Article pubs.acs.org/IECR
Effect of Salt on the Manufacturing and Properties of Hand Dishwashing Liquids in the Coacervate Form Artur Seweryn,*,† Tomasz Wasilewski,† and Tomasz Bujak‡ †
Department of Chemistry, Kazimierz Pulaski University of Technology and Humanities, Chrobrego 27, Radom 26-600, Poland Department of Cosmetology, University of Information Technology and Management in Rzeszow, Sucharskiego 2, 35-225 Rzeszow, Poland
‡
ABSTRACT: The study investigated the possibilities of using different inorganic salts for the production of hand dishwashing liquids in the form of coacervate. A starting formulation was developed and subjected to the process of coacervation using different types of salts including KCl, NH4Cl, MgCl2, and CaCl2. The coacervate phase, which constituted the hand dishwashing liquid, was then isolated from the systems obtained by the procedure explained above. The products thus developed and produced were then assessed to determine their basic physicochemical and functional properties. Salts of monovalent metals were found to produce relatively high coacervate volumes from a given starting formulation, and products obtained from them demonstrate good functional parameters, i.e. washing ability, foaming properties, and fat emulsification ability. In contrast, salts of divalent metals make it possible to obtain products which display a high degree of safety of use.
1. INTRODUCTION From the physicochemical point of view, hand dishwashing liquids (acronym HDLs) are aqueous solutions of anionic, nonionic, and amphoteric surface active agents. They also contain additional substances such as coloring agents, preservatives, fragrances, as well as substances intended to reduce the adverse effect of the product on the skin of the hands. The viscosity of hand dishwashing products is achieved through the addition of inorganic salts. In addition to regulating viscosity, inorganic salts lower the critical micelle concentration (CMC) of surface active agents, thus contributing to an improvement in the detergent properties of the product. In industrial applications, the most commonly used salt is sodium chloride.1−3 Literature reports to date4,5 and own experiences suggest that a possible alternative to hand dishwashing liquids which are currently available on the market are products in the form of coacervate. Products of this type are an aqueous dispersion of lamellar droplets in which surfactant molecules are arranged in layers. A coacervate is composed mostly of active compounds, a small amount of a solvent and salt dissolved in it. A coacervate has a markedly higher concentration of surfactants than the starting formulation from which it is obtained. Assuming that the starting formulation for coacervates can be the composition of a standard hand dishwashing liquid, it can be concluded that the product obtained in the process of coacervation is concentrated.4−11 Coacervation is a phenomenon typical of solutions of colloidal substances. The phase arising in the process of coacervation, called the coacervate, is enriched with a colloidalsized ingredient (e.g., a surface active agent), whereas the diluted phase does not contain it. The process of coacervation may be either simple or complex.12 In simple coacervation, phase separation is induced by the addition of an electrolyte or alcohol or a change in pH or temperature of the colloidal solution of a protein, polymer, or surface active agents. In © XXXX American Chemical Society
complex coacervation, triggering the phase separation requires colloidal solutions of two different substances bearing opposite charges. The literature contains a considerable body of publications on the phenomenon of complex coacervation and its practical applications, for example, in the food and pharmaceutical industries.12,14,15 In contrast, decidedly less attention is given to simple coacervation occurring in aqueous solutions of surfactants. The few available reports discuss mainly coacervate phases obtained from solutions of individual surfactants,6,7 and applications of the process of simple coacervation are limited to the production of cosmetics13 and household chemicals.4,5,12 An interesting application of simple coacervation is the production of hand dishwashing liquids in the form of coacervate. Studies conducted on the topic so far have investigated the effect of the type and concentration of anionic and nonionic surfactants,4,5 salt (NaCl)5 in the context of production technologies, and properties of the finished product. The mechanism of the coacervation process depends to a large extent on the type of salt used. In accordance with the lyotropic series,16−18 an increase in the valency of cations markedly reduces the electrolyte content required to achieve the separation point. The literature contains a number of detailed studies in this area, investigating physicochemical properties of resulting coacervates, particularly for the process of complex coacervation.14,15 However, the effect of salt used in the process on the functional properties of resulting products in the form of coacervate has not as yet been unambiguously explained. The present study is an attempt to determine the effect of selected inorganic salts (KCl, NH4Cl, CaCl2, and MgCl2) on Received: October 27, 2015 Revised: December 29, 2015 Accepted: January 7, 2016
A
DOI: 10.1021/acs.iecr.5b04048 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
were placed in 50-ml beaker. Then, the mixture was stirred with a glass rod for 5 min. The mixture obtained was transferred quantitatively into a 200 cm3 volumetric flask and brought up to volume with distilled water. The flask was closed and shaken intensively for 5 min with rotations of 180°. The resulted emulsion was placed in an incubator (45 °C) for 30 min. The flask was then taken out and the emulsion was assessed. Separation of the oil layer in the flask’s neck or the appearance of one or more drops of colored oil in the upper part of flask’s neck was considered to be a negative result (the liquid was not capable of emulsifying a given weight of fatty soil). When a negative result was obtained, the subsequent trials were carried out, in which the weight of oil was decreased by 0.2 g. If the result obtained was then positive, the subsequent trials were made (with an increase in the oil weight of 0.2 g) until a negative result was obtained. The final result of the ability to emulsify fatty soil by studied dishwashing liquid was given as grams of oil per 1 L of 1% dishwashing liquid solution. Evaluation of Foaming Properties. The experiments were carried out as follows: 100 cm3 of 1% aqueous solution of studied dishwashing liquid was poured into a glass cylinder. Then, the foam was whipped (time of whipping 60 s., number of full hits 60) using a perforated disc placed on a metal bar. The volume of the foam formed was read out after 10 s. Foaming ability is described as foam volume after 10 s after its formation. The final result was the arithmetic mean of three independent measurements. Determination of Chloride Salt Content. Content of chloride salt was determined by Mohr’s method. A 3 g sample of the product was dissolved in 50 g of distilled water and titrated with 0.1 M silver nitrate. Potassium chromate was used as indicator. The same procedure was performed for a sample of 50 mL distilled water as the blank. Chloride content [%] was calculated from the equation
the process of simple coacervation and the properties of hand dishwashing liquids in the form of coacervate obtained in this manner. Prototype products which were developed in the study were subjected to functional tests typical of their product group in order to evaluate their detergent activity and foaming properties. The coacervate products obtained were also assessed to determine their safety of use, mainly in terms of the skin irritating effect.
2. MATERIALS AND METHODS Materials. Raw materials used in the commercial household products industry were used to develop hand dishwashing liquids in coacervate form: Sodium alkylbenzenesulfonate (trade name, Paste ABS Na; supplier, PCC Rokita S.A., Poland), adducts of 7 mol of ethylene oxide to lauryl alcohol (respectively: Laureth-7, Rokanol L7, PCC Rokita S. A., Poland), sodium laureth sulfate (Texapon NSO, BASF, Germany), cocamidopropyl betaine (Dehyton K, BASF, Germany), cocamide DEA (Rokamid KAD, PCC Rokita S. A., Poland), urea (POCH, Poland), potassium chloride (POCH Poland), ammonium chloride (POCH Poland), calcium chloride (POCH Poland), magnesium chloride (POCH Poland), methylchloroisothiasolinone and methylisothiazolinone as preservative (Euxyl K120, Schulke&Mayr), distilled water. Methods. Viscosity Measurements. A Brookfield RV DVIII + rheometer was used. Measurements were carried out at 22 °C with a rotary speed of spindle 10 rpm. Viscosity values presented in the figures below represent average values obtained from five independent measurements. Determination of Washing Ability. The test was carried out as follows: 60 white plates (cleaned, defatted, and dried) of 240 mm diameter were prepared. About 2 g of model soil (soil containing 34 g rapeseed oil, 34 g wheat flour, 20 g milk powder, 7 g egg yolk, and 50 g water) was applied to each plate and left for 24 h. A model bath of about 10 dm3 (0.17% aqueous solution of the model preparation containing: ABS Na 16%, laureth-7 8%, ethyl alcohol 3%, water 73%) and 10 dm3 of 0.25% aqueous solution of each one of the studied hand dishwashing liquids was prepared. Then, the plates were washed in the prepared solutions (30 items in each) at 45 °C. Washing time for one plate was 30 s. After drying, each plate was immersed in iodine solution (5 g of iodine, 10 g of KJ, 3 dm3 of water, HCl to pH = 1) and evaluated in 5-point scale: 5 points, plate without any stains; 3 points, up to 10 stains on a plate; 1 point, above 10 stains on a plate; 0 points, streaks on a plate surface. Washing ability (Z) of a studied hand dish washing liquid was calculated as a percentage according to the equation:
c XCl % =
(V2 − V1)cMx 100 1000m
where V2 is the volume of silver nitrate used for the titration of the sample [cm3], V1 is the volume of silver nitrate used for the titration of the blank [cm3], c is the concentration of silver nitrate [0.1 mol/cm3], m is the mass of the sample used for measurements [g], Mx is the molar mass of salt [g/mol]. The final result was the arithmetic mean of three independent measurements. Determination of Irritant PotentialZein Value (ZV). The irritant potential of the products was measured using the zein test. In the surfactants solution zein protein is denatured and then is solubilized in the solution. This process simulates the behavior of surfactants in relation to the skin proteins.19 To 40 mL of HDLs solution (10 wt % ) was added 2 ± 0.05 g of zein from corn. The solutions with zein were shaken on a shaker with water bath (60 min at 35 °C). The solutions were filtered on Whatman No. 1 filters and then centrifuged at 5000 rpm for 10 min. The nitrogen content in the solutions was determined by the Kjeldahl method. One mL of the filtrate was mineralized in sulfuric acid (98%) containing copper sulfate penthahydrate and potassium sulfate. After mineralization the solution was transferred (with 50 mL of MiliQ water) into the flask of the Wagner−Parnas apparatus. Then 20 mL of sodium hydroxide (25 wt %) was added. The released ammonia was distilled with steam. The ammonia was bound by sulfuric acid (5 mL of 0.1 N H2SO4) in the receiver of the Wagner−Parnas apparatus. The unbound sulfuric acid was titrated with 0.1 N
Z % = (n2 /n1) ·100
where n1 is the number of points for 30 plates cleaned in the model bath, and n2 is the number of points for 30 plates cleaned in a studied dishwashing liquid solution. The final result was the arithmetic mean of three independent measurements. Evaluation of Ability to Emulsify Fatty Soils by Studied Liquids. The maximum weight of rapeseed oil colored with Sudan Red (0.1 g of Sudan IV per 1000 mL of rapeseed oil) capable of being emulsified by 1 dm3 of a 1% aqueous solution of the studied HDLs was determined. The experiments were carried out as follows: 1.4 g of rapeseed oil colored with Sudan Red (model fatty soil) and 2 g of the studied dishwashing liquid B
DOI: 10.1021/acs.iecr.5b04048 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
presented in Table 1, a total of four 100 g samples were made as a starting formulation for the preparation of hand dishwashing liquids in the form of coacervate. Simple coacervation was used to prepare hand dishwashing liquids in coacervate form. A diagram of the simple coacervation process in a solution of surface active agents is shown in Figure 1. The solutions were prepared in accordance with the following procedure. The required quantity of water was weighed, and consecutive components were added to it in the order defined in the composition. After each component was added, the mixture was thoroughly stirred using a magnetic stirrer until completely dissolved. Clear solutions with a viscosity comparable to that of water were obtained. Next, different salts were added in portions (0.5 g/100 g of the starting formulation) to the samples. A different salt was used for every solution. The following salts: KCl, NH4Cl, CaCl2, and MgCl2 were selected for the study. After adding salt the mixture was stirred until the salt was completely dissolved and then set aside for 5 min. If no separation was observed during that time, another portion of salt was added. Salt was added until the formulation separated into two phases (i.e., until the coacervation process occurred). The products were then transferred into separation funnels and left for 48 h to achieve complete phase separation. The technological process of coacervate production is shown in Figure 2. HDL composition, which is a solution of surfactants in water, can be regarded as a special type of colloid. In the literature, it is referred to as an association colloid. The scope of changes in the structural arrangement of such a system depends on the type of cation used. The presence of cations from the added salt in the aqueous solution of surface active agents induces changes in its structure. In contrast, the effect of anions is limited. Changes accompanying the presence of salt in the system are manifested as a destruction of solvation shells around micelles and a change in the electrokinetic potential (zeta potential, ζ), leading to a change of the charge carried by micellar aggregates. The system loses its stability, and the aggregates begin to change their structures, which is evidenced by a change in the viscosity of the solution.16−18,20−23 Ionic surface active agents, which are the base of the starting formulation for producing a coacervate, form micelles with charged surfaces in the aqueous solution. The properties of such micellar solutions can be interpreted by referring to the theory of the electric double layer.24 On the micellar surface, there is an electrical layer consisting of an adsorption layer (composed of counterions) which is permanently bound to the micelle and a diffusion layer which penetrates into the solution. Between the two layers, there is a difference in potential which is referred to as zeta potential. A nonzero value of zeta potential is responsible for the electrostatic repulsion of uniformly charged aggregates. Adding an electrolyte to a micellar solution of an anionic surfactant brings about an increase in the number of counterions both in the adsorption layer and the diffusion layer. Consequently, a decrease in zeta potential and a change in micellar charge are observed. A decrease in the value of zeta potential causes a gradual attenuation of electrostatic repulsion forces between the micelles. An increasing number of counterions bound on the surface of micelles weaken the repulsive interactions between the hydrophilic heads of surfactant molecules.5−7 Nonionic surface active agents are used in hand dishwashing liquids because of their high detergent activity. They also have a significant impact on the structure of the system. Steric
sodium hydroxide. Tashiro solution was used as a indicator. The zein number (ZN) was calculated from the equation: ZN = (10 − V1)100 × 0.7
[mg N/100 mL]
where V1 is the volume (cm3) of sodium hydroxide used for titration of the sample. The final result was the arithmetic mean of three independent measurements. Determination of Dry Mass. Determination of dry mass was performed using a moisture analyzer from Radwag (Poland). About 2 g of the product was weighed and then dried at 105 °C until a constant sample weight was obtained. The final result was the arithmetic mean of three independent measurements. Determination of Turbidity. The test was performed using a turbidity analyzer (turbidimeter) HACH 2100 AN. The coacervate sample was transferred to the cuvette which was then placed in the measuring chamber of a turbidimeter. The results were evaluated after their stabilization. The final result was the arithmetic mean of three independent measurements. Microscopy. A microscope manufactured by PZO Warszawa (Poland) equipped with a digital camera was used. The measurements were conducted at 25 °C and the magnification used was 150×. Error Analysis. The points in the charts represent mean values from a series of three or five independent measurements. The t-distribution was used to calculate confidence limits for the mean values. Confidence intervals, which constitute a measuring error were determined for the confidence level of 0.90. Error values are presented in the Figures.
3. RESULTS AND DISCUSSION Starting Composition (SC) for Preparing Hand Dishwashing Liquids in the Form of Coacervate. On the basis of the literature reports and our own studies, a composition was developed for a starting formulation (SC) to prepare a hand dishwashing liquid in the form of coacervate. 3−5 The composition is shown in Table 1. Table 1. Composition of the Starting Formulation for Obtaining Coacervates (Designated as SC) component (INCI name)
concentration [wt %]
aqua sodium laureth sulfate sodium alkylbenzenesulfonate cocamide DEA cocamidopropyl betaine laureth-7 urea color preservative
ad 100 4.0 1.0 0.5 0.5 1.0 0.5 0.001 0.1
The starting formulation contained a total of 7 wt % of surface active agents. The primary surfactants used in the formulation were sodium laureth sulfate (4 wt %) and sodium alkylbenzenesulfonate (1 wt %). The auxiliary surfactants included cocamidopropyl betaine (0.5 wt %), an amphoteric surfactant, and laureth-7 (1 wt %) and cocamide DEA (0.5 wt %), nonionic surfactants. In addition, the composition contained urea, a coloring agent, a preservative, and water as a base. Technology of Preparing Hand Dishwashing Liquids in the Form of Coacervate. On the basis of the composition C
DOI: 10.1021/acs.iecr.5b04048 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
Figure 1. Diagram of simple coacervation process in solution of surface active agents.
aggregations.5−8 The steric effect of a nonionic surfactant is shown in Figure 3. The present study investigated how salts with different cation types influence the formation of hand dishwashing liquids in the form of coacervate and their properties. The concentrations of different salts and the percentage contents of phases
Figure 2. Schematic representation of the process of producing a hand dishwashing liquid in the form of coacervate.
interactions characteristic of the group of nonionic surface active agents are attributed to the formation of hydrogen bonds between oxygen atoms in oxyethylene chains and water molecules. Hydration of these chains results in the formation of a specific spatial barrier in the solution, preventing bent polyoxyethylene chains from penetrating between one another. Electrolyte addition to an aqueous solution induces dehydration of oxyethylene groups leading to the elimination of the steric (spatial) barrier caused by the “shrinking” of oxyethylene chains. The process makes it possible to bring aggregates together at small distances, and promotes the collisions of micelles and their fusion. Dehydration of an increasing number of these groups results in a decrease of the volume occupied by chains in the solution and an increase in the number of
Figure 3. Steric forces between nonionic surfactants in aqueous solution (A) and in electrolyte aqueous solution (B). D
DOI: 10.1021/acs.iecr.5b04048 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research separated from respective starting formulations are listed in Tables 2 and 3. Table 2. Concentration of Electrolytes Causing the Coacervation Process sample
concentration of salt causing the coacervation process [g salts/100 g starting composition]
SC + KCl SC + NH4Cl SC + CaCl2 SC + MgCl2
separated lower phase coacervate
6.5
K
5.5
NH4
2.8
Ca
5.2
Mg
Figure 4. Turbidity of hand dishwashing liquids in coacervate form.
highest clarity (i.e., lowest turbidity) was noted for the coacervate formulated with KCl. Following separation, the formulations were subjected to further physicochemical and functional tests (but only the lower phase). The coacervates maintained an appropriate physicochemical and microbiological stability. The structure of the products obtained in the study was verified by microscopic tests. Microscopic images of the separated lower phase are shown in Figure 5.
Table 3. Volume of Separated Phases in Coacervation Process volume of separated phase [vol %] sample (HDL in coacervate form)
diluted phase
coacervate phase
K NH4 Ca Mg
45.0 51.0 50.0 40.0
55.0 49.0 50.0 60.0
The type of salt used for obtaining products in the coacervate form has an effect on its concentration required to induce the phenomenon of coacervation (phase separation). By far the highest coacervation rate was noted for CaCl2. A 2.8 g portion of the salt was already sufficient for inducing a separation of the formulation into two phases. In other cases under study, the results ranged between 5.2 and 6.5 g of salt per 100 g of the starting formulation. The type and weight of salt added to the formulation have an impact on the volumes of separated phases. A lower relative volume of coacervate (49 vol %) was observed with ammonium chloride. In turn, the highest volume of the coacervate phase (60 vol %) was achieved for the formulation containing magnesium chloride. A comparison of the effect produced by salts containing monovalent and divalent cations in terms of the concentration inducing the process of coacervation shows that the results conform to the lyotropic series reported in the literature. Divalent ions exhibit markedly higher coagulation ability than monovalent ions.16−18,20−23 Appearance and Stability. Following the addition of salt all the formulations under study became separated into the coacervate phase with a color corresponding to the coloring agent used, and the transparent aqueous phase. In all the cases under study, the coacervate phase resulting from the separation constituted the lower phase. All the resulting products (containing KCl, NH4Cl, CaCl2, and MgCl2) underwent detailed tests with a turbidity meter. Measurement results are shown in Figure 4. In all cases including the calcium chlorides, the coacervate phase is a transparent liquid phase. The tests demonstrated that the majority of coacervates had relatively low turbidity levels, ranging from 9.5 to 16.2 NTU. The only exception was the coacervate produced using calcium chloride, which had a turbidity level of 40.7 NTU. Out of the remaining products, the
Figure 5. Micrographs of coacervates containing KCl (a), NH4Cl (b), CaCl2 (c), and MgCl2 (d).
The round-shaped structures (lamellar droplets) shown in the photograph attest to the coacervation process which occurred in the study samples. The coacervate formulated with the addition of potassium chloride was found to have the highest dispersal of lamellar droplets of all the products under study. The coacervate in question also demonstrated the lowest turbidity levels. In contrast, the coacervate obtained from CaCl2 which achieved the highest turbidity was found to have a structure in the form of small lamellar droplets densely packed in the system. Content of Chloride Salt and Active Matter. To verify the constitution of different phases, an analysis was performed to assess the chloride content (expressed as salt) and dry weight in the coacervates separated from respective starting formulations. On the basis of the results, the approximate content of active substances was estimated. The results are listed in Table 4. As a consequence of the coacervation process, a significant majority of active substances used in the starting formulations (surfactants, urea) pass into the coacervate phase. The results Table 4. Concentration of Chloride Salt, Dry Mass, and Concentration of Active Matter in Coacervate Phases Separated from Starting Compositions
E
sample (cocacervate)
concn of salt [%]
dry mass [%]
concentration of active matter [%]
K NH4 Ca Mg
6.2 3.1 2.5 5.1
21.6 18.4 12.3 14.5
15.4 14.1 9.8 9.4
DOI: 10.1021/acs.iecr.5b04048 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
Foam Properties. Results of tests assessing the foaming properties are shown in Figure 8.
attest that the coacervate phase can represent a concentrated form of a washing product with a high content of active substances.4,5 It was found that the coacervates obtained with salts containing divalent cations have a markedly lower content of active substances than the coacervates formulated using salts containing monovalent cations. Washing Ability. Results recorded in tests investigating the washing ability of formulated hand dishwashing liquids are shown in Figure 6.
Figure 8. Foam properties of hand dishwashing liquids in coacervate form.
The highest foaming ability was noted for the coacervate formulated with KCl. The recorded result was 660 cm3 of foam. The least favorable foaming ability was observed for the coacervate containing CaCl2. The foaming ability of this product is 390 cm3. The results are consistent with the determined active substance concentrations in the products. The study confirmed the literature data in demonstrating that an increase in foaming ability in a solution of surface active agents is determined by the concentration of these agents in the system: the higher is the concentration of surfactants, the greater is the volume of emerging foam.1,25 Determination of Irritant PotentialZein Value (ZV). The results of zein value determinations for the studied group of products are shown in Figure 9.
Figure 6. Washing ability of hand dishwashing liquids in the cocacervate form.
The hand dishwashing liquids in the form of coacervate which were obtained in the study exhibit very good detergent properties. The washing ability of concentrates formulated with different inorganic salts is within a similar range of 94−101%. But the differences for the analyzed HDLs are statistically insignificant. The washing ability levels obtained in the study were found to be correlated with the determined content of active substances in respective products (Table 4). The coacervates in which the recorded active substance content was the highest obtained the highest test scores. Ability to Emulsify Fatty Soils. Results of tests investigating the ability to emulsify fatty soils are shown in Figure 7.
Figure 9. Zein number of hand dishwashing liquids in coacervate form.
The type of salt used for producing hand dishwashing liquids in the coacervate form has a significant impact on their skin irritant activity. The addition of a salt with a divalent cation causes a significant improvement in the safety of product use, which was observed on the basis of zein value determination. The highest result in the study, amounting to 195 mgN/100 mL, was achieved for the coacervate which was formulated with KCl. For the other products, however, the values of the studied parameter were markedly lower. The lowest value was recorded for the formulation containing magnesium chloride (91 mgN/ 100 mL). According to literature reports cleaning products are classified as nonirritating when ZV is less than 200, averagely irritating when ZV is about 200−400, and strongly irritating when ZV is greater than 400 mg N/100 mL. The irritant potential of cleaning products is a consequence of interactions between surfactants and the skin. Surfactants may bind to skin proteins which are present in the stratum corneum. Binding of
Figure 7. Ability to emulsify fatty soils of hand dishwashing liquids in coacervate form.
The highest result (23 g/L) was recorded for the product formulated with KCl. The least effective emulsification of fatty soils (17.0 g/L) was noted for the formulation containing CaCl2. In the coacervates which had NH4Cl and MgCl2 in their compositions, the evaluated parameter reached 21 and 18.5 g/ L, respectively. Differences in results can also be explained by different active substance contents in the coacervate phase (Table 4). Samples containing salts of monovalent metals are characterized by a higher content of surface active agents, which means that their emulsification ability is higher. F
DOI: 10.1021/acs.iecr.5b04048 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
with water and the increase in viscosity observed after the addition of the first several portions of water make coacervate a potentially very interesting product form. It offers the user a possibility of diluting the product to the preferred viscosity. However, there is no obstacle to using the product directly, without a prior addition of water. The pattern of changes in dynamic viscosity (η) in the function of the weight of water added to 100 g of the coacervate is the same in every studied sample. An addition of further portions of water causes a gradual increase in dynamic viscosity of the coacervate phase until the maximum value characteristic of each formulation is achieved (ηmax). Subsequent portions of added water trigger a drop in coacervate viscosity. The type of electrolyte used in coacervate compositions has an effect on the maximum viscosity value that can be achieved during their dilution and the weight of water for which that value is observed. The highest value, ηmax equal to 2750 mPa·s, was noted for the coacervate which was formulated with potassium chloride. This level of viscosity is achieved after adding 120 g of water to 100 g of the coacervate. The lowest value of ηmax (750 mPa·s) was recorded for the formulation containing calcium chloride. In this case, the maximum value is reached after the addition of 40 g of water to 100 g of the coacervate. Markedly higher viscosity values were observed for electrolytes with monovalent cations. The maximum values achieved for the parameter are about three and four times higher than those recorded for the coacervates which were formulated using electrolytes with divalent cations.
proteins with surfactants molecules leads to protein denaturation and it is indicated as the main cause of skin irritation.3,26,28−31,34 The literature data26−32 also indicate that the skin irritating activity is largely attributable to surfactant monomers. Monomers of surfactants molecules, because of their small size (less than the diameter of the skin pores), can penetrate into the deeper layers of the skin.26,29−31,34 The presence of ions of divalent metals in the solution contributes to a large decrease in the CMC value, and thus to the “binding” a relatively large number of monomers in the form of aggregates.25−30 Micelles have larger size (larger than the diameter of the skin pores) and do not penetrate into the skin.26,29−31,34 The results obtained in the study corroborate the correlations observed for solutions of individual surfactants. For example, 1% aqueous solutions of sodium laurylether sulfate are characterized by a zein value which is about twice as high as magnesium laurylether sulfate.26,32,33 Tests on Changes in the Viscosity of Hand Dishwashing Liquids in Coacervate Form Due to Dilution with Water. A test was performed to determine the relationship between dynamic viscosity and the weight of water containing 100 g of the coacervate. The results are shown in Figure 10.
■
CONCLUSIONS Summing up, the study yielded the following results: • The process of coacervation can be used for the production of concentrated hand dishwashing liquids. The coacervate phase contains practically all surfactants (active ingredients) present in the composition of the starting formulation, though the coacervates should preferably be formulated using electrolytes with monovalent cations. • The type of electrolyte used affects the process of coacervate formation. Selecting a salt with monovalent cations results in an increase in electrolyte weight which is necessary for inducing the coacervation process. • The emulsifying properties of coacervates decrease in line with increasing valency of the cation contained in the salt. The tendency can be a consequence of a lower concentration of surface active agents in the product obtained using compounds of this type. • The resultant hand dishwashing liquids exhibit very high washing and foaming abilities, though better parameters were achieved for products formulated using salts with cations having a single electric charge. • The type of electrolyte used has a decisive influence on the zein value which is a measure of the skin irritating potential of products. The study confirmed existing literature reports on a considerable reduction of the studied parameter in the presence of cations carrying a double electric charge such as Mg2+ or Ca2+. • All dishwashing liquids in the coacervate form were found to exhibit an increased viscosity in contact with water. The type of electrolyte used in the formulation affects the susceptibility of coacervates to thickening after the addition of water. Electrolytes with cations carrying a
Figure 10. Influence of water mass introduced into coacervates on their dynamic viscosity.
A distinctive feature of hand dishwashing liquids in the coacervate form is that they themselves do not have a high viscosity, but they thicken in response to water dilution. The phenomenon is similar to that observed, for example, when concentrated solutions of anionic surfactants are dissolved in water. At appropriately high concentrations, anionic surfactants can occur in the form of lyotropic liquid crystals with a lamellar arrangement. Under the effect of dilution, the lamellar arrangement can be transformed into a hexagonal arrangement which is usually characterized by a very high viscosity.4,35 A problem, however, is that the time of combining a lyotropic liquid crystal with water is very long, even up to a dozen minutes. Consequently, using hand dishwashing liquids in the form of liquid lamellar crystals is practically impossible. An increase in viscosity following the addition of water can also be observed in coacervates. However, the lamellar arrangement is found only within small lamellar droplets dispersed in an aqueous salt solution.6,9,36 In response to dilution, the established equilibrium is disturbed, and small lamellar droplets are transformed into cylindrical micelles. It is crucial to note that the addition of water to a dispersion of lamellar droplets is not very difficult. As a result, the time of complete combination of coacervate and water is normally very short (usually several seconds). The ease of mixing coacervate G
DOI: 10.1021/acs.iecr.5b04048 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
Article
Industrial & Engineering Chemistry Research
■
(17) Salis, A.; Ninham, B. W. Models and mechanisms of Hofmeister effects in electrolyte solutions, and colloid and protein systems revisited. Chem. Soc. Rev. 2014, 43, 7358−7377. (18) Lyklema, J. Simple Hofmeister series. Chem. Phys. Lett. 2009, 467, 217−222. (19) Fischer, H.; Scheuermann, F.; Hase, Ch.; Krause, H. J. Mild to the skin anionic tensides of basic protein aminolysates preparations containing them, and their use. U.S. Patent 4,338,214, October 16, 1982. (20) Dutkiewicz, E.; Jakubowska, A. Effect of electrolytes on the physicochemical behaviour of sodium dodecyl sulphate micelles. Colloid Polym. Sci. 2002, 280, 1009−1014. (21) Patón-Morales, P.; Talens-Alesson, F. I. Flocculation of anionic surfactant micelles in the presence of hydrocarbons. Colloid Polym. Sci. 2000, 278, 697−700. (22) Collins, K. D.; Washabaugh, M. W. The Hofmeister effect and the behaviour of water at interfaces. Q. Rev. Biophys. 1985, 18, 323− 422. (23) Gokarn, Y. R.; Fesinmeyer, R. M.; Saluja, A.; Razinkov, V.; Chase, S. F.; Laue, T. M.; Brems, D. N. Effective charge measurements reveal selective and preferential accumulation of anions, but not cations, at the protein surface in dilute salt solutions. Protein Sci. 2011, 20, 580−587. (24) Hunter, R. J. Zeta Potential in Colloid Science: Principles and Applications. Academic Press, New York, 2013, 11− 32. (25) Simjoo, M.; Rezaei, T.; Andrianov, A.; Zitha, P. L. J. Foam stability in the presence of oil: effect of surfactant concentration and oil type. Colloids Surf., A 2013, 438, 148−158. (26) Cohen, L.; Martin, M.; Soto, F.; Trujillo, F.; Sanchez, E. The Effect of counterions of linear alkylbenzene sulfonate on skin compatibility. J. Surfactants Deterg. 2016, 12, 1−4. (27) Denda, M.; Katagiri, C.; Hirao, T.; Maruyama, N.; Takahashi, M. Some magnesium salts and a mixture of magnesium and calcium salts accelerate skin barrier recovery. Arch. Dermatol. Res. 1999, 291, 560−563. (28) Ferreira, M. O.; Costa, P. C.; Bahia, M. F. Effect of Sao Pedro do Sul thermal water on skin irritation. Int. J. Cosmet. Sci. 2010, 32, 205−210. (29) Hall-Manning, T. J.; Holland, G. H.; Rennie, G.; Revell, P.; Hines, J.; Barratt, M. D.; Basketter, D. A. Skin irritation potential of mixed surfactant systems. Food Chem. Toxicol. 1998, 36, 233−238. (30) Moore, P. N.; Puvvada, S.; Blankschtein, D. Challenging the surfactant monomer skin penetration model: Penetration of sodium dodecyl sulfate micelles into the epidermis. J. Cosmet Sci. 2003, 54, 29−49. (31) Lips, A.; Ananthapadmanabhan, K. P.; Vethamuthu, M. Role of surfactant charge in protein denaturation and surfactant-induced skin irritation. In Surfactants in Personal Care Products and Decorative Cosmetics; CRC Press: 2006; pp 177−187. (32) Bigotti, C.; Guaio, F.; Merlo, E.; Gazzaniga, G.; Villa, G. Zinc and its derivatives: their applications in cosmetics. J. Appl. Cosmetol. 2005, 23, 139−147. (33) Singh, S. K. Handbook on Cosmetics (Processes, Formulae with Testing Methods; Asia Pacific Business Press: 2010; pp 5960. (34) Bujak, T.; Wasilewski, T.; Nizioł-Łukaszewska, Z. Role of macromolecules in the safety of use of body wash cosmetics. Colloids Surf., B 2015, 135, 497−503. (35) Holmberg, K.; Shah, D. O.; Schwuger, M. J. Handbook of Applied Surface and Colloid Chemistry; John Wiley & Sons, Inc: NJ, 2001. (36) Cohen, I.; Vassiliades, T. Coacervation in aqueous cationic soap solutions. J. Am. Oil Chem. Soc. 1962, 39, 246−250.
double charge were found to be associated with lower maximum values of dynamic viscosity (ηmax) which can be obtained for coacervates after the addition of water. These products required the addition of a smaller weight of water to achieve ηmax values.
AUTHOR INFORMATION
Corresponding Author
*Tel.: +48 (48) 361 7545. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This paper is a part of Project No. PBS1/A5/18/2012 “Developing a new generation of ecological safe-to-use cosmetics and chemical household products containing vegetable extracts obtained under supercritical CO2 condition”.
■
REFERENCES
(1) Cohen, L.; Soto, F.; Luna, M. S. Sulfoxylated methyl esters as potential components of liquid formulations. J. Surfactants Deterg. 2001, 4, 147−150. (2) Jadidi, N.; Adib, B.; Malihi, F. B. Synergism and performance optimization in liquid detergents containing binary mixtures of anionic−nonionic, and anionic−cationic surfactants. J. Surfactants Deterg. 2013, 16, 115−121. (3) Wasilewski, T.; Przondo, J.; Gorzelak, J. Use of magnesium lauryl ether sulfates and alkylbenzene sulfonates in hand dishwashing liquids. Przem. Chem. 2011, 90, 1586−1592. (4) Wasilewski, T. Coacervates as a modern delivery system of hand dishwashing liquids. J. J. Surfactants Deterg. 2010, 13, 513−520. (5) Wasilewski, T.; Bujak, T. Effect of the type of nonionic surfactant on the manufacture and properties of hand dishwashing liquids in the coacervate form. Ind. Eng. Chem. Res. 2014, 53, 13356−13361. (6) Sein, A.; Engberts, J. Micelle to lamellar aggregate transition of an anionic surfactants in dilute aqueous solution induced by alkali metal chloride and tetraalkylammonium chloride salts. Langmuir 1995, 11, 455−465. (7) Sein, A.; Engberts, J.; van der Linden, E.; van de Pas, J. C. Salt induced transition from a micellar to a lamellar liquid crystalline phase in dilute mixtures of anionic and nonionic surfactants in aqueous solutions. Langmuir 1993, 9, 1714−1720. (8) Lasic, D. Mechanism of Vesicle Formation. Biochem. J. 1988, 256, 1−11. (9) Menger, F. M.; Sykes, B. M. Anatomy of a Coacervate. Langmuir 1998, 14, 4131−4137. (10) Bohidar, H. B. Coacervates: a novel state of soft matterAn overview. J. Surf. Sci. Technol. 2008, 24, 105−124. (11) Wang, R.; Tian, M.; Wang, Y. Coacervation and aggregate transitions of a cationic ammonium gemini surfactant with sodium benzoate in aqueous solution. Soft Matter 2014, 10, 1705−1713. (12) Benite, S. Microencapsulation. Methods and Industrial Applications; Taylor & Francis Group: Boca Raton, FL, 2006. (13) Kalantar, T.; Tucker, C.; Zalusky, A.; Boomgaard, T.; Wilson, B.; Ladika, M.; Jordan, S.; Li, W.; Zhang, X. High throughput workflow for coacervate formation and characterization in shampoo systems. J. Cosmet. Sci. 2007, 58, 375−383. (14) Perry, S. L.; Li, Y.; Priftis, D.; Leon, L.; Tirrell, M. The effect of salt on the complex coacervation of vinyl polyelectrolytes. Polymers 2014, 6, 1756−1772. (15) Jha, P. K.; Desai, P. S.; Li, J.; Larson, R. G. pH and salt effects on the associative phase separation of oppositely charged polyelectrolytes. Polymers 2014, 6, 1414−1436. (16) Wang, M.; Wang, J. Development of surfactant coacervation in aqueous solution. Soft Matter 2014, 10, 7909−7919. H
DOI: 10.1021/acs.iecr.5b04048 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX
