rubber process analyzer rpa applications: bridging the gap ...€¦ · rubber compound process...

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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

What do we want to know about rubber?

Processing

Molding

Molecular Weight

Additives

Performance

Mixing

Aging Curing

0,01 0,1 1 10 100

shear rate, g

cosity

Mooney Tests

Sample

Mooney-V

iscosity [

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

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

500 1000 1500 2000 2500

AMW (kg/mol)

0,01 0,1 1 10 100

shear rate, g

cosity

S* min

• Rheometer, Curemeter• Biconical, closed die• 100 cpm / 1.67 Hz• 0.5° / 7% strain

MDR: Moving Die Rheometer

What does a Rubber Process Analyzer (RPA)

• 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

TA Instruments – RPA elite

0 5 10 15 20 25 30 35 40

Amplitude0.005°…360°

0.07%...5000%

Frequency0.001…50.0 Hz

Rubber Processing: Where does a Rheometer

Additive

FillerElastomer

Rubber

Compound

Finished Rubber

Mixing Processing Cure

Rubber Processing: Where does a Rheometer

fit in?

Mooney Viscosity: single point

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

EPDM Processing Troubleshooting:

Frequency Sweep

Shear - thinning

Nordel Keltan

Viscosity, η* Rate dependentFrequency Sweep:

Viscosity, η*

Frequency Sweep Nordel Keltan

Viscosity, η* Rate dependent

Avg MW Low High

Higher

Narrow

Frequency Sweep:

Modulus crossover

Frequency Sweep

Mooney

Frequency

Nordel Keltan

Avg MW Low High

tan δ (low ω) 1.25 0.9

Frequency Sweep:

Tangent δ

Amplitude Sweep - LAOS

Strain

Nordel Keltan

Avg MW Low High

tan δ (low ω) 1.25 0.9

tan δ (high γ) 9.0 5.0

Amplitude Sweep:

Amplitude Sweep - LCB Nordel Keltan

Avg MW Low High

tan δ (low ω) 1.25 0.9

LCB index -1.25 1.21

Amplitude Sweep:

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

Rubber Compound: Payne Effect – Testing for

Filler Interactions/Distribution

Strain Sweep testing can distinguish

between filler contributions and polymer

contributions.

Delay time before start test

0.5, 1.0, 2.0, 4.0, 8.0 min

Rubber Compound: Structure Recovery

RPA Rheometer

0.01 0.1 1 10 100

Strain (%)

Compound property

change after instrument

CLOSURE!

Non stationary conditions

Sample structure still recovering

Instrument closure

Low strain, time sweep

for structure recovery

0.0 6.0 12.0 18.0 24.0 30.0

l G' [

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

Structure recovery highly

dependent on compound

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

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

Shear thinning

Rubber Compound Testing: Frequency Sweep

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

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

0.1 1 10 100 1000 10000 100000

Frequency (Rad/s)

50° (EPDM3)

125° EPDM3)

50° (EPDM1)

125° (EPDM1)

Crossing 1

Crossing 2

3.5 4.5 5.5 6.5

Log MW (Daltons)

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

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

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]

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…

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]

DE 19720

Test Temp.

Strain

Frequency

130 °C

0.50°

1.67Hz

Minimum of cure curve is identical

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]

DE 19720

Test Temp.

Strain

Frequency

130 °C

0.50°

1.67Hz

Processing Behavior Good Bad

Viscosity, η* SimilarFrequency Sweep:

Viscosity, η*

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]

DE 19720

Test Temp.

Strain

Frequency

130 °C

0.50°

1.67Hz

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

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 13.0 14.0 15.0 16.0 17.0 18.0 19.0 20.0

S' [dNm]

Time [min]

DE 19720

Test Temp.

Strain

Frequency

130 °C

0.50°

1.67Hz

Good Bad

tan δ (low ω) 1.0 0.8

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

More positive LCB index indicates

large amount of branching and high

elasticity

Amplitude Sweep:

Good Bad

tan δ (low ω) 1.0 0.8

LCB Index 0.18 2.73

Energy released at large strains for bad compound is greater.

Premature scorch produced by heat generation in extruder

Amplitude Sweep:

Good Bad

tan δ (low ω) 1.0 0.8

Wdiss 169 J 177 J

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

speed step

Dump temp

step 1

Dump temp

step 2

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

MIXING CYCLE IMPROVEMENT (Payne Diagram)

0.101.00

10.00100.00

1000.00

Strain (% SSA)

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

speed step

Dump temp

step 1

Dump temp

step 2

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

MIXING CYCLE IMPROVEMENT (Payne Diagram)

0.101.00

10.00100.00

1000.00

Strain (% SSA)

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

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

Quality Control: Instrument repeatability, Compound

homogeneity, and production variation

Highly variable mixingLarge difference in Carbon Black dispersion.

Energy dissipation in processLAOS – 90° Arc – 100°C, 0.1 Hz

UNCONTROLLED MIXING PROCESS

gsin d

•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

Important QC Aspects QC Applications for RPA

•Excellent Instrument repeatability

•Additional mixing compound

•Sample number: 15

•CV (Std Dev/Mean) ≈ 0.75%

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)

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

2K/min3K/min

5K/min

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

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.

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

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

For more information…

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