<title>Microencapsulation of Essential Oils for Use in Cold Process Soap</title>

<author><firstname>James</firstname><surname>Baldwin</surname></author>

<author><firstname>Kevin</firstname><othername>M</othername><surname>Dunn</surname></author>

The purpose of this project is to develop a microencapsulation technique to be used in cold process soap making to prevent seizing of the soap. It was found that seizing in soap is caused by an increased rate of reaction due to the introduction of scent oil, such as clove oil, which reacts rapidly with sodium hydroxide. Using physical microencapsulation, a microcapsule consisting of eugenol, carnauba wax, deionized water, and a small amount of 12 ppt NaOH solution can be used to protect the scent oil from reacting with the 333 ppt sodium hydroxide used during the soap making process. It was found that the use of the developed microencapsulation technique shows promising results in protecting the scent oil, eugenol, from the 333 ppt sodium hydroxide solution. Also included in this research investigation is a few quality assurance issues including saponification value determination and residual total alkali determination for the specific soaps produced from this seizing project.

The purpose of this project is to develop a microencapsulation technique to be used in cold process soap making to prevent seizing of the soap. It was found that seizing in soap is caused by an increased rate of reaction due to the introduction of scent oil, such as clove oil, which reacts rapidly with sodium hydroxide. As a result, to better improve the characteristics of soap in Hampden-Sydney College's production of handcrafted soap bars, the creation of a microencapsulation process to protect the scent oils would be very beneficial.

Microencapsulation is a very long, tedious process and unfortunately there is limited research regarding a successfully procedure for using microencapsulation in the soap making business. However, combining many of the procedures currently available can aid the process of developing a procedure. Research states that the microencapsulation process requires the application of a shell material to the particles. Additionally, there are a few processes found for using a benefit agent for encapsulation; note that benefit agents are considered materials that have a positive effect to the substrate, in our case, skin. <xref linkend="R5"/>

Also, benefit agents for the skin are water insoluble products that can protect, moisturize, or condition the skin after using the bar of soap.<xref linkend="R5"/> This procedure involves the application of a shell to the particles. This process involves melting the benefit and carrier agent in a beaker and adding the mixture to a solvent solution of the shell material. As a result, the encapsulating material is established holding the scent. In this case, the benefit agents being used are waxes such as carnauba and beeswax. <xref linkend="R6"/>

Although microencapsulation has not been studied in detail at Hampden-Sydney College, the technology of microencapsulation is a prominent topic in today's scientific community. Most people have come in to contact with the scratch-and-sniff perfume advertisements located in many news stand magazines; the way this technology works is through microencapsulation. Additionally, microencapsulation relies on the rupture of the shell to release its contents. There are various ways in which core material can be freed from a microcapsule including rupture, dissolution, phase separation, melting, and diffusion of the cell wall <xref linkend="R1"/>. For soap making, it seems best suitable to use the mechanism of dissolution of the wall. In addition, this process which is used in many microencapsulation processes is nearly 80% effective <xref linkend="R2"/>.

The reason why much interest is sparked in the soap making community regarding microencapsulation is because this technology is widely and successfully used in many other products including food, perfumes, and laundry detergents. It seems fit that the process in which laundry detergent uses microencapsulation would benefit microencapsulation in handcrafted soap making.

However, the microencapsulation technique used in laundry detergent production makes use of a water-soluble polymer where upon contact with water, shell dissolution occurs and the scent is released<xref linkend="R1"/>. We have found that a physical microencapsulation technique, in which a hard outer shell is ruptured to release the scent oil, is best for handcrafted soap makers. Our technique involves the creation of a microcapsule using clove oil, carnauba wax, water, and a small amount of lye.

Clove oil is the most widely used scent oil in cold process soap making. Additionally, the single largest component of clove oil is eugenol. Therefore, during experimentation eugenol was treated as clove oil. More so, eugenol is a phenol and a very weak acid. ><xref linkend="R3"/>.

<figure id="lab_eugenolstructure"><title>Structure of Eugenol</title> <mediaobject><imageobject><imagedata fileref="lab_eugenolstructure1.pdf" format="PDF" scale="50"/></imageobject></mediaobject> </figure>

Also, carnauba wax is safe from sodium hydroxide because wax does not react with sodium hydroxide. As a result, the eugenol is safely protected within the walls of the carnauba wax. We hypothesized that the use of eugenol as the scent oil and carnauba wax as a coating agent will prevent rapid soldification of our soaps.

The diagram below depicts our hypothesis. Palm oil, lye, and our microcapsules are added to a mixing jar. Upon mixing, soaponification occurs at a normal rate of reaction. As a result, the scent oil remains protected within the walls of the microcapsules.

<figure id="lab_hypothesisdiagram"><title>If Hypothesis Supported</title> <mediaobject><imageobject><imagedata fileref="lab_hypothesisdiagram1.pdf" format="PDF" scale="50"/></imageobject></mediaobject></figure>

On the other hand, the diagram below depicts the addition of eugenol without any form of protection from the sodium hydroxide. Notice that upon mixing, soaponification occurs at a much faster rate of reaction due to the production of sodium eugenolate.

<figure id="lab_fastratediagram"><title>Scent Oil without Protection</title> <mediaobject><imageobject><imagedata fileref="lab_fastratediagram1.pdf" format="PDF" scale="50"/></imageobject></mediaobject></figure>

Also included in this research investigation is a few quality assurance issues including saponification value determination and residual total alkali determination for the specific soaps produced from this seizing project. Because real-world oils are composed of complex mixtures of fatty acid triglycerides, we can never know the exact saponification value of each and every soap. In addition, due to the variation of composition of oils from supplier to supplier it is necessary that we conduct a saponification value investigation of each oil we encounter. More so, saponification values can be calculated using a variety of methods from the use of methanol to the use of ethanol. It will be our purpose to determine which method of saponification value calculations is easiest for hand crafted soapmakers. Lastly, our investigation leads us to test if our sample soap has fully saponified; this process is completed through the residual total alkali test, which "assigns a numerical value which may be tracked as the soap ages." <xref linkend="R21"/>

<bibliomixed id="R1">Franjione, John, Niraj, Vasishtha <citetitle>The Art and Science of Microencapsulation.</citetitle>, Technology Today: 1-6, 1995.</bibliomixed>

<bibliomixed id="R2">Brenner, Joseph <citetitle>Process of encapsulating an oil and product produced thereby</citetitle>, U.S. Patent 3,971,852 , 1976.</bibliomixed>

<bibliomixed id="R3">McDaniels, Robert <citetitle>Essentially Soap.</citetitle> Krause Publications: April 2000.</bibliomixed>

<bibliomixed id="R5">Finucane, Kevin Michael Corr, James Joseph Ornoski, Gregory Alan Coyle, Laurie Ann <citetitle>Extruded soap and/or detergent bar compositions comprising encapsulated compounds. </citetitle>, 2001.</bibliomixed>

<bibliomixed id="R6">Shefer, Adi; Shefer, Samuel David <citetitle>Multi - component controlled delivery system for fabric care products and delivery system production. </citetitle>, 2003.</bibliomixed>

<bibliomixed id="R21">Dunn, Kevin M.<citetitle>Scientific Soapmaking: The Chemistry of Handcrafted Soap </citetitle>, 2005 (Draft).</bibliomixed>

Materials - Investigation One

The materials needed to complete the experimentation includes a 200.00 g balance, plastic cups, carnauba wax, eugenol from Aldrich, 3 vials with caps, 12 ppt sodium hydroxide solution, distilled water, a beaker, a hot plate, a sonic bath, plastic pipettes, a pH meter, ethanol supplied by Aldrich, palm oil, 333 ppt sodium hydroxide solution, mixing jar, oven, calculator, and a notebook.

Methods and Discussion - Investigation One

The figure below depicts the proposed emulsification to produce microcapsules.

<figure id="lab_emulsification"><title>Emulsification to Produce Microcapsules</title> <mediaobject><imageobject><imagedata fileref="lab_emulsification1.pdf" format="PDF" scale="50"/></imageobject></mediaobject></figure>

The first step to begin the production of a physical microcapsule is to prepare a 12 ppt lye solution, standardize the 12 ppt sodium hydroxide solution, determine the endpoint of eugenol, and then proceed to the production of microcapsules.

To prepare the 12 ppt sodium hydroxide solution, mix 998 g of distilled water with 12.XX g of sodium hydroxide. Standardize the 12 ppt solution with KHP. In our experimentation, we standardized 3 times to get mean and standard deviation for 12 ppt dilute NaOH concentration in mol solute/kg solution (molamity). <xref linkend="R7"/> The average molamity was .3206 mol NaOH/ kg lye solution with a standard deviation of .7 ppt.

Because eugenol is a very weak acid, the endpoint is not sharp.

<figure id="lab_titrationcurve"><title>Simulated Titration Curve for 0.5 g eugenol with .3 m NaOH</title> <mediaobject><imageobject><imagedata fileref="lab_titrationcurve1.pdf" format="PDF" scale="50"/></imageobject></mediaobject></figure>

Therefore, we need to determine the endpoint of 0.5XXX g eugenol. Using the calculation below, the expected endpoint should be reached after 9.5XXX g 12 ppt sodium hydroxide solution is titrated.

<figure id="lab_endpointcalc"><title>Example Calculation for the Endpoint of Eugenol</title> <mediaobject><imageobject><imagedata fileref="lab_endpointcalc1.pdf" format="PDF" scale="50"/></imageobject></mediaobject></figure>

Since gravimetric titrations are being employed, we must know the endpoint pH of 0.5XXX g eugenol. Therefore, titrate 0.5XXX g eugenol with 12 ppt sodium hydroxide solution and record the pH. Add 0.5XXX g eugenol, 50 g of distilled H20, and 50 g of ethanol (to dissolve oil) to a flask. Place a cup of 20 g of 12 ppt NaOH solution on a balance and tare balance. Remove NaOH from cup to flask and record pH at each interval. Pay close attention to pH from 9-11 grams because we want to know the pH when 9.5XXX g of sodium hydroxide have been added to the flask! From our results, it was determined the pH for the endpoint of 0.5XXX g of eugenol is 12.46 with a standard deviation of .005. We used our results to complete an interpolation. At a pH of 12.46 the average amount of 12 ppt sodium hydroxide was interpolated to be 9.55 g 12 ppt sodium hydroxide.

<figure id="lab_curve"><title>Actual Titration Curve for 0.5 g eugenol with .3 m NaOH</title> <mediaobject><imageobject><imagedata fileref="lab_curve1.pdf" format="PDF" scale="50"/></imageobject></mediaobject></figure>

Knowing the pH for the endpoint of 0.5 g of eugenol we can create our first emulsion using microencapsulation. The first step is to weigh out 0.50XX g of eugenol into a vial. Next, add 2.00 g of carnauba wax to the vial. Then, add 4.00 g of distilled water the vial. Add 1 drop of 12 ppt lye to the vial; in this case one drop is equivalent to 0.10 g. Place the cap on the vial and add to a hot water bath to melt the mixture. Once the mixture is fully liquefied shake the vial to create and emulsion. The emulsion should appear creamy yellow. After the vial has cooled add to the sonic bath. Remove the vial from the sonic bath. Next, add a 50/50 solution of ethanol and distilled water (50 g / 50 g) into a beaker. Add the emulsion mixture (microcapsules) to the plastic cup. Use gravimetric titrations to titrate the emulsion to a pH of 12.46 with the 12 ppt NaOH solution. Once a pH of 12.46 has been reached use the corresponding amount of 12 ppt lye solution to determine the amount of free eugenol.

<figure id="lab_freecalc"><title>Sample Calculation of % Free Eugenol</title> <mediaobject><imageobject><imagedata fileref="lab_freecalc1.pdf" format="PDF" scale="50"/></imageobject></mediaobject></figure>

From 3 trials, we found that there was an average of about 32.3% <quote>free eugenol</quote> +/- 5.5%. In other words about 70% of the eugenol was protected by the wax.

Next, we wanted to test out the microcapsules in real soap making conditions. Three different 100 g palm oil bars of soap were produced. Add 100 g Palm Oil, 42 g 333 ppt NaOH, and our emulsion to mixing jar. Seizing should not occur! Mix until trace is reached. Pour mixture in mold, place in oven for 4 hours at 150°C. Remove from oven and weigh bar of soap. Next, add 100 g Palm Oil, 42 g 333 ppt NaOH, and 1 g eugenol to mixing jar. Mix until trace is reached. Pour mixture in mold, place in oven for 4 hours at 150°C. Remove from oven and weigh bar of soap. Lastly, add 100 g Palm Oil, 42 g 333 ppt NaOH to mixing jar. Mix until trace is reached. Pour mixture in mold, place in oven for 4 hours at 150°C. Remove from oven and weigh bar of soap. From our results, we calculated that the bar of palm oil soap with the microcapsules weighed 84.9% of original weight, the bar of palm oil soap without any form of scent weighed 87.5% of original weight, and the bar of palm oil soap with eugenol added directly without protection weighed 73.1% of original weight.<xref linkend="T1"/>

<table id="T1"><title>100 g Palm Oil Soap Bars</title>

</table>

<bibliomixed id="R7">Ramette, Richard W. <citetitle>In Support of Weigh Titration Techniques</citetitle>, Chemical Education Today: 81:12, 2004.</bibliomixed>

Materials - Investigation Two

Saponification Value Determination

A 200 g balance, palm oil, 6% ethanolic KOH solution, 6% methanolic KOH solution, 500.0 ppt citric acid solution, six clean 500-mL Erlenmeyer flasks (labeled Blank A, Blank B, Blank C, Soap A, Soap B, Soap C), three watch glasses, three plastic weighing cups (labeled Oil, Acid, and Base), three pipets (labeled Oil, Acid, and Base), and a soap oven.

Residual Total Alkali Determination

A 200 g balance, sample of soaps, distilled wather, 500-mL Erlenmery flask, a soap oven, a knife, 100.0 ppt citric acid standard, two plastic cups (labeled Soap and Acid), a pipet (labeled Acid), 1% Phenolphthalein solution.

Methods and Discussion - Investigation Two

Saponification Value Determination

The first part of this experiment involved determining whether to use an ethanolic KOH solution or a methanolic KOH solution. Therefore, two experiments were completed: the AOCS Recommended Practice Cd 3c-91 - Saponification Value Modified Method Using Methanol and the AOCS Official Method Cd 3-25 Saponification Value experiment. It was found that the AOCS Official Method Cd 3-25 Saponification Value experiment should be the preferred choice of procedure. As for the ease of each each experiment, the ethanol and methanol techniques are very similar. In addition, one experiment does not take any longer than the other experiment. As for the cost of materials to complete each experiment, methanol is much higher in cost than ethanol. In fact, methanol usually cost about double compared to ethanol. In addition, ethanol can be purchased from Wal-Mart for about $7.00 a liter. Lastly, using the methanol technique does not always guarantee the same results when an experiment is repeated whereas, the ethanol technique is reliable for reproduction. Therefore, all saponification values were determined in our experimentation using 6% ethanolic KOH.

A number of SAP determinations were completed using the following technique: first, the oven was preheated to 170 degrees Farenheight. Using the base weighing cup and base pipet, 100.00 g of the 6% ethanolic KOH solution was synthetically weighed into the Blank A flask. Identical amounts of ethanolic KOH solution was weighed into Blank B, Blank C, Soap A, Soap B, and Soap C flasks. Using the oil cup and the oil pipet, 20.00 g of palm oil was weighed into Soap A flask. Identical portions of oil were weighed to Soap B and Soap C flasks. All soap flasks were placed into the soap oven for 1 hour to ensure complete soaponification. Add two or three drops of indicator to each Blank flask. While the soaps were cooking, all Blank flasks were titrated with 500.0 ppt citric acid using the gravimetric titration technique. After an hour, the soap flasks were removed from the oven. Immediately add two or three drops of indication to each soap flask and titrate with 500 ppt citric acid solution. From these titrations, SAP values were calculated using the following calculation:

? g NaOH = 312.3 (YY.YY - ZZ.ZZ / 20.XX) g NaOH, where 20.XX is the exact amount of oil used for each Soap flask, YY.YY is the endpoint for the blank flask, and ZZ.ZZ is the endpoint for the Soap flask.

For our palm oil, our SAP value was determined to be 145.78 +/- .39 g or 145.78 +/- .39 ppt. These values were used to create a number of soaps, which an RTA value was then determined. See the next experiment for results.

Residual Total Alkali Determination

A residual total alkali determination was conducted on soaps produced using the saponification value calculated in the previous experiment. This experiment began by preheating the oven to 200 degrees Fahrenheit. The soap was placed in a cup onto the balance and balance was tarred. The knife was used to carefully shave more than 10.00 grams into the cup. With the Soap cup still on the balance, the balanced was once again tarred. The contents of the soap cup were poured into the Erlenmeyer flask. The amount of soap transferred was recorded. About 250 mL of distilled water was added to the soap flask. The soap was placed into the oven for about 1 hour. The soap was removed from the oven and allowed to cool to room temperature. Two or three drops of indicator were added to the flask. 100.0 ppt citric acid standard was used to titrate by the gravimetric titration technique.

The RTA Value of each soap was calculated and the results are as follows: ? g NaOH = 62.47 (0.YY/10.XX) g NaOH, where 0.YY is the endpoint and 10.XX is the amount of soap used.

<table id="T3"><title>RTA Calculations of Palm Oil Soap Bars</title>

</table>

The results gathered from experimentation are very promising. The results show that the physical microencapsulation technique developed actually protected the eugenol from the sodium hydroxide. As a result, the rate of reaction was not increased and our hypothesis was supported by the data.

Although the data we gathered supports our hypothesis, more work can be completed to improve the quality of the microcapsules. More so, the microcapsules tended to clump together to form a huge ball of microcapsules. Instead of having a huge ball, a method needs to be developed to crush the ball of microcapsules into a fine powder. A great start would be the use of filtration to separate the chunks of microcapsules and the use of a pestle and mortar to finely grind the microcapsules.

All in all, the experimentation completed was a great success. More so, we were able to dive into a project that had never been researched before and develop a new technique that could truly change the face of cold process soap making.

All in all, the experimentation involving saponification values and residual total alkali was a success. In addition, it is very important for handcrafted soapmakers to know that they need to completed each of their experiments based on their own materials. As stated before, each box of oil has its own SAP value and as a result, each SAP value plays a vital role to not only seizing properties but to the entire soapmaking process. As for residual total alkali, again each soapmaker's soap will have an individual RTA number; it should be noted that an accepted bar of soap has an RTA value of less than 1.0 ppt. Although our results were not below 1.0 ppt for any of our soaps, we stand confident that our experimental procedure is acceptable for determining RTA values.

<figureid="lab_eugenolstructure"><title>Structure of Eugenol</title> <mediaobject><imageobject><imagedata fileref="lab_eugenolstructure1.pdf" format="PDF" scale="50"/></imageobject></mediaobject> </figure>

<figure id="lab_hypothesisdiagram"><title>If Hypothesis Supported…</title> <mediaobject><imageobject><imagedata fileref="lab_ hypothesisdiagram1.pdf" format="PDF" scale="50"/></imageobject></mediaobject>

<figure id="lab_fastratediagram"><title>Scent Oil without Protection</title> <mediaobject><imageobject><imagedata fileref="lab_ fastratediagram1.pdf" format="PDF" scale="50"/></imageobject></mediaobject>

<figure id="lab_emulsification"><title>Emulsification to Produce Microcapsules</title> <mediaobject><imageobject><imagedata fileref="lab_emulsification1.pdf" format="PDF" scale="50"/></imageobject></mediaobject>

<figure id="lab_endpointcalc"><title>Example Calculation for the Endpoint of Eugenol</title> <mediaobject><imageobject><imagedata fileref="lab_endpointcalc1.pdf" format="PDF" scale="50"/></imageobject></mediaobject>

<figure id="lab_titrationcurve"><title>Simulated Titration Curve for 0.5 g eugenol with .3 m NaOH</title> <mediaobject><imageobject><imagedata fileref="lab_titrationcurve1.pdf" format="PDF" scale="50"/></imageobject></mediaobject>

<figure id="lab_curve"><title>Actual Titration Curve for 0.5 g eugenol with .3 m NaOH</title> <mediaobject><imageobject><imagedata fileref="lab_curve1.pdf" format="PDF" scale="50"/></imageobject></mediaobject>

<figure id="lab_freecalc"><title>Sample Calculation of % Free Eugenol</title> <mediaobject><imageobject><imagedata fileref="lab_freecalc1.pdf" format="PDF" scale="50"/></imageobject></mediaobject>