Trefor Evans, Ph.D Director of Research & Institute Fellow, TRI-Princeton TEvans@TRIPrinceton.org
The wonderful world of hair
Consumer attributes Anti-breakage Anti-flyaway/static Anti-frizz Body Color Protection Conditioning Control Damage Hold Longevity Manageability Moisturization Protection Repair Shine Strength UV Protection Volume
Consumer language -vs- scientific language Consumer language Anti-flyaway/static Conditioning Moisturization Shine Softness Strength Volume Scientific language - electrostatic properties - lubrication - water content - light scattering - modulus - tensile properties - image analysis Body -??? There is danger in taking consumers words literally.
Technical assessment of hair performance
An experiment you ve all probably tried Conditioner (master batch) Conditioner (sub-batch #1) Conditioner (sub-batch #2) Conditioner (sub-batch #3) Conditioner (sub-batch #4)
Consumer performance -vs- Technical performance Technical performance gives loss Consumer performance gives loss Reformulate for improved performance Technical performance equivalent Consumer performance gives loss Reformulate for improved aesthetics? Is the concept right? Technical performance win Consumer performance gives loss/parity Is the technical win off-set by poor aesthetics? Is the technical parameter important?
The moisture content of hair
Relative Humidity (%) Dynamic Vapor Sorption (DVS) Temperature Controlled Incubator Vapour Humidifier Microbalance Balance Purge Adsorption isotherm for hair and water Regulated Dry Gas Flow Mass Flow Controller 1 Mass Flow Controller 2 Sample Holder Reference Holder Temp/Humidity Probes Speakman & Chamberlain - 1931 20 Evans - 2011 % Increase in weight 125 120 115 110 Weight increase and decrease as fn(humidity) 100 80 60 40 Amount adsorbed (%) 15 10 5 105 20 0 0 10 20 30 40 50 60 70 80 90 100 100 0 1000 2000 3000 Time (mins) 0 Relative humditiy (%)
Inconsistencies between consumer language and hair science 25 DVS Data for virgin vs bleached/waved hair Cumulative increase in weight upon increasing humidity bleached/waved Chemically damaged hair will adsorb more water than healthy hair Increase in weight (%) 20 15 10 Virgin hair Technically, the term dry damaged hair is an oxymoron. 5 0 0 10 20 30 40 50 60 70 80 90 100 Relative Humidity (%) Hair contains highest levels of moisture at high humidity a condition that is synonymous with bad hair days.
F.J.Wortmann, A.Hullmann, C.Popescu, Water Management of Human Hair., IFSCC Magazine, Vol 10(4) (2007) p317-320 It is concluded that human hair exhibits a rather robust static and dynamic water sorption performance that, against initial expectations, is not readily changed by cosmetic processes and ingredients.
P&G Study Presented by MG Davis at 2009 DWI Hair Conference 20g ponytail hair tresses were treated with a non-conditioning shampoo Tresses were equilibrated for 48 hrs at either 15%RH or 80%RH Tresses were transported in plastic containers to maintain RH until evaluated by panelists Blindfolded panelists were asked to feel tresses and answer a series of questions (n=50) Adsorption isotherm for hair and water 20 Amount adsorbed (%) 15 10 5 0 0 10 20 30 40 50 60 70 80 90 100 Relative humditiy (%)
P&G Study Presented by MG Davis at 2009 DWI Hair Conference 100% 90% 80% 15% RH 80%RH No difference % Response 70% 60% 50% 40% 30% 20% 10% 0% More "Moisturized" Smoother More Tangled More Damaged Attribute Thanks to P&G for access and permission to present this data
Scanning electron microscopy pictures of hair
Scanning electron microscopy pictures of hair
Typical wet combing results 60 Influence of hair type on combing results Effect of hair state on wet combing results Untreated Maximum combing force (gmf) 50 40 30 20 10 Untreated XM Untreated XM XM 0 Virgin hair Bleached hair Bleached & waved hair Treatment
Lubrication and hair claims Lubrication is behind claims regarding Manageability Conditioning Protection Moisturization Repair Strengthening
Strong, Healthy Hair
Constant rate extension experiments Schematic of stress-strain curve for wet hair 100 *Note : Break Stress = Force/Cross sectional area 80 Break Force* Force (gmf) 60 40 Modulus = slope of linear region 20 Plateau Load 0 Elastic (linear) region Break Extension 0 10 20 30 40 50 60 % Extension 0. 023 Break Stress for chemically treated hair Wet Tensile Testing (N=40) Stress = force/unit area 0. 021 0. 019 Break Stress 0. 017 0. 015 0. 013 0. 011 V i r n B l B&W Virgin Bleached Bleach & Treatment waved Mean+SD Mean-SD Mean+SE Mean-SE Mean Outliers Extremes
Consumer perception of strength Consumers do not assess the strength of hair by stretching at a constant rate and judging the force to break. Brown & Swift (1975); Robbins (2006) Hair fibers are plucked from the head upon application of forces considerably lower than the break force. W.Hamburger, H.M.Morgan and M.M.Platt, Some aspects of the mechanical behavior of hair, Proc.Sci.Sect., 14, 10-16 (1950) Consumer perception of strength is likely related to number of fibers in brush/comb after grooming; number of fibers in base of shower after washing; and/or visual observation of split ends.
Single fiber fatigue experiments T.A.Evans, Fatigue Testing of Hair A Statistical Approach to Hair Breakage, Journal of Cosmetic Science, 60, 599-616, Nov/Dec, 2009 T.A.Evans and K.Park, A Statistical Approach to Hair Breakage. II. Repeated Grooming Experiments, Journal of Cosmetic Science, 61, 439-455, Nov/Dec, 2010 T.A.Evans, Hair Breakage, in Practical Modern Hair Science, Ed. Trefor Evans & R.Randall Wickett, Allured Books, 2012. T.A. Evans, Measuring Hair Strength, Part 2: Fiber Breakage, Cosmetics & Toiletries, Vol. 128(12), 854-859, December 2013
The S-N Curve Failure cycles versus Stress virgin hair Virgin Caucasian hair at 60% RH 1e+6 1e+5 Cycles to failure 1e+4 1e+3 1e+2 1e+1 0.009 0.010 0.011 0.012 0.013 0.014 0.015 0.016 Stress (g/um 2 ) Break stress by conventional method would be around 0.021 g/um 2 So hair fibers will break (and break in a predictable manner) upon repeated application of stresses considerably below the so-called break stress.
Repeated grooming experiments Cumulative breakage as fn of grooming strokes Unconditioned virgin and bleached Caucasian hair at 60% RH 100 90 Bleached hair Number of broken fibers 80 70 60 50 40 30 20 10 Virgin hair 0 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Brushing Cycles
Repeated grooming experiments Cumulative breakage as fn of grooming strokes Unconditioned and conditioned bleached Caucasian hair at 60% RH 100 Unconditioned Bleached hair 90 Number of broken fibers 80 70 60 50 40 30 20 10 0 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Brushing Cycles Conditioned
X times stronger claims
Fatigue leads to larger differences between samples 0.026 Break stress for virgin Caucasian and Afro hair at 60% RH Failure cycles versus Stress virgin hair Caucasian hair 60% RH 0.024 1e+6 0.022 1e+5 Break stress (g/um 2 ) 0.020 0.018 0.016 9% Cycles to failure 1e+4 1e+3 1e+2 0.014 1e+1 0.012 Caucasian Hair type Afro Mean Mean±SE Mean±SD Outliers Extremes 1e+0 0.009 0.010 0.011 0.012 0.013 0.014 0.015 0.016 Stress (g/um 2 ) Average number of cycles-to-fail for Caucasian and Afro hair under repeated application of a 0.010 g/μm 2 stress at 60% RH Hair type Average cycles-to-fail Caucasian 37,000 Afro 5,500
Fatigue leads to larger differences between samples Box Plot of Break Stress (gmf/sq. microns) grouped by % RH Effect of RH on break stress Virgin Caucasian Hair at Different %RH 0.028 Failure cycles versus Stress virgin hair Caucasian hair as fn(rh) 0.026 1e+5 Break Stress (gmf/sq. microns) 0.024 0.022 0.020 0.018 0.016 0.014 0.012 4% 12% 20 60 90 % RH Mean Mean±SE Mean±SD Outliers Extremes Cycles to failure 1e+4 1e+3 1e+2 20% RH 60% RH 90% RH 1e+1 0.006 0.007 0.008 0.009 0.010 0.011 0.012 0.013 0.014 0.015 0.016 0.017 Stress (g/um 2 ) Average # cycles-to-fail for Caucasian hair under repeated application of a 0.013 g/μm 2 stress as fn RH Relative Humidity Average cycles-to-fail 20% 24,800 60% 2,100 90% 100
Hot-off-the-presses data S-N Curve virgin and treated Caucasian hair 1e+6 1e+5 60% RH 3x bleached Cycles to failure 1e+4 1e+3 1e+2 1e+1 0.006 0.007 0.008 0.009 0.010 0.011 0.012 0.013 0.014 0.015 0.016 Stress (g/um 2 )
Hot-off-the-presses data S-N Curve virgin and treated Caucasian hair 1e+6 1e+5 60% RH 3x bleached Cycles to failure 1e+4 1e+3 Virgin 90% RH 1e+2 1e+1 0.006 0.007 0.008 0.009 0.010 0.011 0.012 0.013 0.014 0.015 0.016 Stress (g/um 2 )
Hot-off-the-presses data Cycles to failure 1e+6 1e+5 1e+4 1e+3 S-N Curve virgin and treated Caucasian hair Virgin 90% RH 60% RH 3x bleached Average number of cycles-to-fail under repeated application of a 0.011 g/μm 2 stress Hair type Average cycles-to-fail Virgin (60% RH) 37,000 Bleached (60% RH) 2,700 Virgin (90% RH) 2,400 Bleached (90% RH) 150 1e+2 3x bleached 90% RH 1e+1 0.006 0.007 0.008 0.009 0.010 0.011 0.012 0.013 0.014 0.015 0.016 Stress (g/um 2 )
Force (gmf) Fatigue testing as fn of RH Failure cycles versus Stress virgin hair Caucasian hair as fn(rh) 1e+5 Schematic of Young s modulus as fn RH Cycles to failure 1e+4 1e+3 60% RH 90% RH 1e+2 20% RH 60% RH 90% RH 1e+1 0.006 0.007 0.008 0.009 0.010 0.011 0.012 0.013 0.014 0.015 0.016 0.017 % extension Stress (g/um 2 )
Glycerol treatment S-N Curve virgin and treated Caucasian hair at 60% RH 1e+5 60% Virgin + 10% glycerol + 20% glycerol Cycles to failure 1e+4 70 Number of broken fibers as a fn of treatment after 10,000 grooming strokes 1e+3 60 50 1e+2 0.006 0.007 0.008 0.009 0.010 0.011 0.012 0.013 0.014 0.015 0.016 Stress (g/um 2 ) # broken fibers 40 30 20 Average # cycles-to-fail for Caucasian hair under repeated application of a 0.011 g/μm 2 stress at 60% RH Relative Humidity Average cycles-to-fail Virgin 33,200 10% glycerol 7,600 20% glycerol 2,600 10 0 Control 10% glycerol Treatment Repeated grooming data Mean Mean±SE Mean±SD Outliers Extremes
Changing the water content of hair carboxylic acids Adsorption isotherm for virgin Caucasian hair 20 Amount adsorbed (%) 15 10 5 5% citric acid 0 0 20 40 60 80 100 Relative humidity (%) C.H. Nicholls, and J.B. Speakman, The adsorption of water by wool. Part IV The influence of combined acid on the affinity of wool for water., J.Tex.Inst., 45, T267-271, 1954
Changing the water content of hair phenols Adsorption Isotherm for Water and Hair 25 Virgin Hair Virgin Hair 20 Amount adsorbed (%) 15 10 5 + 5% resorcinol 0 0 10 20 30 40 50 60 70 80 90 100 Relative Humidity (%) Binding of phenols by hair, Parts I, II and III, M.M.Breuer, J.Phys.Chem, 68, p-2067-2084, (1964). showed that water content is diminished by soaking hair in various phenolic solutions, with resorcinol showing the largest effect.
Changing the water content of hair phenols Reduction in water content of hair after treatment with phenols 25 20 Virgin Hair Amount adsorbed (%) 15 10 5 + 5% Cl-resorcinol 0 0 10 20 30 40 50 60 70 80 90 100 Relative Humidity (%)
Fatigue testing on resorcinol-treated hair Failure cycles versus Stress virgin hair Caucasian hair 1e+5 Cycles to failure 1e+4 1e+3 1e+2 1e+1 Virgin hair Resorcinol soaked hair 0.009 0.010 0.011 0.012 0.013 0.014 0.015 0.016 Stress (g/um 2 )
The effects of acids on hair Some companies are including carboxylic acids as actives Kao s 3 Days Straight product uses lactic and malic acids as the active. Glyoxylic acid is being pushed as an alternative to formaldehyde-based BKT-type products. Olaplex uses maleic acid as an active
Resorcinol activity as a function of soak time Reduction in water content for hair after soaking in 5% resorcinol 35 30 % Reduction in water content 25 20 15 10 5 0 0 20 40 60 80 100 120 Time (minutes)
Citric acid activity as a function of temperature and soak time Reduction in water content for virgin Caucasian hair after soaking in a 5% citric acid solution as a function of time and temperature 25 40 o C % Reduction in water content 20 15 10 5 22 o C 0 0 50 100 150 200 250 Time (minutes)
Dynamic vapor sorption in Organics mode - adsorption rate for hair and ethanol 4 Adsorption of water, ethanol and propanol by hair 0-10% jump in relative vapor pressure Water Amount adsorbed (%) 3 2 1 Methanol Ethanol 0 0 200 400 600 800 1000 1200 1400 1600 Time (minutes)
Propanol adsorption Adsorption of methanol, ethanol and propanol by hair 0-90% jump in relative vapor pressure 20 Methanol Amount adsorbed (%) 15 10 5 Ethanol Propanol 0 0 1000 2000 3000 4000 5000 Time (minutes)
Adsorption testing with decane Adsorption of decane by hair after 0-90% jump in relative vapor pressure 0.5 Amount adsorbed (%) 0.4 0.3 0.2 0.1 Rapid surface adsorption Slow bulk adsorption 0.0 0 500 1000 1500 2000 2500 3000 Time (minutes)
Adsorption testing with cyclomethicone Adsorption and desorption of cyclomethicone on virgin hair after 0-90-0% steps in relative vapor pressure 0.3 Amount adsorbed (%) 0.2 0.1 Cyclomethicone 0.0 0 500 1000 1500 2000 2500 3000 Time (minutes)
Adsorption testing with amyl acetate Adsorption of amyl acetate by hair after 0-90% jump in relative vapor pressure 1.0 Amount adsorbed (%) 0.8 0.6 0.4 amyl acetate 0.2 0.0 0 1000 2000 3000 4000 5000 6000 Time (minutes)
The rigors of hair
Hair Repair
The scope of the problem what happens during bleaching with a simple hydrogen peroxide solution? Penetration of the solution between cuticle scales will weaken the inter-cuticular cement and leave this protective structure more susceptible to deterioration. Oxidative conditions, in combination with elevated ph, will irreversibly increase the swelling capacity of fibers placing additional strain on the cuticle structure each time the hair is wetted. Degradation and dissolving of melanin pigment granules leads to lightening of the hair color while seemingly leaving behind microscopic voids. Oxidative side reactions with hair protein deplete strength-supporting cystine disulfide bonds by conversion to cysteic acid. Individual hair fibers become weaker and more prone to breakage. The dry state modulus increases leaving individual fibers stiffer The lipid layer on the very outside surface of a hair fiber (the f-layer) is removed changing its interaction with water and possibly leading to slower hair drying. Enhanced swelling in combination with a more-hydrophilic character can lead to increased fiber water content. Lipid structure becomes weakened and components are more easily removed.
What happens to hair during simple washing with a standard shampoo? Fibers swell - putting strain on the cuticle. Swollen fibers are subjected to inter-fiber abrasion and friction - likely causing cuticle wear. Bending and twisting of fibers could initiate localized cuticle uplift. Fibers encounter various tugging and fatiguing forces while in a decidedly weaker, plasticized state. Lipids and degraded protein may be leached from the hair.
Hair Damage - where does it occur? Surface (cuticle) (Tactile, manageability, shine) Break Stress for chemically treated hair Wet Tensile Testing (N=40) Inside (cortex) 0. 023 0. 021 0. 019 (Strength, breakage, stiffness) Break Stress 0. 017 0. 015 0. 013 Mean+SD Mean-SD Mean+SE Mean-SE Mean 0. 011 V i r gi n B l eached B&W Virgin Bleached Bleach & Treatment waved Outliers Extremes
Hair Damage - how does it occur? Chemical impetus Mechanical impetus Thermal impetus Photochemical impetus
Hair Damage - how does it manifest to the consumer Manageability issues Sensorial issues Strength/breakage issues
Let s combine the lot Grooming-related Sensorial-compromised surface hair damage due to groomingrelated surface damage Repair Reduce Remove
Let s combine the lot Strength-compromised hair due to chemicalrelated internal protein damage Repair Reduce Remove
Summary Hair care products are sold using consumer language. This is the language of our industry. But, We should not forget we are scientists. Scientists are very precise people who question everything. Upon doing this, it becomes apparent that consumer language and scientific language do not equate. This can severely muddle our industry and the product development process and often sends formulators off on wrong routes. TRI-Princeton
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