APPLICATION OF RESTAURANT WASTE LIPIDS (RWL) AS A …eprints.uthm.edu.my/10255/1/AZRISZUL_MOHD_AMIN.pdf · binder component was monitored base on mixing condition, rheological characteristic,

APPLICATION OF RESTAURANT WASTE LIPIDS (RWL) AS A BINDER

COMPONENT IN METAL INJECTION MOULDING

AZRISZUL BIN MOHD AMIN

A thesis submitted in

fulfillment of the requirement for the award of the

Doctor of Philosophy

Faculty of Mechanical and Manufacturing Engineering

Universiti Tun Hussein Onn Malaysia

APRIL 2017

iii

For my beloved mother PUAN HJH ZAMALIAH BTE SURATDI,

my loving wife SITI NURFAIZAH BINTI MOHSAN, my sons MUHAMMAD

AQEEL IFWAT, AHMAD AL-SHAREEF, my daughters KHAYRA ZAFIRAH,

AREEFA NAFEESAH, my only sister and her husband INTAN KARTINI BTE

MOHD AMIN, DR. HASMADI BIN HASSAN

“THANK YOU for your endless support”

iv

ACKNOWLEDGEMENT

In the name of ALLAH S.W.T, The Most Gracious and The Most Merciful,

Greeting and Blessing to Prophet Muhammad S.A.W

I would like to express my sincere appreciation to my supervisor; Associate Professor

Dr. Mohd Halim Irwan Bin Ibrahim and my co supervisor; Associate Professor Dr.

Md. Saidin Bin Wahab for his thoughtful insights, helpful suggestions and continued

support in the form of knowledge, enthusiasm and guidance throughout the duration

for this research.

My infinite gratitude also goes to our dedication technician members; Mr.

Fazlannuddin Hanur, Mr. Shahrul Mahadi, Mr. Anuar and Mr. Tarmizi for their

support and cooperation during completing the experimental and analysis process.

A millions thanks to my family for their constant encouragement and love I have

relied on throughout my studies. To my PhD colleagues; Dr. Mohd Yussni Hashim,

Mr. Suzairin Md Seri, Mr. Shazarel Shamsudin, Dr. Faizal Mohideen Batcha and Dr.

Zamri Noranai, thank a lot for your ideas, motivations, involvement and support during

my PhD journey. Finally, I would like to express my gratitude and appreciation to

Malaysian Government and Universiti Tun Hussein Onn Malaysia for the financial

support and facilities. THANK YOU.

v

ABSTRACT

Application of Restaurant Waste Lipids (RWL) is introduced as binder component in

metal injection moulding since it’s contains rich amounts of free fatty acids which is

suitable as secondary binder components. Different binder formulation of RWL and

Polypropylene (PP) were prepared as the binders and the mixture of these binders with

water atomized 316L powder were obtained. The suitability application of RWL as

binder component was monitored base on mixing condition, rheological characteristic,

injection moulding, debinding and sintering process. Mixing time of 90 minutes was

obtained as suitable mixing time for producing good homogenise feedstock base on

mixing the polypropylene (PP) and RWL. Binder ratio of 50/50 weight percentage

between PP and RWL was obtained to be good binder ratio although all binder ratio

of 60/40, 40/60 and 30/70 shows pseudoplastic behavior. Taguchi method was

successfully employed for optimizing the injection moulding parameters which

consists of injection temperature, mould temperature, pressure, packing time, injection

time, speed and cooling time. It was found that factors that contribute in injecting good

part density and strength were temperature, pressure and speed. Extraction process of

RWL using solvent debinding process indicates that hexane solution with temperature

of 60ºC and solvent to feeds ratio of 7:1 were better as compare to heptane with respect

to fastest time removal. Good thermal debinding process under air atmosphere

condition with temperature of 400ºC and heating rate of 30ºC/min was obtained.

Sintering of the thermal debound parts also shows good mechanical properties and

microstructure of 316L stainless steel parts.

vi

ABSTRAK

Penggunaan sisa buangan lemak dan minyak dari restoran makanan telah digunakan

sebagai komponen bahan pengikat dalam pembuatan pembentukan suntikan logam.

Nisbah percampuran yang berbeza antara RWL dan polimer polypropylene (PP)

dihasilkan dan nisbah percampuran bahan pengikat yang berbeza ini dicampurkan

bersama serbuk logam keluli tahan karat 316L. Kebolehan bahan ini sebagai

komponen bahan pengikat dalam menghasilkan bahan suapan serbuk logam 316L di

tunjukkan dari segi percampuran sekata, sifat reologi, pembentukan suntikan, proses

pembuangan bahan pengikat dan pensinteran. Masa adunan 90 minit menjadi pilihan

berdasarkan campuran yang sekata antara bahan pengikat. Nisbah 50/50 berat bahan

pengikat antara polimer dan minyak buangan dari restoran dipilih berdasarkan analisa

yang dilakukan walaupun semua nisbah yang terdiri dari 60/40, 40/60 dan 30/70

didapati boleh digunakan sebagai nisbah bahan pengikat. Dalam mencari parameter

acuan suntikan yang optimum bagi isipadu dan kekuatan komponen yang dihasilkan,

kaedah rekabentuk eksperimen Taguhi digunakan dan mendapati bahawa faktor suhu

suntikan, suhu acuan dan tekanan memainkan peranan utama bagi penghasilan

komponen suntikan yang mempunyai ketumpatan dan kekuatan yang baik.

Pengekstrakkan bahan buangan lemak dan minyak dari komponen menggunakan

pelarut hexane didapati lebih berkesan dari bahan pelarut heptane dengan suhu 60ºC

dengan nisbah berat pelarut dan komponen sebanyak 7:1 adalah lebih baik berdasarkan

faktor singkatan masa. Pembuangan bahan pengikat polimer menggunakan kaedah

haba dalam udara terbuka dengan suhu 400ºC dengan kadar 30ºC/min peningkatan

suhu adalah lebih baik tanpa sebarang kecacatan pada komponen berlaku. Proses

pensinteran terhadap bahan yang telah melalui proses pembuangan polimer

menghasilkan pembentukan komponen yang baik dari segi sifat mekanikal dan

mikrostruktur bahan 316L keluli tahan karat.

vii

CONTENTS

DECLARATION OF THESIS STATUS

EXAMINERS’ DECLARATION

TITLE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

CONTENTS vii

LISTS OF TABLES xiii

LISTS OF FIGURES xvi

LISTS OF SYMBOLS AND ABBREVIATIONS xxv

LISTS OF APPENDICES xxviii

CHAPTER ONE INTRODUCTION

1.1 Problems Statement 4

1.2 Objectives 5

1.3 Scopes 6

1.4 Research Methodology 7

CHAPTER TWO LITERATURE REVIEW

2.1 Powder Injection Moulding 9

2.2 Metal Injection Moulding 9

2.3 Binder 11

2.3.1 Backbone binder 12

2.3.1.1 Ethylene Vinyl Acetate (EVA) 13

viii

2.3.1.2 Polyethylene (PE) 14

2.3.1.3 Polymethyl Methacrylate (PMMA) 14

2.3.1.4 Polypropylene (PP) 15

2.3.2 Secondary binder 16

2.3.2.1 Polyethylene Glycol (PEG) 16

2.3.2.2 Paraffin wax (PW) 17

2.3.2.3 Carnauba wax 18

2.3.2.4 Palm kernel and stearin 19

2.3.3 Surfactants 20

2.4 Restaurant waste lipids as binder

(RWL)

21

2.5 Stainless steel 316L powder feedstock 24

2.5.1 Critical Powder Volume

Concentration (CPVC) of SS316L

powder

28

2.6 Feedstock formulation 31

2.6.1 Different binder components 32

2.6.2 Different weight or volume fraction of

binder component

33

2.7 Mixing 34

2.7.1 Mixing rotational speed and time 35

2.7.2 Mixing temperature 37

2.8 Rheology 38

2.8.1 Flow behaviour index, n 41

2.8.2 Activation energy analysis, 𝐸𝑎 44

2.8.3 Mouldability index, 𝛼𝑆𝑇𝑉 46

2.9 Injection moulding 47

2.9.1 Factorial design (DOE) 49

2.9.2 Taguchi design (DOE) 50

2.10 Debinding 51

2.10.1 Single step thermal debinding process 52

2.10.2 Two step debinding via wicking and

thermal debinding process 53

ix

2.10.3 Two step debinding via solvent and

thermal debinding process

53

2.10.4 Thermal debinding after solvent or

wicking peocess

57

2.11 Sintering 61

2.11.1 Sintering atmosphere 62

2.11.2 Heating rate 64

2.11.3 Sintering temperature 64

2.11.4 Cooling rate 65

CHAPTER THREE METHODOLOGY

. 3.1 Introduction 67

3.2 Stainless steel powder used for

feedstock

67

3.3 Binder components of feedstock 70

3.3.1 Polypropylene (PP) and Restaurant

Waste Lipids (RWL)

70

3.4 Mixing 73

3.5 Rheology experimental method 76

3.6 Optimising green density and strength

of the injection moulding processes

78

3.7 Solvent debinding process 82

3.8 Thermal debinding process 84

3.9 Sintering 87

CHAPTER FOUR RESULTS AND DISCUSSIONS: MIXING

AND RHEOLOGICAL

CHARACTERISTIC

4.1 Introduction 93

4.2 Characteristic of SS316L powder and

binder components

93

4.2.1 Characteristic of SS316L powder 93

4.2.2 Characteristic of binder components 94

x

4.3 Mixing homogeneity 95

4.3.1 Homogeneity mixing time 97

4.3.2 Characteristic of mixing binder

components

101

4.4 Effect of binder formulation on

rheological behaviour and

characterization of feedstock

106

4.4.1 Effects of temperature on viscosity

with different binder formulation 110

4.4.2 Effect of binder formulation on

activation energy, viscosity, flow

behaviour index of feedstock 113

4.5 Optimising powder loading 117

4.5.1 Effect of powder loading to

temperature variation with viscosity 121

4.5.2 Effect of powder loading on viscosity,

activation energy, mouldability index

and flow behaviour index of feedstock 125

CHAPTER FIVE OPTIMISING INJECTION MOULDING

FOR DENSITY/STRENGTH OF GREEN

PART

5.1 Introduction 129

5.2 Preliminary study of optimum density

of injected parts (green part) for

feedstock formulation of F1 with ISO

178 flexural bar shape 132

5.3 Optimising the green density of

injection moulded tensile bar shape of

F2 binder formulation 140

xi

5.4 Optimising the F2 binder formulation

for density and strength using L18

Taguchi method 147

5.5 Experimental Layout for Strength

Measurement 152

CHAPTER SIX RESULT AND DISCUSSION:

DEBINDING AND SINTERING

VARIABLES OF INJECTION

MOULDED 316L WITH RWL AS

BINDER

6.1 Introduction 156

6.2 Solvent Debinding 157

6.2.1 Effects of Solvents Temperature on

Weight Loss Percentage of Green

Compacts for F2 Feedstock During

Solvent Debinding 157

6.2.2 Effects of Solvents Temperature on

Diffusion Coefficient of Green

Compacts for F2 Feedstock 160

6.2.3 Effect of Solvent to Feed Ratio on

Solvent Debinding Time 164

6.2.4 Scanning Electron Microscopy

(SEM) and Energy Dispersive X-ray

Spectroscopy (EDS) on F2 Green

Compact Formulation

166

6.3 Thermal Debinding 169

6.3.1 Effect of Temperature in Degradation

of PP During Thermal Debinding 169

6.3.2 Effect of Heating/Cooling Rate on

Weight Loss During Thermal

Debinding 184

6.4 Sintering 185

xii

6.4.1 Surface Appearance Between Green,

After solvent, Brown and Sintered

Part 185

6.4.2 Linear Shrinkage and Density of

Sintered Part 186

6.4.3 Surface Morphology and Mechanical

Properties of Sintered Part 189

CHAPTER SEVEN CONCLUSION

Conclusion 194

REFERENCES 196

APPENDIX 219

xiii

LIST OF TABLES

Table 2 - 1 Fatty acid composition (%) of NIE, EIE and CIE 50:50

PO:PKO blend fractions

19

Table 2 - 2 Reported fatty acids present in grease trap 22

Table 2 - 3 % mass fatty acids profiles of cooking fats and oils 23

Table 2 - 4 Fatty acid and FFA profile of FOG samples and neat palm

oil

23

Table 2 - 5 Fatty acids composition of some vegetable oils and animal

fats

24

Table 2 - 6 Various debinding technique for binder 61

Table 3 - 1 Chemical composition of water atomised SS316L (source

of Epson Atmix Corp)

68

Table 3 - 2 Characteristic of water atomised SS316L 68

Table 3 - 3 Binder Formulation between PP and RWL with 60%

powder loading SS316L

74

Table 3 - 4 Table of selected Injection parameter 80

Table 3 - 5 Injection Moulding Factors and its Levels using Taguchi

L18

81

Table 3 - 6 Injection Moulding Factors and its Levels using Taguchi

L27

82

Table 3 - 7 Temperature of solvent (Hexane and Heptane) used with

time and temperature

84

Table 3 - 8 Experimental heating, cooling rate and temperature setup 86

Table 5 - 1 Injection parameters for optimised 130

Table 5 - 2 Binder components ratio and powder loading 131

xiv

Table 5 - 3 Level of Injection parameters for optimisation 133

Table 5 - 4 Experimental layout of the L16 and density measurement

of the part

134

Table 5 - 5 Analysis of Mean and Signal to Noise Ratio of each factor 134

Table 5 - 6 Response table of variability analysis of S/N ratio 135

Table 5 - 7 Response Table for variability analysis of Mean 137

Table 5 - 8 Confirmation optimised injected part 138

Table 5 – 9 Injection Moulding Factors and its Levels 141


of the part

142


Table 5 - 12 Response Table for variability analysis of S/N ratio 143

Table 5 - 13 Response Table for variability analysis of Mean 144

Table 5 - 14 Confirmation optimised injected part 146

Table 5 - 15 Injection Moulding Factors and its Levels 148


of the part

148


Table 5 - 18 Average S/N ratio table 149

Table 5 - 19 Average Mean table 150

Table 5 - 20 Confirmation optimised density of green part 152

Table 5 - 21 Experimental layout of the L18 and strength measurement

of the part

152


Table 5 - 23 Average S/N ratio table 153

Table 5 - 24 Average Mean ratio table 154

Table 5 - 25 Confirmation optimised strength of green part 155

xv

Table 6 - 1 Carbon and Oxygen contents before and after solvent

debinding process as compare to SS316L powder

167

Table 6 - 2 Weight loss/gain after thermal debound with different

temperature

170

Table 6 - 3 Chemical composition of water atomised SS316L powder

(Epson Atmix Corp.)

172

Table 6 - 4 Shrinkage percentage after sintering process 187

xvi

LIST OF FIGURES

Figure 1 -1 Examples of MIM process sequence 4

Figure 2 - 1 Production of metal powder by gas atomisation, centrifugal

and water atomisation

10

Figure 2 - 2 Examples of polymers used in different binder

formulations

12

Figure 2 - 3 Mean concentrations of fatty acids in the FOG deposits 22

Figure 2 - 4 Powder particle shape of SS316L (a) water atomised (b)

gas atomised

25

Figure 2 - 5 Critical powder loading by means of density measurement 26

Figure 2 - 6 Example of relative viscosity versus volume fraction at

different shear rates

27

Figure 2 - 7 Mixing torque of finding critical solid loading metal

powder

27

Figure 2 - 8 Example of powder particles shape 29

Figure 2 - 9 Brabender Plasti-Corder two screw mixer in open position 37

Figure 2 - 10 Typical (a) pseudoplastic, (b) Newtonian, (c) dilatant flow

behaviour of fluid subtances

39

Figure 2 - 11 Schematic diagram of capillary rheometer components 39

Figure 2 - 12 Examples of pseudoplastic (shear thinning), Newtonian

and dilatant (shear thickening) flow behaviour on viscosity

versus shear rate (force) profile

40

Figure 2 - 13 Examples of poor and well mixed of metal or ceramic

powder and binder on capillary rheometer pressure profile

40

xvii

Figure 2 - 14 Example of pseudoplastic behaviour of feedstock

relationship between viscosity and shear rate

41

Figure 2 - 15 Relationship of flow behavior index (n) or power law

exponent to temperature

42

Figure 2 - 16 Example of flow behavior with different particle size 43

Figure 2 - 17 Arrhenius-type plot for the OA, SA, and HSA suspensions;

different slopes indicate the suspension viscosity exhibiting

a different but specific temperature dependency

46

Figure 2 - 18 General moldability index vs. solid loading % 47

Figure 2 - 19 Moulding variables using factorial design 50

Figure 2 - 20 Effects of different heating rate on degradation temperature

of binder components

58

Figure 3 - 1 Particles analyser machine (Fritsch analysette 22 compact) 68

Figure 3 – 2 JEOL JSM-6380LA Scanning Electron Microscopy 69

Figure 3 - 3 Critical powder volume concentration (CPVC) of SS316L

powder

70

Figure 3 - 4 (a) Polypropylene (PP) and (b) RWL used in the

investigation

71

Figure 3 - 5 Auto Q20 differential scanning calorimeter (DSC) 71

Figure 3 - 6 Linseis Thermal gravimetric Analysis Equipment 72

Figure 3 - 7 Perkin Elmer FTIR equipment 73

Figure 3 - 8 Mattler Toledo density apparatus measurement 73

Figure 3 - 9 Brabender Plastograph EC mixer is used for compounding

SS316L powder, PP and RWL (b) RWL being heated using

hot plate heater

75

Figure 3 - 10 Mixing sequence of feedstock compound using mixer a) PP

into the mixing chamber, b) PP left for melting, c) SS316L

powder left for homogeneously mix with PP, d) RWL

going into chamber, e) feedstock being taken out, f)

feedstock being cooled at room temperature

75

Figure 3 - 11 (a) Crusher machine used in transforming the bulky

feedstock into (b) small pallet feedstock

76

xviii

Figure 3 - 12 Capillary rheometer used in determining the rheological

behaviour and characterization

77

Figure 3 - 13 Schematic diagram of capillary rheometer 77

Figure 3 - 14 Injection moulding machine unit used for green specimens 78

Figure 3 - 15 Mould of specimen ISO 178 flexural bar shape 79

Figure 3 - 16 Mould of specimen MPIF Standard 41 bar shape 80

Figure 3 - 17 Universal flexural/tensile machine 81

Figure 3 - 18 Mould of specimen ISO 527-2 tensile bar shape 82

Figure 3 - 19 Water bath used for solvent debinding process 83

Figure 3 - 20 Colourless heptane change to yellow/brown colour during

solvent debinding process of green compact

84

Figure 3 - 21 High temperature furnace and temperature profile of

thermal debinding process

85

Figure 3 - 22 Alumina crucible 85

Figure 3 - 23 X-ray diffraction Bruker D8 Advance machine 87

Figure 3 - 24 Vacuum Furnace at AMREC Kulim, Kedah 87

Figure 3 - 25 Mould sample holder 88

Figure 3 - 26 Grit size sequence of polishing sintered SS316L part 89

Figure 3 - 27 Grinding and polishing machine 89

Figure 3 - 28 Silicon carbide grinding paper 89

Figure 3 - 29 Polishing process 90

Figure 3 - 30 Samples test after being grinded and polished 90

Figure 3 - 31 Electro etching equipment setup for SS316L sintered part 91

Figure 3 - 32 Microhardness test equipment 91

Figure 3 - 33 Digital microscope used for detrmining the grain size 92

Figure 3 - 34 Tensile machine test of the sintered part 92

xix

Figure 4 - 1 (a) Powder size distribution of SS316L, (b) SS316L

powder morphology

94

Figure 4 - 2 Differential scanning calorimetry curve of RWL 95

Figure 4 - 3 Differential scanning calorimetry curve of PP 95

Figure 4 - 4 Thermalgravimetric analysis of the RWL 96

Figure 4 - 5 Thermalgravimetric analysis of the PP 96

Figure 4 - 6 Fourier Transform Infrared Spectrometry (FTIR) spectrum

of RWL

97

Figure 4 - 7 Surface morphology of the feedstock with binder

formulation (a) F1 (b) F2 (c) F3

98

Figure 4 - 8 TGA comparison of mixing time of Stainless steel powder

316L, RWL and PP for (a) 45 minutes (b) 90 minutes for

F2 binder formulation

99

Figure 4 - 9 TGA profiles of different binder formulation 101

Figure 4 - 10 DSC of F1 relatives to PP and RWL derivatives 103




Figure 4 - 14 DSC scans of the PP, RWL and feedstock formulation 105

Figure 4 - 15 Viscosity versus shear rate graph of binder F1 with 60%

powder loading

107


powder loading

108


powder loading

108


powder loading

109

Figure 4 - 19 Viscosities shear rate of all binder formulations at

temperature 190°C

110

Figure 4 - 20 Logarithmic viscosity against reciprocal temperature of F1

binder formulation at different shear rate

111

xx



111



112



112

Figure 4 - 24 Comparison of logarithmic viscosity against reciprocal

temperature of all binder formulation at different shear rate

113

Figure 4 - 25 Activation Energy and flow behaviour index against binder

formulation profile at shear rate of 1000s-1

114

Figure 4 - 26 Viscosity and flow behaviour index against binder

formulation profile

115

Figure 4 - 27 Activation energy and mouldability index against binder

formulation profile

116

Figure 4 - 28 General moldability index vs. feedstock formulation 117


powder loading

118


powder loading

119


powder loading

119

Figure 4 - 32 Viscosity versus shear rate graph at 190°C for all Powder

loading

120

Figure 4 - 33 Viscosity and flow behaviour index against Volumetric

Powder Loading profile at 1000s-1 shear rate

121

Figure 4 - 34 Logarithmic viscosity against reciprocal temperature of

60% powder volume loading at different shear rate

122



123



123

xxi

Figure 4 - 37 Comparison of logarithmic viscosity against reciprocal

temperature of all powder volume loading at 1000 s-1 shear

rate

124

Figure 4 - 38 Viscosity and activation energy against Volumetric Powder

Loading profile at 190°C

125

Figure 4 - 39 Activation energy and flow behaviour index against

Volumetric Powder Loading profile

126

Figure 4 - 40 Activation energy and mouldability index against


127

Figure 4 - 41 Mouldability index and flow behaviour index against


127

Figure 4 - 42 Viscosity and mouldability index against Volumetric

Powder Loading profile

128

Figure 5 - 1 ISO 178 flexural bar shape 133

Figure 5 - 2 Schematic diagram dimension of ISO 178 flexural bar

shape

133

Figure 5 - 3 S/N ratios variations of green part density at various levels

of injection parameters

137

Figure 5 - 4 Mean variations of green part density at various levels of

injection parameters

137

Figure 5 - 5 Variations of density during the L16 Taguchi DOE

experiments

139

Figure 5 - 6 Injected part shape for solvent debinding (F2 feedstock) 140

Figure 5 - 7 S/N ratio of green part density at various levels of injection

parameters

144

Figure 5 - 8 Mean of green part density at various levels of injection

parameters

145

Figure 5 - 9 Tabulated density of green part density at various levels of

injection parameters

146

Figure 5 - 10 Bar shape injected moulded part 147

Figure 5 - 11 S/N Ratio main effect plot of the control factors 150

Figure 5 - 12 Mean main effect plot of the control factors 151

xxii

Figure 5 - 13 S/N Ratio main effect plot of the control factors 154

Figure 5 - 14 Mean main effect plot of the control factors 154

Figure 6 - 1 Schematic diagram of solvent debinding process inside the

green compact

156

Figure 6 - 2 Solubility of the RWL in (a) Hexane solution after 4 hrs (b)

Heptane solution after 2 hrs with solvent temperature of

50°C respectively

157

Figure 6 - 3 Weight loss percentage of RWL removed for F2 feedstock

during solvent debinding at different temperature using

hexane

158

Figure 6 - 4 Weight loss percentage of RWL removed for F2 feedstock

during solvent debinding at different temperature using

heptane

159

Figure 6 - 5 Injected test specimen of the F2 feedstock (a) green

compact (b) after extraction process

159

Figure 6 - 6 Effect of temperature on weight loss of the green compact

during the first hour for F2 feedstock with different organic

solvent

160

Figure 6 - 7 Diffusion coefficient of RWL for F2 feedstock during

solvent debinding at different temperature using hexane

161

Figure 6 - 8 Diffusion coefficient of RWL for F2 feedstock during

solvent debinding at different temperature using heptane

162

Figure 6 - 9 Effect of temperature on solvent debinding diffusion

coefficient during the first hour for F2 green compact with

different organic solvent

163

Figure 6 - 10 DSC profile of F2 green compact before and after first hour

solvent debinding process using hexane at 60°C taken from

the centre of the compact

163

Figure 6 - 11 Bar shape used for solvent debound process with different

solvent to feed ratio at 60°C

164

Figure 6 - 12 Weight loss percentage profile of different solvent to feed

ratio using hexane solution

165

Figure 6 - 13 Diffusion coefficient profile of different solvent to feed

ratio using hexane solution

165

xxiii

Figure 6 - 14 Evolution of pores from (a) green compact (b) solvent

debinding after 3 hrs (c) solvent debinding after 6 hrs

166

Figure 6 - 15 EDS analysis on solvent debound sample (a) area taken for

carbon analysis, (b) EDS element analysis of green

samples, (c) after solvent samples, (d) after thermal

samples

168

Figure 6 - 16 Comparison in dimension between brown part under

different temperature

170

Figure 6 - 17 TGA profiles of brown compact after solvent debound

process

171

Figure 6 - 18 XRD pattern of SS316L water atomised powder 171

Figure 6 - 19 Schaeffler diagram for determining phases formed upon

solidification, based on chemistry

172

Figure 6 - 20 XRD pattern for (a) part with 500°C (b) part with 600°C

thermal debound

173

Figure 6 - 21 XRD pattern of thermal debound part at 600°C indicates of

oxidation of SS316L brown compact

174

Figure 6 - 22 Example of XRD profile oxidation occurs on SS316L

powder during sintering under different atmosphere

174

Figure 6 - 23 Part sample that undergo temperature of (a) 500°C (c)

450°C (d) 400°C with heating rate of 10°C/min and (d)

swelling and crack of parts surface under 40°C/min at the

temperature of 400°C

175

Figure 6 - 24 Weight loss of thermal debound part with temperatures of

10 replications each

176

Figure 6 - 25 Effect of temperature in weight loss of part after thermal

debinding process

177

Figure 6 - 26 XRD pattern of part under 400°C thermal debound 178

Figure 6 - 27 Peaks of highlighted area from Figure 6-26 shows

increment of α- martensitic peak and decrease in γ-

austenite besides peak shifted

178


xxiv




180





181

Figure 6 - 32 SEM/EDS of water atomised SS316L 181

Figure 6 - 33 SEM of 400°C Thermal debound part morphology and

EDS analysis

182


EDS analysis

182


EDS analysis

182

Figure 6 - 36 Shrinkage value relatives to temperature of debinding

process

183

Figure 6 - 37 Effect of heating rate with 400°C temperature on

percentage of weight loss

184

Figure 6 - 38 Surface morphology of cross sectional (a) green part (b)

after solvent part (c) brown part (d) after sinter part

185

Figure 6 - 39 (a) comparison of part after each process (b) shrinkage

value after each MIM process

186

Figure 6 - 40 Density of part after each process 188

Figure 6 - 41 Density of part after each process in MIM relative to

theoretical density

189

Figure 6 - 42 Surface morphology of the sintered part (a) after polishing

and (b) after etching

189

Figure 6 - 43 Surface morphology of sintered part after etching 190

Figure 6 - 44 SEM and EDS analysis on the etched sintered sample 191

Figure 6 - 45 Section sketch of microhardness test on the sintered part 191

Figure 6 - 46 Hardness test for grip’s cross sectional area (A-A’) 192

Figure 6 - 47 Hardness test value on the surface of Grip area ‘B’ 192

xxv

Figure 6 - 48 Hardness test value on the surface of neck area ‘C’ 193

xxvi

LIST OF SYMBOLS AND ABBREVIATIONS

FOG - Fats, Oils and Grease

RWL - Restaurants Waste Lipids

PMMA - Poly(methyl methacrylate)

PP - Polypropylene

PE - Polyethylene

LDPE - Low Density Polyethylene

HDPE - High Density Polyethylene

CPVC - Critical Powder Volume

Concentration

TGA - Thermal gravimetric Analysis

DSC - Differential Scanning Calorimeter

ASTM - American Society for Testing and

Materials

MPIF - Metal Powder Industries Federation

SEM - Scanning Electron Microscope

XRD - X-Ray Diffraction

μMIM - Micro Metal Injection Molding

PIM - Powder Injection Molding

FCC - Face Center Cubic

BCC - Body Center Cubic

xxvii

PM - Powder Metal

𝐷10 - Distribution of powder at 10%



CHMA - Cyclohexyl Methacrylate

DMPT - Dimethylpara Toluidine

EVA - Ethylene-vinyl acetate

PEG - Polyethylene Glycol

PW - Paraffin Wax

PK/PS - Palm Kernel/Stearin

MW - Microcrystal paraffin wax

SA - Stearic acid

OA - Oleic acid

HSA - 12-hydroxystearic acid

𝑉𝑝 - Volume powder

𝑉𝐿 - Volume liquid

𝜂 - Viscosity, Pa.s

�̇� - Shear rate, 𝑠−1

𝑛 - Flow behavior index

𝐸𝑎 - Activation energy

𝑅 - Gas constant

T - Temperature

B - Reference viscosity

𝛼𝑆𝑇𝑉 - Mouldability index

DOE - Design of Exsperiment

xxviii

𝐷𝑒 - Interdiffusion coefficient

∅ - Removed fraction of soluble binder

A - Area

t - time

𝑁𝐴 - Avogadro constant

𝑁2 - Nitrogen gas

𝐻2 - Hidrogen gas

CIM - Ceramic Injection Moulding

DA - Dissociate Ammonia

Fe - Ferum

Cr - Chromium

Ni - Nickel

𝑆𝑊 - Distribution slope parameter

FTIR - Fourier transform infrared

spectroscopy

𝑊𝐵 - Weight of binder

𝑊𝑃 - Weight of powder

𝜌𝐵 - Density of binder

𝜌𝑃 - Pycnometry Density of powder

�̅� - Average S/N ratio

S/N - Signal to Noise

�̅� - Mean

𝛿𝑁−1 - Standard deviation

xxix

LIST OF APPENDICES

APPENDIX TITLE

PAGE

A Data of binder formulation calculation and rheology 219

B Data of stainless steel (SS316L) powder particle size,

Critical Powder Volume Concentration (CPVC) and

SEM/EDS analysis

230

C List of Publications

236

D Specification of stainless steel powder (SS316L),

Polypropylene, Restaurant waste lipids supplier 238

CHAPTER ONE

INTRODUCTION

Towards implementing the green technology, four pillars are being listed for

improvement, which are energy, which is seeking to attain energy independence and

promote efficient utilizations. Seconds is to enhance national economic development

through the usage of green technology while the third one is more concern on society

where to improve the quality of life for all generations. Finally, it is to conserve and

minimize the impact of development on environment. A sector, which is promising in

the usage of green technology, is identified to be in energy sectors, building, transports

and water waste management sectors. Sustainable Development will require major

changes with respect to production and consumption patterns in our societies,

including materials, energy sources and production processes used in industry, the

products and services offered, as well as the organisation and management of supply

chains and the governance of firms. Industry, and the manufacturing sector in

particular, is therefore one of the key addressees of the Sustainable Development

strategy since a more sustainable manufacturing sector can make significant

contributions to attain the objectives. This is stated in the Brundtland Report [1] about

the key concepts towards Sustainable Development " the idea of limitations imposed

by the state of technology and social organization on the environment's ability to meet

present and future needs" where here the technology is more towards the

manufacturing sectors to implementing the sustainable manufacturing with consuming

less materials resources and energy.

With rapid growth of human population, index of pollution results from RWL

also will increase. It is found that, the change of habits will also increase the solid

waste produce by the human [2]. Urbanisation also lead to change in diets where more

2

food with higher in fat, animal products, sugar and processed food become the priority

[3]. Due to these rapid changes of dietary more pollution is created results from fat, oil

and grease (FOG) to the water stream in sewage. This will results in high toxicity of

the wastewater [4] due to increasing use of oil and grease in high-demanded oil-

processed foods, establishment and expansion of oil mills and refineries worldwide,

as well as indiscriminate discharge of oil and grease into the water drains, domestically

and industrially. It will also increase the government expenditure due to pipe

blockages, pipe break excessive inflows and power failure. Clean up cost could rise

thousands of dollars to the municipalities as claimed by Hong Kong Drainage Service

Department [5]. The increasing of this source of food tend to increase the production

of cooking oil in factory and this is true through its export data of crude palm oil from

Malaysia palm Oil Council [6]. Besides the increasing of cooking oils demand, the

consumption of animal meat also increase which also contribute to the waste water

pollution. Reuse of such wastes as a sustainable construction material appears to be

viable solution not only to pollution problem but also to the problem of the land-filling

and high cost of building materials [7].

Powder injection moulding (PIM) which consists of metal injection moulding

(MIM) and ceramics injection moulding (CIM) is one of the major manufacturing

processes used to generate small parts with intricate geometries, thin walls and in large

production batches [8], [9]. It combines the flexibility and high productivity of the

plastics injection moulding with the powder metallurgy method of sintering.

Therefore, it has the capability to manufacture a wide range of components having

multifaceted shape, high performance, application areas are various ranging from

automotive (locking mechanisms, transmissions synchronisers, and airbag sensors),

electronics (computer hard disk drive magnet), defences and aerospace (rocket nozzle

guidance system, aircraft engine screw seal), to medical industry (orthodontic

brackets, medical forceps) and jewellery (wristwatches). A propose materials,

common metals, alloys, ceramics and carbides are frequently encountered [10].

Then, since the sintering of a compacted powder is similar for a part obtained

by injection or press moulding, the recipe points in MIM turned out to be how to make

the metal flow into the mould and how to retain the shape of the moulded part until it

begins the sintering. Dispersing the powdered metal into a binder to form a gloop that

flows at high temperature and becomes solid at room temperature commonly solves

3

this difficulty. As a result, the moulded part retains its shape after injection moulding

and may be handled and processed safely.

The research of binder is the heart of this technique in particular, the

binders in the feedstock strongly determine MIM quality [11]. The recipe points in

MIM binder turned out to be how to make the metal flow into the mould and how to

retain the shape of the moulded part until it begins the sintering. Dispersing the

powdered metal into a binder to form a gloop that flows at high temperature and

becomes solid at room temperature commonly solves this difficulty. They provide

adhesion among powdered particles and improve the mechanical properties of

feedstock and prevent separation phenomena among binders and powders. As a result,

the moulded part retains its shape after injection moulding and may be handled and

processed safely. cost reduction and less environmental issues of binder also plays

significant role in proper selection of binder besides to achieve low viscosity of the

feedstock [11], [12]. Usually binders are mixture of several organic compounds where

the main ingredients are waxes and synthetic polymers. The purpose of the polymer is

to convey rigidity to the part when cold, while the wax reduces the viscosity and flow

ability of the binder and the additives reduce particle severance and segregation [13].

It is usual to convert the powder-binder mix, the so-called feedstock, into solid pellets

by a granulation process. These feedstock pellets can be stored and fed into the

moulding machine as required.

Parts that are produce from the injection moulding machine are called

green parts where this parts contains of metal powder, polymer, wax and additives.

This is not a finalised part since it will go another process to get the finalized parts.

The green parts will then undergoes another process called debinding process where

the primer and secondary binder will be flowed out of the parts through solvent,

catalyst wicking or thermal debinding. Sometimes this thermal process will

simultaneously prepared with the sintering process since the sintering also required

certain temperature in bonding the metal powder in order to get the desired density,

strength and shape of final products. The full view of the process is shown in Figure

1-1;

4

Figure 1 - 1: Examples of MIM process sequence [14]

Due in promoting the sustainability development in this manufacturing area,

waste materials from the restaurants waste lipids (RWL) or fats, oils and grease (FOG)

derivatives from restaurants will be used here since it is believed that it can contribute

in some area of metal injection moulding process especially in preparing the binder

systems for powder metals feedstock. This abundant resource is increasing with the

increasing human population, which make it possible solution in reducing and

recycling waste as alternative for current binder in the markets for MIM.

1.1 Problems Statement

The use of RWL in MIM process is a new idea besides it’s used in the biodiesel sector.

It is the challenge how this waste can be used in the manufacturing area since it has

composition of different organic materials. It is found that this RWL contains high

energy and oil recovery which can be obtained from this abundant source of energy

[15]. In terms of MIM, process the RWL seems could be used in the production of

MIM feedstock since it has the mixture of animal fats, vegetable oils which compose

of several organic acids [16].

In MIM, the miscible issues of RWL and polymer will be analysed since the

mixing ability of the binder components is very important in providing good

5

interaction of metal powder and binder for flowability of the feedstock. Results of this

analysis could leads to better rheological characteristic of the feedstock.

Since RWL contains high fats and oils recovery which act as a lubricant in

feedstock during injection moulding process [17], other issues such as crack,

distortion, shot short, density and strength of the injected moulded parts or green parts

will be analysed [18]. It is expected that the binder components in MIM should not

retain in green parts and being removed before sintering processes. Therefore finding

the suitable extraction process of the binder need to be considered since improper

removal could results in several defect on the green parts which affect the sintering

process and the materials characteristic of the sintered parts [19].

1.2 Objectives

The main objective of the research is to evaluate the application of RWL in metal

injection moulding. In order to achieve the objective, several sub-objectives need to

be implemented, which are:

a) To investigate the mixing and rheological characterization of different

binder formulation between PP and RWL and optimum powder loading

for metal injection moulding feedstock.

b) Optimising the injection moulding parameters of metal injection

moulding process for highest green density and strength by means of

Taguchi method for RWL as binder component.

c) Determine the optimum effect of debinding conditions in removing

RWL binder component from the green compact.

d) Determine the mechanical and microstructure analysis of the sintered

part under graphite vacuum furnace.

6

1.3 Scopes

Scopes of this research focused on process ability of using novel binder system in order

to produce micro metal parts. In order to obtain this, this research will cover the

following scopes:

a) Feedstocks of the µMIM were prepared base on water atomised

Stainless Steel powder SS316L with mean size of 6µm, Polypropylene

and RWL as a backbone binder and lubrication/surfactant respectively.

b) Mixing homogeneity characteristic was based on mixing time between

45 minutes and 90 minutes. Homogeneity of the feedstock will be

monitored base on density and TGA and DSC analysis of the feedstock.

c) Characteristic of feedstock produced from the mixing were analysed on

rheological properties base on shear rate, shear stress, viscosity,

activation energy, flow index, mouldability index and temperature.

d) Optimization of the metal injection process were done base on Taguchi

Method where the parameter will be analysed are injection pressure,

injection temperature, mould temperature, injection time and holding

time.

e) Optimum solvent debinding was based on type of solvent (hexane and

heptane), solvent temperature, and time and diffusion rate. Optimum

thermal debinding was optimised base on the effect of heating rate and

temperature on oxidation of powder and other defects such as warping,

swelling and crack.

f) Mechanical properties and characteristic of the sintered parts under

heating rate of 5ºC/min, sintering temperature of 1360ºC, sintering

atmosphere under high vacuum furnace and dwell time of 100 minute

were investigated besides the carbon contents by means of SEM/EDS

and XRD.

7

1.4 Research methodology

In order to achieve the objectives of this study, the following methodologies were used

as a guideline during the course of the study.

a) Determination of critical powder volume concentration (CPVC) of

SS316L powder by means of ASTM D-281-31.

b) Determination of degradation and melting temperature of the binder

components which are polypropylene (PP) and restaurant waste lipids

(RWL) for mixing purposes.

c) Determining the optimum binder formulation and powder loading base

on rheological behaviour and characteristic using capillary rheometer

Instron CEAST SmartRHEO 10 (ISO 11443, ASTM D3835 and DIN

54811)

d) Optimizing the injection parameters for density and strength of green

compact by means of MPIF standard 15 and density of specimens

standard ISO 527-2 tensile bar for sintering.

e) After optimising the injection parameter has been done, green parts

were allowed to experience the solvent debound or extraction process

where optimising in terms of temperature, solvent’s type and time of

extraction were done. Effect of weight loss and diffusion coefficient of

RWL with respect to temperature, solvent’s type and extraction time

were analysed.

f) After solvent process, removing the polymer or backbone binder from

the brown compact was done by thermal pyrolysis/debound as suitable

heating rate and temperature. Selection of degradation temperature for

polymer were based on TGA results and temperature, which produced

high weight loss of the brown compact, will be selected without any

defect on the brown compacts.

g) Sintering process will be done base on the previous researchers such as

heating rate, temperature and dwelling time. Mechanical and

microstructure properties of the sintered part was done base on MPIF

standard 10/ASTM E8 for tensile strength, MPIF standard 51 for

8

microhardness properties and ASTM 112-13 for grain size properties

of the sintered parts.

CHAPTER TWO

LITERATURE REVIEW

2.1 Powder Injection Moulding

Powder injection moulding (PIM) process is the adoption process of plastic

injection moulding process. The difference is that the polymer is filled with disperse

metal and ceramic powder and transported into the mould cavity to form the mould

cavity shape. It is a process of capable in producing small intricate complex part shapes

with combining multiple parts into single one and at medium to high quantity

production [10], [20]. It has the ability to handle very fine metals or ceramics powder

that can be sintered to high densities near to its bulk metals or ceramics. Acceptable

ductility and strength could be produced using this technique. Besides its attractive

process, wide range of ceramics and metals could be processed with this technique

ranging from low alloy steels, stainless steel, magnetic alloys, nickel alloys, tool steels

and titanium alloys which become limitation for die casting process. Fine details such

as blind holes, recesses, sharp edges and internal or external threads which becomes

limited process for investment casting becomes much easier using PIM [21]. PIM

could divided into three categories which are ceramics [22]–[28], metals [17], [29],

[30] and cermets [31]–[33].

2.2 Metal Injection Moulding (MIM)

Metal injection moulding is subdivision of powder injection moulding process. The

composites fabricated by MIM can be divided into refractory metal based metal matrix

composites (MMC), titanium based, intermetallic based and steel based. The MIM

direction has enabled the fabrication of MMCs containing ingredient materials that are

10

not compatible in molten state and difficult to fabricate by conventional routes [21],

[34].

MIM relies on shaping metal particles and subsequently sintering those

particles. Hence MIM products are competitive with most other metal component

fabrication routes, and especially are successful in delivering higher strength compared

with die casting, improved tolerances compared with investment or sand casting, and

more shape complexity compared with most other forming routes [35].

MIM production involves several processing steps which are mixing of

binder and powder to form feedstock, injection of green part, debinding and sintering

[36]. Every steps of processing plays significant roles in producing good parts with

acceptable mechanical and dimensional properties. Mistakes could not be repaired in

subsequent process.

Various metals powder have been used ranging from stainless steel, titanium,

high speed steel, Inconel and Nickel Titanium alloy to form a feedstock [33], [37]–

[43]. Various powder particle shapes have been used in MIM process ranging from

sphere, rounded and flaky shapes. This particle shapes were depend on the types of

processing used in producing the metals powder such as air atomising particles which

results in sphere shape particles as compared water atomised which results in rounded

or irregular shapes as shown in Figure 2-1 [44].

Figure 2 - 1: Production of metal powder by gas atomisation, centrifugal and water

atomisation [44]

11

2.3 Binder

Binder plays significant role in transporting the metal powder to the mould cavity

during injection process. It should not interact chemically with the metal powder

during the subsequent process which may alter the composition of the final sintered

products. Many types of polymers range from thermoplastic and thermosetting can be

used as a backbone binder in MIM which hold the part retention during solvent,

wicking or thermal debinding [45]–[48]. Backbone binder itself is unable to produce

good flow in injection moldings process, which results in higher viscosity and shear

rate appreciated in the range of below 1000 Pa.s for viscosity and 102 to 105 s-1 for

shear rate. Therefore waxes in terms of vegetable oils, camphor, naphthalene, dish

soap and fish oil are common for lubrication in MIM feedstock to improve the

flowability of the feedstock.

Waxes commonly has low melting temperature which is an advantages during

debinding process in creating pores for the ease of thermal degradation of backbones

binder. With the help of pores after removing these waxes, quickest time possible for

removing backbone could be done which also reduced the possible defects on the part

in terms of part distortion, swelling and cracks. Waxes also serve as a good wetting

agent due to short molecular chain lengths low viscosities and decompose at low

temperature with small volume change compares to other polymers.

Fraction between polymer and waxes is roughly equal in its proportions. With

the aid of current research, this proportions evolved with just minimum by volume or

weight ratio of polymer is enough in holding the powder particles in place. Nowadays,

proportions of 20 to 80% by volume between polymer and waxes are possible with

appreciation of surfactants such as stearic acids (SA) and oleic acids (OA) [49]–[53].

These surfactants will increase the wettability of the binder constituents on powder

particles surface which results in reducing the amount of polymer in MIM feedstock

that can contribute in minimizing carburization on the sintered part during sintering

which could contributed to carbide formations which results in much brittle part [54]–

[56]. It is clear that the binder is the key that provides the rheological properties and

determines whether the resulting feedstock can be injection moulded without

introducing defects[57].

12

2.3.1 Backbone binder

Since polymer is the preferable backbone binder in producing acceptable feedstock,

many types of polymer have been used. Polymer from thermoplastic gives an

advantage among others type of polymer since the ability of recyclable of the feedstock

as compare to thermosetting which degrade upon reheating. This is due to the

thermosets polymer has the formation of chemical crosslinks by covalent bonds which

upon complete polymerization become infusible solids that will not soften when

reheated. Thermoplastics comprise essentially linear or lightly branched polymer

molecules, while thermosets are substantially crosslinked materials, consisting of an

extensive three-dimensional network of covalent chemical bonding [58]. Relative to

thermoplastic materials, it can be reheated several time, which likely become

favourable in the MIM feedstock. Only several polymers from thermosetting materials

being encountered for MIM feedstock, which is done by Castro et al., [45] where they

used cyclohexyl methacrylate (CHMA), ethylenglycol dimetacrylate (DMEG) and

dimethylpara toluidine (DMPT) for making AISI 316L feedstock in analysis of

mechanical properties and pitting corrosion resistance being explored although much

has been listed by Randall and Bose [59].

Various thermoplastic polymer have been encountered to be backbone

polymer for MIM such as polyethylene (HDPE, LDPE, LLDPE, MDPE),

polypropylene (PP), polystyrene (PS), ethylene vinyl acetate (EVA), polyethylene

glycol (PEG) and polymethyl methacrylate (PMMA) as shown in Figure 2-2 [22], [49],

[60]–[63].

Figure 2 - 2: Examples of polymers used in different binder formulations [62].

13

The selection of polymer usually base on the type of application. Although

polymer as binder in MIM should not dictate the final composition of the molded

materials, selection of the types of polymer also plays critical role in producing good

mechanical properties of the sintered materials due to residue produced from it through

thermal debinding. In some extent polymer selection need to consider environmental

issues due to its degradation has potential effects on human health such as styrene

monomers used in acrylonitrile-butadiene- styrene (ABS), and styrene-acrylonitrile

resins. Styrene is classied by International Agency for the Research on Cancer (IARC)

as possibly carcinogenic to humans[64]. Vinyl Chloride is used essentially to produce

polyvinyl chloride (PVC) resins also has some hazards potential such as halogen

acids[65].

Degrading these polymer during thermal debinding process could introduce

residual carbon on the sintered parts. Therefore such analysis in carbon contents have

become the interesting topic to be discussed. Carbon content after thermal debinding

was much influenced the degradation behaviour of the polymer, interaction of polymer

with the powder particles, chemistry of powder surfaces, thermal debinding

atmosphere and oxidation temperature of the powder [31].

2.3.1.1 Ethylene Vinyl Acetate (EVA)

EVA has low melting temperature which is approximately 86ºC with degradation

temperature of 520ºC [63]. It has some of the properties of a low density polyethylene

but increased gloss (useful for film) and being used as components of binder in MIM

because of its properties of non-toxic materials. It has been used widely ranging from

titanium [33], [36], [66], [67], stainless steel [12], [68]–[70], W–Cu alloys [71],

Inconel 718 Alloy [72]. It was used by Demers et al., [63] in analysing the segregation

measurement of powder injection molding feedstock using thermogravimetric

analysis, pycnometer density and differential scanning calorimetry techniques. Low

pressure MIM is possible with EVA as backbone binder since it has low melting

temperature. Fan et al., [49] used EVA in determining the effect of surfactant addition

on rheological behaviours of ultrafine 98W-1Ni-1Fe suspension feedstock and results

in better rheological properties with additional of surfactant. Youhua et al., [72] used

14

EVA with other components of binder in preparing the Inconel718 Alloy feedstock to

be used for MIM process in investigating the effects of sintering processes, hot

isostatic pressing and heat-treatment on the density, microstructure and mechanical

properties of the alloy for finding a proper way to prepare a high performance nickel

based alloy through MIM-sintering-HIP-heat treatment technology. Highest sintered

relative density of 98% can be achieved with superior mechanical properties was

achieved. Li et al., [73] used EVA in preparing the 17-4PH stainless steel for feedstock

preparation where low pressure injection moulding process was possible with the used

of paraffin wax (PW) and stearic acids. The lowest flow exponent for 68% powder

loading indicates that there is a best powder binder ratio for MIM feedstock to get

quick powder repacking and binder molecule orientation during moulding.

2.3.1.2 Polyethylene (PE)

Polyethylene polymer in MIM can be devided into low density polyethylene (LDPE),

high density polyethylene (HDPE) and medium density polyethylene (MDPE). It is

most common plastic used for packaging, toys and bullet proof vest. It consists of

nonpolar, saturated, high molecular weight hydrocarbons. In MIM, PE has been used

for binder in producing feedstock such as titanium feedstock [74]–[77], stainless steel

[52], [78], [79], zirconia [26], [80], cemented tungsten carbide [81] and among other

materials. The used of this binder shows good flowability of feedstock inside the

mould cavity and rheological characteristic. Subsequent process of the MIM showing

good part retention after solvent debinding without any parts defect such as swelling

or part cracks. The sintering condition with this type of binder shows good mechanical

properties.

2.3.1.3 Polymethyl Methacrylate (PMMA)

Using PMMA as binder in MIM was found in making the feedstock of stainless steel

[82], [83], titanium [84], tungsten carbide cobalt [85] and many other material

applications. The wide used of PMMA as backbone binder was due to its ability to

mix of powder with PMMA at room temperature with the help of acetone. Good part

shape retention also contributes to this wide usage of this polymer in MIM. Good

15

rheological characteristics and high powder loading on water atomised 316L powder

was determined by Ibrahim et al., [86]. Subsequent process of solvent, thermal

debinding and sintering also shows good mechanical properties and characteristic.

Table below shows application of PMMA as binder by other researchers in their

research.

2.3.1.4 Polypropylene (PP)

PP also known as polypropene, is a thermoplastic polymer used in a wide variety of

applications including packaging and labeling, textiles, stationery, plastic parts and

reusable containers of various types, laboratory equipment, loudspeakers, automotive

components, and polymer banknotes. An addition polymer made from the

monomer propylene, it is rugged and unusually resistant to many chemical solvents,

bases and acids. Kong et al., [37] did comprehensive study of determining the best

binder formulation between LDPE and PP as backbone binder. The PP and LDPE was

mixed with secondary binder of carnauba wax (CW) and paraffin wax (PW) with

addition of stearic acids (SA) as wetting and lubrication agents. Different molecular

weight of PP and LDPE have been tested with 60% powder loading of gas atomised

316L stainless steel powder (D50 = 3µm) . The best selection of binder were based on

mixing torque and rheological behaviour of the feedstock with different binder

composition. They found that, binder composition containing the PP with PW and SA

was better since it produced low mixing torque and low viscosity for rheological

behaviour. This binder formulation was then being further analysed for searching the

critical and optimum powder loading of stainless steel powder. From their results a

good sintered parts was obtained and optimal powder loading of 64 vol.% was

achieved. Other researchers also used PP as backbone binder in making their feedstock

for stainless steel powder and found that optimum powder loading were obtained

besides good rheological characteristics and sintered parts [87][88]. Other than that PP

was able to be mixed with other secondary binder like PEG, PW, palm kernel, palm

stearin and CW [10], [51].

Besides its usage in making the MIM feedstock, PP also being used in CIM

as binder in making the CIM feedstock. Onbattuvelli et al., [89] used PP as backbone

binder determining the effects of nanoparticle addition on binder removal of silicon

16

carbide injection moulded specimens. No defects were found for their debinding

analysis with the usage of PP as backbone binder. Aggarwal et al., [90] used PP in

their niobium feedstock for determining the master decomposition curve for binder

used in PIM where this method can predict the remaining amount of binder during the

debinding process, and such can help to optimize the binder composition without

additional experiments.

In making a feedstock of titanium, PP also has been used as backbone binder

by other researchers [91][74] and found that thermal debound and sintered of micro

parts shows no sign of defects. This indicates that the usage of PP as backbone binder

can be used as binder even for the difficult or critical powders such as titanium

feedstock.

2.3.2 Secondary binder

Secondary binder was name because of its ability to decrease the viscosity and increase

the wettability and miscibility of the feedstock during the injection moulding process.

It was not meant for powder particle holder since it has low molecular weight which

results in low melting temperature. Many types of polymer, waxes and plasticizers has

been encountered as secondary binder in MIM and CIM such as polyethylene glycol

(PEG), carnauba wax [92], paraffin wax [70], peanut oil, palm kernel and palm stearin.

2.3.2.1 Polyethylene Glycol (PEG)

PEG is a polyether compound with many applications from industrial manufacturing

to medicine. Due to its low melting temperature, PEG was used as secondary binder

in most MIM application related to feedstock. Unlike the polymer/wax binder systems

which used organic solvents frequently in solvent debinding process which are

flammable, carcinogenic and environmentally unacceptable, PEG is soluble in water.

This advantages contribute to very safe chemicals and are used quite extensively in

food industry and allowed from the local water authorities to dump the water/PEG

containing solvents into the drain after debinding [57], [93]. Yang et al., [57] use

different molecular weight of PEG in determining its effect on rheological behaviour

of injection moulding alumina feedstock. They found that PEG with highest molecular

17

weight (20K) was better as compare to low molecular weight (1K and 1.5K). The

backbone binder they used for their research was polyethylene wax. Chen et al., [77]

used PEG along with PMMA as backbone binder and stearic acid for wettability

agents. Analysis of PEG removal inside the water was increase with temperature and

diffusion of PEG was low at room temperature. Porosity increase with debinding time

base on the surface porosity of the green parts. This shows that PEG usage in MIM as

binder also shows good flowability in MIM. Krauss et al., [93] develop a model for

PEG removal in alumina injection moulded part. They found that the pore diameter

remain the same throughout the debinding time but the volume or number of pores

inside the specimens was increased. Hayat et al., [84] use the same experimental

method by Yang et al., [57] where the same molecular weight of PEG was used. They

conclude that the PEG with higher molecular weight shows good rheological

behaviour due to the interaction between powder and polymeric binder, as a result of

increased number of hydrogen bonds on the longer PEG molecule chains.

The used PEG with cellulose acetate butyrate (CAB) [84], [94], [95] as

backbone binder results in pseudoplastic behaviour and a global viscosity model

involving all of the dependent variables, including shear rate, temperature, solid

loading and particle sizes was achieved. Sharmin and Schoegl [23] used PEG (6000

molecular weight) along with EVA in analysing the two-step debinding and co-

extrusion of ceramic-filled polyethylene butyl acrylate (PEBA) and EVA blends. Good

rheological behaviour was achieved. Results of solvent debinidng of EVA-PEG was

better as compare to PEBA-PEG binder due to compatibilities between PEG and the

thermoplastic binder which in this case EVA shows better compatibility with PEG

than PEBA, and the slower removal rate and higher torque is attributed to a finer

dispersion of PEG within the blend. Thavanayagam et al., used PEG of 8000 molecular

weight as binder in titanium feedstock and good rheological behaviour was achieved.

2.3.2.2 Paraffin wax (PW)

Paraffin wax is a white or colourless soft solid derivable from petroleum, coal or oil

shale, which consists of a mixture of hydrocarbon molecules containing between

twenty and forty carbon atoms. Common applications for paraffin wax

include lubrication, electrical insulation, and candles.

18

Detail used of PW was elaborated by Zaky et al., [96] where they use different

molecular weight of PW ranging from 378 to 572 to investigate the influence of

paraffin wax characteristics on the formulation of wax-based binders and their

debinding from green moulded parts using two comparative techniques. The mixing

time and temperature were fixed at 150ºC and 30 minutes mixing time. Results of their

studies indicates that mixtures of EVA as backbone binder and PW of high molecular

weight was better since it has good compatibility and rheological properties as it has

viscosity below 10Pas which is suitable to fabricate homogenous feedstock during

compression or injection moulding process. They also conclude that solvent

immersion is a preferable technique as it saves the amount of solvent used as compared

with the evaporation–condensation technique.

You et al., [97] use PW as backbone binder in making low pressure injection

moulding in making micro gear. They used nano powder in making the feedstock and

successfully producing moulded gear which had a sound surface, uniform shape and

homogeneous microstructure even after thermal debinding process. The debound gear

of the micro-nano powder underwent isotropic shrinkage and near full densification

during sintering. Other application of PW as binder were shown by Sotomayor et al.,

[98] where they used PW with high density polyethylene (HDPE) as backbone binder

with formulation of 50/50 between secondary and primary binder for fremixed of

ferritic and austenitic stainless steel. Results shows that the PW was successfully

mixed with HDPE and solvent, thermal debinding and sintering process was

successfully being done without any defects. Four composition of binder was used by

Li et al., [99] in producing the molybdenum feedstock where PW as the major

components of the binder beside the HDPE, EVA and stearic acids. These types of

binder composition usually used for thermal debinding process only where solvent

debinding were not been used. All the injected parts were free from defects.

2.3.2.3 Carnauba wax

Carnauba wax is a wax from a plants which is obtained from the leaves of the carnauba

palm by collecting and drying them, beating them to loosen the wax, then refining and

bleaching the wax. Carnauba wax contains fatty acid which known to be good agent

for binder in MIM [100]. In MIM and CIM, carnauba wax has long been known for

19

its suitability as binder components. It has melting temperature of 84ºC which was

higher as compare to other types of waxes [92]. Supriadi et al., [12] used carnauba

wax for their wax binder systems and good mouldability shape was produced due to

its low heat capacity which in turns has high cooling rate and producing good shape

retention. Ahn et al., [101] has include carnauba wax in their analysis of determining

the effect of powders and binders on material properties and molding parameters in

iron and stainless steel powder injection molding process. All the properties of the

binder composition shows good pseudoplastic behaviour.

2.3.2.4 Palm kernel and stearin

Palm kernel and stearin was comes from palm oil plants which contains rich amounts

of fatty acids. The composition of fatty acids from palm kernel is shown in Table 2-1;

Table 2 - 1: Fatty acid composition (%) of NIE, EIE and CIE 50:50 PO:PKO blend

fractions [102]

As can be seen C18:0 and C18:1 were the carbon number of stearic acid and

oleic acid. This shows that this palm kernel were suitable to be used to replace the

function of wax and surfactant in a binder system to ensure good wetting of the powder

[51]. Omar et al., [51], [79], [103] quite intensively used palm kernel or stearin in their

research of producing 316L stainless steel powder feedstock. With this binder

composition, solvent and thermal debinding was successfully being done without any

20

defects. Sintering process of the parts also indicates good achievement where relative

density of 97% was achieved.

2.3.3 Surfactants

Polymeric surfactants are essential materials for preparation of many disperse systems,

of which we mention dyestuffs, paper coatings, inks, agrochemicals, pharmaceuticals,

personal care products, ceramics and detergents [50]. In PIM surfactants was used to

avoid particles agglomeration, wetting agents and lubrication. Surfactants such as oleic

and stearic acids was used to improve powder dispersion during mixing [104]. Several

analysis has been done in determining the influence of surfactant on suspension

structure and green microstructure of injection-moulded parts.

Fraction between polymer and waxes is roughly equal in its proportions. With

the aid of current research, this proportions evolved with just minimum by volume or

weight ratio of polymer is enough in holding the powder particles in place. Nowadays,

proportions of 20 to 80% by volume between polymer and waxes are possible with

appreciation of surfactants such as stearic acids (SA) and oleic acids (OA). The aims

to reduce the amount of polymer in MIM feedstock can contribute in minimizing

carburization on the sintered part during sintering which could contributed to carbide

formations which results in much brittle part. Stearic acids is known for low cost polar

molecule with molecular structure of CH3(CH2)16COOH and low melting temperature.

This wetting agent will improve wettability of the polymer and powder particles by

lowering the contact angle by decreasing the surface energy of the binder-powder

interface[59]. The ability of bridging the property of polymer could increase the

powder loading and results in lowering shrinkage value and reduces the parts from

slumping during thermal debinding and sintering. Surfactants also reacts as internal

lubricant (incorporated into the host resin during production or compounding), which

promotes fusion, and reduce melt viscosity and friction or increase slipperiness

between polymer particles before melting.

Tseng et al., [104] has tested several quantity of stearic acids on the zirconia

feedstock. The range of addition of stearic acid was between 3 vol.% to 17 vol.% and

was found that the pore size of the reduces with increasing the fraction of stearic acids.

This indicates good packing structure of the green parts and also leads to low viscosity

21

of the feedstock. They also found that although higher contents of stearic acid leads to

good viscosity and particles packing, too high fraction of stearic acid also leads to high

cracks during thermal debinding.

Comparison between oleic, stearic and 12-hydroxystearic acids on

rheological behaviour of alumina powders also been done by Tseng [104]. They

conclude that the viscosity of the suspension was lower for stearic acids and followed

by oleic and 12-hydroxystearic acids. Li et al., [105] did the analysis of different

fraction of stearic acids on making the 17-4PH stainless steel feedstock and found that

0.2% theoretical calculation was enough in producing single molecule layer of stearic

acid on the powder surface but higher fraction were needed for irregular shape

particles. They also found that as the fraction of stearic acid increase, the wetting angle

decrease. Fan et al., [49] have determining the influence of stearic acid during ball

milled the ultrafine 98W-1Ni-1Fe and found that it improves the particle sizes

distribution of the ball milled powder, reduce the mixing time for homogeneity of

feedstock, better rheology at lower temperature but opposite when higher temperature

were used and reduces the temperature required for injection moulding of 98W-1Ni-

1Fe powder. Therefore, the used of surfactant especially stearic acid for binder in MIM

becomes common such as in making the water atomised 316L stainless steel feedstock

[52], [106].

2.4 Restaurant waste lipids as binder

Domestic and commercial food establishments generate large volumes of wastewater,

in the form of grey water or sullage that contains significant amounts of fats, oil and

grease (FOG) or RWL. FOG must be separated from wastewater prior to entering the

sewage system, primarily because of its propensity to block municipal sewer lines and

disrupt the effective operation of downstream treatment processes [107]. RWL can be

recovered efficiently from grease interceptors for biodiesel production or other

cosmetics products. RWL is susceptible to hydrolysis because of its inherent high

moisture content and the presence of lipases associated with food residuals in the

grease interceptors. Since the evolved of engine diesel by Rudolf Diesel which tested

his engine with vegetable oils as fuel, many are drawback to see vegetable and animal

fats as biodiesel fuel for substituting the fossil fuel in minimizing the environmental

22

pollutions and reducing the dependence on fossil fuels [108]. The number of waste oils

and fats is expected to increase with urbanization, life style changes and nutrition

transition due to occupational which time consuming which also shifted the diets

towards fast foods [3].

Williams et al., [109] have characterized the FOG deposits in sewers on

several locations such as pumping station, sewers and sewage works. They found that

percentage of free fatty acids (FFA) were shown as Table 2-3 and Figure 2-3. They

also found that the majority of the deposits contain FFA of palmitic, oleic, stearic and

linoleic acid.

Table 2 - 2: % mass fatty acids profiles of cooking fats and oils [109]

Figure 2 - 3: Mean concentrations of fatty acids in the FOG deposits [109]

It is stated that RWL in restaurants sewers line are a major problem and can

cause sewer overflows, resulting in environmental damage and health risks [109]. It is

the challenge how this waste can be used in the manufacturing area since it has

composition of different organic materials. It is found that this RWL contains high

energy and oil recovery which can be obtained from this abundant source of energy

[15]. In terms of Metal Injection Moulding process the RWL seems could be used in

23

the production of feedstock since it has the mixture of animal, vegetable fats and

several organic acids. Table 2-2 shows the reported fatty acids present in restaurant

waste lipids.

Table 2 - 3: Reported fatty acids present in grease trap [110]

Montefrio et al., [107] also found the same FFA in their analysis of fats, oil

and grease from grease interceptors for biodiesel production. They found that higher

FFA in the grease interceptors and the results were compared with FFA contains in

palm oils, animal fats (tallow) and lards as shown in Table 2-4;

Table 2 - 4: Fatty acid and FFA profile of FOG samples and neat palm oil [107]

Since RWL contains of animal fats and vegetable oils, Banković-Ilić et al.,

[111] done some classification of FFA on several types of animal fats and vegetable

24

oil as shown in Table 2-5. All the vegetable oils and animal fats contains stearic acids

and oleic acid which useful as surfactant for dispersing metal powder in MIM

feedstock.

Table 2 - 5: Fatty acids composition of some vegetable oils and animal fats [111]

Although much discussion on FFA contain in RWL, much was concerning

its application on biodiesel [16], [110], [112], [113]. Therefore the use of RWL for

MIM binder seems suitable to replace the function of wax and surfactant in a binder

system to ensure good wetting of the powder since the RWL were either soft or waxy

in room temperature.

2.5 Stainless steel 316L feedstock

Stainless steel powder can be divided into of water atomised and gas atomised powder

particles. Water and gas is named based on its process for producing the powder

particles. Water atomised have round or irregular shapes as compared to gas atomised

which have the spherical shapes. Examples of water and gas atomised 316L stainless

steel powder is shown in Figure 2-4.

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