Carbopol®* is a water soluble vinyl polymer, used as an emulsifying, stabilising, suspending, thickening and gelling agent in many industries. Carbopol® is available in several different grades, which are widely used in manufacture of cosmetics and toiletries, including gels, creams and lotions, detergents, and air fresheners. The gelling effect is activated in two stages, firstly the dispersion and hydration of the Carbopol®, and secondly “neutralising” the solution by the addition of chemicals which increase the pH. Neutralising agents include triethanolamine (TEA), sodium hydroxide and potassium hydroxide.
Manufacturing methods vary according to the type of product, but can generally one of two methods would be used:
The Carbopol® is added to water (the aqueous phase) and mixed until a lump-free dispersion is obtained. Other aqueous phase ingredients e.g. active ingredients, fragrance, colour etc. would then be added. If the product is an emulsion this would then be combined with the oil phase. Finally the neutralising agent would be added, activating the gelling effect. Typically a slow speed stirrer/scraper would be used for this stage.
The Carbopol® is premixed with the oil phase liquid. This reduces the tendency of the polymer to agglomerate. Remaining oil phase ingredients are then added. The aqueous phase is prepared separately; in some cases the neutralizing agent is added to the aqueous phase, alternatively it is added to the product as the two phases are combined, forming the emulsion and activating the gelling effect.
*Registered trademark of Noveon, Inc.
These problems can be overcome using a Silverson high shear mixer to disperse the Carbopol® and other ingredients, and for emulsifying oil and aqueous liquid phases.
Dispersion is completed in a fraction of the time taken by conventional means, avoiding the risk of overshearing the polymer. Operation is described below.
Silverson mixers can be used for the neutralisation stage, depending on percentage and grade of carbomer. For high viscosity products, a low shear stirrer/scraper would be used.
The vessel is charged with appropriate base fluid.The mixer is started, and the solid/powdered ingredients are added. The powerful suction created by the high speed rotation of the rotor draws liquid and solids into the workhead where they are rapidly mixed.
The solids are de-agglomerated in the precision machined workhead before being forced out through the stator and circulated back into the mix. Simultaneously fresh material is drawn into the workhead.
Once the powdered ingredients have been fully dispersed in the "continuous" liquid phase, the "dispersed" phase is added. The high shear mixing action of the workhead rapidly forms a uniform and stable emulsion before the viscosity increase is activated.
The batch size, the grade and percentage of Carbopol®, and the product viscosity (dependant on pH of solution before neutralisation) dictate which Silverson mixer is most suitable for individual process requirements:
High Shear Batch Mixers
High Shear In-Line mixers.
High Shear Bottom Entry Mixers