Melamine formaldehyde microcapsules with fragrance core material: Preparation,properties,and end use

Abstract

The aim of this research was to prepare and analyze suitable microcapsules for the chosen end use—that is, bow-ties. The produced microcapsules were composed of melamine formaldehyde microcapsules with fragrance oils in the core. Regarding the properties, the surface morphology (studied by Scanning electron microscopy (SEM)), thermal properties (measured by Simultaneous Thermal Analysis [STA]), size and size distribution (by SEM and ImageJ software), and release behavior of the microcapsules were analyzed. The microcapsules were further (in two trials) applied with a screen-printing technique to textile materials which were investigated by microscopy (SEM) and tested for thickness, mass per unit area, and crease recovery angle. Finally, the scented bow-ties were designed and a subjective wear test was performed by the participants. According to the results, the prepared microcapsules were undamaged, with a spherical and smooth surface. An impermeable shell enabled the fragrance to be released simply by rupturing the microcapsules. This property was desired, since a stronger release through the permeable shell could be annoying for the wearer. During wear, the fragrance faded, but by rubbing the surface of the bow-tie and consequently rupturing the microcapsules, the release of the fragrance was initiated again, before or after wear.

Keywords

bow-tie microcapsules fragrance oil screen-printing user experience

The importance of scents has been acknowledged by our ancestors.¹ They used different herbal and aromatic substances in aromatherapy and for protection against airborne infections and prevalent disease, noxious odours², unpleasant smells (e.g. of dyes, disuse, humidity),¹ and suchlike. Essential oils were applied to clothes and other textile items and accessories, the most interesting being scented handkerchiefs. According to Victor Hugo, a proper gentleman always had to carry a fragranced handkerchief.¹ Scented textile items have been used for decades. Today, they are present in the market as a very small but interesting niche, with the potential for further development.

The duration of fragrances applied to textiles is limited according to their volatilization and fastness to washing. Therefore, the invention of the microencapsulation process has presented an important innovation that enables prolonged fragrance on textiles. The microencapsulation process was developed in the 1950s and subsequently led to the use of microcapsules in many industries, such as graphics³, food, pharmaceuticals, agriculture, building constructions,⁴ and so on. In microcapsules, the core material is safely entrapped inside the shell and is released by, for example, friction, pressure, change of temperature or pH, biodegradation, diffusion through the shell, or shell dissolution. Exploiting the possibilities of core release techniques, microcapsules have also been introduced into the textile industry, where the core substances used are appropriate for aromatherapy,⁵ scenting,^6–8 cosmetics, as flame retardants,⁹ antimicrobials,^10,11 insect repellents, sensors,¹² and phase change materials in thermal regulation,¹³ amongst others.

The microencapsulated odorants have opened new horizons in scented textiles. In 1989, the Japanese company Kanebo patented the process of preparing a fragrant fibrous structure with incorporated microcapsules with fragrance in the core.¹⁴ In 1998, the French company Neyret made a woman’s bra that released the scents of apple, grapefruit, or watermelon when stretched or caressed.¹⁵ The Sensory Perception Technology (SPT) has been introduced by Woolmark and has been developed in cooperation with International Flavors and Fragrances Inc.¹⁶ In 2007, Cognis introduced the Skintex™ technology. Today, fragranced textile materials can be found in many items, for example, underwear, socks, T-shirts, shoes, linings, kitchen and bathroom textiles, carpets, and upholstery, which have been introduced into the market by different companies, including Invista, Nike, Tisseray et Cie, Le Slip Francais, and Urban Yoga.

The aim of our research was to produce a scented bow-tie. If the textile material is scented by non-microencapsulated fragrance oil, the olfactory performance of the bow-tie is quickly lost during wear.¹⁷ Consequently, the fragrance oils selected for the purpose of this research were microencapsulated. The microcapsules with a melamine formaldehyde shell were produced and analyzed. The melamine formaldehyde type of shell was selected according to our requirements: (a) impermeability¹⁸ of the shell to protect core material against vaporization; (b) suitable mechanical properties of the shell—that is, viscoelastic behavior at small deformation¹⁹ to withstand the pressure of a squeegee in the printing process, and plastic behavior beyond a yield point followed by a burst at higher compression,¹⁹ which enables the release of the fragrance from the core of the microcapsules on rubbing during use; and (c) suitable thermal properties²⁰ of the shell at the temperature up to 150℃ to withstand the drying and curing of the printed material. The drying and curing were omitted in our study; however, the thermal properties of microcapsules were studied, since they are important in the case of the industrial printing process.

The microcapsules with fragrance oil were mixed with the printing ink and applied with the screen-printing technique to different textile materials, which were used for the construction of the designed bow-ties. The presence, intensity, and duration of the fragrance on the bow-ties were determined by the user experience wear test.

Experimental

Materials and methods

Textile materials

Suitable textile materials for a bow-tie have to be soft and willing to fold. Thus, soft 100% polyester satin with a glossy surface was used in the research (thread density: weft 33 threads/cm, warp 42 threads/cm). To gain proper stability of the soft satin, adhesive nonwoven interlining (73% viscose, 27% polyester) was chosen. As the carrier of microcapsules, the lightweight 100% cotton batiste in taffeta weave was selected (thread density: weft 37 threads/cm, warp 45 threads/cm).

Preparation of microcapsules

Microcapsules with a single core were synthesized by modified in situ polymerization. For the microcapsule shells, partially methylated trimethylolmelamine (Melamin, Slovenia) was used. Polyacrylic polymer was used as the modifying agent/poly-condensation initiator for the in situ polymerization. Analytical grade sodium hydroxide (Kemika, Croatia) was used for the termination of the poly-condensation reaction and pH neutralization. To remove the formaldehyde released during the poly-condensation, ammonia (Kemika, Croatia) was added to the suspension of microcapsules as the scavenger. As the core material, two commercial—male and female—fragrance oils were used (Tovarna Organika, Slovenia). The male fragrance oil was a mixture of soft bergamot oil on a base of ambergris, orange blossom, vanilla, sandalwood, and sweet musk, whereas the female fragrance oil was an aquatic floral fragrance with top notes of lotus, freesia, and cyclamen. The specific gravities of the male and female fragrance oil (at 20℃) were 1.008 and 0.9670, respectively.

The modified process of the in situ polymerization microencapsulation was performed in a 1-L laboratory reactor equipped with a turbine stirrer in the following stages: (1) preparation of an aqueous solution of modifying agent; (2) emulsification of core material at room temperature with stirrer speed of 1500 rpm for 20 min; (3) addition of partly methylated trimethylolmelamine amino-aldehyde prepolymer for shell formation; (4) induction of poly-condensation reaction by raising the temperature to 70–80℃; (5) poly-condensation process (approx. 1 hour), That is, the formation of microcapsules; (6) termination of poly-condensation; (7) removal of released formaldehyde by addition of ammonia scavenger at 50℃; and (8) cooling to room temperature. For the printing onto textiles, the microcapsules were suspended in an aqueous solution.

Printing procedure

In the research, commercially available (ready-to-use) printing ink Elastil Comprente (Minerva, Italy; viscosity 110 dPa·s and pH value 8.2) was mixed with 20% mass concentration of fragrance microcapsule suspension. To gain the appropriate viscosity of the printing ink, 8% mass concentration of water was added into the mixture.

The screen-printing technique was performed manually. The screen was made of an aluminum frame and PET mesh with a density of 43 threads/cm, monofilament diameter of 80 µm, thread angle of 0°, and load tension of 15 N. All prints were made with two strokes with a squeegee (hardness of 65 Sh) and were air-dried after the printing.

The satin material was straightened with an adhesive nonwoven interlining. The prepared satin-interlined composition was cut into 25.5 × 14.5 cm rectangles. On the front side of each rectangular composition, decorative patterns were printed. The bow-ties were afterwards designed in two different trials, as follows below.

Trial 1. Microcapsules were mixed with the printing ink and later screen-printed onto the inner side of the satin–interlining composition. The composition was then folded (first by folding backwards the longer sides up to the middle and then in the same manner the shorter sides) into a smaller shape. The folded composition was sewn and formed into the final shape of the bow-tie.

Trial 2. Microcapsules were mixed with the printing ink and later screen-printed onto the surface of the batiste material. The batiste material was then lodged into the inner side of the satin–interlining composition, folded, formed, and sewn as described in Trial 1.

The bow-ties, which were chosen for further testing, were stored in paperboard boxes which were constructed for the purpose of the research (Figure 1). The purpose of the packaging was to protect the product against external effects (dust, dirt) and to retain the fragrance during storage. The packaging was made of paperboard of 700 g/m² and thickness of 1 mm. It was constructed using EngView software (EngView Systems Sofia JSC, Bulgaria), cut out on a Pirina 700 cutter plotter (Pirina Technologies, Bulgaria) and creased with a head pressure of 0.50 MPa.

Figure 1.

Final appearance of bow-tie in packaging.

Bow-tie design and storage

The morphological properties of microcapsules and unprinted and printed textile materials were observed by scanning electron microscopy (SEM, JSM 6060 LV, Jeol). The microcapsule suspension was applied on a specimen stub and allowed to air-dry. The unprinted and printed textile materials were cut to appropriate size and fixed onto the specimen stub. The samples were afterwards covered with an ultra-thin coating of gold (with high vacuum evaporation). On the dried sample of the microcapsule suspension and the samples of printed microcapsules, the following morphological properties were observed: shape (spherical or aspherical), surface (smooth or granulated), and deformation (undamaged or ruptured).

The size of the microcapsules was determined from SEM images with the use of the ImageJ software and from these results the size distribution curves were drawn.

The release behavior of microcapsules was performed by two tests according to Šumiga²¹ and Hwang et al.²² For both tests, the suspension of microcapsules was added to aluminum cups (5 × 7 cm in size) which were then placed into a drying oven.

In the test by Šumiga,²¹ the drying oven was heated to 135℃. The microcapsules were placed into the oven and left for 180 minutes. After every 30 minutes, the samples were weighed and placed back into the oven. With the use of equation (1), the release rate of the tested microcapsules was calculated

Massloss [%] = \frac{A_{0} - A_{n}}{A_{0}} \cdot 100

(1)

where A_n is weight (g) of microcapsules after n minutes of the release test (n = 60, 90, 120, 150, and 180 min) and A₀ is weight (g) of microcapsules suspension before the release test. The first calculated mass loss after 30 minutes corresponds to water evaporation and the residual material corresponds to dry mass/share of microcapsules in an aqueous suspension. Subsequent drying (from 30 to 180 minutes) corresponds to the lost weight after every 30 minutes due to the porosity of the shell.

In the release test by Hwang et al.,²² the oven was heated first to 25℃ and then to 40℃. The microcapsules were heated at both temperature ranges for 5 days. Each day, at the same time, the samples were weighed and placed back into the oven. The mass loss was calculated in the same manner as in the previous test at 135℃ (i.e. using equation (1)).

The thermal stability of non-microencapsulated and microencapsulated male and female fragrance oils was determined on an STA (Simultaneous Thermal Analysis) 449 Jupiter apparatus (Netzsch, Germany), on which thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) data were recorded simultaneously. The samples in the aluminum crucibles were heated at the rate of 10 K/min from 25℃ to 600℃ in an argon atmosphere.

On the textile materials, the following parameters were determined: mass per unit area according to EN 12127,²³ thickness according to ISO 5084,²⁴ and recovery angle according to the standard ISO 2313.²⁵ The mean value of the angle was calculated from the mean values of measurements in warp and weft directions as follows (equation (2))

Crease recovery angle [^{\circ}] = \frac{α_{5 (warp)} + α_{5 (weft)}}{2}

(2)

where α_5(warp) and α_5(weft) present the mean values of the angles obtained in the warp and weft directions, respectively.

The testing of individual bow-ties was performed by the user experience wear test in which 15 male and 16 female test persons participated. Prior to the first testing and after each wear the individual bow-ties were stored in the specially designed packaging (Figure 1). Each test person wore an individual bow-tie 10 times. During the testing, they needed to answer questions relating to the presence, duration, and intensity of the released fragrance.

Results and discussion

Properties of microcapsules

Morphology of microcapsules

Figures 2 and 3 show that both types of microcapsules were undamaged, with a spherical and smooth surface. The surface tension and capillary forces caused the formation of liquid bridges,²⁶ which were formed among the microcapsules during the drying. After the drying, they became solid, most likely since they are composed of the residues of the non-reacted melamine formaldehyde resin and amorphous modifying agent, which were present in the aqueous suspension of microcapsules.

Figure 2.

Microcapsules with male fragrance oil (SEM; 300 × and 3300 × magnification). Arrows indicate solid liquid bridges among particles dried at room temperature.

Figure 3.

Microcapsules with female fragrance oil (SEM; 300 × and 3300 × magnification). Arrows indicate solid liquid bridges among particles dried at room temperature.

Size distribution properties

Microcapsules with the male fragrance were on average slightly larger (23.5 µm; σ = 8.42 µm) than the microcapsules with the female fragrance oil (15.5 µm; σ = 5.10 µm), which can be seen in Figures 4 and 5. During the microcapsule preparation, the synthesis-processing parameters and the components for the shell and final microcapsules formation were the same, while the core fragrant oils composition was different, which could thus be the reason²¹ for a different average size of the male and female microcapsules.

Figure 4.

Size distribution curve of microcapsules with male fragrance oil in core.

Figure 5.

Size distribution curve of microcapsules with female fragrance oil in core.

The size distribution curve of the microcapsules with the male fragrance oil in the core was bimodal (Figure 4) with two distinctive size ranges: from 3 to 15 µm (14.2% of microcapsules) and from 15 to 36 µm (83.1% of microcapsules). The remaining 2.8% was represented by microcapsules larger than 36 µm. The size distribution curve of the microcapsules with the female fragrance oil in the core was only slightly bimodal (Figure 5) with two almost inherent size ranges: from 2.8 to 12.0 µm (24% of microcapsules) and from 12 to 26.4 µm (74.4% of microcapsules). The remaining 1.6% of microcapsules was larger than 26.4 µm. The size of microcapsules is one of the factors influencing the release properties;¹⁷ when microcapsules are too small (below 10 µm), they cannot be easily broken (especially under shear forces), consequently limiting the yield of the released fragrance. In contrast, when microcapsules are too large (above 30–40 µm), they rupture easily, instantly releasing the core material, the smell of the sample being ephemeral. According to Bône et al.,¹⁷ the best compromise is achieved with the microcapsules of 10–40 µm in size. Our male and female fragrance microcapsules were in the proposed range. According to the size, it was expected that the larger microcapsules with male fragrance oil would be ruptured more easily, that the fragrance would be intense, and that it would last for a shorter period of time. In the case of the smaller microcapsules with the female fragrance oil, on the other hand, these would be harder to rupture, the fragrance being discrete and lasting longer. However, as will be seen in the continuation of our research, the results of the subjective bow-tie testing disproved our assumptions.

Thermal analysis (STA)

The thermal analysis of non-microencapsulated and microencapsulated male and female fragrance oil is presented by TG/DSC thermograms in Figure 6 and 7.

Figure 6.

TG/DSC thermogram of (a) male and (b) female fragrance oil.

TG thermograms (Figure 6) show that both fragrance oils, male and female, had a similar pattern of evaporation. The endothermic peak (temperature of the maximum rate of volatilization) was at 276℃ (236.3 J·g^–1) and 218.8℃ (232.0 J·g^–1) for male and female fragrance oil, respectively. The volatilization process of the non-microencapsulated male fragrance oil started at 102℃ and finished at around 280℃ (Figure 6(a)). The volatilization process of the non-microencapsulated female fragrance oil started at the initial temperature of 90℃ and was almost finished at a temperature around 240℃ (Figure 6(b)). The mass loss at 400℃ was 99.25% and 94.50% for the male and female fragrance oils, respectively.

In Figure 7, the TG/DSC thermograms of microcapsules with male (a) and female (a) fragrance oils are presented.

Figure 7.

TG/DSC thermogram of microcapsules with (a) male and (b) female fragrance oil.

The first mass loss on the TG curve and the first endothermic peak on the DSC curve shown on both diagrams in Figure 7 represent the water evaporated from the sample in the 50–100℃ interval. The second interval, 100–180℃, represents the water evaporation due to the condensation process (i.e. self-condensation of methylol groups, leading to the ether bridge formation at 140–160℃, and a condensation reaction between the melamine and methylol group, leading to the methylene bridge of the curing reaction at the temperature above 160℃),²⁰ and most likely also to the partial volatilization of the male and female fragrance oils. The next interval, 180–350℃, could be ascribed to the elimination of formaldehyde from the ether bridge forming methylene bridges; this interval also represents the continued volatilization of fragrance oils in the core²⁰ (endothermic peak at about 318℃ in Figure 7(a). The interval 350–400℃ (where the highest mass loss is observable for both types of microcapsules), overlaps with the second endothermic peak at about 380℃ in the DSC thermogram and represents the breakage of the methylene bridges (degradation of microcapsules’ melamine formaldehyde wall)²⁰ and to the final release of fragrance oils. The fifth interval, 400–600℃, represents the thermal degradation of the triazine ring.²⁰ The mass loss during the TG analysis, read at 420℃ and 405℃, was 80.78% and 79.73% for the microcapsules with the male and female fragrance oils, respectively.

When the core material is microencapsulated, the endothermic peak of the pure core material is usually affected by the microencapsulation;²⁷ consequently, the slight endothermic peak at about 318℃ on the DSC curve in Figure 7(a) could belong to the male fragrance oil shifting from 276℃.

Since the drying and the curing operation of the printing process are conducted in the temperature range from 100℃ (drying) to 150℃ (curing), it is important that the core and shell of the microcapsules withstand those temperatures without major changes. As can be seen from the explanation of the DSC and TGA curves, the water evaporation and the partial volatilization of the male and female fragrance oils occur in this temperature range. Since the fragrance oils are safety entrapped inside the microcapsules, the volatilization probably started with a delay compared to pure oils (Figure 7(a)). This means that at 100℃ or even 150℃, the volatilization of the fragrance oil will be negligible.

Release behavior

Figure 8 and 9 present the release behavior of microcapsules after 180 min at 135℃, and after 5 days at 25℃ and 40℃.

Figure 8.

Residual weight of male/female fragrance microcapsules during 180 minutes at 135℃. MC-MF: microcapsules with male fragrance in the core; MC-FF: microcapsules with female fragrance in the core. The shaded area represents the interval where the dry mass of the microcapsules was determined.

Figure 9.

Residual weight of male/female fragrance microcapsules during 5 days at 25℃ and 40℃. MC-MF: microcapsules with male fragrance in core; MC-FF: microcapsules with female fragrance in core. The shaded area represents the interval where the dry mass of the microcapsules was determined.

Figure 8 shows the proportion of the released core material (diffusion) through the wall of microcapsules during 180 min at 135℃ in the heated oven. The mass loss after 30 minutes corresponds to water evaporation,²¹ while the residue corresponds to the dry mass/share of microcapsules in the aqueous suspension, which was 53.3% and 48.8% for the microcapsules with the male and female fragrance oil in the core, respectively. The mass loss within the subsequent 150 minutes corresponds to the diffusion of the core material through the microcapsule walls. The mass loss of 3.2% and 1.5% for the male and female fragrance oils, respectively, can be observed.

As can be seen from the results, the diffusion (vaporization) of the fragrance oil at higher (135℃) temperature through the wall is rather low for both types of microcapsules; the microcapsules are thus able to withstand the drying (100℃) and curing (150℃) processes. According to the research conducted by Leskovšek,²⁶ microcapsules with a melamine formaldehyde shell heated at lower temperatures (below 180℃) also maintain their shapes without deformations of their shell surface.

These results could be connected with the DSC/TGA results, whereby it can be concluded that, up to 150℃, the volatilization of the fragrance oil is negligible, mostly due to the melamine formaldehyde shell protecting the oil in the core against vaporization (Figure 7). In pure male and female oils (Figure 6), the vaporization has already started in this temperature interval.

Figure 9 shows the proportion of the released core material (diffusion) through the wall of the microcapsules during 5 days of exposure at 25℃ and 40℃. The mass loss after 1 day corresponds to water evaporation,²² while the residue corresponds to the dry mass/share of microcapsules in an aqueous suspension. The dry mass/share of microcapsules at 25℃ was 53.6% and 50.3% for the microcapsules with the male and female fragrance oil in the core, respectively, and at 40℃, it was 54.5% and 49.8% for the microcapsules with the male/female fragrance oil in the core, respectively. After the following 4 days of exposure at 25℃, 0.11% and 0.23% of the male and female fragrance oils, respectively, were released from the microcapsules, while at 40℃, 0.08% and 0.27% of the male and female fragrance oils, respectively, were released from the microcapsules (Figure 9).

The low percentage of the released core materials at 25℃, 40℃, and also 135℃ implies that the microcapsule shell is almost impermeable and that the fragrance will be released by destruction of the wall during use rather than by diffusion.

Properties of textile materials printed with microcapsules

In Trial 1, the microcapsules with the male and female fragrance oils were applied to the interlining side of the satin-interlined composition. The microcapsules were applied with the screen-printing technique. According to the results of the release test (Figure 8), the final percentage of microcapsules (dry mass) in the printing ink was 10.7% and 9.8% for the male and female fragrance oils, respectively (the added quantity of microcapsules water solution into the printing ink was 20% mass concentration, while the dry mass/share of microcapsules in the aqueous suspension was 53.3% and 48.8% for the microcapsules with the male and female fragrance oils, respectively). Figure 10 shows the surface of the interlining adhered to the satin (a) and the screen-printed satin-interlined composition with the male and female fragrance oil microcapsules ((b) and (c)) incorporated into the printing ink.

Figure 10.

Surface images of (a) non-printed satin-interlined composition, and printed satin-interlined composition with (b) male and (c) female fragrance oil microcapsules (SEM; 100 × magnification).

In Figure 10, it can be seen that the larger microcapsules with the male fragrance oil are more concentrated on the surface of the satin-interlined composition (b), while the smaller, female microcapsules (c) penetrated into the structure. The properties of non-printed and printed satin with interlinings are shown in Table 1.

Table 1.

Properties of textile materials, before and after printing with microcapsules with male (MC-MF) and female fragrance oil (MC-FF)

Material sample	Thickness/σ (mm)	Mass per unit area/σ (g/m²)	Crease recovery angle/σ (°)
Non-printed satin	0.269/0.003	143.17/2.83	177.6/4.03
Non-printed satin + interlining	0.468/0.007	170.00/3.08	161.9/4.56
Printed satin + interlining with:
MC-MF	0.490/0.010	256.73/3.05	115.5/9.14
MC-FF	0.483/0.015	262.67/5.76	99.2/10.87

σ: standard deviation.

As it can be seen from Table 1, the satin became thicker when the interlining was fixed onto its inner side and afterwards printed. The mass per unit area increased with printing for both satin–interlining compositions printed with male and female fragrance microcapsules. The satin alone (100% polyester) had a very high crease recovery angle. After the interlining was adhered to the surface, the satin slightly lost its ability to recover after creasing. A significant decrease of crease recovery angle was noticed also after the satin–interlining composition was printed with male or female microcapsules. Since the material lost the ability to recover to its original state after creasing, the required soft folding of the material into a bow-tie was impossible. The printing onto the inner side of satin with interlining was thus omitted, and Trial 2, with the batiste material, was introduced into the bow-tie design, and is described below.

In Trial 2, the microcapsules with the male and female fragrance oils were applied to the batiste material (batiste is a thin, soft, fine material with high thread density) with a manual screen-printing technique. In Figure 11, the surface of the non-printed and printed batiste material with microcapsules is shown, and the properties of the non-printed and printed batiste are presented in Table 2.

Figure 11.

Surface of (a) non-printed and (b) printed batiste material with male fragrance microcapsules (SEM; 100 × magnification).

Table 2.

Properties of non-printed and printed batiste material with male (MC-MF) and female fragrance oil (MC-FF) microcapsules

Material	Thickness/σ (mm)	Mass per unit area/σ (g/m²)	Crease recovery angle/σ (°)
Non-printed batiste	0.144/0.001	58.80/1.46	42.1/4.84
Printed batiste with:
MC-MF	0.212/0.004	121.58/2.54	64.3/5.68
MC-FF	0.205/0.006	118.00/0.55	56.9/18.71

As can be seen from Table 2, the thickness and mass per unit area of the batiste material increased after the printing. Furthermore, the material lost the ability to recover to its original state after creasing. Since this material was integrated inside the bow-tie, the low crease recovery angle was not an intrusive factor which influenced the required soft folding of the material during the bow-tie design. The bow-ties designed in Trial 2 also had suitable aesthetic appearance, with soft edges and proper folding in the tapered middle part. Hence, the bow-ties prepared in this manner were tested by the end users who participated in the research.

Subjective bow-tie testing

In the research, 31 bow-ties were tested, 16 with female and 15 with male fragrance microcapsules. All bow-ties were subjected to a wear test by the end users who participated in the research. The test represented only a subjective and rough evaluation, as the male and female participants were of different ages and were wearing bow-ties at different occasions, which means that the surrounding factors (open/closed area with fewer or more surrounding smells) could have influenced the results. Nevertheless, since our product was intended for the end bow-tie users, we decided that they should wear the bow-ties at different occasions and in different surroundings. Since the test was being performed from November 2015 to January 2016, the users wore bow-ties at concerts, parties, and the like, and also every day at work. Before the test, the bow-ties, stored in the appropriate packaging, together with the questionnaires, were given to each user. The users had to wear the bow-tie on at least 10 occasions, and before and after each wear, they had to fill in the questionnaire about their experience regarding the presence and duration as well as the intensity and fading of the fragrance.

As it can be seen from Figure 12, the fragrance was detected by the majority of users prior to each wear when the bow-ties were taken out of the packaging. Most of the participants (90.9%) felt the fragrance as very gentle.

Figure 12.

Fragrance detection immediately after bow-ties were taken out of packaging, prior to each wear.

The fragrance was released from bow-ties during wearing (Figure 13(a)). Although the users were familiar with the procedure of rupturing the microcapsules by rubbing the bow-ties (they had the possibility to intensify the fragrance before each wear), the bow-ties slightly lost their fragrance from the first to the tenth wear (Figure 13(b)). The results on the presence and fading of the fragrance did not differ between the male and female users. The linear correlation between the presence and fading of the fragrance during wear was strongly negative: ρ = –0.985, α < 0.05.

Figure 13.

Presence (a) and fading (b) of fragrance during wear of bow-ties.

All bow-ties were inspected once again after the wear test was finished. After taking the bow-ties out of the packaging, the fragrance intensity was subjectively evaluated. Among all the samples, most bow-ties (83.9%) were still releasing gentle and discrete fragrance, which was intensified by rubbing the bow-ties between two fingers.

Conclusions

The aim of the research was to create an added value bow-tie, made of textiles. Therefore, knowledge of textile materials, printing, and microencapsulation was combined with the sensory perception (in our case, the senses of smell and vision), which plays an important role, especially in the marketing of a product. Starting with an idea, proceeding to the invention, and final innovation, we managed to develop a new product—a scented bow-tie. The only known patent on scented bow-ties originates from the year 2006,²⁸ in which a device sprayed with different scents is described.

In this research, the scented bow-ties were designed with the use of microcapsules, in the core of which male and female fragrance oils were entrapped. The microcapsules with male fragrance oil were larger (23.5 µm) than the microcapsules with the female fragrance oil (15.5 µm). Since bigger microcapsules are more prone to rupturing,¹⁷ a more intense but short-lasting fragrance was expected for the male microcapsules. According to the results of subjective bow-tie testing, the presence and fading of the fragrance did not differ between the male and female users, which implies that the difference would probably only be sensed if the size differential of the male and female microcapsules was more pronounced.

The DSC/TGA and the release test results performed on the microcapsules showed that the mass loss up to 135℃ is negligible, the drying (at 100℃) and curing (at 150℃) of printed samples thus not influencing the core of the male and female microcapsules.

The low percentage of the released core materials at 25℃, 40℃, and also 135℃ implies that the microcapsule shell is impermeable and that the fragrance will be released only by the destruction of the wall and not by diffusion. This conclusion was proven by the bow-tie subjective testing. The selected melamine formaldehyde shell of the microcapsules seems to be a suitable choice for the scented bow-tie, since a controlled release of the fragrance, stimulated by rubbing the bow-tie between two fingers and rupturing the microcapsules, was well accepted among the users. According to the users’ responses, a continuous release through a permeable shell during wear would be somewhat annoying.

The bow-ties were designed in two manners: with and without an additional batiste layer. When the printing ink with fragrance microcapsules was applied directly to the interlined side of the satin-interlined composition material, the material stiffness increased, which made the folding into the final shape impossible. In contrast, an additional layer of the batiste material, previously printed with fragrance microcapsules, enabled an aesthetic design and the desired additional value—the fragrance to be simultaneously integrated into the bow-ties.

According to the results, the microcapsules which were produced in our research are suitable for the selected end products, and the results obtained from the microcapsule analyses coincide with the results of the end use.

Footnotes

Acknowledgements

The authors gratefully acknowledge Dr Mirjam Leskovšek, Dr Jožef Medved, and Edvard Roglič from the Faculty of Natural Sciences and Engineering, for the assistance on SEM and STA. The developed scented bow-tie is patent pending.

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 received no financial support for the research, authorship, and/or publication of this article.

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