Conditioning Agents for Hair and Skin

Organo-Modifled Slloxane Polymers 173
Table 1 Heat of Vaporization of Common Personal Care Carriers
Material Heat of vaporization (cal/g)
Water 539
Ethanol 210
Cyclotetrasiloxane 32
Qfclopentasiloxane 32
Cycloheptasiloxane), respectively. Volatile (poly)dimethylcyclosiloxanes are
considered non-Volatile Organic Components (VOC) as regulated by the U.S.
federal (19) and state Environmental Protection Agencies (EPA). Cyclomethicone
fluids have unique physical properties that translate into benefits for
personal care applications. These include volatility, low viscosity, and nonresidual
transient skin feel. Cyclomethicone fluids have low heat of vaporization
(Table 1), they are noncooling (i.e., cooling during evaporation from skin
is minimal), and are nonstinging—a combination rare for personal care carriers.
Other attributes of cyclomethicone fluids include: colorless, odorless, nonstaining,
good spreading, detackification, water sheeting, and transient emolliency
properties. The level of use of cyclomethicone in personal care applications
is typically from 0.1% to 85%; the low end represents use levels which
enhance skin feel in creams (e.g., hand and body moisturizers), and the highend
use levels are to carry actives to skin and hair (e.g., antiperspirant salts,
hair cuticle coat). Another aspect of cyclomethicone fluids that make them
functional in the personal care industry is that they have broad compatibility
with most personal care ingredients, including ethanol, mineral oil, and fatty
acid esters.
Another key attribute ot cyclomethicones is their ability to provide appealing
sensorial esthetics to personal care products. Key sensorial esthetics
typically associated with (poly)dimethylcyclosiloxanes, of which cyclopentasiloxane
is a good example, are low residue, low stickiness, low tackiness,
low greasiness, and low waxiness. Using a protocol developed by Dow
Corning Corporation (20) in Figure 4 one sees that cyclopentasiloxane has
sensory properties normally associated with silicones. The scale in Figure 4
that is used to rank each attribute is based on 0 to 10, with 10 representing the
most and 0 representing the least for the attribute measured. As the ring size
of (poly)dimethyl-cyclosiloxane changes, there are minor changes in sensory
effects. Larger-ring-size cyclomethicone fluids are slower to volatilize, and
they reside on the skin longer to give a longer-lasting feel until they totally
evaporate.