Nonionic
surfactants are surface active agents which do not dissociate
into ions in aqueous solutions, unlike anionic surfactants which
have a
negative charge and cationic surfactants which have a positive charge
in aqueous solution. Nonionic surfactants
are more widely used as detergents than ionic surfactants because anionic surfactants are insoluble in
many hard water and cationic surfactants are considered to be poor cleaners. In
addition to detergency, nonionic surfactants show excellent solvency, low foam properties
and chemical stability. It is thought that nonionic
surfactants are mild on the skin even at high
loadings and long-term exposure. The hydrophilic group of
nonionic surfactants is a polymerized alkene oxide (water soluble
polyether with 10 to 100 units
length typically). They are prepared by polymerization of ethylene oxide, propylene oxide, and butylene oxide in the
same molecule. Depending
on the ratio and order of oxide addition, together with the number of carbon atoms
which vary the chemical and physical properties, nonionic
surfactant is used as a wetting agent, a detergent, or an emulsifier. Nonionic
surfactants include alcohol ethoxylates, alkylphenol
ethoxylates, phenol
ethoxylates, amide ethoxylates, glyceride
ethoxylates
(soya
bean oil and caster oil ethoxylates), fatty
acid ethoxylates, and
fatty amine ethoxylates. Another commercially significant nonionic surfactants are the alkyl glycosides
in which the hydrophilic groups are sugars (polysaccharides).
The term
sorbitan describes the anhydride form of sorbitol, whose fatty acids are
lipophilic whereas sorbitol body is hydrophilic. This bifunctionality in one
molecule provides the basic properties useful in cleaners, detergents, polymer
additives, and textile industry as emulsifiers, wetting agents, and viscosity
modifiers. Sorbitan esters are rather lipophilic (or hydrophobic) surfactants
exhibiting low HLB (Hydrophilic-Lipophilic Balance) values; having an affinity
for, tending to combine with, or capable of dissolving in lipids (or
water-insoluble). While, the ethoxylated sorbitan esters are hydrophilics
exhibiting high HLB values; having an affinity for water; readily absorbing or
dissolving in water. The type of fatty acid and the mole number of ethylene
oxide provides diverse HLB values for proper applications.
HLB numbers
describe following characterestics:
<10 : Lipid soluble (or
water-insoluble) >10 : Water Soluble 4-8 : Antifoaming 7-11 :
Water-in-oil emulsion 12-16 : Oil-in-water emulsion 11-14 : Good
Wetting 12-15 : Good detergency 16-20 : Stabilizing
HLB values of
sorbitan compounds are:
Surfactants
|
HLB
Value
|
CAS
RN
|
Sorbitan hexastearate ethoxylate EO 6 mole |
3.0
|
|
Sorbitan isostearate
|
4.3
|
|
Sorbitan laurate
|
8.6
|
1338-39-2 |
Sorbitan monoisostearate ethoxylate EO 20 mole |
15.0
|
66794-58-9 |
Sorbitan monolaurate ethoxylate EO 20 mole |
16.9
|
9005-64-5 |
Sorbitan monooleate ethoxylate EO 20 mole |
15.0
|
9005-65-6 |
Sorbitan monopalmitate ethoxylate EO 20 mole |
15.6
|
9005-66-7 |
Sorbitan monostearate ethoxylate EO 20 mole |
14.9
|
9005-67-8 |
Sorbitan monstearate ethoxylate EO 6 mole |
9.5
|
|
Sorbitan oleate
|
4.3
|
1338-43-8 |
Sorbitan palmitate
|
6.7
|
26266-57-9
|
Sorbitan sesquioleate
|
4.5
|
8007-43-0 |
Sorbitan stearate
|
4.7
|
1338-41-6 |
Sorbitan tetraoleate ethoxylate EO 30 mole |
11.5
|
|
Sorbitan tetraoleate ethoxylate EO 40 mole |
12.5
|
|
Sorbitan tetraoleate ethoxylate EO 6 mole |
8.5
|
63089-86-1 |
Sorbitan tetrastearate ethoxylate EO 60 mole |
13.0
|
66828-20-4 |
Sorbitan trioleate ethoxylate EO 20 mole |
11.0
|
9005-70-3 |
Sorbitan trioleate
|
1.8
|
26266-58-0 |
Sorbitan tristearate ethoxylate EO 20 mole |
10.5
|
9005-71-4 |
Sorbitan tristearate
|
2.1
|
26658-19-5 |
|
Sorbitol
is a white, sweetish, hygroscopic,
crystalline
sugar alcohol of six-carbon. It
is found naturally in various
berries and fruits or it is prepared synthetically by
high-pressure catalytic hydrogenation of glucose sugar
derived from cornstarch.
It
melts
at 93 to 98 C depending on the form. It is used
as a a
food additive, toothpaste, tobacco,
toiletries
and in cosmetics. It is used for vitamin-C
fermentation. It is also used in the manufactue of polyethers
for polyurethanes and surfactants.
|