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to Flavors and Fragrances

Table of Contents Page1. Introduction to Thermal Analysis 2

2. Thermogravimetric Analysis (TGA) 2

3. Characterization of Delivery Systems by Thermogravimetry 3

3.1 Introduction 3

3.2 Experimental details 4

3.3 Theoretical principles 4

3.4 Results and discussion 5

3.5 Conclusions 8

3.6 Literature 8

4. Measurement of Dynamic Water Vapor Sorption Processesby Modified TGA

8

4.1 Introduction 8

4.2 TGA instrument modifications 9

4.3 Sorption experiments 10

4.4 Further applications 11

4.5 Acknowledgements 11

4.6 Literature 12

5. Other Thermal Analysis Techniques 12

5.1 DTA 12

5.2 SDTA 12

5.3 DSC 13

5.4 EGA 13

5.5 TMA 13

5.6 DMA 13

5.7 TOA 13

5.8 TCL 14

5.9 Application Overview 14

6. For More Information 15

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Introduction to Thermal Analysis

Thermal analysis is the name given to a group of techniques used to measure the physical and chemical properties of materials as a function of temperature. In all these methods, the sample is subjected to a heating, cooling or isothermal temperature program.

The measurements can be performed in different atmospheres. Usually either an inert atmosphere (nitrogen, argon, helium) or an oxidative atmosphere (air, oxygen) is used. In some cases, the gases are switched from one atmosphere to another during the measurement. Another parameter sometimes selectively varied is the gas pressure.

Thermogravimetric Analysis (TGA)

When a sample is heated, it often begins to lose mass. This loss of mass can result from vaporization or from a chemical reaction in which gaseous products are formed and evolved from the sample. If the purge gas atmosphere is not inert, the sample can also react with the gas. In some cases, the sample mass may also increase, e.g. in an oxidation reaction if the product formed is a solid.

In thermogravimetric analysis (TGA), the change in mass of a sample is measured as a function of temperature or time.

TGA provides information on the properties of the sample and its composition. If the sample decomposes as a result of a chemical reaction, the mass of the sample often changes in a stepwise fashion. The temperature at which the step occurs characterizes the stability of the sample material in the atmosphere used.Figure 1 shows a typical TGA curve. The composition of a material can be determined by analyzing the tem-peratures and the heights of the individual mass steps.

Volatile compounds such as water, residual solvents or added oils are evolved at relatively low temperatures. The elimination of such components depends on the gas pressure. At low pressures (vacuum), the correspond-ing mass loss step is shifted to lower temperatures, that is, vaporization is accelerated. The analysis of pyroly-sis reactions in an inert atmosphere allows the content (from the step height) and possibly even the type of material to be determined.

The carbon black or carbon fiber content of a sample can be determined from the height of the combustion step after switching to an oxidative atmosphere. The residual filler, glass fiber or ash is determined from the residue. Small changes in the measurement curve due to buoyancy effects and gas flow rate can be corrected by sub-tracting a blank curve.

TGA measurements are often displayed as the first derivative of the TGA curve, the so-called DTG curve. Steps due to loss of mass in the TGA curve then appear as peaks in the DTG curve. The DTG curve corresponds to the rate of change of sample mass.

The temperature range of the decomposition steps is influenced to a certain extent by the ease with which the gaseous products are able to diffuse out of the sample. When reactive atmospheres are used, the efficiency of gas exchange at the surface of the sample is crucial. The effects of diffusion on the measurement can be reduced by using suitable crucibles (e.g. crucibles with low wall-heights such as the 30-µL alumina crucible) and by suitable sample geometry (several small pieces or powder).

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Figure 1. Schematic TGA curve: 1 loss of mass due to the vaporization of volatile components; 2 pyrolysis in an inert atmosphere; 3 combustion of carbon on switching from an inert to an oxidative atmosphere; 4 residue.

In TGA, the change in mass of the sample is measured very accurately. Unfortunately, however, the technique does not provide any information about the nature of the gaseous decomposition products evolved. The products can however be analyzed by coupling the TGA to a suitable gas analyzer (evolved gas analysis, EGA).

Characterization of Delivery Systems by ThermogravimetryDr. V. Normand, K. Aeberhardt, Firmenich S.A., Geneva, Switzerland

Introduction

A “good” perfume is of course expected to provide a pleasant and distinctive odor. At the same time, the fra-grances should remain perceptible for as long as possible at a constant level of intensity. For this reason, the fragrances in perfumes are now being encapsulated in so-called delivery systems. The release of fragrances then occurs under control, allowing the perception of the perfume to be optimized with respect to intensity and lasting effect.

The encapsulation of fragrances in suitable delivery systems is therefore a topic of great importance for produc-ers of perfumes.

To identify the most suitable delivery system from the very large number of possible carriers available requires a rapid analytical screening technique that can describe the stability and release performance of a fragrance from the delivery system. Thermogravimetry (TGA) is an excellent technique for this purpose.

In this article, the release of Romascone® from three different delivery systems has been investigated using thermogravimetry. Romascone® is a fragrance that finds application in women’s perfumes. The delivery systems utilized three different types of polymeric nanoparticles based on crosslinked vinyl acetate.

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Experimental details

The investigations described here were performed with a METTLER TOLEDO TGA851/SDTAe (1) equipped with the small furnace. Samples masses of typically 8 mg (fragrance and nanoparticles together) were measured in aluminum crucibles. The mass fraction of the nanoparticles made up 40% of the total mass. The purge gas was nitrogen at 20 mL/min. The measurements were performed isothermally at different temperatures.

(1) This instrument was recently replaced with the TGA/DSC 1.

Theoretical principles

Evaporation of pure liquidsIf volatile compounds (such as fragrances) are measured in the TGA, a continual loss of mass is expected because the furnace is open and an equilibrium state is never reached.

This is because there is a steady transfer of molecules from the liquid phase to the gas phase. Molecules that reach the boundary layer between the liquid and the gas phase are swept out of the TGA furnace by the purge gas. Under isothermal conditions, this results in a constant rate of loss of mass which is determined by the vapor pressure of the compound and the mass transfer at the boundary layer, i.e.

where m is the mass, k is a constant that describes the mass transfer at the boundary layer between the liquid and the gas phase and Pvap is the vapor pressure.

Evaporation of a compound from a binary mixtureIn a mixture of two compounds, the chemical potentials of the two compounds in the mixture are reduced compared to the chemical potentials of the individual pure compounds.

In a binary mixture of two ideal non-interacting compounds with molecules of equal size, Raoult’s law predicts that the partial pressure of each compound is proportional to the mole fraction of each species in the mixture, that is:

Here P1 and P2 are the partial pressures of the two compounds, x1 and x2 are their mole fractions and P10 and P20 are the vapor pressures under normal conditions. For real compounds and assuming that only one substance is volatile, the Flory approximation applies and the partial pressure of the volatile component is given by:

Here f1 stands for the volume fraction of the volatile component (solvent) and c for the so-called Flory interaction parameter.

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aper For mixing of the two components to occur spontaneously, the mixing enthalpy (expressed here by the Flory interaction parameter, c must be small. Typically c varies between 0 (for good solvents, athermic mixing)

and 0.5 (for bad solvents, endothermic mixing). If the interaction parameter is greater than 0.5, demixing of the system is expected.

If the density of the two compounds in the mixture is about the same, the volume fraction of the solvent (f1) equals its mass fraction (w1). The rate of mass loss is then given by the equation:

If the first derivative of the TGA signal is plotted as a function of the mass fraction of the solvent, the parameters k · Pvap and c can be determined from a fit of this curve with the function according to eq 4.

If several isothermal measurements of the evaporation behavior are performed, the temperature dependence of the two parameters can be investigated. The following relationship is then expected for the interaction param-eter:

where W is the mixing enthalpy of the system, k the Boltzman constant and T the temperature.

Evaporation limited by diffusionIn eq 4 it is assumed that the evaporation rate of the volatile component is given solely by its vapor pressure. In a delivery system, the evaporation rate of the volatile component can also be limited by diffusion of the vola-tile molecules to the surface of the delivery system. In this case Fick’s law applies and we obtain:

Here D stands for the diffusion coefficient in the delivery system, which here depends on whether the delivery system is liquid, rubbery or glassy. A is the surface area of exchange, dc/dr the concentration gradient within the delivery system and a, a′ and a″ are constants that take into account the dependence of the diffusion on the volume or mass fraction of the volatile component in the delivery system.

If the delivery system consists of nanoparticles as in the case described here, it can be assumed that the concentration gradient within the particles is constant after a short time. In this case, the rate of mass loss is proportional to the diffusion coefficient.

Results and discussion

In the delivery system investigated here, Romascone® was encapsulated in nanoparticles made of different types of crosslinked vinyl acetate. With Samples A and B the degree of crosslinking was chosen so that the delivery system was in a rubbery elastic state. With Sample C, more heavily crosslinked nanoparticles were used so that the delivery system was in the glassy state.

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Evaporation of pure Romascone®

Figure 2 shows the isothermal TGA curves of pure Romascone® measured at different temperatures. The curves show that although the rates of mass loss for the various temperatures are different, they do not change during the experiment.

Physically, this means that the rate of evaporation is only determined by the temperature-dependent vapor pres-sure of the fragrance, which means that the evaporation process can be described by eq 1. If the slopes of the curves are plotted logarithmically as a function of the reciprocal temperature in Kelvin (red curve), the straight line expected from the Clausius-Clapeyron equation is obtained.

Evaporation of Romascone® from a rubbery delivery systemIn these experiments, the delivery system was in a rubbery-elastic state. The results (see Figure 3) show that in these samples a bend appears in the TGA curve after a certain time (except for the measurement at 25 °C; in this case the measurement time was not sufficiently long). This bend occurs when evaporation is limited by the transport processes in the polymer (diffusion). The slope of the TGA curves before the bend is not constant either.

According to eq 4, the evaporation rate depends on the Romascone® fraction (the evaporation rate corresponds to the slope of the TGA curve). The evaporation rate as a function of the Romascone® mass fraction can be calculated based on the amount of Romascone® present after a cer-tain time.

The corresponding data for the measurement at 40 °C together with the “best fit” curve according to eq 4 is displayed in Figure 4. In the same figure, the values found with the fit for k · Pvap for the three tem-peratures (25 °C, 40 °C and 70 °C) were compared with the corresponding values for pure Romascone® (calculated from the slopes of the mass loss curves in Figure 2). It was found that the values for k · Pvap for the delivery system are systematically lower than those for pure Romascone®.

The temperature dependence of the interaction parameter, c, is plotted for two different rubbery delivery systems in Figure 5. The two samples (Samples A and B) differ in the degree of crosslinking of the nanopar-ticles used for the delivery system (nanoparticles in Sample A are more strongly crosslinked than those in Sample B). The figure shows the expected linear increase with increasing temperature (see eq 5).

Figure 3. Evaporation of

Romascone® from a delivery system in the rubbery-elastic

state at various temperatures.

Figure 2. Evaporation of

pure Romascone® at various temperatures.

Figure 4. Rate of loss of mass of

Romascone® from a rubbery-elastic delivery

system at 40 °C. Inserted diagram:

the parameter k ·Pvap for the delivery system and

pure Romascone® at various temperatures.

Figure 5. Temperature dependence of the interac-tion parameter, c. The slope of the curve describes the interaction energy between Romascone® and the nanopolymer. It can be seen that the interaction energy between the more lightly crosslinked nanoparticles and Romascone® (Sample B) is larger than that between the more heavily crosslinked delivery system and Romascone®.

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aper Evaporation of Romascone® from a glassy delivery systemIn these measurements, the evaporation of Romascone® from a glassy delivery system (Sample C) was investi-

gated. The results of the measurements at different temperatures are displayed in Figure 6. It shows that in each case the system asymptotically approaches a constant, temperature-dependent composition. This means that in this delivery system, part of the Romascone® remains in the delivery system and is not released. The equilibrium concentration is however not reached with the timescale of the experiment.

The analysis of the data according to the approach of Flory (eq 4) gives unrealistic values for the unknown parameters k · Pvap and c. In fact, in this case the evaporation rate is determined by the diffusion of the Romascone® molecules to the surface of the nanoparticles practically from the beginning, so that the evapora-tion behavior of the fragrance is described by eq 6. Accordingly, a linear relationship between the logarithm of the evaporation rate and the volume fraction of the volatile components is expected.

The results in Figure 7 show that apparently two curves with different slopes are required to describe the data. The reason for this behavior is that Romascone®

acts as a plasticizer for the nanoparticles. Depending on the Romascone® fraction and the temperature, the delivery system is either in the glassy or rubbery state, which leads to the different slopes in the figure: the blue curves describe data for a delivery system in the rubbery elastic state, and the red lines for a deliv-ery system in the glassy state. Whether the delivery system is in the glassy or rubbery state depends on the actual Romascone®mass fraction at a particular temperature. The point of intersection of a red and the corresponding blue curve therefore corresponds to the “critical” Romascone® mass fraction for the tempera-ture: above this mass fraction the delivery system is rubbery elastic, and below it is glassy.

The figure shows that at high temperatures and high Romascone® fractions, the rate of mass loss is higher. In the same way, it is clear that the diffusion of Romascone® in a glassy delivery system is apprecia-bly slower than in the rubbery-elastic delivery system.

The different slopes at the different temperatures there-fore describe the temperature dependence of the dif-fusion coefficient. If the logarithm of the slopes of the curves in Figure 7 are displayed as a function of the reciprocal temperature, the curves shown in Figure 8 are obtained. The evaporation process can therefore be understood as an activated process according to the equation:

Here a(T) represents the slope of the mass loss curve, Ea is the activation energy, R the gas constant and T the temperature.

The blue curve describes the evaporation from the rubbery-elastic delivery system, and the red the evaporation from the glassy delivery system. The two curves have approximately the same slope. This indicates that the activation energy of the evaporation processes is independent of the state of the delivery system (rubbery-elastic or glassy), at whose surface the evaporation takes place. Evaluation of the data gives an activation energy of about 17.2 kJ/g.

Figure 6. Evaporation of Romascone® from glassy polymeric nanoparticles.

Figure 7. Evaporation of Romascone® from a glassy delivery system at different temperatures.

Figure 8. Arrhenius diagram for glassy (red curve) and rubbery elastic (blue curve) delivery systems. The activation ener-gy for both delivery systems is about 17.2 kJ/g.

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Conclusions

The evaporation of volatile substances from delivery systems can be investigated by thermogravimetry. In the example, the evaporation of Romascone® from nanoparticles based on crosslinked vinyl acetate was investigated.

If the delivery system is in the rubbery-elastic state, the evaporation of Romascone® can be described by the Flory theory (evaporation is limited by the volatility of the volatile substance).

If the delivery system is in the glassy state, the evaporation is limited by the diffusion of the volatile substance within the nanoparticles and takes correspondingly longer.

The method described here is simple and allows delivery systems to be quickly characterized and optimized.

Literature

[1] L. Ouali, G. Léon, V. Normand, H. Johnsen, A. Dyrli, R. Schmid and D. Benczédi, Mechanism of Romascone® Release from Hydrolized Vinyl Acetate Nanoparticles, Polymers for advanced Technologies, 2006 (17), 45-52.

Source: METTLER TOLEDO TA UserCom 25 (2007)

Measurement of dynamic water vapor sorption processes by modified TGA

M. Schudel, J.B. Ubbink, and Ch. Quellet, Givaudan Dübendorf AG, CH-8600 Dübendorf, Switzerland

Introduction

This article describes the modification of a TGA instrument to measure dynamic water vapor sorption processes (Dynamic Vapor Sorption, DVS). Instrumentation of this type allows the change in mass of a sample in powder form to be measured as a function of relative humidity and time [1]. This is of particular interest because many water-soluble and powdered foodstuffs are moisture sensitive. If such foodstuffs are stored under conditions where the humidity is too high, they can become lumpy, undergo phase changes and recrystalliza tion, lose aroma or go bad due to the growth of molds.

The DVS method described here is one of many methods that can be used to characterize the behavior of pow-der systems with regard to humidity [1]. Compared with conventional methods, the DVS technique has the advantage that it is rapid and less labor-intensive [1]. With a DVS instrument, it is possible to measure a com-plete sorption isotherm quasi fully automatically with a single sample, and at the same time follow the sorption process dynamically, i.e. as a function of time. A commercially available DVS instrument, however, costs several times more than a standard TGA instrument. We therefore decided, together with METTLER TOLEDO, to modify a TGA instrument to a DVS instrument so that it could be used for either DVS or TGA measurements as desired. An additional advantage is that important thermodynamic quantities such as the enthalpy of sorption can be deter-mined from a combined DVS/TGA measurement. This is not directly possible with conventional DVS instruments.

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aper TGA instrument modifications

A METTLER TOLEDO TGA/SDTA851e/LF1100 (1) was chosen for the construction of the DVS instrument. The large gas outlet makes this model especially suitable for the modifications required. A specially built water vapor gen-erator equipped with a humidity sensor (Rotronic AM3 hygro meter, Rotronic AG) (2) was connected to this gas outlet. The humidity sensor is located in the furnace chamber and is positioned close to the crucible holder with the sample. The humidified gas is passed from the water vapor generator via silicone rubber tubing directly into the furnace chamber. The furnace chamber in fact serves as a controlled environmental chamber. It is main-tained at 25°C by means of a thermostat (Fig. 9) during the DVS measurement.

(1) Current instrument model is TGA/DSC 1(2) Currently it is recommended to use the MHG 32 (ProUmid) vapor generator

The measurement signal of the humidity sensor is transferred to a PC and regulates the water vapor generator so that defined humidity steps can be set. Technical details of the DVS instrument are listed in Table 1.

This type of humidity-sorption measurement places special demands on the thermobalance:• Thehumiditysensorwithits4-pole

cable must be located in the furnace chamber• Thehumidifiedgasmustbesuppliedwithoutcondensationor

cooling oc curring• Theexhaustgasshouldflowoutofthecellinadefinedway

without condensation so that further analysis, e.g. online GC-MS, is possible.

To meet these requirements, a special furnace lid with O-ring seal and wide-diameter stainless steel outlet tube (internal diameter 6.8 mm) was made. The outlet tube is maintained at constant temperature by a heat exchanger. A thermostat regulates the temperature at 25.0 °C and is also used for the water vapor generator, the heat exchanger of the furnace, and the furnace flange assembly. A second thermostat maintains the balance housing at 22.0 °C. The humidity sensor cable as well as the two supply and exhaust gas tubes pass through the outlet tube. They are sealed in the outlet tube with epoxy resin. The position of the humidity sensor can be checked when the furnace is open using a dentist’s mirror. Neither the sensor nor the two tubes should touch the crucible containing the sample or the crucible holder. A flow of 20 ml/min dry gas was used to protect the micro-balance from moisture.

The water vapor generator was specially developed for the DVS modification. The most important parts of the generator are the control unit (PC hardware and software) and the water vapor generator with its humidifying and mixing units.

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Fig. 9. Schematic diagram of the DVS instrument.

Table 1. Technical details of the DVS instrument.

Relative humidity range 1-93%

Humidity stability ± 0.1-1%

Temperature range 0-40 °C

Weighing capacity 1 g

Balance resolution ± 0.1 µg

Max. number of sorption steps 500

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The dry inlet gas (N2) is divided into two parts. One part is at 100% RH (relative humidity), while the other part remains dry (< 2% RH). The desired relative humidity in the furnace chamber is adjusted by mixing dry and moist gas in the right proportions. The mixing ratio from “dry” to “wet” is set by means of computer-controlled valves triggered by the RH program (humidity steps). The control program was written with LabView 4.1 software (National Instruments, USA). The total flow of humidified gas into the TGA furnace chamber was usually 200 ml/min.

Sorption experiments

Dynamic sorption curvesFirst the dynamic sorption curve of microcrystalline cellulose RM 302 (LGC Teddington Ltd., UK) was measured as a standard. The results showed that our DVS measurements were in good agreement with the literature values [2].

As a further example, the humidity sensitivity of maltodextrin (modified starch) was also investigated. This is illustrated in Figure 10, which shows the dynamic water vapor sorption on maltodextrin with a dextrose-equiv-alent (DE) of 6. After drying at < 2% RH over a period of several hours, the humidity is increased to 85% RH in steps of 10% RH (final step 5% RH). The time interval between the individual humidity steps was chosen so that constant mass (equilibrium) was reached.

Fig. 10. Dynamic water vapor sorption on maltodextrin DE 6.

Sorption isothermsThe sorption isotherms can now be calculated from the curve shown in Figure 10 using the end point of each sorption step (equilibrium reached) and the Guggen heim, Anderson and deBoer (GAB) equation [3]. From this one obtains the following GAB parameters for maltodextrin (DE 6): ww,mon 4.1 10-2 wt%; CG 5.6, K 0.97; and AGAB 1.4 m2 g-1. These are typical values for starch products [4]. This of course assumed that equilibrium was reached at the end point of each sorption step. In practice, this is not always so easy because equilibration was not always attained at the same rate (waiting times of different duration, no decision-making criteria in the current software). For this reason, with new materials, it is advisable to perform a trial sorption measurement beforehand to determine the times to reach (approximate) equilibrium.

DiffusionThe dynamic process of the sorption of water on powders can be looked upon as a diffusion process in which water penetrates into the surface layer air/powder to an extent depending on the sensitivity of the powder toward humidity. The dynamic course (i.e. as a function of time) of the sorption process of a particular step can there-fore be described with the aid of diffusion equations. The diffusion coefficient, Dw, of water in these thin layers can be then calculated as a characteristic quantity [5], [6]. This is an important advantage of the dynamic sorp-tion measurement technique using a DVS instrument compared with conventional gravimetric methods.

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Sorption enthalpyAnother application of dynamic sorption measurements is the simultaneous determination of the sorption enthalpy and moisture content, ww , with variable humidity. This quantity allows the temperature dependence of watervaporsorptiontobedescribedatanyhumidity.Theisostericsorptionenthalpy(∆sorption H°) ww of water on a powder can be determined from the temperature dependence of a sorption isotherm [7]. This is however relatively time consuming because several sorption isotherms have to be measured at different temperatures.

Alternatively,thesorptionenthalpy,∆sorption, i→i+1H°,ofarelativelysmallsorptionstep,∆i→i+1ww , can be mea-sured, whereby the heat flow due to sorption of water can be followed using the sample temperature sensor of the TGA instrument (SDTA®). The resulting sorption enthalpy is given by the equation

Here∂T(t)/∂tisthetemperaturechangeofthesampleperunitoftime,mP is the mass of the sample and C a constant that can be determined by calibration with pure water (drop of water in an aluminum crucible on the crucibleholder,nopowder).Thesmallertheinterval,∆i→i+1 ww , chosen for a particular value, ww , the better ∆sorption, i→i+1H°canbeusedasestimatefor(∆sorption H°) ww .

In a measurement similar to that shown in Figure 10 on maltodextrin (DE 6), the temperature, T, was measured as a function of time, t, for the humidity step 80 to90%RH.Thisenabledthesorptionenthalpy,∆80→90%RH H°, to be calculated using equation (8), with C equal to 1.05 . 102 kJ mol-1 K-1 g, mP31.1mgand∆ i→i+1ww 27.7 wt%. The value of 40.3 kJ mol-1obtainedfor∆80→90%RH H° is in good agreement with literature values for modified starch(∆50→60%RH H° of 42.9 kJ mol-1) [4].

Further applications

In the analysis of aroma powders, water sorption, aroma loss and structural changes such as phase changes overlap one another. Online GC-MS, for example, should therefore be used to measure the amount of aroma evolved. This information allows the release behavior of aroma powders to be relatively easily determined or estimated.

The results can then also be described by diffusion models [6], [8].

There is also the possibility of “storing” the sample for a longer period of time (several days) at constant humid-ity (e.g. 70% RH) and temperature (e.g. 37 °C) in the DVS/TGA instrument. This allows storage tests to be simulated and losses of aroma to be followed online using GC-MS.

Acknowledgements

The authors wish to thank the many people involved in this work at Givaudan Düben dorf AG: in particular, Mr. Ch. Montagner and R. Graf of the Creation Tools group for the design and construction of the water vapor generator, and Mr. J. Bouwmeesters of the Delivery Systems group for performing the sorption experiments. Finally, we owe our thanks to the management of Givaudan Dübendorf AG for their financial support for the development of this instrument.

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Literature

[1] Gál, S., Recent Advances in Techniques for the Determination of Sorption Isotherms, in Water Relations in Food, R.B. Duckworth, ed., Academic Press, London (1975).

[2] Jowitt, R., and P.J. Wagstaffe, Community Bureau of Reference, EUR 12429EN.[3] Kontny, M.J., and G. Zografi, Drugs Pharm. Sci., 70 (1995) 387.[4] Mulet, A., J. García, R. Ranjuán, J. Bon, J. Food Sci., 64 (1999) 64.[5] Ogawa, T., T. Nagata, and Y. Hamada, J. Appl. Polym. Sci., 50 (1993) 981.[6] Crank, J., The Mathematics of Diffusion, Reprint 2nd ed., Oxford University Press, Oxford (1992).[7] Atkins, P.W., Physical Chemistry, 5th ed. Oxford University Press, Oxford (1995).[8] Fan L.T., S.K. Singh, Controlled release, a quantitative treatment, Springer, Berlin (1989).

Source: METTLER TOLEDO TA UserCom 17 (2003)

Other Thermal Analysis Techniques

DTA

Differential Thermal AnalysisIn DTA, the temperature difference between the sample and an inert reference substance is measured as a func-tion of temperature. The DTA signal is °C or K. Previously, the thermocouple voltage in millivolts was displayed.

SDTA

Single DTAThis technique was patented by METTLER TOLEDO and is a variation of classical DTA that is particularly advan-tageous when used in combination with thermogravimetric analysis. The measurement signal represents the temperature difference between the sample and a previously measured and stored blank sample.

DTA and SDTA allow you to detect endothermic and exothermic effects, and to determine temperatures that characterize thermal effects.

DSC

Differential Scanning Calorimetry.In DSC, the heat flow to and from a sample and a reference material is measured as a function of tempera-ture as the sample is heated, cooled or held at constant temperature. The measurement signal is the energy absorbed by or released by the sample in milliwatts.

DSC allows you to detect endothermic and exothermic effects, measure peak areas (transition and reaction enthalpies), determine temperatures that characterize a peak or other effects, and measure specific heat capacity.

EGA

Evolved Gas AnalysisEGA is the name for a family of techniques by means of which the nature and/or amount of gaseous volatile products evolved from a sample is measured as a function of temperature. The most important analysis tech-

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niques are mass spectrometry and infrared spectrometry. EGA is often used in combination with TGA instruments because TGA effects involve the elimination of volatile compounds (mass loss).

TMA

Thermomechanical AnalysisTMA measures the deformation and dimensional changes of a sample as a function of temperature. In TMA, the sample is subjected to a constant force, an increasing force, or a modulated force, whereas in dilatometry dimensional changes are measured using the smallest possible load.

Depending on the measurement mode, TMA allows you to detect thermal effects (swelling or shrinkage, soften-ing, change in the expansion coefficient), determine temperatures that characterize a thermal effect, measure deformation step heights, and to determine expansion coefficients.

Figure 11.The techniques used to measure polyamide 6 show different thermal effects. DSC: melt-ing peak of the crystalline part; TGA: drying and decomposition step; TMA: softening un-der load.

DMA

Dynamic Mechanical AnalysisIn DMA, the sample is subjected to a sinusoidal mechanical stress. The force amplitude, displacement (defor-mation) amplitude, and phase shift are determined as a funtion of temperature or frequency. DMA allows you to detect thermal effects based on changes in the modulus or damping behavior.

The most important results are temperatures that characterize a thermal effect, the loss angle (the phase shift), the mechanical loss factor (the tangent of the phase shift), the elastic modulus or its components the storage and loss moduli, and the shear modulus or its components the storage and loss moduli.

TOA

Thermo-optical AnalysisBy TOA we mean the visual observation of a sample using transmitted or reflected light, or the measurement of its optical transmission by means of hot-stage microscopy or DSC microscopy. Typical applications are the investigation of crystallization and melting processes and polymorphic transitions.

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TCL

ThermochemiluminescenceTCL is a technique that allows you to observe and measure the weak light emission that accompanies certain chemical reactions.

Application Overview

Application overview showing the thermal analysis techniques that can be used to study particular properties or perform certain applications.

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Property or application DSC DTA TGA TMA DMA TOA TCL EGA

Specific heat capacity ••• •

Enthalpy changes, enthalpy of conversion ••• •

Enthalpy of melting, crystallinity ••• •

Melting point, melting behavior (liquid fraction) ••• • • •••

Purity of crystalline non-polymeric substances ••• ••• •

Crystallization behavior, supercooling ••• • •••

Vaporization, sublimation, desorption ••• • ••• ••• •••

Solid–solid transitions, polymorphism ••• ••• • •••

Glass transition, amorphous softening ••• • ••• ••• •

Thermal decomposition, pyrolysis, depolymerization, and degradation

• • ••• • • •••

Temperature stability • • ••• • • •••

Chemical reactions, e.g. polymerization ••• • • •

Investigation of reaction kinetics and applied kinetics (predictions)

••• • ••• •

Oxidative degradation, oxidation stability ••• ••• ••• • •••

Compositional analysis ••• ••• •••

Comparison of different lots and batches, competitive products

••• • ••• • • ••• • •••

Linear expansion coefficient •••

Elastic modulus • •••

Shear modulus •••

Mechanical damping •••

Viscoelastic behavior • •••

•••means“verysuitable”,•means“lesssuitable”

15White Paper METTLER TOLEDO

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Outstanding ServicesMETTLER TOLEDO offers you valuable support and services to keep you informed about new developments and help you expand your knowledge and expertise, including:

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The following Collected Applications Handbooks can be purchased as color-printed books:

Title Order Number Title Order Number

Thermal Analysis in Practice 51725244 Elastomers Vol. 1 51725057

Validation in Thermal Analysis 51725141 Elastomers Vol. 2 51725058

Food 51725004 Elastomers Vol. 1 and Vol. 2 51725061

Pharmaceuticals 51725006 Thermosets Volume 1 51725067

Thermoplastics 51725002 Thermosets Volume 2 51725068

EGA Evolved Gas Analysis 51725056 Thermosets Volume 1 + 2 51725069

TutorialThe Tutorial Kit handbook with twenty-two well-chosen application examples and the corresponding test sub-stances provides an excellent introduction to thermal analysis techniques and is ideal for self-study. www.mt.com/ta-handbooks

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51140879

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GTAPTM

1Evaluation

2Selection

5Routine

Operation

3Installation

& Qualification

4Training

www.mt.comFor more information

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Subject to technical changes©11/2013 Mettler-Toledo AG

Good Thermal Analysis Practice™ GTAP™ is a 5 step approach to improve your Lab workflow. METTLER TOLEDO offers comprehensive support for all steps to ensure that you invest in the right area and minimize risks with targeted efforts.GTAP supports you for•Compliancewithregulations•Preservationoftheaccuracyandprecisionofresults•Increasedproductivityandreducedcosts•Professionalqualificationandtraining

1. Evaluation – Thorough requirement analysisSelecting the right analytical sys-tem is not only about knowing your current needs, but must also take into account future requirements.

2. Selection – Optimal instrument selectionOnce actual and future needs have been clearly identified, the best suitable Thermal Analysis system can be selected.

3. Installation – Professional setup and proof of accuracy Installation is crucial to guarantee the best working conditions as well as longevity of the selected system. After installation, the system has to be qualified for operation.

4. Calibration – Well trained users Training of the users is very important to achieve the best possible results. METTLER TOLEDO offers different training possibilities.

5. Routine Operation – Consistent performance and accuracyRegularly maintained instruments reduce the likelihood of day-to-day measurement errors, preventing potentially expensive follow-up costs.

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