15 
INVESTIGATION OF TENSILE PROPERTIES AND 
DURABILITY OF 
COIR FIBRES/GEOTEXTILES 
This thesis was submitted to the Department of Textile and Clothing 
Technology of the University of Moratuwa in partial fulfillment of the 
requirements for the Degree of Master of Science 
Department of Textile and Clothing Technology 
University of Moratuwa 
D. S. K. PATHIRANA 
Sri Lanka 
6 7 7 . 1 8 . o n - 4 
May 2004 UH To so--" c©!J . 
University of Moratuwa 
"I certify that this thesis does not incorporate any material previously submitted for a 
degree or diploma in any university and to the best of my knowledge and belief it does 
not contain any material previously published or orally communicated by another person 
except where due reference is made in the text." 
D.S.K.Pathirana 
(Candidate) 
"To the best of our knowledge the above particulars are correct." 
iiv -
Dr. Nirmali de Silva Dr. U.S.W. Gunasekera 
(Co-Supervisor) (Co-Supervisor) 
II 
ABSTRACT 
Coir is a ligno-cellulosic fibre, cheap and abundantly available in Sri Lanka as a by­
product of the coconut industry. Coir-geotextiles, which are manufactured from coir, 
have been identified as good geotextile material to be used for soil reinforcement in soil 
erosion problems until sustainable vegetation is established. Because of this reason coir 
based geotextiles have the potential to be an exportable product. It has become necessary 
to scientifically study the properties of coir fibres and coir-geotextiles in great detail to 
meet the suitability requirements of the export market as well as the local market. 
Mechanical and physical properties including tensile properties, initial modulus, length, 
mass and diameter of brown and white coir fibre obtained from Kurunegala District have 
been used in the evaluation. Moisture absorption characteristics of coir fibres were also 
evaluated. 
Results show that there is a direct relationship between the length and tenacity as well as 
extension at break of retted brown coir fibre. This relationship is not significant in 
unretted white coir fibre, which is a longer fibre with a higher in tenacity and extension at 
break. 
Wet tensile strength and wet extension at break of coir fibres were found to be greater 
than the tensile strength in the conditioned state. In seawater immersion, coir fibres did 
not lose strength after 24 hours at room temperature. During a 24 hours period coir fibres 
did not lose strength significantly in the pH 5-9 range at ambient temperature. 
At different NaOH concentrations and different time periods at 25°C, coir fibres were 
immersed in alkaline medium to find out whether the strength was affected. After 30min 
in 10 % NaOH brown coir showed highest strength but white coir fibre showed highest 
strength in 25% NaOH concentration after 30min immersion. 
It was attempted to apply the idealized staple fibre yarn model to coir yarns. For this 
purpose coir-yarn initial modulus was calculated using results of strength tests for coir 
III 
fibres and coir yarns. Calculated initial modulus is greater than experimentally obtain 
results but deviate considerably from the actual situvation. 
The durability of coir fibres was investigated by immersing in distilled water, acid 
medium, alkaline medium and saline solution at ambient temperature over a period of 
time and the results showed that brown coir fibre and white coir fibre had similar losses 
in strength in acidic medium after 3 months. White coir fibre lost strength significantly 
after 3 months in distilled water (pH=5.89) treatment. But both coir fibres do not lose 
strength significantly during 3 months time in alkaline medium or saline water. Scanning 
Electron Microscope (SEM) analysis of selected treated coir fibres was carried out to 
investigate the effect on surface structure of fibres. This analysis explained the results of 
tensile strength tests between brown and white coir fibres and untreated and treated 
conditions. 
IV 
ACKNOWLEDGEMENT 
My heartfelt gratitude goes to the two supervisors Dr. Nirmali de Silva and Dr. U.S.W. 
Gunasekera for their guidance, encouragement and assistance given in numerous ways 
throughout the research project. 
Also special thanks go to Prof. Lakdas D. Fernando and Dr. W.D.G. Lanarolle for the 
valuable contributions and suggestions made in progress review committees, which were 
useful to make this research project a success. 
I wish to extend my sincere thanks to all the staff members of the Department of Textile 
and Clothing Technology who helped me in various ways to complete this research 
successfully and especially to the Technical Officers Mrs. D. Dissanayake, Mrs. P. 
Wanniarachchi, Mr. CP. Malalanayake and Lab Attendant Mr. W.Chandradasa for their 
support in supplying all the necessary material whenever necessary. 
I thank the Head of the Mechanical Engineering Department of University of Moratuwa 
who allowed me to use their Incline Plane Tester for my research work. I also thank the 
Head of the Material Department of Industrial Technology Institute for giving me 
permission to use their Scanning Electron Microscope. 
Special mention goes to Mr. N.S.Nawarathna, who gave me suggestions and necessary 
help at the introductory stages and also to my fellow researcher Mrs. K.P.N. Gunarathna 
who was a big helping hand throughout. 
Finally I wish to thank the Asian Development Bank, Science and Technology Personnel 
Development Project for the funding my research project leading to Masters Degree. 
TABLE OF CONTENTS 
Page 
ABSTRACT HI 
ACKNOWLEDGEMENT V 
1 CHAPTER ONE - Introduction and Literature Review 1 
1.1 Introduction 1 
1.2 Literature Review 3 
1.2.1 Geotextiles 3 
1.2.2 Early Applications of Geotextiles 3 
1.2.3 Types of Geotextiles 4 
1.2.3.1 Woven Geotextiles 5 
1.2.3.2 Non-Woven Geotextiles 6 
1.2.3.3 Knitted Geotextiles 7 
1.2.4 Coir Fibre 8 
1.2.5 Crystalline and Non-Crystalline 9 
1.2.6 Cell Wall Constituents 9 
1.2.6.1 Cellulose 10 
1.2.6.2 Hemi-Cellulose 10 
1.2.6.3 Lignin 11 
1.2.7 The Cell Wall Structure of Lignocellulose Fibre 11 
1.2.8 Comparison of Coir fibre with Other Cellulosic Textile Fibres 12 
1.3 Objective 15 
1.4 Scope 15 
2 CHAPTER TWO - Materials and Methods 17 
2.1 Production of Woven Coir-Geotextiles 17 
2.2 Materials 17 
2.2.1 Coir Fibre Sampling Method 17 
2.2.2 Coir Yarn Sampling Method 19 
2.2.3 Chemicals Used in the Experiments 19 
2.3 Methods 20 
2.3.1 Method Used for Coir Fibre Tensile Properties Testing 20 
2.3.2 Wet Strength and Wet Elongation at Break of Coir Fibre 20 
2.3.3 Strength Retention of Coir Fibre in Seawater 20 
2.3.4 Strength of Coir Fibre in Different pH Buffer Environments 20 
2.3.5 Moisture Regain of Coir fibres 21 
2.3.6 Behaviour of Coir Fibres in NaOH 21 
2.3.7 Coefficient of Friction of Coir Fibres 22 
2.3.8 Tensile Properties of Coir Yarns 22 
2.3.9 Twist of Coir Yarns 22 
2.3.10 Linear Density of Coir Yarns 22 
2.3.11 Durability of Coir Fibre in Different Chemical Environments 22 
2.3.12 Microstructure of Coir Fibre 23 
3 CHAPTER THREE - Results and Discussion 24 
VI 
3.1 Physical Properties o f Coir Fibre 2 4 
3.1.1 Length and Fineness o f Coir Fibres 24 
3 .1 .1 .1 Length 2 4 
3 .1 .1 .2 F ineness 25 
3 .1 .1 .3 Length to Diameter Ratio 27 
3 .1 .2 Strength o f Coir Fibre 28 
3 .1 .3 Initial M o d u l u s o f Coir Fibre 3 0 
3 . 1 . 4 Breaking Elongat ion o f Coir Fibre 3 0 
3 .1 .5 Mois ture Regain o f Coir Fibre 32 
3 .1 .6 Relat ionship be tween Fibre Length and Tens i l e Properties 33 
3.2 Behav iour o f Coir Fibre in Different Environments 35 
3.2.1 Comparison o f Wet and Condit ioned State Tens i l e Properties 35 
3 .2 .2 Tens i l e Properties o f Coir Fibre in Seawater 36 
3 .2 .3 Behav iour o f Coir Fibre under Different pH Condi t ions 37 
3 .2 .4 Behav iour o f Coir Fibre in N a O H 3 9 
3.3 Interrelations b e t w e e n the Structure and Properties o f Fibre and Yarn 4 0 
3.3.1 Theoretical Ana lys i s o f Idealized Staple Fibre Yarn Mode l 41 
3 .3 .2 Appl icat ion o f Theoretical Model to Coir Yarn 43 
3 . 3 . 2 1 Coeff ic ient o f Friction o f Coir Fibre 43 
3 . 3 . 2 . 2 Coir Yarn Tens i l e Properties 4 4 
3 .3 .2 .3 Compar i son o f Theoretical and Measured Yarn modulus 45 
3.4 Durability o f Biodegradable Geotext i l es 45 
3.4.1 Chemica l Degradation o f Coir Fibre 4 6 
3 .4 .1 .1 Durability o f Coir Fibre in Dist i l led Water 47 
3 .4 .1 .2 Durabil ity o f Coir Fibre under Ac id ic Condi t ion 4 8 
3 4 1 3 Durability o f Coir Fibre under Bas ic Condi t ion 4 9 
3 .4 .1 .4 Durabil ity o f Coir Fibre in Seawater 4 9 
3 .4 .2 Compar i son o f Durability Tests 50 
3.5 Structural Properties o f Coir Fibres 52 
3.5.1 Comparison o f Tens i le Results with S E M o f Coir Fibre 52 
4 CHAPTER FOUR - Conclusions and Suggestions for Future Work 56 
4 1 C o n c l u s i o n s 56 
4.2 S u g g e s t i o n s for Future Work 58 
REFERENCES 60 
Annex-1: B r o w n Coir Fibres Tensile Properties 64 
Annex-2: White Coir Fibres Tensile Properties 71 
VII 
LIST OF FIGURES 
Page 
VIII 
Figure 1.1 A Woven Tape Geotextile 6 
Figure 1.2 Highly Magnified View of a Non-Woven Geotextile 7 
Figure 1.3 An Example of a Knitted Fabric 7 
Figure 1.4: Cellulose Structure 10 
Figure 1.5: Cell Wall Structure of Cellulose Fibre 11 
Figure 1.6: Classification of Natural Vegetable Fibre According to Origin 12 
Figure 1.7: Cell Wall Polymers Responsible for the Properties (approximate comparison) 
14 
Figure 2.1: Extraction Process of Coir Fibre 18 
Figure 3.1: Variations in Length, Mass and Diameter of between Coir Fibres 26 
Figure 3.2: Strength Variation of Coir Fibres 29 
Figure 3.3: Stress-Strain Curve of Coir Fibre 30 
Figure 3.4: Elongation Variation of Coir Fibres 31 
Figure 3.5: Tenacity vs Length (Brown Fibre) 33 
Figure 3.6: Elongation (%) vs Length (Brown Fibre) 33 
Figure 3.7: Diameter vs Length (Brown Fibre) 33 
Figure 3.8: Tenacity vs Length (White Fibre) 3 4 
Figure 3.9: Elongation (%) vs Length (White Fibre) 34 
Figure 3.10: Diameter vs Length (White Fibre) 34 
Figure 3.11: Comparison between Conditioned and Wet state Tensile Properties 35 
Figure 3.12: Comparison between Conditioned State and in Seawater Tensile Properties 
36 
Figure 3.13: Variation of Tenacity with pH of Brown and White Coir Fibres 3 8 
Figure 3.14: Strength of NaOH Treated coir fibres (a) Brown (b) White at 25°C 39 
Figure 3.15: Interrelations of Fibre, Yarn and Fabric Structure and Properties 41 
Figure 3.16: Tenacity of Coir Fibre after Treatments (a) Brown (b) White 51 
Figure 3.17: Elongation of Coir Fibres after Treatments (a) Brown (b) White 51 
LIST OF TABLES 
IX 
Table 1.1: Chemical Composition of Cellulose Fibres 9 
Table 2.1: Chemicals used to Prepare pH Solutions [33] 21 
Table 3.1: Dimensional Properties & Mass of Coir Fibres 25 
Table 3.2: Diameter of cellulose Fibres 27 
Table 3.3. Strength and C V% of Coir Fibres 28 
Table 3.4: Elongation (%) and CV% of Coir Fibres 31 
Table 3.5: Moisture Regain of Coir Fibre (at 65%RH & 27°C) 32 
Table 3.6: Tensile Properties under Standard and Wet States 35 
Table 3.7: Tensile Properties under Standard State and in Seawater (pH=8) 36 
Table 3.8: Some Typical Minerals and Fills and their Maximum pH Values in Soil 37 
Table 3.9: Influence of pH on Coir Fibre at Ambient Temperature 38 
Table 3.10: Behavior of Coir Fibre under NaOH at 25°C 39 
Table 3.11: Fibre and Yarn Parameters 42 
Table 3.12: Coefficient of Friction of Fibres 44 
Table 3.13: Tensile Properties of Brown and White Coir Fibres 44 
Table 3.14: Measured Tensile Properties of Coir Yarns 45 
Table 3.15: Tensile Properties of Untreated Coir Fibre 47 
Table 3.16: Tensile Properties after Distilled Water Treatment 48 
Table 3.17: Tensile Properties after HC1 Treatment 48 
Table 3.18: Tensile Properties after NaOH Treatment 49 
Table 3.19: Tensile Properties after Seawater Treatment 50 
Table 4.1: Summary of Tensile Properties of Coir Fibres-I 57 
Table 4.2: Summary of Tensile Properties of Coir Fibres-II 57 
Page 
LIST OF PHOTOGRAPHS 
Page 
Photograph 1.1: Application of Coir-Geotextile in Erosion Control 2 
Photograph 3.1: SEM Photographs of Coir Fibres (a) Cross-section (b) Transverse-
section 52 
Photograph 3.2: Brown Coir Fibre Surface 53 
Photograph 3.3: White Coir Fibre Surface 53 
Photograph 3.4: Brown Coir Fibre Surface-After HC1 Treatment for 3 months 55 
Photograph 3.5: White Coir Fibre Surface-After Distilled Water Treatment for 3 months 
55 
LIST OF ABBREVIATIONS 
Scanning Electron Microscopy 
Coefficient of Variation 
International Standards Organisation 
British Standard 
Sri Lanka Standard 
American Association of Textile Chemists & Colourists 
XI