnated by fragrance/β-CD inclusion complexes were tested by SEM. Slow-release experiments of the aromatic cotton fabrics performed by gas chromatography-mass spectrometry and an electronic nose proved that the cotton fabrics impregnated by fragrance/β-CD inclusion complexes had excellent slow-release properties. Moreover, the continuous aroma release time of the cotton fabrics impregnated by fragrance/β-CD inclusion complexes reached up to 80 days.

Keywords

β-cyclodextrin inclusion complexes gas chromatography-mass spectrometry electronic nose aromatic cotton fabrics slow release

With the development of economy, flavors and fragrances play an increasingly crucial role in consumer satisfaction for various products, such as foods, beverages, cigarettes, cosmetics, drugs and leathers.^1–4 Particularly in textiles, consumers are no longer satisfied with the basic performance of warmth for textiles; their demand for fashion and comfort of textiles is increasingly diversified.^5,6 Recently, studies of adding fragrance to textiles have drawn great attention.^7–12 Ibrahim et al.¹³ prepared perfume cotton fabric with different softeners to retain the fragrance. However, the effect of adding perfume directly to cotton fabric was not good,¹⁴ because the active ingredients (including aldehydes, esters and alcohols) of fragrances are typically organic chemical compounds that are volatile and unstable, they are sensitive to light, heat, oxidation and humidity and can be easily degraded if are they not protected from environmental degradation agents. Therefore, adding fragrance to cotton fabric directly does not retain a long-term fragrance.

Encapsulation technology is a good way to deal with these problems. Encapsulation technology can enhance the stability and extend the retention time of fragrance.¹⁵ Thence, the application of encapsulated fragrance to fabrics has been attracted great interest recently.^16–18 Silva et al.¹⁹ reported the preparation of poly(urethane-urea) (PUU) microcapsules containing limonene via interfacial polymerization, which were then applied onto wool/polyester fabrics. In previous researches, the wall materials of microcapsules applied to cotton fabrics were mostly chitosan–sodium alginate²⁰ and poly(L-lactide).²¹ However, toxic substances were used in these methods that can cause health and environmental problems. Alternatively, β-cyclodextrin (β-CD), which is a cyclic oligosaccharide with seven D-glucopyranose units, has been recognized as a non-toxic ingredient to humans. β-CD can encapsulate hydrophobic guest molecules to form a host–guest complex, due to the special structure of the hydrophilic outer edge and the hydrophobic inner cavity.²² β-CD is widely used owing to its suitable cavity size that can encapsulate various guest molecules selectively, especially aromatic molecules.²³ Thus, β-CD has the potential to be applied as an encapsulant to cotton fabrics to prolong their fragrance without health or environmental concerns.

Up to now, little data has been available about the sustained-release properties and the quantitative analysis of encapsulated fragrance from textiles. In this study, apple fragrance was used as a model to prepare fragrance/β-CD inclusion complexes. The slow-release properties of aromatic cotton fabrics were studied at room temperature. This manuscript provides basic research data for studying the slow-release behavior of fragrance from aromatic cotton fabrics.

Materials and methods

Materials

β-CD and anhydrous ethanol were obtained from Titanchem Co., Ltd (Shanghai, China). Citric acid monohydrate (C6H8O7.H2O), urea (CON2H4) and sodium bicarbonate (NaHCO₃) were purchased from Sinopharm Chemical Reagent Co., Ltd. 1,2-Dichlorobenzene was purchased from Adamas Reagent Co., Ltd. The apple fragrance was a commercial grade product, kindly supplied by the Epson Spice Co., Ltd (Shanghai, China). All other reagents used in this study were analytical reagent grade, and they were used without further purification. Deionized water was used throughout the experiments.

The process to prepare inclusion complexes

The inclusion complexes were prepared by coprecipitation according to the report of Petrovic et al.²⁴ with a few modifications. Approximately 10 ± 0.01 g of β-CD was dissolved in 100 ml of an alcohol/distilled water (1:2) mixture. Then the apple fragrance was added to the above solution with a weight ratio of 1:8 (fragrance:β-CD). Afterwards, the mixed solution was stirred for 3 h at 50℃ (±2℃). Finally, the solution was maintained overnight at 4℃. The precipitated material was washed with anhydrous ethanol and deionized water, and then dried at 50℃ for 12 h in an electro-thermostatic drying oven (DHG-9143BS-III, Shanghai Xinmiao Medical Device Manufacturing Co., Ltd) to obtain the apple fragrance/β-CD solid powders. The solid powders were stored for further analysis.

Preparation of the physical mixture

Certain amounts of β-CD and apple fragrance with a weight ratio of 1:8 were added in a mortar, and then they were mixed together until homogeneous.

Scanning electron microscopy analysis of fragrance/β-cyclodextrin inclusion complexes

Scanning electron microscopy (SEM; Hitachi, Japan) analysis was carried out to characterize the structure and shape of the inclusion complexes. The samples were attached to a sample plate using electrically conductive double-sided tape, then were coated with a thin layer of gold (33 A° thickness) in vacuum, and finally were analyzed by SEM.

Fourier transform infrared spectroscopy analysis

A Fourier transform infrared spectroscopy (FT-IR) spectrometer (Thermo Fisher, USA) was used to characterize the chemical structure of the apple fragrance, β-CD, apple fragrance/β-CD physical mixture and apple fragrance/β-CD inclusion complexes. Experiments were performed using the KBr pellet press method and the samples were scanned in the wavelength range of 4000–400 cm^–1 with 2 cm^–1 differentiating ability.

Thermogravimetric analysis

The thermal properties of β-CD and fragrance/β-CD inclusion complexes were detected by a TGA-Q5000IR (TA Instruments, USA). The samples were put in an aluminum crucible and heated from 25℃ to 600℃ at 10℃/min under N₂ atmosphere at a flow rate of 20 ml/min.

Application of apple fragrance/β-CD inclusion complexes in cotton fabrics

Fragrance/β-CD inclusion complexes were added to cotton fabrics by impregnation. The cotton fabrics (100% cotton) were boiled for 30 min at 100℃, and then were taken out and dried naturally. A total of 10 g treated cotton fabrics was dipped into an aqueous emulsion (contained 100 g/l citric acid monohydrate, 100 g/l urea (CON2H4) and 50 g/l sodium bicarbonate (NaHCO₃)) at a bath ratio of 1:20, and stirred at 35℃ for 2 h at 500 rpm. Then, the finished cotton fabrics (cotton fabrics impregnated by fragrance/β-CD inclusion complexes) were taken out and dried at room temperature. The same content of apple fragrance was directly applied to cotton fabrics (cotton fabrics impregnated by impregnated apple fragrance) in the same way.

Morphology of aromatic cotton fabrics

The appearance of the two types of aromatic cotton fabrics were analyzed by SEM (Hitachi, Japan) using the same method as for inclusion complexes.

Slow-release performance of aromatic cotton fabrics by gas chromatography-mass spectrometry

For analysis, the aromatic cotton fabrics were placed at room temperature and analyzed at different times. In this study, a 7890A-5975C gas chromatograph-mass spectrometer (Agilent Technologies, Inc., USA) combined with an automatic headspace sampler was used to analyze the concentration of volatile compounds released from aromatic cotton fabrics. The detection conditions were in accordance with the report of Xiao et al.²⁵ with a few modifications. A total of 1 g of aromatic cotton fabrics was transferred into 15 ml sealed vials, and 30 µl of 1,2-dichlorobenzene with a concentration of 100 ppm was added into the vials as an internal standard. The conditions of headspace extraction were set as follows: the desorption time was 300 s; the agitator speed was 500 rpm; the extraction time was 30 min; and the extraction fiber was preconditioned at 250℃ for 20 min in N₂ at a rate of 1.0 ml/min. The instrument conditions were as follows: the gas chromatographic column was a DB-Innowax capillary column (60 m × 0.25 mm ID, 0.25 -µm film thickness); the inlet temperature was 250℃; the ion source temperature was 230℃; the carrier gas (purity = 99.999%) was helium; the flow rate was 1 ml/min; the injection volume was 1 µl; splitless; temperature ramp-up procedure: solvent delay after 3 min. The initial column temperature was 50℃, and the temperature was increased to 140℃ at 3℃/min and maintained for 5 min, then increased to 230℃ at 5℃/min and maintained for 10 min; electron energy: 70 EV; scanning range: 30–450 amu.

The volatile components of aromatic cotton fabrics at different times were investigated by gas chromatography-mass spectrometry (GC-MS) analysis. The content of each compound was determined by ChemStation software (Agilent Technologies). Based on the database provided by NIST and Wiley 7 n (Hewlett-Packard, Palo Alto, CA), the volatile chemical compounds were identified by comparing with their mass spectrum. The total content of the aromatic compounds was calculated by normalization of the peak area.

Electronic nose analysis of the aromatic cotton fabrics

The slow release of microcapsules reflects the effectiveness of micro-encapsulation. In order to detect the sustained release of aromatic cotton fabrics, a FOX 4000 (Alpha-MOS, France) combined with automatic headspace sampler HS100 was used to analyze the aromatic intensity. The electronic nose (E-Nose) was equipped with 18 sensors that respond to volatile components.

In the experiment, 1 g of aromatic cotton fabrics was weighted accurately and then put into a 10 ml bottle with a cap. The detection conditions were appropriately modified according to Zhu et al.²⁶ The syringe temperature of the sample was 80℃ and the flushing time was set at 120 s. The injection volume was 2.5 ml and the rate was 2.5 ml/s. The agitation speed was set at 500 rpm/min; in addition, the incubation time was 600 s and the incubation temperature was 60℃. Each sample was detected with four repetitions. Finally, the sensors recorded the changes of aromatic intensity of the two types of aromatic cotton fabrics samples by means of a radar chart.

Results and discussion

Characterization analysis

The appearance of samples was characterized by SEM. The inner cavity of β-CD is hydrophobic and can embed guest molecules to form an inclusion complex. Figure 1 shows the surface morphology of pure β-CD and fragrance/β-CD inclusion complexes. Figure 1(a) shows pure β-CD with geometric crystals of different sizes. In addition, some small particles adhered to the surface of the crystals, which has been reported by other authors.²⁷ As shown in Figure 1(b), compared with the morphology of pure β-CD, the appearance of the complex samples were an irregular shape with smaller sizes and some small aggregates. The differences between β-CD and fragrance/β-CD inclusion complexes indicated that the inclusion complexes may be formed.

Figure 1.

Scanning electron microscope images of β-cyclodextrin (β-CD) (a) and fragrance/β-CD inclusion complexes (b).

FT-IR spectroscopic analysis

FT-IR analysis is a useful technique and has been used to characterize the structures of inclusion complexes. Figure 2 shows the infrared spectrum of each sample. The main prominent absorption peaks of pure β-CD (Figure 2(b)) were observed at 3400 and 2140 cm^–1 (-OH), 1640 cm^–1 (H-O-H), 1410 cm^–1 (–C–OH) and 1150 cm^–1 (C–O–C). The FT-IR spectrum of apple fragrance (Figure 2(a)) contained the characteristic absorption bands of 3450 cm^–1 (-OH), 2920 and 2860 cm^–1 (C-H), 1730 cm^–1 (H-O-H), 1450 cm^–1 (–C–OH), 1250 cm^–1 (C–O–C), 1110 cm^–1 (C–O–C) and 950 cm^–1 (=C-H). As shown in Figure 2(c), the infrared spectrum of physical mixtures showed the simple superposition of individual peaks of both β-CD and apple fragrance, while the intensity of the absorption peak was lower than that of β-CD and apple fragrance. The infrared spectrum curve of fragrance/β-CD inclusion complexes (Figure 2(d)) was different from the infrared spectrum of physical mixtures. The absorption bands of apple fragrance at 1410 and 1250 cm^–1 appeared in the infrared image of apple fragrance/β-CD inclusion complexes (Figure 2(d)). The infrared spectrum of apple fragrance (Figure 2(a)) at 1730 cm^–1 and the spectrum of β-CD at 2140 and 1640 cm^–1 disappeared from the infrared image of apple fragrance/β-CD inclusion complexes (Figure 2(d)). The peak of β-CD at 3400 cm^–1 and the peak of apple fragrance at 2920 and 2860 cm^–1 shifted to higher frequencies at 3669, 2978 and 2901 cm^–1 in the curve of apple fragrance/β-CD inclusion complexes, respectively, which illustrated that the absorption spectra of apple fragrance were slightly transformed after encapsulation. Compared with pure β-CD, the spectral changes of apple fragrance/β-CD inclusion complexes were probably attributed to the stretching vibration between molecules during the formation of inclusion complexes.²⁸ These results indicated that the hydrophobic volatile compounds of apple fragrance were effectively embedded into the cavity of β-CD. These findings were consistent with the reports of Kayaci and Uyar¹⁷ and Yang et al.²⁹

Figure 2.

Fourier transform infrared (FT-IR) spectra of apple fragrance (a), pure β-cyclodextrin (β-CD) (b), apple fragrance/β-CD physical mixture (c) and apple fragrance/β-CD inclusion complexes (d).

Thermal analysis

Thermogravimetric analysis (TGA) is an effective method for studying the change of physical and chemical properties of materials.³⁰ The changes of mass and weight loss rate of blank β-CD and inclusion complex samples with increasing temperature conditions are depicted in Figure 3. As shown in Figure 3, there were three phases in the weight loss process of β-CD and fragrance/β-CD inclusion complexes during pyrolysis. Weight loss in the first step of TG curve of β-CD was 2% from 25℃ to 200℃, this was probably attributed to the loss of water molecules combined with β-CD and the volatile compounds. As depicted in Figure 3, although the TG curves of the two samples were similar, the weight loss of the inclusion complexes with fragrance in the first stage was more (7.8%) than that of β-CD. This was probably because the apple fragrance escaped from the inner cavity of β-CD. The main weight loss of β-CD occurred in the second phase ranging from 292℃ to 460℃, where the weight loss was 78.9%, which was attributed to the thermal pyrolysis of β-CD. The weight loss of inclusion complexes with fragrance at this phase was similar to that of blank β-CD at 79.7%. Research on pyrolysis of corresponding sample has been reported by Mohamad et al.³¹ and Zohuriaan and Shokrolah.³² There was a strong peak in the derivative thermogravimetry (DTG) curve of both β-CD and inclusion complexes around 330℃, indicating that the rate of weight loss reached its maximum value and due to the thermal disintegration of β-CD. In the DTG curve of fragrance/β-CD inclusion complexes, a small peak appeared at 292℃ in front of the pyrolysis peak of β-CD. This may be due to the volatility of the apple fragrance encapsulated in the cavity of β-CD. The weight losses of β-CD and fragrance/β-CD inclusion complexes in the first step were 2% and 7.8% respectively. The difference of 5.8% was mainly due to the weight loss of apple fragrance. From the difference of the two weight loss values, the loading of apple fragrance in the inclusion complexes was estimated to be about 5.8%. In the third stage, the mass loss of both β-CD and fragrance/β-CD inclusion complexes began from 460℃ up to the final temperature (600℃). The mass of the sample gradually became constant and there was only a little weight loss in this step; the residue mass of blank β-CD and inclusion complexes was 13.5% and 10%, respectively.

Figure 3.

Thermogravimetry (TG) and derivative thermogravimetry (DTG) curves of β-cyclodextrin (β-CD) and fragrance/β-CD inclusion complexes.

SEM of the cotton fabrics impregnated by fragrance/β-CD inclusion complexes

Figure 4 shows the SEM characterization results of the blank sample and the cotton fabrics impregnated by fragrance/β-CD inclusion complexes, respectively. Figure 4(a) indicates that the surface appearance of the blank cotton fabrics was smooth. As shown in Figure 4(b), a large number of particles were adhered to the surface of the cotton fabrics. This confirmed that the fragrance/β-CD inclusion complexes were successfully applied to cotton fabrics.

Figure 4.

Scanning electron microscopy images of blank cotton fabrics (a) and cotton fabrics impregnated by fragrance/β-cyclodextrin inclusion complexes (b).

Gas chromatography-mass spectrometry

Figure 5 shows the aroma slow-release performance of the cotton fabrics impregnated by apple fragrance (non-encapsulated) and fragrance/β-CD inclusion complexes (encapsulated fragrance) at room temperature with placement time. From Figure 5, the aroma concentration of the two types of aromatic cotton fabric was reduced with time and the aroma evaporated quickly in the first five days. However, the two samples possessed different release characteristics. At first, the aroma concentration of the cotton fabrics impregnated by apple fragrance was higher than that of cotton fabrics impregnated by fragrance/β-CD inclusion complexes. The fast release rate of cotton fabrics impregnated by fragrance/β-CD inclusion complexes could be due to the release of the fragrance, which was not encapsulated into the cavity of β-CD. The aroma concentration of the aromatic cotton fabrics gradually decreased over time. Forty days later, GS-MS could not detect the existence of volatile aroma components in cotton fabrics impregnated by apple fragrance. However, the concentration of aroma in cotton fabrics containing encapsulated fragrance tended to be stable, which was attributed to the encapsulation of the apple fragrance with β-CD. This stage reflected the mainly slow-release properties of cotton fabrics containing encapsulated fragrance. Eighty days later, the cotton fabrics containing β-CD encapsulated fragrance still remained scented. Figure 5 confirms that the cotton fabrics impregnated by fragrance/β-CD inclusion complexes had excellent slow-release properties with a sustained-release time of over 80 days. All these results demonstrated that the cotton fabrics impregnated by fragrance/β-CD inclusion complexes have excellent sustained-release properties when compared with cotton fabrics impregnated by apple fragrance.

Figure 5.

Release of fragrance from the cotton fabrics impregnated by non-encapsulated and by β-cyclodextrin encapsulated fragrance.

Electronic nose analysis

The E-Nose, which has been widely used in many fields, can imitate the human sense of smell and respond to aromatic substances quickly. The E-Nose analysis was carried out to test aromatic compounds from the cotton fabrics in headspace. The response value of the E-Nose can provide an expression for the sensitivity of the sensor to volatile compounds. The sensitivity increases with increasing response value.²⁹

Based on the values of sensors responding to the odor, the radar graphs of the two types of aromatic cotton fabrics were obtained. Differences between the two samples can be obtained from the radar graphs. Through these results, the slow-release performance of aromatic cotton fabrics can be obtained. Figure 6 shows the changes of aroma intensity of the two types of aromatic cotton fabrics at different times. The fragrance concentration affected the radar areas. Due to the volatility of aroma substances, the radar areas gradually decreased as the aroma intensity decreased over time. Figures 6(a) and (b) have similar radar profiles, the fragrance intensity of the two samples decreased with the increasing of placement time and the aroma of cotton fabrics impregnated by apple fragrance released rapidly, however, the aroma of cotton fabrics impregnated by fragrance/β-CD inclusion complexes released slowly. This was because the fragrance substances were incorporated into the cavity of wall materials and were protected, which made the aroma release slowly. Eighty days later, the radar areas of cotton fabrics impregnated by fragrance/β-CD inclusion complexes were still much larger than those of cotton fabrics impregnated by apple fragrance and blank cotton fabric. The fragrance added to the two types of aromatic cotton fabrics was equal, while the content of the fragrance that successfully attached to the cotton fabrics maybe different. This may be because the fabric samples were measured after one day of storage, and apple fragrance is volatile and unstable. Since β-CD can protect apple fragrance, more flavored substances may be retained in the cotton fabrics impregnated by β-CD encapsulated fragrance. This proved that the cotton fabrics impregnated by fragrance/β-CD inclusion complexes had a long lasting fragrance capacity when compared to cotton fabrics impregnated by apple fragrance.

Figure 6.

The radar graph of aromatic cotton fabrics: (a) cotton fabrics impregnated by apple fragrance; (b) cotton fabrics impregnated by fragrance/β-cyclodextrin inclusion complexes.

Conclusion

The present work prepared apple fragrance/β-CD inclusion complexes, then applied them on cotton fabrics by impregnation. The appearance of the characteristic absorption peaks of apple fragrance confirmed the formation of apple fragrance/β-CD inclusion complexes. TGA demonstrated the inclusion complexes had a good thermal stability, and the loading of apple fragrance was estimated to be 5.8%. SEM characterized the surface morphology of the apple fragrance/β-CD inclusion complexes and the aromatic cotton fabrics, indicating that the inclusion complexes can be well adhered to cotton fabrics. In addition, GC-MS and the E-Nose showed that the cotton fabrics impregnated by fragrance/β-CD inclusion complexes had excellent sustained-release properties, which could last for 80 days. On the contrary, the cotton fabrics directly impregnated by apple fragrance had a short scent retention time and no volatile aroma components were detected 40 days later. This study could help to accelerate the further development of aromatic textile products.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Natural Science Foundation of China (No. 21776178), the National Key Research Development Program Nanotechnology Specific Project (2016YFA0200304) and the Shanghai Pujiang Program (18PJD048).

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