44
STUDY OF ADHESION PROPERTIES OF NATURAL RUBBER, EPOXIDIZED NATURAL RUBBER, AND ETHYLENE-PROPYLENE DIENE TERPOLYMER-BASED ADHESIVES KWO HAN KIU UNIVERSITI SAINS MALAYSIA 2007

ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

  • Upload
    vokiet

  • View
    218

  • Download
    0

Embed Size (px)

Citation preview

Page 1: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

STUDY OF ADHESION PROPERTIES OF

NATURAL RUBBER, EPOXIDIZED NATURAL RUBBER, AND ETHYLENE-PROPYLENE DIENE

TERPOLYMER-BASED ADHESIVES

KWO HAN KIU

UNIVERSITI SAINS MALAYSIA

2007

Page 2: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

STUDY OF ADHESION PROPERTIES OF

NATURAL RUBBER, EPOXIDIZED NATURAL RUBBER, AND ETHYLENE-PROPYLENE DIENE

TERPOLYMER-BASED ADHESIVES

by

KWO HAN KIU

Thesis submitted in fulfilment of the requirements

for the Degree of Master of Science

January 2007

Page 3: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

ACKNOWLEDGEMENTS

Heartiest thankful goes to Assoc. Prof. Dr. Poh Beng Teik since he agreed to

become my very Supervisor for the lab work and tried to assist me in filling forms for

pursuing the Degree of Master of Science. He had been providing me a lot of

opportunities and flexibilities in viewing out my own ideas and most of them were

supported by him. The guide that had given by him was remarkably useful and really

helpful. He was never being selfish to view out his opinions for my guidance and he is

definitely a sincere person.

The fully spiritually support, love and care, and partially financial that had given by

my family is gratefully acknowledged. The author has no reason for not to express his

sincere gratitude to his parents for their encouragement between the course of this

research and until the writing of this thesis.

Lastly, the author shall thank Universiti Sains Malaysia (USM) for its wonderful

study environment and beautiful landscape. Special thankful makes for Institute of

Graduate Studies (IPS) and personnel for making this study possible through a

postgraduate assistantship. The author at very last not forget to express his very last

thankful to School of Industrial Technology, USM for providing him facilities and very

much opportunities to work and co-operate with all staffs and lecturers.

Thank you to you all for everything. May God bless you.

Page 4: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

TABLE OF CONTENTS

Acknowledgements ---------------------------------------------------------------------------

Table of Contents ------------------------------------------------------------------------------

List of Tables ------------------------------------------------------------------------------------

List of Schemes --------------------------------------------------------------------------------

List of Figures ----------------------------------------------------------------------------------

List of Plates ------------------------------------------------------------------------------------

List of Abbreviations/Symbols --------------------------------------------------------------

Abstrak -------------------------------------------------------------------------------------------

Abstract ------------------------------------------------------------------------------------------

CHAPTER 1 – INTRODUCTION

General ------------------------------------------------------------------------------------------

CHAPTER 2 – LITERATURE SURVEY

2.1 Historical Background on Rubber ----------------------------------------------------

2.2 Standard Malaysian Rubber (SMR) --------------------------------------------------

2.3 Epoxidized Natural Rubber (ENR) ---------------------------------------------------

2.3.1 Epoxidation -------------------------------------------------------------------------

2.3.1.1 In Situ Epoxidation -------------------------------------------------------

2.3.1.2 ENR and Halogen --------------------------------------------------------

2.4 Ethylene-Propylene Diene Terpolymer (EPDM)

2.4.1 EPDM Background ----------------------------------------------------------------

2.4.2 EPDM ---------------------------------------------------------------------------------

2.4.3 EPDM in Tyres ---------------------------------------------------------------------

2.4.4 Tackifier in EPDM ------------------------------------------------------------------

2.5 Coumarone-indene (CI) Resin --------------------------------------------------------

2.6 Petroresin ----------------------------------------------------------------------------------

2.7 Gum Rosin (Tricyclic Monocarboxylic Acids) --------------------------------------

Page ii iii vii ix x xiii xiv xvi xviii 1 5 7 9 13 13 17 19 20 21 22 23 25 26

Page 5: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

2.8 Toluene (C7H8) ----------------------------------------------------------------------------- 2.9 Two-Roll Mill

2.9.1 Milling ---------------------------------------------------------------------------------

2.9.2 Two-Roll Mill in Laboratory ------------------------------------------------------

2.10 Rotary Viscometer ----------------------------------------------------------------------

2.11 Lloyd Adhesion Instruments ----------------------------------------------------------

2.12 Texture Analyser ------------------------------------------------------------------------

2.13 Adhesion ----------------------------------------------------------------------------------

2.14 Pressure Sensitive Adhesive (PSA)

2.14.1 Rubber-Based PSA -----------------------------------------------------------

2.14.2 Miscibility of Rubber-Based PSA ------------------------------------------

2.15 Tackifying Resin

2.15.1 Resin Tackifier ------------------------------------------------------------------

2.15.2 Resin Types ---------------------------------------------------------------------

2.15.3 Resin Tackifier in PSA --------------------------------------------------------

2.15.4 Selection of Resin Tackifier -------------------------------------------------

CHAPTER 3 – EXPERIMENTAL (MATERIAL AND METHODS)

3.1 Materials ------------------------------------------------------------------------------------

3.2 Apparatus ----------------------------------------------------------------------------------

3.3 Methods

3.3.1 Picking of Raw Material ----------------------------------------------------------

3.3.2 Mastication --------------------------------------------------------------------------

3.3.3 Adhesive Solution Preparation -------------------------------------------------

3.3.4 Adhesive Coating ------------------------------------------------------------------

3.3.5 Testing

3.3.5.1 Peel Test Modes ----------------------------------------------------------

3.3.5.1.1 T-Peel Test -----------------------------------------------------

Page 26 27 28 30 32 34 35 36 40 41 44 46 47 49 52 57 57 59 61 64 65

Page 6: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

3.3.5.1.2 90o Peel Test -------------------------------------------------- 3.3.5.1.3 180o Peel Test -------------------------------------------------

3.3.5.2 Tackiness Tests

3.3.5.2.1 Ball Rolling Tack Test --------------------------------------- 3.3.5.2.2 Viscosity Measurements -----------------------------------

3.3.5.2.3 Loop Tack Test ------------------------------------------------

3.3.5.3 Shear Resistance Test --------------------------------------------------

CHAPTER 4 – EXPERIMENTAL RESULTS AND DISCUSSION 4.1 Cleavage of Raw Rubber Main Chain During Mastication --------------------- 4.2 Miscibility Between Coumarone-Indene (CI) Resin and Rubber-Based Adhesive Solution ---------------------------------------------------- 4.3 Viscosity of CI Resin Filled Rubber-Based Adhesive ---------------------------- 4.4 Tackiness of CI Resin Filled Rubber-Based Adhesive -------------------------- 4.5 Shear Resistance of CI Resin Filled Rubber-Based Adhesive ---------------- 4.6 Peel Strength of CI Resin Filled Rubber-Based Adhesive --------------------- 4.7 Advantages and Disadvantages of Rubber-Based Adhesive ----------------- 4.8 Effects of CI Resin, Petroresin and Gum Rosin

on Viscosity of Rubber-Based Adhesive --------------------------------------------

CHAPTER 5 – SUMMARY AND CONCLUSION -------------------------------------- CHAPTER 6 – RECOMMENDATION FOR FUTURE RESEARCH --------------- References -------------------------------------------------------------------------------------- Appendices

Appendix 1 – Equations ----------------------------------------------------------------------

Appendix 2 – Data of Testing for SMR L-Based Adhesive (in Avg.) --------------- Appendix 3 – Data of Testing for SMR 10-Based Adhesive (in Avg.) -------------

Appendix 4 – Data of Testing for SMR 20-Based Adhesive (in Avg.) ------------- Appendix 5 – Data of Testing for ENR 25-Based Adhesive (in Avg.) ------------- Appendix 6 – Data of Testing for ENR 50-Based Adhesive (in Avg.) -------------

Page 66 67 68 69 70 71 73 78 87 89 99 112 127 128 130 135 137 144 148 151 154 157 160

Page 7: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

Appendix 7 – Data of Testing for EPDM-Based Adhesive (in Avg.) --------------- Appendix 8 – Selected Data for Tested Coumarone-Indene (CI) Resin

Filled ENR 50 and EPDM-Based Adhesive Samples --------------

Appendix 9 – Phase Homogeneity and Colour Comparison Between Coumarone-Indene (CI) Resin, Petroresin, and Gum Rosin Respectively Filled in SMR L, ENR 25 and ENR 50 Solution in the Beaker -------------------------

Appendix 10 – Coumarone-Indene (CI) Resin, Petroresin, and Gum Rosin Before and After Pulverizing --------------------------------------------

Publication List i. Peel Strength of ENR-Based Adhesive (Article for 3rd Life Sciences

Postgraduate Conference, 24th – 27th May, 2006) ii. Peel and Shear Strength of Pressure-Sensitive Adhesives Prepared from

Epoxidized Natural Rubber (Accepted for publication in J. Appl. Polym. Sci.; In press)

Page 163 166 170 172

Page 8: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

LIST OF TABLES Table 2.1: 2 Factors, 2 Levels of Experiment on Effects

of Elastomer and Resin Tackifier ------------------------------------------- Table 3.1: Details of Main Materials and Chemicals Used ------------------------

Table 3.2: Details of Apparatus and Machine for Lab Use ------------------------ Table 3.3: Adhesive Formulation (Milled Rubber of Fixed

Mastication Time) --------------------------------------------------------------

Table I: 90o Peel Test (N/m) -------------------------------------------------------- Table II: 180o Peel Test (N/m) ------------------------------------------------------ Table III: T-Peel Test (N/m) ---------------------------------------------------------- Table IV: Shear Resistance Test (N/m2) ------------------------------------------ Table V: Tackiness Test -------------------------------------------------------------- Table VI: 90o Peel Test (N/m) -------------------------------------------------------- Table VII: 180o Peel Test (N/m) ------------------------------------------------------ Table VIII: T-Peel Test (N/m) ---------------------------------------------------------- Table IX: Shear Resistance Test (N/m2) ------------------------------------------- Table X: Tackiness Test -------------------------------------------------------------- Table XI: 90o Peel Test (N/m) -------------------------------------------------------- Table XII: 180o Peel Test (N/m) ------------------------------------------------------ Table XIII: T-Peel Test (N/m) ---------------------------------------------------------- Table XIV: Shear Resistance Test (N/m2) ------------------------------------------ Table XV: Tackiness Test -------------------------------------------------------------- Table XVI: 90o Peel Test (N/m) ------------------------------------------------------- Table XVII: 180o Peel Test (N/m) ------------------------------------------------------ Table XVIII: T-Peel Test (N/m) ---------------------------------------------------------- Table XIX: Shear Resistance Test (N/m2) ------------------------------------------ Table XX: Tackiness Test -------------------------------------------------------------- Table XXI: 90o Peel Test (N/m) --------------------------------------------------------

Page 43 49

52 59 148 148 149 149 150 151 151 152 152 153 154 154 155 155 156 157 157 158 158 159 160

Page 9: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

Table XXII: 180o Peel Test (N/m) ------------------------------------------------------ Table XXIII: T-Peel Test (N/m) ---------------------------------------------------------- Table XXIV: Shear Resistance Test (N/m2) ------------------------------------------ Table XXV: Tackiness Test -------------------------------------------------------------- Table XXVI: 90o Peel Test (N/m) ------------------------------------------------------- Table XXVII:

180o Peel Test (N/m) ------------------------------------------------------ Table XXVIII: T-Peel Test (N/m) ---------------------------------------------------------- Table XXIX: Shear Resistance Test (N/m2) ------------------------------------------ Table XXX: Tackiness Test --------------------------------------------------------------

Page 160 161 161 162 163 163 164 164 165

Page 10: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

LIST OF SCHEMES

Page

Scheme 2.1: Ziegler-Natta Reaction (Upper); SMR from Cis-1, 4-Polyisoprene Structure (Lower) ------------------------

Scheme 2.2: General Schematic of Epoxidation on NR Latex --------------------- Scheme 2.3: Simple/Low Level of Epoxidation of NR Latex

Using Peroxy Acid via Secondary Ring-Opening by Isolated Epoxide Groups -----------------------------------------------

Scheme 2.4: Cross-Linking of ENR via Ring-Opening

of Oxirane Groups -----------------------------------------------------------

Scheme 2.5: Chemical Structure of Commercially Ethylene/Propylene/ 1, 4 Hexadiene Terpolymer (EPDM) ------------------------------------

Scheme 2.6: Polymerized Coumarone-Indene Resin Combination Between Coumarone and Indene Structure --------------------------

Scheme 2.7: Chemical Structure of Toluene (C7H8) ---------------------------------- Scheme 4.1: Principles for Mastication of Rubbers (Fries et al., 1982) --------- Scheme 4.2: Reactions Sequence for Elastomer Mastication

(Fries et al., 1982) ----------------------------------------------------------

Scheme 4.3: Cleavage in the Cis-1, 4-Polyisoprene Chain During Mastication ----------------------------------------------------------

Scheme 4.4: Proposed Schematic Chemical Structure for Reformed Radicals by Masticated NR and Coumarone-Indene Resin in Solution ----------------------------

Scheme 4.5: Proposed Schematic Chemical Structure for Cross-Linked Radicals by Masticated ENR and Coumarone-Indene Resin in Solution ----------------------------

Scheme 4.6: Proposed Schematic Chemical Structure

for Linkable Radicals by Masticated EPDM and Coumarone-Indene Resin in Solution ----------------------------

8 13 15 15 19 24 26 76 76 77 82 83 84

Page 11: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

LIST OF FIGURES Figure 2.1: A Tape or Label Consisting Raw Rubber-Based PSA

and Elastomer ----------------------------------------------------------------- Figure 2.2: A Mastication Work on Raw Rubber by Two-Roll Mill --------------- Figure 2.3: The Arrangement of Cone-Plate in Rotary Viscometer ------------- Figure 2.4: General Errors that Cause Uncertainty Viscosity

for Test Sample ---------------------------------------------------------------

Figure 3.1: The Samples from SMR 10-Based Adhesive with Different Resin Concentration --------------------------------------

Figure 3.2: A T-Peel Test Sample Dimensioned 10 x 2.5 cm

with Coated Area 5 x 2.5 cm ---------------------------------------------- Figure 3.3: A 90o Peel Test Sample Dimensioned

15 x 7 cm (Lower Part of Sheet); 10 x 2.5 cm (Upper Part of Sheet) with Coated Area 5 x 2.5 cm ----------------

Figure 3.4: A 180o Peel Test Sample Dimensioned

15 x 7 cm (Lower Part of Sheet); 15 x 2.5 cm (Upper Part of Sheet) with Coated Area 5 x 2.5 cm ----------------

Figure 3.5: A Shear Test Sample Dimensioned 15 x 2.5 cm

with Coated Area 5 x 2.5 cm ---------------------------------------------- Figure 3.6: Three-Dimensional (3-D) View of Arrangement

for T-Peel Test ---------------------------------------------------------------- Figure 3.7: Side View of Arrangement for 90o Peel Test -------------------------- Figure 3.8: Side View (Left) and Top View (Right)

of Arrangement for 180o Peel Test -------------------------------------- Figure 3.9: Side View of Arrangement for Ball Rolling Tack Test --------------- Figure 3.10: Front View of Cone-Plate Arrangement

for Viscometer During Measurement ----------------------------------- Figure 3.11: Front View of Different Loop Characteristics

from the Beginning until the End of Testing (from the Left to the Right) ------------------------------------------------

Figure 3.12: 3-D View of Arrangement for Shear Resistance Test -------------- Figure 4.1: Effects of Mastication on Viscosity

of CI Resin Filled Rubber-Based Adhesive --------------------------- Figure 4.2: An Example Showing the Dull Peak

in Peel Test Curve for Immiscible Blends ------------------------------

Page 22 28 30 31 59 61 62 62 62 65 66 67 68 69 71 71 75 80

Page 12: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

Figure 4.3: Colour Characterizing Miscibility of Rubber/

CI Resin Blends ------------------------------------------------------------- Figure 4.4: Viscosity Versus CI Resin Concentration ----------------------------- Figure 4.5: Tackiness Versus CI Resin Concentration --------------------------- Figure 4.6: Tackiness Versus Mastication Duration ------------------------------- Figure 4.7: Tackiness in Distance Versus CI Resin Concentration ------------ Figure 4.8: Tackiness in Distance Versus Mastication Duration ---------------- Figure 4.9: Rubber-Based Sample Showing Their

Single, Clear Peak and Curve Shape by Shear Test --------------- Figure 4.10: Shear Resistance Versus CI Resin Concentration

at 30 μm Thickness of Coating Layer ----------------------------------- Figure 4.11: Shear Resistance Versus CI Resin Concentration

at 60 μm Thickness of Glue Layer --------------------------------------- Figure 4.12: Shear Resistance Versus CI Resin Concentration

at 90 μm Thickness of Gluing Area -------------------------------------- Figure 4.13: Shear Resistance Versus CI Resin Concentration

at 120 μm Thickness of Glue Layering --------------------------------- Figure 4.14: Shear Resistance Versus Thickness of Coating Layer

at 0 phr of Coumarone-Indene Resin Concentration ---------------- Figure 4.15: Shear Resistance Versus Thickness of Coating Layer

at 40 phr of Coumarone-Indene Resin Concentration -------------- Figure 4.16: Shear Resistance Versus Mastication Time

at 20 phr of Coumarone-Indene Resin Concentration -------------- Figure 4.17: Peel Strength Versus CI Resin Concentration

(90o Peel Test) ---------------------------------------------------------------- Figure 4.18: Peel Strength Versus CI Resin Concentration

(180o Peel Test) -------------------------------------------------------------- Figure 4.19: Peel Strength Versus CI Resin Concentration

(T-Peel Test) ------------------------------------------------------------------- Figure 4.20: Peel Strength Versus CI Resin Concentration

for Each Peel Test ------------------------------------------------------------ Figure 4.21: An Excellent Interfacial Interlocking/Anchorage by Adhesive on the Rough Surface of Adherent --------------------- Figure 4.22: Peel Strength Versus Thickness of Coating Layer ------------------

Page 85 88 92 94 95 97 100 101 103 104 106 107 109 110 113 114 116 117 118 119

Page 13: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

Figure 4.23: Peel Strength Versus Mastication Duration

(90o Peel Test) ---------------------------------------------------------------- Figure 4.24: Peel Strength Versus Mastication Duration

(180o Peel Test) -------------------------------------------------------------- Figure 4.25: Peel Strength Versus Mastication Duration

(T-Peel Test) ------------------------------------------------------------------ Figure 4.26: Peel Strength Versus Type of Peel Test ------------------------------- Figure 4.27: Viscosity Versus Type of Resin ------------------------------------------ Figure I: Obvious Peaks Are Shown by 90o Peel Test Using

Lloyd Adhesion Testing Machine LRX Plus with NEXYGEN Software Model LLOYD LRX Plus 104250 for 5 Min Masticated ENR 50-Based Sample Filled CI Resin at 90 Microns Coating Thickness and Speed of 500mm/min; i. 40 phr CI Resin Added; ii. 0 phr CI Resin Added ------------------

Figure II: Several Peaks Are Indicated by 180o Peel Test Using Lloyd Adhesion Testing Machine LRX Plus with NEXYGEN Software Model LLOYD LRX Plus 104250 for Masticated ENR 50-Based Sample Filled 20 phr CI Resin at Layering Thickness of 120 Microns; i. 15 Min Mastication on Rubber; ii. More Peaks for 5 Min Mastication Than the Former --------------

Figure III: Different Number of Peaks Are Displayed by T-Peel Test

by Means of Lloyd Adhesion Testing Machine LRX Plus with NEXYGEN Software Model LLOYD LRX Plus 104250 at Speed of 500 mm/min; Rather Readings in Figure i than in Figure ii; i and ii Are ENR 50-Based Samples at 5 Min Mastication, 90 Microns Layering Thickness, and 20 phr and 80 phr CI Resin Added, Respectively --------------

Figure IV: Comparison of Number of Peaks Are Reported

by 90o Peel Test by Means of Lloyd Adhesion Testing Machine LRX Plus with NEXYGEN Software Model LLOYD LRX Plus 104250; Rather Readings in Figure ii than in Figure i; i and ii Apparently Are EPDM-Based Samples at 5 Min Mastication, 120 Microns Coating Layer, and 0 phr and 60 phr CI Resin Added, Respectively ----------------

Page 120 122 124 125 128 166 167 168 169

Page 14: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

LIST OF PLATES Plate I: Nine Mix Formulations for SMR L, ENR 25,

and ENR 50-Based PSA in Addition of CI Resin, Petroresin, and Gum Rosin, Respectively ---------------------------------------------------

Plate II: Each Formulation of Rubber/Resin Blends

Has Characterized by Their Own Colour Appearance ------------------- Plate III: Resin that Furnished by Euro Chemo-Pharma Sdn. Bhd.,

M’sia Was Pulverized into Powder Form Using a Mortar ----------------

Page 170 171 172

Page 15: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

LIST OF ABBREVIATIONS/SYMBOLS

ASTM b.p.

BrENR BrNR

CI ClENR

ClNR cm cP

CR 3-D

ENR EPDM (EPT)

EVA g

GP h

HENR Ib Ibf

Ibf/In2 kg KJ

kN/m μm

mm mm/min

mm/s Mn

m.p. MPa

Mw N

NBR NMR

NR PF phr

PSA PVC

r RH

rpm RRIM SAN SBR SBS S.D. S.G. SIS

SMR

= American Standard for Testing and Materials, USA = Boiling point = Brominated epoxidized natural rubber = Brominated natural rubber = Coumarone-indene = Chlorinated epoxidized natural rubber = Chlorinated natural rubber = Centimetre = Centipoises = Chlorinated rubber = Three-dimensional = Epoxidized natural rubber = Ethylene-propylene diene terpolymer = Ethylene-vinyl-acetate = Gram = Gutta-percha = Hour = Hydrogenated epoxidized natural rubber = Pound = Pound feet = Pound feet per square inch = Kilogram = Kilo joule = Kilo Newton per metre = Micron = Millimetre = Millimetre per minute = Millimetre per second = Number-average molecular weight = Melting point = Megapascal = Molecular weight = Newton = Nitrile-butadiene rubber = Nuclear magnetic resonance = Natural rubber = Phenol formaldehyde = Parts per hundred parts = Pressure sensitive adhesive = Poly(vinyl chloride) = radius = Relative humidity = Rotation per minute = Rubber Research Institute of Malaysia = Styrene-acrylonitrile = Styrene-butadiene rubber = Styrene-butadiene-styrene = Specific density = Specific gravity = Styrene-isoprene-styrene = Standard Malaysian Rubber

Page 16: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

SMR 5

SMR 5CV

SMR EQ SMR GP

SMR L

SMR 5LV

SOP s.p.

Syn. TPE

Tr UV

VOCs θ α

= Standard Malaysian Rubber

(Impurities ≤ 0.05 %) = Standard Malaysian Rubber Constant Viscosity

(Mooney 60 ± 5) = Standard Malaysian Rubber Extra Quality = Standard Malaysian Rubber General Purpose = Standard Malaysian Rubber

(Like SMR 5 but lighter colour) = Standard Malaysian Rubber Low Viscosity

(Mooney 50 ± 5) = Standard Operation Procedure = Softening point = Synonym = Thermoplastic elastomer = Room temperature = Ultraviolet = Volatile organic contents = Contact angle = Cone-plate angle

Page 17: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

Kajian Mengenai Sifat-sifat Perekatan pada Perekat yang Berasaskan Getah Asli, Getah Asli Terepoksida, dan Etilena-Propilena Diena Terpolimer

ABSTRAK

Kekuatan kupasan, ketahanan ricihan dan sifat-sifat lekitan pada perekat yang

berasaskan getah asli terepoksida (ENR), getah asli (SMR) dan getah sintetik, EPDM

telah dipelajari dan dikaji. ENR terbahagi kepada dua gred, iaitu ENR 25 and ENR 50,

di mana masing-masing mengandungi 25 dan 50 mol % kumpulan epoksi. Sebanyak

tiga gred SMR, iaitu SMR L, SMR 10 dan SMR 20, yang berbeza dari segi kandungan

kotoran khususnya, telah dipelopori dan dikaji. Sumber getah ini telah dikenakan

mastikasi dalam empat jangka masa yang berlainan bagi mempelbagaikan struktur

panjang rantai getah. Resin coumarone-indene (CI) telah dipilih sebagai pelekit dalam

keseluruhan kajian. Selain itu, petroresin dan gum rosin telah juga digunakan secara

berasingan tetapi dalam keadaan terpilih. Kandungan pelekit berbeza dari 0 hingga 80

phr (bahagian per seratus bahagian getah). Pelarut toluena digunakan untuk

meleraikan getah kepada suatu larutan supaya dapat memudahkan lagi pengujian ke

atasnya. Perekat ini kemudian disapukan ke atas substrat dengan menggunakan

SHEEN hand-coater. Setiap sampel disapukan mengikut empat ketebalan permukaan,

iaitu 30, 60, 90, dan 120 μm. Kekuatan kupasan sampel perekat getah ditentukan oleh

alat penguji perekatan Lloyd melalui tiga mod ujian (T-Peel Test, 90o Peel Test, 180o

Peel Test), dengan berpandukan piawaian daripada ASTM. Mesin ini juga dipakai

gunakan untuk Loop Tack Test manakala dua ujian lekitan lain adalah menerusi Ball

Rolling Tack Test dan penentuan likatan. Shear Resistance Test dilakukan dengan

menggunakan Texture Analyser. Daripada keputusan ujian, kekuatan kupasan

tertinggi telah ditunjukkan pada setiap perekat yang berasaskan getah pada ketebalan

120 μm, manakala terendah pada sampel yang berketebalan 30 μm. Dalam setiap

ketebalan ini, diperhatikan satu titik maksimum pada 40 phr resin CI. Jelasnya,

Page 18: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

perekat berasaskan ENR 25 telah menunjukkan kekuatan kupasan dan ketahanan

ricihan yang lebih tinggi berbanding perekat berasaskan ENR 50 dan getah lain.

Sebaliknya, perekat berasaskan EPDM, diikuti SMR L telah memberikan sifat-sifat

lekitan yang lebih baik berbanding SMR lain manakala getah berasaskan ENR 50 dan

ENR 25 adalah kurang memuaskan. Pengaruh masa mastikasi ke atas kekuatan

kupasan, ketahanan ricihan dan sifat-sifat lekitan pada perekat juga dikaji dan

dibincangkan.

Page 19: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

Study of Adhesion Properties of Natural Rubber, Epoxidized Natural Rubber, and Ethylene-Propylene Diene Terpolymer-Based Adhesives

ABSTRACT

The peel strength, shear resistance and tackiness properties of epoxidized natural

rubber (ENR), Standard Malaysian Rubber (SMR), and ethylene-propylene diene

terpolymer (EPDM)-based adhesives were studied. Two grades of ENRs, i.e. ENR 25

and ENR 50 having 25 and 50 mole % epoxidation were respectively used as the

elastomers. Whereas as many as three grades of SMRs, viz. SMR L, SMR 10 and

SMR 20 varying from their dirt content and other foreign substances were studied.

These rubbers were masticated at different mastication times in order to vary the rubber

chain lengths. Coumarone-indene (CI) resin had been chosen as tackifier throughout

the study. As comparison, there is presented two other resins in the selective

conditions, and they were petroresin and gum rosin. The concentration of tackifier

ranged from 0 to 80 phr (parts per hundred parts of rubber). Toluene was used as the

solvent to prepare the adhesives into solution for testing. Coating on substrates was

carried out using a standard SHEEN hand-coater. For each adhesive sample, four

levels of coating thicknesses were carried out, i.e. 30, 60, 90, and 120 μm. Peel

strength of the adhesives was determined by the Lloyd adhesion tester instrument using

three different testing modes (T-Peel Test, 90o Peel Test, 180o Peel Test) in accordance

with ASTM specifications. The machine was also used for Loop Tack Test whilst two

other tackiness tests were via Ball Rolling Tack Test and viscosity measurement.

Another test, named Shear Resistance Test was carried out by means of Texture

Analyser. Results indicated that for all rubber-based adhesives, 120 μm coated

sample showed the highest peel strength whereas the lowest peel strength was

exhibited by 30 μm coated sample. For a fixed thickness of coating, the maximum peel

strength occurred at 40 phr of coumarone-indene resin. Obviously, ENR 25-based

Page 20: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

adhesive showed a better peel strength and shear resistance compared to that of ENR

50, and other rubber-based adhesives. Reversely, EPDM and SMR L-based

adhesives indicated higher tackiness than those from other SMRs-based adhesives

whilst ENR 50 and ENR 25-based adhesives were the lowest. The effect of

mastication time on peel strength, shear resistance and tackiness property of the

adhesives were also studied and discussed.

Page 21: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

1

CHAPTER 1 – INTRODUCTION

General

The adhesion properties of natural rubber (NR) and epoxidized natural rubber (ENR)

were much discussed in this thesis. Discussion is ranged from the historical

background of these rubbers, followed by objective of the rubber research, etc., until the

future prospects in rubber technology.

NR here refers to Standard Malaysian Rubber (SMR). It is sticky, coloured,

produced in large size varying in kilograms (kg). Because of the nature of SMR, a

great potential for various applications may have derived since more than four decades

ago. Rubber Research Institute of Malaysia (RRIM) has very much concentrated on

the quality assurance of the production of rubbers in order to produce as lowest dirt

content as possible by means of manufacturer’s instruments and technologies. SMR

is well-known and recognized throughout the world, especially by developing

industrialized countries like United States of America, European Union (EU), Japan,

Korea, etc. because of its cost effectiveness, usable, harmless especially to one’s

health.

ENR is more or less popular due to two grades of ENRs, viz. ENR 25 and ENR 50.

These ENRs are chosen as their moderate cost, great adhesion properties, and easily

gained by means of the production line via a simple and quite rapid route using peroxy

acid onto NR. A slightly changes in chemical structure in the presence of oxiranes

making possible for ENR to possess other properties such as heat resistance, air

permeability resistance, and stability due to chain re-arrangement.

Page 22: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

2

The only synthetic rubber, ethylene-propylene diene terpolymer (EPDM) was used

for comparison with those of ENRs and SMRs. EPDM is essentially a transparent,

non-tacky, difficult-to-masticate material. EPDM has been largely applied for roofing

and tyres production. Tyre for example, is highly resisted to abrasion at either very

high or low temperature on the road. Recompounding EPDM and reinforcing have

very much studied for improved tack and adhesion for both roofing and tyres use

(Morton, 1987a; Crowther and Melley, 1974). However, is that possible for EPDM to

shift to adhesive level in the future? Yes, it could be, by addition of certain resin, filler, or

accelerator, an EPDM-based adhesive could be prepared and it is possibly used in tape

or label.

All these rubbers made in rubber-based adhesives, separately. A series of testing

had been carried out, of which ranged from Peel Test, Shear Resistance Test to

Tackiness Test, to determine the tack and adhesion properties. Different test mode will

probably be varying the final average value of tackiness and adhesion strength owing to

different evaluation formula. In accordance with ASTM Standard, each adhesion test

should have its own preparation and operation ways. They differ from each other.

Tests are carried out carefully and separately for each sample, without rush. Data

collecting is an important task as there might be occurred data mixing and this should be

avoided.

Moreover, one should be able to carry out a test systematically, for instance one

sample followed by one sample but not mixing the samples from different formulations.

Smart time management is as important as other parts in experimental as a little

mistake may cause serious implication at the end. One may have to repeat again

overall experiment from the beginning. For example, one supposes to measure

viscosity for all adhesive samples on Friday, but he forgets or careless not to do so.

The related adhesive in the beaker is left for another two days before measuring on next

Page 23: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

3

Monday. The viscosity of the sample could possibly be different within two days. A

repetition needs time and energy as well as cost but nothing one could do unless he or

she can manage time wisely.

Furthermore, lab work could be divided into preparation of material and testing of

sample, two major tasks. It is a stringent work of all. One should exactly follow the

Standard Operation Procedure (SOP) of an instrument. The awareness of certain

safety is, as important as learning how to tolerate with each of other students who are

doing the same or another experiment in the same laboratory.

The main idea for the thesis is the adhesion properties of raw rubber-based

adhesive as described in the main title above. The peel strength of rubber-based

adhesive is discussed throughout NRs, ENRs and synthetic rubber, EPDM in addition of

different resin concentration. The influence of mastication time on rubber and

rubber-based adhesive as well as the effects of varying thickness of adhesive which is

applied onto the substrates, are investigated.

Apart from Peel Test, there are two other tests, viz. Tackiness Test and Shear

Resistance Test, of which using the same or other instruments depending on the needs.

The involved parameters are quite the same as described above but giving significantly

different results after having testing for each test. Comparison of adhesion strength

was made for rubber-based adhesives, in accordance with different mastication time,

resin concentration and surface thickness of adhesive on sample.

Page 24: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

4

The experimental’s objectives are to:

I. Develop ENRs, SMRs and EPDM-based adhesives, by blending different resin content to raw rubber solution and the effects of resin on the adhesion properties were studied;

II. Masticate raw rubber using two-roll mill and to coat rubber-based adhesive on the

substrate (PET); III. Test each rubber-based adhesive sample or specimen by means of different

testing modes in accordance with Standard Operation Procedure (SOP) and American Standard for Testing and Materials (ASTM);

IV. Determine or measure viscosity, tackiness, shear resistance, and peel strength of

rubber-based pressure sensitive adhesive (PSA) from a variety formulations; and to

V. Make comparison between results of testing.

Page 25: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

5

CHAPTER 2 – LITERATURE SURVEY

2.1 Historical Background on Rubber

A rubber tree has a long and rough trunk, with dark-green leaves on the top.

Rubber seed, all in three, hiding in a rubber shell when cracks, it drops on the ground, a

new life begins. The latex is found in trunk and in the leaves as well. Latex (white

fluid) shows its nature of tacky. This milky white fluid is a colloidal suspension of

rubber in a liquid consisting mostly of water. This fluid tends to harden upon air

exposure, within a couple hours. Therefore, the rubber estate worker will go to collect

it as fast as possible few moments after tapping in the early morning.

Rubber divides into two, natural rubber (NR) and synthetic rubber. Standard

Malaysian Rubber (SMR) and epoxidized natural rubber (ENR) are belonged to NR

whilst EPDM is one type of the latter. Rubber ball from weeping wood of Haiti origin,

was first brought back by Christopher Columbus to Europe (Spain) as early as 1496 ago.

Though comprising waterproofing usefulness for cloth and footwear, this gum or rubber

ball remained suffering from stickiness in hot weather and brittleness in cold. Until

1770, the English chemist, Priestley, gave a name ‘rubber’ to the raw material as it

conferred rub off characteristics towards pencil marks. He may have unawaredly

became the first one to add carbon black to rubber (Morton, 1987a; Treloar, 1975).

In the early 1800’s, a Scotsman, MacIntosh, had created the first raincoat, by

inserting a layer of rubber in between two separate cloths. Also, the first rubber band

had also been invented by cutting rubber into long strips, through Thomas Hancock in

1823. Until 1839, Hancock and Charles Goodyear from America had not coincidently

found that rubber may be improved by addition of sulphur in the presence of heat. The

Page 26: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

6

new product of so called vulcanized rubber, was not temperature dependant. Thomas

Hancock again made solid tyres for the carriage of Queen Victoria seven years later.

Perhaps that was the starting moment for our recent vast tyre industry.

Rubber tree, Hevea brasiliensis (Kawahara et al., 2000), was first came to

Singapore and Malay Peninsula (now Malaysia Peninsula), in 1877 and 1888

respectively, an effort by Sir Henry Wickham. After taking over the duty of Sir Henry

Wickham, Ridley, H.N. had intended to plant slow-growing rubber trees replacing coffee

crops in Malaya. Hectares and hectares of land and forest had been cultivated for

rubber tree crops since then. He also anticipated that an unprecedented demand on

rubber throughout the world will possibly due to the development of newly invented

pneumatic tyre (by Thomson, R.W., in 1845), credited to John Dunlop in England. He

was right as increasing market value had made possible for rubber to expand rapidly

throughout the world for a great variety of uses until these days. The demand of

rubber increased sharply during the World War I.

Germany had produced methyl rubber during the period of World War I but

production of which ceased after recovery of supplies of NR. Era of synthetic rubber

since then, Buna S and Buna N (modern form called as SBR and NBR),

polychloroprene (Neoprene), polysulphide rubber (Thiokol), butyl rubber, and silicone

rubber lastly had been commercially produced in 1944. World War II broke out in 1939

and it was not until mid-1941 and early of 1942, United States of America had produced

a synthetic rubber of the Buna S type in a slow starting (Craig, 1969).

Rubber is mostly used for tyre making (Kim et al., 2000), parts in automotive, shoe,

etc. Synthetic rubber has gradually developed but not to take over the role of NR,

where to some extent, this rubber possesses the suitability for some other special uses.

Synthetic rubber could be produced massively, and hence reduces production cost.

Page 27: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

7

Besides, the required properties may also be controlled. It is, however, NR has higher

gel content (Li et al., 2000), higher cohesive strength and tack in the unvulcanized state,

high tensile strength and crack growth resistance in vulcanized state (Kawahara et al.,

2000), and higher molecular weight (Mw), than synthetic rubber. All these imply that

better adhesion properties, and rubbery behaviour making possible for NR to withstand

steadily until today.

2.2 Standard Malaysian Rubber (SMR)

Despite numerous local socio-economic and global recession problems, and the

fact that the country’s cultivated land has been reduced to 40 % of its original acreage,

Malaysia remained the world’s largest producer of raw rubber, in the last decade, not

only in quantity but also in quality (Buist, 1987). Malaysian government, through its

Rubber Research Institute of Malaysia (RRIM) agency, has produced better and high

yields of planting materials or rubber clone by Ong (2000), new tapping and exploitation

methods like mechanical tapping knives, polybag collection, new and improved grades

such as Standard Malaysian Rubber General Purpose (SMR GP), new and more

systematic and efficient mini-estates management, and other advantages (Gullen,

1987). Recently, the Malaysian Rubber Board (MRB) official physical price for NR in

sen per kilo for tyre grade SMR 20 has increased to 690.00 compared to only 459.00

nine months ago, by a pleased rise of sharply 231.00 sen, for rubber estate owner.

Details could be referred to The Star daily newsprints dated 22nd March, 2006.

In between 1950’s and 1960’s, the work of Prof. Karl Ziegler and Prof. Giulio Natta

in the field of stereospecific polymerization has opened up a vast area in polymer

synthesis and there are now available cis-, and trans-polyisoprene, EPDM,

trans-polybutadiene and polybutadienes with low and high cis-content (Ciesielski, 1999;

Page 28: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

8

Morton, 1987a). Polyisoprene, a type of diene polymer builds up NR. There are

several thousand units of C5H8 in NR. The single unit, isoprene has 2 carbon-carbon

double bonds.

CH3

H2C═ C─HC═CH2 CH2─ C ═ CH─ CH2 CH3

Isoprene (C5H8) Polyisoprene

H2C CH2

C C

H3C H n

Scheme 2.1: Ziegler-Natta Reaction (Upper); SMR from Cis-1, 4-Polyisoprene

Structure (Lower)

Rubber from trans-1, 4-polyisoprene is not preferably for further enhancing as it is a

tough, horny substance at room temperature (Tr), and will become soft and tacky only

when warmed to about 100oC. Most of these rubbers obtained from the sap of trees of

the Sapotaceae family, which can be found abundantly in Southeast Asia. The raw

rubber of commerce (sheet, crepe, or block rubber) comprises a Mw mainly in the range

of 500,000 to 1,000,000, with extensions into both lower and higher regions (Allen and

Bloomfield, 1963; Nair and Sekhar, 1967; Ng and Schulz, 1969).

SMR is Malaysian-made, and is named so by 1965. For nearly a half century,

SMR is continuously, observed under the RRIM. SMR, a type of natural rubber has

been examined for its usability and quality in packing, grading, tape and labelling,

Page 29: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

9

electricity, oil and air resistance, etc. There are existed in many grades, such as SMR

5, SMR 5L, SMR 10, SMR 20, SMR 50, SMR EQ (light colour; ≤ 0.02 % dirt content),

SMR GP, SMR CV, SMR LV, etc., among the most easiest gained in the market,

covering a wide range of applications.

The grade of SMR is basically determined by its cleanliness or maximum dirt

content and the extent of some other foreign contaminants, such as copper, manganese,

nitrogen, and volatile constituents. They came in very small percentage and seemed

nearly the same for each grade of SMR. Reversely in the case of SMR 10, 20, and

SMR 50, they contain even higher percentage of ash and dirt than others, of which 0.1,

0.2, and 0.5 %, respectively. The bigger the number of SMR, the lower quality and

lower rubbery behaviour performed in rubber.

Most of SMRs are produced in a crumb form by one of several mechanical or

chemical processes. After washing and drying either by air or under sunlight or

assisted heat, the crumb rubber is compressed hydraulically into 60 – 75 pound (Ib)

bales (not exceeding 112 Ib). It is then wrapped in polyethylene bag and ready for

shipment in big mass. Advantages of recently new SMR products as recognized by

customers outside of Malaysia, are including higher uniformity, greatly improved

cleanliness, and better appearance, as well as ease of handling from the producing

workplace.

2.3 Epoxidized Natural Rubber (ENR)

Technology of ENR developed since as long ago as 1922, while NR was reacted

with a peroxy acid. But as a result, there was a weakness encountered on structure

where it supposed to be.

Page 30: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

10

Until early of mid-1970’s, epoxidation was carried out in the latex phase, and the

relatively low cost of reagents involved. Between this, secondary ring-opening reaction

involved in the presence of epoxide group.

ENR is a cis-1, 4-polyisoprene with epoxide groups randomly allocated along the

polymer backbone. The epoxide group in ENR plays a main role in rubber-based

adhesive. ENR possesses high strength that can be increased by increasing epoxide

contents, mostly in between 25 and 50 mole %. This is because of its ability to

undergo strain crystallization, comprising higher glass transition temperatures (Tg) (Poh

et al., 2001) and solubility parameter. Besides, ENR is tested to have increased oil

resistance, enhanced adhesive properties, high degree of damping and reduced gas

permeation (Gelling et al., 1991). It means ENR could not be oxidized easily in the

presence of air and thus prolongs its shelf life.

ENR is synthesized by epoxidation reaction on the polyisoprene backbone of NR

(Hevea brasiliensis type) at the latex stage in a suspension containing a significant

amount of gel particles, with peracetic acid (Gelling, 1991). Glacial acetic acid and

hydrogen peroxide added in epoxidation process is by Mounir El Sayed et al. (2002).

Those particles will tend to cause heterogeneity in sealant and adhesive formulation.

Thus, ENR has to be degraded chemically using peptizers or physically through

mastication. Degraded ENR could be soluble in most common solvents like toluene

and methylenechloride indicating a tacky surface and a transparent appearance.

These are depending on mastication time, set temperature, and the model and type of

two-roll mill used.

Li et al. (1998), in their published paper, mentioned that the ways in producing such

an epoxidized natural rubber latex (ENR L) or more precisely ENR. The raw rubber,

NR latex is first added stabilizer and followed by solution of formaldehyde in stirring.

Page 31: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

11

After 10 min, the latex solution is put in hydrogen peroxide and formic acid. A

continuous stirring and heating up to 50oC is necessary. The reaction is kept in

attention for another 24 h, to prepare required ENR L. Purification is applied for 24 h

afterwards through a dialysis process in deionized water, which should be changed

every 2 h in a pH value of 7 at the end of dialysis. ENR L is coated on a clean glass

and is put in the vacuum chamber at Tr until a transparency looking latex film is gained.

The test sample of ENR L is prepared after removing of water, and is tested to comprise

50 mole % of epoxide group within it.

ENRs that furnished by Guthrie Company, Malaysia, are brought in Universiti Sains

Malaysia (USM) together with SMRs, EPDM and some other laboratory grade

chemicals. ENR is a new, commercialized polymer in Malaysia since the end of 1987.

Such ENR is a potentially useful material, which exhibits unique properties such as

good oil resistance, low gas permeability hence giving excellent ageing resistance,

increased glass transition temperature, and improved wet grip and friction resistance

(Nakason et al., 2004; Hirthammer et al., 1987). At temperature of 20oC, the relative

air permeability is ranged from the highest NR, ENR 25, ENR 50, ENR 70, until the

lowest synthetic rubber.

70 % of overall rubber (natural and synthetic) consumption is emphasized on the

manufacture of the tyres (Kim et al., 2000), belts, cellular products, latex dipped goods,

hose and tubing, and footwear, of which assisted by carbon black, rubber chemicals,

canvas and textiles, leather and poly(vinyl chloride) (PVC) industries (Sarkar et al., 1990;

Parra et al., 2000; Mousa et al., 1998). Technology development will be directed

towards new products, but more importantly is new production method that giving good

results in higher quality, greater efficiency, and cost effectiveness (Buist, 1987).

Page 32: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

12

Among ENR 10, 25, 50, and 70 mole %, the carbon atom of which is epoxidized by

epoxide content, through breaking over the double bond in the backbone of chain

system. More epoxide group content means more expensive ENR costs. For the

commercial purposes, ENR 70 is seldom use as a sealant or an adhesive compared to

those of ENR 25 and ENR 50 (Dynaprene as trade name) (Hirthammer et al., 1987).

Some researchers from India, and Japan as well as Europe Countries imported

Epoxyprene 25 (ENR 25) and Epoxyprene 50 (ENR 50) from Malaysia.

Apart from SMRs and synthetic rubber, ENRs are also belonged to the group of

elastomers or thermoplastic elastomers (TPEs) but not for synthetic ones. TPE here

refers to a group of materials, based on a dynamically vulcanized elastomer and a

thermoplastic, commonly polypropylene.

TPE based on ENR, has covered a wide range of hardness for related product.

Tensile and tear properties are typical of dynamically vulcanized blends of elastomers

and polypropylene, while exhibiting excellent oil resistance and air aging properties as

mentioned repeatedly above.

TPE has also been produced by blending ENR and a styrene-acrylonitrile (SAN)

copolymer. Observing that tensile, tear strength as well as abrasion resistance

increased with increasing SAN content. However, there is decrease in elongation at

break and lower impact resistance. This is partly owing to the ability of ENR to

undergo strain crystallization, and thus suggests a wide range of potential applications

through R & D works in rubber industries (Fisher, 1987).

Page 33: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

13

2.3.1 Epoxidation

O

NR Latex ENR

Scheme 2.2: General Schematic of Epoxidation on NR Latex

NR undergoes epoxidation under a random fashion. At a very low level of

epoxidation, the reaction becomes easier as isolated isoprene units ‘freely’ arranged

along the main chain of molecule. However, the reaction rate is rapidly increased with

increasing peroxy acid content and thus provides more epoxidized blocks up to 15

mole % or above along the backbone of modified ENR.

It is important to know that the epoxidation reaction is a random process and

therefore epoxide-activated double bonds are distributed randomly along the polymer

molecule. This is proved by NMR spectroscopy studies. 13C-NMR or 1H-NMR

studies have also established that in spite of the physical heterogeneity of latex systems

epoxidation is quite random. The higher the concentration of the epoxide group in the

rubber chain, the stronger is the activation of the adjacent double bond (Poh et al., 1991;

Poh et al., 2000).

2.3.1.1 In Situ Epoxidation

The epoxidation rate increases with increasing latex concentration. There are

various methods involved in epoxidation of NR latex. One of them is through in situ

generating by using performic acid, an effort of combination of formic acid and hydrogen

peroxide. This is a famous method for commercial ENR use. Dilute latex with 20 %

Page 34: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

14

of solid content is preferably to epoxidation of NR but higher solid content up to 60 % for

commercial purpose, will result in enhanced reaction rates, and greater output per unit

volume of input.

Vernekar et al. (1992) reported in their paper that both 1H- and 13C-NMR studies

showed that latex concentration has no effect on the sequence distribution of the

polymer (epoxide groups). Even at higher latex concentrations, epoxidation led to

reasonably random placement of epoxy group along the chain.

In situ epoxidation has widely adopted for preparation of ENR in two separated

reactions.

Page 35: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

15

HCOOH + H2O2 HCOOOH + H2O (1) HCOOOH + + HCOOH (2)

O NR Latex ENR

OH

OH

+ H2O +

Trans-diol OH

O

C O R

Scheme 2.3: Simple/Low Level of Epoxidation of NR Latex Using Peroxy Acid via

Secondary Ring-Opening by Isolated Epoxide Groups

OH

Trans-diol + ENR O

X

X = RCOO

Scheme 2.4: Cross-Linking of ENR via Ring-Opening of Oxirane Groups

Page 36: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

16

A systematic change in properties of ENR that observed through the epoxidation

whether it is in low or high reaction rate, is depended on the final outcome. In the

presence of H2O, ENR continues to cross-link with ring-opened product yielding

interchained ENR through ring-opening of the epoxy groups (Hashim et al., 1995).

There are two distinct types of ring-opened products, which basically depended on the

level of epoxidation.

As in in situ epoxidation, formic acid (HCOOH) is reacted with the hydrogen

peroxide (H2O2) to form a rate-determining step which also known as a step of the

formation of performic acid (HCOOOH – a oxidation agent) as shown in stage (1). The

mixture should be stirred continuously until complete conversion of NR isoprene units to

ENR. The rate of reaction could be higher with increasing temperature up to 50oC,

heating of which for 10 – 12 h epoxide content of 50 mole % might be attained in ENR.

Ratio of H2O2 and isoprene units in the backbone determines the degree of epoxidation

towards unsaturated sites of yielded ENR. The raw ENRs are macroscopically stickier

than both SMRs and EPDM due to their epoxide groups.

HCOOOH in stage (2) tends to react with raw NR towards double bonds along the

main chain of molecule. These double bonds are eventually substituted by epoxide

groups, on the one hand but not all of them. HCOOH is formed back after completing a

‘donation’ on the other hand. The reaction rate of peracid (HCOOOH) against double

bonds is faster than its formation and the in situ epoxidation process will rapidly reach a

stationary state which the rate of formation of HCOOOH is equal to its consumption

(Bac et al., 1991).

A pure and ideal raw ENR can be obtained by reacting low concentration of

HCOOH with a large excess of H2O2, without side ring-opening reactions. An ENR

product of lower than 50 mole % epoxide content is also a typical elastomer, of opaque

Page 37: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

17

to translucent aspect, with off-white colour bringing visible yellowish outlook. Moreover,

ENR of higher epoxide content becomes harder, and less elastic due to increasing gel

content. But still ENR is having very good flexibility (lower degree of epoxidation is

better). Other than that, it imparts higher abrasion resistance, moderate solvent

resistance, low gas permeability, and better peel strength than NR and EPDM.

The polar epoxide group will evidently, tend to change the solubility of ENR. It

determines the solving capacity of the initial polyisoprene during the presence of polar

solvent. Toluene is a weak but good commercial polar solvent that could dissolve all

kinds of raw rubbers in the experiment. The effectiveness of toluene towards SMR and

ENR at low degree of epoxidation might not be so vary after all.

2.3.1.2 ENR and Halogen

ENR that derived from NR, has excellent strength, moderately acquired solvent and

oil resistance, and gas impermeability properties due to its epoxide contents.

Generally ENR, as like NR still poor in aging property. In order to prolong the shelf life

of ENR, there is a need to constitute some other elements via halogenation in

specialized conditions. The addition of hydrogen has reduced the unsaturation point

along the main chain of ENR as in the reaction of hydrogenation that providing

hydrogenated epoxidized natural rubber (HENR). The miscibility of blends could be

attained via hydrogen bonding.

Apart from this, the reinforcement could be obtained via reaction of secondary

ring-opening of epoxide group in ENR resulting brand new products, named

halogenated epoxidized natural rubber (XENR). For example in the case of

chlorinated epoxidized natural rubber (ClENR – a white solid; transparent looking in

Page 38: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

18

solution) and brominated epoxidized natural rubber (BrENR – a grey powder), they

possess a good adhesion properties to metal, glass or ceramics. Chlorine or bromine

first attacks the double bonds in ENR and further separation by furanized blocks to

propose ring-opening epoxide groups products. These literatures may refer to Roy et

al. (1993), and Cataldo (1992), in their respective published papers entitled

‘Hydrogenation of Epoxidized Natural Rubber’ and ‘Chlorination and Bromination of

Epoxidized Natural Rubber’ in details.

HENR tends to reduce the possibility of reactivity of double bonds as it has been

saturated by hydrogen (H2). Furthermore, HENR has signified less gel content created

upon aging than that of ENR. The air (oxygen) attacks double bonds in ENR rather

than in HENR. And thus as a result, HENR imparts so much better aging properties

than that of ENR with low level of epoxidation on the one hand, and comparable to

those with high level of epoxidation on the other hand. Moreover, the studies reveal

that the higher thermal stability of HENR over ENR, is closely correlated to different

content of double bonds existed in respective raw rubber.

Similar to the case of ENR, the original raw NR could also be able to undergo a

series of reactions in the presence of bromine or chlorine to give a better adhesion

properties form known as brominated natural rubber (BrNR) or chlorinated natural

rubber (ClNR), respectively. A detail experimental procedure is also being studied and

discussed by Cataldo (1992) in his published paper.

Page 39: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

19

2.4 Ethylene-Propylene Diene Terpolymer (EPDM)

2.4.1 EPDM Background

Ethylene/propylene rubber (usually called as EPDM) had first introduced in the

United States, in 1962. Though commercial production only began in 1963, it has

grown the fastest among other elastomers. The production had expanded to Europe

Countries as well as Japan since then.

Ethylene-propylene diene terpolymer (EPDM) elastomer as classified by ASTM, is a

thermoset polymer. EPDM (EPT) is abbreviation for ethylene-propylene terpolymer, in

accordance with ASTM D1418-67.

Its backbone is constructed by hydrocarbon chain that consisted of both single and

double bonds.

CH3

CH2 – CH2 – CH – CH2 – CH – CH2

CH2 n

CH

CH CH3

Scheme 2.5: Chemical Structure of Commercially Ethylene/Propylene/1, 4

Hexadiene Terpolymer (EPDM)

Page 40: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

20

2.4.2 EPDM

EPDM has a very low level unsaturation compared to that of NR or ENR, SBR, or

NBR, etc. This polymer is non-tacky, colourless, ranging from 0.86 – 0.87 g/cm3 of

specific gravity. It is tested to have 0.52 cal/goC of heat capacity on the one hand, –

95oC of brittle point on the other hand. Its relative air permeability could be quite

similar to that of NR, viz. 100 cm2sec-1atm-1, and obviously higher than SBR (23 % of

styrene), 65 cm2sec-1atm-1. The Mw of an elastomer is commonly reported as the

Mooney Viscosity (ML). ML of EPDM can vary from a low of 20 to a high 100 (Morton,

1987a). Furthermore, it is stable during exposure to sunlight, heat, moisture, or ozone,

and is possessed extraordinary elongation break up to 400 % without damaging on its

original chemical structure (Jablonowski et al., 1991; Kalwara, 1990).

Elongation Break = (Final Length – Original Length) / Original Length x 100 %

EPDM is divided into reinforced and non-reinforced EPDM, two major groups. The

latter is homogenous whilst the former is non-homogenous. Tensile strength could be

carried out in accordance with ASTM D412-68 in the case of homogenous EPDM.

Tensile Strength = Breaking Force / Cross Sectional Area (Ibf/In2) or (MPa), where 1 MPa = 145 Ibf/In2 or psi

Non-homogenous EPDM, according to ASTM D751, is measured on breaking of

fabric to give a unit of Ibf or Newton (N) representing the breaking strength since the

dimension of length x width has been fixed at one inch.

Moreover, ASTM D624-54 has guided out a specific tear test for non-reinforced

EPDM where a specimen is tore by pulling it in the opposite direction at 2 different

edges until it tears off. The result is calculated as Ibf/In or kN/m representing tearing

Page 41: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

21

resistance of specimen.

Similar to the case of breaking strength, by adopting ASTM D751, tearing resistance

of reinforced EPDM that could be stood by a sample, is evaluated. The tearing action

is quite the same as in non-reinforced EPDM. Tearing force is recorded at 5 maximum

peaks for the same group of samples and an average is counted. The unit for tearing

strength is written as Ibf or N.

Both reinforced and non-reinforced EPDM comprise flexibility properties at low

temperature, long shelf life, and greater peeling or tearing resistance. Those are the

reasons for EPDM to be utilized widely in roofing, floor layout. It has been tested and

proved that there only less than 1 % of shrinkage of EPDM, by Gish (1990). Therefore,

EPDM is suited for construction and building purposes, especially the roof constructing

of which prior to high temperature, continuous heat. EPDM can easily be rolled over,

functioning as insulator on the roof, especially in the West, but very rarely seen in Asia

(especially from Southeast).

2.4.3 EPDM in Tyres

EPDM is important in manufacturers of passenger car tyres. Various components

of passenger car tyres, on the selection of compounding recipes has been adjusted to

establish tyre fabrication practices due to the tacky problem of EPDM compound. The

formulation of special treatments has also been adopted to overcome the adhesion

barrier between cords and carcass stocks to ensure a balance of highway, and city

treadwear and skid resistance in conjunction with present-day first grade passenger

tyres. All-EPDM passenger tyre is adequate in durability, safety, and treadwear, as

well as the freedom from cracking and checking of the ozone resistant EPDM sidewall

Page 42: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

22

to some extent.

Again, reinforced EPDM by fabric, resin or cement in the presence of toluene, will

tend to increase the breaking strength. The fabric could be cotton, rayon, nylon, or

from the synthetic ones. In some other formulations, there strictly control over catalyst

and accelerator in order to avoid degradation on whole system. A more detail

procedure had been demonstrated by Crowther and Melley (1974), in accordance with

formulation between EPDM elastomer and polyester fibres.

2.4.4 Tackifier in EPDM

As the nature behaviour of non-tackiness and chemically stable, EPDM faces

difficulty to provide appropriate tackiness to most adherents. Resin tackifier or resin

that formulated with EPDM is one of many purposes where an EPDM-based pressure

sensitive adhesive (PSA) could be produced to suit for certain field of industries.

Generally, resin is added as a tackifier to raw rubber for enhancing tackiness or

tackiness characteristics that may not be performed by single raw rubber. Degradation

may occur to EPDM and other rubber-based PSA via oxidation, UV rays, and atomic

rays on polymer surface.

PSA

Polymer

Figure 2.1: A Tape or Label Consisting Raw Rubber-Based PSA and Elastomer

Page 43: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

23

There are various types of resins that could be compatible with EPDM elastomer.

Among them are rosin ester, phenolic resin, polybutene, terpene combinations, and

combinations between these resins and other hydrocarbons. These resins could be

differentiated from their naturally colour, physical appearance, miscibility and curing rate

when blending with EPDM.

2.5 Coumarone-Indene (CI) Resin

Coumarone-indene (CI) resin, supplied by Euro Chemo-Pharma Sdn. Bhd.,

Malaysia, is a mixed compounding thermoplastic polymerized resin between

coumarone and indene structure. Coumarone resin is one of natural or wood resins.

Coumarone (benzofuran) combines with indene in coal tar naphtha (b.p. 150 – 200oC)

in the presence of other compounds, mainly xylene and cumenes. Resinification is

carried out to separate the resin from those compounds followed by distillation to yield a

solvent-based CI resin. However, hard and brittle CI resin solid is polymerized by

mixing concentrated sulphuric acid or a Friedel-Crafts catalyst to the naphtha at 0oC.

Any found sludge is removed after 5 – 10 min, and neutralization is followed by then.

Residual naphtha is finally washed and distilled off to leave the resin.

Page 44: ADHESION PROPERTIES OF NATURAL RUBBER (NR) AND EPOXIDIZED NATURAL RUBBER (ENR)-BASED ...eprints.usm.my/9470/1/STUDY_OF_ADHESION_PROPERTIES_OF... · 2013-07-13 · study of adhesion

24

CH

CH + O

Coumarone Indene

Polymerization (At 0oC with catalyst)

H2C O H2C HC CH HC CH HC CH

Coumarone-Indene Resin Polymers

Scheme 2.6: Polymerized Coumarone-Indene Resin Combination Between Coumarone and Indene Structure

The hard and brittle to soft and sticky of resin greatly depends on the relative

proportion of coumarone and indene content and polymerization conditions. Usually,

the coumarone content is less than 10 %. This resin is a low surface energy polymer

due to the bulky part of resin which is extended by peripheral hydrocarbon substituents.

It is highly soluble in many organic solvents, including toluene and compatible with a

wide range of other polymers.

The resin that characterized by the m.p. below 50oC, could act as tackifier or

plasticizer in the mixture with rubber. Tackifier here acts as softening tools whereas

plasticizer assists in pigment dispersion apart from holding stress-strain properties at