2. Somashekara Koushik Ayalasomayajula
http://www.iaeme.com/IJMET/index.asp 33 editor@iaeme.com
microscopy. Experimental proceedings and results were discussed separately for
better understanding of the process.
2. EXPERIMENT
Polymeric sample is first inspected visually for the presence of any surface defects
and then microscopy is performed to study morphology followed by Dynamic
Mechanical Analysis (DMA) to analyse the mechanical properties.
2.1. Visual Inspection
Visual inspection by eye is the oldest and widely employed method that provides a
means of detecting and examining inhomogeneity’s such as voids, pores, cracks and
also surface finish.
2.2. Microtomy and Microscopy
Microtomy is a cutting process which cuts the material into extremely thin slices or
organic tissues, known as sections. Microtomes are used in microscopy, allowing for
the preparation of samples for observation under transmitted light or electron
radiation. LEICA RM2165, a fully motorized rotary microtome, known for sectioning
at low temperatures in combination with LN21 Freezing unit and a tissue freezing
medium to hold sample tight is used for this operation [1]. Polymer film is placed
inside a material holder by applying a tissue freezing medium and kept inside the
chamber filled with coolant gas where a glass knife cuts the film into slices of desired
thickness which is controlled by operator. In our case it is 10 µm. Now the slice is
placed on the glass slide by applying oil on it and observed under microscope.
Zeiss Axioplan 2 a high-end imaging platform for complex research optimized for
light transmission and extremely high contrast fluorescence imaging is used for
microscopy [2]. The lenses we used are plan-neofluar lenses with magnifications 10X,
20X, 50X, 100X.
2.3. Annealing conditions
Annealing of polymers is defined as a secondary process wherein the polymer is
brought to a certain temperature (below its glass transition temperature) and then
cooled down to room temperature. It is generally performed to enhance mechanical
properties [3]. Polymeric sample is annealed at a temperature of 120°C for 2 minutes.
2.4. Dynamic Mechanical Analysis (DMA)
Dynamic mechanical analysis (DMA) is a thermal analysis technique that is used to
provide information about the mechanical properties of any viscoelastic material [4]
as they are deformed under periodic stress. Specifically, a variable sinusoidal stress is
applied, and the resultant sinusoidal strain is measured.
A purely elastic material exhibits no phase difference between stress and strain
waves i.e. phase difference is 0o and if the material is viscous it exhibits 90o phase
difference. Polymers generally exhibit viscoelastic behaviour and thus show phase
differences between those extremes. This phase difference along with amplitudes of
stress strain waves, is used to deduce some material parameters such as Storage
Modulus E', Loss Modulus E", Complex Modulus E* and loss tangent tan δ [5].
3. Examining The Mechanical Properties of Annealed and Not Annealed Multilayer Film
(Polyethylene/ Polyethylene Terephthalate/ Polyethylene) by Dynamic Mechanical Analysis
(DMA)
http://www.iaeme.com/IJMET/index.asp 34 editor@iaeme.com
Figure 1 stress-strain behaviour of viscoelastic material
Figure 2 stress-strain behaviour of a purely elastic material
Two dumb bell shaped specimens of the same polymeric material comprising of
PET and PE are prepared as per ISO 6721-1 (Plastics- Determination of dynamic
mechanical properties) standards [6]. One of the samples is annealed at certain
conditions as discussed in earlier section. EPLEXOR® 150 N machine is used to
perform DMA and the test conditions are as follows:
Table 1 Test conditions for performing DMA
Frequency 10 Hz
Temperature -50°C to 180°C
Heat rate 2K/min
Static load 1.0%
Dynamic load 0.3%
Maximum force 80N
Minimum force 40N
Soak time 1800 sec
4. Somashekara Koushik Ayalasomayajula
http://www.iaeme.com/IJMET/index.asp 35 editor@iaeme.com
3. RESULTS AND DISCUSSIONS
Observing the given polymeric sample through naked eye it is clear that the
provided film is colourless, flat with uniform thickness and with no surface defects.
Furthermore light passes through the film which says it is transparent and placing the
film in sunlight we can find the direction of extrusion of the film.
Figure 3 Morphology showing different layers
Fig.3 shows the morphology of the given sample. From the microscopic image we
can infer that the film was composed of 3 layers and the thickness of layers are
137.4µm, 281.75µm and 156.14µm respectively. Furthermore the sealing layers look
alike thus making the film as ABA type. The difference in observed values of
thickness of layers might be because of microtome cut. By observing the morphology
it can be said that core layer is of PET and sealing layers are comprised of PE. The
thickness of core layer is nearly 300µm and the sealing layers 150µm each
constituting for 600µm for the entire film.
The results of DMA scan with a constant heating rate of 2K/min at constant
frequency of 10Hz for both annealed and not-annealed samples are presented in Fig 4
and Fig 5 as variation of E',E",E* and tan δ with temperature which clearly explains
that DMA we performed is temperature sweep but not frequency sweep or
temperature-frequency sweep.
Figure 4 DMA graph for annealed film
Material: PE/PET/PE.
DMA: Frequency: 10 Hz, Temperature: -50o
C – 180o
C, static strain = 1.0 %, dynamic strain =
0.3 %
5. Examining The Mechanical Properties of Annealed and Not Annealed Multilayer Film
(Polyethylene/ Polyethylene Terephthalate/ Polyethylene) by Dynamic Mechanical Analysis
(DMA)
http://www.iaeme.com/IJMET/index.asp 36 editor@iaeme.com
Figure 5 DMA graph for not annealed film
Material: PE/PET/PE.
DMA: Frequency: 10 Hz, Temperature: -50o
C – 180o
C, static strain = 1.0 %, dynamic strain =
0.3 %
Figure 6 Comparison of complex modulus for both samples
Material: PE/PET/PE.
DMA: Frequency: 10 Hz, Temperature: -50o
C – 180o
C, static strain = 1.0 %, dynamic strain =
0.3 %
Primary analysis of complex modulus curve of both samples reveal that the
complex modulus curve for annealed sample is decreasing at slow rate when
compared to that of not annealed sample, which says that annealed material is stiffer
than that of not annealed one. Variation in mechanical loss factor tan δ with
temperature for both samples is shown in Fig 7. Comparing the area under graphs we
can observe that area covered by not annealed film is more than that of annealed film
which clearly states that damping is higher for not annealed film.
The main aim of performing DMA is to determine glass transition temperature Tg.
Tg can be calculated by the following ways [5].
6. Somashekara Koushik Ayalasomayajula
http://www.iaeme.com/IJMET/index.asp 37 editor@iaeme.com
Evaluation of modulus step:
Step method employed for DSC curves (start, half step height and end of glass
transition),
Inflection point method,
2% offset method (start of glass transition),
Tangent method (start of glass transition).
Evaluation of peaks from plots of loss factor and loss modulus:
Maximum loss factor,
Maximum loss modulus.
Evaluating the peak of loss factor is widely employed to determine Tg.
Figure 7 Comparison of loss tangent
Material: PE/PET/PE.
DMA: Frequency: 10 Hz, Temperature: -50o
C – 180o
C, static strain = 1.0 %, dynamic strain =
0.3 %
It is evident from Fig.7 that the Tg of not annealed specimen is about 96o
C and
annealed specimen is about 120o
C which clearly explains that heat treatment process
like annealing increases Tg of material [7].
4. CONCLUSION
Heat treatment process like annealing forms additional crystals while cooling down to
room temperature. From the results of performed Dynamic Mechanical Analysis we
conclude that annealed material has more glass transition temperature when compared
to that of not annealed material. Also annealed sample has high stiffness and less
damping when compared to that of not annealed because of formation of additional
crystals. Glass transition temperature observed using peak analysis of loss modulus is
different from Tg obtained from other methods. Exact reason for this is unknown,
leaving space for research in this area. With the increase in glass transition
temperature the area of application of the polymeric material is increased and also
performing some other thermal analysis techniques like DSC, TGA one can easily
7. Examining The Mechanical Properties of Annealed and Not Annealed Multilayer Film
(Polyethylene/ Polyethylene Terephthalate/ Polyethylene) by Dynamic Mechanical Analysis
(DMA)
http://www.iaeme.com/IJMET/index.asp 38 editor@iaeme.com
understand the behaviour of the material at higher temperatures and also there is a
possibility in achieving traditional polymeric materials with enhanced properties.
5. ACKNOWLEDGEMENT
I would like to thank my Professor Dr. Achim Frick and Mr. Muralidharan
Vibunanthan for providing me the opportunity and for extending their support
throughout the experiment.
REFERENCES
[1] Leica microsystems, operating manual, Nussloch, pp: 6, [online]
http://www.leica-
microsystems.com/fileadmin/downloads/Leica%20RM2165/Brochures/RM2165_
germ.pdf, Viewed on: 11-June-2015.
[2] Zeiss, Axioplan 2 imaging and Axiophot 2 Universal Microscopes Operating
manual, Jena, pp: 83, [online] https://physics.ucsd.edu/neurophysics/
Manuals/Zeiss/Axioplan%202%20imagine%20and%20Axiophot%202.pdf,
Viewed on: 11-June-2015.
[3] LeGrand. D.G, Encyclopedia of Polymer Science and Technology, (Wiley Online
library, John Wiley & Sons, Inc. Feb-2011).
[4] Faria.R, Duncan. J.C, Brereton. R.G. Dynamic mechanical analysis and
Chemometrics for polymer identification. In: Polymer Testing, 26(3), May 2007,
pp: 403.
[5] Erhenstein.G.W, Riedel. G, Trawiel. P, Thermal Analysis of Plastics Munich,
Carl Hanser, 2009, pp: 236-239,243,244,247.
[6] ISO standard; ISO 6721-1 (Plastics- Determination of dynamic mechanical
properties).
[7] Gupta.S, Dixit.M, Sharma.K, Saxena. N.S. Mechanical study of metalized
polyethylene terephthalate (PET) films. In: Surface and Coating technology,
204(5), Dec-2009, pp: 664.
[8] Siddhant Datta, B.M. Nagabhushana, R. Harikrishna, A New Nano-Ceria
Reinforced Epoxy Polymer Composite with Improved Mechanical Properties,
International Journal of Advanced Research in Engineering & Technology
(IJARET), 3(2), 2012, pp. 248 - 256.
[9] N. Kumar, P. L. Meena, A. S. Meena and K. S. Meena, Physico-Mechanical
Properties OF SSBR Styrene 40%, Vinyl Content 46% Based Truck Tyre Tread
Cap Compounds with LPCA and HPCA Oils, International Journal of Advanced
Research in Engineering & Technology (IJARET), 5(2), 2014, pp. 121 - 127.
[10] Jeevan.V , C.S.P Rao and N.Selvaraj, Compaction, Sintering and Mechanical
Properties of Al-SICP Composites, International Journal of Mechanical
Engineering and Technology, 3(3), 2012, pp. 565 – 573.
![Somashekara Koushik Ayalasomayajula
http://www.iaeme.com/IJMET/index.asp 33 editor@iaeme.com
microscopy. Experimental proceedings and results were discussed separately for
better understanding of the process.
2. EXPERIMENT
Polymeric sample is first inspected visually for the presence of any surface defects
and then microscopy is performed to study morphology followed by Dynamic
Mechanical Analysis (DMA) to analyse the mechanical properties.
2.1. Visual Inspection
Visual inspection by eye is the oldest and widely employed method that provides a
means of detecting and examining inhomogeneity’s such as voids, pores, cracks and
also surface finish.
2.2. Microtomy and Microscopy
Microtomy is a cutting process which cuts the material into extremely thin slices or
organic tissues, known as sections. Microtomes are used in microscopy, allowing for
the preparation of samples for observation under transmitted light or electron
radiation. LEICA RM2165, a fully motorized rotary microtome, known for sectioning
at low temperatures in combination with LN21 Freezing unit and a tissue freezing
medium to hold sample tight is used for this operation [1]. Polymer film is placed
inside a material holder by applying a tissue freezing medium and kept inside the
chamber filled with coolant gas where a glass knife cuts the film into slices of desired
thickness which is controlled by operator. In our case it is 10 µm. Now the slice is
placed on the glass slide by applying oil on it and observed under microscope.
Zeiss Axioplan 2 a high-end imaging platform for complex research optimized for
light transmission and extremely high contrast fluorescence imaging is used for
microscopy [2]. The lenses we used are plan-neofluar lenses with magnifications 10X,
20X, 50X, 100X.
2.3. Annealing conditions
Annealing of polymers is defined as a secondary process wherein the polymer is
brought to a certain temperature (below its glass transition temperature) and then
cooled down to room temperature. It is generally performed to enhance mechanical
properties [3]. Polymeric sample is annealed at a temperature of 120°C for 2 minutes.
2.4. Dynamic Mechanical Analysis (DMA)
Dynamic mechanical analysis (DMA) is a thermal analysis technique that is used to
provide information about the mechanical properties of any viscoelastic material [4]
as they are deformed under periodic stress. Specifically, a variable sinusoidal stress is
applied, and the resultant sinusoidal strain is measured.
A purely elastic material exhibits no phase difference between stress and strain
waves i.e. phase difference is 0o and if the material is viscous it exhibits 90o phase
difference. Polymers generally exhibit viscoelastic behaviour and thus show phase
differences between those extremes. This phase difference along with amplitudes of
stress strain waves, is used to deduce some material parameters such as Storage
Modulus E', Loss Modulus E", Complex Modulus E* and loss tangent tan δ [5].](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)