Connecting mechanical testing techniques to user perception · 2016. 5. 10. · Cambridge Polymer...

Cambridge Polymer Group, 56 Roland Street, Suite 310

Boston, MA 02129(617) 629 4400

www.campoly.com

7-17 Presentation (10/1/2010)

Connecting mechanical testing techniques to user perception

“Psychorheology”

Gavin Braithwaite

“Psycho-rheology”

• Where analytical rheology doesn’t provide the complete answer– Rheology reliably analyzes and ranks materials

• Generally linear functions– Consumer perception is overall experience

• “psycho-rheology”• First coined by G.W. Scott Blair (1930’s)

• Real-world usage rarely one deformation– “performance” based tests often useful in linking

“real world” experience with fluid properties– Tests that inherently use multiple relevant

deformations can sometimes provide better insight to consumer perception

– Almost certainly non-linear– Less “transferable”

2 Cambridge Polymer GroupMarch 2015

Origins of the concept

• Psychorheology– Psychology– Physics/rheology– Sensory evaluation (sensory psychology)

• Late 19th century - Introspectionism– True study of perception requires isolation of the perceptual experience

• Mid-20th century - Psychometricians use statistical processes– Texture descriptors correlated with each other– Yields set of texture “primaries”

• Early 1960s Szcesniak et al (General Foods) formalized– Built large number of descriptive terms

• assumed to be independent– Termed the “texture profile system”– Related “ranking” to analytical techniques

3 Cambridge Polymer GroupPsychorheology – its foundations and current outlook, HR Moskowitz (1977) Journal of Texture Studies V8, 229-246

March 2015

Texture Profile Characterization (Szcesniak)

4 Cambridge Polymer GroupClassification of Textural Characteristics, A.S. Szczesniak (1963) Journal of Food Science V28 N4 285-289

March 2015

Psychophysical properties

• Mid-20th C - efforts to correlate analytical parameters to experience– Magnitude estimation

• Generation of a power function by observers• Relates physical intensity (I) to sensory intensity (S)

5 Cambridge Polymer GroupPsychorheology – its foundations and current outlook, HR Moskowitz (1977) Journal of Texture Studies V8, 229-246

March 2015

Texture Analysis

• Initial attempts were instruments for specific applications– Gelometers– Tenderometers– Consistometers– Exact physics of the deformation less important– Difficult to transfer, rarely standardized and subjective use

• First “integrative” machines– General Foods Texturometer

• Imitative of mastication• Coupled to secondary “combined” texture functions

– Allo Kramer Shear Press– Largely superceded

• “Instron” type instruments• Rheometers

• Highly complex correlations6 Cambridge Polymer GroupMarch 2015

General Foods Texturometer

• Based on an MIT design– Hanau articulator simulates mastication through model of the mandible

condyle– Additional added viscosity measurement

• Standardized configuration– Deformation– Sample size/shapes

7 Cambridge Polymer Group

The Texturometer – A New Instrument for Objective Texture Measurement, H.H. Friedman et al. (1963) Journal of Food Science V28 N4 390-396

March 2015

Texturometer parameters

• Hardness - Inverse of modulus on first chew – Highest deflection at A1 normalized by force

• Cohesiveness - work in chewing– Area under second peak (A2) normalized by first peak (A1)

• Elasticity - Recovery– Distance B

• Adhesiveness - negative peak height (A3) – Work required to separate samples

• Brittleness– Height for first break in the peak A1

• Chewiness– Hardness x Cohesiveness x Elasticity

• Gumminess– Hardness x Cohesiveness x 100

• Viscosity– Simple bob-and-cup

8 Cambridge Polymer GroupDevelopment of Standard Rating Scales for Mechanical Parameters of Texture and Correlation Between the Objective and the Sensory Methods of Texture Evaluation, A.S. Szczesniak et al. (1963) Journal of Food Science V28 N4 397-403

March 2015

Rheology

• Modern shear rheometers exceptionally robust tools– Wide torque and strain range

• Many orders of magnitude– Robust control systems with wide dynamic range– Well understood flow-fields– Industry accepted instrumentation and models

• Other geometries– Capillary– Vane– Extensional


Quantitative characterization

• Simplifying flow-fields aids analysis– Shear flows

• Viscosity• Shear thinning/thickening• Elasticity• Temporal evolution• Relaxation times• Yield stress

– Pipe flow• Extensional properties• Melts

– Extensional rheometers• Breakup times• Relaxation times

– Reduce flow-fields and deformations to tractable situations


What tests are “right”?

• What are the dominant deformations?• Two approaches

– Model the process• Texturometer

– Break the process down• Some connections are obvious

– Sticky/slippery• Some are not

– “mouth feel”


0

5

10

15

20

25

dressing 1 dressing 2 dressing 3 dressing 4

Breakup Time [sec]Relaxation Time [sec]

Poor “mouthfeel”

March 2015

Consumer perception

• Consumer perception is not solely one “phase”– Example from foods


Texture Profile Method, M.A. Brandt et al. (1963) Journal of Food Science V28 N4 404-409

March 2015

Case studies

1. Food products– Differentiating milk products

2. Consumer healthcare– Tactile feel of personal care fluids

3. Haircare products– Competitive analysis


Case 1: Milk rheology

• Bovine milk similar composition, with breed variations– Fat

• Holstein/Friesian - 3.6wt%, Jersey - 5.2 wt%– Proteins

• 3.4-3.9 wt%– Lactose

• ~5 wt%

• Proteins act to stabilize fat globules– Strongly influence feel and behavior– Agglomeration and separation important– Other solids impact shear viscosity

• Normally considered Newtonian• Motivation: Replacement of fats and sugars

– Desirable for health reasons– Need to preserve consumer perception


Microalgal flour

• Microalgal biomass contains nutrition-providing materials – carotenoids– dietary fiber– tocotrienols and tocopherols– varying lipid compositions– low levels of saturated lipids


Experimental

• AR-G2 cone-and-plate– 60 mm 1º SS cone, 25 ºC– Stepped shear 0.1-1000 s-1

• Milk (fresh)– Whole (~4% fat)– Skimmed (2% fat)– Skimmed (1% fat)– Non-fat (0.5 wt% fat)

• Starch solutions• Sugar solutions• Proprietary food additives

– Consumer testing indicates best alternative


Impact of composition

• Milk normally considered “newtonian”• Stabilized fat globules

– Deformable spheres– Hydrodynamic interactions dominate

• Einstein/Taylor/Schowalter etc– Spheres in Newtonian solution– Packing fraction depends on proteins

and sugars (~10%)– Not mono-disperse– Globules prone to cluster

• Critical response for mouth-feel – Shear thinning with zero-shear plateau– Fat provides viscosity– Fat % does not change behavior


Fat volume fraction

Shear rate5 s-1

10 s-1

0.1 s-1

Kyazze, G. and Starov, V., Viscosity of Milk: Influence of Cluster Formation. Colloid Journal 66(3),316-321 (2004)

C.W. Macosko Rheology: Principles, Measurements, and Applications, VCH Publishers Inc., New York, 1994.

March 2015

• What is the most relevant deformation?

0.001

0.01

0.1

0.1 1 10 100 1000

She

ar v

isco

sity

[Pa.

s]

Shear rate [s-1]

whole milk (G2)

2% fat (G2)

1% skimmed (G2)

non-fat (G2)

Milk


Error bars SD for three runs

Fat wt% down

March 2015

Reducing fat


0.001

0.010

0.100

1.000

10.000

0.1 1.0 10.0 100.0 1000.0

Shear rate [s-1]

Shea

r Vis

cosi

ty [P

a.s]

Alginate flourAlgal Flourwhole milk2% fat1% skimmednon-fat1% starch2% starch3% starch 5% starch

March 2015

Conclusions

• Consumer testing implies– Algal flour closest to milk response– Shear rheology indicates starch is the best

• Complex fluids can yield deceptively simple responses– Milk (stabilized fat globules)

• Shear thinning• Shear rate response controlled by fat content plus proteins and sugars

– Choosing “dominant” deformation does not always allow replacement of ingredients

• Milk “feel” expected to be dominated by shear viscosity• Corn syrup, algal flour and starch all provide reasonable rheological

responses• But rheology does not provide separation between systems

– So where is the difference?• Wrong deformation?• Wrong range of deformation?


• Consumer products represent a massive market in US– Emulsions, emollients, moisturizers and personal lubricants

• Perception of efficacy influenced by “feel” and “look” of system– Complex interplay of

• Viscosity• Yield stress• Absorption• Wetting • Elasticity• Loading

Case 2: Consumer Products


Personal Lubricants


0102030405060708090Firmness

Thickness

Residue Thickness

Slipperiness

Stickiness

Runniness

Spreadability

Wetness

124568910

AqueousSiliconeEmulsion

March 2015

Consumer ranking (selected)


0

1

2

3

4

5

6

7

8

9Fi

rmne

ss

Thic

knes

s

Stic

kine

ss

Run

nine

ss

Spr

eada

bilit

y

Ave

rage

1

2

4

5

6

8

9

10


March 2015

0.1000 1.000 10.00 100.0 1000Ang. frequency (rad/s)

0.01000

0.1000

1.000

10.00

100.0

1000

G' [

Pa]

0.01000

0.1000

1.000

10.00

100.0

1000

G''

[Pa]

1

10

2

4

56

9

Small Amplitude Oscillatory Shear


1

4

9


March 2015

Yield Stress



1

4

9

0.01000 0.1000 1.000 10.00 100.0 1000Shear stress [Pa]

1.000E-3

0.01000

0.1000

1.000

10.00

100.0

1000

Visc

osity

[Pa.

s]

1

10

2

4

6

9

5

March 2015

0.01

0.1

1

10

0 2 4 6 8 10Time [s]

Diam

eter [m

m]

14925610

Capillary Breakup


• Thermo Haake CaBER

0.01

0.1

1

10

0 2 4 6 8 10Time [s]

Diam

eter [m

m]

14925610

Sample

Laser micrometer

1

99

4


March 2015

Observations

• High ranking materials appear to have– High low-shear viscosity and low high-shear viscosity– High shear viscosity seems to be more important– Elasticity less important– Extensional properties appear related

• What is missing?– “slipperiness” (lubricity)

• Related to shear viscosity and surface chemistry• “Thin” film with gap governed by shear properties• Coefficient of Friction

– “stickiness” (tack)• Related to elasticity and adhesion• Large contact area, dependent on pull speed and fluid properties• Tack test


Lubricity


CoF on a rheometer


1 Kavehpour and McKinley “Tribo-rheometry: from gap-dependent rheology to tribology” Tribology Letters (2004) 17(2) 327-335

Spring

Annulus

Surface

March 2015

Coefficient of Friction

• CoF fixture on AR-G2. Controlled normal stress (82 kPa) and rotation rate


-0.10.00.10.20.30.40.50.60.7

0.1 1 10 100Coe

ffici

ent o

f Fric

tion

[]

Velocity [rad/s]

1

4

9

2

5

8

6

10

water

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.1 1 10 100

Coe

ffici

ent o

f Fric

tion

[]

Velocity [rad/s]

1

49

2

5

8

6

10

Hydrogel

Neoprene

1, 4, 9

4

9

1


March 2015

Comparisons


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

1 4 9 2 5 8 6 10 water

Coe

ffici

ent o

f Fric

tion

[]

Hydrogel Neoprene

Em

ulsi

on

Aqu

eous

NA

• CoF fixture on AR-G2. Controlled normal stress (82 kPa) and rotation rate (0.3 rad/s)– 12 N load, linear velocity of 3 cm/s

Aqu

eous

Aqu

eous S

ilico

ne

Aqu

eous

Aqu

eous

Sili

cone

March 2015

Tackiness

• Combination of accurate vertical position and normal force allow tack to be measured on a conventional rheometer– AR-G2 has a “fast sampling” mode that allows 250 Hz– Squeeze/pull-off allows tack-like test using parallel plates


Normal force

Velocity

March 2015

Tackiness

• 4 cm parallel plate loaded to fixed gap and pulled at 500 micron/s


-20

-15

-10

-5

0300 600 900 1200 1500 1800 2100 2400

Forc

e [N

]

Position (relative to bottom plate) [mm]

1 4 9 2 5 8 6 10

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

300 600 900

Forc

e [N

]

Position (relative to bottom plate) [mm]1

4

9


March 2015

Work of Adhesion


0

0.001

0.002

0.003

0.004

0.005

0.006

1 4 9 2 5 8 6 10

Wor

k of

adh

esio

n [J

]

Sample

Aqu

eous

Aqu

eous

Sili

cone

Aqu

eous

Aqu

eous

Sili

cone

Aqu

eous

Em

ulsi

on

March 2015

Conclusions


Correlation between physical and sensory measures Intimate Health products, (p<0.05)

Shear Viscosity

Oscillatory Viscosity

Lubricity

Extensional Viscosity

Adhesion

FirmnessThicknessResidueSlipperinessStickinessRunninessSpreadabilityControllabilityWetnessCooling

March 2015

Case 3: Hair products

• Commercial hair care comparisons– Hold (how well the style is held)

• Adhesion between strands• Lap shear

– Rehold (ability to reform/restyle)• Adhesion between strands after disruption• 180° peel

– Feel (tactile feel)• Coefficient of Friction

– Conflicting needs?


Lap Shear and 180° Peel test


• Based on – ASTM F2255 “Strength properties of Tissue Adhesives in Lap-Shear by

Tension Loading”• Materials pulled apart at 5 mm/min• Shear loading

– ASTM D1876 “Peel Resistance of Adhesives”• Materials pulled apart at 305 mm/min• Tensile decohesion• After testing, samples were reformed• Retested five times

• Conventional servo hydraulic load frame– Material spread on stainless steel– Mesh pushed on to material with a dead weight– Allowed to dry

March 2015

Lap shear testing


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.2 0.4 0.6 0.8 1

Force

Displacement

0

0.2

0.4

0.6

0.8

1

1.2

Average Peak She

ar Force

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

Average Work To

End

Bad

Good

March 2015

180 ° Peel - Recovery of adhesion


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1R

un 1

Run

2

Run

3

Run

4

Run

5

Run

1

Run

2

Run

3

Run

4

Run

5

Good Bad

Forc

e

Bad

Good

March 2015

Coefficient of Friction


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

CoF

Normal Force

Bad

Good

March 2015

Conclusions

• Test selection– Important to pick relevant deformations– May not be trivial– If the tests are too complex – may not be the right ones

• Good analytical tests should– Be relatively simple– Capture critical aspect(s) of use– Generate a clear picture of sample differences


Lessons and comments

• Understanding the rheology of fluids critical for understanding consumer perception and use

• But mode of use can be just as important– Usage rarely simple shear

• Or only in a limited range– Perception is therefore governed by response to variety of deformations

• Simple shear• Compression• Extension• Pipe-flow etc

• Collating data in more relevant configurations can provide useful correlations with field data

• Superb force and position control of a conventional rheometer still useful


Thank you

Cambridge Polymer Group is a contract research laboratory specializing in polymers and their applications. We provide outsourced research and development, consultation and failure analysis as well as routine analytical testing and custom test and instrumentation design.

Cambridge Polymer Group, Inc.56 Roland St., Suite 310Boston, MA 02129(617) 629-4400http://[email protected]


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Connecting mechanical testing techniques to user perception · 2016. 5. 10. · Cambridge Polymer...

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