The Preparation and Testing of a Common Emulsion and Personal

In the Laboratory

The Preparation and Testing of a Common Emulsion and Personal Care Product: Lotion

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Suzanne T. Mabrouk Chemistry Department, The Citadel, The Military College of South Carolina, Charleston, SC 29409; [email protected]

In addition to the typical chemistry topics, current introductory chemistry textbooks (1–3) present the chemistry of everyday life: the chemistry of the environment, nutrition, personal care products, pharmaceuticals, and polymers. Although many experiments on the aforementioned topics have appeared in this Journal, few have addressed the preparation of moisturizers (4–6). In 1939, Anderson (4) presented a study by high school students on the preparation of cleansers and lotions. The lotions were made from olive oil or lanolin, water, the emulsifier diglycol laurate, scent, and colorant. In 1944, Hunter (5) showed that a cold cream could be made from beeswax, borax, mineral oil, and water. In 1980, Kaye incorporated the preparation of this cold cream formulation into a cosmetic science class at a community college (6). As there are few published lotion formulations and little information on the topic in introductory chemistry courses, this article presents the chemistry of lotions: the classifications of moisturizers and their key ingredients, the classifications of emulsions and methods for their identification, and the preparation of three lotions and related tests. This experiment could serve as an introduction to the chemistry of emulsions in a food or cosmetic science class.

Na2B4O7(s) + 2H2O(l) 2 NaOH(aq) + H2B4O7(aq)

(1)

followed by reaction of the base with the free acids in beeswax, predominately cerotic acid, CH3(CH2)24CO2H (14):

Overview of Moisturizers Moisturizers are stable mixtures composed of water, emollient(s), emulsifying agent(s), humectant(s), preservative(s), thickener(s), and possibly pH adjuster(s). Moisturizers serve three functions. They replenish the skin with water, form a waterproof barrier for the retention of water within the skin, and soften the skin. Moisturizers include creams and lotions. Creams are more nearly solid, whereas lotions are more nearly liquid. Key Ingredients in Moisturizers Commercial lotions contain 76–84% water (7). When using the described equipment, about 70% water and 18% emollient yield a product with the appropriate consistency. Deionized water is used instead of tap water to prevent contamination from hard water ions or other impurities that could cause discoloration with aging. Emollients are substances that soothe or soften the skin, for example, fats and oils. In the described formulations, the emollients are castor, coconut, and sunflower oils, and shea butter. Shea butter, which comes from the seeds of the African karite tree, Butyrosperum parkii, is a more effective emollient than cocoa butter. Petrolatum and mineral oil are the common emollients used in commercial moisturizers, as they are inexpensive. Some of the lotions tested in this experiment contained sesame and wheat germ oils. Emulsifying agents or emulsifiers are compounds that cause one liquid to be dispersed as tiny droplets (0.1–1.0 µm), www.JCE.DivCHED.org

the dispersed phase, within another liquid, the continuous phase. The resulting stable suspension is called an emulsion (8–11). Without the emulsifier, the two phases are immiscible. Emulsifiers are large molecules containing both hydrophilic and lipophilic moieties (12). In moisturizers, the hydrophilic group hydrogen bonds with water, while the lipophilic group exhibits London forces toward the oils present. These forces serve to decrease surface tension between the two phases and decrease the rate of coalescence of the dispersed liquid (9, 10). Coalescence may occur in a few minutes to over a period of years (9). In two of the prepared lotions (see Table 1), the emulsifying agent is emulsifying wax, a vegetable-based mixture containing cetearyl alcohol, polysorbate 60, PEG-150 Stearate, and Steareth-20 (13). The emulsifying wax is 5% of prepared lotions 1 and 2. In formulated lotion 3, soap serves as the emulsifier, similar to early formulations. The soap is made in situ via hydrolysis of borax and water,

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NaOH(aq) + CH3(CH2)24CO2H(s) CH3(CH2)24CO2− Na+(s) + H2O(l)

(2)

Borax and beeswax are 2% and 9% of lotion 3, respectively. Some common emulsifiers include the components of emulsifying wax, as well as carbomer, cholesteryl isostearate, lecithin, and xanthan gum (15). Humectants are substances that attract moisture from the air to themselves via hydrogen bonding. Glycerin is the humectant used in the formulations. It accounts for 1% of each lotion. Commercial lotions also use propylene glycol or sorbitol (15) as humectants. To prevent bacterial and fungal growth in lotions, preservatives are added. Citric acid and Germaben II are used in lotions 1 and 2, where they account for 1% and 0.6%, respectively, of the product. Germaben II can only be used in creams and lotions with a pH of 7.5 or lower (16), as it will react with base. Owing to the incompatibility of Germaben II with borax, grapefruit seed extract is used for 0.6% of lotion 3. Germaben II is a mixture of propylene glycol, diazolidinyl urea, methylparaben, and propylparaben (16). Many of the ingredients of Germaben II are used as preservatives in commercial lotions (15). As moisturizers can sometimes seem thin, thickeners are added. Stearic acid, which is used in many commercial lotions (15), is likewise used in this experiment.

Vol. 81 No. 1 January 2004

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Journal of Chemical Education

83

In the Laboratory Table 1. Ingredients of the Prepared Lotions Lotion 1

Oil Phase

Aqueous Phase

Preservative

3.00 g Castor oil

0.60 g Citric acid

0.34 g Germaben II

3.00 g Emulsifying wax

0.60 g Glycerin

1.80 g Shea butter

41.64 g Deionized water

3.00 g Stearic acid 6.00 g Sunflower oil 2

4.20 g Coconut oil

0.60 g Citric acid

3.00 g Emulsifying wax

0.60 g Glycerin

0.34 g Germaben II

3.00 g Stearic acid


6.60 g Sunflower oil 3

5.40 g Beeswax

1.20 g Borax

0.34 g Grapefruit

3.00 g Castor oil

0.60 g Glycerin

seed extract

1.80 g Shea butter


6.00 g Sunflower oil

Experimental Procedure

Classifications of Emulsions and Methods for Identification Emulsions are classified based on the dispersant. An oilin-water emulsion (o兾w) is a dispersion containing a waterimmiscible liquid, oil, in an aqueous phase. A water-in-oil emulsion (w兾o) is a dispersion containing an aqueous solution in a water-immiscible liquid, oil, as the continuous phase. To distinguish between the two emulsion types, a combination of the following methods is employed: conductivity, dye solubility, fluorescence, phase dilution, and wetting of filter paper (17). As oils are poor conductors, w兾o emulsions will conduct poorly, if at all. O兾w emulsions will conduct, as water is the continuous phase (17, 18). Oil-soluble dyes, like Sudan III or fuchsin, will color w兾o emulsions, whereas water-soluble dyes, like methylene blue or food dyes, will color o兾w emulsions (9, 18, 19). As many oils fluoresce under ultraviolet light, w兾o emulsions will fluoresce. O兾w emulsions will show only spotty fluorescence as a result of the dispersed oil droplets. W兾o emulsions will form one phase with oil and two phases with water, as oil is the continuous phase. O兾w emulsions will form one phase with water and two phases with oil, as the aqueous phase can be diluted with water. A drop of o兾w emulsion will spread quickly on filter paper, whereas a drop of w兾o emulsion will not (17). In this experiment, conductivity, fluorescence, and phase dilution are used to identify the emulsion type. pH of Lotion and Skin As lotions 1 and 2 and some commercial lotions contain citric acid and no pH adjusters, these lotions should be acidic. As lotion 3 contains the emulsifier soap, this lotion should be basic. Commercial lotions that contain pH adjusters, like triethanolamine (TEA), will be basic. By measuring the pH of the prepared lotions, commercial lotions, and the student’s skin, the student can determine which lotion is appropriate for their use. 84


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In one lab period, students can prepare one of the three described lotions and test all three prepared lotions and commercially available lotions for emulsion type and pH. Samples of the prepared lotions can be obtained from classmates for use in the described tests.

Chemicals All the ingredients are available from either From Nature With Love (13) or Majestic Mountain Sage (16). Borax and sunflower oil cost less when purchased at a grocery store. Preparation of Lotions 1, 2, and 3 The ingredients of the oil phase are combined in a 150mL beaker and heated with gentle stirring until melted on a magnetic stirring hot plate (Table 1). Coconut oil must be melted prior to use, as it separates on cooling. In a 100-mL beaker, the ingredients of the aqueous phase are warmed with gentle stirring on a magnetic stirring hot plate. Warming the aqueous solution will prevent precipitation of the fatty acids on combining the two phases. The warmed aqueous phase is then added to the oils. The resultant milky white emulsion is stirred for at least 30 minutes, during which time it thickens. Preservative and essential or fragrance oils (0.34 g) are then added to the lotion. The lotion is stirred an additional five minutes and then transferred to a 2-oz plastic bottle. Determination of Emulsion Classification via Conductivity, Fluorescence, and Phase Dilution A Flinn conductivity meter is used to measure the conductivity of each commercial and prepared lotion and some ingredients of the lotions. Using an ultraviolet lamp, the relative fluorescence is determined for each commercial and prepared lotion and the melted coconut oil. Equal masses of lotion and deionized water or sunflower oil are combined to assess solubility. The collected data are then used to identify the emulsion classification for each lotion.


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In the Laboratory Table 2. Intensity of Light Bulbs, Degree of Conductivity, Strength of Electrolyte, and Emulsion Type for Selected Lotions Degree of Conductivity

Strength of Electrolyte

Off

Medium

Medium

o/w

Medium

Off

Medium

Medium

o/w

Bright

Dim

High

Strong

o/w

Fruit of the Earth

Dim

Off

Low

Weak

w/o

Jergens

Dim

Off

Low

Weak

w/o

Suave

Medium

Off

Medium

Medium

o/w

Vaseline

Medium

Off

Medium

Medium

o/w

Lotion

Red LED

Green LED

1

Medium

2 3

Emulsion Type

NOTE: The complete names for the commercial lotions are: Fruit of the Earth Aloe Vera Lotion, Jergens Replenishing Multi-Vitamin Lotion, Suave Skin Therapy Lotion, and Vaseline Intensive Care Lotion for Dry Skin.

pH Test of Lotions and Student’s Skin Commercial and prepared lotions and deionized water are classified as acidic, basic, or neutral following testing with pHydrion paper. Students’ skin is likewise classified, using a water rinse. The Feel Test The feel of each prepared lotion is determined qualitatively by rolling a small quantity between two fingers. Hazards Gloves and goggles should be worn throughout this experiment, especially when working with Germaben II and essential and fragrance oils. If any of the aforementioned materials come in contact with the skin or eyes, flush the area well. Students who are sensitive to coconut oil should not make lotion 2. Flames should be avoided as many essential and fragrance oils are flammable. If the heated oils scorch in the preparation of lotion, the student should start the experiment again with fresh oils.

According to the data collected from the three tests, all tested lotions appear to be o兾w emulsions (Table 3). The conductivity for Fruit of the Earth and Jergens indicates that these two lotions are w兾o emulsions, however other data contradict this finding. As stated by Becher (20), there may be discrepancies in the collected data. For this reason more than one method is used to identify the emulsion type. Three of the four commercial lotions were found to be basic, as indicated in Table 4. Their basicity is due to the addition of TEA, which raises the pH of the otherwise acidic lotion. As no pH adjusters have been added to the formulation of Jergens or lotions 1 and 2, they were found to be acidic. Lotion 3 was found to be basic owing to the presence of the emulsifier soap. Students found the pH of their skin to be slightly acidic. Following the feel test, some students expressed a preference for the acidic lotions, 1 and 2. They preferred the lotions that had a similar pH to their skin. Others preferred the basic lotion, 3. Some students found the prepared lotions more liquidy or oily than they are accustomed, while others were quite pleased with the finished product.

Results and Discussion All tested lotions were found to conduct, as shown in Table 2. Lotion 3 conducted the most, whereas Jergens and Fruit of the Earth conducted the least. Based on these findings, all of the lotions were classified as o兾w emulsions, except for Jergens and Fruit of the Earth. The conductivity of 3% aqueous borax, 1.5% aqueous citric acid, coconut oil, sunflower oil, and deionized water were measured as references; they gave the expected results. The concentration of the borax and citric acid solutions are the same as in the lotion formulations. Four of the tested lotions were found to fluoresce: lotion 2 and 3 especially weakly and Jergens and Suave weakly. Coconut oil, the reference, fluoresced strongly. Owing to limited fluorescence, all lotions were classified as o兾w emulsions. On diluting each lotion with sunflower oil, two phases were observed. On combining each lotion with water, one phase was obtained. Therefore, water is the continuous phase in each lotion and each lotion is an o兾w emulsion. www.JCE.DivCHED.org

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Table 3. Synopsis of Emulsion-Type Data for Selected Lotions from Performed Tests Lotion

Conductivity Fluorescence

Phase Dilution

Composite of Emulsion Type

1

o/w

o/w

o/w

o/w

2

o/w

o/w

o/w

o/w

3

o/w

o/w

o/w

o/w

Fruit of the Earth

w/o

o/w

o/w

o/w

Jergens

w/o

o/w

o/w

o/w

Suave

o/w

o/w

o/w

o/w

Vaseline

o/w

o/w

o/w

o/w



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85

In the Laboratory

Table 4. pH and Classification of Selected Lotions Lotion

pH

Classification

1

2

Acidic Acidic

2

2

3

9

Basic

Fruit of the Earth

8

Basic

Jergens

6

Acidic

Suave

8.5

Basic

Vaseline

8

Basic


Conclusion According to anonymous surveys, students were interested to learn how to make lotions. They were surprised by the ease of formulation. Many students appreciated the final product that they could take home and use. A few students thought that the required stirring time in the preparation of the lotion was too long, however a minimum of thirty minutes is required to form an appropriate emulsion. The experiment demonstrated the application of chemistry to meeting the needs of everyday life. By preparing a lotion, students learned from experience how to prepare a stable emulsion and to differentiate between w兾o and o兾w emulsions. The experiment made a topic of consumer chemistry, personal care products, more tangible than a lecture. W

Supplemental Material

Instructions for the students and notes for the instructor are available in this issue of JCE Online.

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Literature Cited 1. Joesten, M. D.; Wood, J. L. World of Chemistry: Essentials, 2nd ed.; Saunders: New York, 1999. 2. Hill, J. W.; Kolb, D. K. Chemistry for Changing Times, 9th ed.; Prentice Hall: Upper Saddle River, NJ, 2001. 3. Snyder, C. H. The Extraordinary Chemistry of Ordinary Things, 3rd ed.; Wiley: New York, 1998. 4. Anderson, N. J. J. Chem. Educ. 1939, 16, 160–164. 5. Hunter, G. W. J. Chem. Educ. 1944, 21, 175. 6. Kaye, S. R. J. Chem. Educ. 1980, 57, 641. 7. Mabrouk, P. A.; Castriotta, K. J. Chem. Educ. 2001, 78, 1385– 1386. 8. Grosser, A. E. The Cookbook Decoder or Culinary Alchemy Explained; Beaufort Books: New York, 1981; pp 121–125. 9. Bravo-Diaz, C.; Gonzalez-Romero, E. J. Chem. Educ. 1996, 73, 844-847. 10. Thomssen, E. G. Modern Cosmetics, 3rd ed.; Drug & Cosmetic Industry: New York, 1947; pp 95–100. 11. McGee, H. On Food and Cooking: The Science and Lore of The Kitchen; Fireside: New York, 1997; pp 348–366. 12. Ignatia, S. M. J. Chem. Educ. 1951, 28, 112. 13. Tina Harshbarger. From Nature With Love home page. http:// www.from-nature-with-love.com/soap/ (accessed Sep 2003). 14. Warth, A. H. The Chemistry and Technology of Waxes, 2nd ed.; Reinhold: New York, 1956; p 91. 15. Winter, R. A Consumer’s Dictionary of Cosmetic Ingredients, 5th ed.; Three Rivers: New York, 1999. 16. Majestic Mountain Sage Home Page. http://www.thesage.com (accessed Sep 2003). 17. Hauser, E. A.; Lynn, J. E. Experiments In Colloid Chemistry; McGraw-Hill: New York 1940; pp 129–131. 18. Selinger, B. Chemistry In The Marketplace, 5th ed.; Harcourt Brace: Orlando, FL, 1998; p 145. 19. Robertson, T. B. Kolloid-Z 1910, 7, 7. 20. Becher, P. Emulsions: Theory and Practice; ACS Monograph 135; Reinhold: New York, 1957; p 326.


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The Preparation and Testing of a Common Emulsion and Personal

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