Evaluation of ESCR of PE Resins Using Tensile Strain ...
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Evaluation of ESCR of PE Resins Using Tensile Strain Hardening and Extensional Viscosity Pouyan Sardashti 1 , Costas Tzoganakis 1 , Maria Anna Polak 2 , and Alexander Penlidis 1 Institute for Polymer Research University of Waterloo Converging Flow Technique: Evaluation of Extensional Viscosity Using Cogswell Methodology (Capillary Rheometry) ESCR is the resistance to initiation of cracking and embrittlement of polymeric components; herein applied to polyethylene (PE) resins • Main fracture mechanism involved in polymers (25% of all fractured Mechanical Approach: • Tensile Strain Hardening Stiffness Test (TSHS) 1: Department of Chemical Engineering, 2: Department of Civil Engineering, University of Waterloo Environmental Stress Cracking Resistance (ESCR) Environmental Stress Cracking Resistance (ESCR) Methodology Methodology Rheological Approach: • Converging Flow Technique: Results Results Shear Rates polymers experience ESCR mechanism) • Function of different micromolecular properties (MW, MWD, SCB, etc.) • Occurs when polymers are subjected to low levels of stress over long periods of time, and aggressive environment Mechanism: Slow Crack Growth (SCG) • Polymer chain rearrangement to minimize stress • Craze initiation propagation brittle fracture Linear Elastic Region Cold Drawing/ Plastic Deformation Strain Hardening Region Stress/Load Displacement/Strain • Extensional rheometers: • Sentmanat Extensional Rheometer (SER) • Craze initiation, propagation, brittle fracture Displacement/Strain Displacement/Strain Stress/Load Sentmanat Extensional Rheometer (SER) • Rheotons (Fiber Spinning) Objective: Evaluation of ESCR Objective: Evaluation of ESCR RESULTS RESULTS A potential standard test for evaluation of ESCR Evaluation of ESCR from simple testing in a reliable and more practical fashion Relationship between melt strain hardening and ESCR Insight into the influences of chain entanglements on ESCR Extensional Rheometry: Sentmanat Extensional Rheometer (SER) Need to identify the extent of entanglements Conventional Methods: Low accuracy, high uncertainty, long testing periods • Notch Constant Load Test (NCLT), Pennsylvania Notch Test (PENT), Full Notch Creep Test (FNCT), Notched Pipe Test (NPT) Potential Extensional Characterization Methods: • Uniaxial Tensile Testing • Tensile Strain Hardening Stiffness Test (TSHS) • Rheological Techniques Gel Permeation Chromatography (GPC) NMR Resin M n (g/mol) M w (g/mol) M z (g/mol) PDI M w /M n SCB (/1000C) HDPE 25,236 118,501 336,312 4.70 1.8 LLDPE 18,334 90,101 279,526 4.91 3.5 NMR: Nuclear Magnetic Resonance SCB: Short Chain Branching 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 2 3 4 5 6 7 8 dwt/dLog(Mw) LLDPE HDPE Correlation between strain hardening and extent of 4 5 6 7 8 • Converging Flow Technique • Extensional Rheometry Materials Materials HDPE: High Density Polyethylene (HD 8660.29, ExxonMobil) LLDPE: Linear Low Density Polyethylene (LL 8550.24, ExxonMobil) 7 mm/min 10 mm/min (MPa) s (MPa) HD LLD HS (MPa) 0.019 0.013 Tensile Strain Hardening Stiffness Test (TSHS) • Room Temperature • 7 and 10 mm/min Crosshead Speed Hardening Stiffness (HS)= Log(MW) Future Steps Future Steps Investigation of the validity of the techniques on a broader ranger of PE resins (ESCR between 50 and 800 hours) Optimization of the TSHS test based on specimen dimensions and crosshead rates Development of a standard test for evaluation of the ESCR of PE resins HDPE 1 HDPE 2 HDPE 1 HDPE 2 hardening and extent of entanglements 0 50 100 150 200 250 0 1 2 3 0 1 2 3 4 5 HD HDP LLD Cheng, J.; Polak, M.; Penlidis, A. J. Macromol Sci. Pure & Appl Chem 2008, 45, 599. Cogswell, F. N. J.Non‐Newtonian Fluid Mech 1972, 12, 64. Cheng, J. J. Mechanical and Chemical Properties of High Density Polyethylene Effects of Microstructure on Creep Characteristics; PhD Dissertation, Dept of Chem Eng, University of Waterloo: Waterloo, Ont., 2008. Wright, D. C. 1996. Environmental Stress Cracking of Plastics, Smithers Rapra Technology, 1996. Bernnat,A., Wagner,M.H. Prog Trends Rheol V, Proc Eur Rheol Conf. 5 th , 1998. REFERENCE REFERENCE Density (g/cm 3 ) ESCR (h) Differential Scanning Calorimetry (DSC) Resin Crystallinity (%) Melting Point ( o C) Lamella Thickness (nm) HDPE 0.942 35 56.1 127.5 4.2 LLDPE 0.936 15 48.4 125.5 3.6 ESCR: Notch Constant Load Test (NCLT) Lamella Thickness: Gibbs‐Thomson Equation and DSC Analysis Shifted Strain (%) Shifted Strain (%) Shifted Stress Shifted Stres LLDPE LLDPE IPR 2011
Transcript of Evaluation of ESCR of PE Resins Using Tensile Strain ...
Evaluation of ESCR of PE Resins UsingTensile Strain Hardening and Extensional Viscosity
Pouyan Sardashti1, Costas Tzoganakis1, Maria Anna Polak2, and Alexander Penlidis1 University of Waterloo
Institute for Polymer Research
University of Waterloo
Converging Flow Technique: Evaluation of Extensional Viscosity Using
Cogswell Methodology (Capillary Rheometry)
ESCR is the resistance to initiation of cracking and embrittlement of polymeric components; herein applied to polyethylene (PE) resins
• Main fracture mechanism involved in polymers (25% of all fractured
Mechanical Approach:• Tensile Strain Hardening Stiffness Test (TSHS)
1: Department of Chemical Engineering, 2: Department of Civil Engineering, University of Waterloo
Environmental Stress Cracking Resistance (ESCR)Environmental Stress Cracking Resistance (ESCR) MethodologyMethodology
Rheological Approach:• Converging Flow Technique:
ResultsResults
Shear Rates
polymers experience ESCR mechanism)
• Function of different micromolecular properties (MW, MWD, SCB, etc.)
• Occurs when polymers are subjected to low levels of stress over long periods of time, and aggressive environment
Mechanism: Slow Crack Growth (SCG)
• Polymer chain rearrangement to minimize stress
• Craze initiation propagation brittle fracture
Linear Elastic Region
Cold Drawing/ Plastic Deformation
Strain Hardening Region
Stress/Load
Displacement/Strain
• Extensional rheometers:
• Sentmanat Extensional Rheometer (SER)• Craze initiation, propagation, brittle fracture Displacement/Strain
Displacement/Strain
Stress/Load
Sentmanat Extensional Rheometer (SER)
• Rheotons (Fiber Spinning)
Objective: Evaluation of ESCRObjective: Evaluation of ESCR RESULTSRESULTS
A potential standard test for evaluation of ESCR
Evaluation of ESCR from simple testing in a reliable
and more practical fashion
Relationship between melt strain hardening and ESCR
Insight into the influences of chain entanglements on
ESCR
Extensional Rheometry: Sentmanat Extensional Rheometer (SER) Need to identify the
extent of entanglements
Conventional Methods: Low accuracy, high uncertainty, long testing periods• Notch Constant Load Test (NCLT), Pennsylvania Notch Test (PENT), Full
Notch Creep Test (FNCT), Notched Pipe Test (NPT)
Potential Extensional Characterization Methods: • Uniaxial Tensile Testing
• Tensile Strain Hardening Stiffness Test (TSHS)• Rheological Techniques
Gel Permeation Chromatography (GPC) NMR
ResinMn
(g/mol)Mw
(g/mol)Mz
(g/mol)PDI
Mw/Mn
SCB (/1000C)
HDPE 25,236 118,501 336,312 4.70 1.8
LLDPE 18,334 90,101 279,526 4.91 3.5
NMR: Nuclear Magnetic ResonanceSCB: Short Chain Branching
0
0.1
0.20.3
0.4
0.5
0.6
0.70.8
0.9
2 3 4 5 6 7 8
dwt/dLog(M
w)
LLDPE
HDPE
Correlation between strain hardening and extent of
4
5
HD HDP LLD
6
7
8
HD HDP LLD
g q• Converging Flow Technique• Extensional Rheometry
MaterialsMaterials
HDPE: High Density Polyethylene (HD 8660.29, ExxonMobil)
LLDPE: Linear Low Density Polyethylene (LL 8550.24, ExxonMobil)7 mm/min 10 mm/min
(MPa)
s (M
Pa)
HD LLDHS (MPa) 0.019 0.013
Tensile Strain Hardening Stiffness Test (TSHS)
• Room Temperature
• 7 and 10 mm/min Crosshead Speed
Hardening Stiffness (HS)=
Log(MW) Future StepsFuture Steps
Investigation of the validity of the techniques on a broader ranger of PE
resins (ESCR between 50 and 800 hours)
Optimization of the TSHS test based on specimen dimensions and crosshead
rates
Development of a standard test for evaluation of the ESCR of PE resinsHDPE 1 HDPE 2 HDPE 1
HDPE 2
hardening and extent of entanglements
0 50 100 150 200 2500
1
2
3
0
1
2
3
4
5
HD HDP LLD
Cheng, J.; Polak, M.; Penlidis, A. J. Macromol Sci. Pure & Appl Chem 2008, 45, 599.
Cogswell, F. N. J.Non‐Newtonian Fluid Mech 1972, 12, 64.
Cheng, J. J. Mechanical and Chemical Properties of High Density Polyethylene Effects of Microstructure on
Creep Characteristics; PhD Dissertation, Dept of Chem Eng, University of Waterloo: Waterloo, Ont., 2008.
Wright, D. C. 1996. Environmental Stress Cracking of Plastics, Smithers Rapra Technology, 1996.
Bernnat,A., Wagner,M.H. Prog Trends Rheol V, Proc Eur Rheol Conf. 5th , 1998.
REFERENCEREFERENCEDensity(g/cm3)
ESCR (h)
Differential Scanning Calorimetry (DSC)
Resin Crystallinity (%)
Melting Point (oC)
Lamella Thickness (nm)
HDPE 0.942 35 56.1 127.5 4.2
LLDPE 0.936 15 48.4 125.5 3.6
ESCR: Notch Constant Load Test (NCLT)Lamella Thickness: Gibbs‐Thomson Equation and DSC Analysis
Shifted Strain (%) Shifted Strain (%)
Shifted
Stress
Shifted
Stres
LLDPELLDPE
IPR 20
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