THERMAL PROPERTIES

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THERMAL PROPERTIES
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THERMAL PROPERTIES

• Plays a vital role in evaluating the product
  performance processibilty characteristics in
  polymers.
• Thermal analytical methods monitor differences in
  some sample property as the temperature
  increases, or differences in temperature between
  a sample and a standard as a function of added
  heat. These methods are usually applied to solids
  to characterize the materials.

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THERMAL PROPERTIES

• Heat Deflection Temperature (HDT)
• Vicat Softening Temperature (VSP)
• Thermal Endurance
• Thermal Conductivity
• Thermal Expansion
• Low Temperature Brittleness
• Flammability
• Melting Point, Tm, and Glass Transition, Tg
  (DSC)
• Thermomechanical Analysis

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Heat Deflection Temperature
Defined as the temperature at which a standard
test bar (5 x ½ x ¼ in ) deflects 0.010 inch
under a stated load of either 66 or 264 psi.

• Significance
• HDT values are used to compare the elevated
  temperature performance of the materials under
  load at the stated conditions.
• Used for screening and ranking materials for
  short-term heat resistance.
• HDT values do not represent the upper temperature
  limit for a specific material or application.
• The data are not intended for use in design or
  predicting endurance at elevated temperatures.

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Test Methods, Specimen Conditioning

• Test Method
• ASTMD 648, ISO 75 -1 and 75-2
• Test Specimen
• 127mm (5 in.) in length, 13mm (½ in.) in depth by
  any width from 3mm (? in.) to 13mm ((½ in.)
• Conditioning
• 23 2oC and 50 5 RH for not less than 40 hrs
  prior to test.
• Two replicate specimens are used for each test

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Apparatus

• Specimen Supports Metal supports for the
  specimen of 100 2mm
• Immersion Bath
• Deflection Measurement Device
• Weights 0.455 MPa (66 psi) 2.5 or 1.82 MPa
  (264 psi) 2.5.
• Temperature Measurement System

Apparatus for Determination of HDT
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Procedure

• Measure the width and depth of each specimen
• Position the test specimens edgewise in the
  apparatus
• Position the thermometer bulb sensitive part of
  the temperature
• Stir the liquid-heat transfer medium thoroughly
• Apply the loaded rod to the specimen and lower
  the assembly into the bath.
• Adjust the load to obtain desired stress of 0.455
  MPa (66 psi) or 1.82 MPa (264 psi)
• Five minutes after applying the load, adjust the
  deflection measurement device to zero or record
  its starting position
• Heat the liquid heat-transfer medium at a rate of
  2.0 0.2oC/min.
• Record the temperature of the liquid
  heat-transfer medium at which the specimen has
  deflected the specified amount at the specified
  fibre stress.

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Calculation
The weight of the rod used to transfer the force
on the test specimen is included as part of the
total load. The load (P) is calculated as P
2Sbd2 / 3L Where, S Max. Fibre stress in the
specimen of 66 Psi / 264 Psi b Width of
specimen d Depth of specimen L Width of span
between support (4 in)
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Results Conclusion

• A bar of rectangular cross section is tested in
  the edgewise position as a simple beam.
• Load applied at the center to give maximum fibre
  stresses of 66 /264 psi.
• The specimen is immersed under load in a
  heat-transfer medium provided with a means of
  raising the temperature at 2 0.2oC/min.
• The temperature of the medium is measured when
  the test bar has deflected 0.25mm (0.010 in).
• This temperature is recorded as the deflection
  temperature under flexural load of the test
  specimen.

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Factors influencing

• HDT of unannealed (heat treatment) specimen is
  usually lower than that of annealed specimen.
• Specimen thickness is directly proportional to
  HDT because of the inherently low thermal
  conductivity of plastic materials.
• Higher the fibre stress or loading lower the HDT.
• Injection moulded specimen tend to have a lower
  HDT than compression moulded specimen.
• Compression moulded specimen are relatively
  stress free.

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Vicat Softening Point (VSP)
Defined as the temperature at which a flat ended
probe with 1 mm2 cross section penetrates a
plastic specimen to 0.04 inch (1 mm) depth.

• Significance
• Data obtained by this test method may be used to
  compare the heat-softening qualities of
  thermoplastic materials.
• This test method is useful in the areas of
  quality control, development and characterization
  of plastic materials.

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Test Methods, Specimen Conditioning

• Test Method
• ASTMD 1525 or ISO 306
• Test Specimens
• The specimen shall be flat, between 3 and 6.5mm
  thick and at least 10 by 10mm in area or 10mm in
  diameter.
• Conditioning
• 23 2oC and at 50 5 relative humidity of not
  less than 40 hrs

A minimum of two specimens shall be used to test
each sample.
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Apparatus

• Immersion Bath
• Heat-Transfer Medium
• Specimen Support
• Penetration-Measuring Device Masses 10 0.2N or
  50 1.0N
• Temperature-Measuring Device
• Needle

Fig. 2 Apparatus for Softening Temperature
Determination
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Procedure

• Prepare the immersion bath so that the
  temperature of the heat-transfer medium is
  between 20 and 23oC at the start of the test
• Place the specimen, which is at room temperature,
  on the specimen support.
• The needle should not be nearer than 3mm to the
  edge of the specimen.
• Gently lower the needle rod, without the extra
  mass, so that the needle rests on the surface of
  the specimen and holds it in position.
• Position the temperature-measuring device so that
  the sensing end is located within 10mm from where
  the load is applied to the surface of the
  specimen.
• Lower the assembly into the bath and apply the
  extra mass required to increase the load on the
  specimen to 10 0.2N (Loading 1) or 50 1.0N
  (Loading 2).
• After a 5-min waiting period, set the penetration
  indicator to zero.
• Start the temperature rise.
• Record the temperature of the bath when the
  needle has penetrated 1 0.01mm into the test
  specimen.

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Results Conclusion

• Vicat softening temperature is expressed as the
  arithmetic mean of the temperature of penetration
  of all specimens tested.
• If the range of penetration temperatures for the
  individual test specimens exceeds 2oC, record the
  individual results and repeat the test, using at
  least two new specimens.

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Thermal Conductivity

• Rate at which heat is transferred by conduction
  through a unit cross sectional area of a material
  when a temperature gradient exists perpendicular
  to the area.
• The coefficient of thermal conductivity (K
  factor), is defined as the quantity of heat that
  passes through a unit cube of the substance in a
  given unit time when the difference in
  temperature of the two faces is 10C.
• Mathematically, thermal conductivity is expressed
  as
• K Qt/A(T1-T2)
• Q amount of heat passing through a cross
  section, A causing a temperature difference, ?T
  (T1-T2), t thickness of the specimen.
• K is the thermal conductivity, typically measured
  as BTU.in / (hr.ft2.0F) indicates the materials
  ability to conduct heat energy.

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Significance

• Thermal conductivity is particularly important in
  applications such as headlight housings, pot
  handles hair curlers that require thermal
  insulation or heat dissipation properties.
• Computerized mold-filling analysis programs
  requires special thermal conductivity data
  derived at higher temperatures than specified by
  most tests.

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Test Methods Specimen

• Test method Guarded hot plate test
• ASTM D177, ISO 2582
• Test Specimen two identical specimens having
  plane surface of such size as to completely cover
  the heating unit surface
• The thickness should be greater than that for
  which the apparent thermal resistivity does not
  change by more than 2 with further increase in
  thickness

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Apparatus

• The apparatus is broadly of two different
  categories of the following
• Type I (low temperature) Temperature of cold
  plate 21 K, Temperature of heating unitlt500 K
• Type II (High temperature) Temperature of heating
  unit rangegt550 K -lt1350K
• Heating units
• Gap Metering Area
• Unbalance Detectors
• Cooling units
• Sensors for measuring Temperature difference
• Clamping force
• Measuring system for Temperature detector outputs

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Guarded Hot plate Apparatus
Guarded Hot plate Apparatus Courtesy Bayer
Material Data Sheet
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Procedure

• Two test specimens are sandwiched between the
  heat source (main heater) heat sink one on
  either side of the heat source.
• The clamping force is so adjusted that the
  specimens remain in perfect contact with the
  heater sink
• Guard heaters are provided to prevent heat flow
  in all except in the axial direction towards the
  specimen
• The time of stabilization of input out put
  temperature is noted.
• Temperature difference between the hot cold
  surfaces of the specimen should not be less that
  5 K or suitable differences as required.

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Calculation
The relationship between the quantity of heat
flow and thermal conductivity is defined as Q
K/ x Q Quantity of heat flow K Thermal
Conductivity X The distance the heat must
flow Thermal conductivity is calculated as
K Qt / A (T1 T2) Q Rate of heat
flow (w) T Thickness of specimen (m) A Area
under test (m2) T1 Temperature of hot surface
of specimen (k) T2 Temperature of cold surface
of specimen (k)
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Results Conclusion

• Thermal conductivity is calculated by using the
  value of rate of flow at a fixed temperature
  gradient.
• Data are obtained in the steady state

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Factors influencing

• Crystallites have higher conductivity.
• As the density of the cellular plastic decreases,
  the conductivity also decreases up to a minimum
  value and rises again due to increased convection
  effects caused by a higher proportion of open
  cells.

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Thermal Expansion (Coefficient of Linear Thermal
Expansion, CLTE)

• Measures the change in length per unit length of
  a material, per unit change in temperature.
• Expressed as in/in/0F or cm/cm/0C
• Mathematically, CLTE (a), between temperatures T1
  and T2 for a specimen of length L0 at the
  reference temperature, is given by
• a (L2 L1)/L0(T2 T1) ? L/L0?T

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Significance

• Determines the rate at which a material expands
  as a function of temperature.
• The higher the value for this coefficient the
  more a material expands and contracts with
  temperature changes.
• Plastics tend to expand and contract anywhere
  from six to nine times more than materials that
  are metallic.
• The thermal expansion difference develops
  internal stresses and stress concentrations in
  the polymer, which allows premature failure to
  occur.

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• Test Method ASTMD 696
• Test Specimen
• 12.5 by 6.3mm (½ in. by ¼ in.) 12.5 by 3mm (½ by
  ? in.), 12.5mm (½ in.) in diameter or 6.3mm (¼
  in.) in diameter.
• Conditioning 23 2oC and 50 5 RH for not
  less than 40h prior to test.

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Apparatus

• A vitreous silica dilometer
• Dial gage
• The weight of the inner silica tube the
  measuring device reaction shall not exert a
  stress gt 70 kPa on the specimen so that the
  specimen is not distorted or appreciably
  indented.
• Scale or Caliper
• Controlled Temperature Environment
• Means shall be provided for stirring the bath
• Thermometer or thermocouple

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Procedure

• Measure the length of two conditioned specimen at
  room temperature
• Mount each specimen in a dilatometer, install the
  dilatometer in the 30oC control environment.
• Maintain the temperature of the bath in the range
  32oC to 28oC 0.2oC until temperature of the
  specimen along the length is constant
• Record the actual temperature and the measuring
  device reading.
• Change to the 30oC bath, so that the top of the
  specimen is at least 50mm below the liquid level
  of the bath.
• Maintain the temperature of the bath in the range
  from 28 to 32oC 0.2oC
• Record the actual temperature and the measuring
  device reading.
• Change to 30oC and repeat the above procedure
  measure the final length of the specimen at room
  temperature.
• If the change in length per degree of temperature
  difference due to heating does not agree with the
  change length per degree due to cooling within
  10 of their average investigate the cause of the
  discrepancy and if possible eliminate.
• Repeat the test until agreement is reached.

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Calculation

• Calculate the CLTE over the temperature range as
• a ?L/Lo?T
• a Average coefficient of linear thermal
  expansion degree
• Celsius.
• ?L Change in length of test specimen due to
  heating or to
• cooling,
• Lo Length of test specimen at room
  temperature (?L and Lo being measured in the
  same units), and
• ?T Temperature differences, oC, over
  which the change in the length of
  the specimen is measured.
• The values of a for heating and for cooling shall
  be averaged to give the value to be reported.

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Result Conclusion

• Provide a means of determining the CLTE of
  plastics, which are not distorted or indented by
  the thrust of the dilatometer on the specimen.
• The specimen is placed at the bottom of the outer
  dilatometer tube with the inner one resting on
  it.
• The measuring device, which is firmly, attached
  to the outer tube is in contact with top of the
  inner tube and indicates variations in the length
  of the specimen with changes in temperature.
• Temperature changes are brought about by
  immersing the outer tube in a liquid bath or
  other controlled temperature environment
  maintained at the desired temperature.
• The nature of most plastics and the construction
  of the dilatometer make 30 to 30oC a convenient
  temperature ranges for linear thermal expansion
  measurements of plastics.
• This range covers the temperatures in which
  plastics are most commonly used.

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Factors influencing

• Thermal expansion is substantially affected
• by the use of additives
• especially fillers
• Wt Of loading
• Lowers the coefficient of thermal expansion.

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Differential Scanning Calorimetry (DSC)

• DSC measures the heat flow into or from a sample
  as it is heated, cooled or held under isothermal
  conditions
• Applications of DSC includes characterization of
• Polymers
• fibres
• Elastomers
• Composites
• films
• pharamaceuticals
• foods
• cosmetics

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• DSC provides the following important properties
  of materials
• Glass Transition Temp. (Tg)
• Melting point (Tm)
• Crystallization times Temp.
• Heats of melting crystallization
• Percent Crystallinities
• Heat set temp.
• OIT
• Compositional Analysis
• Heat capacities
• Heats of cure
• Thermal Stabilities

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Apparatus

• DSC apparatus consists of
• Furnace
• Temperature Sensor
• Differential Sensor
• Test Chamber Environment
• Temperature Controller
• Recording Device
• Sealed pans
• Balance

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• Samples Powder, Liquids, crystal

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Procedure

• DSC apparatus consists of two sealed pans sample
  and reference aluminum pans
• The pans are heated, or cooled, uniformly while
  the heat flow difference between the two is
  monitored.
• This can be done at a constant temperature
  (isothermally), but is more commonly done by
  changing the temperature at a constant rate,
  called temperature scanning.
• The instrument detects differences in the heat
  flow between the sample and reference plots the
  differential heat flow between the reference and
  sample cell as a function of temperature.

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First Order Transitions (Tc, Tm)

• Specimen mass appropriate of 5-mg is taken in the
  pan
• Intimate thermal contact between the pan and
  specimen is established for reproducible results.
  
• Heat the sample at a rate of 10oC/min under inert
  gas atmosphere from 50oC below to 30oC above the
  melting point to erase the thermal history .
• The selection of temperature and time are
  critical when effect of annealing is studied.
• Hold temperature for 10min.
• Cool to 50oC below the peak crystallization
  temperature at a rate of 10oC/min and record the
  cooling curve.
• Repeat heating as soon as possible under inert
  purge gas at a rate of 10oC/min, and record the
  heating curve.

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For Second order Transition (Tg)

• Use a specimen mass of 5-mg.
• Perform and record a preliminary thermal cycle as
  up to a temperatures 30oC above the extrapolated
  end temperature, Te, to erase previous thermal
  history, heating at a rate of 20oC/min.
• Hold temperature for 10min.
• Quench cool to 50oC below the transition
  temperature of interest.
• Hold temperature for 10min.
• Repeat heating at a rate of 20oC/min, and record
  the heating curve until all desired transition
  have been completed.

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Typical DSC curves
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Measurement of various Properties/Explanations

• Heat Capacity
• Heating the sample Reference pans, the the
  difference in heat output of the two heaters is
  plotted against temperature. i.e the heat
  absorbed by the polymer against temperature.

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Heat Capacity

• The heat flow at a given temperature is
  represented units of heat, q supplied per unit
  time, t.
• The heating rate is temperature increase T per
  unit time, t.

Dividing,
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Glass Transition

• Property of the amorphous region
• Below Tg Disordered amorphous solid with
  immobile molecules
• Above Tg Disordered amorphous solid in which
  portions of molecules can wiggle around
• A second order transition ( Increase in heat
  capacity but there is no transfer of heat

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Crystallization

• Above Tg, the polymers are in mobile conditions.
• When they reach the right temperature, they gain
  enough energy to move into very ordered
  arrangements, which we call crystals,
• When polymers fall into these crystalline
  arrangements, they give off heat.
• When this heat is dumped out, there is drop in
  the heat flow as a big dip in the plot of heat
  flow versus temperature

We call crystallization an exothermic transition.
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Melting
Above Tc, we reach the polymer's melting
temperature, or Tm, those polymer crystals begin
to fall apart, that is they melt. The chains
come out of their ordered arrangements, and begin
to move around freely. Melting is a first order
transition (Tm).
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Putting it all together
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Polymer crystallinity
Measure the area of under the melting of the
polymer. Plot of heat flow per gram of material,
versus temperature.
multiply this by the mass of the sample
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Degree of crystallinity is given by
X 100 Xc
Where H Heat of Fusion determined from DSC
thermogram Hm Heat of fusion of a 100
crystalline sample
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Results Conclusion

• DSC thermograms provides an elaborate picture of
  various transitions in a polymer.
• The degree of crystallinity in a polymer sample,
  specific heat etc. can be determined.
• Any side reaction (for example, crosslinking,
  thermal degradation or oxidation) shall also be
  reported and the reaction identified if possible.

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Factors affecting

• Addition of fillers affects the transitions in
  DSC
• Previous thermal history of the samples also
  affects the DSC transitions.
• There should be proper contact between the
  samples pans

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Thermo Gravimetric Analysis (TGA)
Changes in weight of the specimen is recorded as
the specimen is heated in air or in a controlled
atmosphere such as nitrogen
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Terminologies

• Highly volatile matter moisture, plasticizer,
  residual solvent or other low boiling (200oC or
  less) components.
• Medium volatile matter medium volatility
  materials such as oil and polymer degradation
  products. In general, these materials degrade or
  volatilize in the temperature range 200 to 750oC.
  
• Combustible material oxidizable material not
  volatile (in the unoxidized from) at 750oC, or
  some stipulated temperature dependent on
  material. Carbon is an example of such a
  material.
• Ash nonvolatile residues in an oxidizing
  atmosphere which may include metal components,
  filler content or inert reinforcing materials.
• Mass loss plateau a region of a
  thermogravimetric curve with a relatively
  constant mass.

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Significance
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Apparatus
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Procedure

• Establish the inert (nitrogen) and reactive (air
  oxygen) gases at the desired flow rates in the
  range of 10 to 100mL/min.
• Switch the purge gas to the inert (nitrogen) gas.
• Zero the recorder and tare the balance.
• Open the apparatus to expose the specimen holder.
• Prepare the specimen of 10 to 30mg and carefully
  place it in the specimen holder.
• Position the specimen temperature sensor
• Enclose the specimen holder.
• Record the initial mass.
• Initiate the heating program within the desired
  temperature range.
• Record the specimen mass change continuously over
  the temperature interval.
• The mass loss profile may be expressed in either
  milligrams or mass percent of original specimen
  mass.
• Once a mass loss plateau is established in the
  range 600 to 1200oC, depending on the material,
  switch from inert to reactive environment.

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Calculation
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Calculation
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Calculation
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Calculation
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Factors influencing

• Oil-filled elastomers have such high molecular
  weight oils and such low molecular weight polymer
  content that the oil and polymer may not be
  separated based upon temperature stability.
• Ash content materials (metals) are slowly
  oxidized at high temperatures and in an air
  atmosphere, so that their mass increases (or
  decreases) with time. Under such conditions, a
  specific temperature or time region must be
  identified for the measurement of that component.
  
• Polymers, especially neoprene and acrylonitrile
  butadiene rubber (NBR), carbonize to a
  considerable extent, giving low values for the
  polymer and high rubber values.
• Others, such as calcium carbonate, release CO2
  upon decomposition at interference is dependent
  upon the type and quantity of pigment present.

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Dynamic Mechanical Analysis (DMA)

• DMA is a technique in which a substance while
  under an oscillating load is measured as a
  function of temperature or time as the
  substance is subjected to a controlled
  temperature program in a controlled atmosphere.
• Dynamic Mechanical Analysis (DMA) examines
  materials between -170C and 1000C.

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DMA - Storage Modulus
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DMA for Testing Recyclates Virgin ABS and ABS
with 25 Recyclate

• The high inherent sensitivity of DMA
  provides a means of testing polymers with
  recyclates
• In this example of virgin ABS and ABS with 25
  recyclates, the effects of the recyclates can
  be easily observed
• Testing was done with 3-point bending probe

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FOURIER TRANSFORM INFRARED TECHNIQUE

• Identification of plastic through structural
  analysis
• Identification of additives, fillers, etc.
• Polymer blend analysis
• Monomer content analysis on plastics
• Compatibility studies on blends
• Curing of polymers
• Degradation studies

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