Optimizing Processing of Masterbatchesby Rheology PAM 2016 PRESENTATIONS U… · 15.01.15 | Sheet 3...
Transcript of Optimizing Processing of Masterbatchesby Rheology PAM 2016 PRESENTATIONS U… · 15.01.15 | Sheet 3...
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Optimizing Processing of Masterbatches by Rheology
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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
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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''
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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’
Frequency Sweep – Master Curve
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
Frequency Sweep – Master Curve
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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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