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TECHNICAL DATA SHEET

TDS-244Edition: January, 2002

Measurement and Understanding of Yield Value inPersonal Care Formulations

What is Yield Value?Yield value is a measurable quantity similar to, butnot dependent on, viscosity. It can be thought of asthe initial resistance to flow under stress, hence, itis also referred to as yield stress. Carbopol

polymer gels exhibit a yield value that allows themto be useful in a variety of applications.

What Does Yield Value Do?Yield value is a property critical to achieving certainphysical characteristics, such as:

Suspension - Particles dispersed in a medium willremain suspended if the yield value of the mediumis sufficient to overcome the effect of gravity orbuoyancy on those particles. On a label, thephrase "Shake well before using" can be read as"Needs a higher yield value".

Emulsion - Insoluble liquid droplets can beprevented from rising and coalescing with yieldvalue. (i.e. hand creams, sunscreens, hairconditioners)

Foam - Gas bubbles can also be suspended anduniformly distributed in a liquid medium using yield

values as a formulating tool. (i.e. shampoos, hairmousses, shave creams)

Surface Cling - With enough yield value, a gelledliquid will not drip or run down a vertical surface.(i.e. hair sprays, face masques)

As examples, to suspend large mineral oil beads ina bath gel, it might take a Brookfield yield value of300 - 450. Whereas to stabilize a mineral oil/wateremulsion might require a Brookfield yield valuerange of only 100 - 200. Similarly, to suspend micain a shampoo could call for a Brookfield yield valueof 130 - 200. Suspending larger particles of pumicein a foot scrub could require a Brookfield yield valuein the range of 250 - 300.

How is Yield Value Measured?The most common way to measure yield value isthe Brookfield yield value extrapolation method. ABrookfield RVT viscometer is used to measure thetorque necessary to rotate a spindle through a liquidsample at speeds of 0.5 to 100 rpm. Multiplying thetorque reading by the appropriate constant for thespindle and speed gives the apparent viscosity.Spindle speed corresponds to shear rate. Yieldvalue is an extrapolation of measured values to a

shear rate of zero. Brookfield yield value (BYV) canbe calculated by the following:

BYV*, dyn/cm2

= 2r1 (

1 -

2) (Eq.1)

100

Where,

1 and

2 = apparent viscosities obtained at two different spindle speeds, r1 and r2, respectively.*Only when r2/r1 = 2

If spindle speeds of 0.5 and 1 rpm are used:

BYV, dyn/cm2

= (

1 -

2) or BYV, Pa = (

1 -

2) (Eq.2)

100 1000

Yield value (stress) can also be measured using a cone-and-plate rheometer. Shear stress is measured as afunction of shear rate. The resultant curve is fitted with what is called the Casson Rheological Model:

1/2

= y1/2

+ (a)1/2

(Eq.3)

Where, shear stress, shear rate, and y yield stress

Lubrizol Advanced Materials, Inc. / 9911 Brecksville Road, Cleveland, Ohio 44141-3247 / TEL: 800.379.5389 or 216.447.5000

For further information, please visit www.personalcare.noveon.com

The information contained herein is believed to bereliable, but no representations, guarantees orwarranties of any kind are made as to its accuracy,suitability for particular applications or the results to beobtained therefrom. The information is based onlaboratory work with small-scale equipment and doesnot necessarily indicate end product performance.Because of the variations in methods, conditions and

equipment used commercially in processing thesematerials, no warranties or guarantees are made as tothe suitability of the products for the applicationdisclosed. Full-scale testing and end productperformance are the responsibility of the user. LubrizolAdvanced Materials, Inc. shall not be liable for and thecustomer assumes all risk and liability of any use ofhandling of any material beyond Lubrizol Advanced

Materials, Inc.s direct control. THE SELLER MAKES NOWARRANTIES, EXPRESS OR IMPLIED, INCLUDINGBUT NOT LIMITED TO, THE IMPLIED WARRANTIESOF MERCHANTABILITY AND FITNESS FOR APARTICULAR PURPOSE. Nothing contained herein isto be considered as permission, recommendation, noas an inducement to practice any patented inventionwithout permission of the patent owner.

Lubrizol Advanced Materials, Inc. / 9911 Brecksville Road, Cleveland, Ohio 44141-3247 / TEL: 800.379.5389 or 216.447.5000

For further information, please visit www.personalcare.noveon.com

The information contained herein is believed to bereliable, but no representations, guarantees orwarranties of any kind are made as to its accuracy,suitability for particular applications or the results to beobtained therefrom. The information is based onlaboratory work with small-scale equipment and doesnot necessarily indicate end product performance.Because of the variations in methods, conditions and

equipment used commercially in processing thesematerials, no warranties or guarantees are made as tothe suitability of the products for the applicationdisclosed. Full-scale testing and end productperformance are the responsibility of the user. LubrizolAdvanced Materials, Inc. shall not be liable for and thecustomer assumes all risk and liability of any use ofhandling of any material beyond Lubrizol Advanced

Materials, Inc.s direct control. THE SELLER MAKES NOWARRANTIES, EXPRESS OR IMPLIED, INCLUDINGBUT NOT LIMITED TO, THE IMPLIED WARRANTIESOF MERCHANTABILITY AND FITNESS FOR APARTICULAR PURPOSE. Nothing contained herein isto be considered as permission, recommendation, noas an inducement to practice any patented inventionwithout permission of the patent owner.

Lubrizol Advanced Materials, Inc. is a wholly owned subsidiary of The Lubrizol Corporation

* Trademark owned by The Lubrizol Corporation Copyright 2007 / The Lubrizol Corporation

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How is Viscosity Different from Yield Value?

Viscous suspensions can and will collapse. It is acommon misconception that if the viscosity of aproduct is high enough, it can be used to suspend.Actually, a higher viscosity only slows down therate of particle movement. Yield value is required

to create a stable suspension.

Table I demonstrates the relationship betweenyield value of a sand suspension and suspendingability.

Silica sand with an average particle diameter of0.6mm was placed in gels made from variousthickener types at different concentrations. Thedata suggests that a critical Brookfield yield valuebetween 90 and 124 is required to produce astable sand suspension. This clearly demon-strates that yield value, not viscosity, is theinfluencing factor in suspension performance.

How Do Carbopol

Polymers Compare in YieldValue?

It can be seen below in Figure 1 that each of thepolymers maintains a useful yield value throughoutthe most common pH use range. They differ in

their relative strengths depending on their type andegree of crosslinking. The data presented show thathe polymers with a higher degree of crosslinking havhigher relative values, as given for Carbopol

940

Those with a lesser degree of crosslinking show lowerelative values, as given for Carbopol

941. Figure

shows the yield value efficiency of Carbopol

ETD anCarbopol

Ultrez polymers.

What Common Factors Affect Yield Value?

The yield value achieved with Carbopol

polymers cabe changed by adding materials that affect the swellinof the polymer. Some materials that can cause change in polymer swelling are alcohols, polyols, ancations. Each of these materials may have the effect oreducing the yield value of the system. The otheprimary factor affecting the yield value is the density othe medium. In this case, the dissolution of othepolymers, polysaccharides for instance, may increasthe medium density and lower the required yield valueSome systems can have more complex interactions othese two effects. Examples of this type can commonbe seen in surfactant formulations, further covered TDS-224.

Table IEffect of Yield Value on a Sand Suspension

Brookfield BrookfieldConcentration Viscosity Yield Suspension

Exp Thickener % (mPa.s (cP), 20 rpm) Value Performance

1 Carbopol

941 polymer 0.15 2,900 500 Stable2 Carbopol

934 polymer 0.25 6,350 410 Stable

3 Gum tragacanth (Homogenized) 3.00 9,740 276 Stable4 Gum tragacanth (set 2 months) 3.00 - 144 Stable5 Carbopol

934 polymer 0.18 2,420 136 Stable

6 Carbopol

941 polymer 0.10 1,950 124 Stable7 Carbopol

934 polymer 0.15 1,600 90 48 hours

8 Locust bean gum 2.50 22,800 80 8 hours9 Polyethylene oxide 1.50 2,040 40 3 hours10 Sodium CMC 1.50 5,900 36 3 hours11 Guar gum 1.50 8,040 32 4 hours12 Sodium Alginate 2.50 8,360 16 2 hours13 Methyl cellulose 2.00 3,200 2 1.5 hours

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Can Yield Value for a System be predicted?

A simple approximation of the required yieldvalue for a system can be obtained if the

density of the medium and the size anddensity of an assumed spherical particle areknown:

Yield Value, dyn/cm2 = 4/3R (p-m)gwhere R radius of the particle, in cm

p density of particle, in g/cm3

m density of medium, in g/cm3

g acceleration due to gravity(980 cm/s2)

Figure 3 shows how yield value is a function of

the density difference (p-m) between theparticle and the medium, and of the particlesize (radius).