Conditioning Agents for Hair and Skin

66 Morrison
Although mineral oil and paraffin wax cannot be mixed to create petrolatum,
various types and grades of petrolatum can be prepared which contain
differing amounts of wax and oil. This allows numerous blends to be prepared,
each designed to meet a specific need. Obviously, petrolatums with high levels
of wax have high melting points and hard consistencies, while those with more
oil are softer and more fluidlike. The waxes which are present in petrolatum
are clearly evident when samples are viewed under a microscope. Figure 2
shows a microphotograph (100 x) of a petrolatum, while Figure 3 is the same
material photographed at 500 x. In both photos, the wax crystals can be seen
quite easily.
In order for petrolatum to be labeled "Petrolatum, U.S.P." or "White Petrolatum,
U.S.P.," it must conform to the requirements described in the United
States Pharmacopoeia. One of the tests it must meet is a consistency test. Since
adding too much oil or too much wax to a petrolatum may cause the final
product to fail this U.S.P. requirement, care must be taken when blending
petrolatums to ensure that the product's consistency does not fall outside the
required range if the final material is to be U.S.P. petrolatum. Note that the
U.S.P. also has other requirements for petrolatums, but these are easily found
in the United States Pharmacopoeia and will not be discussed here, as they are
outside the scope of this chapter.
V. REFINING AND PRODUCTION
As stated previously, petrolatum is a purified, semisolid mixture of hydrocarbons
taken from petroleum (crude oil). Since petroleum is obtained from the
earth, and since the materials it contains are simply refined (i.e., separated
from impurities) and not synthesized, petrolatum can be considered a natural
material in the truest sense of the word (18).
The exact method of production of petrolatum varies depending on several
factors. These factors include the type of crude oil used (the chemical compositions
of crude oils from different sources vary considerably, as do the boiling
range and other physical properties which affect the conditions used to refine
the petroleum) and the types of petroleum products desired at the end of the
refining process. However, a general process for the manufacture of petrolatum,
from crude oil to the final product, is described below.
Figures 4,5, and 6 show the general scheme of a petroleum refinery process,
with focus on the production of petrolatum. First, a crude oil is subjected to
atmospheric distillation, which removes gases and lighter refined products
(i.e., fuels, such as gasoline, kerosene, and Diesel fuel) from the bulk of the
crude oil product at atmospheric pressure. The remaining oil is sent to a vacuum
distillation unit so that the heavier fractions (e.g., lubricating oil fractions)
can be removed without the extreme temperatures which would be required