Do synthetic oils oxidize?

Hello All,

After a lot of doubts I finally ordered several synthetic oils: Mineral Oil, Petrolatum and Hydrogenated Polyisobutene.

I have some experience with vegetable oils, but I don’t know whether synthetic oils are the same. Every time I search for synthetic oils online, to understand how to formulate with them, I either get chemo phobic articles (like 10 reasons to avoid mineral oil etc.) or articles about car engines.

Should I add vitamin E to the formula (let’s say a basic o/w moisturiser), or they don’t oxidize (I understand it sounds silly for professional chemists, but I really can’t find anything reasonable online)? Any other specifics related to synthetic oils?

Thank you in advance.

Comments

  • No, the oils you listed do not generally oxidize.  It has to do with the structure of the compounds.

    Vegetable oils typically contain molecules that have double bonds of carbon to carbon (C=C). These bonds are susceptible to oxidation which is one reaction that happens in rancidity.

    Vegetable oils also have Carbon Oxygen bonds (C-O-C) which can react with water to produce free radicals that can further react to break down compounds in the system.

    Mineral oil, Petrolatum and Hydrogenated Polyisobutene primarily contain single bonded Carbon-Carbon or Carbon-Hydrogen atoms.  C-C  and C-H.  These are generally not subject to oxidation.

    I should note that Mineral Oil and Petrolatum are not synthetic oils. No one synthesizes them in a lab. They are derived from crude oil in the same way that essential oils are derived from plant matter. There is no chemical reactions involved in isolating them from oil. 
  • edited September 26
    It doesn't sound silly at all. As a matter of fact, you post interesting questions.
    I also use synthetic oils, I have the idea that they hardly oxidize or don't oxidize at all, but I'm not totally sure. I use petrolatum quite often. And I love the fact that they're cheap in comparison with veggies.

    Lately I'm not as big a fan of tocopherol anymore, as (alpha)tocopherol paradoxically tends to be pro oxidative in even slightly higher doses. The suppliers of the tocopherol I buy never can tell which type of tocopherol they sell, alpha, gamma, delta, or a combination.
    Right now I've also got BHT and a mixture of rosemary extract+ascorbyl palmitate+gamma & delta tocopherol in sunflower oil and lecithins in stock (Phytrox LTR15-IP MB).
    A while ago I totally forgot about it containing lecithins and I use parabens nearly all the time. I hope the small quantity of lecithin didn't make the parabens totally inactive. 
    There's so much you have to keep in mind. Like a while ago I put allantoin together with an anionic emulsifier together in an acidic emulsion. Totally forgot about allantoin being amphoteric. :confused:
  • Thank you very much @Perry. I know that mineral oil is derived from crude oil, I was just not sure what term to use. So, my conclusion is that if I don't add any vegetable oils, Vitamin E is not required. 
  • @Doreen, I though amphoteric changes charge to anionic at a low pH? I used allantoin in a formula with Sepinov EMT which is anionic.. I guess I shouldn't have done it?

    Do you have any information about tocopherol optimal %? I read somewhere that it shouldn't be used at a concentration higher than 0.2% but can't find any legit source. 
  • edited September 26
    In the time that I was writing my reply, @Perry had already written the answer. :joy:

    Thanks Perry! I was also uncertain, now we know the answer! :+1:
  • Thank you @Doreen, I am excluding allantoin from all formulations contraining Sepinov EMT (and since it's my favorite polymer no more allantoin for me lol)
  • edited September 26
    If you don't have troubles with allantoin and the Sepinov EMT 10 together, maybe you don't need to exclude it. I used a higher dose of allantoin (1.5% together with betaine. Betaine (trimethylglycine) can make salicylic acid and allantoin more soluble in water). If you just use 0.5% allantoin (or less) maybe it's not a 'major interaction'. ;)

    I thought the optimal dose for (alpha)tocopherol, or a combination, is 0.05 - 0.1% and it shouldn't exceed 0.2%.
  • Thank you @Doreen. Yes, I used exatctly 0.5%, but I want to do it right. Also, I don't know what long-term effect it might have on the emulsion stability.

    Any rules for tocopheryl acetate? I noticed that it's used at a higher % in commercial products than tocopherol. 
  • You don't have to worry about pro oxidative activity with tocopheryl acetate (neither anti oxidative as far as I remember).
    Tocopheryl acetate is used as skin active and according to CIR/SCCS you can use higher doses. I'm still not sure how it really benefits the skin, some studies seem to contradict. I haven't been into the whole vitamine E matter for quite a while, so it's all from the top of my head. 
    Maybe the experts can chime in?
  • Frankly, I am just adding 0.2% of tocopherol and 0.5% of tocopheryl acetate, without a deep understanding of how they work, because I saw it in commercial products (worked out % looking at other ingredients such as carbomer and phenoxyethanol). It would be great if experts can shed some light on it. Lotioncrafter states you can use up to 5% of tocopheryl acetate, which doesn't sound right to me..
  • edited September 26
    In some product types, higher concentrations like 5% are seen as safe by FDA and even 36% (in cuticle softeners). It's a document from 2013, I don't know if and what has been changed in the mean time:

    http://www.cir-safety.org/sites/default/files/tocopherols.pdf

    Some people are even allergic to tocopherol:
    https://www.ncbi.nlm.nih.gov/pubmed/20487657
    (Luckily it is "an uncommon phenomenon")
  • You can conduct a Iodine test yourself to test for unsaturated carbon bonds.
    https://en.wikipedia.org/wiki/Iodine_value

    It's actually a simple test to conduct.
    Just be careful not to spill the Iodine. Place a tray underneath in case a spill were to happen.
  • edited September 27
    @Gunther
    I had a chart with info on several kinds of oils and noticed the 'iodine value', never given much thought about it, but now I understand what it means, thanks! :+1:

    Right now I have refined rosehip oil, on the label it also says 'stabilised', do you have any idea what is meant with that? I can only find information on stabilisation of crude oil, to be made safe for shipment on tankers. :neutral:
  • @Doreen think they took care of loose ends I mean the double bonds where they don't cleavage and it stays as it is for longer time. Once the double bonds are attacked, you have rancid smell and many other undesired properties. 
  • @Chemist77
    Ok, thanks! 
  • @Doreen, I like rosehip oil but the oldest product I made with it is only 3 months. Do you know if it's stable? What I mean is, say, grapeseed oil is utterly unstable and gets rancid in months but I can't find information about rosehip oil.
  • @ngarayeva001
    The label says it's 'stabilised' and I do suspect a treatment like Chemist 77 wrote. The oil is now a year old and although it's kept at 4C constantly, it doesn't smell rancid or off. I have opened an closed it numerous times. I don't find any BHT or tocopherol additions in the document that came with it.
    At work we have this handy nitrogen supply (g) for treating several preparations 'under modified atmosphere'. Wish I had it at home sometimes! :wink:
  • @ngarayeva001
    I have a chart here on oils and if I look at the composition, I think it's very sensitive to oxidation, maybe even more so than grapeseed oil.
    @Gunther pointed out the way they use iodine to determine the amount of unsaturation in fatty acids. The higher the number, the more double carbon bonds there are present in the oil.
    The iodine value of rosehip oil is very high (175-185), coconut oil for example is less than 10. Grapeseed oil is 125-142, according to this chart.
    I don't mind sharing it, but it's all in Dutch.
  • edited October 12
    I was looking for fatty acid profile for rosehip oil but didn't find anything comprehensive... @Doreen, is the chart you have list INCI names of oils, or just names of oils in Dutch? I know must of INCI names.
  • @ngarayeva001
    It's all in Dutch only, but if it's only rosehip seed oil you're looking for, I can give the details right here (it's from an Excel file). This is about rosehip in general, if you order the oil, I would ask a CoA from your supplier for exact data.

    As you can see, a high % of (poly)unsaturated fatty acids.

    Linolenic acid (omega 3): 30-40%
    Linoleic acid (omega 6):   40-50%
    Oleic acid (omega 9):       14-18%
    Palmitic acid:   2-5%
    Stearic acid:     1.5 - 3%

    Iodine value: 175-185
    Saponification value: .138
  • @Doreen, thank you very much for this!
  • @ngarayeva001
    You're welcome!
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