SPE Aug15

May 8, 2006 Transmit Technology Group, LLC
Applications of
Thermoformability Analyzer
Amit Dharia
Transmit Technology Group, LLC
Irving, Texas

Objectives
• To demonstrate the need for an industry wide
standard Quantitative test method for
“Measuring” and “Reporting”
Thermoformability of plastic materials (2005)
• To illustrate applications of test equipment and
test method in understanding and resolving
issues related to Thermoformability.

Outline
• Structure-Property- Process relationship
• Current test methods
• Description of Technoform
• Application and data interpretation
• Products – Basic, Standard, Advanced
• Conclusion

Thermoforming Process
• Extruding sheet stock
• Heating sheet above Tg
• Stretching heated sheet in rubbery state
• Cooling
• Trimming
• Finishing
• Regrinding and recycling scrape

Structure - Properties -
Thermoformability
• Rate of change of strength with the change in
strain rate at forming temperature
• % Crystallinity – Breadth of rubbery Plateau
• Molecular weight, Molecular weight
distribution, molecular architecture
(branching, crosslinking) – MFR, Melt
Elasticity, Rheology

Other parameters
• Density - % filler, type of fillers, degassing
• Geometry – Thickness, area, multi-layered
structures, adhesion between layers
• Residual stresses between and within in
extruded layer sheet stock
• Thermal diffusivity (Cp, K. Rho)
• Extrusion quality ( gels, unmelts, thickness
variation, grain patterns)
• Color (IR absorption)

Test Methods
Test Method Major Short coming
MFR Easy, measure of only MW
Melt Tension > Tm, cooling effect, uni-directional, not
applicable to all materials
Sag test No external force, geometry dependent,
measure of only melt strength
Stress
Relaxation
Repeatable, correlates with Sag test,
expensive equipment
DMTA Repeatable, effect of temperature
Hot tensile test Inconsistent results, grip extrusion,
annealing

Major disadvantages of current
methods
• Most tests are conducted in melt or near melt phase
• Test Specimens do not reflect actual test geometry
(shape, size, clamping mode)
• Tests do not account for orientation, thermal stresses,
thickness variations
• Isothermal environment, does not account for transient
nature of heating/ cooling
• Effects of secondary process parameters can not be
evaluated
• Results cannot be directly used.

What processors want to know?
• Will this material thermoform?
• Will this new material process the same?
• Will this lot process the same as the last one?
• Why this lot does not process the same?
• How fast material will heat?
• What is the right forming temperature range?
• Will melt adhesion between layers survive heating and
stretching step?
• Will material discolor, fed or degrade during heating?

What processors want to
know? -II
• What is the maximum draw down?
• How fast part can be made?
• What is the MD and TD shrinkage?
• Will material tear at the corners and ribs?
• How much regrind can I use?
• Will grains retain shape and depth?
• Does extruded sheet have gels or unmelts?

What Industry Needs?
• A standard test method which reflects all unit steps –
heating, 3D stretching, forming, and cooling
• A test equipment which can be precisely controlled, is
rapid, easy to use, provides repeatable and quantitative
information, using the least amount of material.
• Easy to use “Thermoformability Index” standard for
comparing, contrasting effects of selected process/
material variables

Variables
Material Feed Stock Process
Molecular Structure Thickness Forming Method
Tg, Tm, % Xc Residual stresses Part geometry
% LCB, % Xl Layers Plug geometry
ηo, ηel Color Plug material
Rho, k, Cp Volatiles Plug temperature
Type of fillers % regrind Forming speed
% of fillers impurity
Additive package Extrusion, storage
Shrinkage

Desired Test Method
• MEANINGFUL
• Rapid
• Easy to use
• Quantitative
• Repeatable
• A good problem solving tool

Schematics of Technoform

Technoform

Test Input – Output
Input Range Output
Method Plug assist, Vacuum Temp. vs. Time
Resin Type Any type Force vs. Time
Sheet Thickness 10 mil to 375 mil Force vs. Draw
Depth
Forming Temperature 60 C to 280 C Draw vs. time
Heat Soak time Variable Force at Max
Draw Depth
Plug Material Epoxy, Polished Aluminum Force vs. Depth
Plug temperature 23 C to 120 C
Forming Speed 10- 180 mm/second
Plug Dwell time Variable
Maximum Force 100 lb
Cooling Time Variable

Typical GUI Screen
Sag
Elastic
Plastic
Strain
hardening
Thinning

Results
V,T

Melt Strength = Resistance to Deformation @ T
Melt Elasticity =Capability to deform @ T
Stress
(Force)
% Draw or A/Ao
Strain Hardening

Heating rates for various plastic materials
(Heater at 600 C, 3” from upper, 2” from lower)
30
80
130
180
230
0 20 40 60 80
t (seconds)
T(c)
PP
HDPE
HIPS
PVC
ABS
Acetal
PMMA
Nylon

Effect of Crystallinity
0
5
10
15
20
25
30
50 70 90 110 130
Forming distance, mm
Force(N)HDPE PP HIPS PETG ABS PMMA PVC

Comparison of various PE
LDPE, LLDPE, MDPE @ 60 mm/s
0
5
10
15
20
25
30
35
0 20 40 60 80
Depth, mm
Force,lbf
LDPE120
LLDPE120
MDPE120

Effect of Forming Temperature
0
2
4
6
8
10
12
14
125 145 165 185
Temperature (C)
Force(N)
ABS
PP
HDPE
HIPS
PETG
PMMA
ACETAL

Force100 = f (T, V, material)
• F(ABS) =9.2348 -0.0547 T (R2 =99%)
• F(PMMA)=7.1587 -0.0341 T(R2=98%)
• F(PETG)=10.096 -0.0601 T (R2=92%)
• F(HIPS)=9.6782 - 0.0503T(R2=93%)
• F(HDPE)=5.2771 -0.0266 T (R2=86%)

Effect of Melt Strength
(% HMSCOPP in COPP)
0
0.5
1
1.5
2
2.5
0 50 100 150
0
20
40
60
80
100

HMSCOPP
0
10
20
30
40
0 50 100 150
Draw Depth (mm)
Focelbf(170C)
0
1
2
3
4
Forcelbf
170 C
180 C
190 C
210C

COPP vs. HMSCOPP
40
60
80
100
120
170 180 190 200 210
T, C
DrawdepthatYield
COPP
HMSPP

Isothermal vs. Non-Isothermal
20 mm/s, 130 C, HIPS
0
2
4
6
8
10
12
1 2 3 4 5
Draw Depth (Inches)
Force(lb)
130 C-20I 130 C-20NI

Effect of Plug Temperature
HIPS 35 mil, 130 C, 40 mm/s, No control
0
2
4
6
8
10
12
0 20 40 60 80 100 120 140
Draw Depth, mm
Force,Lbf
Series1
Series2
Series3

Effect of Plug Temperature-II
35 mil HIPS, 130 C, 40 mm/s, Plug at 23 C
0
2
4
6
8
10
12
0 20 40 60 80 100 120
Depth, mm
Force,Lbf
#1
#2
#3
#4

Effect of Plug induced cooling -III
HIPS (with and without hole)
0
0.2
0.4
0.6
0.8
1
1.2
0 20 40 60 80 100 120
Draw Depth, mm
Force,lbf
wo with

Effect of Plug Material
35 mm HIPS, 40 mm/s, 130 C
0
1
2
3
4
5
6
0 20 40 60 80 100 120
Depth (mm)
Force(lb)
WF WFT Bix

Effect of Sheet Thickness
on heating rates
0
100
200
300
0 500 1000
time (sec)
Surface
Temperature(C)
100 mil 150 mil 250 mil

Effect of Sheet Thickness
0
1
2
3
4
5
6
7
8
9
0 20 40 60 80 100
Depth (mm)
Froce(lbf)
95 150 250

Effect of Color on heating Rate
32
82
132
0 50 100
time (sec)
Surface
Temperature(C) Red Blue Metalic

Effect of Color
CoPP, 35 mil, 40 mm/s, 160 C
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 20 40 60 80 100 120
Depth (mm)
Force(lb)
0
2
4
6
8
10
12
blue red Metallic

Effect of Lot to Lot Variation
170 C, 40 mm/s, 190 mil TPO
0
1
2
3
4
5
6
7
8
9
10
0 10 20 30 40 50 60 70
Depth (mm)
Froce(lbf)
1-1 1-2 1-3

Effect of Regrind (FR-ABS)
125 mil, 160 C, 40 mm/sec
0
2
4
6
8
10
12
14
0 20 40 60 80 100
Depth (mm)
Froce(lbf)
50% RG 100% RG

Effect of Regrind (GPPS)
125 mil, 190 C, 40 mm/sec
0
2
4
6
8
10
12
14
0 50 100
Draw Depth (mm)
FormingForce(lbf)
PS Virgin
PS Regrind

Processing Window of Commercial TPOs
0
10
20
30
0 20 40 60 80 100
Depth (mm)
Force(lbf)
170 180 190 170TPO

COPP- Nano clay Composites
Force @ yield
0.9
0.95
1
1.05
1.1
1.15
1.2
COPP(0.8) COPP2.6NC COPP2.6C
Fy,190

CoPP-Nano Clay Composites
50
75 COPP(0.8)
COPP2.6N
C
COPP2.6C
DrawDepth@yield
Dy,190/100

How to Standardize?
• Thermoforming Index (TFI)
– Force required to draw a sheet of thickness X at
speed Y mm/second using a Plug of specified
geometry G at Temperature Tf to area ratio A
(or volume ratio V), with plug temperature Tp.
• TFI = [Force (M, Tm)/ Force (GPPS, Ts)]

Thermoforming Index (example)
• 125 mil, GPPS, 40 mm/s force to draw to 45
mm depth @ 160 C is 7 lbs.
• 125 mil, PP, 40 mm/s Force required to
draw to 45 mm depth @ 170 C is 3.5 lbs.
• TFI of PP = F 45,PP * thickness (GPPS)
F 45, GPPS * thickness (PP)
= 3.5*0.125/ 7* 0.325
= 0.5

Relaxation Time (s) Vs. Force @ 75 mm depth
R2
= 0.9968
0
2
4
6
8
10
12
0 2 4 6 8
Relaxation Time (sec)
FormignFroce(75mm)
PP, 165 C
HDPE,140C HIPS,160 C

Conclusions
• Easy and rapid test method with overall operation
similar to actual Thermoforming process
• Economical vs. Field trials
• Test equipment and method can be applied to wide
range of Industrial applications
• TFI offers one simple number (like MFI)
representing material’s Thermoformability
• Test equipment and method can be applied to wide
range of Industrial applications

SPE Aug15

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