Overview of METTLER TOLEDO Thermal Analysis · polymers, polyamides, polyesters. Following on after thesecommonlyused thermoplastic materials, there are someapplications involving

Application Handbook

Thermoplast Collected Applications

Ther

mal

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METTLER TOLEDO Collected Applications THERMOPLASTICS Page 1

Collected ApplicationsThermal Analysis

THERMOPLASTICS

This application booklet presents selected application examples. The experiments were conducted with the utmost careusing the instruments specified in the description of each application. The results were evaluated according to the currentstate of our knowledge.

This does not however absolve you from personally testing the suitability of the examples for your own methods, in-struments and purposes. Since the transfer and use of an application is beyond our control, we cannot of course acceptany responsibility.

When chemicals, solvents and gases are used, general safety rules and the instructions given by the manufactureror supplier must be observed.

® TM All names of commercial products can be registered trademarks, even if they are not denoted as such.


Preface to the first edition, 1997

Thermal analysis is the name given to a group of techniques that are used to determine the physical orchemical properties of a substance as it is heated, cooled or held at constant temperature. The fascina-tion of thermal analysis lies in its dual character: In addition to its purely analytical functions it can beused as an engineering tool. Heat treatment applied to a sample in the first measurement may causephysical and chemical changes. Such effects can be investigated by cooling the sample and measuringit a second time in the same instrument.

This booklet covers the main aspects of thermal analysis, the analytical results and engineering possi-bilities.

The application examples are presented in the following order: polyolefines, styrene polymers, vinylpolymers, polyamides, polyesters. Following on after these commonly used thermoplastic materials,there are some applications involving special polymers that are produced in smaller quantities.

All the evaluated diagrams are available as an option in STARe database as a basis for your own meas-urements.

We would like to thank all involved people, especially Thomas Nitschke for his enthusiasm and en-couragement as well as Helga Judex for designing the layout. We also thank Tom Basalik and Dr. RodBottom for proofreading the manuscript.

Dr. M. Zouheir Jandali, Bielefeld Georg Widmann, Schwerzenbach

Preface to the second edition, 2002

This second edition has been completely revised and extended by Dr. Rudolf Riesen and Dr. JürgenSchawe. It now includes a number of experiments performed by dynamic mechanical analysis, DMA.The text was reviewed by Dr. Dudley May, Greifensee.

Dr. R. Riesen, Schwerzenbach

Page 4 THERMOPLASTICS METTLER TOLEDO Collected Applications

Contents

PREFACE TO THE FIRST EDITION, 1997 ......................................................................................3PREFACE TO THE SECOND EDITION, 2002 .................................................................................3CONTENTS ............................................................................................................................................4APPLICATIONS LIST..........................................................................................................................61. INTRODUCTION TO THERMAL ANALYSIS........................................................................10

1.1. DIFFERENTIAL SCANNING CALORIMETRY (DSC) ........................................................................101.1.1. Conventional DSC ..............................................................................................................101.1.2. Temperature-modulated DSC.............................................................................................11

1.2. THERMOGRAVIMETRIC ANALYSIS (TGA) ...................................................................................121.3. THERMOMECHANICAL ANALYSIS (TMA) ...................................................................................131.4. DYNAMIC MECHANICAL ANALYSIS (DMA) ................................................................................141.5. SIMULTANEOUS MEASUREMENTS WITH TGA (SDTA AND EGA)...............................................16

1.5.1. Differential thermal analysis (DTA, SDTA) .......................................................................161.5.2. Evolved gas analysis (EGA) ...............................................................................................17

2. STRUCTURE AND BEHAVIOR OF POLYMERS ..................................................................192.1. SOME DEFINITIONS IN THE FIELD OF POLYMERS ..........................................................................192.2. PHYSICAL STRUCTURE OF POLYMERS .........................................................................................202.3. THERMOPLASTIC POLYMERS.......................................................................................................21

2.3.1. Amorphous plastics.............................................................................................................212.3.2. Semicrystalline plastics ......................................................................................................22

3. IMPORTANT FIELDS OF THERMOPLASTIC POLYMERS ..............................................234. APPLICATION OVERVIEW OF THERMOPLASTIC POLYMERS ...................................245. TABLE OF CHARACTERISTIC TEMPERATURES OF THERMOPLASTIC

POLYMERS...................................................................................................................................256. PROPERTIES OF IMPORTANT THERMOPLASTIC POLYMERS AND

TYPICAL TA APPLICATIONS..................................................................................................266.1. POLYETHYLENE, PE ...................................................................................................................266.2. ETHYLENE/VINYLACETATE COPOLYMER, E/VAC ......................................................................266.3. POLYPROPYLENE, PP..................................................................................................................266.4. POLYSTYRENE, PS......................................................................................................................276.5. POLYVINYL CHLORIDE, PVC ......................................................................................................276.6. POLYVINYL ACETATE, PVAC.....................................................................................................286.7. POLYAMIDE, PA.........................................................................................................................286.8. POLYETHYLENE TEREPHTHALATE, PET .....................................................................................286.9. POLYCARBONATE, PC ................................................................................................................296.10. POLYOXYMETHYLENE, POM......................................................................................................296.11. POLYTETRAFLUOROETHYLENE, PTFE........................................................................................29


7. APPLICATIONS OF THERMOPLASTICS ..............................................................................307.1. MEASUREMENTS ON POLYETHYLENE..........................................................................................307.2. MEASUREMENTS ON POLYPROPYLENE BASED MATERIAL............................................................557.3. GLASS TRANSITION OF POLYSTYRENE.........................................................................................647.4. TA MEASUREMENTS ON POLYVINYL CHLORIDE ..........................................................................687.5. POLYAMIDES AND THEIR BLENDS................................................................................................787.6. THERMAL BEHAVIOR OF POLYETHYLENE TEREPHTHALATE.........................................................977.7. MEASUREMENTS ON OTHER POLYMERS ....................................................................................1057.8. THERMOPLASTIC ELASTOMERS .................................................................................................1217.9. POLYMER BLENDS AND COPOLYMERS .......................................................................................1257.10. FURTHER MEASUREMENTS OF THERMOPLASTICS AND THEIR PRODUCTS ...................................137

LITERATURE ....................................................................................................................................147SUBJECT INDEX...............................................................................................................................148


4. Application overview of thermoplastic polymers

The table shows the properties that can be investigated by TA. Important applications are marked witha large circle.

DSC TMA TGA DMA

Temperature of fusion

Heat of fusion

Crystallinity

Melting behavior, fraction melted

Temperature of crystallization

Heat of crystallization

Cold crystallization

Polymorphism (change of crystal modification)

Glass transition

Softening

Evaporation, desorption (moisture), vaporization

Thermal decomposition (pyrolysis, depolymerization)

Thermal stability

Oxidative degradation, oxidation stability

Compositional analysis(volatiles, polymer, carbon black, ash, filler, glass fibers)

Specific heat capacity

Viscoelastic behavior

Expansion and shrink behavior

Expansivity (coefficient of linear expansion)

Young’s and shear modulus, stiffness

Damping behavior


7. Applications of thermoplastics

7.1. Measurements on polyethylene

PE, characterization by peak temperature

PE-LD and PE-LLD as pellets, PE-HD as a film.SampleKH@$-H@$-HI=

Measuring cell: DSC821e with air cooling

Pan: Aluminum standard 40 μl, lid hermetically sealed

Sample preparation: PE-LD: Disk of 9.796 mg cut from pelletPE-LLD: Disk of 8.128 mg cut from pelletPE-HD: Disk of 10.314 mg punched from film

DSC measurement: Heating from 30 to 180 °C at 10 K/min

Conditions

Atmosphere: Static air

PE-LD PE-LLD PE-HD

Extrapolated peak temperature in °C 109.6 123.8 133.4

Evaluation

Peak temperature in °C 108.8 123.5 132.9


Note: Two values can be used to characterize the peak temperature: the extrapo-lated intersection point of the inflection tangents, and the maximum of the DSCcurve. The extrapolated peak temperature is not influenced so much by the arbi-trary shape of the peak where random noise may cause the actual maximum todiffer slightly from run to run, leading to an irreproducible «peak temperature».For this reason the reproducibility of the extrapolated value is usually better.

Interpretation The melting peaks are typical for the three different PE qualities with their dis-tinctive peak temperatures.

Conclusion The peak temperature of the DSC melting curve is the most frequently deter-mined property of semicrystalline polymers. It is the key parameter for process-ing and serves generally for identification.


PE, characterization by crystallinity

Sample PE-LD and PE-LLD as pellets, PE-HD as a film


Pan: Aluminum standard 40 μl, lid hermetically sealed

Sample preparation: PE-LD: Disk of 9.796 mg cut from pelletPE-LLD: Disk of 8.128 mg cut from pelletPE-HD: Disk of 10.314 mg punched from film


Conditions


PE-LD PE-LLD PE-HD

Crystallinity in % 25.8 35.3 63.5

Evaluation

Heat of fusion in J/g 75.8 103.5 186.0

Note: A straight baseline has been used for integration. Since the normalizedvalue is used, it is important that the sample weight is accurate.


Interpretation The area under the peak corresponds to the heat of fusion of the sample. It isproportional to amount of crystallites present in the sample. The degree of crys-tallinity is determined by comparing the measured heat of fusion with the theo-retical heat of fusion of 100% crystalline polyethylene of 293 J/g (see table onpage 25).

Conclusions The DSC crystallinity indicates the percentage of the material that is crystallineversus amorphous. The degree of crystallinity depends on how regular the struc-ture of the molecule is (no branches or short branches in regular distance) and onthe thermal history. Since hardness and strength increase with increasing crystal-linity, the DSC result correlates with the mechanical properties.


PE-HD, characterization by conversion curves

Sample Lupolen 4261 pellets and a molded part said to be Lupolen 4261


Pan: Aluminum standard 40 μl, pierced lid

Sample preparation: Disks of approx. 5.0 mg cut from pellet or part

DSC measurement: Elimination of thermal history: 25 to 200 °C at 10 K/min,then cooling at 5 K/min. Actual measurement: secondheating run from 25 to 200 °C at 10 K/min

Conditions

Atmosphere: Nitrogen, 50 cm3/min

Lupolen 4261 Molded part

Heat of fusion in J/g 152.0 177.0

Peak temperature in °C 131.0 130.0

Peak width in K 10.9 8.2

Fraction melted at 80 °C in % 1.8 1.6

100 °C in % 6.8 6.0

120 °C in % 24.5 20.7

Evaluation

140 °C in % 99.8 99.8


Interpretation The melting behavior is characterized by the heat of fusion, the peak temperatureand the peak width at half height (all 3 values together) or by the conversioncurve. The conversion curve, also called the fraction melted, is a measure of thepercentage of crystallites that has melted at the particular temperature. It can bepresented in a tabular or graphical form. In contrast to the degree of crystallinity,conversion is a relative value and is therefore practically independent of weigh-ing uncertainties. The balance used for this work had a resolution of 0.1 mg. Anuncertainty of 0.3 mg can for example lead to a 6% error in the calculated valueof the heat of fusion and hence in the degree of crystallinity.

Conclusion The melting behavior of the two samples is similar. The main difference is seenin the heat of melting. The crystallization behavior of the samples is comparedon the next page.


PE-HD, characterization by crystallization behavior

Sample Lupolen 4261 pellets and a molded part said to be Lupolen 4261

Measuring cell: DSC20


Sample preparation: Disks of approx. 5.0 mg cut from pellet or part

DSC measurement: Melting the sample by heating to 200 °C at 10 K/min. Ac-tual measurement: cooling from 200 to 25 °C at 10 K/min

Conditions


Lupolen 4261 Molded Part

Onset of crystallization in °C 116.8 117.4


Peak width in °C 5.9 5.0

Evaluation

Heat of crystallization in J/g 145.0 170.0


Interpretation The crystallization behavior is characterized by the crystallization onset, thepeak width and the heat of crystallization. In addition, the conversion curve andtable are useful for comparison purposes.

Conclusion The crystallization behavior of the two samples is similar.The melting behavior of the same samples is compared in the previous experi-ment. The heats of crystallization differ by about the same amount as measuredbefore in the melting experiment.


PE-HD from different manufacturers

Sample Vestolen A 6017, Stamylan HD 7771, NCPE 2233, Finathene 58070,Lupolen 4261



Sample preparation: Disk cut from pellet


Conditions


Name Crystallinity

in %

Peak tem-perature

in °C

Peak width

in °C

Sample mass

in mg

Vestolen A 6017 63.7 139.6 14.1 13.3

Stamylan HD 7771 55.7 136.6 15.2 22.5

NCPE 2233 52.4 133.1 10.6 4.9

Finathene 58070 58.4 135.2 12.4 11.3

Evaluation

Lupolen 4261 48.2 131.4 11.5 4.5

Note: For clearness, only the Vestolen curve is evaluated in the diagram.


Interpretation The DSC curves of all samples begin to deviate from baseline between 50 and60 °C. The signal returns to the baseline between 145 and 160 °C.

Conclusions The DSC melting peaks of PE-HD of different quality show characteristic dif-ferences. To eliminate effects due to individual thermal history, the samplesshould have been pre-melted and recrystallized at 10 K/min. In addition, thesample masses should be more uniform, e.g. 5 ± 2 mg. The peak width in par-ticular depends on the sample mass (increasing mass → increasing melting time→ broader peak) .


PE, melting curve and thermal history

Sample PE-HD film


Pan: Aluminum standard 40 μl, lid is hermetically sealed

Sample preparation: Disk of 2.33 mg punched out of film

DSC measurement: Pretreatment: annealing for 60 min at 129 °C followed bycooling to 40 °C at 5 K/minHeating from 40 to 180 °C at 5 K/min (see curve of PE-HD annealed at 129 °C), then cooling from 160 to 40 °Cat 5 K/minSecond heating run from 40 to 180 °C at 5 K/min (seecurve of PE-HD with thermal history eliminated)

Conditions


Evaluation The melting gap can be evaluated as an onset, or the melting behavior can becharacterized by the conversion curve. However, the most important informationit reveals is the temperature at which annealing was performed.


Interpretation Crystallite segregation occurs during annealing at 129 °C: Small crystallites meltand recrystallize to form crystallites with melting points above 129 °C. Crystal-lites with melting points of 129 °C or lower cannot of course be formed duringthis process. As the sample is cooled, small crystallites with lower meltingpoints form again, but a gap at 129 °C (called the melting gap) appears in thesecond heating run of the sample. On complete melting, any thermal history iseliminated.

Conclusions The shape of the DSC melting curve depends on the thermal history of the sam-ple. The melting gap is often used to check that the processing temperature wascorrect, e.g. the annealing of PE high voltage cables. Complete melting elimi-nates any thermal history and is a prerequisite for the comparison of differentraw materials.


PE-HD, identification of cable tubing and recycled material

Sample Two different types of tubing for automobiles and recycled material said to bePE-HD



Sample preparation: Disk cut from material


Conditions


Crystallinityin %

Peak temperaturein °C

Defective tubing 57.8 135.2

Good tubing 55.7 133.2

Evaluation

Recycled material 57.7 134.8


Interpretation The DSC melting curves of all three samples are characteristic for PE-HD.

Conclusions The DSC melting curve allows PE-HD to be clearly identified. The defectivetubing is also made of the correct material. To eliminate the effects of thermalhistory, the samples should be premelted and then cooled at identical rates, e.g.10 K/min.

Recycled material is not delivered in properly labeled original manufacturer’spackaging material. It is therefore very important to confirm that the polymer isthe right material. The recycled material must also be checked to make sure thatthe initial processing and the recycling did not degrade the quality to any signifi-cant extent.


DSC of recycled sheets, said to be PE-HD

Sample Noticeably brittle and distorted sheets, said to be made of PE-HD



Sample preparation: Disk cut from material (6.8 mg)


Conditions


Evaluation The heat of fusion determined for the PP peak (14.3 J/g) allows the approximatecontent of PP to be calculated. If the heat of fusion of pure PP is taken to be60 J/g (typical for polypropylene), then the content is given by:

Content = ΔH/ΔHPP·100%, i.e. 23.9%.

Interpretation The melting curve clearly shows that the material is a blend of PE-HD (peaktemperature of 135 °C) and PP (peak temperature of 163 °C) and not pure PE.

Conclusion DSC proves that the material does not match the quality agreed upon. The sup-plier therefore replaced the sheets free of charge.


PE-LD, comparison of two products

Sample Lupolen 1800 S and Lupolen conz. SL 020 A as pellets



Sample preparation: Disks cut from center part of pellet


Conditions

Atmosphere: Air, 50 cm3/min

Lupolen 1800 S Lupolen conc. SL 020A

Crystallinity in % 29.2 35.6


Onset of oxidation in °C 220.0 217.0

Evaluation

Sample mass in mg 19.5 14.35


Interpretation The DSC melting curves have the typical shape for PE-LD. The exothermic re-action above 200 °C is due to the onset of oxidation.

Conclusions Evaluation of the percentage crystallinity and peak temperature reveal that thesetwo samples are of similar quality and that both are PE-LD. The onsets of oxida-tion around 220 °C indicate they are «processing stabilized» because the onsetsare slightly higher than that expected for basic PE. Lupolen 1800 S is more sta-ble than the other sample. Further stabilization could be achieved by adding ad-ditional antioxidants. This could shift the onset to as high as 260 °C.


PE, oxidation stability

Sample Lupolen GM5040 T12 (stabilized PE-HD film)

Measuring cell: DSC821e with air cooling and gas controller

Pan: Aluminum standard 40 μl without lid,40 μl copper pan without lid, for comparison

Sample preparation: Disk punched out of film

DSC measurement: According EN 728 (European standard):Under nitrogen, 50 cm3/min3 min isothermal at 30 °C, then heating to 200 °C at20 K/min, 2 min isothermal at 200 °C.Under oxygen, 50 cm3/min (automatically switched by thegas controller):Isothermally at 200 °C starts the actual measurement.Since only the onset of oxidation is required, the actualmeasurement time can be reduced using the ConditionalExperiment Termination software option.

Conditions

Atmosphere: Nitrogen and oxygen, respectively, automatically switchedby the gas controller

Evaluation The oxidation induction time (OIT) in the aluminum pan is 15.9 min, in the cop-per pan 9.5 min. The melting curve could also be evaluated.


Interpretation The time after switching to oxygen to the onset of oxidation (intersection ofbaseline with the tangent) is called the induction period or Oxidation InductionTime, OIT. A long OIT indicates good stability and vice versa. Contact withcopper or copper alloys catalyzes the oxidation reaction. Polyolefins that will beexposed to copper require special additives that neutralize this catalytic effect.The efficiency of such additives is determined by carrying out the experimentwith the sample in a copper pan. Good «copper stability» results in an OIT of atleast half the value obtained in the aluminum pan. Without such additives, theOIT is about 10 times shorter in copper pan.

Note: Polyolefines give distinct induction periods. Other polymers are besttested by exposure to oxygen on heating at relatively low rates, preferably5 K/min, until distinct exothermal oxidation is visible.

Conclusion The determination of the oxidative stability by DSC is fast and easy. It is espe-cially recommended for the quality assurance of long-life goods such as electri-cal cables and water pipes. Each batch of the raw material should be measured.In addition, the polymer can be identified from the fusion peak obtained.


Cross-linked PE by dynamic load TMA

Sample Cross-linked polyethylene sheet

Measuring cell: TMA40 with 3-mm ball-point probe

Pan: The sample is measured between fused silica disks of6-mm diameter and 0.5-mm thickness

Sample preparation: A rectangular sample of about 4x4 mm is cut off with aknife. The height of the sample, 5.1 mm, is the same as thethickness of the original sheet

TMA measurement: A first heating run to 150 °C at 10 K/min eliminated thethermal history. After uncontrolled cooling to 25 °C, themeasurement was performed at a heating rate of 10 K/min.Note: the pretreatment was also done under dynamic load.

Load: Periodically changing every 6 s between 0.01 and 0.19 N

Conditions


Evaluation The elastic deformation of 1.9% in the amorphous state allows the complexYoung’s modulus, E, to be calculated as follows:E = ΔF/(A·ΔLr), where ΔF is the change in force, A the cross-sectional area ofthe sample, and ΔLr the relative change in length (1.9%).E = 0.18 N/(4⋅4 mm2⋅0.019) = 0.59 N/mm2.

The onset of the difference of the envelopes at 99.6 °C is related to the crystallitemelting.


The expansion coefficients derived from the slope of the upper envelope (load0.01 N) are:between 40 and 50 °C, semicrystalline 275 ppm/Kbetween 120 and 130 °C, amorphous 353 ppm/K

Interpretation Cross-linked polyethylene below the crystallite melting range is rigid, just likestandard PE. When the crystallites melt the volume increases and the propertiesbecome rubbery-like. There is an elastic deformation of approx. 1.9% caused bythe varying force. The distance between upper and lower envelopes is propor-tional to the compliance (1/E). The overall slope of the curve envelope reflectsthe expansion of the sample.

Note: PE that is not cross-linked would be squeezed out between the disks aftermelting (plastic deformation).

Conclusions The thermomechanical properties of cross-linked polyethylene above the crystal-lite melting range are completely different to those of normal PE. Instead of vis-cous flow there is rubbery elastic behavior. The cross-linked macromoleculesprevent plastic deformation.

Documents

Overview of METTLER TOLEDO Thermal Analysis · polymers, polyamides, polyesters. Following on after thesecommonlyused thermoplastic materials, there are someapplications involving