Characterization of cosmetic cream and body lotion containing xanthan gum, hydroxypropyl methylcellulose (HPMC) and carbopol during storage / Siti Nor Diana Khairuddin

Cosmetic creams and lotions intended for topical application are generally complex mixtures of oil and aqueous components with varied rheological, texture and stability properties depending on their ingredients. The objective of this project is to investigate the effects of concentration and types of thickener: natural (i.e. xanthan gum), semi-synthetic (i.e. hydroxypropyl methylcellulose), and synthetic hydrophilic polymers (i.e. Carbopol® 934, Carbopol® 940; and Ultrez® 21) on rheology, stability and texture profiles of emulsions. For this purpose, 20 oil-in-water (o/w) (Fl-F20) emulsions were prepared: Fl-Fl2 (synthetic); Fl3-Fl6 (semi-synthetic) & Fl 7-F20 (natural polysaccharide). Rheological parameters such as viscosity and mechanical response were determined through shear stress analysis and dynamic oscillatory test, respectively. Meanwhile, textural characterization was performed through back extrusion and spreadability tests in which parameters such as firmness, work of shear, cohesiveness and consistency were determined. Furthermore, droplet size distributions of the emulsions were monitored for over a 7-day period. Stability of the emulsions was investigated using accelerated method (20° C; 31 OOrpm) in order to predict the emulsions stability for one year. Based on the results, 20- emulsions (Fl-F20) exhibited shear thinning (pseudoplastic) behaviour. It was found that emulsions containing synthetic thickeners (F-Fl2) exhibited a higher value of viscosity than those of the natural polysaccharide (Fl 7-F20). Furthermore, at low shear rate of 0.1 rpm, distinct behaviour was observed between the synthetic and the naturally derived thickeners emulsions in which yield stress is observed in Carbopol® containing emulsions and absent in xanthan gum containing emulsion. It was also observed that almost all emulsions (all except F-5) exhibited elastic behaviour; G'>G". In stability study, it was found that only one emulsion demonstrated phase separation and failed the accelerated stability study ( emulsion F3- contain 0.3% w/v Carbopol® 934 formulated using oliwax). Minor behaviour differences were noted between 0.3% and 0.5% w/v of thickener used. In conclusion, the use of different hydrophilic texturizing agents of different concentrations not only affects the rheological and textural properties of o/w emulsions but it also affects the emulsion droplet size. A prominent characteristic of stable emulsions was evidenced in emulsion containing Carbopol® 934; where at low concentration of 30%, solid­ like consistency cream was noted as compared to other synthetic and naturally derived thickeners. Natural polysaccharides on the other hand showed a distinct shear thinning behaviour as compared to those of semi-synthetic and synthetic agents in rheological and textural properties and produce an emulsion of medium sized droplets. However no stable correlation between concentrations with the emulsion properties was found.