First published in 1970.
January 2020 SPRAY 29
(HLB) was created in that year. It considered non-ionic emulsifiers, positioning on a span of
0–40.
The HLB number for an unknown compound was determined by Becher using a procedure
described in various articles and finally in a book titled “The Emulsification Process”
(1973). A summary for aerosol scientists was produced by former Dupont scientist Dr. Paul
A. Sanders in two textbooks, the first titled “Principles of Aerosol Technology” published
by Van Nostrand Reinhold Co. (1970). He described how these non-ionic w/o emulsifiers
could be used for water-based pesticides, air fresheners, furniture polishes, artificial snow
and other aerosols.
A rough guide to the emulsion properties can be illustrated as:
APPEARANCE IN WATER
1–2 HLB No solubility or dispersability
3–6 HLB Poor dispersability (w/o emulsion forms)
6–8 HLB Milky emulsion (usually w/o emulsion forms)
10–11 HLB Translucent emulsion (o/w emulsion forms)
12 and higher HLB Transparent emulsion (o/w emulsion forms)
The type of emulsion can be readily confirmed. A w/o emulsion has oil as the continuous phase. It
will not conduct electricity. A droplet of colored water will not disperse (the colorant is added for better
visibility). Add 15% iso-butane and spray. The w/o emulsion does not foam. The spray is relatively
warm. Dilution with water forms a separate phase.
Examples of various emulsifiers and their HLB values are shown as follows:
TYPICAL HLB VALUES
HLB Value Organic Compound
03.8 Glyceryl Monostearate
05.3 Polyethoxylated (2 moles) cetylalcohol
16.9 Polyethoxylated (23 moles) lauryl alcohol
04.9 Polyethyloxylated (2 moles) stearyl alcohol (Brij 72)
10.0 Polyethyloxylated (5 moles) sorbitan monolaurate
11.0 Polyethyloxylated (20 moles) sorbitan trioleate
Ideally, the low HLB surfactant (or preferably a blend) should have about the same HLB as the
chemical(s) to be emulsified. Typical values are aromatic mineral oil (12.8), kerosenes (10.6), aliphatic
solvents (about C12 9.7), paraffin wax (9.8) and various oils (11). These values must be determined
experimentally. For example, in the development of an aerosol air freshener, the concentrate is placed
in a glass tube and the selected hydrocarbon-hydrofluorocarbon propellant is slowly added. At first,
emulsification is complete. The mixture turns milky white and no separation of the propellant takes
place.
However, when about 15% is added to some formulas, there is a very slow (hours) separation of
a clear layer of liquid propellant at the top. Adding still more propellant will accelerate the rate of
separation, with a clear meniscus visible in perhaps a few minutes. This is normally considered to be
acceptable, provided the separation rate does not increase over several weeks or over anticipatable
temperatures, and if the product is directed to be shaken when used.
This brings up a major problem with the HLB systems. As temperatures rise, more hydration of
hydrophilic groups takes place. If the heat is sufficient, the desired w/o emulsion may invert to the
o/w type. In one unusual case, the unwanted o/w formula was corrected by placing the filled stock
in an ice house. Over a weekend, it reverted to the w/o type. The Phase Inversion Temperature or
“PIT” refinement of HLB is designed to cope with this problem.