DEVELOPMENT OF CONDUCTIVE AND 
BIODEGRADABLE NANOFIBROUS YARNS: STUDY 
OF ELECTRICAL AND MECHANICAL PROPERTIES 
 
 
 
 
 
 
 
Puwakdandawe Vishakha Thilini Weerasinghe 
 
(188058V) 
 
 
Degree of Master of Science 
 
 
 
Department of Textile and Clothing Technology 
 
University of Moratuwa 
Sri Lanka 
 
 
 
January 2020 
DEVELOPMENT OF CONDUCTIVE AND 
BIODEGRADABLE NANOFIBROUS YARNS: STUDY 
OF ELECTRICAL AND MECHANICAL PROPERTIES 
 
 
 
 
 
 
 
 
 
Puwakdandawe Vishakha Thilini Weerasinghe 
 
(188058V) 
 
 
 
Thesis submitted in partial fulfillment of the requirements for the 
degree Master of Science in Textile and Clothing Technology 
 
 
Department of Textile and Clothing Technology 
 
University of Moratuwa 
Sri Lanka 
 
January 2020
i 
 
Declaration 
“I declare that this is my own work and this thesis does not incorporate without 
acknowledgement any material previously submitted for a Degree or Diploma in any 
other University or institute of higher learning and to the best of my knowledge and 
belief it does not contain any material previously published or written by another 
person except where the acknowledgement is made in the text. 
Also, I hereby grant to University of Moratuwa the non-exclusive right to reproduce 
and distribute my thesis, in whole or in part in print, electronic or other medium. I 
retain the right to use this content in whole or part in future works (such as articles or 
books).” 
Signature: ……………………………   Date: ………………….. 
 
“The above candidate has carried out research for the Master’s thesis under my 
supervision.” 
Name of the supervisor: ………………………………………………………………. 
Signature of supervisor: ……………………………  Date: ………………….. 
Name of the supervisor: ………………………………………………………………. 
Signature of supervisor: ……………………………  Date: ………………….. 
 
 
 
 
 
ii 
 
Abstract 
Electrically conductive and biodegradable materials are desired for a vast array of applications 
in wearable and flexible electronic areas to address the growing ecological problem of e-waste. 
Herein, we report on the design and fabrication of all-organic, conductive and biodegradable 
yarn using polyaniline (PANi) and polycaprolactone (PCL). The process of PANi 
incorporation is achieved in two ways; i) electrospinning a blend of PANi and PCL solution 
ii) in-situ polymerization of PANi on the nanofibrous surface of PCL electrospun fibers. The 
electrospun PANi incorporated webs are cut into ribbons and twisted to develop twisted yarns. 
A customized setup was used to produce continuous electrospun yarns. The effect of different 
degrees of PANi blended into PCL was investigated. Moreover, the effect of an array of aniline 
concentrations in coated fibers were studied.  PCL/PANi blended solution with 2% PANi 
resulted in nanofibers with resistance of 10 ± 4 MΩ/cm. Fibers coated with 1% aniline 
concentration resulted in the core-shell fibers with of 50 ± 8 kΩ/cm. Increasing the number of 
plies of yarn to 3 plies resulted in a 3-fold reduction of the resistance. The twisted plied yarns 
were incorporated into fabric by stitching or weaving to demonstrate the stability of 
conductivity over mechanical forces. Both PANi blended and PANi coated yarns were found 
to be biodegradable in controlled environmental conditions. The use of PANi blended yarn as 
a biomaterial for tissue engineering and PANi coated yarns as a wearable electrode for 
capacitive sensors were demonstrated. The electromechanical behavior of PANi coated yarn 
is expected to provide inspiration for the production of highly sensitive strain sensors. This 
approach presents an early step on the way to the realization of all organic conductive 
biodegradable nanofibrous yarns for sustainable smart textiles. 
Key words: Conductive polymers, nanofibrous yarns, biodegradable, electrospinning, 
polyaniline 
 
iii 
 
Dedication 
 
 
 
 
 
 
I dedicate my thesis to all my professors and doctors and scientists for the extensive 
knowledge you share with me. Your unselfish guidance increased my passion for 
nanotechnology. 
 
 
 
 
 
 
 
 
 
 
 
iv 
 
Acknowledgement 
I wish to acknowledge who supported me in numerous ways to achieve my MSc. First,  
I am indebted to research supervisor Dr. N.D. Wanasekara, Senior Lecturer, 
Department of Textile and Clothing Technology, University of Moratuwa for 
invaluable support, and motivation he readily gave me to accomplish this research .His 
patience in guiding me, vast knowledge, advice and experience helped me in many 
ways to conclude my research.   
I would like to express appreciation thanks to Dr. (Mrs.) D.G.K. Dissanayake, Senior 
Lecturer, Department of Textile and Clothing Technology, University of Moratuwa, 
insightful comments and encouragement from the start to the very end of the days I 
worked on this thesis and also, magnanimous way of educating me to the world of 
scientific publication, are very much appreciated. 
Besides my supervisors, I am also thankful towards my progress review committee: 
Dr. Srimala Perera and Dr. T.S.S. Jayawardena for their motivation comments and 
encouragement in each progress review to make my focus to the strategical research 
plan.  
Also, I wish to express gratitude to Sri Lanka Institute of Nanotechnology (SLINTEC) 
to give access to advanced laboratory facilities and scientists, Miss. Nadeeka Tissera, 
Mr. Ruchira Wijesena and Prof. Nalin de Silva who assisted and supported me while 
dedicating their valuable time.  
I also express my sincere gratitude to the academic and nonacademic staff of 
Department of Textile and Clothing Technology, University of Moratuwa for the 
continuous support and guidance given throughout my undergraduate and 
postgraduate life. Furthermore, I thank Nilupuli Rathnayake from the 15th batch and 
Sasini Weerasinghe from the 13th batch, Department of Textile and Clothing 
technology for all the support given to accomplish this research without any stress.  
The financial support for this research was provided through the SRC Grant 
(SRC/LT/2018/ 33) offered by the Senate Research Council, University of Moratuwa. 
v 
 
I would like to extend my sincere thanks to SRC for identifying the value of this 
research and approving the requested budget for this research. I would like to 
acknowledge Dr. (Mrs.) D.G.K. Dissanayake for appointing me as a research student 
to conduct this research under the above SRC grant.  
Last but not least, it is with a heart laden with gratitude that I thank to my family for 
the tremendous support given me and who were always there to lift me up during hard 
times. 
 
 
 
 
 
 
 
 
 
 
 
vi 
 
Table of contents 
 Page 
 
Declaration of the candidate & supervisors                                                                      i 
Abstract ii 
Dedication iii 
Acknowledgements iv 
Table of contents vi 
List of figures x 
List of tables xv 
List of abbreviations xvi 
List of appendices 
CHAPTER 01 xvii 
1. INTRODUCTION 1 
1.1 Introduction 1 
1.2 Problem statement 2 
1.3 Objectives 3 
1.4 Chapter framework 
CHAPTER 02 
2. LITERATURE REVIEW 5 
2.1 Introduction 5 
2.2 Importance of conductive yarns 5 
2.3 Problems of existing conductive yarn manufacturing methods 5 
2.4 Conductive polymers 6 
2.5 Doping of conductive polymers 8 
2.6 Polyaniline 10 
2.7 Nanofibrous yarns 11 
2.8 Electrospinning 11 
2.9 Electrospinning yarns 12 
2.10 Electrospun conductive yarns 15 
2.11 Importance of biodegradability in smart textiles 15 
2.12 Biodegradable applications in smart textiles 16 
vii 
 
2.13 Electrospinning of biodegradable polymers 16 
2.14 Degradation of poly (e-caprolactone) 17 
2.15 Electrospinning of conductive biodegradable polymers 17 
2.16 Electrospun conductive and biodegradable yarns 18 
2.17 Summary 
CHAPTER 03 
3. METHODOLOGY 20 
3.1 Introduction 20 
3.2 Materials and reagents 20 
3.3 Selection of suitable carrier polymer 21 
3.3.1 Preparation of PVA and PCL polymer solution 21 
3.3.2 Conventional electrospinning 21 
3.3.3 Analyzing fiber mats to select the biodegradable polymer 21 
3.4 Preparation of PANi blended yarns 22 
3.4.1 Preparation of PANi solution 22 
3.4.2 Preparation of PANi/PCL casted films 22 
3.4.3 Preparation of PANi/PCL solution 23 
3.4.4 Electrospinning by using rotary collector 23 
3.4.5 Yarn preparation from nanofibrous web 24 
3.4.6 Design and development of collector attachment for production 
of continuous nanofiber yarns 25 
3.4.7 Continuous yarn production by electrospinning 27 
3.5 Preparation of PANi coated yarns 27 
3.5.1 Dip coating of PANi 27 
3.5.2 PANi in-situ polymerization 27 
3.5.3 Preparation of twisted yarns 28 
3.6 Characterization 28 
3.6.1 Fiber Morphology 28 
3.6.2 Conductivity measurement 29 
3.6.3 Tensile strength 31 
3.6.4 DSC Analysis 31 
3.6.5 FTIR analysis 31 
viii 
 
3.6.6 TGA analysis 31 
3.6.7 Conductivity over mechanical deformation 31 
3.6.8 Biodegradation of the material under controlled composting 
conditions 32 
3.7 Applications 33 
3.7.1 Capacitive sensor 33 
3.7.2 Biomaterial 34 
3.7.2.1 Biodegradability 34 
3.7.2.2 Cell cytotoxicity study 35 
3.7.2.3 Cell morphology study 36 
3.8 Summary  
CHAPTER 04 
4. RESULTS AND DISCUSSION 37 
4.1 Introduction 37 
4.2 Electrospinning of PVA and PCL 37 
4.3 PANi blended nanofibrous yarns 41 
4.3.1 Influence of conductivity on electrospinnability 41 
4.3.2 Conductivity measurement 45 
4.3.3 Nanofibrous yarn formation 46 
4.3.4 Continuous yarn formation 48 
4.3.5 Effect of PANi concentration on mechanical properties of yarns
 49 
4.3.6 TGA analysis 51 
4.3.7 DSC analysis 53 
4.3.8 FTIR analysis 55 
4.3.9 Optimizing PANi concentration 56 
4.3.10 Electro-mechanical behaviour of electro-conductive yarn 56 
4.3.10.1 Effect of weaving and sewing on electrical resistance 
of the yarn 56 
4.3.10.2 Effect of strain on electrical resistance of the yarn 58 
4.3.10.3 Effect of twist on electrical resistance of the yarn 59 
4.3.11 Biodegradability 60 
ix 
 
4.4 PANi coated nanofibrous yarns 64 
4.4.1 Effect of dip coating on PANi on fiber morphology, electrical 
and mechanical properties 64 
4.4.2 Studying PANi in-situ polymerization 65 
4.4.2.1 Polymerization of aniline on PCL nanofibers 65 
4.4.2.2 Effect of concentration of reaction mixture on fiber 
morphology 69 
4.4.3 Conductivity measurement 71 
4.4.4 Nanofibrous yarn formation 74 
4.4.5 Effect of aniline concentration on mechanical properties of yarn
 75 
4.4.6 TGA analysis 77 
4.4.7 DSC analysis 79 
4.4.8 FTIR analysis 81 
4.4.9 Electro-mechanical behaviour of electro-conductive yarn 83 
4.4.9.1 Effect of weaving and sewing on electrical resistance of 
the yarn 83 
4.4.9.2 Effect of tensile strain on electrical resistance of the yarn
 86 
4.4.9.3 Effect of twist on electrical resistance of the yarn 87 
4.4.10 Biodegradability 88 
4.5 Comparison of PANi blended and coated yarns and potential 
applications 91 
4.5.1 Capacitive sensor 92 
4.5.2 Biocompatibility 93 
 4.5.2.1 Cytotoxic effects of the PANi blended nanofibers 93 
 4.5.2.2 Cell morphology study 93 
 4.5.2.3 In-vitro degradability 94 
4.6 Summary                                                                                              96 
CHAPTER 05 
5. CONCLUSIONS AND RECOMMENDATIONS 97 
5.1 Introduction 97 
x 
 
5.2 Key conclusions 97 
5.3 Key recommendations 99 
Reference list 100 
Appendix A: Arduino code linked with cap sense library 113 
Appendix B: Publications on this study                                                                         114 
  
xi 
 
List of figures 
 
Figure Description Page 
 
Figure 2.1 Energy band diagram demonstrating band gaps 8 
Figure 2.2 Band structure of a conjugated polymer as a function of p-doping level
 9 
Figure 2.3 Oxidation states of PANi  11 
Figure 2.4 Electrospinning basic setup 12 
Figure 2.5 Electrospinning continuous yarns using one nozzle 14 
Figure 2.6 Electrospinning continuous yarns using two nozzles 14 
Figure 3.1 Designed schematic diagram of modified electrospinning unit with 
rotational drum collector 24 
Figure 3.2 Designed schematic diagram of apparatus for twisting single yarns and 
ply yarn. 25 
Figure 3.3 Designed schematic diagram of continuous yarn forming setup 26 
Figure 3.4 Schematic diagram of test circuit for measuring resistance with the 
four-point probe method 29 
Figure 3.5 Schematic diagram of test circuit for measuring resistance of fiber 
ribbons with the two-probe method using multimeter 30 
Figure 3.6 Schematic diagram of test circuit for measuring resistance of the yarn 
with the two-probe using multimeter 30 
Figure 3.7 Homemade apparatus for measuring resistance vs strain 32 
Figure 3.8 Basic circuit for capacitive sensors 34 
Figure 3.9 Well plate with cells that were treated with nanofibers 35 
Figure 4.1 SEM image and diameter distribution histogram of (a) PCL nanofibers, 
(b) PVA nanofibers 38 
Figure 4.2 Illustration of hydrogen bonding interaction among PVA by water 38 
Figure 4.3 Solutions of (a) emeraldine base (EB) PANi/PCL, (b) emeraldine base 
(EB) PANi/CSA/PCL, (c) emeraldine salt (ES) PANi (PANi doped by 
HCl)/CSA/PCL 40 
xii 
 
Figure 4.4 Casted films of (a) emeraldine base (EB) PANi/PCL, (b) emeraldine 
base (EB) PANi/CSA/PCL, (c) emeraldine salt (ES) PANi (PANi 
doped by HCl)/CSA/PCL 40 
Figure 4.5 Demonstrating conductive nanofiber electrospinning process 42 
Figure 4.6 A photo of the electrospinning step with rotational drum collector 42 
Figure 4.7 Morphology of nanofibers synthesized from different PANi 
concentrations and PCL. (a) pure PCL, (b) PANi 0.5%, (c) PANi 1%, 
(d) PANi 2%, (e) PANi 3% 44 
Figure 4.8 (a) The four probe V - I characteristics of PANi blended electrospun 
mats, (b) PANi concentration vs conductivity measured using four-
probe method 45 
Figure 4.9 PANi 2%(a) Twisting single yarns, (b) twisting ply yarns, (c) 
PCL/PANi 1-ply yarn, (d) PCL/PANi 2-ply yarn, (d) PCL/PANi 3-ply 
yarn 47 
Figure 4.10 Effect of number of plies on resistance 48 
Figure 4.11 (a) Developed continuous yarn manufacturing unit, (b) 3D fibrous cone 
and twisted yarn 49 
Figure 4.12 (a) The stress–strain curves of Pure PCL, PANi 0.5%, PANi 1%, PANi 
2%, (b) effect of PANi concentration on energy at break value of yarns, 
(c) effect of PANi concentration on modulus of yarns 51 
Figure 4.13 TGA profiles of pure PCL and conductive PANi/PCL yarns with 
different PCL to PANI ratio 53 
Figure 4.14 DSC profiles of pure PCL and conductive PANi/PCL yarns with 
different PCL to PANI ratio 54 
Figure 4.15 FTIR spectra of pure PCL and PANi 2% 55 
Figure 4.16 PCL/PANi 2% blended nanofibrous yarns. (a) Image of yarn stitched 
on a nylon fabric, (b) microscopic image of yarn stitched on the nylon 
fabric 57 
 
 
 
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Figure 4.17 Fabric woven with PANi 2% blended nanofibrous yarns and 2-ply 
nylon yarns. (a) Conductivity measuring of unfolded fabric, (b) 
conductivity measuring of folded fabric, (c) microscopic image the 
fabric, (d) demonstrating yarn short circuiting by folding, (e) 
illustrating resistance change by number of folding cycles 58 
Figure 4.18 Effect of tensile strain on electrical resistance of PCL/PANi 2% 
blended yarn 59 
Figure 4.19 PANi 2% nanofibrous fiber ribbons (a) as made, (b) twisted, (c) effect 
of twist on electrical resistance 60 
Figure 4.20 Physical appearance of different stages of biodegradation of cellulose 
filter paper, PCL, PCL/PANi, and polyethylene 61 
Figure 4.21 Residual weight percentages vs number of days in each stage of 
biodegradation 62 
Figure 4.22 SEM images of (a) PCL before and (b) after degradation in soil and (c) 
magnified SEM image of after degradation in soil. (d) PCL/PANi 
blended fibers before and (e) after degradation in soil. (f) Magnified 
SEM image of after degradation in soil 63 
Figure 4.23 (a and b) SEM image and its magnified image of 10% PANi dip coated 
PCL nanofibers. (c) Stress- strain curve of PCL pure and PANi 10% 
dip coated nanofibrous yarns 64 
Figure 4.24 (a) Schematic of the apparatus for producing of continuous PCL twisted 
yarns. (a’) The 3D nanofibrous cone drawing from collector. (b and c) 
SEM image of collected PCL nanofibrous twisted yarn and magnified 
image of aligned nanofibers 66 
Figure 4.25 Sketch illustration of Fabrication of PANi decorated PCL nano-fibrous 
yarns 66 
Figure 4.26 Color change of aniline reaction mixture by adding APS after (a) 60 s, 
(b) 90 s, (c) 120 s, (d) 150 s, (e) 180 s, (f) 220 s, (g) 260 s, (h) 10 
min. 68 
Figure 4.27 SEM images of (a) Pure PCL, (b) aniline 0.5%, (c) aniline 1% (d) 
aniline 2% 70 
xiv 
 
Figure 4.28 Resistance per unit length verses used aniline concentration in reaction 
mixture 71 
Figure 4.29 (a) The four probe V - I characteristics of PANi coated electrospun 
mats, (b) aniline concentration vs log value of conductivity measured 
from four probe 73 
Figure 4.30 SEM images of (a) 1- ply yarn, (b) 2 – ply yarn and (c) 3 – ply yarn 74 
Figure 4.31 Effect of number of plies on resistance 75 
Figure 4.32 (a) The stress–strain curves of Pure PCL, aniline 0.5%, aniline 1%, 
aniline 2%, (b) effect of aniline concentration on energy at break value 
of yarns, (c) effect of aniline concentration on modulus of   yarns 77 
Figure 4.33 TGA profiles of pure PCL, aniline 0.5%, aniline 1%, aniline 2% 79 
Figure 4.34 DSC profiles of pure PCL, aniline 0.5%, aniline 1%, aniline 2% 80 
Figure 4.35 FTIR spectra of pure PCL and aniline 1% 81 
Figure 4.36 Aniline 1 % coated nanofibrous yarns. (a) Image of yarn stitched on a 
nylon fabric, (b) microscopic image of yarn stitched on the nylon fabric
 83 
Figure 4.37 Fabric woven with aniline 1% coated nanofibrous yarns and 2-ply 
nylon yarns. (a) Conductivity measuring of unfolded fabric, (b) 
conductivity measuring of folded fabric, (c) microscopic image the 
fabric, (d) SEM image of the fabric (e) demonstrating yarn short 
circuiting by folding, (f) illustrating resistance change by number of 
folding cycles 85 
Figure 4.38 Effect of tensile strain on electrical resistance of yarn 86 
Figure 4.39 Time-dependent normalized resistance change of the yarn under 
maximum strains of 20% 87 
Figure 4.40 Aniline 1 % nanofibrous fiber ribbons (a) as made, (b) twisted, (c) 
effect of twist on electrical resistance 88 
Figure 4.41 Residual weight percentage versus number of days in each stage of 
biodegradation 89 
Figure 4.42 Physical appearance of different stages of biodegradation of cellulose 
filter paper, PCL, PCL/PANi and polyethylene 89 
xv 
 
Figure 4.43 SEM images of PCL nanofiber (a) before degradation and (b-c) after 
degradation in soil. PANi/PCL nanofibers (d) before degradation and 
(e-f) after degradation in soil 90 
Figure 4.44 Illustration of the electrical conductivity nature for the prepared PANi 
coated PANi /PCL yarns with application of flexible capacitive sensor 
for operation of LED (a) ON (c) OFF by touching 92 
Figure 4.45 In-vitro cytotoxicity effects of the PCL and PANi/PCL electrospun 
nanofibers on Vero cells (green monkey kidney) 93 
Figure 4.46 SEM images of (a) Vero cells seeded PCL nanofibers and (b) 
PCL/PANi nanofibers 94 
Figure 4.47 Degradation profile of the PCL, and PANi blended PCL electrospun 
nanofibers 95 
Figure 4.48 SEM images of the (a) PANi/PCL electrospun nanofibers after 20 days 
soaking in PBS and (b) magnified SEM image 95 
 
 
 
 
 
 
 
  
xvi 
 
List of tables 
 
Table Description Page 
 
Table 3.1 The weight of PCL and PANi taken for preparing solutions and volume 
ratios of each solution in solution mixture 23 
Table 3.2 Amounts of anile and APS taken for solution mixture 28 
Table 4.1 Effect of different dopant on electrospinnability and resistance 41 
Table 4.2 Measuring resistivity by different methods 46 
Table 4.3 TGA data compilation for the tested fibers, including the first peak 
weight loss attributed to HCL, second onset and weight loss attributed 
to PANi, third onset and weight loss attributed to PCL and residual 
weight 52 
Table 4.4 Melting temperature and melting enthalpy of pure PCL and conductive 
PANi/PCL yarns with different PCL to PANI ratio 54 
Table 4.5 Characterization peaks of PCL and PANi 2% 55 
Table 4.6 Volume of aniline in aniline/HCl mixture and the weight of APS in 
APS/HCl mixture 66 
Table 4.7 Measuring resistivity by different methods 73 
Table 4.8 TGA data compilation for the tested fibers, including weight loss 
attributed to HCL and water, second third onset and weight loss 
attributed to PCL and residual weight 88 
Table 4.9 Melting temperature and melting enthalpy of pure PCL, aniline 0.5%, 
aniline 1%, aniline 2% 81 
Table 4.10 Characterization peaks of PCL and PANi 2% for aniline 1% nanofibers
 82 
Table 5.1 Summary of important results of the study  98 
 
 
 
 
 
xvii 
 
List of abbreviations 
 
Abbreviation Description 
 
PANi             Polyaniline 
PCL             Polycaprolactone 
CBNY             Conductive and biodegradable nanofibrous yarn 
NY                      Nanofiber yarn 
SEM                Scanning electron microscope 
FTIR                Fourier transform infrared 
DSC                 Differential scanning calorimetry 
TGA                Thermogravimetric 
PBS                 Phosphate-buffered saline 
ASTM             American Society for Testing and Material 
 
 
 
  
 
 
 
 
 
 
 
xviii 
 
List of appendices 
 
Appendix Description Page 
 
Appendix A Arduino code linked with cap sense library 113 
Appendix B     Publications on this study                                                                         114