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.
The first stage, effectively dispersing the Carbopol into a base liquid can be extremely challenging for a number of reasons; Carbopol is a very light, low density powder. Not only can this make controlled powder addition very difficult, it can cause dusting problems, which in turn leads to waste of an expensive raw material as well as increased cleaning requirements. When the powder is added to water, it tends to float, requiring vigorous agitation to wet it out. As soon as the powder comes into contact with the liquid it begins hydrating, and when powder remains floating on the top of the liquid or within the mix, agglomerates or fish-eyes (where dry powder remains encapsulated within a hydrated outer layer) will form. Long mixing times are required to complete dispersion/hydration and often a filtration stage is needed to remove agglomerates after mixing.
Although vigorous agitation is needed to incorporate the powder, this can lead to excessive aeration which can create a persistent foam which may require chemical additives to disperse. Entrained air can also cause problems as it is very difficult to remove and can result in clear gels appearing cloudy and problems where packaging is filled by volume rather than weight.
These problems come up time and again where conventional mixing equipment is being used for this process. High Shear mixers are much more suitable for this application and can easily overcome these issues.
A recent example of this was with an oral health care manufacturer, who significantly improved their product quality and process by switching from a conventional agitator to a Silverson high shear mixer. Using the high shear mixer in place of the agitator for dispersing Carbopol into their teeth whitening products, they have been able to reduce their mixing times while improving quality.
The company had been mixing in a 20 litre container using an agitator to try and disperse Carbopol. Unsurprisingly, they were struggling to incorporate the Carbopol properly and the inefficient agitator was causing agglomerates to form which were taking a very long time to disperse in a process that was labour intensive and time consuming.
Silverson Machines went to visit them and demonstrated an L5M-A laboratory mixer. The company saw an immediate improvement in their processing times and their dispersion of the Carbopol. With the high shear Laboratory mixer they no longer had to filter out and discard partially hydrated or undispersed Carbopol, reducing their raw material costs and improving the quality of their end product. As a result they purchased the laboratory mixer. As the business continued to grow, the company scaled-up and returned to purchase a production-scale High Shear Batch mixer to increase their batch size and keep up with production demands.
How is a high shear mixer able to do this? The difference to conventional mixing equipment is the rotor/stator workhead. The high speed rotation of the rotor blades creates a powerful suction which draws the liquid and powders down from the surface of the vessel and surrounding mixture into the workhead where they are rapidly mixed.
Centrifugal force drives the powders and liquid towards the periphery of the workhead, where they are subjected to intense high shear in the gap between the rotor and stator wall. The product is forced out of the stator and projected radially back into the body of the mix.
Fresh materials are simultaneously drawn into the workhead. In a short mixing cycle all the material passes many times through the workhead, progressively reducing the particle size and exposing an increasing surface area to the surrounding liquid, accelerating hydration. This results in an agglomerate-free mix so filtration stages and long mixing times can be eliminated.
For larger batches, Silverson have developed a range of powder/liquid mixing systems for high speed dispersion of difficult ingredients such as Carbopol. With Silverson powder/liquid mixers you feed the powder into the hopper and let the machine do the rest. The powder is rapidly incorporated into the liquid stream and passes into the precision engineered rotor/stator workhead, where the materials are intensely mixed before being returned to the vessel by the self-pumping mixer. The Carbopol is fully hydrated after a short recirculation period. The results are a uniform, agglomerate-free mix, maximised yield, minimised aeration and consistent product quality and repeatability.
If you'd like to find out more, please contact Silverson Machines.