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