Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Depigmentation problem

  1. Sep 14, 2012 #1
    Hello All,

    First post here and ill give you guys a quick breakdown,

    I am from Canada currently working as a Paramedic, my knowledge on chemistry probably isn't as superb as some of your, thus the reason I am here for some help!

    Currently my girlfriend are I are trying to figure out how some hair extension companies do a process called "de-pigmentation" to remove the colour from the hair. they claim to use no harsh chemicals in the process because that causes harm to the fibres within the hair causing it to break.

    One of the major companies claims:

    "The hair undergoes a delicate process of de-pigmentation lasting 15 - 20 days.

    The black pigments are slowly removed from inside the hair, not from the outside. The typical method of lightening/bleaching hair using ammonium derivatives damages the cuticle layer, thus compromising the hair's texture and condition! Our de-pigmentation process does not damage the hair and permits the removal of the black pigment without altering the quality of the hair. The color molecules are actually removed rather than bleached."

    they say they do a process of "gentle osmosis", similar to the de-pigmentation of Cashmere

    I am curious if anyone can give me a hand and maybe even discover as to how they do this?
    I understand the basics of osmosis, but I don't understand how they can literally remove the melanin within the cuticle of the hair.

    i have been messaging some Cashmere processing companies, but this all seems to be one big super secret, but one company did reply with this information:

    "Depigmentation Process. The depigmentation process consisted of a mordanting step followed
    by a bleching step and was carried out at the following experimental conditions:
    Mordanting Rinsing Bleaching
    FeSO4°E7H2O: 3.7 g/l
    Na2S2O4: 1 g/l
    HCHO (35-40%): 3 g/l
    L.R.: 1:20-1:50
    pH(HCO2H): 3
    1h 85°C
    Warm water 20 min
    room temperature
    water 20 min
    Na4P2O7: 10 g/l
    EDTA: 2 g/l
    H2O2: 1-8 vol
    L.R.: 1:20-1:50
    pH: 9
    30 min 85°C
    Different concentrations of hydrogen peroxide in the bleaching bath were tested.
    Sample A (16.5 µm) was depigmented at a fibre liquor ratio of 1:20 using an Ahiba –Turbocolor
    100 Laboratory dyeing apparatus. Concentrations of 2-4 and 8 vol of hydrogen peroxide
    were used.
    Sample B (17.1 µm) was depigmented at a fibre liquor ratio of 1:50 in flasks placed in a
    thermostatically controlled shaking water bath (Grant OLS200). Concentrations of 1-2-3-4-5-
    6-7-8 vol of hydrogen peroxide were used."

    I know they use a very weak based hydrogen peroxide, but would that still not harm the hair?

    Thank you for any help!
  2. jcsd
  3. Sep 16, 2012 #2
    Re: Depigmentation

    It is rather difficult to reply to a post like this. There are a lot of pitfalls:
    -- Much of the specialist knowledge is (as you have already found) tied up with commercial secrets rather than available in the open literature
    -- Where does "spin" stop and "misleading" start in advertising a product?
    -- Possibility of connection with litigation by someone claiming that hair has been damaged.

    I will restrict an answer to some very basic considerations of general chemistry.

    (1) Rates of reaction: a) Effect of dilution is to slow down reaction. Depends on the "order" of a particular reaction. Rate is usually first order (directly in proportion to concentration); zero order (no concentration effect) or second order (half the concentration, quarter the rate) are reasonably common, other arrangements possible but rare. Dilution tends to treat all reactions equally, but you might get an advantage from it in particular cases.
    b) Effect of temperature is to slow down reactions. Usually the effect is larger for slower reactions. If you have an undesirable side reaction going on as a minor process alongside your main reaction as the major process, then operating at a lower temperature will slow down your main reaction, but it will probably have a larger effect on your side reaction. You might even be able to almost stop the side process, but you will have to be very patient with the main process.
    c) pH can be a very important factor in aqueous systems, and particularly in biological type systems. pH adjustment and buffering are often vitally necessary to obtain a good and safe result.

    (2) The advertising "spin". A term like "harsh chemicals" is doubly subjective -- "harsh" is a matter of degree, and a subjective judgement after that. And any material in the world has a chemical composition. How do we define when some material is, or ceases to be a "chemical"? Similarly any process that takes 15-20 days might or might not be described as "delicate". Would we consider painting a wall to be a "delicate" process? An oil-based paint dries in 3 stages: solvent evaporation over the first hour or two, continuing polymerization over 12 to 24 hours until the paint is "properly dry", and "curing" over the next month as the polymer reacts with atmospheric oxygen to make cross-links that give the paint film its eventual strength and hardness.

    The manufacturer is here emphasizing "inside" and "outside" as though they were the most important issues. But if you think about it, the melanin has to be removed from "inside" the hair, because that is where it is! Only street dust and oily secretions are on the "outside"! But there is something in the advertising claim here, because some of the cheaper treatments probably bleach the pigment without really effectively removing it.

    Their claim not to damage the hair structure seems to be a very solid one that they should stand by. The claim that melanin is "removed rather than bleached" sounds rather implausible when they are using peroxide in the last step. At best it would seem that the wording should be "removed as well as bleached" Perhaps "bleach" is also a pejorative term in this sort of context.

    (3) Comments on the chemistry required.

    Melanin (check wikipedia) is a black polymer that forms within skin or hair cells. It would not normally pass through a cell wall barrier.

    As with most dyes it can be transformed to a colourless material in a chemical reaction that is either an oxidation or a reduction. Normally oxidative decolouration (bleaching) is more effective than reductive because oxidation can break up the connections between carbon atoms in the main backbone of a molecule, and alter molecules enough that there is no way that the dye can be regenerated; reductive decolouration, on the other hand, is usually easily reversible. It usually leaves the main backbone of the molecular structure intact.

    To remove the dye, in its altered form, requires getting it somehow through the cell wall. There are issues here which I, as an expert non-biochemist, am not familiar with. I think that a polymer molecule would need to be broken down into much smaller chunks, and that it might need to "hitch a lift" as part of a metal co-ordination complex.

    (4) The formulation presented:
    FeSO4 -- looks like a source of Fe2+ for complexation to melanin
    Na2SO4 -- no idea. Possibly something to do with maintenance of ionic strength and charge balance
    HCHO -- is a mild reducing agent and a mild protein denaturant. It is probably present to ensure that iron stays as iron(II) rather than getting oxidized to iron(III). Any use in conditions where it could act as a protein denaturant would throw considerable doubt on the claim that it does not damage the structure of hair.
    HCO2H -- formic acid is an interesting choice for a pH regulator and buffer. The HCHO/HCO2H
    system would also act as a redox buffer.
    then there is an extensive rinse in water
    In the final stage
    Na4P2O7 -- ionic strength booster and pH buffer
    EDTA -- metal complexing agent, probably intended to substitute the ligand from the previous complex
    H2O2 -- a standard oxidative bleach, in a moderate concentration.
    If they claim that it would not harm the hair (and remember that this is a cashmere processing formulation, not a treatment for human hair), they would have to stand by that claim in the face of evidence to the contrary. I believe (with no particular experience or authority) that it would harm the hair or fibre, but perhaps the concentration and pH is such as to minimize any such damage.
  4. Sep 17, 2012 #3


    User Avatar

    Staff: Mentor

    Re: Depigmentation

    Sodium sulfate, or dithionite?

    Actually that's the first time I saw dithionite so I checked its properties in wikipedia. Article there says "used (...) in some industrial dyeing processes, where an otherwise water-insoluble dye can be reduced into a water-soluble alkali metal salt." It also says dithionite reacts with HCHO producing rongalite - again, according to wikipedia "The compound has, in recent years, been used increasingly in commercial cosmetic hair dye colour removers despite the generation of formaldehyde, a known human carcinogen."

    So perhaps it is dithionite that is the active ingredient here?
  5. Sep 17, 2012 #4
    Re: Depigmentation

    Yes it certainly would be; I misread the OP -- saw sodium sulfate, which I was half expecting. Did not notice the S2O4 instead of SO4. Dithionite is a moderately strong reducing agent that might well help solubilize any depolymerized melanin. That helps explain a lot.

    My concern would be that the brew in both of the main stages of this process looks fairly ferocious. I suppose that the formulators have designed it to be as gentle as possible, but the measures required to remove the pigmentation are necessarily fairly strong for the brew to do the job. I will provisionally accept their subjective judgement that the process is non-harsh and non-damaging to materials that it is not supposed to damage, but retain just a touch of scepticism. I have no specific expertise nor experience in this area.
  6. Sep 18, 2012 #5
    Re: Depigmentation

    i would like to thank both of you for the great replies. i guess even i fell for there marketing tactics and should probably read through the lines a bit more aha.

    well i guess the only thing i can really do is try out the solutions that i received from one company, do you think this is something safe to do at home in an well ventilated area or am i just dreaming here?
  7. Jan 26, 2014 #6
    I am a hair stylist who specializes in extensions, and my interest in customizing color for clients has also led me to the same conundrum. While I do suspect this jargon is absolutely spin meant to disguise the actual process, I believe the answer to safely depigmenting hair lies within the textile industry. Specifically the treatment of keratin based protein fibers, such as wool. I found this link when I did my last search. It's a section in a textile book, scroll down to the wool section. They discuss various bleaching methods and the essential rules behind them. I would imagine that any of these methods would require a bleach bath and proper ventilation in a safe environment. Generally, a weak solution at a slower rate, perhaps more than once, will result in more control over the health of the hair and a gentler process. Heat while bleaching is the fastest and lightest results, but does blow out the cuticle with expansion and can lead to weakened fibers.

    http://books.google.com/books?id=e9...#v=onepage&q=bleaching protein fibers&f=false
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook