Properties of plastics

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THERMAL PROPERTIES

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• 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.
THERMAL PROPERTIES

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• 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
THERMAL PROPERTIES

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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 (⅛ 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 for Determination
of HDT
• 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

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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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• 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.
Results & Conclusion

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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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Fig. 2 Apparatus for Softening Temperature Determination
• Immersion Bath
• Heat-Transfer Medium
• Specimen Support
• Penetration-Measuring Device
Masses: 10 ± 0.2N or 50 ±1.0N
• Temperature-Measuring Device
• Needle
Apparatus

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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 unit:<500 K
• Type II (High temperature) Temperature of heating unit
range:>550 K -<1350K
• 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
Courtesy: Bayer Material Data Sheet
Guarded Hot plate Apparatus

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• 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.
Procedure

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

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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 (α), between
temperatures T1 and T2 for a specimen of
length L0 at the reference temperature, is
given by :
• α = (L2 – L1)/[L0(T2 – T1)] = L/L0ΔT

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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 ⅛ 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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• A vitreous silica dilometer
• Dial gage
• The weight of the inner silica tube +
the measuring device reaction shall
not exert a stress > 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
Apparatus

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

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

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

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 Terminologies:
 Glass Transition Temperature (Tg): it is defined as the temperature below
which the polymer is in the glassy state & above which it attains rubbery
state.
 First order transitions: In a first-order transition there is a transfer of heat
between system and surroundings and the system undergoes an abrupt
volume change eg. Melting point (Tm), Crystallization Temperature (Tc)
 Second order transitions: In a second-order transition, there is no
transfer of heat, but the heat capacity does change. The volume changes to
accommodate the increased motion of the wiggling chains, but it does not
change discontinuously..
• 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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 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.
First Order Transitions (Tc, Tm)

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 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.
For Second order Transition (Tg)

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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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Dividing,
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.

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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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We call crystallization an exothermic transition.
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:

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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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multiply this by the mass of the sample
Polymer crystallinity
Measure the area of under the melting of the
polymer.
Plot of heat flow per gram of material, versus
temperature.

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X 100% = Xc
Where H’= Heat of Fusion determined from DSC thermogram
H*m= Heat of fusion of a 100% crystalline sample
Degree of crystallinity is given by

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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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 Thermogravimetric curves (thermograms) provide information regarding
polymerization reactions, the efficiencies of stabilizers and activators, the
thermal stability of final materials, and direct analysis.
Provides a general technique to determine the amount of highly volatile matter,
medium volatile matter, combustible material and ash content of compounds.
 This test method is useful in performing a compositional analysis in polymers
This test method is applicable to solids and liquids.
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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 Highly volatile matter content may be determined by the following equation
V = [(W-R)/W] x 100% (1)
Where:
V = highly volatile matter content, as received basis (%),
W = original specimen mass (mg), and
R = mass measured at Temperature X (mg).
Calculation

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 Medium volatile matter content can be determined using the following
equation:
O = [(R-S)/W] x 100% (2)
Where:
O = medium volatile matter content, as-received basis, %
R = mass measured at Temperature X, (mg),
S = mass measured at Temperature Y, (mg), and
W = original specimen mass, (mg).
Calculation

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Combustible material content may be calculated by the following equation:
C = [(S-T)/W] x 100% (3)
Where:
C = combustible material content, as-received basis, (%),
S = mass measured at Temperature Y, (mg),
T = mass measured at Temperature Z, (mg) and
W = original specimen mass, (mg).
Calculation

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 The ash content may be calculated using the following equation:
A = (T/W) x 100% (4)
Where:
A = ash content, as received basis, (%),
T = mass measured at Temperature Z, (mg) and
W = original specimen mass.
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 -170°C and
+1000°C.

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DMA - Storage Modulus
Storage Modulus
DSC
Tg
Hard and
Brittle
Elastic and
Deformable
Fluid
Tm
10
5
10
6
10
7
10
8
10
9
10
10
Temperature

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DMA for Testing Recyclates
Virgin ABS and ABS with 25%
Recyclate
-150 Temperature (C) 100
E’
E”
DMA of ABS With Recyclates
 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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