MOLD FILLING CHARACTERISTICS AND MOLECULAR ORIENTATION IN INJECTION MOLDING OF LIQUID CRYSTALLINE COPOLYESTERS OF POLY (ETHYLENE TEREPHTHALATE) by Chieu Dinh Nguyen Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE in Chemical Engineering APPROVED: D. G. Baird, Chairman J. E. McGrath G. L. Wilkes December, 1982 Blacksburg, Virginia
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MOLD FILLING CHARACTERISTICS AND MOLECULAR ORIENTATION IN INJECTION MOLDING OF LIQUID CRYSTALLINE COPOLYESTERS
OF POLY (ETHYLENE TEREPHTHALATE)
by
Chieu Dinh Nguyen
Thesis submitted to the Faculty of the
Virginia Polytechnic Institute and State University
in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE
in
Chemical Engineering
APPROVED:
D. G. Baird, Chairman
J. E. McGrath G. L. Wilkes
December, 1982
Blacksburg, Virginia
ACKNOWLEDGEMENTS
The author wishes
Donald G. Baird
to express his appreciation to Dr.
for his advice, criticism and
recommendations during the course of this work. He would
also express thanks to Dr. Garth L. Wilkes and Dr. James E.
McGrath for their interests of being the members of the
graduate committee.
The author also wishes to thank Dr. G. Ifju for his
permission to use the Spencer 860 Sliding Microtome. He
would also like to express his deep appreciation to Billy
Williams for the excellent machine works in constructing the
capillaries and molds.
Last but not least, he would like to express his
sincere gratitude to his friends Eugene Joseph, Ramesh
Pisipati, Dr. Athanasios E. Labropoulos, Kao Chun Hawn and
Din-Shong Done for their help and guidance. All this would
not have been possible without the help, criticism and
encouragement of Thuy Tran.
ii
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ........................................ ii
TABLE OF CONTENTS ...................................... iii
LI ST OF FIGURES .......................................... v
LIST OF TABLE .......................................... xiv
Chapter Page I . INTRODUCTION ....................................... 1
II. LITERATURE REVIEW .................................. 5
Liquid Crystalline Order ........................ 6 General ...................................... 6 The Thermotropic Liquid Crystalline system
Poly (Ethylene Terephthalate) and p-Hydroxybenzoic Acid .................... 9
Rheological Properties of Thermotropic Liquid Crystalline Polymers .................. 14
The Mechanism of Skin-Core Formation in Injection Molding ........................ 22
The Flow of Polymer Melt in Injection Molding ............................... 22
The Skin-Core Morphology of Injection Molded Objects ........................ 26
2.1.1 Schematic representation of Mesophase Type ........ 18
2.1.2 Poly (Ethylene Terephthalate) and its Copolymers with p-Hydroxybenzoic Acid ............ 19
2.1.3 Effect of p-Hydroxybenzoic Acid Content on Melt Viscosity at 275 C (Jackson and Kuhfuss, 1976) ................................... 20
2.1.4 Effect of Shear on Melt Viscosity of PET Modified with p-Hydroxybenzoic Acid (Jackson and Kuhfuss, 1976) ...................... 21
2.2.1 Schematic Representation of the Flow Pattern in the Central Portion of the Advancing Front between two Parallel Plates (Tadmore, 1974) ........................... 28
2.2.2 Flow Pattern in the Advancing Front between Two Parallel Plates (Tadmore, 1974) .............. 29
2.2.3 Effect of Thickness on Along-The-Flow Flexural Modulus of PET Modified with 60 Mole % p-Hydroxy-benzoic Acid (Jackson and Kuhfuss, 1976) ......... 30
2.2.4 Schematic Diagram of the Velosity Profile of The Flow behind the Front and its Corresponding Shear Rate ....................................... 31
2.2.5 Tensile Bar (Schematic) Showing the Arrangement of the Morphologic Zones (Kantz et al., 1972) .... 32
2.3.1 Mold Filling Patterns in Different Geometry ...... 40
2.3.2 Mold Filling Characteristics in Rectangular Cavity ........................................... 41
4.1. 6 Typical Bagley Plot for PET Homopolymer .......... 7 6
4.1.7 Entrance Pressure Loss versus Apparent Shear Rate for 60 Mole% PHB/PET ....................... 77
4.1.8 Entrance Pressure Loss versus Apparent Shear Rate for 80 Mole% PHB/PET ....................... 78
4.1.9 Entrance Pressure Loss versus Apparent Shear Rate for PET Homopolymer ......................... 79
4. 1. 10 Wall Shear Stress versus Apparent Shear Rate for 60 Mole % PHB/PET at 275 c .............. 80
4.1.11 Wall Shear Stress versus Apparent Shear Rate for 80 Mole % PHB/PET at 305 c .............. 81
4 .1.12 Wall Shear Stress versus Apparent Shear Rate for PET Homopolymer at 285 c ................ 82
4.1.13 Melt Viscosity as a Function of Wall Shear Rate for 60 Mole % PHB/PET with Capillary Diameter of 0.027 inch ........................... 83
4.1.14 Melt Viscosity as a Function of Wall Shear Rate for 80 Mole %PHB/PET with Capillary Diameter of 0.05 inch ............................ 84
4.1.15 Melt Viscosity as a Function of Wall Shear Rate for 60 Mole % PHB/PET with Capillary Diameter of 0.07 inch ............................ 85
4.1.16 Melt Viscosity as a Function of Wall Shear Rate for 80 Mole % PHB/PET with Capillary
vi
Diameter of 0.027 inch ........................... 86
4.1.17 Melt Viscosity as a Function of Wall Shear Rate for 80 Mole % PHB/PET with Capillary Diameter of 0.05 inch ............................ 87
4.1.18 Melt Viscosity as a Function of Wall Shear Rate for 80 Mole % PHB/PET with Capillary Diameter of 0. 07 inch ............................ 88
4.1.19 Melt Viscosity as a Function of Wall Shear Rate for PET Homopolymer with Capillary Diameter of 0.027 inch ........................... 89
4. 2. 1 Di stance from Ga.te versus Time for Various Fluid Pigments in a Cold Mold (Mold Temp.= 100 C, Cavity thickness= 0.125 inch, Injection Speed = 40 cm/min) ..................................... 92
4.2.2 Distance from Gate versus Time for Various Fluid pigments in a Hot Mold (Mold Temp.= 200 C, Cavity thickness= 0.125 inch, Injection Speed = 40 cm/min) ..................................... 93
4.2.3 Velocity of Various Fluid Pigments versus Distance from Gate in a Cold Mold (Mold Temp.= 100 C, Cavity thickness= 0.125 inch, Injection Speed = 40 cm/min) ............................... 94
4.2.4 Velocity of Various Fluid Pigments versus Distance from Gate in a Hot Mold (Mold Temp.= 200 C, Cavity Thickness= 0.125 inch, Injection Speed = 40 cm/min) ............................... 95
4.2.5 Longitudinal Section of Short-Shot Type of Injection for 60 Mole% PHB/PET .................. 96
4.2.6 Longitudinal Section of Short-Shot Type of Injection for 80 Mole% PHB/PET .................. 97
4.2.7 Longitudinal Section of Short-Shot Type of Injection for PET Homopolymer .................... 98
4.2.8 Photograph of Section Cut Transverse to the Flow Direction ........................................ 99
4.3.1 Shrinkage of the Microtomed Samples of 60 Mole % PHB/PET (Mold Temp. = 100 C, Melt Temp.= 275 C, Injection Speed= 20 cm/min., Cavity thickness= 0.1250 inch) ................... 102
4.3.2 Shrinkage of the Microtomed Samples of 60 Mole % PHB/PET (Mold Temp.= 100 C, Melt Temp. = 285 C, Injection Speed= 20 cm/min.,
4.3.21 Comparison of the Across the Flow Shrinkage of The Microtomed Samples of 60 Mole % PHB/PET in two Seperate Runs (Injection Speed = 20 cm/min, Cavity Thickness= 0.125 inch) .................. 122
5.1.1 Viscosity versus Wall Shear Rate for PET/60%PHB at 260 c ........................................ 12 8
5.1.2 Viscosity versus Wall Shear Rate for PET/60%PHB at 275 c ........................................ 12 9
5.1.3 Viscosity versus Wall Shear Rate for PET/60%PHB at 285 c ........................................ 13 0
5.1.4 Viscosity versus Wall Shear Rate for PET/80%PHB at 305 c ........................................ 131
ix
5.1.5 Viscosity versus Wall Shear Rate for PET/80%PHB at 315 C ........................................ 132
5.1.6 Viscosity versus Wall Shear Rate for PET Homopolymer at 275 C ....... ~· ................... 133
5.1.7 Viscosity versus Wall Shear Rate for PET Homopolymer at 285 C ............................ 134
5.1.8 Schematic Diagram of Capillary Used in This Work (A) and That Used by Jerman (B), (Jerman, 1980) .................................. 135
5.2.1 Comparison of Viscosity for PET/60%PHB Measured at 260 C Using Capillaries with Different Diameters ........................ 141
5.2.2 Comparison of Viscosity for PET/60%PHB Measured at 275 C Using Capillaries with Different Diameters ........................ 142
5.2.3 Comparison of Viscosity for PET/60%PHB Measured at 285 C Using Capillaries with Different Diameters ........................ 143
5.2.4 Comparison of Viscosity for PET/80%PHB Measured at 305 C Using Capillaries with Different Diameters ........................ 144
5.2.5 Comparison of Viscosity for PET/60%PHB Measured at 315 C Using Capillaries with Different Diameters ........................ 145
5.2.6 Entrance Pressure Loss as Function of Apparent Shear Rate for 60 Mole % PHB/PET Measured at 260 C Using Capillary with Different Diameters .. 146
5.2.7 Entrance Pressure Loss as Function of Apparent Shear Rate for 60 Mole % PHB/PET Measured at 275 C Using Capillary with Different Diameters .. 147
5.2.8 Entrance Pressure Loss as Function of Apparent Shear Rate for 60 Mole % PHB/PET Measured at 285 C Using Capillary with Different Diameters .. 148
5.2.9 Entrance Pressure Loss as Function of Apparent Shear Rate for 80 Mole % PHB/PET Measured at 305 C Using Capillary with Different Diameters .. 149
5.2.10 Entrance Pressure Loss as Function of Apparent Shear Rate for 80 Mole % PHB/PET Measured at 315 C Using Capillary with Different Diameters .. 150
x
5.2.11 Viscosity versus Wall Shear Rate for 60 Mole% PHB/PET at 275 C (without Correcting for Pressure Entrance Loss) .................................. 151
5.3.1 Distribution of Colors in a Molded Plaque of PET Homopolymer (Mold Temp.= 100 C, Melt Temp.= 285 C, Injection Speed= 40 cm/min) .................... 156
5.3.2 Velocity of Various Fluid Pigments versus Time for PET Homopolymer (Mold Temp.= 285 C, Injection Speed = 40 cm/min, Cavity Thickness= 0.1250 inch) ................. 157
5.3.3 Longitudinal Section of Short-Shot type of Injection for 60 Mole% PHB/PET ................. 158
5.3.4 Longitudinal Section of Short-Shot type of Injection for 80 Mole% PHB/PET ................. 159
5.3.5 Proposed Mold Filling Mechanism for PET/PHB Copolymer Systems ............................... 160
5.4.1 Schematic Representation of the Bulk Structure of Liquid Crystalline Copolymers of PET modified with 60 and 80 Mole% PHB ....................... 168
5.4.2 Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to the Flow Direction for 60 Mole % PHB/PET (Mold Temp. = 100 C, Melt Temp. = 275 C Cavity Thickness= 0.125 inch) .................. 169
5.4.3 Effect of Injection Speed on Shrinkage of Microtomed samples Transverse to the Flow Direction for 60 MOle % PHB/PET (Mold Temp.= 100 C, Melt Temp.= 285 C, Cavity Thickness= 0.125 inch) .................. 170
5.4.4 Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to the Flow Direction for 80 Mole % PHB/PET (Mold Temp.= 100 C, Melt Temp.= 305 C, Cavity Thickness= 0.125 inch) .................. 171
5.4.5 Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to the Flow Direction for 60 Mole % PHB/PET (Mold Temp.= 100 C, Melt Temp.= 275 C, Cavity Thickness= 0.0625 inch) ................. 172
5.4.6 Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to the Flow Direction for 60 Mole % PHB/PET (Mold Temp.= 100 C, Melt Temp. = 285 C,
5.4.7 Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to the Flow Direction for 80 Mole % PHB/PET (Mold Temp.= 100 C, Melt Temp.= 305 C, Cavity Thickness= 0.0625 inch) ................. 174
5.4.8 Effect of Cavity Thickness on Shrinkage Transverse to the Flow Direction for 60 Mole % PHB/PET (Mold Temp. = 100 C, Melt Temp.= 275 C, Injection Speed= 20 cm/min) ................... 175
5.4.9 Effect of Cavity Thickness on Shrinkage Transverse to the Flow Direction for 60 Mole % PHB/PET (Mold Temp. = 100 C, Melt Temp.= 285 C, Injection Speed= 20 cm/min) .................... 176
5.4.10 Effect of Cavity Thickness on Shrinkage Transverse to the Flow Direction for 80 Mole % PHB/PET (Mold Temp. = 100 C, Melt Temp.= 305 C, Injection Speed= 20 cm/min) .................... 177
5.4.11 Effect of Cavity Thickness on Shrinkage Transverse to the Flow Direction for 60 Mole % PHB/PET (Mold Temp. = 100 C, Melt Temp.= 275 C, Injection Speed= 40 cm/min) .................... 178
5.4.12 Effect of Cavity Thickness on Shrinkage Transverse to the Flow Direction for 60 Mole % PHB/PET (Mold Temp. = 100 C, Melt Temp.= 285 C, Injection Speed= 40 cm/min) .................... 179
5.4.13 Effect of Cavity Thickness on Shrinkage Transverse to the Flow Direction for 80 Mole % PHB/PET (Mold Temp. = 100 C, Melt Temp.= 305 C, Injection Speed= 40 cm/min) .................... 180
5.4.14 Effect of Injection Speed on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp. = 165 C, Melt Temp.= 275 C, Cavity Thickness= 0.125 inch) .................. 181
5.4.15 Effect of Injection Speed on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp. = 165 C, Melt Temp.= 285 C, Cavity Thickness= 0.125 inch) .................. 182
5.4.16 Effect of Injection Speed on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp. = 165 C, Melt Temp.= 275 C, Cavity Thickness= 0.0625 inch) ................. 183
5.4.18 Effect of Cavity Thickness on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp. = 165 C, Melt Temp.= 275 C, Injection Speed= 20 cm/min) .................... 185
5.4.19 Effect of Cavity Thickness on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp. = 165 C, Melt Temp.= 285 C, Injection Speed= 20 cm/min) .................... 186
5.4.20 Effect of Cavity Thickness on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp. = 165 C, Melt Temp.= 275 C, Injection Speed= 40 cm/min) .................... 187
5.4.21 Effect of Cavity Thickness on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp. = 165 C, Melt Temp.= 285 C, Injection Speed= 40 cm/min) .................... 188
xiii
LIST OF TABLES
3.1.1 Temperature for Viscosity Measurement of Poly (Ethylene Terephthalate) and its Copolymer of PET & p-hydroxybenzoic Acid ...................... 46
3.2.1 Gear Ratio and Speeds for Instron Model 3211 Capillary Rheometer .............................. 50
3.5.1 Compression Molding Temperature for PET and its Copolymer with PHB ............................... 61
Figure 4.2.1: Distance from Gate versus Time for Various Fluid Pigments in a Cold Mold (Mold Temp.= 100°C, Cavity Thiclmess = 0.125 inch, Injection Speed= 40 cm/min.)
Figure 4.2.2: Distance from Gate versus Time for Various Fluid Pigments in a Hot Mold (Mold Temp.= 200°C, Cavity Thiclmess = 0.125 inch, Injection Speed = 40 cm/min.)
El & 0 El 0 & 0 0 ____ ______.__, ________ ________.
0 50 100 150 200 Distance from Gate (mm)
Figure 4.2.3: Velocity of Various Fluid Pigments versus Distance from Gate in a Cold Mold (.Mold Temp.= 100°C, Cavity Thickness= 0.125 inch, Injection Speed= 40 cm/min.)
,_Q l'-
-() Q) rJl ......... ~ ~
$ •r-1 () 0 rl ~
PET HOHOPOLYMER at 285°C 0 now frcmt ~ Violet
0 Orange 8 Green
0 Red
~ EJ Blue
20 8 ~
~
0 00 ~ 0 0 0 0
~ ~
8 0 8
10 ~ 0 8 0 EJ 0
8 ~
EJ 0 0
0
EJ 0 8 EJ 0~ ~ EJ
0 .~ 0 50 100 150 200
Distance from Gate (mm)
Figure 4.2.4: Velocity of Various Fluid Pigments versus Distance from Gat~ in a Hot Mold (Mold Temp.= 200°C, ~,avity Thickness= 0.125 inch, Injection Speed= 40 cm/min.)
'° \J1
96
Figure 4.2.5: Longitudinal Section of Short-Shot type of Injection for 60 Mole % PHB/PET
97
Fisure 4.2.6: Longitudinal Section of Short-Shot Type of Injection for 80 Mole ~ PHB/PET
98
Figure 4.2.7: Longitudinal Section of Short-Shot type of Injection for PET homopolymer
99
Figure 4.2.s: Photograph of Section Cut Transverse to the Flow Direction
100
4.3 SHRINKAGE MEASUREMENT OF MICROTOMED SAMPLES
Molecular orientation generated during the injection
molding of polymer melt influences significantly the proper-
ties of the molding.
face to the core of
This orientation varies from the sur-
the ~njection molded part. Since
shrinkage depends on this state of orientation, one method
to qualitatively rate the degree of orientation is to mea-
sure the shrinkage of the microtomed samples of the injec-
tion molded parts. The state of orientation depends on many
injection molded variables, i.e. speeds of injection, cavity
thicknesses, mold temperatures, type of melt flow. Conse-
quently, the degree of shrinkage will vary with these varia-
bles as well. In this section, the plots of the percent
shrinkage of microtomed samples versus the distance from the
surface of the molded parts are shown for various injection
molded conditions. Figures 4.3.1 to 4.3.12 show the shrink-
age measurement data for the injection molding of liquid
crystalline polymer into a rectangular channel (unidirec-
tional flow). Figures 4.3.1 to 4.3.3 show these data with
injection speed of 20 centimeter per minute and cavity
thickness of 0. 125 inch. Figures 4. 3. 4 to 4. 3. 6 show data
with the same cavity thickness but with a higher injection
speed, 40 centimeter per minute. For a smaller cavity
thickness, 0.0625 inch, figures 4.3.7 to 4.3.9 show shrink-
101
age data with injection speed of 20 centimeter per minute
whereas figures 4. 3. 10 to 4. 3. 12 show shrinkage data with
higher speed of injection, 40 centimeter per minute. With
the same injection molding conditions as in the case of uni-
directional flow above, figures 4. 3. 13 to 4. 3. 18 show the
shrinkage data for radial polymer melt flow.
8
2
0 0
0
o.oo
UNIDIRECTIONAL FLOW 60 MOLE % PHB/PET at 275°C
0 0
0 0 0
[] across-the-flow direction
G) along-the-flow direction
0 0 0 Center
\ G.vi 0.02 O.OJ 0.04 0.06
Distance from Surface (inch)
Figure 4.3.1: Shrinkage of The Microtomed Samples of 60 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 275°C, Injection Speed= 20 Cm/Min., Cavity Thickness= 0.1250 inch)
Figure 5.2.7: Entrance Pressure Loss as F\Jnction of Apparent Shear Rate for 60 Mole % PHB/PET Measured at 275°C Using Capillaries with Different Diameters
Figure 5.2.8: Entrance Pressure Loss as Function of Apparent Shear Rate for 60 Mole % PHB/PET Measured at 285°C Using Capillaries with Different Diameters
-"' • t) Q)
Cl) • ~ ........ ~ ......... ~ 1\1 p..
<l
80 MOLE % PHB/PET at 305°C
105
10 1
'{ (Sec.-' ) w
8 0 0
Capillary Diameter, 1!!£h 0 0.027
0 0.05
6 o.o?
10 u.
Figure 5.2.9: Entrance Pressure Loss as Function of Apparent Shear Rate for 80 Mole % PHB/PET Measured at 305°C Using Capillaries with Different Diameters
Figure 5.3.5: Proposed Mold Filling Mechanism for PET/PHB Copolymer Systems
161
5.4 MOLECULAR ORIENTATION OF LIQUID CRYSTALLINE POLYMERS IN INJECTION MOLDING
Melt flow during the molding of ·plastics parts always
causes an orientation of macromolecules. This molecular or-
ientation influences significantly the properties of the
molding. The crack behavior, tendency to distort, corrosion
and shrinkage depend on this state of orientation (Menges
and Wubken, 1973). For liquid crystalline polymers, oriented
parts show highly anisotropic physical properties (Jackson
and Kuhfuss, 1976). This molecular orientation is due to
both the shear deformation of the melt and the flow front.
The last objective in this work is to qualitatively study
the molecular orientation generated during unidirectional
and radial types of flow. The first type of flow is thought
to result in anisotropic molecular orientation whereas the
second type of flow is thought to result in biaxial orienta-
ti on.
For unidirectional flow, the percent shrinkage of the mi-
crotomed samples as a function of distance from the surface
of the molded parts is shown in chapter 4 for 60 mole %
PHB/PET and 80 mole % PHB/PET. .All shrinkage data show a
negligible amount of shrinkage along the flow direction
whereas across to the flow direction, it is significantly
higher. To qualitatively confirm that no density change oc-
cured, the thfckness of the molded part was measured before
162
and after annealing. It was noticed that a 5 percent in-
crease in thickness results from the annealing process. The
shrinkage across to the flow direction shows a maximum peak
away from the surface of the parts. This maximum peak cor-
responds to high molecular orientation in the shear zone
layer which was discussed in chapter 2. This is not to say
that maximum orientation is found away from the surface of
molded part. According to Menges and Wubken (1973), the ab-
solute maximum orientation is always found at the surface,
since the oriented state is frozen immediately and no possi-
bility for relaxation exists. Away from the shear zone lay-
er, the percent of shrinkage decreases corresponding to less
orientation in the core.
For liquid crystalline polymer, the data in chapter 4
shows a higher shrinkage across the flow direction than that
along the flow direction. This is contrast to amorphous po-
lymer. For the latter type, higher shrinkage would be ob-
served along the flow than that of across to the flow. The
explanation for this phenomena may be found base on the work
by Joseph, Wilkes and Baird (1982). Basically, the polymer
melt of PET/PHB copolymers has been reported to be nonho-
mogenous (Zachariades et al., 1982; Meesiri et al., 1982;
Joseph et al., 1982). Using chemical etching technique on
the pressed film, Joseph et al. have shown that these copo-
163
lymers contain two phases: PET rich and PHB rich phase. For
copolymer of 60 and 80 mole % of PHB, the PHB rich phase ap-
pears to be more continuous than the PET rich phase (figure
5.4.1). They suggested that when the melt undergoes deforma-
tion, the PHB rich region would have a lower viscosity and
thus would orient along the flow and migrate towards the
surface of the injection molded parts while the more viscous
PET phase preferentially remains in the core (Joseph er al.,
1982). Since PHB segments are rigid, they do not relax much
upon annealing. Therefore, along the flow direction, the
maximum shrinkage peak close to the surface is absent.
Furthermore, since not much of shear deformation occurs in
the core and the PHB rich phase is found in the skin region,
negligible shrinkage of the microtomed sample (along the
flow direction) is observed. Consequently, the rest of the
discussion for unidirectional flow will only concern the
shrinkage across to the flow direction.
The effect of injection speed on molecular orientation
can be easily understood. With increasing injection speed,
higher force is applied and thus more oriented molecules
will immediately be frozen at the mold surface as a result
of the increases in rate of elongation and cooling rate.
Therefore, the relative maximum molecular orientation would
move to the surface. This is actually seen in figures 5.4.2
164
to 5.4.7. From these figures, the relative maximum shrinkage
corresponding to the molecular orientation of the shear zone
moves closer to the surface as the injection speed increas-
es. The fact that the magnitude of the relative maximum is
nearly the same at lower and higher injection speed is pro-
bably due to the combination of the relaxation process dis-
cussed above and the slow speed of injection (which is lim-
ited by the capability of the instrument). A lower injection
speed will result in a longer injection time and therefore a
thicker frozen layer. A higher injection speed will result
parts with higher molecular orientation along the flow. This
would give rise to anisotropic mechanical properties of the
molded parts.
The effect of gap thickness on molecular orientation can
be seen in figures 5.4.8 to 5.4.13. In these figures, the
across the flow shrinkage at the same injection speed and
different gap thickness is shown. Similar to the case of
higher injection speed, with constant injection speed, the
smaller the cavity thickness, the larger the rate of shear
deformation and the larger amount of heat removal will oc-
cur( for a smaller cavity). As a result, the thinner the fro-
zen layer will be and therefore, the relative maximum orien-
tation will move toward the surface as the cavity thickness
decreases. This is indeed observed in figures 5.4.8 to
5.4.13 for across the flow direction.
165
The discussion so far about the relative maximum
orientation beneath the surface of the molded parts may also
hold for the case of radial flow. Evidence can be seen in
figures 5.4.14 to 5.4.21. The effect of injection speed on
shrinkage of microtomed samples is shown in figures 5.4.14
to 5. 4. 17. With decreasing injection speed, the relative
maximum orientation (peak) moves toward the center of the
plaque due to a thicker frozen layer developed. The effect
of cavity thickness on the amount of shrinkage is shown in
figures 5.4.18 to 5.4.21. Similar to unidirectional case,
holding the injection speed constant and decreasing the cav-
ity thickness which lead to a larger amount of heat being
removed,. Therefore, the thinner frozen layer will be and the
relative maximum orientation will move toward the surface of
the molded parts.
The major difference between the shrinkage of parts re-
sulting from unidirectional and radial flow is that a signi-
ficant amount of shrinkage along the flow direction exists
in the radial flow case whereas it is negligible in the uni-
directional flow case. For radial flow, the radial velocity
for any type of incompressible fluid is:
Vr = V(r,z) (5.4.1)
166
The equation of continuity is:
\] • v = 0
Therefore:
= 0 and f (z)
r
The rate of deformation tensor becomes:
2 oVr ar
i = 0 -
0
2 Vr r
0
0
0
(5.4.2)
(5.4.3)
The diagonal components are related by the continuity equa-
tion (5.4.2):
d- Vr = - Vr O r r
(5.4.4)
The term on the left side of equation 5. 4. 4, )V,. , reflects or the amount of elongational strain generated along the flow
direction (r-direction). The term on the right side of the
167
equation (5.4.4), V..-. r reflects the amount of elongational
strain generated normal to the flow direction ( e -direc-
tion). These two terms would qualitatively be respossible
for the molecular orientation generated in redial flow. Ac-
cording to this equation 5.4.4, the degree of the molecular
orientation, hence the percent of shrinkage, should be in
the same order of magnitude for the flow direction and its
transverse direction (r and 6-directions respectively). In
the publication by Schmidt (1976), it was found that the ra-
dial flow beyond the entrance region can be described as a
combination of planar extension and simple shear whereas the
equation 5.4.4 only describes the planar extensioal flow be-
havior. Therefore, the magnitude of shrinkage is not the
same in the r and e-directions. Of course, more work must be
done to confirm this explanation.
In summary,from the shrinkage data shown in this section,
biaxial orientation has been generated in radial flow. The
amount of shrinkage in both the e and r-directions becomes
significant. This is the result of planar extension and
shear flow. Increasing injection speed or decreasing cavity
thickness would make the relative maximum shrinkage peak
move toward the surface as a result of higher deformation,
168
PET RICH PHASE
PHB RICH PHASE
Figure 5 .4. 1 Schematic Representation of the Bulk Structure of Liquid erYstalline Copolymers of PET Modified with 60 and 80 Hole % PHB (from Joseph et al., 1982)
Figure 5.4.2: Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to 'lhe Fl.ow Direction for 60 Mole % PHB/PET (Mold Temp..=100°C, Melt Temp •. :;:275° C, Cavity 'lhiclmess==0.125 inch)
8
6
4
2
0 o.oo 0.01
UNIDIRECTIONAL FLOW 60 MOLE % PHB/PET at 285°C
Injection Speed, Cm /Min.
8
0
0.02 0.03 0.04 Distance from Surface {inch)
40
20
0
6
~~nter 0.05 o.06
Figure 5.4.3: Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to The Flow Direction for 60 Mole% PHB/PET {Mold Temp.=100°C, Melt Temp.=285°C, Cavity Thickness=0.125 inch)
Figure 5.4.4: Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to The Flow Direction for 80 Mole % PHB/PET (Mold '.i.'emp.=100°C, Melt Temp.=305°C, Cavity 'l'hiclmess=0.125 inch)
..... -...J .....
UNIDIRECTIONAL FLOW 60 MOLE % PHB/PET at 275°C
16 Injection Speed, Cm /Min.
~ 40
12 0 20 Q)
J ~ ~ 08 Q) 0 0 ~
04 c.ente7r 6
~ 00
o.oo 0.01 0.02 0.03 Distance from Surface (inch)
Figure 5.4.5: Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to The Flow Direction for 60 Mole % PHB/PET (Mold Temp.=100°C, Melt Temp.=275°C, Cavity Thickness=0.0625 inch)
_.. -..J I\)
16
12
08
00 o.oo
UNIDIRECTIONAL FLOW 60 MOLE % PHB/PET at 285°C
0.01
Injection Speed, Cm /Min.
0.02 Distance from Surface (inch)
Center
""' Figure 5.4.6: Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to The Flow D::;rection
Figure 5.4.?: Effect of Injection Speed on Shrinkage of Microtomed Samples Transverse to The Flow D:trection for 80 Mole % PHB/PET (Mold Temp.=100°C, Melt Temp.=305°C, Cavity Thickness=0.0625 inch)
UNIDIRECTIONAL FLOW 60 MOLE % PHB/PET at 275°C
8 Ca.vi ty Thickness, !!!9b.:
~ 0.1250 6 0 0.0625
4
2
Center 0 \
0.02 0.03 0.04 Distance from Surface (inch)
o.o 0.01 0.05 0.06
Figure 5.J,..8: Effect of Cavity Thickness on Shrinkage Transverse to The Fl.ow Direction for 60 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 275°C, Injection Speed= 20 Cm/Min.)
..... -J
"'
UNIDIRECTIONAL FLOW 60 MOLE % PHB/PET at 2a5°c
16
Cavity Thickness, ~:
~ 0.1250 0 0.0625
4
Center
0 ·\ 0 o.o 0.01 0.02 0.03 0.04
Distance from Stn"face (inch) 0.06
Figure 5.4.9: Effect of Cavity Thickness on Shrinkage Transverse to The Flow Direction for 60 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 285°C, Inject;Lon Speed= 20 Cm/Min.)
Figure 5.4.10: Effect of Cavity Thickness on Shrinkage Transverse to The Flow Direction for 80 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 305°C, Injection Speed= 20 Cm/Min.)
UNIDIRECTIONAL FLOW 60 MOLE % PHB/PET at 2?5°C
16
Ca.vi ty Thidmess, E.!£h:
~ 0.1250 12 0 0.0625
8
4
G Center 0 0 ~
o.o 0.01 0.02 0.03 0.04 0.06 Distance from Surface (inch)
Figure 5.4.11: Effect of Cavity Thickness on Shrinkage Transverse to The Flow Direction for 60 Mole % PHB/PET (Mold Temp.= 100°C, Melt Temp.= 2?5°C, Injection Speed= 40 Cm/Min.)
Figure 5.4.12: Effect of Cavity Thickness on Shrinkage Transverse to The Flow Direction for 60 Mole % PHB/PET (Mold Temp.=100°C, Melt Temp.=285°C, Injection Speed.=40 Cm/Min.)
UNIDIRECTIONAL FLOW
8 80 MOLE % PHB/PET at 305°C
Q) 6 Cavity Thiclmess, ~:
J ~ 0.1250 ~ 0 0.0625 ~ C) 4 ~
2
Center 0 ~
o.o 0.01 0.02 0.03 0.04 Distance from Surface (inch)
0.05 o.06
Figure 5.4.13: Effect of Cavity Thickness on Shrinkage Transverse to The Flow Direction for 80 Mole % PHB/PET (Mold Temp.=100°C, Melt Temp.=305°C, Injection Speed=40 Cm/Min.)
-' ()'.) 0
20
15
10
5
0 o.o 0.01
RADIAL FLOW 60 MOLE % PHB/PET at 275°c
Direction/Injection Speed
~ 9-direction, 40 Cm/Min.
0 r-direction, 40 Cm/Min.
~ 8-direction, 20 Cm/Min.
• r-direction, 20 Cm/Min.
0
Center \
0.02 0.03 0.04 0.05 0.06 Distance from Stn"face (inch)
Figure 5.4.14: Effect of Injection Speed on Shrinkage of Microtomed Samples for 60 Mole% PHB/PET (Mold Temp.= 165°C, Melt Temp.= 275°C, Cavity Thickness= 0.125 inch)
Figure 5~4.20: Effect of Cavity Thickness on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp.= 165°C, i"1elt Temp.= 275°C, Injection Speed= 40 Cm/Min.)
RADIAL FLOW 60 MOLE % PHB/PET at 285°C
DirectionLCavit~ Thickness 20 0 e -direction, 0.1250
~ r -direction, 0.1250
• e-direction, 0.0625
• r-direction, 0.0625
10
5
0 o.oo 0.01 0.02 0.03 0.04 0.05 o.06
Distance from Surface (inch)
Figure 5.4.21: Effect of Cavity Thickness on Shrinkage of Microtomed Samples for 60 Mole % PHB/PET (Mold Temp.= 165°C, Melt Temp.= 285°C, Injection Speed= 40 Cm/Min.)
Chapter VI
CONCLUSIONS
The dependence of viscosity on capillary diameters for
PET/PHB copolymer has been investigated. The mold filling
characteristics and molecular orientation in injection mold-
ing have been qualitatively studied. The following conclu-
sions may be drawn from the results of this work.
1. Unlike PET homopolymer, this liquid crystalline po-
lymer system is highly non-Newtonian and pseudoplas-
tic fluid. Increasing the degree of stiffness of the
polymer chain by increase the percentage of PHB con-
tent does not show a decrease in viscosity of the
melt as the 60 mole % PHB/PET copolymer shows lower
viscosity than the 80 mole % PHB/PET copolymer.
2. Melt viscosity of 60 mole% PHB/PET measured at 27S0 c shows a slight dependence on capillary diameter. This
is probably caused by a boundary layer of molecules
oriented parallel to the flow direction. At the
boundary, the viscosity of the melt is less than that
of the core fluid. For smaller capillary diameters,
the boundary occupies a greater percentage of the
flow channel. This explains the decrease in viscosity
with decrease in capillary diameter.
189
190
3. The reverse of the order of colors suggests that the
first material entering the mold would lay on the
wall and remained near the gate. The succeeding ma-
terial accelerates in the core, to the front, splits
and lays on the walls away from the gate.
4. Unlike amorphous polymers where the splitting pat-
terns only occur at the flow front, for liquid crys-
talline polymers, the splitting occurs even when the
fluid pigment is in the core. This splitting magni-
fies gradually and accelerate to the flow front. Upon
contacting with the cold wall, the splitting of the
fluid pigments stops and forms a "V" shape which has
the direction opposite to that of the flow.
5. The negligible amount of shrinkage along the flow di-
rection arises from the orientation of the PHB rich
region at the surf ace of the molded part and the much
less orientation of the PET region in the core. Upon
heating up to annealing temperature, the induced or-
ientation of PHB region relaxes more slowly than that
of flexible chain polymer. Also, the PET region in
the core is not oriented. Therefore, insignificant
amount of shrinkage along the flow direction is ob-
served.
191
6. For unidirectional flow, neglegible shrinkage along
the flow direction and low viscosity observed for li-
quid crystalline polymer suggest a high degree of mo-
lecular orientation developed along the flow direc-
tion during extrusion. Because of this orientation,
the molded parts possess anisotropic mechanical prop-
erties as reported by Jackson & Kuhfus (1976).
7. For radial flow, biaxial orientation was observed.
Flow beyond the gate region is a conmposi tion of
shear and planar extensional flow.
8. In general, maximum orientation due to shear zone
moves to the surface for higher injection speed and
smaller cavity thickness due to a larger rate of
shear deformation and the larger amount of heat remo-
val.
Chapter VI I
RECOMMENDATIONS
Based on the results of this work, the following is the
list of recommendations for future study in the area of pro-
cessing and rheology of copolyester of PET with p-hydroxy-
benzoic acid.
1. The behavior of viscosity for liquid crystalline po-
lymer at high shear rate should be investigated. This
can be done by measuring viscosity of these melt us-
ing capillaries with smaller diameters (i.e. !) =
0. 009 inch).
2. Since the molecular rotation of molecules in isotrop-
ic state is different from that of nematic mesophase,
further work should include NMR studies for the melts
at these states.
3. Future study should investigate the phase transition
of 60 mole % PHB/PET copolymer using differential
scanning calorimetry, X-ray diffraction, and electron
microscopy.
4. Since boundary layer effect occurs at 2 75° C for 60
mole % PHB/PET, injection molding in unidirectional
flow with the wall specially treated is a direct ap-
plication of the boundary layer.
192
193
5. Mold filling studies should be carried out at higher
injection speed for both radial and unidirectional
flow.
6. Center-gated type of injection should be further stu-
died with the lower plate rotating to further inves-
tigate the biaxial orientation of these copolymers.
7. Physical properties of each layer of injection molded
parts (from surface to core) should be measured both
along and across the flow directions to correlate
with the shrinkage data shown in this work.
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Appendix A
COMPUTER PROGRAM FOR VISCOSITY CALCULATION
Comment: c
This program is to calculate the viscosity of polymer melt from the raw data of Instron capillary rheometer model 3211. Entrance pressure loss is also calculated from the linear regression of total pressure drop vs L/D ratio (Bagley plot). Corrected wall shear stress and wall shear rates are thus obtained.
c c c c c c c c c c c c c c
c c c c c c c
c
1 100
101
2
5 6
3
Input: Speed of Plunger and Pressure readings for capillaries with different L/D ratio.
REAL D,TEMP,L(10),SPEED(l8),FORCE(18),LNGAMA(l8) REAL LNPRES(18),C(ll),LNTW(6,30),LNTWS(30) REAL APGAMA(30),PRESS(6,30),RATI0(6),PEN(30),TW(6,30) REAL LNAPGA(30), GAMAW(6,30),ETA(6,30),APRESS(6) REAL FORCES(l8,4),AGAMA(18),PRESUR(l8,4),PRESSE(30,6) INTEGER N,NDATA(18),DATA,M,K,I,S,Y INTEGER DOTS(4,130),DOT,POLYMA,POLYMB,POLYMC DATA DOT/lH*/
The data is input here: N = number of capillary, i.e. 03 D = Capillary Diameter TEMP = Melt Temperature POLYMA, POLYMB, POLYMC = name of polymer
READ (5,100) N,D,TEMP,POLYMA,POLYMB,POLYMC FORMAT (I2,lX,F7.5,lX,F5.l,lX,3A4) IF (N .EQ. 0) GOTO 600 WRITE (6,101) FORMAT (lHl) DO 6 I=l,4 DO 2 J=l,130 DOTS(I,J)=DOT CONTINUE WRITE(6,5) (DOTS(I,J),J=l,130) FORMAT(lX,130Al) CONTINUE WRITE (6,7) WRITE (6,3) POLYMA, POLYMB, POLYMC, TEMP, D FORMAT (lX, 'RHEOLOGICAL PROPERTY OF I ,3A4, 'AT I ,FS.l,lX,
C Input of Raw Data: C L(I) = Length of capillary (inch) C NDATA(I) = number of data points C SPEED(J) = speed of plunger (cm/min) C FORCE(J) = Pressure reading (kg) c
DO 40 I=l,N READ (5,200) L(I),NDATA(I) DATA= NDATA(I) DO 10 J=l,DATA READ (5,300) SPEED(J), FORCE(J) FORCES(J,I)=FORCE(J)
10 CONTINUE c C Calculation of apparent shear rate and total pressure C drop from raw data c
DO 20 K=l,DATA AGAMA(K)=2.0*SPEED(K)*((0.9525)**2)/(15.0*(((D*2.54)**3))) LNGAMA(K)=ALOG(AGAMA(K)) PRESUR(K,I)=(l.375E05)*FORCE(K) LNPRES(K)=ALOG(PRESUR(K,I))
20 CONTINUE c C Using linear least square to compute entrance pressure C loss from Bagley Plot c
CALL LEAST (LNGAMA,LNPRES,l,C,DATA) APGAMA(l)=lO.O DO 30 M=l,28 LNAPGA(M)=ALOG(APGAMA(M)) PRESS(I,M)=EXP((C(2))*LNAPGA(M)+C(l)) PRESSE(M,I)=PRESS(I,M) IF (APGAMA(M).LT.100.0) GOTO 22 IF (APGAMA(M).LT.1000.0) GOTO 24 IF (APGAMA(M).LT.10000.0) GOTO 26 GO TO 31
22 S=M+l APGAMA(S)=APGAMA(M)+lO.O GO TO 30
24 S=M+l APGAMA(S)=APGAMA(M)+lOO.O GO TO 30
26 S=M+l APGAMA(S)=APGAMA(M)+lOOO.O
30 CONTINUE 31 DO 40 Y=l,11
C(Y)=0.0 40 CONTINUE
WRITE (6,7) DO 60 M=l,28 DO 50 I=l,N RATIO(I) = L(I)/D
50 APRESS(I) = PRESS(I,M)
c
207
CALL LEAST (RATIO,APRESS,l,C,N) PEN(M) = C(l) DO 60 J=l,11 C(J) = 0.0
60 CONTINUE WRITE (6,45) (RATIO(I),I=l,3)
45 FORMAT (lX, 'SPEED*******FORCE, L/D = I ,6(2X,F6.2)/) WRITE (6,46)
46 FORMAT (lX, I (CM/MIN)' ,4X, I (KG)'//) DO 41 J=l,DATA WRITE(6,42) SPEED(J),(FORCES(J,I),I=l,N)
42 FORMAT (1X,F4.l,4(5X,F7.2)/) 41 CONTINUE
WRITE (6,7) WRITE (6,47) (RATIO(I),I=l,3)
47 FORMAT (lX, 'APGAMA*******PRESSURE, L/D = I ,6(2X,F6.2)/) WRITE (6,48)
48 FORMAT (lX, I (SEC-1)' ,6X, I (KG/M.SEC2)'//) DO 44 J=l,DATA WRITE(6,43) AGAMA(J),(PRESUR(J,I),I=l,N)
43 FORMAT (1X,F7.l,4(5X,Ell.4)/) 44 CONTINUE
C Write apparent shear rate, total pressure drop for C each capillary and entrance pressure loss. c
c
WRITE (6,7) WRITE (6,66) (RATIO(I),I=l,3)
66 FORMAT (lX, 'APGAMA******PRESSURE, L/D = I ,3(2X,F6.2),3X, +'PRESS. ENTRANCE '/)
WRITE (6,67) 67 FORMAT (lX, I (SEC-1)' ,6X, I (KG/M.SEC2)' ,33X, '(KG/M.SEC2)'//)
DO 64 J=l,28 WRITE (6,63) APGAMA(J),(PRESSE(J,I),I=l,N),PEN(J)
63 FORMAT (1X,F7.l,5(5X,Ell.4)/) 64 CONTINUE
WRITE (6,7) 7 FORMAT(lX,' '//////)
C Calculation of corected wall shear stress from total C pressure drop and entrance pressure loss c
DO 80 I=l,N WR I TE ( 6 I 3 5 0 ) I WRITE (6,400) WRITE (6,450) DO 61 M=l, 28 TW(I,M)=(PRESS(I,M)-PEN(M))*D/(4.0*L(I)) LNTW(I,M)=ALOG(TW(I,M)) LNAPGA(M}=ALOG(APGAMA(M))
61 CONTINUE DO 65 S=l,28 LNTWS(S)=LNTW(I,S)
65 CONTINUE
208
DATA = 28 c C Using Linear least square to compute the power law C index of the polymer c
CALL LEAST (LNAPGA,LNTWS,l,C,DATA) c C Calculation of corrected wall shear rate and its C corresponding viscosity c
c c c c c
c c c c c
70
80 200 300 350
400
450
500
600
DO 70 M=l,28 GAMAW(I,M)=((3.0*C(2)+1.0)/(4.0*C(2)))*APGAMA(M) ETA(I,M)=TW(I,M)/GAMAW(I,M)
WRITE (6,500) PEN(M),TW(I,M),APGAMA(M),GAMAW(I,M),ETA(I,M) CONTINUE DO 80 J=l,11 C(J)=O.O CONTINUE FORMAT (F5.3,1X,I2) FORMAT (F5.2,F7.2) FORMAT(lHl,lX, 'THE CALCULATED RHEOLOGICAL PROPERTIES ',
+I USING CAPILLARY' I I2, lX, I ARE: I//) . FORMAT(lX, 'ENTRANCE PRESSURE' ,13X, 'WALL SHEAR STRESS' ,13X,
+'RATE (SEC-1)' ,19X, I (SEC-1)' ,17X, I (PASCAL.SEC)'//) FORMAT(4X,Ell.4,19X,Ell.4,21X,F7.l,22X,F8.2,18X,F8.2) GOTO 1 STOP END
This subroutine is to calculate the slope and y-intercept of a straight line from a set of data using the linear least square method
SUBROUTINE LEAST (X,Y,M,C,DATA) DIMENSION X(200),Y(200),A(ll,ll),B(ll),C(ll),P(20) INTEGER DATA NUMBER = DATA MX2 = M*2 DO 13 I=l,MX2 P(I) = 0.0 DO 13 J=l,NUMBER
13 P(I) = P(I)+X(J)**I N = M+l DO 30 I=l,N DO 30 J=l,N K =I+J-2 IF(K) 29,29,28
28 A(I,J) = P(K) GO TO 30
29 A(l,l) =NUMBER 30 CONTINUE
B(l) = 0.0 DO 21 J=l,NUMBER
21 B(l) = B(l)+Y(J) DO 22 I=2,N B(I)=O.O DO 22 J=l,NUMBER
209
22 B(I)=B(I)+Y(J)*X(J)**(I-1) NMl=N-1 DO 300 K=l,NMl KPl = K+ 1 L=K DO 400 I=KPl,N IF(ABS(A(I,K))-ABS(A(L,K))) 400,400,401