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Institute for Polymer Research 27th Annual Symposium

Symposium documents for

Costas Tzoganakis

Abstract

Presentation

PROCESSING OF POLYMERS WITH SUPERCRITICAL CO2

Professor Costas Tzoganakis Department of Chemical engineering

University of Waterloo 200 University Avenue West Waterloo, Ontario N2L 3G1

CANADA E-mail: [email protected]

ABSTRACT

Supercritical fluids (SCF) have recently achieved a widespread attention in the synthesis and

processing of thermoplastic polymers. A supercritical fluid (SCF) is a substance that is

compressed beyond the critical pressure and heated above the critical temperature (see figure). At

these conditions, the vapour and liquid phases become

indistinguishable and the substance behaves as a single

phase. Although the SCF remains as a single phase, its

density can be easily “tuned” from gas to liquid values

merely by changing the pressure of the fluid. While the

density of an SCF is liquid like, the diffusivity and

viscosity are intermediate between the gas and liquid

values. The motivation for using SCFs in polymer

processing stems not just from the environmental impetus for their use as benign solvents.

Sorption of SCFs into polymers results in their swelling and changes in mechanical and physical

properties of these polymers. The higher diffusivities of SCFs provide a means of improving mass

transfer characteristics, while lower viscosities assist in reduced energy for pumping. In polymer

extrusion, SCFs are injected in extruders for the purpose of plasticizing a polymer, reducing the

melt viscosity and increasing diffusion rates. This leads to reduced pumping requirements and

thermal degradation as well as it provides interesting potential for chemical modification in

reactive extrusion operations.

In this presentation, results will be presented from studies in four different areas. In the first one,

the effect of supercritical CO2 on the viscosity and elasticity of polymer melts during extrusion

will be highlighted for polyethylene and polystyrene resins. In the second one, the effect of

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supercritical CO2 on the morphology of binary blends will be addressed in view of the influence of

scCO2 on the interfacial tension. In the third study, we will address the role of supercritical CO2 in

reactive extrusion processes by discussing results from grafting and reactive blending experiments.

In the fourth study, the application of scCO2 in an extrusion process for the devulcanization of

rubber crumb will be presented. Finally, current research efforts on the development of a scCO2-

assisted fibre spinning processes will be highlighted.

PROCESSING OF POLYMERSPROCESSING OF POLYMERSWITH SUPERCRITICAL COWITH SUPERCRITICAL CO22

Prof. Costas TzoganakisProf. Costas TzoganakisInstitute for Polymer ResearchInstitute for Polymer Research

Department of Chemical EngineeringDepartment of Chemical EngineeringUniversity of WaterlooUniversity of Waterloo

Waterloo, OntarioWaterloo, OntarioCANADACANADA

•• IntroductionIntroduction•• Supercritical Fluids (Supercritical Fluids (SCFsSCFs) / Applications) / Applications

•• Polymer Extrusion ApplicationsPolymer Extrusion Applications•• Plasticization / Effects on Plasticization / Effects on viscoelasticviscoelastic behaviorbehavior•• Polymer Blending / Interfacial tension and morphologyPolymer Blending / Interfacial tension and morphology•• Reactive ExtrusionReactive Extrusion•• Rubber Rubber DevulcanizationDevulcanization

•• Closing RemarksClosing Remarks•• AcknowledgementsAcknowledgements

OUTLINEOUTLINE

INTRODUCTIONINTRODUCTIONSupercritical Fluids (Supercritical Fluids (SCFsSCFs) / Applications) / Applications

•• vapour and liquid phases are indistinguishablevapour and liquid phases are indistinguishable•• SCF density can be easily SCF density can be easily ““tunedtuned”” from gas to liquid values from gas to liquid values

merely by changing the pressure of the fluidmerely by changing the pressure of the fluid•• density is liquid like / diffusivity and viscosity are density is liquid like / diffusivity and viscosity are

intermediate between the gas and liquid valuesintermediate between the gas and liquid values

INTRODUCTIONINTRODUCTIONSupercritical Fluids (Supercritical Fluids (SCFsSCFs) / Applications) / Applications

Motivation for using sc COMotivation for using sc CO2 2 in polymer extrusionin polymer extrusion

•• Benign solventBenign solvent•• Changes in mechanical and physical properties of polymersChanges in mechanical and physical properties of polymers•• Higher diffusivities improve mass transfer characteristicsHigher diffusivities improve mass transfer characteristics•• Lower viscosities assist in reduced energy for pumpingLower viscosities assist in reduced energy for pumping

ReferencesReferencesA.I. Cooper, A.I. Cooper, J.Mat. Chem.J.Mat. Chem., , 1010, 207, 207--234 (2000).234 (2000).S.G. S.G. KazarianKazarian, , Polymer Science, Ser.C.Polymer Science, Ser.C., , 4242, 78, 78--101 (2000).101 (2000).P.G. P.G. JessopJessop and W. and W. LeitnerLeitner, , ““Chemical Synthesis Using Supercritical FluidsChemical Synthesis Using Supercritical Fluids””, , WeinheimWeinheim, Wiley, Wiley--VCH (1999).VCH (1999).J.L Kendall, D.A. J.L Kendall, D.A. CanelasCanelas, J.L. Young and J.M. , J.L. Young and J.M. DeSimoneDeSimone, , Chem. Rev.Chem. Rev., , 9999, 543 (1999)., 543 (1999).C.A. Eckert, B.L. Knutson and P.G. C.A. Eckert, B.L. Knutson and P.G. DebenedettiDebenedetti, , NatureNature, , 382382, 313 (1996)., 313 (1996).

POLYMER EXTRUSION APPLICATIONSPOLYMER EXTRUSION APPLICATIONS

Extrusion with SCF

Injection of SCF Mixing and dissolution of SCF

On-line measurementof rheological properties

POLYMER EXTRUSION APPLICATIONSPOLYMER EXTRUSION APPLICATIONSPlasticization / Effects on Plasticization / Effects on viscoelasticviscoelastic behaviorbehavior

•• Supercritical COSupercritical CO22 (scCO(scCO22))•• Research StudiesResearch Studies

Capillary, Slit, Wedge Dies

Free Volume Scaling Model

Shear Viscosity

EntranceFlow

Entrance Pressure Drop

Elongational Viscosity

( )2

,,, COCTPγηη &=


Viscosity of PS/COViscosity of PS/CO22 SolutionsSolutions

Gearbox

Extruder

Positive Displacement

Pump

Valve Valve

Pressure Transducers

Control Panel

Opto 22 Data Acquisition System

Feeder

CO2Cylinder

Wedge Die

SecondaryDie

Thermocouples

50 rpm200 C

Polymer(PS)

Twin-screw Extruder


Shear Rate (1/s)0.001 0.01 0.1 1 10 100 1000 10000

Visc

osity

(Pa-

s)

10

100

1000

10000

Cone-Plate Rheometer(220oC-260oC)Capillary Rheometer(220oC-260oC)

Wedge Die Rheometer(203oC-271oC)


Shear Rate (1/s)30 40 50 60 70 8090 200 300 400100

Visc

osity

(Pa-

s)

200

300

400

500600700800900

2000

100

1000

PS viscosity dataPS viscosity data PS/COPS/CO22 viscosity dataviscosity data



η0γ

1e+1 1e+2 1e+3 1e+4 1e+5 1e+6 1e+7 1e+8 1e+9

η/η

0

1e-4

1e-3

1e-2

1e-1

1e+0

Experimental values2nd order C-C model



- Dissolution of 1.0 wt% of CO2 ≈ Decreasing pressure by 9.8 MPa- T-P and T-C interactions depend on the absolute temperature.

Increasing Temperature

Increasing CO2 content

Decreasing Pressure

200°C 210°C

260°C 270°C

1.35 wt%

0.9 wt%

13.3 MPa

8.7 MPa


Entrance Pressure Drop of PS/COEntrance Pressure Drop of PS/CO22 SolutionsSolutions

18

1

52 24 24 24 24 52PT #1 PT #2 PT #3 PT #4 PT #5

TS

Flow

PT — Pressure TransducerTS — Temperature Sensor

Die width is 22All dimensions are in mm



Pressure Profile within the Slit Die

∆ Pent

Pupstream

P

Flow Direction

2nd dieslit dieupstream

ionextrapolatupstreament PPP −=∆



Upstream Pressure, MPa15 20 25 30 35 40

Ent

ranc

e P

ress

ure

Dro

p, M

Pa

0.1

1.0

200 oC, 0% CO2

210 oC, 0% CO2

220 oC, 0% CO2

220 oC, 2% CO2

220 oC, 4% CO2

γapp = 220 s-1



Extension Rate, s-1

100 101 102

Ext

ensi

onal

Vis

cosi

ty, P

a.s

104

105

0% CO2

4% CO2

T = 220 oCPupstream = 27.6 MPa



• Entrance pressure drop of PS and PS/CO2 increases with upstream pressure

• CO2 decreases the entrance pressure drop of PS melts. Entrance pressure drop, plotted versus wall shear stress, coincide on a master curve

• CO2 decreases both shear and extensional viscosities of PS

POLYMER EXTRUSION APPLICATIONSPOLYMER EXTRUSION APPLICATIONSPolymer Blending / Interfacial tension and morphologyPolymer Blending / Interfacial tension and morphology

PS/LDPE BlendsPS/LDPE Blends

Gearbox

Extruder


Pump

Valve Valve


Control Panel


Feeder

CO2Cylinder

Wedge Die

SecondaryDie

Thermocouples

50 rpm200 C

PolymerA+B

Twin-screw Extruder


Shear Rate (1/s)

Visc

osity

(Pa-

s)

10 100 1000100

1000

10000

without CO2

2 wt% CO23 wt% CO24 wt% CO2

Shear Rate (1/s)

Visc

osity

(Pa-

s)

10 100 1000

100

1000

without CO2

3 wt% CO25 wt% CO27 wt% CO2

PS LDPE




0 wt% (x1000)

Schematic

cellcell

cell

0 wt% (x500) 3wt% (x1000)

Schematic

3 wt% (x5000)

PE/PS=80/20


0 wt% CO2 4 wt% CO2PS/LDPE=60/40



0 wt% CO2 4 wt% CO2PS/LDPE=50/50




mη

Γ

γ&

dη

Γ



(a) t = 0.5 hr (b) t = 3 hr (c) t = 6 hr

(f) t = 9 hr(e) t = 8 hr(d) t = 7 hr


Time (hr)0 1 2 3 4 5 6 7 8 9

IFT

(mN

/m)

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

Necking DropStable Drop




CO2 Pressure (MPa)0 4 8 12 16 20

IFT

(mN

/m)

4

5

6

7

200 oC220 oC

Pc

POLYMER EXTRUSION APPLICATIONSPOLYMER EXTRUSION APPLICATIONSReactive ExtrusionReactive Extrusion

Grafting of Grafting of MahMah on PPon PP

CH

CH 3R orI

C

CH3

grafting

OO O

..

C

O

O

O

.CH 3

.

.RH

Rhydrogentransfer

C

O

O

O

.CH3 CH3

O

O

O

C



Die

CO2 2

Cylinder

PP/MAh Peroxide Solution



MAh Content (wt. %)

0.30 0.40 0.50 0.60

Mel

t Flo

w In

dex

(g/1

0 m

in)

10

20

30

40

50 2 % MAh Level without CO 2

2 % MAh Level with CO 2

4 % MAh Level without CO 2

4 % MAh Level with CO 2

T = 190 CLoad = 1.2 kg


Interfacial Reaction (PEInterfacial Reaction (PE--MahMah / PA/ PA--6)6)

O OO

NH2(CH2)5CNHO

+

– H2O

O ON

(CH2)5CNHO

cyclic imide


Interfacial Reaction (PEInterfacial Reaction (PE--MahMah / PA/ PA--6)6)

CO2 Concentration, wt%0 1 2 3 4

MA

Con

vers

ion,

%

0

20

40

60

80

100

30.0 / 00.0 / 70

47.5 / 47.5 / 5

45.0 / 45.0 / 10

40.0 / 40.0 / 20

PE-MA / LDPE / PA-6


Rubber Rubber DevulcanizationDevulcanization

SY

SY

CO2

Vulcanized rubber Crosslink



Gearbox

Extruder


Pump

Valve Valve


Control Panel


Feeder

CO2Cylinder

Wedge Die

SecondaryDie

Thermocouples

50 rpm200 C



Soxhlet extraction

Two-step process to separate gelAcetone : Remove the low molecular weight contentToluene : Extract the sol content

Extrudate Soluble Gel



Rubber flow rate (g/min) – CO2 concentration (wt%)Powder 15-1% 15-2% 15-3% 30-1% 30-2% 30-3%

Wei

ght p

erce

nt o

f who

le s

ampl

e

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Circles: Screw 1Triangles: Screw 2

Soluble content

Sol content

Low molecular weight content

SBR80 / 250 oC

CLOSING REMARKSCLOSING REMARKS

• Highlights from our research work on polymer extrusion with supercritical CO2 have been presented

• Potential innovative applications are numerous

• Our current efforts are focused on membrane and fiber formation as well as on block copolymer and TPV preparation

ACKNOWLEDGEMENTSACKNOWLEDGEMENTS

Funding

Natural Sciences and Engineering Research Council of Canada (NSERC)Materials Manufacturing Ontario (MMO)DuPont Canada Inc.

Researchers

Dr. Minhee LeeDr. Anle XueDr. S. ZhuMs. Beth DorschtMs. Joy Zhang

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