Many reasons can lead to unstable formulations when you first start testing a new formulation or a new ingredient. Some are due to non-optimized use of ingredients such as stabilizers and others are due to formulation processing or incompatibilities. Sounds familiar? We might have good news for you.
The first two problems can be solved by optimizing test conditions and concentrations to overcome instabilities. On the contrary, the problem with incompatibilities means that the construction of the formulation should be completely revised.
In this blog post, I will walk you through some points that show why the use of cellulose fibrils as stabilizers can help with formulation stability.
Why the new technology of cellulose fibrils can give you good stabilization options
High yield stress is important when we refer to stabilization. The yield stress of the material defines the point where a material breaks down under stress. High yield stress will for example maintain particles suspended in the formulation no matter how bumpy the transportation is. It is therefore recommended to use a stabilizer that has a high yield stress and good compatibility with formulation ingredients.
Cellulose fibrils have a very high yield stress and extremely high viscosity at rest as compared to other materials. In addition, due to the physical and three dimensional network, the fibrils are very little affected by the formulation chemistry and therefore, if used in water or polar solvent based media, the chances are very little that incompatibilities occur.
These are the two major reasons why cellulose fibrils is a good option for stabilizing your formulation.
What can cellulose fibrils stabilize
Cellulose fibrils can in general stabilize most materials that can be physically held in their position within the formulation, entrapped within the fibril network as depicted in figure 1.
Cellulose fibrils have shown to stabilize the following:
- oil droplets in an emulsion
- particles or pigments in a water based or polar solvent based formulation as well as in emulsions
Figure 1 above depicts how cellulose fibrils perform as stabilizers in the case of an emulsion. The well dispersed cellulose fibrils build a strong physical three dimensional entangled network in the emulsion. This holds these oil droplets physically in place avoiding destabilization of the emulsion.
In one of our earlier blog posts, we have demonstrated that for 10 similar emulsions with varying amount of cellulose fibril content, the emulsion stability is not the same. It was observed that:
- Appropriate amount of cellulose fibrils are needed to obtain a stable emulsion over time. Otherwise, phase separation can be observed.
- The degree of phase separation is higher when the concentration of fibrils is lower and decreases when the concentration of fibrils increases.
How to know when to utilize cellulose fibrils alone and when not to
The cellulose fibrils technology has one main important rule: to obtain the desired stabilizing properties without the need for a co-stabilizer, the fibril network needs to be dense enough and strong enough. This can be controlled both with the concentration of cellulose fibrils used as described above as well as with the composition of the surrounding matrix. The method of incorporation of the fibrils is also very important. For example, you need to avoid foam formation during the incorporation step.
If the formulation remains unstable after optimizing the incorporation of cellulose fibrils into your specific matrix, it is then recommended to test a higher concentration of cellulose fibrils
If you would like to keep the concentration of cellulose fibrils at the low level already defined, use an emulsifier or a co-stabilizer. At this lower concentrations, if cellulose fibrils do not give the formulation full stability, they will positively impact and enhance the formulation stability.
How can I use this information?
As a conclusion, cellulose fibrils can be a good solution when encountering formulation instabilities. This material is compatible with many different chemistries that are water or polar solvent based and has a very high yield stress.
It is however important to understand that even though cellulose fibrils are good stabilizers, they are not emulsifiers. The stabilizing properties can also be different from one formulation to another and will depend on the concentration used as well as on the type of ingredients present in the formulation.
It is therefore recommended to optimize the concentration depending on the formulation you are making. When using very low concentrations of cellulose fibrils, it might be important to also use an emulsifier or a co-stabilizer depending on what properties, visual and viscosity your formulation should have.
A small advice at the end, since cellulose fibrils can also modify the rheology profile of a system and make a formulation shear thinning, it is worthwhile checking the spraying and non-dripping properties of the thick formulation.
Rebecca Blell first started working with microfibrillated cellulose MFC in 2009. During her studies, she was part of the SustainComp project and her task was to understand and incorporate MFC into thin layers for improved film properties. As a research scientist at Borregaard today, she focuses on the Exilva product and its performance in personal care and home care applications. Rebecca has a PhD in physical chemistry from the University of Strasbourg, France, and experience from international locations.
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