Thermal Analysis of Materials

7/27/2019 Thermal Analysis of Materials

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Hamzah Mukhtar

Pablo Ramos

Vamakshi Khati

Daniel Gomez

Thermal Analysis of Materials

Group-6


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Contents

PROBLEM

INTRODUCTION TO PRODUCT

DSC

DILATOMETRYDMTA

CONCLUSION

SUMMARY

REFERNCES


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Problem

One Asian customer has a problem with a polymergland that fails after a few months. It is observed that

this polymer has multiple fractures and its surface is a

bit harder than the reference sample. This polymer

cable gland is used in power cable.

There are several factors that are to be considered for

failure of a material.


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Introduction to Product

Polymer cable glands attaches and holds the end of acable to the equipment.

Polymer properties specifically depends on some

specific parameters like Tg, Tm, temperature of

crystallisation, degree of crystallinity and degradation.

So to estimate why the polymer becomes harder and

fractures we have to analyse the characteristics of

polymers using DSC, DMTA and Dilatometry.


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Differential Scanning Calorimetry (DSC)

DSC stands for differential scanning calorimetry is athermo-analytical technique.

It measures the amount of heat absorbed or released

when a sample is cooled or heated and thus providing

the data that is related with them.

DSC chambers consist of two more or less equal

chambers one chamber contains the inert reference

sample (usually alumina) where the heat capacitance is

well defined in more or less all temperature ranges and

in the other chamber is our sample.


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Schematic diagram of a typical differential scanning calorimeter.


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DSC determines the thermal transitions in polymers, by

which we can understand the behaviour of our polymer cable

gland and to compare it with our reference sample. The

information thus collected can determine the changes in the

polymer.

The following diagram shows some changes in our material

and they are showed in endothermic/exothermic reactions.


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Dilatometry It is the thermo-analytical method which is used for the

measurement of shrinkage and expansion of the materialsunder controlled temperature range.

The amount of shrinkage or expansion is dependent on

material properties or characteristics.

By using dilatometry following properties can be measured Thermal expansion and coefficient of thermal expansion

Volumetric expansion

Influence of additives/raw materials

Density change

Glass transition temperature (Tg)

Dilatometric softening point (Td)

Phase transition


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Pushrod dilatometry is a method that is used for determination

of dimensional changes versus temperature or time while

sample is subjected to a controlled temperature program.


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L0=Initial sample

length

T=Change intemperature


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Dynamic Mechanical Thermal Analysis

DMTA or DMA measures the temperature dependent visco-elastic properties along with modulus of elasticity.

Strain is measured by applying fluctuating stress and thus

complex modulus is determined. This approach can be used

to locate the Tg of the material, as well as to identifytransitions corresponding to other molecular motions.

Temperature-sweeping DMA is often used to characterize

the glass transition te

DMA measures the visco-elastic properties by transient ordynamic oscillatory tests temperature of a material.


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Transient tests include stress relaxation and creep. In

dynamic oscillatory test, a sinusoidal stress is applied

and sinusoidal strain is measured along with phase

difference. For polymers the phase difference is

intermediate as in next figure.


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In Asia region these glands used for power cables are made ofpolymers with high content in halogens (for instance PVCcan reach 57% of chloride), this is also a problem because itcould lead to degradation of the polymer easily. Degradationcan occur as a result of the formation and then breakage ofdouble bonds (for instance when a Carbon is bond with ahalogen and it breaks). This occurs in PVC in the presence ofan acid species. Active Hydrogen atoms will remove aChlorine atom from the polymer molecule, formingHydrochloric acid (HCl) causing de-chlorination of adjacent

Carbon atoms. These de-chlorinated Carbon atoms tend toform double bonds which can be broken in an ozoneatmosphere (normal conditions).

Polymer Description


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Conclusion Some mechanisms of hardening are related with

recrystallization, as they will increase the percentage

of crystallinity of the polymer. As a result it will get

harder, and get brittle, which along with stresses could

lead to failure.

Introducing oxygen and carbon atoms in the main

chain will lead to hardening, besides C-C bonds,

oxygen atoms are introduced generating a dipole. The

link will be reinforced so there will be an increase in

resistance to being deformed, so atmospheric

conditions should also be taken into account.


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Conclusions are related then to avoid recrystallization

(be aware of Tg and temperature of recrystallization of

the polymer), take into account atmosphere conditionsand content of halogens in the polymer used.


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Summary

Introduction to polymer glands

Discussed about the Problem to the

product

Methods being used to Analyse the

Problem


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References http://en.wikipedia.org/wiki/Differential_scanning_c

alorimetry

http://en.wikipedia.org/wiki/Differential_thermal_an

alysis

http://www.pslc.ws/macrog/dsc.htm

http://www.mate.tue.nl/mate/pdfs/10367.pdf

http://en.wikipedia.org/wiki/Dynamic_mechanical_a

nalysis

http://en.wikipedia.org/wiki/Polyvinyl_chloride

http://www.files.chem.vt.edu/chem-

dept/marand/Lecture23.pdf

Documents

Thermal Analysis of Materials