J Surfact Deterg DOI 10.1007/s11743-017-1970-8
ORIGINAL ARTICLE
Development of Nanoemulsion of Silicone Oil and Pine Oil Using Binary Surfactant System for Textile Finishing Dipak D. Pukale1 • Archana S. Bansode2 • Dipak V. Pinjari1,3 • Usha Sayed2 Rahul R. Kulkarni4
•
Received: 6 January 2017 / Accepted: 27 April 2017 Ó AOCS 2017
Abstract Nanoemulsions of silicone oil and pine oil using a binary surfactant system were prepared. Silicone oil and pine oil were used to achieve softness and mosquito repellency and antibacterial activity respectively when the nanoemulsion was applied on the fabric. A silicone surfactant (AG-pt) and a hydrocarbon surfactant (TDA-6) were used in different proportions to obtain stable nanoemulsions at the lowest possible droplet size. The various emulsification process variables such as ratio of hydrocarbon to silicone surfactant, surfactant concentration, ratio of silicone oil to pine oil, oil weight fraction and sonication time have been studied. The optimal variables include the ratio of hydrocarbon to silicone surfactant of 80:20, surfactant concentration of 8%, ratio of silicone oil to pine oil of 80:20, oil weight fraction of 20% and 15 min of sonication time at 40% of the applied power. Nanoemulsions were found to be very stable with emulsion droplet size around 41 nm. In order to compare different emulsification techniques, emulsions were also prepared using the conventional method. Emulsions analyzed using SEM showed spherical droplets ranging from 40 to 120 nm. Atomic force microscopy was used to evaluate the bounciness, fluffiness and softness of fabric. From this & Dipak V. Pinjari
[email protected] 1
Oils, Oleochemicals and Surfactants Technology Department, Institute of Chemical Technology, Mumbai, India
2
Textile and Fibre Technology and Engineering Department, Institute of Chemical Technology, Mumbai, India
3
Chemical Engineering Department, Institute of Chemical Technology, Mumbai, India
4
Elkay Chemicals Pvt. Ltd., Pune, India
study, it was found that stable nanoemulsion with a lowest possible droplet size of silicone and pine oil could be prepared by ultrasonic emulsification technique in order to deliver multiple properties when applied to fabric. Keywords Nanoemulsion Binary surfactant system Silicone surfactant Amino-modified silicone oil Acoustic cavitation Textile finishing
Introduction Healthy, hygienic and safe textiles allow humans to work with maximum efficiency and effectiveness. Researchers have focused on the development of various fabric finishing chemicals to provide desired properties. Nanoemulsions are one type of finishing chemical used in the textile industry to modify textile morphology, either physically or chemically [1]. Nanoemulsions are colloidal dispersions of two immiscible phases i.e. an oil phase and an aqueous phase where emulsion droplet size ranges from 20 to 200 nm [2]. Nanoemulsions have negligible turbidity and good rheological properties [3]. Stability of nanoemulsions is good due to very small droplet size hence creaming, flocculation, sedimentation of the particles in the emulsion does not occur for a long periods of time [4]. Droplet size of the emulsion is governed by the nature of the surfactants, type of surfactant system (single or binary), surfactant concentration etc. [5–7]. Newly formed small droplets can be stabilized by the surfactant system present at the interface. Development and application of new surfactant molecules along with conventional surfactants has gained interest due to the ability to achieve synergism in binary surfactant systems. Silicone surfactants, mainly non-ionic
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trisiloxane molecules, have been found to be good wetting and foaming agents but the introduction of these surfactants into emulsion development have not been studied much [8]. Molecules can be tailored easily to suit the application by attaching hydrophilic moieties to the silicone backbone [9, 10]. The method of emulsification is also one of the vital factors to obtain the smallest possible droplet size of the emulsion. Many researchers have focused on identifying suitable methods for emulsification which are efficient, competitive and effective [2, 11]. Acoustic cavitation using ultrasound is one of the methods which could be employed for emulsification. Formation and subsequent collapse of microbubbles by pressure fluctuation due to ultrasonic irradiation creates voids. The voids gradually increase in size and collapse to form a hot spot which generates localized turbulence which is responsible for the disruption of the dispersed phase into smaller droplets [12–16]. Several studies have been carried out on the emulsification of single oils to utilize the unique property of the oil [17, 18] but very little work has been conducted on the emulsification of two different oils which have different densities to achieve multiple properties of the emulsion [19]. Silicone oil is widely used in cosmetics, home and personal care, textile finishing, inks etc. due to the unique humectant, lubricant and emollient characteristics. Depending upon the requirements, silicone oil can be functionalized to obtain the desired properties such as softness to fabric. Silicone oil can be further converted into amino-modified silicone oil (AMSO) which is widely used in textile softeners [10, 20, 21]. Pine oil is naturally occurring plant oil, generally used for the protection from mosquito bites. It is also used in the rural areas of India as herbal medicine [18, 22]. Pine oil can be used as an antibacterial, antifungal, insecticide [23]; hence pine oil has been chosen for this study along with silicone oil to obtain multiple properties on the fabric when applied. In the present work, we have developed an emulsion (o/w) of silicone oil and pine oil using a conventional method and by acoustic cavitation. We have studied the effect surfactant ratios, surfactant concentration, oil ratios, oil weight fraction, sonication time on emulsion droplet size and emulsion stability. Emulsion morphology has been visualized using scanning electron microscopy (SEM). This study has focused on the impact of prepared nanoemulsions on the textile fabric surface modification and fabric properties. In the current investigation, we have applied the prepared emulsion to the fabric and studied the surface modification using atomic force microscopy (AFM). Also, we have tested treated fabrics for antibacterial and mosquito repellent activities. The treated fabric showed 21.4% antibacterial activity against Staphylococcus aureus bacteria whereas we obtained 54% activity
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against Klebsiella pneumoniae bacteria. This result clearly indicates that prepared nanoemulsion is suitable for applying as an antibacterial solution in various applications. Also, the treated fabric showed 100% mosquito repellency when 100 gpl solution of prepared nanoemulsion were applied onto the fabric.
Experimental Chemicals Pine oil was purchased from R. K Aroma Shop, Mumbai, India. Amino-modified silicone oil (AMF) and nonionic silicone surfactant (AG-platinum also known as AG-pt) was synthesized at Elkay Chemical Pvt. Ltd., Pune, India and received as gift samples and utilized for the current study without any further purification. Tridecyl alcohol ethoxylate (TDA-6) hydrocarbon surfactant was donated by Elkay chemicals, Pune, India and used as received. Acetic acid was purchased from SD Fine Chemicals Ltd. Mumbai. Water was purified using a Millipore lab scale distilled water plant for emulsion preparation and sample preparation for analysis. Ultrasound-Assisted Emulsification Nanoemulsions of silicone oil and pine oil as an oil phase were prepared using a binary emulsifier system, acetic acid, and distilled water. Blends of nonionic hydrocarbon surfactant and non-ionic silicone surfactant were used at various ratios [hydrocarbon:silicone (HS)—0:100, 10:90, 20:80, 30:70, 40:60, 50:50, 60:40, 70:30, 80:20, 90:10, 100:0%]. Coarse emulsions were prepared by mixing two different surfactants (at various concentrations: 0, 0.25, 0.5, 1, 2, 3, 4, 5, 6.5, 8, 10, 12.5, 15% of the total emulsion) with distilled water followed by the gradual addition of mixtures of silicone oil and pine oil (at different volume fractions: 0.04, 0.08, 0.12, 0.16, 0.2) into the surfactant mixtures with the help of vigorous magnetic stirring at room temperature for 6 min after complete addition of oil phase. The coarse emulsions were further subjected to high energy ultrasonic emulsification. All emulsions were prepared at room temperature for 15 min, where each cycle involved 5 s pulses on and 5 s pulses off. The different emulsification parameters studied in the present work in order to obtain minimum particle size and stable emulsion for the longest period of time, include hydrocarbon and silicone surfactant ratios as mentioned above, surfactant concentrations, silicone oil and pine oil ratios [Si:Pi—100:0, 80:20, 60:40, 40:60, 20:80, 0:100%], volume fraction of oil in the emulsion and sonication time (5, 10, 15, 20 min).
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Conventional Emulsification Method Nanoemulsions were prepared using a high-speed homogenizer at 2500 rpm using a 0.2 oil volume fraction and optimized surfactants’ ratio and concentration at room temperature. Conventional emulsification was carried out for 20 and 120 min. Mean Droplet Diameter (MDD) and Zeta Potential A Zetasizer Nano ZS (Malvern Instruments, UK) was used to determine the droplet size of emulsions prepared by the above methods. This instrument is equipped with dynamic light scattering (DLS) to determine size distribution on the basis of the Brownian motion of the particles and links this to the particle size. For particle size and zeta potential samples were prepared by diluting it with the water by 1:100 ratios to obtain free Brownian motion of the samples. Equilibration time for the analysis kept to 30 s at 25 °C. Zeta potential of the emulsion droplets was determined by evaluating the electrophoretic mobility of the particles expressed in mV. Emulsion Morphology Nanoemulsions were diluted for analysis by scanning electron microscopy (SEM) (Quanta 200 ESEM) to understand the morphology of the nanoemulsion. After dilution of the sample, 1 drop was coated onto the sample stub. Before imaging, a thin layer of gold sputtering was done to prevent surface charging in the electron beam. Physicochemical Characteristics The FTIR spectra of the silicone oil and mixture of silicone oil and acetic acid were recorded using a Shimadzu FTIR spectrophotometer using ATR mode of operation and scanning of the FTIR spectrophotometer was carried out from 4000 to 600 cm-1. A K100 surface tensiometer (Kruss) was used to determine the surface properties of individual surfactants and blends of the surfactant system. Critical micelle concentrations were determined on the basis of surface tension. Interfacial tension between oil mixture (silicone oil and pine oil) and surfactant aqueous solution were determined using the K100 surface tensiometer (Kruss). The Wilhelmy plate of the tensiometer was used to analyze the surface tension, interfacial tension, and CMC of the surfactant system. Emulsion Stability Prepared emulsions were studied for kinetic stability using a centrifuge, and those samples were selected for storage
stability test which had exhibited no phase separations or creaming upon centrifugation. Centrifugation was carried out at 2000 rpm for 3 min to evaluate the kinetic stability. Stable samples were further kept for the storage stability test and periodically analyzed for particles size and visually measurement of the layer of emulsion and separated material. Storage stability was conducted by storing samples at room temperature for 3 weeks. Phase separation of the nanoemulsion was determined as follows: he f ð%Þ ¼ 100; ð1Þ ht where the ‘f(%)’ refers to the fraction of emulsion phase and ‘he’ refers to the height of the emulsion and ‘ht’ refers to the total height of the whole emulsion system comprising the heights of the emulsion as well as the separated phase. Application Methods Terry towel fabric samples were treated by the nanoemulsion using padding mangle followed by oven drying for a softness test. Knitted fabric samples were also treated by the same method for the mosquito repellency and antibacterial activity. Modified WHO/CTD/WHO PES/IC/96.1 mosquito repellent test was conducted for the fabric testing. Mosquitos were released in a Excito repellency chamber made using treated fabric to observe the change in behavior in the form of moving away from treated fabric chamber to untreated one and observations were recorded in 10 min and after 30 min. Antibacterial activity of the treated fabrics was evaluated by the AATCC 100-2012 test. Staphylococcus aureus ATCC 6538 and Klebsiella pneumoniae ATCC 4352 inoculum were used for the study.
Result and Discussion Surface Properties of Surfactant System The resistance of an emulsion droplet to deformation is controlled by the interfacial tension of the surfactant system. It has been known for many decades that blending of two or more surfactants significantly improves the surface properties such as surface tension, interfacial tension, contact angle etc. and exhibits better application properties. In this work, we examined the surface tension, critical micelle concentration and interfacial tension of the individual and mixed surfactants at various proportions in order to select surfactant judiciously for nanoemulsion development. Also, we examined if the addition of silicone surfactant (AG-pt) altered the particle size of the emulsion
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As mentioned previously, emulsions were prepared using TDA-6 and AG-pt. Linear alkyl alcohol ethoxylates surfactants are generally used to stabilize emulsions by
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Fig. 1 The effect of surfactant ratios on surface tension and CMC
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tailoring the hydrophilic and lipophilic units. TDA-6 is a nonionic surfactant having a C13 aliphatic chain with 6 ethylene oxide units at the terminal position. AG-pt is a trisiloxane based nonionic surfactant with 7–8 ethylene oxide units attached to the silicone backbone at the pendant position. In this study, silicone surfactants were intentionally combined with TDA-6 to attain better emulsifying properties as the energy of adsorption at the interface of the oil–water mixture is greater. High molecular weight polymeric or oligomeric silicone surfactants can attach to the interface via several segments which can significantly increase the adsorption energy compared to an individual or single segment of a surfactant. Also, high molecular weight silicone surfactants have a reduced tendency to readily desorb from an interface nor migrate through the bulk phase because of their greater adsorption energy. AGpt belongs to the low molecular weight oligomeric silicone surfactant category hence it provides appreciable adsorption energy along with TDA-6. Selection of the surfactant ratio (hydrocarbon to silicone surfactant) in the blend is vital to achieving the lowest possible emulsion droplet size. Emulsions were prepared using various surfactant ratios (0:100–100:0) of hydrocarbon to silicone surfactant to investigate the effect of the surfactant blend ratio on emulsion droplet size at 8% surfactant concentration and 20% oil weight fraction using ultrasound-assisted emulsification. The observations obtained are shown in Fig. 3. As 105
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droplet stabilized by TDA-6 as a result of surfactant synergy. This surfactant system (TDA-6 and AG-pt) was chosen for the nanoemulsion preparation for two reasons 1. Better compatibility with each other and the known synergistic effect and 2. Because they are safe, cheap, generally available on the market. In the present study, the relationship between surfactant ratio (hydrocarbon, i.e. TDA-6 and silicone, i.e. AG-pt surfactant) and CMC were determined on the basis of surface tension. Figure 1 shows the CMC and surface tension at various surfactant blend ratios. TDA-6 exhibits maximum surface tension (27.7 mN/m) whereas AG-pt exhibits minimum surface tension (21.5 mN/m) because of the quick orientation at the interface and that they retain their aggregation properties at the surface results in improving surface tension reduction as well as CMC reduction [7]. Also, the silicone backbone in the AG-pt has a tendency to contribute a certain level of surface properties hence provides a synergistic effect with TDA-6. Interfacial tension is a critical surface property when it comes to emulsification of two heterogeneous phases, i.e. aqueous phase and an oil phase. Interfacial tension of the individual surfactants and blends at various proportions have been analyzed and results are shown in Fig. 2. (What concentration of surfactant was used?) Interfacial tension between water and oil phase (silicone oil:pine oil = 80:20) is 11.72 mN/m. Addition of surfactant reduced the interfacial tension to 1.28 mN/m because of the orientation of the surfactant molecules partitioned in both phases results in an increase in the interfacial area hence significant reduction in interfacial tension [18]. The added surfactants in the system provide higher adsorption energy at the interface of the heterogeneous phases which results in a dramatically lower interfacial tension.
Interfacial Tension (mN/m)
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Hydrocarbon: silicone surfactant rao
Fig. 3 The effect of surfactant ratios on emulsion droplet size and the fraction emulsion phase (f) of emulsion formulated via ultrasonic emulsification method. Composition: 20% oil weight fraction, 80:20 of Si oil:Pine oil ratio, 8% of surfactant concentration prepared at 40% of applied power and 15 min sonication time
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the contribution of TDA-6 in the blend increases, droplet size decreases gradually to a surfactant ratio of 80:20. The reduction in the emulsion droplet size occurred due to the synergistic effect that arises from having two different surfactants with unique structural properties and packing geometries. The silicone backbone possesses high flexibility with the hydrocarbon surfactant to achieve quick orientation at the interface in a relatively short time [9]. The emulsion phase fraction (f) also increases with increasing TDA-6 up to a surfactant ratio of 80:20. Based on these results, the surfactant ratio (TDA-6:AG-pt) was optimized as 80:20 for further experimentation. Optimization of the surfactant concentration is very critical to achieve the desired emulsion droplet size and also relates to the cost of the emulsion. To study the effect of surfactant concentration on the emulsion stability and properties, emulsions were prepared using various surfactant concentrations ranging from 0.25 to 15% of the total mass of emulsion. The results in terms of emulsion droplet size and emulsion phase fraction (f) under different surfactant concentrations are shown in Fig. 4. It can be seen that mean droplet size of the emulsion decreased from 301.6 to 57.2 nm as surfactant concentration increased from the 0.25 to 6.5%. A further increase in the concentration results in the lowest mean droplet size of 41.1 nm at 8% surfactant. The mean droplet size decreased with increasing concentration due to an increase in the ratio of surfactant film thickness to droplet radius. The interfacial film can provide comparable resistance to emulsion particles agglomerating or flocculating which results in stable droplet size and emulsion stability. Also, an increase in the surfactant concentration provides more interfacial area and decreases the interfacial tension which results in a reduction in mean droplet size. However, a further increase in the surfactant concentration from 10 to 15% had a negative effect on the mean droplet size. The droplet size
Surfactant concentraon (%)
Fig. 4 The effect of surfactant concentration on emulsion droplet size and the fraction emulsion phase (f) of emulsion formulated via ultrasonic emulsification method. Composition: 20% oil weight fraction, 80:20 of Si oil:Pine oil ratio, 80:20 of hydrocarbon:silicone surfactant ratio prepared at 40% of applied power and 15 min sonication time
Table 1 Effect of surfactant concentration on viscosity and zeta potential Surfactant concentration (% of total emulsion volume)
Viscosity (±1.87 cp)
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increased slightly because of increased viscosity due to higher surfactant concentration. The effect of surfactant concentration on viscosity and zeta potential is shown in Table 1. The results may be attributed to the fact that the use of higher surfactant concentration results in high viscosity emulsions which can result in a reduction in sonication efficiency. Particle size distribution of the nanoemulsion is shown in Fig. 5 which shows the emulsion droplet size lies between 20 and 120 nm. From Fig. 4 it can be seen that the fraction emulsion phase (f) at low concentration is lower as there are insufficient surfactant molecules at the oil–water interface to stabilize the emulsion. Constant f is observed at 6.5% surfactant concentration which indicates the stability of the emulsion. As the surfactant concentration increased, maintaining all other parameters constant, increased viscosity of the emulsion was observed (Table 1) due to water molecules becoming trapped in the long alkyl chain of surfactant molecules increasing the effective volume fraction due to an electrical double layer of surfactant as surfactant concentration increases [24, 25]. Oil Ratio and Oil Weight Fraction Optimization Nanoemulsions were prepared using silicone oil and pine oil using various proportions in order to get a stable emulsion and provide desired properties. The purpose of selecting silicone oil for this study is that amino modified silicone oil provides surface modification of the fabric which results in smoothness, softness, bounciness, fluffiness etc. In actual application of silicone oil emulsion, emulsion droplets are adsorbed onto the fabric leading to surface modification. This application seems to ameliorate the electro-kinetic properties of emulsion droplet and fabric substrate [26]. Pine oil shows bactericide and fungicide
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Fig. 5 Particle size distribution of nanoemulsion
Silicone oil: Pine oil rao
Fig. 6 The effect of silicone and pine oil ratios on emulsion droplet size and fraction emulsion phase (f) of emulsion formulated via ultrasonic emulsification method. Composition: 20% oil weight fraction, 8% of surfactant concentration, 80:20 of hydrocarbon:silicone surfactant ratio prepared at 40% of applied power and 15 min sonication time
properties and is used in many cleaning formulations [27]. Also, some researchers have studied pine oil as a mosquito repellent agent and antibacterial agent when it is applied on fabric substrates [1]. Ansari et al. studied the larvicidal and mosquito repellent activities on human volunteers [22]. Past research has shown that 5% pine oil in the emulsion or solution is effective at obtaining mosquito repellent activity; still we have examined the emulsion droplet size and stability using various oil proportions (silicone oil:pine oil) from 0:100 to 100:0 in order to examine the effect of pine and/or silicone oil on the emulsion droplet size and ultimately on the emulsion stability. The oil ratio has been varied and emulsions prepared at 0:100, 20:80, 40:60, 60:40, 80:20, 100:0 (silicone oil:pine oil). It can be seen from the Fig. 6 that the droplet size of silicone oil only emulsion is smaller (35.3 nm) compared to the droplet size of pine oil only emulsions (178 nm). Emulsion droplet size increased slightly (43.21 nm) when the contribution of silicone oil in the oil phase decreased from 100:0 to 80:20. Further increase in the droplet size has occurred hence the oil
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ratio of silicone to pine oil have been optimized as 80:20 for further experimentation. The reason behind the minimum droplet size is 0.4% acetic acid used in the emulsion interacts with the aminomodified silicone oil to obtain a quaternary ammonium moiety which acts as a surfactant as well as oil phase in the emulsion system. Chemical modification of amino-modified silicone oil with acetic acid is depicted in Fig. 7. FTIR analysis of silicone oil only (Fig. 7A1) with a mixture of acetic acid and amino-modified silicone oil (Fig. 7B1) was conducted to examine whether a chemical modification in the emulsion had occurred. The unreacted acetic acid shows carboxyl groups at 1705–1710 cm-1 in Fig. 7B1. Because of this modification, emulsions of silicone oil in water become very stable with minimum droplet size, whereas there is no chemical interaction with acetic acid in the case of pine oil hence silicone oil is responsible for obtaining the lowest droplet size and more stable emulsions. It can be seen that the fraction emulsion phase (f) is 100% for silicone oil-dominated emulsion and decreases when the silicone oil contribution decreases in the oil phase due to the increasing droplet size. The optimized oil ratio may be sufficient in order to obtain the targeted properties, i.e. softness, bounciness, fluffiness, antibacterial and mosquito repellent activities to the fabric when it is applied. More dramatic improvements in droplet size reduction have been observed when the oil weight fraction (%) has been reduced. Emulsions prepared at 4, 8, 12, 16, 20% oil (silicone:pine in 80:20 ratio) based on the total emulsion volume are depicted in Fig. 8. An oil weight fraction of 4% resulted in the smallest droplet size of around 27.5 nm. As the oil weight fraction increases, droplet size also increases due to the higher ratio of oil to surfactant mass in the emulsion system. At the lower oil weight fractions there is more surfactant present. The higher surfactant loading is not desirable as surfactants as such do not contribute any functional properties to the emulsion. In order to obtain the desired properties like antibacterial and mosquito
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Fig. 7 FTIR spectra of A1. Silicone oil B1. Mixture of silicone oil and acetic acid
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Fig. 8 The effect of the oil weight fraction on emulsion droplet size of emulsions formulated via ultrasonic emulsification method. Composition: 8% of surfactant concentration, 80:20 of hydrocarbon:silicone surfactant ratio, 80:20 of silicone oil:pine oil ratio prepared at 40% of applied power and 15 min sonication time
repellency activities of pine oil and fabric surface modification of silicone oil, it is recommended to prepare emulsions of a higher oil weight fraction. Effect of Acoustic Cavitation on the Emulsion Acoustic cavitation has been employed to achieve the smallest possible droplet size at the shortest time span. Silicone oil and pine oil are not miscible and have different densities. Moreover, the oil and aqueous phase are also not miscible. In order to make a homogeneous system from these three phases, an energy intensive technique is required to obtain the desired droplet size. When sonication is employed, the rate of energy dissipation in the system increases which results in increased temperature. Increasing temperature results in decreasing interfacial tension and viscosity which facilitates dispersion of one phase into
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another [14]. Ultrasonication is also responsible for the production of shear forces which causes breakdown of large droplets into smaller droplets and newly generated droplets are stabilized by surfactant. The effect of sonication on emulsion droplet size and stability has been studied by providing different sonication times to prepare the emulsions. Emulsion were prepared at different sonication times i.e. 5, 10, 15, 20, 25 min at a fixed power applied, 20% oil weight fraction, 8% surfactant concentration. The results of the sonication time on droplet size and emulsion fraction phase are shown in Fig. 9. It can be seen that as sonication time increases, emulsion droplet size decreases. An appreciable difference in the particle size has been observed from sonication time from 5 to 15 min. The increase in the sonication time from 15 to 25 min results in only a marginal decrease in emulsion droplet size; hence 15 min sonication time was optimized from the experiments. Morphology of Nanoemulsion Nanoemulsion morphology has been studied using SEM. Images of the nanoemulsion at 10,000 and 20,000 magnification are shown in Fig. 10. It can be seen that droplets present in the emulsion are spherical with droplet size ranging from 40 to 120 nm. Droplet size of the nanoemulsion by SEM agrees with the droplet size analyzed by the Malvern zetasizer. Comparison of Acoustic Emulsification and Conventional Emulsification Method Emulsions were also prepared using conventional methods to compare with the results obtained by acoustic
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Sonicaon Time (minute) Fig. 9 The effect of sonication time on emulsion droplet size and fraction emulsion phase (f) of emulsion formulated via ultrasonic emulsification method. Composition: 8% of surfactant concentration, 80:20 of hydrocarbon:silicone surfactant ratio, 80:20 of silicone oil:pine oil ratio and 20% of oil weight fraction prepared at 40% of applied power
emulsification. Conventional emulsification was conducted for two different time periods i.e. at 20 and 120 min. The emulsion droplet size and a fraction of emulsion phase (f) were analyzed at day 1, after 1 week and after 2 weeks. The optimized parameters such as surfactant ratio of 80:20 (hydrocarbon:silicone surfactant), 8% surfactant concentration, 20% oil weight fraction etc. were also used to prepare the emulsion by the conventional method. Obtained results from both methods are shown in Fig. 11. It can be seen from the figure that acoustic emulsification results in the minimum droplet size after 15 min. A negligible increase in the particle size is observed after 1 and 2 weeks indicating agglomeration of the particles in the emulsion system is not occurring due to the stabilization of the small droplet by the binary surfactant system. The
Fig. 10 SEM images of nanoemulsion a 910,000, b 920,000
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fraction of emulsion phase (f) is 100% after 3 weeks of storage. We have monitored this emulsion for stability for almost 3 months and found that no phase separation. Droplet size of the emulsion prepared by the conventional method after 20 min was 291.3 nm and an increase in droplet size occurred rapidly after 1st and 2nd week. Also, the fraction of the emulsion phase was less than 81% and decreased to 56% after 2 weeks. However, emulsion droplet size dramatically decreased when we increased the time of the conventional emulsification method from 20 to 120 min. Droplet size obtained using this technique was 53.2 nm and varied only slightly after the 1st and 2nd week. The fraction of the emulsion phase was 100% which decreased slightly after the 3rd week of storage. In any emulsification method, there are two processes which occur simultaneously; droplet break-up and droplet recoalescence. Droplet breakup occurs when the applied shear is greater than the Laplace pressure within the emulsion drop. The surfactant system used to prepare the emulsion can ameliorate the breakup rate. Increase in the droplet size occurs due to lack of surfactant molecules adsorbed at the interface around the newly generated droplet. Hence stable nanoemulsions can only be obtained when the droplet break-up process is dominants over the droplet recoalescence. The stability and particle size of emulsions obtained by ultrasound are attributed to the physical effects of the cavitation phenomenon. The generation of high-level intense turbulence and mixing in the emulsion vessel causes diffusivity of the surfactant molecules around the droplets formed due to the formation, growth and collapse of microbubbles. On the other hand, conventional methods lack this phenomenon resulting in larger droplet size.
J Surfact Deterg Fig. 11 Comparison of acoustic emulsification and conventional emulsification method
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54.4
Mean droplet size (nm) (Aer 1 week)
Mean droplet size (nm) (Aer 2 week)
Mean droplet size expressed in ‘nm’
Application of Nanoemulsion as Textile Finishing Agent A textile fabric is a complex microstructure comprised of nano size to micron size voids and spaces as well as similar size surface textures that control the feel of the fabric. The feel of the fabric can be enhanced by surface finishing chemicals. Fabric finishing can be enhanced by the treatment of surface modifying chemicals for desired transport and interfacial properties which result in modification of surface and bulk properties of fabric such as inner softness, bounciness, fluffiness, wet/dry feel, water taking/holding capacity. The prepared nanoemulsions were applied onto terry towel fabric using a padding mangle. Dried samples were analyzed using AFM. Treated and untreated fabric samples were studied using AFM in order to identify the effect of treatment on the fabric sample and difference in their surface properties. The 2D and 3D images of untreated and treated fabric captured by AFM are shown in Fig. 12. It can be seen from Fig. 12a, b that the fibers in the untreated fabric is compact in nature which imparts a rough feel. On the other hand, treated fabric is more uniform and easily relaxed compared to the untreated fabric as shown Fig. 12c, d. Also, it seems that the fabric is divided into various layers after treatment. These changes indicate that the nanoemulsion has a pivotal role in modifying the micro-properties of the fibers and can be used to impart bounciness, softness, fluffiness and other required properties. Figure 13 shows the projected area and actual surface area traveled by the tip of the AFM probe during the
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98.92
43.02
42.38
Hence the acoustic or ultrasonic technique is useful for systems with more than one component present in the oil phase to obtain nanoemulsion with desired droplet size. This process is not harmful to the environment as well as can be demonstrated at the large scale using hydrodynamic cavitation.
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%f (aer 3 week)
Fraction emulsion phase expressed in ‘%’
morphology study. The area covered by the tip on the untreated fabric is more as compared to projected area but significantly less than the area covered by the tip on the treated fabric which indicates that nanoemulsion modified the surface and bulk properties. To test the mosquito repellency, one side of a cage was covered with fabric treated with the oil and the another side was covered with normal untreated fabric. The two sides were separated by an acrylic slit with a circular hole in the center. Mosquitoes were introduced in the treated net side of the cage and then the observations and results were made. All mosquitoes if repelled will go through the hole and sit on the untreated side of the cage. A scheme of the mosquito repellent cage is shown in Fig. 14. Mosquito repellent activity on the fabric has been carried out at different gram per liter (gpl) concentrations, i.e. at 50 and 100 gpl. Observations have been recorded in Table 2. After 30 min, 100% mosquito repellency was obtained when 100 gpl of nanoemulsion were applied on the fabric. At 50 gpl, the mosquito repellency obtained is 80% after 30 min. This can be concluded that pine oil containing nanoemulsion shows mosquito repellency activity. Textiles in contact with the human body exhibit an ideal environment for microbial growth. Microbial infestations pose detrimental effects to both living and non-living matters. Off smell from the inner and undergarments, the spread of diseases, staining and degradation of textiles are some of the undesired effects of bad microbes [28–30]. In order to study antibacterial activity of the prepared nanoemulsion on the fabric, we have tested treated fabric samples using two different types of bacteria. Observations and results are shown in Table 3. After 24 h, Staphylococcus aureus bacteria was reduced up to 21.4% whereas Klebsiella pneumoniae bacteria was reduced up to 54.2%. From these results, we can comment that a pine oil-containing prepared nanoemulsion shows limited antibacterial activity. This can be enhanced by increasing the pine oil content in the emulsion.
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Fig. 12 AFM images of fabrics a untreated fabric 2D image, b untreated fabric 3D image, c treated fabric 2D image, d treated fabric 3D image
Conclusion The present study clearly illustrates the development process, parameter optimization and application of the nanoemulsion on fabric. Ultrasound-assisted emulsification of silicone oil and pine oil stabilized by a binary system of
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surfactant was prepared successfully with lowest possible droplet size, i.e. 41.2 nm. Though nanoemulsion can be produced at any level of parameters, we have identified and optimized all the required variables for the development of a stable emulsion within desired particle size. A blend of TDA-6 and AG-pt has shown better performance at 80:20
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26.10 25.47 25.00
25.00
UT
T
UT
Projected Area
T
Surface Area 5x5
Fig. 13 AFM analysis by area covered for 5 9 5 lm fabric sample
proportion (TDA-6:AG-pt) in obtaining lower particle size stable emulsion. The lowest particle size of 41.2 nm was obtained at 8% surfactant concentration, 15 min sonication time and 20% oil weight fraction using silicone oil and pine
oil in 80:20 proportions. Comparison of sonication with the conventional emulsification method has enabled us to clearly illustrate the role of the ultrasonic field in increasing mixing of two immiscible phases and emulsification giving better particle size. We used SEM technique to study the morphology of the emulsion and results have shown that emulsion droplets are spherical with a particle size of 40 nm to 120 nm. Prepared emulsions were applied to fabric as finishing chemicals and studied the significant different occurred in the microstructure of fabric. We used AFM technique to study the softness, bounciness and fluffiness of the fabric and results have been shown that treated fabric is modified at the surface and in the bulk. We also tested treated fabrics for mosquito repellent and antibacterial activity and we have observed appreciable mosquito repellency at a 100-gpl dosage and moderate antibacterial activity of the fabric.
Fig. 14 Schematic diagram of mosquito repellent cage
Table 2 Mosquito repellent activity of treated fabric at different dosage level Sample name
No. of mosquitoes in treated chamber
No. of mosquitoes on treated fabric
No. of mosquitoes on untreated fabric
No. of mosquitoes showing mobility
Percentage repellency
A (50 gpl)—initial
10
6
4
0
A (50 gpl)—after 30 min
10
2
8
0
80
B (100 gpl)—initial
10
4
6
0
60
B (100 gpl)—after 30 min
10
0
10
0
100
40
Table 3 Antibacterial activity of the treated fabric using Staphylococcus aureus and Klebsiella pneumoniae bacteria Sample name
(A) Treated at 100 gpl
Test culture
S. aureus K. pneumoniae
No. of bacteria per sample (CFU/sample)
Percentage reduction of microorganism (R) (%)
Inoculated sample at 0 h
Inoculated sample at 24 h
1.54 9 105
1.21 9 105
21.4
5
0.87 9 105
54.2
1.90 9 10
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J Surfact Deterg Acknowledgements The authors would like to express their sincere gratitude towards Elkay Chemicals Pvt. Ltd., Pune (India) for providing necessary financial assistance to conduct the research work.
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Dipak D. Pukale is a Master Student in the Oils, Oleochemicals and Surfactants Technology Department at the Institute of Chemical Technology, and his research involves interfacial science, synthesis and application of surfactants, such as silicone surfactant and Gemini surfactant, emulsions, essential oils, and detergents. Archana S. Bansode is a Master Student in the Fibres & Textile Processing Technology Department at the Institute of Chemical Technology, and her research involves the studies in synthesis and formulation of specialty chemicals for textile processing, natural biopolymers, and essential oils for value addition in textiles. Dr. Dipak V. Pinjari is an Assistance Professor of the Chemical Engineering Department at the Institute of Chemical Technology, and
J Surfact Deterg his research is based on the process intensification, surfactant, cavitation engineering and technology, synthesis of nanomaterials, polymers, and sonochemistry. He has a large number of publications in process intensifications. Dr. Usha Sayed is an Associate Professor of the Fibres & Textile Processing Technology Department at the Institute of Chemical Technology, and her research is based on the laundry detergents,
studies in surface active agents for textile processing, studies of biopolymers, synthesis of cationic fixing agent and speciality chemicals and dyes, recycling and reuse, and studies in wet wipes. Dr. Rahul R. Kulkarni is a General Manager at Elkay Chemicals Pvt. Ltd. His research is based on speciality polymers, polymeric silicone, silicone fluid, emulsions, and interfacial science.
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