moisturizing lotion
The effluence of structure of
moisturizing lotion (texture parameter)
on its use properties, and control of its
physical properties
The effluence of structure of moisturizing lotion (texture
parameter) on its use properties, and control of its
physical properties
• 1. Factors influencing the lotion physical
parameter
• 2. The effects on the behavior of lotion
during lotion processing
Table 1. Texture profile
Mechanical
characteristics
Primary
parameter
hardness
Secondary
parameter
Popular terms
Soft→firm→hard
Cohesiveness
Crumbly→crunchy→brittle
viscosity
Thin→viscous
elasticity
Plastic→elastic
adhesiveness
Sticky→tacky→gooey
Geometrical
characteristics
Particle size and shape
Particle shape and orientation
Gritty, grainy, coarse, etc.
Fibrous, cellular, crystalline, etc.
Other
characteristics
Moisture
content
Fat content
Dry→moist→wet→watery
Oiliness
greasiness
oily
greasy
Table 2. texture profile parameter used in
the skin care product evaluation
Stage of
evaluation
Skin care product attribute and
definite
Texture profile
parameter
PICK-UP, product
removed from
container, product
poured or
squeezed from
bottle onto
fingertips, or
product lifted
from jar with
forefinger
THICKNESS-perceived
denseness of product. Evaluated
as force required to squeeze
between thumb and forefinger.
Rated as thin-medium-thick.
Or:
CONSISTENCY-perceived
structure of product. Evaluated as
resistance to deformation and
difficulty of lifting from
container. Rated as lightmedium heavy.
Viscosity for lotions
RUB-OUT
(application),
spread of product
over and into skin
with fingertips
using gentle circular
motion at a rate of
two rub per second
for a specified
period of time,
depending on the
product.
SPREADABILITY-ease of moving
product from point of application
over rest of face. Evaluated as
resistance to pressure. Rated or
described as:
‘slips’-very easy to spread
‘glides’-moderated easy
‘drag’-difficult to spread
ABSORBENCY-Rate at which
product is perceived to be absorbed
into skin. Evaluated by noting
changes in character of product and
in amount of product remaining
(tactile and visual) and by changes in
skin surface. Rated slow-moderatefast.
Viscosity, cohesiveness,
springiness, gumminess,
adhesiveness
Other characteristics –(oil
and water content of
product)
AFTER-FEEL
(and appearance),
evaluation of skin
surface with
fingertips, visually
and kinesthetically
immediately after
product
application and
possible at varying
intervals thereafter.
AFTER-FEEL – Type and
intensity of product residue left on
skin; changes in skin feel/ Product
residue is described by type, i.e.
film(oily or greasy), coating(waxy
or dry), flaky or powdery particles;
the amount of such residue is
identified as slight-moderate-large.
Skin feel is described as dry (taut,
pulled, tight); moist (supple,
pliant), oily(dirty, clogged).
Other sensations are also noted
and identified where applicable,
i.e. clean, stimulated, irritated, etc.
Other characteristics(oil and water content)
Geometrical
characteristics-(gritty,
powdery, etc.)
1. Factors influencing the lotion
physical parameter
• (1). THE EMULSIFIER The emulsifier frequently is
the most important role in the emulsion in producing the
characteristic flow properties. In dilute emulsions this is
more evident because when the concentration of emulsifier
is varied, the effects of change in particle size and particle
size distribution of the disperse phase on the viscosity of
the emulsion are not as big as the change in the viscosity of
the continuous phase brought about by the emulsifier.
Mixed emulsifiers can provide desirable flow properties
(used to thicken lotion, see also table 2) and to reduce
cream of lotion.
(2) THE DISPERSE PHASE
• There are many parameters related to the disperse phase or
internal phase that exert rheological changes in emulsions,
including: nature of the oil; viscosity of the oil; particle
size; particle size distribution; and particle shape. Particle
size and particle size distribution also depend on the
emulsifier concentration.
• The nature of the oil in O/W emulsion exerts its effect on
the emulsion via its interaction with the emulsifier. The
viscosity of the aqueous medium and the particle size
distribution are related to differences in the state of
aggregation of the globules.
(2) THE DISPERSE PHASE
• The mean particle size and particle size
distribution can exert profound effects on the
rheological parameters of an emulsion. The
viscosity of dilute O/W emulsions are influenced
by mean particle size variation of 3 to0.7 microns,
but in concentrated emulsions the product of
relative viscosity and mean particle size did not
change if the distribution of particle size about the
mean value was not very wide.
(3) THE CONTINUOUS PHASE
• The rheological behavior of a lotion is most often
determined by the rheology of the continuous
phase. The rheological behavior of the continuous
phase of O/W emulsions is frequently controlled
by the use of hydrocolloids, which have been
already been discussed. The rheological behavior
properties of the emulsion, in turn, are dependent
on the stability of the hydrocolloidal system
(4) PHASE VOLUME RATIO
• The rheological patterns of dilute emulsions are often
markedly different than those for concentrated emulsions.
Therefore, it is useful to have information concerning the
viscosity dependence on the phase volume ratio in both
areas. Generally, it has been found that the rheological
parameters of an emulsion increase with crease in the
phase volume ratio. It is expected that the limit of φ before
inversion occurs will vary depending on the characteristics
of the system and, in particular, the nature of the
emulsifying agent and its solubility in the continuous phase
of the emulsion
2. The effects on the behavior of lotion
during lotion processing
•
•
•
•
(1) Mixing
(2) Heating and cooling
(3) Shearing
(4) Homogenizing
(1) Mixing
• Mixing is a basic step to the compounding and
processing of lotion in the cosmetic industry.
Mixing is necessary to blend a water phase and oil
phase into an emulsion, but consider the potential
effect of the degree of mixing on the product
viscosity. First of all, a minimum of energy must
be used to evenly mix the two phases and other
additives. A high amount of mixing energy,
however, can decrease the particle size of the
dispersed phase and hence affecting the emulsion
viscosity.
• In case of heat transfer, viscous lotions are usually
handled with a contrarotating agitator.
• Mixing is so basic to the formation of the lotion
and can have such an important effect on product
rheology that the smart formulator will learn to
work with it in achieving the desired end
properties instead of fighting against it in a
dogmatic scaleup from benchtop to plant.
Cosmetic lotion may be shear sensitive to some
degree and mixing can be used as a tool in
achieving the desired product viscosity by
properly manipulating the mixing variables.
(2) Heating and cooling
• Heating is generally less of a problem in cosmetic
processing because the product or phase is usually
fluid at elevated temperatures (viscosity being
inversely proportional to temperature for
emulsions commonly encountered in the cosmetic
industry). The rate of heating is not usually
considered an important parameter, assuming that
the desired end point is not overshot.
• Cooling is more commonly a problem with
cosmetic emulsion because it generally increases
product viscosity greatly.
• In summary, a lotion is usually heated after it has
been formed to reduce its viscosity for filling.
Cooling has a more important relationship to final
product viscosity because of its effect on
crystallite size and dispersion, and because of the
interrelationship of work input and product
viscosity.
(3) Shearing
• Many lotions are shear-thining. In a typical
operation, a finished lotion is cooled to room
temperature in a compounding vessel, and then
pumped through a filter to a storage tank where it
is held for filling. The viscosity of lotion will have
been reduced by this step. Then the product may
be pumped to the filling line. The product usually
has a chance to build a network of bonds. A
portion of these bonds, if broken, are sometimes
permanently destroyed
(4) Homogenizing
• Homogenization, or the reduction of particles to a
small and uniform size and their even distribution in
a medium, is related to shearing in that frequently
used to create the particle breakdown. The cosmetic
industry usually resorts to homogenization for
dispersing solids and insoluble liquids in a liquid
phase and reducing the dispersed particles to a
minimum size. The reasons for doing this are
numerous and include the desire to increase stability
by minimizing globule size and hence decrease the
chances of coalescence, to reduce particle size of
the disperse phase so as to inhibit settling, and to
increase viscosity by forming a finer emulsion.
• If while the emulsion is hot and both phases still liquid,
homogenization will tend to reduce the disperse phase
to a minimum size distribution which will impart
certain properties (such as increased stability) to the
final product when it is cooled down and packaged. If
the product is homogenized after some cooling has
taken place and viscosity has already started to build,
however, the viscosity of the finished product may be
permanently reduced. Timing and process step must be
considered in developing a process to make a product
with the desired end properties.