Thermal Analysis of Cosmetics – Useful Applications
On Demand Webinar

Thermal Analysis of Cosmetics

On Demand Webinar

The webinar "Thermal Analysis of Cosmetics" describes relevant applications for cosmetic industries

Thermal Analysis of Cosmetics
Thermal Analysis of Cosmetics

Cosmetics are used for skin care and for decorative purposes. Nowadays, they have become almost as important for men as for women. Cosmetics include skincare creams and makeup such as lipsticks, eye shadow, nail polishes and hair sprays.
Thermal analysis methods are used for studying raw materials as well as for developing and checking the quality of the final cosmetic products. The different methods are ideal for characterizing cosmetics and their ingredients.

In this Webinar, we will show how thermal analysis is used to analyze cosmetic materials and present typical examples of samples measured by DSC, TGA, TMA as well as by dropping point and melting point instruments.

33:34 min
English

The Webinar covers the following topics:

  • Introduction
  • Cosmetics applications
  • Thermal Analysis
  • Instruments and Applications
    - DSC
    - TGA
    - TMA
    - Thermal values (Dropping point, Melting Point)
  • Summary

The webinar titled "Thermal Analysis of Cosmetics" presents relevant applications for the characterization of cosmetic products and preparations as a function of temperature.

Thermal analysis of cosmetics

Cosmetics include all sorts of substances that are applied to different parts of the human body for enhancing people’s appearance, for skin-, hair- and nail-care, and for cleansing purposes.

This webinar presents a number of interesting application examples that demonstrate the use of thermal analysis techniques in the cosmetics industry. The applications have to do with the measurement of the physical properties and behavior of cosmetic preparations as a function of temperature and include melting, content determination, denaturation studies, curing reactions, and loss on drying.

 

Effects measured by thermal analysis

The most important effects that can be analyzed by DSC are the melting point, melting range, and melting behavior.

For TGA, the main applications are evaporation, content determination and filler determination.

A Dropping Point or DP instrument is used to detect the dropping point of waxes.

A Melting Point or MP instrument is used for automatic melting point determination and melting range detection.

TMA is normally used to study the expansion or shrinkage of materials.

Thermal Analysis of Cosmetics

Slide 0: Thermal Analysis of Cosmetics

 

Ladies and Gentlemen,

Welcome to the METTLER TOLEDO webinar on the “Thermal Analysis of Cosmetics”.

 

Cosmetics include all sorts of substances that are applied to different parts of the human body for enhancing people’s appearance, for skin-, hair- and nail-care, and for cleansing purposes.

The slide shows a good example - lipstick is widely used by women to make them look more attractive and to protect their lips. Cosmetic products like this are generally referred to as makeup.

 

During the course of this webinar, I would like to describe a number of interesting application examples that demonstrate the use of thermal analysis techniques in the cosmetics industry. The applications have to do with the measurement of the physical properties and behavior of cosmetic preparations as a function of temperature and include melting, content determination, denaturation studies, curing reactions, and loss on drying.

 

Slide 1: Contents

 

First, I want to discuss the most important analytical applications and effects shown by cosmetic substances and then describe the four main thermal analysis techniques that are used to investigate them.

The techniques are:

Differential Scanning Calorimetry or DSC;

Thermogravimetric Analysis, or TGA;

Thermomechanical Analysis, or TMA; and

Melting point and Dropping point instruments.

 

I will then present a number of application examples that illustrate the use of these techniques to analyze cosmetic products.

 

Finally, I would like to summarize the different thermal analysis techniques and their application fields, and list a number of useful references for further information and reading.

 

Slide 2: Introduction

Mascara is a well-known type of eye makeup that is used to darken, thicken and lengthen women’s eyelashes.

In the picture on the right, the mascara has become smeared from the eyelid to below the eye. This undesirable effect may have been caused through the wrong application procedure or through inadequate binding of the ingredients.

 

Slide 3: Introduction

The slide shows DSC heating curves of Vaseline, a brand of petroleum jelly that is often used in the cosmetics industry. The substance is a mixture of solid and liquid hydrocarbons with a broad melting range from well below zero up to about 70 degrees Celsius. The melting curves provide information about the composition of different samples and enable products to be modified and improved.

 

The diagram shows the first and second heating runs of two Vaseline products, A and B, measured from minus fifty degrees to plus eighty degrees at ten Kelvin per minute without removing the sample from the DSC. The results show that the melting behavior of each sample is different and that there are differences between the first and second heating runs.

These differences are associated with variations in crystalline content of the two products. Vaseline B melts over a significantly higher temperature range than Vaseline A and contains a greater portion of solid hydrocarbons.

DSC measurements give an insight into the melting range of products. This provides information on the liquid hydrocarbon content, which is responsible for lowering the melting range.

DSC is a very convenient technique for characterizing the properties of Vaseline or similar skin care products. It offers a rapid approach for monitoring products and for the development of new formulations.           

 

Slide 4: Analytical Applications

Thermal analysis has many potential applications and is used in practically all fields of the cosmetic industry. Thermal analysis techniques are easy to use and require only small amounts of sample.

 

The table summarizes different types of products ranging from skin-, eye-, nail- and hair-cosmetics and the applications most frequently performed to investigate them.

 

Thermal analysis methods are mainly used to measure the melting point, purity and content determination of skin- and eye-cosmetics. They can also provide information on protein denaturation, moisture determination and the shrinkage behavior of hair.

 

Slide 5: Thermal Analysis

What exactly do we mean by thermal analysis? The definition given by ICTAC is given in the slide, namely:

“A group of techniques in which a physical property of a substance is measured as a function of temperature whilst the substance is subjected to a controlled temperature program”.

The schematic diagram on the right shows such a simple linear temperature program.

 

The lower half of the slide illustrates typical events that occur when the sample is heated. For example, initial melting, in which the sample changes from the solid to the liquid state. If the sample is exposed to air or oxygen, it will start to oxidize and finally decompose. Thermal analysis techniques are widely used in research and development to investigate these effects.

 

Slide 6: Thermal Analysis

The slide shows the most important thermal analysis techniques used to characterize cosmetic substances and products. The techniques include:

 

Differential Scanning Calorimetry, or DSC. This is the most widely used thermal analysis technique. The picture shows a DSC sensor with a crucible containing a sample on the left, and a reference crucible on the right.

 

Thermogravimetric Analysis, or TGA. This technique continuously measures the weight of the sample using a highly sensitive electronic balance.

The picture shows a view of the sample holder with a crucible containing a sample. The standard crucibles are made of alumina.

 

Thermomechanical Analysis, or TMA, is used to measure dimensional changes of a sample.

The picture shows the sample support with a sample and the fused silica probe for measuring expansion or shrinkage.

 

And finally, Melting Point and Dropping Point instruments.

The picture shows a dropping point instrument with sample cups ready for insertion into the instrument. Two samples can be measured at the same time.

 

I will explain these techniques in more detail in the following slides and describe some application examples.

 

Slide 7: DSC

Let’s begin with Differential Scanning Calorimetry, or DSC. This technique allows us to determine the energy absorbed or released by a sample as it is heated or cooled.

 

The standard METTLER TOLEDO DSC 1 instrument measures from minus one hundred and fifty degrees Celsius to plus seven hundred degrees at heating rates of up to three hundred Kelvin per minute. Samples are normally measured in small crucibles made of aluminum, alumina or other materials, using sample amounts of one to ten milligrams.

 

The schematic diagram shows a typical DSC measurement curve of a crystalline substance. Exothermic effects point in the upward direction and endothermic effects downward. The curve is plotted as heat flow in milliwatts against temperature.

The different effects are numbered next to the curve and include:

One, the initial deflection or start-up transient of the DSC;

Two, the evaporation of moisture;

Three, part of the curve where no thermal effects occur. This is often referred to as the baseline and is proportional to the heat capacity of the sample;

Four, melting of crystalline fraction; and finally

Five, the onset of exothermic oxidation in air.

 

Slide 8: Differential Scanning Calorimetry (DSC)

The table summarizes the main analytical applications of DSC for cosmetic substances and products.

DSC is used to study the thermal behavior of cosmetic materials and to investigate events and processes that characterize them such as melting, crystallization and evaporation. DSC methods also provide information about the enthalpy of transitions and the influence of impurities on melting behavior. Most of the effects are related to enthalpy changes initiated by increasing or decreasing temperature.

The picture on the right shows a view of an open DSC furnace with sample and reference crucibles. The standard crucibles are made of aluminum.

 

Slide 9: Application 1: DSC                                          Identification of lipsticks

Lipsticks contain waxes, oils, pigments, and emollients commonly known as moisturizers. The products give the lips color, texture, and provide protection.

 

The first DSC application example shows the heating curves of five different lipsticks labeled Lipstick A, B, C, D, and E measured in the range minus fifty degrees Celsius to plus one hundred and forty degrees. Measurements like these are typically performed at heating rates of 5 or 10 Kelvin per minute.

The waxes and oils are initially solid but melt on heating, giving rise to endothermic peaks on the DSC curves. DSC analysis can be used as a quality control tool to obtain melting profiles and to characterize and distinguish between different lipsticks.

The results also provide information about the practical performance of lipsticks. For example, we expect a lower-melting lipstick like Lipstick D to spread well, and a higher-melting lipstick like Lipstick C to wear well.

 

Slide 10: Application 2: DSC                                        Melting behavior of beeswax

This application example shows DSC heating and cooling curves obtained from the analysis of a sample of beeswax.

Beeswax is a natural wax and consists mainly of hydrocarbons, free fatty acids and esters, and long chain alcohols. Both purified and bleached beeswax are used in the cosmetic industry, for example in lipsticks.

The diagram displays the first heating run, the cooling curve, and the second heating run of a sample of beeswax. The measurements were performed from minus thirty degrees Celsius to plus one hundred and thirty degrees at ten Kelvin per minute.

The first heating run in the middle of the diagram shows a broad melting peak with a maximum at about 64 degrees. This melting point is characteristic for this type of substance.

The top curve was obtained by cooling the sample at ten Kelvin per minute and shows the crystallization behavior. The bottom curve is the second heating run; the melting range is similar to that observed in the first heating run.

The experiment demonstrates that DSC can be used to characterize the melting behavior of beeswax and so gain a better understanding of its complex structure.

 

Slide 11: Application 3: DSC                            DSC fingerprints of O/W creams

This slide compares the melting behavior of two different cosmetic creams.

Creams are semi-solid emulsions and consist of mixtures of oil and water. Oil-in-water or O/W creams are more convenient to use than water-in-oil creams because they are less greasy and easier to wash off with water compared with water-in-oil creams, which are more moisturizing.

DSC measurements were performed to compare two oil-in-water (O/W) creams labeled in the diagram as Cream A and Cream B. Differences in the content of constituents can affect the consistency and quality of the finished cream formulation.

Both DSC curves exhibit a large melting peak in the range fifty-five to sixty-five degrees Celsius. This peak is due to the presence of glyceryl monostearate, which is an emulsifier and is commonly used as an excipient in creams. It acts as a thickening agent and stabilizer.

Cream A, however, has three additional peaks in the region 25 to 45 degrees, which are the typical melting points of mono-, di- and tri-glycerides. These inactive ingredients are used in the manufacture of O/W creams; with the addition of water, they form three-dimensional structures of different types and strengths.

The DSC curves can be used as fingerprints for characterizing and differentiating between different O/W formulations.

 

Slide 12: Application 4: DSC                                        Identification of PEG

Polyethylene glycols, or PEGs, are widely employed in cosmetic products as thickeners, solvents, softeners, and moisture-carriers. They often form the basis of cosmetic creams.

The diagram displays DSC curves of PEG samples with molecular masses ranging from four hundred to ten thousand (400 to 10,000). The melting points of the various polyethylene glycols increase with increasing chain length or increasing molecular mass. The longer the chain length, the less the melting points of the polyethylene glycols differ from one another.

The enthalpy of fusion cannot be used to differentiate the polyethylene glycols because the difference due to chain length is not significant and also depends on the crystallinity.

In summary, polyethylene glycols can be characterized by DSC by measuring their melting range, even though the differences become smaller with increasing chain length.

 

Slide 13: Application 5: DSC                            Hair protein denaturation study

The protein denaturation temperature of human hair can be investigated by DSC.

The diagram displays DSC heating curves of six hair samples labeled Sample A, B, C, D, E, and F. The curves exhibit three thermal events between 25 and 300 degrees Celsius.

The broad endothermic peak between 40 and 160 degrees (°C) is due to the elimination of water from the capillary tissue.

The endothermic peak observed at around 230 degrees (°C) is attributed to the melting of the alpha-form (α-form) crystallites in human hair keratin. The spiral form of alpha-keratin (α-keratin) gives the hair support.

The third effect is due to the overlapping of melting and possibly decomposition.

The DSC measurement curves show great similarity with regard to protein denaturation of the α-form crystallites in human hair keratin. The peak temperatures and the respective enthalpies are however not identical and allow the samples to be differentiated.

 

Slide 14: TGA/DSC

Now let’s turn our attention to Thermogravimetric Analysis, or TGA.

In this technique, the mass of a sample is measured as it is heated in a defined atmosphere. We simply put a few milligrams of a sample into a crucible, heat it and continuously record the weight change. The resulting weight-loss curve yields information about the composition of the sample.

The schematic diagram on the left shows a typical TGA measurement curve of a pharmaceutical preparation. The different effects are numbered next to the curve and explained in the table, namely.

 

One, heating begins and volatile components vaporize;

Two, loss of water of crystallization;

Three, at three hundred degrees Celsius, the sample undergoes decomposition; and

Four, inorganic fillers or a decomposition residue are left behind.

 

Some TGA instruments also provide simultaneous DSC or DTA curves and thereby supply information on effects due to enthalpy changes as we discussed earlier on.

 

Slide 15: Thermogravimetric Analysis (TGA)

TGA is used to investigate processes such as vaporization or decomposition.

The table summarizes the main analytical applications of TGA for cosmetic materials. The technique allows us to measure the evaporation, desorption and vaporization of materials quantitatively as well as to investigate thermal stability, reaction kinetics and reaction stoichiometry.

If necessary, evolved gases can be analyzed online using hyphenated techniques such as TGA-MS or TGA-FTIR.

The picture on the right side shows a view of the open furnace and the sample holder with positions for the sample and reference crucibles in a TGA/DSC instrument. The standard crucibles are made of alumina.

 

Slide 16: Application 1: TGA                Characterization of perfume delivery systems

The encapsulation of fragrances in suitable delivery systems is a topic of great importance for producers of perfumes. Thermogravimetric analysis an excellent technique to study the stability and release-behavior of fragrances from delivery systems.

In this example, the fragrance was trapped in polymeric nanoparticles. The delivery systems used two different types of nanoparticles based on crosslinked vinyl acetate.

 

In the first experiment, the encapsulated fragrance was measured isothermally at 25, 40 and 70 degrees Celsius (°C) using a delivery system in the rubbery elastic state. A bend appears in the TGA curve except for the measurement made at 25 degrees where the time chosen was not long enough. This bend occurs when evaporation is limited by diffusion processes in the polymer. In this delivery system, the evaporation is limited by the volatility of the volatile substance.

In the second experiment, the delivery system was in the glassy state. The results of measurements at 25, 40, 70, 90 and 180 degrees show an asymptotic approach to a constant, temperature-dependent composition. This indicates that part of the fragrance remains in the delivery system and is not released.

This means that, in this delivery system, evaporation is limited by the diffusion of the volatile substance within the nanoparticles and therefore takes longer than in the delivery system in the rubbery elastic state.

 

Slide 17: Application 2: TGA               Carbon black content of mascara

Thermogravimetric analysis can be use to determine the content of carbon black in mascara formulations and requires only a small amount of sample.

The slide displays the TGA heating curves of two different samples of mascara. Both curves exhibit several weight loss steps. The main ingredients of mascara are oils and waxes like beeswax, pigments and other preservatives. Carbon black is commonly used as the pigment.

In the diagram, the first and second weight-loss steps of both samples correspond to the evaporation and decomposition of waxes and preservatives.

The carbon black decomposes when the atmosphere is switched from nitrogen to air at 600 degrees Celsius. Evaluation of the step height yields carbon black contents of 0.7% for Sample A and 0.2% for Sample B.

The inorganic residue of both samples was approximately 12% at 800 degrees Celsius.

 

The United States Food and Drug Administration (FDA) code of federal regulations issues rules and regulations concerning the content of carbon black permitted in different cosmetics. We see that TGA can play an important role in checking that official limits are not exceeded.

 

Slide 18: TMA

We now move on to Thermomechanical analysis, or TMA. This technique measures the dimensional changes of a sample as it is heated or cooled under a defined force or load.

The schematic diagram shows a typical TMA heating curve of the coating of a capsule. The main effects are numbered next to the curve and explained in the table. These are:

One, expansion below the glass transition;

Two, softening with plastic deformation;

 

Slide 19: Thermomechanical Analysis (TMA)

The table lists some of the analytical applications of TMA for cosmetic materials.

The main application is the determination of the coefficient of thermal expansion, or CTE The technique is also excellent for determining glass transition temperatures, for studying softening behavior, and for measuring the swelling of materials in solvents at constant temperature.

The picture on the right shows the typical experimental setup with a ball-point probe resting on the sample specimen.

The following slide describes a specific application example.

 

Slide 20: Application 1: TMA                                       Shrinkage behavior of hair

The TMA application summarized in the following two slides illustrates the use of TMA for hair studies.

Nowadays, natural protein or keratin treatment is applied to straighten hair and stop hair from frizzing and at the same time make it look shinier. There are, however, risks associated with many types of treatments and customers should be fully aware of the process and possible adverse effects before choosing a safe treatment.

The shrinkage or expansion of hair can be easily characterized by TMA. Even very fine hairs can be mounted in the tension accessory using copper clips.

 

In this application example, two different hairs, one natural and one treated, were measured in the tension mode up to a temperature of 230 degrees Celsius

The first two curves are displayed up to 140 degrees and illustrate the shrinkage behavior of natural and treated hairs. Both hair samples shrink up to about 110 degrees due to drying. For natural hair, this amounts to about 0.7% of the original sample length, and for treated natural hair to about 1.0%.

 

The next slide displays the same TMA curves in the temperature range above 140 degrees.

 

Slide 21: Application 1: TMA                           Expansion coefficient of hair

The curves show that decomposition begins above 220 degrees Celsius (°C) and that the hairs rapidly tear. In this case, the mean value of the onset of melting calculated for natural hair was 223 degrees (°C) and for treated natural hair 226 degrees (°C). The standard deviation values obtained show excellent reproducibility. The thermal stability of the treated natural hair is therefore greater than for natural hair and confirms the positive effect of the hair treatment.

 

Slide 22: Thermal Values                                 Melting Point / Dropping Point

The innovative METTLER TOLEDO Melting Point and Dropping Point systems automatically determine the melting point or melting range of a substance, or the dropping point of a sample, with excellent accuracy. The instruments can however do much more, for example investigate color changes, clear points and decomposition temperatures with video recording.

The picture on the left shows a view of the Melting Point instrument with colored substances filled in six melting-point capillaries.

The picture on the right shows a Dropping Point instrument. The dropping point is the temperature at which the first drop of a melted sample flows through the 2.8-mm opening of a standard dropping-point sample-cup on slow heating.

 

Slide 23: Application:                                                  Dropping point of Vaseline

Let me now briefly introduce you to an application involving the Dropping Point instrument.

As I mentioned before, Vaseline is a mixture of solid and liquid hydrocarbons with a broad melting range from well below zero up to about 70 degrees Celsius. It protects the skin from effects of cold and extreme weather conditions and acts as a sealant for the skin.

The table summarizes the results of dropping point measurements performed according to the ASTM D 3954-94 standard. Four different samples were measured to study the reproducibility of the dropping point values. The results obtained were very reproducible. This means that the four samples can easily be differentiated for quality control purposes.

 

Slide 24: Summary

The table summarizes the most important thermal properties and events that characterize cosmetic materials as well as the techniques recommended to investigate them. A box marked red means that the technique is recommended as a first choice; a box marked blue indicates that the technique can also be used.

 

The most important effects that can be analyzed by DSC are the melting point, melting range, and melting behavior.

 

For TGA, the main applications are evaporation, content determination and filler determination.

 

A Dropping Point or DP instrument is used to detect the dropping point of waxes.

 

A Melting Point or MP instrument is used for automatic melting point determination and melting range detection.

 

TMA is normally used to study the expansion or shrinkage of materials

 

Slide 25: Summary

This slide presents an overview of the temperature ranges of the METTLER TOLEDO instruments for DSC, TGA, TMA and Thermal Values.

 

In general, DSC experiments are performed at temperatures between minus one hundred and fifty degrees Celsius and plus seven hundred degrees. The temperature ranges may be different if special equipment or accessories are used.

 

TGA measurements usually begin at room temperature. The maximum possible temperature is about sixteen hundred degrees. However, for cosmetic applications, a maximum temperature of 900 degrees (°C) is normally sufficient.

 

TMA experiments can be performed between minus one hundred and fifty degrees Celsius and plus eleven hundred degrees.

 

Thermal Values instrumentation includes Melting- and Dropping-Point instruments. The temperature range for the Melting-Point instrument is from room temperature up to four hundred degrees and for the Dropping-Point instrument from minus twenty to plus four hundred degrees.           

 

Slide 26: For More Information on Cosmetics

Finally, I would like to draw your attention to information about applications in the field of cosmetics that you can download from the Internet.

METTLER TOLEDO publishes articles and applications on thermal analysis twice a year in UserCom, the well-known METTLER TOLEDO biannual technical customer magazine. Back issues can be downloaded as PDFs from www.mt.com/ta-usercoms as shown in the slide.

 

Slide 27: For More Information on Thermal Analysis

In addition, you can download details about webinars, application handbooks or information of a more general nature from the Internet address given on this slide.

 

Slide 28: Thank You

This concludes my presentation on the Thermal Analysis of Cosmetics. Thank you very much for your interest and attention.

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