Chemistry Reference
In-Depth Information
TABLE 9.1. Some Calculated HLB Values for Typical
Nonionic Surfactant Structures
Surfactant
a
HLB
Sorbitan trioleate
1.8
Sorbitan tristearate
2.1
Propylene glycol monostearate
3.4
Glycerol monostearate
3.8
Sorbitan monooleate
4.3
Sorbitan monostearate
4.7
Polyoxyethylene(2) cetyl ether
5.3
Diethylene glycol monolaurate
6.1
Sorbitan monolaurate
8.6
Polyoxyethylene(10) cetyl ether
12.9
Polyoxyethylene(20) cetyl ether
15.7
Polyoxyethylene(6) tridecyl ether
11.4
Polyoxyethylene(12) tridecyl ether
14.5
Polyoxyethylene(15) tridecyl ether
15.4
a
Numbers in parentheses indicate the average number of OE units
in the hydrophilic chain.
HLB of 16.7. For materials that cannot be saponified, an empirical formula of the
form
E
þ
P
5
HLB
¼
ð
9
:
9
Þ
can be employed. In the equation, E is the weight percent of oxyethylene chains
and P is the weight percent of polyhydric alcohol (glycerol, sorbitan, etc.) in the
molecule.
Although the HLB system has proved to be very useful from a formulation
chemist's point of view, its empirical nature did not satisfy the desire of many
for a sounder theoretical basis for surfactant characterization. It was subsequently
suggested that HLB numbers could be calculated on the basis of group contribu-
tions according to the formula
X
X
HLB
¼
7
þ
ð
hydrophilic group numbers
Þ
ð
hydrophobic group numbers
Þ
ð
9
:
10
Þ
Some typical group numbers are listed in Table 9.2.
The use of the HLB system for choosing the best emulsifier system for a given
application originally required the performance of a number of experiments in
which surfactants or surfactant mixtures with a range of HLB numbers are
employed to prepare emulsions of the oil in question, and the stability of the result-
ing emulsions is evaluated by measuring the amount of creaming that occurred with
time. The use of surfactant mixtures can become complicated by the fact that such
