SUSPENSION AIDS
8 7 6 5 4 3 2 1 0
0 0.05 0.1 0.15
% Commercial MFC by formulation weight
Temperature (˚C) 25
45 60
Yield (Pa) 1.6
1.7 1.5
Figure 7: Yield values vs. concentration of commercial MFC in a generic surfactant- thickened bodywash with a pour viscosity of 3500 cP (20 sec–1
) (12% active surfactants,
2% NaCl). [Yield values obtained using a Brookfield DV-III Ultra (RV or LV) with EZ-yield software, 0.05 rpm, #71 spindle].
that is now available for household and personal care applications is a polymer blend of MFC, xanthan gum, and cellulose gum (sodium carboxymethylcellulose or CMC). The xanthan gum and CMC are co-processing aids used to enable the recovery of MFC as a powder. The commercial names for these products are AxCel CG-PX cellulose for personal care applications and Cellulon PX cellulose for household and general industrial applications. These commercially-available forms of
MFC retain all the important features of pure MFC except that these powdered products require incorporation into fresh water prior to use. The dispersion steps typical of most rheology modifiers are needed with the powdered MFC products since lumping can occur. Once good dispersion in water has been achieved, the MFC needs to be ‘activated’ or highly dispersed to be fully functional. This activation is accomplished by using a high shear device with a very fine rotor- stator assembly (eg Ross Mixer Quad-Slot or MegaShear mixing head). Several passes may be required and can be monitored with a simple microscope with 12-16x magnification. After MFC activation has taken place, the solution (up to 1% commercial MFC product) can be used
Figure 8: Picture of generic bodywash (12% active surfactants) with 0.08% commercial MFC and suspended exfoliant beads. (The yield value was about 1.6 Pa).
in the final formulation, typically as the first ingredient added. Activated MFC can be used in a wide
variety of formulations. One of its most valuable properties is its ability to provide good suspension at very low use levels. An advantage of these low use levels is the fact that MFC will not contribute much viscosity at the shear rates typical of pouring so the ‘pour’ viscosity of the product looks very similar to the original product except in its ability to suspend particles. MFC can even be used to make clear formulations when used at low use levels of 0.05%-0.15%. The ability to make these high clarity formulations appears to be not only dependent on the MFC level, but also on the index of refraction of the formulation. This dependency on index of refraction is due to the fact that MFC is insoluble. However, for most surfactant applications, the index of refraction is relatively high (e.g. 1.35-1.42) and the MFC use levels low, so and the fibres become transparent except for perhaps a slight hazing. Another useful aspect of MFC is its
ability to suspend in the presence of high micelle development such as in surfactant- thickened bodywashes, shampoos, and liquid hand soaps. This is an area that is currently dominated by synthetic polymers. However, aside from the non-biodegradability of these synthetic
0.2
polymers, their use levels are generally quite high (typically 5%-7% as a 30% emulsion) and therefore the cost-in-use is a problem for many formulators. With MFC, however, the use level can be much lower (typically 0.05%-0.1% of the commercial MFC product). In these formulations, the base viscosity is obtained by the surfactant micelle development (with salt and/or a synergist surfactant) while the MFC is used at low levels to provide suspension. MFC contributes very little to the perceived viscosity of these formulations and in fact, can even be used to create suspending systems that are water-thin, such as in foaming hand soap formulations. Clarity can also be quite good in these surfactant-thickened formulations but will depend on both the MFC use level and on the index of refraction of the formulation.
Conclusion As consumer trends push the personal and home care markets towards more environmentally friendly formulations and practices, these industries will need alternative, ‘green’ technology to provide reliable suspension. Microfibrous cellulose is a powerful option for both performance and sustainability. MFC is naturally-derived, biodegradable, and made from the sustainable process of microbial fermentation. MFC offers excellent suspensional properties, low cost-in-use, and due to its insolubility, unmatched limits of compatibility. The development of MFC is proof that naturally-derived products cannot only replace some of the synthetic polymers used today but, in some cases, outperform them.
PC
Figure 9: Picture of low viscosity, foaming hand soap made with 0.125% commercial MFC.
March 2012 PERSONAL CARE 71
Yield stress (Pa)
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