Dispersants are critical ingredients found in most personal care products that contain pigments or other types of powders. They can have a profound impact on processing and formulation performance.
Dispersants are materials which improve the separation of particles in a suspension or colloid and reduce settling/agglomeration and can be surfactants or polymeric materials. Polymeric materials are generally preferred and offer improved color development, significant viscosity reduction, faster dispersion, less settling of dispersed particles, and higher particle loading.
Three stages of the particle dispersion process are wetting, dispersion (agglomerate/particle size reduction), and stabilization.
- A good dispersant can displace gases, liquids, and other contaminants from a pigment surface increasing the surface area available for wetting and reducing the need for mechanical energy.
Dispersion (particle size reduction)
- Mechanical action leading to agglomeration size reduction. A good dispersant will wet the new particle surface quickly preventing the agglomerate from reforming.
- A good dispersant will keep pigment particles separated by adsorbing onto the pigment particle and providing a barrier against particle re-agglomeration.
Dispersants function by charge (electrostatic) stabilization, steric (entropic) stabilization, and electrosteric stabilization (combination of both). Electrostatic stabilization occurs only in an aqueous media and is dependent on repelling forces to maintain particle separation. Steric stabilization occurs in aqueous and non-aqueous mediums and is dependent on anchoring groups on the polymeric dispersing agent to provide a strong interaction with the pigment surface. Electrosteric stabilization works by a combination of steric/electrostatic mechanisms and works well in aqueous systems.
- Reduction in viscosity and improved stability are good predictors of dispersion quality.
- For pigments, increased color development is a useful indicator of dispersion quality.
- Try combinations of dispersants that work by different mechanisms.
- Polymeric dispersants normally work better than surfactants.
- Many dispersants also have good metal chelating properties.
Recommended dispersants for water based suspensions
- E-Sperse PDD (Ethox)-claimed to be highly effective in aqueous or non-aqueous formulations.
- Easy-Sperse P20 (Monobutyl Ethyl Ester of Poly (methyl vinyl ether/maleic acid) Copolymer, Sodium salt and Polyvinylpyrrolidone (EU)-Ashland (EU))
- Ganex P 904 (Butylated Polyvinylpyrrolidone-Ashland)
- Acusol 460N (Dow Chemical (EU))
- Acusol 531 (Dow Chemical)
- Acusol 588 (Dow Chemical)
- Prayphos S5PP FG (Sodium Pentapolyphosphate-Prayon), also is a good chelant
- DSP5K (Polyitaconate-Itaconix), also is a good chelant
Recommended dispersants for oil based suspensions
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