Lip balm stick cracking. - Cosmetic Science Talk

Lip balm stick cracking.

Hi all,

I seem to have some sort of conundrum. I'm trying to make a stick lip balm molded into a bullet and in a dial up case. I'm having problems with the bullets cracking on the suface, making them weak.

At first I thought the culprit was shea butter, which is known for its propensity to crystallize. I figured it was providing seeds, causing the rest of the formula to follow, and the cracks were actually boundaries between large crystals. Now I'm not convinced that this is the case anymore, because even without shea butter this persists. I think it's a mild form of brittle failure and my wax ratio is off.

Here's the original formula.

Wax Phase
Candelilla wax - 8%
Carnauba wax - 2%
Microcrystalline wax - 5%
Ozokerite wax - 5%
Cocoa butter - 5%

Emollient Phase
Rice Bran Oil - 44%
Fractionated Coconut Oil - 5%
C12-15 Alkyl Benzoate - 5%
Shea Butter - 9%
Sesame Oil - 9%

Flavor Phase
Sugar Baby (sweetener) - 1%
Peppermint EO - 0.3%

Preservation Phase
Phenonip - 1%
Tocopheryl Acetate - 0.7%

I have tried adding Nylon 12 (hoping a solid would interrupt crystal formation), I have tried removing the shea butter, I have tried removing the shea butter and adding polyamide-3 at 9%, versagel ME750 at 9%, and polyamide-3 and Versagel ME750 at 4.5% each, and all of those still cracked.

Interestingly, the lipstick formula this is based on does not crack at all. It doesn't contain Shea butter either, which is why I got suspicious of it.

Any ideas what I may be doing wrong?

Thank you for any help!

Comments

  • personally, I'd be tempted to remove the cocoa butter - that's notorious for crystallising in the cooldown phase, and causing products to become grainy / crumbly / otherwise unsatisfactory if it's cooled too slowly
    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
  • That's a good point, cocoa butter is really no better than shea in this respect.
  • You may try one of the waxes like rice bran that forms a gel with oils. Also, cetyl esters may help.
  • What are the in-use spreading properties? Brittle failure suggests to me that the stick would be very unpleasant to use.

    Castor oil as the major oil phase in what is basically a lipstick formula is difficult to improve on.
  • I agree with you, the wax ratio is off.  You must have a high melting point...more than 62 d Celsius.  Try to reduce your Ozokerite, which provides the hard and less flexible part of your formula.  I would use less than 2%.  Also, which grade of Microcrystalline cera do you use?  Do you know its melting point?.  When you end up with your correct, combination of waxes, (melting point, should not exceed 55degrees)  then try and play around with different ratios of your oils, to achieve good spreadability and sensorial properties
  • @johnb surprisingly it feels quite nice, smooth with good slip, leaving behind a nice, occlusive layer. No grittiness, no grabbyness (though it got a bit tacky in the shea-less versions).

    The original formula had castor oil as part of the pigment dispersion (so 66% of the dispersion used at 18%, so a total of 11.8%) so that's something to try out.

    @HelenB I forgot to mention, a version without ozokerite also misbehaved, though having it here is probably not hugely improving matters. The melting point of the crystalline wax I use is 51.6C, so the supplier tells me (haven't actually tested it).

    Do you know of any way to estimate the MP of a blend of waxes? Somehow I don't think it'll be just a weighted average of component melting points.


  • In my days in soap the way of measuing the titre (melting point) of the fatty acids released in soap was to decompose a soap solution with acid, allow the fatty acids to float to the top and then quickly insert a stick thermometer through the fatty layer.

    The fat coated thermometer was then placed in a water bath where the temperature was slowly increased until the fatty coat just melted. The temperature was noted.

    There are more modern instrumental techniques now.
  • Lipstick melt point is usually indirectly measured using a drop point test:
    http://www.koehlerinstrument.com/products/K19490.html
    Robert Zonis, Sr. Formulation Chemist, Beaumont Products "All opinions and comments expressed are my own, have no relation to Beaumont Products, are fully copyrighted, and may not be used without written permission."
  • The following method is a cheap method to give you approx. drop points, just to give you an idea.

    The drop point is the temperature at which the first drop of the melting substance to be examined falls from the tip of the thermometer

    The apparatus, consists of a mercury thermometer, which covers the range of 0-110°C, a test tube, and when in use, it is fixed to the test tube, by means of a stopper through which the thermometer passes.  The whole device is immersed in a beaker with a capacity of about 0.25 L, filled with water.  The bottom of the test tube, is placed about 50 mm from the bottom of the beaker. A stirrer is used to ensure that the temperature of the water remains uniform. Wrap around the bulb of the thermometer the substance to be tested.  Fix the thermometer as suggested above in the test tube.  Do not to get in contact with the test tube wall.

    Heat the water-bath and when the temperature is at about 10 °C below the presumed drop point, adjust the heating rate to about 1 °C/min. Note the temperature at the fall of the first drop. The reading of temperature at the fall of the first drop is regarded as the drop point of the substance. Carry out at least 3 determinations, each time with a fresh sample of the substance.  The difference between the readings, must not exceed 3°C.  The mean of three readings is the drop point of the substance.

  • Thanks for the tip @HelenB, I'll be trying that! 

    @johnb, @Bobzchemist, @HelenB y'all have been wonderful <span>:smiley:</span> As soon as I get out to the lab again I'll be trying all of these!
  • The plot has thickened.

    I added castor oil at 10% (took away from the rice bran oil), still cracked.

    Then I took 10g rice bran oil and 10g of the above, melted it all together, basically to halve the amount of wax in the formula roughly, and not only it cracked, but catastrophically so, as the stick with so much oil was too soft to hold itself in one piece.

    Haven't measured melting point yet, but I know it's way too low on the second bullet and it still cracked the same way, so I don't think MP is related at this point.

    I am truly stumped.
  • I think you need one or two advanced materials in there. Perhaps including a silicone will produce an amorphous rather than crystalline mass.
    Design of anti-aging creams, gels, and serums; shampoos; and therapeutic cosmetics. In-house label and box design capability.
  • Try Dow Corning® SW-8005 C30 Resin Wax
    Robert Zonis, Sr. Formulation Chemist, Beaumont Products "All opinions and comments expressed are my own, have no relation to Beaumont Products, are fully copyrighted, and may not be used without written permission."
  • I think I might be on to something. I think my mold is too cold because it's winter and it's really cold here. So I warmed my little four cavity mold until it was nice and toasty, poured, parked the mold in a container with water for a slow cool (didn't want to overwhelm the fridge), and when I went to unmold it, I found both halves of the split mold were now firmly shut together because it got flooded with hot wax (next time more elbow grease on the screw). Once I managed to separate the two halves, have broken the top half of the bullet off in the process with my delicate touch, I took a hard look at the two pieces and no cracking was found. This needs to be tested again, preferably without causing a calamity, but I think this may be it.

    My theory is that because the mold was so cold, an instant layer of cold balm formed without any inside support, allowing it to contract too much and crack. That same coldness prevented the liquid part of the balm from seeping into the cracks and filling them, but the inside cooled more slowly, preventing the cracks from propagating all the way inside (at least until some force was applied). Will be testing again (time to go now before I get stranded sans train).

    I feel like Chew in Blade Runner:
    https://s-media-cache-ak0.pinimg.com/originals/3d/1c/9f/3d1c9fc3f6cec0f6da0fff855fe469a9.jpg



  • Today I poured the same recipe into a four cavity split mold warmed to 40C and left to cool in air on a steel table, and the result was four perfect bullets, no cracks or any other appearance issues. I dripped some onto the metal table itself, which is quite cold, as a test, and that cracked instantly. I think this settles the question.

    To everyone who helped, thank you so much! I can't say how grateful I am that you all took time to share your hard-earned knowledge with me. You are wonderful! <3 I have learned a lot with this thread!

    Thank you!
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