Rubber Process Analyzer RPA Applications: Bridging the Gap Between Polymer/Compound Properties and Processing Behavior

Transcription

1 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

2 What do we want to know about rubber? Performance Molecular Weight Additives Processing Molding Mixing Aging Curing

3 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, Sample Rotor. shear rate, g

4 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 MML MML MML MML May decrease with very high Mw polymers. due to polymer fracture in viscometer cavity AMW (kg/mol)

5 viscosity h MDR: Moving Die Rheometer 1 0,1 S* min 0,01 0,01 0, shear rate, g Rheometer, Curemeter Biconical, closed die 100 cpm / 1.67 Hz 0.5 / 7% strain

6 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

7 Amplitude Amplitude TA Instruments RPA elite g Frequency Hz Time Zeit g g Amplitude % % -2-3 Time Zeit

8 Rubber Processing: Where does a Rheometer fit? Mixing Processing Cure Filler Elastomer Additive Rubber Compound Finished Rubber

9 Rubber Processing: Where does a Rheometer fit in? Mooney Viscosity: single point

10 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] Ethylene [%] ENB content [%] Distribution medium medium

11 EPDM Processing Troubleshooting: Frequency Sweep Frequency Sweep: Viscosity, η* Viscosity, η* Nordel Keltan Rate dependent Shear - thinning

12 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

13 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) Mooney

14 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) tan δ (high γ)

15 EPDM Processing Troubleshooting: Amplitude Sweep - LCB Nordel Keltan Amplitude Sweep: LCB Viscosity, η* Rate dependent Avg MW Low High tan δ (low ω) tan δ (high γ) LCB index

16 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 Chalk Paraffinic Oil ZnO 6 6 Stearic acid 1 1 Drying agent 9 9 Antiaging agent Sulfur and accelerator

17 Rubber Compound: Payne Effect Testing for Filler Interactions/Distribution Strain Sweep testing can distinguish between filler contributions and polymer contributions.

18 Rubber Compound: Structure Recovery Delay time before start test 0.5, 1.0, 2.0, 4.0, 8.0 min RPA Rheometer

19 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 Strain (%)

20 Schubmodul G' [kpa] Rubber Compound: Structure Recovery Scarabaeus GmbH Meß- und Produktionstechnik SIS V50 Structure recovery highly dependent on compound Zeit [min] SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6403/9034-0

21 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] S' Max [dnm] ENB content [%] branched linear

22 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

23 Rubber Compound Testing: Frequency Sweep 5% Shear thinning 15%

24 Rubber Compound Extrusion Machine parameters Extrusion Keltan compound Nordel compound Temp. extruder [ C] Pressure die [bar] Current [A] Speed [m/min] Temp. Mass [ C]

25 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.

26 dwt/d(logm) Tangent d (-) Effect of Molecular Weight Distribution (MWD) on compound extrusion behavior Rubber Compound Crossing Bad 50 (EPDM3) Bad 125 EPDM3) Good 50 (EPDM1) Good 125 (EPDM1) Crossing 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 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

27 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

28 Rubber Compound: Similar cure, Different Processing Behavior TA Instruments 159 Lukens Drive New Castle DE S' [dnm] Test Temp. Strain Frequency 130 C Hz 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 BAD GOOD Time [min] SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6441/

29 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 S' [dnm] 15.0 Frequency 1.67Hz Time [min] SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6441/

30 Rubber Compound: Similar cure, Different Processing Behavior Good Bad Frequency Sweep: Low frequency tan δ Viscosity, η* Similar tan δ (low ω) TA Instruments Test Temp. 130 C 159 Lukens Drive New Castle Strain 0.50 DE S' [dnm] 15.0 Frequency 1.67Hz Time [min] SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6441/ Bad sample exhibiting slightly lower tan delta, indicating more elasticity

31 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) TA Instruments Test Temp. 130 C 159 Lukens Drive New Castle Strain 0.50 tan δ (high γ) DE Frequency 1.67Hz Modulus values similar at small strains Time [min] SCARABAEUS GMBH - info@scarabaeus-gmbh.de - Tel.:+49 (0) 6441/ Bad compound has higher G, indicating more elastic, solid-like behavior than good compound

32 Rubber Compound: Similar cure, Different Processing Behavior Amplitude Sweep: LAOS Viscosity, η* Good Similar Bad tan δ (low ω) tan δ (high γ) LCB Index More positive LCB index indicates large amount of branching and high elasticity

33 Rubber Compound: Similar cure, Different Processing Behavior Amplitude Sweep: LAOS Viscosity, η* Good Similar Bad tan δ (low ω) tan δ (high γ) Wdiss 169 J 177 J Energy released at large strains for bad compound is greater. Premature scorch produced by heat generation in extruder

34 Silica Compound Processing: Tread compound formulation Silica compound Ingredient PHR Buna VSL Buna CB Ultrasil 3370GR 80.0 Silane X50S 12.5 High aromatic oil 5.0 ZnO 2.5 Stearic acid PPD 2.0 Wax 1.5 Patent Application EP , Michelin, R. Rauline, February 25th, 1991

35 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 Sample Sample Sample MS(1+4) 100 C Sample Sample Sample Sample At first, Mooney viscometer was used for QC of silica compounds Very little difference in Mooney viscosity

36 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 Sample Sample MIXINGCYCLEIMPROVEMENT(PayneDiagram) Sample G' (KPa) 1, Increasingreaction SiO2>Silane Less hydrogen bonding due to hydroxy groups consumed C, 0.1 Hz Uncured No 1 (65 RPM) No 2 (55 RPM) No 3 (45 RPM) No 4 (65&45 RPM) increasedsilane Difficult to degradation process Strain (% SSA) 100

37 Silica Compound Processing: Mixing Conditions and Payne Diagram MS(1+4) 100 C strain (kpa) strain (dnm) Sample Sample Sample Sample 4MIXINGCYCLEIMPROVEMENT(PayneDiagram) G' (KPa) 1, Increasingreaction SiO2>Silane Less hydrogen bonding due to hydroxy groups consumed C, 0.1 Hz Uncured No 1 (65 RPM) No 2 (55 RPM) No 3 (45 RPM) No 4 (65&45 RPM) increasedsilane Difficult to degradation process Strain (% SSA) 100

38 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.

39 Quality Control: Instrument repeatability, Compound homogeneity, and production variation Highly variable mixing Large difference in Carbon Black dispersion.

40 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

41 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

42 Additional Techniques: Cure Kinetics Analysis

43 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)

44 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

45 Additional Techniques: Non-isothermal Kinetics 5K/min 3K/min 2K/min

46 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

47 Additional Techniques: Foaming and Sponge Rubber

48 Additional Techniques: Foaming and Sponge Rubber Accurate cure and blowing reaction testing requires: Identical material quantity: sample mass +\ g Identical shape, minimizing material flow in the test chamber.

49 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

50 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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