Optimizing Processing of Masterbatchesby Rheology PAM 2016 PRESENTATIONS U… · 15.01.15 | Sheet 3 Solid or Liquid additive for Plastics Coloring or additive Masterbatch Concentrated

www.anton-paar.com15.01.15 | Sheet 1

Optimizing Processing of Masterbatches by Rheology


World Market Leader in Rheometry

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▸ Solid or Liquid additive for Plastics▸ Coloring or additive Masterbatch▸ Concentrated mixture of pigment or additive in a carrier▸ Carrier can be simple wax or resin or linear polymer or even filled

polymer

Masterbatch

Applications of Additive Masterbatches▸ ultraviolet light resistance▸ flame retardant▸ anti-fouling▸ anti-static▸ lubrication▸ anti-slip▸ corrosion inhibitors for metals packaged in plastic▸ anti-microbials▸ anti-oxidants▸ extrusion aids▸ phosphorescence © CC BY-SA 3.0

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MELT RHEOLOGY

PP25 (PP35), CP25-3/TG (CP35-3/TG)

FLOW CURVE, FREQUENCY SWEEP

Zero shear viscosity

Relaxation time

Power law exponent

Deborah number

Master Curve

Mw, MMD (relative)

Shear-rheology

Rheology in Shear Mode

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▸ Melting temperature and glass transition temperatureimportant information for processing and for properties of final products Temperature test

▸ Zero-shear viscosity and low shear rate behavior correlates often to manufacturing problems like irregularities in molded parts Flow curve, frequency sweep, stress relaxation, flow inception, creep, master

▸ High shear viscosity correlates to processing condition: extrusion, injection molding, film blowing Frequency sweep, master curve

▸ Average molar mass and molar mass distributionabsolute determination Frequency sweep, creep test, master curve, relaxation time spectra, MMD calculation

▸ Crossover point G’ = G” relative determination Frequency sweep, master curve

Rheology Characterization: The Most Important Parameters

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Neat Polymer and Polymer with MB Additive with Filler

100

101

102

Pas

10-2

10-1

100

101

102

1/s

Shear Rate .

Polymer with Fillers

Viscosity

Neat Polymer

Viscosity

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Low concentration of filler

High concentration of filler

▸Finding structures…▸ Lower shear rates: more sensitive to

interacting forces▸ High shear rates: orientation of structure

Viscosity Curve

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cv

Particles are “free” to move within the matrix liquid

Particle-Particle interactions Friction due to high concentration

Solid-volume concentration Cv [%]

10% 20%5%

▸Finding structures▸ By regression the viscosity for any concentration can be found

can be done by copying viscosity values into Excel

Viscosity Curve

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Viscosity Curve – Carreau-Yasuda Regression

η0 Zero shear viscosity = proportional to molar massn Power law exponent = qualitative measure for the macro molecules to orient

in shear direction and to reduce flow resistancea Width of transition range = proportional to MMD and PDI

-> narrow MMD=steep, broad MMD=flat)l Relaxation time = time dependent recovery of internal stresses

De Deborah Number

Rule of thumb for processingMake sure that De value is as low as possible

Time ProcessingTime RelaxationDe

*

What‘s the meaning of the 3 ranges?

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▸Vector diagram▸ G* [Pa]: complex shear modulus ▸ Elasticity law of Hooke (for oscillation):

▸ G' [Pa]: storage modulus, elastic portionG'' [Pa]: loss modulus, viscous portionof the viscoelastic behavior

▸ Physically:G' for the stored and G'' for the lost (dissipated) deformation energy

▸ tan [1] = G''/G' damping or loss factor as quotient of the viscous and elastic portions

Oscillatory Tests: Recap

A

A*

G

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▸ Melt mixing is a powerful method to disperse CNT into polymers▸ Masterbatch dilution technique (based on a PC masterbatch)

▸ percolation in the range of 1.0 wt% MWNT ▸ suitable processing conditions can shift percolation to lower values (0.5wt%)▸ effects of mixing equipment and PC viscosity on percolation are small

▸ Direct incorporation method▸ percolation strongly depends on the kind of CNT, production method

(resulting in different sizes, purity and defect levels), and the purifying/modification steps

▸ for commercial MWNT percolation occurs between 1.0 and 3.0 wt% and is lower at lower MWNT diameters and higher purity

▸ HipCO-SWNT (CNI) percolation between 0.30 and 0.35 wt% ▸ stress-strain behavior of the composites: modulus and stress are

enhanced, elongation at break reduced especially above percolation concentration Reference

Masterbatch dilution technique for NT Loading

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▸Too much elasticity and relaxation issues▸ Unwanted side effects due to long relaxation times and high shear processing

speeds▸ Strategy

▸ MB additives => e.g. reduced risk of melt fracture during extrusion▸ Modification of MMD(insitu plasticizer with MB) => lower storage modulus

G’ at higher frequencies (shifted cross over towards higher frequencies) ▸ Deborah-Number De = processing shear rate (smallest diameter) * relaxation

time

Solving Processing Issues

Melt fracture limited processing speed

Die swell after leaving the nozzle

Sharkskin often found with LLDPE and HDPE

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▸ Time dependence (sedimentation) ▸ Short and long time behavior

▸Process behavior▸ Slow/fast, extrusion

▸Structure characterization▸ Polymer: cross linked / non

cross linked dispersions: stable / unstable

▸Material characterization▸ Polymer: molecular structure

Frequency Sweep

Amplitude = const. Frequency = variable

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Frequency Sweep (ISO 15798 2010)Stability of suspensions/emulsions/dispersions

t = 1 / omega

Time dependent structural strength

Time

G‘‘

2

G‘

1

G’ decreasing - Long term behavior = Fluid -like- Strength of the structure G’ decreases- Good flow characteristics- Low stability

G’ constant, light decreasing - Long time structural strength G‘ - Bad flow characteristics - High stability

1

1 2

2


Shelf Life – Long Term Storage

0.001

0.1

10

Pa

10-3

10-2

10-1

100

101

102

rad/s

Comparison of two Dispersion Stability

Long - term storage stability:Evaluation at a low frequencyG' > G'' hence „gel - like“,stable dispersionG'' > G' hence „liquid - like“,unstable dispersion

= 1 %T = +23°C

angular frequency lg

lg G'

lg G''


Frequency Sweep of a Polymer Melt

100

101

102

103

104

105

106

Pa

G'

G''

102

103

104

105

Pas

|*|

10-3

10-2

10-1

100

101

102

103

1/sAngular Frequency

PDMS

G'

G''

|*|

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▸Average Molar Mass M▸ Position of the crossover

point G' = G'', depends on M (here: M1 > M2)

▸Maxwellian Behavior▸ In the range of low

frequencies G''(w) and G'(w) show the slopes of 1:1 and 2:1

Frequency Sweep - Unlinked Polymer Deciphered

Unlinked Polymers: Analysis

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▸Visco-elastic liquid (no gel, unlinked, no filter)▸ Long term: newtonian behavior▸ Short term: viscoelastic behavior

Angular frequency

Complex viscosity

G‘‘ G‘1

12

1

No network structure No links between

macro-molecules

Frequency Sweep

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▸Visco-elastic, linked▸ No long term relaxation▸ Gel stability due to 3D-network structure

Slope: Strength of structure

at rest

Absolute value: Stiffness

Damping G”/G’ Damping behaviour

Frequency Sweep

Angular frequency

G’

G”

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Frequency Sweep: Molar Mass Mw

G'(

) G''(

)

1 10 100

1000G'G''

Angular Frequency

higher average MW

lower average molar mass MW

narrow distribution

broad distribution

longer or branched moleculesshorter or less branched molecules

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Measurements on Three Different Polyethylene Melts

103

104

105

106

Pa

G'

G''

0.01 0.1 1 10 1001/s

Angular Frequency

HDPECOP = 0.22s-1

G’COP = 19,292Pa

LLDPECOP = 52.48s-1

G’COP = 183,050Pa

LDPECOP = 2.18s-1

G’COP = 13,145Pa

low moderate highAverage Molar Mass

LLDPEx 1

LDPEx 24

HDPEx 238

narrow moderate broadMMD LLDPE

x 1HDPEx 9.5

LDPEx 14

▸ An increasing average molar mass is expressed in a COP moved to lower angular frequencies

▸ A vertical shift of the COP towards lower modules (G’COP) indicates a wider MMD

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▸ (1) polymer with unlinked molecules degrees of cross-linking and a narrow MMD

▸ (2) polymer with unlinked molecules and a wide MMD

▸ (3) sparsely cross-linked polymer, flexible gel or dispersion low structural strength at rest

▸ (4) densely cross-linked polymer, rigid gel or dispersion with high structural strength at rest

Frequency Sweep: Polymers, Gels, Dispersions

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▸Time temperature superposition

Frequency Sweep – Master Curve

Background: Due to increasing T the relaxation times are getting shorter Shift factor aT=l(T)/l(Tref) or based on viscosity aT=h(T)/h(Tref) Frequency sweeps (FS) measured at various T can be shifted horizontally Only applicable for unlinked and unfilled polymers Each FS measured at T can be shifted by aT to the so called reference temperature T0

(+) Enlarged frequency range(+) Information about practically relevant shear rates up to 100.000s-1

(+) Determination of the zero shear viscosity

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▸Horizontal shift towards the reference temperature T0▸ TTS example: horizontal shift of storage modulus G’


Angular frequency

Storage modulus G’

260°C

160°C

180°C

200°C

230°C

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▸Horizontal shift towards the reference temperature T0▸ TTS example: shift of storage modulus G’▸ The range above the transition region is called glassy region


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Cox-Merz-Rule…..Example: Liquid MB ( Color)

100

101

102

Pa·s

|*|

10-2

10-1

100

101

103

Pa

G'

G''

0.01 0.1 1 10 100 1,0001/sAngular Frequency

10-1

100

101

102

Pa·s

10-3

10-2

10-1

100

101

102

104

Pa

10-5

10-4

10-3

10-2

10-1

100

101

102

104

1/s

Shear Rate .

0.1

1

10

100

Pa·s

10-5

10-4

10-3

10-2

10-1

100

101

102

104

1/s

Shear Rate .

Flow Curve

Frequency Sweep

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Frequency sweeps of two polymers with different MMDs

Frequency Sweep on a Polymer Melt

Angular frequency

G‘

G‘‘ narrow MMD

wide MMD

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From Master Curve to the Continuous Relaxation Time Spectrum

Rheological fingerprint Basis for further conversions: G(t), MMD

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000Pas

H(

10210

0

101

102

103

104

105

107

Pa

H()

10-3 101 s

SHORTMOLECULES

- 1st cross over region in FS -

LONGMOLECULES

- zero shear voscosityregion in FS -

Distribution

Shoulderinspectrum?-> bimolar

10-2

10-1

100

Relaxation Time

SHEAR [s-1]

TIME [s]

CONVERSION t = = 1 /

LONGMOLECULES

SHORTLONG SHORTMOLECULES

Entanglement region

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From Continuous Relaxation Time Spectrum to Molar Mass Distribution (MMD)

MMD kernels with parameter settings available for the following standard polymers PP PE HDPE PS

LONGMOLECULES

SHORTMOLECULES

LONGMOLECULES

SHORTMOLECULES

101

102

103

104

105

Pa

H()

10-3

10-2

10-1

100

101

102

sRelaxation Time

0

5,000

10,000

15,000

20,000

Pas

H()

H(lambda) [s]

Mass [kg/mol]

CONVERSIONwith THIMM Kernel 0

0.2

0.4

0.6

0.8

1

wi

10 100 1,000 10,000kg/mol

Molar Mass Mi

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Example Molar Mass MW… Calculated Using a Master Curve

0

0.2

0.4

0.6

0.8

1

wi

10,000 100,000 1,000,000g/molMolar Mass Mi

Rheol Acta (2001) 40: 322-328

Weight-AverageMolar Mass Mw : 140,200 g/mol

101

102

103

104

105

Pa·s

|*|

101

102

103

104

105

107

Pa

G'

G''

10-2

10-1

100

101

102

103

105

1/sAngular Frequency

Master Curve 170°C

|*|

G'

G''

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Rheology Analysis Pathways

Frequency Sweep G’(), G’’(), *()

Stress RelaxationStep Strain G(t)

Creep TestStep Stress J(t)

Relaxation Time SpectraH()

Retardation Time SpectraL()

Master CurveFrequency Sweep

Master CurveRelaxation Modulus

Master CurveCreep Compliance

Molar Mass Distribution MMD

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Thank You

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Documents

Optimizing Processing of Masterbatchesby Rheology PAM 2016 PRESENTATIONS U… · 15.01.15 | Sheet 3 Solid or Liquid additive for Plastics Coloring or additive Masterbatch Concentrated