information Value of Sultaines - HARKE Group

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JANUARY 2012
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Surfactants
The value of sultaines
Regina Cosby and Frank Wagner of Rhodia take a new look at amphoteric surfactants*
Amphoteric surfactants are commonly used by
formulators in personal care applications, such as
body washes, shampoos and facial cleansers, and
in home care formulations like hard surface cleaners and
laundry and dish detergents. They typically allow
formulators to reduce the irritation potential of anionic
surfactants, develop formulation viscosity and enhance
foam quality in terms of texture, volume and stability.
Cocamidopropyl betaine (CAPB, Figure 1a) is a widely
used amphoteric surfactant in the home and personal
care industries, although it can limit formulators in
developing higher performance products at a lower
formulation cost. Sultaines, such as cocamidopropyl
hydroxysultaine (CAPHS, Figure 1b) are an amphoteric
option that offer improved foam quality, enhanced
mildness and cost-effectiveness and are environmentally
favourable.
The molecular design of sultaines enhances mildness
and foam performances and can solve key formulation
challenges of sulfate- and ethoxylate-free formulations in
personal care. Sultaines bring extra clarity and stability
when compared to betaines, due to their stronger
hydrotroping properties, and are extremely tolerant in
hard water environments. They have identical viscosity
development to betaines and can easily replace them in
home and personal care formulations.
Chemistry of sultaines
Sultaines are the inner sulfonic acid salt of a strong
inorganic acid and are commonly referred to as
‘sulfobetaines.’ They are similar to betaines, which are
inner carboxylic acid salts of a weak organic acid. 1
Both molecules are considered zwitterionic at neutral
pH where the nitrogen on the hydrophobic tail is
quaternary (cationic); the polar head groups are anionic
and add to the hydrophilic properties of the molecule.
Because the quaternary nitrogen is always positive, these
molecules cannot obtain anionic nature at any pH and are
not truly amphoteric, although they are commonly
referred to as such.
The alkyl chain length varies, depending on the
feedstock used. In personal care formulations, higher
hydrophobic alkyl chain lengths of C 12-14 are preferred for
optimum foaming, mildness and viscosity building
properties.
Foam volume (ml)
500
400
300
200
100
With disodium
Lauryl sulfosuccinate
CAPHS-FA
CAPB-FA
LAPHS-FA
LAPB-FA
CAPHS-T
CAPB-T
Figure 1 - CAPB & CAPMS
Figure 2 - Foam volume of
betaines & sultaines of
varying feedstocks with
common anionics
With sodium coco-sulfate
CAPH-FA
CAPB-FA
LAPHS-FA
LAPB-FA
CAPHS-T
CAPB-T
a - Cocamidopropyl
betaine
b - Cocamidopropyl
hydroxysultaine
O
CH 3
R N N + O -
H
Although sultaines and betaines are similar in structure,
the slight difference in the head group of the molecule is
what gives sultaines their different properties. A betaine’s
head group is a weakly anionic carboxylic acid that binds
easily to divalent cations, such as calcium and
magnesium. Sultaines consist of a strong anionic
sulfonate group that overpowers the cationic properties
of the quaternary nitrogen.
This small difference in the molecule is what gives
sultaines their enhanced properties over their betaine
counterparts, such as strong alkali stability, excellent lime
soap dispersion and enhanced coupling. When
manufactured, sultaines are naturally higher in terms of
active content than betaines without the use of solvents
and they are free of preservatives, processing aids and
chelants.
Improved foam properties
Foam tests of various anionic: amphoteric combinations
were evaluated at 0.1% actives at a ratio of 1.5:1 to
study further the properties of sultaines in personal care.
Since amphoterics display different properties at various
pH ranges, foam volume was measured at both pH 4.0
and 7.0. The testing parameters for all foam studies were:
no soil, an ambient temperature of 22°C and water with
a hardness of approximately 150 ppm calcium and
magnesium ions.
The process used an automatic cylinder shake foam
apparatus from Guam that consisted of placing 100 ml of
test solution in a 500 ml graduated cylinder and inverting
it ten consecutive times and at a frequency of 30 rpm. The
foam volume, expressed in ml, is measured immediately
following last inversion, t=0, and after five minutes, t=5.
The initial foam volume indicated flash foam properties
and the reading after five minutes indicated foam
stability. All samples were run in duplicate using a least
significant difference of 90%.
Figure 2 shows the foam volume of betaines and
sultaines of varying feedstock combined with two of the
anionic surfactants tested, disodium lauryl sulfosuccinate
and sodium coco-sulfate. The feedstock varieties included
betaine and sultaines derived from triglycerides (CAPB-T
and CAPHS-T), those derived from coconut fatty acid
(CAPB-FA and CAPHS-FA) and those derived from lauric
acid (LAPB-FA and LAPHS-FA).
26 Speciality Chemicals Magazine January 2012 www.specchemonline.com
R
O
N
H
CH 3
O
CH 3
N + S O
O O
CH 3 OH

Surfactants
Foam volume (ml)
500
450
400
350
300
250
SLES-2
SLES-3
Anionic neat
SLES-2
Combos
Triglyceride
Sultaines
Betaines
SLES-3
Combos
In all cases, at a 90% confidence level, sultaines
statistically outperformed their betaine counterpart of the
same feedstock in both pH environments. In terms of
foam stability, betaines and sultaines displayed similar
abilities to stabilise foam volume at five minutes. During
the study, it was observed that the sultaine combination
solutions were clear and the betaine combinations were
hazy when combined with each of the high Kraft point
anionics.
This mimics the hydrotroping properties of sultaines
that have been studied in hard surface cleaners. The
superior performance is most likely due to the greater
charge neutralisation of the molecule. Further studies are
planned to evaluate these coupling properties
quantitatively in a personal care formulation.
Sodium coco-sulfate has a dense, creamy foam quality
that is further stabilised with the addition of amphoterics.
Figure 2 shows that there was a significant improvement
in the foam quantity of sultaines over betaines with
sodium coco-sulfate in all feedstock cases.
Using the same conditions as this study, further foam
work focused on standard, triglyceride-based amphoterics
to explore the effect of the ethoxylation of the anionic on
the foam performance of sultaines. The triglyceride-based
sultaines outperformed the betaines and the foam volume
of the sodium laureth sulfate (SLES)/sultaine combinations
were significantly impacted by the degree of ethoxylation
on the SLES molecule (Figure 3).
SLES-3/sultaine foamed significantly higher than the
SLES-2/sultaine yet the ethoxylation differences did not
have an effect on the SLES/betaine combinations. All
anionic/amphoteric surfactant combinations have a
denser and more stable foam quality and do not have as
high a foam volume as the neat anionic surfactants.
Viscosity building
Viscosity comparisons used two base formulations that
only varied the test surfactant to evaluate viscosity
building properties with electrolytes. Viscosity readings
were measured when the samples reached 25°C in a
water bath by using a Brookfield LVT Viscometer, spindle
#3, after one minute. The speed on the viscometer was
adjusted accordingly from 3 to 12 rpm or when the
sample measured 50% torque.
Two common surfactant systems were analysed, based
on 12% active SLES-2/3% active test surfactant and 16%
active SLES-1/1.6% active cocamide MEA/1.5% active test
surfactant respectively. Similar to the foam studies, the
test surfactants consisted of sultaines and betaines
derived from various feedstocks including triglycerides
(whole coconut oil), coconut fatty acid or lauric fatty acid.
Figure 3 - Foam volume of
SLES-3/sultaine
combination
The objective was to determine if sultaines of various
feedstocks built viscosity as well as their corresponding
betaine counterparts. Each system was balanced to 100%
by weight with distilled water and adjusted to pH 7.0±0.2
using citric acid. Initial readings were measured, then
sodium chloride was added in 0.2-0.5% increments.
The results (Figure 4) demonstrate that a sultaine and
betaine derived from the same feedstock build viscosity in a
similar way. The addition of an alkanolamide made more of
an impact on viscosity response due to its strong hydrogen
bonding with electrolytes. For example, a sultaine and a
betaine, both based on coconut fatty acid, both built
viscosity in a similar way in the system that contained an
amide and in the one without it.
In the formulation without amide, both test
formulations with coconut fatty acid-based amphoterics
reached an ideal personal care formulation viscosity of
10,000-15,000 cps with 1.5% sodium chloride. When an
amide was present, the formulations reached this same
viscosity range at 0.5% sodium chloride, even though
half the amount of coconut fatty acid-based amphoterics
was used.
The same patterns were observed for lauric fatty acidor
triglyceride-based sultaines and their betaine
counterparts. Viscosity response showed the following
sequence between alkyls as contributors to the viscosity
build of amphoterics: in both systems tested, with or
without the addition of a non-ionic, lauric fatty acid >
coconut fatty acid > coconut oil.
Viscosity build is therefore a function of the alkyl chain
length and/or chain distribution of the amphoteric.
Betaines and sultaines build viscosity in a similar way.
Based on the two systems tested, sultaines can replace
betaines with minimal difference in viscosity building in
personal care formulations.
Reduced irritation
MatTek’s patented EpiOcular test was used to evaluate
and compare the effect that a sultaine and a betaine has
on reducing the irritation of anionic surfactants. Mildness
was evaluated in vitro by MatTek using its corneal model
that consists of cultured epidermal cells similar to those
found in the cornea. The model provides a predictive
means to assess ocular irritancy in vitro.
Table 1 - EpiOcular test results of SLES-2 or sodium coco-sulphate, sultaine & betaine
combinations
Sodium
laureth-2
sulfatebased
combinations
Sodium
cocosulfatebased
combinations
Sample description Draize Sample description Draize
score
score
15% active SLES-2 48.9 Johnson & Johnson NMT 9.1
15% active CAPHS 67.2 15% active CAPB 67.2
11.25% active SLES-2 11.25% active SLES-2
4.75% active CAPHS 40.7 4.75% active CAPB 37.1
7.5% active SLES-2 7.5% active CAPHS
7.5% SLES-2 14.4 7.5% active CAPB 18.0
4.75% active SLES-2 4.75% active SLES-2
11.25% active CAPHS 6.6 11.25% active CAPB 22.4
10% active coco-sulfate 102.5 Johnson & Johnson NMT 9.1
10% active CAPHS 97.0 10% active CAPB 65.4
7.5% active coco-sulfate 7.5% active coco-sulfate
2.5% active CAPHS 75.7 2.5% active CAPB 58.3
5.0% active coco-sulfate 5.0% coco-sulfate
5.0% active CAPHS 20.1 5.0% active CAPB 20.4
2.5% active coco-sulfate 2.5% active coco-sulfate
7.5% active CAPHS 13.8 7.5% active CAPB 17.3
www.specchemonline.com January 2012 Speciality Chemicals Magazine 27

Surfactants
Viscosity (cps)
120,000
100,000
80,000
60,000
40,000
20,000
0
0.0 0.5 1.0 1.5 2.0 2.5
NaCl (%)
Hydroxysultaines
SLES-1/CMEA
systems
CAPB-FA
LAPB-FA
LAPHS-FA
CAPHS-FA
CAPHS-T
CAPB-T
Betaines
SLES-2
systems
CAPB-FA
LAPB-FA
CAPHS-FA
LAPHS-FA
CAPHS-T
CAPB-T
CAPHS-FA LAPHS-FA CAPHS-T CAPB-FA LAPB-FA CAPB-T
The procedure uses a water-soluble, yellow tetrazolium
salt (MTT {3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium
bromide}), which is reduced by succinate
dehydrogenase in the mitochondria of viable cells to a
purple, insoluble formazan derivative. Substances which
damage this mitochondrial enzyme inhibit the reduction
of the tetrazolium salt. The amount of MTT reduced by a
culture is therefore proportional to the number of viable
cells.
As per MatTek’s protocol, the samples are diluted to a
20% solution and the appropriate tissue preparation is
made. 100 microlitres of the test article and distilled
water (negative control) were added to the micelles
containing the EpiOcular samples. The six-well plates
containing the dosed EpiOcular samples were then
incubated at 37°C, 5% CO 2 and >90% humidity. The
results were then converted from an ET-50 value into a
familiar estimated Draize score.
According to this test, the ingredient is considered
more or less irritating depending on the Draize Score: 0-
15 means non-irritating, minimal, 15.1-25 is mild, 25.1-
50 is moderate and 50.1-110 is considered severely
irritating or extreme. Traditionally, true amphoterics or
highly ethoxylated nonionics are used to reduce or
minimise eye irritation of alkyl ethoxylated sulfates and
alkyl sulfates. Previous studies show that betaines have
minimal impact on this property. 2
EpiOcular comparisons were made for two anionic
combinations, one with SLES-2 and one with sodium
coco-sulfate to determine if sultaines displayed similar
Figure 4 - Viscosity
responses of sultaines &
betaines
References
1. McIntyre Group, McIntyre
Chemistry Manual 1997, 46-60
2. T. Schoenberg, Formulating
with Betaine and Amphoteric
Surfactants 1997, 2.
3. F. Wagner, D. Colovic, J.
Kiplinger, G. Cosby & E. Leroy, A
Novel Look at Amphoteric
Surfactants, Poster, 2010.
Contact
Denis Bendejacq
Rhodia CTRA
Labo Home & Personal
Care
52, rue de la Haie Coq
F-93308 Aubervilliers
France
E-mail: denis.bendejacq@
eu.rhodia.com
Website: www.rhodia.com
behaviour to betaines. The results (Table 1) show that,
although all surfactants tested individually at 10-15%
active were severely irritating, the combination of an
anionic with either a betaine or sultaine starts to mitigate
the irritation potential.
Sultaines especially reduced the irritation when
incorporating more sultaine than anionic in the SLES-
2/amphoteric combinations. For example 11.25% CAPHS
and 4.75% SLES-2 had a score of 6.6, non-irritating and
the corresponding CAPB was 22.4, or mild. The score of
this SLES-2/CAPHS combination was even lower than the
benchmark baby shampoo that claims ‘no more tears’.
Similarly, the estimated Draize scores of sodium cocosulfate
were reduced when incorporating a betaine or
sultaine. The impact of the ethoxylation of the alkyl
sulfate in combination with a sultaine was more dramatic
than the sulfate/betaine combinations, as also indicated in
the foam studies.
Conclusion
Sultaines molecular design makes them an ideal
amphoteric choice for personal care formulations where
mildness and foam are important. They are free of
processing aids and preservatives and are able to reduce
the irritation of common anionics more efficiently than
betaines.
Sultaines are highly compatible with anionic surfactants
and enhance foaming properties of ethoxylate-free
surfactants such as sodium coco-sulfate and also sulfatefree
surfactants such as disodium lauryl sulfosuccinate. In
every combination of anionic/amphoteric, sultaines
delivered superior or equal foam when compared to
betaines at the 90% confidence level.
Chain length of the betaine or sultaine and anionic
selection is more important in boosting foam than pH
effect. The degree of ethoxylation on an alkyl sulfate in
combination with a triglyceride-based CAPHS has a
favourable impact on mildness and foam. Sultaines build
viscosity similarly to their betaine counterpart and can
easily substitute them into a personal care formulation
while simultaneously boosting foam and mildness.
* - The authors would like to thank Dusanka Colovic Vos of
Rhodia, University Park, for her assistance in running many of the
foam and viscosity tests, Jon Kiplinger and Tom Ruch of Rhodia
CRTA for their assistance with EpiOcular correspondence and
interpretation of results and Eric Leroy of CRTA for his guidance
on relating the results to molecular structure as originally
published in a poster format. 3 They would especially like to thank
Denis Bendejacq of CRTA for all of his assistance and guidance in
writing this article.
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