Connecting mechanical testing techniques to user perception

Size: px

Start display at page:

Download "Connecting mechanical testing techniques to user perception"

Andra Thomas
5 years ago
Views:

1 Connecting mechanical testing techniques to user perception Psychorheology Gavin Braithwaite Cambridge Polymer Group, 56 Roland Street, Suite 310 Boston, MA (617) Presentation (10/1/2010)

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

2 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 Group

3 Origins of the concept Psychorheology Psychology Physics/rheology Sensory evaluation (sensory psychology) Late 19 th century - Introspectionism True study of perception requires isolation of the perceptual experience Mid-20 th 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 Psychorheology its foundations and current outlook, HR Moskowitz (1977) Journal of Texture Studies V8, Cambridge Polymer Group

4 Texture Profile Characterization (Szcesniak) Classification of Textural Characteristics, A.S. Szczesniak (1963) Journal of Food Science V28 N Cambridge Polymer Group

5 Psychophysical properties Mid-20 th 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) Psychorheology its foundations and current outlook, HR Moskowitz (1977) Journal of Texture Studies V8, Cambridge Polymer Group

6 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 correlations 6 Cambridge Polymer Group

configuration Deformation Sample size/shapes The Texturometer A New Instrument for Objective

7 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 The Texturometer A New Instrument for Objective Texture Measurement, H.H. Friedman et al. (1963) Journal of Food Science V28 N Cambridge Polymer Group

8 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 Group Development 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 N

9 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 9 Cambridge Polymer Group

10 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 10 Cambridge Polymer Group

What tests are right? What are the dominant deformations?

process down Some connections are obvious

Time [sec] Relaxation Time [sec] 15 Poor mouthfeel 10 5

11 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 25 mouth feel 20 Breakup Time [sec] Relaxation Time [sec] 15 Poor mouthfeel dressing 1 dressing 2 dressing 3 dressing 4 11 Cambridge Polymer Group

12 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 N Cambridge Polymer Group

13 Case studies 1. Food products Differentiating milk products 2. Consumer healthcare Tactile feel of personal care fluids 3. Haircare products Competitive analysis 13 Cambridge Polymer Group

Case 1: Milk rheology Bovine milk similar composition, with breed variations Fat Holstein/Friesian - 3.6wt%, Jersey - 5.2 wt% Proteins 3.4-3.

14 Case 1: Milk rheology Bovine milk similar composition, with breed variations Fat Holstein/Friesian - 3.6wt%, Jersey wt% Proteins 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 14 Cambridge Polymer Group

fiber tocotrienols and tocopherols varying lipid

15 Microalgal flour Microalgal biomass contains nutritionproviding materials carotenoids dietary fiber tocotrienols and tocopherols varying lipid compositions low levels of saturated lipids 15 Cambridge Polymer Group

Experimental AR-G2 cone-and-plate 60 mm 1º SS cone, 25 ºC Stepped shear 0.

16 Experimental AR-G2 cone-and-plate 60 mm 1º SS cone, 25 ºC Stepped shear 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 16 Cambridge Polymer Group

17 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 C.W. Macosko Rheology: Principles, Measurements, and Applications, VCH Publishers Inc., New York, Shear rate 5 s s s -1 Fat volume fraction Kyazze, G. and Starov, V., Viscosity of Milk: Influence of Cluster Formation. Colloid Journal 66(3), (2004) 17 Cambridge Polymer Group

18 Milk 0.1 What is the most relevant deformation? Error bars SD for three runs whole milk (G2) 2% fat (G2) 1% skimmed (G2) non-fat (G2) Shear viscosity [Pa.s] 0.01 Fat wt% down Shear rate [s -1 ] 18 Cambridge Polymer Group

19 Reducing fat Shear Viscosity [Pa.s] Alginate flour Algal Flour whole milk 2% fat 1% skimmed non-fat 1% starch 2% starch 3% starch 5% starch Shear rate [s -1 ] 19 Cambridge Polymer Group

20 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? 20 Cambridge Polymer Group

Case 2: Consumer Products Consumer products

of system Complex interplay of Viscosity Yield

21 Case 2: Consumer Products 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 21 Cambridge Polymer Group

22 Personal Lubricants Wetness Firmness Thickness Aqueous Silicone Emulsion 50 Spreadability Residue Thickness Runniness Slipperiness Stickiness 22 Cambridge Polymer Group

23 Consumer ranking (selected) Aqueous Silicone Emulsion Cambridge Polymer Group Firmness Thickness Stickiness Runniness Spreadability Average

Small Amplitude Oscillatory Shear 1000 100.0 Aqueous Silicone Emulsion 1000 100.0 1 10.00 9 10.00 G' [Pa] 1.000 0.

24 Small Amplitude Oscillatory Shear Aqueous Silicone Emulsion G' [Pa] G'' [Pa] Ang. frequency (rad/s) 24 Cambridge Polymer Group

Yield Stress 1000 1 9 100.0 4 Aqueous Silicone Emulsion Viscosity [Pa.s] 10.00 1.000 0.

25 Yield Stress Aqueous Silicone Emulsion Viscosity [Pa.s] E Shear stress [Pa] 25 Cambridge Polymer Group

26 Capillary Breakup Sample Thermo Haake CaBER 10 Laser micrometer Aqueous Silicone Emulsion Diameter [mm] Time [s] 26 Cambridge Polymer Group

27 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 27 Cambridge Polymer Group

28 Lubricity 28 Cambridge Polymer Group

29 CoF on a rheometer Spring Annulus Surface 1 Kavehpour and McKinley Tribo-rheometry: from gap-dependent rheology to tribology Tribology Letters (2004) 17(2) Cambridge Polymer Group

30 Coefficient of Friction Aqueous Silicone Emulsion Coefficient of Friction [] CoF fixture on AR-G2. Controlled normal stress (82 kpa) and rotation rate Coefficient of Friction [] , 4, Hydrogel Velocity [rad/s] water Neoprene Velocity [rad/s] 30 Cambridge Polymer Group

31 Comparisons 0.7 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 0.6 Hydrogel Neoprene Coefficient of Friction [] Aqueous Aqueous Emulsion Aqueous Aqueous Aqueous Silicone Silicone water NA 31 Cambridge Polymer Group

32 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 Velocity Normal force 32 Cambridge Polymer Group

33 Tackiness 4 cm parallel plate loaded to fixed gap and pulled at 500 micron/s Position (relative to bottom plate) [mm] Force [N] Force [N] 0.5 Position (relative to bottom plate) [mm] Aqueous Silicone Emulsion Cambridge Polymer Group

Work of Adhesion 0.006 0.005 0.004 0.003 0.

34 Work of Adhesion Work of adhesion [J] Aqueous Aqueous Emulsion Aqueous Aqueous Aqueous Silicone Silicone Sample 34 Cambridge Polymer Group

35 Conclusions Correlation between physical and sensory measures Intimate Health products, (p<0.05) Shear Viscosity Oscillatory Viscosity Lubricity Extensional Viscosity Adhesion Firmness Thickness Residue Slipperiness Stickiness Runniness Spreadability Controllability Wetness Cooling 35 Cambridge Polymer Group

36 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? 36 Cambridge Polymer Group

37 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 37 Cambridge Polymer Group

38 Lap shear testing Force Bad Average Peak Shear Force Good Average Work To End Displacement 38 Cambridge Polymer Group

39 180 Peel - Recovery of adhesion Good Run 1 Run 2 Run 3 Run 4 Run 5 Run 1 Run 2 Run 3 Run 4 Run 5 Force Bad Good Bad 39 Cambridge Polymer Group

Coefficient of Friction 1 0.9 0.8 Bad 0.7 0.6 CoF 0.5 0.4 0.3 0.2 0.

40 Coefficient of Friction Bad CoF Good Normal Force 40 Cambridge Polymer Group

41 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 41 Cambridge Polymer Group

42 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 42 Cambridge Polymer Group

We provide outsourced research and development, consultation and failure analysis as well as routine

43 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 310 Boston, MA (617) info@campoly.com 43 Cambridge Polymer Group

By Dr. Robert Marsh, Bohlin Instruments, 2003

A R H E O L O G I C A L V I E W P O I N T O F T H E R M O P L A S T I C M E L T S By Dr. Robert Marsh, Bohlin Instruments, 2003 Introduction Rheology is the science of studying the flow and deformation