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STRETCHABLE STRAIN SENSORS BASED ON POLYPYRROLE
/THERMOPLASTIC POLYURETHANE BLENDS
By
Group No. 05
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
BSc IN POLYMER ENGINEERING
in the Department of Polymer and Process Engineering
Nauman Aslam (2017pe21@student.uet.edu.pk)
Thesis Supervisor: Dr Rabia Nazar, Assistant Professor
July, 2021
UNIVERSITY OF ENGINEERING AND TECHNOLOGY, LAHORE
Mian Husnain Iqbal (2017-PE-21)
Shahroz Sarwar (2017-PE-28)
Mian Arslan Sarwar (2017-PE-37)
STRETCHABLE STRAIN SENSORS BASED ON POLYPYRROLE
/THERMOPLASTIC POLYURETHANE BLENDS
By
Group No. 05
We have jointly examined the candidates today through viva voce examination
and evaluated thesis submitted by them. We jointly agree on the result of the
thesis examination and evaluation as follows:
1. Thesis is approved.
2. Thesis is rejected.
3. Thesis is returned to candidates for incorporating
additions/modification
Internal Examiner
Sign:
Name: Dr Rabia Nazar
Internal Examiner
Sign:
Name: Dr. Faheem
Chairman
Sign:
Name: Prof Dr Asif Ali Qaiser
Dated: _______
UNIVERSITY OF ENGINEERING AND TECHNOLOGY, LAHORE
Mian Husnain Iqbal (2017-PE-21)
Shahroz Sarwar (2017-PE-28)
Mian Arslan Sarwar (2017-PE-37)
iii
Thesis Supervisor: Assistant Professor Dr. Rabia Nazar (Ph.D.)
ABSTRACT
The advancement of stretchable strain sensors has capable applications in the human motion
detection, medical and soft robotics. For applications, highly stretchable, stable, and sensitive
strain sensors are required. Good stretch ability is the key features. Recently, the technique of
hybridization is applied to overcome the challenges associated with wide strain range and
sensitivity of strain sensors. In this research work, we propose a simple solution casting
technique to fabricate piezoresistive strain sensors by incorporating conductive materials
such as pyrrole as a conducting material. The development of thermoplastic
polyurethane(TPU)/polypyrrole(PPy) 4.5, 9, 18 wt% pyrrole based strain sensors are
synthesized in solution technique of in-situ polymerization of acid doped PPy with TPU in
different percentage. Different characterization techniques employed to monitor different
properties FTIR for amine and carbonyl group interaction, TGA heat stability
characterization, UTM for mechanical analysis and electrical properties by Multi-meter.
Keywords: Strain sensors, Pyrrole, TPU, solution casting, wearable sensors, piezoresistive
conductivity
iv
Table of Contents
ABSTRACT.................................................................................................................................... iii
ACKNOWLEDGEMENTS............................................................................................................. v
List of Glossary............................................................................................................................. vii
Chapter: 1 Introduction .................................................................................................................2
1.1 Applications.............................................................................................................................6
1.1.1 Application of strain sensor in medical field......................................................................6
1.1.2 Application in Sports.........................................................................................................9
Chapter: 2 Literature Review ......................................................................................................11
Chapter: 3 Experimental Methods..............................................................................................21
3.1 Materials Required................................................................................................................21
3.2 Strain sensors prepared by in Situ Polymerization process.....................................................21
3.3 Characterization ....................................................................................................................22
Chapter no 4 Results and Discussion..........................................................................................23
4.1 Thermogravimetric Analysis...................................................................................................23
4.2 Fourier transforms infrared spectroscopy..............................................................................24
4.3 Future Prospect.....................................................................................................................26
Chapter: 5 Conclusion..................................................................................................................28
v
ACKNOWLEDGEMENTS
It's always a joy to thank the wonderful folks at the University of Engineering and
Technology (UET) for their unwavering support in helping me maintain my
practical and laboratory polymer abilities. First and foremost, I want to express my
gratitude to my parents for their unwavering support, enthusiasm, and tremendous
assistance. I might not be able to finish this subject adequately if I don't have all of
this. Second, I'd want to express my gratitude to Dr. Rabia Nazar for allowing us to
participate in polymeric material testing and formulation. She also provides us with
his undivided attention and assistance. Finally, I'd like to convey my gratitude to all
Lab Attendants for their assistance with Polymer.Finally, I'd want to express my
gratitude to all Lab Attendants for their Polymer Department guidance, which has
really aided me in dealing with experimental training placement. They had backed
me up by demonstrating various methods for gathering data for the trial. In
addition, I'd like to express my gratitude to Prof. Dr. Asif Ali Qaiser (Chairman and
Senior Professor/Department of Polymer and Process Engineering), who oversaw
the department's rules and regulations and met all of the laboratory's requirements,
as well as extending his friendship to the staff and creating a pleasant training
environment. A paper is insufficient to express my gratitude for their assistance and
direction throughout practically all of my work in the department. Finally, I
apologise to all those anonymous individuals that assisted me in various ways in
order for me to have a successful training.
vi
List of Figures
Figure 1.1. Diverse functional, sensors composed of nanomaterials for human action measure. a)
Resistive-type sensors, and b) capacitive-type sensors.. ....................................................................5
Figure 1.2 A conceptual schematic of strain sensors operating in the case of emergency by collecting
patients’ physiological information and then transferring the data to a medical Center through
wireless devices, thereby, alerting the physician medical assistant ...................................................8
Figure 1.3 The operation of portable and skin attached - stretched sensors in the biomedical field: a)
A capacitive-kind strain sensor covered near the hreat. b) he astrain sensor's reply in blood
measurement. c) Strain sensor mounted on the chest for the breathing ...........................................8
Figure 1.4 Implementation of wearable sensors for measuring physical performance on body joints.
a) Strain sensor attached on the wrist and elbow joints. b) The reply of skin-mountable strain
sensors to leveling and twisting movement of the hand and elbow joints c)....................................10
Figure 2.1Spray Coating process of the soft finger ..........................................................................13
Figure 4.1 TGA curves for pure TPU and TPU/PPy.DBSA blends in PPy weight percentages of 4.5, 9,
and 18. respectively ........................................................................................................................23
Figure 4.2 FTIR/ATR spectra of pure TPU and TPU/PPy.DBSA blends in PPy weight percentages of 4.5,
9, and 18. respectively.....................................................................................................................25
vii
List of Glossary
TPU Thermoplastic Polyurethane
PPy Polypyrrole
DBSA Do decyl benzene Sulphonic Acid
APS Ammonium Per Sulphate
CB Carbon Black
PANI Polyaniline
GF Gauge Factor
FTIR Fourier Transform infrared spectroscopy
SEM Scanning Electron Microscopy
EIS Electrochemical impedance spectroscopy
DMTA Dynamic Mechanical Thermal Analysis
GNPs Graphene Nano Platelets
CNT Carbon Nano Tubes
A Ampere
V Voltage
GNPs Graphene nan platelets
MWCNT Multi wall carbon nano tube
FLG Graphene composite fiber
viii
PDMS Polydimethylsiloxane
PSS Polystyrene sulfonate
NBR Nitrile butadiene rubber
SWNT Single Wall Nano tube
LED Light emitting diode
∆R/RO Relative Change in Resistance
2
Chapter: 1 Introduction
The incorporation of different nanoparticles and response of these advanced
nanomaterials into strain sensors have modernized the application of these
intellectual devices in various sectors [1]. Due to their innovative benefits in
numerous areas, the flexible and sensitive strain sensors have risen in popularity in
research for their use in many applications .i.e. structural health monitoring (SHM),
soft robotics, and pressure sensing etc [2]. The strain sensors function by perceiving
the human body motions triggered by mobility, breathing, and pulse, and are also
able to detect significant body stresses caused by joints twisting. Besides, These
sensing may be integrated into wearable electronic devices that connect to clothes
and the human tissue [3]. Moreover, they can also be utilized to measure the
movements of robotic joints and successfully record and improve the living
environment of human beings. The sensing mechanism is triggered upon stretching
the strain sensors that are followed by various processes, such as propagation of the
crack, tunnelling effect and increase in distance between the adjoining nanomaterial
[4]. Traditionally, metal-based strain gauges were fabricated but they exhibited
lower strain (<5%) due to low elongation at break. Therefore, elastomeric or
polymeric based materials were used because they exhibited much higher strains (10
to 800%) [4].
Flexible strain sensors necessitate the incorporation of several conductive
nanoparticles into the elastomeric substrate. To create sensors with a large level of
elasticity, the most common polymers employed are different elastomers such as:
NBR, EPDM etc. That sensing characteristic of strain sensors is activated by mixed
with conductive nanomaterial for example carbon black (CB),
3
(CNTs) [5], (GNPs) [6] and (Ag-NWs) [7] etc. However, the majority of nano
particles communicate great sensitivity as sensors but are relatively costly. As a
result, hence the necessity to consider more affordable options. This can be resolved
by utilizing low resistance polymers such as : (PPY) and polyaniline (PANI). The use
of polyaniline, as a conductive filler, is gradually increasing due to its easy synthesis,
processability and cheapness. To improve its electrical conductivity, it is converted
(ES) through various form chemical means and doped it such as power acids HCl,
H2SO4, DBSA etc. [8] [9]. The conductivity of PANI can be tuned by doping it with a
certain amount of acid and thus falls into the category of metals and conductor.
Hence, it is an excellent choice of a conductive material for increasing the strain
sensor's effectiveness. However, it has a disadvantage of being incompatible with
different polymers. There are three different approaches to making polyaniline
compatible with different polymers such as molten blends, liquid polymerization
and in-situ polymerization are all methods of polymerization. The process of in-situ
polymerization, as compared to others, uniformly disperses the polyaniline into the
base matrix and improves the electromechanical properties of the strain sensors [10].
Though, to achieve a strain sensor with improved mechanical, thermal and electrical
properties, strong compatibility, and interaction is required between filler and
polymer. Some research have previously been published in which PANI was
utilized as a potential filler for stretch sensors Gong et al. created elastic strain
sensors out of PANI as a conducting polymer and integrated it into
polydimethylsiloxane (PDMS), reporting a 50% strain value [11].
The required characteristics of the strain sensors such as flexibility, conductivity,
stability, sensitivity and mechanical properties of substrate for the application in
structural health monitoring must be considered. Therefore, to achieve these
requirements, higher interfacial bonding and compatibility between carbon
4
nanomaterials and polymers are essential [4]. By integrating carbon nanotube (CNT)
thin films on piezoelectric materials, strain sensors with great ductility are created;
nevertheless, these strain sensors have limited responsiveness [12]. Although, the
limitation of low stretchability of the reported strain sensors rendered them
unsuitable for large motion detection application [13].
The electrical percolation network of fillers is highly dependent on the geometry,
size and structure of nanomaterial. As a result, the piezoresistive behavior of 2D
nanofill is higher than those of nanowires and enhances the sensitivity of the strain
sensors [14]. Due to graphene and CNTs are expensive, there is a limitation of cost
control for the manufacturing of sensors. Therefore, there remains a challenge in the
achieving strain sensors with high durability, accuracy, resilience, and cheap price
[2]. There are two types of approaches employed in the manufacturing of stretchable
strain sensors first is resistive-type and second is capacitive-type. The most
preferable is the resistive-kind sensors owing to its straightforward and easy
manufacturing procedure, operating principle and minimal energy usage under
application [15]. A huge number of research have been conducted on the
piezoresistive behavior of TPU nanocomposites including carbon-based
nanoparticles [16]. The results demonstrated that under tensile strain, the adjacent
neighboring fillers lose contact due to deformation of TPU matrix producing a
resistance-strain response.
Because of its intrinsic characteristics such as low aspect ratio, cheap price in
comparison to other carbonaceous nanoparticles such as graphene and CNT, and
high conductivity, zero-dimensional (0D) carbon black (CB) is a viable option as
conductive filler.The electrical and mechanical characteristics of the strain sensors
containing carbon black as a nanofiller are enhanced due to its reinforcing effect.
Silver nanoparticles (AgNPs) are also becoming attractive as a conductive candidate
due to their improved effect on the strain sensing performance. When AgNPs are
5
hybridized with other conductive materials, they produce a synergic effect and are
prone to produce microcracks under tensile strain [16].
The electrical and mechanical properties of the strain sensors can be the filling level
in elastomeric substrates may be readily regulated by fine-tuning the loading rate.
The hybridization technique is attracting emphasis is drawn to the combination of
distinct filler characteristics, decreased filler loading, and improved electrically and
structural characteristics because of the synergistic impact of both additives The
physical and electric characteristics of a strain sensor are evaluated under statically
and kinetic circumstances to assess resistance fluctuation and to validate the strain
sensor's sensibility and endurance. Moreover, the testing findings allow the
constructed strain sensors to identify human actions such as thumb twisting, hand
rotation, and knee extension, as demonstrated. in Fig. 1.1 [17]
Figure 1.1. Diverse functional, sensors composed of nanomaterials for human
action measure. a) Resistive-type sensors, and b) capacitive-type sensors [2].
6
1.1 Applications
Stretchable strain sensor has large number of applications in various fields. For
example, pressure measure gadgets , structural health-monitoring. Flexible and
stretchable strain sensor also used in electronic circuit and machine for the detection
human motion and convert data in the form of human readable information They
can be used as wearable gadgets that are directly attached to human body or
clothing for the body strain measured These ultra-sensitive sensors can detect
actions as small as breathing and heartbeat to huge strain-induced body joint
bending and straightening. Additionally, these sensitive strain sensors are beneficial
for the observing the robot activity and motion detection
1.1.1 Application of strain sensor in medical field
Human Healthcare and high -quality drugs are becoming more difficult and
complex as the population grows. Wearable electronics are gaining popularity due
to their ease of use and long-term monitoring capabilities. These individualized
health-monitoring technologies have promise for enhancing the capabilities of
present medical systems. systems [18].
Fig. 2.1 shows the conceptual illustration of health-monitoring devices using
wearable sensors [18]. These wearable strain sensors function by assembling the
health and physical information from the human body and is represented in the
form of heart rate , respiratory rate [19], pressure of blood and oxygen level [15],
human body temperature and movements etc. The sensors send the evaluated
statistics from wearing sensors to a smartphone or wireless accessible hotspot an
alert message is delivered to a call for assistance center for quick assistance. After a
patient has received adequate medical therapy, health-care providers can monitor
person Condition of health person the condition and make medical choices [20]. The
strain sensors may also be used in biological devices to check complicated and
7
massive displacements of human skin or clothes, and their excellent detecting
capability allows them to detect small skin straining caused by breathing or pressure
of blood Fig. 1.2 (a) uses a stretchable capacitive-type sensor to measure blood
pressure in viva [2]. The sensors reacted to fluctuating heart rate with excellent
strains detecting capabilities in Fig. 1.2 (b). stimulate accurate, skin movable, and
wearable strain sensors that detect tiny body motion.by phonation, body posture,
skin, expansion, injury recovery, respiratory, and heartbeat rate [21]. The illustration
of a resistance-kind of sensor attached to the human body is shown in Fig. 1.2 (c)
exhibiting the response of the sensor to the motionless (black) and moving (red)
sates of breathing. The peak of the statistics shows expands and does not expand the
chest When breathing accordingly. Strain sensor implemented on the wrist to
measure heart rate is shown in Fig. 1.2 (d). The pulse numbers are 38 and 46 is
subjects were in the motionless (black) and activity (red) states of modes for 30 s
correspondingly [22]. Individualized health-monitoring systems can accurately
important role in human health indicators like long time. Measurement of vascular
circulation, pulse, and respiration, signaling initial disease diagnosis When a person
sat with a regularly stretched leg, an elastic capacitive-type strain sensor was
attached to the knees to perform a patellar reflex examination, as illustrated in Fig.
1.2. (e). During the bending state of the knee, the sensors measured a large strain.
The patellar knee ligament was tapped with a mallet during the leg reflex
examination. The striking motion led the leg to stretch and quickly return to its
original position Fig. 1.2 (f) illustrates that the capacitance decreased suddenly
during straightening and then back to original the bio-compatible and portable
strain sensors can be used in a variety of biomedical applications. Because of their
great sensitivity, conductive sensors are excellent for measured low-strain motions,
whereas detection systems function better for high-strain movements in aspects of
uniformity, minimal hysteresis, and quick reply.
8
Figure 1.2 A conceptual schematic of strain sensors operating in the case
of emergency by collecting patients’ physiological information and then
transferring the data to a medical Center through wireless devices,
thereby, alerting the physician medical assistant [2]
Figure 1.3 The operation of portable and skin attached - stretched sensors in the
biomedical field: a) A capacitive-kind strain sensor covered near the hreat. b) he
astrain sensor's reply in blood measurement. c) Strain sensor mounted on the chest
for the breathing
9
1.1.2 Application in Sports
Adjustable strain sensors connected to several body parts measure exercise ability.
The signals measured by the strain sensors wrapped around the wrist and elbow are
demonstrated in Fig. 2.3 (a) and 2.3 (b) [6]. The resistance of strain sensors increases
during the rotating action of the arm and hand. After the straightening of wrist and
elbow, the change in resistance It has regained its original value The body
movement analysis can be performed through the data measured by the w strain
sensors. A rosette-type stretchable strain sensor is fabricated from 3s self-runing
CBs, PDMS strain sensors at an angle of 120° of each other [13]. The function of
rosette-type strain sensors is to measure the principal strains under in-plane
directions of displacements [5]. The response of elongated sensor in the uniaxial
direction of S1 is shown in Figure 2.3 (c). In Fig. 2.3 (d), the change in resistance for
the S1 was larger than that of S2 and S3. The information reported from these
sensors can be used for body fitness analysis Fig. 2.3 (e) demonstrates another
application in which Flexible strain sensors were connected to the knee joint to study
different knee movement Moving, walking, and leaping from a seated posture are
examples of sequences [5]. As a result, skin launch, and portable strain sensors are
useful for large period structural human health observing reintegration and
evaluating players' athletic performance.
10
The use of elastic stretch sensors on robotic a) Measured signals from stretched
sensor to the sensors to leveling and twisting movement of hands joints. b)
Resistivity changes as the twisting position of the elastic strain sensor changes. c)
Strain sensor mounted on gloves to control the movement of a gripper robot flexible
sensors resulting in dummy electronic skin. e) The piezoresistive reply of the
dummy skin positioned on the top of the skin [2].
Figure 1.4 Implementation of wearable sensors for measuring physical
performance on body joints. a) Strain sensor attached on the wrist and elbow
joints. b) The reply of skin-mountable strain sensors to leveling and twisting
movement of the hand and elbow joints c)
11
Chapter: 2 Literature Review
A brief literature review is conducted, underlining the usage of different conductive
and sensing materials, various forms of additives, different building techniques and
performance characteristics such as sensitivity and stretch ability of strain sensors.
Due to the increasing demand for automation and lack of resources the industrialists
are demanding robots that can perform their tasks precisely and accurately. For their
accurate working, flexibility is needed in their manufacturing and sensors are their
most important parts so it needs some flexibility this requirement cannot be fulfilled
by using typical metallic strain sensors whose maximum strain sustainability is ~5%
but polymers can fulfill this requirement. S. Tadakaluru et al. [19] manufactured a
sensor made up of natural rubber having carbon nanotube and graphite films
sandwiched between its layers and measured their strain sustainability. Graphite
and carbon sensors give 246% and 620% strains which are ~50 and ~120 times
greater than a conventional metallic sensor respectively. R. Zhang et al. [23]
observed the strain sensing behavior of polyurethane- urea/ amino-functionalized
MWNTs composite prepared using a solution casting technique. Appreciable
recoverability was noticed in it at a 5% strain.
M. Kotal et al. [24] worked on the up-gradation of the high-temperature stability and
conductivity of the nano blends based on thermoplastic polyurethane and
polypyrrole (PPy) doped with dodecyl benzenesulfonic acid (DBSA) by adopting
two processing methods namely in situ (IS) and solution intercalation (SB) methods.
Increase in the conductivity was observed by incorporating DBSA doped PPy.
However, a sharp increase in the conductivity manifested by a specimen with 2.5
wt% of DBSA doped PPy by adopting in situ technique. The highest value of
electrical conductivity observed by utilizing the SB technique was 0.26 S cm-1
at 30
wt% of DBSA doped PPy. The decomposition temperature was observed to be about
12
382o
C, 384o
C, and 414o
C for TPU, DBSA doped PPy /TPU by IS technique, and
DBSA doped PPy /TPU by SB respectively. A.S. Kurian, H. Souri, V.B. Mohan et al.
[6] prepared stretchable sensors of polypyrrole (PPy) and silicone rubber (SR) which
are used to detect the movement of the humans by utilizing the solution casting
method. The gauge factor obtained with different amounts of PPy in SR was in
between 1.15 and 1.58. PPy/SR is more suitable for the strain in large values due to
their low hysteresis, sensitivity, and durability.
A.P. Tjahyono et al. [25] manufactured a strain sensor based on the conductive
polymer polypyrrole (PPy) and a matrix of natural rubber (NR) adopting vapor
phase polymerization method under evacuation. The gauge factor was appeared to
be 1.86 while hysteresis shown by the sensor was its major demerit.
J. Chen et al. [26] reported the stretching ability, flexibility, and quick self-healing
properties of flexible stretchable sensors of elastomer doped with polypyrrole
prepared by using in situ polymerization of pyrrole in the elastomer substrate
having abundant hydrogen bonding. The conductive filler PPy incorporation up to
7.5 wt. % gives 2.4% enhancement in the fracture resistance from 0.3 to 0.72 MPa
while on the other hand the stretchability was reduced by 18% from 500 to 410 %.
The electrical conductivity with 7.5 wt. % of PPy was about 0.88 Sm-1
. High strain
sensitivity up to 300% elongation was observed and hence it is used for the detection
of motion. P. Cisell et al. [27] prepared a piezoresistive strain sensor based on
Ethylene-Propylene-Diene-Monomer (EPDM)/ multi-wall carbon nanotubes
(MWNTs) composite by solution casting technique. The results show that its
conductivity is a linear function of strain up to 10% strain.
F. Martinez et al. [28] formulated a silicone/carbon nanofillers based flexible
standing strain sensor to measure electrical conductance. The electrical conductivity
13
of 0.3-0.4 mS/cm is obtained from the different sensors having conductivities
between 0.03-5mS/cm.
Z. Levin et al. [29] prepared a polyaniline(PANI)/ poly(vinyl acetate) (PVAc) based
sensor using a solution casting method. 4wt.% PANI proved to be highly sensitive
and have a gauge factor between 6 and 8 approximately triple than any typical
metallic sensor. Y. Li et al. [30] reported a polypyrrole coated fiber strain sensor. Its
sensitivity and conductivity were tried to be enhanced by using different techniques
i.e. thin coating by a vapor deposition method, polymerization of pyrrole at low
temperature. The strain and electrical characterization suggest a high strain
sensitivity of ∼80 for 50% strain.V. Sencadas et al. [31] prepared an ultra-thin Multi-
walled carbon nanotube (MWCNT)/styrene butadiene styrene (SBS) based
piezoresistive sensor for fingers skin used in robots. It gives a gauge factor of ∼1.
Zhou et al. [32] manufactured an exceptionally stretchable and super touchy strain
sensor utilizing single-walled carbon nanotubes (SWCNTs) joined into the PDMS
substrate by scattering technique in methane sulfonic corrosive and acquired
greatest extending up to 50 % strain and bestow the worth of affectability i.e., 750.
Wang et al. [21] introduced a strain sensor that accomplished the good stretch ability
of 100% and high affectability up to 1020.2 dependent on bright/ozone (UV/O3)
beams broke and carbon nanotubes/elastomer (CNTs/PDMS). The revealed
Figure 2.1Spray Coating process of the soft finger [15]
14
exceptionally touchy strain sensor has expected application in the recognition of
human body movement like eye squinting, wrist and beating.
Niu et al. [33] manufactured an adaptable based strain sensor comprised on
nanocomposite made up with graphene nan platelets (GNPs) and
polydimethylsiloxane(PDMS) elastomer as a base material and furthermore
appropriate for pressure recognition having a affectability up to 20% strain inferable
from high stretch ability and adaptability of PDMS elastomer. GNPs/PDMS
piezoresistive sensor likewise showed most extreme affectability of 140 at 5 wt %
fixation which could be constrained by the fuse of GNPs into PDMS elastomer.
GNPS/PDMS based adaptable sensors showed the diversion after bowing as well as
showed the identification of the finger movement and made it reasonable for fake
skin and wearable applications.
Wang et al. [18] manufactured a productive stretchable and exceptionally delicate
piezoresistive sort strain sensor comprised of polystyrene butadiene styrene (SBS) as
a conductive material with a couple of layers of graphene composite fiber (FLG)
utilizing a wet-turning measure. The revealed showed super strain range more
prominent than every available ounce of effort and super sensitivity esteem with a
(GF) 2546 up to 100% strain.
Wang et al.[5] made multi-walled carbon-nanotubes (MWCNTs)/(TPU) elastomer
fiber-shaped high stretchable sensor having a permeable structure by a cost-effective
wet twisted method that is possible as a continuous and large-scale preparation
process. MWCNTs/TPU based strain sensor showed better studied through the
tunneling theory and gave efficient balance in between the ultra-wide response
having a range for strain (320%) and the value of sensitivity having GF 97.1 as a
resistive type based stretchable strain sensor in the uniaxial stretching test.
15
Zheng et al.[21] created a stable and exceptionally stretchable strain sensor i.e., a
conductive composite comprised of crossover carbon Nano fillers (CNTs–CB) with
polydimethylsiloxane (PDMS) elastomer substrate for powerful human movements
checking applications. This (CNTs - CB)/PDMS based strain sensor was
manufactured by utilizing the arrangement blending and projecting method and
displayed a high stretch ability up to 300% strain. Higher affectability with a
measure factor of 0.91 was gotten after extending from 0% - 100%, 100% - 225% with
a GF of 3.25 also, 225% - 300% showed a greatest measure factor of 13.1 separately.
Raju et al. [34] created two sorts of strain sensors dependent on graphene – polymer
(PDMS) composite coatings that displayed a wide reach strain sensor tested by
Raman spectroscopy i.e., substance fume statement (CVD) covering based example
and the dry changed precisely shed based example. In any case, the Raman two-
dimensional band having shift-pace of shed graphene are 35% more noteworthy
than CVD-graphene focusing on the previous high strain touchy. The shed graphene
covering on PDMS by Raman spectroscopy showed a GF of 2 while CVD graphene
covering on polydimethylsiloxane introduced a GF of 6.1 for an applied strain of
30% individually.
Knite et al.[35] manufactured a sensor-dependent on two kinds of fillers, one was
high construction carbon nanoparticles (CNPs) and second was multiwall carbon
nanotubes (MWCNTs) in polyisoprene lattice by arrangement blending technique.
The detailed sensor shown a greatest extending up to 40% with the check factor GF
of 6 for carbon nanotubes filler-based composite while 4 worth of GF for multi-
walled carbon nanotubes-based composite under 40% applied strain. Wichmann et
al.[36] announced the manufacture of a profoundly touchy also, stretchable strain
sensor dependent on multiwall carbon nanotubes (MWCNTs)/Epoxy grid
nanocomposite by means of blending technique and showed a greatest extending
16
worth of 500% strain and high affectability esteem with GF of 10 toward 900 or 2700
directions.
Martinez et al. [28] introduced a polymer based highly flexible strain sensor by
using smart materials (Electrical conducting liquid silicon rubber of Elastosil and
carbon nanotubes conductive fillers) achieving a maximum of elongation of 410% at
the time of breaking point of sample. The fabricated strain sensor was used for the
extent of biological signals such as joint position and its movement,
electrocardiogram, breathing and skin temperature. Sekitiani et al.[37] manufactured
a sensor as natural light discharged diode (LED) show by utilizing stretchable
dynamic grid covered on a printable flexible conductor through vacuum dissipation
and mechanical punching strategy or cutting cycle in which a light-radiating diode
was made out of graphene movies and single wall carbon nanotubes. This method
significantly improves the stretch ability and conductivity of the strain sensors.
Yu Chang et al. [38] created 3x3 dimensional adaptable strain sensor comprised of
conductive materials like carbon nanotubes (CNTs) and carbon nanofiber (CNF)
composite miniature dainty movies in the type of clusters that were implanted on
the thermoplastic polyurethane (TPU) network by utilizing the designed surface
treatment and shifted drop measure. It reacted by estimating the measure factor in
the scope of 0.34 to 7.98 under the applied strain 3 to 7% individually. The proposed
creation strategy was equipped for making conductive sort polymer-based sensors
through profoundly troublesome plans, with more consistency just as exceptionally
productive for mass creation.
Ciselli et al.[27] made a composite kind strain sensor comprised of multi-walled
carbon nanotubes (CNTs) utilized as a conductive filler and inserted it on to the
ethylene propylene diene monomer (EPDM) substrate. The manufactured strain
sensor displayed the upgrade in the mechanical properties when contrasted with the
17
most perfect type of the EPDM. A high stretch ability of up to 10% of strain was
achieved and showed straight connection with the conductivity which worked on its
application towards the pressing factor sensor just as strain sensor.
Cochrane et al. [39] introduced an adaptable strain sensor that was manufactured
from conductive sort polymer-based composite (CPC) for deciding the size of the
parachute-shade bending. Evoprene, a class of thermoplastic elastomers (TPE), was
utilized as a polymer framework and calcium carbonate as a filler to assembling
profoundly stretchable strain sensors. The scattering of filler confers a high strain
rate from 10 to 1000 mm/min and twisted at a greatest extending of 9% during 15
testing on the parachute overhang.
Martinez et al.[28] detailed a polymer-based strain sensor having a self-flexing
capacity created from Elastosil, a fluid silicone elastic comprising of great
mechanical, electrical, maturing and vulcanization properties, built up with high
viewpoint proportion conductive-nanoparticles showed a decent conductivity of 0.3
to 0.4 mS/cm and most extreme strain of up to 410% lengthening at the hour of the
break with an elasticity of 5.4 N/mm2 .
Yamada et al. [40] manufactured a stretchable strain sensor comprised of the slight
movies of single-walled carbon nanotubes (CNTs) covered on the canine bone shape
bits of polydimethylsiloxane (PDMS) polymer lattice for the movement recognition
of the human body. It reacted to a novel strain sensor that surrendered high
extending to 280% and 0.06 worth of check factor up to 200% of strain.
Ku-Herrera et al.[41] announced a piezo resistivity of carbon nanotube with vinyl
ester-based composites i.e., the utilization of strain sensor reacted in cyclic pressure
and strain mode in the versatile systems and showed affectability esteem with a
measure factor of 2.60 upon a normal extreme strain of 1.40% and showed a straight
18
piezoresistive conduct in pressure and non-direct conduct in pressure up to the
break of the example.
Xiao Li et al.[42] manufactured a delicate and profoundly stretchable strain sensor
utilizing graphene woven textures (GWFs) layered onto a polydimethylsiloxane
(PDMS) polymer grid and came about with a most extreme malleable strain of 6%
with a check factor of 103 and for higher strain (>6%) the check factor esteem was up
to 106 because of its woven cross section design and crack conduct, showing higher
affectability under each extending cycle.
J. Lipomi et al. [43] detailed a pressure strain sensor grounded on straightforward,
versatile and biocompatible conductive carbon nanotubes CNTs films and
polydimethylsiloxane (PDMS) material as a polymer substrate. The last shaped
strain sensor reacted high stretchability with a greatest strain up to 150% with high
conductivity of 2200S cm-1 in the full extended state. These straightforward and
biocompatible strain sensors are profoundly reasonable for human wearable
electronic applications.
Nanshu Lu et al.[44] introduced a skin mountable strain sensor that showed high
affectability what's more, was manufactured by utilizing polydimethylsiloxane
(PDMS) elastomer and exceptionally conductive carbonaceous materials like the
carbon dark CB and the carbon nanotubes (CNTs) as detecting 16 materials in the
improvement of strain sensors. CB and CNTs were doped onto a PDMS polymer
substrate and gave great affectability having check factor (GF) 29 and the most
extreme extending estimated was in the middle of the scope of 11.2% to 22.6%.
Slobodian et al. [45] manufactured an electrically conductive composite dependent
on the interlaced organization of carbonbased nanotubes CNTs in thermoplastic
polyurethane (TPU) framework. This CNT/TPU based composite showed greatest
19
prolongation through extending as 400% with multiple times more expansion in
opposition that empowered it to be material for exceptionally distorted strain
detecting component, electro-attractive field safeguarding and so forth.
P. Tjahyono et al. [25] created a profoundly adaptable strain sensor by utilizing slim
layers of polypyrrole as a conductive polymer covered on the regular elastic
substrate by means of fume stage polymerization strategy through a vacuum
climate. The came about strain sensor displayed better security with a greatest check
factor of 1.86 upon 20% strain of the last example. The created sensor was totally
applied to compression and expansion-based applications like an air muscle and can
likewise be executed for computing the huge twisting strain applications.
Hwang et al.[46] manufactured electromechanical strain sensor dependent on
crossover composite sheets that include carbon nanotubes CNTs and graphene
nanoplatelets GNPs impregnated on to polycarbonate PC through vacuum incited
filtration strategy. The subsequent half breed sensor exhibited a high flexural strain
of up to 2% with a measure factor in the scope of 0.56 – 0.64.
Ning Hu et al.[47] introduced a super delicate strain sensor created from carbon
nanofillers CNFs that was metal-covered in nature and epoxy lattice was utilized as
a polymer framework for making CNF/epoxy-based composite. The subsequent
sensor was produced using two sorts of nanofillers, one depended on fume
development carbon fiber (VGCFs) with silver or nickel coatings and different was
created by utilizing the metal-covered CNF. The created sensor showed high
affectability with a check factor of 155 for VGCFs with silver covering and around
multiple times expansion in the incentive for metal foil based strain checks upon
+6000 miniature strain level.
20
Hoon Bae et al.[48] created a straightforward type strain sensor produced using
graphene as a detecting filler into the stretchable elastic substrate in a type of rosette
through particle carving and stepping strategies. The subsequent straightforward
strain sensor showed affectability as far as measure factor in the scope of 4 to 14
upon 7.1% applied strain. These outcomes were shown by utilizing a
straightforward glove every which way and their sizes were estimated by applying
the gloves on to fingers actuated by the movement of finger [99].
Cai et al. [22] introduced a very stretchable capacitive sort strain sensor comprised of
multi-walled carbon nanotubes (MWCNTs) inserted onto the polydimethylsiloxane
PDMS substrate that was straightforward and utilized for movement identification
of human joints. The subsequent strain sensor showed high stretchability with a
most extreme strain of 300% with the upgraded toughness even in the wake of
finishing many cycles.
21
Chapter: 3 Experimental Methods
3.1 Materials Required
Materials which are required for the manufacturing of sensors are thermoplastic
polyurethane (TPU – hardness = 87 shore D - ester-based, China) as the base
polymer, Pyrrole monomer Tetrahydrofuran (THF Sigma – Aldrich chemicals,
Germany), Ammonium persulfate (APS Dae – Jung, chemicals China), Dodecyl
benzenesulfonic acid (DBSA)
3.2 Strain sensors prepared by in Situ Polymerization process
By in situ polymerization process TPU and PPy are and polymerized, first of all 4.1g
of TPU is added in 10mL THF and dissolved with continuous stirring for half or an
hour so TPU can dissolve completely in solvent. Then (4.5, 9 and 18) wt. percentage
of pyrrole with respect to of TPU was added in solution TPU solution, DBSA as a
dopant for pyrrole monomer is added in the solution meanwhile (0.005 mole) APS is
added drop wise through the burette and the solution is kept at 5o
C for 12 hrs. under
stirring for the completion of polymerization. As the polymerization initiates the
color of the solution turns from greenish to black. After 12 hours of stirring the
polymer is precipitated out by adding the excess amount of methanol in solution
and washed several times with distilled water after precipitation. This washing will
remove the unreacted monomers. After the washing precipitated mass is filtered out
using filter paper and dried at 60-70 o
C for 1 hour. Then the dried black colored mass
is dissolved in the THF, and solution was molded in the handmade tape molds on a
glass plate, the sample is subjected to [24].
22
3.3 Characterization
FTIR/ATR spectrum of TPU and its different blends with Polypyrrole were recorded
using FT/ IR-4100 infrared spectrometer (JASCO, Japan). The spectrum of the
specimens were obtained in the wave number range of 400–4000 cm−1
.
Thermogravimetric Polymer Bulletin 1 3 analysis of pure TPU film, PANI.DBSA and
different blends of TPU/Aniline. DBSA was performed using thermogravimetric
analyzer TGA-50 instrument (Shimandzu, Japan) at heating rate of 20 °C/min under
nitrogen atmosphere and above ambient temperature 25–600 °C. Efect of
concentration of aniline was observed on the thermal degradation of the blends.
Samples were completely dried in a vacuum chamber before analysis.
Figure 3.1 Schematic representation of the in-situ polymerization and solution casting
technique resulting in the fabrication of PPy/TPU hybrid sensor.
23
Chapter no 4 Results and Discussion
4.1 Thermogravimetric Analysis
The Thermogravimetric Analysis (TGA) analysis of Thermoplastic Polyurethane (TPU) and
Polypyrrole (PPy), TPU/PPy.DBSA blends at (4.5, 9, 18) PPy wt.% are shown in the Figure
4.1. All curves represent the three major regions of weight loss that are detected during TGA
study. The very first decay area up to 250 °C temperature is due to the drying up of the
water deposited on the surfaces. The next degradation area ranging from 250 °C to 450 °C
temperature shows the decay of Dodecylbenzene sulphonic acid (DBSA) and the and the
oxidized PPy and TPU polymers present in them. The last region ranges from 450 to 550 °C
temperature depicts the deprivation of hemmed in DBSA, PPy and TPU [49].
Figure 4.1 displays that the neat TPU sample remains stable up to 340 °C. The dip in the
Figure 4.1 TGA curves for pure TPU and TPU/PPy.DBSA blends in PPy
weight percentages of 4.5, 9, and 18. respectively
24
weight prior to 340°C is due to the elimination of humidity from the TPU surface. The decay
initiates at 340 °C and then offsets at 430 °C. Total mass loss of neat TPU is 82% at the offset.
The blends of TPU/PPy.DBSA synthesized via in situ polymerization shows varying weight
loss values. The 4.5 PPy wt.% displays the beginning at 250 °C before the beginning point a
weight loss up to 4 % occurs due to the thermally volatile elements like contaminants and
humidity present in the blend. The onset started at 250 °C due to the presence of some
unreacted pyrrole monomers and solvent present in the blends. Blend is stable at higher
temperatures and the mass loss is up to 62% at the offset temperature of 410 °C. The trend in
the Figure 4,1 portrays the mass loss decreases with the increase in the PPy concentration,
Blend with PPy 9 wt. % shows the onset at 250 °C and offset at 395 °C. The blend is more
stable at higher temperatures. The mass loss is up to 58 % till the offset temperature. Blend
with PPy 18 wt. % shows the onset at 210 °C and offset at 375 °C. this blend is highly stable
at higher temperatures and shows the mass loss up to 50 % at its offset temperature.
For every blend, the region of 150–410 °C shows greater mass loss as in comparison to the
neat TPU. This mass loss portrays the lower thermal stability of urea linkages between
PPy.DBSA and TPU. Above 410 °C, the mass loss is higher for the TPU and lower for the
blends and the mass loss is dependent on the PPy added.
4.2 Fourier transforms infrared spectroscopy
The infrared spectroscopy study is conducted to analyze the interaction PPy.DBSA
macromolecules with the Thermoplastic polyurethane matrix present within the in situ
polymerized blend. Literature reported that the FTIR analysis TPU blended with PPy shows
the interaction of TPU carbonyl groups with the PPy amine functional groups [12]. Figure
4.2 shows FTIR spectra of TPU and PPy.DBSA/TPU blends with varying percentages. The
peaks ranging 3000 to 3300 cm-1 shows the amine functional groups absorption and the
dominant peaks at 3335 cm-1 are linked to the stretching of the amine functional groups.
The peaks at the 2947 cm-1 shows the stretching of CH, CH2 and CH3 groups symmetrically
and asymmetrically.
25
0 wt% PPy 1220
1513
1080
3338
1527
1010
10200
1160
1160
1527
4.5 wt Py
3329
1527 1160
1040
3319
9 wt% PPy
1720
3324 2947
2947
2947
2947
18 wt% PPy
4000 3500 3000 2500 2000 1500 1000 500
Wavenumber (cm
-1
)
Absorbance
1720
1720
1720
Figure 4.2 FTIR/ATR spectra of pure TPU and TPU/PPy.DBSA blends in PPy weight
percentages of 4.5, 9, and 18. respectively
The absorption observed at 1720 cm-1
provide the information at about the
asymmetrical stretching of TPU carbonyl group. The FTIR bands of the in situ
polymerized blends exhibited that amine peak sharpness is displaced from 3338 cm−1
in 0 wt % PPy (neat TPU) to lesser wave number, i.e., 3329, 3324 cm−1
, and 3319 cm−1
for 4.5 wt.% PPy, 9 wt.% PPy and, 18 wt.% PPy, respectively. This shift of amine
group peaks indicates that the existence of interacting bonding between the carbonyl
groups of TPU and amine groups of PPy. As the TPU is the matrix and higher in
26
percentage so it is dominant, this behavior is indicated in the narrow peak
difference. The absorption peak at 1080 cm-1
indicates the aromatic C-H bending in
plane. The same peak is moved from 1080 to 1040, 1020, and 1010 cm-1
for 4.5 wt.%
PPy, 9 wt.% PPy and, 18 wt.% PPy, respectively with the increase in the loading of
PPy. The peaks are more sharpe in the case of blends. The existence of varied
morphologies and mutually free and bound carbonyl groups in both blends is
shown by the extent of the asymmetric carbonyl absorption peak at the 1732 cm-1
wave number in both blends [50].
4.3 Future Prospect
The aim and objectives our project were to fabricate the highly stretchable and sensitive
strain sensor based on Polypyrrole and thermoplastic urethane blend. But because of the
time constrains and COVID situation we would not do that. But soon our juniors will do
that.
In the future, we are aiming to synthesis Piezoresistive strain sensor based on PPy/TPU
blend. Piezoresistive strain sensor consist of the electrically conductive film on flexible
material and sense the change in resistance by change in geometry of sensor.
M. Kotal et al. [4] worked on the up-gradation of the high-temperature stability and
conductivity of the nano blends based on thermoplastic polyurethane and polypyrrole (PPy)
doped with dodecyl benzenesulfonic acid (DBSA) by adopting two processing methods
namely in situ (IS) and solution intercalation (SB) methods. Increase in the conductivity was
observed by incorporating DBSA doped PPy. However, a sharp increase in the conductivity
manifested by a specimen with 2.5 wt% of DBSA doped PPy by adopting in situ technique.
The highest value of electrical conductivity observed by utilizing the SB technique was 0.26
S cm-1 at 30 wt% of DBSA doped PPy. The decomposition temperature was observed to be
about 382 oC, 384 oC, and 414oC for TPU, DBSA doped PPy /TPU by IS technique, and DBSA
doped PPy /TPU by SB respectively. A.S. Kurian, H. Souri, V.B. Mohan et al. [9] prepared
stretchable sensors of polypyrrole (PPy) and silicone rubber (SR) which are used to detect
27
the movement of the humans by utilizing the solution casting method. The gauge factor
obtained with different amounts of PPy in SR was in between 1.15 and 1.58. PPy/SR is more
suitable for the strain in large values due to their low hysteresis, sensitivity, and durability.
28
Chapter: 5 Conclusion
In this research project, a facile fabrication route and characterization of hybrid
fillers-based flexible strain sensors has been presented to study the behavior of the
designed sensors. Thermoplastic polyurethane (TPU) has been selected as base
polymer because of its excellent characteristics such as good stretchability , excellent
mechanical properties and compatibility With polypyrrole (ppy) nanofillers.The
thermal stability of TPU/PPY blend sensor increases with the increasing conductive
nanofillers ( PPY) loading(0%,4.5%,9%,18%) in thermoplastic polyurethane matrix.
Which gives 80% to 50% loss in mass respectively. As we increase the loading of
nanofillers ( PPY) (0%,4.5%,9%,18%) we get more sharp peaks which indicates that's
interaction between TPU and PPy.DBSA increased. Because TPU carbonyl grou and
amine group from ppy interactions.These results confirmed by FTIR test.
29
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[48] S. H. Bae, Y. Lee, B. K. Sharma, H. J. Lee, J. H. Kim, and J. H. Ahn, “Graphene-
based transparent strain sensor,” Carbon N. Y., vol. 51, no. 1, pp. 236–242, 2013,
doi: 10.1016/j.carbon.2012.08.048.
[49] I. A. Rashid et al., “Stretchable strain sensors based on
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pp. 1081–1093, 2020, doi: 10.1007/s00289-019-02796-x.
[50] P. C. Rodrigues and L. Akcelrud, “Networks and blends of polyaniline and
polyurethane : correlations between composition and thermal , dynamic
mechanical and electrical properties,” vol. 44, pp. 6891–6899, 2003, doi:
10.1016/j.polymer.2003.08.024.

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STRETCHABLE STRAIN SENSORS BASED ON POLYPYRROLE AND THERMOPLASTIC POLYURETHANE BLENDS.pdf

  • 1. STRETCHABLE STRAIN SENSORS BASED ON POLYPYRROLE /THERMOPLASTIC POLYURETHANE BLENDS By Group No. 05 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF BSc IN POLYMER ENGINEERING in the Department of Polymer and Process Engineering Nauman Aslam (2017pe21@student.uet.edu.pk) Thesis Supervisor: Dr Rabia Nazar, Assistant Professor July, 2021 UNIVERSITY OF ENGINEERING AND TECHNOLOGY, LAHORE Mian Husnain Iqbal (2017-PE-21) Shahroz Sarwar (2017-PE-28) Mian Arslan Sarwar (2017-PE-37)
  • 2. STRETCHABLE STRAIN SENSORS BASED ON POLYPYRROLE /THERMOPLASTIC POLYURETHANE BLENDS By Group No. 05 We have jointly examined the candidates today through viva voce examination and evaluated thesis submitted by them. We jointly agree on the result of the thesis examination and evaluation as follows: 1. Thesis is approved. 2. Thesis is rejected. 3. Thesis is returned to candidates for incorporating additions/modification Internal Examiner Sign: Name: Dr Rabia Nazar Internal Examiner Sign: Name: Dr. Faheem Chairman Sign: Name: Prof Dr Asif Ali Qaiser Dated: _______ UNIVERSITY OF ENGINEERING AND TECHNOLOGY, LAHORE Mian Husnain Iqbal (2017-PE-21) Shahroz Sarwar (2017-PE-28) Mian Arslan Sarwar (2017-PE-37)
  • 3. iii Thesis Supervisor: Assistant Professor Dr. Rabia Nazar (Ph.D.) ABSTRACT The advancement of stretchable strain sensors has capable applications in the human motion detection, medical and soft robotics. For applications, highly stretchable, stable, and sensitive strain sensors are required. Good stretch ability is the key features. Recently, the technique of hybridization is applied to overcome the challenges associated with wide strain range and sensitivity of strain sensors. In this research work, we propose a simple solution casting technique to fabricate piezoresistive strain sensors by incorporating conductive materials such as pyrrole as a conducting material. The development of thermoplastic polyurethane(TPU)/polypyrrole(PPy) 4.5, 9, 18 wt% pyrrole based strain sensors are synthesized in solution technique of in-situ polymerization of acid doped PPy with TPU in different percentage. Different characterization techniques employed to monitor different properties FTIR for amine and carbonyl group interaction, TGA heat stability characterization, UTM for mechanical analysis and electrical properties by Multi-meter. Keywords: Strain sensors, Pyrrole, TPU, solution casting, wearable sensors, piezoresistive conductivity
  • 4. iv Table of Contents ABSTRACT.................................................................................................................................... iii ACKNOWLEDGEMENTS............................................................................................................. v List of Glossary............................................................................................................................. vii Chapter: 1 Introduction .................................................................................................................2 1.1 Applications.............................................................................................................................6 1.1.1 Application of strain sensor in medical field......................................................................6 1.1.2 Application in Sports.........................................................................................................9 Chapter: 2 Literature Review ......................................................................................................11 Chapter: 3 Experimental Methods..............................................................................................21 3.1 Materials Required................................................................................................................21 3.2 Strain sensors prepared by in Situ Polymerization process.....................................................21 3.3 Characterization ....................................................................................................................22 Chapter no 4 Results and Discussion..........................................................................................23 4.1 Thermogravimetric Analysis...................................................................................................23 4.2 Fourier transforms infrared spectroscopy..............................................................................24 4.3 Future Prospect.....................................................................................................................26 Chapter: 5 Conclusion..................................................................................................................28
  • 5. v ACKNOWLEDGEMENTS It's always a joy to thank the wonderful folks at the University of Engineering and Technology (UET) for their unwavering support in helping me maintain my practical and laboratory polymer abilities. First and foremost, I want to express my gratitude to my parents for their unwavering support, enthusiasm, and tremendous assistance. I might not be able to finish this subject adequately if I don't have all of this. Second, I'd want to express my gratitude to Dr. Rabia Nazar for allowing us to participate in polymeric material testing and formulation. She also provides us with his undivided attention and assistance. Finally, I'd like to convey my gratitude to all Lab Attendants for their assistance with Polymer.Finally, I'd want to express my gratitude to all Lab Attendants for their Polymer Department guidance, which has really aided me in dealing with experimental training placement. They had backed me up by demonstrating various methods for gathering data for the trial. In addition, I'd like to express my gratitude to Prof. Dr. Asif Ali Qaiser (Chairman and Senior Professor/Department of Polymer and Process Engineering), who oversaw the department's rules and regulations and met all of the laboratory's requirements, as well as extending his friendship to the staff and creating a pleasant training environment. A paper is insufficient to express my gratitude for their assistance and direction throughout practically all of my work in the department. Finally, I apologise to all those anonymous individuals that assisted me in various ways in order for me to have a successful training.
  • 6. vi List of Figures Figure 1.1. Diverse functional, sensors composed of nanomaterials for human action measure. a) Resistive-type sensors, and b) capacitive-type sensors.. ....................................................................5 Figure 1.2 A conceptual schematic of strain sensors operating in the case of emergency by collecting patients’ physiological information and then transferring the data to a medical Center through wireless devices, thereby, alerting the physician medical assistant ...................................................8 Figure 1.3 The operation of portable and skin attached - stretched sensors in the biomedical field: a) A capacitive-kind strain sensor covered near the hreat. b) he astrain sensor's reply in blood measurement. c) Strain sensor mounted on the chest for the breathing ...........................................8 Figure 1.4 Implementation of wearable sensors for measuring physical performance on body joints. a) Strain sensor attached on the wrist and elbow joints. b) The reply of skin-mountable strain sensors to leveling and twisting movement of the hand and elbow joints c)....................................10 Figure 2.1Spray Coating process of the soft finger ..........................................................................13 Figure 4.1 TGA curves for pure TPU and TPU/PPy.DBSA blends in PPy weight percentages of 4.5, 9, and 18. respectively ........................................................................................................................23 Figure 4.2 FTIR/ATR spectra of pure TPU and TPU/PPy.DBSA blends in PPy weight percentages of 4.5, 9, and 18. respectively.....................................................................................................................25
  • 7. vii List of Glossary TPU Thermoplastic Polyurethane PPy Polypyrrole DBSA Do decyl benzene Sulphonic Acid APS Ammonium Per Sulphate CB Carbon Black PANI Polyaniline GF Gauge Factor FTIR Fourier Transform infrared spectroscopy SEM Scanning Electron Microscopy EIS Electrochemical impedance spectroscopy DMTA Dynamic Mechanical Thermal Analysis GNPs Graphene Nano Platelets CNT Carbon Nano Tubes A Ampere V Voltage GNPs Graphene nan platelets MWCNT Multi wall carbon nano tube FLG Graphene composite fiber
  • 8. viii PDMS Polydimethylsiloxane PSS Polystyrene sulfonate NBR Nitrile butadiene rubber SWNT Single Wall Nano tube LED Light emitting diode ∆R/RO Relative Change in Resistance
  • 9. 2 Chapter: 1 Introduction The incorporation of different nanoparticles and response of these advanced nanomaterials into strain sensors have modernized the application of these intellectual devices in various sectors [1]. Due to their innovative benefits in numerous areas, the flexible and sensitive strain sensors have risen in popularity in research for their use in many applications .i.e. structural health monitoring (SHM), soft robotics, and pressure sensing etc [2]. The strain sensors function by perceiving the human body motions triggered by mobility, breathing, and pulse, and are also able to detect significant body stresses caused by joints twisting. Besides, These sensing may be integrated into wearable electronic devices that connect to clothes and the human tissue [3]. Moreover, they can also be utilized to measure the movements of robotic joints and successfully record and improve the living environment of human beings. The sensing mechanism is triggered upon stretching the strain sensors that are followed by various processes, such as propagation of the crack, tunnelling effect and increase in distance between the adjoining nanomaterial [4]. Traditionally, metal-based strain gauges were fabricated but they exhibited lower strain (<5%) due to low elongation at break. Therefore, elastomeric or polymeric based materials were used because they exhibited much higher strains (10 to 800%) [4]. Flexible strain sensors necessitate the incorporation of several conductive nanoparticles into the elastomeric substrate. To create sensors with a large level of elasticity, the most common polymers employed are different elastomers such as: NBR, EPDM etc. That sensing characteristic of strain sensors is activated by mixed with conductive nanomaterial for example carbon black (CB),
  • 10. 3 (CNTs) [5], (GNPs) [6] and (Ag-NWs) [7] etc. However, the majority of nano particles communicate great sensitivity as sensors but are relatively costly. As a result, hence the necessity to consider more affordable options. This can be resolved by utilizing low resistance polymers such as : (PPY) and polyaniline (PANI). The use of polyaniline, as a conductive filler, is gradually increasing due to its easy synthesis, processability and cheapness. To improve its electrical conductivity, it is converted (ES) through various form chemical means and doped it such as power acids HCl, H2SO4, DBSA etc. [8] [9]. The conductivity of PANI can be tuned by doping it with a certain amount of acid and thus falls into the category of metals and conductor. Hence, it is an excellent choice of a conductive material for increasing the strain sensor's effectiveness. However, it has a disadvantage of being incompatible with different polymers. There are three different approaches to making polyaniline compatible with different polymers such as molten blends, liquid polymerization and in-situ polymerization are all methods of polymerization. The process of in-situ polymerization, as compared to others, uniformly disperses the polyaniline into the base matrix and improves the electromechanical properties of the strain sensors [10]. Though, to achieve a strain sensor with improved mechanical, thermal and electrical properties, strong compatibility, and interaction is required between filler and polymer. Some research have previously been published in which PANI was utilized as a potential filler for stretch sensors Gong et al. created elastic strain sensors out of PANI as a conducting polymer and integrated it into polydimethylsiloxane (PDMS), reporting a 50% strain value [11]. The required characteristics of the strain sensors such as flexibility, conductivity, stability, sensitivity and mechanical properties of substrate for the application in structural health monitoring must be considered. Therefore, to achieve these requirements, higher interfacial bonding and compatibility between carbon
  • 11. 4 nanomaterials and polymers are essential [4]. By integrating carbon nanotube (CNT) thin films on piezoelectric materials, strain sensors with great ductility are created; nevertheless, these strain sensors have limited responsiveness [12]. Although, the limitation of low stretchability of the reported strain sensors rendered them unsuitable for large motion detection application [13]. The electrical percolation network of fillers is highly dependent on the geometry, size and structure of nanomaterial. As a result, the piezoresistive behavior of 2D nanofill is higher than those of nanowires and enhances the sensitivity of the strain sensors [14]. Due to graphene and CNTs are expensive, there is a limitation of cost control for the manufacturing of sensors. Therefore, there remains a challenge in the achieving strain sensors with high durability, accuracy, resilience, and cheap price [2]. There are two types of approaches employed in the manufacturing of stretchable strain sensors first is resistive-type and second is capacitive-type. The most preferable is the resistive-kind sensors owing to its straightforward and easy manufacturing procedure, operating principle and minimal energy usage under application [15]. A huge number of research have been conducted on the piezoresistive behavior of TPU nanocomposites including carbon-based nanoparticles [16]. The results demonstrated that under tensile strain, the adjacent neighboring fillers lose contact due to deformation of TPU matrix producing a resistance-strain response. Because of its intrinsic characteristics such as low aspect ratio, cheap price in comparison to other carbonaceous nanoparticles such as graphene and CNT, and high conductivity, zero-dimensional (0D) carbon black (CB) is a viable option as conductive filler.The electrical and mechanical characteristics of the strain sensors containing carbon black as a nanofiller are enhanced due to its reinforcing effect. Silver nanoparticles (AgNPs) are also becoming attractive as a conductive candidate due to their improved effect on the strain sensing performance. When AgNPs are
  • 12. 5 hybridized with other conductive materials, they produce a synergic effect and are prone to produce microcracks under tensile strain [16]. The electrical and mechanical properties of the strain sensors can be the filling level in elastomeric substrates may be readily regulated by fine-tuning the loading rate. The hybridization technique is attracting emphasis is drawn to the combination of distinct filler characteristics, decreased filler loading, and improved electrically and structural characteristics because of the synergistic impact of both additives The physical and electric characteristics of a strain sensor are evaluated under statically and kinetic circumstances to assess resistance fluctuation and to validate the strain sensor's sensibility and endurance. Moreover, the testing findings allow the constructed strain sensors to identify human actions such as thumb twisting, hand rotation, and knee extension, as demonstrated. in Fig. 1.1 [17] Figure 1.1. Diverse functional, sensors composed of nanomaterials for human action measure. a) Resistive-type sensors, and b) capacitive-type sensors [2].
  • 13. 6 1.1 Applications Stretchable strain sensor has large number of applications in various fields. For example, pressure measure gadgets , structural health-monitoring. Flexible and stretchable strain sensor also used in electronic circuit and machine for the detection human motion and convert data in the form of human readable information They can be used as wearable gadgets that are directly attached to human body or clothing for the body strain measured These ultra-sensitive sensors can detect actions as small as breathing and heartbeat to huge strain-induced body joint bending and straightening. Additionally, these sensitive strain sensors are beneficial for the observing the robot activity and motion detection 1.1.1 Application of strain sensor in medical field Human Healthcare and high -quality drugs are becoming more difficult and complex as the population grows. Wearable electronics are gaining popularity due to their ease of use and long-term monitoring capabilities. These individualized health-monitoring technologies have promise for enhancing the capabilities of present medical systems. systems [18]. Fig. 2.1 shows the conceptual illustration of health-monitoring devices using wearable sensors [18]. These wearable strain sensors function by assembling the health and physical information from the human body and is represented in the form of heart rate , respiratory rate [19], pressure of blood and oxygen level [15], human body temperature and movements etc. The sensors send the evaluated statistics from wearing sensors to a smartphone or wireless accessible hotspot an alert message is delivered to a call for assistance center for quick assistance. After a patient has received adequate medical therapy, health-care providers can monitor person Condition of health person the condition and make medical choices [20]. The strain sensors may also be used in biological devices to check complicated and
  • 14. 7 massive displacements of human skin or clothes, and their excellent detecting capability allows them to detect small skin straining caused by breathing or pressure of blood Fig. 1.2 (a) uses a stretchable capacitive-type sensor to measure blood pressure in viva [2]. The sensors reacted to fluctuating heart rate with excellent strains detecting capabilities in Fig. 1.2 (b). stimulate accurate, skin movable, and wearable strain sensors that detect tiny body motion.by phonation, body posture, skin, expansion, injury recovery, respiratory, and heartbeat rate [21]. The illustration of a resistance-kind of sensor attached to the human body is shown in Fig. 1.2 (c) exhibiting the response of the sensor to the motionless (black) and moving (red) sates of breathing. The peak of the statistics shows expands and does not expand the chest When breathing accordingly. Strain sensor implemented on the wrist to measure heart rate is shown in Fig. 1.2 (d). The pulse numbers are 38 and 46 is subjects were in the motionless (black) and activity (red) states of modes for 30 s correspondingly [22]. Individualized health-monitoring systems can accurately important role in human health indicators like long time. Measurement of vascular circulation, pulse, and respiration, signaling initial disease diagnosis When a person sat with a regularly stretched leg, an elastic capacitive-type strain sensor was attached to the knees to perform a patellar reflex examination, as illustrated in Fig. 1.2. (e). During the bending state of the knee, the sensors measured a large strain. The patellar knee ligament was tapped with a mallet during the leg reflex examination. The striking motion led the leg to stretch and quickly return to its original position Fig. 1.2 (f) illustrates that the capacitance decreased suddenly during straightening and then back to original the bio-compatible and portable strain sensors can be used in a variety of biomedical applications. Because of their great sensitivity, conductive sensors are excellent for measured low-strain motions, whereas detection systems function better for high-strain movements in aspects of uniformity, minimal hysteresis, and quick reply.
  • 15. 8 Figure 1.2 A conceptual schematic of strain sensors operating in the case of emergency by collecting patients’ physiological information and then transferring the data to a medical Center through wireless devices, thereby, alerting the physician medical assistant [2] Figure 1.3 The operation of portable and skin attached - stretched sensors in the biomedical field: a) A capacitive-kind strain sensor covered near the hreat. b) he astrain sensor's reply in blood measurement. c) Strain sensor mounted on the chest for the breathing
  • 16. 9 1.1.2 Application in Sports Adjustable strain sensors connected to several body parts measure exercise ability. The signals measured by the strain sensors wrapped around the wrist and elbow are demonstrated in Fig. 2.3 (a) and 2.3 (b) [6]. The resistance of strain sensors increases during the rotating action of the arm and hand. After the straightening of wrist and elbow, the change in resistance It has regained its original value The body movement analysis can be performed through the data measured by the w strain sensors. A rosette-type stretchable strain sensor is fabricated from 3s self-runing CBs, PDMS strain sensors at an angle of 120° of each other [13]. The function of rosette-type strain sensors is to measure the principal strains under in-plane directions of displacements [5]. The response of elongated sensor in the uniaxial direction of S1 is shown in Figure 2.3 (c). In Fig. 2.3 (d), the change in resistance for the S1 was larger than that of S2 and S3. The information reported from these sensors can be used for body fitness analysis Fig. 2.3 (e) demonstrates another application in which Flexible strain sensors were connected to the knee joint to study different knee movement Moving, walking, and leaping from a seated posture are examples of sequences [5]. As a result, skin launch, and portable strain sensors are useful for large period structural human health observing reintegration and evaluating players' athletic performance.
  • 17. 10 The use of elastic stretch sensors on robotic a) Measured signals from stretched sensor to the sensors to leveling and twisting movement of hands joints. b) Resistivity changes as the twisting position of the elastic strain sensor changes. c) Strain sensor mounted on gloves to control the movement of a gripper robot flexible sensors resulting in dummy electronic skin. e) The piezoresistive reply of the dummy skin positioned on the top of the skin [2]. Figure 1.4 Implementation of wearable sensors for measuring physical performance on body joints. a) Strain sensor attached on the wrist and elbow joints. b) The reply of skin-mountable strain sensors to leveling and twisting movement of the hand and elbow joints c)
  • 18. 11 Chapter: 2 Literature Review A brief literature review is conducted, underlining the usage of different conductive and sensing materials, various forms of additives, different building techniques and performance characteristics such as sensitivity and stretch ability of strain sensors. Due to the increasing demand for automation and lack of resources the industrialists are demanding robots that can perform their tasks precisely and accurately. For their accurate working, flexibility is needed in their manufacturing and sensors are their most important parts so it needs some flexibility this requirement cannot be fulfilled by using typical metallic strain sensors whose maximum strain sustainability is ~5% but polymers can fulfill this requirement. S. Tadakaluru et al. [19] manufactured a sensor made up of natural rubber having carbon nanotube and graphite films sandwiched between its layers and measured their strain sustainability. Graphite and carbon sensors give 246% and 620% strains which are ~50 and ~120 times greater than a conventional metallic sensor respectively. R. Zhang et al. [23] observed the strain sensing behavior of polyurethane- urea/ amino-functionalized MWNTs composite prepared using a solution casting technique. Appreciable recoverability was noticed in it at a 5% strain. M. Kotal et al. [24] worked on the up-gradation of the high-temperature stability and conductivity of the nano blends based on thermoplastic polyurethane and polypyrrole (PPy) doped with dodecyl benzenesulfonic acid (DBSA) by adopting two processing methods namely in situ (IS) and solution intercalation (SB) methods. Increase in the conductivity was observed by incorporating DBSA doped PPy. However, a sharp increase in the conductivity manifested by a specimen with 2.5 wt% of DBSA doped PPy by adopting in situ technique. The highest value of electrical conductivity observed by utilizing the SB technique was 0.26 S cm-1 at 30 wt% of DBSA doped PPy. The decomposition temperature was observed to be about
  • 19. 12 382o C, 384o C, and 414o C for TPU, DBSA doped PPy /TPU by IS technique, and DBSA doped PPy /TPU by SB respectively. A.S. Kurian, H. Souri, V.B. Mohan et al. [6] prepared stretchable sensors of polypyrrole (PPy) and silicone rubber (SR) which are used to detect the movement of the humans by utilizing the solution casting method. The gauge factor obtained with different amounts of PPy in SR was in between 1.15 and 1.58. PPy/SR is more suitable for the strain in large values due to their low hysteresis, sensitivity, and durability. A.P. Tjahyono et al. [25] manufactured a strain sensor based on the conductive polymer polypyrrole (PPy) and a matrix of natural rubber (NR) adopting vapor phase polymerization method under evacuation. The gauge factor was appeared to be 1.86 while hysteresis shown by the sensor was its major demerit. J. Chen et al. [26] reported the stretching ability, flexibility, and quick self-healing properties of flexible stretchable sensors of elastomer doped with polypyrrole prepared by using in situ polymerization of pyrrole in the elastomer substrate having abundant hydrogen bonding. The conductive filler PPy incorporation up to 7.5 wt. % gives 2.4% enhancement in the fracture resistance from 0.3 to 0.72 MPa while on the other hand the stretchability was reduced by 18% from 500 to 410 %. The electrical conductivity with 7.5 wt. % of PPy was about 0.88 Sm-1 . High strain sensitivity up to 300% elongation was observed and hence it is used for the detection of motion. P. Cisell et al. [27] prepared a piezoresistive strain sensor based on Ethylene-Propylene-Diene-Monomer (EPDM)/ multi-wall carbon nanotubes (MWNTs) composite by solution casting technique. The results show that its conductivity is a linear function of strain up to 10% strain. F. Martinez et al. [28] formulated a silicone/carbon nanofillers based flexible standing strain sensor to measure electrical conductance. The electrical conductivity
  • 20. 13 of 0.3-0.4 mS/cm is obtained from the different sensors having conductivities between 0.03-5mS/cm. Z. Levin et al. [29] prepared a polyaniline(PANI)/ poly(vinyl acetate) (PVAc) based sensor using a solution casting method. 4wt.% PANI proved to be highly sensitive and have a gauge factor between 6 and 8 approximately triple than any typical metallic sensor. Y. Li et al. [30] reported a polypyrrole coated fiber strain sensor. Its sensitivity and conductivity were tried to be enhanced by using different techniques i.e. thin coating by a vapor deposition method, polymerization of pyrrole at low temperature. The strain and electrical characterization suggest a high strain sensitivity of ∼80 for 50% strain.V. Sencadas et al. [31] prepared an ultra-thin Multi- walled carbon nanotube (MWCNT)/styrene butadiene styrene (SBS) based piezoresistive sensor for fingers skin used in robots. It gives a gauge factor of ∼1. Zhou et al. [32] manufactured an exceptionally stretchable and super touchy strain sensor utilizing single-walled carbon nanotubes (SWCNTs) joined into the PDMS substrate by scattering technique in methane sulfonic corrosive and acquired greatest extending up to 50 % strain and bestow the worth of affectability i.e., 750. Wang et al. [21] introduced a strain sensor that accomplished the good stretch ability of 100% and high affectability up to 1020.2 dependent on bright/ozone (UV/O3) beams broke and carbon nanotubes/elastomer (CNTs/PDMS). The revealed Figure 2.1Spray Coating process of the soft finger [15]
  • 21. 14 exceptionally touchy strain sensor has expected application in the recognition of human body movement like eye squinting, wrist and beating. Niu et al. [33] manufactured an adaptable based strain sensor comprised on nanocomposite made up with graphene nan platelets (GNPs) and polydimethylsiloxane(PDMS) elastomer as a base material and furthermore appropriate for pressure recognition having a affectability up to 20% strain inferable from high stretch ability and adaptability of PDMS elastomer. GNPs/PDMS piezoresistive sensor likewise showed most extreme affectability of 140 at 5 wt % fixation which could be constrained by the fuse of GNPs into PDMS elastomer. GNPS/PDMS based adaptable sensors showed the diversion after bowing as well as showed the identification of the finger movement and made it reasonable for fake skin and wearable applications. Wang et al. [18] manufactured a productive stretchable and exceptionally delicate piezoresistive sort strain sensor comprised of polystyrene butadiene styrene (SBS) as a conductive material with a couple of layers of graphene composite fiber (FLG) utilizing a wet-turning measure. The revealed showed super strain range more prominent than every available ounce of effort and super sensitivity esteem with a (GF) 2546 up to 100% strain. Wang et al.[5] made multi-walled carbon-nanotubes (MWCNTs)/(TPU) elastomer fiber-shaped high stretchable sensor having a permeable structure by a cost-effective wet twisted method that is possible as a continuous and large-scale preparation process. MWCNTs/TPU based strain sensor showed better studied through the tunneling theory and gave efficient balance in between the ultra-wide response having a range for strain (320%) and the value of sensitivity having GF 97.1 as a resistive type based stretchable strain sensor in the uniaxial stretching test.
  • 22. 15 Zheng et al.[21] created a stable and exceptionally stretchable strain sensor i.e., a conductive composite comprised of crossover carbon Nano fillers (CNTs–CB) with polydimethylsiloxane (PDMS) elastomer substrate for powerful human movements checking applications. This (CNTs - CB)/PDMS based strain sensor was manufactured by utilizing the arrangement blending and projecting method and displayed a high stretch ability up to 300% strain. Higher affectability with a measure factor of 0.91 was gotten after extending from 0% - 100%, 100% - 225% with a GF of 3.25 also, 225% - 300% showed a greatest measure factor of 13.1 separately. Raju et al. [34] created two sorts of strain sensors dependent on graphene – polymer (PDMS) composite coatings that displayed a wide reach strain sensor tested by Raman spectroscopy i.e., substance fume statement (CVD) covering based example and the dry changed precisely shed based example. In any case, the Raman two- dimensional band having shift-pace of shed graphene are 35% more noteworthy than CVD-graphene focusing on the previous high strain touchy. The shed graphene covering on PDMS by Raman spectroscopy showed a GF of 2 while CVD graphene covering on polydimethylsiloxane introduced a GF of 6.1 for an applied strain of 30% individually. Knite et al.[35] manufactured a sensor-dependent on two kinds of fillers, one was high construction carbon nanoparticles (CNPs) and second was multiwall carbon nanotubes (MWCNTs) in polyisoprene lattice by arrangement blending technique. The detailed sensor shown a greatest extending up to 40% with the check factor GF of 6 for carbon nanotubes filler-based composite while 4 worth of GF for multi- walled carbon nanotubes-based composite under 40% applied strain. Wichmann et al.[36] announced the manufacture of a profoundly touchy also, stretchable strain sensor dependent on multiwall carbon nanotubes (MWCNTs)/Epoxy grid nanocomposite by means of blending technique and showed a greatest extending
  • 23. 16 worth of 500% strain and high affectability esteem with GF of 10 toward 900 or 2700 directions. Martinez et al. [28] introduced a polymer based highly flexible strain sensor by using smart materials (Electrical conducting liquid silicon rubber of Elastosil and carbon nanotubes conductive fillers) achieving a maximum of elongation of 410% at the time of breaking point of sample. The fabricated strain sensor was used for the extent of biological signals such as joint position and its movement, electrocardiogram, breathing and skin temperature. Sekitiani et al.[37] manufactured a sensor as natural light discharged diode (LED) show by utilizing stretchable dynamic grid covered on a printable flexible conductor through vacuum dissipation and mechanical punching strategy or cutting cycle in which a light-radiating diode was made out of graphene movies and single wall carbon nanotubes. This method significantly improves the stretch ability and conductivity of the strain sensors. Yu Chang et al. [38] created 3x3 dimensional adaptable strain sensor comprised of conductive materials like carbon nanotubes (CNTs) and carbon nanofiber (CNF) composite miniature dainty movies in the type of clusters that were implanted on the thermoplastic polyurethane (TPU) network by utilizing the designed surface treatment and shifted drop measure. It reacted by estimating the measure factor in the scope of 0.34 to 7.98 under the applied strain 3 to 7% individually. The proposed creation strategy was equipped for making conductive sort polymer-based sensors through profoundly troublesome plans, with more consistency just as exceptionally productive for mass creation. Ciselli et al.[27] made a composite kind strain sensor comprised of multi-walled carbon nanotubes (CNTs) utilized as a conductive filler and inserted it on to the ethylene propylene diene monomer (EPDM) substrate. The manufactured strain sensor displayed the upgrade in the mechanical properties when contrasted with the
  • 24. 17 most perfect type of the EPDM. A high stretch ability of up to 10% of strain was achieved and showed straight connection with the conductivity which worked on its application towards the pressing factor sensor just as strain sensor. Cochrane et al. [39] introduced an adaptable strain sensor that was manufactured from conductive sort polymer-based composite (CPC) for deciding the size of the parachute-shade bending. Evoprene, a class of thermoplastic elastomers (TPE), was utilized as a polymer framework and calcium carbonate as a filler to assembling profoundly stretchable strain sensors. The scattering of filler confers a high strain rate from 10 to 1000 mm/min and twisted at a greatest extending of 9% during 15 testing on the parachute overhang. Martinez et al.[28] detailed a polymer-based strain sensor having a self-flexing capacity created from Elastosil, a fluid silicone elastic comprising of great mechanical, electrical, maturing and vulcanization properties, built up with high viewpoint proportion conductive-nanoparticles showed a decent conductivity of 0.3 to 0.4 mS/cm and most extreme strain of up to 410% lengthening at the hour of the break with an elasticity of 5.4 N/mm2 . Yamada et al. [40] manufactured a stretchable strain sensor comprised of the slight movies of single-walled carbon nanotubes (CNTs) covered on the canine bone shape bits of polydimethylsiloxane (PDMS) polymer lattice for the movement recognition of the human body. It reacted to a novel strain sensor that surrendered high extending to 280% and 0.06 worth of check factor up to 200% of strain. Ku-Herrera et al.[41] announced a piezo resistivity of carbon nanotube with vinyl ester-based composites i.e., the utilization of strain sensor reacted in cyclic pressure and strain mode in the versatile systems and showed affectability esteem with a measure factor of 2.60 upon a normal extreme strain of 1.40% and showed a straight
  • 25. 18 piezoresistive conduct in pressure and non-direct conduct in pressure up to the break of the example. Xiao Li et al.[42] manufactured a delicate and profoundly stretchable strain sensor utilizing graphene woven textures (GWFs) layered onto a polydimethylsiloxane (PDMS) polymer grid and came about with a most extreme malleable strain of 6% with a check factor of 103 and for higher strain (>6%) the check factor esteem was up to 106 because of its woven cross section design and crack conduct, showing higher affectability under each extending cycle. J. Lipomi et al. [43] detailed a pressure strain sensor grounded on straightforward, versatile and biocompatible conductive carbon nanotubes CNTs films and polydimethylsiloxane (PDMS) material as a polymer substrate. The last shaped strain sensor reacted high stretchability with a greatest strain up to 150% with high conductivity of 2200S cm-1 in the full extended state. These straightforward and biocompatible strain sensors are profoundly reasonable for human wearable electronic applications. Nanshu Lu et al.[44] introduced a skin mountable strain sensor that showed high affectability what's more, was manufactured by utilizing polydimethylsiloxane (PDMS) elastomer and exceptionally conductive carbonaceous materials like the carbon dark CB and the carbon nanotubes (CNTs) as detecting 16 materials in the improvement of strain sensors. CB and CNTs were doped onto a PDMS polymer substrate and gave great affectability having check factor (GF) 29 and the most extreme extending estimated was in the middle of the scope of 11.2% to 22.6%. Slobodian et al. [45] manufactured an electrically conductive composite dependent on the interlaced organization of carbonbased nanotubes CNTs in thermoplastic polyurethane (TPU) framework. This CNT/TPU based composite showed greatest
  • 26. 19 prolongation through extending as 400% with multiple times more expansion in opposition that empowered it to be material for exceptionally distorted strain detecting component, electro-attractive field safeguarding and so forth. P. Tjahyono et al. [25] created a profoundly adaptable strain sensor by utilizing slim layers of polypyrrole as a conductive polymer covered on the regular elastic substrate by means of fume stage polymerization strategy through a vacuum climate. The came about strain sensor displayed better security with a greatest check factor of 1.86 upon 20% strain of the last example. The created sensor was totally applied to compression and expansion-based applications like an air muscle and can likewise be executed for computing the huge twisting strain applications. Hwang et al.[46] manufactured electromechanical strain sensor dependent on crossover composite sheets that include carbon nanotubes CNTs and graphene nanoplatelets GNPs impregnated on to polycarbonate PC through vacuum incited filtration strategy. The subsequent half breed sensor exhibited a high flexural strain of up to 2% with a measure factor in the scope of 0.56 – 0.64. Ning Hu et al.[47] introduced a super delicate strain sensor created from carbon nanofillers CNFs that was metal-covered in nature and epoxy lattice was utilized as a polymer framework for making CNF/epoxy-based composite. The subsequent sensor was produced using two sorts of nanofillers, one depended on fume development carbon fiber (VGCFs) with silver or nickel coatings and different was created by utilizing the metal-covered CNF. The created sensor showed high affectability with a check factor of 155 for VGCFs with silver covering and around multiple times expansion in the incentive for metal foil based strain checks upon +6000 miniature strain level.
  • 27. 20 Hoon Bae et al.[48] created a straightforward type strain sensor produced using graphene as a detecting filler into the stretchable elastic substrate in a type of rosette through particle carving and stepping strategies. The subsequent straightforward strain sensor showed affectability as far as measure factor in the scope of 4 to 14 upon 7.1% applied strain. These outcomes were shown by utilizing a straightforward glove every which way and their sizes were estimated by applying the gloves on to fingers actuated by the movement of finger [99]. Cai et al. [22] introduced a very stretchable capacitive sort strain sensor comprised of multi-walled carbon nanotubes (MWCNTs) inserted onto the polydimethylsiloxane PDMS substrate that was straightforward and utilized for movement identification of human joints. The subsequent strain sensor showed high stretchability with a most extreme strain of 300% with the upgraded toughness even in the wake of finishing many cycles.
  • 28. 21 Chapter: 3 Experimental Methods 3.1 Materials Required Materials which are required for the manufacturing of sensors are thermoplastic polyurethane (TPU – hardness = 87 shore D - ester-based, China) as the base polymer, Pyrrole monomer Tetrahydrofuran (THF Sigma – Aldrich chemicals, Germany), Ammonium persulfate (APS Dae – Jung, chemicals China), Dodecyl benzenesulfonic acid (DBSA) 3.2 Strain sensors prepared by in Situ Polymerization process By in situ polymerization process TPU and PPy are and polymerized, first of all 4.1g of TPU is added in 10mL THF and dissolved with continuous stirring for half or an hour so TPU can dissolve completely in solvent. Then (4.5, 9 and 18) wt. percentage of pyrrole with respect to of TPU was added in solution TPU solution, DBSA as a dopant for pyrrole monomer is added in the solution meanwhile (0.005 mole) APS is added drop wise through the burette and the solution is kept at 5o C for 12 hrs. under stirring for the completion of polymerization. As the polymerization initiates the color of the solution turns from greenish to black. After 12 hours of stirring the polymer is precipitated out by adding the excess amount of methanol in solution and washed several times with distilled water after precipitation. This washing will remove the unreacted monomers. After the washing precipitated mass is filtered out using filter paper and dried at 60-70 o C for 1 hour. Then the dried black colored mass is dissolved in the THF, and solution was molded in the handmade tape molds on a glass plate, the sample is subjected to [24].
  • 29. 22 3.3 Characterization FTIR/ATR spectrum of TPU and its different blends with Polypyrrole were recorded using FT/ IR-4100 infrared spectrometer (JASCO, Japan). The spectrum of the specimens were obtained in the wave number range of 400–4000 cm−1 . Thermogravimetric Polymer Bulletin 1 3 analysis of pure TPU film, PANI.DBSA and different blends of TPU/Aniline. DBSA was performed using thermogravimetric analyzer TGA-50 instrument (Shimandzu, Japan) at heating rate of 20 °C/min under nitrogen atmosphere and above ambient temperature 25–600 °C. Efect of concentration of aniline was observed on the thermal degradation of the blends. Samples were completely dried in a vacuum chamber before analysis. Figure 3.1 Schematic representation of the in-situ polymerization and solution casting technique resulting in the fabrication of PPy/TPU hybrid sensor.
  • 30. 23 Chapter no 4 Results and Discussion 4.1 Thermogravimetric Analysis The Thermogravimetric Analysis (TGA) analysis of Thermoplastic Polyurethane (TPU) and Polypyrrole (PPy), TPU/PPy.DBSA blends at (4.5, 9, 18) PPy wt.% are shown in the Figure 4.1. All curves represent the three major regions of weight loss that are detected during TGA study. The very first decay area up to 250 °C temperature is due to the drying up of the water deposited on the surfaces. The next degradation area ranging from 250 °C to 450 °C temperature shows the decay of Dodecylbenzene sulphonic acid (DBSA) and the and the oxidized PPy and TPU polymers present in them. The last region ranges from 450 to 550 °C temperature depicts the deprivation of hemmed in DBSA, PPy and TPU [49]. Figure 4.1 displays that the neat TPU sample remains stable up to 340 °C. The dip in the Figure 4.1 TGA curves for pure TPU and TPU/PPy.DBSA blends in PPy weight percentages of 4.5, 9, and 18. respectively
  • 31. 24 weight prior to 340°C is due to the elimination of humidity from the TPU surface. The decay initiates at 340 °C and then offsets at 430 °C. Total mass loss of neat TPU is 82% at the offset. The blends of TPU/PPy.DBSA synthesized via in situ polymerization shows varying weight loss values. The 4.5 PPy wt.% displays the beginning at 250 °C before the beginning point a weight loss up to 4 % occurs due to the thermally volatile elements like contaminants and humidity present in the blend. The onset started at 250 °C due to the presence of some unreacted pyrrole monomers and solvent present in the blends. Blend is stable at higher temperatures and the mass loss is up to 62% at the offset temperature of 410 °C. The trend in the Figure 4,1 portrays the mass loss decreases with the increase in the PPy concentration, Blend with PPy 9 wt. % shows the onset at 250 °C and offset at 395 °C. The blend is more stable at higher temperatures. The mass loss is up to 58 % till the offset temperature. Blend with PPy 18 wt. % shows the onset at 210 °C and offset at 375 °C. this blend is highly stable at higher temperatures and shows the mass loss up to 50 % at its offset temperature. For every blend, the region of 150–410 °C shows greater mass loss as in comparison to the neat TPU. This mass loss portrays the lower thermal stability of urea linkages between PPy.DBSA and TPU. Above 410 °C, the mass loss is higher for the TPU and lower for the blends and the mass loss is dependent on the PPy added. 4.2 Fourier transforms infrared spectroscopy The infrared spectroscopy study is conducted to analyze the interaction PPy.DBSA macromolecules with the Thermoplastic polyurethane matrix present within the in situ polymerized blend. Literature reported that the FTIR analysis TPU blended with PPy shows the interaction of TPU carbonyl groups with the PPy amine functional groups [12]. Figure 4.2 shows FTIR spectra of TPU and PPy.DBSA/TPU blends with varying percentages. The peaks ranging 3000 to 3300 cm-1 shows the amine functional groups absorption and the dominant peaks at 3335 cm-1 are linked to the stretching of the amine functional groups. The peaks at the 2947 cm-1 shows the stretching of CH, CH2 and CH3 groups symmetrically and asymmetrically.
  • 32. 25 0 wt% PPy 1220 1513 1080 3338 1527 1010 10200 1160 1160 1527 4.5 wt Py 3329 1527 1160 1040 3319 9 wt% PPy 1720 3324 2947 2947 2947 2947 18 wt% PPy 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber (cm -1 ) Absorbance 1720 1720 1720 Figure 4.2 FTIR/ATR spectra of pure TPU and TPU/PPy.DBSA blends in PPy weight percentages of 4.5, 9, and 18. respectively The absorption observed at 1720 cm-1 provide the information at about the asymmetrical stretching of TPU carbonyl group. The FTIR bands of the in situ polymerized blends exhibited that amine peak sharpness is displaced from 3338 cm−1 in 0 wt % PPy (neat TPU) to lesser wave number, i.e., 3329, 3324 cm−1 , and 3319 cm−1 for 4.5 wt.% PPy, 9 wt.% PPy and, 18 wt.% PPy, respectively. This shift of amine group peaks indicates that the existence of interacting bonding between the carbonyl groups of TPU and amine groups of PPy. As the TPU is the matrix and higher in
  • 33. 26 percentage so it is dominant, this behavior is indicated in the narrow peak difference. The absorption peak at 1080 cm-1 indicates the aromatic C-H bending in plane. The same peak is moved from 1080 to 1040, 1020, and 1010 cm-1 for 4.5 wt.% PPy, 9 wt.% PPy and, 18 wt.% PPy, respectively with the increase in the loading of PPy. The peaks are more sharpe in the case of blends. The existence of varied morphologies and mutually free and bound carbonyl groups in both blends is shown by the extent of the asymmetric carbonyl absorption peak at the 1732 cm-1 wave number in both blends [50]. 4.3 Future Prospect The aim and objectives our project were to fabricate the highly stretchable and sensitive strain sensor based on Polypyrrole and thermoplastic urethane blend. But because of the time constrains and COVID situation we would not do that. But soon our juniors will do that. In the future, we are aiming to synthesis Piezoresistive strain sensor based on PPy/TPU blend. Piezoresistive strain sensor consist of the electrically conductive film on flexible material and sense the change in resistance by change in geometry of sensor. M. Kotal et al. [4] worked on the up-gradation of the high-temperature stability and conductivity of the nano blends based on thermoplastic polyurethane and polypyrrole (PPy) doped with dodecyl benzenesulfonic acid (DBSA) by adopting two processing methods namely in situ (IS) and solution intercalation (SB) methods. Increase in the conductivity was observed by incorporating DBSA doped PPy. However, a sharp increase in the conductivity manifested by a specimen with 2.5 wt% of DBSA doped PPy by adopting in situ technique. The highest value of electrical conductivity observed by utilizing the SB technique was 0.26 S cm-1 at 30 wt% of DBSA doped PPy. The decomposition temperature was observed to be about 382 oC, 384 oC, and 414oC for TPU, DBSA doped PPy /TPU by IS technique, and DBSA doped PPy /TPU by SB respectively. A.S. Kurian, H. Souri, V.B. Mohan et al. [9] prepared stretchable sensors of polypyrrole (PPy) and silicone rubber (SR) which are used to detect
  • 34. 27 the movement of the humans by utilizing the solution casting method. The gauge factor obtained with different amounts of PPy in SR was in between 1.15 and 1.58. PPy/SR is more suitable for the strain in large values due to their low hysteresis, sensitivity, and durability.
  • 35. 28 Chapter: 5 Conclusion In this research project, a facile fabrication route and characterization of hybrid fillers-based flexible strain sensors has been presented to study the behavior of the designed sensors. Thermoplastic polyurethane (TPU) has been selected as base polymer because of its excellent characteristics such as good stretchability , excellent mechanical properties and compatibility With polypyrrole (ppy) nanofillers.The thermal stability of TPU/PPY blend sensor increases with the increasing conductive nanofillers ( PPY) loading(0%,4.5%,9%,18%) in thermoplastic polyurethane matrix. Which gives 80% to 50% loss in mass respectively. As we increase the loading of nanofillers ( PPY) (0%,4.5%,9%,18%) we get more sharp peaks which indicates that's interaction between TPU and PPy.DBSA increased. Because TPU carbonyl grou and amine group from ppy interactions.These results confirmed by FTIR test.
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