Tea tree oil can be solubilised in water using a variety of surfactants. In our laboratories we found it necessary to use four parts of polysorbate 20 to one part of tea tree oil to produce a clear solution on subsequent dilution with water. This is in contrast to about one to one and a half parts of the surfactant polyoxyl 35 castor oil. The method of preparation is of vital importance. The method can be summarised as follows:
1. The tea tree oil is first mixed with the surfactant and allowed to stand for several minutes.
2. Add small aliquots of water gradually with constant stirring. This results in a thick gel due to hydration.
3. Further gradual additions of water result in a lowering of the viscosity and a clear liquid.
Should the initial addition of water be done too quickly or the tea tree oil not adequately mixed, then at best an opalescent solution results.
The addition of polyhydroxy alcohols such as glycerol or propylene glycol can effect solubilisation without having to go through the initial gelling phase. This can be achieved by triturating the glycerol with the mixture of the surfactant and tea tree oil, prior to the addition of water. The addition of alcohol to the formulation greatly enhances solubilisation producing a clear solution. Typically a range of 5 to 10% alcohol is employed.
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