Thermogravimetric Analysis.pptx

Thermogravimetr
ic Analysis
Sohail AD

What is TGA?
06/06/2023 12:49 saaku Thermogravimetric Analysis 2
• Thermogravimetric analysis or thermal gravimetric analysis
(TGA) is a method of thermal analysis in which the mass of a
sample is measured over time as the temperature changes.
• This measurement provides information about physical
phenomena, such as phase transitions, absorption and
desorption as well as chemical phenomena including
chemisorption's, thermal decomposition, and solid-gas
reactions (e.g., oxidation or reduction)

Types of TGA
1) Isothermal or static thermogravimetry: In this technique the sample
weight is recorded as function of time at constant temperature.
2) Quasistatic thermogravimetry: In this technique the sample is heated
to constant weight at each of series of increasing temperatures.
3) Dynamic thermogravimetry: In this technique the sample is heated in
an environment whose temperature is changing in a predetermined
manner generally at linear rate. This type is generally used.

Principle of the Instrument
• In thermo-gravimetric analysis, the sample is heated in a given
environment (air, N2, CO2, He, Ar, etc.) at controlled rate. The change in
the weight of the substance is recorded as a function of temperature or
time.
• The temperature is increased at a constant rate for a known initial weight
of the substance and the changes in weights are recorded as a function of
temperature at different time interval.
• This plot of weight change against temperature is called thermo-
gravimetric curve or thermo-gram, this is the basic principle of TGA.

TGA Curve
Thermogravimetric Analysis 5
• The instrument used for thermo-
gravimetry is a programmed precision
balance for rise in temperature known
as Thermo-balance.
• Results are displayed by a plot of mass
change versus temperature or time and
are known as Thermogravimetric
curves or TG curves.
06/06/2023 12:49 saaku

TGA Curve
• TG curves are normally plotted with the mass change (Dm) in percentage
on the y-axis and temperature (T) or time (t) on the x-axis.
• There are two temperatures in the reaction, Ti(procedural decomposition
temp.) and Tf (final temp.) representing the lowest temperature at which
the onset of a mass change is seen and the lowest temperature at which
the process has been completed respectively.
• The reaction temperature and interval (Tf-Ti) depend on the experimental
condition; therefore, they do not have any fixed value.

Instrument Detail
The instrument consist of five major elements;
1) Recording balance
2) Sample holder
3) Furnace
4) Temperature programmer /controller (thermocouple)
5) Recorder

Instrument Detail
1. Recording Balance
A microbalance is used to record a change in mass of
sample/substance.
An ideal microbalance must possess following features:
• It should accurately and reproducibly record the change in mass of
sample in ideal ranges of atmospheric conditions and temperatures.
• It should provide electronic signals to record the change in mass
using a recorder.

Instrument Detail
• The electronic signals should provide rapid response to change in mass.
• It should be stable at high ranges, mechanically and electrically.
• Its operation should be user friendly.
After the sample has been placed on microbalance, it is left for 10-15min to
stabilize. Recorder balances are of to types:
a) Deflection-type instruments
b) Null-type instruments

Instrument Detail
Deflection-type balances: When balance arm is deflected by a change in weight, the
relative illumination of photocells from light source changes due to the movement of shutter
attached to the balance beam, resulting in flow of compensating current through one of the
pair of photocells. The current produced is proportional to the change in sample weight and
after amplification is passed to the coil thus restoring it to its original position.
Deflection balances are following types;
i. Beam type
ii. Helical type
iii. Cantilevered beam
iv. Torsion wire

Instrument Detail
Null point balances: As weight change occurs, the balance beam
starts to deviate from its normal position, a sensor detects the
deviation and triggers the restoring force to bring the balance beam
back to the null position. The restoring force is directly proportional to
the weight change.

Instrument Detail
2. Sample Holder
• The sample to be studied is placed in sample holder or crucible.
It is attached to the weighing arm of microbalance.
• There are different varieties of crucibles used. Some differ in
shape and size while some differ in materials used.
• They are made up from platinum, aluminum, quartz or alumina
and some other materials like graphite, stainless steel, glass
etc.

Instrument Detail
2. Sample Holder
Crucibles: Crucibles should have temperature at least 100K greater than
temperature range of experiment and must transfer heat uniformly to sample.
Therefore the shape, thermal conductivity and thermal mass of crucibles are
important which depends on the weight and nature of sample and temperature
range.
There are different types of crucibles;
a. Shallow pans(used for volatile substances)
b. Deep crucibles (Industrial scale calcination)
c. Loosely covered crucibles (self generated atm. Studies)
d. Retort cups (Boiling point studies)

Instrument Detail
3. Furnace
• The furnace should be designed in such way that it produces a linear
heating range.
• It should have a hot zone which can hold sample and crucible and its
temperature corresponds to the temperature of furnace.
• There are different combinations of microbalance and furnace
available. The furnace heating coil should be wound in such a way
that there is no magnetic interaction between coil and sample or
there can cause apparent mass change

Instrument Detail
4. Temperature programmer /controller (thermocouple)
Temperature measurement is done in no. of ways thermocouple is the
most common technique.
The position of the temperature measuring device relative to the
sample is very important.
The major types are:
a. The thermocouple is placed near the sample container and it has
no contact with the sample container. This isn’t a good
arrangement where low-pressure are employed.

Instrument Detail
b. The sample is kept inside the sample holder but not in contact
with it. This arrangement is better than that of (a) because it
responds to small temperature changes.
c. The thermocouple is placed either in contact with sample or
with the sample container. This is the best arrangement of
sample temperature detection.

Instrument Detail

Instrument Detail
5. Recorder
The recording systems are mainly of 2 types;
a) Time-base potentiometric strip chart recorder.
b) X-Y recorder.
• In some instruments, light beam galvanometer, photographic paper
recorders or one recorder with two or more pens are also used.
• In the X-Y recorder, we get curves having plot of weights directly against
temperatures.
• However, the percentage mass change against temperature or time would
be more useful.

Scope of the Instrument
• From TGA, we can determine the purity and thermal stability of
both primary and secondary standard.
• Determination of the composition of complex mixture and
decomposition of complex OR composition of complex
systems.
• For studying the sublimation behavior of various substances.
• TGA is used to study the kinetics of the reaction rate constant.

• Used in the study of catalyst: The change in the chemical states
of the catalyst may be studied by TGA techniques. (ZnZnCrO4)
Zinc-Zinc chromate is used as the catalyst in the synthesis of
methanol.
• Analysis of the dosage form.
• Oxidative stability of materials.
• Estimated lifetime of a product.

• TGA is often used to measure residual solvents and moisture,
but can also be used to determine solubility of pharmaceutical
materials in solvents.
• The effect of reactive or corrosive atmosphere on materials.
• Moisture and volatiles contents on materials.

Advantages of Instrument
• A relatively small set of data is to be treated.
• Continuous recording of weight loss as a function of
temperature ensures Equal weightage to examination over the
whole range of study.
• As a single sample is analyzed over the whole range of
temperature, the variation in the value of the kinetic parameters,
if any, will be indicated.

Limitations of Instrument
• The Chemical or physical changes which are not accompanied
by the change in mass on heating are not indicated in
thermogravimetric analysis.
• During TGA, Pure fusion reaction, crystalline transition, glass
transition, crystallization and solid state reaction with no volatile
product would not be indicated because they provide no change
in mass of the specimen.

Practical Usage of Instrument
Sample size: The sample should weigh about 50 milligrams.
Sample type and compatibility: TGA is typically used for
pharmaceutical substances.
Unique capabilities: TGA records weight loss as a function of
temperature.
Timing: Typical analysis time is about 1 hour

Instrument Parameters & Effect: Furnace heat rate and furnace
atmosphere are the factors which might affect the outcomes of TGA
analysis.
Furnace Heating rate: The temperature at which the compound (or
sample) decompose depends upon the heating rate. When the
heating rate is high, the decomposition temperature is also high. A
heating rate of 3.5°C per minute is usually recommended for reliable
and reproducible TGA.

Furnace atmosphere: The atmosphere inside the furnace surrounding the
sample has a profound effect on the decomposition temperature of the
sample. A pure N2 gas from a cylinder passed through the furnace which
provides an inert atmosphere.
• Other factors affecting TGA curve:
o Sample holder
o Heat of reaction
o Compactness of sample
o Previous history of the sample

Illustrations
Research Paper-1
• Nguyen et al. investigated the detection of suspected carcinogen azo
dyes in textiles using thermogravimetric analysis. TGA was
performed on 18 samples of women panties comprising of different
colors and made from cotton, polyester and nylon.
• The nature of fabrics was identified based on their unique
thermogravimetric analyses (TGA) pattern. Aromatic amines
produced from thermal degradation of the samples were identified
using NIST mass spectra data base.

Illustrations
Research Paper-1
• Quantitative TGA data were categorized into four groups: Temperature (C), time
(s), weight loss % and first derivative of weight loss/time.
• Cotton, polyester, and nylon materials showed unique behavior in the TGA
experiment regardless of their colors or origin of manufacturing. All cotton,
polyester and nylon samples were found to be degraded maximumly between
350 to 390 OC, 448 to 450 OC and 460–470 OC, respectively. Red cotton sample
was made of material composition of 40% cotton and 60% polyester showing that
the cotton fraction showed DTG consistent with the cotton materials. Sample’s
descriptions and their TGA and DG results are shown in Table.

Illustrations
Research Paper-1

Illustrations
Research Paper-1
Data obtained experimentally by TGA/GCMS provided information
about the thermal stability of cotton, polyesters and nylon textiles and
their coloring dyes. The results showed that TGA and DG experiments
can be used to identify the materials used in making the textile as
cotton, nylon or polyester base form their degradation pattern. The
method can also be used for quick screening test for textiles that may
contain azo dyes. The procedure does not require any sample
preparation and can be automated and finished in less than 30 min
compare to several hours using standard procedures.

Illustrations
Research Paper-2
• Satheesh Kumar et al. investigated the Thermogravimetric
Analysis and Morphological Behavior of Melamine-
Formaldehyde Filled Polyvinyl Acetate—polyester Nonwoven
Fabric Composites.
• From the thermogravimetric analysis, the improvement in
thermal stability of the composites was noticed with increase in
the MF content.

Illustrations
Research Paper-2

Illustrations
Research Paper-2
• TGA and its derivative thermograms for different amounts of MF-
incorporated PVAc-polyester nonwoven fabric composites are shown
in Figure. From the thermograms, it is found that all the samples
undergone two-step degradation processes.
• The temperature range of decomposition, the percentage weight loss
in each step and the percentage ash content for different amounts of
MF-incorporated PVAc-polyester nonwoven fabric composites are
given in Table.

Illustrations
Research Paper-2
• It can be observed that, the onset degradation temperature of the composites increased
with increase in the MF content. This can be attributed to the formation of hydrogen bond
between the PVAc and MF resin. The percentage ash content of the composites
increases with increasing the MF content in the system. This increased percentage ash
content is also an indication for the enhancement of thermal stability of the composites.
• The thermograms obtained during the TGA scans were analyzed to give the percentage
weight loss as a function of temperature. T0 (temperature of onset decomposition), T10
(temperature for 10% weight loss), and Tmax (temperature for maximum weight loss) are
the main criteria to indicate their thermal stability of the composites.

Illustrations
Research Paper-3
• Kanakannavar et al. investigated Biodegradation properties and
thermogravimetric analysis of 3D braided flax PLA textile
composites.
• To study the thermal stability of the prepared bio-composites
thermogravimetric (TG) analysis is carried out. Results showed that
biodegradability, tensile properties and thermal stability of the
composites are enhanced significantly with the reinforcement of 3 D
braided yarn fabric.

Illustrations
Research Paper-3

Illustrations
Research Paper-3
• Thermal degradation of materials is divided into two stages based on the nature of the graph. The first stage of the degradation starts at
the temperature range of 30 OC to 250 OC. In this stage, there is a small weight loss or thermal degradation of materials occurs in the
range of 0.82% to 10.87%. This degradation occurs by evaporation of moisture content from the flax fiber, PLA and composites.
• Observation shows that the flax fiber has a higher content of moisture about 10.87%. The hydrophilic nature of the natural fiber is
responsible to absorb moisture from the surrounding environment. The pure PLA has very less moisture content and the moisture content
of the composite increased with the fiber content. Composite with 33 wt.% of NFBF showed higher weight loss due to moisture
evaporation of about 5.18%.
• A very deep reduction in the percentage of weight loss is observed for a temperature range of 230 OC to 350 OC. This demonstrates the
drastic decrease in thermal or heat stability of the flax fiber, PLA and NFBF/PLA composites in the 230 OC to 350 OC temperature range.
In the second stage, the shoulder is obtained at the end of the process around 280 OC – 350 OC as shown in Figure. This is due to the
residual mass of fiber, polymer and composites left after thermal degradation and this residual mass is called char.
• These results represent that the thermal stability of the composites is enhanced with the reinforcement of the NFBF. This is might be due
to good interfacial bonding between fiber and matrix.

Illustrations
Research Paper-4
• Guizani et al. introduced fast and quantitative compositional analysis of
hybrid cellulose-based regenerated ﬁbers using thermogravimetric
analysis and chemometrics.
• The TGA and the DTG curves of the cellulose-lignin samples are shown in
Figure. The TGA curves of the two repeatability tests for each sample are
almost superimposed.
• The thermograms and their derivatives showed clear changes when
increasing the share of lignin in the hybrid ﬁber. The characteristic
parameters of the thermograms are summarized in Table.

Illustrations
Research Paper-4

Illustrations
Research Paper-4
• Chitosan and cellulose have very different thermal behavior despite
their structural similarity. Chitosan has also a lower thermal stability
than cellulose and start to decompose at a lower Tonset. The hybrid
ﬁbers showed consequently a lower thermal stability and a higher
char yield as the share of chitosan increased in the ﬁbers. However,
those changes were not linear since the char yields were not additive
and the cellulose maximum decomposition peak shifted to lower
temperatures.

Illustrations
Research Paper-5
• Fukatsu et al. investigated thermogravimetric analysis on thermal degradation of novoloid
fiber/cotton fiber blend.
• The thermogravimetric weight loss(TG) and differential thermogravimetric(DTG) curves of
novoloid fiber and cotton fiber are shown in figure, employing a 10K/min heating rate in air
atmosphere. Cotton fiber degraded into two stages, the first weight loss centered taking
place at 300~370 OC, where ca.70% of weight was degraded., and the carbonized
residue was gradually lost by 520 OC at the second stage.
• On the other hand, the degradation temperature of novoloid fiber was very much higher
than that of cotton fiber because of a heat-resistant fiber, and the TG curves in figure
shows that this degradation was gradually generated by the one step having a small
shoulder peak observed in DTG curve.

Illustrations
Research Paper-5

Thank you
06/06/2023 12:49
saaku
Thermogravimetric Analysis 43
Sohail AD
E-mail: sohail.ad3@gmail.com
Mob.: +92-301-4106739

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