46 MANUFACTURE
Figure 2: Orean develops new products in-house, taking into consideration the scale-up process and how best to achieve efficiencies on plant
oil can vary in colour due to variations in the raw materials. These materials are derived from natural sources, so the ‘strength’ of the colour will vary according to where the crop was grown, soil conditions, weather conditions, time of year and so on. During scale-up, these materials will be added during a colour-match process to ensure the colour of the end product matches the colour of the sample made during development. Providing the inclusion level of the colourant is less than 1%, it can be included in the INCI list in any position; therefore, amending the amount required during scale-up should not incur a change to the product’s artwork.
The water-free trend All-oil batches have increased in popularity in recent years for several reasons, such as having no requirement for preservatives (and therefore preservative efficacy testing). However, they are more challenging for large-scale manufacturing equipment. Each piece of equipment that comes into
contact with the batch must be water-free to prevent contamination – this is achieved by flushing the vessels, pumps, valves, and pipework with a low-cost carrier oil. This is much harder than simply drying out a glass beaker during development! Similarly, cleaning equipment on plant is
significantly more difficult than in the lab. This could lead to issues in products using solely natural preservatives, as they are less efficacious than traditional synthetic preservatives. In these cases, factories utilise extra cleaning
measures to ensure the natural preservatives are sufficient to keep the product safe throughout its shelf life. This is an important consideration in terms of time, resources, and costs of producing this kind of batch on a large scale, and should be assessed during development when weighing up the preservative options available.
Achieving homogeneity in emulsions Emulsions made on a large scale are assessed
PERSONAL CARE April 2024
Figure 3: Large scale mixing vessels utilise contra-rotating blades to ensure homogeneity For robust formulations, including a
for homogeneity using various methods. Samples can be viewed under a microscope to ensure the particle size distribution matches the development samples, and can be centrifuged to observe whether the phases separate. Both these methods give a good indication
of the long-term stability of the bulk, so it is crucial that similar tests were carried out during development and can be cross-referenced during scale-up. Emulsions are also assessed using a tile test,
whereby a small sample of bulk is placed onto a black tile and spread down to leave an even coating. This can be scrutinised for signs of oil droplets that still require homogenisation. In cases where the water and oil phases
have been sufficiently homogenised but are still experiencing phase separation, an additional emulsifier may be required to bind the batch together. It is, therefore, important to ensure the correct emulsifier is chosen during the development process using the HLB method (hydrophilic-lipophilic balance).
water-phase thickener such as xanthan gum or cellulose is also useful. This will ensure the water is held in the emulsion and prevents the risk of water pooling on the surface when produced on a large scale.
Issues with viscosity During scale-up, the resulting product may have a greater viscosity compared to samples created during development. This occurs mainly for products that utilise pH-dependent thickeners, such as carbomer – when the pH is adjusted into the middle of the specification range, the viscosity may become too thick. In these instances, the pH can be reduced
to deactivate some of the thickener and reduce the viscosity. It is therefore essential to ensure that the amount of thickener used in development enables the viscosity to reach mid-specification, to allow for tolerances at either end of the range on scale-up. Similarly, if thickeners such as gums or
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