Improving Benzoyl Peroxide stability in emulsions - TODO and NOT DOs

ZinkZink Member
edited March 12 in Formulating
Benzoyl Peroxide is notoriously unstable being a potent oxidizer. I remember testing a dozen emulsifiers to find something it didn't tear apart, synthetics like Sepiplus 400 did well, then getting to a 1 year shelf-life with less than 10% BP degradation can be a challenge. 

What to avoid
Ingredients that can be oxidized, like water soluble antioxidants
Amine groups (don't use TEA, use Sodium Hydroxide instead to adjust pH)

What to try
More synthetics (typically less prone to oxidation, e.g. squalane vs squalene)
Adding more solvents like ethanol or DMI
Encapsulated Benzoyl Peroxide (at a cost)
Increasing viscosity might help?
Air and UV proof packaging might help?

Are there any ingredients or other tricks that could protect free Benzoyl Peroxide from degradation?

Comments

  • I don't have any knowledge in this area but the popular topical for acne which is a mix of adapelene + benzoyl peroxide (trade: tactupump, epiduo) has the following formula:

    acrylamide/sodium acryloyldimethyltaurate copolymer, docusate sodium, disodium edta, glycerin, isohexadecane, poloxamer 124, polysorbate 80, propylene glycol, sorbitan oleate, and purified water.

    Maybe some of those ingredients could give you some clues as to what is helpful in a benzoyl peroxide formulation?
  • Bill_TogeBill_Toge Member, Professional Chemist
    try etidronic acid or one of its salts - it's a chelator that also suppresses radical formation, and is used to stabilise hydrogen peroxide solutions
    UK based formulation chemist. Strongest subjects: hair styling, hair bleaches, hair dyes (oxidative and non-oxidative) I know some stuff about: EU regulations, emulsions (O/W and W/O), toothpaste, mouthwash, shampoos, other toiletries
  • ZinkZink Member
    Thanks Bill, very good thinking. Have you tried it or is it a hypothesis? Regardless seems worth a shot.
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