Why is salt (sometimes) added at the beginning?
This is a question I have been curious about for a while and have not been able to find concrete answer to: Why in formulae is salt addition occasionally broken into multiple stages of addition (typically before the primary surfactant)?
For ex (not an actual formula just threw values out for the relevant raw materials):
A) Water q.s
b) SLES (70%) 15.0%
C) CAPB (30%) 5.0%
D) Salt 2.0%
If I was making this formula I would make it as above. A -> B -> C -> D. However I often find the following variation for a similar formula:
A) Water q.s
b) Salt 1.5%
C [or B.5]) SLES (70%) 15.0%
D) CAPB (30%) 5.0%
E) Salt 0.5%
A majority of the intended salt is added before or with SLES. Why? The initial salt is typically not enough to begin any real viscosity I have found. I have heard from another that salt can help SLES dissolve; though I have never seen any evidence of this myself trying it at lab or production scale sizes. Is it just a time management strategy? SLES can occasionally take a while to dissolve so might as well dissolve the bulk of the salt while your at it? (Though salt doesn’t take that long to dissolve so is that much time being saved)? Is this just an artefact of an older manufacturing system being passed down?
I have omitted many raw materials that may be added (chelators, colours, preservatives, marketing materials) so let me know if the answer involves them.