Rubber Process Analyzer RPA Applications: Bridging the Gap Between Polymer/Compound Properties and Processing Behavior Greg Kamykowski, PhD Alina Latshaw, PhD TA Instruments Waters LLC Akron, OH September 2017
What do we want to know about rubber? Performance Molecular Weight Additives Processing Molding Mixing Aging Curing
Mooney-Viscosity [MU] viscosity h Mooney Tests 1 0,1 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 0,01 ML1+4 0,01 0,1 1 10 100 Sample Rotor. shear rate, g
ML(1+4), 125 C Mooney viscosity: meaning and limitations Mooney viscosity Increases approx. linearly with polymer Average Molecular Weight (AMW) plateau at high Mw Vistanex (exxon Mobil) Average molecular Weight 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 80 70 60 50 May decrease with very high Mw polymers. due to polymer fracture in viscometer cavity 40 500 1000 1500 2000 2500 AMW (kg/mol)
viscosity h MDR: Moving Die Rheometer 1 0,1 S* min 0,01 0,01 0,1 1 10 100. shear rate, g Rheometer, Curemeter Biconical, closed die 100 cpm / 1.67 Hz 0.5 / 7% strain
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
Amplitude Amplitude TA Instruments RPA elite g 1.5 1 0.5 0 0 5 10 15 20 25 30 35 40 Frequency 0.001 50.0 Hz -0.5-1 -1.5 Time Zeit 3 2 1 0-1 0 5 10 15 20 25 30 35 40 g g Amplitude 0.005 360 0.07%...5000% -2-3 Time Zeit
Rubber Processing: Where does a Rheometer fit? Mixing Processing Cure Filler Elastomer Additive Rubber Compound Finished Rubber
Rubber Processing: Where does a Rheometer fit in? Mooney Viscosity: single point
EPDM Processing Troubleshooting Filler Elastomer Additive Case Study Company tried to switch from Keltan EPDM to Nordel EPDM, but significant processing differences were observed Keltan 6950 Nordel 5565 Mooney ML 1+4 [MU] 65 65 Ethylene [%] 48 50 ENB content [%] 9 7.5 Distribution medium medium
EPDM Processing Troubleshooting: Frequency Sweep Frequency Sweep: Viscosity, η* Viscosity, η* Nordel Keltan Rate dependent Shear - thinning
EPDM Processing Troubleshooting: Frequency Sweep Nordel Keltan Frequency Sweep: Modulus crossover Viscosity, η* Rate dependent Avg MW Low High Narrow MWD Higher AMW Lower AMW Broad MWD
EPDM Processing Troubleshooting: Frequency Sweep Frequency Sweep: Tangent δ Low Frequency Viscosity, η* Nordel Keltan Rate dependent Avg MW Low High tan δ (low ω) 1.25 0.9 Mooney
EPDM Processing Troubleshooting: Amplitude Sweep - LAOS Amplitude Sweep: LAOS High Strain Viscosity, η* Nordel Keltan Rate dependent Avg MW Low High tan δ (low ω) 1.25 0.9 tan δ (high γ) 9.0 5.0
EPDM Processing Troubleshooting: Amplitude Sweep - LCB Nordel Keltan Amplitude Sweep: LCB 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
Recipe of Compounds Rubber Compound How does presence of branching affect filler distribution, compound properties and processing behavior? 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
Rubber Compound: Payne Effect Testing for Filler Interactions/Distribution Strain Sweep testing can distinguish between filler contributions and polymer contributions.
Rubber Compound: Structure Recovery Delay time before start test 0.5, 1.0, 2.0, 4.0, 8.0 min RPA Rheometer
G' (kpa) Rubber Compound: Structure Recovery Instrument closure Low strain, time sweep Compound for structure property recovery change after instrument CLOSURE! Non stationary conditions Sample structure still recovering 1800 1600 1400 1200 1000 800 600 400 200 0 0.01 0.1 1 10 100 Strain (%)
Schubmodul G' [kpa] Rubber Compound: Structure Recovery Scarabaeus GmbH Meß- und Produktionstechnik SIS V50 Structure recovery highly dependent on compound 800.0 700.0 600.0 500.0 400.0 0.05 5744 0.05 5747 300.0 200.0 100.0 0.0 0.0 6.0 12.0 18.0 24.0 30.0 Zeit [min] SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6403/9034-0
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 Rubber Compound Linear polymer shows poor distribution Tensile Strength [Mpa] Keltan branched 9.25 Nordel - linear 8.32 Poorly dispersed CB leads to decreased tensile strength
Rubber Compound Testing: Frequency Sweep 5% Shear thinning 15%
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 Rubber Compound Surface defect as «shark skin»on extrusion Tentative conclusion Shark skin effect in extrusion is due to MWD effect and not LCB effect.
dwt/d(logm) Tangent d (-) Effect of Molecular Weight Distribution (MWD) on compound extrusion behavior Rubber Compound 1 0.9 0.8 Crossing 1 0.7 0.6 0.5 0.4 0.3 0.2 0.1 Bad 50 (EPDM3) Bad 125 EPDM3) Good 50 (EPDM1) Good 125 (EPDM1) Crossing 2 0 0.1 1 10 100 1000 10000 100000 Frequency (Rad/s) 1 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. 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 3.5 4.5 5.5 6.5 Log MW (Daltons) Production Good line 1 Production Bad line 2 Maximum extrusion speed for no surface defect Production line 1: 25 m/min Production line 2: 2 m/min
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
Rubber Compound: Similar cure, Different Processing Behavior TA Instruments 159 Lukens Drive New Castle DE 19720 S' [dnm] 15.0 14.0 13.0 12.0 11.0 10.0 9.0 8.0 7.0 6.0 5.0 Test Temp. Strain Frequency 130 C 0.50 1.67Hz Minimum of cure curve is identical MDR cure curves look similar Bad sample shown to cure more slowly, but shows issues in production BAD GOOD 4.0 3.0 2.0 BAD GOOD 1.0 0.0 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 Time [min] SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6441/56777-0
Rubber Compound: Similar cure, Different Processing Behavior Good Bad Frequency Sweep: Viscosity, η* Viscosity, η* TA Instruments Test Temp. 130 C 159 Lukens Drive New Castle Strain 0.50 Similar DE 19720 S' [dnm] 15.0 Frequency 1.67Hz 14.0 13.0 12.0 11.0 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 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 Time [min] SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6441/56777-0
Rubber Compound: Similar cure, Different Processing Behavior Good Bad Frequency Sweep: Low frequency tan δ Viscosity, η* Similar tan δ (low ω) 1.0 0.8 TA Instruments Test Temp. 130 C 159 Lukens Drive New Castle Strain 0.50 DE 19720 S' [dnm] 15.0 Frequency 1.67Hz 14.0 13.0 12.0 11.0 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 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 Time [min] SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6441/56777-0 Bad sample exhibiting slightly lower tan delta, indicating more elasticity
Rubber Compound: Similar cure, Different Processing Behavior Amplitude Sweep: High Strain tan δ 15.0 Viscosity, η* S' [dnm] Good Similar Bad tan δ (low ω) 1.0 0.8 TA Instruments Test Temp. 130 C 159 Lukens Drive New Castle Strain 0.50 tan δ (high γ) 5.7 3.0 DE 19720 Frequency 1.67Hz 14.0 13.0 12.0 11.0 10.0 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 Modulus values similar at small strains 1.0 0.0 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 Time [min] SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6441/56777-0 Bad compound has higher G, indicating more elastic, solid-like behavior than good compound
Rubber Compound: Similar cure, Different Processing Behavior Amplitude Sweep: LAOS Viscosity, η* Good Similar Bad tan δ (low ω) 1.0 0.8 tan δ (high γ) 5.7 3.0 LCB Index 0.18 2.73 More positive LCB index indicates large amount of branching and high elasticity
Rubber Compound: Similar cure, Different Processing Behavior Amplitude Sweep: LAOS Viscosity, η* Good Similar Bad tan δ (low ω) 1.0 0.8 tan δ (high γ) 5.7 3.0 Wdiss 169 J 177 J Energy released at large strains for bad compound is greater. Premature scorch produced by heat generation in extruder
Silica Compound Processing: Tread compound formulation Silica compound 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 Processing: Mixing Conditions 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 viscometer was used for QC of silica compounds Very little difference in Mooney viscosity
Silica Compound Processing: Mixing Conditions and Payne Diagram 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 MIXINGCYCLEIMPROVEMENT(PayneDiagram) Sample 4 65 45 153 155 4.133 G' (KPa) 1,000 100 10 0.10 Increasingreaction SiO2>Silane Less hydrogen bonding due to hydroxy groups consumed 1.00 100 C, 0.1 Hz Uncured No 1 (65 RPM) No 2 (55 RPM) No 3 (45 RPM) No 4 (65&45 RPM) 10.00 increasedsilane Difficult to degradation process 100.00 Strain (% SSA) 100
Silica Compound Processing: Mixing Conditions and Payne Diagram 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 4MIXINGCYCLEIMPROVEMENT(PayneDiagram) 60.5 448 19.04 G' (KPa) 1,000 100 10 0.10 Increasingreaction SiO2>Silane Less hydrogen bonding due to hydroxy groups consumed 1.00 100 C, 0.1 Hz Uncured No 1 (65 RPM) No 2 (55 RPM) No 3 (45 RPM) No 4 (65&45 RPM) 10.00 increasedsilane Difficult to degradation process 100.00 Strain (% SSA) 100
Silica Compound Processing: Test Conclusions 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.
Quality Control: Instrument repeatability, Compound homogeneity, and production variation Highly variable mixing Large difference in Carbon Black dispersion.
Quality Control: Instrument repeatability, Compound homogeneity, and production variation Energy dissipation in process LAOS 90 Arc 100 C, 0.1 Hz UNCONTROLLED MIXING PROCESS g sin d
Quality Control: Instrument repeatability, Compound homogeneity, and production variation Important QC Aspects Excellent Instrument repeatability Additional mixing compound Sample number: 15 CV (Std Dev/Mean) 0.75% QC Applications for RPA 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
Additional Techniques: Cure Kinetics Analysis
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
Additional Techniques: Non-isothermal Kinetics 5K/min 3K/min 2K/min
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
Additional Techniques: Foaming and Sponge Rubber
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.
Additional Techniques: Activation energy of blowing reaction Insulation foam NBR-PVC blend Car door seal EPDM 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
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