The beauty and cost-saving benefits of inverse emulsions

For the longest time, w/o emulsions were reserved for use in sunscreens, waterproof makeup and nappy (barrier) creams. Yet over the years, emulsion technology has evolved widening the range of applications for emulsions to almost all personal care products. Jacques Strydom, technical manager for personal care and home care at AECI Specialty Chemicals explains the history behind the technology and how the application focus has changed.

I T’S IMPORTANT TO understand the main difference between water-in-oil (w/o) and oil-in-water (o/w) emulsions. Water and oil are not miscible with each other, so emulsifiers are needed to mix the two parts and create a stable end-product. In colloidal science, the ‘inside’ phase is called the dispersed phase while the ‘outside’ phase is referred to as the continuous phase. In a w/o emulsion, the water is the dispersed phase and the oil, the continuous phase. W/o offers a number of practical advantages, because the oil is on the “outside”. For example, the end-product feels oily to the touch – this is commonly experienced with sunscreens. The characteristic enables water resistance, which is why w/o is the preferred emulsion type for sunscreens, waterproof makeup and barrier creams. The lipid barrier also locks in moisture, so w/o emulsions are great for problematic skin, prone to psoriasis, eczema and dryness. This begs the question, why are the majority of personal care creams o/w, which is the opposite type of emulsion?

SELECTING W/O EMULSIFIERS AND EMOLLIENTS

In the past, w/o emulsions were perceived as sticky, greasy, heavy, hard to stabilise and expensive. However, scientific advances have addressed and counteracted these issues over time. It is now possible to easily produce w/o emulsions that are cost-effective, easy to stabilise, fast absorbing, feel light on skin (where required), and are non-tacky. These factors are addressed by two main components of the formulation, being the choice of emulsifier and the selection of emollients. AECI Specialty Chemicals has a solution for both of these ingredient types. Its easyto-use w/o emulsifier base is supplied in a viscous liquid format and is used at very low dosages between 1.8% and 3%.

In w/o emulsions, increasing the dispersed phase content increases the viscosity of the final emulsion. Thus, oil phases in the order of 10% to 15% yield thick creams, while oil phases in the range of 18% to 35% yield lower viscosity lotions. The other advantage of w/o is that the viscosity of the oil phase is proportional to the final emulsion viscosity, due to the oil phase being the continuous phase. This means that adding cosmetic waxes, butters and even petrolatum, will significantly alter the structure of the emulsion, allowing applications like beauty balms and body butters.

The choice of emollient is critical to the sensory experience of a final product. Selecting more volatile emollients with high spreading coefficients, such as silicones, squalanes and certain alkanes, achieves light emulsions that penetrate the skin easily. Similarly, when more occlusive emollients are used, like mineral oil and certain vegetable oils, heavier emulsions are created. A heavier emulsion performs better at preventing transepidermal water loss, effectively increasing moisturisation.

EQUALLY BENEFICIAL FOR HAIR CARE

Of course, the technology is not limited to skin care. Because these emulsions can be designed with such large quantities of oil, makes them perfect for certain hair care products such as oil moisturisers, masks, hair foods and serums. Imagine combining a blend of nourishing oils that are highly favoured by consumers, such as argan oil, coconut oil, Abyssinian oil and sapote oil, and saving costs in the process. The cost savings are made possible by the emulsifier, which allows for water to be included in the formulation without hampering the performance of the oils. Table 1 features an example of a formulation for a highly cost-effective tissue oil lotion. The formulation uses minimal ingredients and yet it yields a beautifully glossy, rich cream that radiantly moisturises the skin. •

AECI Specialty Chemicals – jacques.strydom@aeciworld.com or thureya.sarlie@aeciworld.com