MICROEMULSION FORMATION OF VEGETABLE OILS USING MIXED EXTENDED SURFACTANT FOR CLEANING APPLICATIONS

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1 MICROEMULSION FORMATION OF VEGETABLE OILS USING MIXED EXTENDED SURFACTANT FOR CLEANING APPLICATIONS Siriluk Jariyawattanarat a, Chodchanok Attapong b, David A. Sabatini c, John F. Scamehorn c, Ampira Charoensaeng*,a a The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok, Thailand b Faculty of Engineering King Mongkut's Institute of Technology Ladkrabang, Bangkok, Thailand c School of Civil Engineering and Environmental Science, Institute of Applied Surfactant Research, University of Oklahoma, USA Keywords: Middle phase microemulsion, Extended surfactant, HLD, Optimum salinity, IFT measurement ABSTRACT In water washing, some vegetable oils can form semi-solid crystalline. The formation of semi-solid fat or waxy soils results in weak interactions between the oil and surfactant during the cleaning process. In this study, the anionic extended surfactant (C PO-SO 4 ) systems were applied to form a middle phase microemulsion with various vegetable oils with the aim to improve the interaction of oil phase. The middle phase with high oil solubilization and low interfacial tension were formulated for semi-solid fats removal. The addition of co-surfactant (C 16-18, 4EO-2PO) in the mixed surfactant systems was also evaluated to observe the solubility enhancement. The Hydrophilic-Lipophilic Deviation (HLD) concept was conducted to estimate the required Cc and K parameter for examination the correlation with the experiment. The IFT measurement of formulated surfactant systems was evaluated at different salinities and surfactant concentrations to determine the optimum salinity. It was found that the extended surfactant systems formed the middle phase microemulsion with coconut, soybean and palm oil at the optimum salinity of 7 wt%, 9 wt% and 8 wt% NaCl, respectively. For the system with the co-surfactant, the middle phase microemulsion formed at lower optimum salinity. * ampira.c@chula.ac.th INTRODUCTION Triglyceride is the main component of vegetable oil which has low solubilization capacity because of their large structure. Some vegetable oils have a melting point below the water washing temperature that can form semi-solid fat. The semi-solid fat results weak interactions between the oil and surfactant (Do et al., 2014). The surfactants are useful in detergent and cleaning applications that they can reduce the interfacial tension (IFT) between the wash solution and the cloth and the wash solution and the oil. Microemulsions are thermodynamically stable mixtures of water oil and surfactant. Microemulsions are divided into four types, Winsor Type I (oil-in-water), Winsor Type II (water-in-oil), Winsor Type III (bicontinuous phase) and Winsor Type IV(single phase). The middle phase microemulsion or Winsor Type III can provide not only high oil solubilization but also low interfacial tension (Do et al., 2009). The extended surfactants are surfactants that have intermediate ethylene oxide (EO) and propylene oxide (PO) groups inserted between the Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 1

2 hydrophilic head and hydrophobic tail. Due to their unique structure, the extended surfactants can improve the solubilization of oil in microemulsion and provide ultralow IFT (Phan et al., 2010). This study interested in the extended surfactants to form microemulsions with long chain triglycerides oil at ambient temperature (25 2 o C) that can provide minimum IFT value with enhancing oil removal efficiency for cleaning application. Co-surfactants are often used to improve the effectiveness of a surfactant. They can increase the oil solubilization capacity of microemulsion surfactant systems. The extended anionic surfactant used in this study is C PO-SO 4 which contains eight PO groups in the structure. The middle phase microemulsions together with IFT measurement are evaluated at different salinities, surfactant concentrations to confirm the optimum salinity. The addition of co-surfactant, C 16-18,4EO-2PO in the mixed surfactant system is evaluated to observe the solubility enhancement. The HLD (Hydrophilic-Lipophilic Deviation) values have been used to explain the microemulsion systems. HLD < 0 for Winsor type I microemulsion, HLD > 0 for Winsor type II microemulsion and HLD = 0 for Winsor type III microemulsion (Salager et al., 1979). In this work, the HLD is conducted to estimate the required Cc and K values. In application, hard surface cleaning or the oil solubilization test with palm sterin as a semi/solid fat is studied to find the optimum condition of each formulated surfactant system for maximizing oil removal efficiency EXPERIMENTAL A. Materials The anionic extended surfactant, C PO-SO 4 (30%) and the nonionic surfactant, C EO-2PO (99%) were obtained from Sasol North America. The conventional surfactant (SDBS, C 18 H 29 NaO 3 S) with 30 % purity was purchased from Sigma-Aldrich (Thailand). All vegetable oils are food grade and purchased from local market, including soybean oil (York Industrial (Thailand) Co., Ltd), Coconut oil (Pure life industrial Company) and palm oil (Morakot Industries Public Company Limited). Alkane oils (Hexane, Dodecane, and Hexadecane) were purchased from Merck (Thailand). Sodium Chloride (99%) was purchased from RCL Labscan (Thailand). Table 1. Properties of chemicals Type Chemical Molecular Weight Active Matter or EACN (g/mol) Purity Surfactant C PO-SO Co-surfactant C EO-2PO Soybean oil - Food grade 17.7 a Vegetable oil Palm oil - Food grade 14 b Coconut oil - Food grade 12 c Hexane Alkane oil Dodecane Hexadecane Salt NaCl Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 2

3 a The data from Do et al., 2014 b The data from Witthayapanyanon et al., 2006 c The data from Do et al., 2009 B. Microemulsion Formation Microemulsion phase scan experiments were conducted by varying surfactant concentrations from 1 to 4 wt% and the salinity concentrations from 1 to 10 wt%. The microemulsion was formed in a 15 ml with PTFE screwed cap vial, containing equal volume (5 ml) of the oil phase and an aqueous phase (Do et al., 2014). The solutions were mixed well to form a microemulsion under room temperature (25 2 o C). After 48 hrs, the samples were observed the microemulsion by visual and then they were left for a month to ensure equilibrium. C. IFT Measurement The dynamic interfacial tension (IFT) experiments were performed using a spinning drop tensiometer (SITE 04, Krüss GmbH, Hamburg). The IFT measurements were conducted using 1-2 μl of oil injected into 300 μl of the aqueous phase. The diameter of the oil drop was measured at equilibrium after 20 min at 7000 rpm of rotational velocity. In this study, the interfacial tension at the middle phase formed have been known as the minimum IFT value of which below 10-3 mn/m is defined as the ultralow IFT (Nguyen et al., 2009), and this point the required salinity is called as the optimum salt. D. HLD Calculation The HLD which developed by Salager and coworkers (1979) was conducted to estimate K and Cc values. The HLD equation is as follow; HLD = ln(s*) - K (EACN)- f(a) + Cc - α T ΔT (Eq.1) Where, S is the salt concentration at middle phase microemulsion, f(a) represents alcohol or alcohol-free f(a) equal to 0, α T is the temperature coefficient and has a value of For most ionic surfactants, ΔT is the temperature difference between the studied surfactant (25± 2 C) and the reference temperature equal to 25 C. The HLD equation indicates K and Characteristic curvature (Cc) values of each surfactant and oil. The HLD value equals to zero for middle phase microemulsion. K and Cc values are determined by the slope and y- intercept of the plot between ln S* (optimum salt) and EACN number, respectively. E. Hard surface cleaning Palm stearin used as a semi-solid fat. It was dyed by Oil-red-O, and 0.2 g of palm stearin was added into a 15mL flat-bottom and filled with the aqueous phase. The sample was placed in a horizontal position shaker. After that, the sample was washed with DI water. The 5mL limonene was used to remove the dyed oil in the tubes. The amount of remaining oil (died oil) in the tube was measured by a UV/VIS spectrophotometer (1800 Shimadzu, liquid) for absorbance at λmax. The concentration of the remaining oil was calculated throughout the material balance equation. The percentages of oil removal were calculated followed by the Eq. 2. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 3

4 Oil removal (%) = (A-B) 100/(A) (Eq.2) Where A is the average concentration before washing, while B is the average concentration after washing with limonene after 24 hours. RESULTS AND DISCUSSION A. Middle Phase Microemulsion Formation In this work, the microemulsions were formulated with three vegetable oils at the room temperature using the single anionic extended surfactant, C 14-15, 8PO-SO 4 and its mixed systems with the nonionic extended surfactant, C EO-2PO as a co-surfactant. The mixed system with the co-surfactant was fixed at the ratio of 9:1 (C 14-15, 8PO-SO 4 to C EO-2PO). All surfactant systems formed microemulsion from Winsor Type I, III and II, respectively when the salinity increased. The middle phase or Winsor Type III microemulsions of the single and mixed surfactant systems occurred at the optimum salinity. Table 2 summarizes the results of middle phase microemulsion formation study. Table 2. Summarize the optimum salinity Oils EACN Sufactant Co-surfactant Optimum salt (S*) Soybean oil 17.7 C 14-15, 8PO-SO 4 C 14-15, 8PO-SO 4 - C EO-2PO 9 8 Palm oil C 14-15, 8PO-SO 4 C EO-2PO 7 C, 8PO-SO - 8 Coconut oil 12 C 14-15, 8PO-SO 4-7 C 14-15, 8PO-SO 4 C EO-2PO 6 From Table 2, the middle phase microemulsion formed with soybean oil, palm oil, and coconut oil. It was found that the optimum salinity decreases with decreasing EACN of oil. For the system containing C EO-2PO as a co-surfactant, it can be observed that the middle phase microemulsion formed at lower optimum salinity because C EO-2PO can improve the oil solubilization capacity due to its hydrophobicity structure. Similar to the results of Acosta and coworkers (2008), the addition of nonionic surfactant (C alcohol exthoxylate-6.5eo) can reduce the optimum salinity of extended surfactant system. B. IFT measurement The IFT measurement of surfactant system was performed to determine the optimum salinity. Generally, the middle phase occurs with the minimum IFT value and the required salt to form the middle phase is called the optimum salinity. At this point, the surfactants have an equal affinity for solubilization both oil and water phase. The minimum IFT was determined by the plot of IFT values versus NaCl concentrations. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 4

5 Figure 1. Microemulsion formulation (Winsor I, II and III) of 0.5 wt% C 14-15,8PO-SO 4 with coconut, palm and soybean oil Figure 1 plots the interfacial tension between excess oil and excess water of the middle phase microemulsion formulations as a function of salinity for soybean oil, palm oil, and coconut oil, using anionic extended surfactant at 0.5 wt%. The results show that the minimum IFT values of 0.5 wt% C 14-15,8PO-SO 4 with coconut, palm, and soybean oil were achieved at 7%, 8% and 9% NaCl concentrations, respectively. The minimum IFT values of those three oils occurred at Type III microemulsion region. The achieved IFTs of coconut, and soybean oil are an ultralow IFT (<10-3 mn/m) and similar to the results that obtained from the middle phase scan study. C. HLD calculation In this study, we used simplified HLD model developed by Salager and coworkers (1979) as shown in Eq. 1. The HLD calculation was conducted to determine Cc and K value from the plot between the optimum salt from the IFT measurement and EACN of alkane oils. For the middle phase microemulsion, HLD value equal to zero (Nguyen and Sabatini, 2011) Table 3. Summary of the optimum salinity (S*) and the minimum interfacial tension (IFT*) of 0.5 wt% C 14-15, 8PO-SO 4 with alkane oils Alkane oils EACN Co-surfactant S*(wt%) IFT*(mN/m) Hexane ± Dodecane ± Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 5

6 Hexadecane ± Hexane ± Dodecane 12.0 C EO-2PO ± Hexadecane ± The calibration curve plots between the optimum salt and EACN of alkane oils from Table 3. K and Cc values are determined by the slope and y-intercept of the plot between ln S* (optimum salt) and EACN number, Table 4. K-values and Cc-values of the surfactant systems obtained from HLD calculation Surfactant K Cc C 14-15, 8PO-SO C 14-15, 8PO-SO 4/ C EO-2PO (9:1) For the HLD equation, the Cc value has been used to determine the hydrophobicity of a surfactant. From Table 3, the calculated Cc and K values of extended surfactant, C 14-15, 8PO-SO 4 alone was and , respectively. Kiran and Acosta (2010) reported that Cc and K values of C (PO) 8 SO 4 Na are and 0.087, respectively. The obtained Cc and K values for extended surfactant system is in the similar ranges of the Cc and K value of C (PO) 8 SO 4 Na. When compared the extended surfactant system alone with the extended surfactant mixed with the co-surfactant system, the C 14-15, 8PO-SO 4 system alone was achieved more negative Cc value than that of the system with cosurfactant, indicating that the C 14-15, 8PO-SO 4 system alone is more hydrophobicity. D. Hard surface cleaning Palm stearin has a melting point about C (Ghosh and Bhattacharyya, 1997) which turns to be a semi-solid fat at room temperature (25 ± 2 C). It was used as fat in hard surface cleaning experiment for determined the efficiency of the surfactant system. Amount of oil removal was determined for estimating the performance of surfactant system, as shown in Figure 3 Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 6

7 Figure 2. The oil removal efficiency of C 14-15,8PO-SO 4 alone, C 14-15,8PO-SO 4 mixed with C 16-18, 4EO-2PO and SDBS using palm oil as the semi-solid fat. Figure 2. shows the plot between the percentage of oil removal and NaCl concentration using 3 wt% C 14-15,8PO-SO 4 alone, 3 wt% C14-15,8PO-SO4 mixed with C 16-18, 4EO-2PO and 3 wt% SDBS. The results show that the maximum oil removal of the mixed system of C 14-15, 8PO-SO 4 / C 16-18, 4EO-2PO was about 63%. The anionic extended surfactant system alone had the maximum oil removal about 59%. While the maximum oil removal of the conventional surfactant was achieved about 21%. The oil removal efficiency of the mixed anionic and nonionic extended surfactant is much more than that of the conventional surfactant (SDBS) system by 42%. This result indicated that the addition of co-surfactant could enhance interactions of the semi-solid fat and the surfactant molecules. Figure 3. Correlations between the oil removal efficiency and microemulsion types using 3 wt% C 14-15,8PO-SO 4 with palm olein and palm stearin, respectively. Figure 3 presents the maximum oil removal of C 14-15,8PO-SO 4 alone with palm oil occurred in Type III region that correlated with the microemulsion formation experiment. The middle phase microemulsion can achieve high maximum oil removal. This result similar to Tanthakit and coworkers (2010), the maximum oil removal efficiency of palm oil was achieved at the optimum salinity. CONCLUSIONS The middle phase microemulsion was formed with soybean, palm and coconut oil using anionic and nonionic extended surfactant can provide minimum IFT value resulting in an enhancement of oil removal efficiency for cleaning application. The extended surfactant systems were able to form a middle phase microemulsion with coconut, palm and soybean oils. The addition of co-surfactant in the surfactant system can enhance the solubilization capacity that the middle phase microemulsion can form at lower optimum salinity. For IFT measurement, the minimum IFT value can point the optimum salinity that correlated with the middle-phase microemulsion formation. K and Cc values obtained from HLD equation can be used for the extended surfactant system with vegetable oils. The oil removal Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 7

8 efficiency of extended surfactant with co-surfactant is higher than the extended surfactant system alone and the conventional surfactant system. ACKNOWLEDGEMENTS This work is funded by The Petroleum and Petrochemical College and surfactant obtained from Sasol. REFERENCES Do, L.D., Withayyapayanon, A., Harwell, J.H., and Sabatini, D.A. (2009). Environmentally Friendly Vegetable Oil Microemulsions Using Extended Surfactants and Linkers. Journal of Surfactants and Detergency, 12, Do, L.D., Attaphong, C., Scamehorn, J.F., and Sabatini, D.A. (2014). Detergency of Vegetable Oils and Semi-Solid Fats Using Microemulsion Mixtures of Anionic Extended Surfactants: The HLD Concept and Cold Water Applications. Journal of Surfactants and Detergency, 18, Kiran, S., and Acosta, E.J. (2010). Predicting the morphology and viscosity of microemulsions using HLD-NAC model. Industrial and Engineering Chemistry Research, 49, Nguyen, T.T., and Sabatini, D. A. (2009). Formulating alcohol-free microemulsions using rhamnolipid biosurfactant and rhamnolipid mixtures. Journal of surfactants and detergents 2, Phan, T.T., Witthayapanyanon, A., Harwell, J.H., Sabatini, D.A. (2010). Microemulsion-Based Vegetable Oil Detergency Using an Extended Surfactant. Journal of Surfactants and Detergents, 13, Salager, J. L., Morgan, J. C., Schecher, R. S., Wade, W. H., and Vasquez, E. (1979). Optimum formulation of surfactant/water/oil systems for minimum interfacial tension or phase behavior. Society of Petroleum Engineers Journal, 2, Tanthakit, T., Ratchatawetchakul, P., Chavadej, S., Scamehorn, J.F., Sabatini D.A., Tongcumpou, C. (2010). Palm Oil Removal from Fabric Using Microemulsion-Based Formulations. Journal of Surfactants and Detergency, 13, Thu, T. N., Sabatini, D.A. (2009). Formulating alcohol-free microemulsions using rhamnolipid biosurfactant and rhamnolipid mixtures. Journal of surfactants and detergents, 12, Witthayapanyanon, A., Acosta, E.J., Harwell, J.H., and Sabatini, D.A. (2006). Formulation of ultralow interfacial tension systems using extended surfactants. Journal of surfactants and detergents, 4, Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 8

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