Thermal Analysis of Biopolymers
On Demand Webinar

Thermal Analysis of Biopolymers

On Demand Webinar

"Thermal Analysis of Biopolymers" presents techniques used to characterize biopolymers

Thermal Analysis of Biopolymers
Thermal Analysis of Biopolymers

In the webinar titled "Thermal Analysis of Biopolymers", we describe a number of techniques and methods that can be used to characterize the physical properties of biopolymers.

What is a biopolymer?

The terms biopolymers and bioplastics are not precisely defined and are often used differently. Frequently, the two expressions are used to mean plastics from bio-based raw materials, or to mean biologically degradable plastics. Many biopolymers satisfy both points.

With bio-based plastics, the main focus is on the source of the starting material, namely renewable raw materials in contrast to fossil petroleum oil. Not all bio-based polymers are biodegradable.

Biodegradable plastics are a source of food and energy for microorganisms and are decomposed through the metabolism of microorganisms or their enzymes to form carbon dioxide, water and biomass. These polymers are not necessarily produced from renewable raw materials.

Thermal analysis of biopolymers

The most important effects that can be analyzed by DSC are the glass transition, melting, crystallization behavior, reaction enthalpies and kinetics, and the influence of fillers.

For TGA, the main applications are content analysis and thermal stability.

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

DMA is the best method for characterizing the frequency-, force-, and amplitude-dependent mechanical behavior of materials.


Thermal Analysis of Biopolymers

Thermal Analysis of Biopolymers


First, I would like to differentiate between biopolymers and conventional polymers.


I then want to discuss some questions regarding the use of different thermal analysis techniques for the analysis of biopolymers.


After this, I will present a number of examples that illustrate how thermal analysis can be used to investigate the physical behavior of biopolymers.


Finally, I will 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

We encounter plastics everywhere in our daily life. The advantages of plastics are readily apparent – plastic materials are light, have a long life cycle, are cheap, and are extremely versatile.


In this connection, I want to discuss the production and disposal of polymers.

Conventional synthetic plastics are mainly produced from petroleum oil and natural gas. If renewable raw materials are used, the consumption of fossil raw materials can be reduced.

About 30% of the worldwide plastics production is used for packaging materials and throw-away articles that are disposed of within one year of their manufacture.


Although significant advances have been made in disposal and recycling in recent decades, a large part of the worldwide plastic waste still ends up uncontrolled in the environment as the picture of the polluted seashore shows.

The enormous amount of plastic waste drifting around in the oceans is now recognized as a major environmental problem.


Biopolymers could be an alternative to the long-life-cycle polymers manufactured from oil and fossil raw materials – that is, polymers made from biobased raw materials, or polymers that are degradable. This is the topic of the next slide.


Slide 3: Introduction

The terms biopolymers and bioplastics are not precisely defined and are often used differently. Frequently, the two expressions are used to mean plastics from biobased raw materials, or to mean biologically degradable plastics. Many biopolymers satisfy both points.


With biobased plastics, the main focus is on the source of the starting material, namely renewable raw materials in contrast to fossil petroleum oil. Not all biobased polymers are biodegradable.

Biodegradable plastics are a source of food and energy for microorganisms and are decomposed through the metabolism of microorganisms or their enzymes to form carbon dioxide, water and biomass. These polymers are not necessarily produced from renewable raw materials.


The slide shows typical representatives of each group - we will encounter one or the other again in the applications.


Biopolymers are by no means a modern new discovery. One of the first polymers was natural rubber or caoutchouc and is a biopolymer; cellulose acetate has been made from the cellulose of plants for more than 150 years.


Slide 4: Thermal Analysis

What exactly do we mean by thermal analysis? The definition given by the International Confederation of Thermal Analysis and Calorimetry is:

“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 a simple linear temperature program.


The lower half of the slide illustrates typical events that occur when a 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. We use thermal analysis techniques to investigate these effects.


Slide 5: Thermal Analysis Techniques

Let’s now take a look at the individual thermal analysis techniques.


The slide shows the most four most important techniques used in thermal analysis to characterize biopolymers, namely:


Differential Scanning Calorimetry, or DSC. This is the most widely used technique. The picture shows a DSC sensor with a crucible containing a sample (colored red), and a reference crucible.

In contrast to conventional DSC, the Flash DSC provides heating and cooling rates that are more than one thousand times higher.


Thermogravimetric Analysis, or TGA. The picture shows the TGA balance with its automatic internal ring weights.


Thermomechanical Analysis, or TMA. The picture shows the sample area with a sample (colored red) and the quartz probe and sensor.


And finally, Dynamic Mechanical Analysis, or DMA. The picture shows one of the several different sample-clamping assemblies.


Slide 6: Thermal Analysis of Biopolymers

The slide displays an overview of typical measurement curves of polylactide, or PLA for short, obtained from all four techniques.

The TGA curve at the top records the change in mass of a sample as a function of temperature and allows you to derive information on its stability and decomposition behavior.

The DSC curve provides information about transition temperatures such as the glass transition temperature (Tg), the melting point (Tm), the degree of crystallinity, and transition enthalpies, all of which influence the processing conditions.

TMA and DMA are used to determine mechanical properties such as the coefficient of expansion or the elastic modulus. These methods of course also supply transition temperatures. The measurements can also be performed under different atmospheric conditions, for example to study the influence of relative humidity on mechanical properties.


Slide 7: Industries and Applications

Biopolymers have very many potential applications and are used in practically all industries and in our daily lives.


Biodegradable polymers are particularly important if we want the material to decompose after a certain time when it has fulfilled it purpose. This is the case with medical implants or threads as well as films and packaging for use in agriculture and domestic households.


Biopolymers are also used wherever the advantages of polymers such as low production price, low weight, colorful design and versatility are of advantage.


I now want to look at the individual thermal analysis techniques and discuss some typical application examples.


Slide 8: Differential Scanning Calorimetry (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.


DSC instruments exist in different versions depending on their temperature range, their heating and cooling rates, and the type of sensor used:


The standard METTLER TOLEDO DSC instrument measures from negative temperatures close to the boiling point of liquid nitrogen to about plus seven hundred degrees (700 °C) at heating rates of up to several hundred Kelvin per minute. Samples are normally measured in small crucibles made of aluminum, alumina or other materials, using sample amounts between two and twenty milligrams.


The fast scanning METTLER TOLEDO Flash DSC 1 expands the heating rate to two million four hundred thousand Kelvin per minute (2,400,000 K/min) and the cooling rate to two hundred and forty thousand Kelvin per minute (240,000 K/min). To achieve this, the Flash DSC uses very small sample sizes of about one hundred nanograms (100 ng) and no sample crucibles - the sample is in direct contact with the sensor. The ultra-fast heating and cooling rates allow industrial process conditions to be simulated in which materials undergo extremely rapidly cooling.


Another useful DSC technique is high-pressure DSC or HPDSC for short. The METTLER TOLEDO HP DSC 1 can analyze samples under inert or reactive gases at high pressures. This suppresses undesired vaporization of samples or enables the stability of samples under increased oxygen pressures to be studied.


The schematic curve on the left shows a typical DSC measurement curve of a semicrystalline polymer. Exothermic effects point in the upward direction and endothermic effects downward. The different effects are numbered next to the curve and explained in the table, namely

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

Two, the baseline where no thermal effects occur;

Three, a glass transition with enthalpy relaxation;

Four, cold crystallization;

Five, melting of the crystalline fraction; and finally

Six, oxidative exothermic decomposition.


Slide 9: Differential Scanning Calorimetry (DSC)


Differential Scanning Calorimetry is used to study thermal behavior, reaction kinetics and events such as melting, solid-solid transitions, or chemical reactions.


The table summarizes the analytical applications of DSC for biopolymers.

The main applications have to do with melting behavior and the glass transition temperature. Several standard procedures are routinely used to determine oxidation stability and the influence of additives. DSC measurements also provide information about the composition and the thermal history of materials.

The picture on the right of the slide shows a view of an open DSC furnace with sample and reference crucibles.


Slide 10: Application1: DSC

Now let’s look at some DSC applications involving biopolymers:


The slide shows the first heating run of a semicrystalline polylactide pellet measured at a heating rate of 10 Kelvin per minute (10 K/min). The curve exhibits two main thermal events:

First there is the glass transition in the temperature range 60 to 80 degrees Celsius (60 to 80 °C). This is characterized by an endothermic displacement in the heat flow curve with a relaxation peak that can vary in intensity. The glass transition temperature occurred at 68 degrees (68 °C) and the delta cp step height (cp) was zero point one four joules per gram Kelvin (0.14 J/gK).

After the glass transition, reorganization processes occur in the polymer crystals in which both endothermic melting and exothermic crystallization take place. The two processes overlap each other. In the temperature range 160 to 180 degrees, the polymer crystals finally formed melt with a melting peak maximum at 172 degrees. The enthalpy of fusion normalized to mass was 42 point 5 joules per gram (42.5 J/g).


The example shows the type of information that can be obtained from a single DSC measurement. The measurement is rapid and only a small amount of sample is needed.


Slide 11: Application 2: HPDSC

Depending on the process, the temperature range of processing is restricted by the glass transition temperature or the melting point.

If the materials involved are temperature sensitive and careful processing is required, it is often beneficial to lower these two temperatures. This can be done with some polymers by processing the material in a carbon dioxide atmosphere.

In this example, polylactide was measured in the high-pressure DSC. The CO2 pressure was varied. The measurement curves displayed are second heating runs.

The curves show quite clearly that the glass transition temperature, the crystallization peak and the melting point are shifted to lower temperatures at higher CO2 pressures.

This effect could be used to advantage for example for packaging pharmaceutical drugs.


Slide 12: Application 3: Flash DSC

Polymers undergo reorganization processes at the heating rates normally used in conventional DSC instruments. The melting point measured in the first heating run does not correspond to the melting point of the original polymer crystals. To suppress reorganization, much higher heating rates are necessary: These can easily be achieved using the Flash DSC 1.

The slide displays DSC and Flash DSC measurement curves of a bio-copolymer as an example. The first heating run in the DSC at 10 Kelvin per minute (10 K/min) shown in the upper diagram exhibits a peak melting point of 96 degrees Celsius (96 °C).

In the lower diagram, we see the first heating run measured using the Flash DSC 1. The heating rate was one thousand Kelvin per second (1000 K/s), or sixty thousand Kelvin per minute (60,000 K/min). This is fast enough to suppress reorganization. In this case, the melting point of 81 degrees (81 °C) is lower. The enthalpy of melting was about the same in both cases.

To obtain good thermal contact for the first heating run, a small amount of a special oil was applied between the sample and the sensor.


Slide 13: Thermogravimetric Analysis (TGA)

Now let’s turn our attention to thermogravimetric analysis, or TGA.


In this technique, the mass of a sample is continuously measured as it is heated or cooled in a defined atmosphere. We simply put a few milligrams of the sample into a crucible, weigh the sample, heat it and record the change in mass. From this, we can obtain information about the composition of the sample such as the polymer and filler content.


The schematic curve on the left shows a typical TGA measurement curve of a polymer. Initially, before the heating ramp begins, the TGA measures the mass of the sample. At the end of the measurement at about one thousand degrees Celsius (1000 °C), inorganic fillers such as silicates may remain behind as a residue. The steps due to loss of mass give us valuable information about the composition of materials.


The steps are numbered next to the curve and explained in the table, namely:

One, heating begins and volatile components vaporize;

Two, pyrolysis of organic substances and polymers;

Three, at six hundred degrees Celsius (600 °C), the atmosphere is switched from nitrogen to oxygen to obtain oxidative conditions;

Four, carbon black or carbon fibers burn;

Five, inorganic fillers such as silicates are left behind as a residue.


Slide 14: Thermogravimetric Analysis (TGA)

Thermogravimetric Analysis is used to investigate processes such as vaporization or decomposition, evaluate the stability of compounds, and to determine inorganic residues. Evolved gases can be analyzed online using hyphenated techniques such as TGA-MS or TGA-FTIR.


The table summarizes the main analytical applications of TGA for biopolymers. The technique provides information about the composition of samples including their filler content. Furthermore, it allows us to check the thermal or oxidative stability of products such as biodegradable polymers, or to analyze the content of moisture or volatiles in formulated products.


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


Slide 15: Application 1: TGA/DSC                    Decomposition

The first TGA application shows the weight loss curves of the decomposition of a polylactide sample using two different purge gases - red using air, and blue using nitrogen. The heating rate was 20 Kelvin per minute (20 K/min).

The decomposition in air begins at a lower temperature than in nitrogen. This is shown by the mid point temperatures of the two curves measured at half the step height. Decomposition in air takes place in two well-separated steps. In the first step, 98% of the material burns, the remaining 2% burns at a temperature about 80 degrees higher. In contrast, decomposition in nitrogen is not complete - a residue of about 1% is left behind.


In the next example, I want to discuss the kinetics of such decomposition processes.


Slide 16: Application 2: TGA/DSC        Kinetics of decomposition

The kinetic evaluation of thermal analysis curves is an extremely valuable tool for analyzing reactions and making predictions about the stability of materials. A powerful software to evaluate reaction kinetics is the METTLER TOLEDO model-free-kinetics-software called MFK for short.

The slide illustrates some of the application possibilities and summarizes the results obtained for the thermal decomposition of polylactide in oxygen.

An evaluation using model free kinetics requires at least three measurement curves recorded at different heating rates.

The upper left diagram shows weight-loss curves measured at heating rates of 5, 10, and 20 Kelvin per minute (5 K/min, 10 K/min and 20 K/min). The conversion curves are calculated from each weight-loss curve as shown in the upper right diagram. These curves are then used by the model-free-kinetics-software to calculate the apparent activation energy curve as a function of conversion.

The activation energy curve provides information about the reaction mechanism. It also allows predictions to be made about the course of the reaction under other conditions.

A good example is the calculation of isothermal-conversion-curves. The diagram in the lower left corner displays such so called iso-conversion curves for temperatures of 300, 320, and 340 degrees Celsius (300 °C, 320 °C and 340 °C). This shows, for example, that at 340 degrees a conversion of 90% is reached after about 15 minutes, whereas at 320 degrees the same conversion needs a reaction time that is four times longer.

Measurements and evaluations like this can be used to evaluate and compare the thermal stability of materials.


Slide 17: Thermomechanical Analysis (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 in a defined atmosphere.


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

One, expansion below the glass transition;

Two, the glass transition point at which the rate of expansion changes;

Three, expansion above the glass transition; the steeper slope indicates a greater rate of expansion;

Four, softening with plastic deformation;


Slide 18: Thermomechanical Analysis (TMA)

The table summarizes the analytical applications of Thermomechanical Analysis for biopolymers.

The main application is the determination of the expansion behavior and the coefficient of thermal expansion, or CTE.

TMA is also excellent for determining the glass transition temperature, and for studying softening behavior, creep, or swelling in solvents. The picture on the right shows the typical experimental setup with a ball-point probe resting on the sample specimen.

The following slides describe some common application examples.


Slide 19: Application 1: TMA/SDTA                              Shrinkage

In this example, I want to discuss the results of TMA tension measurements of a cellulose acetate film used for packaging fruit and vegetables.

The film was measured in the tension sample holder using a tensile force of zero point zero two newtons (0.02 N) as shown in the photograph on the right.


The orientation of the polymer chains in the processing direction and at right angles to this are different. For this reason, the expansion behavior of the film depends on the direction of measurement. The curve measured in the processing direction (longitudinal) is colored red, and the curve measured at right angles to this (across) is blue.

The measurement curves in the temperature range from room temperature to 80 degrees Celsius (80 °C) are shown on an expanded scale in the inset diagram. The curves show that the samples expand in this temperature range. The thermal expansion in the processing direction is less than that at right angles to this direction. 

From about 90 degrees onward, the films shrink depending on the orientation. In the processing direction, the maximum shrinkage of the sample length at a temperature of 160 degrees is more than twice as large as that at right angles to the processing direction.

On further temperature increase, the films are pulled apart due to softening.

Tension measurements like this can also be performed on fibers using suitable clamping accessories.


Slide 20: Application 2: TMA/SDTA                 Compression mode

This slide shows the TMA measurement of a wood-plastic-composite, or for short, WPC.

WPCs are composite materials that can be thermoplastically processed. They are manufactured  from different amounts of wood, plastics, and additives. The advantages of this type of material compared with traditional wood materials such as chipboard, plywood or wallboard are the free, 3-dimensional possibilities for molding the material and its better resistance to moisture.

In this measurement, the swelling behavior in water was determined. The measurement setup is shown in the small inset diagram. A small cube of the material was placed in the cylindrical accessory, which was filled with water. The height of the sample was measured by the TMA probe resting on the sample with a very low force. The measurement was performed at thirty degrees Celsius (30 °C).

The TMA curve shows the sample height as a function of time. In fact, the material was very resistant to water. After more than 50 hours immersion in water, the increase in height or thickness was less than 1%.


Slide 21: Dynamic Mechanical Analysis (DMA)

Dynamic mechanical analysis or DMA is a technique that is used to measure the mechanical properties of a viscoelastic material as a function of time, temperature and frequency when the material is deformed under a periodic oscillating stress.


The schematic diagram on the left shows the results of a DMA measurement of a polymer measured in the shear mode. The curves display the storage modulus (G′), the loss modulus (G″), and tan delta as a function of temperature.

The different effects are numbered next to the curve and explained in the table, namely

One, secondary relaxation, observed as a peak in tan delta;

Two, the glass transition, seen as a decrease in the storage modulus;

Three, cold crystallization begins with increasing temperature;

Four, recrystallization accompanied by a peak in tan delta;

Five, melting of the crystalline fraction with a decrease in the storage modulus.


Slide 22: Dynamic Mechanical Analysis (DMA)

The table lists the main analytical applications of Dynamic Mechanical Analysis for biopolymers.

In general, DMA provides information about the mechanical modulus, compliance, damping, and viscoelastic behavior. The glass transition temperature, softening temperatures, or beta relaxation processes are detected as peaks in tan delta or through changes in the modulus.

The picture on the right shows a sample installed in the DMA ready for measurement in the bending mode.


Slide 23: Application 1: DMA                                       Tension mode

In this slide, we see the results of a DMA measurement of a biodegradable composite film.


The measurement was performed in the tension mode in the temperature range minus 175 degrees Celsius to plus 140 degrees (-175 °C bis 140 °C) at a heating rate of 2 Kelvin per minute (2 K/min) and a frequency of 5 hertz (5 Hz). In the diagram, the Young’s Modulus ee prime (E’) curve is colored red and the loss factor, tan delta, curve is blue.


At very low temperatures, the sample shows a weak secondary or beta-relaxation peak. At minus 35 degrees (-35 °C) and plus 65 degrees (65 °C) the modulus decreases by more than a decade while the loss factor, tan delta exhibits a peak. This behavior is typical for a glass transition or alpha-relaxation.

The composite material therefore consists of at least two materials with different glass transition temperatures. At about 100 degrees (100 °C), the modulus increases by more than half a decade. This behavior is typical for cold crystallization – the part of the composite with the higher glass transition temperature crystallizes. The sample becomes stiffer and the modulus increases. At about 120 degrees (120 °C), the modulus shows a marked decrease, tan delta increases, and the polymer crystals melt.


Slide 24: Application 2: DMA               Master curve for tension

In the previous application, we looked at the temperature dependence of different relaxation processes measured at a single frequency.

Now we want to look at the storage modulus, ee prime (E’), and the loss modulus, ee double prime (E’’), as a function of frequency for a so-called reference temperature. Normally, only a certain frequency range is available for the measurement.

The Time-Temperature-Superposition-principle however allows a so-called master curve to be constructed from isothermal frequency-dependent measurements, the so-called Time-Temperature-Segments (TTS), for a particular reference temperature. The reference temperature corresponds to the temperature of the TTS segment that is not shifted. The TTS segments measured at higher temperatures are shifted to lower frequencies, and the TTS segments measured at lower temperatures are shifted to higher frequencies until the best possible overlap of the ends of the individual segments is achieved. The prerequisite for this is that the sample is homogeneous, isotropic and amorphous.

The slide shows the results of the master curve construction for a biodegradable copolymer for a frequency range of 10 to the minus 12 hertz, to, 10 to the minus 18 hertz (10-12 Hz bis 1018 Hz). The measurements were performed with the DMA 1 in the temperature range minus 80 to plus 80 degrees Celsius (-80 °C bis 80 °C) at temperature intervals of 5 Kelvin (5 K). Each color corresponds to an isothermal measurement at five different frequencies from 1 to 20 hertz (1 Hz bis 20 Hz).

Two relaxation processes can be seen: at higher frequencies the glass transition of the soft polymer segments, and at lower frequencies the glass transition of the hard segments.

The results show quite clearly that mechanical spectroscopy allows detailed information to be obtained on material properties over an extremely wide frequency range.


Slide 25: Application 3: DMA               Stress-Strain tension

The final application shows the Stress-Strain behavior of a commercially available cotton fiber. In the wider sense, cotton can be looked on as a biopolymer because it consists mainly of cellulose.

The quasi-static mechanical properties can be described over a large deformation range by a Stress-Strain curve. In this, the fiber is subjected to an increasing tensile stress and the resulting change in length is measured.

The diagram shows the Stress-Strain curve at 30 degrees Celsius (30 °C). For low deformation a linear relationship is found between Stress and Strain. The slope of the curve up to about 0.5% deformation is the elastic modulus with a value of about 20 giga-pascals (20 GPa). In the non-linear region, the curve flattens off and the modulus decreases.

Stress-Strain experiments in the DMA allow the strength, stiffness, and expansion behavior of fibers to be measured and compared. In addition, these material properties can be investigated under different conditions of relative humidity or in a water bath. Finally, measurements like this allow conclusions to be drawn about the properties of textiles made from different fibers.


Slide 26: Summary 1

The table summarizes the most important events that characterize biopolymers as well as the techniques recommended for investigating the effects. A box marked red means that the technique is strongly recommended; a box marked blue indicates that the technique can also be used.


The most important effects that can be analyzed by DSC are the glass transition, melting behavior, reaction enthalpies, and the influence of fillers.


For TGA, the main applications are content analysis, thermal stability and evaporation behavior.


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


DMA is the best method for characterizing the viscoelastic behavior of materials.


Slide 27: Summary 2

This slide presents an overview of the temperature ranges of the METTLER TOLEDO DSC, TGA, TMA, and DMA instruments


In general, DSC experiments are performed at temperatures between minus one hundred and fifty degrees Celsius (–150 °C) and plus seven hundred degrees (700 °C). The temperature ranges may be different if special equipment or accessories are used.


TMA experiments can be performed between minus one hundred and fifty degrees Celsius (–150) and plus eleven hundred degrees (1100 °C).


DMA samples are measured in the range minus one hundred and fifty degrees Celsius (–150 °C) to plus six hundred degrees (600 °C).


TGA measurements normally begin at room temperature. The maximum possible temperature is about sixteen hundred degrees (1600 °C).



Slide 28: For More Information on Biopolymers

Finally, I would like to draw your attention to information about the thermal analysis of biopolymers that you can download from the Internet.

METTLER TOLEDO publishes articles on thermal analysis and applications from different fields twice a year in UserCom, the well-known METTLER TOLEDO biannual technical customer magazine. Back issues can be downloaded as PDFs from as shown in the middle of the slide.

A compilation of applications can be found in the “Thermoplastics” and the “Thermal Analysis in Practice” handbooks.


Slide 29: 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 addresses given on this slide.


Slide 30: Thank You

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

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