Recycling

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Recycling RheologyWarwick Manufacturing
Group28th November 2000

• Don Fleming
• FLEMING Polymer Testing Consultancy

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Contents

• Introduction-Don Fleming
• FLEMING Polymer Testing Consultancy
• Polymer Rheology

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Introduction-Don Fleming

• 1985-1989, Mechanical Engineering degree
• 1989-1993, PhD in Mechanical Engineering -
  In-Line Rheometry studies in Reactive Extrusion
• Design, Instrument Install In-Line Rheometer on
  APV 30mm twin screw extruder. In-Line monitoring
  of the reactive extrusion of peroxide X linked
  LLDPE. Study of residence time distribution in
  TSE using Raman Spectroscopy (Journal of Applied
  Spectroscopy, Volume 50 (6) (1996))
• 1993-1994, Post-Doctural research with Shell
  Chemicals-reactive extrusion of PET foam using a
  twin screw extruder
• Create, sustain reaction and foam in one twin
  screw extruder
• Reduce foam density and optimise reaction by
  manipulation of screw configuration
• 1994-1998, Rosand Precision-UK Sales Manager
• Instruments-Twin Bore Capillary Rheometer
  Instrumented Falling Weight (IFW) Impact Tester
• Niche market products-low volume high cost
• Limited sales-many companies unable to justify
  financial time investment

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FLEMING Polymer Testing Consultancy

• 1/6/1998 to date, FLEMING Polymer Testing
  Consultancy - Principal Specialisation-Rheometry
  and Instrumented Impact
• Equipment - Rosand RH7-2 Twin Bore Capillary
  Rheometer, Rosand IFW 413 Instrumented Impact
  tester, CEAST Pendulum
• Some Current Projects

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Conference Presentations

• To Date
• Fleming, D.J., Analytical and Computational
  approaches for Wall Slip calculation in Polymeric
  materials, Mechanics in Design 98, Paper written
  and presented by the author at The Nottingham
  Trent University, 6-9 July 1998.
• Fleming, D.J., First Normal Stress Difference via
  Capillary Rheometry-Fact or Fiction?, Rheology-A
  Practical Approach to Quality Control, Paper
  written and presented by the author at RAPRA on
  1st October 1998.
• Fleming, D.J., Capillary Rheometry-a technique
  sensitive to molecular architecture, Paper
  written and presented by the author at Molecular
  Mass Charactersiation of Synthetic Natural
  Polymers, MOLMAS 99, Oulton Hall, Leeds on 30th
  March 1999.
• Fleming, D.J., and Renolds, N, Observation of
  progressive damage in Plytron using instrumented
  falling weight and thermal imaging techniques,
  Breaking Plastics 99, Telford Golf Country
  Club, Telford, 22nd-23rd September 1999.
• Fleming, D.J., Capillary Rheometry-melt fracture,
  Polymer Rheology 99, Paper written and presented
  by the author at RAPRA, 13th -14th October 1999.
• Fleming, D.J., Capillary Rheometry and beyond !
  Progress in Rubber and Plastics Technology,
  September 1999.

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Polymer Rheology

• Rheology-the science of deformation flow
• Capillary Rheometry is a technique used to
  accurately reproduce deformation
• Most polymer production processes exploit
  deformation and flow to form a useful product
• It is often a materials resistance to
  deformation that can yield the most intriguing
  insights
• How can rheology give us an insight into such
  areas as mixing molecular architecture?

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MFI-simple capillary rheometry

• Melt Flow Index was one of the 1st techniques
  used to indicate polymer structure
• Developed by ICI to grade oelefin
  production-early difficulty in the control of Mw
• MFI-a simple robust, one number technique used
  to indicate viscosity (resistance to deformation)
  and correlate Mw
• MFI uses a heated barrel and a mass driven piston
  to force melt through a die (capillary)-more
  mass/unit time greater MFI no. lower Viscosity
  lower Mw
• Historical difficulties - testing very high or
  very low viscosity mtls, poor operator
  repeatability

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PP _at_ 230C having an MFI value of 2.4
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Shear Viscosity Function

• Polymer melt viscosity changes with deformation
  rate (shear rate)
• Viscosity is a function of shear rate-hence
  viscosity function-MFI only indicative of one
  rate
• Rheometer is capable of generating the viscosity
  function over a range of deformation rates
• Fortuitously melt viscosity reduces with rate-as
  an anisotropic microstructure is created on
  alignment
• The degree of alignment influences viscosity
  function and microstructure

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a wide range of polymers
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Different shear viscosity functions created by
the reactive extrusion of LLDPE over a range of
flow rates using a 0.1 peroxide concentration.
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Curious results

• Peroxide concentration kept constant
• Expect viscosity not to change degree of
  cross-linking to remain constant irresp of
  throughput M
• Peroxide half life well exceeds Rt at 2kg/hr
• Viscosity degree of cross-linking increases
  with M
• Mixing is poor at low M although Rt is less
  than half life at 12kg/hr mixing is better and
  cross-linking more efficient - greater viscosity
• Shear viscosity function sensitive to deg of X
  linking
• Shear viscosity function is sensitive to changes
  in Mw
• GPC appears to be insensitive to degree of
  X-linking

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Melt Fracture in HDPE
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Melt Fracture in Metalocene catalysed LLDPE
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Shear Viscosity Function

• Viscosity is a function of shear rate
• Viscosity needs to be measured over a range of
  shear rates
• Viscosity function is sensitive to molecular
  alignment
• Viscosity function is sensitive to Mw changes
• Viscosity function can expose Melt fracture

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Elongational Viscosity

• So far we have talked about Shear viscosity
• Polymer melts are highly complex visco-elastic
  materials-they also stretch!
• Polymers deform in both shear and elongation in a
  typical deformation
• Resistance to elongation, elongational viscosity
  is also sensitive to molecular architecture-specif
  ically MWD

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Where do we encounter elongational viscosity-Film
Blowing
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Catalyst Effects on MWD

• Near identical shear viscosity functions in High
  Density Polyethylene

Data HDPE1 HDPE 2 MFI (g/10mins) 0.21
0.23 Density (Kg/m3) 954
958 Mw 155,000 200,000 Polydispersity
8.1 16
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Significant Changes in Elongational Viscosity

• Elongational Viscosity differences suggest
  dissimilar MWD
• Dissimilar catalyst types confirm MWD changes
• Broader MWD expected from Phillips catalyst

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Radiation Cross-linking

• Radiation X-linked LLDPE
• No differentiation possible in MFI -despite
  increasing irradiation levels
• No differentiation possible in shear
• Grades very different on film blowing

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Radiation Cross-linked LLDPE

• Differentiation clearly seen in extension
• Identical shear viscosity functions indicate
  similar Mw
• Dissimilar elongational viscosity functions
  indicate MWD changes

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Elongational Viscosity Function

• Polymers deform in both shear and elongation
• Resistance to elongation is sensitive to MWD

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Conclusions

• Capillary rheometry is a technique that is
  sensitive to molecular architecture
• Shear Viscosity function can provide a good feel
  for the Mw and degree of molecular alignment
• Elongational Viscosity function can illuminate
  differences in MWD