thermal character is at ion of polymers
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THERMALCHARACTERISATION
OF POLYMERS
THERMALCHARACTERISATION
OF POLYMERS
PRESENTED BY MALLIKA JOLLY
UNDER THE GUIDANCE OF
Dr.(Mrs).VARSHA POKHARKAR
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THERMAL ANALYSISTHERMAL ANALYSIS DEFINITION: A branch of materials science where the
properties of materials are studied as they change with
temperature.
ConventionalTA
techniques:DTA temp. diff.
DSC - enthalpy
TGA mass
TMA - deformation
DMA deformation
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Advantages ofTAover other analytical methods:Wide temperature range
Any physical form of sample can be accommodated using variety of vessels
Small amount of sample is required (0.1g-10mg)Atmosphere in vicinity of sample can be standardized
Time required can range from several minutes to several hours
Instruments are priced resonably
T.AInstrumentation:
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DIFFERENTIAL THERMAL
ANALYSIS
DIFFERENTIAL THERMAL
ANALYSIS DTA measures temperature difference between a sampleand an inert reference (T= TS-TR ) while heat flow to the
reference and the sample remains the same
Instrumentation:
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Furnace temperature is recorded as a function of time
Minimum T measured by DTA : 0.01K
Crystallization: exothermic
Melting: endothermic
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DIFFERENTIAL SCANNING
CALORIMITRY
DIFFERENTIAL SCANNING
CALORIMITRY
The basicdifference betweenDTAandDSCDSC- calorimetric method, energy differences measured.
DTA- temperature differences measured.
The applications of both techniques are similar, but DSC is now morepopular.
DTA is used for higher temperature and qualitative applications.
DSC is used for calorimetric determinations, sample purity
determinations and kinetics
The sample and reference are maintained at the same temperature,
even during a thermal event (in the sample)
DSC measures the energy required to maintain zero temperature
differential between the sample and the reference(dq/dt)
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Two major types ofDSC instruments areavailableHeat fluxdevice more popular;more stable baseline and more durable cell.
Difference in heat flow into S and R is measured with (linear) change in sample
temperature.
Power compensationdevice betterresolution; faster heating and coolingrates.
S and R heated by separate heaters to keep same temperature, as T is changed
linearly
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accurately-weighed samples (~3-20 mg, usually 3-5 mg for simple
powders) small
sample pans (0.1 mL) of inert or treated metals (Al, Pt, stainless)
several pan configurations, e.g., open , pinhole, or hermetically-sealed
pans
same material and configuration should be used for the sample and the
reference material should completely cover the bottom of the pan to
ensure good thermal contactavoid overfilling the pan to minimize thermal lag from the bulk of the
material to the sensor
small sample masses and low heating rates increase resolution, but at
the expense of sensitivity
Sample Preparation
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Packing schemes for open type
and hermetically sealed-type
sample vessels. Only samples I
and IV are correctly packed
Sample Packing
Selection of sample vessels used inDSC andDTA
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Purge GasesSample may react with air - oxidising or burning
Control moisture content of atmosphere
Use inert gas e.g. nitrogen or argon
Flowing purge gasIn some cases deliberately choose reactive gas, e.g.
hydrogen to reduce an oxide to metal
carbon dioxide which affects decomposition of metal carbonate
Removes waste products from sublimation or decomposition
Endothermic events
meltingSublimation
Desolvation
chemical reactions
solid-solid transitions
Exothermic eventsCrystallization
Decomposition
chemical reactions
solid-solid transitions
Baseline shiftsglass transition
TypicalFeatures of aDSCTrace
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Examines the mass change of a sample as a function of
temperature in the scanning mode or as a function of time in the
isothermal mode.
Thermo gravimetric AnalysisThermo gravimetric Analysis
Ti :
Tf :
Lowest temperature at
which theonset of amass change can be
detected
Lowest temperature by
which the process
resp
onsibl
efor
the
m
asschange has been
completed
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TG curves are recorded using a thermo balance
Instrumentation:
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1. no change
2. desorption/drying
(rerun)
3. single stage
decomposition
4. multi-stage
decomposition
5. as 4, but no
intermediates or heating rate
too fast
6. atmospheric reaction
7. as 6, but product
decomposes at higher
temperature
Typical TG curves
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The following experimental parameters shouldbenoted: sample identification;
form and dimensions of sample; mass of sample, initial and final;
preconditioning of sample;
crucible shape, size and material;
type and position of sample thermocouple;
atmosphere and gas flow rate; heating rate or isothermal temperature;
reference material used for temperature calibration;
type of instrument used.
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Applications ofThermalA
nalysis
Applications ofThermalA
nalysisGlass Transition TemperatureMelting Point
Heat Capacity Measurement by DSC
Purity Determination by DSC
Crystallinity Determination by DSCPolymorphism
Phase Transition
Gel- Sol Transition
Temperature measurement
Enthalpy measurementReaction rate kinetics
Molecular Rearrangement during Scanning
Annealing
BoundWater Content
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GLASS TRANSITIONThe glass transition temperature, Tg, is the temperature at which a
glassy polymer becomes rubbery (soft and flexible) on heating and arubbery polymer becomes glassy (hard and brittle) on cooling.
More specifically, it defines a pseudo second order phase transitionin which a supercooled melt yields, on cooling, a glassy structure
and properties similar to thoseof crystallinematerials e.g. of anisotropic solid material.
Physical properties that undergo changes at Tg:
Hardness
Volume
Modulus% elongation to break
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MeltingProcesses byDSC
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Heat CapacityMeasurement UsingDSC
Baseline change h occurs for substances with different Cp, or for same
substance after phase change.
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Purity byDSC
Peak width a valuablemeasure of purity:
impurities lower themelting point
Less pure (non-perfect) crystals melt
first followed by purer larger crystals
polymorphism interferes with
purity determination, especially
when a transition occurs in the
middleof themelting peak
Accuratemeasurement of
Hf needs pure samples of
polymorphs
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CrystallinityPolymers
Crystalline Amorphous
Molecules are
arranged in
regularorder
Molecules are
arranged in random
disordered state
Crystallinity is the amount of crystallineregion in polymerw.r.t.
amorphous content.
Crystallinity influences polymer properties
Polymers are semi- crystallineDegreeof crystallinity is determined by:
Structureregularity
Compactness
flexibility
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Polymorphism is the term used to describe the occurrence of different
structural forms of a material,and is observed in polymers such as polyamides, polypropylene,
polysaccharides and fluorinated polymers.
X-ray diffractometry is the principal technique used to probe the
polymorphic nature of polymers.
The temperature and enthalpy change associated with crystal to crystaltransitions are measured using DSC.
Polymorphism
A phase diagram is a graphical representation of the relationship
between a given set of experimental parameters and the phase changesoccurring in a material. Sample volume, transition temperature and
enthalpy, pressure and composition of the material are commonly used
parameters in phase diagrams
Phase Diagrams
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Polymer chains can form infinite networks by either physical or chemical
association. Reversible networks in the presence of a solvent formreversible gels. The cross-links between individual chains in a reversible gel
are localized, but not permanent, and the interacting groups dissociate and
reassociate according to the conditions of thermodynamic equilibrium. The
gel structure present at low temperatures is transformed on heating and a
liquid state is observed. This process, which can be reversed on cooling, iscalled the gel-sol transition.
Gel-SolTransition
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Characterization ofPTFEusingadvancedthermal analysis techniques
CASESTUDYCASESTUDY
Introduction:Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer often referred to by its
trademark name, TEFLON
PTFE generally has a high density (around 2.2 g/cm) and high melting point
(approximately 327C)
At atmospheric pressures , crystallineor partially crystalline PTFE undergoes
several phase changes from sub-ambient temperatures up to themelting point.
Below19C, a well-ordered hexagonal crystal structure is obtained. When heating
to higher temperatures, the crystalline PTFE turns into a partially ordered
hexagonal phase. Above 30C, thematerial converts into a pseudohexagonal, very
disordered phase. This phase is stable until thematerial reaches themelting
region around 330C.
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Various thermal analysis techniques wereemployed for the
characterization of PTFE
:
Heat Flux DSC : Specific heat
Dialatometer : Thermal expansion measurements
Laser Flash apparatus :T
hermal diffusivityDynamic Mechanical Analyzer : Viscoelastic properties
Experimental:
The system allows measurement of different thermophysical properties
between -125C and 1100C (using two interchangeable furnaces).
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Apparent specific heat (specific heat and overlapped transition
enthalpies) of the PTFE
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Thermal diffusivity of the PTFE
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Thermal conductivity of PTFE=
thermal diffusivity specific heat density
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Conclusion:
Various thermophysical and thermomechanical properties were
measured on Polytetrafluoroethylene (PTFE) from -170C to 370C.
Comparison of the different physical properties allows more
detailed insight into the changes inside thematerial during the
phase transitions around room temperature.
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