MANUFACTURE
polymers are not allowed to hydrate sufficiently before taking a viscosity reading during development, they could cause products to become much thicker on a large scale. In these cases, the viscosity may need to be
reduced by adding extra water; consideration must be taken of the preservative system to ensure the efficacy is not compromised with the additional water. Other factors to consider include the fragrance,
to ensure it is not diluted down and causes the product to smell weaker than intended. If the product is a water-based batch, additional preservatives and fragrances would require solubilising before being added to the bulk. It is also important to consider the impact of
increased product viscosity. Some products may be acceptable slightly thicker, such as creams in jars, and the specification may be expanded to accommodate the scaled-up bulk. However, products that will be filled into a pump need the correct viscosity to ensure the dispensability throughout its shelf life is not affected and the product is fit for use. The most common issue encountered in
scale-up, however, is related to oil-in-water emulsions which are too thin compared to samples made during development. The primary reason for this is energy input. In development, bench-top homogenisers
allow a large volume of liquid to flow easily through the homogeniser head and, as a result, a substantial amount of energy can be applied to the emulsion. This will ensure the particle size
of the oil droplets is as small as possible and well dispersed throughout the external water phase, creating a stable emulsion with a high viscosity. Most large-scale mixing vessels, however, have a smaller homogeniser head relative to the volume of liquid that the vessel can hold. The action of the mixing blades draws the
liquid into the homogeniser head and allows the liquid to flow through, though this will be proportionally smaller than the bench- top equivalent. It is therefore important to consider the capabilities of the manufacturing equipment during the development stage, and make accommodations to manage any differences that have been identified. There is potential for less energy to be applied to the emulsion in large-scale production, and as a result the viscosity may not be as high. This can be mitigated by ensuring bench-top homogenisers are used at speeds that can be achieved during large-scale manufacture (this will be dependent on specific factory capabilities). This can help ensure the energy input during
development can be replicated in large-scale mixing vessels. Homogenisation times should also be kept to a minimum to help ensure the formulation is reproducible on plant. During development, ingredients that may
be required to increase the viscosity of the final product can be included in the INCI list in order to safeguard the formulation against issues during scale-up. Including pre-neutralised, liquid polymers such as polyacrylates or
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taurates during development allows these materials to be incorporated at up to 1% during scale-up without affecting the artwork on pack. These are also excellent ingredients
to utilise because they are cold-process materials: they can be incorporated at the end of the manufacturing process without needing to reheat the batch, and can be easily homogenised into the product with minimal energy input.
Cost optimisation With the rising cost of energy, it is advisable to consider how to create a cost-optimised product on plant when developing a formulation. The energy required to heat multiple-tonne mixing vessels to 70°C or above can be incredibly costly and will incur a higher production charge than cold process formulations. It is more cost and energy effective to
develop emulsions using a one-pot method where possible. This yields several benefits versus a traditional two-pot method. Firstly, using two mixing vessels to make one product on plant is an inefficient use of equipment and essentially halves the output of the factory, as otherwise two products would be made in parallel in the two mixers. Additionally, heating both vessels to 70°C
rather than just one will incur much higher energy costs and is far less environmentally friendly. Manufacturing facilities look to reduce energy usage whenever possible, and the one- pot method is an excellent way to achieve this.
www.personalcaremagazine.com
April 2024 PERSONAL CARE
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