fundamentals of rheology; concepts and measurements

(c) 2016 Elementis Specialties ACS 2012-Elementis Specialties, Inc.

Fundamentals of Rheology;

Concepts and Measurements

Mihai Polverejan, Ph.D.

PNW Society for Coatings

Technology

January, 2016

(c) 2016 Elementis Specialties

Agenda

• Current WB Thickener Technologies

– Clays, HEC, ASE/HASE, NiSATs

• Rheological Concepts

– Viscosity, Shear Rate, Yield Point

• Evaluation Methods

– Rotational and Oscillatory Rheometry

• Examples


Thickener Types for Waterborne Coatings

• Inorganic Thickeners

– Attapulgite / Bentonite clays / Hectorite clays

– Fumed Silica

• Cellulosic Thickeners

– HEC

– HMHEC

• Alkali-Responsive Thickeners

– ASE

– HASE

• Nonionic Synthetic Thickeners

– NiSAT- HEUR

– NiSAT - HMPE


• Naturally occurring layered aluminum silicate

minerals

• Rarely used as a sole thickener

• There are two types of clays; Swelling and non-

Swelling

CLAYS

• Viscosity build

• Sag control

• Pigment suspension

• Metal flake control


BENTONITE

HECTORITE

SMECTITE CLAY

SWELLING

KAOLIN

MICA

NON-SWELLING

CLAYS

Clay Minerals Family


Gel-structure

Flocculation

Swelling

Hydration

Water

(Osmosis)

Deagglomeration

Water

Shear force

Smectite agglomerate

Na- Ions +

Clay Thickening Mechanism


Silica Alumina Silica

8000 Å

10 Å

BENTONITE

Silica Magnesia

Silica

800 Å

10 Å

HECTORITE

Bentonite and Hectorite

Bentonite [Na-Al-Mg-Silicate]

Hectorite [Na-Mg-Li-Silicate]

H2O 13.7 12.5 Colour green cream

Platelet shape equidimensional elongated

Platelet size 0.8 x 0.8 x 0.001 µm 0.08 x 0.8 x 0.001 µm

Swelling ability 16 x 24 x


Hectorite vs. Bentonite - Viscosity

1120

1920

3740

01000

2000

3000

4000

Bro

ok

fie

ld v

isco

sit

y,

cp

s

Bentonite clay BENTONE CT BENTONE MA (SD)

• Hectorite requires

more shear

• Hectorite has slower

hydration rate

• More efficient

• More effective:

• Syneresis control

• Suspension

stability

• Greater thixotropic

behavior

• Sag resistance

5% water gels


Hectorite Clay Products

PRODUCT DESCRIPTION % ACTIVE MATTER

BENTONE® OC Unrefined hectorite clay 40 - 60

BENTONE® CT Unrefined hectorite clay 50

BENTONE® GS Refined hectorite clay 100

BENTONE® DE Refined hectorite clay

Hyperdispersible 100

BENTONE® MA Refined hectorite clay 100

BENTONE® LT Organically modified refined

hectorite 100

BENAQUA® 4000 Hectorite/polymer composite 100

BENTONE® DY-CE Organically modified clay 100

BENTONE® DH Organically modified hectorite 100


NonSwelling Clay e.g.. Attagel 40,50

• Colloidal, inorganic mineral thickeners

• Optimum dispersion (high speed) is necessary to attain maximum viscosity – 3 -10 lbs./100 gal. added as last part of pigment

• 3 - 5 lbs. in semi gloss

• 3 - 7 lbs. in interior flat

– Should avoid excessive amount of dispersants

physical appearance micronized powders

pH 7.5 - 9.5

average particle size (microns) 0.1

color light cream

bulking value (gal/lbs.) 0.0507


SILICAS

• Advantages – low cost

– provides settling resistance

– provides sag resistance

– Imparts thixotropy

• Disadvantages – pH sensitive

– powder (low density)

– decreases gloss

– cannot be used as sole thickener

• Commonly occurring

mineral

• forms loosely-woven lattice-

like network by hydrogen

bonding between particles

– network is stable at rest

– network is disrupted by

the application of an

applied stress or force,

but rebuilds when stress

is removed

(c) 2016 Elementis Specialties (c) 2016 Elementis Specialties

12

• naturally-occurring polysaccharide

• insoluble in water

• hydroxyl groups hinder solubility by promoting hydrogen bonding

- results in highly ordered crystalline structure

Structure of Cellulose

2OH 2OH

anhydrous ring

Hydroxy Ethyl Cellulose - HEC


Cellulose Ether Thickeners

Advantages vs. Disadvantages

• Advantages

– reasonable properties for most paints as a single thickener

– provides good resistance to sagging and some settling and syneresis control

• Disadvantages

– increase probability of flocculation and lower gloss

– reduces washability

– lower film builds

– promotes roller spatter

– prone to microbial attack

• Solution viscosity increases

when HEC is dissolved in

water or other aqueous system

– polymer chains become

uncoiled and hydrated

– entanglement of hydrated

polymer chains in solution

– proportional to the polymer

chain length and polymer

molecular weight

13


14

• Thicken through volume exclusion

– hydrophilic backbone tends to associate with the

surrounding water molecules

• Viscosity dependent upon the molecular weight (chain

length) and nature of the polymer :

• linear

• branched

• cross-linked

Modified Acrylics - ASE

Non-Associative: Alkali Soluble Emulsions


OH-

pH > 7

COOH

COOH COOH COOR COOH

COOH COOH COOR

COOR COO-

COO- COO-

COO- COO-

COO- COOR

ester group

carboxylate anion

COOR

COO -

ASE Thickening Mechanism

COOR COO-

COO- COO-

COO- COO-

COO- COOR


Alkali Swellable Emulsions Comparison with Cellulosics

• Advantages over Cellulosics

– Easier handling in production

– Not susceptible to microbial attack

– Lower cost

• Drawbacks

– More water sensitive

– Fairly pseudoplastic

– Poor resistance to roller spatter


OH-

pH > 7

COOH

COOH COOH COOR COOH

COOH COOH COOR

COOR COO-

COO- COO-

COO- COO-

COO- COOR

hydrophobic group ester group

carboxylate anion

COOR

COO - binder

HASE Thickening Mechanism


RHEOLATE ® ASE / HASE Series:

Rheological Additives – Acrylic/ Alkali Swellable

Alkali Swellable Emulsion

Hydrophobically Modified ASE

• High thickening efficiency:

• pH activated: 8.0 +

• VOC Free

• Easy to incorporate

• Use alone or with other thickeners


RHEOLATE® Type VOC %

Active

Shear

Range

% Use

Level Applications

1 ASE none 30 Mid 0.3 -1.0 Across the board; industrial

& deco

125

150

ASE

HASE

none

none

30

30

Low-Mid

Low

0.3 -1.0

0.3 – 1.0

General Industrial

High efficiency low to mid-

shear- deco & industrial

175 HASE none 30 Mid 0.3 – 1.0 Mid-shear good leveling-

deco

420 HASE none 30 Mid 0.3 – 1.0 Across the board- Industrial

& deco

475 HASE none 30 Mid 0.3 – 1.0 Across the board; excellent

flow & leveling; good gloss

450 HASE none 30 Mid-High 0.3 – 1.0 High PVC systems- mainly

deco

RHEOLATE® ASE / HASE Series


Associative Thickeners

• NiSAT = Non-Ionic Synthetic Associative Thickeners

(HEUR & HMPE)

• HEUR = Hydrophobically Modified Ethyleneoxide

Urethane

• HMPE = Hydrophobically Modified PolyEther

Associative Thickener - Structure

Surfactant

Associative Thickener

Hydrophilic Tail

Hydrophilic

Backbone

21

hydrophobes

hydrophilic Polymer

Hydrophobic Head


Associative Thickener – Surfactant:

Reason of Mechanism of Viscosity Loss

Once surfactant levels reach

critical levels they form their

own micelles which further

disrupt the AT mechanism as

the hydrophilic (water soluble)

tails cannot associate with

anything

Closed Micelle Structure


Thickening Mechanism Associative Thickener Only

Hydrophobic

Particle

Hydrophobic

Particle

Hydrophobic

Particle

Fully Networked


Network Totally

Disrupted

Hydrophobic

Particle

Hydrophobic

Particle

Hydrophobic

Particle

Mechanism of Viscosity Loss Associative Thickener With High Levels of Surfactant


0

200

400

600

800

1000

1200

1400

1600

1800

0 0.2 0.4 0.6 0.8 1

Wt % Surfactant

Bro

okfi

eld

Vis

co

sit

y, cp

s

HLB = 3.6

HLB = 10.0

HLB = 12.4

Anionic

Effect of Surfactants

Ingredient effects on thickener response


NiSAT (Associative) Thickeners

Superior Performance:

• pH independent

• ability to tailor rheology

• good leveling

• spatter resistance

• ease of use

• broad application

• newer technologies offer more resistance to

surfactant interactions


Rheology Modifiers for Various Shear Rates

Bentone® EW, Bentone® DH (clays)

Rheolate® 666 Rheolate® 150

Rheolate® CVS-10, Rheolate® CVS-11

Rheolate® 310, Rheolate® 678

Rheolate® 475 (HASE)

Rheolate® 212, Rheolate® 644

Rheolate® 350, Rheolate® HX 6050

BROOKFIELD cPs or mPas STORMER

KU

Cone & plate ICI


Rheological Additives - Why?

• Storage stability: Antisettling / Syneresis

• Application behavior

–Sag resistance

–Levelling

–Roller-spatter resistance


Viscosity (η)

(Resistance to Flow) =

Shear Stress

Shear Rate

(t)

(g) .

Definition of Viscosity

Newton´s Law: τ= γxη .


F [N] A= area [m²]

Shear Stress

t = shear stress = F/A [N/m²]


F [N]

Shear Rate

g = shear rate = v/d [1/s]

d [m]

v = velocity [m/s]

.


Assumption:

linear velocity (V) = 0.5 m/s

d = 0.2 mm

shear rate =

v

d = 0.5 m/s

0.0002 m

shear rate = 2500 1/s

d= 0.2 mm

V= 0.5 m/s

Shear Rate - Roller Application


V= 5 s/m = 0.2 m/s

Film thickness = 50 µm

Shear Rate – Brush Application

0.2 m

5 x 10-5 m s = 4000 s-1 shear rate [1/s] =


V= 0.1 m/s

Film thickness = 5 mm

shear rate [1/s] = 0.1 m = 20 s-1

0.005 m s

Shear Rate – Trowel Application


Newtonian Viscosity is independent of shear rate

Viscosity profiles - Newtonian


Viscosity profiles - Dilatant

dilatant Viscosity is increasing with increasing shear rate


Viscosity profiles - Pseudoplastic

pseudoplastic Viscosity is decreasing with increasing shear rate


Viscosity profiles - Thixotropic

thixotropic time dependent recovery after shear is removed


Cone Plate (ICI) Viscometer

Rotor

Stator

Measures Absolute Viscosity

at constant shear of 10000 1/s

(Inclined plane varies film

thickness “d” at the same rate as

the velocity “V” is changing.


Shear

rate varies from zero to

upper limit defined by

rotational speed & disk diameter

Spindle Disk Viscometer


Measures “single point”

quasi-viscosity. Shear

rate varies from zero to

upper limit defined by

rotational speed & paddle length

Krebs Stormer Viscometer


Flow curve - Emulsion paint

0.1

1

10

100

1,000

Pa·s

10-1

100

101

102

103

1/s

Shear Rate g.

RHEOLATE® 278, PVC 50% HEC, PVC 50%

Two paints with

very different flow

properties


Viscosity measurement for coatings

ICI

Cone & Plate

Brookfield

Krebs Stormer

Rheometer

Oscillation


Viscometer / Rheometer

Din Cylinder

Cone / Plate

50 µm gap

Plate / Plate


processing

application

transportation storage

sag

levelling

settling

package viscosity brushing

rolling

spraying

post-application

Coating properties and shear rate


0.001 0.01 0.1 1 10 100 1000 10000

0.01

0.1

1

10

100

1000

10000

100000

g shear rate (sec ) . -1

HEC/

CLAYS

ASE

HASE

HEUR

PEPO

vis

cosity

(Pa·s

)

Flow Profile Comparison

Equal Mid-Shear Viscosity


Structural Recovery – viscosity vs. time

Preset of 3 steps:

low – high – low shear rate

Result:

time-dependent viscosity curve


Time (s)

slow recovery

(Thixotropy)

fast recovery

V

isco

sity (

Pa

· s)

0.1 s-1 1000 s-1 0.1 s-1

Viscosity Recovery


"Minimum shear stress required to induce flow"

Yield Value Viscosity

Pa Pa s

Honey 0 11.0

Ketchup 14 0.1

Mayonnaise 85 0.6

.

Yield Value


Yield Value - Measurement

pseudoplastic flow behaviour with yield point


Oscillation


Viscometer / Rheometer

Rotation Oscillation


ideal-viscous

e.g. mineral oil

viscoelastic

e.g. gum

ideal-elastic

e.g. steel

Viscoelasticity

Newton´s Law: τ= γxη Hooke´s Law: τ= G x γ .


Viscoelasticity

A viscous material flows irreversibly when stress is applied.

An elastic material flows reversibly when stress is applied.

Viscoelastic materials have an intermediate behaviour.


Oscillation Measurements

• An oscillating stress is applied to the sample

and the responding strain wave pattern is measured.

• The sample is stressed in a sinusoidal way.

Input

Output

δ

δ = 0° ideal elastic material

δ = 90° ideal viscous material


Oscillation Experiments

G´

G´´

δ

G* G`` = loss or viscous modulus

G` = storage or elastic modulus

tan δ = G``/ G´ = damping (loss) factor

δ = 0° ideal elastic material

δ = 90° ideal viscous material

Viscous Viscoelastic Elastic

G``>> G` G``> G` G= G` G``< G` G``<< G`

Liquid-like structure Gel point Gel-like structure

tan δ>>1 tan δ>1 tan δ=1 tan δ<1 tan δ<<1


Amplitude Sweep D

efo

rmation

γ

Frequency Hz

Strain – Amplitude

The amplitude of oscillation is increased at constant frequency

to find the limit of the linear- viscoelastic LVE range


Amplitude Sweep

0.01

0.1

1

10

100

1000

10000

0.01 0.1 1 10 100

Shear Stress [Pa] or Deformation [%]

Mo

du

lus [

Pa]

G`

G``

LVE Range

Yield point (end of LVE range)

Flow (crossover)

point


Frequency Sweep D

efo

rmation

γ

Frequency Hz

Strain - Frequency

The frequency of the oscillation is increased at

constant amplitude to examine stability and long-

range interactions


0.1

1

10

100

1000

10000

0.001 0.01 0.1 1 10 100

Angular frequency [1/s]

Mo

du

lus [

Pa]

Frequency Sweep

G`

G``


Frequency Sweep

Long-term storage stability:

•Sedimentation, Settling

•Syneresis

•Appearance (consistency)

•Transport stability


Interpretation of results

Results are useful for relative comparisons

For good storage stability and sag control. Elasticity

should dominate after stresses are removed

For good levelling and flow. Viscosity should

dominate after stresses are removed

Data can be used to perfect a coating system


Viscoelasticity

initial after 5 minutes

salad

dressing

olive

oil

salad

dressing

olive

oil


Viscoelasticity - Frequency sweep

10-8

10-7

10-6

10-5

10-4

10-3

10-2

10-1

100

102

Pa

G'

G''

0.1 1 10 1001/s

Angular Frequency

G' Salad dressing G' Olive oil G'' Salad dressing G'' Olive oil

stable

unstable

practically no G ´ (structure)


Examples


Latex Paint

Test System:

- Latex paint pvc 50% based on acrylic binder (spatter and poor levelling).

Thickeners:

- Mid-range HEC (0.6% on total)

- Newtonian associative thickener RHEOLATE® 212 (0 – 2.0 % on total)


Flow Behaviour

0.1

1.0

10.0

100.0

1000.0

0.1 1 10 100 1000

Shear rate [1/s]

Vis

co

sit

y [

Pa

.s]

mid-range HEC thickener

RHEOLATE® 212 associative thickener


Latex Paint - Flow Behaviour

10-1

100

101

102

103

Pa·s

10-1

100

101

102

103

1/s

Shear Rate .

blank

+ 0.5% RHEOLATE® 212




increased mid

and high shear viscosity


Latex Paint – Frequency Sweep e

lastic

ity d

ecre

ases

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

tan( )

0.1 1 10 100rad/s

Angular Frequency

tan( ) blank

tan( ) 0.5% RHEOLATE® 212




tan(δ)=G”/G’


Latex Paint - Brush-out

blank (0) + 0.5% RHEOLATE 212 (2) + 1.0% RHEOLATE 212 (3)

+ 1.5% RHEOLATE 212 (4) + 2.0% RHEOLATE 212 (5)

ranking: 0= poor; 5= excellent


Latex Paint - Roller Spatter Resistance

ranking: 0= poor; 5= excellent

blank (0) + 0.5% RHEOLATE 212 (2) + 1.0% RHEOLATE 212 (3)

+ 1.5% RHEOLATE 212 (4) + 2.0% RHEOLATE 212 (4-5)

New Folder Structure/various projects/Actual Projects/L 290 PVK50_Rh.212/spatter test_0004.wmv


Summary

Formulation of the RHEOLATE 212 associative thickener into a standard latex paint improves: • Mid and high-shear viscosity (film build and brush drag) • Brush-out levelling • Roller-spatter resistance - by decreasing the elasticity of the latex paint


Epoxy Coating

• Evaluate various rheological additives in an epoxy

coating Part A to improve syneresis and settling

characteristics.

Level

RHEOLATE 288 1%

RHEOLATE 288 3%

RHEOLATE 299 1%

BENTONE GS 1%

BENTONE GS 2%

BENTONE LT 0.5%

BENTONE LT 1%


Rheological Profile-Flow

Performed flow curves on the Anton Paar MCR 301 rheometer using the 50 mm parallel plate configuration at 25°C

with a 1 mm gap. A logarithmic ramp from 0.1 to 100 s-1 shear rate.

1

10

100

Pa·s

0.1 1 10 100 1,0001/s

Shear Rate .

CTRL Rh 299 1% Rh 288 1% Rh 288 3%


Rheological Profile-Flow

Performed flow curves on the Anton Paar MCR 301 rheometer using the 50 mm parallel plate configuration at 25°C

with a 1 mm gap. A logarithmic ramp from 0.1 to 100 s-1 shear rate.

1

10

100

Pa·s

0.1 1 10 100 1,0001/s

Shear Rate .

CTRL Bentone GS 1% Bentone GS 2% Bentone LT 1% Bentone LT 0.5%


Rheological Profiles-Frequency Sweep

tan(δ)=G’’/G’

100

101

102

103

tan( )

0.1 1 10 1001/s

Angular Frequency

CTRL RH 299 1% Rh 288%


Rheological Profiles-Frequency Sweep

tan(δ)=G’’/G’

100

101

102

103

tan( )

0.1 1 10 1001/s

Angular Frequency

CTRL Bentone GS 2% Bentone LT 0.5% Bentone LT 1%


Heat Aging 140F, 7 Days

0.08% GS 0.16% GS

Level Syneresis (mm)

Base Part A 5

RHEOLATE 288 1% 20

RHEOLATE 288 3% 22

RHEOLATE 299 1% 20

BENTONE GS 1% 1

BENTONE GS 2% <1

BENTONE LT 0.5% <1

BENTONE LT 1% <1


Summary

• BENTONE® GS and LT:

Improved syneresis/settling (elastic) properties of the

epoxy coating without majorly impacting the overall

viscosity.


Yield Point and Sag Correlation

Large Format Tile

(8 lb./sq. feet)

Mortar

Yield Point

(Pa)

Sag (mm)

3 min./10 min.

HEC 27 30/32

0.4% Bentone MA

0.1% Rh 101 61 8/17

0.25% Bentone MA

0.25% Rh 101 109 2/3

The Yield Point is determined using Amplitude Sweep


Thixotropy- Structural Decomposition

and Regeneration (ORO)

REST REST HIGH

SHEAR

Rotation

ỳ

Oscillation

γ, ω

Oscillation

γ, ω

t1 t3 t2 t0

1 2 3

1. Structure at rest

2. Structural decomposition

3. Structural regeneration


Oscillation-Rotation-Oscillation Study

Eggshell white acrylic based paint

Evaluate various mid-shear thickeners to

improve the sag resistance (the paint originally

sags after spray application).


Oscillation-Rotation-Oscillation Study

101

102

Pa

G''

G'

100

101

100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400s

Time t

CTRL KU-1 KU-3

Sample Crossover

time (s)

CTRL 50

KU-1 25

KU-3 <5

Eggshell white acrylic based paint

Rotational

Interval


For further information please refer to

www.Elementis-Specialties.com

[email protected]

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