Microsoft School Of Rheology Part 2 Capillary RH2000
User Manual: RH2000
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Brno, 28-29th march 2012 – School of Rheology Part II: Capillary Rheometry A method to predict flow properties under processing conditions Outline • Range of Applications for Capillary Rheometry • Introduction into capillary rheometry: Principle of Operation and theoretical background • Test results on LDPE: Complete Capillary Characterisation • Advanced Test Types: pVT, Relaxation, Thermal Degradation etc. Capillary Rheometry: Main Applications Repeat from the previous session: Basic Terms Displacement u Normal Force ! Shear Force F d, L area A = a · b Height = d Initial length = L a u γ = d γ d γ& = dt Ftan τ = A Strain [] Shear Rate [1/s] Shear Stress [Pa] b ε = ln l L ε& = 1 d l L dt Fnor σ= A Extension [] Extensional Rate[1/s] Extensional Stress [Pa] Typical Shear Rate Ranges Sagging, Levelling Extrusion, Injection Moulding Roll Coating, Spraying Mixing, Blade Coating, Brushing 10-3 10-1 100 101 102 103 104 106 s -1 Rotational-Rheometer Sample: Water up to solids Results: Shear-Viscosity, Yield Stesses, Visco-Elasticity, Relaxation... High Pressure Capillary-Rheometer Sample: Water up to high viscous Results: Shear-Viscosity, Elongational-Viscosity, Wall Slip... Principle of Operation Given quantity: piston speed ⇒ wall shear rate Measured quantity: pressure drop ⇒ wall shear stress v Bore Full pressure drop = P L P1 Entrance pressure drop + Fully developed flow region 2R Pw entry 0 L 0 Z ⇒ small ram extruder Shear pressure drop Laminar Pipe Flow Isothermal, stationary Flow of an incompressible fluid Newtonian γ app = τ app = 4⋅Q 3 πR R ⋅∆P 2⋅L d (log τ) n= d (log γ) Non-Newtonian Index (Ostwald-de Waele) Volumen./s . Shear Rate v Newtonian -R 0 -R 0 0 ∆Ρ R R NonNewtonian What are we doing to get flow curves? measurement : v Ramp in steps ∆p t t . γ app = τ app = 4⋅Q 3 πR R ⋅∆P 2⋅L corrections η = τ true . γ true Correction: Entrance zone of a capillary die Pressure transducer Convergent Flow Capillary die Aim of the test: to separate entrance pressure and shear pressure drop! Rosand Twin Bore Principle v v Pfull pentrance L Pfull= Pshear + Pentrance 2R left: capillary pentrance pshear right: orifice How do we get the Extensional Viscosity? Cogswell`s Convergent Flow Model ⇒ Extensional Viscosity Pfull= Pshear + Pentrance λ= 9 (n+1)2 (Ps)2 . 32 η γ 2 • Special Orifice Die according to Uni Zlin Model enables characterisation of very small extensional rates too. . d (log τ) n= d (log γ) Non-Newtonian Index (Ostwald-de Waele) ε ≈ 10-1 - 103 s-1 F. Cogswell, “Polymer Melt Rheology”, Woodhead Publishing Limited (1981) Zatloukal, Vlcek, Tzoganakis, Saha J. Non-Newtonian Fluid Mech. 107 (2002) 13–37 Example LDPE LDPE at 190°C Shear Viscosity / Extensional Viscosity (Pas) 1,0E+05 Low Shear Test Zero Shear Viscosity Low Shear 2.0mm 1,0E+04 Standard Shear 1mm Standard Shear Melt Fracture High Shear 0.5mm 1,0E+03 Low Extension 2.0mm Standard Extension 1mm 1,0E+02 Standard Extension Melt Rupture High Extension 0.5mm 1,0E+01 1,0E-04 1,0E-02 1,0E+00 1,0E+02 1,0E+04 Shear Rate / Extensional Rate (1/s) 1,0E+06 Extensional Rheology of LDPE Blow Moulding ⇒ Blow Moulding is mainly influenced by Extension! Surface Instabilities LDPE Surface shape Cooling air Surface Instabilities LDPE How can the process be improved? Dehnviskosität - Vergleichskurven zwischen Homopolymer PE und Polymerblend PE-PP 1,0E+05 Extensional Viscosity (Pas) Sample 2 1,0E+04 Sample 2 Sample 2 Sample 2 1,0E+03 Sample 1 1,0E+02 1,0E-04 1,0E-02 1,0E+00 1,0E+02 Extensional Rate (1/s) 1,0E+04 1,0E+06 Another Example: Co-Extrusion Similar instabilites High acceleration Low acceleration LDPE in Co-Extrusion Die Instabilities caused by Extensional Flow Behaviour of LDPE Zatloukal et. al. Journal of Applied Polymer Science, 98 (2005) 153 Further Examples: Dispersions Scherviskositätskurven bei 40°C 1.0E+04 Rotationsrheometer Bohlin Gemini Kapillarrheometer Rosand RH10 Probe 1 Kapillar Test 1 Probe 1 Kapillar Test 2 Probe 2 Kapillar Test 1 1.0E+03 Scherviskositätskurven (Pas) Probe 3 Kapillar Test 1 Probe 1 Rotation Test 1 Probe 1 Rotation Test 2 1.0E+02 Probe 2 Rotation Test 1 Probe 2 Rotation Test 2 Probe 3 Rotation Test 1 1.0E+01 Düsenverstopfung durch Agglomeration bei Probe 3 1.0E+00 Besseres Standvermögen 2. Newtonsches Plateau Probe 2 (ca. 170 mPas) Probe 3 Rotation Test 2 Rotational: Bohlin Gemini, Peltier Option, Cone Plate CP 4°/40 1.0E-01 Bessere Verarbeitbarkeit 1.0E-02 1.0E-03 1.0E-02 2. Newtonsches Plateau Probe 1 (ca. 96 mPas) 1.0E-01 1.0E+00 1.0E+01 1.0E+02 1.0E+03 1.0E+04 1.0E+05 1.0E+06 Capillary: Rosand RH10-D, capillary die 0.4mm diameter / 32mm length, pressure sensors 500psi, Rabinowitsch corrected Scherrate (1/s) ⇒ Capillary Rheometry can predict Die Blocking Example: Dispersion Adhesive for Spray Coating ⇒ Shear Thickening effect depends on the particle volume fraction Wide Shear Rate Range ⇒ Rotational and Capillary Rheometry cover approx 13 decades in shear Further Applications: Wall Slip Wall Slip Velocity of chromium catalyzed HDPE at 190°C No wall slip Wall slip Vmax Vmax Vw = 0 Vw = 0 Wandgleitgeschwindigkeit bei 190°C 0,9 0,8 Wall slip velocity increases dramatically at just above 0.1 MPa. Wall Slip Velocity (m/s) 0,7 0,6 0,5 Wall Slip according to Mooney Model 0,4 Critical Stress 0,3 0,2 critical stress 120 kPa 0,1 0 -0,1 0 50 100 150 200 250 Shear Stress (kPa) 300 350 400 Equilibrium Pressure: Homogeneity Pressure drop is important homogeneous inhomogeneous ⇒ For polymer blens, filled polymers, suspensions, emulsions, composites etc. Thermal degradation / Curing Thermischer Abbau at 260°C 6 60 5 50 v Pressure (MPa) 4 40 3 30 2 20 t 1 10 0 0 1000 2000 3000 4000 real time (sec) ⇒ Gives max process time 5000 0 6000 Shear Rate (/s) / Extruded Volume (cm 3) Prinzip: 70 Pressure Drop Shear Rate Extruded Volume Stick-Slip Flow Instabilities Linear Ramp v t Melt fracture ⇒ What is the max processing pressure / Shear Rate? Melt Fracture Unstable flow, poor product quality. ? 100000 100 10 Pressure (Mpa) Shear Stress (Pa) 1000000 10000 1 10 100 Shear Rate (1/s) 1 PO PC 1,000s-1 0.1 0 50 100 150 Time 200 250 300 Relaxation LDPE What happens after processing Relaxation 190°C LDPE 25 12000 10000 20 Pressure Drop (MPa) Prinzip: v 8000 15 6000 Relaxation Time λ = 26.75 sec ( Mono-exp. Decay) 10 5 Online Pressure Drop Shear Rate 4000 2000 Thermal Equilibrium Time 0 t 0 0 50 100 150 200 250 300 350 400 Real Time (sec) ⇒ inner stresses can lead to surface crack (automotive industry) Compressibility PV-Isotherm pV Isotherme bei 190°C 250 Pressure (MPa) 200 150 PV-Isotherm 100 dV/V = 1/K·p 50 0 0 2 4 6 8 10 12 14 16 dV/V0 (%) PVT: • Mainly needed for flow simulation Rheometer Types Benchtop RH2000 and Floor Standing RH7/10 Example: Test Run at RH7 Conclusion The complete flow behaviour under processing conditions Rosand Double Capillary System with Orifice Die: • • • • • • direct measurement of the entrance pressure drop - no extrapolation needed calculation of extensional viscosity according Cogswell method flow curve up to very high shear end extensional rates ability to detect wall slip by Mooney‘s method correlation with structural changes during processing additional Options for detection of elastic behaviour (Die-Swell) Thank you for your attention.
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