@Emna - Since you are a new formulator the first thing you need to do is to set your expectations.
“what ingredients can bring the hair back to its “nature” ? I want to bring structure and life to damaged hair , i don’t aim to straighten a curly hair or to make it look silky, just make it “healthy”
The reality is that there are NO ingredients that can bring back your hair structure. Damaged hair is damaged and there are no chemicals you can put on hair that will repair that damage.
Hair is a dead fiber. It is no more alive than a shoelace or the fibers used to make your clothes.
This is how you can think about it. Imagine you have a blouse or t-shirt and it gets a hole in it (damage). There is no liquid or chemical that you could pour onto that hole to fix it. You may be able to take needle & thread and close the hole but that is much more complicated than dunking it in a liquid, and even sewing it doesn’t actually “bring it back to its nature.”
The BEST you can hope for is that you can coat the hair with a thin, smooth film that makes hair look, feel and behave in a way that it would if it weren’t damaged. The best ingredients to achieve this goal are silicones like Dimethicone.
But if you are following a “natural” formulating strategy your choices are less effective and more limited. The proteins do have the potential to form a film although since these ingredients are water soluble, when you rinse your hair you’ll lose much of the film. You might experiment with other hydrolyzed proteins.
Coconut oil will penetrate the fiber slightly so that can help improve the fiber flexibility. Lexfeel may give a decent feel but some people may find it heavy on hair. Plus it might make hair fibers stick together. So will the Shea Butter.
In my experience Panthenol has no positive impact on hair. It’s a humectant and since you’ve got glycerin in there, you will see no additional benefit from panthenol. In the cosmetic business, panthenol is used only as a claims ingredient & no benefit is ever expected from it. Raw material suppliers will tell you a different story, but I know many formulas on the market right now use panthenol at levels of 0.1% or less because it’s expensive and has no real, noticeable effect.
Of all the things in this formula, your quat will be the main conditioning ingredient. The one you have chosen is not a particularly good one (in terms of performance). You would have a more effective product if you chose something like Stearalkonium Chloride or Cetrimonium Chloride or even Behentrimonium Methosulfate.
Finally, you don’t have to leave the mask on for hours. Leaving it on your hair longer won’t actually improve the performance. Quats bind to damaged proteins immediately upon application. Oils also spread on the fiber pretty much immediately. The “mask” piece is simply a gimmick that makes people feel like they are doing something special.
Ultimately, you have to decide what type of formulator you want to be. Do you want to make products that perform the best? Or do you want to make products that align with your personal beliefs while compromising performance? It’s really up to you.