thermal character is at ion of polymers

8/8/2019 Thermal Character is at Ion of Polymers

1/30

THERMALCHARACTERISATION

OF POLYMERS

THERMALCHARACTERISATION

OF POLYMERS

PRESENTED BY MALLIKA JOLLY

UNDER THE GUIDANCE OF

Dr.(Mrs).VARSHA POKHARKAR


2/30

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


3/30

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:


4/30

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:


5/30

Furnace temperature is recorded as a function of time

Minimum T measured by DTA : 0.01K

Crystallization: exothermic

Melting: endothermic


6/30

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)


7/30

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


8/30

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


9/30

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


10/30

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


11/30

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


12/30

TG curves are recorded using a thermo balance

Instrumentation:


13/30

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


14/30

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.


15/30

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


16/30

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


17/30

MeltingProcesses byDSC


18/30

Heat CapacityMeasurement UsingDSC

Baseline change h occurs for substances with different Cp, or for same

substance after phase change.


19/30

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


20/30

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


21/30

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


22/30

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


23/30

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.


24/30

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).


25/30


26/30

Apparent specific heat (specific heat and overlapped transition

enthalpies) of the PTFE


27/30

Thermal diffusivity of the PTFE


28/30

Thermal conductivity of PTFE=

thermal diffusivity specific heat density


29/30

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.


30/30

THANKYOUTHANKYOU

thermal character is at ion of polymers

Documents