11

Ultrasonic treatment of Ultrasonic treatment of PEN/LCP blends PEN/LCP blends during extrusionduring extrusion

by

Kaan Gunes and A. I. Isayev

Presented at

Conference on Graduate and Undergraduate ResearchThe University of Akron

March 27, 2008

22

OutlineOutline

� Objectives

� Liquid crystalline polymers (LCP)

� Blends of LCP/thermoplastics

� Compatibilization of LCP blends

� Effect of Ultrasound

� Materials

� Ultrasound assisted extrusion

� Experimental methods

� Results and discussion

� Summary

33

ObjectivesObjectives

Problem:Problem:� Blends of wholly aromatic LCPs with thermoplastics not fully

utilized� Optimum degree of compatibilization necessary to preserve

fibrillar LCP structure and improve interfacial adhesion

Research Objectives: Research Objectives: � To design a new ultrasonic single screw extrusion process to

effectively mix blends and induce in situ compatibilization at low residence times

� To study the effect of processing parameters in ultrasonic extrusion on PEN/LCP blends in order to create in situ polymer composites with enhanced mechanical properties

44

Liquid Crystalline PolymersLiquid Crystalline Polymers

Lyotropic: solution processible

e.g. poly(p-phenylene-terephtalamide)

C

O

C

O

N

H

N

H

n

Origin of liquid crystallinity

� Rod like structure� Mesogenic groups in backbone/side chains

Greater rigidityMelting temperature ↑

Stiffness and strength ↑

Processibility ↓

Thermotropic: melt processible

HBA/PET

HBA/HNA

Kevlar ®

1 Wissbrun, K. F., Journal of Rheology, 25(6), 619-662 (1981)

e.g.

55

LCP/Thermoplastic BlendsLCP/Thermoplastic Blends

Desirable properties of LCP blends� High tensile strength and modulus� Toughness� Dimensional stability� Chemical resistance� Low gas permeability

To achieve these properties:� Fine uniform fibrils� Good interfacial adhesion

In situ fiber reinforced composites�Low melt viscosity�LCP fibrillar structure�Fibrils created by elongation flows:

•Fiber spinning / injection molding

LCP fibrils in fiber spinning2

2 Sawyer, L.C. and Jaffe M., Journal of Materials Science, 21 (6), 1897-1913 (1986)

66

Application of LCPs and Application of LCPs and their blendstheir blends

� Typical applications of LCPs, and their blends include3

� Electronics interconnects

� Medical technology

� Automotive engineering

� Chemical process equipment

� Fuel cells

� Weathering-resistant fibers

� Packaging

3 Vectra LCP Application Database, Ticona.com

77

Compatibilization of LCP/Polyester Compatibilization of LCP/Polyester BlendsBlends

Traditional methods:�Addition of block copolymers�Transesterification by internal mixing or annealing for long times

OO

OHA

C

∆, ))))

B

O O

OH

A

B

O

Transesterification of polyesters

Heat / Mechanochemistry

Generation of copolymers through transesterification in the interface of polymer blends promotes compatibility through improved interfacial adhesion4

4 Porter, R. S., Wang, L-H, Polymer 33(10), 2019-2030 (1992)

88

Mechanism of UltrasoundMechanism of Ultrasound

Ultrasonic cavitation� High amplitude alternating pressure created by ultrasound.

� Oscillating forces nucleate bubbles at sites of material defects

5 Price, G. J. in “New Methods of Polymer Synthesis,”Edbon, J. R., Eastmond, G, Eds.,Chapman Hall: NY (1995)

Defects can be:

•Dissolved gasses

•Cryst. lattice imperfections

•Polymer/filler interface

•Immiscible blend interface

Mechanism of Cavitation5

99

In situ Ultrasonic CompatibilizationIn situ Ultrasonic Compatibilization

Ultrasonic cavitation in polymer melts

� Ultrasonic cavitation in melts can lead to� Chain scission� Formation of reactive end groups� Formation of interfacial graft/block copolymers� Creation of high MW species� Mn ↓, Mw ↑

� Recorded improvements in� Tensile strength� Elongation at break� Young’s modulus� Toughness

� Benefits:� Single step, continuous and fast operation, can be scaled up� Residence time is ultrasonic zone controlled

6Gunes, K., Isayev, A. I., ANTEC-SPE, 1533-1537 (2007)7 Lin, H., Isayev, A. I., Journal of Applied Polymer Sci., 102(3), 2643-2653 (2006) 8 Isayev, A. I., Ghose, S. in Rubber Recycling, De, S. K., Isayev, A. I., Khait, K eds., Boca Raton, FL: Taylor & Francis/CRC Press (2005)

Studied blends include: 6,7,8

�PET/LCP�PA6/PP�PP/NR�PP/EPDM�PP/EPDM�HDPE/NR�HDPE/EPDM�HDPE/SBR

1010

MaterialsMaterials

LCP: Vectra A950, Ticona (Tm=275oC)� Wholly aromatic copolyester containing 73% HBA and 27% HNA

PEN: VFR 40046, Shell Chemical Company (Tm=275oC)

1111

The Ultrasonic ExtruderThe Ultrasonic Extruder

Screw flightsScrew flightsScrew flightsScrew flights

•7 s residence time

•Frequency: 20 KHz

•Amplitude: 0-10 µm

PEN and PEN/LCP blends:

•260°C Feed, 300°C other zones

•10 rpm screw speed

•1 kg/hr flood feeding

Pure LCP was processed at 260°C feed, 285°C other zones, 15 rpm, 1 kg/hr flood feeding6

1212

Animation of Animation of copolymer copolymer formation in formation in ultrasonic extrusionultrasonic extrusion

1313

Experimental MethodsExperimental Methods

Injection molding: Van Dorn 55 HP-2.8F� Impact (ASTM D 256-05) & mini tensile bars (ASTM D 638-03)� 260°C Feed/ 285°C other zones; 27oC mold, 150 mm/s, 55 ton Clamping force, 4 MPa holding

pressure for 5 s, 25 s cooling

Rheological measurement: RH7 Advanced Capillary Rheometer, Bohlin Instruments� 300oC, 1:24 die, Ф=1 mm. Apparent shear rate: 20-2877 s-1 in 10 logarithmic steps, 69 MPa PTMorphological studies: Hitachi S-2150 SEM � Cryofractured injection molded mini tensile bars, skin-core micrographsMechanical tests:� Instron 5567 tensile tester

� 10 kN load; 5 mm/min crosshead speed; extensometer with 7.62 mm gauge length� Average of 6 samples

� Izod impact tester (Testing Machines Inc.) � Unnotched; Blends: 907 g load, LCP and PEN: 4536 g load� Average of 20 samples

Dynamic mechanical thermal analysis:� Elmer Pyris Diamond

� Oscillatory tension, frequency 1 Hz, Heating 20 to 150oC at 2oC/min

1414

Results and Discussion

1. Process characteristics2. Rheology3. Mechanical properties4. Microscopic Analysis

1515

Process CharacteristicsProcess CharacteristicsPressure (PEN & blends)

Pressure ↓ w/ ultrasonic amplitude due to:

Acoustic cavitation in melt:

�Permanent and thixotropicviscosity change

�Possible slip of polymer melt along the solid surface

Pressure greater in blends:

�Greater viscosity of blends with and without treatment for the low shear rate in extrusion of ~10 s-1

�Higher pressure at 7.5 µm indicates less degradation with presence of LCP

Pressure before ultrasonic treatment zone vs. ultrasonic amplitude

Ultrasonic amplitude (µm)

-2 0 2 4 6 8 10 12

Pre

ssu

re b

efo

re u

ltras

ou

nd z

one

(M

Pa)

0

1

2

3

4

5

6

PEN 90/10 PEN/LCP 80/20 PEN/LCP

1616

Process CharacteristicsProcess CharacteristicsUltrasonic Power Consumption (PEN & blends)

�Power consumption ↑ with ultrasonic amplitude

�Similar effect of ultrasound on PEN and blends

Ultrasonic power consumption vs. ultrasonic amplitude

Ultrasonic amplitude (µm)

0 2 4 6 8 10

Ultr

aso

nic

po

wer

co

nsu

mpt

ion

(W

)

0

50

100

150

200

250

PEN 90/10 PEN/LCP 80/20 PEN/LCP

1717

Process CharacteristicsProcess CharacteristicsUltrasonic Power Consumption & Pressure for LCP 6

Ultrasonic Amplitude

0 2 4 6 8 10

Pre

ssur

e (M

Pa)

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

Ultr

aso

nic

Po

wer

Con

sum

ptio

n (

W)

0

20

40

60

80

100

120

140

160

180

200

PressureUltrasonic power consumption

�Pressure greater due to processing at 15 RPM

�Pressure decreases at 5 µm and is similar at higher amplitudes

�Similar change in power consumption as in PEN and blends

Values shifted along abscissa for clarity

6Gunes, K., Isayev, A. I., ANTEC-SPE, 1533-1537 (2007)

1818

ViscosityViscosityPEN and LCPPEN and LCP

γ& γ&

γ&

•Viscosity of PEN ↓ w/ ultrasonic treatment � Degradation of PEN•Degradation of virgin PEN by extrusion without treatment•PEN: Newtonian, LCP: shear thinning•Less significant effect of extrusion and ultrasonic treatment on viscosity of LCP•Low �LCP viscosity highest at 7.5 µm. High �overlap, oriented domains.

Apparent shear rate (s-1)

10 100 1000 10000

App

aren

t vis

cosi

ty (

Pa

*s)

10

100

1000

PEN 0 µm PEN 5 µm PEN 7.5 µm PEN 10 µmPEN virgin

Apparent shear rate (s-1)

10 100 1000A

pp

are

nt V

isco

sity

(P

a*s

)10

100

LCP 0 µm LCP 5 µm LCP 7.5 µm LCP 10 µm LCP virgin

γ& γ&

1919

ViscosityViscosityPEN/LCP blendsPEN/LCP blends

Apparent shear rate (s-1)

10 100 1000

Ap

par

ent V

isco

sity

(P

a*s)

10

100

1000

90/10 PEN/LCP 0 µm 90/10 PEN/LCP 5 µm 90/10 PEN/LCP 7.5 µm 90/10 PEN/LCP 10 µm

Apparent shear rate (s-1)

10 100 1000

Ap

pare

nt V

isco

sity

(P

a*s

)

10

100

1000

80/20 PEN/LCP 0 µm 80/20 PEN/LCP 5 µm 80/20 PEN/LCP 7.5 µm 80/20 PEN/LCP 10 µm

•Viscosity of 80/20 PEN/LCP > that of 90/10 PEN/LCP•Blend viscosities do not decrease until 10 µm � different effect than for PEN•Blend more shear thinning with increasing LCP content•Slight increase in viscosity of 90/10 PEN/LCP with treatment at 5 µm

2020

DMADMAPENPEN

Storage (A) and loss (B) modulus vs. temperature for PEN without and with ultrasonic treatment

Temperature (oC)

60 80 100 120 140

E' (

Pa)

1e+6

1e+7

1e+8

1e+9

1e+10

PEN 7.5 µm

PEN 10 µm

PEN 5 µm

Virgin PEN

PEN 0 µm

(A)

Temperature (oC)

60 80 100 120 140

E"

(Pa)

1e+6

1e+7

1e+8

1e+9

PEN 7.5 µm

PEN 10 µm

PEN 5 µm

Virgin PEN

PEN 0 µm

(B)

2121

DMADMAPEN tan PEN tan δδ

Tg of PEN (tan δ peaks)

tanδ (oC) PENVirgin 1300um 1315um 1307.5um 12910um 126

Temperature (oC)

60 80 100 120 140

tan

δ

0.01

0.1

1

10

PEN 7.5 µm

PEN 10 µm

PEN 5 µm

Virgin PEN

PEN 0 µm

Severe degradation of PEN at 10 µm

2222

Mechanical PropertiesMechanical PropertiesTensile strength & Young’s modulus

�Tensile strength and Young’s moduli ↑ w/ LCP content. �With ultrasonic treatment, increase for 90/10 PEN/LCP at 7.5 µm and decrease for PEN and blends at 10 µm

Ultrasonic Amplitude (µm)

0 2 4 6 8 10

Ten

sile

str

engt

h (

MP

a)

20

40

60

80

100

120

140

160

180

200

220

Pure PEN 90/10 PEN/LCP 80/20 PEN/LCP Virgin PEN

Ultrasonic Amplitude (µm)

0 2 4 6 8 10

Yo

un

g's

mo

du

lus

(GP

a)

0

2

4

6

8

10

Pure PEN 90/10 PEN/LCP 80/20 PEN/LCPVirgin PEN

2323

�Elongation ↓ with LCP content and at 10 µm for PEN and blends� Impact strength more sensitive to polymer degradation� Improvement in impact strength at 7.5 µm for 90/10 blends.

Mechanical PropertiesMechanical PropertiesElongation & Impact strength

Ultrasonic amplitude (µm)

0 2 4 6 8 10

Elo

ngat

ion

at y

ield

(%

)

1

2

3

4

5

6

7

8

9

Pure PEN 90/10 PEN/LCP 80/20 PEN/LCP Virgin PEN

Ultrasonic Amplitude (µm)

-2 0 2 4 6 8 10 12

Imp

act s

tre

ng

th (

kJ/m2 )

0

20

40

60

80

100

120

140

160

180

200

Unextruded PENPure PEN 90/10 PEN/LCP 80/20 PEN/LCP

2424

Mechanical PropertiesMechanical PropertiesEffect of ultrasound on LCP 5

� Impact strength 261 kJ/m2 untreated LCP ↑ to 346 kJ/m2 at 7.5 µm. � Tensile strength 262 MPa untreated LCP ↑ to 273 MPa at 7.5 µm. � Ultrasound could have led to structural changes of LCP melt

Ultrasonic Amplitude ( µµµµm)

0 2 4 6 8 10

Impa

ct S

treng

th (kJ

/m2 )

220

240

260

280

300

320

340

360

Ten

sile

Stre

ngth

(M

Pa)

240

250

260

270

280

You

ng's

Mod

ulus

(G

Pa)

8.0

8.5

9.0

9.5

10.0

10.5

11.0

Young's modulus

Impact strength

Tensile strength

5Gunes, K., Isayev, A. I., ANTEC-SPE, 1533-1537 (2007)

2525

Microscopic AnalysisMicroscopic Analysis

�LCP droplets in core&fibrils in skin—Larger at 10 µm due to low η of PEN

90/10 7.5 µm 90/10 10 µm90/10 0 µm

Skin

Core

2626

Microscopic AnalysisMicroscopic Analysis

80/20 7.5 µm 80/20 10 µm80/20 0 µm

Skin

Core

�LCP droplets/fibrils in core/skin larger in 80/20 than in 90/10 and also at 10 µm

2727

Microscopic AnalysisMicroscopic AnalysisInterfacial thicknessInterfacial thickness

Ultrasonic Amplitude (µm)

0 2 4 6 8 10 12

Inte

rfac

ial t

hick

ness

( µm)

0.04

0.06

0.08

0.10

0.12

0.14

90-10 PEN-LCP80-20 PEN-LCP

90/10 PEN/LCP 7.5 µm

�Decrease in interfacial thickness suggests improved interfacial adhesion through possible copolymerization reactions.

2828

SummarySummary

�The novel ultrasonic extrusion method has been used to study compatibilization of PEN/LCP blends with the possibility of improving their mechanical properties.

�Ultrasonic treatment leads to competition between fibrillation and compatibilization

�PEN viscosity decreases with extrusion and with ultrasonic treatment, its Tg is lower with treatment at an amplitude of 10 µm

�Slight increase in LCP viscosity occurs with treatment at 7.5 µm, but otherwise there is little effect of ultrasound on its viscosity.

�Increases in Young’s modulus, tensile strength and impact strength of 90/10 PEN/LCP suggest improved interfacial adhesion with minimal change in LCP fibrillation through possible copolymerization during ultrasonic treatment

2929

Thank you for your attention