Thermal Analysis of Composites
On Demand Webinar

Thermal Analysis of Composites

On Demand Webinar

"Thermal Analysis of Composites" presents techniques used to characterize these versatile materials

Thermal Analysis of Composites
Thermal Analysis of Composites

Composite materials are widely used in many industries because of their unique properties such as low weight, attractive price, wide stiffness range, long fatigue life and good wear resistance. Thermal analysis techniques such as DSC, TGA, TMA, and DMA are ideal for characterizing such materials. The most important advantage is that properties can be measured as function of temperature or time over a wide temperature range, from –150 to 1600 °C.

In this Webinar, we will show how thermal analysis is used to analyze composite materials and present some typical examples of samples measured by DSC, TGA, TMA, or DMA.

41:29 min
English

The Webinar covers the following topics:

  • Introduction
  • Composites
  • Thermal analysis
  • Industries and applications
  • Instrumentation and applications
    - DSC
    - TGA
    - TMA
    - DMA
  • Summary

In the webinar titled "Thermal Analysis of Composites", we describe a number of typical application examples that illustrate how thermal analysis can be used for the routine testing and development of modern composite materials based on polymers in various industry segments.

What is a composite material?

The term composite means that two or more constituent materials are combined together on a macroscopic scale to form a new material. The individual components remain separate and distinct within the finished composite material. The functional properties of the composite are however better than those of the individual constituents. For example, higher stiffness in a polymer is achieved by incorporating fibers into the polymer to reinforce it.

Industrial applications

In many industries, composites are replacing metals because of their comparatively light weight, low price and better performance. Composites are widely used as high-performance engineering materials in the aerospace, aviation, automobile, building, electronics, sports-goods, and other industries.

 

Thermal analysis of composites

The most important effects that can be analyzed by DSC are melting behavior and the glass transition. DSC can also be used to determine the curing kinetics of matrix resins and influence of additives.

For TGA, the main applications are compositional analysis, for example filler and fiber content, and thermal stability.

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

DMA is the most sensitive method for measuring the glass transition, modulus values, and the viscoelastic properties of materials as well as for investigating the influence of measurement frequency and displacement amplitude.

Thermal Analysis of Composites

Slide 0: Composites

Ladies and Gentlemen,

Welcome to the METTLER TOLEDO webinar on the Thermal Analysis of Composites.

 

A composite or composite material consists of two (or more) distinct materials: One is the matrix or binder, and the other the reinforcement or filler.

The matrix material binds together the fibers or material used as the reinforcement or filler to produce a composite material whose properties are superior to those of the individual constituents.

Natural composites exist in plants and animals, for example the structures of wood (cellulose fibers and lignin), and bone in your body.

Man-made composites date back thousands of years.

Early forms of composites were bricks made of mud and straw.

Later on came concrete, in itself a composite of stones and cement, which is nowadays usually reinforced with metal rods and wires.

Modern examples of composites are the ever-increasing number and variety of polymers reinforced with glass and carbon fibers.

In this webinar, I want to concentrate on this latter class of composites.

 

Slide 1: Contents

Thermal analysis is an excellent method for identifying and characterizing composites because their physical and chemical properties are strongly dependent on temperature.

 

The slide lists the topics I would like to cover.

 

First, I will give an overview of the different classes of composites and briefly describe the four main thermal analysis techniques used to investigate their behavior.

The techniques discussed are:

Differential Scanning Calorimetry or DSC;

Thermogravimetric Analysis, or TGA;

Thermomechanical Analysis, or TMA;

and Dynamic Mechanical Analysis, or DMA.

 

I will then describe a number of typical application examples that illustrate how thermal analysis can be used for the routine testing and development of modern composite materials based on polymers in various industry segments.

 

Finally, I want 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

As I have already mentioned, the term composite means that two or more constituent materials are combined together on a macroscopic scale to form a new material. The individual components remain separate and distinct within the finished composite material. The functional properties of the composite are however better than those of the individual constituents.

For example, higher stiffness in a polymer is achieved by incorporating fibers into the polymer to reinforce it. Or, the wear performance of automobile tires is greatly improved by the addition of carbon black.

In many industries, composites are replacing metals because of their comparatively light weight, low price and better performance. Composites are widely used as high-performance engineering materials in the aerospace, aviation, automobile, building, electronics, sports-goods, and other industries.

 

Slide 3: Introduction: Design of Composites

A well-designed composite exhibits properties that are optimum for the particular application envisaged and superior to those of the individual constituent materials.

A composite can be a combination of different materials such as polymers, metals and ceramics, or simply just a mixture of different polymers.

 

A composite is designed by selecting a suitable matrix, and an appropriate reinforcement material with a view to achieving certain specifications.

The final composite enables products to be manufactured that exhibit properties such as optimum strength, stiffness, wear behavior, thermal conductivity, low weight, lifetime, and so on.

 

Slide 4: Introduction: Types of Matrices

This slide shows different types of matrix materials that are used for composites. The matrix can be a polymer, a metal, ceramic material, or subdivisions of these three main types as shown in the tree diagram.

 

Composite materials have long history.

For example, the ancient Egyptians used a type of plywood because they realized that layers of wood could be arranged to achieve superior strength and resistance to thermal expansion as well as to swelling caused by the absorption of moisture.

Medieval swords and armor were constructed with layers of different metals to achieve high mechanical strength.

Nowadays fiber-reinforced, resin-matrix-composite materials that have high strength and stiffness-to-weight ratios have become very important in weight-sensitive applications in the aerospace, aviation, and automobile industries.

In this webinar, I want to focus on modern composites involving polymer matrices.

 

Slide 5: Introduction: Types of Composites

In the previous slide, we saw that composites involving polymer matrices can be subdivided into categories depending on whether the matrix material used is

a thermoplastic,

a thermoset, or

an elastomer.

 

Another classification criterion is the structure of the composite, that is, how the materials are combined together structurally to form a composite. The three basic types are shown in the slide, namely:

1) fibrous composite materials,

2) laminated composite materials, and

3) particulate composites, consisting of small particles embedded in the matrix,

 

as well as combinations of these three types .

 

Some of the criteria for selecting the matrix and the reinforcement or filler materials are summarized at the bottom of the slide. Ultimately, the aim is to improve the performance and reduce the overall price of a product.

 

Whether the term reinforcement or filler is used depends on the degree of bonding and interaction between the reinforcement or filler and the matrix. 

 

Slide 6: Thermal analysis

What is Thermal Analysis?

The ICTAC definition of thermal analysis 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 in which the temperature of a sample is increased at a constant heating rate.

 

The lower half of the slide illustrates typical events and processes that occur when the sample is heated. For example, initially 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 quality control and in research and development to investigate effects like these.

 

Slide 7: Thermal Analysis                                                           Techniques

The slide shows the four most important thermal analysis techniques used to study composite materials:

 

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 (colored red), and a reference crucible.

 

In Thermogravimetric Analysis, or TGA, the weight of the sample is measured as a function of temperature using a highly sensitive electronic balance.

 

Thermomechanical Analysis, or TMA, is used to measure dimensional changes of a sample with increasing temperature. The picture shows the sample support with a sample (colored red), the quartz probe and sensor.

 

And finally, Dynamic Mechanical Analysis, or DMA, which measures the mechanical properties of a sample as a function of time, temperature, and frequency.

The picture shows one of the several different sample-clamping assemblies.

 

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

 

Slide 8: Industries and Applications       

The table summarizes some of the industries in which composites are used and the thermal analysis techniques that can be employed for quality control, and research and development.

For example, in the automotive and aviation industry, composites are used in the body and wings of aircraft to achieve high mechanical strength but with lighter weight. TGA, DSC and DMA techniques are used to determine properties such as thermal stability, thermal resistance, and mechanical behavior.

Similarly in the electronics industry, printed circuit boards can be investigated by TGA and TMA techniques to evaluate thermal stability and determine expansion coefficients.

In the foodstuffs industry, the thermal behavior and oxidative stability of multi-layer packaging laminates can be analyzed by DSC or TGA, and expansion or shrinkage behavior by TMA.

 

Slide 9: DSC, Flash DSC, HPDSC

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

 

DSC instruments are available in different versions depending on their temperature range, the type of sensor, and the heating and cooling rates.

 

The standard METTLER TOLEDO DSC 1 instrument measures from minus one hundred and fifty degrees Celsius (–150 °C) to plus seven hundred degrees (700 °C) at heating rates of up to three hundred Kelvin per minute (300 K/min). Samples are normally measured in small crucibles made of aluminum, alumina or other materials, using sample amounts of two to twenty milligrams.

 

The 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 1 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 pressures of up to ten megapascals (10 MPa). This suppresses undesired vaporization of samples or enables the stability of samples to be studied under increased oxygen pressures.

 

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. These are:

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 10: Differential Scanning Calorimetry (DSC)

The table summarizes some of the applications used to investigate and characterize composite materials.

The main applications have to do with the measurement of melting behavior and the glass transition.

DSC measurements also provide information about the enthalpy of transitions, heat capacity, and the influence of impurities, additives or fillers on melting behavior.

The rate of curing reactions of thermosetting matrixes and the degree of cure is also an important field.

 

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

 

Slide 11: Application 1: DSC                              Identification of film layers

Nowadays, the flexible packaging films used in the food and pharmaceutical industries are very often laminates made of several thin thermoplastic polymer films bonded together in different ways. This type of multilayer film composite ensures good mechanical and barrier properties.

The most common DSC application is to identify the individual polymers films that make up the composite multilayer film. Most polymers used as films exhibit unique melting behavior, which can easily be measured by DSC.

The slide displays the DSC heating curve of a multilayer film measured at a heating rate of 20 Kelvin per minute. Four main events can be seen:

First, a broad peak with peak temperature at about 108 degrees Celsius. This is due to the melting of low-density polyethylene, so-called PE-LD. The peak is followed by a shoulder at about 120 degrees that can be assigned to the melting of linear low-density polyethylene, or PE-LLD.

The peaks labeled PA 12 and PA 11 at 177 and 191 degrees are due to the melting of polyamide 12 and polyamide 11, respectively.

The small step at about 40 degrees is due to the glass transition of the polyamide.

The size of the peaks depends on the thickness of the layer and the degree of crystallinity of the particular polymer.

The DSC measurement resolves the four melting peaks corresponding to the four polymer layers of the composite film. The polymers can be identified by comparing their peak temperatures with reference values.

 

Slide 12: Application 2: DSC                              Influence of accelerator on curing

Accelerators are added to matrix resins to speed up the curing reaction and so lower the curing temperature.

DSC can be used to measure the influence of a particular accelerator on the curing process. This example describes curing measurements of samples of a glass-fiber-reinforced vinyl-ester-resin-composite containing different concentrations of an accelerator. The material is used for the manufacture of plastic molding parts.

The diagram displays the DSC heating curves of three samples of the composite material containing different concentrations of the accelerator. Each curve exhibits an exothermic peak proportional to the heat produced during the exothermic curing reaction. Increased accelerator concentration speeds up the reaction and causes the reaction peak to shift to lower temperatures.

The sample without any accelerator shows a rather narrow exothermic peak with a peak temperature of 122 degrees Celsius.

The reaction peaks of the samples containing the accelerator are broader and occur at lower temperature. The curves show quite clearly that the reaction has already begun well below 50 degrees, in marked contrast to the sample without any accelerator.

This type of DSC measurement allows production processes to be adapted and optimized by choosing the right accelerator, its concentration, and the curing temperature.

Measurements like this can also be used as an additional quality control criterion for checking incoming resin mixtures.

 

Slide 13: Application 3: DSC                              Curing kinetics of a composite

Curing kinetics have an important influence on the design of processes.

In this example, DSC experiments were performed to investigate the relationship between the curing time and the reaction temperature of a urea-based resin composite used for the manufacture of parts for housings from filled molding compounds.

Samples were first measured at three different heating rates, in this case at 5, 10 and 20 Kelvin per minute. The measurement curves are displayed in the upper left diagram. Due to kinetic processes, the reaction peaks shift to higher temperatures with increasing heating rate.

The conversion curves displayed in the upper right diagram were calculated by integrating the reaction peaks in the range 90 to 180 degrees Celsius. The Model Free Kinetics software program, MFK, was then used to calculate the apparent activation energy shown in the bottom right diagram. The evaluation shows that the activation energy is more or less constant from 35% conversion onward but before this is very different, indicating that initially the curing reaction proceeded differently.

 

The Model Free Kinetics software allows predictions to be made for the isothermal conversion at any particular temperature of interest, in this case for 80, 100, and 120 degrees, as shown in the lower left diagram.

For example, the isothermal conversion curve calculated for 100 degrees shows that a conversion of 90% is reached after about 130 minutes at this temperature. This indicates the processing time necessary to achieve this particular degree of conversion.

 

The data obtained from experiments like this can be used to optimize production processes and conditions.

 

Slide 14: TGA/DSC

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 weight change. 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, inorganic fillers such as glass fibers are left behind as a residue after heating to temperatures of one thousand degrees Celsius (1000 °C). The steps due to the 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. These are:

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, residue of inorganic fillers such as glass fibers.

 

Slide 15: Thermogravimetric Analysis (TGA)

TGA is used to investigate processes such as vaporization or decomposition. The combination of a TGA instrument with a mass spectrometer or a Fourier transform infrared spectrometer provides information about the composition of samples by analyzing the evolved gases.

The table on the left summarizes the main analytical applications of TGA for composite materials. Besides content determination, the technique allows us to check the thermal stability of substances and the kinetics of decomposition reactions.

The picture on the right is a view of the open furnace, showing a sample holder with two positions for the sample and reference crucibles in a TGA/DSC instrument. The standard crucibles are made of alumina to withstand high temperatures.

 

Slide 16: Application 1: TGA                                           Compositional analysis

As I explained earlier on, polymers are often filled or reinforced with different types of materials in order to improve their mechanical and thermal properties. For example, the addition of fibers can result in a major increase in stiffness and strength. Glass-fiber-reinforced thermoplastics are widely used for technical products - they can be processed by injection molding or extrusion and exhibit excellent mechanical properties. The quality assurance of such composite materials consists primarily of checking the fiber content. This is very easily done by thermogravimetric analysis.

The diagram displays the TGA heating curves of samples of polyamide 6 (PA 6) with and without glass fibers. The samples weighed about 11 milligrams and were heated up to 800 degrees Celsius in a nitrogen atmosphere.

The PA 6 sample without glass fibers lost about 2.5% of its mass up to 200 degrees. This effect is due to the loss of moisture and is well known for polyamides. The polymer then decomposed almost completely in the range 400 to 500 degrees.

 

As expected, the glass-fiber-reinforced sample behaved similarly except that the weight-loss effects were reduced in proportion to the amount of glass fiber. The residue of 24.3% that remained corresponds to the glass fiber content of the sample.

Quantitative content determination is therefore a simple matter because the glass fiber does not decompose under the experimental conditions used, but remains behind as a residue while the polymer undergoes complete degradation.

 

Slide 17: Application 2: TGA                   Thermal endurance by ASTM E1877

This application describes the determination of the activation energy of a decomposition reaction using dynamic TGA measurements according to the ASTM E1641 test method. This is used in the ASTM E1877 test method for estimating the isothermal long-term stability or thermal endurance of a material,

The sample in this application was a printed circuit board, or PCB. If printed circuit boards are heated to high temperatures, the matrix resin begins to decompose and gases are evolved. This process causes delamination of the layered structure of the printed circuit board and leads to ultimate destruction of the board.

To determine the activation energy of the decomposition reaction according to ASTM 1641, four samples were heated to temperatures well above their decomposition temperatures at heating rates of 1, 2, 5 and 10 Kelvin per minute. The resulting curves displayed in the diagram on the left show that the mass loss was about 30%.

The temperature corresponding to a certain conversion, typically 10% of the mass loss up to 380 degrees Celsius, was determined for all four TGA curves. The activation energy to be calculated is independent of the reaction order, which is assumed to be one in the ASTM E1641 method, but only at the beginning of the decomposition reaction.

The activation energy is the parameter needed to determine the lifetime as a function of the isothermal temperature of use according to ASTM E1877. This test method describes the Standard Practice for Calculating Thermal Endurance of Materials from Thermogravimetric Decomposition Data.

In this case, the lifetime was calculated assuming that the level of decomposition can reach 0.1%, 0.5% or 1.0% before the printed circuit board becomes unusable. The resulting curves are shown in the diagram on the right and are referred to as Iso-Conversion plots. For example, if 1% is set as the limit, the iso-conversion curve shows that the board must not be heated for more than 5 minutes at 250 degrees (a temperature that could occur in a soldering bath).

Iso-Conversion curves and predictions for the lifetime of a material at different temperatures can be used for quality control or development purposes.

 

Slide 18: TMA/SDTA

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

 

The schematic curve on the left shows a typical TMA measurement curve of a polymer under a small sample load. The different effects are numbered next to the curve and explained in the table. These are:

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 19: Thermomechanical Analysis (TMA)

The table on the left summarizes the analytical applications of TMA for composite materials.

Generally, the main application is the determination of the coefficient of thermal expansion, or CTE. The method is based on the measurement of the change in thickness of a sample on heating.

TMA is also an excellent technique for determining the glass transition temperature, and for studying softening behavior, especially for thin layers or coatings. The picture on the right shows an experimental setup with a ball-point probe in contact with the sample specimen mounted on a flat support.

The following two slides describe specific application examples.

 

Slide 20: Application 1: TMA                              Effect of fiber orientation

Most materials expand on heating. Polymer composites reinforced with glass fibers usually have expansion coefficients that are direction-dependent.

The example describes the TMA measurement of a machine component shaft made of glass-fiber-filled polyphenylene sulfide, PPS. For trouble-free operation, it is important to know the expansion coefficients of the shaft in the axial and in the radial directions.

In this investigation, sample specimens were prepared from the shaft, one in the radial direction and the other in the axial direction. To maximize accuracy, the specimens were carefully prepared so that all the surfaces were flat, smooth and parallel with a thickness of at least 5 millimeters (5 mm).

The specimens were measured from 30 to 200 degrees Celsius at a heating rate of 1 Kelvin per minute. The resulting measurement curves are displayed in the diagram and show that the glass transition temperatures are practically the same for both directions, differing only by about one Kelvin.

However, the expansion coefficients in the axial and radial directions differ by about 30% below the glass transition, and by a factor of two above the glass transition temperature. This effect is due to the orientation of the fibers and shows that fiber orientation has a considerable effect on the coefficient of thermal expansion.

 

Slide 21: Application 2: TMA                                          Delamination of a PCB

TMA is one of the best techniques to study the dimensional changes of small samples.

In the case of printed circuit boards, it helps us determine the onset of delamination. This is the temperature at which decomposition of the epoxy matrix resin begins with the release of gaseous products and separation of the layers.

If PCBs are exposed to excessive heat, there is the risk that the individual layers of the board separate. This is hardly visible but is nonetheless sufficiently large to destroy electrical connections. If the temperature of the board is too high, decomposition continues, and gases are evolved that cause further damage.

In this experiment, the 3-mm ball-point probe was positioned directly on the sample. The force applied was 0.05 newtons (0.05 N). The sample was then heated from 30 to 650 degrees Celsius at 20 Kelvin per minute. The TMA curve records the dimensional changes of the printed circuit board up to 500 degrees. The change in the slope of the TMA curve at about 92 degrees corresponds to the glass transition of the matrix resin. The sudden dimensional changes above 323 degrees are due to delamination of the board.

This is shown in more detail in the zoomed curve in the inset diagram. Above about 300 degrees, delamination and degradation begins with the formation of gaseous products.

In another experiment, bromine-containing compounds were clearly identified using evolved gas analysis during the delamination of a printed circuit board that contained a brominated flame retardant in the matrix material.

 

Slide 22: DMA and DMA/SDTA

The final technique I would like to discuss is Dynamic Mechanical Analysis or DMA.

DMA 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 shock-cooled semi-crystalline polymer measured in the shear mode. The curves display the storage modulus, gee prime (G′), the loss modulus, gee double-prime (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 shown by a peak in tan delta;

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

 

Slide 23: Dynamic Mechanical Analysis (DMA)

The table on the left lists the main analytical applications of DMA for composites.

DMA is a very sensitive technique for measuring the glass transition temperature of amorphous components of a polymer. The glass transition is detected as a step in the storage modulus curve or as a peak in the loss modulus and tan delta curves. 

In general, DMA provides information about the mechanical modulus, damping properties, and viscoelastic behavior as a function of temperature and frequency.

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

 

Slide 24: Application 1: DMA      Glass transition of an epoxy composite

The glass transition temperature of the matrix resin is important for guaranteeing the properties and performance of the composite material. As we have just heard, DMA determines the glass transition by measuring changes in mechanical properties such as the elastic modulus or the loss factor, tan delta.

The diagram displays the storage modulus, ee prime (E’), loss modulus, ee double prime (E”), and tan delta curves of a carbon-fiber reinforced epoxy composite measured in the 3-point bending mode in the range 30 to 100 degrees Celsius.

The storage modulus curve exhibits a step-like decrease, whereas the loss modulus and tan delta curves show a peak in the range of 50 to 80 degrees. These effects can be attributed to the glass transition of matrix resin. This defines the upper temperature limit of use for the composite material.

 

Slide 25: Application 2: DMA                  Metal/elastomer laminate

DMA can be used to measure the glass transitions of individual polymers of a laminate.

The diagram displays the curves obtained from the measurement of a metal/elastomer laminate consisting of a 0.4 millimeter (0.4 mm) thick aluminum foil coated with two different elastomers. Two sample specimens measuring about 4 by 4 millimeters and 1.57 millimeters thick were measured in the shear clamping assembly parallel to the direction of the layers in the temperature range minus 45 to plus 90 degrees Celsius.

The top diagram displays the storage and loss modulus curves. Only one relaxation transition is observed because the change is dominated by the softer material. This is also the case in the tan delta curve where the glass transition that occurs first, predominates.

The glass transition of the second polymer layer is however visible as the second peak at about plus 15 degrees in the corresponding loss compliance curve, jay prime (J”). This is due to the fact that compliance is additive when shear measurements are performed parallel to the direction of the thin layers. This allows both transitions to be observed.

 

Slide 26: Application 3: DMA                  Influence of carbon black content

In this application, the mechanical properties of four natural rubber samples with different contents of carbon-black filler were investigated. Here, phr, means parts by weight of carbon-black per hundred parts of rubber.

The curves displayed in the upper diagram were measured in the shear mode at room temperature and a frequency of one hertz (1 Hz). The displacement amplitude was varied in steps between thirty nano-meters (30 nm) and one millimeter (1 mm) and the force was measured.

In the lower diagram, the storage modulus of the unfilled material is practically independent of the displacement amplitude. The other three curves, however, show that the storage modulus increases with increasing carbon-black content and that the modulus for a particular carbon-black content decreases as the displacement amplitude increases. This indicates non-linear behavior and is due to the reversible destruction of carbon-black clusters.

The data obtained therefore provides information about the linear elastic range and the interaction between the polymer and the carbon black.

The upper diagram shows that a large force of up to forty newtons (40 N) is essential for measurements like this. This of course requires an instrument with a correspondingly high performance specification.

 

Slide 27: Summary

The table summarizes the most important thermal events that characterize composite materials as well as the techniques recommended for measuring 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 for some applications.

 

The most important effects that can be analyzed by DSC are melting behavior and the glass transition. DSC can also be used to determine the curing kinetics of matrix resins and influence of additives.

 

For TGA, the main applications are compositional analysis, for example filler and fiber content, and thermal stability.

 

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

 

DMA is the most sensitive method for measuring the glass transition, modulus values, and the viscoelastic properties of materials as well as for investigating the influence of measurement frequency and displacement amplitude.

 

Slide 28: For More Information on Composites

Finally, I would like to draw your attention to information about applications involving composites 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 www.mt.com/ta-usercoms as shown at the bottom of the slide.

 

Slide 29: For More Information on Thermal Analysis

In addition, you can download details about webinars, application handbooks, training, 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 Composites. Thank you very much for your interest and attention.

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