72
Introduction
JOURNAL OF COSMETIC SCIENCE
SrtUTEGIES AND TECHNl{JUES FOR TROUBLE-FREE
MANUFACTURING OF COSMETIC EMULSIONS
T. Joseph Lin, Ph.D.
628 Enchanted Way, Pacific Palisades, CA 90272
Faced with fierce competition and ever-changing market demands, cosmetic chemists are increasingly
under pressure to formulate large numbers of new products quickly. Frequently, insufficient time is
allowed for conducting stability tests and pilot batch experiments which are essential to assure sufficient
shelf life and trouble-free manufacturing operation. Among the various types of cosmetic preparations,
emulsion-based products, including suspensions, are most vulnerable to batch-to-batch variations in
product quality and stability. Such variations often result in QC rejection, causing time-consuming
reprocessing, inevitable delay in new product introduction or even expensive product recall. To reduce
processing costs, many manufacturers have increased batch size, and a batch failure can be very
expensive, not only in terms of the raw material cost but also the expense of disposi�g of the rejected bulk.
Clearly, the ability to ensure consistently uniform product quality in manufacturing a wide_range of
emulsion-based products is more important than ever for our industry.
Defining the Problem and Understanding the Causes
Key to developing a sound strategy for consistently producing trouble-free batches of diverse emuJsion
products is defining problems dearly and seeking to understand their true causes. Some problems, such
as pH value of a certain batch not meeting specifications, are usually not very difficult to define and the
extent of deviation from the norm can be measured objectively and accurately. Since there are only a
Jimited number of ingredients in the product which can contribute to the pH variation, isolating possible
variables and investigating the cause may not be very difficult.
However, there are other more complex problems involving certain visual characteristics such as
..product texture" which are more difficult to define and measure objectively. A sample of a cream from a
certain production batch may pass all measurable specifications such as pH, viscosity, specific gravity, and
yet its texture may appear different from that of the laboratory sample or previous batches. Whether this
variance should be sufficient to cause alarm may depend on the chemist's perception. An inexperienced
worker may ignore it whereas an experienced formulator may see it as a sign of something going wrong
with the batch and suggest further investigation. Ignoring signs of a potential problem can invite an
expensive product recall in the future. However, an error in identifying a non-problem as a problem can
also cause unnecessary delay in production -and resulting expense. Clearly, accurate definition and
evaluation of the problem is a very important first step in sohing the often complex problems involving
cosmetic emulsions.
Batch failure can result from many possible factors, and identifying the correct cause or causes requires
good understanding of the effects of key variables. Since consumer satisfaction is essential for cosmetic
products, any change in product properties that can affect consumers' perception of quality, safety, or
effectiveness needs to be controlled. For cosmetic emulsions these properties may incJude product
appearance incJuding color, opacity, and tex1ure, as well as other sensory properties such as fragrance,
odor and skin feel. Control of rheological properties is essential for emulsion products as they can
strongly affect consumer perception of product qualities like "richness," "smoothness," and
••stickiness"( I). In addition, change in rheological properties of an emulsion can strongly affect product
stability as, for example, a reduction in }ield value can cause serious phase separation which will almost
certainly be interpreted by consumers as a sign of an inferior or defective product.

2006 ANNUAL SCIENTIFIC MEETING 73
Investigating and Identifying Factors Affecting Emulsion Quality
Precise control of chemical composition in the production batch is crucial, as inaccurate weighing or
the use of the wrong raw materials can certainly cause variations in many important chemical/physical
properties related to product quaJity and shelf life. Equally important, however, are "Process Variables,"
which can also exert strong influence on perceived product quality. Most cosmetic emulsions on the
market are processed by a batch process, using kettles and mixers. By nature, batch processing is
accompanied by numerous process variables which are difficult to control precisely, and which may affect
emulsion quality. Process variables are those variables introduced during the manufacturing process
including emulsification temperature, mixing speed, the rate and the order in which the two phases are
combined, cooling rate and even filling speed. Depending on the type of product and formulation, some
process variables can be very important while others may be insignificant. Better control of process
variables can often be attained by adopting a continuous process, but this method is not often used in
cosmetic production because of the high engineering and equipment costs and the lack offlexibility.
Understanding the Nature of Emulsion Products
One reason why so many emu1sion products are tricky to manufacture and pose difficu1ty in controlling
the quality of every batch is that most emulsions, except microemulsions, are non-equilibrium systems.
As such, they are subject to the Second Law of thermodynamics and there is a strong tendency for the oil
phase to become separated from the water phase, even when surfactants and polymers are used to retard
this process. In general, a non-equilibrium product such as an 0/W cream, consisting of incompatible oil
and water phases, is much more susceptible to process variables and more troublesome to process than is a
single phase product like a toning lotion consisting mainly of water and ethanol in an equilibrium state.
Many process variables, such as shear stress from mixing and even the speed of adding one phase to
another, if not carefully controlled, can affect emu1sion properties and shelf life. Thus, a 1000 gram
sample of a new cream made in a beaker in the product development laboratory may have a shelf life of 3
years while the first production batch from the same formula, produced in a I 000 gallon tank, may end up
having only a 6-month shelf life. If the shortened shelf life is not detected before shipment, a costly
product recall could result. Scaling-up of a new product from the laboratory to production is a very
important step in prudent emulsion product development and carefully controlled piJot batch experiments
go a long way in preventing production disasters.
Manufacturing Trouble Prevention Program
To avoid problems in manufacturing a new emulsion formulation, it is essential for the development
chemists, quality control staff and process engineers to work together to develop an effective trouble
prevention program. Early detection and identification of potential manufacturing problems is crucial.
The product development chemists in charge of the new product should be alert to communicating
potential processing problems to the QC and engineering staff. Since each emulsion formulation is
unique and may be affected differently by different process variables, it is often advisable to carry out pilot
process experiments to determine the best way of processing and scaling up a new emulsion.
The importance of staff training cannot be overemphasized in our fast-changing industry. Companies
are expanding production by installing larger kettles and bigger mixers. Changing batch size often means
introduction of many process variables which can affect product quality and stability. It is not surprising
that some emulsions made in a new larger kettle can often produce batches having lower quality or
shortened shelf life. An experienced staff may be able to detect signs pending trouble from the appearance
of a batch sample and take corrective, or at least cautionary action. Proper staff training and open
communication among manufacturing staff, QC and development chemists are very important in
formulating a sound strategy for trouble-free manufacturing of cosmetic emulsions.
References
(1) T. J. Lin, Rheology Fundamentals and Applications in Cosmetics Formulation, Manufacturing and
Quality Control, The Chemistry and Manufacture of Cosmetics, M. L. Schlossman, editor, Allured
Publishing Corp. volumel, pp 341-371 (2000)