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Belinda Carli from IPCS explains the differences between the many types of micro-capsules and how to pick the right material for each application. She points out that micro-capsules are often used for visual and other benefits and shows why the different types of filling for micro-capsules are an important issue.

Micro-capsules: For visual and other benefits

Micro-capsules are increasingly used in personal care formulations for visual and other benefits. With a growing number of variants now available for formulators to choose from, it becomes more difficult to choose the right material for each application need, and to assess the differences between the many types now available. What are the benefits of using micro-capsules? This is not the only question that comes up in this context. It is also important to know what types are available, in what way they differ, what needs to be known for formulating and processing, what to look for when selecting micro-capsules and what are some examples of the many varieties now available.

Formulating with micro-capsules

Micro-capsules are generally designed to be used at an input of 0.5–5.0%. Some micro-capsules with selected actives, UV filters or colour may be recommended at higher inputs than this. This is why it is always a good idea to refer to supplier information sheets for specific internal content details and external shell/matrix details. It is also extremely important to check for the recommended use range and any pH compatibility requirements in the finished product. It is also necessary to check the temperature at which they must be added, as some internal components such as waxes, or the external matrix, may be susceptible to breakages at elevated temperatures (above 50°C). This may also cause false ‘positives’ to occur during accelerated stability testing where elevated temperature conditions are used. In addition, all types of micro-capsules need to be stabilised well. They are of significant size and will have considerable weight compared to the rest of the emulsion or gel formula, so a suitable polymer will have to help to hold the micro-capsule in place throughout its shelf life. Suppliers will inform about the gums or polymers they have and usage rates to ensure appropriate suspension depending on the size and input of micro-capsules you intend to use. The more micro-capsules need to be suspended, and the larger they are, generally the more gum or polymer is required to hold them stable throughout a product’s shelf life.

Filling of micro-capsules: Another important issue

Only gravity feed or piston fillers are recommended while centrifugal and gear pumps must be avoided. Wide pipes and filling nozzles should be used, ideally 12.5 mm diameter or larger. This means that the formulation needs to accommodate these requirements. Micro-capsules will generally start to soften after 24–48 hours, so filling should be done within the first 24 hours or at worst, 48 hours from production, otherwise excessive breaks may occur. Finally, micro-capsules with a small diameter (less than 100 microns) and thick walls are the most robust and resilient to shear during manufacture and filling. If you are using large micro-capsules, beware: the larger the micro-capsule, the more fragile they generally become.

Do certain ingredients need to be avoided?

If certain ingredients need to be avoided, either internally or in the shell/matrix, then this will limit the choices available. The full INCI names have to be checked with the supplier before ordering samples to avoid issues with labelling later if certain ingredients have to be avoided as part of a certain ingredient philosophy.

Do you need a customised option?

Most suppliers of micro-capsules can provide customised options to suit specific needs including internal contents, external shell/matrix and colour; but they will have large minimum order quantity requirements (typically around 25 kg). It is important to calculate out inputs of the micro-capsules in comparison to the active content needed. In addition, an efficacious quantity has to be used to obtain the desired effect in the end. It is important to make further checks as necessary to ensure aspects such as compatible pH, temperature, continuous phase as well as manufacturing method.

AUTHOR:

Belinda Carli, Director Institute of Personal Care Science (IPCS)

www.personalcarescience.com.au

belinda@personalcarescience.com.au

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