Microfibrillated cellulose (MFC) is an exciting new technology. The capability of MFC in coatings can be exemplified by its ability to work both as a substitute for HASE (Hydrophobically modified Alkali Swellable Emulsions) technology but also as a synergetic material. For decades, producers of fluid materials have used HASE as the fundamental technology to control flow. Will the new kid on the block, MFC, challenge HASE's position? If so, in what areas? Or is it possible that these two could work together?
Similarities and differences
The first and most striking difference between the two additives is their physical and chemical nature. HASE, a water-soluble polymer, is a synthetically derived product with various product types based on its molecular composition (weight and chain length). It is, as the name suggests, swellable only in alkali environments. This can be seen as both an opportunity and a limitation.
MFC is an insoluble fiber network not dependent on the same alkali environments to work. Its effect on rheology and thickening varies across the pH ranges but is stable from pH 1-13 (source: Borregaards Exilva product).
Microfibrillated cellulose (Borregaard's Exilva MFC) seen in microscopy. The insoluble fibrils can be seen in the picture.
The degree of shear thinning of MFC and HASE are also different. This difference in rheological properties is relevant for time delay in visocity recovery (thixotropy). In certain applications, it might be a good option to combine HASE and MFC to achieve a desirable rheology profile (for example, good leveling vs. anti-sag performance in coatings). MFC can also boost the effect on open-time control, anti-cracking behaviours and emulsion stability, providing a good synergetic effect with the HASE’s rheology control.
HASE is a so-called associative polymer. When the hydrophobic parts of HASE associate with each other and the latex droplets in the final formulation, a thickening effect is achieved. In general terms, HASE works well in systems where a limited amount of water is allowed. MFC, on the other hand, will stabilize a larger amount of water. In systems where the room for introduction of water is larger, MFC can be a very interesting alternative to the synthetic acrylic technology. Thus, MFC can prevent phase separation and provide good syneresis resistance.
Addition: pre-addition and post-addition
HASE and MFC are different when it comes to the addition to the manufacturing process. HASE is a technology which is famous for its ability to fine tune the properties of, for instance coatings, at the end of the manufacturing process. This is due to its low viscosity and how alkali environments activates its thickening properties. MFC can also be post-added, but is more vulnerable to the need for high shear to be present (see our blog post on the subject). A manufacturer of coatings should rather add MFC in the grinding phase to ensure the necessary shear.
Application example and sustainability
HASE is currently popular in the field of coatings. This is an application field where both the post-addition and pre-addition (during grinding phase) are highly applicable. In tests, MFC has shown interesting properties on anti-sag, water sensitivity, shear thinning capabilities and stability at rest. In paint systems with high particle loadings, MFC may actually give better performance on stability than HASE. This is due to its physical network which keeps the pigments well dispersed. In addition, MFC has shown neutral behaviour on scrub resistance, while HASE can give somewhat negative impact on this parameter.
MFC can provide a fairly good alternative to the HASE technology. In hydrophilic systems with sufficient room for water, it can present you with new and exciting possibilities. Consider also it’s no-VOC, and it can be worthwhile to test the next time you screen for something to change your formulations.