imaging and rheology techniques · laser diffraction user day and complementary imaging and...

$: Imaging and Rheology techniques · Laser diffraction User day and complementary Imaging and Rheology techniques Rheology Introduction Plastics and polymers injection moulding efficiency,$
Laser diffraction User day and complementary Imaging and Rheology techniques

Etten-Leur 2015

Rheology


Rheology“The science of deformation and flow”

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RheologyIntroduction



Why- Can my product not be pumped to the next production location?

- Is my paint still wet after 3 hours?

- Does it take an hour to drop some glue on my paper?

For all these questions the answer is;

Rheology helps to understand

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RheologyIntroductionRheology Importance to Various Industries

● Pharmaceuticals and personal care products● shelf life, sensory perception, yield point, gel strength, syneresis, consistency

● Foods● texture perception, storage stability, ‘mouth feel’, cooking characteristics, ● processability, extrusion, spreadability

● Ceramics● stability, pouring, pumping, casting performance

● Petrochemicals● lubricant formulation, temperature-viscosity profiles for engine

performance, drilling fluids – suspending capacity and pumpability, ● elevated temperatures and high pressure

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● Plastics and polymers● injection moulding efficiency, extrusion variations, molecular weight determination, dimensional

stability, surface finish, impact strength, glass transition temperature

● Paints, inks and coatings● spatter and fly in roller-coating, spray atomisation, film thickness, colour density, duct flow out,

dot retention and definition, sagging, pigment sedimentation under storage

● Asphalt● binder stiffness, fatigue, rutting, thermal cracking, SHRP specification testing

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Rheological measurements

Depending on the rheometer a sample is loaded between 2 plates or in a bore barrel.

After loading a sample; stress (force) is applied to the sample.

The sample experiences a strain or shear rate depending on the type of stress applied.

Shear rate is an indication of how fast you are deforming a material.

The sample experiences a shear profile.

Typical material properties can be calculated.

Like; Viscometry, Yield stress, Thixotropy and Viscoelatic behaviour.

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FLOW● Viscosity (flow) measurements.

● The resistance to flow.

● How thick is a paint sample.● Will the sample be pumped?

● Types of experiment:- Viscometry- Yield stress- Thixotropy

DEFORMATION● Viscoelastic (Oscillation)

measurements● How does a sample behave

before a sample flows…?

● Predicts sample properties.● Toothpaste – deforms and then

flows out of the tube.

● Types of experiment:- Complex modulus - Phase angle- Creep, Relaxation

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Rheology measurements can be divided into:


Viscosity is defined as “resistance to flow”● To measure viscosity; we measure the resistance (i.e.

stress) when a material is flowing at a certain shear rate● A rheometer measures the push (stress) needed to get

the material to move at a certain speed (shear rate)

Viscosity test:1. Apply a constant shear rate (= force (f or p) per area (a))2. Measure the stress the material requires to flow

(=Shear (strain) rate: change in strain with time)

RateShear

StressShearViscosity

Top plate, surface area (a) rotates

with force (f)

RheologyIntroduction (Flow)


Flow Curves Viscosity is a function of shear rate

Three general flow behaviours

› Most, real, samples are shear thinning with Newtonian regions



Yield Stress Measurement

Apply an increasing rotational “squeeze”, i.e. shear stress to a material

● A To measure viscosity; we measure the resistance (i.e. stress) when a material is flowing at a certain shear rate

● A material with yield stress will stretch easily, until the yield point, then flow

● The stress at the peak in viscosity is the force required to go from solid like to liquid like, i.e. the yield stress

● No peak (black line), no force needed

Stre

ss

Time



Thixotropic Measurement

Viscosity is not only dependent on shear rate it is also time dependent.

Example: Paint.

● Thick in the can on stock

● Thins when stirred.

● It is thixotropic as it does not rebuild straight away on stopping the stirring.





Store paint

Low shear rate

Appears “thick”

Stir paint

High shear rate

Becomes thinner, shear

thinning.

Apply paint

Low shearrate

Termed thixotropic: it takes time to

become thick again / rebuild




Bad PaintGood Paint




● The longer it takes to rebuild, the more thixotropic the sample is

● Thixotropy also affects how long a sample takes to get to steady flow

● Thixotropy is not only an important material parameter. It is important to understand for reproducible measurements, i.e. repeat when fully rebuilt


Most materials are not completely solid nor completely liquid like…

They are

viscoelastic

RheologyIntroduction (Deformation)


Principles – Viscoelastic (Oscillation) testing

● Instead of rotating on a sample, we now oscillate back and forth● We typically apply a sinusoidal signal to the sample● This is non-destructive testing, so can show the properties under

deformation, before flow


From this we can predict sample properties


Complex Modulus – G*From oscillation we can measure the materials complex modulus, the stiffness of a material



Phase AnglePhase Angle can be calculated Different types of materials have a different log / phase angle between the applied and measured sinusoidal signal



Phase AngleFor a Purely Elastic Material – Solid-like behaviourThe stress and strain are exactly in phasePhase angle is zero (Yogurt is elastically dominated, behaves solid like)

For a Purely Viscous Material – Liquid-like behaviourStress and strain are 1/4 of a cycle out of phasePhase angle is 90° (Honey is viscously dominated, behaves as a liquid)



Rheology language tends to use a combined form of complex modulus and phase angle.

● If G’ > G’’, phase angle less than 45° - SOLID LIKE● If G’’ > G’, phase angle greater than 45° - LIQUID LIKE

● G* - modulus, is still a measure of toughness



Oscillation ProceduresThere are fundamentally two parts of the oscillation that we can control:


1. The oscillation AMPLITUDE,stress or strain:

› Run an amplitude sweep experiment to determine the Linear ViscoElasticRegion

2. The oscillation timescale / FREQUENCY:

› Run an frequency sweep experiment to determine the response for different timescales


Amplitude SweepThis tests records the:• Linear Viscoelastic Region (LVER) of a material• Indicates the stability of a suspension.


Small LVR

G’ S

tora

ge M

odul

us

Strain

Large LVR

› Can calculate the “Cohesive Energy” to quantify stability.

› How much energy required to break suspension.

› The larger, the more stable.


Frequency Sweep● A frequency sweep records a

fingerprint spectrum of the material● It can also classify a material into

three general behaviours● The material property at rest (0Hz) classifies behaviour



Frequency Sweep

On studying the phase angle…VISCOELASTIC SOLID: phase angle 0° at 0Hz

(45° 0°) SOLID LIKEVISCOELASTIC LIQUID: phase angle 90° at 0Hz

(45° 90°) LIQUID LIKEGEL : phase angle independent of frequency



Kinexus

RheologyKinexus


Kinexus series rheometers

RheologyKinexus

● Liquids to soft solids● Processability to product performance● Temperature to time dependence● From simple viscosity to complex

viscoelastic parameters


Kinexus series rheometers

RheologyKinexus


Interaction with hardware

● Auto-detection of accessoriesEnvironmental controllers and geometries

● Calibration and configuration data is stored on the instrument Auto-initialization of instrument on accessory change Always know what environmental cartridge is loaded and system

sets up accordingly Changing cartridge or geometry will prompt a re-zero of geometry

– best rheological practice

● System is always ready to measure

● Intelligent, automatic……and simple

RheologyKinexus


Interchangeable lower cartrige system

Self-contained cartridges with unique functionality

● Provide lower geometry interchange and temperature and environmental control for sample

● Fully-integrated into Kinexus chassis● ‘Plug and play’

– all connections made/automatic recognition● Life-tested – repeatable mechanical alignment

(over 12000 operations)

RheologyKinexus


Interchangeable lower plate● Interchangeable lower plates

Match upper and lower geometries for different sample types

Interchange between types of finish to optimize for different sample types

Easy cleaning● Consistent, repeatable and accurate mechanical alignment

● Thermal performance controlled

Stability, ramp performance, minimal thermal gradients Resolution 0.01°C

RheologyKinexus


Temperature control

Plate Cartridge -40C to 200C●Peltier heating and cooling●Additional boost heater design● Improves heating performance●Minimises thermal gradient across Peltier

element lengthening life time●Dedicated protection thermocouples to

prevent overdriving Peltier element●Thermally-modelled – stability, ramp performance, gradient-free

RheologyKinexus


Temperature controlActive Hood Cartridge (-40°C to 200°C)

● Minimized thermal gradients for plate measuring systems● Highly thermally-sensitive samples ● Proprietary design to control radial and vertical thermal losses from

local sample environment● Inlet for inert gas feed

Peltier Cylinder Cartridge (-30°C to 200°C)

● For concentric cylinder-type measuring systems● Highly fluid-like samples through to high concentration yield stress

dispersions

RheologyKinexus


Geometry

Interchange: Quick-connect & releaseNew chuck mechanism for upper geometry

● Easy, quick, positive, reliable‘Plug and play’ configuration for quick start-up

● Auto-recognition● Set up into working state (zeroed and ready for sample loading) in

<30secs

RheologyKinexus


Geometry

Viscometry: Cone (real viscosity)

Oscillation: Cone or plate (gap normally 0.5 – 1mm).

Size of geometry (guidelines):

● Viscosity ca. 1Pa.s: 40mm plates● Viscosity >> 1 Pa.s: 20mm plates● Viscosity << 1 Pa.s: 50-60mm plates

No grip on the sample/slippage:

● Serrated: 700um pyramids● Sand blasted: ca. 30um roughness

RheologyKinexus


GeometryBob systems● Low viscosity samples

● Cup and Bob etc.

● Avoid breaking structure, avoid wall slib (yoghurt)

● Vane Tool

● Slippery samples:

● Sandblasted, Splined, Groved cup and bob

● Very low viscous samples

● Double gap (couette)

RheologyKinexus


Solvent Trap Systems – minimize evaporation

Kinexus Active solvent trap cover (SS) (KNX2514)

● For Active Hood Cartridge ONLY ● Stainless Steel (SS)

Kinexus Passive solvent trap cover (SS) (KNX2513)

● For Standard Plate and Cylinder Cartridges ONLY ● Includes thermal cover to 200°C

and purge gas option

RheologyKinexus


The Kinexus software:

r-Space

RheologyKinexus

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