Ole Martin Kristiansen | June 5, 2018
Are you looking for a new additive for controlling rheology? In this article if will give you an explanation of the typical and well known rheology additive, and the Exilva Microfibrillated cellulose.
Your toolbox of rheology modifiers is growing
There are currently a high number of alternatives to provide you with a solution, which can be grouped accordingly:
- Soluble polymers
- HEUR
- HASE
- ASE
- Cellulose Ethers
- Insoluble additives
- Clays
- Fumed Silica
- Cellulose Fibrils, like Exilva microfibrillated Cellulose
The first alternatives, soluble polymers, are the most common technology today. There are mainly three ways of a soluble polymer to thicken: hydrodynamic volume exclusion, by associative thickening and particle-particle interactions.
Hydrodynamic volume exclusion simply means that the polymer chains occupy the space in the formulation which the other ingredients can’t take, reducing the flowability of the formulation. ASE polymers swell and uncoil in alkali conditions since functional groups on the polymer chains are charged which thickens the formulation. HASE polymers thicken by associative thickening which means that the hydrophobic parts of the polymer tend to interact with each other in hydrophilic environment since that lowers the overall free energy in the system. The third mechanisms, particle-particle interactions refer to dispersing effect. The polymer chains can adsorb on the solid particle creating repulsion between them and thus stabilizing the formulation.
The insoluble additives thicken the formulation by forming a network which expands throughout the formulation and stabilizes the other ingredients within that network. Clays and fumed silica interact with surrounding solvent (water) when wetted and form the network. Cellulose fibrils, like Exilva microfibrillated cellulose, have, in addition, physical linkages in the network since the long fibrils can entangle with each other, offering extra strength for the network.
So many alternatives! Which one to choose when robustness is needed?
As mentioned above, the thickening mechanisms for the different rheology additives differ drastically. For the polymers, the mechanism is often a mixture of volume exclusion, associative thickening and particle-particle interaction. The downside of these thickening mechanism is that they are not so robust since they are dependent on the physico-chemical environment. To achieve the increased viscosity by volume exclusion, the pH needs to be alkaline. Similarly, a high amount of surfactants disturbs the associative thickening mechanisms, leading to lower viscosity. In addition, salts can disturb the adsorption of the polymers on the solid particles and thus interfere with the particle-particle interaction mechanism.
Insoluble additives instead form a physical network throughout the formulation and stabilize in that way. This is generally a robust way to stabilize a formulation. However, the strength of this network varies from additive to additive and Exilva microfibrillated cellulose has some advantages over the clays and fumed silica. Clays and fumed silica form the network based on the solvent – particle interactions (for example, the silanol groups on fumed silica).
This means that the interactions are vulnerable for the changes in the chemical environment. Instead, Exilva microfibrillated cellulose form partly the network through their physical form, since the slender, long fibrils which can entangle with each other. This makes the network more stable against changes in pH, salinity or temperature. Insoluble rheology additives have some other advantages over the soluble polymers. For example, viscosity recovery after shear is quicker for the solid network. In addition, polymer chains might break down at very high shear conditions, whereas clays, fumed silica and cellulose fibrils, like Exilva MFC, withstand high shear conditions extremely well.
Do not miss out on the chance to order your free sample of Exilva MFC today, and start formulating.
