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Rubber Process Analyzer – RPA Applications: Bridging the Gap Between Polymer/Compound
Properties and Processing Behavior
Greg Kamykowski, PhDAlina Latshaw, PhD
TA Instruments – Waters LLCAkron, OH
September 2017
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What do we want to know about rubber?
Processing
Molding
Molecular Weight
Additives
Performance
Mixing
Aging Curing
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0,01 0,1 1 10 100
0,01
0,1
1
.
h
shear rate, g
vis
cosity
ML1+4
Mooney Tests
Sample
Rotor
Mooney-V
iscosity [
MU
]
Time [min]
• Mooney Viscosity•One point method•Single shear rate: 1.6 s-1 (2 rpm)
• Mooney Relaxation•Sensitive to elasticity•Relates to die swell
•Mooney Scorch
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Mooney viscosity: meaning and limitations
Average molecular Weight
Mooney viscosity
• Increases approx. linearly with polymer Average Molecular Weight (AMW)… plateau at high Mw
• May decrease with very high Mw polymers…. due to polymer fracture in viscometer cavity
Vistanex (exxon Mobil)
AMW(k. g/Mole)
ML(1+4)125° C
MML80 900 69.0
MML100 1240 57.0
MML120 1660 51.1
MML140 2150 48.0
40
50
60
70
80
500 1000 1500 2000 2500
ML
(1+
4),
12
5°C
AMW (kg/mol)
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0,01 0,1 1 10 100
0,01
0,1
1
.
h
shear rate, g
vis
cosity
S* min
• Rheometer, Curemeter• Biconical, closed die• 100 cpm / 1.67 Hz• 0.5° / 7% strain
MDR: Moving Die Rheometer
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What does a Rubber Process Analyzer (RPA)
do?
• Measures material response to shear deformation or force as a
function of time, temperature, frequency, or deformation
▪ Typically reports viscoelastic properties of storage modulus (G’), loss
modulus (G”), and tan delta
• Common Uses:
▪ Complete pre and post cure viscoelastic characterization
▪ Identifying differences in material properties unable to be
detected by MDR or Mooney – relate to processing behavior
Frequency dependence
Strain dependence
Stress relaxation
▪ Effects of filler/vulcanization network
Payne Effect
• Key Instrument Attributes:
▪ Excellent strain control and torque sensitivity
▪ Uniform temperature profile and control
▪ Low instrument compliance/ rigid test frame
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TA Instruments – RPA elite
Zeit
g
-1.5
-1
-0.5
0
0.5
1
1.5
0 5 10 15 20 25 30 35 40
Zeit
g
-3
-2
-1
0
1
2
3
0 5 10 15 20 25 30 35 40
g
Amplitude0.005°…360°
0.07%...5000%
Frequency0.001…50.0 Hz
Am
plit
ud
e
Time
Am
plit
ud
e
Time
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Rubber Processing: Where does a Rheometer
fit?
Additive
FillerElastomer
Rubber
Compound
Finished Rubber
Mixing Processing Cure
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Rubber Processing: Where does a Rheometer
fit in?
Mooney Viscosity: single point
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EPDM Processing Troubleshooting
Keltan 6950 Nordel 5565
Mooney ML 1+4 [MU] 65 65
Ethylene [%] 48 50
ENB content [%] 9 7.5
Distribution medium medium
Case Study
Company tried to switch from Keltan EPDM to Nordel EPDM, but significant
processing differences were observed
Additive
FillerElastomer
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EPDM Processing Troubleshooting:
Frequency Sweep
Shear - thinning
Nordel Keltan
Viscosity, η* Rate dependentFrequency Sweep:
Viscosity, η*
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EPDM Processing Troubleshooting:
Frequency Sweep Nordel Keltan
Viscosity, η* Rate dependent
Avg MW Low High
Lower
AMW
Higher
AMW
Narrow
MWD
Broad
MWD
Frequency Sweep:
Modulus crossover
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EPDM Processing Troubleshooting:
Frequency Sweep
Mooney
Low
Frequency
Nordel Keltan
Viscosity, η* Rate dependent
Avg MW Low High
tan δ (low ω) 1.25 0.9
Frequency Sweep:
Tangent δ
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EPDM Processing Troubleshooting:
Amplitude Sweep - LAOS
High
Strain
Nordel Keltan
Viscosity, η* Rate dependent
Avg MW Low High
tan δ (low ω) 1.25 0.9
tan δ (high γ) 9.0 5.0
Amplitude Sweep:
LAOS
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EPDM Processing Troubleshooting:
Amplitude Sweep - LCB Nordel Keltan
Viscosity, η* Rate dependent
Avg MW Low High
tan δ (low ω) 1.25 0.9
tan δ (high γ) 9.0 5.0
LCB index -1.25 1.21
Amplitude Sweep:
LCB
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Recipe of Compounds
Keltan
compound
Nordel
compound
phr phr
EPDM (LCB) 100
EPDM, linear 100
Fast Extrusion Furnace (FEF)
carbon black 95 95
Chalk 50 50
Paraffinic Oil 65 65
ZnO 6 6
Stearic acid 1 1
Drying agent 9 9
Antiaging agent 0.5 0.5
Sulfur and accelerator 4.5 4.5
How does presence of branching affect filler distribution,
compound properties and processing behavior?
Rubber
Compound
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Rubber Compound: Payne Effect – Testing for
Filler Interactions/Distribution
Strain Sweep testing can distinguish
between filler contributions and polymer
contributions.
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Delay time before start test
0.5, 1.0, 2.0, 4.0, 8.0 min
Rubber Compound: Structure Recovery
RPA Rheometer
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Rubber Compound: Structure Recovery
0
200
400
600
800
1000
1200
1400
1600
1800
0.01 0.1 1 10 100
G' (
kPa)
Strain (%)
Compound property
change after instrument
CLOSURE!
Non stationary conditions
Sample structure still recovering
Instrument closure
Low strain, time sweep
for structure recovery
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0.0
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200.0
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400.0
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600.0
700.0
800.0
0.0 6.0 12.0 18.0 24.0 30.0
Sch
ub
mo
du
l G' [
kPa
]
Zeit [min]
SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6403/9034-0
0.05° 5744
0.05° 5747
Scarabaeus GmbHMeß- und Produktionstechnik
SIS V50
Rubber Compound: Structure Recovery
Structure recovery highly
dependent on compound
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Rubber Compound Testing: Cure
Linear polymer has
higher S’max,
indicating stronger
rubber and more
crosslinks, but ENB is
higher in Keltan
Keltan
compound
Nordel
compound
S' Min [dNm] 1.21 1.4
S' Max [dNm] 20.44 23.17
ENB content [%] 9 7.5
branched linear
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Rubber Compound Testing: Payne Effect
Tensile Strength [Mpa]
Keltan – branched 9.25
Nordel - linear 8.32
Rubber
Compound
Linear polymer shows
poor distribution
Poorly dispersed CB
leads to decreased
tensile strength
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Shear thinning
15%
5%
Rubber Compound Testing: Frequency Sweep
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Rubber Compound Extrusion – Machine
parameters
Extrusion Keltan compound Nordel compound
Temp. extruder [°C] 70 70
Pressure die [bar] 91.3 102
Current [A] 111.5 124
Speed [m/min] 10.5 10.5
Temp. Mass [°C] 114 114-125
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Effect of Molecular Weight Distribution
(MWD) on compound extrusion behavior
Surface defect as« shark skin »on extrusion
Tentative conclusionShark skin effect in extrusion is due to MWD effect and not LCB effect.
Rubber
Compound
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0.1 1 10 100 1000 10000 100000
Tan
gen
t d
(-)
Frequency (Rad/s)
50° (EPDM3)
125° EPDM3)
50° (EPDM1)
125° (EPDM1)
Crossing 1
Crossing 2
0
0.1
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Log MW (Daltons)
dw
t/d
(lo
gM
)
Production line 1
Production line 2
Maximum extrusion speed for no surface
defect
Production line 1: 25 m/min
Production line 2: 2 m/min
• LCB content of both polymers was
very similar
• Extrudability problem (shark skin) was
found in the large reduction of small
molecules in the problem polymer
• Very small molecules act in compound
as excellent processing aid
• The higher tangent d value at high
frequency for the good processing
polymer confirmed this result.
Effect of Molecular Weight Distribution
(MWD) on compound extrusion behavior
Rubber
Compound
Bad
Bad
Good
Good
Bad
Good
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Rubber Compound Process Troubleshooting
Case Study
Bad sample exhibiting extrusion instabilities indicating scorching in extruder at
current processing conditions. Could the RPA determine differences in the materials?
Summary of observations:• Bad batch shows higher extrusion head pressure and
temperature, higher swell and surface defect (“Orange skin”)
• Indicating scorching within extruder
• All batches passed standard QC tests (MDR only)
• Bad batch compared to a trouble free batch to troubleshoot
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0.0
1.0
2.0
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5.0
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15.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0
S' [dNm]
Time [min]
SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6441/56777-0
BAD
GOOD
TA Instruments159 Lukens Drive New Castle
DE 19720
Test Temp.
Strain
Frequency
130 °C
0.50°
1.67Hz
Rubber Compound: Similar cure, Different
Processing Behavior
MDR cure curves look
similar
Bad sample shown to
cure more slowly, but
shows issues in
production…
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0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0
S' [dNm]
Time [min]
SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6441/56777-0
BAD
GOOD
TA Instruments159 Lukens Drive New Castle
DE 19720
Test Temp.
Strain
Frequency
130 °C
0.50°
1.67Hz
Minimum of cure curve is identical
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0.0
1.0
2.0
3.0
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0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0
S' [dNm]
Time [min]
SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6441/56777-0
BAD
GOOD
TA Instruments159 Lukens Drive New Castle
DE 19720
Test Temp.
Strain
Frequency
130 °C
0.50°
1.67Hz
Rubber Compound: Similar cure, Different
Processing Behavior Good Bad
Viscosity, η* SimilarFrequency Sweep:
Viscosity, η*
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0.0
1.0
2.0
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15.0
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S' [dNm]
Time [min]
SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6441/56777-0
BAD
GOOD
TA Instruments159 Lukens Drive New Castle
DE 19720
Test Temp.
Strain
Frequency
130 °C
0.50°
1.67Hz
Rubber Compound: Similar cure, Different
Processing Behavior Good Bad
Viscosity, η* Similar
tan δ (low ω) 1.0 0.8Frequency Sweep:
Low frequency tan δ
Bad sample exhibiting slightly
lower tan delta, indicating
more elasticity
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Rubber Compound: Similar cure, Different Processing Behavior
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
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14.0
15.0
0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0
S' [dNm]
Time [min]
SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6441/56777-0
BAD
GOOD
TA Instruments159 Lukens Drive New Castle
DE 19720
Test Temp.
Strain
Frequency
130 °C
0.50°
1.67Hz
Good Bad
Viscosity, η* Similar
tan δ (low ω) 1.0 0.8
tan δ (high γ) 5.7 3.0
Amplitude Sweep:
High Strain tan δ
Modulus values similar
at small strains
Bad compound has higher
G’, indicating more elastic,
solid-like behavior than
good compound
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Rubber Compound: Similar cure, Different Processing Behavior
More positive LCB index indicates
large amount of branching and high
elasticity
Amplitude Sweep:
LAOS
Good Bad
Viscosity, η* Similar
tan δ (low ω) 1.0 0.8
tan δ (high γ) 5.7 3.0
LCB Index 0.18 2.73
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Rubber Compound: Similar cure, Different Processing Behavior
Energy released at large strains for bad compound is greater.
Premature scorch produced by heat generation in extruder
Amplitude Sweep:
LAOS
Good Bad
Viscosity, η* Similar
tan δ (low ω) 1.0 0.8
tan δ (high γ) 5.7 3.0
Wdiss 169 J 177 J
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Silica Compound Processing:Tread compound formulation
Ingredient PHR
Buna VSL 4020-1 103.1
Buna CB 10 25.0
Ultrasil 3370GR 80.0
Silane X50S 12.5
High aromatic oil 5.0
ZnO 2.5
Stearic acid 1.0
6 PPD 2.0
Wax 1.5
Patent Application EP 0501 227, Michelin, R. Rauline, February 25th, 1991
Silica compound
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Mixer
speed step
1
Mixer
speed step
2
Dump temp
step 1
Dump temp
step 2
Total
mixing
energy
Sample 1 65 65 155 180 4.123
Sample 2 55 55 145 161 4.076
Sample 3 45 45 146 146 4.067
Sample 4 65 45 153 155 4.133
MS(1+4)
100°C
Sample 1 68.7
Sample 2 65.4
Sample 3 68.1
Sample 4 60.5
At first, Mooney viscometerwas used for QC of silica
compounds
Very little difference in Mooney viscosity
Silica Compound Processing: Mixing Conditions
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MIXING CYCLE IMPROVEMENT (Payne Diagram)
0.101.00
10.00100.00
1000.00
Strain (% SSA)
10
100
1,000
G' (KPa)
No 1 (65 RPM)
No 2 (55 RPM)
No 3 (45 RPM)
No 4 (65&45 RPM)
100° C, 0.1 HzUncured
Increasing reaction SiO2 > Silane increased silane
degradation
Mixer
speed step
1
Mixer
speed step
2
Dump temp
step 1
Dump temp
step 2
Total
mixing
energy
Sample 1 65 65 155 180 4.123
Sample 2 55 55 145 161 4.076
Sample 3 45 45 146 146 4.067
Sample 4 65 45 153 155 4.133
Difficult to
process
Silica Compound Processing: Mixing Conditions and Payne Diagram
Less hydrogen
bonding due to
hydroxy groups
consumed
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MIXING CYCLE IMPROVEMENT (Payne Diagram)
0.101.00
10.00100.00
1000.00
Strain (% SSA)
10
100
1,000
G' (KPa)
No 1 (65 RPM)
No 2 (55 RPM)
No 3 (45 RPM)
No 4 (65&45 RPM)
100° C, 0.1 HzUncured
Increasing reaction SiO2 > Silane increased silane
degradation
Difficult to
process
Silica Compound Processing: Mixing Conditions and Payne Diagram
Less hydrogen
bonding due to
hydroxy groups
consumed
MS(1+4) 100°C G’@1% strain (kPa) S’@450% strain (dNm)
Sample 1 68.7 448 27.69
Sample 2 65.4 568 23.75
Sample 3 68.1 754 19.75
Sample 4 60.5 448 19.04
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Careful visco-elasticity measurements on masterbatch can rapidly and easily:
• Fully characterize Payne diagram• Payne diagram low strain elastic modulus provides essential
information of silica/silane chemical reaction• Payne diagram high strain elastic modulus or better elastic
torque provides information on the uncured compound processability
2 industrial uncured compounds• Compound 1 can be processed
but won’t provide adequate cured properties
• Compound 2 will provide adequate cured properties but cannot be processed.
Silica Compound Processing:Test Conclusions
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Quality Control: Instrument repeatability, Compound
homogeneity, and production variation
Highly variable mixingLarge difference in Carbon Black dispersion.
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Quality Control: Instrument repeatability, Compound
homogeneity, and production variation
Energy dissipation in processLAOS – 90° Arc – 100°C, 0.1 Hz
UNCONTROLLED MIXING PROCESS
gsin d
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•Identify compound homogeneity and
quality of mixing
•Test multiple samples within
same batch
•Identify batch to batch production
variability in compound processing
•Requires low variability within
batch – excellent compound
homogeneity
•Unable to perform if variation
within one batch is greater than
between batches
Quality Control: Instrument repeatability, Compound
homogeneity, and production variation
Important QC Aspects QC Applications for RPA
•Excellent Instrument repeatability
•Additional mixing compound
•Sample number: 15
•CV (Std Dev/Mean) ≈ 0.75%
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Additional Techniques: Cure Kinetics Analysis
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Additional Techniques: Cure Kinetics Analysis
Activation energy is calculated using
Arrhenius Equation
Software can use model to calculate time until
compound cures at user specified temperatures
(ex: storage time at 30 deg C or 0 degC)
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Additional Techniques:
Modeling Curing Reaction
Calculated
Measured
Kinetics model can be used to model curing reaction of compound at other
temperatures or temperature profiles.
Able to compare to measured data to confirm accuracy of model
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2K/min3K/min
5K/min
Additional Techniques:
Non-isothermal Kinetics
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Additional Techniques:
Non-isothermal Kinetics
Non-isothermal kinetic model clearly shows rate of
reaction changes as reaction proceeds. Shape of curves
clearly indicate order of reaction ≠ 1
Can use information to help optimize processing conditions
when trying to match curing profiles of different compounds
when molding together
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Additional Techniques:
Foaming and Sponge Rubber
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Additional Techniques:
Foaming and Sponge Rubber
Accurate cure and blowing reaction testing requires:• Identical material quantity: sample mass +\- 0.01 g• Identical shape, minimizing material flow in the test
chamber.
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Additional Techniques:
Activation energy of blowing reaction
Insulation foamNBR-PVC blend
Car door sealEPDM compound
Conversion rate constant and kinetic analysis on pressure curve to calculate activation energy of blowing reaction
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Summary
• Mooney and MDR testing alone has limitations
▪Mooney viscosity is only one point!
▪Smin only one time scale compared to many others in a process
• RPA testing capable of distinguishing differences in materials unable to be detected by Mooney and MDR tests
▪Raw Elastomers:
MWD, AMW, and branching differences directly affect processing
▪Mixed Compounds:
Structural changes in raw elastomers affect compound processing and performance
Mixing and processing times change compound structure and properties
▪Payne Effect and Filler distribution
• Cure kinetics measurements and modeling can be used to tailor compound composition and optimize processing parameters
• RPA can produce pressure and cure curve measurements, providing insight into blowing reaction for foaming and sponge applications
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