FUNCTIONAL INGREDIENTS
Long-chain alcohols and their derivatives are widely used in household and personal care products. They are often manufactured by hydroformylation (with carbon monoxide and hydrogen, so-called synthesis gas) of a long chain olefin to give an alcohol. In the case of Shell Chemicals, this hydroformylation process termed “modified oxo” in the industry results in a lightly branched chemical composition, branded as NEODOL®, and with about 80% linear and 20% branched chains on the second carbon (Figure 10). Different grades of alcohols are available with a mixture of chain lengths, C9 to C15, which are a mixture of odd and even carbons. The composition of carbon numbers and branching gives some benefits in personal care products. Branching in a hydrocarbon gives more structural irregularity and less opportunity for neighbouring chains to interact and aggregate. For the alcohol and its derivatives, this
lowers the pour point (related to melting point) which is desirable for handling and processing at room temperature without additional heating. Branching also affects the properties and performance of the end molecule. Alcohol grades can be converted into alcohol
ethoxylates by reaction with one or more ethylene oxide (EO) units. The ethylene oxide chain modifies the properties of the alcohol and the resulting alcohol ethoxylate retains to an extent the properties of the parent alcohol properties in terms of effects of carbon chain length and branching. Alcohol ethoxylates are versatile building blocks for ingredients in personal care formulations; there are two generic types of alcohol ethoxylates used in the industry: 1. When several EO units are added (say 5 to 8, the number chosen can depend on the alcohol chain length) the resulting alcohol ethoxylate becomes a surfactant as there are enough EO chains with oxygen atoms (each which with a lone pair of electrons) that will hydrogen bond with water molecules and give this part of the molecule water solubility, in contrast to the carbon chain which is oil soluble. 2. When only a few EO units are added,
Figure 8: Examples of bio-based mass balance alpha olefin structures, what they can be converted into, and their end uses
SO3 Figure 9: Schematic structure of a C14 alpha olefin sulfonate
e.g. 1 to 3 EO, the resulting alcohol ethoxylate is not a surfactant. It remains (like the parent long chain alcohol) insoluble in water as there is insufficient hydrogen bonding with water molecules. In this case the alcohol ethoxylate is usually functionalized by sulfation (reaction with SO3 followed by neutralization described earlier for the alpha olefin) to give an alcohol ethoxy sulfate molecule with a water-soluble part (the ionic sulfate). The most commonly used alcohol ethoxy sulfate in the industry is sodium lauryl ethoxy sulfate (SLES) that is manufactured from palm kernel or coconut oil. The addition of a few EO units to the alcohol chain before sulfation
rather than sulfation of the alcohol directly imparts properties to the alcohol ethoxy sulfate molecule such as increased tolerance to calcium ions (preventing precipitation) and reduced skin harshness compared to an alcohol sulfate. Examples of alcohol ethoxylate grades, their uses (including as sulfates), and INCI names is given in Table 3. Being colourless and ranging from liquids to low-melting point solids, they can be used in multiple formulations. The alcohols have chain lengths from C9 to C15 and are ethoxylated with various average EO numbers, enabling them to be used in a variety of products including body wash, cosmetics, hair care, and skin care. Alcohol sulfate and alcohol ethoxy sulfates
give excellent foaming and cleansing properties which are comparable to derivatives made from palm kernel and coconut oil, making them suitable for use in liquid soap, body wash, and shampoo formulations. A back-to-back comparison of the
˜80% Linear
foaming performance of a sulfate based on C12,13 alcohol compared to the oleo C12,14 analogue (aka sodium lauryl sulfate) is shown in Figure 11 with SLES being present as a common ingredient. The prototype liquid soap formulation shown in Table 4 was used. The two charts show that, within test
˜20% Branched at 2-Alkyl position
Figure 10: Schematic visualizing the linear and branched structures in Shell alcohol composition
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repeatability, the C12,13 alcohol sulfate is a good substitute for sodium lauryl sulfate, giving a similar foam formation rate and foam stability (foam height) in all tests: with deionised water, in the presence of hard water, and with an oily soil. This is because the C12,13 alcohol, with 80% linearity and an average carbon number of 12.6, is structurally similar to the fully linear lauryl C12,14 alcohol.
March 2024 PERSONAL CARE Na
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