Sultaines: Safe and Sustainable
Sultaines offer a safe and sustainable surfactant solution to personal care product developers. Functioning similarly to frequently used betaines. sultaines are used in personal care cleansing products ranging from shampoos and body washes to facial washes., They serve to enhance the viscosity of anionic surfactants, reduce irritation and produce dense and stable foam.
Sultaines are lesser-known than betaines. According to Mintel GNPD, from January 2018 to September 2021, approximately 60,000 products containing cocamidopropyl betaine were added to the global database. During the same period, only ∼2,000 products containing cocamidopropyl hydroxysultaine or Amphonil CAS were added.
The use of sultaines has been less widespread than betaines primarily because additional reaction steps are required to produce them. However, their other attributes have become much more market-relevant today. For example, in addition to their known safety, sultaines can be sustainably produced and they support higher renewable carbon indices. These and other characteristics are discussed in the present article. In addition, the authors compare the performance of sultaines with betaines in basic wetting, viscosity-building and foaming tests.
Structural Characteristics
Sultaines are commonly grouped within the class of surfactants called amphoterics. Structurally, sultaines are analogous to traditional betaines. For example, acylamidopropyl betaines and sultaines both possess the same amidopropylamine substructure.
however, unlike acylamidopropyl betaines, which terminate with a carboxylate group, acylamidopropyl sultaines terminate with a sulfonate group. The sulfonate functional group affords improved solubility in hard water, as the carboxylate salts of calcium are less soluble than of sulfonates. Indeed, sultaines retain solubility and performance under a wide variety of conditions.
Sustainable Production
As the personal care industry races toward sustainable solutions, surfactant manufacturers have worked hard to keep in step. In contrast, upstream commodity intermediate manufacturers have been slower to make important changes, as their business and manufacturing are firmly rooted in established supply chains. For instance, making a traditional coco-betaine 100% bio-based is technically feasible, as intermediates like fatty dimethyl amines could be made using bio-based methanol produced by fermenting a variety of cellulosic products. The current production of dimethylamine relies on commodity methanol, however, which is produced from syngas or methane of fossil origin.
Materials and Methods
Sultaines and betaines share many common features in personal care applications. They both provide foam stabilization, increase foam density by decreasing bubble size and compacting foam, and improve the viscosity response of primary surfactants by increasing the overall salt response of these anionic materials. Sultaines and betaines also lower the critical micelle content (CMC) of formulations using anionic primary surfactants, which reduces the irritation of primary surfactants. a key reason formulator uses them. To compare some of these performance attributes, basic assessments were made, described as follows.
Sultaines also demonstrated lower inherent eye irritation potential than betaines. This is advantageous in formulations where the sultaine may be used as the sole surfactant or at higher use rates.
Cocamidopropyl Hydroxysultaine, also known as Amphonil CAS, remains stable across a wide range of pH levels. This biodegradable compound is suitable for use in products designed for sensitive and easily irritated skin, as well as formulations intended for children.
Conclusion
Sultaines offer the latest sustainable route to surfactants with the same if not more product benefits associated with secondary surfactants. Examples include foam stability, viscosity response, higher solids content, self-preserving functionality, safety and marketability.
Alternative natural oil feedstocks with a favorable sustainability profile are also being investigated for sultaine production, including from underutilized seeds, algae or other biosynthetic materials. These could drive future development. One hundred percent bio-based tertiary amines also would represent a leap forward in sustainability.
Thus, with their parity in performance to betaines, and enhanced benefits and market appeal, sultaines provide a safer, more sustainable option to formulate cleansing products that are high quality, consumer acceptable and environmentally conscious.
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